JPS6264293A - Motor driving circuit - Google Patents

Abstract

PURPOSE:To prevent a torque ripple from generating even when an output torque is increased by correcting to cancel the tertiary torque ripple when the value of an exciting current increases. CONSTITUTION:A correcting circuit 9 generates a correction signal which is four times in frequency as large as exciting currents IA, IB (sinusoidal signals Ss, Sc) on the basis of the rotating angle thetam of a rotor generated from an angle calculator circuit 3 and proportional to the cube of a control signal Si in magnitude, and adds the signal to the signal Si. When signals having four times in frequency as large as the signals Ss, Sc are used as correction signals to be added to the signal Si if the amplitudes of the currents IA, IB become large, the tertiary torque ripple can be cancelled to obtain an output torque having less ripple.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention eliminates torque unevenness by supplying a sinusoidal excitation current with a different phase to a plurality of t-mature coils, and also eliminates torque unevenness. The present invention relates to a motor drive circuit configured to change the amplitude of the output torque according to a control signal and arbitrarily control the magnitude of the output torque.

[Conventional technology]

As mentioned above, as an example of a motor drive circuit that is free from torque unevenness and can arbitrarily control the magnitude of the output torque, the applicant of the present application has already developed a motor drive circuit in U.S. Pat.
There is a motor drive circuit filed as No. 030.

FIG. 3 is a configuration diagram showing an example of such a motor drive circuit. In the figure, l is a two-phase excitation type pulse motor,
2 is a high-resolution encoder connected to this pulse motor 1 and generates an output signal Sf according to the rotation angle θ of the pulse motor 1; 3 is a high-resolution encoder that calculates the rotation angle θm with respect to the magnetic pole of the pulse motor 1 from the output Sf of this encoder 2; 4 is a function generating circuit that generates sine wave signals Ss and Sc having a phase difference of 90'' depending on the rotation angle θm; 5.6 is a function generating circuit that generates sine wave signals Ss and Sc that have a phase difference of 90'' according to the rotation angle θm; a multiplier that changes the amplitude of the sinusoidal signals Ss, Sc;7.
8 is a power amplifier. Output IA of power amplifier 7.8,
rB is supplied to the armature coil of the pulse motor 1, respectively. That is, the position of the rotor in the pulse motor 1 is detected by the encoder 2 and the angle calculation circuit 3, and the excitation current IA according to the position (rotation angle θm) is detected by the encoder 2 and the angle calculation circuit 3.
, IB are supplied to each single child coil.

Here, the magnitudes of the outputs Ss and Sc of the function generation circuit 4 are as follows: 5s=sin(θm+w/2) Sc=cos(0m+r/2), and when the magnitude of the control signal 54 is taken as IO, Excitation current kon, I supplied to the armature coil of pulse motor 1
The size of B is IA m lo-5in (θm+w/2) IB -I
o-cos(θH+f/2).

As is clear from the above equation, the excitation current islands, IB, supplied to each armature coil have a phase difference of 90°, and their sum [vector composition] is always constant, so This means that a constant torque with no torque unevenness is generated. Moreover, its magnitude is the magnitude I of the control signal Si
It is proportional to o. Therefore, when the load is zero, if the magnitude IO of the control signal Si is zero, the pulse motor 1 is stopped, and if the magnitude Io of the control signal Si increases, the speed increases accordingly. It will start rotating.

Furthermore, the example in FIG. 3 shows the case where the pulse motor 1 is driven like a DC motor, so the exciting currents IA, I
The electrical angle in the composite current of B always has a phase difference of 90° with respect to the mechanical angle (rotation angle θm) of the rotor, and the maximum torque is generated in this state.

In this way, in the motor drive circuit as shown in Fig. 3,
By supplying sinusoidal excitation currents IA and IB with different phases to a plurality of armature coils, it is possible to eliminate torque unevenness, and by changing the magnitude ro of the control signal Si, the pulse motor 1 can be arbitrarily controlled.

[Problem that the invention seeks to solve]

However, in a general motor, the relationship between the excitation current and the magnetic flux density in the magnetic path is not linear, and has nonlinearity as shown in FIG. 4.

Therefore, in the motor drive circuit configured as described above, in order to increase the output torque, the excitation current IA
If the amplitude of , IB is increased, the magnetic flux density in the magnetic path will be saturated, resulting in ripples in the output torque. This phenomenon is particularly noticeable in motors such as pulse motors in which the magnetic flux density in the magnetic path is high.

The present invention aims to eliminate the drawbacks of the conventional device as described above and realize a motor drive circuit with a simple configuration that can prevent the occurrence of torque ripple even when the output torque is increased. It is.

[Means for solving problems]

The motor drive circuit of the present invention eliminates torque unevenness by supplying sinusoidal excitation currents with different phases to a plurality of armature coils, and also changes the amplitude of these excitation currents in accordance with a control signal to generate an output. In a motor drive circuit configured to arbitrarily control the magnitude of torque, the bending control signal has a frequency of 4 to 8 of the NjJ magnetic current, and its magnitude is proportional to the square or cube of the control signal. The corrected signals are added together.

[For production]

In this way, the control signal that determines the magnitude of the excitation current is
If we add a correction signal whose frequency is four times the excitation current and whose magnitude is proportional to the square or cube of the control signal,
4, which appears most significantly when the value of the excitation current increases.
The magnitude of the control signal, that is, the excitation current, can be corrected so as to cancel out the next torque ripple, and a constant output torque with less ripple can be obtained.

〔Example〕

FIG. 1 is a configuration diagram showing an embodiment of a motor drive circuit of the present invention. In the figure, the same parts as in the old figure 3 are designated by the same reference numerals. Reference numeral 9 denotes a correction circuit whose frequency is determined by the excitation current IA based on the rotation angle θm of the rotor generated from the angle calculation circuit 3.

, IB (sine wave signals Ss, Sc) of 4 (8), and the magnitude thereof is proportional to the cube of the control signal Si, and this correction signal is added to the control signal Si.

The magnitude of the correction signal at this time is set according to the actual driving state, and is set to the optimum magnitude using a variable resistor while measuring the output torque state.

Now, as mentioned above, between the excitation currents rA, IB and the magnetic flux generated thereby, there exists a saturation characteristic as shown in FIG. , the waveform of the magnetic flux is distorted, and ripples (harmonic components) occur in the output torque.

Therefore, the saturation characteristics shown in FIG. 4 are approximated by a quadratic curve,
When determining the magnitude of the ripple included in the output torque, the amplitude of this ripple is proportional to the cube of the amplitude of the excitation current I^, IB, and the amplitude of the ripple is proportional to the excitation current IA.

It can be seen that it has a frequency (fourth harmonic component) four times rB.

Therefore, when the amplitude of the excitation currents IA, TB becomes large, the torque ripple having the fourth harmonic component appears the most with respect to the frequency of the excitation currents IA, TB. Ss,
By adding a signal having a frequency four times that of Sc to the control signal Sj as a correction signal, it is possible to obtain an output torque with less fourth-order torque ripple as described above.

Also, the magnitude of the correction signal is determined by the excitation current IA. A suitable value is IB, that is, a magnitude proportional to the cube of the magnitude of the control signal Si, and as the magnitude of the excitation current I^, IB (control signal Si) increases, the magnitude of the correction signal also increases.

Note that it is also effective to make the magnitude of the correction signal proportional to the square of the control signal Sj.

From the above relationship, if the magnitude of the correction signal is expressed by the formula, the first
As shown in the figure, - K Io'' cos4θm K: proportionality constant. Also, when making the magnitude proportional to the square of the control signal Sj, the absolute value of Io'' is used.

FIG. 2 is a diagram showing the correction effect by the motor drive circuit of the present invention. As is clear from the figure, exciting currents TA, TB
When the ratio of It can be suppressed to about 115.

Here, when the magnitude of control No. 18 Si is corrected, the torque ripple does not become completely 7 because the torque ripple is somewhat suppressed by harmonic components other than the fourth order.

In the above description, a case has been exemplified in which a two-phase excitation type pulse motor is driven by the motor drive circuit of the present invention, but the type of motor to be driven is not limited to this. In addition, in the above explanation, the exciting current IA
, IB (sine wave signal Ss.

Although the correction circuit 9 generates a correction signal having a frequency four times that of Sc), the means for generating the correction signal is not limited to this. Corresponding sine wave signal Ss
, Sc as well as a signal with a frequency four times that of the frequency signal, and supply it to the correction circuit 9, the same operation can be performed.

〔Effect of the invention〕

As explained above, the motor drive circuit of the present invention eliminates torque unevenness by supplying sinusoidal excitation currents with different phases to a plurality of armature coils, and also uses the amplitude of these excitation currents as a control signal. In a motor drive circuit configured to arbitrarily control the magnitude of output torque by changing the magnitude of the output torque according to Since a correction signal proportional to the power of This makes it possible to realize a motor drive circuit with a simple configuration that can prevent the occurrence of torque ripple even when the output torque is increased.

[Brief explanation of drawings]

FIGS. 1 and 2 are block diagrams showing one embodiment of a motor drive circuit of the present invention, and FIGS. 3 and 4 are circuit diagrams showing an example of a conventional motor drive circuit. 1...Pulse motor, 2...Encoder, 3...
Angle calculation circuit, 4... Function generation circuit, 5, 6... Subtraction =, 7, 8... Power amplifier, 9... Correction circuit. Figure 3 Figure 4 Torque ripple (N-m)

Claims (1)

[Claims] In a motor drive circuit configured to eliminate torque unevenness by supplying sinusoidal excitation currents with different phases to a plurality of armature coils, there is a constant phase relationship, and the phase of the combined current is similar to that of the rotor. A function generating circuit generates a plurality of sine wave signals that always have a constant phase difference with respect to the mechanical angle, and a control signal that commands the value of output torque has a frequency four times that of the sine wave signal and is larger than that of the sine wave signal. a correction circuit that adds a correction signal proportional to the square or cube of the control signal; and a plurality of circuits that change the amplitudes of the plurality of sine wave signals according to the magnitude of the control signal corrected by the correction circuit. multipliers; and a plurality of power amplifiers that receive the outputs of these multipliers and supply excitation currents proportional to the outputs to the plurality of armature coils, respectively.