Abstract:
A line printer is provided in which disturbances during the start of printing are prevented with low power consumption. The printer has a motor control section which performs a stop printing operation by driving a stepping motor in a direction reverse to that in which print paper is fed by a predetermined number of steps and then turns off the stepping motor to stop printing and performs a start printing operation in which the stepping motor is driven in a forward direction by the same predetermined number of steps before starting a printing operation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a line printer for simultaneously printing characters etc, while feeding print paper in units of lines. 
     2. Description of the Related Art 
     Heretofore, a line printer for simultaneously printing characters etc. according to a print signal input from a host, feeding print paper in units of line has been used. 
     FIG. 4 is a side view showing the outline of a print paper feeding mechanism in a general line printer. 
     As shown in FIG. 4, when a stepping motor  401  is rotated counterclockwise by a predetermined amount as shown by an arrow, the above-mentioned rotation is transmitted to a platen roller  404  via two gears  402  and  403 . As a result, the platen roller  404  is rotated clockwise and feeds print paper  405  in units of lines. In a synchronous matter therewith, the printer prints characters etc. in response to a print signal from a host (not shown) by driving a print head  406 , while feeding the print paper  405  in units of lines. 
     FIG. 5 is a timing chart showing a conventional driver signal in the case that the stepping motor  401  is driven. When printing according to a print signal is executed in an area A and is completed, a driver signal to the stepping motor  40 i is stopped in an area D and the stepping motor  401  is stopped. In the next operation, first, a driver signal of the same phase as a supplied phase when the stepping motor  401  is stopped, is supplied, to align the position (area E). Thereafter, the printing operation is started (area G) by supplying a driver signal of the next phase. 
     When a driver signal sent to the stepping motor  401  is stopped and the stepping motor is in a state in which it is not excited, a counterclockwise force is applied to the shaft of the platen roller  404  by the spring force of the platen roller  404 , because the print head  406  is fixed. As a result, a clockwise torque is applied to the stepping motor  401  via the gears  403  and  402 . When the above-mentioned torque exceeds inhibiting torque that the stepping motor  401  per se has, the stepping motor  401  is rotated clockwise. 
     Therefore, when the stepping motor  401  is next driven, a phase output from a motor control circuit and the actual phase of the stepping motor  401  are asynchronous. Therefore, when a driver signal of the same phase as a phase when the stepping motor  401  is stopped, is supplied to the stepping motor  401  (area E of FIG. 5) so as to drive the motor next, if the stepping motor  401  is reversed by more than two steps, the motor is reversed to the same phase before four steps or steps of a multiple of four from a position where the stepping motor  401  is stopped, and printing is started from the above-mentioned position (area G of FIG.  5 ). Accordingly, there arises a problem in that printing for the four steps or the steps of the multiple of four is packed at the head. 
     To prevent the above-mentioned situation, a method of supplying holding current of low voltage to the stepping motor  401  while the stepping motor  401  is stopped is also conceivable. However, consumed current is increased and it is particularly a large problem in a line printer driven by a cell. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the abovementioned problems, and therefore an object of the invention is to provide a line printer in which large power consumption is not required and turbulence when printing is started, can be inhibited. 
     According to the present invention, there is provided a line printer for rotating a platen roller by forwardly rotating a motor by motor control means to feed a print paper by a fixed amount, and synchronously therewith, for effecting printing by driving a print head in accordance with a print signal, characterized in that: 
     the motor control means turns off the motor after reversing the motor by a predetermined amount when the motor is turned off to stop printing; and the motor control means starts printing operation after forwardly rotating the motor by the same predetermined amount to start printing. The motor control means turns off the motor after reversing the motor by the predetermined amount when the motor is turned off to stop printing, and starts a printing operation after forwardly rotating the motor by the above-mentioned predetermined amount to start printing. 
     The above-mentioned motor control means may be configured so that the motor control means turns off the motor after reversing the motor by a predetermined amount in case that a printing condition is not met within-a predetermined time after the printing of one line is completed. 
     Also, the above-mentioned motor may be composed of a stepping motor, and configured so that the motor control means turns off the stepping motor after reversing the stepping motor by a predetermined number of steps when the stepping motor is turned off to stop printing; and the motor control means starts printing operation after forwardly rotating the stepping motor by the predetermined number of steps to start printing. 
     Further, the above-mentioned motor control means may be configured so that the motor control means forwardly rotates the stepping motor by the predetermined number of steps after outputting the same phase as a phase output immediately before turning off the stepping motor, to the stepping motor when the stepping motor is driven to start printing, and then starts the printing operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a block diagram showing a line printer according to to an embodiment of the present invention; 
     FIG. 2 is a timing chart showing the line printer according to the embodiment of the present invention; 
     FIG. 3 is a flowchart showing the line printer according to the embodiment of the present invention; 
     FIG. 4 is a partially side view showing a general line printer; and 
     FIG. 5 is a timing chart showing a conventional type line printer. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram showing a line printer according to an embodiment of the present invention. As shown in FIG. 1, a read only memory (ROM)  102 , a random access memory (RAM)  103 , a head driver  104 , and a motor control section  106  are connected to a central processing unit (CPU)  101  to which a print signal such as print data is input and which constitutes motor control means. The read only memory (ROM)  102  stores a processing program for execution by the CPU. A random access memory (RAM)  103  is used to store print data, etc. A head driver  104  serves for driving a print head  105 . A motor control section  106  controls the rotation of a stepping motor  107  and constitutes together with the CPU motor control means. 
     FIG. 2 is a timing chart showing a driver signal output from the motor control section  106  to the stepping motor  107 . FIG. 3 is a flowchart showing processing by the CPU  101 . 
     Referring to FIGS. 1 to  3 , the operation of this embodiment will be described below. 
     First, the CPU  101  judges whether the stepping motor  107  is turned off or not in step S 301 . The CPU  101  forwardly rotates the stepping motor  107  by four steps in a step S 302 , if the stepping motor is turned off to execute the printing of one line in step S 303 . That is, as shown in FIG. 2, after an OFF state in an area D, a driver signal immediately before driving is stopped, is outputted in an area E, and a signal for forwardly rotating the stepping motor  107  by four steps is output in an area F, to start the printing of one line. 
     In the meantime, in step S 301 , if the stepping motor  107  is not turned off, processing proceeds to step S 303 . This indicates a state in an area A shown in FIG. 2, and the printing of one line is successively executed without forwardly rotating the stepping motor  107  by four steps. 
     Next, a 100 msec timer is started to start a timing operation for 100 msec in a step S 304 . 
     Next, whether a printing condition is established or not is judged, and if the printing condition is established such that the print data of the next line is input, processing is returned to step S 303  (step S 305 ). 
     On the other hand, the above-mentioned printing condition is not established, whether 100 msec has elapsed or not is judged in step S 306 . If 100 msec has not elapsed, processing is returned to step S 305 . After the stepping motor  107  is reversed by four steps in step S 307 , if 100 msec has elapsed, the stepping motor  107  is turned off in step S 308 . 
     That is, as shown in FIG. 2, the same phase is excited for 100 msec in an area B. If the above-mentioned state is continued for 100 msec, in an area C, the stepping motor is reversed by four steps, and thereafter, the stepping motor  107  is turned off. 
     By this, series of operations convention of operation can be prevented wherein every time the printing of one line is completed, the reverse and forward rotations of the stepping motor  107  are repeated to thereby lower the printing speed. 
     As described above, according to this embodiment, it is characterized in that the CPU  101  and the motor driver  106  turn off the stepping motor after reversing the stepping motor  107  by four steps when the stepping motor  107  is turned off to stop printing, and start a printing operation after forwardly rotating the stepping motor  107  by the same four steps as the number of steps reversed when the stepping motor is stopped to start printing. Accordingly, such a line printer can be provided in which misalignment caused by a spring force of a platen roller  404  is prevented, and turbulence when printing is started can be restrained. 
     Also, while the stepping motor  107  is turned off, driving current is not required to flow, thereby reducing power consumption. Particularly, for a line printer that is driven by a secondary cell, the life of the cell can be extended. 
     Further, as the stepping motor  107  is driven by four steps immediately before printing, the rotation of the stepping motor  107  can be accelerated for the while, and printing of high quality, which is also substantially free of turbulence at the time when printing is started, can be obtained. 
     Furthermore, if a printing condition is not established within a predetermined time after the printing of one line is completed, the conventional operation can be prevented where the reverse and forward rotation of the stepping motor  107  are repeated at every printing of one line to lower the printing speed. 
     In this embodiment, the device is configured such that when the driving of the stepping motor  107  is stopped, the stepping motor is allowed to rotate by four steps. However, it may configured such that the spring force of the platen roller  404  is released to reverse the stepping motor by only the number of steps necessary such that the stepping motor  107  is not rotated. The number of steps may be set to a suitable value in accordance with the spring force of the platen roller  404 , the inhibiting torque of the stepping motor  107  and the like. In this case, when the driving of the stepping motor  107  is started, a printing operation has only to be started after the stepping motor is forwardly rotated by the same number of steps as that of reversed steps. The present invention can also be applied to the case of a motor other than the stepping motor. 
     According to the present invention, turbulence when printing is started can be inhibited at low power consumption. 
     Particularly, in the line printer that is driven by a cell, the life of the cell can be extended.