JPH0632583B2 - Current detection circuit for servo motor control - Google Patents

Description

The present invention relates to a servo motor control which detects a phase current of a rectangular wave drive type brushless servomotor and outputs a current detection signal for controlling the servomotor. The present invention relates to an electric current detection circuit.

[Prior Art] Conventionally, a current feedback signal for controlling a servomotor based on the above current detection signal has been obtained by a feedback signal generation circuit as shown in FIG. 5, for example. 1u and 1 in FIG.
All of v are current detectors, the former detecting U-phase current of a rectangular wave drive type brushless servomotor (not shown), and the latter detecting V-phase current. In order to insulate the input side and the output side from these current detectors,
It is often used as a current transformer using a Hall element (so-called Hall CT). 20 is an inverting addition amplifier, 21-23
Are inverting amplifiers, and 24 is a multiplexer.

In the circuit of FIG. 5, the current detectors 1u and 1v detect the U-phase and V-phase currents of the servomotor, respectively, and output detection output signals U and V corresponding to the magnitudes of the respective currents. The W-phase current detection signal W is obtained by adding and inverting the detection output signals U and V of the current detectors 1u and 1v by the inverting and adding amplifier 20. Further, signals whose polarities are inverted by the inverting amplifiers 21 to 23 are obtained from the above detection signals U, V and W, respectively. Then, the six types of signals are input to the multiplexer 24. This multiplexer is controlled by the rotor position detection signal Vθ of the servo motor.

The waveforms of the above detection signals U and V are as shown in (3) and (4) of FIG. 6, respectively, and current conduction depends on the armature angle position θ of the rotor of the servomotor shown in (1) of FIG. The periods A and C are set, and the current quiescent period B is set. Therefore, by selecting the phase current detection signal in the current conduction period by the multiplexer 24 according to the rotor position θ and combining the signals, a stable current feedback signal as shown in (5) of FIG. 6 is obtained. Get Icom.

[Problems to be Solved by the Invention] In the feedback signal generation circuit as described above, since the Hall detector CT or the like is used for the current detectors 1u and 1v as described above, the Hall detector is used during the rotation of the servo motor. Even when the phase current to be detected is zero due to factors such as remanence of the magnetic circuit in CT, temperature fluctuations, or fluctuations in the base point of current transformation, for example, the current detection described above is performed as shown in (6) of FIG. The signal U does not become zero, but an apparent offset voltage Vof occurs. Therefore, the current detection signal U is shifted upward by the offset voltage Vof as a whole. As a result, the current feedback signal Icom ′ to the servo system fluctuates depending on the rotor position θ as shown in (7) of FIG. 6, which causes a problem of torque fluctuation and speed fluctuation of the servo motor. there were.

An object of the present invention is to detect the offset voltage Vof appearing in the detection output of the current detector and cancel the voltage from the detection output to obtain a good current detection signal. To provide.

[Means for Solving Problems] A configuration of the present invention for solving the above problems will be described below with reference to FIG. 1 corresponding to an embodiment.

A servo motor control current detection circuit according to the present invention detects a phase current of a servo motor for controlling a brushless servo motor driven by a rectangular wave current, and outputs a current detection signal. In the circuit, a current detector 1 that detects a predetermined phase current of the servo motor, and a rotor position detection circuit 3 that detects a rotational position of the rotor of the servo motor and outputs a rotor position signal.
And a sample and hold circuit 4 which receives a detection output signal of the current detector 1 to hold and output an offset signal instructed to sample by a predetermined position signal of the rotor,
And a signal correction circuit 7 for correcting the detection output signal of the current detector 1 with the offset signal and outputting the current detection signal.

[Operation of the Invention] In the servo motor control current detection circuit configured as described above, the current detector 1 detects a predetermined phase current of the servo motor, and the detected output signal is input to the sample and hold circuit 4. It On the other hand, the rotor position detection circuit 3 detects the rotor position of the servo motor, the sample hold circuit 4 is instructed to sample by a predetermined rotor position signal, and the offset signal included in the detection output signal of the current detector 1 is sampled. It is held in the hold circuit 4.
Then, the detection output signal of the current detector 1 is corrected by the signal correction circuit 7 by the offset signal. As a result, a good current detection signal in which the offset signal included in the detection output signal of the current detector 1 is erased can be obtained.

[Embodiment] An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 1 is a current detector that detects a predetermined phase current i of a servo motor and outputs a detection output signal Vi, 2 is a noise signal elimination circuit connected to the output end of the current detector 1, 3
Is a rotor position detection circuit for detecting the electrical angle position θ of the rotor of the servo motor (not shown), and 4 is a rotor position detection circuit 3
Is a sample and hold circuit that receives an output of the noise signal removing circuit 2 and outputs an offset voltage Vof, which is sampled by a predetermined rotor position signal (a position signal corresponding to a phase current rest period) from. 5 is this offset voltage
An inverting circuit which receives Vof and outputs a signal -Vof whose polarity is inverted, 6 is an adder circuit which receives the detection output signal Vi of the current detector 1 and the output signal -Vof of the inverting circuit 5 as an input signal. 5 and the addition circuit 6 constitute a signal correction circuit 7. The current detection circuit configured as shown in FIG. 1 is provided for each predetermined phase of the servo motor.

In the current detection circuit having the above configuration, the current detector 1 detects a predetermined phase (for example, U phase) current of the servo motor and outputs the detection output signal Vi. The noise signal removing circuit 2 receives the signal Vi to remove the noise voltage, and outputs the signal Vi.
When the offset voltage Vof is included in the above, the offset voltage Vof of the DC component is output during the idle period of the phase current of the motor. On the other hand, the rotor position detection circuit 3 detects a pause period [B in FIG. 6 (3)] of the phase current of the motor, and the noise core elimination circuit 2 is detected during each current pause period B.
The offset voltage Vof output from is input to the sample and hold circuit 4 to hold the voltage. Then, during the current conduction period C or A following each of the periods B, the voltage −Vof obtained by inverting the polarity of the holding voltage Vof by the inverting circuit 5 is input to the adding circuit 6. The adder circuit 6 detects the detection output signal V including the offset voltage Vof as described above.
i and the above voltage −Vof are added, and the offset voltage Vof is erased from the signal Vi and corrected to obtain a good current detection signal V.
Output ic. By using such a current detection signal Vic, a stable current feedback signal as shown in (5) of FIG. 6 can be obtained.

Next, a modified example of the portion of the signal correction circuit 7 in the embodiment of FIG. 1 will be described with reference to FIG. Reference numeral 8 in FIG. 2 is an inverting amplifier that receives the detection output signal Vi from the current detector 1 shown in FIG. 1 and outputs a signal i of opposite polarity, and 9 is an offset output from the sample and hold circuit 4 in FIG. Voltage Vo
The current detection signal Vic with f and the above output signal i as input
Is an inverting addition amplifier that outputs
And the inverting addition amplifier 9 constitute the signal correction circuit 7.

By the way, when the sample / hold circuit 4 in FIG. 1 is configured by an analog circuit, the held offset voltage Vof may change if the signal holding time becomes long. Therefore, two examples of the configuration of the sample and hold circuit 4 which improves this are shown in FIG. 3 and FIG.

First, in FIG. 3, 4a receives the position detection signal Vθ of the rotor position detection circuit 3 and receives the output signal Vi of the noise signal removal circuit 2 in the period B of (3) in FIG. A-D converter for conversion, 4b is this A-
A digital latch circuit for holding the digital signal output from the D converter for a predetermined time, 4c is a DA converter for converting the digital signal held by the latch circuit into an analog signal and outputting it as the offset voltage Vof. Is.

In the sample and hold circuit of FIG. 3, the offset voltage
Since the Vof equivalent value is held in a digital amount, there is an advantage that the holding voltage value does not change even if the holding time becomes long.

Next, in FIG. 4, 4d is the noise signal removing circuit 2 described above.
Of the output signal i of the DA converter 4c and the comparator 4e for comparing the output signal i of the DA converter 4c with the counting operation thereof are controlled by a predetermined clock signal given from the other, and the position detection signal Vθ of the rotor position detection circuit 3 is controlled. It is an up / down counter that receives and counts the output signal of the comparator 4d in the period B. In this example, the comparator 4d and the up / down counter 4e are
It acts as a -D converter.

In the sample and hold circuit of FIG. 4, during the period B, the output signal i of the noise signal elimination circuit and the D / A converter 4 are
The output signal Va of c is compared, the up / down counter 4e is operated so that they match each other, and the count value DA converter 4c held by the up / down counter 4e when the period B ends It is converted to an analog quantity and output as an offset voltage Vof.

In the sample hold circuit of FIG. 4 as well, the offset voltage equivalent value is held as a digital amount, so that the hold voltage value does not fluctuate even if the hold time becomes long.

In the embodiment of FIG. 1, the noise signal removing circuit 2 is used to remove the noise signal contained in the detection output signal of the current detector 1, but this noise signal removing circuit may be omitted depending on the case. Good.

[Effects of the Invention] As described above, according to the present invention, the detection output signal of the current detector for detecting the phase current of the servomotor is sent to the sample and hold circuit sampled by the rotor position detection signal of the motor. Since the offset signal included in the input signal is held by the input, and the detection output signal of the current detector is corrected by the offset signal, the offset signal included in the detection output signal is erased, which is favorable. A current detection signal can be obtained. If such a good current detection signal is used, a good current feedback signal for controlling the servo motor can be obtained, and it is possible to effectively prevent the torque and speed from varying in the control of the servo motor. .

[Brief description of drawings]

FIG. 1 is a block diagram showing an outline of an embodiment of the present invention, and FIG.
FIG. 4 is a block diagram showing a modified example of the signal correction circuit used in the present invention, FIGS. 3 and 4 are block diagrams showing different configuration examples of the sample and hold circuit used in the present invention, and FIG. FIG. 6 is a block diagram showing an example of a circuit that generates a current feedback signal used for controlling a motor.
The figure is a signal wave system diagram for explaining the operation of the circuit of FIG. 1 ... Current detector, 2 ... Noise signal elimination circuit, 3 ... Rotor position detection circuit, 4 ... Sample and hold circuit, 7
...... Signal correction circuit, 4a ...... A-D converter, 4b ...... Digital latch circuit, 4c ...... D-A converter, 4d ......
Comparator, 4e ... Up-down counter.

Claims (3)

[Claims] 1. A brushless driven by a rectangular wave current.
A servo motor control current detection circuit for detecting a phase current of the servo motor and outputting a current detection signal for controlling the servo motor, comprising: a current detector for detecting a predetermined phase current of the servo motor; A rotor position detection circuit that detects the rotational position of the rotor of the motor and outputs a rotor position signal, and a offset position signal that is sampled by a predetermined position signal of the rotor and receives the detection output signal of the current detector. A servo motor control current detection circuit comprising: a sample and hold circuit for outputting; and a signal correction circuit for correcting the detection output signal of the current detector with the offset signal and outputting the current detection signal. . 2. An A / D converter for converting a detection output signal of the current detector into a digital amount, the sample and hold circuit being instructed by a predetermined position signal of the rotor.
A digital latch circuit that holds the output signal of the A-D converter, and a D- that receives the held signal of the digital latch circuit and converts it into an analog amount and outputs the offset signal.
The servo motor control current detection circuit according to claim 1, comprising an A converter. 3. The sample / hold circuit calculates and holds the output signal of the comparator instructed by a comparator receiving a detection output signal of the current detector at one input terminal and a predetermined position signal of the rotor. An up / down counter, a DA converter for receiving the signal held by the up / down counter, converting the analog signal into an analog amount, outputting the offset signal, and applying the offset signal to the other input terminal of the comparator. The current detection circuit for controlling a servo motor according to claim 1.