JPS5817370A - Rotation detector - Google Patents

Abstract

PURPOSE:To prevent mistaken judgement of stopping at any speed in a rotation detection device for detection of rotation stopping of a reel by generating pulses that have at least two kinds of periods in one rotation. CONSTITUTION:In a rotation stopping detection device for a reel of a tape recorder, etc. a light shielding disc 7 is used for making rotation into pulses. Notches 7a and notches 7b that have width three times as wide as the notches 7a are formed alternately as in 7a1, 7b1, 7a2, 7b2 in the disc 7. Frequency of the generated rotation pulses gradually falls from reel-winding starting to its end as shown in A-D. In a pulse level height is judged by the timings denoted by the arrow marks, continuous high level is detected from the pulse Pa at 7a1 section, but soon low level is detected for the pulse Pb at 7b1 section as in B. Accordingly mistaken judgement of high level (i.e. stopping) all the time can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotation detection device, which is configured to take out a rotation pulse having a period of at least 211 types per rotation of a rotating body, and when detecting a change in the level of the rotation pulse at a fixed timing, It is an object of the present invention to provide a rotation detection device that can detect both the H level and L level of a rotation pulse within a predetermined time at any rotation speed, and can reliably detect whether or not a rotating body is rotating.

For example, in a video tape recorder, a circuit for detecting whether or not a reel disk is rotating is provided separately from a circuit for detecting the rotational speed of a capstan in a capstan servo system. This is different from a capstan servo system, and simply determines whether or not the reel disk is rotating.For example, if the magnetic tape becomes tangled for some reason and stops moving, the reel disk motor can be left as it is. If you leave it on, there is a risk of burning it out.
In order to prevent this, a circuit is included that detects when the reel disc motor stops rotating and cuts off the power supply to the motor.

For example, as shown in FIG. 1, a light-shielding disc 2 having notches provided on the circumference at predetermined intervals is attached to the rotating shaft of a reel disc motor l that drives a reel disc, and the notches of the disc 2 are The light from the light emitting diode 3 provided on one side of the notch is passed through and blocked by the rotating disk 2, and is supplied to the phototransistor 4 provided on the opposite side of the notch. The electric signal is waveform-shaped into an alternating pulse signal by a waveform shaping circuit 5, and is supplied to a detection section 6, which is constituted by, for example, a microcomputer, to detect a change in the level of the pulse signal. The detection unit 6 is provided with a level judgment time of, for example, 3 seconds, and when the motor 1 is rotating, the pulse signal from the waveform shaping circuit 5 is a repetition of H level and L level, so this repetition is The motor is activated after determining that it is continuing for 3 seconds.
A signal is supplied to the motor 1 to cause the motor to rotate as it is.

On the other hand, if the motor l stops rotating for some reason even though power is being supplied to the motor l, the pulse signal from the waveform shaping circuit 5 disappears and becomes a signal at the same level, and the detection unit 6 outputs the same level. After determining that the signal continues for 3 seconds, a signal is supplied to the motor 1 to cut off the power supply to the motor 1.

By the way, for example, the rotational speed of the take-up reel in the playback mode is fast at the beginning of tape winding and slows down as it approaches the end of the tape, and as shown in FIG. The frequency of the signal becomes progressively lower. In this case, the conventional disk 2 is as shown in FIG.
Since the notches 2a are provided at equal intervals on the circumference, the frequency of the pulse signal changes gradually, but the determination time in the detection section 6 is constant for 3 seconds. On the other hand, the timing at which the detection unit 6 detects the level of the pulse signal from the waveform shaping circuit 5 differs depending on each mode such as fast forward, rewind, and playback, but is constant within a certain mode. The mode is as shown in FIG. 2 with an arrow (↓) on the plow.

In this way, in this conventional device, since the notches 21 of the disk 2 are provided at equal intervals on the circumference, for example, as shown in FIG.
B) As is clearer, there is a period during which the level detection timing in the detection section 6 and the timing of the H level of the pulse signal coincide for a judgment time of 3 seconds or more in the detection section 6.

For this reason, the detection unit 6 detects only the H level for 3 seconds or more even though the pulse signal in which the H level and L level repeatedly occur is extracted from the waveform shaping circuit 5, and the reel A signal to cut off the power supply to the motor 1 is supplied to the motor 1 even though the motor 1 is rotating normally, resulting in problems such as low operational reliability.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described with reference to FIG. 4 and the following figures.

FIG. 4 shows a light-shielding disc 7 used in the rotation detection device according to the present invention.
1 shows a plan view of an embodiment of the invention. - In the figure, 7a is a notch having the same spacing as the notch 2a shown in the third diagram, and 7b is a notch 7
Notch groups 7a, 7a2 each having a width that is, for example, three times as wide as the width of a, and are constituted by a plurality of notches 7a.
7b is one place on each circumference, 7am is one place on each circumference, and 7am is a notch group.

7b, 7a, 7b, and 2 are successively provided on the circumference in this order. Specifically, the notches of the notch group 7sis t 7a2 are connected from the waveform shaping circuit 5 to the part shown in FIG.
When the disk 7 is rotated at a speed at which a pulse signal with a frequency as shown in FIG. They are provided at equal intervals so that the period during which P persists is less than the judgment time (3 seconds) in the detection unit 6.

When using a disc in which some of the notches are provided at irregular intervals in this way, the pulse signal obtained by the rotation of the reel on the winding side in the playback mode will be generated as shown in Figure 5, from the beginning to the end of the tape winding. During one rotation of the disc 2, a pulse P obtained by the notch 7a and a pulse Pb obtained by the notch 7b are generated, and the pulse width is produces a changing part. Therefore, as shown in FIG. 5 03), even if the generation timing of the pulse Pa in the reproduction mode coincides with the level detection timing (↓) in the detection section 6, the cut section group 7m,
Alternatively, since 7h is provided as described above, the detection unit 6
The time it takes for the signals from the waveform shaping circuit 5 to be determined to be at the same level (H level in this case) is less than 3 seconds, and when the notch group 7a1 finishes sustaining the pulse PR, the notch group 7b, the Nyoru pulse, P .

Detects the L level.

That is, at the level detection timing within the judgment time in the detection unit 6, the H level due to the pulse P and the L level due to the pulse Pb are detected.
Since there are two levels, the detection unit 6 detects both the H level and the L level. As a result, even if there is a period during the playback mode in which the level detection timing of the detection section 6 and the H level of the pulse P match, this is less than the judgment time of the detection section 6. If the H level continues as described above, a signal to cut off the power supply to the motor l will not be supplied to the motor l, but a signal to rotate the motor l will be supplied to the motor l as it is.

Even in modes other than playback mode, pulse signals as shown in Figure 5 (5) to (to) are extracted depending on the tape winding diameter, although the frequency differs, and the level detection timing also varies depending on the mode. 5(B) may occur in any mode. In this embodiment, since the disk 7 is formed as described above, the above-described operation does not cause any inconvenience as in the conventional case as long as the reel disk rotates normally in any mode.

Further, the shape of the light-shielding disk is not limited to the shape shown in FIG. 4, and for example, the shape of the light-shielding disk is not limited to the shape shown in FIG. It may be a circular plate in which a notch 8b having a width three times the width of the notch 8m and a light shielding part 8d having a width three times the width of the light shielding part 8c are provided on the top (note that the notch 8c and The relative position with respect to the light shielding part 8d is not limited to that shown in the figure, but may be set to any positional relationship such as, for example, so that the two are in symmetrical positions with respect to the center of the rotation axis). As shown in the figure, there is a notch 98 in the part marked ■ on the circumference, and a notch 9 in the remaining part marked ■.
It may also be a disc provided with a notch 9b having a width three times the width of a. Each disc has a notch 8a or 9. ! The duration during which the H level of the pulse obtained by 1 and the level detection timing in the detection section 6 match is set to be less than the level determination time in the detection section 6.

Further, the means for obtaining the pulse signal is not limited to the light-shielding disk provided with a notch as in the above embodiment, but may also be a disk provided with holes, for example. An apparatus may also be used in which a disc coated with different colors so as to have two different aging periods is used to irradiate this area with light and to receive the light reflected from the disc.

As described above, the rotation detection device according to the present invention is configured so that pulse signals having at least two types of periods are extracted per rotation of the rotating body when the rotating body is rotating at a substantially constant speed. Even if the timing at which a level change is detected coincides with one period of the pulse, the pulse of the other period will not coincide with this detection timing, and at any rotation speed, it will always be delivered to one revolution of the rotating body, that is, within a predetermined time. It is possible to detect both the H level and L level of the pulse, and as a result, unlike conventional devices, it is possible to detect the same level of the pulse at the portion where the detection timing and the pulse match, even if the rotating body is rotating. However, there is no possibility that the rotating body is mistakenly determined to have stopped rotating, and it is possible to reliably determine whether the rotating body is rotating or not, and the operation reliability can be improved.

[Brief explanation of the drawing]

Figure 1 is a block diagram of an example of a general rotation detection device.
Figure 2 4-(to) are signal waveform diagrams for explaining the operation of the conventional device;
Fig. 3 is a plan view of an example of a light-shielding disc used in the conventional device i;
FIG. 4 is a plan view of an embodiment of the light-shielding disc used in the device of the present invention, FIGS. 5 (5) to (2) are signal waveform diagrams for explaining the operation of the device of the present invention, and FIGS. 6 and 7 are FIG. 6 is a plan view of another embodiment of the light-shielding disc used in the device of the present invention. l...Reel motor, 3.Working/Light emitting diode, 4.
■Phototransistor, 60/Detection section, 7... Clear light disk, 7a, 7b, 8a, 8b, 9a. 9b...notch part, 8c, 8d...light shielding part.

Claims (1)

[Claims] '(1) Rotation detection that detects level changes of a pulse signal of a frequency corresponding to the rotational speed of a rotating body at a constant timing, and detects whether or not the rotating body is rotating based on the presence or absence of the level change. In the device, means to obtain said PAL No. 718? A rotation detection device characterized by 5i-, which is configured such that pulse signals having at least two types of periods are extracted for one rotation of the rotating body when the rotating body is rotating at a substantially constant speed. Device. (2) The means for detecting a level change is a means for detecting a level change of the cough pulse signal within a preset level judgment time, and the means for obtaining the pulse signal is a means for detecting a level change of the cough pulse signal within a preset level judgment time. 2. The rotation detection device according to claim 1, wherein the rotation detection device is configured to obtain pulse signals having two types of periods.