Abstract:
A recording apparatus includes a conveying mechanism control unit which performs a first processing and a second processing almost simultaneously, when it is detected that a recording medium has reached a stop position. The first processing is to make invalid the output of a servo computing device and make effective the output in accordance with an output-for-stop setting register. The second processing is to generate an auto stop interrupt to inform that the output in accordance with the output-for-stop setting register is made effective. With this configuration, the recording apparatus enables the increase in speed of a stop operation control processing of a DC motor for use in conveying a recording medium and the improvement of the stop position accuracy of the recording medium.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to control of a recording medium conveying mechanism of a recording apparatus which produces records with recording heads and conveys a recording medium in a predetermined amount by means of a DC motor. 
     2. Related Background Art 
     Ink-jet recording apparatus, which are mounted on printers, facsimiles and copiers, are widely used as means for recording images (including characters and symbols) on recording media, such as paper and plastic thin sheet (OHP), based on image information. 
     There is shown in FIG. 8 a schematic structural view of the recording medium conveying unit of one example of the above described ink-jet recording apparatus. 
     A recording medium  201  is supported by a conveying roller  202  placed in a recording section and conveyed in the direction shown by the arrow α in the figure by the conveying roller  202  when driving a conveying motor  203 . As the conveying motor  203 , a stepping motor or a DC motor is used. Nowadays, however, a DC motor is used more often because of its quietness, etc. When using a DC motor, a rotary encoder, not shown in the figure, is installed in the conveying roller  202  and the conveying motor  203  is controlled based on encoder signals sent from the encoder. 
     In front of the conveying roller  202 , shafts  204  are provided in parallel therewith. And a carriage  205  performs a reciprocating motion on the shafts  204  in the direction shown by the arrow β when the drive action of a carriage motor  206  is transmitted to the carriage  205  via a belt  207 . Between the shafts  204  and the carriage  205 , lubricating oil such as grease is applied so as to decrease the mechanical loading caused due to the friction between them. As the carriage motor  206 , a stepping motor or a DC motor is used, like the conveying motor  203 . Nowadays, however, a DC motor is used more often because of its quietness, etc. When using a DC motor as the carriage motor  206 , a linear encoder, not shown in the figure, is arranged on the carriage  205  and a linear encoder scale, not shown in the figure, is arranged in parallel with the shafts  204 . And the carriage motor  206  is controlled based on signals obtained from the linear encoder. 
     The carriage  205 , as means for moving recording heads, is mounted with recording heads  208  and tanks  209  which contain recording ink. The recording heads  208  shown in FIG. 8 are for use in producing color images, and a head for black  208 -BK, a head for cyan  208 -C, a head for magenta  208 -M and a head for yellow  208 -Y are arranged in this order in a scan direction of the carriage  205 . And tanks  209 -BK,  209 -C,  209 -M,  209 -Y for respective black (BK), cyan (C), magenta (M) and yellow (Y) supply the inks to the heads corresponding to the respective colors. On the front surface of each recording head  208 , that is, on a surface which faces the recording area of the recording medium  201  spaced at a fixed distance (eg. 0.8 mm) apart therefrom, an ink ejection portion is provided in which multiple (for example, 48 or 64) ink ejection orifices are arranged in a column in the direction intersecting the scanning direction of the carriage. 
     A control unit containing a control circuit (CPU) of the recording apparatus and ROM and RAM, all of which are not shown in the figure, receives information on a recording mode and recording data from a controller of an external host computer via, for example, the interface. And the control unit controls each recording head via head driving circuits and the driving sources such as various types of motors, based on the received information and data, whereby ink, etc. is ejected and records are produced on the recording medium  201 . 
     As a method of controlling motor torque when using a DC motor for each of the carriage motor and the conveying motor, one is known in which an enable signal, which controls on/off of motor driver output, and phase signal, which controls the direction of motor rotation, are subjected to PWM (Pulse Width Modulation) control. 
     The relationships between the motor supply torque and the control waveform (duty factor DUTY) at the time of subjecting the enable signal to PWM control are shown in FIGS. 9A to  9 C and those at the time of subjecting the phase signal to PWM control are shown in FIGS. 10A to  10 C, respectively. The enable signal determines on/off of the output directed to the motors; for example, when the enable signal is low, output is disabled and when the enable signal is high, output is enabled. As shown in FIGS. 9A to  9 C, when high level duty factor of the waveform is 0%, the motor supply torque output is 0%, when the duty factor 50%, the torque output 50%, and when the duty factor 100%, the torque output 100%, provided that the maximum output torque of the motors is 100%. 
     On the other hand, the phase signal determines the direction of motor rotation; for example, when the phase signal is low, the motor rotates in the reverse direction and when the phase signal is high, the motor rotates in the forward (or normal) direction. As shown in FIGS. 10A to  10 C, when the high level duty factor of the waveform is 50%, the motor generates the same magnitude of torque in the forward and reverse directions, and therefore, is in the stopped state. In other words, when the high level duty factor of the waveform is 50%, the motor supply torque generated is 0%, when the duty factor is 75% (duty factor 25%), the torque generated is 50% in the forward direction (50% in the reverse direction), and when the duty factor is 100% (duty factor 0%), the torque generated is 100% in the forward direction (100% in the reverse direction). 
     Then, a control flowchart when using a DC motor as the conveying motor is shown in FIG.  11 . The control in a DC motor servo has been performed by software computing via CPU. The information required for the servo is obtained from the encoder signal, and the encoder signal is processed using hardware such as ASIC. The software reads the position and speed information obtained from the encoder signal at intervals of servo cycle, for example, of 1 ms and performs servo computing processing to control the DC motor. The stop position of the recording medium is detected by the hardware, such as ASIC, which sends an interrupt signal to the CPU, and this interrupt allows the software to know that the recording medium reaches the stop position. After the Start (s 501 ), upon the occurrence of interrupt (s 502 ), the software decides what the content of the interrupt is (s 503 ). If the decision is that the interrupt is not stop position interrupt, the software performs regular interrupt handling corresponding to the content of the interrupt (s 504 ). If the interrupt is decided to be stop position interrupt, the software sets PWM output for stop and drives accordingly (s 505 ), and then resets the interrupt (s 506 ). Then the software verifies the stop position (s 507 ); and, if the stop position is out of position, the stop position is corrected (s 508 ). After verifying the stop position, a recording operation (s 509 ) is executed and the control is completed (s 510 ). 
     However, in the motor control of the prior art described above, the motor does not stop until multiple steps, that is, occurrence of interrupt, decision of the content of interrupt and setting/execution of PWM output for stop are executed after the recording medium reaches the stop position. Since the conveying motor continues to operate during the execution of each of the above steps, a problem of lowering the stop position accuracy has sometimes arisen. 
     Further, in order to avoid causing variation in time of executing PWM output for stop due to the occurrence of waiting for the interrupt, it has been necessary to raise the priority of stop position interrupt to the highest. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of this invention is to provide a recording apparatus which enables the speed up of a stop operation control processing of a DC motor for use in conveying a recording medium and the improvement of the stop position accuracy of the recording medium. 
     Another object of this invention is to provide a recording apparatus which is independent of the priority of an interrupt process related to the stop position of a DC motor, and hence high in degree of design freedom. 
     Still another object of this invention is to provide a recording apparatus which includes conveying means for conveying a recording medium, a conveying motor for driving the conveying means, servo computing means for controlling the output directed to the conveying motor based on servo computing results obtained using software, position detecting means for detecting the position of the recording medium by counting the number of encoder signal edges, a stop position setting register for setting a stop position of the recording medium, position comparing means for comparing the position detected by the position detecting means with that set by the stop position setting register, and conveying motor output switching means for selectively switching the output from the servo computing means and the output from an output-for-stop setting register. The recording apparatus further includes a conveying mechanism control unit which performs a first processing and a second processing almost simultaneously, when it is detected by the position comparing means that the recording medium has reached the stop position. The first processing is to make invalid the output of the servo computing means by the conveying motor output switching means and make effective the output in accordance with the output-for-stop setting register. The second processing is to generate an auto stop interrupt to inform that the output in accordance with the output-for-stop setting register is made effective. 
     Another object of this invention is to provide a recording apparatus which includes conveying means for conveying a recording medium, a conveying motor for driving the conveying means, servo computing means for controlling the output directed to the conveying motor based on the servo computing results obtained using software, position detecting means for detecting the position of the recording medium by counting the number of the encoder signal edges, a stop position setting register for setting a stop position of the recording medium, a position comparing means for comparing the position detected by the position detecting means with that set by the stop position setting register, and conveying motor output switching means for selectively switching the output from the servo computing means and the output from an output-for-stop setting register. The recording apparatus further includes a conveying mechanism control unit in which when it is detected that the recording medium has reached the stop position by the position comparing means, and the conveying motor output switching means, the position comparing means generates an auto stop interrupt to inform that the output in accordance with the output-for-stop setting register is made effective, and make the output from the output-for-stop setting register effective a certain time after the occurrence of the auto stop interrupt. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic structural view of the recording medium conveying unit of an ink-jet recording apparatus in accordance with a first embodiment of the present invention; 
     FIG. 2 is a control block diagram illustrating the control of a DC motor of a recording medium conveying mechanism in accordance with the first embodiment of the present invention; 
     FIGS. 3A,  3 B,  3 C,  3 D,  3 E,  3 F and  3 G are timing charts illustrating the control of the DC motor of the recording medium conveying mechanism in accordance with the first embodiment of the invention; 
     FIG. 4 is a flowchart illustrating the control of the DC motor of the recording medium conveying mechanism in accordance with the first embodiment of the present invention; 
     FIG. 5 is a control block diagram illustrating the control of a DC motor of a recording medium conveying mechanism in accordance with a second embodiment of the present invention; 
     FIGS. 6A,  6 B,  6 C,  6 D,  6 E and  6 F are timing charts illustrating the control of the DC motor of the recording medium conveying mechanism in accordance with the second embodiment of the present invention; 
     FIG. 7 is a flowchart illustrating the control of the DC motor of the recording medium conveying mechanism in accordance with the second embodiment of the present invention; 
     FIG. 8 is a schematic structural view of a recording medium conveying unit of an ink jet recording apparatus of the prior art; 
     FIGS. 9A,  9 B and  9 C are graphs illustrating the waveforms subjected to PWM control by the enable signal; 
     FIGS. 10A,  10 B and  10 C are graphs illustrating the waveforms subjected to PWM control by the phase signal; and 
     FIG. 11 is a flowchart illustrating the control of a DC motor in a recording medium conveying mechanism of the prior art. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following the embodiments of the invention will be described in detail with reference to the accompanying drawings. 
     It should be noted that the present invention is not limited to these embodiments as illustrated in the drawings. 
     First Embodiment 
     Referring first to FIG. 1, there is shown a schematic structural view of a recording medium conveying unit of an ink-jet recording apparatus of the first embodiment. 
     A recording medium  1  is supported by conveying rollers  2  which are arranged in a recording area and conveyed in the direction shown by the arrow α in the figure by driving a conveying motor (DC motor)  102 . In the conveying roller  2  a rotary encoder, not shown in the figure, is installed, and the conveying motor  102  is controlled based on an encoder signal given by the encoder. 
     In front of the conveying rollers  2 , shafts  4  are provided in parallel therewith. A carriage  5  performs a reciprocating motion on the shafts  4  in the direction shown by the arrow β when a driving action of a carriage motor  6  is transmitted to the carriage  5  via a belt  7 . Between the shafts  4  and the carriage  5 , lubricating oil such as grease is applied so as to decrease the mechanical loading caused due to the friction between them. A linear encoder, not shown in the figure, is arranged on the carriage  5  and a linear encoder scale, not shown in the figure, is arranged in parallel with the shafts  4 . The carriage motor  6  is controlled based on signals obtained from the linear encoder. 
     The carriage  5 , as means for moving recording heads, is mounted with recording heads  8  and tanks  9  which contain recording ink. The recording heads  8  are for use in producing color images, and a head for black  8 -BK, a head for cyan  8 -C, a head for magenta  8 -M and a head for yellow  8 -Y are arranged in this order in a scan direction of the carriage  5 . Tanks  9 -BK,  9 -C,  9 -M,  9 -Y for respective black (BK), cyan (C), magenta (M) and yellow (Y) colors supply ink to the heads corresponding to the respective colors. On a front surface of each recording head  8 , that is, on a surface which faces the recording area of the recording medium  1  spaced at a fixed distance (e.g., 0.8 mm) apart therefrom, an ink ejection portion is provided in which multiple (for example, 48 or 64) ink ejection orifices are arranged in a column in the direction intersecting the scan direction of the carriage. 
     A control unit, which will be described later, containing a control circuit (CPU) of the recording apparatus and ROM and RAM receives information on a recording mode and recording data from the controller of an external host computer via, for example, the interface. And the control unit controls each recording head via head driving circuits and driving sources such as various types of motors, based on the received information and data, whereby inks are ejected and recording is conducted on the recording medium  1 . 
     Referring now to FIG. 2, there is shown a control block diagram illustrating the control of the DC motor of a recording medium conveying mechanism of this embodiment. 
     The control block of the recording medium conveying mechanism of this embodiment includes a CPU (servo computing unit)  106  for controlling an output directed to the DC motor  102  based on the servo computing results obtained using software; an ASIC 104 including a position detecting unit  105  for detecting a position of the recording medium  1  by counting the number of the edges of the encoder signal  103 , a stop position setting register  108  for setting a stop position of the recording medium  1 , a PWM for stop setting register  109  for setting an output of the DC motor  102  for stop, a position comparator unit  115  for comparing a position of the recording medium  1  detected by the position detecting unit  105  with that set by the stop position setting register  108 , and a PWM selection unit  111  for selectively switching the output from the CPU (servo computing unit)  106  and the output from the PWM for stop setting register  109 ; and a motor driver  113  for controlling the DC motor  102  based on the PWM signal  112  output from the PWM selection unit  111 . 
     An encoder  101  outputs the encoder signal  103  according to the motion of the DC motor  102 . The encoder signal  103  is sent to the position detecting unit  105  within the ASIC  104 , and the position detecting unit  105  performs position counting at all times. The CPU (servo computing unit)  106  writes on each register or reads from it selectively via a register control unit  107  within the ASIC  104 . The CPU (servo computing unit)  106  sets the stop position in the stop position setting register  108  and a PWM value for stop in the PWM for stop setting register  109  before starting to drive the DC motor  102 . The CPU (servo computing unit)  106  reads position information from the position detecting unit  105  at intervals of servo cycle, performs computation based on the information it has read, and sets the thus computed PWM value in a servo PWM setting register  110 . The PWM selection unit  111  generates a PWM signal according to the PWM value set in the servo PWM setting register  110 . The generated PWM signal  112  is sent to the DC motor driver  113 , and the motor output in accordance with the PWM signal  112  is directed to the DC motor  102 , whereby the DC motor  102  is driven. When the DC motor  102  is driven and the recording medium reaches the stop position, the position comparator unit  115  comparing the position information  114  counted by the position detecting unit  105  with the value of the stop position setting register  108  detects that the recording medium has reached the stop position. Upon that detection, the position comparator unit  115  sends an auto stop signal  116  to the PWM selection unit  111  and also sends an auto stop interrupt signal  117  to the CPU (servo computing unit)  106 . The PWM selection unit  111  into which the auto stop signal  116  is entered outputs immediately the PWM signal  112  in accordance with the PWM for stop setting register, and at the same time inhibits the acceptance from the servo PWM setting register  110 . Thus, the DC motor driver  113  sends to the DC motor  102  the output in accordance with the PWM signal  112  indicating the stop state, whereby the DC motor is suspended. The CPU (servo computing unit)  106  having received the auto stop interrupt signal  117  detects the DC motor going into the stop mode, reads the position information from the position detecting unit  105 , verifies the stop position, and executes recording operations. 
     Referring now to FIGS. 3A to  3 G, there are shown timing charts illustrating the control of the DC motor of the recording medium conveying mechanism of this embodiment. 
     An encoder detected position  601  is the position of the recording medium  1  detected by increasing/decreasing the counted value in accordance with the encoder signal  103 . A stop position ( 6 ) is set in a stop position setting register  602  and a PWM value for stop (α) is set in a PWM for stop setting register  603  before driving the DC motor. In a motor output PWM setting register  604  for the DC motor being driven are set PWM values (A, B, C, D . . . ) set by the CPU (servo computing unit)  106 , and in accordance with these values, PWM signals for controlling the DC motor are generated. Immediately when the encoder detected position  601  and the value of the stop position setting register  602  coincide, an auto stop signal  605  is made low (PWM output for stop) and an auto stop interrupt signal  606  is made low (auto stop operation occurrence). When the auto stop signal  605  becomes PWM output for stop (low), the PWM value for stop (α) in the PWM for stop setting register  603  is automatically input into a motor output PWM setting register  604  and PWM output in accordance with this value is generated. If the servo computing unit sets a PWM value while the auto stop signal  605  is low, the setting is ignored and the value of the PWM for stop setting register  603  remains effective. Then, if an end of recording detection signal  607  occurs, the auto stop signal  605  is changed to servo PWM output (high), and the control of the DC motor is returned to the regular DC motor driving by the servo. The end of recording detection signal  607  occurs when recording by the recording heads  8  terminates, but it may be output when it is required that the auto stop signal  605  changes from the PWM output for stop (low) to the servo PWM output (high). 
     Referring now to FIG. 4, there is shown a flowchart illustrating the control of the DC motor of the recording medium conveying mechanism of this invention. 
     After the starting (s 701 ), upon knowing the occurrence of interrupt (s 702 ), the control decides what the content of the interrupt is (s 703 ). If the interrupt is not an auto stop interrupt, the control performs a regular interrupt process corresponding to the content of the interrupt (s 704 ). If the interrupt is the auto stop interrupt, the control resets it (s 705 ). Then the control verifies the stop position (s 706 ), and if the stop position is out of position, the control corrects it (s 707 ). After verifying the stop position, the control executes a recording operation (s 708 ) and ends (s 709 ). 
     As described so far, according to the recording apparatus of this embodiment, the control related to the stop operation of the DC motor is not executed by the servo computing unit of the CPU, but performed within the ASIC, so that the speed-up of processing is realized. The DC motor goes into the stop mode immediately when the recording medium reaches the stop position, and thus the stop position accuracy is improved. 
     Further, according to the recording apparatus of this embodiment described above, it is not necessary to raise the priority of the interrupt handling related to the stop operation of the DC motor to the highest. Therefore, the degree of design freedom can be enhanced. 
     Second Embodiment 
     Referring to FIG. 5, there is shown a control block diagram illustrating the control of the DC motor of the recording medium conveying mechanism of the second embodiment. 
     First, the difference in control between the first and second embodiments will be roughly described. 
     In the first embodiment, the auto stop signal  116  is input into the PWM selection unit  111 , which inhibits the acceptance from the servo PWM setting register  110 . And at the same time, the PWM signal  112  in accordance with the PWM for stop setting register is directed to the DC motor driver  113 . In other words, the DC motor  102  is stopped by the signal from the PWM selection unit  111 , and even if the CPU (servo computing unit)  106  outputs an operation instruction, since the PWM selection unit  111  does not accept the servo PWM setting register  110 , the operation instruction is never output from the PWM selection unit  111  to the DC driver  113  as a PWM signal  112 . This allows the DC motor  102  to remain in the stopped state. 
     On the other hand, in this embodiment, in order for the CPU (servo computing unit)  806  to have time to fully identify the auto stop interrupt, the CPU (servo computing unit)  806  outputs no signal which operates a DC motor  802  after the DC motor  802  enters in the stopped state. 
     In the following, this embodiment will be described in detail. However, the structure of the ink-jet recording apparatus of this embodiment is the same as that of the ink-jet recording apparatus shown in FIG. 1, except that the method of controlling the recording medium conveying mechanism, which is to be described below, is different from that of the first embodiment. Therefore, the detailed description will be omitted in other parts. In the following description, reference numerals different from those of FIG. 1 will be used to denote each constituent, signal, etc. For example, the DC motor  102  shown in FIG. 1 is denoted with reference numeral  802 . 
     For the regular operations of an encoder  801 , a DC motor  802 , an encoder signal  803 , an ASIC  804 , a position detecting unit  805 , a CPU (servo computing unit)  806 , a register control unit  807 , a stop position setting register  808 , a PWM for stop setting register  809  and a servo PWM setting register  810 , the description will be omitted since they are the same as those of FIG.  1 . However, a PWM value for stop set in the PWM for stop setting register  809  is not sent to the PWM selection unit  811  until a stop position arrival signal  816  is sent from the position comparator unit  815 . 
     The PWM selection unit  811  generates a PWM signal according to the PWM value set in the servo PWM setting register  810 . The PWM selection unit  811  generates the PWM signal  812  according to the value sent last between the PWM for stop setting register  809  and the servo PWM setting register  810 . The generated PWM signal  812  is sent to the DC motor driver  813 , and the motor output in accordance with the PWM signal  812  is directed to the DC motor  802 , whereby the DC motor  802  is driven. 
     When the DC motor  802  is driven and the recording medium reaches the stop position, the position comparator unit  815  comparing the position information  814  counted by the position detecting unit  805  with the value of the stop position setting register  808  detects that the recording medium has reached the stop position. Upon that detection, the position comparator unit  815  sends an auto stop interrupt signal  817  to the CPU (servo computing unit)  806 . Then, after a certain time has elapsed which allows the CPU (servo computing unit)  806  to fully identify the above auto stop interrupt and stop the servo output, the position comparator unit  815  sends the stop position arrival signal  816  to the PWM for stop setting register  809 . The PWM for stop setting register  809  into which the stop position arrival signal  816  is entered transfers the PWM value for stop to the PWM selection unit  811 . And the PWM selection unit  811  immediately outputs the PWM signal  812  in accordance with the PWM value for stop. This allows the DC motor driver  813  to direct the output in accordance with the PWM signal  812  in the stopped state to the DC motor  802  to enter in the stopped state. The CPU (servo computing unit)  806  having received the auto stop interrupt signal  817  detects that the DC motor has fallen into the stop mode, reads the position information from the position detecting unit  805 , verifies the stop position, and executes the recording operation. 
     Referring now to FIGS. 6A to  6 F, there are shown timing charts illustrating the control of the DC motor of the recording medium conveying mechanism of this embodiment. 
     An encoder detected position  901  is the position of the recording medium  1  detected by increasing/decreasing the counted value in accordance with the encoder signal  803 . A stop position ( 6 ) is set in a stop position setting register  902  and a PWM value for stop (α) is set in a PWM for stop setting register  903  before driving the DC motor. In a motor output PWM setting register  904  for the DC motor being driven are set PWM values (A, B, C, D . . . ) set by the CPU (servo computing unit)  806 , and in accordance with these values, PWM signals for controlling the DC motor are generated. Immediately when the encoder detected position  901  and the value of the stop position setting register  902  coincide, an auto stop interrupt signal  905  is made low (auto stop operation occurrence). Then, after a certain time d has elapsed which allows the servo computing unit to fully identify the change in the auto stop interrupt signal  905  and stop the servo output, a stop position arrival signal  906  (one shot) is produced. When the stop position arrival signal  906  (one shot) is produced, the motor output PWM setting register  904  is rewritten with the information (α) stored in the PWM for stop setting register  903 , and PWM output in accordance with this value is generated. 
     Referring now to FIG. 7, there is shown a flowchart illustrating the control of the DC motor of the recording medium conveying mechanism of this invention. 
     After the starting (s 1001 ), upon knowing the occurrence of interrupt (s 1002 ), the control decides what the content of the interrupt is (s 1003 ). If the interrupt is not an auto stop interrupt, the control performs a regular interrupt process corresponding to the content of the interrupt (s 1004 ). If the interrupt is the auto stop interrupt, the control stops the servo output (s 1005 ) and then resets the interrupt (s 1006 ). Thereafter, the control verifies the stop position (s 1007 ), and if the stop position is out of position, the control corrects it (s 1008 ). After verifying the stop position, the control executes the recording operation (s 1009 ) and ends (s 1010 ). 
     As described so far, according to the recording apparatus of this embodiment, the control related to the stop operation of the DC motor is not executed by the servo computing unit of the CPU, but performed within the ASIC, just like the first embodiment, so that the speed-up of processing is realized. The DC motor goes into the stop mode immediately when the recording medium reaches the stop position, and thus the stop position accuracy is improved. 
     Further, according to the recording apparatus of this embodiment described above, it is not necessary to raise the priority of the interrupt handling related to the stop operation of the DC motor to the highest. Therefore, the degree of design freedom can be enhanced. 
     As described above, according to this embodiment, the control related to the stop operation of the conveying motor is not performed based on the servo computing results obtained by using the software of the servo computing means, but executed by the conveying mechanism control unit. Therefore, the servo computing means need not take over a burden and the processing is speeded up. 
     Further, since the servo computing means does not participate in the control of the stop operation of the conveying motor, it is not necessary to consider the priority of the interrupt handling related to the stop operation of the conveying motor toward the servo computing means, resulting in enhancement of the degree of design freedom.