JPH0456558B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for a DC motor used in a tape drive system.

Generally, in a tape drive device using a DC motor such as a VTR capstan or reel,
To change the tape transport direction, an electronic switch is used to change the direction of the current flowing through the DC motor. A conventional switch circuit of this type is shown in FIG.

In FIG. 1, 101 is a DC power supply, 102 is a DC motor for driving the tape, 103 to 106 are switching elements for switching the current direction, and the switching elements 103 and 106 are the forward rotation command input terminal 107.
It opens and closes in conjunction with the input from the user. Switching elements 104 and 105 are reverse command input terminals 108
It opens and closes in conjunction with the input from the user. Therefore, when there is an input to terminal 107 and no input to terminal 108, switching elements 103 and 106 are closed, and switching elements 104 and 105 are opened. Then, current flows from one end P of the motor 102 to the other end Q of the motor 102, and the motor 102 rotates normally. The same can be said for the case of reversing.

However, the positive and negative input terminals 107 and 108
When inputs are simultaneously applied to the switching element 10
All 3 to 106 are closed, switching element 1
03 to 105, and switching element 104
An excessive short circuit current flows from the power source 101 to the power source 106, which not only causes destruction of the switching element but also
It may also cause damage. Therefore, this type of DC motor control circuit generally requires a special protection circuit when both forward and reverse inputs are applied.

Further, when both the forward and reverse inputs are turned off, all of the switching elements 103 to 106 are opened, and both ends P and Q of the motor are in an open state. Therefore, when it is desired to suddenly stop tape transport, a special brake device is required.

Furthermore, in the circuit shown in FIG. 1, the voltage applied to the motor 102 is only applied by switching the DC fixed voltage source 101 with the switching elements 103 to 106, so the rotation speed of the motor 102 can be changed or the rotation speed can be changed. To precisely control the power supply voltage, separate control of the power supply voltage is required.

The present invention has been made in order to eliminate the drawbacks of the conventional devices as described above, and is capable of reversing the tape transport direction and transporting the tape using a simple electric circuit including transistors and diodes in a tape drive device such as a VTR capstan. It is an object of the present invention to provide a DC motor control circuit for a tape drive device that can control speed variation, stoppage of transport, etc.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 shows an example in which a DC motor control circuit for a tape drive device according to an embodiment of the present invention is applied to a capstan drive device for a VTR. In this device,
The tape 1 is pressed by a pinch roller 4 to a capstan 3 driven by a DC motor 2 and transferred.

The DC motor control circuit 5 is provided with an input terminal 6 for specifying the motor rotation direction in the forward direction and an input terminal 7 for specifying the motor rotation direction in the reverse direction. The voltage between the output terminals 8 and 9, that is, the voltage applied to the motor 2, is controlled by the voltage applied to the motor 2, and short-circuit braking can also be applied to the motor 2.

FIG. 3 is an electrical circuit diagram showing one embodiment of the DC motor control circuit 5. FIG. In the figure, an NPN Darlington transistor 2 as the first control element
The collector of 0 is connected to the positive terminal of power supply 100.
Further, the collector of the NPN Darlington transistor 21 as the second control element is also connected to the DC power supply 100.
connected to the positive terminal of the The emitter of the Darlington transistor 20 is connected to one connection point a of the DC motor 2, and the collector of an NPN transistor 22 as a first switching element is connected to this connection point a. The emitter of transistor 22 is then grounded. The emitter of the Darlington transistor 21 is connected to the other connection point b of the DC motor 2, and the collector of an NPN transistor 23 as a second switching element is connected to this connection point b. and transistor 23
The emitter is grounded. In parallel with the Darlington transistor 20, its cathode is connected to the DC power supply 10.
A diode 24 is provided, which is connected to the positive electrode of 0 and whose anode is connected to connection point a. Further, a diode 25 is provided in parallel with the Darlington transistor 21, the cathode of which is connected to the positive electrode of the DC power supply 100, and the anode of which is connected to the connection point b. A diode 26 whose cathode is connected to the connection point a and whose anode is grounded is provided in parallel with the transistor 22, and in parallel with the transistor 23, whose cathode is connected to the connection point b.
Diode 2 connected to
7 is provided.

The base of the transistor 22 is connected to the collector of a transistor 28 as a third switching element. A connection point between the base of transistor 22 and the collector of transistor 28 is connected to the positive electrode of power supply 100 via resistor 30 . The emitter of transistor 28 is grounded. The base of the transistor 23 is connected to the collector of a transistor 29 as a fourth switching element. Base of transistor 23 and transistor 2
The connection point of the collector of 9 is connected to the power supply 1 through a resistor 31.
Connected to the positive terminal of 00. The emitter of transistor 29 is grounded. The base of the Darlington transistor 20 is connected to the normal input terminal 6. The base of the transistor 28 is also connected to the input terminal 6 via a resistor 32. The base of the Darlington transistor 21 is connected to the inversion input terminal 7. The base of the transistor 29 is also connected to the input terminal 7 via a resistor 33.

The input terminal 6 for forward rotation is connected to the two-contact F, S1 circuit switch 34 for forward rotation. This switch 34
The F contact of is connected to the control voltage source 36 for forward rotation,
The S contact is grounded. Further, the switch 34 is set to the F contact when rotating the motor 2 in the forward direction (corresponding to current flowing from the connection point a to the connection point b),
When stopping, the S contact is set.

The reversing input terminal 7 is connected to a two-contact R, S1 circuit switch 35 for reversing. This switch 35
The R contact of is connected to the reverse control voltage source 37,
The S contact is grounded. Further, the switch 35 is set to the R contact when the motor 2 is reversed (corresponding to the current flowing from the connection point b to the connection point a),
When stopping, the S contact is set.

The circuit configuration shown in Figure 3 is designed to control the motor 2 in both forward and reverse directions.
It should be pointed out in advance that although the circuit configuration is symmetrical between the left and right sides, the circuit configuration is not limited to such a symmetrical circuit configuration.

Next, the operation will be explained. Now, set the forward rotation command switch 34 to the F contact and the reverse rotation command switch 35 to the S contact.
The operation when it is set as a contact point will be described. At this time, a base current is supplied from the control voltage source 36 to the transistor 28 via the switch 34 and the resistor 32, and the collector and emitter of the transistor 28 are closed. Since the base of the transistor 22 is grounded through the transistor 28, the collector and emitter thereof are opened. On the other hand, since the base of the transistor 29 is grounded via the switch 35, the collector and emitter thereof are opened. Since the transistor 29 is open, the base current of the transistor 23 is supplied through the resistor 31, and the collector and emitter of the transistor 23 are closed. The base of Darlington transistor 21 is grounded via switch 35, and the emitter is grounded via transistor 23, so that it is in a cut-off state. Connection point b of motor 2 is also connected to transistor 2.
It is grounded via 3. Here, since the motor 2 serves as a load for the emitter follower of the Darlington transistor 20, the control voltage 3 is applied to the connection point a.
6 is applied, a current flows through the motor 2 from the connection point a to the connection point b, and the motor 2 rotates in the normal direction.

Next, turn the switch 34 to S to stop forward rotation.
The case where it is connected to a contact will be explained. At this time, the base of the transistor 28 is grounded via the switch 34, so that the collector and emitter are opened. Therefore, a base current is supplied to the transistor 22 via the resistor 30, and the collector and emitter thereof are closed. The base of the Darlington transistor 20 is grounded via the switch 34, and the emitter is also grounded via the transistor 22, so that it is in a cut-off state. Also, Darlington transistor 21 remains cut off as described above. Therefore, the electric current 100 is not supplied to the motor 2 and the motor 2 attempts to stop. However, motor 2
Since inertia remains in the rotor, the motor 2 generates a starting force based on this inertia. The direction of the starting force is the direction in which a positive voltage is applied to the connection point a. This applies a positive voltage to the collector of the transistor 22, so the transistor 22 is closed and the connection point a is grounded. Therefore, a negative voltage will be generated at the right end of the motor, that is, at the connection point b. Then, the transistor 23 cannot remain closed and becomes open. On the other hand, the diode 27 becomes conductive when the connection point b becomes a negative voltage. Motor 2 is thus short-circuited through diode 27 and transistor 22. As a result of this short circuit, motor 2 is suddenly subjected to electromagnetic braking.
It stops almost without over-revving.

Furthermore, when the motor 2 is reversed or stopped from a reversed state, the same operation as in the case of normal rotation described above is performed.

Further, according to the present invention, the voltage applied to the motor 2 can be controlled by the voltage applied to the input terminals 6 and 7. Therefore, when it is desired to vary the tape feeding speed, several control voltage sources are prepared and a switch can be used as appropriate. It is also possible to switch by using a variable voltage source or to use a variable voltage source as the control voltage source.

Furthermore, in the present invention, if Darlington transistors 20, 21 and transistors 22, 23 are selected to have a small collector-emitter saturation voltage,
It is possible to operate even when the voltage of the DC power supply 100 is low, and applications in a wide voltage range are possible.

Furthermore, in the DC motor control circuit shown in FIG. 3, when the voltage applied to the normal rotation input terminal 6 is gradually increased from the ground level, the transistor 2
Since the base voltage that closes the collector and emitter of the Darlington transistor 20 needs to be higher than the base input voltage that closes the collector and emitter of the Darlington transistor 20, the transistor 28 always precedes the Darlington transistor 20. conduction, and thus transistor 22 opens prior to conduction of Darlington transistor 20, so that transistor 22 and Darlington transistor 20 are not closed at the same time;
Darlington transistor 2 during switching
0 collector-emitter and transistor 2
This has the advantage of being able to protect the device from excessive current flowing between the collector and emitter of the device, resulting in damage.
Moreover, since the left and right circuits operate completely independently with the motor 2 in between, even if input is applied to both the forward and reverse input terminals 6 and 7 at the same time, the above action will act on both the forward and reverse circuits, as shown in Figure 1. Unlike conventional DC motor control circuits, it is possible to avoid damage to the transistor during both forward and reverse inputs, and there is no need for a special circuit to protect the transistor.

Also, if high _hFE transistors are selected for transistors 22 and 23, resistors 30 and 31 can be made larger, so
This has the advantage of reducing current consumption when stopped.

FIG. 4 shows a DC motor control circuit 5 according to the present invention.
This is an example of applying this to precise rotational speed control of a DC motor with a feedback servo loop, taking advantage of the advantage of being able to obtain a motor applied voltage proportional to the input control voltage.

A frequency proportional to the rotational speed of the motor 2 obtained by a frequency generator 40 attached to the rotor shaft of the DC motor 2 is led to a frequency comparator 42 and compared with the frequency from a reference signal source 41. The error output from the frequency comparator 42 is led to a forward/reverse/stop switching circuit 44 via an error amplifier 43. The forward/reverse/stop switching circuit 44 has the role of distributing the input error signal to the forward rotation input terminal 6 or the reverse rotation input terminal 7, and lowering the terminals 6 and 7 to the ground level when braking the motor 2. The motor control circuit 5 generates a voltage applied to the motor according to the input error signal, thereby trying to keep the rotational speed of the motor 2 constant.

In addition, in FIG. 3, the transistor 20 and the transistor 22 are prevented from being closed at the same time, thereby preventing the two transistors from being destroyed. In order to make this possible, the transistor 20 is a Darlington transistor, but the present invention is not limited to this, and a constant voltage element 20b is connected to the base of the transistor 20a.
Fig. 5 shows the transistor 20a connected in series, Fig. 6 shows the base voltage of the transistor 20a divided by resistors 20c and 20d, and Fig. 6 shows the transistor 22a collector connected in series with the constant voltage element 22b. You can use the method shown in Figure 7. Further, the constant voltage element may be a general diode.

Note that the DC motor control circuit of this tape drive device is not limited to a capstan drive, but can also be used to control the drive of a reel motor or a loading motor, producing the same effects as in the above embodiment.

As described above, according to the present invention, since the device is configured with a simple electric circuit including transistors and diodes, normal rotation of the DC motor,
Controls such as reverse rotation switching, variable speed operation, and braking are extremely easy to perform. In addition, the DC motor control circuit of the tape drive device according to the present invention consumes little current during standby, can be used over a wide power supply voltage range, and has a transistor protection function when forward and reverse inputs are input simultaneously. It also has other features such as:

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a DC motor control circuit of a conventional tape drive device, FIG. 2 is a diagram showing a DC motor control circuit of a tape drive device according to an embodiment of the present invention, and FIG. 3 is a circuit diagram of a DC motor control circuit of a tape drive device according to an embodiment of the present invention. An electric circuit diagram of one embodiment of the control circuit, FIG. 4 is a circuit diagram showing an example in which the circuit of FIG. 3 is applied to a tape drive device having a feedback servo mechanism, and FIGS. FIG. 7 is a diagram showing another example of the structure of the first control element shown in FIG. 3, and FIG. 7 is a diagram showing another example of the structure of the first switching element shown in FIG. 100...DC power supply, 2...DC motor, 20,2
1... Darlington transistor (first, second control element), 22, 23, 28, 29... transistor (first to fourth switching element), 24
~27...first to fourth diodes, 6, 7...
First and second input terminals. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A control circuit for a DC motor driven by a DC power source in a tape drive device, wherein a collector and an emitter are connected between one end of the DC power source and one end of the DC motor. a first Darlington transistor; a second Darlington transistor having a collector and an emitter connected between one end of the DC power supply and the other end of the DC motor; the other end of the DC power supply and one end of the DC motor; a first transistor having an emitter and a collector connected between the transistors and not being activated at the same time as the first Darlington transistor; and a collector and an emitter connected between the other end of the DC power supply and the other end of the DC motor. a second transistor connected and not active at the same time as the second Darlington transistor; a third transistor having its collector and emitter connected to the base and emitter of the first transistor for opening and closing; a fourth transistor whose collector and emitter are connected to the base and emitter of the second transistor in order to open and close the second transistor;
a diode connected in a direction that is in a cutoff state when the Darlington transistor is in an active state;
a diode connected in a direction that is in a cutoff state when the Darlington transistor is in an active state; a first input terminal for serving as the base of the third transistor and an input of the first Darlington transistor; 4 and a second input terminal for serving as an input to the second Darlington transistor, the first input terminal or the second input terminal when the DC motor is driven by the DC power supply. When it is desired to control the direction of rotation of the DC motor and the magnitude of the voltage applied to the DC motor by the voltage input to the first and second
A DC motor control circuit for a tape drive device, characterized in that an input terminal thereof is at ground potential.