JPS62213596A - Speed setter for motor - Google Patents

Abstract

PURPOSE:To eliminate the possibility of damaging a motor and a load due to resonance vibration by outputting a speed command signal to avoid an operating avoiding speed range. CONSTITUTION:When the output of an accelerating/decelerating calculator 12 falls within an operation avoiding speed range, comparators 24, 25 and exclusive OR gate 26 detect it to operate a signal switching unit 27. Thus, the output signal of a predetermined speed setter 21 is applied as a speed command signal to a speed controller instead of the output signal of the calculator 12. Since the speed signal set by the setter 21 is set to a speed as near as the speed range outside the operating avoiding speed range, the motor does not stay in the avoiding speed range but rapidly becomes the speed set by the setter 21.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a speed setting device for an electric motor that commands a speed excluding a speed range that is desired to be avoided by an electric motor operating at variable speed.

[Prior art and its problems]

FIG. 3 is a circuit diagram showing a conventional example of a speed control device for a variable speed motor, and shows a case where an induction motor is driven by a transistor inverter that outputs alternating current power of variable voltage and frequency. . That is, in FIG. 3, AC power from AC power source 2 is passed through diode rectifier 3
The AC power converted by the transistor inverter 5 is supplied to the induction motor 6 to drive the load 7. The speed of the induction motor 6 is controlled as follows.

The speed command means 10 includes a speed setting device 11 and an acceleration/deceleration calculator 12
When the speed setter 11 is set to a desired speed position, the acceleration/deceleration calculator 12 receives this setting signal and outputs a speed command signal that changes at a predetermined rate of change over time. This speed command signal is converted into a frequency command signal by a voltage/frequency converter 13, and is also converted by a function generator 14 into a voltage command signal having a fixed functional relationship with this frequency command signal. The pulse width modulation circuit 15
Frequency command signal from frequency converter 13 and function generator 1
Since the voltage command signal from 4 is input and a pulse train signal corresponding to these input signals is output, this pulse train signal is inputted to the base of each transistor constituting the transistor inverter 5 via the base drive circuit 16. By turning these on and off sequentially, the transistor inverter 5 outputs AC power with a frequency and voltage corresponding to the speed command signal, allowing the induction motor 6 to operate at the set speed. . Therefore, by changing the setting value of the speed setting device 11, the speed of the induction motor 6 can be changed freely.

By the way, when a mechanical system consisting of an induction motor 6 and a load 7 driven by the induction motor 6 is operated at a specific speed, resonance vibration occurs in this mechanical system. This may cause problems such as damage to the load 7. Therefore, it is necessary to avoid operation within a certain speed range centered around the speed at which resonance imaging occurs.Therefore, in the conventional example circuit shown in FIG. It is artificially set so that the speed is away from the speed that causes the movement, but if it is set at the wrong position, it will damage the mechanical system, so great care must be taken when setting it.

Furthermore, even if the set speed is sufficiently higher than the speed that causes resonance vibration, if the total force of the load 7 and the motor 6 is large, the acceleration/deceleration calculator 12 outputs Since the speed command signal has a gradual rate of change over time, there is a risk that the mechanical system will remain in a dangerous speed range for a long time during acceleration, causing problems such as damage to the mechanical system. There is.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electric motor speed setting device that can automatically prevent a mechanical system consisting of a variable speed electric motor and its load from operating near a speed that causes resonance vibration.

[Key points of the invention]

This invention provides a setting device that separately sets the upper and lower limits of a speed range that the motor should avoid, and a predetermined speed setting device that sets a predetermined speed outside the speed range that the motor should avoid. By configuring the logic circuit so that the setting signal from the predetermined speed setting device is given to the motor speed control device as a speed command signal during the period when the command signal is within the speed range that should be avoided, human setting errors can be avoided. Alternatively, it is intended to automatically avoid the risk of resonance vibration occurring due to staying within the avoidance speed range for a long time during the acceleration/deceleration period.

[Embodiments of the invention]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and only shows the portion corresponding to the speed command means 10 in the conventional circuit shown in FIG. 3, and the remaining portions are omitted. .

Considering the case where you want to start a stopped electric motor and increase it to a desired speed, in this figure 1, the speed setting device 1
1 to output a desired speed command signal, but if the step-like speed command signal output by the speed setter 11 is directly applied to the motor, problems such as overcurrent will occur, so acceleration/deceleration calculations are necessary. The stepwise speed command signal is converted into a slowly changing speed command signal by the switch 12, and this signal is applied to the subsequent speed control device through one contact of the signal switch 27. For example, when driving a load with an extremely large flywheel effect, the time rate of change of the speed command signal output from acceleration/deceleration calculation 6/2 is reduced so that the motor speeds up very slowly. .

If the electric motor passes through a point that causes resonance vibration while increasing its speed to the desired speed, it is possible to quickly pass through a constant speed range around the point that causes resonance vibration. No damage will occur due to vibration. Therefore, the lower limit speed of the speed range in which the motor should avoid operation is set using the lower limit speed setter 22, and this setting signal is sent to the first
Let it be input to the controller 24. Further, the upper limit speed of the driving avoidance speed range is set by the upper limit speed setter 23, and this setting signal is input to the second comparator 25. Further, a speed command signal outputted from the acceleration/deceleration calculator 12 and changing at a predetermined rate of change is inputted to the first comparator 24 and the i2 comparator 25.

If the motor is speeding up and the speed command signal output by the acceleration/deceleration calculator 12 has not reached the lower limit speed of the extreme operation avoidance speed range, the speed command signal from the lower limit speed setter 22 is higher than this speed command signal. Since the setting signal is larger, the first comparator 24 outputs a logical signal, and the second comparator 25 also outputs a logical signal since the upper limit speed setting value is larger. ing. Therefore, the output of the exclusive OR element 26 is also a logic signal, and the signal switch 2
7 does not operate and is in the state shown. Therefore, the output signal of the acceleration/deceleration calculator 12 directly serves as the speed command signal.

When the output of the acceleration/deceleration operation Although the output is changed from a logic high signal to a logic high signal, the magnitude relationship between the two signals input to the #E2 comparator 25 remains the same, so the second comparator 25 still outputs a logic high signal. Therefore, exclusive OR element 26
The output of is switched to a logic H signal to operate the signal switch 27. Therefore, the output signal of the predetermined speed setter 21 is given to the speed control device as a speed command signal instead of the output signal of the acceleration/deceleration calculator 12, but the speed signal set by the predetermined speed setter 21 is Since the speed is set outside the above-mentioned driving avoidance speed range and as close to this speed range as possible, the motor quickly reaches the speed set by the predetermined speed setting device 21 without staying in this driving avoidance speed range.

Even when the electric motor is operating at the speed set by the predetermined speed setter 21 as described above, the output of the acceleration/deceleration calculator 12 increases the speed command value at a predetermined rate of change, and that value is the upper limit. When the value exceeds the set value of the speed setter 23, the second comparator 25 detects the reversal of the magnitude relationship between the two input signals and changes its output from a logic high signal to a logic high signal. At this time, since the output of the first comparator 24 is still a logic H signal, the output of the exclusive OR element 26 becomes a logic logic signal again, returning the signal switch 27 to its original state.

Therefore, the exclusion signal output from the acceleration/deceleration calculator 12 is again given to the motor speed control device as a speed command signal.

FIG. 2 is a graph showing changes in the output signals of each part of the embodiment circuit shown in FIG. 1, and FIG. Figure 2) shows the change in the output signal of the exclusive OR element 26, and Figure 2) shows the change in the speed command signal output from the signal switch 27. It's raining. In this Figure 2, A is the lower limit speed of the driving avoidance speed range, B is the upper limit speed of the driving avoidance speed range, and C is the upper limit speed of the driving avoidance speed range.
inputs the speed set by the predetermined speed setter 21.

As is clear from FIG. 2, the acceleration/deceleration calculator 12
Exclusive OR element 2 only when the signal output from is within the driving avoidance speed range (between A and B in Fig. 2 (a))
6 becomes a logic H signal and outputs the speed signal set by the predetermined speed setter 21 (C in FIG. 2 (c)) via the signal switch 27, so the speed command signal becomes
The speed changes as shown in Figure (C), and the danger of the motor staying within the avoidance speed range can be avoided.

〔Effect of the invention〕

According to this invention, the upper and lower limits of the speed range in which the motor should avoid operation are set using separate setters, and the speed command of the motor is set by a logic circuit composed of a comparator and an exclusive OR element. When the signal is within the driving avoidance speed range,
Since a speed command signal set outside this operation avoidance speed range is output, if the speed is set incorrectly or the speed command signal changes slowly, the motor speed will be lower than the operation avoidance speed. This has the effect of automatically avoiding staying within the range for a long time, thereby avoiding the risk of damage to the motor and its load due to resonance vibration, etc. Furthermore, according to the present invention, even if the speed at which resonance W motion is generated changes due to a change in the load condition, the setting values of the upper limit speed setter, lower limit speed setter, and predetermined speed setter can be changed quickly. It also has the advantage of being able to easily respond to changes in resonance speed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a graph showing changes in output signals of various parts of the embodiment circuit shown in Fig. 81, and Fig. 3 is a speed diagram of an electric motor operating at variable speed. 1 is a circuit diagram showing a conventional example of a control device. 2...AC power supply, 3...diode rectifier, 4...
・Smoothing capacitor, 5...transistor inverter,
6... Induction motor, 7... Load, 10... Speed command means, 11... Speed setter, 12... Acceleration/deceleration calculator, 13... Voltage/frequency converter, 14... ...Function generator, 15...Pulse width modulation circuit, 16...Base drive circuit, 21...Predetermined speed setter, 22...Lower limit speed setter, 23...Upper limit speed setting n, 24... first comparator, 25... second comparator, 26.
...Exclusive OR element, 27...Signal switching throat ←
(trans) vine.

Claims (1)

[Claims] 1) Speed command means that outputs a command to operate a variable speed electric motor at a desired speed, and lower limit speed setting means and upper speed limit setting means that separately sets the lower limit speed and upper limit speed of the speed range in which the electric motor wants to avoid operation. means, a predetermined speed setting means for setting a predetermined speed outside the driving avoidance speed range, a first comparator for comparing the output signal of the speed command means with a setting value of the lower limit speed setting means, and an output signal of the speed command means. a second comparator for comparing the set value of the upper limit speed setting means; a means for detecting whether the motor speed is within the operation avoidance speed range from the output signals of the first and second comparators; A speed setting device for an electric motor, comprising a signal switching means for outputting a setting signal from a predetermined speed setting means instead of the speed command means if the speed is within this avoidance speed range.