JP3800917B2 - Motor control device and storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a motor control device suitable for controlling a paper feeding motor in, for example, a line printer, and a storage medium storing an execution program for operating the motor control device.
[0002]
[Prior art]
  In general, a stepping motor dominates a paper feeding motor used in a line printer from the viewpoint of feeding a paper with a certain amount of movement with high accuracy. On the other hand, ink jet printers and the like belonging to line printers often employ a direct current motor (hereinafter abbreviated as “DC motor”) as a carriage head moving motor.
[0003]
  Since these motors have advantages and disadvantages, they are applied according to each operation mode. However, since the stepping motor for paper feeding has a loud operation sound, a DC motor with quiet operation sound is adopted as the paper feeding motor. There is also a line printer. When this DC motor is used for paper feeding, the motor control device needs to control the motor speed with high accuracy in order to perform constant paper feeding as in the case of the stepping motor.
[0004]
[Problems to be solved by the invention]
  Here, considering the case of feeding paper while controlling the motor speed of the DC motor, it is not so difficult to control the motor speed at the time of acceleration or constant speed. The motor must always be stopped at an accurate position (time) with a feed amount, and in this respect, motor speed reduction control is the most important point. A conventional motor controller for a DC motor performs feedback control using an encoder signal from a rotary encoder, and performs PWM (Pulse Width Modulation) control so as to match an ideal deceleration curve as much as possible. The motor was decelerating.
[0005]
  However, in the conventional method of reducing the motor speed, when the deceleration becomes excessive, the edge of the encoder signal from the rotary encoder does not appear for a long time, and during that time, the speed is not changed by PWM control. Sometimes it stopped. In other words, the motor may suddenly stop before reaching the target stop position, which has a problem as a reduction control of the motor speed.
[0006]
  The present invention has been proposed in view of the above points, and provides a motor control device that can stop a motor accurately and smoothly when the motor speed is reduced, and an execution program for operating the motor control device. An object is to provide a stored storage medium.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, a motor control device according to a first aspect of the present invention provides:Decrease the motor rotation speed step by step to stop the motor at the target stop positionA motor control device,A rotational position detecting means for detecting the rotational position of the motor at a predetermined pitch; and a first rotational speed detecting means for decreasing the rotational speed of the motor stepwise each time the rotational position of the motor is detected by the rotational position detecting means. A speed control means, a judgment means for judging whether or not a predetermined time has elapsed from the detection time of the previous rotational position before the rotational position of the motor is detected by the rotational position detection means; And a second speed control means for increasing the rotational speed of the motor when the judgment means judges that the predetermined time has elapsed.It is characterized by that.
[0008]
  According to such a motor control device, the motorRotationSpeedStep by stepDuring deceleration,Its rotationIf it is judged that the vehicle is decelerating excessively even if an excessive deceleration state that causes the speed to stall occursIncrease motor rotation speedSo the motorRotationThe motor does not stop suddenly before reaching the target stop position when the speed is reduced, and the motor can be stopped smoothly with high accuracy.
[0009]
  A motor control device according to a second aspect of the present invention is the motor control device according to the first aspect,The rotational position detecting means comprises an encoder provided on the rotational shaft of the motor, and the first speed control means increases the rotational speed of the motor stepwise each time a pulse signal is output from the encoder. The determination means determines whether or not the predetermined time has elapsed since the previous pulse signal was output before the pulse signal was output from the encoder..
[0010]
  According to such a motor control device, in addition to the effect of the motor control device according to claim 1,The interval of the pulse signal output from the encoder exceeds the specified timeIf the length is longer than necessary, the motor is being decelerated.RotationThe speed can be accelerated very slightly. In other words, at the point just before the target stop positionrotationEven if the speed drops more than necessary, make a complete turn from deceleration so that the target stop position can be reached.rotationSpeed can be accelerated.
[0011]
  Furthermore, the motor control device of the invention described in claim 3 is the motor control device according to claim 2,The determining means includes a time measuring means for starting time measurement every time a pulse signal is output from the encoder, and a time measurement by the time measuring means before the next pulse signal is output from the encoder. The second speed control means increases the rotation speed of the motor when the time over judgment result is outputted by the judgment means..
[0012]
  According to such a motor control device, in addition to the effect of the motor control device according to claim 2,, DecreasePulse during speedSignal intervalIs too long and slows down too much,TimingmeansInThanIncrease the rotation speed of the motor when the time is measuredSo until you reach the target stop positionrotationIt is possible to avoid a situation in which the state of excessively low speed continues for a long time and stops.
[0013]
  A motor control device according to a fourth aspect of the present invention is the motor control device according to the third aspect,The determination means starts the time measuring operation of the time measuring means from the time when the time interval of the rotational position of the motor detected by the rotational position detecting means becomes equal to or greater than a predetermined time interval when the motor is stopped. Make.
[0014]
  According to such a motor control device, in addition to the effect of the motor control device according to claim 3, the motorRotationEven if the speed is almost the end of the stop due to the very low speed operation,rotationThe target stop position is too low for too long.in frontSo as not to stop atMotor rotationThe speed can be fine-tuned.
[0015]
  Furthermore, the motor control device of the invention described in claim 5 is the motor control device of claim 3 or claim 4, whereinThe time counting means is reset every time the predetermined time is counted until the next pulse signal is output from the encoder and repeats the time counting operation for the predetermined time, while the output means is configured to repeat the predetermined time. The second speed control means outputs the rotation speed of the motor each time the time-over determination result is continuously output from the output means. Step by step.
[0016]
  According to such a motor control device, in addition to the effect of the motor control device according to claim 3 or claim 4,RotationThe target stop position is too low for a long time.in frontSo as not to stop atTiming a predetermined timeModerate motor according to the number of timesRotationSpeedRiseCan be made.
[0017]
  The storage medium of the invention described in claim 6Computer, motor stop target position The first speed control means for stepwise decreasing the rotational speed of the motor each time a pulse signal is output from the encoder provided on the rotating shaft of the motor, and the pulse signal from the encoder A determination means for determining whether or not a predetermined time set in advance from the time when the pulse signal was output before the output, and the determination means determines that the predetermined time has elapsed. A program for functioning as second speed control means for increasing the rotational speed of the motor is recorded.It is characterized by that.
[0018]
  According to such a storage medium, the operation of the motor control device according to claim 1 can be realized by operating a CPU such as a so-called microcomputer based on the stored execution program.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, preferred embodiments of the present invention will be specifically described with reference to the drawings.
[0020]
  FIG. 1 is a block diagram showing a circuit configuration as an embodiment of a motor control device according to the present invention. This motor control device is provided in a line printer in a facsimile machine or the like as a device for controlling the speed of the DC motor M for paper feeding.
[0021]
  As shown in FIG. 1, the motor control device includes a CPU 1, ROM 2, RAM 3, EEPROM 4, DMAC 5, interface 6, encoder 10, encoder processing unit 11, acceleration / deceleration control unit 12, drive control unit 20, H-type bridge circuit 30, And a drive DC power supply E and the like. The CPU 1, ROM 2, RAM 3, EEPROM 4, DMAC 5, and interface 6 are parts that form the core function of a so-called microcomputer, and are connected to each other via a bus line. The bus line includes an address bus, a data bus, and a control signal line. The interface 6 is connected to an encoder processing unit 11, an acceleration / deceleration control unit 12, and a drive control unit 20. An encoder 10 is connected to the encoder processing unit 11, and an H-type bridge circuit 30 is connected to the drive control unit 20. A DC (direct current) motor M as a control object is connected to the H-type bridge circuit 30.
[0022]
  The CPU 1 controls the operation of the entire motor control device. In particular, the main function of the CPU 1 is an arithmetic processing function for generating a signal for driving the motor M (hereinafter referred to as “PWM drive signal”) by a pulse width modulation (PWM) method as will be described later. Is mentioned. The ROM 2 stores an execution program of the CPU 1 and the like. The RAM 3 is used as a work area or a data development area for the CPU 1. The EEPROM 4 stores various flags and data. The DMAC 5 directly exchanges data between the RAM 3 and the interface 6 in place of the CPU 1. The interface 6 functions as an input / output contact of each part that is not directly connected to the bus line. Although details will be described later, the interface 6 has a built-in timer circuit (not shown), and the CPU 1 performs predetermined control while referring to the time (timer value) counted by the timer circuit.
[0023]
  The encoder 10 mainly detects the rotational speed (motor speed) of the DC motor M using, for example, a rotary optical system and generates an encoder signal corresponding to the rotational speed. The encoder processing unit 11 creates various necessary signals based on the encoder signal output from the encoder 10. The acceleration / deceleration control unit 12 instructs a shift point that changes from acceleration to constant speed or from constant speed to deceleration. The drive control unit 20 directly controls the operation of the H-type bridge circuit 30 by generating an appropriate motor drive signal corresponding to the level of the PWM drive signal and outputting it to the H-type bridge circuit 30. That is, the duty ratio of the motor drive signal is determined according to the level of the PWM drive signal, and the motor is PWM controlled.
[0024]
  The H-type bridge circuit 30 is provided in order to switch the DC motor M at high speed. The H-type bridge circuit 30 has a configuration in which the DC motor M is bridged in the center and a total of four transistors Tr1 to Tr4 above and below both ends of the bridge line. It is configured by connecting and arranging. Specifically, in the H-type bridge circuit 30 illustrated as an example, the positive electrode end of the DC power source E is positioned on the upper side of the entire circuit, and the negative electrode end is positioned on the lower side thereof. On each connection line connecting the upper positive electrode end and both ends of the bridge line, a diode D is connected in parallel to connect the PNP transistors Tr1 and Tr2, while the lower negative electrode end and both ends of the bridge line are connected. NPN transistors Tr3 and Tr4 are connected to the connection lines connecting the two by connecting diodes D in parallel. Each of the transistors Tr <b> 1 to Tr <b> 4 individually performs an on / off operation in accordance with a motor drive signal from the drive control unit 20. When the motor M performs acceleration or constant speed operation, only a pair of transistors (Tr1 and Tr4 or Tr2 and Tr3) positioned obliquely to each other are turned on. For example, when only the transistors Tr1 and Tr4 are in the on state, a current path passing through these transistors Tr1 and Tr4 is formed, and the motor M rotates in the forward direction. Conversely, when only the transistors Tr2 and Tr3 are on, the motor M is reversed. In the present embodiment, since the DC motor M is used as a paper feeding motor, it is rotated only in a certain direction, and during acceleration and constant speed operation, only the transistors having the symbols Tr1 and Tr4 are turned on. Shall be assumed.
[0025]
  Briefly speaking, the present invention has a feature in the deceleration control of the motor speed, and especially during the extremely low speed state in which the motor speed is almost stopped, the motor speed is too low and the target speed is reduced. This prevents a situation where the vehicle stops before the stop position. When decelerating the motor speed, the CPU 1 controls the motor M based on the pulse width modulation method by feedback control using an encoder signal. That is, the CPU 1 generates a PWM drive signal based on the encoder signal, and also generates a motor drive signal with a duty ratio corresponding to the level of the PWM drive signal, and turns on the transistors Tr1 to Tr4 at a high speed by this motor drive signal. The DC motor M is operated via the H-type bridge circuit 30. The motor drive signal for switching the transistors Tr1 to Tr4 is generated by varying the duty ratio according to the level of the PWM drive signal, and the motor speed is determined according to the pulse width. . The motor speed gradually decreases as it is decelerated. At this time, if the pulse width of the encoder signal is extended for a predetermined time or longer, the motor speed may be stalled before the target stop position accordingly. . For this reason, the CPU 1 refers to the timer value counted by the timer circuit, and when the pulse width of the encoder signal is too long, the CPU 1 changes the motor speed during deceleration slightly.
[0026]
  2 and 3 are time charts showing various signal levels during deceleration. FIG. 2 shows an intermediate stage during deceleration, and FIG. 3 also shows a final stage. Describing based on these figures, the PWM drive signal is generated in steps with each falling edge of the encoder signal (enc1) as a delimiter. According to this PWM drive signal, one cycle of the encoder signal (in the figure) The motor speed is reduced at every interval indicated by the alternate long and short dash line. Referring to FIG. 2, in the intermediate stage in the middle of deceleration, the motor speed gradually decelerates and the pulse width of the encoder signal becomes longer. In such a state, the timer value is counted by the timer circuit. In principle, the timer value is reset at every end of the pulse width of the encoder signal, that is, every falling edge of the encoder signal (enc1). During such operation, if the timer value exceeds a certain value (broken line) until the end of each pulse width is detected, the CPU 1 exceptionally increases the PWM speed to slightly increase the motor speed. Step up the level of the drive signal. As a result, even if the pulse width of the encoder signal is extended and the motor speed is likely to stall, the motor speed is maintained to the target stop position without stopping completely because the speed is slightly increased. It can be made.
[0027]
  On the other hand, in the final stage in the middle of deceleration, as shown in FIG. 3, the pulse width of the encoder signal is further extended, and the motor speed is likely to be stalled. Even in such a situation, as a result of the timer value exceeding a certain value and the time-over being repeated continuously, the CPU 1 steps up the level of the PWM drive signal in an accumulative manner by the number of times the time-over has continued. Thereby, since the duty ratio of the motor drive signal increases, the motor speed can be maintained up to the target stop position without the motor M completely stopping even immediately before the target stop position.
[0028]
  In other words, the CPU 1 realizes a speed adjusting means for slightly increasing the motor speed by determining that the motor speed is excessively reduced when the feedback information does not satisfy a predetermined condition while reducing the motor speed based on the feedback information (pulse wave signal). is doing. The ROM 2 is a storage medium that stores an execution program for operating a motor control device that controls the motor speed based on feedback information from the motor. During the deceleration of the motor speed based on the feedback information, the ROM 2 If the feedback information does not satisfy a predetermined condition, a storage medium is realized that includes in the execution program a speed adjustment program for slightly increasing the motor speed by determining that the speed is excessively slow.
[0029]
  Next, the operation at the time of motor speed reduction by the motor control device will be described with reference to the drawings.
[0030]
  FIG. 4 is a flowchart showing a deceleration processing procedure when the motor speed is reduced, and FIG. 5 is an explanatory diagram shown for explaining an example of a motor speed curve. In the state immediately before starting the deceleration process, the speed of the motor M is in a constant state.
[0031]
  4 will be described mainly with reference to FIGS. 2 to 5. First, the CPU 1 determines whether or not to change the motor speed from a constant speed to a deceleration according to an instruction from the acceleration / deceleration control unit 12. Is determined (S1).
[0032]
  When the process proceeds to the deceleration process (S1: YES), the CPU 1 acquires the encoder signal output from the encoder processing unit 11 at the present time (S2). As described above, the encoder signal is generated by the encoder processing unit 11 based on the signals (enc1, enc2) output from the encoder 10.
[0033]
  The CPU 1 that has acquired the encoder signal at the present time generates a PWM drive signal having a level corresponding to the pulse width of the encoder signal (S3). Then, a motor drive signal having a duty ratio corresponding to the level of the PWM drive signal is input to the H-type bridge circuit 30, and the motor M shifts from a constant speed to a decelerated state by the switching operation of the H-type bridge circuit 30. is there.
[0034]
  During the deceleration operation as described above, the CPU 1 uses the timer circuit to count the timer value (S4). This timer value counting operation is continued until the motor M stops, except when reset as described later. The timer value counting operation may not be started until the motor speed is lowered to a predetermined level, but may be started from an intermediate point in the middle of deceleration where there is a possibility of stalling in a state where the motor speed is sufficiently decelerated. In that case, the start time may be determined based on the motor speed determined based on the encoder signal.
[0035]
  In a state in which the timer value counting operation is continued, the CPU 1 determines a time-over depending on whether or not the timer value has reached a predetermined upper limit reference value (broken line shown in FIGS. 2 and 3) (S5).
[0036]
  If it is not determined that the time is over (S5: NO), the CPU 1 subsequently determines whether or not the end of the pulse width of the encoder signal has been detected (S6).
[0037]
  When the end of the pulse width of the encoder signal is detected (S6: YES), the CPU 1 determines that the motor speed has slightly decreased at this time, causes the timer circuit to reset the timer value, and immediately after that, the timer value is reset again. The count operation is started (S7). The starting point of this counting operation corresponds to the time point indicated by the one-dot chain line and the downward arrow in FIGS.
[0038]
  Furthermore, the CPU 1 steps down the PWM drive signal according to the pulse width of the encoder signal at the start of the timer value counting operation (S8). As the PWM drive signal is stepped down as time passes, the motor speed is gradually reduced and decelerated.
[0039]
  The CPU 1 determines whether or not the target stop position (time point) has been reached by referring to, for example, the cumulative number of pulses of the encoder signal for every fixed cycle after the above process is completed (S9).
[0040]
  When the target stop position is reached (S9: YES), the CPU 1 stops the motor M by stopping the output of the motor drive signal, and ends this deceleration process. Note that after the deceleration process is completed, the motor M is kept stopped for a very short time for recording. Thereafter, the motor M starts acceleration for paper feeding and shifts to a constant speed operation, and then the deceleration process is performed again at an appropriate time.
[0041]
  If it is not determined in S9 that the target stop position has been reached (S9: NO), the CPU 1 returns to S5.
[0042]
  In S6, when the end of the pulse width of the encoder signal is not detected (S6: NO), the CPU 1 returns to S5 to repeatedly determine the time over in a fixed cycle.
[0043]
  In S5, when the time is over (S5: YES), the CPU 1 resets and counts the timer value as in S7 (S11). At this time, the PWM drive signal is stepped up (S12). . Here, the start time of the counting operation in S11 corresponds to the time point indicated by an upward-pointing arrow with a one-dot chain line in FIGS. In other words, when the pulse width of the encoder signal becomes longer than ideal, it is determined that the motor speed is excessively low at that point in time, and the motor speed is slightly increased slightly. This avoids a situation where the motor M stalls and stops before reaching the target stop position.
[0044]
  Further, as shown in FIG. 3, immediately before the target stop position where the motor M should be stopped, the operations of S5, S11, S12, and S9 shown in the flowchart of FIG. At this time, the PWM drive signal is stepped up in a cumulative addition manner by the number of consecutive times of time over. As a result, even when the motor M is very slow and easily stalled, as shown by the broken line in FIG. 5, a deceleration state that falls below the ideal curve of the motor speed does not occur, and the target stop position can be reliably reached. Can do.
[0045]
  In S1, when there is no instruction from the acceleration / deceleration control unit 12 (S1: NO), the CPU 1 performs other control operations without executing this deceleration process, and the motor M is accelerated or operated at a constant speed. .
[0046]
  Therefore, according to the motor control apparatus having the above-described configuration and operation, the motor speed is reduced too much and the target stop is performed based on the encoder signal from the encoder 10 that detects the rotational speed of the motor M while the motor speed is being reduced. If it is determined that the vehicle stalls before reaching the position, the motor speed changes from deceleration to slightly increases, so that the motor M does not stop suddenly before reaching the target stop position, and it is smooth with high accuracy. The motor M can be stopped.
[0047]
  In addition, this invention is not limited to said embodiment.
[0048]
  For example, the H-type bridge circuit 30 as a switching circuit is not constituted by the transistors Tr1 to Tr4, but may be constituted by other switching elements such as thyristors.
[0049]
  The operation of the entire motor control device is controlled by a microprogram system by a microcomputer having the CPU 1 as a core, but may be controlled by a hardware circuit configured by wired logic.
[0050]
  The rotary encoder 10 for detecting the number of rotations of the motor M is not limited to an optical type but may be an electrical contact type or the like, and any device other than an encoder can be used as long as the motor speed can be output as an electrical detection signal. There may be.
[0051]
  The motor control device can be applied not only to line printers, but also to facsimile machines, copiers, image scanners, etc. Of course, it can be used for various other applications without defining the application to paper feeding. it can.
[0052]
  In addition, the structure and operation other than the above-described features of the present invention can be appropriately changed as long as the effects of the present invention are not impaired.
[0053]
【The invention's effect】
  As described above, according to the motor control device of the invention described in claim 1, the motorRotationWhile decelerating,Its rotationIf it is judged that the vehicle is decelerating excessively even if an excessive deceleration state that causes the speed to stall occursIncrease motor rotation speedSo the motorRotationThe motor does not stop suddenly before reaching the target stop position when the speed is reduced, and the motor can be stopped smoothly with high accuracy.
[0054]
  Moreover, according to the motor control device of the invention described in claim 2, in addition to the effect of the motor control device of claim 1,The interval of the pulse signal output from the encoder exceeds the specified timeIf the length is longer than necessary, the motor is being decelerated.RotationThe speed can be accelerated very slightly. In other words, at the point just before the target stop positionrotationEven if the speed drops more than necessary, make a complete turn from deceleration so that the target stop position can be reached.rotationSpeed can be accelerated.
[0055]
  Furthermore, according to the motor control device of the invention described in claim 3, in addition to the effect of the motor control device according to claim 2,, DecreasePulse during speedSignal intervalIs too long and slows down too much,TimingmeansInThanIncrease the rotation speed of the motor when the time is measuredSo until you reach the target stop positionrotationIt is possible to avoid a situation in which the state of excessively low speed continues for a long time and stops.
[0056]
  According to the motor control device of the invention described in claim 4, in addition to the effect of the motor control device of claim 3, the motorRotationEven if the speed is almost the end of the stop due to the very low speed operation,rotationThe target stop position is too low for too long.in frontSo as not to stop atMotor rotationThe speed can be fine-tuned.
[0057]
  Furthermore, according to the motor control device of the invention described in claim 5, in addition to the effect of the motor control device according to claim 3 or claim 4,RotationThe target stop position is too low for a long time.in frontSo as not to stop atTiming a predetermined timeModerate motor according to the number of timesRotationSpeedRiseCan be made.
[0058]
  According to the storage medium of the invention described in claim 6, the operation of the motor control device according to claim 1 is realized by operating a CPU such as a so-called microcomputer based on the stored execution program. Can do.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a circuit configuration as an embodiment of a motor control device according to the present invention.
FIG. 2 is a time chart showing various signal levels during deceleration.
FIG. 3 is a time chart showing various signal levels during deceleration.
FIG. 4 is a flowchart showing a deceleration processing procedure when the motor speed is decreased.
FIG. 5 is an explanatory diagram showing an example of a motor speed curve.
[Explanation of symbols]
  1 CPU
  2 ROM
  3 RAM
  4 EEPROM
  5 DMAC
  6 Interface
  10 Encoder
  11 Encoder processing unit
  12 Acceleration / deceleration control unit
  20 Drive control unit
  30 H type bridge circuit
  M DC (direct current) motor

Claims (6)

A motor control device that reduces the rotational speed of a motor stepwise to stop the motor at a target stop position ,
Rotational position detecting means for detecting the rotational position of the motor at a predetermined pitch;
First speed control means for reducing the rotational speed of the motor stepwise each time the rotational position of the motor is detected by the rotational position detection means;
Determining means for determining whether or not a predetermined time has elapsed from the time of detection of the previous rotational position before the rotational position of the motor is detected by the rotational position detecting means;
A second speed control means for increasing the rotational speed of the motor when the determination means determines that the predetermined time has elapsed;
Motor control apparatus characterized by comprising a. The rotational position detection means comprises an encoder provided on the rotational shaft of the motor,
The first speed control means decreases the rotational speed of the motor stepwise each time a pulse signal is output from the encoder.
2. The motor control according to claim 1, wherein the determination unit determines whether or not the predetermined time has elapsed since a previous pulse signal was output before a pulse signal was output from the encoder. apparatus. The determining means includes a time measuring means for starting time measurement every time a pulse signal is output from the encoder, and a time measurement by the time measuring means before the next pulse signal is output from the encoder. , And output means for outputting the determination result of time over,
3. The motor control device according to claim 2, wherein the second speed control unit increases the rotation speed of the motor when the determination result of the time over is output by the determination unit. The determination means starts the time measuring operation of the time measuring means from the time when the time interval of the rotational position of the motor detected by the rotational position detecting means becomes equal to or greater than a predetermined time interval when the motor is stopped. let, the motor control device according to claim 3. The time counting means is reset every time the predetermined time is counted until the next pulse signal is output from the encoder and repeats the time counting operation for the predetermined time, while the output means is configured to repeat the predetermined time. The time over judgment result is output every time is counted,
5. The second speed control unit according to claim 3, wherein the second speed control unit increases the rotational speed of the motor in a stepwise manner every time the time-over determination result is continuously output from the output unit. Motor control device. Computer
First speed control means for stepwise decreasing the rotational speed of the motor each time a pulse signal is output from an encoder provided on the rotational shaft of the motor in order to stop the motor at the target stop position;
Determining means for determining whether or not a predetermined time has elapsed from the time when the previous pulse signal was output before the pulse signal was output from the encoder;
A second speed control means for increasing the rotational speed of the motor when the determination means determines that the predetermined time has elapsed;
A computer-readable storage medium having recorded thereon a program for causing it to function .

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