Abstract:
Control of a motor in a device in which a mechanism is driven using the motor as the power source is achieved by providing velocity servo-control means for outputting first command information regarding the motor based upon a preset velocity profile and information relating to velocity of the mechanism, and position servo-control means for outputting second command information regarding the motor based upon a preset position profile and information relating to position of the mechanism. A motor driving signal is generated, based upon the first and second command information, in a region in which the mechanism is to be accelerated in the velocity profile. As a result, target-velocity attainment time is shortened and velocity fluctuation after attainment of the target velocity is reduced.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method and apparatus for controlling a motor and, more particularly, to control executed when a mechanism is driven using a motor as a power source.  
         BACKGROUND OF THE INVENTION  
         [0002]    Currently, motors are used as power sources of various apparatuses. Especially, many OA devices and home electric appliances use DC motors because they have simple structures, require no maintenance, generate little rotation variation and vibration, and are capable of high-speed operation and accurate control.  
           [0003]    In recent years, printers, and especially general commercial printers that are often for home use, are required to have not only higher image quality but also lower operation noise. Noise generated in operation includes that generated in printing and that generated in driving mechanical portions. In inkjet printing apparatuses which have only a few noise sources in printing, noise generated in driving mechanical portions is reduced.  
           [0004]    An inkjet printing apparatus has, as its main mechanical portions, a printhead scanning mechanism and a printing medium convey mechanism. Noise is reduced by using a DC motor and linear encoder as a driving means for the printhead scanning mechanism. Today, a DC motor and rotary encoder are also being employed as a driving means for the printing medium convey mechanism in many cases.  
           [0005]    From the viewpoint of noise reduction, an effect can be expected when a DC motor is employed. From the viewpoint of accurate printing medium conveyance, more advanced position control is required in addition to a mechanical accuracy.  
           [0006]    In an inkjet printing apparatus, the printhead is mounted on a carriage, which is driven by a motor. By way of example, control of the motor can be divided broadly into three control regions, namely an acceleration control region, a constant-velocity control region and a deceleration control region. In general, the printing operation is performed in the constant-velocity control region in order to assure image quality by holding the ink ejection interval constant. Though there are also systems in which printing is carried out also in the acceleration and deceleration control regions in order to raise printing speed, in all cases it is desired that any fluctuation in carriage velocity be made as small as possible during execution of printing. Accordingly, velocity servo control is suited as the feedback control method in the period during which printing is performed, i.e., in the constant-velocity control region. The reason for this is that velocity servo control is feedback control the aim of which is to make the velocity of the controlled system at a certain time coincide with a target velocity.  
           [0007]    The specification of Japanese Patent Application Laid-Open No. 2001-63168 describes a motor control apparatus for performing stable control at the timing of a change from velocity control to position control. A conventional example of motor control, inclusive of the content set forth in the above specification, will now be described.  
           [0008]    [0008]FIG. 4 is a block diagram illustrating the ordinary feedback control procedure of a motor employing velocity servo control. Such velocity servo control is performed by a technique referred to as PID control or classical control. This procedure will now be set forth.  
           [0009]    First, a target velocity desired to be imparted to a controlled system is applied in the form of an ideal velocity profile  4001 . The profile provides velocity command values at applicable times. This velocity information changes with the passage of time. Drive is controlled by performing variable-value control with regard to the ideal velocity profile.  
           [0010]    In velocity servo control, a PID operation generally is carried out. This is an operation involving a proportionality term P, an integration term I and a differentiation term D. The difference is found between encoder velocity information, which is obtained by encoder velocity information conversion means  4005  based upon information detected by an encoder sensor  4004 , and the velocity command value obtained from the ideal velocity profile  4001 . This numerical value is delivered to a PID arithmetic circuit  4002  as a velocity error, which is the velocity shortfall relative to the target velocity. Through a technique referred to as a PID operation, the PID arithmetic circuit  4002  calculates the energy that is to be applied to a DC motor  4003  at this time. Upon receiving this energy, the motor driver circuit regulates the current value by changing the duty of the applied voltage through, e.g., pulse-width modulation (PWM) control, thereby effecting velocity control by regulating the energy applied to the DC motor  4003 .  
           [0011]    The DC motor, which is rotated owing to application of the current value, rotates physically while being influenced by an external disturbance  4006 . The output of the motor is fed back by being sensed by the encoder sensor  4004 .  
           [0012]    [0012]FIG. 5 is a graph illustrating an example of the relationship between time and both velocity and present position owing to the above-described control. In FIG.  5 , time is plotted along a horizontal axis  5051 , velocity along a vertical axis  5052  on the left side and position along a vertical axis  5053  on the right side.  
           [0013]    With regard to position indicated along the vertical axis on the right side, numeral  5043  denotes the position at which printing starts and  5042  the position at which printing ends. The interval between points  5043  and  5042  represents the printing region. Numeral  5041  denotes an arrival position, namely the position eventually reached by rapid deceleration following the end of printing.  
           [0014]    With regard to velocity indicated along the vertical axis on the left side, numeral  5031  denotes attainment velocity of the carriage sought in order to implement an ink ejection frequency desirable for printing. Numeral  5032  denotes the initial velocity in the ideal profile.  
           [0015]    Further, the ideal velocity profile is indicated at  5001 . This signifies the best velocity profile in which the printing region between the printing starting position  5043  and printing end position  5042  is traversed by the attainment velocity  5031 , with the carriage coming to rest at the arrival position  5041  upon being promptly decelerated. The ideal velocity profile  5001  is composed of an acceleration control region  5011 , an ideal constant-velocity control region  5012  and an ideal deceleration control region  5013  along the time axis.  
           [0016]    Numeral  5004  denotes an ideal position profile, which indicates the transition of position in a case where drive is performed in accordance with the ideal velocity profile  5001 . Time that passes through the printing starting position  5043  in the ideal position profile  5004  is an ideal time  5021  for starting printing. This generally indicates the ideal time at which constant-velocity control begins. Similarly, time that passes through the printing end position  5042  in the ideal position profile  5004  is an ideal time  5023  for ending printing. This generally indicates the ideal time at which deceleration control begins.  
           [0017]    Numerals  5003  and  5005  denote actual velocity and actual position profiles, respectively. The actual velocity profile  5003  is composed of the acceleration control region  5011 , an actual constant-velocity control region  5014  and an actual deceleration control region  5015  along the time axis.  
           [0018]    If variable-value control is applied to the ideal velocity profile  5001  by the velocity servo control described in FIG. 4, the actual velocity will always follow up the ideal velocity with a certain delay. This means that even if the ideal time  5021  for starting printing arrives, the attainment velocity  5031  will not be reached and neither will the printing starting position  5043 . The printing starting position  5043  is reached only when the actual time  5022  for starting printing arrives. During travel through the printing region from this point onward, constant-velocity control is required in order to suppress a fluctuation in velocity; hence, a transition to deceleration control is not allowed. As a result, the printing end position  5042  is reached after a delay similar to the delay involved in arriving at the printing starting position  5043 . This moment in time is an actual time  5024  at which printing ends. This is the actual time at which deceleration control starts.  
           [0019]    Numeral  5002  denotes an ideal velocity profile that has been re-calculated based upon the actual time  5024  at which deceleration control starts. Actual deceleration control is carried out by variable-value control with regard to the ideal velocity profile  5002 .  
           [0020]    With the control described above, however, the delay in time involved in reaching the printing starting position  5043  lengthens the time needed for overall control. As a consequence, time until the end of printing lengthens and the overall printing speed declines.  
           [0021]    In order to solve this problem, consider a technique in which the above-described control is applied only to the regions from the constant-velocity control region onward and position servo control is applied to the acceleration control region. An instance where position servo control is applied to the acceleration control region in this technique will now be described.  
           [0022]    [0022]FIG. 6 is a block diagram illustrating ordinary feedback control of a carriage motor using position servo control. Components in FIG. 6 identical with those shown in FIG. 4 are designated by like reference characters.  
           [0023]    First, a target position desired to be imparted to a controlled system is applied in the form of an ideal position profile  6001 . The profile provides position command values at applicable times. This position information changes with the passage of time. Drive is executed by performing variable-value control with regard to the ideal position profile.  
           [0024]    The apparatus is provided with the encoder sensor  4004 , which senses physical rotation of the motor. Encoder position information conversion means  6003  counts the number of slits sensed by the encoder sensor  4004  and obtains absolute-position information. The encoder velocity information conversion means  4005  calculates the actual driving velocity of the motor from the signal provided by the encoder sensor  4004  and a clock built in the printer.  
           [0025]    A value that is the result of subtracting the actual physical position obtained by the encoder position information conversion means  6003  from the ideal position profile  6001  is delivered to subsequent position servo-control feedback processing (a major loop for position servo control)  6002  as a position error, which is the position shortfall relative to the target position. The major loop  6002  for position servo control generally is means for performing a calculation relating to the proportionality term P.  
           [0026]    A velocity command value is output as the result of the calculation performed by the loop  6002 . The velocity command value is delivered to velocity servo-control feedback processing starting with circuit  4002 . In the minor loop for velocity servo control, generally the PID operation is performed, namely the operation involving the proportionality term P, integration term I and differentiation term D.  
           [0027]    In the minor loop for velocity servo control, a numerical value that is the result of subtracting the encoder velocity information from the velocity command value is delivered to the PID arithmetic circuit  4002  as the velocity error, which is the velocity shortfall relative to the target velocity. Through the technique referred to as PID, the PID arithmetic circuit  4002  calculates the energy that is to be applied to a DC motor  4003  at this time. Upon receiving this energy, the motor driver circuit regulates the current value by changing the duty of the applied voltage through, e.g., PWM control, thereby implementing velocity control by regulating the energy applied to the DC motor  4003 .  
           [0028]    The DC motor, which is rotated owing to application of the current value, rotates physically while being influenced by the external disturbance  4006 . The output of the motor is fed back by being sensed by the encoder sensor  4004 .  
           [0029]    [0029]FIG. 7 is a graph illustrating an example of the relationship between time and both velocity and position in control for a case where position servo control shown in FIG. 6 is applied to the acceleration control region and velocity servo control shown in FIG. 4 is applied to the regions from the constant-velocity control region onward. Portions in FIG. 7 identical with those shown in FIG. 5 are designated by like reference characters.  
           [0030]    In comparison with the example shown in FIG. 5, the actual position profile  5005  follows the ideal position profile  5004  in extremely accurate fashion, and the difference between the ideal time  5021  for starting printing and the actual time  5022  for starting printing is very small. This alleviates the aforementioned drawback encountered in velocity servo control, namely the fact that the delay in time involved in reaching the printing starting position  5043  lengthens the time needed for overall control, resulting in diminished printing speed overall.  
           [0031]    If control is exercised in this manner, however, the following problem arises owing to execution of position servo control in the acceleration control region  5011 :  
           [0032]    Since precise control of velocity cannot be performed in the position servo-control interval, the occurrence of a fluctuation in velocity cannot be suppressed. As a consequence, it is not possible to control velocity at the moment of changeover from position servo control to velocity servo control, i.e., at the moment constant-velocity control starts, and velocity fluctuates even after the transition is made to the printing region. As a result, the driving frequency of the printhead cannot be held constant in the printing region, a variation occurs in the size of the ink drops ejected in an inkjet printer, and the original printing performance of the apparatus cannot manifest itself.  
         SUMMARY OF THE INVENTION  
         [0033]    Accordingly, a first object of the present invention is to provide a motor control method through which target-velocity attainment time is shortened and velocity fluctuation reduced after the target velocity is attained.  
           [0034]    A second object of the present invention is to provide a motor control apparatus through which target-velocity attainment time is shortened and velocity fluctuation after attainment of the target velocity is reduced.  
           [0035]    According to the present invention, the first object is attained by providing a motor control method of controlling a motor in a device in which a mechanism is driven using the motor as a power source, comprising: a velocity servo-control step of outputting first command information regarding the motor based upon a preset velocity profile and information relating to velocity of the mechanism; a position servo-control step of outputting second command information regarding the motor based upon a preset position profile and information relating to position of the mechanism; and a driving signal generating step of generating a driving signal of the motor, based upon the first and second command information, in a region in which the mechanism is to be accelerated in the velocity profile.  
           [0036]    According to the present invention, the second object is attained by providing an apparatus for controlling a motor in a device in which a mechanism is driven using the motor as a power source, comprising: velocity servo-control means for outputting first command information regarding the motor based upon a preset velocity profile and information relating to velocity of the mechanism; position servo-control means for outputting second command information regarding the motor based upon a preset position profile and information relating to position of the mechanism; and driving signal generating means for generating a driving signal of the motor, based upon the first and second command information, in a region in which the mechanism is to be accelerated in the velocity profile.  
           [0037]    Thus, in accordance with the present invention, control of a motor in a device in which a mechanism is driven using the motor as the power source is achieved by providing velocity servo-control means for outputting first command information regarding the motor based upon a preset velocity profile and information relating to velocity of the mechanism, and position servo-control means for outputting second command information regarding the motor based upon a preset position profile and information relating to position of the mechanism, wherein a motor driving signal is generated, based upon the first and second command information, in a region in which the mechanism is to be accelerated in the velocity profile.  
           [0038]    Adopting such an arrangement makes it possible to achieve motor control that incorporates both the advantage of position servo control, namely a short period of time until attainment of target position, and the advantage of velocity servo control, namely attainment of velocity target velocity in smooth fashion.  
           [0039]    As a result, target-velocity attainment time is shortened and velocity fluctuation after attainment of the target velocity is reduced.  
           [0040]    Preferably, the driving signal may be generated by multiplying the second command information by a coefficient that varies depending upon time.  
           [0041]    Preferably, the coefficient takes on a maximum value at start of acceleration and a minimum value at end of acceleration.  
           [0042]    The driving signal of the motor may be generated based upon the first command information alone in a region in which the mechanism is to be driven at a constant velocity in the velocity profile.  
           [0043]    Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.  
         [0045]    [0045]FIG. 1 is a perspective view showing the overall arrangement of a serial inkjet printer according to an embodiment of the present invention;  
         [0046]    [0046]FIG. 2 is a block diagram for explaining the control arrangement of the printer shown in FIG. 1;  
         [0047]    [0047]FIG. 3 is a block diagram for explaining the detailed arrangement of a printer controller shown in FIG. 2;  
         [0048]    [0048]FIG. 4 is a block diagram illustrating a control procedure based upon ordinary velocity servo control;  
         [0049]    [0049]FIG. 5 is a graph illustrating an example of the relationship between time and both velocity and position in a case where a motor is driven by the velocity servo control of FIG. 4;  
         [0050]    [0050]FIG. 6 is a block diagram illustrating a control procedure based upon ordinary position servo control;  
         [0051]    [0051]FIG. 7 is a graph illustrating an example of the relationship between time and both velocity and position for a case where position servo control shown in FIG. 6 is applied to the acceleration control region and velocity servo control shown in FIG. 4 is applied to the regions from the constant-velocity control region onward;  
         [0052]    [0052]FIG. 8 is a block diagram illustrating a control procedure applied to the acceleration control region in an embodiment of the present invention; and  
         [0053]    [0053]FIG. 9 is a graph illustrating an example of the relationship between time and both velocity and position for a case where the control shown in FIG. 8 is applied to the acceleration control region and the velocity servo control shown in FIG. 4 is applied to the regions from the constant-velocity control region onward.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0054]    A preferred embodiment of the present invention will now be described in detail in accordance with the accompanying drawings. The invention will be described taking as an example a serial inkjet printer on which a printhead having a removable ink tank is mounted. The inkjet printer according to this embodiment applies the motor control method of the present invention to control of a conveyance motor and carriage motor.  
         [0055]    [0055]FIG. 1 is a perspective view showing the overall arrangement of the serial inkjet printer. Referring to FIG. 1, a printhead  101  has an ink tank. The printhead  101  is detachably mounted on a carriage  102 . A guide shaft  103  is inserted to the bearing portion of the carriage  102  so as to be slidable in the main scanning direction. The two ends of the shaft are fixed to a chassis  114 . A driving motor  105  serving as a carriage driving means transmits driving power through a belt  104  serving as a carriage drive transmission means engaged with the carriage  102  so that the carriage  102  can move in the main scanning direction.  
         [0056]    In a printing standby state, printing paper sheets  115  are stacked on a feed base  106 . At the start of printing, a printing paper sheet is fed by a feed roller (not shown). To convey the fed printing paper sheet, a convey roller is rotated by the driving force of a paper convey motor ( 107 ), i.e., a DC motor through a gear train (motor gear  108  and convey roller gear  109 ) serving as a transmission means. The printing paper sheet  115  is conveyed by an appropriate feed amount by a convey roller  110  and pinch rollers  111  that are pressed by the convey roller  110  and makes follow-up rotation. The convey amount is managed by detecting and counting, with an encoder sensor  117 , slits of a code wheel (rotary encoder film  116 ) pressed and fitted into the convey roller gear  109 . Hence, accurate feeding is possible.  
         [0057]    [0057]FIG. 2 is a block diagram for explaining the control arrangement of the printer shown in FIG. 1.  
         [0058]    Referring to FIG. 2, reference numeral  401  denotes a CPU for controlling the printer of the printer apparatus. The CPU  401  controls printing processing using a printer control program stored in a ROM  402  or printer emulation and print fonts.  
         [0059]    A RAM  403  stores rasterized data for printing or received data from a host. Reference numeral  404  denotes a printer head; and  405 , a motor driver. A printer controller  406  controls access to the RAM  403 , exchanges data with the host apparatus, and sends a control signal to the motor driver. A temperature sensor  407  formed from a thermistor or the like detects the temperature of the printer apparatus.  
         [0060]    The CPU  401  reads out from the I/O data register in the printer controller  406  information such as an emulation command sent from the host apparatus to the printer apparatus and writes/reads control corresponding to the command in/from the I/O register and I/O port in the printer controller  406 , while mechanically and electrically controlling the main body in accordance with the control program in the ROM  402 .  
         [0061]    [0061]FIG. 3 is a block diagram for explaining the detailed arrangement of the printer controller  406  shown in FIG. 2. The same reference numerals as in FIG. 2 denote the same parts in FIG. 3.  
         [0062]    Referring to FIG. 3, an I/O register  501  exchanges data with the host at the command level. A reception buffer controller  502  directly writes received data from the register in the RAM  403 .  
         [0063]    In printing, a printing buffer controller  503  reads out print data from the print data buffer of the RAM and sends the data to the printer head  404 . A memory controller  504  controls three-directional memory access with respect to the RAM  403 . A printing sequence controller  505  controls a printing sequence. A host interface  231  communicates with the host.  
         [0064]    [0064]FIG. 8 is a block diagram useful in describing control applied to the acceleration control region in this embodiment of the present invention. Portions in FIG. 8 identical with those shown in FIGS. 4 and 6 are designated by like reference characters.  
         [0065]    First, a target position desired to be imparted to a controlled system is applied in the form of the ideal position profile  6001 . The profile provides position command values at applicable times. This position information changes with the passage of time. Drive is executed by performing variable-value control with regard to the ideal position profile.  
         [0066]    The apparatus is provided with the encoder sensor  4004 , which senses physical rotation of the motor. The encoder position information conversion means  6003  counts the number of slits sensed by the encoder sensor  4004  and obtains absolute-position information. The encoder velocity information conversion means  4005  calculates the present driving velocity of the conveyance motor from the signal provided by the encoder sensor  4004  and a clock built in the printer.  
         [0067]    A value that is the result of subtracting the ideal position profile  6001  from the actual physical position obtained by the encoder position information conversion means  6003  is delivered to position servo-control feedback processing from  6002  onward as a position error relative to the target position. The major loop  6002  for position servo control generally is means for performing a calculation relating to the proportionality term P. In this embodiment, multiplying means  8001  multiplies the output of the major loop  6002  by Kx, which is the output of a function having time as an input. The product that is the output of the multiplying means  8001  is subtracted from the ideal velocity profile  4001 , as a result of which a command velocity  8002  is obtained. The value of the command velocity  8002  obtained by the above calculation has the meaning set forth below.  
         [0068]    First, assume that the motor is being driven with absolutely no error relative to the ideal position profile  6001 . In such case the output of the multiplying means  8001  is zero and, hence, the value of the command velocity  8002  is that of the ideal velocity profile  4001  per se.  
         [0069]    In general, however, the actual arrival position involves a temporal delay with respect to the ideal position profile  6001  and therefore the output of the multiplying means  8001  has a negative value. As a result, the value of the command velocity  8002  exceeds the ideal velocity profile  4001 .  
         [0070]    In other words, a value for the purpose of following up the ideal position profile  6001  while preventing a drastic departure from the ideal velocity profile  4001  is output as the command velocity  8002 , and the motor is driven by performing variable-value control with respect to the command velocity  8002 .  
         [0071]    In velocity servo control, the PID operation generally is performed, namely the operation involving the proportionality term P, integration term I and differentiation term D. The difference is found between the command velocity  8002  and the encoder information, which has been obtained by the encoder velocity information conversion means  4005  based upon the information detected by the encoder sensor  4004 , this numerical value is delivered to the PID arithmetic circuit  4002  as a velocity error, which is the velocity shortfall relative to the target velocity, and the PID arithmetic circuit  4002  calculates the energy, which is to be applied to the DC motor  4003  at this time, through the PID calculation method. Upon receiving this energy, the motor driver circuit regulates the current value by changing the duty of the applied voltage through, e.g., PWM control, thereby implementing velocity control by regulating the energy applied to the DC motor  4003 .  
         [0072]    The DC motor  4003 , which is rotated owing to application of the current value, rotates physically while being influenced by the external disturbance  4006 . The output of the motor is fed back by being sensed by the encoder sensor  4004 .  
         [0073]    [0073]FIG. 9 is a graph illustrating an example of the relationship between time and both velocity and position for a case where drive is controlled according to this embodiment. According to this embodiment, the control depicted in FIG. 8 is applied to the velocity control region, and the velocity servo control shown in FIG. 4 is applied to regions from the constant-velocity control region onward. Portions in FIG. 9 identical with those in the graphs of FIGS. 5 and 7 are designated by like reference characters. Further, the transition of the command velocity  8002  is indicated at  9001 .  
         [0074]    In comparison with the example shown in FIG. 5, the actual position profile  5005  follows the ideal position profile  5004  accurately and the difference between the ideal time  5021  for starting printing and the actual time  5022  for starting printing is very small. This alleviates the aforementioned drawback encountered in the example shown in FIG. 5, namely the fact that the delay in time involved in reaching the printing starting position  5043  lengthens the time needed for overall control, resulting in diminished printing speed overall.  
         [0075]    In comparison with the example shown in FIG. 7, the advantages of velocity servo control can be attained even in the acceleration control region, as a result of which the occurrence of a fluctuation in velocity can be suppressed comparatively effectively. Accordingly, velocity at the moment of changeover from position servo control to velocity servo control, i.e., at the moment constant-velocity control starts, can be made more accurate, and it is possible to avoid a fluctuation in velocity after the transition is made to the printing region.  
         [0076]    In order to obtain these advantages, however, the setting of the coefficient Kx in the multiplying means  8001  is important.  
         [0077]    As a specific example of the setting of Kx, the setting can be made in accordance with the following equation:  
           Kx=K× ( Tflat−Tx )/ Tflat    
         [0078]    where K represents a constant, Tflat the time at which the acceleration control region  5011  ends, and Tx the present time.  
         [0079]    More specifically, Kx takes on the maximum value at time 0 and becomes zero at the instant the acceleration control region  5011  ends. When Kx is zero, the output of the multiplying means  8001  becomes zero and therefore the command velocity  8002  becomes equal to the ideal velocity profile  4001 . This means that control based upon velocity servo control exactly the same as that of FIG. 4 is carried out in the constant-velocity control region.  
         [0080]    Accordingly, when the transition is made from the acceleration control region  5011  to the actual constant-velocity control region  5014 , an extreme or sudden changeover of the control method does not occur and smooth control can be exercised as a result.  
         [0081]    Further, since the gain of position servo control increases when acceleration control starts, good tracking of the ideal position control profile can be expected. As a result, the delay in terms of position in the initial phase of acceleration can be eliminated more effectively, and it is possible to perform position control that makes up for the temporal delay in control from the quiescent state to the moment at which motion begins.  
         [0082]    Furthermore, toward the end of the acceleration control region, the gain of position servo control declines. As a result, velocity servo control becomes more efficacious and a fluctuation in velocity when the transition is made to the actual constant-velocity control region  5014  can be suppressed.  
         [0083]    [Other Embodiments] 
         [0084]    In the embodiment set forth above, the present invention is applied to control of a carriage motor in a serial inkjet printer. However, the present invention is not limited to an inkjet printer and can be applied to various devices that use motors.  
         [0085]    Further, in the foregoing embodiment, the present invention is applied to control of a DC motor. However, the present invention can be applied also to motors other than DC motors so long as these motors can be subjected to feedback control such as the above-described variable-value control.  
         [0086]    Further, the object of the present invention can also be achieved by providing a storage medium storing program codes for performing the aforesaid processes to a computer system or apparatus (e.g., a personal computer), reading the program codes, by a CPU or MPU of the computer system or apparatus, from the storage medium, then executing the program.  
         [0087]    In this case, the program codes read from the storage medium realize the functions according to the embodiments, and the storage medium storing the program codes constitutes the invention.  
         [0088]    Further, the storage medium, such as a floppy disk, a hard disk, an optical disk, a magneto-optical disk, CD-ROM, CD-R, a magnetic tape, a non-volatile type memory card, and ROM can be used for providing the program codes.  
         [0089]    Furthermore, besides aforesaid functions according to the above embodiments being realized by executing the program codes which are read by a computer, the present invention also includes a case where an OS (operating system) or the like working on the computer performs parts or entire processes in accordance with designations of the program codes and realizes functions according to the above embodiments.  
         [0090]    Furthermore, the present invention also includes a case where, after the program codes read from the storage medium are written in a function expansion card which is inserted into the computer or in a memory provided in a function expansion unit which is connected to the computer, a CPU or the like contained in the function expansion card or unit performs a part or entire process in accordance with designations of the program codes and realizes functions of the above embodiments.  
         [0091]    As is apparent, many different embodiments of the present invention can be made without departing from the spirit and scope thereof, so it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.