JPS6035912B2 - Motor speed control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a motor speed control circuit suitable for application to, for example, a rotating magnetic head device of a VTR.

The rotating magnetic head device of a VTR has not only a pair of rotating magnetic heads but also a rotating drum that is rotationally integrated with the magnetic head, and these heads and rotating drums are generally controlled by a control circuit as shown in FIG. Its rotation is controlled by The control circuit consists of a speed control system IA for controlling the rotational speed of the rotating drum, which is a rotating body, and a rotational phase control system IB for controlling the rotational position of the rotating drum, that is, the rotational phase of the rotating magnetic head. The control signals obtained by these control systems IA and IB are supplied to the drive source of the rotating drum, for example, a DC motor M, which controls the rotating drum to a normal rotational speed, and also connects the magnetic head with an external synchronizing signal (video signal). The rotational phase with the vertical synchronization signal (or a signal similar thereto is used) is regulated.

Let's add an explanation starting with the speed control system IA.

Reference numeral 2 indicates a detection element of the head structure constituting the frequency generator G, and a rotation signal S'F (see FIG. 2A) relating to the rotation of the rotary drum is obtained from this detection element 2.

Note that although the rotation signal S'F in this example is selected to have a frequency of about 2 every 360 days, the frequency can be arbitrarily selected. By supplying the rotation signal S'F to the waveform shaping circuit 3, it is converted into a rectangular waveform signal SF as shown in FIG. 2B, and this signal SF is thereafter used as the rotation signal. The rotation signal SF is supplied to a delay circuit 4 whose delay time is set to W.

This delay circuit 4 is composed of a mono multi-channel circuit that operates at the falling edge of the rotation signal SF, and the mono multi-channel output obtained here, that is, the delayed output So (shown in FIG. As a result, the comparison signal Ss shown in FIG. 2D is generated.The comparison signal generating circuit 5 is given an operation in which it is set at the fall of the delayed output So as shown in the figure.

The comparison signal Ss is supplied to a sampling and holding circuit 6, and a speed control signal for controlling the motor M is formed. That is, this sampling and hold circuit 6 receives the comparison signal S
The sampling signal SP (Fig. 2E) is based on the rotation signal SF. It is formed by 7 shows a forming circuit for this purpose, and in this example, as shown in the figure, the sampling signal SP is formed using the rising edge of the rotation signal SF.

The comparison signal Ss sampled by the sampling signal SP is held by the subsequent hold circuit 6B,
This hold output is output from a DC multiplier 8 consisting of an arithmetic multiplier, etc.
The speed control signal So (FIG. 2F) is supplied to the motor M as the speed control signal So (FIG. 2F).

That is, since the sampling position of the comparison signal Ss differs depending on the rotation state (slow and far) of the motor M, the DC level of the speed control signal So changes based on the difference.
This controls the rotational speed of motor M. Next, the rotational phase control system IB will be explained.

This rotational phase control signal is formed from a reference external synchronization signal Sv and a pulse signal pc related to the rotational position of the rotating drum. ) is provided. The head 11 shown in the figure constitutes a pulse generator. Synchronization signal Sv
is supplied to a generating circuit 12 similar to that described above in order to convert it into a sawtooth comparison signal, and then supplied to a sampling and holding circuit 13 where an error in the rotational phase is detected. 14 indicates a pulse shaping circuit for obtaining the sampling signal SG. This rotational phase control signal SE, which corresponds to the rotational phase error, is supplied to the above-mentioned control system IA via the DC multiplier 15.

Normally, by varying the delay time 7 of the delay circuit 4 using the phase control signal SE, the speed of the motor M is controlled and the magnetic head is synchronized with the synchronization signal SP. In this way, two control systems IA÷IB are provided to control the rotating drum and magnetic head.

By the way, if the speed control circuit for the motor M is configured in this way, it is possible to perform both the formation of the comparison signal and the sampling thereof by just using one delay circuit 4, so that the circuit configuration is simplified. On the other hand, there are drawbacks as described below. That is, as shown in FIG. 2, the comparison signal Ss is formed using the falling part of the rotation signal SF as a reference, but the sampling signal SP, on the contrary, is formed using the rising part of the rotation signal SF as a reference. Therefore, when waveform-shaping the sinusoidal rotation signal S'F to obtain the signal SF,
If the level at the time of shaping (slice level) fluctuates, it is not possible to form a complete signal SF with a duty of 50%. Therefore, the time point at which the falling portion is obtained differs from time to time, and therefore the delayed output S. The disadvantage is that the reference time of the speed changes, and accurate speed control cannot always be performed. The present invention eliminates these drawbacks and makes it possible to always achieve accurate speed control regardless of duty fluctuations. The circuit of the present invention will be explained below with reference to the drawings.

FIG. 3 shows an example of a speed control circuit according to the present invention. 1st
Parts corresponding to those in the figure are given the same reference numerals, and their explanations are omitted. This is a case where the output S^ is supplied via the gate circuit 20 instead of being supplied by the generation circuit 5 of Ss. This gate circuit 20G is configured as an AND circuit, and one input terminal is supplied with the delayed output So, and the other input terminal is supplied with the rotation signal SF itself.

The control operation based on such a configuration will be explained with reference to the waveform diagram of FIG. 4.

However, for convenience of explanation, this example describes the operation when the motor M is in a normal rotation state, and in this case, the relationship between the unmeasured a of the rotation signal sF and the delay time is Ta< It satisfies the time relation a.

When the rotation signal SF and the delayed output So shown in FIG. 4A and B arrive, the AND output (gate output) S shown in FIG.
Since A is obtained, if the comparison signal Ss is formed at the falling edge of this AND output SA, a comparison signal Ss as shown in FIG.

This comparison signal Ss is reset at the rising edge of the AND output S^. On the other hand, the sampling pulse SP is a delayed output S. This method uses the reference time axis used when forming the . That is, the sampling signal SP is formed based on the falling portion of the rotation signal SF. Therefore, the present invention is configured so that its operation is opposite to that of the conventional forming circuit 7 shown in FIG. The comparison signal Ss is sampled with the sampling signal SP obtained in this way, but the subsequent operation is the same as that of the slave, so the explanation thereof will be omitted. In addition, when the motor speed decreases and the actual water flow exceeds the delay time 7 as shown in Fig. 5, the AND output S^
cannot be obtained.

When the motor rotation speed becomes less than the set rotation speed, the starting circuit 21 shown in FIG. 3 comes into operation. This starting circuit 21 is composed of an AND circuit 24 having inverters 22 and 23 at its inputs, and the above-mentioned rotation signal SF and delayed output SD are supplied to these inverters 22 and 23 (each waveform is (See Figures 5 A to D).

Therefore, if the motor M is rotating even a little, the starting signal Po shown in FIG. When this is supplied, the motor M is accelerated and returns to a constant speed state. By providing the delay circuit 4 and the AND circuit 20, the motor operates only when the motor rotation speed is equal to or higher than the set frequency, so these provide a frequency discrimination function, and when the rotation frequency is lower than the set rotation frequency, the motor M The motor M is accelerated by the output Po of the starting circuit 21 obtained during the rotation of the motor M, and can be raised to the set rotation frequency in a shorter time. As explained above, in the present invention, the gate circuit 20 is provided, and the gate output S obtained from the falling part of the rotation signal SF is used as a reference for signal formation.
Since the delayed output SD is formed at the falling edge of A and the sampling signal SP is formed at the falling edge similarly to the rotational signal SF, in addition to the feature that it can be configured with one delay circuit, the rotational signal SF If the duty of 1-to-1 changes, both the delayed output So and the sampling signal SP will change simultaneously, so there will be no fluctuation in the reference time axis used for forming various signals, and therefore the change in duty will There is no effect on speed control.

- Therefore, the accuracy of speed control is high, and its operation is always stable. In addition, according to the above configuration, since the rotation frequency of the motor M is controlled by sampling the rotation frequency every one rotation period, the followability of the speed servo system is better than when the sampling period is, for example, two rotation periods. speed control accuracy can be further improved. In addition, in the above-mentioned embodiment, an example was described in which the falling part of the rotation signal SF was selected as the reference for signal formation, but it goes without saying that the same effect as described above can be achieved even if the rising part is used.

In addition, in the example of FIG. 3, the AND output S based on the delayed output So
In this example, the comparison signal Ss is formed from ^.
The comparison signal Ss may be directly generated from the rotation signal SF.

In that case, as shown in FIG.
An AND circuit 20 and a delay circuit 4 are installed before and after the P formation circuit 7.
All you have to do is set A. However, the AND output SA may be further supplied to the delay circuit 4B designated as 7' and added to the formation circuit 7. FIG. 7 shows the waveforms of each part. However, the explanation thereof will be omitted.

[Brief explanation of the drawing]

FIG. 1 is a system diagram of a motor speed control circuit to explain the present invention, FIG. 2 is a waveform diagram to explain its operation, FIG. 3 is a system diagram of essential parts showing an example of the circuit of the present invention, and FIG. 5 and 5 are waveform diagrams for explaining the operation, FIG. 6 is a system diagram showing another example of the circuit of the present invention, and FIG. 7 is a waveform diagram for explaining the operation. IA is a speed control system, IB is a rotational phase control system, M is a motor, 4, 4A, 4B are delay circuits, 5 is a comparison signal generation circuit, 6 and 13 are sampling and hold circuits, SF is a rotation signal, and So is speed A control signal, Sv is an external synchronization signal, Pc is a rotational position signal, SE is a rotational phase control signal, a two-way gate circuit, 21 is a starting circuit, and 7 is a gate pulse Sc forming circuit. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7

Claims (1)

[Claims] 1 Falling portion (or rising portion) of a waveform-shaped rotation signal indicating the rotational speed of a rotating body rotated by a motor
a mono multi circuit triggered by a mono multi circuit, a gate circuit that AND-gates the mono multi output formed by this and the rotation signal, and a gate circuit that performs an AND gate on the mono multi output formed by this circuit and the rotation signal; forming a sampling pulse based on the falling part (or rising part) of the rotation signal or the gate output;
A motor speed control circuit that performs a phase comparison operation by sampling the above-mentioned slope signal with the above-mentioned sampling pulse, and controls the rotational speed of a motor that drives the above-mentioned rotating body using the comparison output.