Printing medium transport apparatus and method and printing apparatus

A printing medium transport apparatus and method and printing apparatus which is capable of properly transporting a printing medium by the cooperation of two rollers under independent drive without incurring the complication, size increase and price increase of the apparatus. In the course of transporting a sheet by the cooperation of feed and transport rollers, deceleration/stop control is made on feed and transport motors to be respectively driven such that the rollers are simultaneously stopped from rotating. When the transport roller stops from rotating that is located downstream side on a transport path of a printing medium in case the feed roller is rotating that is located upstream side on the transport path, the feed motor driving the feed roller is forcibly stopped.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printing-medium transport apparatus and method for transporting a printing medium by use of two rollers to be driven independently, and to a printing apparatus having such a transport apparatus. The invention is suited particularly for use on an apparatus that handles a highly rigid printing medium.

2. Description of the Related Art

In the printing apparatus as represented by the inkjet printer, a feed mechanism is provided to separate one by one a paper sheet as printing medium, from the holder tray and then transport it by a feed roller toward a transport roller. The transport roller is provided in the printing zone where an image is to be printed. In such a feed mechanism, it is a general practice to place the feed and transport rollers under drive control of separate motor drive systems for the purpose of adjusting the sheet feeding conditions and simplifying the drive mechanism.

Such a feed mechanism must be properly set with timing of drive start and stop in consideration of the load burdened on the sheet being transported by the cooperation of the feed and transport rollers.

For example, Japanese Patent Laid-Open No. 2005-67805 discloses a structure that clutches are provided in the respective drive systems for the feed and transport rollers so that the clutch and drive motor, in each drive system, can be controlled associatively. Meanwhile, Japanese Patent Laid-Open No. H1-271335 describes a structure that tension detecting means is provided to detect a tension in a sheet lying between the feed and transport rollers so that the feed and transport rollers can be placed under drive control associatively depending upon the tension in the sheet detected by the tension detecting means.

However, the provision, of such an especial mechanism as a clutch or such an especial detector as tension detecting means as in the existing art, possibly incurs the complication, size increase and price increase of the transport mechanism and ultimately of the resulting printing apparatus.

SUMMARY OF THE INVENTION

The present invention provides a printing-medium transport apparatus and method and printing apparatus capable of properly transporting a printing medium by the cooperation of two rollers to be independently driven without incurring the complication, size increase and price increase of the apparatus.

In a first aspect of the present invention, there is provided a transport apparatus for transporting a printing medium through a transport path by cooperation of a first roller located upstream side on the transport path and a second roller located downstream side on the transport path, the transport apparatus comprising: a first drive system that drives the first roller by a first drive motor; a second drive system that drives the second roller by a second drive motor; and control means that places the first and second drive motors under deceleration/stop control respectively to simultaneously stop the first and second rollers from rotating, in a course of transporting the printing medium by cooperation of the first and second rollers; wherein the control means forcibly stops the first drive motor in a case the first roller is rotating when the second roller stops from rotating.

In a second aspect of the present invention, there is provided a transport method for transporting a printing medium through a transport path by cooperation of a first roller located upstream side on the transport path and a second roller located downstream side on the transport path, the transport method comprising the steps of: driving the first roller by a first drive motor; driving the second roller by a second drive motor; placing the first and second drive motors under deceleration/stop control respectively to simultaneously stop the first and second rollers from rotating, in a course of transporting the printing medium by cooperation of the first and second rollers; and forcibly stopping the first drive motor in a case the first roller is rotating when the second roller stops from rotating.

In a third aspect of the present invention, there is provided a printing apparatus comprising: a transport apparatus according to the first aspect of the present invention; and a printing portion where an image is to be printed on a printing medium being transported through the transport path.

According to the invention, the first and second drive motors, under separate driving to those, are placed under deceleration/stop control to stop simultaneously the first and second rollers from rotating, in the course of transporting a printing medium by the cooperation of first and second rollers. Where the first roller located upstream on the printing-medium transport path is rotating upon a stop of the second roller located downstream on the transport path, the first drive motor is forcibly stopped. Owing to controlling the first and second drive motors in this manner, the printing medium can be properly transported without incurring any complication, size increase and price increase of the apparatus. Specifically, the printing medium can be suitably transported without applying such an excessive load as a tension to the printing medium or without applying an excessive load to the drive motor where transporting a printing medium particularly high in rigidity.

DESCRIPTION OF THE EMBODIMENTS

With reference to the drawings, description will be now made on embodiments according to the present invention.

First Embodiment

FIG. 1is a schematic perspective view for explaining the interior construction of an inkjet printing apparatus of a serial scan system to which the invention can be applied.FIG. 2is a schematic side view for explaining a structural example of a feed mechanism provided on the printing apparatus.FIG. 3is a block configuration diagram of a control system of the printing apparatus.

An inkjet print head (printing means)7, capable of ejecting ink, is removably mounted on a carriage21movable in a main scanning direction along an arrow A. The print head7may constitute an inkjet cartridge together with an ink tank. As shown inFIG. 2, a printing zone6is formed at between the print head7and a platen22. A sheet1, as a printing medium, is to be transported in a sub-scanning direction shown at an arrow B, along a transport path passing through the printing zone6. By repeating the ejection of ink at the print head7moving in the main scanning direction and the transport of the sheet1in the sub-scanning direction, an image is printed in order on the sheet1.

The sheets1, stacked on a holder tray2, are to be separated one by one and fed onto the transport path by means of a feed roller (first roller)3and a separating roller4that constitute a feeding roller pair5. The feed roller3is to be rotated by a feed motor104(seeFIG. 3) while the separating roller4touches the feed roller3. In the vicinity of the printing zone6, a transport roller (second roller)8and a driven roller9are provided constituting a transport roller pair10. The transport roller8is to be rotated by a transport motor105(seeFIG. 3) while the driven roller9touches the transport roller8. The sheet1is to be held by the feed roller pair5and fed to the printing zone6. In this manner, the feed roller3and the transport roller8, as described below, are to be driven separately by respective motor driving systems, in order to adjust the feeding conditions and simplify the drive mechanism.

Between the transport roller pair10and the feed roller pair5, a guide portion11is arranged including a rib to guide the sheet1at its leading edge. In a position above the guide portion11and upstream the transport roller pair10with respect to the transport direction, a sheet-edge sensor12is arranged to detect the leading edge of the sheet1.

The feed roller3generally uses a rubber-made roller formed non-rigid and highly frictional, in order to draw the sheet1out of the holder tray2. Meanwhile, the transport roller8uses a roller formed by a metal shaft polished on its surface in order to improve the transport accuracy of the sheet1at the printing zone6. The transport roller8is set with a sheet-transport power higher than that of the feed roller3.

InFIG. 3, a CPU100is to perform control processing of motions, data processing, etc. for the printing apparatus. A ROM101stores a program for those processing, and a RAM102is to be used as a work area for executing such processing. Ink is ejected from the print head7by driving an ejection-energy producing element of the print head7by means of the CPU100depending upon printing data. The ejection-energy producing element can use an electrothermal conversion element (heater) or a piezoelectric element. Where using the electrothermal conversion element, bubble is caused in ink by heat generation so that ink can be ejected through an ink ejection port by utilization of the energy of bubble generation. Printing data is to be inputted from a host apparatus200in the form of a computer or the like. Through a motor driver103A, the CPU100controls the carriage motor103to move the carriage21in the main scanning direction. Meanwhile, through motor drivers104A and105, the CPU100controls the feed motor (first drive motor)104and transport motor (second drive motor)105as described below, according to the program stored in the ROM101.

The feed motor104and the transport motor105can use a DC motor13as shown inFIG. 4.

The DC motor13is provided with an optical encoder wheel14on a rotary shaft thereof. In a fixing portion of the DC motor13, an optical sensor15is provided to detect encoder slits formed in the wheel14. The rotation number of the DC motor13can be detected depending upon a detection signal of the encoder slits detected by the optical sensor15. In order to detect the rotation number of the DC motor13, the encoder may be provided in a drive system at between the DC motor13and the rollers (feed roller3and transport roller8).

The rotation number per unit time can be detected as to the DC motor13by measuring the detection interval of the encoder slits by use of the optical sensor15. The rotation speed can be adjusted by regulating the application voltage to the DC motor13placed under feedback control. The optical sensor15, using a two-channel type whose output is deviated in phase, also can detect a rotating direction of the DC motor13.

(Drive System Particularity for Feed and Transport Rollers3,8)

In this manner, the drive systems for the feed and transport rollers3,8are structured independently from each other, whose drive systems have respective DC motors13to be placed under servo control separately. In the drive systems for the two DC motors13, there is a possibility to cause a difference in the inertia moment on the elements lying from the DC motor13to the rollers (feed and transport rollers3,8) and in the output characteristics of the two DC motors13. Because the difference of between the drive systems is influential particularly upon the acceleration and deceleration time of the rollers (feed and transport rollers3,8), there is a difficulty in decelerating and stopping the two DC motors13at the same time.

In addition to such a difference of between the drive systems, there is a possibility to cause a transport amount difference of the sheet1at between the rollers resulting from the frictional force difference of between the two types of rollers (feed and transport rollers3,8). This readily causes a looseness or tightness in the sheet1at between the feed and transport roller pairs5,10due to the push or pull of the sheet1.

Pushing a sheet1refers to a state that feed amount is excessive at the feed roller3relative to the transport roller8whereas pulling a sheet1refers to a state that feed amount is deficient at the feed roller3relative to the transport roller8. It is generally considered preferable that the sheet1is suitably loose under the condition not to cause, in the sheet1, wrinkles, folds and tightness in a push direction. For this reason, a space is formed to provide a proper looseness in the sheet1, on the guide portion11constituting the sheet path extending between the feed roller3and the transport roller8. This can prevent the sheet1from being tightened by pulling thereof. The existence of proper flexure in the sheet1provides an effect to eliminate the effect of feed accuracy caused by the feed roller3contrary to the transport roller8requiring transport accuracy.

Meanwhile, it is desirable to eliminate the tightness, constituting a load in the sheet1, in both the push and pull directions of the sheet1at a start of accurately transporting the sheet1. Namely, when the sheet1is transported to the printing zone6by the cooperation of the feed and transport rollers3,8(hereinafter, referred also to as “cooperative transport”) followed by being accurately transported for printing, the feed roller pair5is preferably released of its transport force thereby eliminating the tightness from the sheet1. For this reason, there are cases to use a structure that the rotation amount of the feed roller3is regulated by means of a cam or the like so that the feed roller3can be released of its drive/transport force after cooperatively transporting the sheet1a given amount.

However, where rectifying a skew of the sheet1depending upon the type thereof as referred later, the feed and transport rollers3,8stop simultaneously in timing in various ways. Accordingly, in such various situations the feed and transport rollers3,8stop simultaneously, the transport force must be maintained at the feed roller3. Namely, there is a need to retain a tail portion of the sheet1by means of the feed roller pair5, in the upstream of the transport roller pair10with respect to the sheet transport direction. In this case, the feed roller3is difficult to be controlled by the utilization of a cam and the like.

Furthermore, the feed mechanism recently has reduced in size wherein a rigid special sheet is required to handle as the sheet1, or printing medium. In the specifications of such a feed mechanism, there is a difficulty in securing a sufficient space allowing the sheet1to sag. The printing medium, if highly rigid, is placed in a situation ready to cause a tightness without obtaining a less effect of such sagging wherein a great influence encounters even where slight is the difference of transport amount of the printing medium between the feed roller3and the transport roller8. For example, where the transport roller8stops earlier than the feed roller3after cooperatively transporting a rigid printing medium, the printing medium cannot be fed by the feed roller3being decelerated. In this case, the drive system to the feed roller3becomes possibly inoperative because of load applied thereto. Where allowance is less given to the backlash or mechanism strength of a drive system reduced in size, the sheet1possibly undergoes the effect of tightness loading in the push direction thereof during cooperative transport of the sheet1. Namely, immediately after the feed and transport rollers3,8are stopped, spring-back action takes place at the feed mechanism thereby possibly shifting the feed roller3or the sheet1.

(Control Example of Feed and Transport Motors104,105)

FIG. 5is a flowchart for explaining the feed stop control of the sheet1to be performed at a time of detecting the leading edge of the sheet1by the sheet-edge sensor12after starting to cooperative transport the sheet1by the cooperation of the feed and transport rollers3,8. The control procedure constitutes a part of a control processing of a series of sheet feed operations (including those upon printing) of the sheet1.

In the outset, at step S101, the feed and transport rollers3,8are started to rotate respectively by the feed and transport motors104,105. The sheet1, separated out of the holder tray2, is fed in the arrow direction by the rotation of the feed roller3, as shown inFIG. 6. At this time, the feed speed of the sheet1is equal at the feed roller3and at the transport roller8. The sheet1, being fed by the feed roller3, is moved along the guide portion11and advanced toward the transport roller8. The sheet1, as described below, is detected at its leading edge by the sheet-edge sensor12and then caught at the leading edge by the nip of the transport roller pair10.

When the sheet-edge sensor12detects the leading edge of the sheet1and turns on, the process proceeds from step S102to step S103inFIG. 5, thus starting deceleration/stop control as to the feed and transport motors104,105. Namely, a deceleration/stop command is issued to decelerate and stop the motors such that, after the sheet-edge sensor12detects the leading edge of the sheet1, the feed and transport rollers3,8are rotated equal in transport amount and then the feed and transport motors104,105are stopped at the same time. The transport amount, in this case, is given as a specified amount established by a detection signal related to the encoder slits.

By means of the deceleration/stop command, the sheet1comes to a rest in a state being fed a somewhat amount in the arrow direction after caught at the leading edge by the nip of the transport roller pair10, as shown inFIG. 7. Namely, the feed and transport rollers3,8go into stop simultaneously after the sheet1is caught at the leading edge by the nip of the transport roller pair10and then fed somewhat in amount by the cooperation thereof.

At the next step S104, it is determined whether or not stop control on the transport motor105has completed, i.e. whether or not the transport motor105has stopped. In the case the transport motor105has stopped, it is determined whether or not stop control of the feed motor104has completed, i.e. whether or not the feed motor104has stopped. In the case the feed motor104has stopped, theFIG. 5process is terminated. Accordingly, in the case the feed motor104is at stop when the transport motor105is in stoppage, theFIG. 5process is terminated.

Meanwhile, in the case the feed motor104is not yet stopped at the time of step S105, the current supply is shut off to the feed motor104. Namely, after issuing a command to forcibly terminate the deceleration/stop control on the feed motor104, theFIG. 5process is terminated.

FIGS. 8 to 10are figures for explaining a change of rotation speed V and application current I under the deceleration/stop control of the feed and transport motors104,105. In the figures, time t is taken on the abscissa while the rotation speed V detected by the encoder and the application voltage I under control are taken on the ordinate. The speed of and application voltage to the feed motor104are shown at v1and i1while the speed of and application voltage to the transport motor105is shown at v2and i2.

FIG. 8shows a case that the feed motor104stops at the time point t0that the transport motor105stops. InFIG. 8, the change of speed is ideal wherein stop timing is identical between the feed motor104and the transport motor105, thus cooperatively transporting the sheet1smoothly. In this case, theFIG. 5process is terminated without proceeding the process from step S105to step S106inFIG. 5.

FIG. 10shows a case that the feed motor104comes to a stop earlier in timing than the transport motor105wherein the transport roller8stops later than the feed roller3. However, because transport force is greater at the transport roller8than the feed roller3, the difference between those causes a slippage at between the feed roller3and the sheet1, thus not raising a trouble in driving the transport motor105. In this case, theFIG. 5process is terminated similarly to theFIG. 8ideal situation without proceeding the process from step S105to step S106inFIG. 5.

FIG. 9shows a case that the transport motor105comes to a stop earlier in timing than the feed motor104. For example, where the transport roller8stops earlier during transporting a rigid sheet1, the sheet1cannot be fed by the feed roller3being decelerated. In such a case, the feed drive system including the feed motor104possibly becomes inoperative because of load applied thereto. Accordingly, in this case, the process proceeds from step S105to step S106inFIG. 5where application voltage i1is cut off to the feed motor104being decelerated, thus interrupting the deceleration servo control on the feed motor104. Due to this, the feed motor104stops after decelerated on inertia.

By thus executing theFIG. 5processing, the deceleration/stop control is completed as to the transport motor105regardless of the stop timing of the feed and transport motors104,105. Thus, accurate management is available as to the stop position of the sheet1.

After stopping the sheet1as shown inFIG. 7, the feed and transport rollers3,8are driven simultaneously. By the cooperation of those, the sheet1is transported (cooperatively transported) to the printing zone6at its print start point. Thereafter, image printing is made onto the sheet1being intermittently fed by the cooperation of the feed and transport rollers3,8. TheFIG. 5processing can be executed in any operation of the printing apparatus. Namely, the FIG.5processing may be executed at any time provided that they are stopped at the same time during cooperative transport (including during skew rectification, referred later) of the sheet1.

Before or after a stop of the sheet1as shown inFIG. 7, skew rectification can be made to rectify the skew of the sheet1.

For example, before stopping the sheet1as shown inFIG. 7, the skew of the sheet1is rectified by pushing the leading edge of the sheet1into the nip of the transport roller pair10through use of the transport force of the feed roller3. Namely, the skew is rectified by abutting the leading edge of the sheet1against the transport roller8being stopped from rotation. As another example of skew rectification, there is a method that the transport roller8is rotated reverse while keeping the feed roller3at stop after the leading edge of the sheet1is once caught in the nip of the transport roller pair10by the cooperation of the feed and transport rollers3,8. In such a case, the amount of reverse rotation of the transport roller8is given greater than the catch amount of the sheet1in the transport roller pair10. This method can relieve the load imposed upon abutting the leading edge of the sheet1and improve the effect of rectifying the skew of the sheet1. After rectifying the skew of the sheet1by reverse rotating of the transport roller8in this manner, the sheet1is fed to the printing region6.

Those methods of skew rectification are to be applied depending upon sheet type, etc. wherein it can cope with a change of rotation speed or amount of the roller even on the same printing apparatus.

Second Embodiment

FIG. 11is a flowchart for explaining control to perform after stopping the sheet1from moving by the cooperation (cooperative transport) of the feed and transport rollers3,8. The control procedure constitutes a part of the control processing of a series of feed operations (including those in printing) of the sheet1.

At the time of step S501where to start theFIG. 11process, the feed and transport rollers3,8have already completed the cooperative transport of the sheet1as shown in theFIG. 5flowchart. Consequently, the sheet1is in a state being caught in the nip of the transport roller pair10, as shown inFIG. 7. The step S502represents a situation that the feed and transport motors104,105are once stopped wherein the sheet1is completed in its cooperative transport, i.e. immediately before the movement to the next step.

At the next step S503, with respect to the detection result as to the encoder slits in the drive system of the feed roller3, determination is made as to the presence/absence and direction of a change caused after terminating the deceleration/stop control. When there is a change or no change in the encoder-slit detection result toward the forward rotation of the feed roller3(in the direction of transporting the sheet1toward the downstream of the transport path) after a simultaneous stop of the feed and transport motors104,105, theFIG. 11process is terminated. Meanwhile, when there is a change of encoder-slit detection result toward the reverse rotation of the feed roller3(in the direction of returning the sheet1toward the upstream of the transport path) after a simultaneous stop of the feed and transport motors104,105, the process proceeds to step S504. At the step S504, drive start timing is controlled to advance at the feed motor104earlier than the transport motor105.

The deviation amount of drive timing at the step S504can be defined in terms of the encoder slits or of time. The deviation amount of drive timing can be adjusted in accordance with the reverse rotation amount of the feed roller3such that the deviation amount of drive timing increases with an increase in the detected reverse rotation amount of reverse rotation of the feed roller3.

FIGS. 12 and 13show examples in a change of feed motor104speed and encoder output, at a completion of cooperative transport. In the figures, time t is taken on the abscissa while a rotation speed v of the feed motor3detected by the encoder and an application current i under control are taken on the ordinate.

The encoder is of a two-channel system having phases A and B to be detected in a rotating direction. The outputs20,21in phases A, B from the encoder of the feed motor104are compared with a speed v of the feed motor104.FIG. 12shows a case that the application voltage i becomes zero at a completion time t0of the deceleration/stop control on the feed motor104, followed by reverse rotation of the feed motor104thus changing the encoder outputs.FIG. 13shows a case that the application voltage i becomes zero at a completion time t0of the deceleration/stop control on the feed motor104, followed by forward rotation of the feed motor104thus changing the encoder outputs.

As apparent fromFIGS. 12 and 13, by comparing the phase-A and phase-B outputs20,21with the speed v of the feed motor104, determination can be made as to whether or not the feed roller3has rotated after the deceleration/stop control on the feed motor104. Furthermore, in the case the feed roller3has rotated, determination can be made as to the rotating direction thereof.

Other Embodiments

The invention can be broadly applied as a transport apparatus in various type for transporting a printing medium, wherein the printing medium to transport may be not only an unprinted one but also a printed one. The transport apparatus may be structurally incorporated in a printing apparatus or structurally arranged separately from the printing apparatus. Meanwhile, where the transport apparatus is incorporated in the printing apparatus, the control function for the transport apparatus may be partly or wholly provided on the printing apparatus or on a host apparatus.

The invention is applicable broadly for various printing apparatuses besides the serial-scan type inkjet printing apparatus. The printing apparatuses, the invention is applicable, includes, say, a full-line type printing apparatus having, in a constant position, an elongate printhead extending over the entire width of a printing medium and for printing an image while transporting the printing medium. Meanwhile, printing is not limited to the inkjet printing system but may be desirably, e.g. in a thermal transfer system.

This application claims the benefit of Japanese Patent Application No. 2006-227180, filed Aug. 23, 2006, which is hereby incorporated by reference herein in its entirety.