JPS58186812A - Speed control circuit - Google Patents

Abstract

PURPOSE:To control the rotating speed of a rotating body with high precision by using the output of a rotation period detecting circuit of the rotating body for correcting a rotating speed signal based upon the time during which the rotating body passes between a couple of detecting elements fitted to the rotating body. CONSTITUTION:A capstan 1 is fitted with the rotating body 2 of a frequency generator as an element to be detected and a detecting element 3 is disposed at the position opposing to it. The element 3 is composed of a couple of heads Ha and Hb arranged at an interval l, and detecting outputs Sa and Sb corresponding to the rotating speed of the rotating body 2 are outputted from the heads Ha and Hb. Signals Sa and Sb are inputted to a rotating speed detecting circuit 6 through wave form shaping sections 4 and 5. The circuit 6 outputs the rotating speed signal Sa1 based upon the time difference between the two heads to a speed comparator 8. The rotation period detecting circuit 12 inputs the signal Sb to output a speed signal SD2 corresponding to the rotation period and a comparison 13 with the reference signal SR is made to input a comparison output SC2 to a corrected signal generating circuit 14. The circuit 14 outputs a corrected signal DV, and a comparison 8 between the sum signal S'R of the corrected signal and signal DV obtained by addition 15 is made to perform control so that SD1 is equal to S'R, driving a motor 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating body speed control circuit suitable for application to a capstan servo system of a VTR.

In order to accurately run the tape at a specific speed required for variable speed playback in variable speed playback mode, it is necessary to ensure that the rotational speed of the capstan is always at the standard rotational speed required for that variable speed playback mode. It is necessary to apply a speed servo to For this purpose, a capstan servo recess is usually provided.

Among the speed control circuits used in this servo circuit, there is one that obtains speed information of the capstan from a frequency generator (FC) provided in the capstan.

In this type, speed information is detected by counting frequency signals obtained from the FC, and the rotational speed of the capstan is controlled based on this speed information.

In a speed control circuit using an FG, it usually takes about 1 second to obtain frequency data from the FG and control the capstan, so the rotation speed of the capstan can be adjusted from 0 to
It cannot be applied to high-precision servo systems that are designed to suppress speed errors to 1%.

On the other hand, some devices obtain capstan speed information by detecting the rotation period of the capstan. An FG rotating body is attached to the capstan and has N magnets magnetized at a predetermined pitch. in this case,
If the FG rotating body has uneven magnetization pitch, the detection output of the rotation period will have jitter, and this jitter will fluctuate the rotation speed of the capstan, so it cannot be applied to high-precision servo systems as mentioned above. .

In addition, by arranging a pair of detection elements at a predetermined interval as detection elements of the FG rotating body and measuring the time of the FC rotating body passing between these detection elements,
Some control the rotation speed of the capstan. Although this configuration can avoid the above-mentioned drawbacks, the accuracy of the mounting interval of the detection elements may differ depending on the mounted VTR, so the control accuracy of the servo circuit in this case depends on the mechanical accuracy of the detection elements. Depends on installation accuracy. Normally, it is quite difficult to keep this mounting accuracy within a predetermined range.

Therefore, in this invention, in consideration of these points, in order to compensate for each of the above-mentioned drawbacks, 2i or more different speed information detection means, in particular, a capstan rotation period detection means and a transit time detection means are provided in this invention. A speed servo circuit is constructed by providing a detection means.

Next, a case in which an example of the present invention is applied to the speed control circuit of the capstan servo system described above will be explained with reference to FIG. 1 and subsequent figures.

In FIG. 1, an FG rotating body (2) used as a detected element is attached to a capstan (1).

On the circumferential surface of the FG rotating body (2), N poles and 8 poles are magnetized at a predetermined pitch as shown in the figure to form magnetic poles. In this example, one in which the number of magnetic poles P is 96 is used.

On the other hand, a detection element (3) is arranged at a position facing the FG rotating body (2). The detection element (3) consists of a pair of heads Ha and Hb arranged at a predetermined distance l as shown in the figure.
In this example, the heads Ha and Hb are integrated. The predetermined interval 1 is, for example, about one length of the magnetic difference pitch. However, this value is just an example.

Magnetoresistive elements whose resistance value changes depending on the strength of the magnetic field are used as the heads Ha and Hb.

From heads Ha and Hb, as shown in Figure 2, FG
Detection output 8 with period T corresponding to the rotational speed of the rotating body (2)
a, 8b are obtained. If one of the detection outputs 8a is output from the head Ha that precedes the rotation direction of the FG rotating body (2), then the detection output that is output from the head Hb that follows based on this detection output Sa. sb (corresponding to the time it takes for the same magnetic pole to pass through the heads Ha and Hb), and the speed of the capstan (1) is controlled so that this becomes the reference value.

This is because the time difference ΔT corresponds to the speed change of the FG rotating body (2). Therefore, this detected time difference ΔT has no relation to the unevenness of the magnetization pitch of the FG rotating body (2). However, the setting value is 1 for the actual mounting interval 1 of heads Ha and Hb. Then, the time difference ΔT is expressed by the head Ha mounted on the VTR.

If the mounting interval l of the Hb is different, the absolute rotational speed of the capstan (1) will be slightly different even if ΔT is controlled to the same value.

In order to ensure that the absolute rotational speed also reaches a set value, the present invention includes a detection means for detecting the rotation period of the capstan (1) in addition to the transit time detection means for the FG rotating body (2). provided. In this example, the transit time detection means shown in FIG. 1 is also used as rotation period detection means.

FIG. 3 shows an example of a speed control circuit using these detection means.

Detection output S output from a pair of heads Ha and Hb
a and Sb are limiter amplifiers (4) for waveform shaping, respectively.
, (5) to the rotational speed detection circuit (6), and the instantaneous time difference ΔT of the FG rotating body (2) is detected. At the same time, this time difference ΔT is calculated as the rotational speed 1 degree VD (this is referred to as ■ゎ). is converted into a speed signal SD□ related to

On the other hand, a reference signal SR corresponding to the reference speed (the value differs depending on the playback mode) is supplied to the terminal (7), and this is applied to the first speed comparator (8
), the speed fluctuation in a predetermined reproduction mode is detected, and the comparison output is supplied to the motor drive circuit (9) to create a closed loop so that the rotational speed of the capstan motor (11) becomes the reference speed ■8. controlled.

Since the time difference ΔT is proportional to the mounting interval l of the heads Ha and Hb as shown in equation (1), if there is variation in the mounting interval l and is between l and lo, the capstan (1) will change as a result of closed loop control. Even if the rotational speed ■9□ matches the reference speed ■, it does not absolutely match the reference speed ■□.

Therefore, for high-precision speed control, the rotation speed ■.

It is necessary to further control the output of the capstan (1), and therefore, in the present invention, the output of either the head Ha or Hb, in this example the detection output 8b, is supplied to the rotation period detection circuit (12) to detect the rotation period of the capstan (1). The rotation period (average value) is detected, and the output of this rotation period is output to the capstan (1).
is converted into a speed signal 5Dll related to the rotational speed VD (this is referred to as vD2).

Since the average value of the rotation period is not affected by magnetization pitch unevenness, it is extremely accurate speed information.

This speed signal SD jl, which is related to the rotation period, is
Since it does not depend on the mounting interval j of a and Hb and is determined only by the rotational speed of the capstan (1), this speed signal S and the reference signal SR are supplied to the second speed comparator 2 (13). The speed error is determined. Il”f
l.

If not, even if 8D□=SR, 8Dla
"8R", the comparison output "CS1" at this time is supplied to the correction signal forming circuit (14) to form the speed correction signal DV, which is sent to the synthesizer (15) as the reference signal 8.
R and the reference signal S/ after the addition is supplied to the first speed comparator (8).

Therefore, the rotational speed of the capstan (1) is controlled to match this reference signal S/. If SD□=wax, it becomes 8D2 "" SR, and at this time the speed control loop becomes stable.

In this way, the detection output 8a of the pair of heads Ha and Hb
.

sb and the rotation speed detection circuit (6), the capstan (1
) instantaneous rotational speed ■. , is detected, and the rotation speed vDI is controlled so as to be equal to the reference speed si set in each variable speed reproduction mode. Then, the rotation speed vDI based on the average value of the rotation period of the capstan (1) detected by the rotation period detection circuit (12) is the reference speed V
It is controlled to be equal to R.

By this instantaneous value control and average value control, the capstan (
1) is controlled with high precision to a set rotational speed. In the rotation period speed control system, control is performed to compensate for variations in the mounting distance between the heads Ha and Hb. The capstan (1) can be controlled extremely precisely to the absolute reference speed regardless of variations in speed.

The embodiment shown in FIG. 4 is a partial modification of the embodiment shown in FIG. 3, and the correction signal forming circuit (14) shown in FIG. The correction coefficient generator (16) is configured as a correction coefficient generator (16). Accordingly, a coefficient unit (17) consisting of a multiplier or the like is used, and the output of the coefficient unit (reference signal S'R) is changed in accordance with the correction coefficient.

The embodiment shown in FIG. 5 directly connects the first speed comparator (8) to
This is a case where the reference signal SR is supplied and instead of this, the speed signal sD□ supplied to the first speed comparator (8) is configured to be corrected by the speed signal sD2 related to the rotation period (9). For this purpose, the speed signal SDI is converted into a coefficient multiplier (
17), and the corrected speed signal B'
The speed of D is compared with the speed signal SD regarding the rotation period by the second speed comparator (13), and the output thereof controls the correction coefficient generator (16) to determine the correction coefficient to be added to the coefficient unit (17). Be changed.

Therefore, the speed signal S/ after coefficient correction based on the time difference ΔT
Closed-loop I control is performed so that the signal approaches the reference signal 8R, and the correction coefficient is controlled so that the corrected speed signal 8/D0 becomes equal to the speed signal 8□ regarding the rotation period.

In the embodiment shown in FIG. 6, the coefficient unit (17) is controlled by the reference signal field and the output of the correction coefficient generator (16), and the output of the coefficient unit (17) and the speed signal S are controlled.
An adder (18) for adding DI is provided.

According to this configuration, when the tape speed in the variable speed playback mode is changed, the data of the coefficient unit (17) is immediately changed, so the correction coefficient of the correction coefficient generator (16) does not need to be changed and can be used as is.

(10) In the example of FIG. 5, the coefficient multiplier (17
), so if you change the tape speed, the correction factor generator (1
The correction coefficient 6) is also changed at the same time.

In the embodiment shown in FIG.
) is provided. A speed command signal C is supplied to the terminal (20). The speed command signal C8 is a signal regarding the ratio of the reference playback speed and the commanded speed, that is, the speed ratio. This speed command signal C8 is supplied to the first and second coefficient multipliers (17) and (19).

The output of the first coefficient unit (17) is added to the speed signal SD0 in the adder (21), and then added to the speed signal SD0 in the second speed comparator (
In step 13), the speed is compared with the speed signal 5D11. If there is a speed error, the correction signal CD obtained from the correction coefficient generator (16) changes, and the output of the first coefficient unit (17) is changed. This control loop controls the speed signal S'D0 to become the speed signal SD related to the rotation period.

The correction signal CD is also supplied to the second coefficient multiplier (19), and speed control is performed such that the speed signal SDI matches the reference signal 8'R output from the second coefficient multiplier (19).

In FIG. 7, the terminal (22) is supplied with a reference speed signal (fixed value) SRR for giving the necessary tape speed in the recording mode.
The combined output of the correction signal CD and the correction signal CD is supplied to the R2 coefficient unit (19). (23) shows the subtraction formula for composition.

According to the configuration shown in FIG. 7, since the first coefficient multiplier (17) only multiplies each data of the speed command signal C8 and the correction signal CD, it is possible to use one with a small pit capacity.

As explained above, according to the present invention, the rotation speed detector (6) measures the instantaneous rotation speed of the capstan (1) to control the rotation speed of the capstan (1), and the rotation period detector (6) measures the instantaneous rotation speed of the capstan (1). 12), the capstan (1
), and the rotation speed is calculated from this to control the rotation speed of the capstan (1).

Accordingly, first, the instantaneous rotational speed of a pair of heads Ha
, Since it is calculated from the time of passing through Hb, F
Even if there is magnetization pitch unevenness in the G rotating body (2), this does not affect the speed control of the capstan (1). In addition, since the speed is controlled by the output that detects the rotation period of the capstan (1), even if there is an error in the installation interval l between the pair of heads Ha and Hb, this will not affect the rotation speed control accuracy. Never happened.

Of course, since the speed control is based on the average value output of the rotation period, it is possible to reliably eliminate period errors that cannot be corrected by instantaneous speed control.

Note that the present invention can also be applied to speed control circuits for rotating bodies other than capstans.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of means for detecting the rotational speed of the capstan, Figure 2 is a waveform diagram of the detection signal, and Figures 3 to 7.
Each figure is a system diagram showing an example of a speed control circuit according to the present invention. (1) is a capstan, (2) is a rotating body which is a detected element, (3) is a detection element consisting of heads Ha and Hb, (
6) is rotation (13) speed detection circuit, (7) is rotation period detection circuit, (8),
(13) is a speed comparator, (14) is a correction signal CD forming means, and (11) is a capstan driving motor. (14)

Claims (1)

[Claims] a pair of detection elements arranged close to a rotating body at a predetermined interval; a detected element attached to the rotating body and detected by the detection element; and the detected element passing between the pair of detection elements. A circuit that detects the rotational speed of the rotating body based on time, a circuit that detects the rotational period of the rotating body based on the detection output from the detection element, and an output from the rotational period detection circuit that detects the rotational speed of the rotating body. A speed control circuit for a rotating body, comprising a circuit for correcting the rotational speed of the rotating body.