JPS6011552B2 - DC motor speed control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control method using back electromotive force of a DC motor.

In a speed control circuit for a sewing machine electric motor or the like, torque compensation is generally required for changes in load, and the amount of compensation is desired to be larger as the speed becomes lower.

As this type of speed control circuit, a circuit as shown in FIG. 1 is known.

This circuit consists of a full-wave rectifier consisting of diodes D, ~D4, a diode D5, a DC motor M, a transistor Q2,
Capacitor C charged via resistor R and variable resistor VR, energizer diode ZD, comparator COMP
, a transistor Q for detecting the voltage due to the back electromotive force of the motor M as a speed feedback voltage, a combination of a resistor R4 to a horse, a diode DB, and a resistor R2 forming a voltage divider for dividing the detected speed feedback voltage. and R3, Zener diode ZD2, transistor Q, and resistor R
7 and R8. The capacitor C repeats charging and discharging every half wave in synchronization with the AC power supply voltage, and provides a sawtooth wave voltage Vc as shown in FIG. Variable resistance VR is capacitor C. The speed can be adjusted by changing the charging time constant. The charging voltage Vc of the capacitor CI is determined by the comparator CO
A voltage Vf obtained by dividing the detected speed feedback voltage by voltage dividing resistors R2 and R3 is applied to one input of the comparator COMP, and to the other input of the comparator COMP. The comparator COM determines the speed of the motor by determining the conduction angle of the transistor Q2 based on the point in time when both input voltages match, which is essentially the period of Vf minus Vc. Shown in the mouth and mouth. Note that FIG. 2A shows the motor at low speed, and the opening shows the motor at high speed. Here, it is well known that the back electromotive force of an electric motor is proportional to the rotation speed, but if we consider the case where the rotation speed decreases due to an increase in load, and if this occurs at low speed, then Figure 2 In A, Vf is a
A direction that descends from point to point b and expands the conduction angle Q to Q',
In other words, it acts to compensate for the decrease in rotational speed, and conversely,
When the rotational speed increases due to a decrease in load, the opposite action acts to suppress the rotational speed, and the speed is controlled by capacitor C,
is maintained at the desired value determined by the time constant of .

In order to sufficiently obtain such a compensation effect, it is necessary that the amount of change in Vf with respect to a change in speed, that is, the feedback gain G3 of the back electromotive force, be sufficiently large. By the way, if we apply the case where the feedback gain is large enough to high speed, we get
At high speeds, Vf also rises steeply in proportion to the number of rotations, so as shown by the dotted line at the top of Figure 2, a comparison with Vc cannot be obtained and control becomes uncontrollable. To avoid this, the rise in Vf is suppressed by the Zener diode ZD2, but Vf is equal to the Zener voltage V of the Zener diode ZD2.
In the range higher than zo2, that is, in the range Vf>V2.2, the above-mentioned compensation effect cannot be obtained.

Therefore, only at high speeds, it is necessary to set the feedback gain G to a low value in order to obtain sufficient compensation, but if this is done, the compensation at low speeds becomes insufficient. Put it away. In the end, with the circuit configuration shown in Figure 1,
There is a drawback that the compensation action in either the high-speed or low-speed range must be unique. SUMMARY OF THE INVENTION It is an object of the present invention to provide a speed control scheme for a DC motor which eliminates the above-mentioned drawbacks and which provides sufficient compensation over the entire speed range without introducing any additional circuit complexity.

In the present invention, in the circuit shown in FIG. 1, the resistance related to the charging time constant of the capacitor C is a fixed resistance,
The part of the resistance related to the feedback gain with respect to the speed feedback voltage is a variable resistor, and this variable resistor is adjusted so that the feedback gain has a large value when the speed is set, and the feedback gain gradually decreases as the speed is set. achieve that purpose by doing so.

The invention will now be described with reference to illustrated embodiments.

FIG. 3 shows an embodiment of the invention. The circuit in Figure 3 replaces the variable resistor VR in Figure 1 with a fixed resistor R9,
The fixed resistor R3 is replaced with a variable resistor VR', and the Zener diode ZD2 is removed. The principles of speed adjustment and compensation are as described above, but the present invention conventionally changes the slope of the charging characteristic of the capacitor C, and changes the charging voltage waveform to a voltage proportional to the speed feedback voltage. The conduction angle was determined based on the matching point of C, but the same speed control can be performed even if the gradient of the charging voltage of capacitor C is constant and the proportional coefficient to the speed feedback voltage is changed according to the motor speed. We are focusing on the scales.

In FIG. 3, the feedback gain G' of the back electromotive force is large at low speeds, gradually decreases as the speed increases, and is adjusted so that it becomes 0 at the maximum distance.

Thereby, it is possible to obtain a sufficient compensation effect over the entire speed range while obtaining a large feedback gain on the low speed side where a large amount of feedback is required. Further, in this case, if the speed is set by adjusting the variable resistor VR', the speed setting and the compensation function can be performed at the same time. As can be understood from the above explanation, the present invention provides a speed control method for a DC motor that can perform good speed control while obtaining a sufficient compensation effect over the entire speed range of the motor, and that has a simple configuration. do.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventionally known DC motor speed control circuit, FIG. 2 is a diagram showing the principle of speed adjustment, and FIG. 3 is a diagram showing an embodiment of the present invention. D. ~〇4...Diode, D5...Diode, M.
...DC motor, Q2...Transistor, Q. ...Transistor for detecting back electromotive force, R2
...Fixed resistance for voltage division, VR'...Variable resistance for voltage division, R,, R9...Charging resistance, ZD.・
・・・・・・Ener diode, C, ・・・Capacitor,
COMP... Comparator. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. A rectifier circuit, a series circuit of a DC motor and a controllable semiconductor element connected via a diode placed in the forward direction between the DC output terminals of the rectifier circuit, and a back electromotive force of the DC motor for speed feedback. means for detecting the voltage, a capacitor connected via a charging resistor between the DC output terminals of the rectifier circuit and repeatedly charged and discharged every half wave in synchronization with the AC power supply voltage, and the detected speed feedback. and means for comparing a voltage obtained by dividing a voltage with a voltage divider with a charging voltage of the capacitor and determining a conduction angle for the controllable semiconductor element based on a point in time when the former voltage matches the latter voltage. In a speed control system for a DC motor, the charging resistor is a fixed resistor, the voltage divider is configured with a series circuit of a variable resistor part that determines a feedback gain, and a fixed resistor part, and the variable resistor part is used for speed setting. A speed control method for a DC motor, characterized in that the feedback gain is increased when the motor is running at low speed and gradually reduced as the motor speed increases by adjusting the feedback gain.