JPH10132861A - Current detector of ac servo driver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the control performance of a motor by generating a voltage that is proportional to a current value from an inverter that is subjected to current control based on a current command value and amplifying and ADD- converting a voltage value with a variable amplification rate according to the current command value. SOLUTION: A three-phase current generated by an inverter 1 is supplied to an AC servo motor 3 for drive control. The U phase current is detected by a current detector 2 and is inputted to an operational amplifier 4, and a detection voltage is amplified and is outputted to an A/D converter 5 and is processed as current detection data. When a current command value is large, a switch 6 is tuned on by the output of a comparator 7 for short-circuiting a feedback resistor R3, and the amplification rate of the operational amplifier 4 is reduced by R2/R1, thus detecting a large current. When a current command value is small, the switch 6 is turned off by the output of the comparator 7 and the feedback resistor R3 is inserted and then the amplification rate of the operational amplifier 4 increases by (R2+R3)/R1. Therefore, by suppressing a current detection resolution, vibration can be suppressed when the motor stops.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current detection device for an AC servo driver, and more particularly to a current detection device for an AC servo driver capable of increasing the resolution of current detection.

[0002]

2. Description of the Related Art Conventionally, in the current detection of an AC servo driver, when a current loop is formed by an analog circuit, the current detection is also configured by an analog circuit, and the resolution is theoretically infinite. However, in recent years, with the improvement of digital technology, the case where the current loop is configured by a digital circuit or software has become mainstream. Therefore, current detection also needs to be processed with digital data, and the motor current value is converted into digital data by an A / D converter or the like. However, in this case, there is a problem that the resolution of the A / D converter is finite, that having a high resolution is expensive, and that lowering the resolution makes the motor more likely to vibrate when stopped.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems of the prior art and to increase the resolution of current detection as required with a simple and inexpensive structure. An object of the present invention is to provide an AC servo driver current detection device capable of improving performance.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a means for generating a voltage proportional to a current value flowing through an AC servomotor from an inverter that is current-controlled based on a current command value; An AC servo, comprising: an operational amplifier for amplifying a voltage; and means for converting a voltage value to which the output of the operational amplifier is input into digital data, wherein an amplification factor of the operational amplifier is made variable according to the magnitude of a current command value. It is a current detection device for a driver. Also,
The variable timing of the amplification factor of the operational amplifier has a hysteresis characteristic. According to the present invention, the amplification factor of the operational amplifier that amplifies the voltage proportional to the current flowing through the AC servomotor is made variable, and when the current command value is large, the amplification factor is set low in relatively dynamic operation to increase the large current. By enabling detection, the entire operating range of the current can be controlled, and when the current command value is small, that is, when the movement is relatively static, the amplification factor is set high to increase the current detection resolution. Vibration can be suppressed.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described based on embodiments. FIG. 1 is an electric circuit diagram showing the configuration of the embodiment of the present invention. In the figure, P and N represent the positive and negative sides of the DC voltage. Reference numeral 1 denotes a three-phase PWM inverter including a plurality of switching elements, and these constitute an AC servo driver. Reference numeral 3 denotes an AC servomotor driven by applying a voltage from the three-phase outputs U, V, and W of the inverter 1;
The drive of the AC servomotor is controlled by a control unit (not shown) or the like via an AC servo driver based on the current detection value and the current command value in a known manner. Reference numeral 2 denotes a current detector for detecting a U- or V-phase current flowing to the AC servomotor 3. 4 is an operational amplifier for amplifying the detection output of the current detector 2; Reference numeral 5 denotes an A / D converter that digitizes the output voltage of the operational amplifier 4 and outputs it as a detected current value. Reference numeral 7 denotes a comparator for comparing the U-phase current command value with the level 1 or the level 2 by switching between the level 1 and the level 2 so that the input / output characteristic has a hysteresis characteristic. ON / O of the short-circuit switch 6 for short-circuiting the feedback resistor R3 of the operational amplifier 4 based on the comparison result of the comparator 7
FF control and switching between level 1 and level 2 are performed.

The operation of the embodiment of the present invention will be described.
The following description is for the case of U-phase current detection. A three-phase current generated by the inverter 1 controlled to be conductive by a control unit (not shown) is supplied to the AC servomotor 3,
The drive control of the AC servomotor 3 is performed. The supply current to the U phase of the AC servomotor 3 is detected by the current detector 2,
The detection output is input to the operational amplifier 4. The operational amplifier 4 amplifies the current detection voltage detected by the current detector 2 and outputs the amplified voltage to the A / D converter 5, which processes the current detection data. Here, when the current command value in the AC servomotor control is large, that is, when the servo motor is relatively dynamic, the switch 6 is turned on by the output of the comparator 7 and the feedback of the operational amplifier 4 based on the large current command value. Since the resistor R3 is short-circuited, the amplification factor of the operational amplifier 4 is reduced to R2 / R1 so that a large current can be detected (where R1 is the operational amplifier 4).
Input resistance).

When the current command value is small, that is,
In the case of a relatively static movement, the switch 6 is turned off by the output of the comparator 7 and the feedback resistor R3 of the operational amplifier 4 is inserted, so that the amplification factor becomes large as (R2 + R3) / R1, and the current detection resolution is increased. Thereby, vibration when the motor is stopped can be suppressed. Further, when the current detection value is near the switching level of the operational amplifier, the control becomes unstable due to chattering in which the gain is repeatedly switched in a short cycle. On the other hand, in the present embodiment, the level 1 is detected by the output of the comparator. , 2 and the short-circuit switch switching timing is provided with a hysteresis characteristic, so that chattering does not occur even when the current detection value is near the switching level. Furthermore, in the calculation of the current loop after the conversion by the A / D converter, the magnitude of the current detection data can be converted and processed based on the magnitude of the current command value, that is, the magnitude of the amplification factor. That is, it can be used to perform an operation for matching the current command value with the output level of the operational amplifier.

The above description also applies to the case of detecting the V-phase current shown in the figure.

[0009]

As described above, according to the present invention, the resolution of current detection can be increased as necessary with a simple and inexpensive structure, and the control performance of the motor can be improved. .

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram showing a configuration of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Inverter 2 Current detector 3 AC servo motor 4,4 'Operational amplifier 5,5' A / D converter 6,6 'Feedback resistance short-circuit switch 7,7' Comparator

Claims (2)

[Claims] A means for generating a voltage proportional to a value of a current flowing through an AC servomotor from an inverter that is current-controlled based on a current command value; an operational amplifier for amplifying the voltage; and a voltage having the output of the operational amplifier as an input Means for converting a value into digital data, wherein the amplification factor of the operational amplifier is made variable according to the magnitude of the current command value. 2. The current detection device for an AC servo driver according to claim 1, wherein a hysteresis characteristic is provided at a timing at which the amplification factor of the operational amplifier is changed.