JPS6125081Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a magnetic tape device that drives a magnetic tape by frictionally driving the magnetic tape using a capstan directly connected to a DC motor. The present invention relates to a control circuit for canceling the control of.

In a magnetic tape recording and reproducing apparatus for a computer, a tape driving electric motor M is controlled as shown in FIG. The electric motor M has a low moment of inertia and a low torque constant, and a large current is temporarily passed during start-up and stop control. This is because it is necessary to control the magnetic tape TP, which is frictionally driven by the capstan CPS directly connected to the electric motor M, so that it repeatedly runs forward, stopped, and reversed at high speed in the shortest possible time. The child is a moving coil type and uses thin windings. Therefore, since the continuous rated current value of the electric motor M is extremely small, starting and stopping are controlled in the shortest possible time. After a predetermined period of time has elapsed since startup, constant speed control is established to form a feedback loop. A digital tachometer DT is attached to the shaft of the electric motor M to obtain a predetermined number of pulse signals per revolution of the electric motor, and a pulse train of a frequency proportional to the motor rotation speed is obtained in the tachometer circuit TCC. Next, the pulse counting circuit CT counts the number of pulses of the reference clock signal generated between adjacent pulses. The constant speed control circuit CVC compares the counted value with a speed reference value given as a rotational speed reference signal to obtain a value proportional to the difference in speed, which is converted into an analog signal by the digital-to-analog converter DA.
Depending on the magnitude of this value, the output current of the constant current drive circuit CID is slightly changed to maintain constant speed rotation.

During constant speed control operation or when an abnormal condition occurs such as the motor stopping, the count value of the pulse counting circuit CT becomes extremely large, causing the output current of the constant current drive circuit CID to become extremely large. A large current flows continuously through the armature, leading to armature burnout.

The purpose of the present invention is to provide a DC motor control circuit that is capable of canceling constant speed drive control by providing a device that detects the generation of an abnormal signal when the capstan drive motor in a magnetic tape device becomes abnormal during constant speed drive control. It is about providing.

FIG. 2 shows a configuration diagram of an embodiment of the present invention, and the same reference numerals as in FIG. 1 indicate the same parts. UND is a device that detects the occurrence of a signal that does not normally occur during constant speed control, and specifically consists of a dimer circuit TM and a comparator circuit CP. The comparator circuit CP emits an output signal when the count value of the pulse counter circuit CT exceeds a predetermined value or an overflow occurs.The timer circuit TM outputs an output signal for the duration of the output signal of the comparator circuit CP. If the measured time exceeds the specified time, it means that a signal that does not normally occur during constant speed drive control continues to be generated, so the timer circuit
The TM emits an abnormality detection signal. Timer circuit TM
It is desirable that the abnormality detection signal from the constant speed control circuit CVC is applied to the constant speed control circuit CVC to release the constant speed control of the motor by disconnecting the control operation circuit, and further to make the output current of the constant current drive circuit CID zero.

In addition, when a start signal is applied to the timer circuit TM and when a stop signal is applied during constant speed driving, the comparator circuit CP and timer circuit TM will be in the same abnormal state as described above even if there is no abnormality in the motor M. It is preferable to temporarily stop the operation of the timer circuit TM for a predetermined period of time after application of the start signal and the stop signal, and for this purpose each of the above-mentioned signals is applied to the timer circuit TM.

As described above, the DC motor that drives the capstan of a magnetic tape device has a low moment of inertia and a low torque constant, so the armature uses a thin winding. Therefore, if an abnormal state such as armature stop occurs during constant speed control and a large current flows, it will burn out in a short period of time, so this abnormal state must be detected accurately and quickly, but according to the present invention, The rotational speed of the electric motor during this constant speed control is measured using a tachometer.
Since abnormal conditions are detected using a tachometer circuit and a counter, and an abnormal state is detected using a comparison circuit and a timer, it can be detected accurately and quickly, and even a capstan electric motor will not burn out.

[Brief explanation of the drawing]

FIG. 1 is an explanatory block diagram of a motor of a conventional magnetic tape recording/reproducing apparatus, and FIG. 2 is a block diagram of an embodiment of the present invention. M...Electric motor, CPS...Capstan, TP...
...Magnetic tape, DT...Digital tachometer,
TCC...tachometer circuit, CT...counter, CID
...Constant current drive circuit, DA...Digital analog converter, CVC...Constant speed control circuit, TM...Timer circuit, CP...Comparison circuit.

Claims (1)

[Scope of utility model registration request] In an electric control circuit for driving a capstan in a magnetic tape device that applies a starting current to a DC motor and controls a constant speed after starting, a tachometer that is directly connected to the DC motor and detects the rotation of the motor; A tachometer circuit that obtains a pulse train with a frequency proportional to the rotational speed of the motor,
A counter that counts the number of pulses of the reference clock signal between adjacent pulses of the pulse train output from the tachometer circuit, and outputs an output signal when the count value of the counter exceeds a predetermined value. The motor is characterized by comprising a comparison circuit, a timer circuit that measures whether the output of the comparison circuit continues for a predetermined time or more, and a constant speed control circuit that releases constant speed control of the DC motor based on the output of the timer circuit. A DC motor control circuit for driving a capstan in a magnetic tape device.