JPS6350778B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a reel motor control circuit for a tape recorder such as a VTR.

In tape recorders such as VTRs, the tape may be wound or rewound at high speed, and a constant voltage is usually applied to the reel motor.

A block diagram of the reel motor direct drive system is shown in FIG. 1, and a conventional reel motor drive circuit is shown in FIG. 2. In the figure, 1 is a tape cassette, 2 is a magnetic tape (hereinafter referred to as tape), 3 is a take-up reel (hereinafter referred to as TU reel), 4 is a take-up reel disk (hereinafter referred to as TU reel disk), and 5 is a take-up reel disk (hereinafter referred to as TU reel disk). Take-up reel motor (hereinafter referred to as TU motor), 6 is a supply reel (hereinafter referred to as SP reel), 7 is a supply reel disk (hereinafter referred to as SP reel disk), 8 is a supply reel motor (hereinafter referred to as SP motor) ), 9
is a reel motor (TU motor or SP motor),
10 is a buffer amplifier for driving the reel motor (hereinafter referred to as buffer amplifier).

Next, the operation will be explained. tape cassette 1
Tape 2 inside is TU reel 3 or SP reel 6
wrapped around. Now, consider winding tape 2 in the forward direction (arrow direction) (usually called winding FF). The TU motor 5 is driven by the output V _D of the buffer amplifier 10. The rotation of the TU motor 5 is caused by the TU reel disk 4 which is directly connected to the motor shaft.
This causes the rotation of TU reel 3. Therefore, the tape 2 travels in the direction of the arrow in the figure, and the tape 2 wound on the SP reel 6 is wound on the TU reel 3. Conversely, when rewinding the tape 2 in the opposite direction (usually called rewinding, REW), the SP motor 8 is driven, the SP reel disk 7 and the SP reel 6 rotate, and the tape 2 is reeled onto the SP reel 6. . In addition, the reel motor drive circuit simply connects the reel motor 9 with an output V _D equal to the control voltage V _C.
It is composed of a buffer amplifier 10 that outputs.

Note that the difference between FF and REW is simply whether the reel drive motor is a TU motor or an SP motor, so the following explanation will not distinguish between FF and REW.

Now, let's talk about winding a VHS T-120 cassette (cassette tape for two-hour recording and playback). To completely wind the tape on a T-120 cassette, the reel must rotate approximately 1450 revolutions. Therefore, if the tape winding time for a T-120 cassette is set to 5 minutes, the average reel rotation speed will be approximately 290 rpm. Here for simplicity
Set it to 300 rpm. Incidentally, the reel diameter changes depending on the amount of tape being wound. In the case of a T-120 cassette, the maximum reel diameter is approximately 8.0 cm and the minimum reel diameter is approximately 2.6 cm. Therefore, the motor torque required for winding changes depending on the reel diameter. Here, the reel diameter is 2.6cm.
Assume that it is 40g・cm when , and 400g・cm when 8.0cm. Taking into account various conditions such as winding torque, winding speed, cost, circuit (power supply voltage), etc., we adopted a reel motor whose characteristic curves (NT curve, IT curve) are shown in Figure 3, for example. shall be. If the reel motor drive voltage V _D is set to 7.5V, the third
As shown in the figure, the reel on the take-up side rotates at approximately 680 rpm when the reel diameter is the smallest (2.6 cm), and at 150 rpm when the reel diameter is the largest (8.0 cm). In addition, the reels on the winding side rotate at approximately 220 rpm and approximately 460 rpm, respectively. When the reel rotates at a high speed of about 700 rpm,
Phenomena such as cassette noise occurred, which could even damage the tape. As a way to avoid such problems, a motor with a small rotational speed change due to torque fluctuations, such as a motor with a low no-load rotational speed (V _D = 7.5V and N = 350 rpm) and a high static torque (V _D = 7.5 There is a method of suppressing the rotational speed fluctuation to 350 to 250 rpm by using a motor (T = 1400 g cm), but it is disadvantageous in terms of cost because it is small and special.
(In addition, in belt drive systems, etc., the reduction ratio between the reel motor and the reel is increased, equivalently lowering the no-load rotation speed and increasing the static torque. However, when using a belt, the (Maintenance is required, which is not desirable in terms of maintenance.) Also, since the reel on the take-up side has a rotation speed of 114 to 770 rpm, compared to 350 to 250 rpm for the reel on the take-up side, cassette noise and tape damage occur in this case as well. there is a possibility.

As described above, in the conventional constant voltage application type reel drive system, the reel on the winding side or the winding side rotates at high speed, which may cause damage to the cassette or tape.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by controlling the drive voltage V _D in accordance with the load of the reel motor, the rotation speed changes greatly in response to load torque fluctuations. It is an object of the present invention to provide a reel motor drive circuit that can keep the rotation speed of the reel on the winding side low by rotating the motor at a constant speed and setting an upper limit on the value of V _D. Another object of the present invention is to provide a reel motor drive circuit that can reduce the rotational speed of the reel motor near the end of winding.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram of a reel drive circuit according to the present invention. In FIG. 4, 9 is a buffer amplifier for the reel motor 10, and 11 is a voltage corresponding to the voltage V _S that sets the no-load rotation speed of the reel motor 9 and the voltage drop V _M due to the internal resistance of the reel motor 9.
V _FL is added, and the control voltage of buffer amplifier 10 is V _C
12 is a current detection circuit for detecting the current I _M flowing through the reel motor 9; 13 is a voltage component equal to the voltage drop V _M due to the internal resistance of the reel motor 9 using the output V _CS of the current detection circuit 12; A multiplication circuit 14 that calculates and outputs V _F is an amplitude limiter that limits the upper limit of its input V _FL in order to limit the upper limit of the output V _C of the adder circuit 11 .

Next, the operation will be explained. When winding a tape, the load on the reel motor increases as the diameter of the reel on the take-up side increases and as the diameter of the reel on the take-up side decreases, so that the number of rotations gradually decreases. Generally, in order to rotate a DC motor at a constant rotation speed regardless of the load torque, a voltage V _E is required to provide the specified rotation speed (or a back electromotive force when rotating at a specified rotation speed), and a torque is generated. Therefore, the motor can be driven by the sum of the voltage drop V _M generated within the motor due to the current I _M flowing through the motor. That is, the drive voltage V _D when rotating the reel motor at a constant speed can be calculated using the following formula.

V _D = V _E + V _M = V _E + R _M・I _M ...(1) However, R _M is the motor winding resistance.

By the way, when the take-up reel is rotated at a constant speed, the rotation of the take-up reel increases near the end of winding, so it is necessary to limit the reel motor drive voltage near the end of winding. If the steady rotation speed of the reel motor is 300 rpm and the rotation speed near the end of winding is 150 rpm, the upper limit of V _D may be set to 7.5 V in FIG. 3. At this time, the rotation speed-torque curve of the reel motor is at point A and point B in the diagram.
It becomes a broken line connecting point C and point C. In other words, the reel motor drive voltage V _D can be expressed by the following equation.

V _D = 3 (V) + R _M I _M (However, I _M < 300mA, or T < 300g・cm) V _D = 7.5 (V) (However, I _M ≧300mA, or T ≧ 300g・cm
...(2) In Fig. 4, assuming that the reel motor 9 is rotating with no load, I _M =0 (mA) (Actually, some current flows, but for the sake of simplicity, assume that no current flows) Therefore, V _FL =0 (V). The adder circuit 11 is connected to resistors R1, R2 with equal resistance values,
When configured with R3, R4 and the operational amplifier OPA1, the output V _C of the adder circuit 11 is expressed by the following equation.

V _C =V _S +V _FL (3) By the way, since it is assumed that V _FL =0 (V), V _C =V _S. Since the buffer amplifier 10 has a gain of 1,
V _D = V _C = V _S. Also, in equation (1), I _M =0
(mA), then V _D =V _E. That is, V _S is a voltage that sets the rotation speed when the reel motor 9 rotates without load. Next, if a load is applied to the reel motor 9 and a current I _M flows, this current causes a voltage drop of R _M · I _M inside the reel motor 9, and in the current detection circuit 12, the current detection resistor R5 causes a voltage drop of R5 · A voltage drop occurs in I _M. At this time, if the reel motor 9 is rotating at a predetermined rotation speed, a back electromotive force V _E is generated inside the motor, so the reel motor drive voltage V _D is expressed by the following equation.

V _D = V _E + I _M (R _M + R5) ...(4) By the way, if the relationship V _E = V _S is maintained, V _FL
= V _F , so V _D = V _S + I _M (R _M + R5) ...(6) Also, from the characteristics of the adder circuit 11 and buffer amplifier 10, V _D = V _C = V _S + V _FL = V _S + V _F ... (7). By comparing equations (6) and (7), V _F =I _M ( _RM + R5) ... (8) is obtained. R6 and C1 of the current detection circuit 12 are I _M
generally has a ripple component, so it is used to smooth it with a time constant of R6·C1. Therefore, if I _M is an average current, the input voltage of the multiplier circuit 13 V _CS
=R5・_IM . From the characteristics of the multiplier circuit 13, the output voltage V _F is expressed as V _F =R7+R8/R8·V _CS =R7+R8/R8·R5·I _M (9). It can be seen from equations (8) and (9) that the gain of the multiplier circuit 13 must be R7+R8/R8= _RM /R5+1 (10).

Next, set an upper limit to the reel motor drive voltage V _D ,
This is defined as V _D max. If the input V _F of the adder 11 at this time is V _FL max, then from equation (7), V _FL max = V _D max - V _S (11). This can be achieved by providing the amplitude limiter 14 with the following characteristics.

V _FL = V _F (however, V _F <V _FL max) V _FL = V _FL max (how, V _F ≧V _FL max) ...(12) In the above, using a motor with the characteristics shown in Fig. 3, Load current I _M and reel motor drive voltage V _D when V _S = 3.0 (V) and V _D max = 7.5 (V)
The relationship is shown in Figure 5.

In the above embodiment, the reel motor drive circuit is described in the case where the reel is directly driven by the reel motor, but it is also effective in the case where the rotation of the reel motor is transmitted to the reel by changing the speed via a gear, an idler, a belt, etc. . Further, although an amplitude limiter is used to set an upper limit on the reel motor drive voltage, it goes without saying that equivalent characteristics may be obtained using the saturation voltage of a buffer amplifier or the like. In addition, although an operational amplifier was used as an amplifier,
It goes without saying that the amplifier may be configured with transistors and the like.

As described above, according to the present invention, the reel motor drive voltage is the voltage generated inside the reel motor by the back electromotive force V _E generated when the reel motor rotates at a predetermined rotation speed and the current flowing through the reel motor. A resistor that detects the current flowing through the reel motor in order to make it the sum of the drop V _M , a circuit that calculates V _M from the voltage across this resistor, and V _E
Since it is composed of a circuit that calculates the sum of V _M and a buffer amplifier, the rotation speed of the take-up reel can be controlled to be constant regardless of fluctuations in load torque without using a means to detect the rotation speed of the reel motor. be able to. In addition, since the reel motor uses a motor that is susceptible to rotation speed fluctuations due to load torque fluctuations, by adding a circuit to the above configuration to set the upper limit of the reel motor drive voltage, the reel diameter on the winding side can be adjusted. Reduce the rotation of the reel motor only if the diameter of the reel on the take-up side is large compared to the diameter of the reel on the take-up side, and if the reel on the take-up side rotates at a constant speed, the rotation of the reel on the take-up side becomes abnormally high. This makes it possible to set the rotation speed of the reel on the winding side to an appropriate value,
It has become possible to control fine-grained reel motors using relatively simple electric circuits and low-cost motors.

However, the above control is not necessarily effective when a single motor drives multiple loads with different characteristics, such as a reel and a capstan.

[Brief explanation of the drawing]

1 is a configuration diagram of a reel motor direct drive system, FIG. 2 is a conventional reel motor drive circuit diagram, FIG. 3 is a characteristic curve diagram of a DC motor, and FIG. 4 is a reel motor drive circuit according to an embodiment of the present invention. FIG. 5 is a characteristic diagram of current flowing through a reel motor versus drive voltage according to an embodiment of the present invention. 1 is a tape cassette, 2 is a magnetic tape, 3 is a
TU reel, 4 is TU reel disk, 5 is TU motor, 6 is SP reel, 7 is SP reel disk,
8 is an SP motor, 9 is a reel motor, 10 is a buffer amplifier, 11 is an addition circuit, 12 is a current detection circuit, 13 is a multiplication circuit, and 14 is an amplitude limiter.
In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In the reel motor drive circuit during winding or rewinding of a tape recorder, there is a DC motor that exclusively drives the reel, a buffer amplifier that drives the motor according to the input voltage, and a current that flows through the motor. a current detection circuit;
a multiplier circuit that calculates a voltage drop occurring inside the motor due to the current based on the output of the current detection circuit; an amplitude limiter that limits the amplitude of the output of the multiplier circuit; and an amplitude limiter that limits the amplitude of the output of the multiplier circuit; 1. A reel motor drive circuit for a tape recorder, comprising an adder circuit that adds a rotation speed setting voltage required to obtain a predetermined rotation speed and the output of the amplitude limiter and inputs the sum to the buffer amplifier.