Printing apparatus to dry sheets on which ink is applied

An apparatus includes a printing unit and a drying unit. The printing unit performs printing on a sheet using ink. The drying unit dries the sheet on which the ink is applied at the printing unit as the sheet is conveyed in the drying unit. The drying unit causes hot air heated by a heater to circulate through a housing and blows the hot air to the sheet. The housing includes an opening through which movement of gas between inside and outside the housing can be adjusted. When conveyance of the sheet in the drying unit stops, the apparatus is controlled to reduce an output of the heater and to increase the movement of the gas through the opening.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printing apparatus which makes prints with ink.

2. Description of the Related Art

Printing apparatus ink typically is dried at some point in the printing process to avoid streaking or “offsetting,” in which wet ink smears or transfers from one sheet to an adjacent sheet. Japanese Patent Laid-Open No. 2001-71474 discloses an inkjet image forming apparatus provided with a drying unit (i.e., a drying and fixing unit) for drying ink. In the drying unit, heated air is blown onto a sheet surface by an air blowing unit constituted by a heater and a fan. The blown air is collected in an air collecting chamber and is made to recirculate to the air blowing unit.

In the apparatus disclosed in Japanese Patent Laid-Open No. 2001-71474, air is made to circulate through a substantially closed space in the drying unit. When such an apparatus is used for long time continuous printing or high-duty printing with heavy ink consumption, the ink evaporates and generates steam, which stays in a circulation flow path. Thus, humidity in the air in the circulation flow path gradually increases. As humidity increases, dew-point temperature is raised. When sheet temperature is at or below the dew point, condensation occurs on a sheet surface, whereby the sheet becomes harder to dry and moisture content in the sheet increases. Thus, efficiency in drying the sheet decreases.

In addition, when the printing apparatus jams and conveyance of a sheet is stopped in a printing process, an operator should perform an unjamming operation by removing the sheet from the drying unit. However, workability of the operator in such an unjamming operation is not considered in the apparatus disclosed in Japanese Patent Laid-Open No. 2001-71474.

SUMMARY OF THE INVENTION

An apparatus according to the present invention includes a printing unit and a drying unit. The printing unit performs printing on a sheet using ink. The drying unit dries the sheet on which the ink is applied at the printing unit as the sheet is conveyed in the drying unit. The drying unit causes hot air heated by a heater to circulate through a housing and blows the hot air to the sheet. The housing includes an opening through which movement of gas between inside and outside the housing can be adjusted. When conveyance of the sheet in the drying unit stops, the apparatus is controlled to reduce an output of the heater and to increase the movement of the gas through the opening.

DESCRIPTION OF THE EMBODIMENTS

One of the aspects of embodiments provides a printing apparatus that includes a drying unit that keeps high drying efficiency even after a long time continuous operation and has high energy utilization efficiency. One of the aspects of embodiments also provides a printing apparatus with excellent maintenance workability. With the printing apparatus, an operator can perform an unjamming operation promptly and properly when conveyance of a sheet is stopped due to, for example, a sheet jam in a drying unit.

According to the printing apparatus of the present embodiment, high drying efficiency can be kept even after a long time continuous operation and energy utilization efficiency is high. The printing apparatus of the present invention has excellent maintenance workability. An operator can perform an unjamming operation promptly and properly when conveyance of a sheet is stopped due to, for example, a sheet jam in a drying unit.

FIG. 6Ais a sectional view of a main body of the printing apparatus. Hereinafter, an embodiment of an inkjet printing apparatus will be described. The printing apparatus according to the present embodiment is a high-speed line printing apparatus switchable between simplex and duplex printing modes. A unit of printing is referred to as one page, a page, one unit image, or a unit image and an elongated continuous sheet is longer than repeated units of printing in the conveying direction of the sheet. An elongated continuous sheet is used in the printing apparatus. For example, the printing apparatus is suitable for printing a large number of sheets in a printing laboratory. When a plurality of small images, text and space are included in one unit of printing (i.e., one page), those included in the unit of printing are collectively referred to as one unit image herein. That is, the unit image is one unit of printing (i.e., one page) in a process of sequentially printing a plurality of pages on a continuous sheet. The length of the unit image varies depending on the sizes of images to be printed. For example, the length of a 127 mm-long and 89 mm-wide photograph is 135 mm in the conveying direction and the length of a DIN A4-sized sheet is 297 mm.

The present invention is widely applicable to printing apparatuses, such as a printer, a printer multi-functional peripheral, a copier, a facsimile machine and apparatuses for manufacturing various devices. Any printing system may be selected, including an inkjet printing system, an electrophotography printing system, a heat transfer printing system, a dot impact printing system and a liquid development printing system. The present invention is also applicable to other sheet processing devices which perform various processes that require drying of a continuous sheet (e.g., recording, processing, application, irradiation, reading and inspection).

FIG. 1is a schematic sectional view of an internal configuration of a printing apparatus. The printing apparatus of the present embodiment is capable of printing on a first surface and a second surface positioned opposite to the first surface of a rolled-up sheet. The printing apparatus mainly includes therein a sheet feeding unit1, a decurling unit2, an skew correcting unit3, a printing unit4, an inspection unit5, a cutting unit6, an information recording unit7, a drying unit8, a reverse unit9, a discharge conveying unit10, a sorting unit11, a discharge unit12, and a control unit13. A sheet is conveyed along a sheet conveyance path illustrated as a solid line inFIG. 1by a conveyance mechanism, which consists of a pair of rollers or a belt, and is processed in each of the units. The sheet is conveyed downstream along the sheet conveyance path while printing. At an arbitrary position in the sheet conveyance path where the sheet is conveyed from feeding means to discharging means, a side toward the feeding means is referred to as “the upstream side”, and the opposite side toward the discharging means is referred to as “the downstream side”.

The sheet feeding unit1supports and feeds a rolled-up continuous sheet. The sheet feeding unit1can accommodate rolls R1and R2, one of which is selectively drawn and supplied. The number of rolls in not limited to two and one or three or more rolls may be accommodated. As long as it is continuous, the sheet is not necessarily rolled up. For example, a continuous sheet with perforations formed for each unit length may be folded at the perforations and stacked in the sheet feeding unit1.

The decurling unit2reduces the curling (i.e., warping) of the sheet fed from the sheet feeding unit1. In the decurling unit2, the curling is reduced by applying decurling force to the curled sheet which is made to pass through two pairs of pinch rollers driven by a single driving roller such that the sheet might be curled in an opposite direction.

The skew correcting unit3corrects an skew (i.e., an inclination to a direction in which the sheet should travel) of the sheet which has passed through the decurling unit2. The skew of the sheet is corrected by forcing a reference end of the sheet on a guide member.

While the sheet is being conveyed, the printing unit4makes printing on the sheet from above by print heads14and forms an image. The printing unit4also includes a plurality of conveying rollers which convey the sheet. Each of the print heads14is a linear printing head constituted by an array of inkjet nozzles disposed over the maximum width of a sheet expected to be used. A plurality of print heads14are arranged in parallel along the conveyance direction. In the present embodiment, seven print heads are provided for seven colors of cyan (C), magenta (M), yellow (Y), light cyan (LY), light magenta (LM), gray (G) and black (K). The numbers of the colors and the print heads are not limited to seven. The inkjet printing system may be, for example, a thermal inkjet printing system, a piezoelectric inkjet printing system, an electrostatic inkjet printing system and a MEMS inkjet printing system. Each of the colored ink is supplied to each print head14via an ink tube from an ink tank.

The inspection unit5optically reads, with a scanner, an inspection pattern and an image printed on the sheet in the printing unit4, inspects, for example, a state of the nozzles of the print heads, a state of conveyance of the sheet and image positions and determines whether the image has been printed correctly. The scanner includes a CCD image sensor or a CMOS image sensor.

The cutting unit6includes a mechanical auto cutter which cuts the sheet after the printing to predetermined lengths. The cutting unit6also includes a plurality of conveying rollers which sends the sheet to subsequent next processes after the cutting.

The information recording unit7records print information (inherent information), such as a serial number and a printed date, on a non printed area of the cut sheet. Texts or codes are recorded by inkjet printing or heat transfer printing.

The drying unit8heats the sheet with an image formed thereon in the printing unit4and dries the applied ink in a short time. As the sheet passes through the drying unit8, hot air is blown at least from below on the sheet and an ink-applied surface is dried.

The sheet conveyance path from the sheet feeding unit1to the drying unit8described above will be referred to as a first path. The first path turns around between the printing unit4and the drying unit8. The cutting unit6is provided in the middle of the turning around portion.

The reverse unit9temporarily takes up the continuous sheet which has completed the printing on the front surface thereof and reverses the sheet for duplex printing. The reverse unit9is provided in the middle of a path established from the drying unit8to the printing unit4via the decurling unit2(i.e., a loop path; hereinafter, referred to as a “second path”) such that the sheet which passed through the drying unit8might be fed to the printing unit4again. The reverse unit9includes a winding rotary member (i.e., a drum) which rotates to winding the sheet. The continuous sheet which is still uncut after the printing on the front surface is temporarily taken up on the winding rotary member. After the sheet is taken up, the winding rotary member rotates in an opposite direction and the taken up sheet is fed to the decurling unit2and sent to the printing unit4. Since the sheet has been reversed, printing can be made on a back surface of the sheet in the printing unit4. Detailed description of the operation of the duplex printing will be given later.

The discharge conveying unit10conveys the sheet to the sorting unit11after the sheet is cut in the cutting unit6and dried in the drying unit8. The discharge conveying unit10is provided in a path different from the second path on which the reverse unit9is provided (hereinafter, referred to as a “third path”). A path switching mechanism with a movable flapper is provided in a branching position of the paths for a selective guide of the sheet conveyed on the first path to either one of the second or third path.

The sorting unit11and the discharge unit12are provided at a side of the sheet feeding unit1and at an end of the third path. The sorting unit11sorts the printed sheet into groups as necessary. The sorted sheet is discharged to the discharge unit12which consists of a plurality of trays. As described above, the sheet is discharged along the third path which is disposed below the sheet feeding unit1and at a side of the sheet feeding unit1opposite to the printing unit4and the drying unit8.

The decurling unit2, the skew correcting unit3, the printing unit4, the inspection unit5, the cutting unit6, the information recording unit7, the drying unit8, the reverse unit9and the discharge conveying unit10are independent process units. In order to simplify the maintenance operation, such as an unjamming operation, the operator can manually draw an arbitrary unit independently from the main body of the printing apparatus.

Each of these units is provided with cutters for cutting the continuous sheet. The cutters are each provided in the upstream and the downstream of the sheet conveyance path near each of the units. The operator can use the cutter to cut the sheet near the upstream or downstream of the unit to be drawn for the unjamming operation, whereby the unit can be drawn easily. The cutters are hand cutters operated manually by the operator. The cutters are operated by hand of the operator or driven by an actuator in accordance with an instruction from the operator. As illustrated inFIG. 1, nine hand cutters of first cutter17to ninth cutter25are provided at nine places along the sheet conveyance path in the printing apparatus. The first cutter17is provided between the sheet feeding unit1and the decurling unit2. Similarly, the second cutter18is provided between the decurling unit2and the skew correcting unit3, the third cutter19is provided between the skew correcting unit3and the printing unit4, the fourth cutter20is provided between the printing unit4and the inspection unit5and the fifth cutter21is provided between the inspection unit5and the cutting unit6. In the downstream of the cutting unit6, the sixth cutter22is provided between the cutting unit6and the information recording unit7, the seventh cutter23is provided between the information recording unit7and the drying unit8and the eighth cutter24is provided near and in the downstream of the drying unit8. The ninth cutter25is provided between the reverse unit9and the decurling unit2. It is not necessary to provide a cutter for cutting the continuous sheet in the downstream of the discharge conveying unit10since no continuous sheet is conveyed there.

The control unit13manages the control of each component of the entire printing apparatus. The control unit13includes a CPU, a storage device, a control unit (i.e., a control unit) provided with various control units, an external interface and a manipulation unit15for the user input and output. The operation of the printing apparatus is controlled in accordance with instructions from a host device16, such as a control unit or a host computer connected to the control unit via an external interface.

FIG. 2is a block diagram illustrating a concept of the control unit13. The control unit (a range surrounded by a dashed line) included in control unit13is constituted by a central processing unit (CPU)201, a ROM202, a RAM203, a hard disk drive (HDD)204, an image processing unit207, an engine control unit208and an individual unit control unit209. The CPU201collectively controls the operation of each unit of the printing apparatus. The ROM202stores programs to be implemented by the CPU201and fixed data necessary for various operations of the printing apparatus. The RAM203is used as a work area of the CPU201, as a temporary storing region of various types of received data or as storage for various types of setting data. The HDD204is capable of storing programs to be implemented by the CPU201, print data and setting information required for various operations of the printing apparatus. The manipulation unit15is a user I/O interface. The manipulation unit15includes an input section consisting of a hard key and a touch panel, and an output section consisting of a display device on which information is displayed and a sound generator. For example, the manipulation unit15may be a display device with a touch panel on which an operation status, printing status, maintenance information (e.g., a remaining amount of ink, a remaining amount of the sheets and a maintenance status) of the apparatus are displayed to a user. The user can input various types of information through the touch panel.

A dedicated processing section is provided for units that require high-speed data processing. The image processing unit207performs image processing of the print data processed in the printing apparatus. A color space (e.g., YCbCr) of the input image data is converted into a standard RGB color space (e.g., sRGB). Various image processing, such as resolution conversion, image analysis and image correction, is performed as necessary to the image data. The print data obtained through the image processing is stored in the RAM203or the HDD204. The engine control unit208controls driving of the print head14of the printing unit4in accordance with the print data on the basis of the control commands received from, for example, the CPU201. The engine control unit208also controls the conveyance mechanism of each component of the printing apparatus. The individual unit control unit209is a sub control unit which individually controls the sheet feeding unit1, the decurling unit2, the skew correcting unit3, the inspection unit5, the cutting unit6, information recording unit7, the drying unit8, the reverse unit9, the discharge conveying unit10, the sorting unit11and the discharge unit12. The individual unit control unit209controls the operation of each unit in accordance with the instructions from the CPU201. The external interface205is a local I/F or a network I/F provided for connecting the control unit to the host device16. The components described above are connected by system bus210.

The host device16is a source of supply of image data to be printed on the printing apparatus. The host device16may be a general purpose computer or a dedicated computer, or may be dedicated image equipment, such as, a digital camera, a photograph storage device and an image capturer with an image reader. If the host device16is a computer, an OS, application software for generating the image data and a printing device driver for the printing apparatus are installed in a storage device of the computer. It is not necessary to implement all of these processes by software, but a part or all of them may be implemented by hardware.

Next, a basic operation for the printing will be described. The simplex printing mode and the duplex printing mode have different print operations, which will be described separately.

In the simplex printing mode, printing is made in the printing unit4on the front surface (i.e., the first surface) of the sheet which is fed from the sheet feeding unit1and processed in the decurling unit2and the skew correcting unit3. Images of the predetermined unit length in the conveyance direction (i.e., unit images) are printed sequentially on the elongated continuous sheet and a plurality of images are formed and arranged. The printed sheet is made to pass through the inspection unit5and is cut for each unit image in the cutting unit6. Print information is given on the back surface of the cut sheet as necessary in the information recording unit7. The cut sheet is then conveyed to the drying unit8one at a time and is dried. The sheet is then conveyed via the discharge conveying unit10and is sequentially discharged and stacked in the discharge unit12of the sorting unit11. The sheet left in the printing unit4after the last unit image is cut is made to return to the sheet feeding unit1and is taken up on the roll R1or R2. In this manner, in the simplex printing mode, the sheet is conveyed along the first path and the third path for the processing and is not conveyed along the second path.

In the duplex printing mode, after a print sequence for the front surface (i.e., the first surface) is completed, a print sequence for the back surface (i.e., the second surface) is performed. First, in the print sequence for the front surface, the sheet feeding unit1to the inspection unit5each operate in the same manner as in the above-described simplex printing mode. The sheet is not cut in the cutting unit6and is conveyed as the continuous sheet to the drying unit8. After the ink on the front surface is dried in the drying unit8, the sheet is guided not to the path at the side of the discharge conveying unit10(i.e., the third path) but to the path at the side of the reverse unit9(i.e., the second path). The sheet is wound by the winding rotary member of the reverse unit9which is rotating in a forward direction (i.e., the counterclockwise direction in the drawing) in the second path. When all the scheduled printing on the front surface is completed in the printing unit4, a trailing end of the printing area of the continuous sheet is cut in the cutting unit6. The continuous sheet in the downstream of the conveyance direction (i.e., the printed side) from the cut position is completely taken up to the trailing end (i.e., the cut position) of the sheet in the reverse unit9via the drying unit8. At the same time with the winding operation in the reverse unit9, the continuous sheet left at the upstream side (i.e., the side of the printing unit4) from the cut position in the conveyance direction is returned to the sheet feeding unit1and wound on the roll R1or R2such that the leading end of the sheet (i.e., the cut position) might not be left in the decurling unit2. Such a back feeding system avoids collision with a sheet which is fed again for the subsequent print sequence for the back surface.

After the above-described print sequence for the front surface is completed, the print sequence for the back surface is started. The winding rotary member of the reverse unit9rotates in a reverse direction of the winding direction (i.e., a clockwise direction in the drawing). An end of the wound sheet (the trailing end of the sheet at the time of winding becomes the leading end of the sheet at the time of sending out) is sent to the decurling unit2along the path of the dashed line inFIG. 1. The decurling unit2corrects the curling given by the winding rotary member. The decurling unit2is provided between the sheet feeding unit1and the printing unit4in the first path and is provided between the reverse unit9and the printing unit4in the second path. Thus, the decurling unit2is commonly used for decurling in both the paths. The reversed sheet is sent to the printing unit4via the skew correcting unit3, and printing is made on the back surface thereof. The printed sheet is conveyed through the inspection unit5and is cut in the cutting unit6to each predetermined unit length. Since printing is made on both surfaces of the cut sheet, no information is recorded in the information recording unit7. The cut sheet is conveyed to the drying unit8one at a time and is then conveyed via the discharge conveying unit10and is sequentially discharged and stacked in the discharge unit12of the sorting unit11. In this manner, in duplex printing mode, the sheet is processed while passing through the first path, second path, the first path and the third path in this order.

Next, the drying unit8in the thus-configured printing apparatus will be described in more detail.FIG. 3is a perspective view of an internal structure of the drying unit8.FIG. 4is a sectional view of the drying unit8seen from the direction of arrow Y inFIG. 3. The sheet on which ink is applied in the printing unit4is conveyed through the cutting unit6and the information recording unit7and is introduced into the drying unit8from a direction of arrow X inFIG. 3. The drying unit8includes a heating unit42and a conveying unit43. The conveying unit43includes a conveying belt34and a plurality of conveying rollers (i.e., follower rollers)35. The conveying belt is an endless belt which is driven to rotate. The conveying rollers35are arranged along a conveyance direction facing the conveying belt34. A distance between adjacent conveying rollers35is shorter than the length of the smallest cut sheet. The sheet, either a continuous sheet or a cut sheet, introduced into the drying unit8smoothly advances in the drying unit8while being held by the conveying belt34and the conveying roller35.

The heating unit42causes the hot air to circulate through the housing of the drying unit8and blows the hot air on the sheet. The heating unit42includes a heater36and a fan37. The heater36raises the temperature of (i.e., heats) the air and produces the hot air. The fan37causes the hot air to circulate and blows the hot air on the sheet. The hot air sent by the fan37is moved upward through a plurality of slit-shaped ejection ports41provided in positions corresponding to the clearances between the conveying rollers35and is blown on the sheet surface. The hot air is then returned to the fan37and is made to circulate through the housing. A temperature sensor45, such as a thermistor, for detecting temperature of the hot air is provided on an inner wall surface of the housing near the ejection ports41. A hygrometer46(i.e., a humidity detector) for detecting humidity of the hot air is provided near the temperature sensor45. The humidity detector for detecting humidity information is not limited to that which directly detects humidity using a hygrometer. For example, humidity may also be indirectly detected by detecting temperature using a temperature sensor or by estimating humidity with parameters such as ink depth and printing duty.

A heat transfer plate38and a surface heating element39are provided as an integrated structure inside the conveying belt34. Heat generated in the surface heating element39is transferred to the heat transfer plate38which is a thermal conductor. As the conveying belt34is rotated, the inner surface of the conveying belt34slides in surface contact with a surface of the heat transfer plate38. Since the conveying belt34and the heat transfer plate38are in contact with each other, heat is transferred from the heat transfer plate38to the conveying belt34and the temperature of the entire conveying belt34increases. When the sheet is conveyed inside the drying unit8, the outer surface of the conveying belt34is in surface contact with the sheet and the sheet is heated. Thus, the sheet is dried in an accelerated manner. That is, the sheet is dried highly efficiently by being heated from both surfaces. In particular, the heater42blows the hot air on the front surface and the conveyer belt34heats the sheet on the back surface.

The heating unit42and the conveying unit43are accommodated in the housing of the drying unit8which consists of a first housing segment52(i.e., an upper cover) and a second housing segment53(i.e., a main part of the housing). The heating unit42and the conveying unit43(i.e., the conveying roller35) are partially held by the second housing segment53. As described later, the first housing segment52and the second housing segment53are hinged together and can be disengaged as an alligator mouth such that the operator might access the inside the drying unit8easily.

A first sheet sensor62for detecting existence of the sheet is provided near an inlet of the sheet in the drying unit8(i.e., the upstream side when seen from the drying unit8). A second sheet sensor63for detecting existence of the sheet is provided near an outlet of the sheet in the drying unit8(i.e., the downstream side when seen from the drying unit8). These sheet sensors function as a part of a jam detector which detects occurrence of a jam during the conveyance of the sheet in the drying unit8. A sensor (i.e., a drawing detector) which detects that the drying unit8has been drawn from the main body of the printing apparatus is provided in the main body of the printing apparatus. The seventh cutter23and the eighth cutter24each include a sensor (i.e., a sheet cutting detector) which detects operations of cutting the sheet S by each of the cutters. With the sensor, the control unit can recognize that the operator has operated the cutter.

Here, circulation of the hot air inside the drying unit8will be described.FIG. 5is a sectional view of the drying unit8seen from the direction of arrow X inFIG. 3. An opening50(i.e., a first opening) for introducing ambient air into the housing is provided at an upper surface of the second housing segment53. The opening50includes a movable lid55which can adjust the opening amount of the opening50. The lid55is opened or closed to adjust an amount of movement of the gas (i.e., efficiency in the introduction of the gas) through the opening50from outside the housing. An opening51(i.e., a second opening) for exhausting air from inside the housing is provided at a side surface of the second housing segment53. The opening51includes a movable lid56which can adjust the opening amount of the opening51. The lid56is opened or closed to adjust an amount of movement of the gas (i.e., efficiency in the exhaustion of the gas) through the opening51from inside the housing. These lids55and56pivot open and close about a hinge when being driven by an actuator such as a solenoid or a motor controlled by the control unit. Instead of the pivotation about the hinge, the lids55and56may be slid laterally to open and close the openings50and51.

As a variant example, the openings50and51may each include a fan which rotates at varying rotational state (i.e., with varying blowing capacity). The amount of movement of the gas can be adjusted by the rotational state of the fan. With active supply and exhaust ventilation using the fans provided in the openings, the air is ventilated in a shorter time. Although a functional separation is made between the introducing opening50and the exhausting opening51in this example, such a functional separation is not necessary: a single opening may alternatively be provided for both the introduction and exhaustion. Further alternatively, three or more openings may be provided.

FIG. 5Aillustrates a state in which both the openings50and51are closed. In this state, the inside the housing of the drying unit8is substantially closed except for the inlet and outlet of the sheet. The fan37creates an air current, which is heated by the heater36to produce the hot air. The hot air is made to circulate through the closed space in the directions of arrows inFIG. 5A. The hot air is blown on the sheet through the clearances between a plurality of conveying rollers35.

FIG. 5Billustrates a state in which both the openings50and51are opened. The hot air circulates through the housing of the drying unit8in the directions of arrows inFIG. 5B. During the circulation, a part of the hot air is exhausted outside through the opening51and ambient air is introduced into the housing through the opening50in an amount equivalent to that of the exhausted air.

When an air current is created by the fan37, an upstream side of the fan37is slightly negatively pressurized and a downstream side of the fan37is slightly positively pressurized along the direction of the air current. InFIGS. 5A and 5B, a dark gray region represents a negative pressure region70and a light gray regions represents a positive pressure region71. The opening50is located as close to the fan37as possible in the negative pressure region70(i.e., a position with larger negative pressure) such that the ambient air might be naturally introduced by the negative pressure. The opening51is located in the positive pressure region71such that air inside the housing might be naturally exhausted by the positive pressure. The amount of air which passes through the openings50and51is set so as not to significantly disturb the air current of the hot air which circulates through the housing. The air inside the housing can be ventilated efficiently when the amount of air passing through the openings50and51and the amount of air of the circulating air are well-balanced.

If the temperature of the introduced ambient air is below the temperature of the air inside the drying unit8, the temperature of the air inside the drying unit8will also decrease. Usually, since a relative temperature difference between the room temperature in which the printing apparatus is installed and the heated air in the drying unit8is large, the temperature of the air inside the drying unit8can be reduced rapidly. If the humidity of the introduced ambient air is below the humidity of the air inside the drying unit8, the humidity of the air inside the drying unit8will also decrease. Usually, since a relative humidity difference between the humidity in the room in which the printing apparatus is installed and the inside the drying unit8is large, the humidity of the air inside the drying unit8can be reduced rapidly.

FIGS. 6A and 6Bare sectional views of a main body of the printing apparatus, illustrating a section of the printing unit4and the drying unit8.FIG. 6Aillustrates a state in which the unit is accommodated inside the main body of the printing apparatus and the first housing segment52is closed.FIG. 6Billustrates a state in which the first housing segment52of the drying unit8is opened. A part of the drying unit8slides along a rail57provided in the main body of the printing apparatus and is drawn from the printing apparatus toward an operator. When the drying unit8is drawn as illustrated inFIG. 6B, the unit which includes the conveying unit43and the unit which includes the heating unit42are separated and the heating unit42remains in the main body of the printing apparatus.

As illustrated inFIG. 7, the heating unit42and the conveying unit43are electrically connected by a drawer connector30. Power is supplied to the conveying unit43via the drawer connector30. A signal wire for control is further connected via the drawer connector30. When the drying unit8is mounted on the main body of the printing apparatus (i.e., the state ofFIG. 6A), the drawer connector30is connected between the heating unit42and the conveying unit43and when the drying unit8is drawn from the main body of the printing apparatus (i.e., the state ofFIG. 6B) the drawer connector30is disconnected. With this configuration, the high temperature heating unit42remains in the main body of the printing apparatus and is not exposed when the drying unit8is drawn, whereby the operator can easily and reliably perform a recovery operation.

When the drying unit8is drawn, the first housing segment52pivots about a distal hinge54as a rotation axis and the side of the operator opens as an alligator mouth. The opened first housing segment52keeps its open state by an urging mechanism (e.g., a gas spring, a hinge spring and a torsion spring). The first housing segment52holds an upper part of the conveyance mechanism of the drying unit8(i.e., the conveying belt34, the heat transfer plate38and the surface heating element39). The second housing segment53holds a lower part of the conveyance mechanism (i.e., the conveying roller35). Thus, when the first housing segment52is opened, the conveyance mechanism is separated to expose the sheet S inserted between the conveying belt34and the conveying roller35whereby the operator can remove the sheet S easily.

FIG. 8Aillustrates a configuration of a variant example ofFIG. 6AandFIG. 8Billustrates a configuration of a variant example ofFIG. 6B. In these examples, when the drying unit8is drawn, the heating unit42and the conveying unit43are also drawn in an integrated manner. The second housing segment53also holds the heating unit42(i.e., the heater36and the fan37), which is located further than the hinge54in the drawing direction. Even after the drying unit8is drawn to the maximum, most of the heating unit42remains in the housing of the main body of the printing apparatus. Also in this variant example, the high temperature heating unit42remains in the main body of the printing apparatus and is not exposed when the drying unit8is drawn, whereby the operator can perform a recovery operation easily and reliably.

Next, occurrence of a jam in the thus-configured printing apparatus and an accompanying unjamming operation will be described with reference toFIGS. 9A-9D. The printing apparatus includes a jam detector which detects occurrence of a jam during the printing operation and detects a location of the jam. The jam detector detects a jam by detecting an abnormality in the conveyance at a leading end of the sheet or in the middle of the sheet. In the former method, position information about the theoretical leading end of the sheet calculated based on the control information of the rollers is collated with detection results of the sheet sensor disposed between adjacent rollers. The jam detector determines a jam has occurred when the sheet sensor does not detect the leading end of the sheet during a period in which the leading end of the sheet is estimated to pass through, or when there is a significant delay in the detection of the leading end of the sheet with respect to the theoretical value. In the latter method, if a sheet conveyance failure occurs at a certain place while the continuous sheet is conveyed on a sheet conveyance path, the conveyance speed is reduced at the place and, in the worst case, the conveyance stops. When it happens, a subsequent sheet is continuously sent in that place and accumulated in a looped manner. The jam detector determines occurrence of a jam by detecting a decrease in a rotational state of a motor of the conveying rollers or detecting an abnormality in a motor load. As another method, a direct sensor which directly measures a movement state of a sheet surface (i.e., speed and displacement) may be provided at a plurality of positions along the sheet conveyance path and occurrence of a jam can be determined upon detection of an abnormality in the conveyance speed of the sheet. As further method, a size of a loop is measured by a sensor at a place at which a loop of a sheet is intentionally formed on the sheet conveyance path. If the measured size of the loop differs from a proper size, occurrence of a jam can be determined.

Upon detection of occurrence of a jam by the jam detector, the control unit stops the driving motors of all the conveying rollers related to the conveyance of the sheet in the sheet conveyance path. This is for the purpose of limiting the influence of the jam within the place in which the jam occurred and avoiding the influence from extending to the rest of the components. The control unit displays the jammed place and instructions on a display device of the manipulation unit15or the host device16to encourage the operator to manually perform the unjamming operation. In response to the instructions, the operator performs a manual unjamming operation by manually removing the jammed sheet left in a troubled place.

In the following description, an example will be described in which a jam occurs in a region including the drying unit8in the printing sequence for the first surface in the duplex printing mode. In the printing sequence for the first surface in the duplex printing mode, the continuous sheet passes through the drying unit8(seeFIG. 9A). If a jam occurs in this process, the continuous sheet stops over the drying unit8. When the operator tries to draw the drying unit8for the unjamming operation, the continuous sheet left in the sheet conveyance path hinders smooth drawing of the drying unit8. When the operator tries to draw the drying unit8with excessive force, the continuous sheet may be drawn to damage the drying unit8and adjacent units, or the continuous sheet may be torn and pieces of the continuous sheet may remain in an irremovable manner. To address this problem, the operator cuts the continuous sheet at two places, i.e., the upstream and downstream of the continuous sheet, in the drying unit8using the seventh cutter23and the eighth cutter24which are disposed near the drying unit8before drawing the drying unit8(seeFIG. 9B). The operator then draws the drying unit8from the main body of the printing apparatus along the rail57. Since the sheet has been cut, the drying unit8can be drawn smoothly (seeFIG. 9C). Then, the operator opens the first housing segment52of the drawn drying unit8, removes a sheet piece remaining in the conveyance mechanism and removes the jam (seeFIG. 9D). After the unjamming operation, the operator closes the first housing segment52and returns the drying unit8to the original position in the main body of the printing apparatus. After the maintenance door is closed, the jam detector detects the state of the jam again. If the jam detector still detects a jam, a warning is issued to encourage the operator to perform a manual unjamming operation again. Upon detection of no jam, the jam detector determines that the jammed sheet has been removed. Then, the maintenance mode is completed and the printing operation mode is resumed.

In the simplex printing mode or in the printing sequence for the second surface in the duplex printing mode, a sheet cut for each unit image in the cutting unit6is made to pass through the drying unit8. If a jam occurs and the conveyance is stopped, the leading and trailing ends of the sheet left in the drying unit8are already cut. Thus, the operator can draw the drying unit8without the need of cutting the sheet using the hand cutter. That is, the sheet cutting operation illustrated inFIG. 9Bcan be omitted.

A method of controlling the thus-configured drying unit8will be described. Occurrence of a jam of a sheet being conveyed in the drying unit8is detected by the above-described jam detector. Upon occurrence of a jam, the control unit decreases the output of the heater36of the heating unit42(i.e., turns the heater36off). At the same time, the control unit increases the amount of movement of the gas through the opening by increasing the opening (at least one of the openings50and51). Due to a synergistic effect of stopping the heating by the heater36and the ventilation with ambient air through the opening, the air temperature inside the drying unit8decreases quickly. Accordingly, when the conveyance of the sheet is stopped in the drying unit, the operator can start the unjamming operation quickly. Thus, maintenance workability is improved. When the conveyance of the sheet is stopped by reasons other than the jam, similar operations can be performed.

If the temperature detected by the temperature detector becomes lower than the predetermined value at the time of such a rapid decrease in temperature, the control unit controls the amount of movement of the gas through the opening to be decreased by switching the opening (at least one of the openings50and51) from the opened state to the closed state. Such a configuration prevents an unnecessary decrease in the temperature in the drying unit8and thereby shortens the standup time after the unjamming operation is completed and the printing is resumed. From another point of view, energy consumption in the drying unit8is reduced.

As described above, when a printing apparatus is used for long time continuous printing or high-duty printing with heavy ink consumption, humidity in the air inside the drying unit8increases while efficiency in drying the sheet decreases. Even if the air temperature is kept constant, as the humidity increases, the ink becomes harder to evaporate when the hot air is blown on the sheet. As a result, the humidity as well as the temperature should be managed. When the humidity detected by the humidity detector (e.g., the hygrometer46) exceeds a first predetermined value during the printing process (i.e., during the operation of the drying unit8), the control unit controls the opening (at least one of the openings50and51) to be switched to the opened state. The ventilation of the air through the opening prevents an excessive increase in the humidity in the air inside the drying unit8. However, as the humidity decreases, the temperature also decreases and it is possible that an excessive decrease in the temperature might impair the sheet drying performance in the drying unit8. To address this problem, when the detected humidity is below a second predetermined value (which is smaller than the first predetermined value), the control unit controls the opening (at least one of the openings50and51) to be switched to the closed state. With these operations, the humidity and the temperature of the air inside the drying unit8can be kept in suitable ranges after a long time continuous printing.

The main body of the printing apparatus includes a locking mechanism for operator safety. In a locked state, the locking mechanism prevents drawing of the drying unit8. Since the temperature inside the drying unit8becomes high during the printing operation, the drying unit8is locked such that the operator cannot draw the same at least during the printing operation (i.e., during operation of the drying unit8.). Upon detection of a jam, the lock is released under predetermined conditions to allow the operator to draw the drying unit8. In order to satisfy the predetermined conditions, all of the following conditions should be satisfied.

(1) The jam detector detects a jam during the printing operation on the first surface in the duplex printing mode.

(2) The internal temperature of the drying unit8detected by the temperature detector is lower than a predetermined temperature.

In addition to the above conditions (1) and (2), the following conditions may be added such that the lock is released only after it is confirmed that the continuous sheet has been cut at two places. In this manner, the operator safety is enhanced.

(3) Both the first sheet sensor62and the second sheet sensor63detect the sheet.

(4) The sheet cutting detector detects that the seventh cutter23and the eighth cutter24have been operated.

The locking mechanism may alternatively lock the first housing segment52and the second housing segment53from opening. In this case, in addition to the above conditions (1) and (2), an additional condition will be given that the drawing detector detects that the drying unit8has been drawn.

According to the embodiment described above, high drying efficiency can be kept even after a long time continuous operation and energy utilization efficiency is high. The printing apparatus of the present invention has an excellent maintenance workability. An operator can perform an unjamming operation promptly and properly when conveyance of a sheet is stopped due to, for example, a sheet jam in a drying unit. Even if the continuous sheet is stopped over a unit upon occurrence of a jam during the printing process, the continuous sheet can be cut with a cutter and the unit can be drawn reliably. With this configuration, the operator can perform the unjamming operation with less time and effort. Thus, maintenance workability is improved.

This application claims the benefit of Japanese Patent Application No. 2010-099148 filed Apr. 22, 2010, which is hereby incorporated by reference herein in its entirety.