Printer and method of controlling it

Abstract: Disclosed is a printer for printing on roll paper, comprising a roll paper holder (22) having an opening for loading a paper roll, a cover supported to be movable relative to the roll paper holder (22) between a first position in which it covers the opening and a second position in which it exposes the opening, a feed roller (26) and a first gear (31) both attached to the cover and coupled to each other, a motor (61) for rotatively driving the feed roller (26) via a first gear train (71-73), said first gear train including a second gear (73) fixed relative to the roll paper holder (22), wherein the first gear (31) is engaged with the second gear (73) when the cover is in its first position and is disengaged from the second gear when the cover is in its second position, and the first gear (31) is arranged to rotate relative to the second gear (73) until it has disengaged from the second gear when the cover (30) is moved from said first toward said second position, wherein said second gear (73) is adapted to be driven by said motor (61) such as to rotate in a first direction to advance said roll paper (4) via said feed roller (26), and releasing means are provided for allowing the second gear (73) to rotate in a second direction opposite said first direction, when the cover is moved from said first toward said second position.

Description: The present invention relates generally to printers. More particularly, the invention relates to a printer capable of printing on roll paper supplied from a paper roll in a roll paper holder having an opening for loading the paper roll and a cover for opening/closing the opening. Printers for printing on roll paper using an ink jet head, a wire dot head, or a thermal head as the print head are generally known. JP-B-6-79855, for instance, discloses a thermal printer having a roll paper supply portion including a roll paper cabinet for accommodating a paper roll as a supply of roll paper. The roll paper cabinet has an opening for allowing a paper roll to be installed. A cover is provided that normally closes that opening but can be fully opened so that replacing or loading of roll paper can be accomplished easily. In this printer, the cover comprises a first and a second cover frame that are both pivotally supported by means of the same pivot axis. A first one of the cover frames has a holder for the paper roll and also supports a platen roller (roll paper feed roller). When the cover is closed the platen roller is positioned opposite to a thermal print head. The platen roller has its shaft supported in elongated holes in side portions at the end of the first cover frame remote from the pivot axis. The second cover frame is closed after the first cover frame has been closed already. While the second cover frame is pivoted into the closed position relative to the first cover frame, cam elements fixed to the second cover frame engage the shaft of the platen roller and move it in the elongated holes so as to press the platen roller against the elastically biased thermal head. In the prior art described above, the platen roller is a non-driven freely rotatable roller. EP-A-0 925 947 (prior art according to Art. 54(3) EPC) discloses a structure in which a platen roller mounted on a cover, which is movable with respect to a main frame, is a driven platen roller used as a paper feed roller. In such case, means must be provided to transfer rotary motion from a motor fixed relative to the main frame to the platen roller on the cover. As described in EP-A-0 925 947 such transfer is accomplished by means of a paper feed gear mounted coaxially to the platen roller and a drive gear coupled to the motor and arranged such that the two gears engage each other when the cover is closed and are disengaged from each other when the cover is open. In such case, when the cover is being closed, the freely rotatable paper feed gear first approaches and then contacts the drive gear, and then typically turns by a certain angle until the teeth on the two gears mesh. Because the platen roller is integrally attached to the paper feed gear, the platen roller also turns slightly as the paper feed gear engages the drive gear. When the cover is opened, the paper feed gear likewise rotates through a certain angle in the opposite direction to disengage from the drive gear. The platen roller obviously also turns in the opposite direction at the same time. It is to be noted that the drive gear is typically linked to the drive motor through a gear train. This means that rotation of the drive gear is normally constrained. In such a printer, when a paper jam occurs in that the paper is advanced into and becomes jammed in a gap between the platen roller and another member, the platen roller and, thus, the paper feed gear may no longer be rotatable. When opening the cover requires the paper feed gear to rotate relative to the drive gear until the two gears become disengaged from one another and the rotation of the drive gear is constrained as explained above, it becomes very difficult if not practically impossible to open the cover in order to remove the paper jam. JP-A-5-147284 discloses a printer capable of printing on both roll paper and cut-sheet paper or slip forms. A printer having a switching mechanism for allowing the rotation of a common drive motor to be selectively transferred to either a roll paper transportation mechanism or a slip form transportation mechanism is known from US-A-5,061,095, for example. JP-A-10-20414 teaches a cover opening/closing mechanism comprising a cover pivotally attached to the body of a facsimile machine, for example, and an sensor for detecting whether this cover is open or closed. The cover has locking means for locking the cover in its closed position. When a release lever for releasing this locking means is operated, the sensor detects that the cover lock has been released. It is an object of the present invention to improve a printer of the type explained above and having a cover movable relative to a roll paper holder, a paper feed gear fixed relative to the cover and a drive gear fixed relative to the roll paper holder, in such a way that the cover can be opened using little force even when rotation of the paper feed gear is constrained due to a paper jam. Another object of the invention is to provide a method of controlling such printer. These objects are achieved with a printer as claimed in claim 1 and a method as claimed in claim 12, respectively. Preferred embodiments of the invention are subject-matter of the dependent claims. The invention is based on the recognition that, when the paper feed gear is assumed to be blocked such as by a paper jam, the relative rotation between the drive gear (second gear) and the paper feed gear (first gear) that is required for disengaging the two gears from one another and allow the cover to be opened, can still be made possible by allowing the drive gear to rotate in a direction (second direction) opposite to the direction (first direction) in which it is normally driven to rotate the platen roller via the paper feed gear so as to advance the roll paper. There are several ways for allowing the drive gear to rotate in the second direction. Among these several ways are "passive" alternatives which remove the constraining force exerted by the motor, such as decoupling the drive gear from the gear train normally connecting it to the motor, decoupling that gear train from the motor, or cutting off the holding current to the motor. Included is also an "active" alternative, however, i.e.; reversing the motor so as to actively turn the drive gear in the second direction for a certain time, sufficient for the cover to be opened far enough to disengage the paper feed gear from the drive gear. There are also various possibilities for determining the timing at which the drive gear shall be allowed to rotate in the second direction. Among these possibilities are: in response to a cover-unlocked signal generated upon detection that the cover is unlocked (assuming that the unlocking is an indication that the cover is intended to be opened); in response to a signal generated by a manually operable switch; and in response to a signal generated by a paper jam detector, e.g., a torque detector associated with the drive motor. While the possibilities listed so far require some kind of electric control, the invention also allows use of various kinds of mechanical means such as a mechanically operated clutch for decoupling the drive gear from the motor. It goes without saying, that each of the above listed ways for allowing the drive gear to rotate in the second direction may be combined with some or all possibilities for determining the timing. Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. Fig. 1 is a perspective view of one embodiment of an ink jet printer according to the present invention; Fig. 2 shows the paper transportation path in the ink jet printer shown in Fig. 1; Fig. 3 is a side view of the drive force transfer mechanism in the ink jet printer shown in Fig. 1; Fig. 4(A) is a top view of the drive force transfer mechanism of Fig.3, 4 (B) shows an exemplary clutch mechanism of the drive force transfer mechanism; Fig. 5 is a timing chart of the operation changing the drive force transfer mechanism from the roll paper drive side to the slip form drive side; Fig. 6 is a timing chart of the operation changing the drive force transfer mechanism from the slip form drive side to the roll paper drive side; Fig. 7 is a partial perspective view of the roll paper supply portion in the ink jet printer shown in Fig. 1; Fig. 8 is a side view of the roll paper supply portion in Fig. 7 with a cover closed; Fig. 9 is a side view of the roll paper supply portion in Fig. 7 with the cover in a first intermediate position; Fig. 10 is a side view of the roll paper supply portion in Fig. 7 with the cover in a second intermediate position; Fig. 11 is a side view of the roll paper supply portion in Fig. 7 with the cover fully opened; Fig. 12 (A) and (B) illustrate means for mounting a slide frame to a first cover frame of the cover; Fig. 13 shows the characteristic mechanical parts of the printer shown in Fig. 1 in conjunction with the control system therefor; Fig. 14 shows the operation of a detecting mechanism for detecting locking and unlocking of the cover; and Fig. 15 shows an alternative means for releasing a constraining force. As a preferred embodiment of the present invention an ink jet printer for a POS terminal is described below with reference to the accompanying figures. General configuration of the printer Fig. 1 is a perspective view of an ink jet printer 1 according to the preferred embodiment, and Fig. 2 shows its paper path along which paper is transported. As shown in these figures, the paper path of printer 1 has a roll paper supply portion 2 including a roll paper loading mechanism and a slip form insertion opening 3 for inserting various types of cut-sheet forms of A4 or other size. The paper path carries roll paper 4 supplied from the supply portion 2, or a slip form 5 inserted into the insertion opening 3, past a common printing position 11 (indicated in Fig. 1 by a single dot-dash line). Roll paper 4 is typically used for printing receipts. The roll paper 4 is pulled from a paper roll 4A loaded in the supply portion 2, travels between paper guide 27 and pressure roller 15, past the printing position 11, and between platen roller 26 (also referred to as roll paper feed roller) and pressure roller 16. Note that the roll paper 4 is advanced by rotation of the platen roller 26. Slip forms 5 are used for printing sales records and similar forms. A slip form 5 is inserted into the insertion opening 3 and caught by paper feed roller 51 and pressure roller 52, advanced between paper feed roller 53 and pressure roller 54 past the printing position 11, and is then ejected from the printer after having passed between paper feed roller 55 and pressure roller 56 (see Fig. 3). A guide shaft 6 is disposed in parallel to the common printing position 11. An ink jet head 8 is mounted on a carriage 7, which travels bidirectionally along the guide shaft 6. It is therefore possible to print, by means of this ink jet head 8, as desired on the surface of either roll paper 4 or slip form 5 advanced to the common printing position 11. Ink is supplied through an ink tube (not shown in the figure) to the ink jet head 8 from an ink supply 10 disposed at a position typically adjacent to the roll paper supply portion 2. Drive transfer assembly A typical configuration of a drive force transfer mechanism for use in printer 1 is described next with reference to Fig. 3 and Fig. 4. This drive force transfer mechanism uses a clutch mechanism to transfer rotation (torque) from a single drive motor to either a first gear train for roll paper transportation or a second gear train for slip form transportation, thereby rotatively driving platen roller 26 or paper feed rollers 51, 53, and 55. For better identification the platen roller 26 and the paper feed rollers 51, 53, and 55 are shaded in Fig. 3. Referring to Fig. 3 and Fig. 4, the drive force transfer mechanism comprises: a single drive motor 61; the first gear train for transferring motor rotation from a pinion 61a to the platen roller 26; the second gear train for transferring the motor rotation to paper feed rollers 51, 53, and 55; and a switching gear 62 for switching between these two gear trains. It is to be noted that the switching gear 62 constantly engages the pinion 61 a which is provided on and fixed to the motor shaft. The first gear train includes a first gear 71 for engaging switching gear 62, a second gear 72 coaxial with and fixed to first gear 71, a third gear 73, referred to as drive gear hereinafter, engaged with this second gear 72, and a paper feed gear 31, which is normally engaged with the drive gear 73. As described more fully below, the platen roller 26 is mounted on one end of a slide frame 25, which is a component of a cover 30 (see Fig. 7) for covering the roll paper supply portion 2. The paper feed gear 31 is fixed on one end of a center shaft 26a of platen roller 26 and coaxial therewith. When the cover is completely closed and locked, the paper feed gear 31 engages the drive gear 73. When the cover is open, the paper feed gear 31 is disengaged from the drive gear 73. As will be understood, gears 71 to 73 are fixed relative to a printer main frame 12 while paper feed gear 31 is fixed relative to the cover (in fact, the cover's slide frame 25 in this embodiment where the cover comprises multiple parts movable with respect to one another). Drive gear 73 is the last gear in the first gear train on the main frame side. The second gear train for slip form transportation includes a first gear 81 for engaging switching gear 62; a second gear 82 coaxial with and fixed to this first gear 81; a third gear 83 engaging this second gear 82; fourth and fifth gears 84 and 85 engaging this third gear 83; a sixth gear 86 engaging this fourth gear 84; a seventh gear 87 engaging this fifth gear 85; a paper feed roller drive gear 88 engaging this sixth gear 86; a paper feed roller drive gear 89 engaging the third gear 83; and a paper feed roller drive gear 90 engaging the seventh gear 87. The paper feed roller drive gear 88 is linked coaxially to paper feed roller 51; paper feed roller drive gear 89 is linked coaxially to paper feed roller 53; and paper feed roller drive gear 90 is linked coaxially to paper feed roller 55. The clutch mechanism for switching the transfer path of the drive motor's torque (referred to as drive train below) is described below with reference to Fig. 4. This clutch mechanism comprises the above-noted switching gear 62, and a solenoid 62B for moving the switching gear 62 along its center shaft 62a between a roll paper transport position, in which the gear's position is as indicated in Fig. 4 by a solid line, and a slip form transport position, in which the gear's position is as indicated by a dotted line in Fig. 4. As shown in Fig. 4 (B), the switching gear 62 comprises: a cylindrical part 621 disposed so that it can rotate freely and slide on center shaft 62a; an external gear 623 having its teeth formed on the outer circumferential surface of a ring flange 622, which has a cup-like shape to widen from the outside circumference of cylindrical part 621; and a ring flange 624 formed at a position on the outside circumference of cylindrical part 621 separated in the axial direction from ring flange 622. An annular channel 625 is formed between these ring flanges 622 and 624. One end of operating lever 626 used to slide switching gear 62 along the shaft 62a is inserted into this annular channel 625. The other end of this operating lever 626 is linked to an end part of operating rod 629 of solenoid 62B by way of intervening lever support 628 formed to support a bracket 627. It is therefore possible to slide the switching gear 62 and thereby switch the drive train simply by energizing or deenergizing the solenoid 62B. As will be understood from Fig. 3 and Fig. 4, motor rotation is transferred through first to third gears 71, 72, and 73 to the paper feed gear 31 when the switching gear 62 is in the roll paper transport position (indicated by the solid line in Fig. 4 (A)). Platen roller 26 is thus rotatively driven, and roll paper 4 is advanced. When the switching gear 62 is moved to the slip form transport position (indicated by the dotted line in Fig. 4 (A)), motor rotation is transferred through first to seventh gears 81 to 87 to paper feed roller drive gears 88, 89, and 90, and the corresponding paper feed rollers 51, 53, and 55 are thus rotatively driven. In this case, slip form 5 is advanced. Switching the drive train Fig. 5 and Fig. 6 are timing charts referred to below to describe the switching operation (receipt to slip form or R/S switching) whereby the switching gear 62 is moved from the roll paper transport position to the slip form transport position, and the switching operation (slip form to receipt or S/R switching) whereby the switching gear 62 is moved from the slip form transport position to the roll paper transport position, respectively. As illustrated in these timing charts, the R/S switching is activated by an R/S switching signal. In this embodiment, this R/S switching signal is a cover-unlocked signal output from a detector for detecting whether the cover is locked or unlocked as described more fully below. Note, that the R/S switching signal can also be generated manually using an appropriate manual switch, for instance. When the R/S switching signal is applied, the solenoid 62B is operated (deenergized in Fig. 5, energized in Fig. 6) and the drive motor 61 is driven forward and rearward (i.e., clockwise and counterclockwise) to adjust the position of the switching gear 62 relative to the gear 71 (or 81) so that it may separate from the gear 71 (or 81) with which it is engaged (periods A and D in Fig. 5 and Fig. 6, respectively). Depending on whether the switching gear 62 is engaged with gear 71 or 81 at the start of this operation, switching gear 62 slides along shaft 62a in either period A or D, and separates from gear 71 or 81. It is important to note, however, that the switching gear 62 will not necessarily disengage from gear 71 (or 81) within period A (or D). There is, therefore, a delay (periods B and E, respectively) of a specified time during which the controller for driving the clutch waits for the switching gear 62 to separate completely from gear 71 (or 81). The drive motor 61 is then again turned forward and rearward to allow the switching gear 62 to slide and adjust its position so that it engages the other gear 81 (or 71). It should be further noted that in this embodiment the drive train is normally set to the roll paper transport side, and switching gear 62 is normally held in the position indicated by the solid line in Fig. 4 (A). As will be described more fully below, when the cover-unlocked signal indicating that the cover has been unlocked is applied, the switching gear 62 is slid to the position indicated by the dotted line in Fig. 4 (A) by means of the clutch mechanism, thereby switching the drive train to the slip form transport side. It is yet further important to note that by thus switching the drive train, the first gear train for roll paper transportation is decoupled from the motor and, thus, released from the rotation constraining force exerted by the drive motor 61 when the latter is not driven. As a result, the drive gear 73 and the paper feed gear 31 that engages drive gear 73, are disengaged from the motor and can turn freely. The operating force required to release engagement between these two gears in order to open the cover is thus small, and the cover can be opened easily with little force. Roll paper supply portion The roll paper supply portion 2 of this embodiment is described next with reference to Figs. 7 to 12. Referring to these figures, roll paper supply portion 2 has a mounting frame 21 affixed to the main frame 12. This mounting frame 21 comprises a roll paper holder 22 into which roll paper 4 is loaded in the form of a paper roll 4A. The roll paper holder 22 has a semicircular curved part 22a of a specific width, and a rectangular opening 22b above the curved part 22a. Paper roll 4A can be replaced or loaded through this opening 22b. The opening 22b can be opened/closed by means of cover 30 comprising a first cover frame 23, the slide frame 25, and a second cover frame 28. The first cover frame 23 has a top plate part 23a with substantially the same rectangular shape as the opening 22b, and sides 23b and 23c, which have a specific height and are formed by bending the right and left sides of top plate part 23a perpendicularly to the top. The rear end of each side 23b and 23c extends further downward, forming bottom ends 23d and 23e. These bottom ends 23d and 23e are pivotally supported on a shaft 24. The ends of shaft 24 are supported by mounting frame 21. The first cover frame 23 can thus pivot around shaft 24 between a closed position (shown in Fig. 8) whereat it closes the opening 22b, and an open position (shown in Fig. 11) whereat the opening 22b is open and unobstructed. Slide frame 25 is mounted on this first cover frame 23. Slide frame 25 both pivots in conjunction with the first cover frame 23 and slides relative to the first cover frame 23. The platen roller 26 and the paper guide 27 for guiding roll paper 4 to the platen roller 26 are mounted at the front edge of the slide frame 25. The means that mount slide frame 25 slidably at the first cover frame 23 is described next with reference to Fig. 12 ((A) and (B)). Note that first cover frame 23 and the slide frame 25 are shown upside down in Fig. 12. The slide frame 25 has a rectangular top plate 25a that contacts the inside of the top plate part 23a of first cover frame 23, and sides 25b and 25c, which have a specific height and are formed by bending the right and left sides of top plate 25a perpendicularly to the top. Guide slots 25d and 25f are formed in the front-to-back direction in the top plate 25a. Guide pins 23q and 23r fixed to top plate part 23a of first cover frame 23 pass through these guide slots 25d and 25f. A snap ring 23h and 23i is attached at the projecting bottom ends of these guide pins 23q and 23r to hold the slide frame 25 so that it is slidably held on the inside of first cover frame 23 as shown in Fig. 12 (A). A coil spring 23g is connected between the rear guide pin 23r and a spring catch 25g disposed at the front end of the slide frame 25. This coil spring 23g biases the slide frame 25 to the rear. Referring again to Fig. 7, the platen roller 26 is disposed between front ends 25h and 25i of sides 25b and 25c of the slide frame 25 with the ends of the platen roller shaft rotatively supported at the front ends 25h and 25i. Paper guide 27 is formed below the platen roller 26 and has a convex circular arc shaped surface tangential to the outside surface of platen roller 26. When the platen roller 26 supported at the end of slide frame 25 is in its operating position, pressure roller 16 presses against the outside surface of the platen roller 26 with a specific elastic force. More specifically, the center shaft 16a of pressure roller 16 can be moved slightly to approach or separate from platen roller 26, and is normally urged to platen roller 26 by spring tension. Therefore, when the platen roller 26 is positioned in its operating position in resistance to this spring tension, roll paper 4 is pressed against the outside surface of the platen roller 26 by means of pressure roller 16 as a result of this constant spring tension. Roll paper 4 thus held between these two rollers can then be advanced by rotatively driving platen roller 26. When platen roller 26 is in the operating position, surface 27a of paper guide 27, which is also disposed at the end of the slide frame 25, likewise displaces pressure roller 15, also mounted on the printer, in resistance to the elastic force of the roller. Pressure roller 15 thus pushes with constant force against this surface 27a of paper guide 27 with the roll paper 4 disposed in between. A slightly larger second cover frame 28 is disposed over first cover frame 23. This second cover frame 28 comprises top panel 28a and sides 28b and 28c, which are bent perpendicularly from both sides of top panel 28a. The rear ends of sides 28b and 28c extend further downward, and are pivotally supported on shaft 24. Starting from the positions illustrated in Fig. 11, when this second cover frame 28 is pivoted to close the cover, first cover frame 23 to which slide frame 25 is attached also pivots. After the first cover frame 23 has closed the roll paper loading opening 22b as shown in Fig. 9 (illustrating a first intermediate position of the cover 30), the second cover frame 28 continues to pivot independently. This independent pivoting action of the second cover frame 28 causes the slide frame 25 to slide forward or rearward relative to the first cover frame 23. A linkage mechanism 29 for converting the independent pivoting motion of the second cover frame 28 to the sliding motion of the slide frame 25 comprises a connecting shaft 28d and three oval connecting holes 25j. The connecting shaft 28d spans the distance between the sides 28b and 28c of second cover frame 28 at a position above and at the rear of the second cover frame 28. The connecting holes 25j are provided at the rear of slide frame 25. The connecting shaft 28d passes through the connecting holes 25j. The long axis of the oval connecting holes 25j is oriented substantially perpendicularly to the slide frame 25 so that the connecting holes 25j do not interfere with the independent pivoting action of the second cover frame 28. As a result, when the first cover frame 23 has closed the roll paper loading opening 22b, as shown in Fig. 9, the connecting shaft 28d is positioned so that when the second cover frame 28 is further pivoted toward the horizontal position shown in Fig. 8, the connecting shaft 28d moves downward and forward of the center of shaft 24 defining the center of rotation. While the connecting shaft 28d moves freely downward in the vertically long oval connecting holes 25j, the connecting holes 25j are pushed forward at the same time. This causes the entire slide frame 25 with respect to which the position of connecting holes 25j is fixed to also move forward. More specifically, slide frame 25 slides forward on first cover frame 23, thus projecting platen roller 26 and paper guide 27 on the front end thereof into the printing position 1 with a specific gap held to the opposing ink jet head 8 whereby printing is accomplished. This position of platen roller 26 is referred to herein as the operating position. When the second cover frame 28 is conversely pivoted from the horizontal position shown in Fig. 8 to the position shown in Fig. 9, the movements described above are reversed. That is, the slide frame 25 slides to the back, and the platen roller 26 and paper guide 27 at the front end thereof are retracted from the operating position to a retracted position. As noted above the slide frame 25 is urged constantly in the retracting direction by coil spring 23g. The tension of the extended coil spring 23g thus causes the slide frame 25 to return to the retracted position when the force holding the second cover frame 28 horizontal and closed as shown in Fig. 8 is released. This sliding action also causes the second cover frame 28 to pivot in the opening direction to the posture shown in Fig. 9. A locking lever 280 is disposed at a front part of the second cover frame 28 as a means of locking the second cover frame 28 in the closed position shown in Fig. 8. When the second cover frame 28 is thus closed, hooks 28g and 28h formed on the end of each locking lever 280 engage a corresponding catch 21g and 21h on the edge of the opposing mounting frame 21. Note that the hooks 28g and 28h engage the catches 21g and 21h by rotating back and engaging the catches 21g and 21h from below. A torsion spring (not shown in the figure) constantly urges locking lever 280 in the direction causing the hooks to rotate forward and up against the catches. Therefore, when the second cover frame 28 is closed further from the position shown in Fig. 9, hooks 28g and 28h are forced to pivot slightly back in resistance to the torsion spring until the hooks pass the edge of the corresponding catch and then travel forward and up again to engage the respective catch 21g and 21h on the mounting frame 21. To release the locking, end 28i of the locking lever 280 is raised, thereby causing the hook on the bottom end of the locking lever 280 to rotate downward and disengage the catch. Roll paper supply portion 2 according to this embodiment also has a mechanism for precisely positioning the platen roller 26 in its operating position when the second cover frame 28 is closed as described above. More specifically, positioning pins 25k and 25l project horizontally to both sides at the front of sides 25b and 25c of slide frame 25. Corresponding to these positioning pins 25k and 25l on the mounting frame 21 are semicircular channels 21k and 21l so that when the slide frame 25 is closed the positioning pins 25k and 25l slide horizontally into the positioning channels 21 k and 21l. It is to be noted that the position of these channels 21k and 21l is fixed. As a result, fitting the positioning pins 25k and 25l of the slide frame 25 into these channels 21 k and 21l accurately defines the operating position of the platen roller 26. When the platen roller 26 is in this operating position, the platen roller surface becomes the printing surface against which paper is held in the printing position 11. The ink jet head 8 travels bidirectionally from side to side with a specific gap held to the printing surface. As a result, a constant gap can be held between the platen roller 26 and the nozzle face of the ink jet head 8. A respective coil spring 23j and 23k (only 23j is shown in the figures) is stretched between the sides 21b and 21c of the mounting frame 21 and the corresponding sides 23b and 23c of the first cover frame 23. These coil springs 23j and 23k are disposed such that when the second cover frame 28, slide frame 25, and first cover frame 23 are opened and closed by being pivoted on shaft 24 and pass the pivot position shown in Fig. 10 (illustrating a second intermediate position of the cover) where the center of gravity of the frames is directly above shaft 24, the distance between the catches on the ends of each spring increases as the frames 28, 25, and 23 continue to move. This means that when the second cover frame 28 is opened beyond the pivot position shown in Fig. 10, the coil springs 23j and 23k stretch, creating spring tension pulling the second cover frame 28 in the closing direction. This prevents the second cover frame 28 from springing open rapidly and forcefully, and thus avoids potential damage caused by the frame 28 striking another object. Likewise when the second cover frame 28 is closed beyond the pivot position shown in Fig. 10, the coil springs 23j and 23k stretch, creating spring tension preventing the second cover frame 28 from closing forcefully and thus avoiding damage resulting from the frame 28 striking the opening 22b to the roll paper holder. Locked/unlocked detection mechanism for the cover 30 Printer 1 of this embodiment further comprises a locked/unlocked detection mechanism (simply called LUD mechanism below) for detecting whether the cover 30 is locked in the closed position or whether the locking has been released. Fig. 13 shows the part of the printer where the LUD mechanism is mounted, and the major components of the printer control system. Fig. 14 illustrates how the LUD mechanism works. It is to be noted that this LUD mechanism is omitted from Figs. 1 to 12 for the convenience of showing the other component parts. The LUD mechanism detects whether the locking lever 280 is locked to the mounting frame 21 or has been released from the locked position. As shown in Fig. 13, the LUD mechanism comprises a basically L-shaped pivoting lever 285, which pivots around an axis of rotation when pushed by the hook 28g, 28h of the corresponding locking lever 280, and an optical sensor, here in the form of a photointerrupter 288 for detecting the position of the pivoting lever 285. The pivoting lever 285 and photointerrupter 288 are supported on the mounting frame 21. The pivoting lever 285 is, more specifically, pivotally mounted by means of a pivot pin 289 attached at the bend in the pivoting lever 285. The pivoting lever 285 is normally urged in the direction opposite to arrow 285A in Fig. 13 by a spring (not shown in the figure). An engaging pin 286 is disposed at the top end of pivoting lever 285. When the cover 30 is being closed, this engaging pin 286 contacts the front edge of one locking lever hook 28h just before the cover reaches its final closed position. As the cover 30 then continues to move into its final closed position illustrated in Fig. 8, hook 28h pushing against this engaging pin 286 thereby causing pivoting lever 285 to pivot in the direction of arrow 285A to the position indicated by the solid line in Fig. 13. As noted above, when the second cover frame 28 is completely closed, the hooks 28g and 28h of the locking lever 280 engage the catches 21g and 21h, respectively, on the mounting frame 21 and, thus, lock the cover 30 in the closed position. This locked position is shown in Fig. 14 (a). In this locked position, the other end 287 of the pivoting lever 285 extends into the detection slot 288a of the photointerrupter 288. The photointerrupter 288 thus outputs a detection signal (referred to as cover-locked signal) indicating that the hook 28h of the locking lever 280 is locked. When the cover 30 is to be opened and the end 28i of locking lever 280 is lifted in the direction of arrow 28A in Fig. 13 and Fig. 14 (a) from the locked position, the locking lever hooks 28g and 28h pivot around axis 28B and separate from the catches 21 g and 21 h, respectively, on the mounting frame 21. When the locking is thus released, the above-noted spring tension returns the pivoting lever 285 to the initial unlocked position as shown in Fig. 14 (b) and by the dotted line in Fig. 13, thus also removing the other end 287 from the detection slot 288a of the photointerrupter 288. The output level of the photointerrupter output signal thus changes, and the photointerrupter 288 outputs a detection signal indicating that the locking lever 280 is now unlocked (referred to as cover-unlocked signal). When the locking lever 280 is thus unlocked, the cover 30 is moved toward its fully open position by the applied spring tension as described above. Fig. 14 (c) shows the cover 30 when it has pivoted slightly towards the fully open position. Controller Fig. 13 shows the controller and corresponding mechanical parts of printer 1. In this embodiment, the controller of printer 1 comprises a drive control unit 39 typically having a microprocessor with a CPU, a ROM for storing the program to be run by the CPU, and a working RAM, similar to a common ink jet printer. That is, the controller described below is composed of primarily the same CPU, ROM, and RAM as conventional printers with the CPU performing the process for reducing or releasing the constraining force on the paper feed gear described below according to a program stored in ROM and/or RAM. It is to be further noted that drive control of the ink jet head 8 and paper feed control of roll paper and slip forms by this drive control unit 39 is substantially the same as in a common ink jet printer. Further description and presentation in the accompanying figures is therefore omitted herein; only those parts associated with drive control as it relates to the present invention are described. The drive control unit 39 controls drive motor 61 by means of motor driver 38, and controls operation of the solenoid 62B by means of driver 40. The detection signal 288S generated and output by the photointerrupter 288 of the LUD mechanism as described above is supplied to the drive control unit 39. When the cover 30 is closed and locked, drive gear 73 and paper feed gear 31 are engaged and thus may constrain opening the cover 30 as described above. When it is detected that the locking has been released, the drive control unit 39 performs an operation for releasing the force, if any, that prevents or hinders the meshing drive gear 73 and paper feed gear 31 to disengage from one another and thus constrains opening the cover. This operation is referred to below as a constraint releasing operation. To accomplish this operation, this embodiment has the drive control unit 39 driving the above-noted clutch mechanism to switch the drive train downstream from the drive motor 61 from the roll paper transportation gear train to the slip form transportation gear train. As shown in Fig. 4 (A) and explained before, this clutch mechanism comprises solenoid 62B, switching gear 62, first gear 71, and first gear 81. Operation of the roll paper supply portion Opening and closing roll paper holder 22 of the roll paper supply portion 2 in printer 1 of this embodiment is described next below with reference to Figs. 8 to 11, 13, and 14. Fig. 8 shows the cover 30 in a first or closed position in which the first cover frame 23 covers the opening 22b, the slide frame 25 is in its projected position holding the platen roller 26 in its operation position with drive gear 71 and paper feed gear 31 engaged with one another, and the second cover frame 28 is locked in its closed position. Fig. 11 shows the cover in a second or open position with the first cover frame 23, the slide frame 25 and the second cover frame 28 each in its fully open position. Figs. 9 and 10 illustrate a first and a second intermediate position on the cover's way from the first position of Fig. 8 to the second position of Fig. 11. Note that in this embodiment the paper feed gear 31 becomes disengaged from the drive gear 73 while the cover is moving from the first position in Fig. 8 to the first intermediate position, i.e., before the second position is reached. Starting from the closed position as shown in Fig. 8 and Fig. 13, when the top end 28i of the locking lever 280 is pulled up, the right and left hooks 28g and 28h on the locking lever disengage from the catches 21 g and 21 h, respectively. The locking is thus released. The pivoting lever 285, therefore, leaves the detection slot 288a of the photointerrupter 288, and the photointerrupter 288 thus detects that the locking of cover 30 has been released. More specifically, the detection signal of the photointerrupter 288 is output as a cover-unlocked signal to the drive control unit 39 of the ink jet printer 1. When the drive control unit 39 detects this signal, it applies a drive signal to the solenoid 62B of the clutch mechanism, thereby causing the switching gear 62 to slide from the roll paper transport position (indicated with a solid line in Fig. 4) to the slip form transport position (indicated with a dotted line in Fig. 4). This switching operation follows the sequence shown in Fig. 5 and explained before. The roll paper transportation gear train (gears 71 to 73 and 31) is thus disengaged from the drive train connected to the drive motor 61, thereby reducing or releasing the constraining force preventing free gear rotation. The drive gear 73 on the main frame side and the paper feed gear 31 engaged therewith are thus both able to turn freely. It is therefore possible to easily disengage the meshed drive gears. As a result, the cover 30 can be opened with little force. This is true even if the paper feed gear is blocked by such as a paper jam. In that case only the drive gear 73 is freely rotatable which is sufficient, however, to allow the two gears to rotate relative to each other and, thus, to disengage from each other. When the locking is thus released and the cover 30 opened, the second cover frame 28, slide frame 25, and first cover frame 23 of the cover 30 pivot in conjunction to the position shown in Fig. 9. This pivoting operation is accomplished primarily by the tension of coil spring 23g stretched between slide frame 25 and first cover frame 23. When the second cover frame 28 is then pivoted further to the back through the position shown in Fig. 10 to the position shown in Fig. 11 in resistance to the tension of coil springs 23j and 23k, the opening 22b is completely opened. That is, the second cover frame 28, slide frame 25, and first cover frame 23 are retracted from above the opening 22b. After thus fully opening the roll paper holder, the paper roll 4A (see Fig. 10) in the roll paper holder can be replaced. The paper roll 4A can be easily placed into and removed from the roll paper holder because the opening 22b is unobstructed. It is also easy to position the leading part 4a of the roll paper 4 because the platen roller 26 and paper guide 27 are also removed from the roll paper holder together with the slide frame 25. After loading a paper roll 4A, the second cover frame 28 is rotated in the closing direction. The second cover frame 28, slide frame 25, and first cover frame 23 thus pivot together through the position shown in Fig. 10 until the first cover frame 23 closes the opening 22b as shown in Fig. 9. The first cover frame 23 thus engages the edge of the opening 22b and pivots no further. The slide frame 25 disposed slidably on the first cover frame 23 also stops pivoting. The second cover frame 28, therefore, pivots independently as it continues to close from this position. When the second cover frame 28 is then pushed to pivot to the position shown in Fig. 8, the pivoting motion of the frame is converted by linkage mechanism 29 to a sliding motion of slide frame 25. That is, the slide frame 25 slides forward relative to the first cover frame 23 to the operating position at which the platen roller 26 and paper guide 27 are held to oppose the ink jet head 8 with a specific gap in between. When the slide frame 25 slides forward, the positioning pins 25k and 25l at the front sides of the slide frame 25 enter the channels 21k and 21l in the mounting frame 21, thus stopping the sliding motion and defining the operating position. In other words, the channels 21k and 21l assure that the platen roller 26 and paper guide 27 are held in a predetermined operating position at which a specific gap to the ink jet head 8 is established and held. Sliding the slide frame 25 forward also causes the paper feed gear 31 on one end of the platen roller 26 to move horizontally forward and completely engage drive gear 73 by the time it moves from the side to a position directly above the drive gear 73 on the mounting frame 21. At this point the locking lever hooks 28g and 28h are locked to the frame-side catches 21g and 21 h. The pivoting lever 285 in the front of the hook 28h on one side thus pivots, causing its bottom end 287 to interrupt the light ray of the photointerrupter 288. It is thus detected that the cover 30 is closed and locked and the photointerrupter 288 outputs the cover-locked signal. When the drive control unit 39 then detects this cover-locked signal, it drives the solenoid 62B of the clutch mechanism to slide the switching gear 62 from the slip form transport position (dotted line in Fig. 4) to the roll paper transport position (solid line in Fig. 4). The operating sequence in this case is as shown in Fig. 6 and explained before. This operation completes the drive train for roll paper transportation. Thereafter, the drive control unit 39 drives drive motor 61 through motor driver 38 to advance the roll paper, and synchronously drives the ink jet head 8 to print as desired on the roll paper. It goes without saying that additional means are provided for switching the clutch mechanism between the two gear trains depending on whether roll paper or slip forms are to be printed. Such means are not directly related to the invention and will not be described in further detail. Alternative embodiment of a controller When the controller of the ink jet printer 1 described above generates the cover-unlocked signal, the drive train is switched to the slip form side to release or reduce any constraining force that may oppose the rotation of the paper feed gear 31 relative to the drive gear 73 which relative rotation is necessary to allow the two gears to disengage from one another in response to the application of only a little force. It is alternatively possible, as shown in Fig. 15 for example, for this controller to stop, when the photointerrupter 288 detects that the cover is unlocked, supplying the holding current typically applied to drive motor 61 to hold it in a fixed position. With the holding current removed, the drive motor is allowed to turn freely. This can be accomplished by the motor controller 39B of the drive control unit 39. This configuration also effectively reduces or releases the constraining force of drive motor 61 on the roll paper transportation gear train. Little force is therefore required to disengage the paper feed gear 31 from the drive gear 73. Using the motor controller 39B of the drive control unit 39, the controller can also be comprised to actively disengage the paper feed gear 31 and the drive gear 73 by driving the drive motor 61 reverse to the paper transportation direction for a specified time when the photointerrupter 288 detects the cover to be unlocked. In this case, too, the paper feed gear 31 can be disengaged from the drive gear 73 with little force required. This configuration is particularly advantageous when the roll paper jams. More specifically, when the roll paper jams the roll paper is typically stuck in the gap between the platen roller 26 and the member opposing the outside surface of the platen roller 26. When this happens the platen roller 26 cannot turn, and the paper feed gear 31 affixed coaxially to the platen roller 26 also cannot turn. As a result, the cover 30 to which the platen roller 26 is attached cannot be opened as explained before. To recover from such a paper jam, the cover 30 must be opened and the jammed roll paper removed. Even though the cover 30 itself is blocked in such case, the locking lever 280 will not be affected and can be pivoted to the unlocked position (indicated by the dotted line in Fig. 8), thereby causing the cover-unlocked signal to be output from the photointerrupter 288. When the motor controller 39B of the drive control unit 39 detects this signal, the drive motor 61 is driven in reverse for a specific time by the motor driver 38. If the cover 30 is opened in conjunction with the reverse motor rotation, the paper feed gear 31 and the drive gear 73 can be easily disengaged. It is thus even easier to open the cover 30. Jammed roll paper can then be removed, and the platen roller 26 can again be turned. It is to be noted that while the above preferred embodiment of the present invention has been described with reference to a printer for printing on both roll paper and slip forms, the invention is not limited to such case and can obviously be adapted for use with printers capable of printing on roll paper only. In this case the mechanism for switching the drive train needs only to disengage the roll paper drive gear train from the drive motor or the drive gear from the gear train. While the present invention is applicable to a variety of different printer structures it is particularly advantageous in case of the embodiment explained above in which the paper feed gear 31 engages the drive gear 73 (or disengages from it) while moving in a direction substantially tangential to the drive gear. Because the platen roller 26 and the paper feed gear 31 are mounted on the slide frame 25, the axis of paper feed gear 31 performs a translational motion relative to the drive gear 73 as the two gears are engaged with or disengaged from one another. The drive gear is located at such position that the locus of paper feed gear's axis during the engaging and disengaging motion is parallel to a line more or less tangential to the drive gear. Therefore, more relative rotation between the two gears is required to engage or disengage them as may be the case if the two gears are arranged such that the locus of the paper feed gear during engagement and disengagement is a line radial to the drive gear or at least having a greater component in the drive gear's radial direction.

Claims: A printer for printing on roll paper (4), comprising: a roll paper holder (22) having an opening (22b) for loading a paper roll (4A), a cover (30) supported to be movable relative to the roll paper holder (22) between a first position in which it covers the opening (22b) and a second position in which it exposes the opening (22b), a feed roller (26) and a first gear (31) both attached to the cover (30) and coupled to each other, a motor (61) for rotatively driving the feed roller (26) via a first gear train (71-73), said first gear train including a second gear (73) fixed relative to the roll paper holder (22), wherein the first gear (31) is engaged with the second gear (73) when the cover (30) is in its first position and is disengaged from the second gear when the cover is in its second position, and the first gear (31) is arranged to rotate relative to the second gear (73) until it has disengaged from the second gear when the cover (30) is moved from said first toward said second position, wherein said second gear (73) is adapted to be driven by said motor (61) such as to rotate in a first direction to advance said roll paper (4) via said feed roller (26), and releasing means for allowing the second gear (73) to rotate in a second direction opposite to said first direction, when the cover (30) is moved from said first toward said second position. The printer as set forth in claim 1 wherein said releasing means is responsible to an activating signal. The printer as set forth in claim 2 further comprising: a locking device (21 g, 21 h, 28g, 28h, 280) movable between a locking position in which the cover (30) is locked in said first position and an unlocking position in which the cover is unlocked, and a detecting device (285, 288) for generating, as said activating signal, a cover-unlocked-signal when the locking device is in its unlocking position. The printer as set forth in claim 3, wherein the locking device comprises a locking lever (280) pivotally supported on said cover (30) between a locked position and an unlocked position; a hook (28g, 28h) formed as part of the locking lever; and a catch (21 g, 21 h) fixed relative to the roll paper holder (22) for catching the hook when the locking lever reaches its locked position. The printer as set forth in claim 4, wherein the detecting device comprises a pivoting lever (285) and a sensor (288) for detecting whether or not the pivoting lever is in a first position, wherein the pivoting lever is arranged to be engaged and moved to said first position by a part of the locking lever (280) as the locking lever pivots into its locked position, while the pivoting lever (285) leaves its first position when the locking lever (280) leaves its locked position. The printer as set forth in any one of claims 2 to 5, wherein said releasing means comprises a controller (39) adapted to stop supply of a holding current to the motor (61). The printer as set forth in any one of claims 2 to 5, wherein said releasing means comprises a controller (39) adapted to drive the motor (61) such that said drive gear (73) is rotated in said second direction. The printer as set forth in any one of claims 2 to 5, wherein said releasing means comprises a clutch (62, 62B) for disengaging the first gear train (71-73) from the motor (61) and a controller (39) for controlling the clutch in response to said activating signal. The printer as set forth in claim 8, wherein the clutch comprises: a solenoid (62B); and a switching gear (62) adapted to be slid by the solenoid between a first position in which the switching gear (62) engages a gear of the first gear train (71-73) and a second position in which the switching gear (62) is separated from the first gear train. The printer as set forth in any one of the preceding claims, further comprising: another feed roller (51, 53, 55) for advancing a recording medium other than said roll paper (4); and a second gear train (81-90) for transferring rotation of the motor (61) to said other feed roller (51, 53, 55); wherein said releasing means comprises: a clutch (62, 62B) switchable between a first condition in which it couples the first gear train (71-73) to the motor (61) and a second condition in which it couples the second gear train (81-90) to the motor (61); and a controller (39) for switching the clutch into said second condition in response to said activating signal. The printer as set forth in claim 10, wherein the clutch comprises: a solenoid (62B); and a switching gear (62) adapted to be slid by the solenoid between a first position in which the switching gear (62) engages a gear of the first gear train (71-73) and a second position in which the switching gear (62) engages a gear of the second gear train (81-90). A method of controlling a printer as defined in claim 2, said method comprising the steps of: (a) detecting the activation signal; and (b) allowing, in response to the detection in step (a), the second gear (73) to rotate in said second direction. The method as set forth in claim 12, wherein step (b) includes stopping supply of a holding current to the motor (61) thereby allowing the second gear (73) to rotate freely in said second direction. The method as set forth in claim 12, wherein step (b) includes driving the motor (61) such that the second gear (73) is rotated in said second direction. The method as set forth in claim 12, wherein step (b) includes disengaging the first gear train (71-73) from the motor (61) thereby allowing the second gear (73) to rotate freely in said second direction.

Inventors: NAKAYAMA HIROYUKI, OSAWA KOHEI, NAKAYAMA, HIROYUKI, OSAWA, KOHEI, Nakayama, Hiroyuki, c/0 Seiko Epson Corporation, Osawa, Kohei, c/0 Seiko Epson Corporation
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1999
Main classification: B41J29
IPC codes: B41J15, B41J29