JPH0218700Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a characteristic testing device for an amplifier for a two-phase AC servo motor, which automatically measures the characteristics of an amplifier for a two-phase AC servo motor.

A two-phase AC servo motor is sometimes used in a position control servo mechanism used in a recorder or the like. This servo motor includes two-phase coils: an excitation coil to which an alternating current excitation signal of constant amplitude is applied, and a control coil to which a control signal is applied. The control signal is output from an amplifier installed in front of the servo motor, and is a signal for controlling the rotation speed and direction of the servo motor. In an amplifier that sends out such a control signal, important characteristics include offset voltage, residual voltage, gain, and maximum output voltage. Conventionally, these characteristics of an amplifier have been measured by manually adjusting the input to the amplifier while visually observing the state (rotational speed and direction) of the AC servo motor.
In this case, there were drawbacks such as poor measurement accuracy and time-consuming measurement.

The present invention was developed in view of these points, and is a servo motor that can automatically measure each characteristic of an amplifier by using a circuit equivalent to a motor without using a two-phase AC servo motor. The purpose of this project was to provide a characteristic testing device for amplifiers.

The present invention will be explained in detail below using the drawings. FIG. 1 is an explanatory diagram of the electrical configuration of an embodiment of the servo motor amplifier characteristic testing device according to the present invention. In Fig. 1, 1 is an amplifier under test for a two-phase AC servo motor, 2 is a phase detection circuit, 3 is a subtracter,
4 is an integrator, 5 is a divider, and 6 is an average value rectifier circuit.

The amplifier 1 generates an AC signal (a sine wave modulated with a phase shift of ±90° from the excitation input of the two-phase servo motor) according to the output signal (DC voltage) of the integrator 4 applied to the input terminal. This is what is output.
The amplitude of this AC signal (that is, the control signal) is proportional to the magnitude of the input signal, and its phase is shifted by ±90° from the excitation input of the two-phase AC servo motor, but which polarity it takes is determined by the input signal. Depends on polarity.

The phase detection circuit 2 is an equivalent circuit of a two-phase AC servo motor (why it can be an equivalent circuit will be explained later),
The output of the amplifier 1 (control signal to the two-phase AC servo motor) is input to one input terminal, and a signal corresponding to the excitation signal to the two-phase AC servo motor is input to the other input terminal. The subtracter 3 provides the integrator 4 with the difference between the output of the phase detection circuit 2 and the reference value V _ref .

The divider 5 has its numerator input terminal connected to the output terminal of the phase detection circuit 2 and its denominator input terminal connected to the output terminal of the integrator 4, so that the output of the phase detection circuit 2 is connected to the integrator 4.
It is divided by the output of . Average value rectifier circuit 6
converts the alternating current signal of the amplifier 1 into direct current, and its input end is connected to the output end of the amplifier 1. Next, the principle of the phase detection circuit 2 will be explained. FIG. 2 is a configuration explanatory diagram showing a specific example of the phase detection circuit 2. As shown in FIG. In Fig. 2, 21 is a multiplier, and the input e ₁
(corresponding to the control signal to the two-phase AC servo motor) and the reference input e ₂ (corresponding to the excitation signal to the two-phase AC servo motor).

22 is a first-order lag circuit with a transfer function of 1/(1+T ₁ ·S), the input end of which is connected to the output end of the multiplier. Here, it is assumed that the input e ₁ and the reference input e ₂ are each expressed as follows.

e ₁ = e _s (t) sin (ω _c・t+φ) (1) e ₂ = Asinω _c・t (2) However, e _s (t) is the peak value of e ₁ , and
This is a signal containing very low frequency components compared to ω _c .

Further, A is a constant, ωc is an angular velocity, and φ is a phase.

The output e ₁₂ of the multiplier 21 is e ₁₂ = e _s (t)・A・sin(ω _c・t+φ)×sinω _c・t e _s (t)・A・cosφ +e _s (t)・A・(sin (ω _c ·t)×cos (ω _c ·t) sinφ −cos ² (ω _c ·t) cosφ) (3), and this output signal is given to the first-order lag circuit 22. Here, if the time constant T ₁ of the first-order lag circuit 22 is selected so that 1/T ₁ ≪ω _c , the circuit 22
The output Y of is the first-order lag circuit 22 whose term includes _ω
Since it is filtered and attenuated by , it can be approximated by the following equation.

Y=A・cosφ/1+T ₁・_S・es (t) (4) However, S is Laplace's operator.

What is shown in FIG. 3 is a block diagram of a two-phase AC servo motor, in which the control signal e _c given to the control coil is transferred via a transfer element 31 with a transfer function K _T to a transfer function K _n /(1+T _n S ) first-order lag circuit 32
given to.

In the present invention, the final output of the two-phase AC servo motor is the rotational speed of the motor, and the reason is as follows. The motor displacement of a two-phase AC servo motor is the integral of the motor rotational speed generated by the residual voltage and offset voltage, and its value changes depending on the initial value of the displacement and the transient state of the test. Therefore, it is extremely inconvenient to use the motor displacement as the final output of the two-phase servo motor, and it is appropriate to use the motor rotational speed as the final output here.

Now, the output of the first-order delay element 32 is the rotational speed of the motor, and is expressed as follows.

=Km・K _T /1+Tm・S・e _c =Km・K ₀・e _r・sinα/1+Tm・S・e _c ……(5) However, K _T =K ₀・e _r・sinα K ₀ : Constant e _r : Peak value of excitation signal (sine wave) (constant value) e _c : Peak value of control signal (amplifier output = sine wave) α: Phase difference between excitation signal and control signal K _n : Constant T _n : Hours Constant Here, if we adjust each component of the phase detection circuit so that φ=α−90° A=K _n・K ₀・e _r T ₁ =T _n , we can obtain the equation (4) above. Equation (5) is isomorphic, e _c corresponds to e _s (t), and corresponds to Y, respectively.
The phase detection circuit 2 is equivalent to a two-phase AC servo motor.

A specific example of such a phase detection circuit is shown in the fourth section.
As shown in the figure. In the multiplier 21, A1 is an operational amplifier, which has an input resistor _R1 and a feedback resistor _R2 , and has an input _e1
It is an inverting amplifier that inverts and amplifies. The output of this inverting amplifier is led to _FETQ1 via resistor _R4 . Furthermore, the input e ₁ is led to the output of the FET via a resistor R ₅ having a sufficiently large resistance value.

The diodes D ₁ and D ₂ are connected in antiparallel between the input end of the FET and the common line, so that only a voltage smaller than about ±0.5V is applied to the FET.

Q ₂ is a pnp type transistor, and the reference input e ₂ is applied to its base via a resistor R ₆ , and a diode D ₃ is connected between the base and emitter to prevent current from flowing into the base. It acts to branch. In addition, the emitter of transistor Q ₂ is connected to the common line (OV line), and the collector is connected to a negative voltage −V _E through resistor R ₇ .
is applied. And the collector output is as above
It is guided by the FET gate.

In such a multiplier, transistor Q ₂
The collector voltage of is −V _E when the reference input e ₂ corresponding to the excitation signal of the servo motor is positive, and becomes a negative voltage corresponding to e ₂ when it is negative. This collector voltage is applied to the gate of the FET, but if -V _E is applied, the FET is in the off state (approximately 0.5V between the drain and source of the FET), and is input via the resistor _R5. Only the current corresponding to e ₁ is output.
(However, this current is small enough).

When the reference input e ₂ is negative, the corresponding collector voltage (a negative voltage close to OV) is
Since the voltage is applied to the gate of the FET, the FET enters the active region and performs amplification on the current corresponding to the voltage when the input _e1 is positive. Note that at this time, the resistance
A current is output through _R5 , but this current value is sufficiently small.

This ensures that when input e ₁ is positive and the reference input
Multiplication of both signals is performed only when e ₂ is negative, and therefore a current (pulsating current) approximately corresponding to the multiplied value is output.

The first-order lag circuit 22 has a parallel connection circuit of a resistor R ₈ and a capacitor C ₁ connected to the feedback path of the operational amplifier A2, and has a transfer function of 1/(1+T ₁ ) and a time constant T ₁ of 1/T ₁ 《 The output of the _FET is filtered to obtain the output voltage Y expressed by the equation (4).

In such a feedback loop of the phase detection circuit 2, integrator 4, and amplifier 1, the subtracter 3
is automatically controlled so that the output is zero. In other words, since the DC gain of the integrator can be considered infinite,
The output X of the integrator 4 is given to the amplifier 1 so that the output Y of the phase detection circuit 2 and the reference value V _ref match. In other words, the rotation speed of the two-phase AC servo motor can be specified by the reference value V _ref .

Measurement of each characteristic is performed as follows.

Note that the rotational speed of the motor is related not only to the output voltage of the amplifier (control signal e _c ), but also to the phase difference α between the excitation signal and the control signal, as shown in equation (5) above. Therefore, when measuring the effective values of offset voltage, residual voltage, gain, and maximum output voltage below, observe the values based on the output of the phase detection circuit, which is the product of the peak value and sin α. There is a need.

(b) Measurement of offset voltage The reference value V _ref corresponds to when the motor stops rotating with the gain of amplifier 1 maximized.
Measure the input voltage X of amplifier 1 when is 0.

(b) Measurement of residual voltage The output of the amplifier 1 in the state of item (a) above is read by the average value rectifier circuit 6.

(c) Measurement of gain Read the output Z of divider 5. In this case, it is advantageous to set the reference value V _ref to as large a value as possible within a range that does not saturate the amplifier 1, since the calculation error in the divider 5 will be reduced.

(d) Measurement of the maximum output voltage Set the reference value V _ref to a value much larger than the expected maximum output voltage of the amplifier 1, and measure the output Y of the phase detection circuit 2 or the output AV of the average value rectifier circuit 6 at this time. I Read.

In this way important characteristics of the amplifier 1 can be measured automatically.

As explained above, according to the servo motor amplifier characteristic testing device of the present invention, a phase detection circuit equivalent to a two-phase AC servo motor is used without connecting the motor, and the amplifier under test and By configuring a feedback loop with a phase detection circuit and an integrator that compares the output of this phase detection circuit with a reference value and integrates the difference, each important characteristic of the amplifier, namely offset voltage, residual voltage, The gain and maximum output voltage can be easily and automatically measured by setting the reference value V _ref , which has the advantage of being effectively used for adjusting or inspecting the amplifier.

[Brief explanation of drawings]

FIG. 1 is an electrical configuration diagram showing an embodiment of the servo motor amplifier characteristic testing device according to the present invention, and FIG. 2 is a configuration diagram showing an embodiment of the phase detection circuit used in the device shown in FIG. 1. 3 is a block diagram of a two-phase AC servo motor, and FIG. 4 is a configuration diagram showing a specific example of a phase detection circuit. 1... Amplifier, 2... Phase detection circuit, 3... Subtractor, 4... Integrator, 5... Divider, 6... Average value rectifier circuit, 21... Multiplier, 22... First-order lag circuit.

Claims (1)

[Claims for Utility Model Registration] Receiving a DC voltage, the excitation signal of a two-phase AC servo motor is phase modulated by +90° or -90° depending on its polarity, and the peak value corresponds to the magnitude of the DC voltage. A device for testing the characteristics of an amplifier for a two-phase AC servo motor that outputs a control signal of a sine wave corresponding to the multiplication value of the output signal of the amplifier for the two-phase AC servo motor and the excitation signal. The multiplier that obtains the output and the transfer function are 1/(1+T ₁・S) [where T ₁ is the time constant, S is Laplace's operator, and 1/
T ₁ is sufficiently smaller than the angular velocity ω _C of the output signal of the amplifier, and the input signal corresponds to the output of the amplifier for the two-phase AC servo motor. When the input signal e ₁ and the input signal e ₂ corresponding to the excitation signal of the two-phase AC servo motor are expressed by the following equations (1) and (2), the rotational speed of the two-phase AC servo motor is expressed by the following equation (3). A phase detection circuit that sends out a corresponding output Y, and integrating the difference between the output of this phase detection circuit and a reference value corresponding to the rotational speed given from the outside, and sending the integrated output to the amplifier for the two-phase AC servo motor. a divider that divides the output of the phase detection circuit by the output of the integrator, and an average value rectifier circuit that rectifies the output of the two-phase AC servo motor amplifier to obtain an average value thereof. , set the reference value appropriately and equivalently set 2.
By controlling the rotation speed of the phase AC servo motor and measuring the outputs of the integrator, average value rectifier circuit, divider, and phase detection circuit, the offset voltage, residual voltage, and gain of the amplifier for the two-phase AC servo motor can be determined. , a characteristic testing device for a servo motor amplifier, characterized in that it is capable of measuring the maximum output voltage, respectively. e ₁ = e _s (t) sin (ω _c・t+φ) (1) e ₂ = Asinω _c・t (2) where A is a constant, ω _c is angular velocity, and φ is phase Y=A・cosφ/1+T ₁・S・e _s (t) (3)