JPH0552158B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to ripple reduction in a circuit that detects a current flowing through a coil of a servo motor and feeds back a detection signal to drive the servo motor.

[Prior Art] As a voltage detection circuit for detecting the current flowing in the coil of a servo motor,
A "current detection circuit" was filed on November 6, 1961.
This circuit will be explained below.

The configuration of this current detection circuit is shown in FIG.

In the figure, _X1 is an input circuit, _X2 is an output circuit, and TR is a transformer.

The transformer TR has a primary winding n ₁ to which input circuit X ₁ is connected, and a secondary winding n ₂ to which output circuit X ₂ is connected.
and a tertiary winding n ₃ placed between the primary and secondary windings.

In the input circuit _X1 , 1 and 2 are input terminals to which line l is connected, and r is a resistor connected between input terminals 1 and 2. Since line l is connected in series with the coil of the motor, the resistor r is connected in series with the coil of the motor via terminals 1 and 2.

A series circuit of a resistor R ₁ and a capacitor C ₁ is connected in parallel to the resistor r. The resistance value of the resistor r is, for example, about 5 mΩ, which is sufficiently smaller than the resistance value of the resistor _R1 . Furthermore, a series circuit of a parallel diode circuit D ₁ and a primary winding n ₁ is connected in parallel with the capacitor C ₁ . The parallel diode circuit _D1 has diodes _D1 and _D12 connected in parallel with opposite polarities.

In the output circuit _X2 , 3 and 4 are output terminals. A low-pass filter (hereinafter referred to as
A series circuit consisting of LPF 5, resistor R ₂ and capacitor C ₂ is connected. A series circuit of a parallel diode circuit D ₂ and a winding n ₂ is connected across the capacitor C ₂ . Capacitor C ₂ constitutes the averaging means. The parallel diode circuit _D2 has the same configuration as the parallel diode circuit _D1 .

Voltage applied to parallel diode circuit _D1 , D2
The relationship between e ₁ and the flowing current i ₁ is a nonlinear relationship as shown in FIG.

OS is a pulse generator, connected to winding n ₃ through resistor R ₃ and capacitor C ₃ .

In a circuit configured in this way, if the turns ratio of the primary winding n ₁ of the transformer TR and the secondary winding n ₂ is 1:1, and an impulse signal with positive and negative symmetry is applied to the tertiary winding n ₃ , the equivalent The circuit becomes as shown in FIG.

In the equivalent circuit of Fig. 5, the input voltage E _i is rI
(The resistance value of the resistor r is also expressed by r).

Switches S ₁ and S ₂ are diodes D ₁₁ , D ₁₂ , D ₂₁ ,
This shows the switching operation of D _22. When a positive impulse is applied from the pulse generator OS, switches S ₁ and S ₂ are connected to the contact a side (diodes D ₁₁ and D ₂₁ are turned on). ), when a negative impulse is applied, switches S ₁ and S ₂ are connected to the contact c side (diodes D ₁₂ and D ₂₂ are conductive). Also, when no impulse is applied,
Switches S ₁ and S ₂ are connected to contact b (both diodes are non-conducting). Each diode D ₁₁ ~ _{D 22}
are both forward voltage Δ dynamic resistance (forward resistance)
It is represented by a series connection with r.

Now, when the positive impulse IO is being applied from the pulse generator OS, the switches S ₁ and S ₂
is equivalent to connected to contact a (diode
D ₁₁ and D ₂₁ are conductive), and the inverse io is connected to the diode D ₁₁ side and the diode D ₂₁ side as shown in the figure.
Divides the flow equally by io/2. In this state, the output voltage Eo ₁ between the output terminals 3 and 4 can be expressed by the formula.

Eo ₁ = Ei + Δ ₁₁ + io/2 (r ₁₁ − r ₂₁ ) − Δ ₂₁ In addition, when a negative polarity impulse io (the amplitude is the same as the positive polarity case) is applied, the voltage between output terminals 3 and 4 The output voltage Eo ₂ of can be expressed by the formula.

Eo ₂ = Ei + Δ ₁₂ + io/2 (r ₁₂ − r ₂₂ ) − Δ ₂₂ The impulses of positive and negative polarity from the pulse generator OS are:
As shown in Fig. 6A, if the voltage is applied at a repetition period T and the capacitances of capacitors C ₁ and C ₂ are made sufficiently large so that potential changes due to charging and discharging of impulses are small, the output voltage Eo becomes Eo ₁ and Eo ₂
It is the average value of , and can be expressed by the following equation.

Eo=E ₀₁ +E ₀₂ /2=Ei+1/2 (Δ ₁₁ −Δ ₁₂ −Δ ₂₁ +Δ ₂₂ )+io/4 (r ₁₁ − r ₁₂ − r ₂₁ + r ₂₂ ) In the formula, Δ ₁₁ = Δ ₁₂ , Δ ₂₁ =Δ ₂₂ r ₁₁ = r ₁₂ and r ₂₁ = r ₂₂ , the second term and the third term are both 0, and the output voltage Eo becomes equal to the input voltage Ei.
Therefore, the voltage Ei applied to the input circuit can be electrically isolated and taken out from the output circuit side.

Here, the conditions shown in the formula can be easily realized by using elements D ₁₁ and D ₁₂ and D ₂₁ and D ₂₂ that constitute the parallel diode circuit, respectively, of the same standard, or by maintaining them at the same temperature.

Figure 6 is an operating waveform diagram in Figure 5, where A is the impulse of positive and negative polarity from the pulse generator OS, B is the current shunted to the parallel diode circuits D ₁ and D ₂ ,
C is the output voltage. Here, the ripple portion of the output voltage Eo is exaggerated.

This voltage detection circuit can output a voltage equal to the input voltage with high precision even if the input voltage is small, so the resistance value of the resistor r connected to the input side can be reduced, reducing power consumption on the input side. It has the advantage of

When this current detection circuit is used in a servo motor drive circuit, the structure of the drive circuit becomes as shown in FIG. 7, for example.

In the figure, G ₁ to _{G 4} are the gates of transistors that control the current flowing to the coil L of the servo motor M, and 5
is a gate driver that drives gates _G1 to _G4 , 6
7 is a current detection circuit (corresponding to the current detection circuit in FIG. 3) that detects the current flowing through the coil L based on the voltage across the resistor r connected in series with the coil L;
8 is a high frequency cut filter that cuts the high frequency range of the detection signal of the current detection circuit 6; 8 is a subtracter that takes the difference between the current command value u and the current detection signal after passing through the high frequency cut filter 7; 9 is a phase of the difference signal. 10 is a pulse width modulation circuit that provides the gate driver 5 with a pulse width modulation signal generated based on the phase compensated signal.

[Problems to be Solved by the Invention] In such a drive circuit, when the response frequency of the current detector 6 is increased, the high-frequency cut filter 7 is essential to prevent large ripples from occurring in the output. Since this filter causes a phase delay in the feedback signal, there is a problem that harmful phenomena such as oscillation are likely to occur in the motor.

The present invention has been made to solve the above-mentioned problems, and provides a motor drive circuit that can effectively prevent ripples contained in the output of a current detection circuit without providing a high-frequency cut filter in the return path. The purpose is to

[Means for solving the problem] In a circuit that detects the current flowing through the coil of a servo motor using a current detection circuit and feeds back the detection signal to drive the servo motor, the current detection circuit isolates minute voltage signals. A circuit for detecting current at the timing of a timing clock using a transmitting small signal isolator, the first pulse generator generating a control clock when the timing clock is at a high level; A second pulse generator generates a control clock when the timing clock is at a low level, and a detection signal generated by the current detection circuit when the first pulse generator generates a pulse is held. a first sample and hold circuit that holds a ripple signal on the positive side; and a ripple signal on the negative side by holding a detection signal generated by the current detection circuit when the second pulse generator generates a pulse. A second sample-and-hold circuit holds the signals, and the signals held by the first sample-and-hold circuit and the second sample-and-hold circuit are added together to cancel the ripple signals on the positive and negative sides, and this signal is fed back. This is a motor drive circuit characterized in that it is provided with an adder that performs the following steps.

[Example] Hereinafter, the present invention will be explained using the drawings.

FIG. 1 is a configuration diagram of an embodiment of a motor drive circuit according to the present invention. In the figure, the same parts as in FIG. 7 are given the same reference numerals.

In the figure, 11 is the control clock CLK1
(hereinafter simply referred to as CLK1); 12 is a control clock;
A second clock generator generates CLK2 (hereinafter referred to simply as CLK2); 13 is a first sample and hold circuit that holds the output A of the current detection circuit 6 at the timing given by CLK1; 14 is a
A second sample-and-hold circuit that holds output A at the timing given by CLK2, 15
are the outputs B and C of sample and hold circuits 13 and 14.
This is an adder that adds up the addition signal D and returns the addition signal D to the subtracter 8.

The operation of such a drive circuit will be explained.

FIG. 2 is a time chart for explaining the operation.

In the figure, CLK is a timing clock that provides drive timing to the current detection circuit 6, which is generated by the pulse generator OS in FIG.

The current detection circuit 6 outputs an output A for an input waveform V.
A ripple occurs in synchronization with CLK. CLK1
is synchronized with the high level timing of CLK,
CLK2 is set to synchronize with the low level timing of CLK. As a result, the first sample and hold circuit 13 outputs A when CLK is at a high level (hereinafter referred to as positive ripple).
The second sample and hold circuit 14 samples and holds the output A (hereinafter referred to as negative ripple) when CLK is at a low level.

Since the ripple component of the output A is symmetrical with respect to the input waveform V, the sample and hold circuits 13 and 14
By adding the sum of the signals B and C held in the adder 15, the ripples on the positive side and the negative side are canceled and a signal like D is obtained.

[Effects] According to the present invention, since the ripples on the positive side and negative side of the output of the current detection circuit 6 are added and canceled, a high frequency band for ripple prevention is provided in the feedback path of the current detection circuit 6. There is no need to provide a cut filter. This improves the phase and frequency characteristics of the feedback signal, and prevents problems such as motor oscillation that would otherwise occur if a high-frequency cut filter is provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of a motor drive circuit according to the present invention, FIG. 2 is an explanatory diagram of the operation of FIG. 1, FIG. 3 is a diagram showing an example of the configuration of a current detection circuit, and FIG. FIG. 6 is an explanatory diagram of the operation of the circuit of FIG. 3, and FIG. 7 is a diagram showing an example of the configuration of a motor drive circuit to which the circuit of FIG. 3 can be applied. M... Servo motor, L... Coil, r... Resistor, 11... First clock generator, 12... Second clock generator, 13... First sample and hold circuit, 14... Third 2 sample hold circuit, 15...adder.

Claims (1)

[Claims] 1. In a circuit that detects a current flowing through a coil of a servo motor using a current detection circuit, and feeds back a detection signal to drive the servo motor, the current detection circuit is a micrometer that insulates and transmits a minute voltage signal. A circuit that detects current at the timing of a timing clock using a signal isolator, the circuit comprising: a first pulse generator that generates a control clock when the timing clock is at a high level; a second pulse generator that generates a control clock when the current detection circuit is at a low level; and a second pulse generator that generates a control clock when the first pulse generator is at a low level; a first sample-and-hold circuit that holds the ripple signal of the second pulse generator; and a second sample-and-hold circuit that holds the ripple signal on the negative side by holding the detection signal that the current detection circuit generates when the second pulse generator generates a pulse. an adder that adds the signals held by the first sample and hold circuit and the second sample and hold circuit, cancels the positive side and negative side ripple signals, and feeds back this signal. , A motor drive circuit characterized in that it is provided with the following.