Double-sided stencil printing apparatus

A double-sided printing apparatus using a double sided printing with one plate cylinder and one pressing means system, that is capable of carrying out double-sided printing simply and at low cost, with little deviation in the position of the printed image and with satisfactory resist. Printed matter with little deviation of the image position with respect to the sheet position and with good resist can be obtained, by eliminating delay in feeding sheets due to slippage between roller and press roller by operating the transport belt on the upstream side, and so on, and by eliminating resistance during sheet transportation due to contact with the guide member provided along the circumferential surface of the press roller, when pressing sheets against the press roller with a roller or the like, and transporting the sheets along the guide member or the like provided along the peripheral surface of the press roller. After the resist roller has eliminated the contact between the sheet and the stopper, the transport belt starts to be driven. If the printing speed is low, this timing is taken as the timing that the resist roller contacts the press roller. For both low speeds and high speeds, this may be after passage of a predetermined period of time from the operation command signal for the resist roller.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a double-sided printing apparatus, and more particularly to a double-sided printing apparatus including double-sided stencil printing apparatus.

2. Description of the Related Art

Technologies relating to the present invention are disclosed in the following:

A commonly known example of a printer is a thermal digital double-sided stencil printing apparatus (hereafter simply referred to as a stencil printing apparatus). This printing method uses a stencil plate master (hereafter simply referred to as a “master”), which has a laminated structure formed from a thermoplastic resin film applied to a porous support member. The thickness of the thermoplastic resin film is normally between 1 to 2 μm. The porous support member is made from Japanese paper fibers, or synthetic fibers, or a mixture of Japanese paper fibers and synthetic fibers. The thermoplastic film surface of the master is thermally stenciled to form the master by contacting heating elements of a thermal head operated in the main scanning direction of the thermal head. The master that has been stenciled (hereafter sometimes referred to as a stenciled master) is transported in the sub scanning direction, which is normal to the main scanning direction, by master transport means such as platen rollers or the like, and wound around a porous cylindrical shaped rotatable plate cylinder. The plate cylinder is formed by winding a plurality of layers of resin or metal mesh screens. Ink is supplied to the stenciled master on the plate cylinder from an ink supply member within the plate cylinder. Using pressure means such as a press roller, pressure cylinder, or intermediate pressure roller (hereafter generically referred to as “press roller”) the stenciled master on the plate cylinder is directly and continuously pressed against a sheet shaped recording medium such as for example print sheets (hereafter referred to simply as “sheets”). Printing is carried out by forcing ink through the perforations on the plate cylinder and the master, and transferring the ink to the sheets. Also, a stencil transfer printing apparatus is commonly known, in which ink forced from the perforations of the plate cylinder is temporarily transferred to a transfer cylinder having a rubber sheet, and then indirectly printed onto sheets (for example, see Prior Art 1).

Note that “plate cylinder” sometimes refers to a printing drum, or sometimes to the outer periphery of a printing drum. However, in this patent specification “plate cylinder” refers to the entire printing drum.

In recent years most stencil printing apparatus carry out double-sided printing on both the front and reverse sides of a sheet to reduce the consumption of sheets and storage space for documents, in addition to single-sided printing on one side of a sheet only. Conventionally the double-sided printing method and format uses the normal stencil printer apparatus that carries out single-sided printing as described above. Sheets stacked in the sheet supply unit are supplied to the printing unit, where printing is carried out on one side (the front side). The printed sheets are then discharged and stacked in the discharge tray. The sheets are then reversed, and again supplied to the printing unit, where printing is carried out on the remaining side (the reverse side), to obtain double-sided printing. In this double-sided printing method, the total printing time is very long because printing is carried out twice, and waiting time is necessary after completion of single-sided printing until the ink has dried on the front side, or, as it is referred to, until the front side has set. In addition the work of re-arranging the single-sided printed matter or re-setting the single-sided printed matter in the sheet supply unit was very labor intensive.

In order to improve this manual operation associated with the conventional double-sided printing method, there has been vigorous development of double-side printing apparatus that can automatically carry out double-sided printing, and several methods have been proposed for the format of the double-sided printing apparatus.

For example, in Japanese Patent Application Laid-open No. 2003-266906 (Prior Art 8 shown above), conventional double-sided printing apparatus is generally classified into six methods. In (1) the two drum in opposition one pass simultaneous double-sided printing method, two plate cylinders are provided in mutual opposition, and a sheet can be printed on both sides in one pass. In this method, the apparatus is large, and there is the restriction that when carrying out single-sided printing it is necessary to fit an unstenciled master to one plate cylinder to prevent transfer of ink from that cylinder. This results in wasteful consumption of masters, the work is troublesome, and other problem points (see for example, Prior Art 2).

The other remaining five types of double-sided printing method are: (2) the two pass double-sided printing method with stock re-supply after single-sided printing (see for example, Prior Art 3), (3) the single pass double-sided printing method with two drums in opposition and a transfer cylinder in between (see for example, Prior Art 4), (4) the double-sided printing method with a single drum sub-divided and simultaneous reversal (see for example, Prior Art 5), (5) the double-sided printing method with a single drum sub-divided printing and transfer drum (see for example, Prior Art 6).

Finally, although there are restrictions on sheet size and sheet type, (6) is a revolutionary single process double-sided printing apparatus that generally solves the problem points of (1) through (5) above, that is capable of single-sided printing without using masters unnecessarily, and is capable of providing high quality printed matter when double-sided printing. Further, the increase in installation space can be reduced. This adopts the double-sided format of (4) as the basic method (hereafter referred to as the “one drum one pressing means double-sided printing method” or the “one plate cylinder one pressing means double-sided printing method”). This is a new low cost double-sided printing apparatus that has been proposed to solve and provide measures against problem points such as soundness and reliability of sheet transport, and lack of adaptability to high speed printing (see for example, Prior Art 7 through 9).

This is a method of carrying out double-sided printing in which a single stenciled master wound around a single plate cylinder is divided into the master for printing the front side and for printing the reverse side, as shown in Prior Art 8. This format carries out double-sided printing by continuously pressing the unprinted side of sheets that have been printed on the front side (sheets that have been printed on one side) using one of the sub-divisions of the sub-divided master on the plate cylinder. This is accomplished by re-supplying sheets by clever use of sheet reversal and transport by the rotation of the single pressing means (in particular, a press roller having a diameter smaller than the external diameter of the plate cylinder).

In the double-sided printing apparatus disclosed in Prior Art 7 and elsewhere, for resist of reversed sheets that have been printed on one side and to correct skew, and so on, the front edge of a sheet is temporarily stopped by predetermined sheet re-supply stopping means (equivalent to the sheet re-supply position determination member in the prior art documents). Then the sheet is slightly moved and stopped by a sheet re-supply transport device (equivalent to the sheet re-supply transport member in the prior art documents) as sheet re-supply transport means. Then at a predetermined timing a sheet re-supply resist roller (equivalent to the sheet re-supply resist member in the prior art documents) as sheet re-supply resist means, provided in a stopper member positioning unit as sheet re-supply stopping means, operates and rotates. Then the sheet that is printed on the front side contacts the press roller, and is transported reversed to the printing unit by the rotation transport operation of the press roller, where double-sided printing is carried out.

The reversed sheet is temporarily stopped by the predetermined stopping means in order to carry out resist, correction of skew, and so on. Thereafter at a predetermined timing transport means transports the sheet to the printing unit again, where printing is carried out. However, after stopping the sheet is again suddenly transported at the linear speed of the drum, so there is variation in the position of the leading edge of the sheet when it arrives at the nip between the plate cylinder and the pressing means. This has the problem that there is variation in the resist after printing.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a double-sided printing apparatus using the 1 plate cylinder1pressing means double sided printing format, that is capable of cheaply and simply carrying out double-sided printing, with little deviation in the position of the printed image and with good resist.

In an aspect of the present invention, a double-sided stencil printing apparatus has a plate making device that makes masters divided into front and rear surfaces along the direction of transport of a stencil blank sheet. The double-sided stencil printing apparatus comprises a transport device which transports the sheet, and which has a stopper that receives, comes into contact with, and holds the sheet printed on a first side, when printing on both sides by interchanging the front and rear sides of the sheet that is to be printed; and a stopper release mechanism for releasing the contact between the sheet and the stopper when printing a second side. The contact between the sheet and the stopper is released, and the sheet is re-supplied to the printing position with the front and rear of the sheet being reversed. The transport device is operated after the contact between the stopper and the sheet is released.

In another aspect of the present invention, a double-sided stencil printing apparatus has a plate making device that makes masters divided into front and rear surfaces along the direction of transport of a stencil blank sheet. The double-sided stencil printing apparatus comprises a press roller that is pressed against the interchanged front and rear sides of the sheet that is to be printed; a transport device that receives the sheet that has been printed on a first side and re-supplies the sheet to a printing position with the front and rear sides of the sheet being reversed, when printing on a second side; and a resist roller that brings the sheet into contact with the press roller when printing the second side. Start of feeding by the transport device is commenced in use of an operation command signal of the resist roller as a reference.

In another aspect of the present invention, a double-sided stencil printing apparatus has a plate making device that makes masters divided into front and rear surfaces along the direction of transport of a stencil blank sheet. The double-sided stencil printing apparatus comprises a press roller that is pressed against the interchanged front and rear sides of the sheet that is to be printed; a transport device that receives the sheet that has been printed on a first side and re-supplies the sheet to the printing position with the front and rear sides of the sheet being reversed, when printing on a second side; a resist roller that brings the sheet into contact with the press roller when printing the second side; and a detection device for detecting contact between the resist roller and the press roller. When a printing speed for which delay time in starting to drive the transport device can be ignored, start of feeding by the transport device is commenced after the detection of contact between the resist roller and the press roller by the detection device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is an explanation of the best mode for carrying out the present invention (hereafter referred to as the “embodiments”), with reference to the drawings. Throughout the embodiments and modifications, members and other constituent elements having the same function and shape, and so on, are given the same reference numeral. After explaining the member or element once, further repeated explanation is omitted. To simplify drawings and explanations, constituent elements that should be represented in drawings may be omitted as appropriate if there is no particular necessity to explain them. When constituent elements of a laid-open patent application are referenced and explained as they are, their reference numerals are put within parentheses, in order to distinguish them from those of each embodiment.

First Embodiment

First, the overall constitution of a double-sided stencil printing apparatus300as an example of a double-sided printing apparatus that applies a first embodiment of the present invention is explained, with reference toFIG. 1and others.

Referring toFIG. 1of the drawings, the double-sided stencil printing apparatus300includes a plate making unit15, a printing unit16, a plate discharge unit17, a sheet supply unit30, a sheet discharge unit19, a main body frame130, and an image reading unit18. The plate making unit15makes plates from a master8(sometimes referred to as stencil blank sheets before stenciling. However, in this document it is referred to as a master both before and after plate making) wound in a roll shape, as shown in the top left ofFIG. 1. The printing unit16includes a plate cylinder1around the outer periphery of which the stenciled master is wound, ink supply means, which is described later, which supplies ink to the stenciled master on the plate cylinder1, a press roller21as pressing means that presses sheets36against the stenciled master on the plate cylinder1and which can freely contact and separate from the outer periphery of the plate cylinder1, and other elements, as shown in the center ofFIG. 1. The plate discharge unit17is disposed in opposition to the plate making unit15with the plate cylinder1sandwiched between the plate making unit15and the plate discharge unit17. The plate discharge unit17separates and discharges used masters from the plate cylinder1. The sheet supply unit30is disposed below the plate discharge unit17, and supplies sheets36in a sheet supply tray35as sheet supply platform to the printing unit16. The sheet discharge unit19is disposed in opposition to the sheet supply unit30and below the plate making unit15. The sheet discharge unit19separates printed sheets36from the plate cylinder1and discharges the printed sheets36to a sheet discharge tray172, which is a sheet discharge platform. The main body frame130is the body of the apparatus, within which the plate cylinder1, the plate making unit15, and the plate discharge unit17are disposed, as shown inFIG. 12. The image reading unit18is disposed on the top of the main body frame130. The image reading unit18reads images of documents133transported from a document receiving platform134, or reads images of documents, which are not shown on the drawings, loaded on a contact glass135as a reading unit.

Also, the double-sided stencil printing apparatus300includes a sheet re-supply unit48, a switching guide46, and so on. As described later regarding the printing unit16, the sheet re-supply unit48temporarily holds sheets that have been printed on the front side. Then the sheet re-supply unit48transmits the sheets that have been printed on the front side towards the press roller21where the sheets are reversed and transmitted to the printing unit16. The switching guide46guides sheets that have passed through the printing unit16(either sheets printed on the front side or sheets printed on both sides) to either the sheet re-supply unit48or the sheet discharge unit19.

The sheet re-supply unit48includes a movable guide81, moving means87, a release cam98and a release pin99, sheet re-supply means45, and so on, as shown inFIGS. 1 through 8. The movable guide81as sheet holding means holds the leading edge portion which includes the leading edge (hereafter sometimes referred to as the “leading edge”) of a sheet36athat has been printed on the front side near the moving position P1as the first position near the printing unit16. At an initial position P2(or standby position P2) as the second position near the upstream side of the sheet re-supply means45which is lower than the moving position P1, the movable guide81releases the leading edge of sheets36athat have been printed on the front side. The moving means87reciprocates the movable guide81between the moving position P1and the initial position P2, as shown inFIG. 7. As shown inFIG. 8, the release cam98and the release pin99constitute operation time control means. The release cam98and the release pin99operate the movable guide81to hold the leading edge of the sheets36athat have been printed on the front side after temporarily releasing the movable guide81when the movable guide81is in the moving position P1. Also, the release cam98and the release pin99operate the movable guide81to release the leading edge of sheets that have been printed on the front side when the movable guide81is in the initial position P2. As shown inFIGS. 1 through 6, the sheet re-supply means45temporarily holds sheets that have been printed on the front side that have been received from the movable guide81, then transmits the sheets that have been printed on the front side to the press roller21, the sheets are reversed at the press roller21and transmitted to the printing unit16.

The double-sided stencil printing apparatus300includes a single ink supply means, the single plate cylinder1, and the single press roller21. As stated later, the single plate cylinder single pressing means double-sided printing method is adopted, that is capable of printing on both sides of a sheet by a single rotation of the plate cylinder1. The double-sided stencil printing apparatus300includes the plate making unit15, the printing unit16, the plate discharge unit17, the sheet supply unit30, the sheet discharge unit19, the image reading unit18, the sheet re-supply means45in the sheet re-supply unit48, the movable guide81, the moving means87, the operation time control means, and the switching guide46as devices that are described later.

The plate making unit15has the function and constitution to make masters8. As shown inFIG. 9, the plate making unit15can make stenciled masters8X for double-sided printing (hereafter also referred to as “sub-divided stenciled master8X”) and stenciled masters8Y for single-sided printing. The stenciled masters8X for double-sided printing include a first stenciled image8A (hereafter also referred to as “front side stenciled image8A”) for printing on the front side, and a second stenciled image8B (hereafter also referred to as “reverse side stenciled image8B”) for printing on the reverse side, along the rotation direction of the plate cylinder1(which is the same as the sheet transport direction X, or the master transport direction X1). The stenciled master8Y for single-sided printing has a third stenciled image8YA (hereafter also referred to as the “single-sided stenciled image8YA”) having the image area of the front side stenciled image8A and the reverse side stenciled image8B along the rotation direction of the plate cylinder1, as shown inFIG. 9. When the sub-divided stenciled master8X is wound around the external surface of the plate cylinder1, the front side stenciled image8A forms the position corresponding to the front side area1A shown inFIG. 1. Also, the reverse side stenciled image8B forms the position corresponding to the reverse side area1B shown inFIG. 1.

InFIGS. 1 and 9, the stenciled master8Y is shown within parentheses, to distinguish it from the sub-divided stenciled master8X. InFIG. 9, the extent of the area of the single-sided stenciled image8YA formed on the stenciled masters8Y is indicated with a dotted line. The boundary line of this area in the direction of transport of the master X1overlaps with those of the front side stenciled image8A and the reverse side stenciled image8B. Therefore, inFIG. 9the area of the single-sided stenciled image8YA has been shown slightly larger. However, the extent of the area of the single-sided stenciled image8YA is the total of the front side stenciled image8A, the reverse side stenciled image8B, and an intermediate unstenciled area8C that is the unstenciled blank area located between the front side stenciled image8A and reverse side stenciled image8B.

The plate making unit15includes a master support member8cthat can support the master8so that it can be fed out in the master transport direction X1; a thermal head11that thermally stencils the fed out master8in accordance with image information; a platen roller9that presses the master8against the thermal head11while rotating to transport the master8towards the downstream side in the master transport direction X1; a pair of transport rollers13that further transports the master8transported by the platen roller9towards the downstream side in the master transport direction X1while applying a suitable tension force to the master8; a cutter12disposed between the platen roller9and the pair of transport rollers13, that cuts the stenciled master8or unstenciled master8to a predetermined length; a master guide plate14that guides the leading edge of the master8transported by the platen roller9and the pair of transport rollers13to an open clamper7on the plate cylinder1, and so on.

The master8is formed from a master roll8awound around a roll core8b. The master roll8ais supported at both ends of the roll core8bby the master support member8c, so that the master roll8acan freely rotate in the counterclockwise direction, and the master roll8acan be freely inserted into and removed from the master support member8c. The master support member8cat both sides is installed in and fixed to a pair of plate making side plates, that are not shown in the drawings, that are disposed to the left and right along the direction of transport of the master in the plate making unit15. Therefore, the master8is supported by the master support member8cso that it can be fed from the master roll8ain the direction of transport of the master X1.

The master8has a laminated structure in which thermoplastic resin film of thickness 1 to 5 μm, for example, is applied to a porous support layer made from synthetic fibers or the like. The master is not limited to this, but may be made from thermoplastic resin film applied to a porous support layer made from Japanese paper fibers, or a mixture of Japanese paper fibers and synthetic fibers, or the like, or a master made substantially from thermoplastic resin film only may be used.

The thermal head11is provided extending parallel to the axis of the platen roller9from the near side to the far side relative to the plane of the paper inFIG. 1(this direction is referred to as the main scanning direction). The thermal head11can contact or separate from the platen roller9via the master8, using a contact and separation mechanism provided with a cam and spring member, which is not shown in the drawings. The thermal head11is pressed towards the platen roller9by the spring member. A plurality of heating elements (not shown in the drawings) is disposed in the main scanning direction of the thermal head11in the part that contacts the platen roller9via the master8. The thermal head11has the commonly known function as plate making means of selectively thermally stenciling the master8by selectively heating the heating elements based on digital image signals transmitted from an A/D conversion unit and image signal processing unit, neither of which is shown on the drawings, and processed in a plate making control device and thermal head drive circuit (neither of which is shown in the drawings).

The platen roller9is formed integrally with the platen roller shaft. The platen roller9is rotatably supported at the two ends of the platen roller shaft by the pair of plate making side plates. The platen roller9is connected to a master transport motor10via a rotation transmission member (which is not shown in the drawings) such as a timing belt or gear or the like. The platen roller9is driven to rotate in the clockwise direction by the master transport motor10. The master transport motor10is for example a stepping motor. With this configuration, the master8is drawn out from the master roll8aby the platen roller9being driven by the master transport motor10to rotate in the clockwise direction.

The pair of transport rollers13is provided mutually pressing towards each other with a suitable pressing force by impelling means such as a spring or the like. Each roller shaft is rotatably supported at both ends by the pair of plate making side plates, so that the pair of transport rollers13freely rotate in mutually opposite directions. The pair of transport rollers13is set to rotate with a circumferential speed (transport speed) that is slightly faster than the circumferential speed (transport speed) of the platen roller9by a rotation transmission member that includes the master transport motor10. In this way, with slippage between the pair of transport rollers13and the master8, a suitable front tension is applied to the master8.

The cutter12is a commonly known guillotine type having a fixed blade12band a movable blade12a. The cutter12is not limited to the guillotine type, and a rotating blade moving type in which a movable blade moves while rotating across the width direction of the master at right angles to the master transport direction X1may be used.

The plate making unit15includes constituent elements that are included in plate supply means that is capable of delivering the stenciled master8to and wrapping it around the plate cylinder1. The plate supply means includes the platen roller9, the pair of transport rollers13, and the master guide plate14of the plate making unit15, and the clamper7of a plate cylinder, which is described later, an opening and closing device as opening and closing means that is not shown on the drawings and that opens and closes the clamper7, a main motor20that drives the rotation of the plate cylinder1, and so on, on the plate cylinder1which is described later.

In the plate making unit15shown inFIG. 14, drive means subject to control of the plate making unit15, including the thermal head11that is driven by a thermal head drive circuit (not shown in the drawings) and the master transport motor10, are collectively included as a plate making drive means124.

The plate cylinder1has a two layer structure made from a porous cylindrical shaped support cylinder, and several layers of resin or metal mesh screen (not shown in the drawings) wound around and covering the outer periphery of the support cylinder. The plate cylinder1includes a porous portion1awith many holes through which ink can pass where printing is possible (hereafter also referred to as the “image forming area”), and a non-porous area where the clamper7and so on are provided and where printing is not possible (hereafter also referred to as the “non-image forming area”) formed along the direction of rotation of the plate cylinder1indicated by the arrow inFIG. 1. The image forming area includes at least a first image area1A (hereafter referred to as the front side area1A) in the plate cylinder inFIG. 1, an intermediate area1C, and a second image area (hereafter referred to as the reverse side area1B).

The plate cylinder1is wound around and fixed to end plate flanges, which are not shown in the drawings, and is rotatably supported around an ink pipe that combines with a support shaft5, which is described later. The size of the plate cylinder1is sufficient to obtain an A3 size printed document, for example, in an implementation example if when printing single-sided a maximum A3 size sheet36is printed. In other words, the size is such that a single A3 size master8can be wound, so the outer diameter is set to 180 mm (giving a perimeter of the plate cylinder1of about 565 mm), and the dimension in the width direction (the direction of the axis of the center of rotation) is set to 350 mm.

The plate cylinder1is connected to the main motor20by a gear or belt or another drive transmission means as plate cylinder drive means. For example, the plate cylinder1is driven to rotate in the direction of the arrow inFIG. 1(the clockwise direction) by the main motor20that can be for example a control DC motor. An optical rotary encoder (which is not shown on the drawings) and a plate cylinder sensor (not shown on the drawings) clamped to the optical rotary encoder that generates a pulse by cooperative action with the rotary encoder are provided on the output shaft of the main motor20. The plate cylinder sensor is a transmission type optical sensor that includes a light emitting unit and a light receiving unit (hereafter simply referred to as “transmission type optical sensor”). The plate cylinder sensor is used for controlling the rotation speed (printing speed) and for determining the rotational position of the plate cylinder1.

An ink roller2, a doctor roller3, and the ink pipe5are disposed within the plate cylinder1. The ink roller2is rotatably supported by the side plates that are not shown in the drawings. The ink roller2is driven to rotate in the direction of the arrow inFIG. 1(the clockwise direction) in synchronization with the rotation of the plate cylinder1by rotational drive power transmitted from the main motor20by drive transmission means such as a gear or the like, which is not shown in the drawings. The doctor roller3is disposed parallel to the ink roller2with a small gap between the doctor roller3and the ink roller2. An ink pool4forms in the wedge-shaped cross-section between the doctor roller3and the ink roller2. The ink pipe5supplies ink to the ink pool4. The ink roller2, the doctor roller3, and the ink pipe5constitute the single ink supply means that supplies ink to sub-divided stenciled masters8X or stenciled masters8Y on the plate cylinder1.

The ink in the ink pool4is supplied from an ink pack or the like, which is not shown in the drawings, provided outside the plate cylinder1. The ink is drawn in by an ink pump, which is not shown on the drawings, and supplied and mixed from a supply hole in the ink pipe5. The ink in the ink pool4is supplied as a thin film on the outer peripheral surface of the ink roller2, and measured by the doctor roller2. Further, the ink is supplied to the porous portion1aof the plate cylinder1by contact of the outer peripheral surface of the ink roller2with the inner peripheral surface of the support cylinder of the plate cylinder1.

A stage6and the clamper7are provided in part of the non-porous outer peripheral surface of the plate cylinder. The stage6is made from strong magnetic material and is provided along one generating line of the plate cylinder1. The clamper7has a rubber magnet that can open and close with respect to a plane portion of the stage6, and is rotatably installed on a clamper shaft provided at both ends of the stage6. The clamper7is opened and closed at a predetermined location by an opening and closing device (not shown on the drawings) provided on the main body frame. The plate cylinder1stops with the clamper7in virtually the topmost position shown inFIG. 1, in other words, in the plate supply standby position. The plate cylinder1together with an ink pack installation stand (not shown on the drawings) on which the ink pack can be freely inserted and removed, the ink pump, and other elements constitute an integral plate cylinder unit. The plate cylinder unit can be inserted into and removed from the main body frame of the double-sided stencil printing apparatus300in the direction of the axis of the ink pipe5.

Elements that provide start up and trigger information to a sheet supply motor37and a resist motor41in the sheet supply unit30by detecting the rotation position of the plate cylinder1, as shown inFIGS. 1 and 11, are disposed on the end plate flange of the plate cylinder1on the far side relative to the plane of the paper inFIG. 1and on the body frame near this end plate flange, as shown inFIG. 10. In other words, a sheet supply start light shield plate121and a resist start light shield plate122are installed on the external wall of the end plate flange on the far side of the plate cylinder1, on the same circumference and at a predetermined distance apart and in predetermined positions.

On the other hand, a sheet supply resist sensor120is installed on the side of the main body frame near the light shield plates121,122, in opposition to the circumference on the plate cylinder1on which the sheet supply start light shield plate121and the resist start light shield plate122are installed, so as to sandwich the light shield plates121,122. The sheet supply resist sensor120is a transmission type optical sensor.

In the present embodiment, the home position (initial position) of the plate cylinder1is with the clamper7in virtually the topmost position. This position is set to be the same position as the plate supply standby position in which sub-divided stenciled masters8X or stenciled masters8Y transported from the plate making unit15are received and held. A home position light shield plate, which is not shown on the drawings, is installed at a predetermined position on the external wall of the end plate flange on the far side of the plate cylinder1, in order to detect the home position of the plate cylinder1. A home position sensor (not shown on the drawings) is installed on the side of the main body frame near the home position light shield plate, in opposition to and sandwiching the home position light shield plate on the plate cylinder1. The home position sensor is a transmission type optical sensor.

InFIG. 14, the plate cylinder sensor, the sheet supply resist sensor120, and the home position sensor are given the collective name plate cylinder position detection sensor29, as plate cylinder position detection means that detects the rotational position of the plate cylinder1.

The single press roller21is disposed in opposition to the ink roller2near the bottom of the outer peripheral surface of the plate cylinder1. The press roller21includes an elastic body integrally fixed to a press roller shaft21a, and is provided extending in the axial direction of the plate cylinder1. The press roller21is formed to have virtually the same transverse width as the transverse width of the plate cylinder1. As shown inFIGS. 2 through 4, the press roller21is rotatably supported by a pair of printing pressure arms22via the two ends of the press roller shaft21a. The pair of printing pressure arms22as printing pressure means support members is disposed in the near side and the far side relative to the plane of the paper (the printing pressure arm22on the near side of the plane of the paper is omitted in the drawings).

The size of the plate cylinder1is shown in the drawings as exaggeratedly large compared with the press roller21. For the embodiment, as disclosed for example in Prior Art 7, in order make it easier for the circumferential speed of the press roller21to be the same as that of the plate cylinder1, it is preferable that the ratio of the diameter of the press roller21to the diameter of the plate cylinder1be 1:2 or 1:3. Naturally, if this advantage is not necessary, a press roller21with a length in the circumferential direction that is longer than the length in the circumferential direction of the front side area1A or the reverse side area1B on the outer peripheral surface of the plate cylinder1may be used.

Each printing pressure arm22on the near side and the far side relative to the plane of the paper has virtually the same shape and the same phase. Each of the printing pressure arms22is made integral by an arm shaft22ainstalled and fixed in a position near a bend in the printing pressure arms22, and a connection reinforcing member, which is not shown in the drawings. At the bottom end of the printing pressure arm22shown in the drawings, a notch22bis formed that selectively latches with a latching claw60ain a latching member60that is described later. The arm shaft22ais supported so that it can freely rotate through a predetermined angle between a pair of body side plates, which are not shown in the drawings, provided in the sides of the main body frame (see the pair of body side plates130a,130binFIG. 7) via bearings (not shown in the drawings).

The press roller21is formed from an elastic material having resistance to oil, for example nitrile rubber (NBR). The outer peripheral surface of the rubber at least is uniformly covered with glass beads as a film that has been surface processed to give fine irregularities, similar to the glass fine particles used in offset printing machines, in order to prevent dirt on the printed matter. However, this film is not limited to glass particles, ceramic particles may also be used. In this way, when there is contact with the outer peripheral surface of the plate cylinder1or the sub-divided stenciled master8X or the stenciled master8Y on the plate cylinder1, or when there is contact with the ink on the printed image side of a sheet36athat has been printed on the front side as described later with reference toFIG. 4, swelling and contamination with ink can be kept to a minimum.

The press roller21can be freely displaced via printing pressure range variation means28, latching means64, and each printing pressure arm22, as shown inFIGS. 2 to 4, between a printing position and a non-printing position. The printing position is the position in which unprinted sheets36or sheets36athat have been printed on the front side are pressed against the sub-divided stenciled master8X or the stenciled master8Y on the plate cylinder1, as shown inFIGS. 3 and 5. The non-printing position is the position separated from the printing position shown inFIGS. 1 and 2, and includes the initial position. As stated previously, the pair of printing pressure arms22rotatably support the press roller21as pressing means. Also, the press roller21is constituted so as to be capable of contacting and being separated from the plate cylinder1. The printing pressure range variation means28is also referred to as the press roller contact and separation mechanism as pressing means contact and separation means.

InFIG. 2, reference numeral54indicates a press roller rotation drive means as pressing means drive means that drives the rotation of the press roller21. The press roller rotation drive means54mainly includes a press roller drive motor55and drive power transmission means. The press roller drive motor55as drive means drives the press roller21to rotate at virtually the same circumferential speed of the plate cylinder and in the opposite direction (in the counterclockwise direction) to the rotation direction of the plate cylinder1. The drive power transmission means transmits the rotational drive power of the press roller drive motor55to the press roller21. The press roller drive motor55is installed and fixed to the outside wall of the printing pressure arm22on the far side relative to the plane of the paper inFIG. 2.

As shown inFIG. 2, the drive power transmission means includes a drive pulley56, a driven pulley57, and an endless belt58. The drive pulley56has teeth and is fixed to the output shaft55aof the press roller drive motor55. The driven pulley57has teeth and is fixed to the press roller shaft21aprojected further than the printing pressure arm22to the far side relative to the plane of the paper. The endless belt58has teeth and is wound between the drive pulley56and the driven pulley57.

The press roller21is rotated by the press roller drive motor55at appropriate timing to press unprinted sheets36, sheets36athat have been printed on the front side, or sheets36cthat have been printed on one side against a sub-divided stenciled master8X, or a stenciled master8Y on the plate cylinder1. The operation of the press roller55is controlled by a control device100shown inFIG. 14. The rotational speed of the press roller drive motor55is controlled so that via the drive power transmission means the circumferential speed of the press roller21is virtually the same as the circumferential speed of the plate cylinder1, as stated above. According to the example of the present embodiment, the press roller21is rotated by the press roller drive motor55at a circumferential speed that is virtually the same as the circumferential speed of the plate cylinder1. Therefore, it is possible to obtain good printed matter with no deviation in printed image position.

As shown inFIGS. 1 through 6, besides the press roller21, members which form part of the sheet re-supply means45include a sheet re-supply transport device104, sheet re-supply resist contact and separation means70which is only shown inFIG. 5, a stopper member53, a roller guide plate50, and so on, which are disposed between the printing pressure arms22.

The sheet re-supply means45mainly includes the sheet re-supply transport device104, the stopper member53, a sheet re-supply resist roller51, the sheet re-supply resist contact and separation means70, and the roller guide plate50. The sheet re-supply transport device104as sheet re-supply transport means is capable of stopping and starting at predetermined times, by temporarily holding sheets36aon which a printed image has been formed on the front side in the printing unit16, and transporting it to the press roller21via the stopper member53. The stopper member53as sheet re-supply stopping means temporarily stops the leading edge (the “trailing edge” with respect to the sheet transport direction X. However, this is the “leading edge” or “front edge” with respect to the direction of transport of the sheet36athat has been printed on the front side. Therefore it has been referred to as the “leading edge”) of a sheet36athat has been printed on the front side and that has been transported by the sheet re-supply transport device104in order to determine the position. The sheet re-supply resist roller51as sheet re-supply resist means can freely be displaced between a contact position and a non-contact position that is separated from the contact position. The contact position is the position in which the leading edge of the sheet36athat has been printed on the front side and is temporarily stopped by the stopper member53is released at predetermined timing, and the leading edge of the sheet36athat has been printed on the front side is brought into contact the press roller21. The non-contact position is separated from the contact position. The sheet re-supply resist contact and separation means70displaces the sheet re-supply resist roller51between the contact position and the non-contact position. The roller guide plate50is provided near the outer peripheral surface of the press roller21on the right hand side of the press roller21. The roller guide plate50as sheet re-supply guidance means guides sheets36athat have been printed on the front side and that have been brought into contact with the outer peripheral surface of the press roller21by the sheet re-supply resist roller51towards a nip portion16aformed in the printing unit16.

The sheet re-supply transport device104, as shown inFIGS. 1 to 6, is disposed extending below the trajectory of reciprocation of the movable guide81and to the left of the sheet re-supply resist roller51. The sheet re-supply transport device104mainly includes a sheet re-supply frame110, a rear transport roller107, a front transport roller106, a plurality of transport belts108, a belt drive motor105, and a suction fan109, as shown inFIGS. 2 through 6. The sheet re-supply frame110rotatably supports a drive shaft107aand a driven shaft106a. The rear transport roller107is a drive roller integral with the drive shaft107a. The front transport roller106is a driven roller integral with the driven shaft106, disposed near the sheet re-supply resist roller51on the upstream side of the sheet transport direction X relative to the drive shaft107a. The plurality of transport belts108is a plurality of endless belts wound around and tensioned between the rear transport roller107and the front transport roller106, and contains a plurality of holes108afor air suction. The plurality of transport belts108holds and transports sheets36athat have been printed on the front side that have been received from the movable guide81. The belt drive motor105as belt drive means is connected to the drive shaft107avia drive power transmission means such as a gear or the like, and drives the rotation of the transport belts108by driving the rear transport roller107. The suction fan109attracts and holds sheets36athat have been printed on the front side received from the movable guide81onto the top surface of the transport belts81by drawing air through the plurality of holes108a. For convenience of drawing, the distance between the sheet re-supply resist roller51and the front transport roller106has been shown as reasonably separated. However, it should be noted that they are disposed close to each other.

The sheet re-supply frame110is open on its top surface, and its width is formed slightly smaller than the distance between the two printing pressure arms22. The side cross-section is formed in a channel shape. A plurality of holes or slits is formed in the bottom surface wall of the sheet re-supply frame110to permit the downward flow of air due to the suction fan109. The sheet re-supply frame110has bearings which are not shown on the drawings at both side surfaces in the upstream and downstream sides of the direction of transport of sheets. These bearings rotatably support the drive shaft107aand the driven shaft106a. The drive shaft107apenetrates both side surfaces of the sheet re-supply frame110at the two end portions of the drive shaft107a, and the two ends of the drive shaft107aare rotatably supported by bearing members that are not shown in the drawings.

A drive gear that is not shown in the drawings is installed on one end of the drive shaft107a(the far side of the plane of the paper inFIGS. 2 through 5). The drive shaft107ais driven by the belt drive motor105via the drive gear. The transport belts108are driven to rotate intermittently at special timing in accordance with the type of sheet as explained later, by the belt drive motor105based on command signals from the control device100shown inFIG. 14. The belt drive motor105is for example a stepping motor, and is provided fixed to the side of the main body frame. The driven shaft106adoes not penetrate the two side surfaces of the sheet re-supply frame110at the two ends of the driven shaft106a.

Pins111are fixed projecting to the outside from the two side walls of the sheet re-supply frame110at the upstream end in the direction of transport of sheets X. Each pin111is loosely fitted into holes, which are not shown on the drawings, formed in each printing pressure arm22. In this way, when the press roller21is brought into contact with and separated from the plate cylinder1by the printing pressure range variation means28which is described later, the sheet re-supply frame110of the sheet re-supply device104can swivel at the end where the pins111are disposed about the drive shaft107aas center, to accompany the swiveling motion of the printing pressure arms22.

The rear transport roller107and the front transport roller106are formed from sub-divided rollers formed like on skewers and provided with teeth, for example, and made from high friction material. Incidentally, preferably the rear transport roller107and the front transport roller106are formed from high friction material such as nitrile rubber (NBR) or a suitable resin, or the like, having resistance to oil (resistant to ink corrosion). The transport belt108is for example formed from a plurality of belts with teeth, that are separate from each other and wound around and tensioned between the rear transport roller107and the front transport roller106. Incidentally, preferably the transport belt108is formed from an elastic material with resistance to oil (resistant to ink corrosion) such as for example nitrile rubber (NBR).

The suction fan109includes a fan drive motor as fan drive means to rotate the suction fan109so that sheets36athat are printed on the front side received from the movable guide81are held on the top surface of the transport belts108by drawing in air from the plurality of holes108ain the transport belts108. In the following the suction fan drive motor is simply referred to as the “suction fan109”.

The stopper member53has the function of temporarily stopping the leading edge of sheets36athat have been printed on the front side at a position where they can be passed over to the press roller21, and determining the position of the leading edge of the sheets36athat have been printed on the front side and correcting skew, and so on. The stopper member53is made from sheet metal or a suitable resin, for example, with a cross-section formed in an L-shape. The stopper member53includes a stopper surface53ato which the leading edges of sheets36athat have been printed on the front side butt, to determine the position. The stopper member53is formed with a plurality of notched openings so that when the sheet re-supply resist roller51, which is made from a plurality of roller-shaped members, is displaced to contact the press roller21, the stopper member53does not contact the sheet re-supply resist roller51. The stopper member53is fixed to the sheet re-supply frame110at the left hand end inFIG. 2. In this way, the stopper member53swivels together with both the sheet re-supply transport device104and the press roller21. The stopper member53can also be provided separate from the sheet re-supply transport device104.

The sheet re-supply transport means and the sheet re-supply stopping means are not limited to the sheet re-supply transport device104and the stopper member53according to the present embodiment. For example, as disclosed in FIGS. 1 through 4 and elsewhere in Prior Art 8 and Prior Art 9, a sheet re-supply position determination member (24) in which a sheet re-supply transport unit (25) and an auxiliary tray (8) are integrally installed may be used.

As shown inFIGS. 2 through 4andFIG. 6, a sheet re-supply sensor52is disposed at the upstream end in the direction of transport of sheets X in the stopper member53. The sheet re-supply sensor52is sheet printed on the front side detection means which detects when a sheet36athat has been printed on the front side is in contact with the stopper member53. The sheet re-supply sensor52is a reflection type optical sensor that has the function of detecting the leading edge (the right hand edge inFIG. 4of the sheet36athat has been printed on the front side) and the trailing edge (the left hand edge inFIG. 4of the sheet36athat has been printed on the front side) of sheets36athat have been printed on the front side.

As shown inFIG. 5, the sheet re-supply resist contact and separation means70mainly includes a support shaft72, a pair of swivel arms71, a solenoid73, and a tension spring75, and functions as stopper release means. The sheet re-supply resist roller51is an elastic body formed in a roller shape, made from a high friction material having oil resistance (resistant to ink corrosion), for example a nitrile rubber (NBR), sub-divided and integral with a shaft51a, like on a skewer. The sheet re-supply resist roller51is rotatably installed at both ends of the shaft51aon a first end of each swivel arm71, which is formed in an approximate “A” shape. The sheet re-supply resist roller51normally occupies a non-contacting position below the press roller21and the stopper member53. Each swivel arm71is fixed at its bend portion to the support shaft72which is rotatably supported between the printing pressure arms22. In this way, when the sheet re-supply resist roller51occupies the contact position, contact between the sheet36aand the stopper member53is released. The rotation power of the press roller21acts on the sheet re-supply resist roller51so that the sheet re-supply resist roller51follows by rotating in the opposite direction (the clockwise direction) to the direction of rotation of the press roller21(the counterclockwise direction).

A second end of the swivel arm71on the far side relative to the plane of the paper in the drawing is connected to a plunger74of the solenoid73. The solenoid73is a pull type solenoid, that is installed and fixed to one printing pressure arm22via a fixing member such as a bracket, which is not shown in the drawing. Also, the tension spring75is fixed at one end to one printing pressure arm22and is fixed at the other end to the second end of the swivel arm71. The tension spring75pulls the swivel arm71about the support shaft72so that the sheet re-supply resist roller51normally occupies the non-contact position. The solenoid73has the function as sheet re-supply resist drive means of displacing the sheet re-supply resist roller51at predetermined timing so that it occupies the contact position.

According to the configure described above, when the solenoid73operates against the resistance of the force of the tension spring75(ON operation), the outer peripheral surface of the sheet re-supply resist roller51occupies the contact position where it contacts the outer peripheral surface of the press roller21at a predetermined pressure. In this way, the sheet36athat has been printed on the front side contacts the outer peripheral surface of the press roller21at a predetermined time. Then, under the rotational power of the press roller21, the sheet re-supply resist roller51follows the rotation of the press roller21by rotating in the clockwise direction opposite to the direction of rotation of the press roller21, and assists transport of the sheet36athat has been printed on the front side. When the operation of the solenoid73is released (OFF operation) the outer peripheral surface of the sheet re-supply resist roller51is separated by the force of the tension spring75from the outer peripheral surface of the press roller21and occupies the non-contact position.

The roller guide plate50has the function of guiding sheets36athat have been printed on the front side that are transported by the rotational power of the press roller21towards the plate cylinder1while maintaining contact with the outer peripheral surface of the press roller21. The roller guide plate50is formed in a partial cylindrical shape curved about a press roller shaft21aas center. The roller guide plate50is fixed between the two printing pressure arms22, with a predetermined gap with the outer peripheral surface of the press roller21. In this way the roller guide plate50guides the sheets36athat have been printed on the front side along the outer peripheral surface of the press roller21. The surface of the side of the roller guide plate50that guides the sheets36athat have been printed on the front side is smoothly coated with a film that has a low coefficient of friction with respect to the sheets36athat have been printed on the front side, and that is resistant to ink and oil, such as a poly-tetrafluoroethylene resin or similar.

InFIG. 14, the drive means subject to control of the sheet re-supply means45includes the press roller drive motor55, the solenoid73, the belt drive motor105, the suction fan109, and so on. The sheet re-supply means45includes the sheet re-supply sensor52and so on, as means for detecting several parameters.

Next, the configuration around the printing pressure range variation means28that determines the printing pressure range of the press roller21is simply explained. As shown inFIGS. 1 and 9, in the present embodiment it is possible to selectively switch to one of at least three printing pressure range patterns: printing pressure range pattern I, printing pressure range pattern II, and printing pressure range pattern III. The printing pressure range pattern I is the first printing pressure range pattern, in which printing pressure is applied only to the front side area1A which corresponds to the front side stenciled image8A on the sub-divided stenciled master8X on the plate cylinder1. The printing pressure range pattern II is the second printing pressure range pattern, in which printing pressure is applied only to the reverse side area1B which corresponds to the reverse side stenciled image8B on the sub-divided stenciled master8X on the plate cylinder1. The printing pressure range pattern III is the third printing pressure range pattern, in which printing pressure is applied from the front side stenciled image8A to the reverse side area1B which corresponds to the single-sided stenciled image8YA on the stenciled master8Y on the plate cylinder1. A part of the structure of the printing pressure range variation means28that selectively switches to one among these three printing pressure range patterns is shown inFIGS. 2 and 3. The printing pressure range variation means28has the configuration and function to displace the press roller21between the printing position and the non-printing position.

The printing pressure range variation means28has a similar configuration to the press roller contact and separation mechanism (55) shown in FIGS. 2 through 4 of Prior Art 7, which includes a stepping motor (52) that drives the rotation of a multi-stage cam (43) and a step cam (49), and so on. Incidentally, a part of the printing pressure range variation means28is shown inFIGS. 2 and 3with reference numerals obtained by adding “200” to the reference numerals of the constituent elements of the press roller contact and separation mechanism (55), such as the multi-stage cam (43), the step cam (49), the stepping motor (52). The printing pressure range variation means28includes the arm shaft22a, the pair of printing pressure arms22, a pair of cam followers241, a pair of printing pressure springs242, a printing pressure cam shaft244, a pair of multi-stage cams243, and so on. A stepping motor252is only shown in the printing pressure range variation means28shown inFIGS. 14 and 15.

As shown inFIGS. 2 and 3, each of the constituent elements of the printing pressure range variation means28are disposed in both the near side and the far side of the press roller21relative to the plane of the paper shown inFIG. 1(the elements on the near side of the plane of the paper are omitted). This is so that a uniform pressure force is applied from the press roller21to the outer peripheral surface of the plate cylinder1. Therefore, the explanation of the constituent elements on the far side is taken to be representative, and the explanation for the elements on the near side is omitted. If the advantage referred to above is not required in the printing pressure range variation means28, then the constituent elements constituting the printing pressure range variation means28may be provided, for example, only on the far side as shown inFIGS. 1 through 4.

As shown inFIGS. 2 and 3, the cam follower241is rotatably supported on a shaft on the outside of the far side wall in the center of the printing pressure arm22that opposes on the inner side of the printing pressure arm22that supports the press roller21. The cam follower241is a rolling bearing capable of contacting the multi-stage cam243with low frictional resistance.

One end of a printing pressure spring242(tension spring) that impels the press roller21to press against the outer peripheral surface of the plate cylinder1is connected to the second end of the printing pressure arm22. The other end of the printing pressure spring242is connected to the side plate of the main body frame. The printing pressure spring242impels the second end of the printing pressure arm22to swivel in the clockwise direction about the arm shaft22aas center, in the direction so that the press roller21will contact the outer peripheral surface of the plate cylinder1. The notch22bis integrally formed in the second end of the printing pressure arm22and is capable of latching with the latching claw60aof the latching member60, and capable of being unlatched from the latching member60.

On the other hand, a printing pressure cam shaft244to which the pair of multi-step cams243is fixed and that rotates in synchronization with the rotation of the plate cylinder1is rotatably supported by the side plates of the main body frame near each cam follower241. The multi-stage cam243is for example a plate cam formed with a small diameter portion (depressed portion) and a large diameter portion (projecting portion).

The printing pressure cam shaft244is fixed to a belt pulley or gear or the like, which is not shown in the drawings, and connected to the main motor20via drive transmission means such as a belt pulley or a gear. In this way, the multi-stage cam243rotates in synchronization with the rotation of the plate cylinder1. The cam follower241is pressed to be always in contact with the multi-stage cam243by the printing pressure spring242. Therefore, the cam drive means that drives the rotation of the multi-stage cam243is mainly constituted by the main motor20.

The multi-stage cam243has three cam plates,243A,243B, and243C, fixed at appropriate spacing on the printing pressure cam shaft244. The printing pressure cam shaft244is capable of moving the three cam plates,243A,243B, and243C by predetermined amounts in the axial direction. When necessary a specific cam is selected and moved to a position in opposition to the cam follower241. Each cam plate243A,243B,243C is set in the order cam plate243B, cam plate243A, and cam plate243C from the near side relative to the plane of the paper inFIGS. 2 and 3. Each cam plate243A,243B,243C has a small diameter portion (depression portion or base portion) which is a circular plate concentric with the cam shaft244, and a large diameter portion (projection portion) that projects by the same amount. The cam shaft244of the multi-stage cam243is driven to rotate in the clockwise direction inFIG. 2by rotational power transmitted from the main motor20. In other words, the plate cylinder drive means (121) drives the cam shaft (44) via the drive gear (45) mounted on the cam shaft (44) and the transmission gear (47) mounted on the support shaft (46) rotatably supported on the main body frame, as shown in FIG. 4 of Prior Art 7.

When the large diameter portion of any of the cam plates243A,243B,243C is in contact with the cam follower241, the surface of the press roller21separates from the outer peripheral surface of the plate cylinder1and occupies the non-printing position as shown inFIGS. 2 and 4. When contact between the large diameter portion and the cam follower241is released, the surface of the press roller21contacts the outer peripheral surface of the plate cylinder1as a result of the force of the printing pressure spring242, and occupies the printing position as shown inFIGS. 3 and 5. Each cam plate243A,243B,243C is configured so that when the press roller21is in the printing position, the small diameter portion (base portion) does not contact the cam follower241.

The shape of the large diameter portion of the cam plate243A,243B and243C is formed so that the range of contact between the press roller21and the plate cylinder1is the total of the front surface area1A, the intermediate area1C, and the reverse area1B shown inFIG. 1(see printing pressure range pattern III inFIG. 9). The shape of the large diameter portion of the cam plate243B is formed so that the range of contact between the press roller21and the plate cylinder1is the same as the front surface area1A (see printing pressure range pattern I inFIG. 9). The shape of the large diameter portion of the cam plate243C is formed so that the range of contact between the press roller21and the plate cylinder1is the same as the rear surface area1B (see printing pressure range pattern II inFIG. 9).

As shown inFIGS. 2 and 3, the latching means64maintains the press roller21in the non-printing position shown inFIGS. 1 and 2except when sheets are being passed through. The latching means64mainly includes the latching member60, a support shaft61, a solenoid62, and a tension spring63. The latching means64is disposed in the far side relative to the plane of the paper.

The latching member60is supported so that it can freely swivel about the support shaft61which is mounted on the side plate of the main body frame on the far side relative to the plane of the paper. The latching claw60a, which can be selectively latched onto the notch22bof the printing pressure arm22, is formed in a first end of the latching member60. On a second end of the latching member60one end of the tension spring63is connected so that the tension spring63impels the latching member60in the direction that the latching claw60ais normally latched to the notch22bof the printing pressure arm22. The other end of the tension spring63is connected to the side plate of the main body frame on the far side relative to the plane of the paper. The solenoid62is fixed via a fixing member such as a bracket which is not shown in the drawings to the side plate of the main body frame on the far side relative to the plane of the paper. Also, a plunger62aof the solenoid62is connected via a pin to the side of the second end of the latching member60in opposition to the portion where the tension spring63is disposed. The solenoid62is a pull-type solenoid.

According to the configuration described above, when the solenoid62is electrified and turned on, the printing pressure range variation means28is operated, and the press roller21occupies the printing position as a result of the operation which is described later. In this way, the press roller21continuously presses sheets36against sub-divided stenciled masters8X or stenciled masters8Y on the plate cylinder1while rotating. When the electricity to the solenoid62is stopped and the solenoid62is turned off, the printing pressure range variation means28stops operating, and the press roller21separates from the printing position and occupies the non-printing position (initial position) shown inFIGS. 1 and 2as a result of the operation which is described later.

The solenoid62is controlled to turn on or off by the control device100which is described later. By controlling the switching on and off of the solenoid62by the control device100, it is possible to selectively switch between a state in which the printing pressure arm22is held and a state in which the printing pressure arm22is released. As stated later, the solenoid62is turned on when the cam follower241contacts the large diameter portion of the multi-stage cam243(seeFIG. 2).

FIG. 9shows the printing pressure ranges of the press roller21developed for ease of understanding. InFIG. 9, the sub-divided stenciled master8X wound around the porous portion1aof the plate cylinder1, which is not shown onFIG. 9, is provided with a front stenciled image8A area, a reverse stenciled image8B area, and an unstenciled blank intermediate unstenciled area8C. Here, the leading edge of the sub-divided stenciled master8X, which is also referred to as the leading edge blank portion, which is held by the clamper7of the plate cylinder1, which is not shown inFIG. 9, is on the left hand side.

During normal printing including single-sided printing, the printing pressure range pattern is pattern III. In other words, in printing pressure range pattern III printing pressure is applied continuously from the front side stenciled image8A area, through the intermediate unstenciled area8C, to the reverse side stenciled area8B. To continuously print the single-sided stenciled image8YA of the stenciled master8Y onto sheets36, the printing pressure range variation means28is operated by a command from the control device100shown inFIG. 14to select the cam plate243A, which is driven to rotate so that the small diameter portion of the cam plate243A is in opposition with the cam follower241.

When printing on the front side, the printing pressure range pattern is pattern I. To print corresponding to the front side stenciled image8A area, the printing pressure range variation means28is operated by a command from the control device100to select the cam plate243B. Then the cam plate243B is driven to rotate so that the small diameter portion of the cam plate243B is brought into opposition with the cam follower241, and then the printing pressure is released at the intermediate unstenciled area8C.

When printing on the reverse side, the printing pressure range pattern is pattern II. The printing pressure range variation means28is operated by a command from the control device100to select the cam plate243C. The large diameter portion of the cam plate243C is brought into opposition with the cam follower241so that on the initial front side stenciled image8A area the printing pressure is released. Next the small diameter portion of the cam plate243C is rotated to be brought into opposition with the cam follower241.

According to the present embodiment, the printing pressure range variation means28is provided, so it is possible to appropriately set the range over which the printing pressure is on. Therefore it is possible to prevent problems such as contamination with ink when a print image is transferred to the outer peripheral surface of the press roller21when the printing is on but there is no sheet.

The printing pressure range variation means28is not limited to a configuration that includes the multi-stage cam (43), the stepped cam (49), and the press roller contact and separation mechanism (55) as shown in FIGS. 2 and 4 and elsewhere in Prior Art 7. For example, an emergency pressing release means (79) as shown in FIGS. 1 through 4 of Japanese Patent Application Laid-open No. 2003-237030 may be applied.

As shown inFIG. 1, the sheet discharge unit19is provided close to the outer peripheral surface of the plate cylinder1. The sheet discharge unit19mainly includes a separation claw170, a separation fan171, a sheet discharge transport device152, and the sheet discharge tray172. The separation claw170separates single-side printed sheets36cfrom stenciled masters8Y on the plate cylinder1. The separation fan171blows air between the leading edge of the single-side printed sheet36cthat has been separated by the separation claw170and the plate cylinder1to assist the separation operation by the separation claw170. The sheet discharge transport device152sucks in and transports single-side printed sheet36cor double-sided printed sheets36bseparated by the separation claw170and the separation fan171.

The separation claw170is provided near the downstream portion of the nip portion16aformed by the contact of the press roller21against the outer peripheral surface of the plate cylinder1. The separation claw170can be freely displaced between a separation position and a non-separation position by separation claw displacement means (not shown in the drawings), such as a cam and spring, or the like, that can be rotated in synchronization with the rotation of the plate cylinder1. The separation position is a position close to the outer peripheral surface of the plate cylinder1where a single-side printed sheet36ccan be forcibly separated from the stenciled master8Y on the plate cylinder1. The non-separation position is a position separated from the separation position that avoids contact with the clamper7that projects from the outer peripheral surface of the plate cylinder1. The separation fan171includes a fan drive motor that drives the rotation of the separation fan.

As shown inFIGS. 1 through 5, the sheet discharge transport device152is disposed below the separation claw170and to the left of the switching guide46. The sheet discharge transport device152includes a rear sheet discharge roller154as the drive roller, a front sheet discharge roller156as the driven roller, a sheet discharge belt158which is an endless belt, a suction fan159, and so on. The rear sheet discharge roller154is formed in a roller shape, with a plurality of rollers fitted at predetermined intervals to a drive shaft154arotatably supported on the side plates of the main body frame. The front sheet discharge roller156is also provided with a plurality of rollers at the same intervals as the rear sheet discharge roller154, on a drive shaft156arotatably supported on the side plates of the main body frame. The sheet discharge belt158is wound around and tensioned by the rear sheet discharge roller154and the front sheet discharge roller156. A drive gear or drive pulley, which is not shown on the drawings, is installed on the drive shaft154a(for example, on the far side relative to the plane of the paper inFIGS. 1 through 5). The drive shaft154ais connected to a sheet discharge belt drive motor153via drive power transmission means, which is not shown on the drawings, such as a motor gear meshing with the drive gear, or a belt provided between the drive pulley and a pulley, which are not shown on the drawings. In this way, the sheet discharge belt158is driven to rotate in the direction of the arrow shown inFIG. 1(the counterclockwise direction) by the sheet discharge belt drive motor153.

The suction fan159is disposed below the sheet discharge belt158. The suction fan159includes a fan drive motor that drives the rotation of the suction fan. As a result of the suction force of the suction fan159, the sheet discharge transport device152draws single-side printed sheets36cor double-side printed sheets36bonto the sheet discharge belt158, and transports them in the direction of the arrow shown inFIG. 1by the rotation of each rear sheet discharge roller154.

InFIG. 14, the fan drive motor of the separation fan171, the sheet discharge belt drive motor153, and the fan drive motor of the suction fan159are collectively referred to as sheet discharge drive means127of the sheet discharge unit19.

The switching guide46is disposed on the sheet transport path between the nip portion16aand the sheet discharge transport device152, as shown inFIGS. 1 through 5. The nip portion16ais the printed image formation portion in the printing unit16formed by the press roller21pressing against the plate cylinder1. The switching guide46is a plate member having a width that is virtually the same as that of the plate cylinder1and the press roller21. The base end portion (the downstream end portion in the direction of transport of sheets X) of the switching guide46is fixed to a shaft46athat is supported by the side plates of the main body frame so that it can rotate through a predetermined angle. The free end portion (the upstream end portion in the direction of transport of sheets X) can freely swivel about the shaft46aas center. The outer peripheral surface of the switching guide46is preferably coated with a film that is ink resistant and oil resistant, such as for example a poly-tetrafluoroethylene resin or the like.

The switching guide46can be selectively positioned in a first displacement position or a second displacement position by the action of a solenoid47as switching drive means shown inFIGS. 2 and 14operating against the resistance force of a tension spring as impelling means, which is not shown in the drawings. The first displacement position is the position in which the free end portion which is formed with an acute angled cross-section is positioned as shown by the solid lines inFIG. 1. The second displacement position is shown by the double-dashed lines inFIG. 1. The switching guide46is given the tendency to swivel into the first displacement position, which is also the initial position shown inFIG. 1, by the impelling force of the tension spring. When the switching guide46is in the first displacement position, the tip of the switching guide46is near the outer peripheral surface of the press roller21, and in a position that will not interfere with the clamper7. When the switching guide46is in the second displacement position, the tip is positioned close to the peripheral surface of the plate cylinder1. When the switching guide46is in the first displacement position, double-side printed sheets36bor single-side printed sheets36cthat pass between the plate cylinder1and the press roller21are guided to the sheet discharge unit172. When the switching guide46is in the second displacement position, sheets36aprinted on the front side are guided by the switching guide46to the movable guide81. The switching drive means that displaces the switching guide46between the first displacement position and the second displacement position is not limited to a combination of the solenoid47and the tension spring. For example, the switching guide46may be driven by a stepping motor or a rotary solenoid, or the like.

As shown inFIGS. 1 through 5, the movable guide81is disposed below the sheet discharge transport device152and the switching guide46, and above the sheet re-supply transport device104. As shown inFIGS. 3,7, and8, the movable guide81has the function and constitution as sheet holding means to take hold of the leading edge portion, which includes the leading edge, of sheets36aprinted on the front side that are ejected from the nip portion16a, at the moving position P1, and release the leading edge of sheets36aprinted on the front side at an initial position P2. The moving position P1is the first position near the printing unit16. The initial position P2is the second position which is lower than the moving position P1and which is near the upstream side of the sheet re-supply device45, as shown inFIGS. 7 and 8.

The movable guide81mainly includes a holding platform81f, an end fence81d, projections81c, a clamping claw81b, a clamping shaft81a, a pair of bearing brackets81g, a coil spring which is not shown on the drawings, and a pair of release levers upper82, and release levers lower83. The holding platform81fis for holding and loading the leading edge portion of sheets36athat have been printed on the front side. The end fence81dis formed integrally with the holding platform81fon the downstream side in the direction of movement Xa of sheets36athat have been printed on the front side that have been ejected from the nip portion16a. The end fence81dincludes a sheet contact surface81eagainst which the leading edges of sheets36athat have been printed on the front side contact. The projections81care projections formed integrally as guides at four positions in pairs in the direction of reciprocation on the holding platform81fat both the near side and the far side relative to the plane of the paper. The clamping claw81bis a holding member that is capable of opening and closing with respect to the holding platform81f, and that releases and holds the leading edge portion of sheets36athat have been printed on the front side. The clamping shaft81ais a member on which the base end of the clamping claw81bis installed and fixed, and that is capable of swiveling (rotating freely about a predetermined angle). A pair of the bearing brackets81gare integrally installed on the two side ends of the holding platform81fto support the clamping shaft81aso that the clamping shaft81acan freely rotate through the predetermined angle. The bearing brackets81gare shown onFIG. 7only. The coil spring, which is not shown on the drawings, is impelling means that presses the free end of the clamping claw81bin the direction of the arrow shown inFIG. 4against the top surface of the holding platform81f. The pair of release levers upper82, and release levers lower83is shown inFIG. 8, and is installed and fixed to the clamping shaft81ain the far side relative to the plane of the paper.

The movable guide81is formed in an L-shaped cross-section by the holding platform81fand the end fence81d. The four projections81cfit loosely into guide grooves88formed in the pair of side plates130a,130bof the main body frame, as shown inFIG. 7. The clamping claw81bis slanted at an angle that forms an acute angle with the direction of movement Xa (transport direction) of sheets36athat have been printed on the front side ejected from the nip portion16a. The base end of the clamping claw81bis installed on and fixed to the clamping shaft81a, and the free end is formed in an acute angle shape. In addition, the clamping claw81bis made from a metal or resin thin plate member that is fixed to the clamping shaft81aextending in the sheet width direction Y, to hold or release the leading edge of sheets36aprinted on the front side ejected from the nip portion16a. An installation portion84is provided integrally on the bottom portion of the holding platform81fin the far side relative to the plane of the paper, as shown inFIG. 7. The installation portion84is fixed to a timing belt89that forms part of movement means87.

The release lever upper82and release lever lower83are formed as plate shaped members. The projections81care not limited to being formed integrally with the holding platform81f, and they may be provided as rollers that can roll with low friction on the internal walls of the guide grooves88.

According to the movable guide81of the present embodiment, the clamping claw81bis provided slanted at an angle that forms an acute angle with the direction of movement Xa (transport direction) of sheets36athat have been printed on the front side ejected from the nip portion16a. Therefore, when a sheet36athat has been printed on the front side is being transported, if a load or the like acts in the direction to pull out the sheet36athat has been printed on the front side, a moment will act on the clamping claw81bin the direction to increase the holding force (pressing force). In other words the moment acts to rotate the clamping claw81bin the counterclockwise direction. Therefore, the holding force (pressing force) increases, and pull out of the sheet36athat has been printed on the front side is prevented. In addition, this has the advantages that it is possible to set the holding force of a torsional coil spring, which is not shown in the drawings, smaller, and there is no necessity to make it stronger so the cost can be reduced.

Preferably the parts of the constituent elements of the movable guide81that come into contact with sheets36athat have been printed on the front side are formed from a metal material to prevent static electricity, or are subjected to a vapor deposition process or plating process to prevent static electricity.

The moving means87is disposed to the outside of the side plate130bof the main body frame on the far side relative to the plane of the paper, as shown inFIG. 7. The moving means87has the function and constitution to reciprocate the movable guide81between the moving position P1and the initial position P2. The moving means87mainly includes the guide grooves88, a drive pulley90, a driven pulley91, the timing belt89, a plurality of tension rollers95, a drive gear92, a drive motor94, and a motor gear93. The guide grooves88are formed in a circular arc shape penetrating the pair of side plates130a,130bof the main frame, and sloping downwards to the left to follow virtually the same transport path as the sheet transport direction Xa of the sheets36athat have been printed on the front side. The drive pulley90has teeth and a shaft90a, and is rotatably supported on the side plate130bof the main body frame near the downstream end of the guide groove88in the sheet transport direction Xa of the sheets36athat have been printed on the front side. The driven pulley91has teeth and a shaft91a, and is rotatably supported on the side plate130bof the main body frame near the upstream end of the guide groove88in the sheet transport direction Xa of the sheets36athat have been printed on the front side. The timing belt89is wound around and tensioned on the drive pulley90and the driven pulley91. The plurality of tension rollers95is disposed to contact and apply tension to the timing belt89, and is rotatably supported on the side plate130bvia shafts that are not shown on the drawings. The drive gear92is installed on and fixed to the shaft90aof the drive pulley90. The drive motor94is drive means capable of rotating in the forward and reverse directions, installed on and fixed to the side plate130bof the main body frame near the shaft90aof the drive pulley90. The motor gear93is installed on and fixed to the output shaft94aof the drive motor94and meshes with the drive gear92.

The timing belt89is connected to the movable guide81via the installation portion84integrally formed in the bottom of the holding platform81fof the moving guide81. The drive motor94is for example a stepping motor. As described above, the drive motor94constitutes drive means of the moving means87; the guide grooves88constitute guide means of the moving means87; the timing belt89, the drive pulley90, the driven pulley91, the drive gear92, and the motor gear93constitute drive power transmission means for transmitting the drive power of the drive motor94to the moving guide81.

In accordance with the configuration described above, the moving guide81can be reciprocated by the forward or reverse rotation of the drive motor94via the drive power transmission means to selectively occupy the moving position P1(the first position), or the initial position or standby position (the second position). The moving position P1(the first position) is the position near the printing unit16where the leading edge of sheets36athat have been printed on the front side is clasped, and is indicated by a solid lines inFIGS. 3,7, and8. The initial position or standby position (the second position) is lower than the moving position P1near the upstream side of the sheet re-supply means45(near the rear of and above the transport roller107of the sheet re-supply transport device104). The initial position or standby position (the second position) is the position where the leading edge of sheets36athat have been printed on the front side is released, and is indicated by solid lines inFIGS. 1 and 2, and by double-dashed lines inFIGS. 7 and 8. A home position sensor85is disposed near the drive pulley90to detect when the moving guide81is in the second position that is the home position P2(initial position P2).

The release cam98and the torsional coil spring have the function of operation time control means. As shown inFIG. 8, when the movable guide81occupies the moving position P1indicated by solid lines, the clamping claw81bis temporarily released by being swiveled in the clockwise direction (rotation through a predetermined angle) via the release lever lower83and the clamp shaft81aas a result of the contact between the release lever lower83of the movable guide81and the release cam98, against the resistance of the torsional coil spring. Then, when the movable guide81starts to move from the moving position P1towards the initial position P2indicated by double-dashed lines, the contact between the release cam98and the release lever lower83is eliminated. As a result, the clamping claw81bswivels in the counterclockwise direction due to the impelling force of the torsional coil spring. Therefore the leading edge portion of the sheet36athat has been printed on the front side is held. As shown inFIG. 8, when the movable guide81occupies the initial position P2, the release lever upper82of the movable guide81contacts the release pin99. In this way the clamping claw81bis swiveled in the clockwise direction via the release lever upper82and the clamp shaft81a, against the resistance of the impelling force of the torsional coil spring, which is not shown in the drawings. Therefore the leading edge of the sheet36athat has been printed on the front side is released.

According to the present embodiment, the release cam98is provided, which has the following advantages compared with the case where the release cam98is not provided. Consider for example, a configuration without the release cam98. When the movable guide81is occupying the moving position P1, the leading edge of the sheet36aprinted on the front side swivels the clamping claw81bin the clockwise direction and is inserted into the release portion (the release portion between the front end of the clamping claw81band the top surface of the holding platform81f), using the transport force applied by the nip portion16a, against the impelling force of the torsional coil spring which is not shown on the drawings. Even if the impelling force of the torsional coil spring is set to suit weak sheets, it is conceivable that the leading edge of the sheet will get deformed, or that the holding force will not be stable. In contrast to this, according to the present embodiment, when the movable guide81is occupying the moving position P1, as a result of the action of the release cam98as described, the leading edge of the sheet36aprinted on the front side is smoothly inserted into the release portion (the release portion between the front end of the clamping claw81band the top surface of the holding platform81f), using the transport force applied by the nip portion16a. Therefore it is possible to securely hold and clamp the leading edge of sheets36aprinted on the front side between the front end of the clamping claw81band the top surface of the holding platform81f, regardless of the strength of the sheets. In this way, it is possible to transport the sheets36aprinted on the front side in a stable manner without meandering or skewing. In addition, it is possible to prevent inclination of the image or poor resist due to inclination when printing on the reverse side. Also, it is possible to set the release time longer to a certain extent when clasping the leading edge of the sheet36aprinted on the front side by design and adjustment of the shape of the release cam98. Therefore, even for weak sheets it is possible to insert the leading edge of the sheet without resistance, so the leading edge of sheets36aprinted on the front side can be held well.

As a result of the action and operation of the release pin99, when the movable guide81is in the initial position P2, the leading edge of the sheet36aprinted on the front side that is held between the front end of the clamping claw81band the top surface of the holding platform81fis released. Then the sheet36aprinted on the front side is dropped onto the transport belt108of the sheet re-supply transport device104from its leading edge. At this time the sheet36aprinted on the front side is temporarily held on the top of the transport belt108by the suction force of the suction fan109, and then transported by the rotation of the transport belts108. Of course the length of the transport belts108and the initial position P2of the movable guide81and so on must be set to a suitable length in accordance with the length in the sheet transport direction X of the sheets36used in double-sided printing.

The plate discharge unit17includes an upper plate discharge member160, a lower plate discharge member161, a plate discharge box162, a compression plate163, and so on. The upper plate discharge member160includes a drive roller164, a driven roller165, an endless belt166, and so on. The drive roller164is driven to rotate in the counterclockwise direction inFIG. 1by plate discharge drive means126(seeFIG. 14) that includes a plate discharge motor which is not shown in the drawings. In this way the endless belt166moves in the direction of the arrow shown inFIG. 1. The lower plate discharge member161includes a drive roller167, a driven roller168, an endless belt169, and so on. The drive power of the plate discharge roller that drives the rotation of the drive roller164is transmitted to the drive roller167by drive power transmission means, such as a gear or a belt, which is not shown in the drawings. Therefore the drive roller167is driven to rotate in the clockwise direction inFIG. 1, and the endless belt169moves in the direction of the arrow inFIG. 1. Also, the lower plate discharge member161can be moved by moving means that is not shown in the drawings that is included in the plate discharge drive means126. In this way the lower plate discharge member161can selectively occupy the position shown in the drawings, and a position in which the endless belt169at a position on the outer peripheral surface of the driven roller168contacts the outer peripheral surface of the plate cylinder1.

The plate discharge box162stores used masters, and is provided so that it can be freely inserted into and removed from the main body frame130. The compression plate163is supported so that it can be moved vertically with respect to the main body frame130, so that it can compress used masters transported by the upper plate discharge member160and the lower plate discharge member161into the plate discharge box162. The compression plate163is moved vertically by vertical moving means which is not shown in the drawings, and which is included in the plate discharge drive means126.

InFIG. 14, the plate discharge motor of the plate discharge unit17, the moving means, and the control drive means of the plate discharge unit17which includes the vertical moving motor, is collectively referred to as the plate discharge drive means126.

As shown inFIGS. 1,10, and11, the sheet supply unit30includes the sheet supply tray35, a sheet supply roller33, a separation member34, a sheet size detection sensor117, a pair of resist rollers31a,31b(hereafter referred to as the “pair of resist rollers31”), and so on. The sheet supply tray35is capable of moving vertically, and stacks sheets36so that they can be dispensed. The sheet supply roller33and separation member34as sheet supply means contacts the sheets36on the sheet supply tray35, and separates and transports sheets36one at a time towards the nip portion of the pair of resist rollers31aand31b. The sheet size detection sensor117as sheet size detection means detects the sheet size of the sheets36. The pair of resist rollers31as resist means supplies sheets36between the outer peripheral surface of the plate cylinder1and the press roller21, at timing that is explained later.

A sheet thickness sensor79as sheet type detection means is disposed in the sheet supply path between the pair of resist rollers31and the sheet supply roller33and separation member34, to measure the thickness of sheets36. The sheet thickness sensor79has been explained for convenience in the present embodiment, and although used in modifications described later and so on, the present embodiment is explained for the case that the sheet thickness sensor79is not included.

The sheet supply tray35is raised and lowered by drive means (not shown in the drawings) that includes a sheet supply raising and lowering motor as raising and lowering means and a wire type raising and lowering mechanism, which are not shown on the drawings, or the like. In this way the top of the stacked sheets36contacts the sheet supply roller33with a predetermined pressing force (a pressing force at which sheets36can be transported). In other words, the sheet supply tray35is raised or lowered as the number of sheets decreases or increases, while the sheets36maintain contact with the sheet supply roller33with a pressing force in the range for which the sheets36can be transported. The sheet supply tray35has a structure that enables most sheet types and sheet sizes to be used. In addition, the sheet supply tray35has a structure to permit 500 or more sheets of for example A3 size (placed sideways: indicates the state viewed by a user standing to the near side relative to the plane of the paper) or A4 size sheets36to be stacked, as appropriate for the stencil printing apparatus.

A pair of side fences, which is not shown in the drawings, is disposed in the sheet supply tray35to be able to freely move in the sheet width direction perpendicular to the sheet transport direction X, so that the position of both ends of the sheets36can be determined in accordance with the sheet size.

Near the bottom of the sheet supply tray35, sheet length size detection sensors117a,117b,117c(each made from reflection type optical sensors) are disposed to detect the length of the supplied sheets36. Also, sheet width size sensors (for example, made from transmission type optical sensors coupled to the movement in the sheet width direction of the pair of side fences), which are not shown in the drawings, that detect the sheet width of the supplied sheets36are disposed in the near side and the far side relative to the plane of the paper in the drawings. The size of the supplied sheets36is detected by the sheet length detection sensors117a,117b,117c, and the sheet width size detection sensors, and hereafter these sensors are collectively referred to as the sheet size detection sensor117.

The sheet supply roller33is formed integrally with a sheet supply roller shaft33a, as shown inFIGS. 1 and 11. One end of the sheet supply roller shaft33ais rotatably supported on a side plate of the main body frame. At least the surface of the sheet supply roller33is made from a high frictional resistance material, such as rubber. A toothed sheet supply roller pulley39is installed on one end of the sheet supply roller shaft33a. A one way clutch (not shown on the drawings) is disposed between the sheet supply roller shaft33aand the sheet supply roller pulley39, in order that the sheet supply roller33is rotated so that sheets36are only transported in the sheet transport direction X. The separation member34is formed from a material with a high coefficient of friction with sheets36, such as rubber or resin, or the like. The separation member34includes a member referred to as the separation pad, that is capable of contacting the sheet supply roller33. The sheet supply roller33is pressed by impelling means such as a compression spring, which is not shown in the drawings, against the separation pad.

The sheet supply motor37as sheet supply drive means drives the rotation of the sheet supply roller33, and is disposed below the sheet supply roller pulley39and fixed to a side plate of the main frame. The sheet supply motor37is for example a stepping motor, on the output shaft of which a toothed sheet supply motor pulley38is fixed. A toothed sheet supply motor belt40is wound between the sheet supply roller pulley39and sheet supply motor pulley38. In this way, a rotation drive power transmission relationship is formed between the sheet supply roller33and the sheet supply motor37, via the sheet supply motor belt40and the one way clutch.

As shown inFIGS. 1 and 11, the upper resist roller31ais formed integrally with a resist roller shaft, and the lower resist roller31bis formed integrally with a resist roller shaft31c. Both ends of each resist roller shaft31care rotatably supported on the side plates of the main body frame. A toothed resist roller pulley43is installed on one end of the lower resist roller shaft31c. The lower resist roller31bis supported by the side plates of the main body frame via the resist roller shaft31cso that the lower resist roller31bcan freely rotate but not move. The upper resist roller31acan contact and be separated from the lower resist roller31bat predetermined timings via resist roller contact and separation means, which is not shown in the drawings.

The resist motor41as resist drive means is fixed to a side plate of the main body frame, is provided below the lower resist roller31b, and drives the rotation of the pair of resist rollers31. The resist motor41is for example a stepping motor, and a toothed resist motor pulley42is fixed to the output shaft. A toothed resist motor belt44is fitted between the resist roller pulley43and the resist motor pulley42. In this way, a rotation drive power transmission relationship is formed between the lower resist roller31band the resist motor41, via the resist motor belt44.

InFIG. 1, a sheet detection sensor32as sheet detection means is disposed in the sheet transport path XA from between the plate cylinder1and the press roller21, to the nip portion of the pair of resist rollers31. The sheet detection sensor32detects the leading edge and trailing edge of sheets36dispensed from the pair of resist rollers31. The sheet detection sensor32has the function of detecting jams of sheets36in the sheet transport path XA upstream of the installation position (the position where the leading edge of the sheets36can be detected) of the sheet detection sensor32. The sheet detection sensor32is a reflection type optical sensor.

InFIG. 14, the drive means subject to control of the sheet supply unit30that includes the sheet supply tray raising and lowering motor of the sheet supply unit30, the sheet supply motor37, and the resist motor41is collectively referred to as sheet supply drive means125.

As shown inFIG. 12, the image reading unit18includes the document receiving platform134, the contact glass135, a pair of document transport rollers136, a document transport roller137, guide plates138,139, a plurality of document transport belts140, a document tray141, a pressure plate142, reflection mirrors143,144, a fluorescent light145, a lens146, and an image sensor147. A plurality of sheets of document133is stacked in the document receiving platform134. The contact glass135is a reading unit on which documents133are loaded. The pair of document transport rollers136and the document transport roller137transport the documents133. The guide plates138,139guide the documents133being transported. The plurality of document transport belts140transport the documents133along the contact glass135. The document tray141stacks documents133that have been read. The pressure plate142can be opened and closed with respect to and separated from the contact glass135, and supports each member that has been mentioned, except the contact glass135. The reflection mirrors143,144, and the fluorescent light145are used for scanning and reading the documents133while the image is lit. The lens146focuses the reflected light from the scanned and read image. The image sensor147includes a charge coupled device (CCD) that carries out a photoelectric conversion process on the focused reflected light from the image.

In the configuration described above, the document receiving platform134, the pair of document transport rollers136, the document transport roller137, the guide plates138,139, the document transport belts140, and the document tray141constitute an automatic document feeding device (hereafter referred to as the “ADF”)148as automatic document feeding means that transports documents133one sheet at a time onto the contact glass135(the reading unit). Also, the contact glass135, the reflection mirrors143,144, the fluorescent light145, the lens146, and the image sensor147constitute a scanner device132as document reading means that reads images of the documents133on the contact glass135(the reading unit). Also, the reflection mirrors143,144, the fluorescent light145, and the lens146constitute the document scanning optical system.

The pair of document transport rollers136, the document transport roller137, and the document transport belts140are driven by a document transport motor, which is not shown in the drawings. The scanner device132includes a scanner motor (not shown in the drawings) that drives the scanner device132. The image signal obtained by photoelectric conversion of the reflected light received by the image sensor147is input to an A/D conversion unit.

Document length size detection sensors149a,149b, that detect the length of transported documents133or the length in the transport direction in the drawings (left to right direction) of documents133, which are not shown in the drawings, loaded on the contact glass135, are disposed below and close to the contact glass135. Also, document width size detection sensors which are not shown in the drawings, that detect the width of transported documents133or the width from the near side to the far side relative to the plane of the paper in the drawings of documents133, which are not shown in the drawings, loaded on the contact glass135, are disposed below and close to the contact glass135. The document length size detection sensors149a,149band the document width size detection sensors detect the size of transported documents133or the size of documents133loaded on the contact glass135, and hereafter are collectively referred to as the document size detection sensor149.

The document length size detection sensors149a,149band the document width size detection sensors of the document size detection sensor149are reflection type optical sensors. The document size detection sensor149detects the outline and size of documents133and the presence or absence of documents133on the contact glass135from differences in the amount of reflection. The signal from the document size detection sensor149is input to the control device100which is described later. Based on the signal from the document size detection sensor149, the control device100determines and recognizes the document size (the size of the plate image that should be formed on the stenciled master8when the magnification factor is one). A document detection sensor131is disposed below the document receiving platform134to detect documents133remaining on the document receiving platform134. When there are no more documents133on the document receiving platform134, the document detection sensor131outputs a signal to the control device100.

InFIG. 14, the drive means subject to control of the image reading unit18, which includes the scanner motor and the document transport motor of the image reading unit18, is collectively referred to as document reading drive means128.

The detailed configuration of an operation panel173that issues commands and the like for specific operation of the double-sided stencil printing device300is explained referring toFIG. 13. The operation panel173is disposed near the image reading unit18shown inFIG. 12. The operation panel173includes on its top surface a plate making start key174, a printing start key175, a trial print key176, a continuous key177, a clear/stop key178, a numerical keypad179, an enter key180, a program key181, a mode clear key182, a print speed setting key183, a print speed display device183A made from light emitting diodes (LEDs), four direction keys184, a sheet size setting key185, a sheet type setting key186, a double-sided printing key187, a single-sided printing key188, a display device189made from a seven segment LED, a display device190made from a liquid crystal display (LCD), and so on.

The plate making start key174is pressed when the plate making operation is carried out in the double-sided stencil printing device300. When the plate making start key174is pressed, the plate making operation is carried out, after the plate discharge operation and document reading operation are carried out. Then, the plate installation operation is carried out, and the double-sided stencil printing device300enters the printing standby state. The printing start key175is pressed when the printing operation is carried out in the double-sided stencil printing device300. After the double-sided stencil printing device300enters the printing standby state and the various printing conditions have been set, printing the set number of copies is carried out by pressing the printing start key175. The trial print key176is pressed when the trial print operation is carried out in the double-sided stencil printing device300. After the various printing conditions have been set, printing a single sheet only is carried out by pressing the trial print key176.

The clear/stop key178is pressed to stop the operation of the double-sided stencil printing device300, or to clear an entered number. The numerical keypad179is used for entering numerical values, and so on. The enter key180is pressed when setting a numerical value for the various settings. The program key181is pressed to register or to call up frequently used operations. The mode clear key182is pressed to clear various modes and to restore the initial condition.

The print speed setting key183is pressed when setting the printing speed prior to the printing operation. When a denser image is expected, or when the ambient temperature is low, the printing speed is set slow. When a lighter image is expected, or when the ambient temperature is high, the printing speed is set fast.

The printing speeds of the print speed display device183A and the “Print speed: speed 3” blacked out in the center portion are standard printing speeds that correspond to the normally used printing speeds. When the print speed setting key183is not pressed, the printing speed is automatically set. For example, the leftmost “Print speed: speed 1” displayed as “slow” is the slowest print speed 16 sheets per minute: 16 rpm, adjacent to this to the right the “Print speed: speed 2” is a print speed of 60 sheets per minute: 60 rpm, the “Standard print speed: speed 3” is a print speed of 90 sheets per minute: 90 rpm, to the right of this the “Print speed: speed 4” is a print speed of 105 sheets per minute: 105 rpm, and the rightmost “Print speed: speed 5” displayed as “fast” is the fastest print speed 120 sheets per minute: 120 rpm. The print speed display device183A sets the print speed by switching the print speed between 1 to 5 in five stages by pressing the print speed setting key183(the speed up key and the speed down key on the left and right) once every time, and the print speed is displayed by a light lighting up.

The four direction keys184include an up key184a, a down key184b, a left key184c, and a right key184d. These keys are pressed when adjusting the image position during image editing, or when selecting numbers or items for various settings, and so on. The sheet size setting key185is pressed when inputting the sheet size. The sheet size input using the sheet size setting key185has priority over the sheet size detected by the sheet size detection sensor117.

The sheet type setting key186is pressed when inputting the sheet type prior to double-sided printing. In the present embodiment, sheet types are classified into three types: “normal sheets” which are also referred to as standard sheets, “thin sheets”, and “thick sheets”. Furthermore, one type is selected from among the sheet types which are classified in detail corresponding to these three types. In other words, in the present embodiment, it is possible for example to select and set the sheet thickness characteristics from among the thickness and strength of the sheet from among the sheet types, by the operation of inputting using the sheet type setting key186. This is because in general, as the sheet thickness increases the strength tends to increase.

Thin sheets include groundwood paper, and high quality 45 kg paper, and so on; normal paper (standard paper) includes copier paper, medium quality paper, high quality 55 kg paper, recycled paper, stencil high quality paper, and so on. Thick paper includes drawing paper, postcard, envelope, high quality 135 kg paper, high quality 180 kg paper, and so on.

The double-sided printing key187is pressed before pressing the plate making start key174when carrying out double-sided printing operations in the double-sided stencil printing device300. When the double-sided printing key187is pressed the LED187adisposed close to the double-sided printing key187lights up, indicating that the double-sided printing mode has been set. The single-sided printing key188is also pressed before pressing the plate making start key184when carrying out single-sided printing operations in the double-sided stencil printing device300, similar to the double-sided printing key187. When the single-sided printing key188is pressed the LED188adisposed close to the single-sided printing key188lights up, indicating that the single-sided printing mode has been set. In the double-sided stencil printing device300, after a power switch which is not shown in the drawings is turned on, the LED188alights up in the initial condition, indicating that the single-sided printing mode has been set.

The display device189mainly displays numbers such as the number of sheets printed, and so on. The display device190has a layered display structure. By selecting and pressing selection setting keys190a,190b,190c,190dprovided below the display device190, it is possible to adjust the magnification or image position, and so on, change various modes, and carry out settings in each mode. Also, when the sheet type setting key186is pressed, the sheet types that can be selected and set are displayed in the display device190. Also, the status of the double-sided stencil printing device300is displayed in the display device190, such as “plate making and printing can be carried out” as shown inFIG. 13. In addition warnings regarding plate making or plate making jams, or sheet supply or sheet discharge jams, and so on, and notifications regarding supply of sheets, masters, ink, and other supplies are displayed in the display device190.

When the sheet type setting key186is initially pressed one time, the sheet types that can be selected and set are displayed in the display device190as thin sheets: groundwood paper, high quality 45 kg paper, and so on, normal paper: copier paper, medium quality paper, high quality 55 kg paper, recycled paper, stencil high quality paper, and so on, and thick paper: drawing paper, postcard, envelope, high quality 135 kg paper, high quality 180 kg paper, and so on. Therefore, when the sheet is selected and specified using the four direction keys184, the selected and specified sheet is displayed in the display device190with black and white reversed, and when finally the enter key180is pressed the setting is confirmed. Therefore, in this example the sheet type setting key186, the enter key180, and the four direction keys184constitute sheet type setting means for setting the sheet type.

The sheet type setting means is not limited to the above combination of keys. For example, numeric keys may be allocated to the sheet types that can be selected and set, or the function may be allocated to the selection and setting keys190athrough190d.

Next, the main control configuration of the double-sided stencil printing device300is explained with reference toFIG. 14. InFIG. 14, the control device100has the function and constitution as means to control mainly the document reading operation, plate making and plate supply operation, the sheet supply operation, and the printing operation in the double-sided stencil printing device300. The control device100includes a microcomputer that includes a CPU101(central processing unit), an I/O (input/output) port which is not shown in the drawings, a ROM102(read only memory device), a RAM103(random access memory device), and a timer or similar that is backed up by a battery or similar, which are not shown in the drawings, connected together with a signal bus which is not shown in the drawings.

The control device100is provided on a control board within the main body frame130, as shown inFIG. 1. The CPU101of the control device100(hereafter simply referred to as the “control device100” to simplify the explanation) controls the operation of the double-sided stencil printing device300by controlling the operations of the main motor20of the printing unit16, the stepping motor252of the printing pressure range variation means28, the solenoid62of the latching means64, the plate making unit15, the sheet supply unit30, the plate discharge unit17, the sheet discharge unit19, each drive means subject to control provided in the image reading unit18, the press roller drive motor55provided in the sheet re-supply means45, the suction fan109of the sheet re-supply transport device104, the belt drive motor105, the solenoid73, the solenoid47of the switching guide46, and the drive motor94provided in the moving means87, based on various signals from the operation panel173, detection signals from various sensors provided within the main body frame130, operation programs called up from the ROM102, and related data. Also, the control device100determines the rotational position of the plate cylinder1and the printing speed, and so on, based on various plate cylinder positional signals from that which is collectively indicated as the plate cylinder position detection sensor29inFIG. 14.

The overall operation program for the double-sided stencil printing device300and necessary related data are recorded in advance in the ROM102. This operation program is called up by the CPU101as appropriate. The related data includes related data set for each printing speed for sheet types including thicknesses of sheets36and rotation speed (in other words, the transport speed as the linear speed of the transport belts108) of the belt drive motor105of the sheet re-supply transport device104, related data set for each printing speed for sheet types, and stoppage timing of the belt drive motor105after contact of the leading edge of the sheet36athat has been printed on the front side with the stopper surface53a. This related data is for example obtained in advance by testing or the like, and recorded in the ROM102in a data table for varying the transport speed of the transport belt108for each printing speed and in accordance with the sheet type, or a data table for varying the stop timing of the belt drive motor105for each printing speed in accordance with the sheet type similarly obtained in advance by testing or the like.

For example, in the case of weak sheets36whose thickness is small, such as groundwood paper, compared with thick paper or similar which is heavier, the sheet mass is lighter and there is little slippage relative to the transport belt108. Therefore, the transport speed is set taking into account the transport stop timing of the transport belts108, which is explained later. In other words, when the sheet36athat has been printed on the front side is released from the movable guide81, and the leading edge of the sheet36ais brought into contact with the stopper surface53aof the stopper member53and stops on account of the transport belts108, the subsequent waiting time until the sheet36ais transported at a predetermined timing by the sheet re-supply resist roller51is minimized.

If the sheet36is light and thin, the transport stop timing of the transport belt108is set on the early side. Conversely, if the sheet36is heavy and thick, the transport speed is set higher in anticipation of slippage relative to the transport belt108, and the transport stop timing is set on the late side.

Besides the ROM102, it is possible to use a programmable PROM, or the like. In this way, if it becomes necessary due to design changes or similar, the related data can be read in.

The RAM103has the function of temporarily storing calculation results of the CPU101, and the function of storing at any time settings and input data from the various keys of the operation panel173and the various sensors, and ON and OFF signals.

The control device100determines the rotational speed of the plate cylinder1when necessary, based on plate cylinder position signals from the plate cylinder position detection sensor29. In addition, the control device100determines the rotational position (rotation phase position) of the plate cylinder1in real time.

The control device100varies the transport speed of the transport belts108of the sheet re-supply transport device104, in accordance with the sheet type. In addition, the control device100has the function as control means for varying the transport stop timing of the transport belts108after contact of the leading edge of the sheet36athat has been printed on the front side with the stopper member53. The transport operation of the transport belts108of the sheet re-supply transport device104includes transport until the sheet36acontacts the stopper member53, and transport when sheet re-supply starts and the sheet is removed from the stopper member. The transport speeds should be set separately for these two transport operations in accordance with the sheet type.

In other words, the control device100has the function as control means to control the belt drive motor105to vary the transport speed of the transport belts108of the sheet re-supply transport device104, in accordance with the sheet type selected and set using the sheet type setting key186, the enter key180, and the four direction keys184. In addition, the control device100has the function to control the belt drive motor105to vary the transport stop timing of the transport belts108after contact of the leading edge of the sheet36athat has been printed on the front side with the stopper member53a, in accordance with the sheet type selected and set using the sheet type setting key186, the enter key180, and the four direction keys184.

In further detail, based on the sheet type data signal associated with the sheet type selected and set using the sheet type setting key186, the enter key180, and the four direction keys184, the control device100has the function as control means to call up from the ROM102a data table for varying the transport speed of the transport belts108set in accordance with the sheet type for each printing speed, a data table for varying the stop timing of the belt drive motor105, and a data table for varying the drive start timing of the transport belts108when re-supplying sheets. By extracting the rotational speed of the belt drive motor105and the stop timing after contact of the sheet36athat has been printed on the front side with the stopper surface53a, in accordance with the sheet type, the belt drive motor105is controlled so that the transport speed of the transport belts108corresponds with that for the selected and set sheet type, and the transport stop timing of the transport belts108corresponds with that for the selected and set sheet type.

Based on the configuration described above, the operation including the operating sequence of the double-sided stencil printing apparatus300according to the present embodiment is explained with reference toFIGS. 1 through 14. This operation is carried out under the control of the control device100. Therefore, when explaining the detailed operation of the various motors, solenoids, actuators, and so on, including start up, operation, and stopping, expressions to the effect that these operations are based on instructions or command signals from the control device100have been omitted as much as possible.

OPERATION EXAMPLE 1

First, operation example 1 is explained, in which the single-sided printing mode is set and single-sided printing is carried out. Operation example 1 is virtually the same as the operation of carrying out single-sided printing in a conventional stencil printing apparatus. Also, the operation is substantially the same as carrying out single-sided printing as disclosed in Prior Art 7, so the explanation is simplified. In the single-sided printing operation, printing pressure range pattern III is used, and for normal printing the cam plate243A from among the constituent elements of the printing pressure range variation means28is selected and used. For ease of understanding each operation in operation example 1, the master size is A3 size, and the document and sheet sizes are also A3 size.

The user stacks A3 size sheets36as the sheet size to be used for printing, in the sheet supply tray35. The pressure plate142is opened, the A3 size document that is to be printed is loaded on the contact glass135, and again the pressure plate142is closed. Then, after setting the plate making conditions with various keys on the operation panel173, the single-sided printing key188is pressed to set the single-sided printing mode.

After the user confirms that the single-sided printing mode is set from the LED188a, the plate making start key174is pressed. When the plate making start key174is pressed, the sheet size detection signal from the sheet size detection sensor117, and the document size detection signal from the document size detection sensor149are sent to the control device100. The control device100compares the signals received. In this case, if the sheet size and the document size are the same, the image reading operation is immediately carried out. If the sheet size and the document size are different, the control device100displays a warning to this effect on the display device190, to bring this fact to the attention of the user.

In the single-sided printing mode, the switching guide46is maintained static in the home position which is the first displacement position (initial position) shown inFIG. 1and elsewhere. When the plate making start key174is pressed, a start signal is generated, and when this start signal is input to the control device100the series of operations from plate discharge to sheet discharge is automatically carried out. Before and after this, the sheet supply tray35is raised when the sheet supply tray raising and lowering motor is turned on. When the uppermost sheet36contacts the sheet supply roller33, the control device100determines from the ON detection of a sheet supply position detection sensor, which is not shown in the drawings, that the uppermost sheet36is in the state that it can be supplied, and the sheet supply device30enters the sheet supply standby state.

First, the plate discharge operation, in which the used master is separated from the outer peripheral surface of the plate cylinder1is carried out in the plate discharge unit17. When the start signal is input to the control device100, the plate cylinder1starts to rotate. When the plate cylinder1reaches the home position in which the clamper7is virtually at the top, operation of the main motor20stops, and the plate cylinder1stops in the plate discharge position. Next, the plate discharge drive means126operates, and each roller164,167are driven to rotate. In addition, the lower plate discharge member161is moved towards the plate cylinder1, and the endless belt169positioned on the outer peripheral surface of the driven roller168contacts the used master. After the operation of the plate discharge drive motor126, the main motor20starts up, and the used master is separated from the plate cylinder1and taken and transported between the lower plate discharge member161and the upper plate discharge member160by the rotation of the plate cylinder1and the movement of the endless belt169. After the separated used master has been disposed into the plate discharge box162, the separated used master is compressed by the compression plate163.

After the used master has been completely separated from the outer peripheral surface of the plate cylinder1, the plate cylinder1continues to rotate, and stops rotating at the plate supply standby position, when the clamper7is in virtually the topmost position. Simultaneously the clamper7is opened by the operation of an opening device, which is not shown in the drawings, and the double-sided stencil printing apparatus300enters the plate supply standby state.

In parallel with the plate discharge operation, the operation of reading the document image is carried out in the document reading unit18. Reading the document image is carried out by reflecting the reflected light of the fluorescent light145by the reflection mirrors143,144, and after the reflected light from the read document image is focused by the lens146, the light is input to the image sensor147and photoelectric conversion is carried out. The photoelectric converted electric signal is input to an A/D conversion device, which is not shown on the drawings, within the main body frame130. Then the signal is transmitted to a thermal head drive circuit, which is not shown on the drawings, via a plate making control device (which may be disposed within the control device100), which is not shown on the drawings.

The plate making operation is carried out in the plate making unit15, partially in parallel with the plate discharge operation and the image reading operation. In other words, the digital image signals for heating drive control of the heating elements of the thermal head11are transmitted to the thermal head11via the plate making control device and the thermal head drive circuit. In this way, the heating elements in the thermal head11are selectively heated by electrification with pulses in the main scanning direction. In this way the thermoplastic resin film portion of the master8is selectively thermally stenciled in accordance with the image information, while the platen roller9and the pair of transport rollers13start to rotate as a result of rotational drive from the master drive motor10, and the master8is fed out from the master roll8aand transported in the master transport direction X1.

Then the leading edge of the stenciled master8Y is guided by the master guide plate14and inserted between the clamper7which is open relative to the stage6. When the number of steps of the master transport motor10reaches a predetermined value, it is determined that the leading edge of the stenciled master8Y has arrived between the stage6and the clamper7. Then the clamper7is closed by the opening and closing device, and the leading edge of the stenciled master8Y is fixed and held between the stage6and the clamper7.

After clamping the leading edge of the stenciled master8Y, the plate cylinder1starts to rotate again due to the rotational drive of the main motor20, with a circumferential speed that is virtually the same as the master transport speed. The stenciled master8Y is transported by the platen roller9and the pair of transport rollers13and supplied to be wound around the outer peripheral surface of the plate cylinder1. When the rotational drive of the master transport motor10reaches a predetermined number of steps, it is determined that the plate making on the master8and the set amount of transport of the stenciled master8Y has been completed. Therefore the cutter12is operated and the stenciled master8Y is cut. In addition, rotation of the platen roller9and the pair of transport rollers13stops as a result of the master transport motor10stopping. The trailing edge of the cut stenciled master8Y is pulled out of the plate making unit15by the rotation of the plate cylinder1. At the stage where the stenciled master8Y is fully wound around the outer peripheral surface of the plate cylinder1, winding the stenciled master8Y around the plate cylinder1is complete, so the plate supply operation terminates.

When winding the stenciled master8Y around the plate cylinder1is finished, the plate cylinder1again starts to rotate at a predetermined circumferential speed in the direction of the arrow shown inFIG. 1. With this the sheet supply and printing processes for the plate installation operation start. The solenoid62of the latching means64is maintained off by the control device100until the leading edge of the sheet36intercepts and passes the sheet detection sensor32, in other words, until the leading edge of the sheet36is detected by the sheet detection sensor32. Therefore, the printing pressure range variation means28is in the non-operational state, and as a result the press roller21is maintained in the non-printing position, in other words, the initial position separated from the outer peripheral surface of the plate cylinder1.

The plate cylinder1rotates at low speed in the direction of the arrow. First, the sheet supply start light shield plate121engages with the sheet supply resist sensor120, as shown inFIG. 10, the sheet supply resist sensor120turns on, and generates a sheet supply start signal. Using this signal as a trigger, the sheet supply motor37starts up (starts to drive and rotate). As a result of the rotation of the sheet supply motor37in the clockwise direction ofFIG. 11, the sheet supply roller shaft33aand the sheet supply roller33rotate in the clockwise direction via the operation of the mechanism shown inFIG. 11. The uppermost sheet36in the sheet supply tray35in contact with the sheet supply roller33is transported and separated as a single sheet by the cooperative action with the separating member34, and transported towards the nip portion of the pair of resist rollers31downstream in the sheet transport direction X.

Next, the plate cylinder1rotates further in the direction of the arrow inFIG. 1. When the resist start light shield plate122engages with the sheet supply resist sensor120, the sheet supply resist sensor120turns on and generates a resist start signal. Using this signal as a trigger, the resist motor41starts up. The timing of the start up of the resist motor41, in other words the timing of driving the rotation of the lower resist roller31b, is set so that it is the specific timing that the leading edge of the image area of the single-sided stencil image8YA of the stenciled master8Y in the direction of rotation of the plate cylinder1reaches the position corresponding to the press roller21.

The resist motor41is driven to rotate in the counterclockwise direction inFIG. 11, and rotate the lower resist shaft31cand the lower resist roller31bin the counterclockwise direction via the operation of the mechanism shown inFIG. 11. The leading edge of the sheet36that contacts and is on standby at the nip portion of the pair of resist rollers31is transported while being pressed against by the upper resist roller31a, and is transported between the plate cylinder1and the press roller21.

Next, when the leading edge of the sheet36propelled forward by the pair of resist rollers31has normally penetrated, in other words, when the leading edge of the sheet36has been detected by the sheet detection sensor32within a predetermined time measured by the timer (or within a predetermined number of pulses provided by the resist motor41), this signal is input to the control device100. Based on the detection signal of the leading edge of the sheet36from the sheet detection sensor32and rotational position information of the plate cylinder1from the plate cylinder position detection sensor29, the control device100outputs a command signal to electrify the solenoid62of the latching means64. As a result the solenoid62is turned on, and the cam plate243A of the printing pressure range variation means28is operated.

As a result of turning the solenoid62on, the plunger62ais pulled in, and the latching member60is swiveled in the counterclockwise direction about the support shaft61, against the resistance of the impelling force of the tension spring63. When the latch is released, the second end of the printing pressure arm22which is latched to the latching claw60aby the notch22bswivels in the clockwise direction about the arm shaft22aby the impelling power of the printing pressure spring242. As a result of the second end of the printing pressure arm22swiveling, the outer peripheral surface of the cam follower241comes into opposition with but without contacting the peripheral surface of the small diameter portion of the cam plate243A which rotates in synchronization with the rotation of the plate cylinder1. The pair of printing pressure arms22swivel in the clockwise direction about the arm shaft22aand rise up as a result of the impelling force of the printing pressure spring242at the rotation position (for example, the rotation position shown inFIG. 3) of the cam plate243A.

In this way, as shown inFIG. 9, the outer peripheral surface of the press roller21displaces to the printing position and applies printing pressure to the sheet36to press against the leading edge blank portion slightly to the left of the single-sided stencil image8YA of the stenciled master8Y wound around the front side area1A through to the reverse side area1B of the plate cylinder1as shown inFIG. 1, to form the nip portion16a(see for exampleFIG. 3). At the same time, the press roller drive motor55rotates the press roller21with a circumferential speed that is virtually the same as the circumferential speed of the plate cylinder1. The press roller21continuously presses the sheet36against the stenciled master8Y on the plate cylinder1while rotating in the opposite direction to the direction of rotation of the plate cylinder1. The stenciled master8Y is closely wound around the outer peripheral surface of the plate cylinder1, so ink fills the stenciled master8Y, or so-called installation of the master is carried out. In this process, ink penetrates from the porous portion1aof the plate cylinder1to the perforated portions of the stenciled master8Y, and is transferred onto the surface of the sheet36so that stencil printing is carried out.

At this time, the ink roller2rotates in the same direction as the direction of rotation of the plate cylinder1. The ink in the ink pool4adheres to the surface of the ink roller2due to the rotation of the ink roller2, and is regulated when it passes through the gap between the ink roller2and the doctor roller3, and supplied to the inner peripheral surface of the plate cylinder1. On the other hand, the sheet re-supply transport device104, coupled with the rising and lowering action of the press roller21, swivels about the drive shaft107avia the sheet re-supply frame110. In the single-sided printing mode, the belt drive motor105and the suction fan109of the sheet re-supply transport device104do not operate. In addition, the drive motor94of the moving means87does not operate, and the movable guide81occupies the initial position P2.

In this way, printing of the single-sided stencil image8YA of the stenciled master8Y on the plate cylinder1is carried out. The plate cylinder1rotates further, and at the trailing edge blank portion slightly to the right of the trailing edge of the single-sided stencil image8YA, the large diameter portion of the cam plate243A which rotates in synchronization with the plate cylinder1contacts the outer peripheral surface of the cam follower241. In this way, the pair of printing pressure arms22swivel about the arm shaft22ain the counterclockwise direction against the resistance of the impelling force of the printing pressure spring242. In addition, the press roller21is displaced downwards to occupy the non-printing position, and the state of applying printing pressure by the press roller21is eliminated.

As the plate cylinder1rotates in the direction of the arrow inFIG. 1, when the clamper7approaches the position where the press roller21is in contact with the plate cylinder1, the cam plate243A which rotates in synchronization with the rotation of the plate cylinder1rotates to the position where the peripheral surface of the large diameter portion of the cam plate243A contacts the cam follower241. Therefore, the press roller21separates from the clamper7which projects from the outer peripheral surface of the plate cylinder1, and interference between the press roller21and the clamper7is avoided.

The single-sided printed sheet36cis further transported by the rotation of the plate cylinder1in the direction of the arrow inFIG. 1, while being pressed by the press roller21. The leading edge of the single-sided printed sheet36cis positively separated from the stenciled master8Y on the plate cylinder1by the separation claw170which is close to the outer peripheral surface of the plate cylinder1and by the air blown from the separation fan171. The separated single-sided printed sheet36cdrops downwards and is transported by the sheet discharge belt158of the sheet discharge transport device152. The single-sided printed sheet36cis held by the suction force of the suction fan159on the top surface of the sheet discharge belt158which rotates in the direction of the arrow inFIG. 1(the counterclockwise direction) and is transported downstream in the sheet transport direction X. The single-sided printed sheet36cis then discharged into the sheet discharge tray172while being arranged on both sides by a pair of sheet discharge end fences172a,172b.

On the other hand, when the plate cylinder1has rotated through about ¾ of a revolution from the time of contact of the press roller21with the plate cylinder1, when the large diameter portion of the peripheral surface of the cam plate243A contacts the cam follower241, in other words at the time when the latching claw60aand the notch22bof the printing pressure arm22can be latched together, electrical power to the solenoid62is turned off by a command from the control device100. Then the latching member60swivels in the clockwise direction about the support shaft61due to the impelling force of the tension spring63, and the latching claw60ais latched onto the notch22bof the printing pressure arm22. In this way, the press roller21is restored to and maintained at the non-printing position where it is separated from the outer peripheral surface of the plate cylinder1. In addition, the plate cylinder1rotates again to the home position, and stops. After completion of the printing operation, the double-sided stencil printing apparatus300enters the printing standby status.

Also, during the sheet supply and installation of the master operations, the platen roller9and the pair of transport rollers13start to rotate again, and transport the leading edge of the cut master8is transported towards the nip portion of the pair of transport rollers13. When it is determined from the number of pulses of the master transport motor10that the leading edge of the cut master8has arrived at and is held in the nip portion of the pair of transport rollers13, rotation of the platen roller9and the pair of transport rollers13is stopped, the plate making standby state in preparation for the next plate making operation is established.

After the double-sided stencil printing apparatus300enters the printing standby state, the printing conditions are set with the printing speed setting key183and various other keys on the operation panel173. Then the trial print key176is pressed to carry out a trial print. When the trial print key is pressed, the plate cylinder1is driven to rotate at the set printing speed, and one sheet36is supplied from the sheet supply unit30. After the supplied sheet36is temporarily stopped at the pair of resist rollers31, the sheet36is supplied at the same timing as for the installation of the master operation, and pressed against the stenciled master8Y on the outer peripheral surface of the plate cylinder1by the press roller21. The single-sided printed sheet36con which the printed image is formed is positively separated from the stenciled master8Y on the plate cylinder1by the separation claw170and the separation fan171, the same as described above. The separated single-sided printed sheet36cis transported by the sheet discharge transport device152with the same operation as described above, and discharged into the sheet discharge tray172.

With the setting of the printing speed, the speed or timing of drive means subject to control such as the drive motors or solenoids in the printing pressure range variation means28, the sheet supply unit30, the sheet discharge transport device152, and so on, are controlled to be compatible with the printing speed. Using the trial print, the image position, the density, and so on, are checked. Then the number of sheets to be printed is input using the numerical keypad179, and the print start key175is pressed. Then sheets36are continuously fed from the sheet supply unit30, and the printing operation is carried out the same as the trial print operation. Then, when the set number of printed sheets is used, the plate cylinder1stops at the home position, and the double-sided stencil printing apparatus300again enters the printing standby state. In normal printing operations, the main differences compared with the printing operation when installing the master are only that the number of sheets36used in printing when installing the master are not counted as normal printed sheets, and each operation such as sheet supply and printing is carried out at a speed corresponding to the printing speed set by the user.

Sheet detection means equivalent to the sheet detection sensor32described above may be disposed on the transport path to detect the leading edge and the trailing edge of the sheets36cthat have been printed on the front side and being held on the outer peripheral surface of the press roller21and being transported through the nip portion16a. Besides the operation described above, the reading operation in the image reading unit18may also use the ADF148. In this case the point of difference from operation example 1 is only the following point. The user sets the A3 size document133in the document receiving platform134of the ADF148. Then in parallel with the plate discharge operation the ADF148of the image reading unit18transports one sheet of the document133to the contact glass135which is the reading unit. Thereafter the image of the document133is read as optical information by the operation of the scanner device132, as described above.

OPERATIONS EXAMPLE 2

Next, operation example 2 in which the double-sided printing mode is set and double-sided printing is carried out is explained. Operation example 2 uses all the printing pressure ranges I, II, III shown inFIG. 9. For this purpose all the cam plates243A,243B,243C of the multi-stage cam243that forms one element of the printing pressure range variation means28are used. In operation example 2, for ease of understanding each operation, the master size is A3 size, but the document size and the sheet size is A4. Hereinafter, explanation mainly on features different from those of the operation example 1 is provided. The user stacks A4 size sheets36in the sheet supply tray35, for use in printing. The pressure plate142is opened, the first A4 size document to be printed on the front side is placed on the contact glass135, and the pressure plate142is closed again. Then, the user presses the sheet type setting key186of the operation panel173, and all the sheet types that are used in the double-sided stencil printing apparatus300are displayed in the operation panel173. Then using the four direction keys184, for example “groundwood paper” which is classified as a thin paper is selected as the sheet type to be used in double-sided printing, and is displayed with black and white reversed. Finally the enter key180is used to confirm the selection. Further, after setting the plate making and printing conditions using various keys on the operation panel173, the double-sided printing key187is pressed to set the double-sided printing mode. Then, the user confirms that the double-sided printing mode has been set from the LED187a. Next, the plate making start key174is pressed, and a start signal is generated and input to the control device100, the same as for single-sided printing.

As in operation example 1, the sheet size detection signal from the sheet size detection sensor117, and the document size detection signal from the document size detection sensor149are transmitted to the control device100. The control device100compares the two signals received. In the present embodiment, the maximum sheet size that can be printed with the plate cylinder1during single-sided printing is A3 size in landscape format. Therefore, in double-sided printing up to A4 size sheets can be used in portrait format.

If the result of the comparison is that the document size and the sheet size are both the same, the image reading operation is immediately carried out. If the two sizes are different, the control device100displays a warning to this effect on the display device190, to bring this fact to the attention of the user. In cases where the sheet size is larger than the A4 size in portrait format, the control device100prohibits double-sided printing and induces the display device190to display to the effect that single-sided printing is required.

When the plate making start key174is pressed, the series of operations from plate discharge to sheet discharge is carried out, similar to operation example 1. As in operation example 1, when the control device100determines that the topmost sheet36in the sheet supply tray35is in the state where it can be supplied, the sheet supply unit30enters the sheet supply standby state. After completion of the plate discharge operation similar to operation example 1, the plate cylinder1from which the used master has been removed stops in the plate supply standby position, and the clamper7is opened by the opening and closing device which is not shown in the drawings, the same as for operation example 1.

The operation of reading the document image of the first sheet for printing on the front side is carried out in the image reading unit18, partially in parallel with the plate discharge operation, as in operation example 1. The image data signal is transmitted to the thermal head drive circuit via the plate making control device or similar. The plate making operation is carried out in the plate making unit15by the thermal head11as in operation example 1, partially in parallel with the image reading operation. The master8is drawn out from the master roll8aby the rotation of the platen roller9and the pair of transport rollers13, and transported in the master transport direction X1. At the same time the thermoplastic resin film portion of the master8is selectively stenciled by heating in accordance with the image information, and the front side stenciled image8A for printing on the front side is formed on the front half portion of the master8(see the sub-divided stenciled master8X shown inFIG. 9).

Then, the leading edge portion of the sub-divided stenciled master8X is guided by the master guide plate14, and inserted between the clamper7which is open with respect to the stage6. When the number of steps of the master transport motor10reaches a predetermined value, it is determined that the leading edge portion of the sub-divided stenciled master8X has arrived between the stage6and the clamper7. Then the clamper7is closed by the opening and closing device, and the leading edge portion of the sub-divided stenciled master8X is fixed and held between the stage6and the clamper7.

After the leading edge portion of the sub-divided stenciled master8X is clamped, the main motor20starts up and the plate cylinder1again starts to rotate at a circumferential speed that is virtually the same as the master transport speed. The sub-divided stenciled master8X is transported by the platen roller9and the pair of transport rollers13and supplied to be wound around the outer peripheral surface of the plate cylinder1. When the control device100determines that stenciling the front surface stenciled image8A of the sub-divided stenciled master8X as shown inFIG. 9is complete from the number of steps of the master transport roller10, rotation of the platen roller9, the pair of transport rollers13, and the plate cylinder1is stopped. Then the plate making standby state is established in which the reverse side stenciled image8B, for printing on the reverse side, is stenciled on the next sub-divided stenciled master8X.

Next, the user again opens the pressure plate142, and loads the second A4 size sheet that is to be printed on the reverse side on the contact glass135, and closes the pressure plate142again. Then, the plate making start key174is pressed again, and a start signal is generated and input to the control device100. At this time, similar to the case for the first sheet of the document, the document size and the sheet size are compared by the control device100, and the same operation is carried out as described above. In the image reading unit18, the reading operation for the document image for the second document image for printing on the reverse side is carried out the same as for the first sheet of the document. The image data signal is transmitted to the thermal head drive circuit via the plate making control device, which are not shown in the drawings. Plate making is carried out in the plate making unit15by the thermal head11, same as for the first sheet of the document. The master transport motor10starts to rotate again, and rotate the platen roller9and the pair of transport rollers13, which draws the master8out of the master roll8aand transports it in the master transport direction X1. The thermoplastic resin film portion of the master8is selectively stenciled by heating in accordance with the image information, and the reverse side stencil image8B for printing on the reverse side is formed on the rear half of the master8(seeFIG. 9).

At this time, the plate cylinder1starts to rotate again at virtually the same circumferential speed as the master transport speed, drawing the rear half of the sub-divided stenciled master8X from within the plate making unit15to be wound around the outer peripheral surface of the plate cylinder1. Also, when it is determined by the control device100from the number of steps of the master transport motor10that stenciling of the final reverse side stencil image8B of the sub-divided stenciled master8X has been completed, the cutter12is operated, and the trailing edge portion of the sub-divided stenciled master8X is cut. In addition, rotation of the platen roller9and the pair of transport rollers13is stopped, and the trailing edge of the sub-divided stenciled master8X which has been cut to provide one plate master is completely pulled out from the plate making unit15by the rotation of the plate cylinder1, and the operation of winding and providing the sub-divided stenciled master8X onto the plate cylinder1is completed.

The operations of reading the document image and inputting the image data are not limited to the example described above. For example, the document133can be automatically fed to the contact glass135by the ADF148, or image data can be input from an external device which is not shown on the drawings.

In the present embodiment, when stenciling of the front side stenciled image8A of the sub-divided stenciled master8X is completed, rotation of the platen roller9and the pair of transport rollers13in the plate making unit15and the plate cylinder1is temporarily stopped, and the plate making standby state is entered for stenciling the reverse side stenciled image8B in the sub-divided stenciled master8X for printing on the reverse side. However, the following is preferable. In addition to an operation to automatically transport the document133by the ADF148, the second sheet of the document is scanned in advance, and image memory such as bit map memory or the like, which is not shown on the drawings, is provided to record and store the image data of the document image that was read. The image data for the first and second sheets of document is recorded and stored in the image memory. Plate making is then continuously carried out while calling up the image data in sequence from the image memory. This is preferable because the plate making time is shortened, which shortens the first print time (FPT).

After the plate supply operation, the operation of installation of the master is carried out. When the plate cylinder1stops at the home position, the control device100operates the printing pressure range variation means28. In the following, when carrying out installation of the master corresponding to the front side stenciled image8A of the sub-divided stenciled master8X on the plate cylinder, or carrying out the first front side printing in the formal double-sided printing operation, the printing pressure range variation means28is controlled by instructions from the control device100to select the printing pressure ON timing by the press roller21of the printing pressure range pattern I ofFIG. 9. In other words, a stepping motor252that is only shown inFIG. 14is rotated, and via a commonly known detailed operation via the rotation of the stepped cam (49), the cam plate243B is selected, and the outer peripheral surface of the cam plate243B is brought into contact with the cam follower241.

When winding of the sub-divided stenciled master8X onto the plate cylinder1is completed, the plate cylinder1starts to rotate in the direction of the arrow shown inFIG. 3at a predetermined circumferential speed (normally, a low speed for installation of the master). As in operation example 1, the solenoid62of the latching means64is controlled to be off until the leading edge of the sheet36is detected by the sheet detection sensor32. Therefore, the printing pressure range variation means28is not operational, and the press roller21is maintained in the non-printing position.

The plate cylinder1rotates in the direction of the arrow, the same as in operation example 1. First, the sheet supply start light shield plate121engages with the sheet supply resist sensor120as shown inFIG. 10, and the sheet supply motor37starts up. The topmost sheet36in the sheet supply tray35in contact with the sheet supply roller33is transported, and one sheet is dispensed towards the nip portion of the pair of resist rollers31by the cooperative action of the separation member34.

After the leading edge of the sheet36dispensed in this way contacts the nip portion of the pair of resist rollers31, the leading edge portion of the sheet36is maintained in a predetermined curved state. Next, the plate cylinder1rotates further in the direction of the arrow inFIG. 1. When the resist start light shield plate122engages with the sheet supply resist sensor120, the resist motor41starts up, as in operation example 1. Then the leading edge of the sheet36that was on standby in contact with the nip portion of the pair of resist rollers31is transported between the plate cylinder1and the press roller21by the rotation of the pair of resist rollers31at a predetermined timing. At this time, as in operation example 1, the normal advance of the leading edge of the sheet36by the pair of resist rollers31is detected by the sheet detection sensor32.

Next, based on the detection signal of the leading edge of the sheet36from the sheet detection sensor32and the rotational position information for the plate cylinder1from the plate cylinder position detection sensor29, the control device100turns the solenoid62on, as in operation example 1, and the printing pressure range variation means28operates the cam plate243B. By turning the solenoid62on, the detailed operation of the latching means64is carried out, as in operation example 1. The outer peripheral surface of the cam plate243B is brought into contact with the outer peripheral surface of the cam follower241. Then when the rotational position of the cam plate243B is such that the outer peripheral surface of the cam follower241is in opposition with the small diameter peripheral surface of the cam plate243B but in a non-contacting state, the pair of printing pressure arms22swivel in the clockwise direction about the arm shaft22aand rise due to the impelling force of the printing pressure spring242.

In this way, as shown inFIG. 9, the outer peripheral surface of the press roller21displaces to the printing position and applies printing pressure to the sheet36to press against the leading edge blank portion slightly to the left of the front side stencil image8A of the sub-divided stenciled master8X wound around the front side area1A of the plate cylinder1as shown inFIG. 1, to form the nip portion16a(see the printing pressure ON timing of the press roller21in the printing pressure range pattern I shown inFIG. 9). At the same time, the press roller drive motor55rotates the press roller21with a circumferential speed that is virtually the same as the circumferential speed of the plate cylinder1. The press roller21continuously presses sheets36against the front side stenciled image8A portion of the sub-divided stenciled master8X on the plate cylinder1while rotating in the opposite direction to the direction of rotation of the plate cylinder1. The front side stenciled image8A of the sub-divided stenciled master8X is closely wound around the outer peripheral surface of the plate cylinder1, so ink fills the sub-divided stenciled master8X, or so-called installation of the master occurs. In this process, ink penetrates from the porous portion1aof the plate cylinder1to the perforated portions of the sub-divided stenciled master8X, and is transferred onto the surface of the sheet36so that stencil printing is carried out.

At this time, the ink roller2rotates in the same direction as the rotation direction of the plate cylinder1, as in operation example 1. Therefore ink in the ink pool4is supplied to the inner peripheral surface of the plate cylinder1. In this way installation of the master printing is carried out corresponding to the front side stenciled image8A of the sub-divided stenciled master8X on the plate cylinder1. When the plate cylinder1rotates further and reaches the rotational position in which the portion near the trailing edge of the front side stenciled image8A is in the nip portion16a, the large diameter peripheral surface of the cam plate243B contacts the cam follower241, and the printing pressure arms22rotate in the counterclockwise direction about the arm shaft22a, and the press roller21is maintained in the state of occupying the non-printing position. At this time, the solenoid62of the latching means64is already turned off by a command from the control device100, so the press roller21is restored to and maintains the initial position which is the non-printing position.

In parallel with the installation of the master operation described above, after the clamper7of the plate cylinder1has passed the press roller21in the non-printing position, the solenoid47is turned on, and the switching guide46swivels in the counterclockwise direction about the shaft47aand stops in the second displacement position, as shown inFIG. 3. At the same time, the drive motor94of the moving means87starts up (for example, starts to drive with positive rotation). The movable guide81moves upwards to the right from the initial position P2(the standby position) to the moving position P1, guided by the four projections81cin the guide grooves88. In this way the movable guide81can clamp the leading edge of the sheet36athat has been printed on the front side, as shown inFIG. 3. When the number of steps of the drive motor94reaches a predetermined number, the movable guide81reaches the moving position P1. As shown by the solid lines inFIG. 8, the release lever lower83contacts and rises up on the outer peripheral surface of the release cam98. Therefore, the clamping claw81bis swiveled in the clockwise direction, contact with the top surface of the holding platform81fis eliminated, and the movable guide stops in the standby position.

When the movable guide81has stopped in the moving position P1, as shown inFIG. 3, the leading edge portion of the sheet36athat has been printed on the front side is positively separated from the sub-divided stenciled master8X (seeFIG. 9) on the plate cylinder1by the action of the switching guide46which is stopped occupying the second displacement position and the separation fan171(seeFIG. 1). The leading edge portion of the sheet36athat has been printed on the front side is guided by the slanting surface of the clamping claw81bprovided on the movable guide81and inserted into the gap between the top surface of the holding platform81fand the free end of the open clamping claw81b. Next, the leading edge portion of the sheet36athat has been printed on the front side butts up against and contacts the sheet contact surface81eof the end fence81d. When the leading edge portion of the sheet36athat has been printed on the front side is inserted into the gap between the top surface of the holding platform81fand the free end of the open clamping claw81b, the drive motor94starts up (for example, starts to drive with reverse rotation) with virtually the same speed as the transport speed (virtually the same as the circumferential speed due to rotation of the plate cylinder1and the press roller21) of the sheet36athat has been printed on the front side. Hence the movable guide81starts to move downwards to the left towards the initial position P2.

At this time, inFIG. 8, the release lever lower83separates from the outer peripheral surface of the release cam98, so the clamping claw81bswivels in the counterclockwise direction due to the impelling force of the torsional coil spring. Therefore, the leading edge portion of the sheet36athat has been printed on the front side is held and clamped between the free end of the clamping claw81band the top surface of the holding platform81f. The movable guide81moves downwards to the left towards the initial position P2with a speed of movement virtually the same as the transport speed of the sheet36athat has been printed on the front side, with the leading edge portion of the sheet36athat has been printed on the front side fixed and held as described above, and with the leading edge of the sheet36athat has been printed on the front side butting against the sheet contact surface81e.

As stated above, after the installation of the master printing corresponding to the front side stenciled image8A on the sub-divided stenciled master8X on the plate cylinder1is completed, the press roller21is restored to and maintained in the initial position which is the non-printing position, in the sheet supply standby state for the supply of the next sheet.

On the other hand, usingFIG. 4for explanation, the sheet36athat has been printed on the front side, held and clamped between the free end of the clamping claw81band the top surface of the holding platform81fof the movable guide81, is transported towards the initial position P2by the moving means87. When the movable guide81reaches the initial position P2and stops, this time the release lever upper82shown by double-dashed lines inFIG. 8contacts the release pin99, the clamping claw81bis swiveled in the clockwise direction, and the leading edge portion of the sheet36athat has been printed on the front side is released from being in the held and fixed state.

The rear portion of the sheet36athat has been printed on the front side is drawn to and held by the action of the sheet re-supply transport device104. At this time it is desirable that the leading edge of the sheet36athat has been printed on the front side be released from between the free end of the clamper81band the top surface of the holding platform81f, so that there be little disturbance to the sheet36athat has been printed on the front side so that the positional accuracy of the sheet36ais improved, and subsequent deviation from the printing position is maintained at a minimum.

When the trailing edge of the sheet36athat has been printed on the front side has passed the switching guide46, the solenoid47is turned off. As a result the switching guide46is swiveled by the impelling force of the tension spring about the shaft46ain the clockwise direction and restored to the first displacement position (initial position), as shown by the solid lines inFIG. 1, and stops.

In accordance with a command from the control device100, first the suction fan109of the sheet re-supply transport device104is driven. As a result the reverse side with no printed image of the sheet36athat has been printed on the front side is drawn to the top surface of the transport belts108and temporarily held there. Next, as shown inFIG. 4, the belt drive motor105is driven to rotate with a particular rotational speed corresponding to the sheet type in the opposite direction to the direction up till this point in time. Then immediately afterwards, the belt drive motor105is temporarily stopped at a particular timing corresponding to the sheet type. In other words, the rear transport roller107rotates in the clockwise direction so that the transport belts108transport the leading edge in the new direction of movement of the sheet36athat has been printed on the front side at a transport speed that corresponds with the sheet type (for example, in the present operation example, groundwood paper) to contact the stopper surface53a. Immediately after the leading edge of the sheet36athat has been printed on the front side contacts the stopper surface53a, transport is stopped at a timing that corresponds to the sheet type. The belt transport motor105is controlled so that the occurrence of bending of the leading edge portion of the sheet36athat has been printed on the front side, due to the energy with which the sheet36athat has been printed on the front side contacts the stopper surface53a, is made as small as possible.

Next, when it is determined by the control device100based on rotational position information of the plate cylinder1from the plate cylinder position detection sensor29that the plate cylinder1is in a predetermined position, the solenoid73is turned on. The predetermined position is that rotational position of the plate cylinder1at which the reverse side of the sheet36athat has been printed on the front side can be printed, corresponding to the reverse side stenciled image8B of the sub-divided stenciled master8X on the plate cylinder1. As a result the sheet re-supply resist roller51is raised towards the outer peripheral surface of the press roller21. The contact of the leading edge portion of the sheet36athat has been printed on the front side with the stopper surface53ais eliminated, and the leading edge portion of the sheet36athat has been printed on the front side is pressed against and makes contact with the outer peripheral surface of the press roller21. Also, at the same time the press roller drive motor55is driven to rotate, as shown inFIG. 2, and the press roller21is rotated in the counterclockwise direction. The sheet36athat has been printed on the front side is pressed between the press roller21which rotates in the counterclockwise direction and the sheet re-supply resist roller51which is driven by the press roller21to rotate in the clockwise direction. As a result of the rotational power of the press roller21, the sheet36athat has been printed on the front side is transported at virtually the same circumferential speed as the circumferential speed of the plate cylinder1, and guided along the outer peripheral surface of the press roller21by the roller guide plate50. The sheet36athat has been printed on the front side is then transported towards the nip portion16aformed by the contact of the plate cylinder1and the press roller21with front and reverse sides reversed.

The sheet36athat has been printed on the front side is drawn to the transport belts108with a comparatively weak force by the action of the suction fan109. Therefore, when the transport belt108stops, and when the sheet36athat has been printed on the front side which is held between the sheet re-supply resist roller51and the press roller21starts to move, frictional resistance is generated between the trailing edge portion of the sheet36athat has been printed on the front side and the transport belts108, and slippage occurs between the sheet36aand the press roller21. Therefore, it is necessary to start driving the transport belts108at appropriate timing.

Basically, it is preferable that the sheet36athat has been printed on the front side starts to move after the time that the contact between the leading edge portion of the sheet36athat has been printed on the front side and the stopper surface53ahas been eliminated. This timing is a predetermined period of time after the operation command signal of the sheet re-supply resist roller51, which is characteristic of the device, and which can be determined from tests. Alternatively, detection means may be disposed to detect the contact of the press roller21and the sheet re-supply resist roller51via the sheet36a, and the detection means may be used to start driving the transport belts108. Detection means for detecting contact could be a sensor that detects the position of the sheet re-supply resist roller51. For example, an optical sensor indicated by the reference numeral71ainFIG. 5can be made to detect a part of the swivel arm71, and adjusted so that the sensor provides an output when the sheet re-supply resist roller51arrives at the position where it contacts the press roller21.

As a general rule, the transport belts108are driven at the same speed as the circumferential speed of the plate cylinder1, however there is no particular problem if the speed is slightly faster. If the speed is too fast, too much bending occurs between the transport belts108and the sheet re-supply resist roller51, which causes creases, so about +20% is the limit. Conversely, if the transport belts108are driven slower than the circumferential speed of the plate cylinder1, the frictional resistance will be small provided that difference is small, so about −20% is permissible.

If the belt drive motor105is a stepping motor, if the printing speed is low it is possible to reach the standard speed in a comparatively short period of time. However, if the printing speed is fast, a certain amount of time is required to reach the standard time.

FIGS. 16 and 17are line diagrams showing the drive start up speed of the transport belts108.FIG. 16is a schematic diagram showing the ideal situation, whileFIG. 17is a schematic diagram showing the actually occurring speeds. In both figures the belt speed is conceptually indicated by thick lines.

In the case of the low printing speeds at 16 rpm and 60 rpm, the standard speed is reached without a delay being indicated on the graph.

In the case of the high printing speeds at 90 rpm and 120 rpm, although at 60 rpm the rise in speed is almost instantaneous, thereafter the speed increases at a virtually constant rate of acceleration until the standard speed is reached. Therefore, when the printing speed is high, if the transport belts108start to be driven at the instant that the sheet re-supply resist roller51contacts the press roller21, the movement speed of the sheet36awill not be able to catch up. Therefore, the motor is started up early by the characteristic predetermined period of time, so that at the instant that the sheet re-supply resist roller51contacts the press roller21, the transport belt will have just attained the standard speed.

If the printing speed is low, then the output of the detection means for detecting contact between the sheet re-supply resist roller51and the press roller21may be used to drive the transport belts108. However, if the printing speed is high, the rate of increase of the speed of the transport belts108will be insufficient.

In the present embodiment, it is known that the delay time from applying the operation command signal to the solenoid73for contact between the sheet re-supply resist roller51and the press roller21until actual contact occurs is about 50 ms, although there is a certain amount of variation. Therefore, in the case of high speed printing, the application of the operation command signal to the solenoid73may be used as a criterion. If the printing speed is 120 rpm, when the operation command signal is applied to the solenoid73, the transport belts108are driven after a delay of 25 ms from this criterion. In other words, the transport belts108are driven after a time lag of 25 ms. If the printing speed is 90 rpm, the transport belts108are driven after a time lag of about 38 ms after the operation command signal is applied to the solenoid73. In this way, at the instant that the sheet36astarts to move, the transport belt108is moving at virtually the same speed as the circumferential speed of the plate cylinder1. Even if the transport belt108is driven early, the sheet36ais stopped by the stopper53, so movement does not start.

The same method may also be used if the printing speed is low. In other words, if the printing speed is 16 rpm or 60 rpm, using the operation command signal to the solenoid73as a criterion, the transport belts108may be driven after a time lag of 50 ms.

The amount of variation in the operation delay time 50 ms of the solenoid73is sufficiently smaller than +20%, so there is no problem with adopting this method.

In the above explanation, an example was explained where the range over which the delay time in starting to drive the transport belts108could be ignored was 60 rpm or less. However, this range will vary depending on the type of stepping motor actually used, the constitution of the belt drive mechanism, and soon. Therefore, it is possible to start driving when contact between the sheet re-supply resist roller51and the press roller21is detected in cases where the printing speed is such that the delay time in starting to drive the transport belts108can be ignored.

Also, the time lag after applying the operation command signal to the solenoid73until driving the transport belts108varies depending on the configuration, so values measured on the actual configuration are used.

When carrying out installation of the master operation corresponding to the reverse side stenciled image8B of the sub-divided stenciled master8X on the plate cylinder1, or when carrying out the reverse side printing of the subsequent formal double-sided printing operation, the printing pressure range variation means28is controlled by the control device100so that printing pressure ON timing by the press roller21is selected in accordance with printing pressure range II shown inFIG. 9. In other words, the stepping motor252shown inFIGS. 14 and 15is rotated and via a commonly known detailed operation via the rotation of the stepped cam (49), the cam plate243C is selected, and the outer peripheral surface of the cam plate243C is brought into contact with the cam follower241.

In parallel with this transport, at a predetermined rotational position of the plate cylinder1, that is a predetermined rotational position when the leading edge portion of the reverse side stenciled image8B of the sub-divided stenciled master8X on the plate cylinder1reaches a rotational position corresponding to the nip portion16a, when the small diameter portion of the cam plate243C which rotates in synchronization with the rotation of the plate cylinder1is in opposition with the cam follower241and in the non-contacting state, the press roller21applies printing pressure to press the reverse side (the top surface inFIG. 4) of the sheet36athat has been printed on the front side slightly to the left of the reverse side stenciled image8B of the sub-divided stenciled master8X wound around the reverse side area1B of the plate cylinder1, as shown inFIG. 9. As a result of the impelling force of the printing pressure spring242the nip portion16ais formed, and double-sided printing for installation of the master is carried out (see the ON timing of the press roller21in accordance with the printing pressure range pattern II shown inFIG. 9).

In this way, ink fills the reverse side stenciled image8B of the sub-divided stenciled master8X on the plate cylinder1, and the reverse side printed image is formed on the reverse side of the sheet36athat has been printed on the front side. After the double-sided printing has been carried out, the leading edge portion of the double-sided printed sheet36bfor installation of the master is positively separated from the sub-divided stenciled master8X on the plate cylinder1by the separation claw170near the outer peripheral surface of the plate cylinder1and the air blown from the separation fan171, the same as for the single-sided printed sheet36c. The separated double-sided printed sheet36bdrops downwards onto the sheet discharge transport device152, is drawn to and held by the suction force of the suction fan159, and is transported downstream, to the sheet discharge tray172, in the sheet transport direction X on the top surface of the sheet discharge belt158which rotates in the counterclockwise direction as shown inFIG. 4.

On the other hand, when the plate cylinder1has rotated about ¾ of a revolution from the time that the press roller21has contacted the outer peripheral surface of the plate cylinder1, when the large diameter peripheral surface of the cam plate243C contacts the cam follower241, the press roller21is restored to and maintained at the non-printing position separated from the outer peripheral surface of the plate cylinder1, via the same detailed operation as for operation example 1. In addition, the plate cylinder1rotates to the home position again and stops, thereby completing the installation of the master operation, and the double-sided stencil printing apparatus300enters the standby state for the formal double-sided printing operation.

After the double-sided stencil printing apparatus300enters the printing standby state, the printing conditions are entered using the printing speed setting key183and various keys on the operation panel173. Then, the image positions or the densities or the like are checked with a trial print. After the number of printed sheets has been entered using the numerical keypad179, the printing start key175is pressed. Then sheets36are continuously supplied from the sheet supply unit30, and the double-sided printing operation is carried out for the set number of sheets as set using the numerical keypad179.

The points of difference of the formal double-sided printing operation for the set number of sheets differs basically from the installation of the master operation described above are summarized below. The other details of the operation can be easily understood and implemented by a person skilled in the art to which this patent application pertains from the installation of the master operation described above, the double-sided printing operation disclosed in Prior Art 7 through 9, and so on, so their explanation is omitted.

The first point is that each unit and device constituting the double-sided stencil printing apparatus300directly associated with operations such as sheet supply, sheet re-supply, front side printing, reverse side printing, sheet discharge, and so on, is driven with a speed corresponding to the printing speed set by the printing speed setting key183or the automatically set standard printing speed.

The second point is the belt drive motor105is controlled to rotate by a command from the control device100at the characteristic rotation speed set for each printing speed that depends on the sheet type, and then temporarily stops at the characteristic timing set for each printing speed that depends on the sheet type. In other words, the leading edge of the sheet36athat has been printed on the front side is transported at the transport speed set for each printing speed that depends on the sheet type by the transport belts108via the clockwise rotation of the rear transport roller107, to contact the stopper surface53a. Immediately after the leading edge of the sheet36acontacts the stopper surface53a, transport is stopped at the timing set for each printing speed that depends on the sheet type. In this way bending of the leading edge of the sheet36athat has been printed on the front side due to the energy of the contact between the sheet36athat has been printed on the front side and the stopper surface53ais minimized.

The third point is when printing the second sheet corresponding to the front side stenciled image8A of the sub-divided stenciled master8X on the plate cylinder1, inFIGS. 4 and 9, and subsequently when printing the first sheet36athat has been printed on the front side that has been reversed and transported in the sheet re-supply device45corresponding to the reverse side stenciled image8B of the sub-divided stenciled master8X on the plate cylinder1, the printing pressure range variation means28is controlled to select the printing pressure ON timing by the press roller21in accordance with the printing pressure range pattern III as shown inFIG. 9, the same as for the normal single-sided printing mode (see operation example 1). At this time, the detailed operation of the printing pressure range variation means28is carried out the same as for operation example 1 described above. As shown inFIG. 4, the second sheet is pressed against the front side stenciled image8A of the sub-divided stenciled master8X on the plate cylinder1by the press roller21. Then as a continuation, the first sheet36athat has been printed on the front side and that has been reversed and transported in the sheet re-supply device45is pressed against the reverse side stenciled image8B of the sub-divided stenciled master8X on the plate cylinder1by the press roller21, with the press roller21remaining in the printing position.

In the following, the printing operation has been repeated for (N−1) sheets out of the N sheets set using the numerical keys179. When carrying out the double-sided printing on the reverse side of the Nth(the final sheet) sheet36athat has been printed on the front side that is temporarily held in the sheet re-supply transport device104, immediately prior to completing the printing operation, the printing pressure range variation means28is controlled to select the printing pressure ON timing by the press roller21in accordance with the printing pressure range pattern II, as shown inFIG. 9. In other words, the reverse side of the Nthsheet36athat has been printed on the front side is pressed by the press roller21against only the reverse side stenciled image8B of the double-sided stenciled master8X on the plate cylinder1. Then, after the sheet discharge operation as described above, the double-sided printing operation of the set Nthsheet is completed, and the double-sided stencil printing apparatus300enters the printing standby state.

In this way, in normal double-sided printing, double-sided printing of the set number of sheets is carried out one per revolution of the plate cylinder1. In roughly the first half revolution of the plate cylinder1, the front side is printed corresponding to the front side stenciled image8A of the double-sided stenciled master8X. Then in the remaining half revolution of the plate cylinder1the reverse side is printed corresponding to the reverse side stenciled image8B of the double-sided stenciled master8X.

The fourth point is that compared with the double-sided printing operation for installation of the master, in the formal double-sided printing operation the number of sheets36used in the installation of the master printing operation is not counted as part of the normal number of sheets in the formal printing operation.

According to the present embodiment, it is possible to prevent poor resist caused by deformation of the leading edge portion of sheets due to bending when comparatively light thin sheet types contact the stopper surface53aof the sheet re-supply means45. Therefore, when the sheets36are thin and light, the transport speed (linear transport speed) of the transport belts108is reduced compared with the case where the sheets are thicker and heavier. In addition, the timing of stopping the transport belts108after contact of the sheet36athat has been printed on the front side with the stopper surface53ais earlier. Therefore bending of the sheet36athat has been printed on the front side after contact with the stopper surface53ais minimized. Also, the belt drive motor105is controlled so that bending of the sheet36athat has been printed on the front side after contact with the stopper surface53adue to excessive transport of the sheet36ais minimized. Therefore deformation of the leading edge portion of the sheet36athat has been printed on the front side is minimized, so it is possible to obtain double-sided printed matter in which deviation of the image position and poor resist is minimized.

Also, according to the present embodiment, the above advantages and effects are obtained, and in addition it is possible to carry out single-sided printing without wastefully using masters, as in the double-sided printing apparatus (1) according to Prior Art 7 and 9, referred to above. In addition, it is possible to obtain printed matter with no unevenness in the printed image or differences in printed image density when carrying out double-sided printing easily and at low cost. Further, it is possible to provide a new 1 step double-sided printing apparatus using the 1 plate cylinder1pressing means double sided printing format that is capable of minimizing the increase in installation space.

Modification 1 of the First Embodiment

FIG. 15shows modification 1 of the first embodiment shown inFIGS. 1 through 14.

The main points of difference of modification 1 are that modification 1 has an operation panel173A from which the sheet type setting key186, that is included in the sheet type setting means disposed in the operation panel,173is eliminated. Then instead of the sheet type setting means (sheet type setting key186, the enter key180, and the four direction keys184) the sheet thickness sensor79is disposed as the sheet type detection means as shown inFIG. 15, at the predetermined location shown in FIG.1.

In other words, the control device100of modification 1 has the function as control means of controlling the belt drive motor105to change the transport speed of the transport belts108until the leading edge of the sheet36athat has been printed on the front side contacts the stopper surface53ain accordance with the sheet type pertaining to the thickness or similar of the sheet36detected by the sheet thickness sensor79or similar. In addition, the control device100of modification 1 has the function as control means of controlling the belt drive motor105to change the transport stop timing of the transport belts108when the leading edge of the sheet36athat has been printed on the front side contacts the stopper surface53a. Further, the control device100has the function as control means of controlling the belt drive motor105so that during sheet re-supply also, the transport speed of the transport belts108is the transport speed corresponding to the detected sheet type.

The sheet thickness sensor79may for example be a type that measures the thickness of the sheet36from the transmission ratio of light passing through the sheet36, or a type that measures the thickness of the sheet36by measuring the reflected wave from the sheet36using an ultrasonic wave, or a type that measures the thickness of the sheet36by measuring the distance to the surface of the sheet36using laser light, and so on. Of these methods, the method of using the transmission ratio of light has been commercialized and is in actual use.

The operation of modification 1 can be easily implemented by one skilled in the art to which the present invention pertains, from the configuration of the modification 1 as described above and from the operation of the first embodiment described above, and so on. Therefore, the explanation of the operation of modification 1 has been omitted.

According to modification 1, it is possible to eliminate the effort in manually setting the type of the sheet36every time, and the other advantages and effects are basically the same as for the first embodiment.

Modification 2 of the First Embodiment

FIG. 15shows modification 2 of the first embodiment shown inFIGS. 1 through 14.

The main point of difference of modification 2 is that besides the sheet type setting means (sheet type setting key186, the enter key180, and the four direction keys184) disposed in the operation panel173, in addition the sheet thickness sensor79is disposed as sheet type detection means as shown inFIG. 15.

In other words, the control device100of modification 1 has the function as control means of controlling the belt drive motor105to change the transport speed of the transport belts108of the sheet re-supply transport device104, in accordance with the sheet type pertaining to the thickness or similar of the sheet36detected by the sheet thickness sensor79or similar. In addition, the control device100of modification 2 has the function as control means of controlling the belt drive motor105to change the transport stop timing of the transport belts108when the leading edge of the sheet36athat has been printed on the front side contacts the stopper surface53a.

In modification 2, it is possible for example to configure the control device100with the control function so that the data signal for the thickness of the sheet36selected and set using the sheet type selection means (sheet type setting key186, the enter key180, and the four direction keys184) has priority over the data signal for the sheet thickness36transmitted and input to the control device100from the sheet thickness sensor79.

The operation of modification 2 can be easily implemented by one skilled in the art to which the present invention pertains, from the configuration of the modification 2 as described above and from the operation of the first embodiment described above, and so on. Therefore, the explanation of the operation of modification 1 has been omitted. Modification 2 has the same basic advantages and effects as the first embodiment.

Second Embodiment

If the particular advantages and effects of the first embodiment are not necessary, then compared with the first embodiment shown inFIGS. 1 through 14, in the second embodiment the function of the control device100of the first embodiment the function of changing the transport stop timing of the transport belts108when the leading edge of the sheet36athat has been printed on the front side contacts the stopper member53in accordance with the sheet type is omitted from the control device100of the first embodiment. The control device, which is not shown in the drawings, is configured to have only the function of changing the transport speed of the transport belts108until the leading edge of the sheet36athat has been printed on the front side contacts the stopper member53, and the function of changing the transport speed of the transport belt108during sheet re-supply, in accordance with the sheet type.

In this case, two types of data table, in which the sheet type and the rotational speed of the belt drive motor105are set for each printing speed, are recorded in advance in the ROM of the control device which is not shown in the drawings.

The operation of the second embodiment can be easily implemented by one skilled in the art to which the present invention pertains, from the configuration of the first embodiment described above, and soon. Therefore, the explanation of the operation of the second embodiment has been omitted. Also, the application of modification 1 and modification 2 to the second embodiment can also be easily implemented by one skilled in the art to which the present invention pertains, so its explanation has been omitted.

Third Embodiment

If the particular advantages and effects of the first embodiment are not necessary, then compared with the first embodiment shown inFIGS. 1 through 14, in the third embodiment the function of changing the transport speed of the transport belts108until the leading edge of the sheet36athat has been printed on the front side contacts the stopper member53in accordance with the sheet type is omitted from the control device100of the first embodiment. The control device, which is not shown in the drawings, is configured to have only the function of changing the transport stop timing of the transport belts108when the leading edge of the sheet36athat has been printed on the front side contacts the stopper member53, and the function of changing the transport speed of the transport belts108during sheet re-supply, in accordance with the sheet type.

In this case, a data table in which the sheet type and the stop timing of the belt drive motor105after contact of the sheet36athat has been printed on the front side with the stopper member53are set for each printing speed, and a data table in which the sheet type and the rotational speed of the belt drive motor105are set for each printing speed are recorded in advance in the ROM of the control device which is not shown in the drawings.

The operation of the third embodiment can be easily implemented by one skilled in the art to which the present invention pertains, from the configuration of the first embodiment described above, and so on. Therefore, the explanation of the operation of the third embodiment has been omitted. Also, the application of modification 1 and modification 2 to the third embodiment can also be easily implemented by one skilled in the art to which the present invention pertains, so its explanation has been omitted.

If the advantages described above are not necessary, the configuration of the press roller rotation drive means54shown inFIG. 2is not essential, and for example a configuration in which the press roller21is driven to rotate by contact with the plate cylinder1, as disclosed in Prior Art 7 and 8, may be used.

According to the present invention, printed matter with little deviation of the image position with respect to the sheet position and with good resist can be obtained, by eliminating delay in the sheets due to slippage between roller and press roller by operating the transport belt on the upstream side, and so on, and by eliminating resistance when transporting due to contact with the guide member provided along the circumferential surface of the press roller, when pressing sheets against the press roller with a roller or the like, and transporting the sheets along the guide member or the like provided along the peripheral surface of the press roller.