JPH0958081A - Controlling device for stop of spacing motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop a printing head in an accurate position at every printing. SOLUTION: A printing head 3 is driven in the main scanning direction by a spacing motor 1. When the printing head 3 is stopped, a stop position monitoring part 10 detects the stop position and informs a control part 7 about it. An error at this time is stored in an error, storage part 14. In the case of printing of the next line, the error is read from the error storage part 14 and stop control is performed by considering the error. Therefore, even if the error is caused in the stop position by change in motor load or change in the other conditions, the error is rapidly corrected and accurate stop position control is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spacing motor stop control device for accurately controlling a stop position when driving a spacing motor in an impact printer or the like.

[0002]

2. Description of the Related Art An impact printer mounts a print head on a carriage and prints on a sheet on a platen while moving the print head in the main scanning direction. When printing for one line is completed, the paper is conveyed by a fixed amount in the sub-scanning direction. The print head then starts printing again. Printing is executed by repeating such operations.

[0003]

By the way, the conventional device as described above has the following problems to be solved.
When printing is performed while the print head moves in the main scanning direction, the print head is accelerated at the start of printing and braked and stopped at the end of printing. The spacing motor, which is the drive source of the print head, is set with precise operating conditions for such variable speed control. However, due to variations in the load on the motor and the like, variations in control occur such that the stop position exceeds or is ahead of schedule. Such variations in the stop position of the print head affect the accuracy of the print start position particularly when the print operation is performed both in the forward and backward passes.

[0004]

The present invention adopts the following constitution in order to solve the above problems. A stop control device for a spacing motor according to the present invention includes a spacing motor that drives a print head that is arranged to face a platen in a main scanning direction,
A motor drive circuit that drives the spacing motor and supplies a brake current to stop the print head at a target stop position to perform stop control, and a print head when the spacing motor is stopped by the brake circuit. Stop position monitoring unit that detects and stores the error that occurs between the actual stop position and the target stop position, and in order to reduce the error in the stop position that occurred last time during the next spacing motor stop control. And a controller that calculates a correction value of the brake current and supplies it to the motor drive circuit.

The print head is driven in the main scanning direction by a spacing motor. When the print head is stopped, the stop position monitoring unit detects the stop position and notifies the control unit. The error at this time is stored in the error storage unit. When printing the next line, this error is read from the error storage unit and stop control is performed in consideration of the error. Therefore, even if an error occurs in the stop position due to a change in the motor load or a change in other conditions, the error is promptly corrected for each line, and accurate stop position control can be performed.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a block diagram of a stop control device for a spacing motor according to the present invention. Prior to this description, the mechanism of the impact printer will be described first. FIG. 2 is a perspective view of the main parts of the mechanism of the impact printer. As shown in the figure, in the impact printer, the print head 3 prints on a sheet of paper placed on a platen (not shown). The print head 3 is supported by a carriage 21 so as to reciprocate in the main scanning direction on a main shaft 22 and a slide beam 27 mounted in parallel with the platen. A mini pitch belt 26 is stretched between the drive shaft 23 of the DC servo motor (spacing motor) 1 and the idle pulley 25, and this drives the carriage 21 in the main scanning direction. By the rotation of the spacing motor 1 in the direction of the arrow 24, the print head 3 reciprocates along the platen to perform printing.

Next, the structure of the apparatus shown in FIG. 1 will be described. FIG.
The apparatus of the present invention shown in FIG. 1 includes a print head 3 driven by a spacing motor 1 via a belt 2. The print head 3 is driven in the main scanning direction 4 as described above. For controlling the driving of the spacing motor 1, a slit disk 5 for detecting the rotation, a sensor 6,
A control unit 7, a ROM 8, a motor drive circuit 9, and a stop position monitoring unit 10 are provided. The slit disk 5 is fixed to the drive shaft of the spacing motor 1 and has a large number of slits arranged on the circumference.

This is a so-called rotary encoder and is used to detect the rotation angle and the rotation direction. The sensor 6 is a photointerrupter type rotation detection device, and is a device that, when the light passing through the slits of the slit disk 5 is periodically interrupted, changes in the signal are taken in as an electric signal and supplied to the stop position monitoring unit 10. is there.
The sensor 6 detects two rows of slits of equal pitch, which are provided on the slit disk 5 and have a phase difference of 90 °, and the rotation direction and the rotation are determined by the count of the slits and the phase difference between the two kinds of signals. It is configured to detect speed.

The motor drive circuit 9 is a well-known PWM (pulse width modulation) control circuit that supplies a drive current to the spacing motor 1 to perform a predetermined variable speed control. The control unit 7 is composed of a microprocessor or the like, and supplies a drive control signal to the motor drive circuit 9. A ROM (Read Only Memory) 8 is a storage element that stores an operation program of the control unit 7 and the like. The stop position monitoring unit 10 includes an edge detection circuit 11, a position counter 12, a digital filter 13, an error storage unit 14, and the like.

The edge detection circuit 11 receives the rotation detection signal of the slit disk 5 detected by the sensor 6 to detect the rotation direction of the spacing motor 1 and the output edge of the signal, and outputs an up count pulse in the case of normal rotation. , A circuit that generates a down-count pulse in the case of reverse rotation. The position counter 12 is composed of a counter that counts the pulses output from the edge detection circuit 11. The output of the position counter 12 is sent to the control unit 7,
The count value and the rotation direction of the spacing motor 1 are read by the control unit 7.

The digital filter 13 receives the output of the edge detection circuit 11, adjusts the timing with the drive speed of the print head 3, and outputs an interrupt signal to the control unit 7. As a result, the control unit 7 is configured to know the print timing of the print head 3. Also, RO
M8 stores firmware for the operation of the control unit 7. The control unit 7 reads the count value output from the position counter 12 and manages the position of the print head 3. Further, the spacing motor 1 is controlled so as to rotate stably at a designated speed based on the speed data output from the digital filter 13.

The spacing motor 1 is composed of a DC servo motor as described above, and the control unit 7 calculates a DC control pulse and outputs it to the motor drive circuit 9. The motor drive circuit 9 generates a drive signal for the spacing motor 1 by PWM (pulse width modulation). In addition,
This drive signal is a pulse signal, which is smoothed to be the overdrive voltage of the spacing motor 1. The duty ratio of the drive signal pulse of the spacing motor 1 can be changed by firmware to about 0 to 28%. By changing this duty ratio, the average current IM flowing through the coil of the spacing motor 1 is changed, and its rotational torque is controlled.

As will be described later, the error storage unit 14 detects and records an overrun or underrun error when the print head 3 is driven to stop at the target position after printing is completed. It is a part for. The error is used for the next stop control of the print head as described later.

FIG. 3 shows a basic operation flowchart of the motor drive circuit at the time of printing operation. First, the drive control is provided with an acceleration region, a constant velocity region, and a deceleration region for applying a brake. The acceleration region is steps S1 to S
3. The constant speed region is composed of steps S4 to S6, and the deceleration region is composed of steps S7 and thereafter.

First, in step S1, the spacing motor is unconditionally accelerated when printing is started.
Next, in step S2, the print head is skipped to the print position. Then, in step S3, it is determined whether or not the print position has reached one inch (2.54 cm) before the print position. If not, step S
Steps S2 and S3 are repeated, and when they reach each other, in step S4, the printing speed is switched to a predetermined value. Below, step S
In S5 and S6, the printing process and the judgment as to whether or not the printing is completed are performed, and printing is performed at a constant speed. When printing is completed, deceleration processing is started in step S7. Then, the speed is gradually reduced to the speed VMIN immediately before the stop, and the final deceleration is started in step S8. The final brake is applied in step S9, and the motor is stopped in step S10.

FIG. 4 is an explanatory view of the driving current of the spacing motor in this case. The spacing motor changes its speed as shown in the upper half of this figure, and at that time, the drive current as shown in the lower half is supplied. First, in the acceleration region, the maximum current in the positive direction is supplied to the motor, and when the target speed is reached, the supplied current is reduced to enter the constant speed region. When printing is completed, the reverse negative braking current is supplied to the motor. When entering the deceleration area in this way, the braking current decreases linearly as shown in the figure,
Match the braking force to the printhead speed.

VMIN is the minimum controllable speed at which final braking is applied. The final brake applies maximum negative current to the motor for a certain period of time. The control unit 7 shown in FIG. 1 detects that the spacing motor 1 has stopped rotating, and reads the position of the print head 3 at that time from the output of the position counter 12. Thus, the current final stop position of the motor is detected.

Here, as shown in the figure, the target stop position is P, the stop position in the case of overrun due to the weak final braking force is Q, and the stop position R in the case of underrun. When the final brake is applied, not only the braking force is too strong to stop early, but the print head may return after the stop. Underrun also occurs in such a case. In the present invention, such a difference between the overrun stop position Q and the underrun stop position R with respect to the target stop position P is called an error, and this error is corrected.

The contents of the output signal of the above position counter will be described with reference to FIGS. 5 and 6. FIG. 5 shows an output signal of the position counter at the time of forward rotation. FIG. 6 shows an output signal of the position counter at the time of reverse rotation. In both cases, (a) and (b) are outputs of the sensor 6 which are 90 ° out of phase with each other. The rotation direction is determined by the phase relationship of this output. In the case of FIG. 5, the forward direction, FIG.
In the case of, it is a pulse when rotating in the opposite direction.

As a result, a rotation direction detection signal as shown in (c) is output. In the forward direction, it is "0", that is, low level, and in the reverse direction, it is "1", that is, high level. The UP (up) pulse shown in (d) is a pulse output according to the rotation speed when rotating in the positive direction. Further, the DOWN (down) pulse shown in (e) is a pulse output according to the rotation speed when rotating in the reverse direction. With such a signal,
The control unit 7 shown in FIG. 1 detects the rotation direction, the stop position, etc. of the spacing motor 1.

FIG. 7 is an explanatory diagram of the PWM control pulse when performing the variable speed drive and stop control of the motor as described above. The motor drive circuit 9 shown in FIG. 1 includes a PWM circuit 31 and a switching transistor 32 as shown in FIG. When the switching transistor 32 is turned on / off at a predetermined timing by the PWM circuit 31, a driving current is supplied to the spacing motor 1.

The drive current waveform is shown in (b).
As shown in the figure, a signal W2 having a duty ratio of 50% or more and a signal W3 having a duty ratio of 50% or less are shown with respect to a signal W1 having a duty ratio of 50%. A signal W2 having a large duty ratio is added to increase the rotation speed, and a signal W3 having a small duty ratio is added to decrease the rotation speed. In this way, the speed control of the spacing motor 1 is performed. As shown in (c) of the drawing, the spacing motor 1 has an intermediate current I1 when the duty ratio is 50%, and a larger current I2 and duty ratio when the duty ratio is large. When it is small, a smaller current I3 flows. This corresponds to the average value of drive pulses.

FIG. 8 shows a flowchart of the control operation for detecting the error and reflecting the error in the next drive control according to the present invention. This flowchart therefore follows FIG.
The description is started from the final braking process in the second half of the deceleration region described using. That is, first, step S1
When the final braking process is started in step S2, it is detected in step S2 whether the motor rotation has stopped. If it detects that the motor rotation has stopped,
The head position is calculated in step S3 as described above. Then, in step S4,
The stop target position and the actual stop position are compared.

If the two are equal, the process is terminated. If there is an error, it is determined in step S5 whether the vehicle has stopped by overrun or underrun. When the vehicle has overrun and stopped, the over amount is calculated in step S6. If the vehicle is underrun and stopped, the under amount is calculated in step S7. When error detection is performed in this way,
In step S8, the control unit 7 converts the calculation result into a pulse width duty value. Here, the pulse width duty set value corresponding to the error from the target value with respect to the target value is called by a program to be corrected, and the current flowing to the motor at the time of the final printing brake of the next line is set.

FIG. 9 shows an explanatory diagram of this error correction method. The vertical axis in the figure represents the pulse width duty ratio, and the horizontal axis represents the error. With a duty ratio of 50% as a set value, in this case, the driving condition is determined so as to accurately stop at the target stop position. Both the speed control and the brake control change the pulse width duty ratio on the solid line TYP. When a minus error occurs and a plus error occurs at the stop position, the operating point shifts in the direction of the broken line MIN or MAX. Therefore, this may be returned to the position of the solid line TYP.

More specific contents of the stop control will be described with reference to FIGS. 10 and 11. 10 (a), (b)
Shows the output from the sensor, and the wider the pulse width, the slower the spacing motor is rotating.
(A), (b) shows the output of the sensor when just stopped at the target position. On the other hand, (c) and (d) are cases of underrun, in which the output of the two kinds of signals of the sensor does not stop even when the final brake area is entered, and after the suspension, the phases are inverted and then It has reached the final stop. That is, it can be seen that the motor has rotated in the minus direction here. Also, (e) and (f) are outputs in the case of overrun,
The phases of the two kinds of signals from the sensor remain unchanged, and the rotation in the plus direction is detected by exceeding the target position. The stop position can be known by counting the number of pulses.

FIG. 11 is an explanatory view of the stop position control according to the present invention. In the present invention, as shown in this figure,
As in the conventional case, a constant reverse braking current is supplied to the motor in the deceleration region, and a braking current IBRK is supplied in the final braking region. The brake current IBRK is supplied by determining the duty ratio from the graph shown in FIG. Underrun,
The stop position in the case of overrun can be corrected.

The present invention is not limited to the above embodiments. In the present invention, when the motor is stopped, the amount of overrun or underrun is detected, the error from the target position is temporarily stored in the storage unit, and is used in the stop control of the next line. Therefore, the detection of such a stop position, the calculation process, and other mechanisms and calculation methods may be freely changed without departing from the spirit of the invention. Also, an example using a DC servo motor as the spacing motor has been shown.
Others such as a stepping motor and an AC servo motor can be freely used. Further, as for the print head, not only the impact printer but also a thermal head or other various printer heads can be used.

[0029]

According to the stop control device for a spacing motor of the present invention described above, a motor drive circuit for driving the spacing motor and supplying a brake current for stopping at a target stop position to perform stop control. On the other hand, since the error at the time of the previous stop is detected, the correction value for reducing the error is calculated and the supply is controlled, the load variation of the motor and the variation of the stop position due to other reasons are corrected each time, The spacing motor can be driven with high accuracy. As a result, the printing quality of the printer can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram of a stop control device for a spacing motor according to the present invention.

FIG. 2 is a perspective view of a mechanism main part of the impact printer.

FIG. 3 is a diagram illustrating a basic operation of a motor drive circuit.

FIG. 4 is a diagram illustrating a driving current of a spacing motor.

FIG. 5 is an explanatory diagram of signals during forward rotation.

FIG. 6 is an explanatory diagram of signals during reverse rotation.

FIG. 7 is an explanatory diagram of a PWM control pulse.

FIG. 8 is an explanatory diagram of a control operation according to the present invention.

FIG. 9 is an explanatory diagram of an error correction method.

FIG. 10 is an explanatory diagram (Part 1) of stop control according to the present invention.

FIG. 11 is an explanatory diagram of the stop control according to the present invention (No. 2).

[Explanation of symbols]

 1 Spacing Motor 3 Print Head 7 Control Unit 9 Motor Drive Circuit 10 Stop Position Monitoring Unit 14 Error Storage Unit

Claims (1)

[Claims] 1. A spacing motor for driving a print head arranged in opposition to a platen in a main scanning direction, and a brake current for driving the spacing motor and stopping the print head at a target stop position. Stop control to detect and store the error that occurs between the actual stop position of the print head and the target stop position during the stop control of the spacing motor by this motor drive circuit And a control unit for calculating a correction value of the brake current for reducing the error of the previously generated stop position and supplying it to the motor drive circuit at the time of the next spacing motor stop control. Stopping control device for the characteristic spacing motor.