JPH01298995A - Driving circuit for stepping motor - Google Patents

Abstract

PURPOSE:To prevent a driving torque from decreasing, stepping out and a life from reducing by providing a resistor for detecting the heat generated in a motor. CONSTITUTION:When the temperature of a motor is gradually raised upon lapse of the rotating time of the motor, the resistances of windings 2A, 2B are increased, and currents flowing to the windings are reduced. The reduction in the current is detected by a detecting resistor 6, and the fact that the winding current of the motor is reduced, i.e., that the temperature of the motor is raised to possibly cause the motor to step out is notified to a CPU 14. Then, the CPU 14 temporarily stop the motor or rotates a fan attached to the vicinity of the motor, thereby lowering the temperature of the motor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit that detects the heat generation state of a stepping motor and performs drive control.

[Prior Art] A motor for driving a carriage of a printer has been known as one of the stepping motors. This carriage driving stepping motor is driven by a driving circuit as shown in FIG. 5, for example. In Figure 5, 1
2A and 2B are motor windings; 3, 4A, and 4B are Zener diodes and diodes for absorbing back electromotive force; and 5A and 5B are transistors for driving the motor windings.

[Problems to be Solved by the Invention] However, in the conventional example shown in FIG. 5, the following drawbacks were observed due to heat generation in the stepping motor (heat generation in the motor windings).

■The heat generated by the motor increases the winding resistance, which causes the current to drop, causing a drop in drive torque and loss of synchronization.

■Shorten the life of the motor itself.

SUMMARY OF THE INVENTION In view of the above-mentioned points, an object of the present invention is to provide a drive circuit that can perform appropriate drive control depending on the heat generation state of a stepping motor.

[Means for Solving the Problems] In order to achieve such an object, the present invention includes a current detection resistor that allows the current flowing in the stator winding of a stepping motor to pass through, and a voltage across the terminals of the resistor that is set for a predetermined period of time. The stepper motor is equipped with a measuring means for measuring heat generation of the stepping motor.

[Function] In the present invention, heat generation of the stepping motor can be detected by providing a winding current detection resistor.

[Example] Hereinafter, the present invention will be described in detail based on Examples.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. At Kiguchi, l is the power supply for driving the motor.

2A and 2B are motor windings, 3 and 4A, and 4B are Zener diodes and diodes for absorbing back electromotive force.

58 and 5B are transistors for driving motor windings; 6
is a resistor for winding current detection, 7 is a comparator, 8 is a reference voltage source, and 9 is an AND circuit. IO is a gate signal input terminal, and a signal A which becomes high level only when the motor speed is constant as shown in FIG. 2(a) is input manually. 11 is a pulse counter, 12 is a reference pulse number generator, 13 is a comparator, and 14 is a CPU.

Now, a case in which the printer carriage (not shown) moves from the left end to the right end will be described. At this time, the voltage between the terminals of the winding current detection resistor 6 changes as shown in FIG. 2(b). However, due to the action of the AND circuit 9, the output signal of the comparator passes only when the motor is at a constant speed, so its operation will be explained only when the motor is at a constant speed.

As the rotation time of the motor passes, the temperature of the motor gradually increases. At the same time, the resistance of the windings 2A and 2B increases, and the current flowing through these windings decreases. As a result, the output drive torque decreases, eventually causing step-out.

FIG. 3(a) shows the voltage across the terminals of the resistor 6 during normal operation. Further, a solid line drawn in the middle of the figure indicates the reference voltage of the reference voltage source 8. Therefore, the output of the comparator becomes as shown in FIG. 3(b).

Next, the current in the windings 2A and 2B decreases due to heat generation, and the third
If it becomes as shown in FIG. 3(C), the output of the comparator 7 at that time will be as shown in FIG. 3(d). Furthermore, if the motor heats up and the winding current decreases, as shown in Figure 3(e), the output of the comparator 7 at that time is as shown in Figure 3(e).
f) Therefore, no pulse is output from the comparator 7.

When pulses corresponding to the above three types (b), (d), and (f) are manually input to the counter 11, the counter 11
outputs "7", °3", and "0", respectively. By inputting this count value to the comparator 13 and comparing it with the reference pulse number (for example, 7"), the CPU 14
This alerts you that the motor winding current is decreasing, which means that the temperature of the motor is rising and there is a possibility of a step-out. Therefore, the CPU 14 temporarily stops the motor or installs a fan (
(not shown) lowers the temperature of the motor, thereby preventing a decrease in torque, loss of synchronization, and shortening of motor life.

FIG. 4 is a circuit diagram representing a second embodiment according to the present invention. At the end, 15 is an integrator, 16 is a reference value generator, and 17 is a comparator. The other symbols are as described in connection with FIG.

In this embodiment, the amount of voltage drop representing the winding current of the motor, that is, the voltage between the terminals generated in the detection resistor 6, is input to the integrator 15, and the integral value over a predetermined operating time is calculated.

Next, the integrated output is compared with a reference value by the comparator 17, and when the integrated value becomes smaller than the reference value, in other words, the temperature of the motor increases, the winding resistance increases, and the winding current decreases. When there is a possibility of step-out, the CPU 14 is notified of this, and the motor is temporarily stopped or a fan installed near the motor is activated, thereby lowering the temperature of the motor itself.

[Effects of the Invention] As described above, according to the present invention, by providing a resistor for detecting heat generation of the motor, it is possible to prevent reduction in drive torque, step-out, and reduction in service life.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams showing the operation of FIG. 1, respectively, FIG. 4 is a circuit diagram showing another embodiment, and FIG. 5 is a circuit diagram showing a conventional technique. 1... Power supply, 28, 2B... Motor winding, 3... Zener diode, 4A, 4B... Diode, 5A, 5B... Transistor, 6... Resistor, 7... Comparator, 8... Reference voltage source, 9... AND circuit, 10... Input terminal for gate signal that becomes high level at constant speed, 11... Pulse counter, 12... Reference pulse number generator , 13... comparator, 14... cpu. 15... Integrator, 16... Reference value generator, 17... Comparator. Figure 2 (b) (d) Figure 3

Claims (1)

[Scope of Claims] 1) A current detecting resistor for passing a current flowing through a stator winding of a stepping motor, and a measuring means for measuring a voltage between terminals of the resistor over a predetermined period of time, to reduce heat generation in the stepping motor. A stepping motor drive circuit characterized by detecting.