JPH04255486A - Capstan motor speed detecting mechanism of vtr - Google Patents

Abstract

PURPOSE:To get the enlargement effect of a servo control band equal to having doubled the number of magnetic poles without increasing the number of mag netic poles on the periphery of a capstan flywheel. CONSTITUTION:This is composed of a pair of magnetic heads 3 and 9, which generate two-phase capstan signals, whose phases are different by 90 deg. from each other, an exclusive OR circuit 6, a servo microcomputer 7, and a inter- digital filter, which is constituted in software manner inside this microcomputer, whereby the effect of the phase shift of the two-phase FG signals can be removed.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention is applicable to VT such as movies.
This relates to the R capstan motor speed detection mechanism.

0002

[Prior Art] Conventionally, as a capstan motor speed detection device for a VTR, a magnetic element such as an MR element is used, in which N and S poles are magnetized at equal intervals on the outer periphery of a capstan flywheel, and are placed opposite to the N and S poles. 2. Description of the Related Art There has been known a capstan motor speed detection device that detects a frequency signal (hereinafter referred to as an FG signal) proportional to the rotational speed of a capstan motor using a head or the like. On the other hand, as a capstan motor stop detection device or a capstan motor rotation direction detection device, another magnetic head is provided in addition to the above magnetic head, facing the magnetized portion on the outer periphery of the flywheel, and its output signal is transmitted to the above magnetic head. It is known that the output signal is placed at a position with a phase difference of 90° with respect to the output signal.

Since the above-mentioned conventional capstan motor speed detection device is a well-known technology, a description of its operation will be omitted, and the operation of the above-described conventional capstan motor stop detection device or rotation direction detection device will be explained. . N-poles and S-poles are magnetized at equal intervals on the outer periphery of the capstan flywheel, and from the MR element head A and MR element head B arranged opposite to the capstan FGA as shown in FIG. and capstan FG
The output of B is obtained. These outputs have a phase difference of 90 degrees from each other. Now, if the capstan motor is rotating in the forward rotation direction, as shown in Figure 6, the capstan F
Output 2 of capstan FGB at rising point 1 of GA
When is at HI level, when the capstan motor rotates in the reverse direction, as shown in Fig. 7, the capstan FGA
The output 2 of the capstan FGB at the rising point 1 of is L
It becomes O level, and the direction of forward rotation and reverse rotation can be determined. Such detection technology is generally used for stop control in intermittent drive of the capstan during intermittent slow playback in consumer VTRs. Alternatively, only one of the capstan FGB was used as a speed detection signal.

0004

[Problem to be solved by the invention] As VTRs, especially movies, have become smaller in recent years, capstan wheels have also become smaller, and the number of magnetic poles that can be magnetized on the outer periphery of the flywheel is physically limited. Become. Generally, if the capstan FG wave number is reduced, the servo control band is reduced, and therefore a considerably sophisticated technique is required to accurately magnetize a small flywheel in large numbers. In addition, in special playback of consumer VTRs and long-term monitoring VTRs, the capstan motor may be rotated at an extremely low speed, and when the capstan motor is rotated at an extremely low speed in this way, the sampling frequency of the FG will increase. As the rotational speed decreases, the servo control band decreases, and as the rotational speed decreases, there is an inconvenience that many magnetic poles must be magnetized.

[0005] This invention was made to solve the above-mentioned problems, and has the same effect as doubling the number of magnetic poles without increasing the number of magnetic poles on the outer circumference of the capstan flywheel. It is an object of the present invention to provide a capstan motor speed detection mechanism for a VTR that can expand the servo control band.

[0006]

[Means for Solving the Problems] A capstan motor speed detection mechanism for a VTR according to the present invention includes two-phase F detected by a pair of speed detectors with a phase difference of 90 degrees from each other.
By taking the exclusive OR of the G signal, a speed detection signal obtained by multiplying the FG signal by 2 is obtained, and this multiplied signal is input to a software-based servo microcontroller, and the comb-shaped digital filter inside this servo microcontroller is input. The two-phase F
It is characterized in that it is configured to remove the influence of phase shift of the G signal.

[0007]

[Operation] According to the present invention, the FG signal obtained by multiplying the two-phase FG signal detected by a pair of speed detectors by 2 is used as the speed detection signal without increasing the number of magnetic poles on the outer circumference of the flywheel. Therefore, it is possible to expand the servo control band equivalent to doubling the number of magnetic poles on the outer circumference of the flywheel. In addition, when obtaining an FG signal that is multiplied by 2 times the 2-phase FG signal mentioned above, the synchronization unevenness of the FG signal due to variations in the mounting accuracy of the speed detector, etc. is removed using a comb-shaped digital filter inside the software-based servo microcontroller. Therefore, high accuracy is not required for mounting the speed detector, and the two-phase FG signal conventionally used for detecting stoppage of a capstan motor can be used as is.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a VTR capstan motor speed detection mechanism according to an embodiment of the present invention. In the same figure, 8 is a capstan flywheel, and N poles and N poles are arranged at equal intervals on the outer circumference of the capstan flywheel. The S pole is magnetized. Reference numerals 3 and 9 designate MR element heads, which are arranged to face magnetic poles magnetized on the outer periphery of the capstan flywheel 8. 4 and 10 are FG amplifiers that increase the outputs of the MR element heads 3 and 9; 5 and 11 are FG Schmitt amplifiers; 6 is an exclusive OR circuit;
7 is a software type servo microcomputer.

FIG. 2 is a block diagram showing the configuration of a comb-shaped digital filter configured in software inside a servo microcomputer. In the figure, 14 is a subtracter, 15 is a multiplier, and 16 is a two-stage delay device. , 17 is an adder, 12 is a switch circuit, and 13 is a switch control circuit for controlling opening/closing of the switch circuit 12.

Next, the operation of the above configuration will be explained. When the capstan flywheel 8 rotates, one MR
An output with a frequency proportional to the flywheel rotational speed is generated from the element head 3, which is amplified by the FG amplifier 4 and waveform-shaped by the Schmitt amplifier 5 to become a capstan FGA signal as shown in FIG. 3(a). . Similarly, the output of the other MR element head 9 becomes a capstan FGB signal as shown in FIG. 3(b). The phase difference π between the capstan FG signal A and the capstan FG signal B is always 90° regardless of the rotational speed of the flywheel 8 due to the relationship between the mounting positions of the MR element head 3 and the MR element head 9.
° is set. Next, the capstan FG signal A and the capstan FG signal B are input to an exclusive OR circuit 6, and the exclusive OR circuit 6 calculates the exclusive OR (OR) of both FG signals A and B. The output from has the waveform shown in FIG. 3(c). This means that capstan FG signal A or capstan FG signal B is
The signal has been doubled. Subsequently, the output from the exclusive OR circuit 6 is input to the servo microcomputer 7. The servo microcomputer 7 measures the period at both the rising and falling edges of the signal multiplied by 2 as described above to control the speed of the capstan motor. Here, since the capstan FG signal is doubled, the sampling frequency is doubled, the servo control band is expanded, and the effect is equivalent to doubling the number of magnetic poles on the outer circumference of the flywheel 8. can get.

By the way, due to the variation in the mounting position accuracy of the MR element head 3 and the MR element head 9, etc.,
As shown in Figures 4(d) and (e), the capstan FGA
The phase difference π between the capstan FGB and the capstan FGB may not be exactly 90°. The output of the exclusive OR circuit 6 at this time becomes a signal with different periods of T1 and T2, as shown in FIG. 4(f). That is, an uneven capstan motor speed detection signal is input to the servo microcomputer 7, which causes a problem. However, in this embodiment, a comb-shaped digital filter as shown in FIG. 2 is configured in software inside the servo microcomputer 7, so that the above-mentioned periodic unevenness is removed. In FIG. 2, switch 12
The comb-shaped digital filter transfer function when closed is given by the following equation (
It can be expressed as 1).

0012

[Math 1]

In equation (1), X(z) is the input signal,
Y(z) is an output signal, and K is a coefficient value of the multiplier 15. This comb-shaped digital filter is sampled at both the rising and falling edges of the output of the exclusive OR circuit 6, and the capstan motor speed detection signal is uneven due to the phase difference between the capstan FGA and capstan FGB. can be removed. For example, 360 SN poles are magnetized on the outer periphery of the flywheel 8, and when this is rotated at a rotation speed of 1 Hz, the output of the exclusive OR circuit 6 is 360 Hz. Since the servo microcomputer 7 measures the period of both edges, the sampling frequency is 720 Hz, and the influence of the period unevenness appears as a 360 Hz component.

The characteristics of the above-mentioned comb-shaped digital filter are shown in FIG.
As shown in , since the gain is attenuated at the frequencies of OHz, 360Hz, and their harmonics, the influence of the above-mentioned periodic unevenness is eliminated. On the other hand, since it no longer responds to disturbances of 360Hz and its harmonic components, switch 1 in FIG.
Opening/closing control is performed such that, for example, the switch 2 is turned ON only for two consecutive sampling periods every rotation of the flywheel 8. When the switch 12 is opened, it does not operate as a comb-shaped filter, but operates as an unevenness canceller that subtracts the periodic unevenness stored in the delay device 16 from the original signal, and does not affect disturbance suppression.

[0015]

[Effects of the Invention] As described above, according to the present invention, the servo control band can be expanded to the same extent as doubling the number of magnetized poles on the capstan flywheel without increasing the number of magnetized poles. It can be effectively applied as a speed detection mechanism for capstan motors in movies that use small motors where it is physically difficult to increase the number of magnetic poles, special playback that rotates the motor at ultra-low speed, and long-duration VTRs. It has the effect of being able to

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a capstan motor speed detection mechanism according to an embodiment of the present invention.

FIG. 2 is a block diagram of a comb filter according to an embodiment of the invention.

FIG. 3 is a timing chart showing the operation according to an embodiment of the present invention.

FIG. 4 is a timing chart showing the operation according to an embodiment of the present invention.

FIG. 5 is a characteristic diagram of a comb-shaped filter according to an embodiment of the present invention.

FIG. 6 is a timing chart of two-phase FG during normal rotation of the capstan.

FIG. 7 is a timing chart of two-phase FG when the capstan is reversed.

[Explanation of symbols]

3 MR element head 6 Exclusive OR circuit 7 Servo microcomputer 8 Capstan flywheel 9 MR element head

Claims (1)

[Claims] Claim 1: A pair of speed detectors that generate two-phase speed detection signals having a phase difference of 90 degrees from each other; A device that doubles the speed detection signal, a software-based servo microcontroller that uses a microcomputer to digitally process the servo function that controls the speed of the capstan motor, and a comb-shaped digital controller configured in software inside this servo microcontroller. A capstan motor speed detection mechanism for a VTR, characterized by comprising a filter.