JPH04117198A - Ac servo motor controller - Google Patents

Abstract

PURPOSE:To reduce a cost by deenergizing during rotation, measuring a voltage between phases from arbitrary two terminals, calculating an intrinsic phase angle, correcting a phase angle including a phase error to a true phase angle, and controlling a current. CONSTITUTION:A 3-phase AC servo motor is current-controlled by using a function of a phase angle thetaalpha having possibility of including an error to be rotated, a driving current is set to '0' during rotation to rotate the motor in an deenergized state. Induced voltages proportional to a rotating speed are generated in the phases of the motor rotating in the deenergized state. In this case, the voltage of U phase with V phase as a reference has a predetermined relation, and the voltage generated at this time has a function of the true phase angle and the speed. The motor is rotated by using the true phase angel theta. That is, the angle is obtained from the observed value of the voltage between terminals, and the motor is rotated by a driving current having the true phase angle from the driving current of the phase angle including an error.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is used in control devices for robots, machine tools, automatic assembly machines, etc. equipped with AC servo motors.

[Summary of the invention]

In the present invention, a three-phase AC servo motor that rotates at a drive current phase angle θα that may include an error is reduced to zero drive current.
By setting the AC servo motor in a non-excited state and measuring the phase-to-phase current from any two of the three current terminals, the true phase angle θ is calculated, and from this the true phase angle θ is calculated. The present invention provides an AC servo motor control device that maximizes the power factor at the corrected angle by correcting the phase angle θα including a phase error to the true phase angle θ.

[Conventional technology]

In each of the U, V, and W phases of a three-phase AC servo motor using a permanent magnet as a rotor, a magnetic field is generated that is uniquely determined by the phase angle as shown in Equation 1. However, for convenience, each of the three phases is
, V, and W phases. At this time, when a current expressed by the second equation is passed through each phase, a torque expressed by the fourth equation is generated. This is the principle of torque generation in an AC servo motor.

KTLl= Kro ・sinθ KTV= KTO' 5tn(θ-2π/3) Krw=
Kto-sin(θ+2π/3) (1st formula) Iu
"Io -5inθa Iv = T, -5in(01~2π/3)T,
= I, -5in (θ1+2π/3) (2nd equation)
K tus K 79% K yw is U, V, W
For each phase, it represents the torque generated per unit drive flow and is a function of the phase angle. K. is a proportionality constant.

Iu, ■9.1 HA U, V, w are the driving fl currents of each phase, and Io represents the amplitude of the current value. A sinusoidal t current value corresponding to the second waveform is artificially generated using a current control circuit or the like.

However, the third equation is established between the first equation and the second equation, and α in the equation is the error between the true phase angle θ and the drive current phase angle θα for IIT flow control.

At this time, the phase angle error satisfies -π≦α≦π.

Further, it is clear that the differential value of the phase angle including the phase error and the differential fall of the true phase angle match because the differential value of the phase error becomes 0.

θ α= θ + α - θα = θ (3rd formula) % formula % - 1.5 ・KTO・I o ・cosα (
Equation 4) If the phase angle error can be set to α-0, it is proven from Equation 4 that the AC motor can be driven with the maximum power factor.

Conventionally, methods for determining the phase angle θ used in AC motor current control include mounting an absolute encoder that outputs an absolute angle, and providing a position detector with a function that outputs a signal pulse representing the origin of one revolution of the motor. can be mentioned. When manufacturing both motors, it is necessary to match the phase angle of the signal from the position detector and the magnetic field.

At this time, when the signal is detected, the control device corrects the phase angle of current control to the true phase angle.

Another known method is to measure and utilize the induced voltage, but this method controls the current in a rectangular waveform by comparing the magnitude of the phase-to-phase voltage of a type of AC motor that generates a trapezoidal induced voltage. there were.

[Problem to be solved by the invention]

If you use the conventional method to control the gL flow in a sinusoidal manner as in the second equation according to the rotation angle, you can use an absolute encoder or
Using a position detector that has a phase detection signal synchronized with the three phases of W, perform rectangular wave type current control and rotate until the origin position is recognized. After detection, the phase angle is corrected again and the sine wave type The only option is to switch to current control.

However, the former method may increase the volume of the position detector to some extent, which is unreasonable for today's robots and small equipment where only a narrow space is allowed for motor placement during design, and increases costs. There are cases where this happens. In the latter case, the number of wires increases, making it difficult to incorporate it into devices that allow only a narrow space for wiring, as in the former case.

Further, in a control device that performs rectangular wave current control using induced voltage as described above, there is a risk that torque ripple may occur, causing noise and vibration.

[Means to solve the problem]

In order to solve the above problems, the present invention provides a driving current that is a function of the phase angle θα that may include an error.
By rotating the AC servo motor by current control, then returning the drive current to O during rotation to make it in a non-excited state, and further measuring the phase-to-phase voltage from any two of the three rotating terminals, The true phase angle θ is calculated, and the phase angle θα including the phase error that was previously used for current control is corrected to the true phase angle θ. From then on, the current control is performed using the corrected phase angle. This is an AC servo motor control device that maximizes the power factor by realizing this.

[Effect]

When an AC motor is driven and rotated, and each terminal is in a dynamically excited state during rotation, the drive torque becomes 0, but since the motor is rotating, only the induced voltage is generated between the two terminals. Therefore, observing the voltage between the terminals is equivalent to observing the induced voltage.

The true phase angle is determined from the observed value of the voltage between the terminals,
The motor is rotated by a drive current having a true phase angle from a drive current having a phase angle including an error.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

In this example, an example will be explained based on two phases, the U and V phases, among the U, V and W phases, but it can also be applied to other two phases by replacing them with the V, W phase or the U phase. The same can be applied.

Using the second equation, which is a function of the phase angle θα, which may include an error, the 3-phase AC servo motor is controlled by W! It is rotated by controlling, and during rotation, the drive current is set to O and A
Rotate the C servo motor in a non-excited state. As shown in FIG. 2, an induced voltage proportional to the rotational speed is generated in each phase of a motor rotating in a non-excited state. KE is the induced voltage constant, which is physically. is equivalent to At this time,
The voltage of the U phase based on the phase (2) is expressed by the fifth equation.

However, the voltage generated at this time is a function of the true phase angle and speed.

VLI-V-su-Vv=KEsinθ・θ-KHsi
n(θ-2π/3)-θ-Kt ・19 (s1nθ-
5in(θ-2π/3))=KE' θ((1-c
os(2π/3) s inθ+5in(2π/3)
cosθ)"Kv' /j (3/2 ・sinθ÷
31't/2・Cosθ−(3) ””・Kt−e
-5in (θ1/6) (Equation 5) Since the induced voltage between the terminals satisfies Equation 5, the phase angle θ can be determined from Equation 5. Then, the motor is rotated using the obtained true phase angle θ.

A detailed explanation will be given below based on FIG.

AC servo motor 1 has three terminals U for driving tJVW phase.
, V, and W, and also has a position detector 2 consisting of a rotary encoder that generates a pulse every time the rotation angle of the rotor changes by the resolution. However, it is assumed that the position detector 2 does not have the function of holding phase angle information.

The U, V, and W terminals are connected to a power amplifier circuit 3 called a PWM inverter in the m-control device. The output of the current control circuit 4 is input to the PWM inverter, and the output of the current control circuit 4 receives the U-phase and V-phase B? Feedback signals FU and Fv corresponding to the detected values of the currents flowing through the X command signals 1u and Iv and the terminals of the U phase and ■phase are input, and an input signal for the PWM inverter is created and output.

The reason why there are only two phases of current command signal and t-current feedback fs is that the remaining third phase current has a current value that is the negative sum of the two phases, and is usually omitted.

The output of the phase detector 2 is input to a counter circuit 5. In the counter 5, since the initial value corresponding to the initial phase angle is unknown when the power is turned on, the control section 6 gives an arbitrary phase angle value θα as the phase angle command value. Therefore, any phase angle value θα includes an error with respect to the true phase angle θ, and there exists an initial jiJl error angle α between the true phase angle θ and the counter value θα given by the third equation. do.

Therefore, when the AC servo motor rotates thereafter, the phase angle value θα inside the counter 5 will continue to be updated by the pulses generated by the position detector 2.

The control unit 6 calculates the phase angle θ of the counter 5 based on the second equation.
Current command signals 1u and Iv are calculated using α and output to the current control section 4. The current control unit 4 controls the current flowing through the terminal U to a t-flow command 8. The current is controlled so that the t-flow flowing through the terminal V matches the t-flow command 1v. Then, as a result, the AC servo motor generates a torque represented by No. 4, and the motor starts rotating.

Note that if cosα in the fourth equation is close to 0 and the motor does not rotate due to friction etc., the control unit 6 adjusts the phase angle θα held in the counter 5 by a fraction of the rotational resolution. - is corrected by addition or subtraction of an appropriate phase difference, and outputted again to the counter circuit 5 as a phase angle command value θα, and the motor is rotated by performing t-flow control based on the second equation.

Next, a procedure for determining the true phase angle in the control section ε and controlling the rotation of the motor using the determined phase angle will be described with reference to FIGS. 4 and 5. FIG. 5 is a detailed explanatory diagram of the phase angle correction algorithm in 5T-6 of FIG. 4. Control unit 6
First, the arbitrary phase angle command value θα according to the second formula is output to the counter circuit 5, and the motor is rotated by performing the t-flow control as described above (ST~1).Next, the control unit 6 The counter circuit 5 samples the phase angle data θα twice and calculates the rotation direction based on the sign of the difference. Alternatively, the differential velocity data θα−cut of the phase angle value θα obtained from the counter circuit 5 may be calculated (see equation 3), and the rotation direction may be determined using the sign thereof (ST-2).

Next, while the AC servo motor is rotating, the control unit 6 sets the current command value to 0 to put it in a non-excited state and rotates the motor (βT-3).

During this rotation in the non-excited state, the voltage VU-V between the two terminals of the U phase and ■ phase is detected by the differential amplifier circuit 7. The signal is taken into the control unit 6 via the A/D conversion circuit 8 and observed.

That is, the voltage between the two terminals that is output to the control unit 6 is sampled twice at a sufficiently short sampling time (for example, several m5ec) with respect to the rotation period of the motor in the non-excited state.
Read the voltage between two terminals. From these two data, it is also possible to know the increase or decrease in the voltage between the terminals (ST-4).

This two-terminal voltage satisfies the fifth equation as described above.

V u−v= (3)””・KE・θ・5in
(θ1π/6) (Formula 5) Therefore, θU−V−θ−π
/6, and the phase angle (θ-π/6) is calculated using the 6th point from the terminal voltage of VU-9 and θ obtained by (ST-2).
That is, θ, -9 is obtained (ST-5).

θLl-V-θ+π/6=sin-' (VU-v/(
3”” ・ni, ・θ) (6 formulas) θ−θ, −1−π/6 (7 formulas)
The true phase angle θ can be found by knowing 7th 2<vll-9.

By the way, the value of VU-V and the phase angle θ obtained in the 6th step from i. As shown in FIG.
Even if U-v is originally a value in the second or third quadrant, a solution cannot be obtained, so next we perform quadrant correction based on the rotation direction, the sign of the induced voltage, and the amount of change in the induced voltage ( ST~
6).

Using Figures 5, 6, and 7, 5T-6 in Figure 4
The method of quadrant correction will be explained below.

5T-51 in Fig. 5 is a branch determined by the rotation angle direction obtained in Fig. 4 5T-2, and if it is positive, 5T-52
Proceed to. 5T-52 is the terminal voltage ■ sampled twice in Figure 4, 5T-4. This is a branch determined by the sign of the change of -1, and if it is positive, the process moves to the next step without performing quadrant correction. The above corresponds to ■ and ■ in FIG. If 5T-52 in FIG. 5 is negative, the inter-terminal voltage ■ proceeds to 5T-54. It branches at the sign of -9 and performs 5T-56 or 57 quadrant correction.

This corresponds to ■ and ■ in Figure 6.

If 5T-51 in FIG. 5 is negative, proceed to 5T-53.

If the result in FIG. 4, 5T-4, is negative, the process returns to no quadrant correction. This corresponds to ■ and ■ in Figure 7. If positive, proceed to 5T-55, branch depending on the sign of observed voltage Vυ1, and proceed to 5T in Figure 5.
-58, 59, 0 or more corresponding to ① and ② in Fig. 7 are explanations of Fig. 5, and correspond to 5T-6 in Fig. 4.

By performing quadrant correction of θゎ−1 in this way, the fifth
As shown in the figure, one of the solutions for θu-v from ■ to ■ is obtained.

Here, the explanation will be given by returning to FIG. 4 again. 5T- in Figure 4
In step 7, the true phase angle θ is calculated using equation 7 based on the solution of θu-v obtained through quadrant correction in 5T-6. Then, the control unit 6 outputs the calculated true phase angle θ as a phase angle command value, and newly writes it into the counter circuit 5.

With the above procedure 111N, the phase angle error α automatically becomes 0, and subsequent current control is performed at a power factor of 100%.

〔Effect of the invention〕

As described above, according to the present invention, sinusoidal current control of an AC servo motor can be performed without using an absolute encoder or an origin signal. Also, is there a general-purpose AC servo motor system that does not affect the detection function even if you use an absolute encoder with a different NM for each motor or a motor with a different type of home position signal? 11 device.

The above control allows the AC servo motor to generate a drive torque independent of the phase angle, making it easy to appropriately configure speed control, position control, and force/compliance control loops outside the control circuit.

[Brief explanation of drawings]

The first panel shows an embodiment of the present invention, and shows a diagram of an AC servo motor and its control device. Figure 2 shows the induced voltage generated in the AC servo motor. Figure 3 shows a sine wave signal. Figure 4 shows the phase angle calculation algorithm. Figure 5 shows the angle correction method. In the figure, Δθ represents the amount of rotational change when sampling twice or multiple times, and ΔθU-V represents the same amount of rotation. Figures 6 and 7 show the amount of voltage change during sampling, and Figure 7 shows the phase angle of the sinusoidal voltage generated between two terminals for positive and negative rotation directions, respectively. figure,
Conditions (1) to (2) in FIG. 7 correspond to each other. AC servo motor position detector Power amplifier circuit Current control circuit Counter circuit Control section Differential amplifier circuit A/D conversion circuit

Claims (1)

[Claims] For three sets of AC servo motors that use permanent magnets in their rotors, the induced voltage generated in each phase during rotation due to the magnetic field generated by the permanent magnets is measured by detecting the voltage between two of the three terminals. means for estimating and calculating the phase angle of the magnetic poles of the motor based on the measurement signal;
An AC servo motor control device comprising means for controlling current using the phase angle.