Printing apparatus, method of controlling it and data storage medium

Abstract: Paper jams and damage to a printing medium resulting from movement of a print head carriage are prevented in a printing apparatus in which a print head unit (11) moves orthogonally to the direction in which the printing medium (P) is transported through a transportation path past the printing unit (10) for printing. A pair of transportation rollers (15a, 5b) is supported on opposite sides of the transportation path in a manner enabling the transportation rollers to close and open. The transportation rollers are closed to hold and transport the printing medium (P) in the transportation path to the printing unit (10). A drive means is controlled to open and close the transportation rollers according to a control command. When a non-print control command involving print head movement is received, the drive means is controlled to close the transportation rollers.

Description: The present invention relates to a printing apparatus in which the print head travels orthogonally to the direction in which the printing medium travels in order to print on the printing medium. The present invention also relates to a control method for such printing apparatus, and a data storage medium storing the control method of the invention. Impact printers, thermal printers, inkjet printers, and other printers that print by moving a carriage-mounted print head orthogonally to the direction in which the printing medium travels are widely used and commonly available. Most printers used in conjunction with cash registers and point-of-sale terminals for printing slip forms are of this type. This category of printers includes printers requiring the user to place the printing form (printing medium) at a particular location relative to a printing unit, and having an openable/closable transportation rollers for clamping and holding the form for printing. When the user then initiates printing and a print command is sent from a host device to the printer, the transportation rollers close to clamp and hold the form. The transportation rollers are then driven to advance the form into the printing unit, and printing begins. As taught by JP-U-5-68989, this type of printer can automatically eject any medium present in the transportation path when the power is turned on as a means of preventing paper jams. In this type of printer, when a "return to home position" or similar command is received from the host after the power is turned on and a form is set in the printing unit, the carriage moves across the form to the home position also known as "standby position". The form, however, may be wrinkled, have folded corners, or otherwise be proud of the platen and interfere with print head movement at this time because the form is not clamped by the transportation rollers. The carriage may therefore catch on the form or tear the form, resulting in a paper jam. This is a particular problem in printers having a straight transportation path for printing on slip forms. In printers with a curved transportation path the curves in the transportation path increase the stiffness of the printing medium, and help to keep the printing medium away from the carriage path. This is not the case in printers with a straight transportation path, and the loose printing medium thus tends to wander into the path of the print head carriage. It is an object of the present invention to provide a printing apparatus and a method of controlling it whereby paper jams and damage to the printing medium can be positively prevented. This object is achieved with a printing apparatus as claimed in claim and a method as claimed in claim 11, respectively. In accordance with the present invention, when a non-print control command involving print head movement, for example, a return home command moving the print head to a standby position, or a printer initialization command, is received, transportation means is brought into a closed state so that the printing medium is always held by the transportation rollers when the print head moves. In a preferred embodiment, the transportation means is not closed when no printing medium is present in the transportation path, and noise accompanying operation of transportation rollers can be reduced. It is possible to open the transportation means after closing them and executing a control command involving print head movement. This enables the user to remove and reinsert a printing medium as necessary or desired. The above mentioned ones and other preferred embodiments of the invention are subject-matter of dependent claims. These and other objects and features of the present invention will be readily understood from the following detailed description of preferred embodiments taken in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals, and in which: Fig. 1 is an oblique view of a printing apparatus according to a preferred embodiment of the present invention; Fig. 2 is an oblique view of the major parts of the printing unit in the printing apparatus shown in Fig. 1; Fig. 3 is a typical side view of the printing unit in the printing apparatus shown in Fig. 1; Fig. 4 is a functional block diagram of the printing apparatus shown in Fig. 1; Fig. 5 is a flow chart of a control method for handling carriage movement commands according to a first embodiment of the present invention; Fig. 6 is a flow chart of a control method for handling carriage movement commands according to a second embodiment of the present invention; and Fig. 7 is a flow chart of a control method for handling carriage movement commands according to a third embodiment of the present invention. In the following description a dot impact printer for printing checks and other slip forms in combination with a cash register or point-of-sale (POS) terminal is used as being exemplary of the printing apparatus 1 of the present embodiment. As shown in Fig. 1, a tray 2 for setting slip forms P to be printed is disposed at the front of the printing apparatus 1 as viewed in Fig. 1. This tray 2 leads to the printing unit 10 located inside the front cover 3. A slip form P is manually placed on the tray 2 with its leading edge inserted into the printing unit 10, and is transported linearly along the tray 2 by means of a pair of transportation rollers 15a and 15b described further below. A paper guide 4 on the tray 2 is adjustable to the width of the slip forms P, and can thus guide slip forms P of different widths. An operating panel 5 is disposed to the right of the tray 2. The operating panel 5 contains buttons for feeding, ejecting, and releasing the slip forms P, as well as LEDs for indicating various printer states. Referring to Fig. 2 and Fig. 3, the printing unit 10 of this printing apparatus 1 comprises a print head unit 11. A dot impact type print head 11a is disposed on the bottom of the print head unit 11 facing the tray 2. The print head unit 11 is replaceably mounted to a carriage 12, which is supported on a guide shaft 13. The print head unit 11 can thus travel freely widthwise to the printing medium by driving a drive motor 14 to move the carriage 12 along the guide shaft 13. The transportation rollers 15 are disposed in the transportation path in front of the print head unit 11 as seen in Fig. 2. Of the two transportation rollers 15a and 15b, one is a drive roller connected to a drive power source, and the other is an idler roller that follows the rotation of the drive roller. One of the transportation rollers 15 (roller 15a in this embodiment) is movable relative to the other by means of an actuator between a closed state and an open state. In the closed state, the rollers 15 clamp a slip form P in between which has been inserted into the printing unit 10 to transport the form in the direction of arrow A in Fig. 2. A slip form can also be transported in the direction opposite to arrow A by simply driving the transportation rollers 15 in the opposite direction. In the open state of the transport rollers 15, a slip form held therebetween is released. When a slip form P is inserted into the printing unit 10, the transportation roller 15a is separated from the transportation roller 15b as shown in Fig. 3. When the slip form P is transported, the transportation roller 15a descends in the direction of arrow B and presses the form against roller 15b, thereby enabling form transportation. A stepping motor can be used to drive the transportation rollers 15. It will obvious that using a stepping motor makes it possible to accurately control the distance a form is transported based on the rotary angle of the motor, that is, the number of steps the motor advances. A form stop 16 is provided for positioning the slip form P in the transportation direction. When the user inserts a slip form P into the printing unit 10, the form stop 16 obstructs the path at a point inside from the tray 2 as indicated by the solid line representation of the form stop 16 in Fig. 3. When a slip form P is placed in the printing unit and transportation by the transportation rollers 15 begins, the form stop 16 is retracted from the transportation path by a plunger 17 as indicated by the solid line in Fig. 3, thereby enabling the slip form P to advance. The printing apparatus 1 further comprises two form detectors 18 and 19. As shown in Fig. 3, the one detector 18 comprises an optical emitter 18a and a receptor 18b disposed opposite to one another above and below the transportation path in proximity to the form stop 16. When a slip form P is placed in the printing unit 10 and the leading edge thereof advances between the optical emitter 18a and receptor 18b, light from the optical emitter 18a is interrupted by the form. It can therefore be confirmed that a slip form P is set in the transportation path. The other detector 19 is disposed at one side of the tray 2 as shown in Fig. 2. This detector 19 also comprises an optical emitter and a receptor, housed in a U-shaped frame. As a result, the detector 19 can determine when the edge of a slip form P has been inserted. The form stop 16 and transportation rollers 15 work with the form detector 18 to index and position the leading edge of the form. At the start of this process the form stop 16 blocks the transportation path. When a user inserts a slip form P to the tray 2, the leading edge of the form abuts the form stop 16, and is prevented thereby from advancing further. When the form detector 18 detects a slip form P, the transportation roller 15a descends and the transportation rollers 15 clamp the slip form P. The transportation rollers 15 are then driven in reverse direction, that is, opposite to the direction the form is fed for printing, until the form detector 18 detects that the leading edge of the slip form P has backed out of the form detector 18. As a result of this sequence, the slip form P is indexed to a precise location. After the slip form P is positioned as described above, the location of the leading edge of the form in the transportation path can be estimated from the distance between the form detector 18 and the transportation rollers 15, and the distance corresponding to the rotary angle through which the transportation rollers 15 turned. Referring to Fig. 4, a central processing unit (CPU) 6 of the printing apparatus 1 is able to determine that the slip form P is set to the appropriate position in the printing unit based on the detection results of the form detectors 18 and 19. The CPU 6 reads the current state of the form detectors 18 and 19, and controls and drives the form stop 16, transportation rollers 15, and printing unit 10 as required. The control program executed by the CPU 6 is read by the CPU 6 from read-only memory (ROM) 7 when the printing apparatus 1 is turned on. An interface 8 of the printing apparatus 1 receives control commands sent from a host 20, and buffers the received commands to a random access memory (RAM) 9. RAM 9 also functions as temporary data storage. The CPU 6 interprets control command buffered to RAM 9. When a character print command is received, the CPU 6 reads the font definition from ROM 7 develops a print image and writes the print image to RAM 9. If a form is loaded to the printing unit 10, the CPU 6 drives the printing unit 10 to print the developed print image, and drives the transportation rollers 15 to advance the form after completing a print line. The processes whereby these control commands are received and interpreted, print images are developed, and characters are printed on a form are known in the art, and further description thereof is thus omitted. The CPU 6 is connected to the form detectors 18 and 19, plunger 17 for moving form stop 16, the drive power source for transportation rollers 15, printing unit 10, operating panel 5, ROM 7, interface 8, and RAM 9 via a signal bus or other means known in the art. The operation whereby the printing apparatus 1 prints to a slip form P is described below. When a user inserts a slip form P into the printing unit 10 after a print command has been sent from the host 20 (for example, a cash register) connected to the printing apparatus 1, the form detectors 18 and 19 detect form presence and notify the CPU 6. If the CPU 6 determines that a slip form P is appropriately set in the printing unit 10, that is, is positioned for printing, an actuator (not shown in the figures) is driven to lower the transportation roller 15a, and plunger 17 is driven to retract the form stop 16 from the transportation path. The print head unit 11 is then moved widthwise to the slip form P and the slip form P is printed. The slip form P is advanced one line at a time by the transportation rollers 15 to sequentially supply a fresh printing area to the print head 11a as each line is printed. Non-print commands can also be supplied to the printing apparatus 1, including commands for moving the carriage 12. A return home command (ESC <) causing the carriage 12 to return to the home position, and a printer initialization command (ESC @) are examples of these non-print commands. The printer initialization command (ESC @) cancels any printer mode settings, line feed distance settings, and other user-controllable settings to restore the default settings, and is output when the power to the printing apparatus 1 is turned on and when the printer is reset. A control method for a printing apparatus 1 according to the present invention is described next. Fig. 5 is a flow chart of a control method used when a command involving a carriage movement is received by a printing apparatus according to the present embodiment. Operation of the printing apparatus when such a command is received is described with reference to Fig. 3 and Fig. 5. When a command involving carriage movement (simply called "carriage movement command" below) is received (S501), the printing apparatus 1 lowers the transportation roller 15a (S502) irrespective of whether or not a slip form P is on the tray 2. If a slip form P is on the tray 2 at this time, the slip form P is thus clamped between the transportation rollers 15a and 15b. The drive motor 14 of carriage 12 is then driven, and the carriage 12 is moved according to the carriage movement command (S503). If the carriage movement command is a return home command, the carriage 12 is moved to the home position. When the carriage 12 stops moving, the transportation roller 15a is raised (S504). Any slip form P clamped between the transportation rollers 15a and 15b is thus released. It should be noted that the transportation rollers 15 can be driven by a specific amount after step S502 and before the carriage 12 is moved in step S503. If the transportation rollers 15 are driven, they are driven in the direction opposite to arrow A in Fig. 2, that is, toward the open end of the tray, by an amount sufficient to eject the slip form P. If a slip form P is not appropriately positioned, for example, if a slip form P is inserted diagonally to the transportation path, advancing the slip form P in the direction of arrow A has a good chance of causing a paper jam. As a result, the slip form P is transported in the opposite direction to eject the slip form P and prevent a paper jam from occurring. Fig. 6 is a flow chart of a control method used when a command involving carriage movement is received by a printing apparatus according to a second embodiment of the invention. With the control method illustrated in Fig. 5, the transportation roller 15a is raised and lowered and the rollers 15 possibly driven rotationally irrespective of whether a slip form P is on the tray 2. While this method simplifies the procedure to be executed when a carriage movement command is received, it also involves needless operation of the transportation rollers when no slip form P is present, and creates unnecessary noise. In the present second embodiment, therefore, the presence of a slip form P is detected before the transportation roller 15a is driven, and the transportation rollers are operated only when a slip form P is determined present. When a carriage movement command is received (S601) by the printing apparatus 1 using the control method shown in Fig. 6, the first step is to detect whether a slip form P is present (S602). This is accomplished using the form detectors 18 and 19. Note that this operation does not detect whether the slip form P is appropriately positioned, but simply determines whether either of the form detectors 18 and 19 detects a slip form P. If a slip form P is detected, the transportation roller 15a is lowered, and the slip form P is clamped (S603). The drive motor 14 is then driven to move the carriage 12 (S604). When carriage 12 movement ends, the transportation roller 15a is raised to release the slip form P (S605). If a slip form P is not detected in step S602, the carriage 12 is simply moved (S606) without operating the transportation roller 15a. As a result, raising and lowering the transportation roller 15a when a slip form P is not present is eliminated. The transportation rollers 15 can be driven by a specific amount after step S603 to eject the slip form P before proceeding from step S604. The operation in this case involves the same process as that optionally inserted between steps S502 and S503 in Fig. 5 and described above. Fig. 7 is a flow chart of a control method used when a command involving carriage movement is received by a printing apparatus according to a third embodiment of the invention. This method is the same as that shown in Fig. 6 through carriage movement (S701 - S704 and S705). It differs from the method shown in Fig. 6 in the procedure following carriage movement in step S704, that is, the procedure for releasing the clamped slip form P. In the present method, the form detectors 18 and 19 are used to determine, after the carriage is moved, whether the slip form P is correctly positioned (S706). As described above, the slip form P is assumed to be correctly positioned when it is detected by both form detectors 18 and 19. If the slip form P is not positioned correctly, it is released (S707). If the slip form P is positioned correctly, it is ready for printing and is therefore not released but remains held. By detecting whether the printing medium is appropriately positioned when it is clamped, and then holding the printing medium clamped after moving the carriage, printing can be started immediately after the carriage is moved. Unnecessary operations of the transportation roller 15a can thus be reduced. The slip form P can also be released as required by simply operating the appropriate control button on the operating panel 5. If the slip form P is not appropriately positioned in step S706, the transportation rollers 15 can be driven by a specific amount after step S706 to eject the slip form P before proceeding to step S707. Operation in this case involves the same process as that optionally inserted between steps S502 and S503 in Fig. 5 and described above. The user can be prompted to reset the printing medium correctly by ejecting the printing medium when it is positioned incorrectly. The control methods shown in Fig. 5 to Fig. 7 can be achieved by the CPU 6 of the printing apparatus 1 and a program implemented by the CPU 6. The program itself can be stored in ROM 7 or another semiconductor memory or storage device provided in or connected to the printing apparatus 1. The preceding embodiments of the present invention have been described with reference to a dot impact printer as an example of a printing apparatus used in connection with a cash register or other point-of-sale terminal for printing checks and other slip forms. The invention is not, however, limited to dot impact printers, and can be readily applied to thermal printers, inkjet printers, and other printers in which the print head is moved for printing. The printing apparatus of the invention can also be adapted for printers using a variety of recording media, including receipts, slip forms, labels, checks, invoices, delivery tickets, credit card charges, and other types of cut-sheet forms. The printing apparatus can comprise a plurality of transportation roller pairs, of which all or any part can be openable and closable. The form stop is not essential to the invention, and can be removed from the printing apparatus. In a printing apparatus according to the present invention as described above, the printing medium is always held by a transportation roller whenever the carriage moves, thereby preventing the printing medium from protruding into the path of the carriage, and preventing paper jams and damage to the printing medium resulting from contact between the carriage and printing medium. While this is particularly effective when the transportation path is straight because there is a greater tendency for the printing medium to lift into the carriage path the invention is also applicable to printing apparatus having a curved transportation path. Furthermore, the same effect can be achieved when the printing apparatus is configured to eject the printing medium after it is clamped by the transportation rollers. The present invention allows a data storage medium having recorded thereon a program implementing the method of the invention to be distributed and sold independently of the printing apparatus as a software product.

Claims: A printing apparatus comprising: a print head (11a) supported for reciprocating movement along a first direction, a transportation path into which a printing medium (P) to be printed by said print head (11a) can be inserted, transport means (15) for transporting said printing medium along said transportation path past said print head in a second direction orthogonal to said first direction, said transport means including a first and a second roller (15a, 15b) disposed on opposite sides of the transportation path; drive means for moving said rollers relative to each other between a closed state in which one roller is urged against the other so as to pinch a printing medium which is in between the rollers, and an open state in which the rollers are separated from each other so as to release a printing medium which is in between the rollers, receiving means (8) for receiving commands for controlling the operation of the printing apparatus, and control means (6) responsive to a print head moving command among those commands for causing said print head (11a) to move along said first direction, wherein said control means is adapted to cause, in response to each print head moving command, said drive means to bring said rollers (15a, 15b) into said closed state prior to causing said print head to move. The apparatus as set forth in claim 1, further comprising: medium detection means (18, 19) for detecting if a printing medium (P) is inserted into the transportation path; wherein the control means (6) is responsive to said detection means for causing the drive means to bring said rollers (15a, 15b) into said closed state only when insertion of a printing medium is detected. The apparatus as set forth in claim 1 or 2, wherein the control means (6) is adapted to cause the drive means to bring said rollers (15a, 15b) back to the open state after a print head movement in accordance with a print head moving command has been completed. The apparatus as set forth in claim 1, 2 or 3 further comprising: medium position detection means (18, 19) for detecting if a printing medium (P) is correctly inserted into the transportation path; wherein the control means (6) is responsive to the medium position detection means for controlling the drive means and the transport means (15) so as to eject the printing medium (P) when the printing medium is detected not to be correctly inserted. The printing apparatus as set forth in claim 3, further comprising: medium position detection means (18, 19) for detecting if a printing medium (P) is correctly inserted into the transportation path; wherein the control means (6) is responsive to the medium position detection means for causing the drive means to bring said rollers (15a, 15b) back to the open state only when the printing medium is detected not to be correctly inserted. The apparatus as set forth in claim 5, wherein the control means (6) is responsive to the medium position detection means detecting that the printing medium (P) is not correctly inserted, for controlling the drive means and the transport means (15) so as to eject the printing medium (P) before causing the drive means to bring said rollers (15a, 15b) back to the open state. The apparatus as set forth in claim 4 or 6, wherein the printing medium (P) is ejected in a direction opposite to the direction in which it is inserted into the transportation path. The apparatus as set forth in any one of claims 4 to 7, wherein the medium position detection means comprises first detection means (18) for detecting the leading edge of the printing medium (P) and second detection means (19) for detecting the side edge of the printing medium. The apparatus as set forth in any one of the preceding claims, wherein said print head moving command is a command to move the print head (11a) to a standby position. The apparatus as set forth in any one of the preceding claims, wherein said transportation path is straight. A method of controlling a printing apparatus as defined in any one of the preceding claims, comprising the steps of: (a) controlling the drive means so as to bring the rollers (15a, 15b) into the closed state in response to each print head moving command received by said receiving means (8); and then (b) moving the print head (11a) according to the command. The method as set forth in claim 11 wherein step (a) comprises: detecting, in response to a print head moving command received by said receiving means (8), whether a printing medium (P) is inserted into the transportation path, and controlling the drive means so as to bring the rollers (15a, 15b) into the closed state only when a printing medium is detected to be inserted. The method as set forth in claim 11 or 12, further comprising the step of: (c) bringing said rollers (15a, 15b) back to the open state after step (b) has been completed. The method as set forth in claim 11, 12 or 13 further comprising the steps of: (d) detecting if a printing medium (P) is correctly inserted into the transportation path; and (e) ejecting the printing medium (P) when the printing medium is detected in step (d) not to be correctly inserted, steps (d) and (e) being performed prior to step (b). The method as set forth in claim 11 or 12, further comprising the steps of: (f) detecting if a printing medium (P) is correctly inserted into the transportation path, and (g) controlling the drive means, after step (b), to bring the rollers (15a, 15b) into the open state when the printing medium is detected not to be correctly inserted while controlling the drive means to keep the transportation rollers in the closed state when the printing medium is detected to be correctly inserted. The method as set forth in claim 15, wherein step (g) comprises ejecting the printing medium (P) by means of the rollers (15a, 15b) prior to bringing the rollers (15a, 15b) into the open state when the printing medium is detected not to be correctly inserted. A data storage medium carrying a control program for implementing the method according to any one of claims 11 to 16.

Inventors: ITO YOSHIKAZU, ITO, YOSHIKAZU
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1998
Main classification: B41J11
IPC codes: B41J11, B41J13