JPH0381213B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a reel drive motor in a magnetic tape recording/reproducing device, and more particularly to a control device for a servo for high-speed tape running.

A conventional device of this type is shown in FIG.

In the figure, 1 is a head for recording on tape 2 or reproducing signals recorded on tape 2, 3 and 4 are guide rollers for tape 2, and 5 is a head for pressing tape 2 against head 1. 6 is a reel collar fixed to the rotating shaft of a reel motor 8 for winding, 7 is a reel collar fixed to the rotating shaft of a reel motor 9 for supplying, 8 is a reel motor for winding, and 9 is a supplying reel motor. 10 is a tape winding hub for winding the tape around its outer periphery, 11
12 is the tape wound on the tape winding hub 10 on the winding side; 13 is the tape wound on the winding hub 10 on the winding side;
14 is a control circuit for controlling the take-up reel motor 8; and 15 is a control circuit for controlling the supply reel motor 9.

Further, FIG. 2 shows a control circuit for the reel motor. Since the control circuits 14 and 15 have exactly the same configuration, 1
4 will be explained. In the figure, 141 is a resistor connected in series to the motor 8, 142 is a resistor, and 14
3 is a resistor connected in series with the resistor 142, 144
145 is a differential amplifier whose inverting input terminal is connected to the connection point between the motor 8 and the resistor 141, and A connection point between resistors 142 and 143 is connected to the inverting input terminal. The output terminal 145 is connected to the connection point between the resistor 141 and the resistor 142. 146 is a resistor, 147 is a diode connected in series to this resistor, and the series circuit of this resistor and diode is connected to the motor 8 in parallel. Terminal 140 is a control terminal for turning on/off the output of differential amplifier 145.

The operation of the above configuration will be explained.

The operation of feeding the tape 2 in the direction of the arrow in FIG. 1 will be described below. First, turn on the output of the differential amplifier 145 to the control terminal 140 of the control circuit 14.
A signal is given by means not shown. At the same time, a signal is applied to the control terminal 150 of the control circuit 15 to turn off the output of the differential amplifier 155. As a result, the motor 8 is driven by the control circuit 14, and the tape 2 is wound in the direction of the arrow. Since the control circuit 15 is OFF, the motor 9 does not generate any driving force, but is pulled by the tape 2 and rotates in the reverse direction. The control circuit 14 includes resistors 141, 142, 143
A bridge circuit is formed by the internal resistance Ra of the motor 8 and operates so that the back electromotive voltage Ea generated in the motor 8 becomes equal to the voltage Vref of the reference power supply 144. In this bridge circuit, the resistor 141 is R ₁ , 14
2 is R ₂ , 143 is R ₃ , the back electromotive constant of motor 8 is K _E [v/rpm], and the torque constant is K _T [gr.cm/A]
Then, the load characteristic of the rotation speed of the motor 8 determined by the balance state of the bridge η (rpm/gr.cm)
is given by η=(RaR ₂ −R ₁ R ₃ )/(R ₂ ×K _T ×K _E ) ……(1). Also, the rotational speed N _M when the motor load T _L is T _L = 0 is given by N _M [rpm] = Vre [V] ÷ K _E [V/rpm] ... (2). The rotational speed N _MT of the motor 8 is expressed as N _MT =N _M −η×T _L (3) where T _L is the load torque. When the bridge is perfectly balanced, the term (RaR ₂ −R ₁ R ₃ ) in equation (1) becomes zero, and −η=0. Therefore, formula (3) becomes N _MT = N _M ...(4), and the rotation speed is a constant value N _M regardless of the load T _L
I become confused. In this case, as the tape winding diameter increases, the tape speed increases, and the tape speed changes greatly between the beginning and end of tape winding. Therefore, the bridge was unbalanced and η was set to an appropriate value to reduce the difference in tape speed between the beginning and end of winding. In other words, when the tape winding diameter is small, the load torque T _L is small, and T _L increases in proportion to the increase in the winding diameter, so the rotation speed of the motor 8 is calculated according to equation (3).
N _MT is largest at the beginning of winding and smallest at the end of winding. Further, when the motor 8 is being driven, the resistor 146 and the diode 147 are in a reverse bias state because a positive voltage is applied to the motor 8, so that no current flows through this circuit. On the other hand, since the motor 9 is rotating in the opposite direction, a negative voltage (back electromotive force) Eas proportional to the rotational speed of the motor 9 is generated at the terminals of the motor 9. Here, if the value of the forward voltage drop of diode 157 is V _F , then Eas
When the absolute value of becomes larger than V _F , a current I _MS flows through the closed circuit of motor 9, resistor 156, and diode 157.
begins to flow. I _MS causes the motor 9 to generate a reverse torque. That is, when I _MS flows, the load T _L of the motor 8 is further increased. R156 is this I _MS
It is intended to limit the Therefore, the resistor 156, the diode 157 and the motor 9 perform a so-called braking action. Further, the rotational speed N _MB k of the supply side motor 9 at which the brake starts is the rotational speed at which the back electromotive force Eas becomes equal to the V _F of the diode. In other words, if the back electromotive force constant of the motor is K _E (V/rpm), then N _MBk (rpm)
is given by N _MBk = V _F (V)/K _E (v/rpm) [rpm] (4).

Here, find the tape speed υ _T (cm/s) when there is no brake circuit.

The radius of the tape wound on the take-up hub 10 is
When r _T and the rotational speed of the motor 8 are N _MT , υ _T is given by υ _T = 2π/60N _MT (rpm) x r _T (cm) (5). Also, the load torque of the motor 8 is given by T _L = T _B (gr) x r _T (cm) [gr cm) (6), where T _B is the back tension of the tape, so it is given by Equation (3). ), the rotation speed of motor 8
N _MT (rpm) is obtained as N _MT (rpm) = N _M −ηT _BrT ……(7). According to equations (7) and (5), υ _T is υ _T (cm/S) = 2πηTB/60r _T (No/ηT _B −rT)...
It is given by (8). In equation (8), if the back tension T _B is constant, υ _T becomes a quadratic expression of the winding radius r _T.
r Draw a parabola with respect to _T. Here, the error ε _TB due to the back tension T _B is determined by ε _TB = (1/υ _T ) × dυ _T /dT _B ...(9), then ε _TB = π/30ηrT ² /υ _T [1/gr ] ……(10) is obtained. It can be seen that the error ε _TB is proportional to r _T ² . r _T
increases toward the end of winding, so the error becomes maximum near the end of winding. The maximum value of r _T is approximately 2.5 (cm) in a so-called compact cassette, and this cannot be reduced. Therefore, in order to reduce the error, it is effective to reduce the motor load characteristic η. However, if we reduce η from equation (8),
υ _T increases near the maximum value of r _T. Therefore, the aforementioned brake circuit increases TB to suppress the increase in tape speed near the end of tape winding.

In the above explanation, the motor 8 is used as the take-up side and the motor 9 is used as the supply side. However, when the tape is run in the direction opposite to the arrow in FIG. 1, the terminal 140 in FIG. The output of the width filter 145
A signal to turn OFF is connected to the differential amplifier 1 at the terminal 150.
Just add a signal to turn on the output of 55, and the operation will be exactly the same.

Since the conventional reel motor control device is configured as described above, the motor load characteristic η must be set by adjusting the bridge balance.
In addition, since the brake is applied by the brake circuit, the back tension increases near the end of tape winding, resulting in the tape being wound tightly, making it easy to wear out the tape. Also, since η is large, it is a cassette.
If the back tension T _B differs depending on the half, there are drawbacks such as tape speed errors.

The present invention was made in order to eliminate the above-mentioned drawbacks of the conventional tape, and eliminates the brake circuit and achieves constant tape speed control characteristics without being affected by the magnitude of back tension. The purpose is to provide a control device for a reel motor.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

In FIG. 3, 8 is the reel motor on the winding side, 141 is a resistor connected to the terminal of this reel motor 8, 142 is a resistor connected to the other end of this resistor 141, and 143 is the other end of this resistor 142. The connected resistor 145 is a differential amplifier, whose inverting input is the connection point between the resistor 141 and the terminal of the motor 8, its non-inverting input is the connection point between the resistors 142 and 143, and its output terminal is the connection point between the resistor 141 and the terminal of the motor 8. is connected to the connection point of resistors 141 and 142. A diode 149 has its anode connected to the other end of the resistor 143 and its cathode connected to one end of the resistor 148. The other end of the resistor 148 is connected to a connection point between the resistor 141 and the terminal of the motor 8. 9 is a reel motor on the supply side, 151 is a resistor connected to the terminal of this reel motor 9, 152 is a resistor whose one end is connected to the other end of this resistor 151, and 153 is one end connected to the other end of this resistor 152. is connected to the resistor, 15
5 is a differential amplifier, and its inverting input has a resistor 151.
The connection point between the terminals of the motor 9 and the motor 9 is connected to the connection point of the resistors 152 and 153 to its non-inverting input, and the connection point of the resistors 151 and 152 is connected to its output terminal. 159 is a diode whose anode is connected to the other end of the resistor 153, and its cathode is connected to the resistor 158.
connected to one end of the The other end of the resistor 158 is connected to the resistor 151 and the terminal of the reel motor 9. Reference numeral 160 denotes a current source, one end of which is grounded and the other end connected at a point to a connection point between resistor 143 and diode 149 and a connection point between resistor 153 and diode 159. Here, resistor 141 and resistor 142
, motor 8, resistor 143, diode 15
9, resistor 158, and motor 9 constitute a bridge on the take-up reel motor side, and resistor 1
51, resistor 152, motor 9, resistor 15
3, diode 149, resistor 148, motor 8
It constitutes a bridge on the supply reel motor side whose sides are and.

Next, the operation of this invention will be explained.

The case where the tape 2 is fed in the direction of the arrow in FIG. 1 will be described below. First, the control terminal 140
A signal for turning on the output of the differential amplifier 145 is applied by means not shown. At the same time, control terminal 15
0, a signal that turns off the output of the differential amplifier 155 is added. Here, if R152, 153, and 158 are selected so that the sum of resistor 152 and resistor 153 is sufficiently larger than resistor 158 and internal resistance Ra of motor 9, that is, (R152+R153)≫R158, Ra, then equivalently It will look like Figure 4. Here, the reference voltage Vref of the bridge circuit is Eas, the back electromotive force of the supply side motor 9, Is, the current of the current source 160, and the diode 1.
Letting the forward voltage drop of 59 be _VF , it is given by Vref= _VF −Eas+Is(Ra+R158)...(11). In equation (11), if the internal resistance Ra of motor 9 is sufficiently small compared to R158, equation (11) becomes Vref=V _F +IsR158−Eas =V _S −Eas ……(12) (V _S =V _F +I _S R158 ). In equation (12), V _S is diode 1
59 forward voltage drop V _F and current source 160 current I _S
and a constant voltage source determined by a resistor 158. Formula (12)
Therefore, the reference voltage Vref becomes smaller as the back electromotive force Eas of the motor 9 on the supply side becomes larger. That is, back electromotive force
Since Eas is proportional to the rotation speed of the motor 9, the reference voltage Vref becomes smaller as the rotation speed of the supply side reel increases. In other words, at the beginning of winding when the tape winding diameter on the take-up side is small, the reel rotation speed on the supply side is low.
Vref takes a large value. Therefore, at the beginning of winding, the rotational speed of the winding motor 8 becomes a large value.
As the winding diameter increases, the rotational speed of the reel motor on the supply side increases, so Vref gradually decreases. As a result, the number of rotations of the reel motor on the winding side gradually decreases. Therefore, in the present invention, unlike the conventional example, there is no need to upset the balance of the bridge and increase the load characteristic η, and it is possible to set the load characteristic η so that η=0.

Next, find the tape running speed υ _T. tape.
Speed υ _T is the winding radius of the tape on the winding side r _T
(cm), the tape winding radius on the supply side is rs (cm), the rotation speed of the winding side motor 8 is N _T (rpm), and the reel on the supply side. If the rotation speed of the motor 9 is N _S (rpm), υ _T (cm/s) = 2π/60N _T (rpm) x r _T (cm) = 2π/60N _S (rpm) x rS (cm)... (13) holds, and the back electromotive force constants of motor 8 and motor 9 are both equal K _E (V/rpm) and motor 9
Letting the back electromotive voltage of Eas (V), the rotation speed N _T of motor 8 and the rotation speed N _S of motor 9 are respectively, N _T = Vref (V) / K _E (v/rpm) ... (14) N _S =Eas (V)/K _E (v/rpm)...(15) It is given as follows.

Here, the projected area of the tape wound on the tape winding hub 11 on the supply side is S _S (cm ² ), and the projected area of the tape wound on the tape winding hub 10 on the winding side is S _T (cm 2 ). ² ), then the sum of S _T and S _S
Since S _O is always constant from the beginning to the end of tape winding, the following relationship holds: S _O (cm ² ) = S _T (cm ² ) + S _S (cm ² ) ...(16), where S _O Tape during normal tape playback. If the speed is υ _TP (cm/s), the one-way playback time is T (minutes), and the tape thickness is d (cm), then S _O (cm ² ) = υtp (cm/s) x 60 x T (minutes). )×d
... is given by (17). S _T (cm ² ) is the radius of the tape winding hub as ro (cm) and the tape winding diameter as r _T , and S _T (cm ² ) = π (r _T ² − ro ² ) ……(18) Same S _S (cm ² ) is given by S _S (cm ² )=π(r _S ² −ro ² )...(19). Equations (12), (13), (14), (15), (16
),
From (17), (18), and (19), tape speed υ _T (cm/
s), we get Or υ _T (cm/S) = 2π/60×V _S /K _E ×r _T × [1−r _T /r _S +
r _T ]...(21) Then, we obtain N _T (rpm) + N _S (rpm) = V _S /K _E ...(22). Using formula (20), C-60 tape (plane 30
Fig. 7 shows the changes in r _T and υ _T in the case of double-sided 60-minute tape).

In the figure, the winding radius r _T of the tape on the winding side is
The tape running speed υ _T reaches its maximum at 1.886 cm, and its maximum value υ _Tnax is υ _Tnax = 18 x 4.76 (cm/
S). In addition, back electromotive force constant K _E and constant voltage V _S
(=V _F +I _S R158) is K _E =2×10 ^-3 (V/
rpm) and V _S =1.73 (V).

Further, in the present invention, the case where the motor 8 is used for winding has been described, but the same applies to the case where the motor 9 is used for the winding side.

In the above embodiment, a current source 160 is provided to generate a constant voltage V _S , but it may be replaced with a resistor R _S as shown in FIG. However, in this case, the value of R _S is set so that R _S ≫ R158, and the power supply Vcc applied to the resistor R _S is a constant voltage.

Further, in the above embodiment, a series circuit of a resistor 158 and a diode 159 was used in the circuit for obtaining the constant voltage V _S , but as shown in FIG.
159 may be used in series. In this case, V _S is calculated as V _S =nV _F when n diodes are connected, where V _F is the forward voltage drop per diode.

As described above, according to the present invention, since the back electromotive voltage of the supply side motor is negatively fed back to the speed reference Vref of the winding side motor, there is no need for a brake on the supply side motor. The increase in buck tension near the end is eliminated.
Therefore, the tape is not wound too tightly, and wear and tear on the tape can be prevented. Furthermore, since the load characteristic η can be made small, the influence of load variations can be suppressed, and differences depending on the tape can be almost ignored.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a conventional reel motor control device, FIG. 2 is a diagram showing a specific circuit of the device shown in FIG. 1,
FIG. 3 is a diagram showing an embodiment of the present invention, FIG. 4 is a diagram showing an equivalent circuit of FIG. 3 for explaining the operation of the present invention, and FIGS. FIG. 7 is a diagram showing an example of the characteristics of the winding radius of the tape on the winding side and the tape running speed according to the present invention. 1... Head, 2... Magnetic tape, 3... Guide roller, 5... Head pad, 6, 7... Reel collar,
10, 11... Tape winding hub, 12... Winding side tape, 13... Supply side tape, 14, 15...
Motor control circuit, 145, 155...error amplifier,
149, 159...diode, 160... current source,
Vref…Reference power supply.

Claims (1)

[Claims] 1. A first reel stand for winding the magnetic tape,
a second reel stand for sending out the magnetic tape; a first motor having a shaft directly connected to the first reel stand; a second motor having a shaft directly connected to the second reel stand; One side is the first impedance element, the second side is the first motor, the third side is the second impedance element, and the fourth side is the third impedance element in series with the reference power supply. consisting of a circuit, one end of the first side is connected to one end of the third side, the other end of the first side is connected to one end of the second side, and the third side is connected to one end of the third side. The other end is connected to one end of the fourth side, the other end of the fourth side is connected to the other end of the second side, and the inverting input is connected to the first side and the second side. an error amplifier having a non-inverting input connected to a connection point between the sides, an error amplifier connected to a connection point between the third side and the fourth side, and an output connected to the connection point between the first side and the third side; 1. A control device for a reel motor, characterized in that the reference power source is constituted by a series circuit of a constant voltage source and the second motor.