JPS60245497A - Correcting method for torque of pulse motor - Google Patents

Abstract

PURPOSE:To always hold the prescribed torque in a pulse motor by varying the resistance value of a torque correcting resistor, and maintaining the voltage generated at the resistor constant, thereby reducing the irregular torque of the motor. CONSTITUTION:A voltage generated by a current flowed to a current detecting resistor 6 is compared with a reference voltage E to control a transistor 3 ON or OFF, thereby flowing the constant current to an exciting winding 1. If the torque of a pulse motor becomes insufficient even by the exciting current, the resistor 6 is replaced by that having small resistance value. Thus, the current flowed to the winding 1 increases, the amount decreased in the resistance value is supplemented to rise the voltage of the resistor 6. On the contrary, if the torque of the motor is excess, the resistor 6 is replaced by that having high resistance value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling excitation current of a pulse motor, and particularly to a method for correcting variations in torque of a pulse motor.

In printing devices used in various information processing systems, a pulse motor is used to rotate a type wheel, etc. in order to select a type, and after selecting a predetermined type, the rotation of the type wheel, etc. is stopped, and the selected type is printed. There is a method that prints by pressing it onto printing paper.

In such a printing apparatus, when the pulse motor is controlled in an open-loop manner, the excitation phase of the pulse motor is switched by time control to position the type.

FIG. 2 is a diagram illustrating the torque characteristics of a two-phase excitation pulse motor. The vertical axis represents the torque T, and the horizontal axis represents the rotation angle θ of the pulse motor.

For example, first excite the A and B phases, switch to the BC phase at the point A in the same figure, then switch to the CD phase at the point A, switch to the DA phase at the point C, and switch to the AB phase at the second point. By sequentially switching each excitation phase, the rotating shaft of the pulse motor is accelerated and reaches a constant speed.

That is, the diagonally shaded portion shown by the solid line in the figure is the excitation range in which the acceleration occurs. Then, when each excitation phase is switched in the same manner as described above and excitation is performed in the diagonally shaded portion shown by the dotted line, torque is applied in the direction of deceleration to stop the rotating shaft.

FIG. 3 shows the control characteristics of type selection. By applying torque as described above, an acceleration region as shown in FIG. 3(1) is obtained, and then a constant speed region as shown in FIG. 3(II) is obtained. Then, by excitation in the deceleration direction, the deceleration region (III) is obtained. That is, by switching the excitation phase at an appropriate time as described above, the characteristics of each region can be obtained.

Now, the excitation phase of the pulse motor is switched as described above, and the rotation of the pulse motor is controlled through the acceleration region (■), constant speed region (■), and deceleration region (I[I) shown in Figure 3. Then, the selected type is brought to a predetermined position, but the selected type must reach the predetermined position within a predetermined time and remain stationary.

[Conventional technology]

FIG. 4 shows an example of a conventional pulse motor phase control circuit. 1 is an excitation winding, which corresponds to one phase of the pulse motor. 2 is a correction resistor that corrects the torque of the pulse motor. Reference numeral 3 denotes a transistor for switching excitation phases and controlling current to flow through the excitation winding 1. 4 is a Zener diode, and 5 is a diode which absorbs the energy of the excitation winding 1 when the transistor 3 is turned off. A constant current, which is limited by the resistor 2, flows through the excitation winding 1 from the power supply element 2 when the transistor 3 is turned on.

Now, if θ is the rotation angle, J is the inertia, T is the torque, and t is the time, then T=Ji ■ θ=±it2 ■ holds true.

By eliminating the acceleration θ from formula (2) and formula (0), θ−±(engine) t2 ■ J is obtained. Since the excitation phase is switched at a fixed time t, if there are variations in the pulse motor torque T,
(2) As can be seen from the equation, since the inertia J remains unchanged, the angle θ varies. In other words, excitation phase switching is not performed at a predetermined angle,
This indicates that the stop position of the rotation axis of the pulse motor fluctuates, and selected printed characters overshoot or undershoot with respect to a predetermined position, resulting in irregular printing.

[Problem that the invention seeks to solve]

When Pulsmoke is mass-produced in large quantities, there are variations in torque depending on the production lot. Eliminating this variation in the production process is not a good idea as it would lead to a significant increase in costs. Therefore, when using the control circuit shown in Figure 3, even if proper control is performed in one production lot, the generated torque will not be the same in another production lot even if the same constant current is passed through the excitation winding as described above. , overshoot or undershoot, resulting in irregular printing.

The present invention aims to solve these conventional problems.

[Means for solving problems]

The above problem is solved by comparing the transistor that controls the excitation current supplied to the excitation winding of Pulsmoke, which corrects the torque by connecting a resistor to the excitation winding, and the voltage generated in the resistor with a reference voltage. and supplying the output of the comparing means to the transistor, the torque correction method according to the present invention changing the resistance value of the resistor to keep the voltage generated across the resistor constant. Ru.

[Effect]

In other words, the resistor connected to each excitation winding of the pulse smoke is also used as a torque correction resistor, and the resistance value of this resistor is changed so that even if the torque of the motor changes, the same torque is always generated. It is something to control.

In other words, when the torque of the pulse motor is low, the current in the excitation winding is increased by lowering the resistance value of the torque correction resistor, and when the torque is high, the current in the excitation winding is increased by increasing the resistance value of the torque correction resistor. This reduces the

By doing this, regardless of the production lot,
This allows a predetermined torque to be obtained.

〔Example〕

1(a) is a circuit diagram showing an embodiment of the present invention, and FIG. 1(b) shows the waveform of the current flowing through the current detection resistor 6 of FIG. 1(a).

In Figure 1 (al), 1.3 and 4.5 correspond to those in Figure 4. 6 is a current detection resistor, and the excitation winding 1
In addition to detecting the excitation current flowing through the motor, it also serves to correct the torque of the pulse motor. Reference numeral 7 denotes an operational amplifier which compares the voltage generated across the current detection resistor 6 with a reference voltage E set in the operational amplifier 7, and when a voltage exceeding the reference voltage E is generated across the current detection resistor 6, the transistor 3 It sends out an output that turns off the transistor 3, and when the voltage of the current detection resistor 6 falls below the reference voltage E, it sends out an output that turns on the transistor 3.

When the base current flows through the transistor 3 due to the excitation phase switching signal, the transistor 3 turns on and the excitation winding 1
An excitation current limited by the current detection resistor 6 flows from the power supply +■. Since the operational amplifier 7 operates as described above, the transistor 3 is turned off when the voltage generated by the current flowing through the current detection resistor 6 becomes larger than the reference voltage E as shown in FIG. 1(b). Therefore, when the voltage drops, the transistor 3 is turned on again. Therefore, the reference voltage E
A constant current regulated by will flow through the excitation winding 1.

If the torque of the pulse motor is insufficient even with this excitation current, replace the current detection resistor 6 with one having a smaller resistance value. As a result, the current flowing through the excitation winding 1 increases, and the voltage across the current detection resistor 6 increases to compensate for the decrease in resistance value.

Therefore, the operational amplifier 7 controls the current value of the excitation winding 1 with a voltage regulated by the reference voltage E in the same manner as described above. Therefore, the torque increases by the amount of current increase in the excitation winding 1.

Contrary to the above, if the torque of the pulse motor is excessive,
Replace the current detection resistor 6 with one with a higher resistance value. Since the operational amplifier 7 operates in the same manner as described above, a current regulated by the reference voltage E flows through the excitation winding, and as a result, the current flowing through the excitation winding 1 decreases, and the torque also decreases by the amount of the decrease.

〔Effect of the invention〕

As explained above, according to the present invention, by varying the resistance value of the torque correction resistor, it is possible to always maintain a predetermined torque due to variations in the torque of the pulse motor caused by the production loft.

[Brief explanation of drawings]

Figure 1 is a diagram showing a circuit showing an embodiment of the present invention and the current waveform flowing through the current detection resistor, Figure 2 is a diagram explaining the torque characteristics of a two-phase excitation pulse motor, and Figure 3 is a type selection FIG. 4 is a diagram showing an example of a conventional pulse motor phase control circuit. 1 is the excitation 1 wire, 2 is the torque correction resistor, 3 is the transistor, 4 is the Zener diode, 5 is the diode, 6
is a current detection resistor, and 7 is an operational amplifier. Figure 1 and ≦1 Figure 2 Figure 3 41"4

Claims (1)

[Claims] A transistor for controlling an excitation current supplied to an excitation winding of a pulse motor, and a comparison means for comparing a voltage generated in a resistor connected to the excitation winding with a reference voltage, and an output of the comparison means is provided to the transistor. A method for correcting torque of a pulse motor, characterized in that the resistance value of the resistor is changed to keep the value of the voltage generated across the resistor constant.