JPS59124054A - Speed controlling method of capstan motor of magnetic tape device - Google Patents

Abstract

PURPOSE:To perform optimum speed control over a capstan by driving the short-period speed variation and long-period speed variation of a capstan motor, and summing up both speed variations to perform speed control. CONSTITUTION:An averaging circuit 15 calculates the mean value of the period counted values of tachometer pulses up to now including the current value every time a tachometer pulse is generated, and a register 16 holds the mean value. A comparator 17 compares the mean value from the register 16 with a reference mean value S4 to obtain information on long-period speed variation and its difference is outputted to an adder 18. A comparator 12, on the other hand, compares the period counted value of the tachometer pulses with a reference value S2 and outputs its difference to the adder 18. The adder 8 sums up those difference signals to generate a speed difference signal. This speed difference signal is converted by a D/A converter 13 into a voltage corresponding to the speed difference signal and the signal is amplified by a power amplifier 14, whose output is inputted to the capstan motor 9 to generate torque proportional to the level of the voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a capstan motor speed control method, and in particular a speed control method for maintaining the speed of a capstan motor for magnetic tape feeding at a reference speed over short and long periods of time. This relates to a control method.

(2) Background of the Technology In a device as shown in Fig. 1, in which a magnetic tape 1 is fed from a payout reel 2 to a take-up reel 3 by a capstan 4, the capstan motor rotates in order to run the magnetic tape 1 at a constant speed. The speed is controlled to be constant. In general, the capstan 4 is directly connected to the capstan motor shaft, and the capstan motor is equipped with a tachometer that works with it.By measuring the pulse period of the pulse train emitted from the tachometer, the rotational speed of the capstan 4 and the reference The speed is controlled by detecting the slowness of the speed and accelerating or decelerating the capstan motor. However, in such a tape feeding device, in order to truly match the tape running speed during tape recording and playback, speed control is performed not only for a short period of time but also for a long period of time, and the tape is moved at a constant speed. Getting it to run has become an important issue. In addition, the first
In the figure, reference numeral 5 indicates a tape guide, reference numeral 6 indicates a magnetic head, and reference numerals 7 and 8 indicate a panzer column, respectively.

(3) Prior Art and Problems An example of a conventional speed control method for the capstan 4 is shown in FIG. This is a system in which the speed of the capstan is controlled by a control circuit that is sequentially connected to a capstan motor 9 for driving the capstan 4 and a tachometer lamp 14. In FIG. 1, in order to cause the tape 1 to run at a constant speed, it is sufficient to control the period of the pulses generated by the tachometer sum to be kept constant. Therefore, in the control circuit, the period of the tachometer pulse is counted by the period counter 11 using the clock signal S1 obtained from the high precision oscillator. This count? , is compared with a reference period count value S2 corresponding to the speed to be controlled in the comparator 12. A control signal S is input to the comparator 12 so that the reference value S2 can be changed.

The difference between the above count value and the reference value S2 represents the difference between the current speed and the set speed of the capstan motor 9, so this is
-'A converter 13 converts the voltage into a voltage proportional to the value and applies it to the power amplifier 14. And this voltage at power amplifier 14? The voltage is amplified and input to the capstan motor 9 to generate a torque proportional to the magnitude of the voltage.

In this speed control method, the current speed of the capstan motor 9 is slower than the set speed v8 when measured in a human condition in FIG. 3 (the period T of the tacho pulse at A is long).
In this case, since the count value of the period counter 11 becomes larger than the reference value S2, a positive voltage is output from the DA converter 13.

Therefore, a positive voltage is applied to the power amplifier, and a larger current flows through the capstan motor 9, so a larger torque is generated, accelerating the capstan motor 9 and the capstan 4, and approaching the set speed V. go. Then, when the set speed is reached, the difference between the count value and the reference value S2 disappears, the torque no longer increases, and the acceleration ends.

Conversely, when the current speed of the capstan motor 9 is faster than the set speed, as in the case of measurement in state B in FIG.
3 outputs a negative voltage. As a result, the output current of the power amplifier 14 decreases, the motor torque decreases, and the capstan speed is reduced due to friction between the capstan motor 9 and the load, and approaches the set speed.

In this way, the tape is controlled so that it always runs at a predetermined speed.

By the way, some recent magnetic tape devices have two or more tape running speeds, high and low, in the same device, but when recording and reproducing information on a magnetic tape, regardless of the running speed, The tape must be started and stopped at defined distances from each other. For this purpose, since it is most difficult to start and stop the tape at the fastest running speed of the various running speeds, the capstan motor 9 and its speed control circuit must be adjusted in accordance with this fast running speed. is determined. However, when controlling high and low running speeds using the same speed control circuit, the above speed control method requires that each time a tough pulse is output, it corresponds to the running speed at that time. In order to compare the counted value and the reference value, for example, as shown in FIG. 4, when the tape is running at a low speed, the sampling period is longer than when it is running at a high speed. On the other hand, since the change in the capstan motor 9 current, that is, the increase or decrease in torque in response to the increase or decrease in the difference between the period count value of the tacho pulse and the reference value, is the same at both high speed and low speed, the acceleration of the capstan motor 9 is too large when traveling at low speed, and the speed fluctuation range δ becomes large.

Therefore, in such a magnetic tape device, when running at low speed, the conversion rate of the motor current to the difference between the count value and the reference value is reduced, and the sampling period is lengthened as shown in Figure 4 (d). Also, make sure that the speed fluctuation range does not become large.

However, with the conventional speed control method in which the capstan motor 9 generates a motor torque proportional to the difference between the count value of the period of the tacho pulse and the reference value, long-term fluctuations such as load friction are added to the tape running system. In some cases, sufficient control may not be possible. For example, if the load due to friction increases on the bearings or magnetic tape of the capstan motor 9, in order for the capstan 4 to maintain the same speed against this increase in load, the torque generated by the motor must be increased. However, with the above control method, the rotational speed of the capstan motor 9 is unbalanced in that even if the torque increases, the traveling speed becomes slower than the set speed.

In particular, when driving at low speeds, the conversion ratio of motor current to the difference between the counted value and the reference value is set small, so the balance point Va is far away from the set speed ■2 for the same load fluctuation (Figure 4 (d)). (indicated by α), which results in a long-term speed fluctuation range.

(4) Purpose of the Invention The present invention has been made by focusing on the above-mentioned conventional problems.The purpose of the present invention is to prevent short-term damage to the tape running system when performing constant speed control of the capstan of a magnetic tape device. Or, in the case 11 where long-term load fluctuations are added, the present invention aims to provide a speed control method that can control both short-period fluctuations and long-period fluctuations and optimally control the capstan.

A second object of the present invention is to provide a speed control method that prevents speed fluctuations from being sensitive to instantaneous disturbances such as noise by setting response sensitivities to short-period fluctuations and long-period fluctuations. That's true.

(5) Structure of the Invention In order to achieve the above object, the present invention connects a tachometer to the capstan motor, measures the period of the tacho pulse obtained by the tachometer, and applies the measured value to the set speed of the capstan motor. While comparing with a first reference value of the corresponding tacho pulse period to calculate the difference, an average value is obtained for the plurality of measured values, and this average value is compared with a second reference value of the tacho pulse period to calculate the difference. The present invention is characterized in that the current or voltage to the capstan motor is controlled according to the calculated value and the sum of the differences between the two, and the speed of the capstan motor is controlled to match the set speed.

(6) Embodiments of the invention Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. - FIG. 5 is a diagram showing an embodiment of the present invention.

In this figure, circuits that are the same as those used in the speed control circuit shown in FIG. 2 are given the same reference numerals and designations. That is, capstan 4, capstan motor 9, tachometer 10, period counter 11, comparator 12, D-A
The converter 13 and power amplifier 14 are used in the same manner as before. In the speed control circuit according to this embodiment, the averaging circuit 1
5, a register 16, and a second comparator 17, and further includes an adder 18 that receives signals from both the comparator 12 and the second comparator 17 and outputs them to the DA converter 13. ing. The averaging circuit 15, the register 16, and the second comparator 17 are connected to the period counter 11 in a parallel relationship to the comparator 12.

This averaging circuit 15 adds up the current tough pulse period count value and the average value of the tacho pulse period count values up to the previous time and calculates the average value, thereby calculating the past several times including the current one. Average value of tacho pulse period count? Calculate each time a tacho pulse appears. The register 16 holds the average value calculated by the averaging circuit and outputs it to the second comparator 17, while outputting it to the averaging circuit 15 to calculate the next cycle count average value. Second comparison 517
compares the cycle count average value sent from the register 16 with the second reference value, that is, the average reference value S4, obtains relatively long-term speed fluctuation information, and outputs the difference to the adder 18. . Also, in the comparator 12, the tacho pulse period count value sent from the period counter 11? It is compared with a reference value 82 (which is used as the first reference value with respect to the second reference value S4), and outputs the difference to the adder 18. The adder 18 is
A difference signal between the tacho pulse period count value and the first reference value S2 and a difference signal between the period count average value and the second reference value S4 are added to form a speed difference signal. Note that a control signal S is input to the comparator 12 and the second comparator 17, and the respective first and second reference values S, , S are input.

? In conjunction with switching between low speed and high speed, or switching operation of tape running speed, a command is given as to whether or not to execute speed control using the period count average value. Note that the same value may be used for the reference values S2 and 84.

Addition-a By the addition operation of two difference signals in a,
A speed difference signal is obtained which is a combination of the speed difference between the current speed and the set speed of the capstan motor 9, that is, a short-term speed fluctuation component and a long-term speed fluctuation component due to frictional fluctuations in the tape running system.

Therefore, by applying this speed difference signal to the DA converter 13, converting it into a voltage corresponding to the speed difference signal, amplifying it in the power amplifier 14, and inputting it to the capstan motor 9, the magnitude of the voltage can be adjusted. Generates proportional torque.

As described above, in the speed control method according to the present embodiment, it is possible to control the speed of the capstan motor by detecting not only short-term speed fluctuations but also long-term speed fluctuations. Capstan motor 9 due to etc.
As shown in Fig. 4(d), the rotational speed will not be balanced at a point far away from the set speed. There is a method. For example, each time a tacho pulse appears, the cycle count value at that time may be stored, and the cycle count value for several past cycles (for example, 5 cycles) may be taken out and used as the cycle count average value. In adder 18, when adding the difference signal based on short-term speed fluctuations and the difference signal based on long-term speed fluctuations, both difference signals are multiplied by a predetermined proportional coefficient, and the addition specific gravity changes depending on the tape running speed. By doing so, it is possible to differentiate the response sensitivity to short-term and long-term speed fluctuations, and to minimize speed fluctuations at each tape running speed.

(7) As described in detail, the present invention determines short-term speed fluctuations and long-term speed fluctuations of the capstan motor of a magnetic tape device,
Since the speed is controlled by adding both speed fluctuations,
Optimal speed control of the capstan can be performed against relatively long-term speed fluctuations caused by load friction fluctuations applied to the tape running system. In addition, since it has a function to average the speed information and feed it back, even if there is a momentary disturbance such as noise, it is possible to suppress the oversensitive reaction of the capsulator/motor.

Furthermore, if the magnetic tape device has multiple tape running speeds, the speed control most suitable for the set speed is performed by differentiating the response sensitivity to short-term and long-term speed fluctuations when switching the control circuit system. Various effects can be obtained, such as the ability to

[Brief explanation of the drawing]

Fig. 1 is a front view showing a general example of a magnetic tape device, Fig. 2 is a block diagram showing an example of a capstan speed control method conventionally employed in magnetic tape devices, and Fig. 3 is a conventional speed control method. FIG. 4 is a diagram showing the control state of the motor speed in the control method, (a) is the tacho pulse, (b) is the motor voltage applied to the u capstan motor, (C) is a diagram showing the balance state of the motor speed, and FIG. This figure shows the conventional speed control state during low-speed running of a magnetic tape device with multiple tape running speeds, in which (a) shows the tacho pulse, (b) shows the motor voltage, and (c) shows the motor speed with a large fluctuation range. FIG. 5 is a block diagram showing a capstan speed control method according to an embodiment of the present invention.

Claims (1)

[Claims] 1) Connect a tachometer to the capstan motor, measure the period of the tacho pulse obtained by the tough meter, and use the measured value as the first reference value of the tacho pulse period corresponding to the set speed of the capstan motor. While comparing and calculating the difference, calculate the average value of multiple measured values, compare this average value with a second reference value of the entire tacho pulse period, calculate the difference, and add the difference between both of these values. 1. A method for controlling the speed of a capstan motor in a magnetic tape device, comprising: controlling current or voltage to a capstan motor according to the set speed, and controlling the speed of the capstan motor to match the set speed. 2) In the process of adding the difference between the measured value of the tacho pulse period and the first reference value and the difference between the average value and the second reference value, the addition ratio K is changed between the two differences. A method for controlling the speed of a capstan motor of a magnetic tape device according to claim 1, characterized in that: