JP2839603B2 - Tape running device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a video cassette recorder. More specifically, the present invention relates to a tape running device in a computer magnetic tape device or the like, in which a tape slack prevention technology during tape acceleration is improved.

(Prior art) Video cassette recorder. In a tape drive system for a computer magnetic tape device (hereinafter referred to as a VTR), a tape is driven by a capstan and a pinch roller, pulled out from a supply reel and wound on a take-up reel, or the tape is driven by a take-up reel. In general, a system is drawn from a supply reel and wound on a take-up reel. At this time, an appropriate back tension is applied to the supply reel, and the state of pulling out the tape is controlled.

In such a system, when the tape speed is suddenly changed from a low speed to a high speed, such as when switching from a normal playback to a rewind playback mode, the tape accelerated by a rapidly accelerated capstan shaft and a pinch roller is used. The head and various guides act as loads before being wound by the take-up reel, causing the tape to loosen momentarily. For this reason, the head touch of the tape is deteriorated, and noise is generated on the screen in the video cassette recorder.

Further, when the tape is rapidly decelerated as in a recording bose from the recording travel, the reel on the supply side continues to rotate due to inertia, and tape slack occurs.

Tape slack from low speed to high speed can be suppressed if the capstan motor is not accelerated rapidly but accelerated gradually according to the inertia of the supply reel or the load of the cylinder and various tape guides. . This method can also be applied to tape slack at the time of deceleration, and gradually applies a brake to the capstan motor.

In the case of a voltage-driven drive circuit, the current flowing through the coil of the motor is proportional to the voltage applied to the drive circuit, so the speed control signal that gradually increases or decreases the rotation speed must be adjusted to the speed. Continuous waveform
The loosening phenomenon can be prevented relatively easily. However, recently, in order to reduce power consumption, a current control type drive circuit for controlling a current value flowing through a coil of a motor itself has been used. In the case of a current drive type motor drive circuit, the current flowing through the coil of the motor is proportional to the load, but has no relation to the rotation speed. Therefore, a discrete signal is used as the speed control signal applied to the input terminal of the drive circuit. By applying a pulse signal or a pulse signal, a driving mode like a stepping motor is set. In such control,
Slow acceleration / deceleration cannot be performed, and the motor is accelerated / decelerated in steps. For this reason, every time the motor changes the speed, it affects the screen and generates a mechanical sound, thereby deteriorating the product quality.

(Problems to be Solved by the Invention) As described above, in a conventional apparatus that performs tape running by capstan control using a current control type motor drive circuit, the current value flowing through the motor is proportional to the load. Therefore, when accelerating or decelerating the capstan motor, a continuous waveform in consideration of the over / deceleration due to the load cannot be used as the speed control signal applied to the input terminal of the motor drive circuit. Therefore, if a control method using a discrete signal or a pulse signal such as a stepping motor is adopted, the motor is accelerated or decelerated in a stepwise manner, and there is a problem that the tape running performance is deteriorated every time the gear is shifted.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a tape traveling device which eliminates the above-mentioned problems, corrects the acceleration characteristics of a capstan motor so as to match the winding performance of a take-up reel, and performs tape traveling smoothly.

[Means for Solving the Problems] The present invention relates to a current control type motor drive circuit for controlling a current flowing through a coil of a DC motor according to a speed control signal, and detecting rotation of the motor. A motor rotation detecting means for outputting a rotation detection signal, and an error detection circuit for comparing the rotation detection signal with a target blood and outputting an error control signal, wherein the error detection circuit is used when the motor is started or accelerated. A limiter circuit that limits the lower limit level of the signal from the error detection circuit when stopping or decelerating, and forms the speed control signal based on the output from the limiter circuit. It is characterized by having done.

(Operation) In a feedback control system of an asynchronous motor such as a brushless motor, a speed control error signal formed by comparing a feedback signal with a target value is processed by an adjusting unit to form a speed control signal. According to the configuration of the present invention, the level of the speed control error signal is limited so as not to exceed a predetermined level at the time of starting, accelerating, and stopping or decelerating the motor in the adjusting unit. If you do,
Deceleration performance can be reduced. For this reason, even if the brushless motor is driven like a stepping motor, the rotational speed is not accelerated or decelerated, and the rotation can be controlled in accordance with the reeling capacity of the reel base.

Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is a block diagram showing one embodiment of a tape running device according to the present invention, and FIG. 2 is a configuration diagram based on FIG.

First, in FIG. 2, (1) a capstan motor drive circuit, the bridge circuit 4 ₁ by the drive element in a semiconductor, instead of the power supply voltage + B, the speed control signal 16 added as an input signal to the terminal P _1, capstan each U-phase of the motor 4 _2, V-phase, a controllable current-driven current flowing through the W-phase coil, a detailed configuration is as follows.

(A) a bridge circuit 4 ₁ comprises a circuit for switching the current flowing through each phase coil by FG signal from the Hall element for detecting the position of the rotating magnetic field, is driven by the power supply voltage + B.

The (b) terminal P _2, forward / reverse rotation switching signal 3a from the rotation direction control circuit 3 is applied, the signal 3a switches the current flowing in the coil is input to the bridge circuit 3 _1.

The (c) terminal P ₅ is connected the current detection resistor R, the terminal voltage of the resistor R is fed back to the bridge circuit 4 _1.

(D) external reference bias voltage from an external reference bias circuit 5 of the control system is applied to the terminal P _3, the speed control signal
16 is the difference between the external reference bias voltage is inputted to the bridge circuit 4 ₁ with a feedback signal from the current detection resistor R.

Although the (c) terminal P ₄ in this embodiment is an empty terminal, the said terminal P ₄ current limiter circuit is connected.

(2) The servo control circuit 1, the speed switching circuit 2 and the rotation direction switching circuit 3 are circuits for calculating control target values determined for each mode such as start-up, acceleration, deceleration, braking, and steady state. . (A) The servo control circuit 1 outputs a mode signal to designate each mode such as recording, reproduction, fast-forward, and reverse reproduction. The mode signal is supplied to the limiter value setting circuit 9 according to the present invention.

(B) The speed switching circuit 2 calculates and outputs a speed target value 2a and a phase target value 2b according to the mode signal.

(C) The rotation direction switching circuit 3 generates the forward / reverse switching signal 3a according to the mode signal.

(3) detection pulse generated from the speed detection pulse generating circuit 24 is formed from a FG signal detected by the capstan motor 4 _second Hall element. Speed detection pulse and phase detection pulse generation circuit (control pulse regeneration circuit)
Each detection pulse from 34 is a Schmitt circuit 23,3
The waveform is shaped in 3 and input to the frequency dividers 22 and 32 as a feedback signal.

(4) The frequency divider 22 outputs a signal obtained by dividing the speed feedback signal by the ratio indicated by the target speed value.
A signal obtained by dividing the phase feedback signal by the ratio indicated by the phase target value is output.

(5) The circuit shown in the dotted line constitutes an adjustment section of a feedback control system using the capstan motor as an actuator. The adjusting unit has the following configuration.

(A) The speed error detection circuit 21, the phase error detection circuit 31, and the mix circuit 10
The speed and phase error amounts for each target value are detected and mixed to form a speed control error signal 10a for forming the speed control signal 16. The speed control error signal 10a from the mix circuit 10 is input to the bias shift correction circuit 12,
The bias value is corrected to the bias value from the bias shift detection circuit 11. This is because the speed control error signal 10a obtained from the mix circuit 10 causes an offset with the reference bias level set in the control system by the external reference bias circuit 5, so that this offset amount is detected and the internal bias addition circuit 13 at the subsequent stage detects the offset amount. The internal bias of the adjustment unit to be set is corrected.

(B) The limiter value setting circuit 9 is the servo control circuit 1
A limit value for limiting the signal from the internal reference bias adding circuit 13 of the control system at a predetermined level is generated in accordance with the mode signal from the control system. The signal from the internal reference bias adding circuit 13 is limited in a limiter circuit 7 so as not to exceed the above limit value. From the limiter circuit 7, a final speed control error signal 7a is obtained.

(6) The PWM (pulse width modulation) circuit 14 and the LPF (low-pass filter) 15 constitute a digital conversion circuit and an analog conversion circuit. The PWM circuit 14 outputs a PWM signal whose pulse width is controlled according to the level of the final speed control error signal 7a, that is, the amount of error displacement from the target value. LPF15 is PWM above
The signal is smoothed and a speed control signal 16 in the form of an analog signal is output.

With this configuration, the acceleration or when starting the capstan motor 4 ₂ (hereinafter referred to as the time of acceleration), the level of the speed error signal 10a is restricted so as not to exceed a predetermined level, the capstan acceleration performance Can be dropped.

The above specific configuration is represented by blocks shown in FIG.

That is, in FIG. 1, the elements corresponding to those in FIG. 2 are denoted by the same reference numerals. In the figure, the circuit on the left side of the alternate long and short dash line is the adjustment unit. Further, the control section and the PWM circuit 14 are integrated on the same chip. Bias shift detection circuit 11
Is a configuration in which the output from the delay element and the adder is multiplied by an integer (n) by a factor of 1 to detect a bias shift amount. The bias shift correction circuit 12 is constituted by an adder.

According to the above, as in the inverse backward reproduction mode from the playback mode, when increasing the rotation speed of the capstan motor 4 _2,
A mode signal indicating a limiter value suitable for reverse playback is input from the servo control circuit 1 to the limiter value setting circuit 9. As a result, a limiter value based on the mode signal is output from the limiter value setting circuit 9 and is supplied to the limiter circuit 7, whereby the internal reference bias circuit 13
Is regulated by the level of the limiter value. The final speed control error signal 7a thus obtained is PW
The pulse width modulation range related to the output of the M modulation circuit 14 is controlled to be narrower than when the limiter value is not set,
The speed control signal 16 based on this limits the peak value of the current flowing through the motor coil and reduces the acceleration rate as compared with the case where no limiter value is set. In this embodiment, the drop of the acceleration rate, head, by aligning the winding capacity shortage of the take-up reel by the running load of various tape guides, to suppress the acceleration performance of the capstan motor 4 _2, It is possible to match the capstan acceleration ability with the winding ability of the reel base on the winding side. Therefore, the head touch of the tape does not deteriorate.

Note that the limiter operation period of the limiter circuit 7 is limited to a certain period during acceleration.

In short, current limit control is performed in which the start-up current during acceleration is limited. According to such setting of the limit value, as shown in FIG. 3, the terminal P ₄ of the motor drive circuit 4, by connecting a current limiter circuit 35, the same as the mode signal and the embodiment, the limiter value May be set. However, as can be seen by comparing FIG. 2 and FIG. 3, in FIG. 2, the current limit function can be included in the adjustment unit, and therefore, as shown in FIG. No need to connect 35. In FIG. 3, the same components as those in FIG. 2 are denoted by the same reference numerals. However, the circuit of FIG.
The bias shift correction circuit 12 and the like as shown in the figure are omitted.

4 and 5 are a configuration diagram and a block diagram showing another embodiment of the present invention.

The feature of the present embodiment is that the bias correction is also performed on the limiter value for the speed control signal according to the present invention. That is, a bias shift correction circuit 8 is provided between the limiter value setting circuit 9 and the limiter circuit 7, and the bias for the limiter value is corrected by using the detection output 11a from the bias shift detection circuit 11 in the bias shift correction circuit 8. It does.

This makes it possible to correct the variation in the bias value output from the external reference bias circuit 5. 2 has no problem if the internal bias added by the internal reference bias adding circuit 13 and the internal reference bias actually applied to the motor drive circuit 4 are the same. , Also affects the internal reference bias. Bias shift correction circuit 8 of the present embodiment
Is obtained by correcting the variation of the external reference bias circuit 5.

With the configuration shown in FIG. 4 (FIG. 5), this configuration can be used without being affected by the variation of the bias caused by the variation of each circuit element in the control system and the variation of the external reference bias caused by the variation of the external circuit element. Acceleration and start-up current limiting according to the invention can be performed. Such a correction is a merit that cannot be realized by the method of FIG. 3 in which the current limiter circuit 5 is provided outside to limit the current.

In the embodiment shown in FIG. 6, the limit operation according to the present invention is performed even at the time of stop or deceleration (hereinafter referred to as deceleration) such as recording → recording pause.

In general, at the time of deceleration as described above, the motor is set in a free-run state, and servo is applied when the motor reaches a target value. However, also in this case, when the tape running load is light, the tape may be loosened.

In the present embodiment, the setting of the limiter value in the embodiment of FIG. 1 is separated into an upper limiter value setting circuit 9a and a lower limiter value setting circuit 9b. In the upper limiter value setting circuit 9a, a limiter value for limiting the upper limit level of the speed control error signal 10a during acceleration is set by the mode signal a supplied from the servo control circuit 1, as in the embodiment of FIG. You. In a lower limiter value setting circuit 9b, a limiter value for limiting a lower limit level of the speed control error signal 10a at the time of deceleration is set by a mode signal b generated from the servo control circuit 1 at the time of deceleration.

Further, in the present embodiment, the limiter values set in the upper and lower limiter value setting circuits 9a and 9b are adjusted by bias shift correction circuits 8a and 8b which perform the same bias shift correction as the embodiment of FIG. The bias level is corrected by the detection signal 11 a from the bias shift detection circuit 11 and supplied to the limiter circuit 7.

As described above, at the time of deceleration, the speed and phase error detection circuit
By regulating the signal level of the speed control error signal 10a based on the error outputs from the motors 21 and 31, the current flowing through the motor is limited so as not to be lower than a predetermined value. Thus, the deceleration characteristic of the motor is slowly decelerated similarly to the characteristic at the time of acceleration, and the tape does not loosen. In addition, since the bias at the lower limit level at that time is corrected in accordance with the reference bias set in the control system, it is not necessary to correct the motor drive circuit 4 by directly limiting the current.

When the present invention was actually applied to a video cassette recorder, the limiter control could be performed with higher precision than before, the response during acceleration or deceleration could be arbitrarily selected, and the limit value could be changed according to the tape speed. Power supply fluctuations due to peak currents during acceleration / deceleration could be reduced.

[Effects of the Invention] As described above, according to the present invention, tape slack during acceleration and deceleration of the capstan motor can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a tape running device according to the present invention, FIG. 2 is a block diagram of the above-described embodiment, FIG. 3 is a block diagram in the case where current limiter control is performed outside a control system,
FIGS. 4 and 5 are a configuration diagram and a block diagram showing another embodiment of the present invention, and FIG. 6 is a block diagram showing still another embodiment. 1 servo control circuit 2 speed switching circuit 3 rotation direction switching circuit 4 capstan drive circuit 5
…… External reference bias circuit, 7 …… Limiter circuit, 9…
... Limiter value setting circuit, 10 ... Mix circuit, 11 ... Bias shift detection circuit, 12 ... Bias shift correction circuit, 13
…… Internal reference bias addition circuit, 14… PWM circuit, 15…
... low-pass filter, 22 ... frequency divider, 24 ... speed detection pulse generation circuit, 32 ... frequency divider, 34 ... phase detection pulse generation circuit.

Claims (2)

(57) [Claims] 1. A motor drive circuit of a current control type for controlling a current flowing in a coil of a DC motor in accordance with a speed control signal, a motor rotation detecting means for detecting rotation of the motor and outputting a rotation detection signal, An error detection circuit that compares the rotation detection signal with a target value and outputs a speed control error signal; and, when starting or accelerating the motor, limits an upper limit level of a signal from the error detection circuit, and stops or decelerates. A limiter circuit for limiting a lower limit level of a signal from the error detection circuit, and a drive signal processing circuit for forming the speed control signal based on an output from the limiter circuit and for limiting a current flowing to the motor. A tape running device, comprising: A bias shift detecting circuit for detecting an offset between a reference bias level set in a control system and a bias level at an output of the error detecting circuit, wherein an upper limit level and a lower limit level limited by the limiter circuit are set. 2. The tape running device according to claim 1, wherein the correction is performed based on a detection output of a bias shift detection circuit.