JPH0779587A - Circuit for detecting rotating speed of motor - Google Patents

Abstract

PURPOSE:To highly accurately switch heads to each other by performing the switching based on the edge of the signal of one phase of either the back electromotive voltage waveform of a driving coil or the position detecting signal of a position detector. CONSTITUTION:Head positioning signals the one period of which is made equal to one rotation of a rotor 2 from a PG sensor 3 and rotating speed signals from a rotating speed detector 8 are inputted to a head switching device 4 and head switching is performed at the edge of a prescribed pulse of the rotating speed signals on the basis of the head positioning signals. Namely, the back electromotive voltage shaping waveform which is induced when an electric current is supplied to a driving coil L become 6 pulses/rotation and the rotating speed signals from the detector 8 become 18 pulses/rotation. Therefore, the head switching signals can be switched at the rising position of the rotating speed signal corresponding to the rising position of the edge of the back electromotive voltage shaping waveform of one phase only and the changing period of the rotation can be minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor rotation speed detection circuit.

[0002]

2. Description of the Related Art Conventionally, a cylinder motor used in, for example, a VTR is provided with a rotation speed detection circuit, and a video or audio signal is switched based on the rotation speed signal detected by the rotation speed detection circuit. ing. The structure of this motor rotation speed detection circuit is the same as that shown in FIGS. 1 and 2 showing the embodiment of the present application, and therefore the description will be given below with reference to FIGS. 1 and 2, reference numeral 1 denotes a rotary cylinder, the outer periphery of the rotary cylinder 1, as shown enlarged in FIG. 2, the magnetic head for video V _L, V _R, magnetic audio Heads A _L and A _R are attached. These video heads V _L , V _R and audio heads A _L , A _R have, for example, an angle between the centers of the video head V _L and the audio head A _R of 60 ° and a center of the audio head A _R and the video head V _R. The angle is 120 °, and the angle between the centers of the video head V _R and the audio head A _L is 60 °.

The rotary cylinder 1 is driven to rotate by a cylinder motor, and a rotor 2 of the motor is used.
A PG magnet 2a is attached to the outer peripheral surface of the. A PG sensor 3 for detecting the magnetic field of the PG magnet 2a is arranged at a position facing the outer peripheral surface of the rotor 2, and a head switching device 4 is connected to the PG sensor 3.

A drive magnet (not shown) in which the N poles and the S poles of the drive magnetic poles are alternately magnetized is attached to the rotary shaft of the cylinder motor, and the drive magnet is provided at a position facing the drive magnet. Hall elements 5a, 5b, 5c are provided as position detectors for detecting the magnetic field of the magnetic poles. A drive circuit 6 is connected to the respective output terminals of these Hall elements 5a, 5b, 5c, and they are connected to the three-phase drive coils L, L, L in accordance with the position detection signals from the Hall elements 5a, 5b, 5c. The drive current can be delivered.

A waveform shaper 7 is connected to the output terminals of the drive coils L, L, L to shape the back electromotive force waveform induced when the drive coils L, L, L are energized. The midpoint voltage of the drive coils L, L, L is also input to the waveform shaper 7. The waveform shaper 7 is connected to a rotation speed detection device 8 that synthesizes waveform-shaped three-phase pulse signals and outputs a rotation speed signal. The above-mentioned head switching device 4 is connected to the rotation speed detection device 8, and based on the rotation speed signal and the head positioning signal, the above-mentioned video heads V _L , V _R and the audio head A _L ,
A head switching signal for switching A _R can be sent to the changeover switch 11.

Further, an F / V converter 9 is connected to the rotation speed detecting device 8, an amplifier 10 is connected to the F / V converter 9, and the drive circuit 6 is connected to the amplifier 10. The rotation speed signal from the rotation speed detection device 8 is used as a rotation speed control signal through the F / V converter 9 and the amplifier 10 to drive the drive circuit 6.
To get feedback.

Next, the operation of the circuit thus configured will be described with reference to the timing chart shown in FIG. When a predetermined voltage is applied to the drive coils L, L, L, the drive magnet rotates together with the rotor 2, and the N poles and S poles of the drive magnets alternately face the Hall elements 5a, 5b, 5c, and their magnetic fields A sine wave waveform as a position detection signal is output from the Hall elements 5a, 5b, 5c according to the direction of. These position detection signals are input to the drive circuit 6, and the drive coils L,
The drive current is sent to L and L, respectively, and the rotor 2 rotates.

The counter electromotive voltage waveform and the midpoint voltage of the coils L, L, L induced at this time are input to the waveform shaper 7, and the waveform shaper 7 is shown in FIGS. As shown, for example, a pulse wave of 8 pulses / 1 rotation (b)
Waveforms are shaped in (d). These pulse waves (b)
(D) is input to the rotation speed detection device 8 and synthesized, and from the rotation speed detection device 8, as shown in FIG.
A rotation speed signal (e) of 24 pulses per rotation (three times the frequency of the pulse wave of each phase), which is a combination of the phase pulse waves, is transmitted.

On the other hand, the magnetic field of the PG magnet 2a is detected by the PG sensor 3, and from the PG sensor 3, the magnetic field shown in FIG.
A pulse signal (a) having one cycle of one rotation of the rotor 2 as shown in (a) is transmitted. 1 of this rotor 2
A head positioning signal (a) having one cycle of rotation and the above-described rotation speed signal (e) are input to the head switching device 4, and the head switching device 4 performs head positioning as shown in FIG. 9 (f). A predetermined order of rotation speed signals (e) (head V _L ,
V _R, A _L, arrangement position of A _R, or head V _L, V
Head switching that is switched at the edge position (rising or falling position; rising position in this circuit) of the pulse of _R , A _L , and A _R (determined by the angle between the centers of _R , A _L , and A _R and the number of pulses per rotation) The signal (f) is transmitted. The head switching signal (f) is input to the changeover switch 11, and video or audio signal processing is performed according to the head switching signal (f).

[0010]

However, the above-described motor rotation speed detection circuit has the following problems. That is, as shown in an enlarged manner in FIG. 9, the rotation speed signal (e ′) is a three-phase back electromotive voltage shaping waveform (b ′)-
Since (d ') is synthesized, the cycle fluctuates as shown by the error (variation) component of each phase, and the head switching signal (f') is 1 pulse / 15 °.
The switching is performed according to the edge position of the rotation speed signal (e ′), that is, the switching is performed corresponding to the edge positions of the two-phase back electromotive force shaping waveforms (b) and (d). As shown in FIG. 9 (f '), the switching is deviated from the normal position (see FIG. 9 (F)), and the signal (video, audio) detected by the head is disturbed. There is.

Here, in order to solve this problem, it is conceivable to improve the detection accuracy of the number of revolutions or correct the above-mentioned periodic fluctuation, but this is not preferable because the mechanism and the circuit become complicated and the cost increases. .

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a motor rotation speed detection circuit which has a simple structure and which can perform head switching with high accuracy and prevents disturbance of a detection signal.

[0013]

In order to achieve the above object, a motor rotation speed detection circuit according to the present invention has a rotating body which is rotationally driven by the motor and a plurality of magnetic heads attached to the rotating body. And three position detectors arranged near the rotating body to detect the position of the rotating body, and any one phase of the back electromotive voltage waveform of the drive coil and the position detection signal from the position detector is provided. The magnetic heads are switched based on the edge of the minute signal.

[0014]

According to the circuit for detecting the number of rotations of the motor in the above means, the switching of the magnetic head is performed by the edge of the signal for one phase of the back electromotive voltage waveform of the drive coil and the position detection signal from the position detector. Therefore, the periodic fluctuation is minimized, and the heads are switched with high accuracy. Moreover, the structure is very simple without using a complicated mechanism or circuit.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of a motor rotation speed detection circuit showing a first embodiment of the present invention, and FIG. 2 is a diagram showing an arrangement of heads in a cylinder shown in FIG. Since it is exactly the same, the description here is omitted. The motor rotation speed detection circuit of the first embodiment is different from that of the prior art in that one of the back electromotive force shaping waveforms of the waveform-shaped drive coils L, L, and L is the signal for one phase. The point is that the video heads V _L and V _R and the audio heads A _L and A _R are switched based on the rising edge position.

The operation of this circuit will be further described below with reference to the timing chart shown in FIG. In the first embodiment, the back electromotive force shaping waveform is as shown in FIG.
As shown in (b) to (d), the number of pulses is 6 pulses / revolution, and the rotation speed signal sent from the rotation speed detection device 8 is as shown in FIG. 3 (e). In addition, 18 pulses / revolution (1 pulse / 15 °). Therefore, the head switching signal can be switched at the rising position of the rotation speed signal (e) corresponding to the rising position of the edge of the back electromotive voltage shaping waveform (b) of only one phase, and the fluctuation cycle thereof Can be minimized.

As described above, in the first embodiment, the video head V _L , V _L , is generated based on the rising position of the edge of the signal of only one phase of the back electromotive voltage shaping waveform of the drive coils L, L, L. Since all switching of V _R and the voice heads A _L and A _R is performed, the period fluctuation can be minimized, and the heads V _L , V _R , A _L and A
It is possible to make the switching position of _R approximately coincide with the normal position shown in FIG. Therefore, the heads V _L , V _R , A _L , and A _R can be switched with high accuracy, and it is possible to prevent the disturbance of the detection signal (video, audio). Moreover, the configuration is not so different from the conventional one as described above, and it is very simple because it does not use a complicated mechanism or circuit, so that the circuit can be constructed at low cost.

FIG. 4 is a diagram showing a head arrangement inside a cylinder applied to a rotation speed detection circuit of a motor according to a second embodiment of the present invention, and an overall structure thereof is the first structure described above. Since it is the same as that of the embodiment, its description is omitted here. The motor rotation speed detection circuit of the second embodiment differs from that of the first embodiment in that the head structure on the outer circumference of the rotary cylinder 11 is changed as shown in FIG. That is, an intermediate portion between the video head V _L and the audio head A _R (30 from the video head V _L and the audio head A _R , respectively)
Video position V _L 'at this position)
_The point is that image heads V _R 'are newly provided at positions (180 ° opposite positions) opposite to _L '.

Even if the head is constructed as described above, FIG.
The head switching signal shown in (3) can be fully switched at the rising and falling positions of the rotation speed signal (e) corresponding to the rising and falling positions of the edge of the back electromotive force shaping waveform (b) of only one phase. Therefore, it is possible to minimize the fluctuation period as in the first embodiment.

In the second embodiment, since switching is performed at both the rising and falling positions of the edge, the high and low times of the pulse are equal and the so-called duty 50 condition is not satisfied. It goes without saying that it will not happen.

FIG. 6 is an overall configuration diagram of a motor rotation speed detection circuit showing a third embodiment of the present invention. The motor rotation speed detection circuit of the third embodiment is different from that of the first embodiment in that a one-phase back electromotive force shaping waveform is directly input to the head switching device 4 instead of the rotation speed signal. As shown in FIG. 7, all the heads are switched at the rising position of the edge of the one-phase back electromotive force shaping waveform (b).

It is apparent from FIG. 7 that the same effects as those of the first embodiment can be obtained even with such a configuration. The waveforms (a) to (f), (b ') to (f') shown in FIGS. 3, 5, and 7 are
Regarding (F), the description of the same as the prior art shown in FIG. 9 or the previous embodiment is omitted to avoid duplication.

Although the invention made by the present inventor has been specifically described based on the respective embodiments, the present invention is not limited to the respective embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say, for example, in each of the above embodiments, the heads are switched based on the edge of the one-phase back electromotive force shaping waveform, but as shown by the dotted line in FIG. In addition, one of the three-phase position detection signals is waveform-shaped, and the head is switched based on the edge of the waveform-shaped position detection shaping signal instead of the one-phase back electromotive voltage shaping waveform. It is also possible to do so.

The waveform shaping device 7 for the back electromotive voltage waveform or the position detection signal is not always required in the circuit. For example, as described in Japanese Patent Application No. 4-324766, the back electromotive voltage waveform or position is detected. The rotation speed signal may be directly synthesized from the detection signal.

It should be noted that, as shown in FIG. 8, heads arranged at two positions facing each other are outside the scope of the present invention.

[0026]

As described above, according to the motor rotation speed detection circuit of the present invention, the back electromotive voltage waveform of the drive coil and the position detection signal from the position detector are applied to the edge of the signal for one phase. Since the magnetic heads are switched on the basis of this, the periodic fluctuation is minimized, and therefore the heads can be switched with high accuracy, and the disturbance of the detection signal can be prevented. Moreover, since the structure does not use a complicated mechanism or circuit, it is very simple and the circuit can be formed at low cost.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a motor rotation speed detection circuit according to a first embodiment of the present invention.

FIG. 2 is a view showing a head arrangement in a cylinder in FIG.

FIG. 3 is a timing chart for explaining the operation of the circuit shown in FIG.

FIG. 4 is a diagram showing a head arrangement inside a cylinder applied to a motor rotation speed detection circuit according to a second embodiment of the present invention.

FIG. 5 is a timing chart for explaining the circuit operation of the second embodiment.

FIG. 6 is an overall configuration diagram of a motor rotation speed detection circuit showing a third embodiment of the present invention.

FIG. 7 is a timing chart for explaining the operation of the circuit shown in FIG.

FIG. 8 is a diagram showing an example of a head arrangement that is not applied to the present invention.

FIG. 9 is a timing chart for explaining a circuit operation of a conventional technique.

[Explanation of symbols]

1,11 rotary body 4 head switching devices 5a, 5b, 5c position detector 11 changeover switch _{A L, A R, V L} , V R, V L ', V R' magnetic head L drive coil

Claims (1)

[Claims] 1. A rotating body rotationally driven by a motor, a plurality of magnetic heads attached to the rotating body, and a magnetic head arranged near the rotating body to detect the position of the rotating body.
A number of position detectors, based on the back electromotive voltage waveform of the drive coil and the edge of the signal for one phase of the position detection signal from the position detector,
A rotation speed detection circuit for a motor, which switches the magnetic head.