JPS63136990A - Control circuit for servo motor - Google Patents

Abstract

PURPOSE:To stabilize the controlling characteristic of a control circuit for a servo motor and to save the heat generation of the control circuit by inserting a regenerative power consumption resistor when the negative potential of a smoothing condenser becomes lower than the negative potential of a reference voltage power source circuit by more than set. CONSTITUTION:If the negative potential (e) of a smoothing condenser C becomes lower than the negative potential (b) of a reference voltage power source 3 by more than set when the regenerative current of a DC motor M is consumed at a dummy resistor Rd and the condenser C, a Zener diode ZD1 becomes conductive to turn ON a thyristor SCR. Thus, a switching transistor Q6 and a voltage control element Q5 conduct, and the regenerative current is consumed at a resistor Rs. When the terminal voltage of a Zener diode ZD2 becomes smaller than the sum of the supply voltage to a DC power source E1, the breakdown voltage of the diode ZD2 and a set voltage, the thyristor SCR is turned OFF.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention provides a direct current power supply comprising a full-wave rectifier circuit and a smoothing capacitor for application to servo motors for driving manipulators in automatic machine tools and automatic assembly machines. The present invention relates to a control circuit for a servo motor, including a bridge transistor circuit connected between both ends of the DC power supply circuit, and a servo motor connected between an intermediate point of the bridge transistor circuit.

(Prior art and its problems) Conventionally, this type of circuit has been as follows.

(1) First conventional example (Japanese Patent Publication No. 56-26231) FIG. 4 is a circuit diagram of the one shown in the above publication. In FIG. 4, Ql, Q2. Q3. Q4 is an NPN type power transistor, and the power transistor Ql
the emitter side of the power transistor Q2 and the collector side of the power transistor Q2,
The emitter side of the power transistor Q3 and the collector side of the power transistor Q4 are connected to each other.

The collector sides of power transistors Ql and Q3 are connected to the anode side of DC power supply E, and the emitter sides of power transistors Q2 and Q4 are connected to the cathode side of DC power supply E, respectively. A series circuit including a DC servo motor M and a reactor L is inserted and connected between the emitters of power transistors Q1 and Q3.

Furthermore, each power transistor Ql, Q2 . Between the emitter and collector of Q3゜Q4, there are diodes DI, D2゜D 3 , D 4 for releasing the induced voltage in the opposite direction, one each.
is connected. These constitute a Pritsuno transistor circuit, in which two predetermined power transistors Q
The direct current servo motor M is rotated in forward and reverse directions by turning on L and Q4 or power transistors Q2 and Q3.

Rd is a dummy resistor with a relatively high resistance value connected to the DC power source E, and the induced voltage is consumed by this dummy resistor Rd.

Further, Rs is a discharge resistor for abnormal voltage discharge with a relatively low resistance value connected to the DC power supply E, and Q5 is connected in parallel with the dummy resistor Rd and in series with the discharge resistor Rs.
This is an NPN type transistor as a switching element. The input side of a voltage detector De, such as a constant voltage diode, which outputs an ON signal when a predetermined voltage value is exceeded is connected to the anode side of the DC power supply E, and the output of the voltage detector De is connected to the anode side of the DC power supply E. The side is the transistor Q5
is connected to the base side of the

As a result, when power transistors Q1 and Q4 or Q2 and Q3 are turned off to apply the brakes, even if a regenerative current flows and an abnormal voltage exceeding a predetermined voltage value set by the voltage detector De is induced. , the abnormal voltage is detected by the voltage detector De, and accordingly, the transistor Q5 is turned on, and a discharge resistor R8 with a relatively low resistance value is connected in parallel to the bypass path, which until now had only a dummy resistor Rd with a high resistance value. In addition, the regenerated power due to the abnormal voltage is consumed and clipped by the discharge resistor Rs, thereby suppressing the abnormal voltage and protecting the power transistor.

By the way, if the supply power voltage fluctuates (AC85~1
30V), when the regeneration start voltage of the regeneration circuit is constant, the control characteristics change depending on whether the supply voltage is low or high.

Also, when changing the supply voltage to the power supply in this way,
In the case of the conventional example having the above-mentioned configuration, each time the supply voltage changes, the set voltage of the voltage detector De must be changed to match the rated voltage.

Therefore, considering the range of rated voltages that are normally used, for example, in the case of direct current, set the voltage on the voltage detector De to at least 6180■ or more. It is conceivable to set the voltage of the device De.

However, the pulse width for controlling the servo motor using pulse width variable M (PWM) varies significantly between when the voltage supplied to the power source is the lowest and when it is the highest.

For this reason, when the voltage is rising immediately after regeneration, when the supply current of the servo motor is reduced in order to drive the servo motor at very low speed or low speed, the pulse width will decrease due to the voltage during regeneration. This has the disadvantage that it becomes narrower and the control characteristics deteriorate.

Further, when the power is turned off, it is necessary to rapidly discharge the electric charge stored in the electrolytic capacitor to prevent fire during maintenance. (In FIG. 4, this corresponds to the resistor RD.

(It becomes 50 to 20 V or less after 1 minute.) Therefore, a bleeder resistor with a high resistance value is required, and there is also a drawback that heat is generated due to discharge.

(2) Second Conventional Example (Japanese Unexamined Patent Publication No. 57-78382) FIG. 5 is a circuit diagram of the one shown in the above publication. In FIG. 5, 11 is a DC motor, and 12 is a transistor bridge circuit, which is composed of transistors 21, 22, 23, 24 and diodes 25, 26, 27, 28.

A discharge contact 14 is connected in parallel between both terminals of the DC motor 11 .

Base current drive circuits 31, 32, 33.34 are connected to transistors 21.22, 23.24, respectively.

A discharge circuit 15 is connected between the input terminals of the transistor bridge circuit 12. 16 is a diode rectifier circuit composed of rectifier diodes 61, 63, 64, 65, and 66.

71.72.73 is an electromagnetic switch.

The discharge circuit 5 includes a discharge transistor 51, a current limiting resistor 52, first and second capacitors 53, 54, a diode 55, and a discharge control circuit 56. When regenerative power exceeding the setting is generated, the reverse voltage generated across the diode 55 exceeds the setting, which is detected by the discharge control circuit 56, and the base current is accordingly applied to the discharge transistor 5I. The regenerated power is consumed as Joule heat by the current limiting resistor 52.

Further, a monitoring circuit 18 is connected to the discharging transistor 51 to monitor its conduction state, and when it detects that the duration of the conduction state of the discharging transistor 51 exceeds a set time, it issues an alarm and This makes it possible to prevent poor control of the motor 11 and damage to the discharge transistor 51.

However, in the case of this second conventional example, since the current supplied to the DC motor 11 flows through the diode 55, a large diode 55 must be selected so that it can withstand the peak current to the DC motor 11. . In addition, even though the capacitor 53 does not have the role of absorbing power during regeneration, the DC motor 1
It has a drawback that it requires a large capacity that can tolerate a ripple current value due to a load current of 1.

(Objective of the Invention) The present invention has been made in view of the above circumstances, and is intended to provide good protection to the circuit regardless of voltage changes in the power supply supplied to correspond to the rated voltage of the servo motor. The purpose of this invention is to stabilize the control characteristics of the servo motor and reduce heat generation in the control circuit.

(Structure and Effects of the Invention) In order to achieve such an object, the present invention provides a regenerative power consumption resistor connected between both ends of the bridge transistor circuit in the servo motor control circuit described at the beginning. a discharge circuit consisting of a switching element connected in series to the resistor; a reference voltage power supply circuit of negative polarity; and a switching transistor that outputs a conductive output to the switching element in response to a decrease in the potential on the negative electrode side of the smoothing capacitor that exceeds a set value.

According to this configuration, when regenerative power is generated from the bridge transistor circuit as the servo motor decelerates or stops, the smoothing capacitor is charged with electric charge and its negative electrode potential decreases. When the regenerative power becomes higher than the supply power supply voltage, the negative potential of the smoothing capacitor becomes lower than the negative potential of the reference voltage power supply circuit by more than a setting, which causes the switching transistor to conduct and the switching element to conduct, causing the regenerative current to flow. flows through the resistor, the regenerative power is consumed by discharge there, and it is possible to prevent the voltage immediately after the regenerative operation from rising significantly higher than the supply voltage.

Therefore, the voltage at which regenerative power should be consumed changes depending on the supply voltage to the power supply, so even if the supply voltage changes, there is no need to change the set voltage of the voltage detector like in the past. It is now possible to protect the circuit and stabilize the control characteristics of the servo motor by consuming regenerated power without any effort.

Moreover, the switching transistor is connected to the negative side of the negative reference voltage power supply circuit, and the switching transistor is activated in response to the negative side potential of the smoothing capacitor dropping by more than a set value, with the negative side potential as a reference. For example, compared to the case where the voltage increases by more than a set value than the reference potential, the voltage applied to the switching transistor can be reduced when the power is turned off, and a switching transistor with a low withstand voltage can be used, resulting in lower voltage. This makes it possible to save heat in the control circuit and make it inexpensive, and it also simplifies measures against heat generation, making it possible to effectively implement a hybrid IC.

(Description of Examples) Hereinafter, the present invention will be described in detail based on examples shown in the drawings.

(First Embodiment) FIG. 1 is a circuit diagram according to a first embodiment of a servo motor control circuit of the present invention. In this figure, Ql, Q2.
Q3. Q4 is an NPN type power transistor, M is a DC servo motor, and DI.

D 2 , D 3 , and D 4 are diodes for releasing induced voltage, and these constitute a bridge transistor circuit. The power transistors Ql, Q2 . Q3. Servo amplifier (
(not shown) input pulse signals at predetermined intervals to control the current supplied to the servo motor M. E
is an AC power supply, and rectifier diodes D8. D9. D.I.
The AC power source E is connected to the AC power source E through the DC power source circuit El, which consists of a full-wave rectifier circuit consisting of O, DI l, and a smoothing capacitor C.
DC power is obtained from the Rd is a dummy resistor connected to both ends of the smoothing capacitor C and having a relatively high resistance value. These operations are the same as those described above, and their explanation will be omitted.

2 is a discharge circuit, which includes a low-resistance resistor Rs for regenerative power consumption connected between the DC power supply circuit 91, and this resistor Rs.
and a voltage control element (MOSFET) Q5 as a switching element connected in series.

2 is a voltage difference detection means for detecting a voltage difference between the power supply voltage supplied to the DC power supply circuit El and the regenerated power from the bridge transistor circuit;
A negative reference voltage power supply circuit 3 consisting of rectifying diodes D 6 , D 7 , a smoothing capacitor Cs and a bleeder resistor R3 for monitoring the voltage of the AC power supply as the supply voltage to the Resistors R4, R5, R6,
R7 and the first and second Zener diodes ZD 1
, ZD2, a Cyrisk SCR, a capacitor CI, a PNP switching transistor Q6, and voltage dividing resistors R8 and R9.

D5 is a protection or malfunction prevention diode, ZD3
is a Zener diode for protecting the gate of voltage control element Q5.

Next, the operation of this embodiment will be explained using the time chart shown in FIG.

As shown in Fig. 2 (a), a current corresponding to the desired rotational speed is passed through the servomotor M, and after the specified rotational speed is obtained, the servomotor M resists frictional resistance. A low current of only Then, when the energization is stopped, the servo motor M acts as a generator, and the regenerative current I
b occurs.

In the servo motor M, depending on its supply current, the switching transistor Ql is also turned on.

By the combination of Q 2 , Q 3 and Q 4, the second
As shown in the figure (b), the rotation speed reaches a predetermined speed while being accelerated sequentially, and the rotation speed is rotated clockwise CW or counterclockwise CCW.
Rotate to .

In the above operation, the negative electrode side potential e of the smoothing capacitor C
is on one side with respect to the positive electrode side potential a of the reference voltage power supply circuit 3, and as shown in FIGS. 2(C) and (E), the smoothing capacitor C is charged at the same time as the current is supplied. Therefore, the voltage rises temporarily with respect to the negative electrode side potential of the reference voltage power supply circuit 3, then stabilizes at a predetermined potential, and then, as the current supply is stopped, the smoothing capacitor C
The potential decreases due to the regenerative current with a time constant of .

When the negative potential e of the smoothing capacitor C decreases beyond the set value with respect to the negative potential of the reference voltage power supply circuit 3 as regenerative power increases, the first Zener diode ZDI
When the terminal voltage VD of the thyristor S becomes larger than the sum of the supply voltage Vs of the power supply E-\ and the breakdown voltage Vzl of the first Zener diode ZD1 (VD>Vs+Vzl), the thyristor S
When CR is turned on, the switching transistor Q6 becomes conductive, and a gate current as a conduction output flows through the voltage control element Q5. As a result, the voltage control element Q5 becomes conductive, and regenerative current flows through the resistor Rs, and the regenerated power is transferred to the resistor. Rs.
This prevents the regenerated power from rising above the set voltage.

When the power is turned on again immediately after that, the smoothing capacitor C
Since the battery is charged to 100%, the voltage increase is smaller than at the initial stage [see Fig. 2 (c)].

The collector potential C of the switching transistor Q6 is as shown in FIG.
6 is in the cut-off state, it is equal to the negative electrode side potential e of the smoothing capacitor C, and as it becomes conductive, it rises to a potential almost equal to the negative electrode side potential of the reference voltage power supply circuit 3. and,
The drain side potential d of the voltage control element Q5 is as shown in Fig. 2 (G).
As shown in Fig. 2, it drops as the conduction occurs.

Further, when the terminal voltage VD of the second Zener diode ZD2 becomes smaller than the sum of the supply voltage Vs to the DC power supply circuit El, the breakdown voltage Vz2 of the second Zener diode ZD2, and the set voltage α (V D <Vs The thyristor 5CRh is designed to turn OFF when the voltage is 10Vz2 +a, where a: 3 to 5V), and its operating voltage -Va and release voltage -
It is designed to have hysteresis between it and vb.

Figure 2 (d) shows the voltage change when the regenerative power is not consumed as described above. The voltage is low even when the servo motor M starts to be energized, and this voltage causes a change in the pulse width of the servo motor M and causes damage to the circuit. In the case of the conventional example described above, the voltage rise can be suppressed to the voltage set by the voltage detector De, but since the set voltage inevitably becomes high, the rated voltage of the servo motor M is low and the power supply E
When the supply voltage is lowered, almost the same phenomenon as in the case of FIG. 2 (d) occurs. On the contrary,
In the present invention, even if the supply voltage to the DC power supply circuit El is low, regenerative power is consumed corresponding to the supply voltage, and high voltage is prevented from being applied to the circuit. It can be avoided that the voltage is in a high state at the start of energization.

In addition, the smoothing capacitor C in the reference voltage power supply circuit 3
The relationship between the time constant of s and the resistor R3, and the time constants of the smoothing capacitor C in the DC power supply circuit El, the resistor Rs of the discharge circuit 1, and the dummy resistor Rd is expressed as C-R8<C3.
By setting -R3 to C-Rd, when the supply voltage is cut off, the charge on the smoothing capacitor Cs will be transferred to the resistance R.
3, it is discharged and decreases. Further, the charge of the smoothing capacitor C is discharged by the dummy resistor Rd, but the drop is smaller than that of the smoothing capacitor Cs. When this voltage difference reaches the operating voltage -Va, it is discharged by the resistor Rs due to the conduction of the voltage control element Q5. On the other hand, when the voltage difference reaches the return voltage -vb, the voltage control element Q5 is cut off, and the terminal of the smoothing capacitor Cs is again turned off. When the voltage drops, it performs the same operations as described above, repeats these operations, and stops at the voltage determined by the operating voltage -Va. This results in
The dummy resistor Rd can be selected to have a small power capacity, or it can be eliminated.

(Second Embodiment) FIG. 2 is a circuit diagram according to a second embodiment of the servo motor control circuit of the present invention. This second embodiment is applied to a servo motor M operated by three-phase AC power.

DI2. D13. D14. D15, D16. D17 is
Rectifier diode of the full-wave rectifier circuit constituting the DC power supply circuit E1, DI8°D19. D20 is a rectifying diode.

Q7. QB', Q9. Q10. Q l l, Q l
2 are NPN type power transistors, M is a servo motor, D21. D22. D23. D24. D2
5°D26 are diodes for releasing induced voltage, and these constitute a bridge transistor circuit. The operation is the same as in the first embodiment, and will therefore be omitted.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a first embodiment of a servo motor control circuit of the present invention, Fig. 2 is a time chart explaining the operation of the first embodiment, and Fig. 3 is a circuit diagram of a second embodiment. , FIG. 4 is a circuit diagram of the first conventional example, and FIG. 5 is a circuit diagram of the second conventional example. 1...Discharge circuit, 3...Reference voltage power supply circuit, C.
...Smoothing capacitor, Q8. Q9. D10. D 11, Q12. Q13. D
i4, D 15. D16. D l 7... Rectifier diode that constitutes a full-wave rectifier circuit, El... DC power supply circuit, M... Servo motor, Ql
, Q2. Q3. Q4, Q7. Q8. Q9. Q10゜Ql
l, Q12...NPN power transistor constituting the bridge transistor circuit, Q5...voltage control element (MOSFET) as a switching element, Q6...switching transistor, Rs...for regenerative power consumption resistance.

Claims (1)

[Claims] (1) A DC power supply circuit consisting of a full-wave rectifier circuit and a smoothing capacitor, a bridge transistor circuit connected between both ends of the DC power supply circuit, and a servo connected between the intermediate points of the bridge transistor circuit. A control circuit for a servo motor comprising a motor, comprising: a discharge circuit connected between both ends of the bridge transistor circuit and comprising a resistor for regenerative power consumption and a switching element connected in series with the resistor; and a negative polarity. a reference voltage power supply circuit; and a switching element connected to the negative electrode side of the reference voltage power supply circuit, in response to a decrease in the negative electrode side potential of the smoothing capacitor by more than a setting with respect to the negative electrode side potential of the reference voltage power supply circuit. A servo motor control circuit equipped with a switching transistor that outputs a conductive output.