JPH0452482B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention can be used to measure and adjust the characteristics of servo circuits when mass producing servo circuits for tape recorders, VTRs, record players, compact disc players, etc. The present invention relates to a suitable loop gain measurement method for a servo circuit.

Background technology and its problems Tape recorders, VTRs, record players,
In compact disc players and the like, a servo circuit as shown in FIG. 1 is used to control driving means such as motors. In FIG. 1, 1 is a drive amplifier circuit that generates a drive signal to drive a drive means 2 such as a motor, and 3 is a drive amplifier circuit that determines whether or not the drive means 2 such as a motor is being driven at a predetermined speed, for example, at a predetermined rotation speed. This is an error amplification circuit that detects the error and generates a control signal according to the detected error. In FIG. 1, a drive amplifier circuit 1 is controlled by a control signal output from an error amplifier circuit 3, a drive signal corresponding to this control signal is generated, and this drive signal is used to drive a motor or other drive means. 2.

Conventionally, open-loop and closed-loop characteristics (gain, phase) measurement of such a servo circuit was performed by disconnecting the output side of the error amplifier circuit 3 and the input side of the drive amplifier circuit 1, as shown in FIG. 3 is connected to the non-inverting input terminal of the operational amplifier circuit 4 via a resistor R having a predetermined resistance value R, and this non-inverting input terminal is grounded via a resistor 6 having a resistance value R. The disturbance signal V _G from the signal source 8 is supplied to the inverting input terminal of the operational amplifier circuit 4 through a resistor R having a resistance value R, and the output terminal of the operational amplifier circuit 4 is connected to the output terminal through a resistor R having a resistance value R. The output terminal of the operational amplifier circuit 4 is connected to the input terminal of the drive amplifier circuit 1, and the voltage V _Y between the output terminal of the error amplifier circuit 3 and the ground is measured and calculated. This was done by measuring the voltage _VX between the output terminal of the amplifier circuit 4, that is, the input terminal of the drive amplifier circuit 1, and the ground. In this case, the gain of the drive amplifier circuit 1 is G ₁ ,
When the gain of the error amplifier circuit 3 is G ₂ and the gain of the driving means 2 such as a motor is G _T , the total open loop gain G ₀ of this servo circuit is G ₀ =G ₁・G ₂・G _T , Also, if the voltage of the disturbance signal is V _G , then V _G −V _Y = V _X V _Y = V _X・G ₁・G ₂・G _T. Therefore, this open-loop gain G ₀ is G ₀ = |V _Y |/|V _X |, and this closed-loop gain G _C is G _C =G ₀ /|G ₀ +1=|V _Y |/|V _G | It is. Therefore, as mentioned above, the disturbance signal V _G given to the servo circuit, the resulting error signal V _Y , and the disturbance signal
The gain and phase of the servo circuit can be measured by the difference between V _G and the error signal V _Y (V _G −V _Y ).

However, in the conventional method of measuring the loop gain of a servo circuit, it is necessary to disconnect between the output side of the error amplifier circuit 3 and the input side of the drive amplifier circuit 1 of the servo circuit, and it is necessary to disconnect the loop gain on the printed circuit board. In the case of a servo circuit that cannot be cut, such as a formed servo circuit, it is necessary to construct the servo circuit in advance in such a way that the servo circuit can be cut only for this loop gain measurement and that the above-mentioned arithmetic circuit 4 etc. can be connected. It was hot.

OBJECTS OF THE INVENTION In view of the above, an object of the present invention is to enable loop gain measurement without disconnecting the servo circuit.

Summary of the Invention The present invention provides a first resistor connected between an error amplification circuit and a drive amplification circuit of a servo circuit, the drive amplification circuit side of which is grounded via a second resistor, and the first resistor connected between an error amplification circuit and a drive amplification circuit. A disturbance signal is supplied to the drive amplifier circuit side of the first resistor via a third resistor, and a first voltage between the error amplifier circuit side of the first resistor and the ground and the drive of the first resistor are supplied. The second voltage between the amplifier circuit side and the ground is measured, and a loop is created from the first and second voltages, the voltage of the disturbance signal, and the resistance values of the first, second, and third resistors. According to the present invention, the loop gain can be measured without disconnecting the servo circuit.

Embodiment An embodiment of the method for measuring the loop gain of a servo circuit according to the present invention will be described below with reference to FIG. In FIG. 3, parts corresponding to those in FIG. 2 are designated by the same reference numerals, and detailed explanation thereof will be omitted.

In this example, connection terminals 6a and 6b are provided at both ends of a resistor 5 having a predetermined resistance value, which is connected between the error amplification circuit 3 and the drive amplification circuit 1 of the servo circuit.

When measuring the loop gain of this servo circuit, connect terminal 6 of this resistor 5 on the drive amplifier circuit 1 side.
b is grounded via a resistor 7 having a predetermined resistance value, and a disturbance signal V _G from a disturbance signal source 8 for measurement is supplied via a resistor 9 to this connection terminal 6b.
The resistors 7 and 9 are used to supply a disturbance signal V _G from the outside to this servo circuit, and the resistance value of the resistor 9 is compared with the signal source impedance of the disturbance signal source 8 and is set to a sufficiently large value. In this case, it is assumed that the input impedance of the drive amplifier circuit 1 is sufficiently high and the output impedance of the error amplifier circuit 3 is sufficiently low.

The voltage V _Y between the connection terminal 6a of this resistor 5 on the error amplification circuit 3 side and the ground, and the connection terminal 6
Measure the voltage _VX between b and the ground using voltmeters with sufficiently high impedance.

The open loop gain G ₀ in FIG. 3 is calculated as G ₀ = |V when the resistance value of resistor 9 is R ₁ , the resistance value of resistor 5 is R ₂ , and the resistance value of resistor 7 is R _{3 Y ｜ / ｜ V _ _ _ _ _ _ _ _ _ _} If it is determined, the open loop gain G ₀ can be determined by measuring the voltages V _X and V _Y without disconnecting the servo circuit.

The closed loop gain G _C is as follows. _{Here , G 0 = KV Y / V X V _ _ _ _ _ _ _ _} /R ₃ R ₂ +R ₁ K ₂ =R ₁ R ₃ /R ₁ R ₃ +R ₂ =
KV _Y /G ₀ = K ₁ V _G −K ₂ V _Y K ₁ K _G = K (1 + G ₀ / G ₀ ) V _Y , and the closed loop gain G _C is G _C = G ₀ /1 + G ₀ = V _Y /V _G K ₁・K.

Therefore, if the constant _K1 ·K is found in Figure 3, the closed loop gain G _C of the servo circuit can be found without disconnecting the servo circuit by measuring the voltage V _Y and the voltage V _G of the disturbance signal. can.

It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations may be adopted without departing from the gist of the present invention.

Effects of the Invention According to the present invention, the loop gain of the servo circuit can be measured without cutting the loop. Therefore, the present invention is extremely effective when used for measuring, adjusting, etc. the characteristics when mass-producing servo circuits.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an example of a servo circuit, Fig. 2 is a block diagram illustrating an example of a conventional method for measuring loop gain in a servo circuit, and Fig. 3 is a block diagram showing an example of a method for measuring loop gain in a servo circuit according to the present invention. FIG. 2 is a configuration diagram for explaining an example. 1 is a drive amplifier circuit, 2 is a drive means, 3 is an error amplifier circuit, 5, 7 and 9 are resistors, and 8 is a disturbance signal source.

Claims (1)

[Claims] 1. The drive amplifier circuit side of the first resistor connected between the error amplifier circuit and the drive amplifier circuit of the servo circuit is grounded via a second resistor, and the drive amplifier circuit side of the first resistor is grounded via a second resistor. A disturbance signal is supplied to the circuit side via a third resistor, and a first voltage is applied between the error amplifier circuit side of the first resistor and the ground, and a drive amplifier circuit side of the first resistor is supplied. A loop gain is determined from the first and second voltages, the voltage of the disturbance signal, and the resistance values of the first, second, and third resistors. A method for measuring loop gain of a servo circuit, characterized in that the loop gain of a servo circuit is obtained.