Ink jet printer and movement control method for carriage

An inkjet printer includes a carriage motor that moves a carriage, a carriage driving part that drives the carriage motor, a control value calculating part that calculates a total control value (Wt) composed with a control value for a feedback control and a control value for a feedforward control, which are respectfully referred as a feedback control value (Wb) and a feedforward control value (Wf), and an abnormality judging part that judges whether an abnormality has occurred to the carriage movement based on whether a proportional component (Wp) of the feedback control value has exceeded a threshold value.

TECHNICAL FIELD

This invention relates to an inkjet printer and a movement control method for a carriage.

BACKGROUND

Conventionally, an inkjet printer is designed to perform printing by moving a carriage in the main scanning direction, supplying ink from an ink cartridge to a recording head mounted on the carriage, ejecting ink droplets from the recording head and letting them adhere to (land on) a recording medium, thereby forming an image such as a character or picture consisting of multiple dots.

By the way, in moving the carriage in the inkjet printer, a target velocity that is the velocity targeted by the carriage is set as a target value, and the target velocity is categorized into an acceleration region where the carriage is accelerated from a stopped state, a uniform velocity region where the carriage is moved at a constant velocity, and a deceleration region where the carriage is decelerated and stopped.

In the uniform velocity region, by stably moving the carriage at a constant velocity, the tracks of ink droplets from their ejection from the recording head to their adhesion to the recording medium become uniform, and as the result, dots can be formed in target dot positions on the recording medium. However, if the carriage cannot be stably moved and unevenness occurs in its velocity for example, dots cannot be formed in their target dot positions on the recording medium, degrading the image quality.

Then, in the inkjet printer, feedback control is performed so that the carriage can stably move at a constant velocity in the uniform velocity region.

In the feedback control, based on the above-mentioned target velocity of the carriage, an actual velocity that is the actual velocity of the carriage, a gain, etc., control values including a proportional component and an integral component for the feedback, in other words, feedback control values, are calculated, and the feedback control values are supplied to a carriage driving part for driving the carriage, thereby performing carriage movement control so that the actual velocity becomes the target velocity.

By the way, if an abnormality occurs to the carriage movement, an image cannot be normally formed on the recording medium. For example, if the recording medium hits the carriage, causing a jam, the carriage cannot be moved, and an image cannot be formed on the recording medium. Also, if a foreign body enters inside a chassis of the inkjet printer, the recording medium could become warped, and if the warped recording medium hits the carriage, the carriage cannot be moved at a constant velocity, and dots cannot be formed in the target dot positions on the recoding medium, degrading the image quality.

Then, an inkjet printer has been offered, the inkjet printer being designed to judge whether a deviation between the target velocity and the actual velocity of the carriage has exceeded a threshold value, and if the deviation has exceeded the threshold value, judges that an abnormality has occurred to the carriage movement (see Patent Document 1 for example).

RELATED ART

One Subject to be Solved

However, in the above-mentioned conventional inkjet printer, because carriage movement control is performed by feedback control, the actual velocity is delayed relative to the target velocity, and the deviation between the target velocity and the actual velocity becomes large, which could cause an error in judging whether an abnormality has occurred to the carriage movement.

Then, in order to judge accurately whether an abnormality has occurred to the carriage movement, one idea thought of is to increase the threshold value according to the above-mentioned deviation. However, if the threshold value is increased, when a minor abnormality such that the recording medium becomes distorted and slightly touches the carriage has occurred, the deviation may not exceed the threshold value. In that case, it becomes impossible to judge that an abnormality has occurred to the carriage movement.

As the result, blurring occurs in a formed image, degrading the image quality.

The objective of this invention is to offer an inkjet printer and a carriage movement control method that can solve the above-mentioned problem of the conventional inkjet printer and accurately judge whether an abnormality has occurred to the carriage movement.

SUMMARY

Considering the above objects, a controller of the invention controls a movement of carriage using not only a feedback value but a feedforward value also. Further, the feedback control value is composed with two components, which are a proportional component (Wp) and a integral component (Wi). Using the proportional component, the controller accurately determines if an abnormality of the carriage happens.

More specifically noted, an inkjet printer includes a carriage motor that moves a carriage, a carriage driving part that drives the carriage motor, a control value calculating part that calculates a total control value (Wt) composed with a control value for a feedback control and a control value for a feedforward control, which are respectfully referred as a feedback control value (Wb) and a feedforward control value (Wf), and an abnormality judging part that judges whether an abnormality has occurred to the carriage movement based on whether a proportional component (Wp) of the feedback control value has exceeded a threshold value.

In this case, because carriage movement control is performed using both feedback control and feedforward control, control values for feedback control can be decreased by the amount that control values for the feedforward control are calculated, and therefore the proportional component can be decreased.

Therefore, in judging whether the proportional component has exceeded the threshold value, because the threshold value can be decreased, even if the abnormality in the carriage movement is small, whether the proportional component has exceeded the threshold value can be securely judged.

As the result, whether an abnormality has occurred to the carriage movement can be accurately judged.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Below, an embodiment of this invention is explained in details referring to drawings. In this case, an inkjet printer as an image forming apparatus of an inkjet system is explained.

FIG. 2is a perspective view of the inkjet printer in the embodiment of this invention.

In the figure, indicated as10is the inkjet printer, Fr is a frame of the inkjet printer10, and the frame Fr comprises an upper frame Fr1and an under frame Fr2.

The above-mentioned upper frame Fr1is provided with a receiving plate PB arranged extending from the left end to the right end when seen from the front side of the inkjet printer10(front side in the figure), an outer side plate PL1as a first main supporting part formed standing up from the left end of the receiving plate PB, an outer side plate PR1as a second main supporting part formed standing up from the right end of the receiving plate PB, an inner side plate PL2as a first sub supporting part formed standing up from the receiving plate PB at a prescribed distance rightward of the above-mentioned outer side plate PL1, and an inner side plate PR2as a second sub supporting part formed standing up from the receiving plate PB at a prescribed distance leftward of the above-mentioned outer side plate PR1.

A rail15is erected between the above-mentioned outer side plates PL1and PR1, and a carriage17is arranged in a freely movable manner in the left-right direction along the rail15. Therefore, arranged in a freely rotatable manner are a driving-side pulley18on the above-mentioned outer side plate PR1and a driven-side pulley19on the outer side plate PL1, an endless belt21is stretched in a freely travelable manner between the pulleys18and19, and the carriage17is attached to a prescribed place of the endless belt21. Then, connected to the above-mentioned pulley18is a below-mentioned carriage motor M2(FIG. 1) as a drive part for moving the carriage. Also, attached to the above-mentioned carriage17are below-mentioned multiple, four in this embodiment, recording heads Hi (i=1, 2, . . . , 4) (FIG. 1).

Then, the carriage17is moved in the left-right direction (main scanning direction) by driving the above-mentioned carriage motor M2, and by the individual recording heads Hi being moved in the left-right direction accompanying the movement of the carriage17, printing can be performed on an unshown recording medium.

In this embodiment, the above-mentioned recording heads Hi are recording heads of an inkjet system, where four recording heads Hi that eject black (Bk), yellow (Y), magenta (M), and cyan (C) ink droplets are mounted on the carriage17so that a color image can be formed. Note that the color reproducibility can be improved by using recording heads of other colors than the recording heads Hi of the above-mentioned colors. Also, used as an organic solvent as a solvent in this embodiment is a solvent ink containing a pigment as a colorant.

Unshown multiple nozzles are formed in an array shape on the nozzle face of each of the recording heads Hi, and a color image can be formed by attaching the recording heads Hi to the carriage17so that the nozzle faces oppose the recording medium, and having ink droplets of individual colors ejected through the nozzles according to image data and adhere onto target dot positions on the above-mentioned recording medium while reciprocating the carriage17.

Note that as the recording medium, other than sheets of paper, films made of resins such as vinyl chloride and PET can be used, and the recording medium is carried in a direction perpendicular to the moving direction of the carriage17.

Also, a linear scale23is arranged along the above-mentioned rail15, and by reading the divisions of the linear scale23using a below-mentioned encoder Se (FIG. 1) arranged on the carriage17, the position of the carriage17can be detected.

Then, a medium center guiding part25is arranged between the inner side plates PL2and PR2on the above-mentioned receiving plate PB. The medium center guiding part25is provided with a platen unit u1as a supporting unit that is arranged extending between the inner side plates PL2and PR2, has a plate shape, and supports the recording medium, and an unshown air suction mechanism for drawing from below the recording medium carried on the platen unit u1toward the platen unit u1side with a negative pressure.

The above-mentioned platen unit u1is provided with a platen45as a supporting member having a plate shape, an unshown linear heater that is laid on the rear face of the platen45and heats the recording medium by heating the platen45, and an unshown platen cover as a covering member that has a plate shape, is attached to the rear face of the platen45, and covers the above-mentioned heater.

When the platen45is heated by the above-mentioned heater to make the platen45become a constant temperature, the recording medium carried on the platen45is heated. In this case, by making the temperature of the platen45uniform, an image of uniform quality can be formed. Also, by maintaining the temperature of the recording medium at the most appropriate temperature according to the property of the recording medium and the properties of the inks, ink droplets can be let adhere well to the recording medium, and thus the image quality can be enhanced. If there is unevenness in temperature of the recording medium, differences in drying speed of the individual ink droplets cause differences in their wetting and spreading, and as the result, differences in fusability occur, thereby a specific pattern such as a linear one occurs on the image, degrading the image quality. Furthermore, if the temperature of the platen45is too high, the recording medium becomes warped, making it impossible to carry the recording medium stably.

Also, multiple suction holes are formed on the platen45, a suction chamber is arranged in the above-mentioned air suction mechanism, and a fan is arranged on the suction chamber. By exhausting air inside the suction chamber with the fan and generating a negative pressure in the suction chamber, air can be sucked through each of the suction holes, and the recording medium can be drawn toward the platen unit u1side.

On the rear side (deeper side in the figure) of the above-mentioned upper frame Fr1, an unshown rear paper guide as a medium rear guiding part is arranged. The rear paper guide guides the recording medium, that is forwarded from an unshown forwarding roll and carried up, to the above-mentioned medium center guiding part25. Therefore, between the above-mentioned rear paper guide and the medium center guiding part25in the carrying direction of the recording medium, a carrying roller pair30as a carrying member is arranged in a freely rotatable manner.

The carrying roller pair30comprises a carrying roller31as a first roller arranged in a freely rotatable manner extending along the platen unit u1, and multiple pinch rollers32as second rollers that are arranged in a freely rotatable manner above the carrying roller31and press the recording medium onto the carrying roller31. Once a below-mentioned carrying motor M1as a drive part for carrying is driven to rotate the carrying roller31, the individual pinch rollers32are rotated by drag turning, thereby the recording medium is forwarded from the forwarding roll and carried in a state sandwiched between the carrying roller31and the individual pinch rollers32. Note that the above-mentioned individual pinch rollers32are supported in a freely swingable manner by an unshown arm, and each of them is independently biased toward the carrying roller31by an unshown spring as a bias member, constituting a pinch roller unit.

In this case, the above-mentioned carrying motor M1is driven to carry the recording medium by a prescribed distance, afterwards the carrying motor is stopped, the carriage17is moved in that state, and ink droplets of individual colors are ejected from the individual recording heads Hi, thereby one scan is performed to form one line of image. Once one scan is finished, the above-mentioned carrying motor M1is driven again to carry the recording medium by a prescribed distance, afterwards the carrying motor M1is stopped, the carriage17is moved in that state, and ink droplets are ejected from the individual recording heads Hi, thereby performing one scan and forming one line of image. By repeating this operation, an image is formed on the recording medium.

Note that although printing is performed by a single-pass system in this embodiment, if printing is performed by a multi-pass system, the distance to carry the above-mentioned recording medium is made shorter than the nozzle array of the recording head Hi, and one line of image is formed by performing multiple scans.

Arranged on the front side of the above-mentioned upper frame Fr1is a front paper guide33as a medium front guiding part for guiding the recording medium after printing is performed. The front paper guide33has a curved shape for guiding downwards the recording medium ejected horizontally from the above-mentioned medium center guiding part25. Note that an unshown heater is arranged on the rear face of the above-mentioned front paper guide33, and the front paper guide33is heated by the heater to heat the recording medium.

The above-mentioned under frame Fr2is provided with pedestals35and36arranged in parallel at a prescribed distance between the left-end vicinity and the right-end vicinity of the inkjet printer10, props37and38formed standing up from the center of the respective pedestals35and36, and holding plates PL3and PR3attached to the respective props37and38.

Between the holding plates PL3and PR3, an unshown paper tube (winding roll) is arranged in a freely rotatable manner for winding the recording medium that is ejected from the medium center guiding part25and guided by the above-mentioned front paper guide33. In order to hold the paper tube at the left end and the right end, roll bearings26and27are arranged in a freely rotatable manner on the above-mentioned holding plates PL3and PR3, respectively. By rotating the above-mentioned paper tube by an unshown winding device, the recording medium can be wound.

Also, in the front side of the above-mentioned paper tube, a tension roller28is arranged in a freely movable manner in the up-down direction extending between the holding plates PL3and PR3. The tension roller28gives tension to the recording medium that is guided by the front paper guide33and wound up by the paper tube so that the recording medium should not develop any slack. Therefore, a groove mt is formed extending in the up-down direction on the inner face of each of the above-mentioned holding plates PL3and PR3, and the tension roller28is moved in the up-down direction along the grooves mt.

By the way, as mentioned above, in this embodiment, the above-mentioned rail15is erected between the outer side plates PL1and PR1, and the medium center guiding part25is arranged between the inner side plates PL2and PR2.

Therefore, printing by the individual recording heads Hi is performed while the carriage17is being moved over the medium center guiding part25, and printing by the individual recording heads Hi is not performed while the carriage17is placed between the outer side plate PL1and the inner side plate PL2or between the outer side plate PR1and the inner side plate PR2.

Then, in this embodiment, the space between the outer side plate PR1and the inner side plate PR2is made a home position for performing the origin adjustment of the position of the carriage17and performing the maintenance of the individual recording heads Hi, and the space between the outer side plate PL1and the inner side plate PL2is made a retreat position for letting the carriage17retreat from over the medium center guiding part25.

Then, in the above-mentioned home position, a maintenance unit41is arranged opposing the individual recording heads Hi, and an operation panel43is arranged as an operation/display part for operating the inkjet printer10. In order to maintain the nozzles of the recording heads Hi in a fine state, the above-mentioned maintenance unit41is provided with a wiper to wipe the nozzle face of each of the recording heads Hi, a cap to prevent drying of the nozzles, a suction mechanism to suck ink whose viscosity increased inside a nozzle, etc. Also, the above-mentioned operation panel43is provided with an operation part where operation buttons etc. are arranged, and a display part where a display lamp etc. are arranged.

Next, explained is the control device of the above-mentioned inkjet printer10.

FIG. 1is a block diagram showing the control device of the inkjet printer in the embodiment of this invention.

In the figure, indicated as80is a controller that controls the whole inkjet printer10,81is ROM as a first memory part that records a control program, initial values, etc., and82is RAM as a second memory part used as a work area for the controller80to perform arithmetic operations and also as a buffer for temporarily recording various kinds of data.

Also, indicated as83is a setting value storing part as a third memory part for recording various kinds of setting values in the inkjet printer10. Recorded in the setting value storing part83are target values in moving the carriage17such as target velocity Vs of the carriage17and target position of the carriage17at every unit time (every 1 ms in this embodiment), and a control value for below-mentioned feedforward control, that is, a feedforward control value Wf at every unit time. The individual target values are set by performing experiments or the like in advance. Note that because movement control of the carriage17is performed at every unit time, the shorter the unit time that regulates the individual setting values, the better trackability to the target velocity Vs can become.

Furthermore, recorded in the above-mentioned setting value storing part83are threshold values εj (j=1, 2, 3) for judging whether an abnormality has occurred to the movement of the carriage17. The threshold values εj are set differently according to the peak values of the proportional component Wp in the acceleration region, the uniform velocity region, and the deceleration region of the target velocity Vs, and recorded in the setting value storing part83.

Note that in this embodiment, in order to judge whether an abnormality has occurred to the movement of the carriage17, it is judged whether the proportional component Wp calculated based on the deviation between the target position and the actual position of the carriage17, the deviation between the target velocity Vs and the actual velocity of the carriage17, the gain, etc. has exceeded the threshold value εj (whether the proportional component Wp is greater than the threshold value εj). If delays occur in the actual position and the actual velocity of the carriage17, thus the deviation between the target position and the actual position of the carriage17and the deviation between the target velocity Vs and the actual velocity of the carriage17increase, because the proportional component Wp also increases, it is possible to judge whether an abnormality has occurred to the movement of the carriage17based on whether the proportional component Wp has exceeded the threshold value εj.

Then, indicated as84is a timer as a clocking part that is operated by the controller80and measures time as time information.

The above-mentioned controller80is provided with a control value calculating part Pr1and an abnormality judging part Pr2, and following the control program recorded in the above-mentioned ROM81, an unshown CPU of the controller80operates the control value calculating part Pr1and the abnormality judging part Pr2mentioned above, and also operates a head driving part85, a carrying motor driving part86, a carriage driving part87, a carriage position detection circuit88as a carriage position detecting part, a carriage velocity calculation circuit89as a carriage velocity detecting part, etc. to perform various kinds of processes. One of the carriage position detection part and the carriage velocity detection part or both of these parts function as a carriage detection part. The carriage detection part functions to detect an actual status of the carriage. The actual status means an indicator to represent the actual status of the carriage, and may be composed with an actual position, an actual velocity and/or an actual travel time f the carriage, which are measured at a certain moment.

The above-mentioned head driving part85drives the recording heads Hi according to print data to have ink droplets ejected from the recording heads Hi.

Also, the above-mentioned carrying motor driving part86drives the carrying motor M1to rotate the carrying roller31, thereby carrying the recording medium, and the above-mentioned carriage driving part87drives the carriage motor M2to move the carriage17in the main scanning direction.

Then, the above-mentioned carriage position detection circuit88reads the divisions of the linear scale23with the encoder Se, thereby detecting the actual position of the carriage17as position information, the above-mentioned carriage velocity calculation circuit89calculates the period of a signal output from the encoder Se and divide the distance between the divisions of the linear scale23by the period of the signal, thereby calculating the actual velocity of the carriage17and detecting it as velocity information. Therefore, the above-mentioned actual position is the position detected by the carriage position detection circuit88, and the actual velocity is the velocity detected by the carriage velocity calculation circuit89.

Note that although in this embodiment the actual velocity Vr of the carriage is detected by dividing the distance between the divisions of the linear scale23by the period of the signal, the moving distance of the carriage17can be calculated based on the position of the carriage17detected last time and the position of the carriage17detected this time by the carriage position detection circuit88, elapsed time can be calculated based on the time when the position of the carriage17was detected last time and the time when the position of the carriage17is detected this time, and the actual velocity of the carriage17can be calculated by dividing the moving distance by the elapsed time.

Next, explained is an example of movement control of the carriage17.

First, explained is the operation of the inkjet printer10when carriage movement control is performed using feedback control only.

FIG. 3is a time chart for explaining the operation of the inkjet printer when carriage movement control is performed using feedback control only. Note that the horizontal axis indicates time (unit: ms), the left vertical axis the proportional component Wp and a total control value (final control value) Wt that is the final control value, and the right vertical axis the target velocity Vs and the actual velocity Vr. Also, the proportional component Wp, the total control value Wt, the target velocity Vs, and the actual velocity Vr are dimensionless quantities.

In the figure, indicated as Ar1is the acceleration region where the carriage17is accelerated from a stopped state, Ar2is the uniform velocity region where the carriage17is moved at a constant velocity, and Ar3is the deceleration region where the carriage17is decelerated and stopped. Note that the acceleration region Ar1, the uniform velocity region Ar2, and the deceleration region Ar3are all categorized by preset changes of the target velocity Vs, where the target velocity Vs is increased at a constant slope (or constant rate) from0to a prescribed value in the acceleration region Ar1, maintained at the above-mentioned prescribed value in the uniform velocity region Ar2, and decreased at a constant slope from the above-mentioned prescribed value to 0 in the deceleration region Ar3.

In this case, because movement control of the carriage17is performed using feedback control only, and the feedback control is performed with PI control, the total control value Wt is equal to a control value for feedback control, that is, a feedback control value Wb, which becomes the proportional component Wp with an unshown integral component Wi added and can be expressed as
Wt=Wb=Wp+Wi
Note that the proportional component Wp constitutes a proportional element control value in the feedback control value Wb, and the integral component Wi an integral element control value in the feedback control value Wb. Also, because the integral component Wi has smaller variation than the proportional component Wp, it is not shown inFIG. 3.

By the way, the above-mentioned total control value Wt is a command value for driving the carriage motor M2, and upon calculating the above-mentioned total control value Wt, the controller80sends it to the carriage driving part87. The carriage driving part87is provided with an unshown pulse width modulation signal generating part and a switching circuit, and upon receiving the total control value Wt, has a PWM control signal according to the total control value Wt generated in the above-mentioned pulse width modulation signal generating part, has current according to the duty of the PWM control signal generated in the above-mentioned switching circuit, and sends the current to the carriage motor M2to drive the carriage motor M2. In this case, the greater the above-mentioned total control value Wt is, the greater the value of the current sent to the carriage motor M2becomes, and the smaller the above-mentioned total control value Wt is, the smaller the value of the current sent to the carriage motor M2becomes.

In feedback control, based on the actual position and the actual velocity Vr of the carriage17detected at the current timing, the feedback control value Wb is calculated at the next timing, and the carriage motor M2is driven based on the feedback control value Wb, therefore delays in the actual position relative to the target position and in the actual velocity Vr relative to the target velocity Vs occur.

For example, as shown in the figure, when the target velocity Vs is in the acceleration region Ar1, separation between the target velocity Vr and the actual velocity Vs, that is, deviation δV gradually increases, and at the timing when the target velocity Vs shifts from the acceleration region Ar1to the uniform velocity region Ar2, it becomes an extremely large value δV1, thereby trackability to the target velocity Vs declines.

Therefore, after the target velocity Vs shifted to the uniform velocity region Ar2, prescribed time becomes necessary until the delays in the actual position and the actual velocity Vr are dissolved and the actual velocity Vr becomes the target velocity Vs in the uniform velocity region Ar2, and during that time ink droplets cannot be ejected from the recording heads Hi. That is, a first waiting region Ar21is formed for waiting until it becomes possible to eject ink droplets form the recording heads Hi, and during that time the carriage17is uselessly moved. Accompanying it, a print region Ar22where actual printing is possible becomes fairly shorter than the uniform velocity region Ar2.

Also, after the target velocity Vs shifted from the uniform velocity region Ar2to the deceleration region Ar3, when it has become 0, prescribed time becomes necessary until the actual velocity Vr becomes 0, and during that time the carriage17need be moved continuously. That is, a second waiting region Ar31is formed for waiting for the actual velocity Vr to become 0, and during that time the carriage17is uselessly moved.

In this manner, if movement control of the carriage17is performed using feedback control only, delays in the actual position relative to the target position and in the actual velocity Vr relative to the target velocity Vs occur, thereby trackability to the target velocity Vs declines. Therefore, for example, in order to have the carriage17shift from the acceleration region Ar1to the uniform velocity region Ar2or from the uniform velocity region Ar2to the deceleration region Ar3, necessity to perform excess control such as providing an excess margin occurs, thereby the movement time, one-scan distance, etc. of the carriage become longer, worsening the printing throughput.

Next, explained are changes in the proportional component Wp while performing movement control of the carriage17using feedback control only if no abnormality has occurred to the movement of the carriage17, or if an abnormality has occurred to the movement of the carriage17.

FIG. 4is a time chart for explaining the operation of the inkjet printer if no abnormality has occurred to the carriage movement while performing carriage movement control using feedback control only, andFIG. 5is a time chart for explaining the operation of the inkjet printer if an abnormality has occurred to the carriage movement while performing carriage movement control using feedback control only. Note that the horizontal axis indicates time (unit: ms), the left vertical axis the proportional component Wp and the total control value Wt, and the right vertical axis the target velocity Vs and the actual velocity Vr.

In the figure, indicated as Vs is the target velocity, Vr is the actual velocity, Wp is the proportional component, and Wt is the total control value. The proportional component Wp is calculated based on the deviation between the target position and the actual position, the deviation δV between the target velocity Vs and the actual velocity Vr, the gain, etc. Relationships between the deviation values and the control values, which correspond to the deviation values, are determined in advance and stored in ROM81. For example, an equation for obtaining a control value corresponding to a deviation value, or a table in which control values and corresponding deviation values are aligned are stored in ROM81. The control part80obtains an intended control value Wp by a calculation using a target value and a deviation value obtained from an actual measured value.

When the target velocity Vs is in the acceleration region Ar1(FIG. 3), and if no abnormality has occurred to the movement of the carriage17, as shown inFIG. 4, the proportional component Wp gradually increases according to delays occurring in the actual position and the actual velocity Vr, and after reaching a peak value Wpmax1, gradually decreases. In this case, because the peak value Wpmax1never exceeds a threshold value β, it is not judged that an abnormality has occurred to the movement of the carriage17.

As opposed to this, as shown inFIG. 5, if an abnormality occurs to the movement of the carriage17at timing t1, the actual velocity Vr of the carriage17decreases, the deviation δV increases, and accompanying it, the proportional component Wp increases.

At this time, if the abnormality in the movement of the carriage17is a small one to the extent that the recording medium is distorted and slightly touches the carriage, a peak value Wpmax2of the proportional component Wp never exceeds the threshold value β, therefore it is not judged that an abnormality has occurred to the movement of the carriage17.

On the other hand, if the movement of the carriage17is greatly delayed as in the case where the recording medium has hit the carriage and caused a jam, the proportional component Wp becomes large and exceeds the threshold value β as shown in a broken line, therefore it is judged that an abnormality has occurred to the movement of the carriage17.

Based on this, this embodiment is designed so that the proportional component Wp is suppressed not to increase beyond the threshold value β, and that it is accurately judged whether an abnormality has occurred to the movement of the carriage17.

FIG. 6is a flow chart showing the operation of the inkjet printer in the embodiment of this invention, andFIG. 7is a time chart for explaining the operation of the inkjet printer when performing carriage movement control in the embodiment of this invention. Note that inFIG. 7, the horizontal axis indicates time (unit: ms), the left vertical axis the proportional component Wp, the integral component Wi, an acceleration corresponding control value Wα, a velocity corresponding control value Wv, and the total control value Wt, and the right vertical axis the target velocity Vs and the actual velocity Vr. Also, the proportional component Wp, the integral component Wi, the acceleration corresponding control value Wα, the velocity corresponding control value Wv, the total control value Wt, and the target velocity Vs and the actual velocity Vr of the carriage17are dimensionless quantities.

In this embodiment, the carriage17is designed to be reciprocated. In this case, explained here is a one-scan process of the carriage17when moving the carriage17from a starting point Ps for turning back the carriage17in the home position side toward (or to) an ending point Pe for turning back the carriage17in the retreat position side shown inFIG. 7. Because a one-scan process when moving the carriage17from the ending point Pe to the starting point Ps is the same except having the moving direction of the carriage17reversed, its explanation is omitted.

First of all, the controller80(FIG. 1) reads and acquires the actual position of the carriage17detected by the carriage position detection circuit88.

Subsequently, the controller80reads and acquires time measured by the timer84. In this case, the time measured by the timer84is regarded as elapsed time while the carriage17moves from the starting point Ps to the ending point Pe.

Then, the controller80reads and acquires the actual velocity Vr of the carriage17that is calculated and detected by the carriage velocity calculation circuit89.

Next, the control value calculating part Pr1of the controller80calculates the feedback control value Wb. In this case, because feedback control is performed with PI control, the feedback control value Wb becomes a value that is the proportional component Wp with the integral component Wi added, that can be expressed as
Wb=Wp+Wi

In this embodiment, the proportional component Wp and the integral component Wi are calculated based on the deviation between the target position and the actual position and the deviation between the target velocity Vs and the actual velocity Vr of the carriage17, the gain, etc. so that the actual position becomes the target position and the actual velocity Vr the target velocity Vs.

Therefore, the above-mentioned control value calculating part Pr1reads the target velocity Vs and the target position from the setting value storing part83, calculates the deviation between the target position and the actual position and the deviation δV between the target velocity Vs and the actual velocity Vr, and calculates the proportional component Wp and the integral component Wi.

By the way, the target velocity Vs in this embodiment is set to change as shown inFIG. 7, which is made different from the target velocity Vs when movement control of the carriage17is performed using feedback control only as shown inFIGS. 3-5.

Then, set for the above-mentioned target velocity Vs are the acceleration region Ar1where the carriage17is accelerated from a stopped state, the uniform velocity region Ar2where the carriage17is moved at a constant velocity, and the deceleration region Ar3where the carriage17is decelerated and stopped.

The above-mentioned acceleration region Ar1consists of a first acceleration region portion from the starting point Ps to an intermediate point P1where the actual velocity Vr is increased by gradually increasing the target acceleration of the carriage17, that is, target acceleration, in this case positive target acceleration, from the state where the carriage17is stopped, a second acceleration region portion from the intermediate point P1to an intermediate point P2where the actual velocity Vr is increased by maintaining the positive target acceleration at a constant value, and a third acceleration region portion from the intermediate point P2to an intermediate point P3where the actual velocity Vr is increased by gradually decreasing the positive target acceleration, and once the third acceleration region portion is finished, a shift occurs from the acceleration region Ar1to the uniform velocity region Ar2, where the target velocity Vs is kept constant.

Then, the deceleration region Ar3consists of a first deceleration region portion from an intermediate point P4to an intermediate point P5where the actual velocity Vr is decreased from the target velocity Vs by gradually decreasing (increasing in the absolute value) negative target acceleration, a second deceleration region portion from the intermediate point P5to an intermediate point P6where the actual velocity Vr is decreased by maintaining the negative target acceleration at a constant value, and a third deceleration region portion from the intermediate point P6to the ending point Pe where the actual velocity Vr is decreased by gradually increasing (decreasing in the absolute value) the negative target acceleration, and once the third deceleration region portion is finished, the carriage17is stopped.

Subsequently, the abnormality judging part Pr2of the controller80reads the threshold value εj corresponding to each region of the acceleration region Ar1, the uniform velocity region Ar2, and the deceleration region Ar3mentioned above for the target velocity Vs, compares the proportional component Wp and the threshold value εj, and judges whether an abnormality has occurred to the movement of the carriage17based on whether the proportional component Wp has exceeded the threshold value εj. Threshold value ε1is shown inFIG. 8.

If the proportional component Wp has exceed the threshold value εj (the proportional component Wp is greater than the threshold value εj) and it is judged that an abnormality has occurred to the movement of the carriage17, the above-mentioned abnormality judging part Pr2sends a stop instruction to the carriage driving part87, and upon receiving the stop instruction, the carriage driving part87stops the carriage motor M2to stop the carriage17. Then, the controller80shows a prescribed display on the display part of the operation panel43(FIG. 2) to notify the user of the inkjet printer10that an abnormality has occurred to the movement of the carriage17.

Subsequently, the controller80moves the carriage17to the home position or the retreat position, ends the process, and waits for the user of the inkjet printer10to remove the cause of the abnormality occurrence and release the abnormality in the movement of the carriage17.

On the other hand, if the proportional component Wp has not exceeded the threshold value εj (the proportional component Wp is equal to or smaller than the threshold value εj) and it is judged that no abnormality has occurred to the movement of the carriage17, the above-mentioned control value calculating part Pr1reads and acquires the feedforward control value Wf from the setting value storing part83.

The above-mentioned feedforward control value Wf is a control value that combines the acceleration corresponding control value Wα and the velocity corresponding control value Wv. The value Wα is a control value that is set based on a variation amount of the target acceleration, and corresponds to the acceleration component. The value Ww is another control value that is set based on the target velocity Vs, and corresponds to the velocity component. The acceleration corresponding control value Wα and the velocity corresponding control value Wv are independently recorded in the setting value storing part83.

Then, the above-mentioned acceleration corresponding control value Wα is used in the acceleration region Ar1and the deceleration region Ar3, and the velocity corresponding control value Wv is used in the acceleration region Ar1, the uniform velocity region Ar2, and the deceleration region Ar3.

Therefore, the feedforward control value Wf is expressed as
Wf=Wα+Wv
in the acceleration region Ar1and the deceleration region Ar3, and as
Wf=Wv
in the uniform velocity region Ar2.

The acceleration corresponding control value Wα linearly increases at a constant slope in the first acceleration region portion, becomes a constant value in the second acceleration portion, and linearly decreases at a constant slope in the third acceleration region portion of the acceleration region Ar1. Also, the acceleration corresponding control value Wα linearly decreases at a constant slope in the first deceleration region portion, becomes a constant value in the second deceleration portion, and linearly increases at a constant slope in the third deceleration region portion of the deceleration region Ar3.

In this embodiment, the acceleration corresponding control value Wα is set corresponding to the variation amount of the target acceleration, that is, a jerk that is a value calculated by differentiating the target acceleration, and consists of a part where the jerk takes a positive value, a part where it takes 0, and a part where it takes a negative value.

Note that although the target velocity Vs is set to draw a curve in the first and the third acceleration region portions of the acceleration region Ar1and the first and the third deceleration region portions of the deceleration region Ar3in this embodiment, it can be set not to draw a curve in the acceleration region Ar1and the acceleration region Ar3. In that case, it is preferred to set the acceleration corresponding control value Wα so that the jerk takes a negative value in a part immediately before shifting from the acceleration region Ar1to the uniform velocity region Ar2, and a part immediately after shifting from the uniform velocity region Ar2to the deceleration region Ar3.

Also, the velocity corresponding control value Wv is set corresponding to the target velocity Vs so as to draw a curve in the first and the third acceleration region portions of the acceleration region Ar1and the first and the third deceleration region portions of the deceleration region Ar3, and draw a line in the second acceleration region portion of the acceleration region Ar1and the second deceleration region portion of the deceleration region Ar3.

That is, the velocity corresponding control value Wv has its positive slope gradually increased in the first acceleration region portion, its positive slope kept constant in the second acceleration region portion, and its positive slope gradually decreased in the third acceleration region portion of the acceleration region Ar1of the target velocity Vs, and once a shift occurs from the acceleration region Ar1to the uniform velocity region Ar2, its value is kept constant.

Then, the negative slope is gradually increased in the first deceleration region portion, the negative slope is kept constant in the second deceleration region portion, and the negative slope is gradually decreased to make the value 0 in the third deceleration region portion of the deceleration region Ar3of the target velocity Vs.

Next, the above-mentioned control value calculating part Pr1calculates the total control value Wt based on the feedback control value Wb and the feedforward control value Wf.

Subsequently, the controller80sends the total control value Wt to the carriage driving part87. Upon receiving the total control value Wt, the carriage driving part87has a PWM control signal generated according to the total control value Wt in the above-mentioned pulse width modulation signal generating part, has current generated according to the duty of the PWM control signal in the above-mentioned switching circuit, and sends the current to the carriage motor M2to drive the carriage motor M2.

Then, the controller80judges whether one scan is finished, if one scan is not finished, sets the next scan and acquires the actual position of the carriage17again, and if one scan is finished, ends printing one line and places the carriage17at the starting point Ps.

As the result, the occurrences of delays in the actual position relative to the target position and in the actual velocity Vr relative to the target velocity Vs can be suppressed, therefore trackability to the target velocity Vs can be improved.

Also, because movement control of the carriage17is performed using both feedback control and feedforward control, and the feedforward control value Wf is not set to a constant value such as an offset value but consists of the acceleration corresponding control value Wα and the velocity corresponding control value Wv, the feedforward control value Wf can be easily changed according to the elapsed time while the carriage17is moved from the starting point Ps to the ending point Pe.

For example, if there is a region where the carriage17is desired to be rapidly accelerated or rapidly decelerated, or the actual velocity Vr is desired to be smoothly changed, by setting the acceleration component control value Wα in a prescribed pattern, the deviation δV between the target velocity Vs and the actual velocity Vr can be reduced. As the result, the occurrences of delays in the actual position relative to the target position and in the actual velocity Vr relative to the target velocity Vs can be suppressed, therefore trackability of the control can be improved.

Also, because the target acceleration a is set to 0 at the timing of shifting from the acceleration region Ar1to the uniform velocity region Ar2, the total control value Wt needs to be rapidly reduced. However, in this embodiment, because the acceleration corresponding control value Wα is reduced in the third acceleration region portion of the acceleration region Ar1and the first deceleration region portion of the deceleration region Ar3, variation of the feedback control value Wb can be reduced, therefore variation of the total control value Wt can be reduced.

As the result, because the actual velocity Vr of the carriage17can be prevented from varying greatly, there is no waiting region formed for waiting until it becomes possible to eject ink droplets from the recording heads Hi, allowing an improvement in the printing throughput.

Furthermore, because the velocity corresponding control value Wv changes drawing a curve immediately before the target velocity Vs shifts from the acceleration region Ar1to the uniform velocity region Ar2and immediately after it shifted from the uniform velocity region Ar2to the deceleration region Ar3, the peak value Wpmax of the proportional component Wp in the acceleration region Ar1and the peak value Wpmin of the proportional component Wp in the deceleration region Ar3can be reduced, and also variation of the proportional component Wp when shifting from the acceleration region Ar1to the uniform velocity region Ar2and variation of the proportional component Wp when shifting from the uniform velocity region Ar2to the deceleration region Ar3can be reduced.

Next, explained is the flow chart.

S1: The controller80acquires the actual position of the carriage17.

S3: The controller80acquires the actual velocity Vr of the carriage17.

S4: The control value calculating part Pr1calculates the feedback control value Wb.

S5: The abnormality judging part Pr2compares proportional component Wp with the threshold value εj.

S6: The abnormality judging part Pr2judges whether an abnormality has occurred to the movement of the carriage17. Specifically, it is determined if proportional component Wp is larger than threshold value εj. If an abnormality has occurred to the movement of the carriage17, it proceeds to S7, and if no abnormality has occurred to the movement of the carriage17, it proceeds to S9.
S7: The carriage driving part87stops the carriage17.
S8: The controller80moves the carriage17to the home position or the retreat position, and ends the process.
S9: The control value calculating part Pr1acquires the feedforward control value Wf.
S10: The control value calculating part Pr1calculates the total control value Wt.
S11: The carriage driving part87drives the carriage motor M2.
S12: The controller80judges whether one scan is completed. If one scan is completed, it ends the process, and if one scan is not finished, proceeds to S13.
S13: The controller80sets the next scan and returns to S1.

Next, explained are changes in the proportional component Wp if no abnormality has occurred to the movement of the carriage17or if an abnormality has occurred to the movement of the carriage17while performing movement control of the carriage17using both feedback control and feedforward control in this embodiment.

FIG. 8is a time chart for explaining the operation of the inkjet printer if no abnormality has occurred to the carriage movement while performing carriage movement control in the embodiment of this invention, andFIG. 9is a time chart for explaining the operation of the inkjet printer if an abnormality has occurred to the carriage movement while performing carriage movement control in the embodiment of this invention. Note that in the figures, the horizontal axis indicates time (unit: ms), the left vertical axis the proportional component Wp, the integral component Wi, the acceleration corresponding control value Wα, the velocity corresponding control value Wv, and the total control value Wt, and the right vertical axis the target velocity Vs and the actual velocity Vr. Also, the proportional component Wp, the integral component Wi, the acceleration corresponding control value Wα, the velocity corresponding control value Wv, the total control value Wt, and the target velocity Vs and the actual velocity Vr of the carriage17are dimensionless quantities.

In the figures, denoted as Vs is the target velocity, Vr is the actual velocity, Wp is the proportional component, Wt is the total control value, Wα is the acceleration corresponding control value, and Wv is the velocity corresponding control value. The proportional component Wp is calculated based on the deviation between the target position and the actual position, the deviation δV between the target velocity Vs and the actual velocity Vr, the gain, etc.

In this embodiment, as mentioned above, because the deviation between the target position and the actual position and the deviation δV between the target velocity Vs and the actual velocity Vr can be reduced in the acceleration region Ar1and the deceleration region Ar3, the proportional component Wp can be reduced.

Also, variation of the proportional component Wp when the target velocity Vs shifts from the acceleration region Ar1to the uniform velocity region Ar2, and variation of the proportional component Wp when it shifts from the uniform velocity region Ar2to the deceleration region Ar3can be reduced.

Therefore, in the acceleration region Ar1, the uniform velocity region Ar2, and the deceleration region Ar3, the threshold value εj can be set small to the extent that it is not misjudged whether an abnormality has occurred to the movement of the carriage17, considering scatters among different units of the inkjet printer10.

When the target velocity Vs in the acceleration region Ar1, and if no abnormality has occurred to the movement of the carriage17, as shown inFIG. 8, the proportional component Wp gradually increases according to delays occurring in the actual position and the actual velocity Vr, and after reaching a peak value Wpmax11, gradually decreases. In this case, because the peak value Wpmax11never exceeds a threshold value ε1, it is never judged that an abnormality has occurred to the movement of the carriage17.

Also, in the uniform velocity region Ar2, because a peak value Wpmax12of the proportional component Wp is lower than the peak value Wpmax11, a threshold value ε2is set smaller than the threshold value ε1.

As opposed to this, as shown inFIG. 9, if an abnormality has occurred to the movement of the carriage17at timing t11, the actual velocity Vr of the carriage17decreases, the deviation δV increases, and accompanying it, the proportional component Wp increases and exceeds the threshold value ε1.

At this time, even if the abnormality in the movement of the carriage17is small to the extent that the recording medium is distorted and slightly touches the carriage, if the delay in the actual velocity Vr relative to the target velocity Vs of the carriage17increases even slightly, it is judged that an abnormality has occurred to the movement of the carriage17.

In this manner, in this embodiment, because movement control of the carriage17is performed using both feedback control and feedforward control, the feedback control value Wb can be reduced, and the proportional component Wp can be reduced.

Therefore, in judging whether the proportional component Wp has exceeded the threshold value εj, because the threshold value εj can be reduced, even if the abnormality in the movement of the carriage17is small, it can be securely judged whether the proportional component Wp has exceeded the threshold value εj.

As the result, it can be accurately judged whether an abnormality has occurred to the movement of the carriage17.

Then, because there will be no case where an image is formed on the recording medium without judging that an abnormality has occurred to the movement of the carriage17, degradation in the image quality can be prevented.

Also, because the above-mentioned threshold value εj is set according to the peak value of the proportional component Wp for each of the acceleration region Ar1, the uniform velocity region Ar2, and the deceleration region Ar3, it can be even more accurately judged whether an abnormality has occurred to the movement of the carriage17.

Furthermore, in this embodiment, as mentioned above, because the target velocity Vs changes so as to draw a curve in the first and the third acceleration region portions of the acceleration region Ar1and the first and the third deceleration region portions of the deceleration region Ar3, the deviation δV between the target velocity Vs and the actual velocity Vr can be reduced, and the proportional component Wp can be reduced.

Therefore, it can be accurately judged whether an abnormality has occurred to the movement of the carriage17.

Furthermore, in this embodiment, as mentioned above, because the acceleration corresponding control value Wα is reduced in the third acceleration region portion of the acceleration region Ar1and the first deceleration region portion of the deceleration region Ar3, variation of the feedback control value Wb can be reduced, and variation of the proportional component Wp can be reduced.

Therefore, it will never be misjudged that an abnormality has occurred to the movement of the carriage17.

Also, in this embodiment, as mentioned above, because the velocity corresponding control value Wv changes drawing a curve immediately before the target velocity Vs shifts from the acceleration region Ar1to the uniform velocity region Ar3and immediately after it shifted from the uniform velocity region Ar2to the deceleration region Ar3, the proportional component Wp in the acceleration region Ar1and the deceleration region Ar3can be reduced, and also variation of the proportional component Wp when shifting from the acceleration region Ar1to the uniform velocity region Ar2and shifting from the uniform velocity region Ar2to the deceleration region Ar3can be reduced.

Therefore, it can be accurately judged whether an abnormality has occurred to the movement of the carriage17, and there will be no misjudgment that an abnormality has occurred to the movement of the carriage17.

In this embodiment, the proportional component Wp and the integral component Wi are calculated based on the deviation between the target position and the actual position and the deviation δV between the target velocity Vs and the actual velocity Vr of the carriage17, the gain, etc. However, they can be calculated based on the deviation between the target position and the actual position, the gain, etc., or based on the deviation δV between the target velocity Vs and the actual velocity Vr, the gain, etc.

Also, the proportional component Wp and the integral component Wi can be calculated having as parameters the deviation between the target position and the actual position, and the deviation δV between the target velocity Vs and the actual velocity Vr. In this case, if those two parameters are assigned with prescribed weights in calculating the proportional component Wp and the integral component Wi, trackability to the target velocity Vs can be further improved.

Note that this invention is not limited to the above-mentioned embodiment but can be modified in various kinds of manners based on the purpose of this invention, and they are not excluded from the scope of this invention. Especially, the total control value Wt, feedback control value Wb, feedforward control value Wf are not limited by the disclosed components above. In view of conventional control technology, various types of components are available to compose these values. Also, proportional component Wp, integral component Wi, velocity and acceleration corresponding control values Wv and Wα are not limited within the above embodiments. In the light of conventional technologies, various components including velocity and acceleration are available.

In the invention, the target values, thresholds (or threshold values) and feedforward control values are determined in advance (or prior to the image forming process) from experiences under various conditions or try and error experiences. For example, when moving the carriage from one end of the reciprocation area, the one end is used as a staring point and an elapsed time counts after the carriage leaves form the starting point. The elapsed time is segmented with a predetermined interval so that many measured points are created. A velocity of the carriage is measured at each of the measured points, making the velocity the target value at the measured point. The velocity is illustrated as a line with Vs. The predetermined interval may be ranged within 0.001 to 0.1 seconds.

The threshold values are determined through experiences in which a carriage is caused to collide against a sheet as the control values change. In these experiences, it is observed whether or not any deficiency occurs. When an inacceptable control value is found, the value or near value may be used as the threshold value.

The feedforward control values are determined through many experiences that are performed under various value Wα. When a value Wα that is following well to the target is found, such a value may be used as the feedforward control value.

These above three values are determined at each of the measured points, the points being repeatedly disposed and separated one another with an interval. As described above, the interval may be based on an elapsed time (or a time unit that is obtained based on a measured time), but it may be based on a travel distance (or a moving distance unit) for which the carriage moves from the starting point.