Motor control system of printer
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to control of the motor of a printer and, more particularly, to a motor control system of a printer of the type wherein printing of characters is performed while effecting slow-up over a space or interval between characters, which operates in such a manner that slow-up is effected even in a zone exceeding the space between characters and a print action is performed while slow-up is taking place. 
     2. Description of the Prior Art 
     As shown in FIG. 1, the printer comprises a platen 1, a carriage 3 for moving relatively a head 2, a carriage shaft 4 for supporting the carriage, and the combination for moving actually the carriage, composed of a transmission system 5, A-pulley 6, B-pulley 7, and stepping motor 8. Print action is performed in such a manner that a paper is colored by applying some print commands to the head 2 in synchronization with rotation of the stepping motor 8. As shown in FIG. 2, a printer drive circuit drives, by means of a microprocessor 9, the head 2 and stepping motor 8 by the use of a head driver 10 and motor driver 11. FIG. 3 is a drive timing chart showing a print action according to the prior art, of the head 2 and stepping motor 8, with showing the amount of head movement in correlation with the former. In this drawing, the abscissa indicates the time, and the ordinate indicates drive pulses applied to the head 2 and stepping motor 8 as well as the amount of movement of the carriage 3 when these pulses are applied. 
     In the conventional drive system, as represented by the curve A of FIG. 4, the drive frequency of the stepping motor 8 is slowed up from f 1  to f 2  by making use of steps corresponding to the number of characters, then, after the drive frequency required is attained, the stepping motor 8 is further driven at a constant speed, during which the print command is applied to the head 2 under the state of constant speed. 
     In the foregoing operation, by making use of the space between characters, slow-up is effected over that space. 
     It is desired to increase the print speed; however, according to the prior art, it is hardly possible to effect slow-up successfully thereby resulting in a desired high-speed state within the space between characters. That is, it is undesirable to try to attain a more high print speed than that attained in the prior art within the same number of steps as counted at the stepping timing of the stepping motor. The reason is that if the slow-up of the motor were effected rapidly, the movement of the carriage caused by rotation of the motor becomes not smooth, the quality of print is actually degraded, and there arises the phenomenon that characters are misaligned. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to solve the foregoing problem, thus, to enhance the print speed while maintaining the quality of print. 
     To achieve the foregoing object, according to the present invention, slow-up of a stepping motor is effected for a longer interval than the extent of space between characters and a print action is commenced well within the period of the slow-up. 
     The foregoing technical measures are put into practice in the following manner: slow-up is commenced by the use of pulses of the maximum frequency within the self-startable frequency limits of the stepping motor, a nonprint zone is defined within the extent of space between characters, in the nonprint zone, after completion of about half, for example, of the slow-up, smooth rotation of the motor is maintained, and in the remaining steps, printing is started while effecting slow-up further, whereby the print speed can be enhanced while maintaining the quality of print. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a configuration diagram of an example of a printer to which the present invention is applicable; 
     FIG. 2 is a block diagram of a printer control circuit; 
     FIG. 3 is an operation timing chart of the printer and its control circuit; and 
     FIG. 4 is an explanation chart showing the operation (B) of an embodiment of the present invention, compared with the operation (A) of the conventional print system. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will now be described with reference to FIG. 4. 
     The curve A illustrated relates to the conventional control system of the stepping motor 8, whereas the curve B relates to the control system of the stepping motor 8 which is the embodiment of the present invention. 
     With respect to both the conventional and present control systems whose operations are illustrated in FIG. 4, a similar configuration to that of FIG. 1 is employable in the printer, and a similar configuration to that of FIG. 2 is employable in the printer control circuit. 
     According to the curve B of the present embodiment, the stepping motor 8 slows up from its self-startable frequency f 3  to the print frequency f 4 , and after completion of a few steps falling under the nonprint zone, the print command is applied to the head 2 to commence printing. 
     Even during the foregoing operation, slow-up is effected, and as the slow-up terminates at f 4 , the stepping motor 8 is driven at a constant speed. The print action is performed within the print zone illustrated. In the action above, the number of steps required in the slow-up varies dependig upon the type of printer. 
     By actualizing a drive system involving the feature of the curve B which represents the embodiment, at the moment of completion of the nonprint zone, the movement of the carriage 3 has passed through its transient state appearing in the beginning of start, and is smooth since then; thus, misalignment of characters is effectively prevented from occurring. 
     As described hereinabove, according to the present invention, the print speed in enhanced, but the quality of print can not be degraded. Further, because of driving at a high frequency, the current of the stepping motor decreases and the consumption power lessens; thus, the present invention is very advantageous. Furthermore, regarding a mechanical vibration, because the motor is driven at a high frequency, the vibration diminishes and noise lowers.