JPS6330704B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a servo circuit for a reel motor suitable for application to a VTR.

For example, in a VTR, when the take-up side and supply side reel shafts are driven by separate motors and a tension servo is applied to the reel motors, a tape tension detector is provided, and the tape tension detection signal from the tape tension detector is is supplied to a phase compensation circuit, its output is supplied to a level comparison circuit and compared with a reference voltage for setting tape tension, and the reel motor is controlled based on the comparison output.

By the way, when changing the tape running mode,
When the tape tension detection signal is first supplied to the phase compensation circuit, due to the rise time constant of the phase compensation circuit, the reel motor is not servoed properly, and the tape tension may become excessive or the tape may become loose. This may cause damage to the tape or tape running system.

In view of this, the present invention proposes a servo circuit for a reel motor that can properly control the tension even when changing the tape running mode.

The present invention includes a phase compensation circuit to which a tape tension detection signal is supplied, and a level comparator to which the output of the phase compensation circuit and a reference voltage for setting tape tension are supplied and compared, and controls the reel motor based on the comparison output. , and an initial value voltage generation source that applies an initial value voltage to the phase compensation circuit when the tape tension detection signal is not supplied to the phase compensation circuit.

An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1 is a diagram showing the entire tape running drive device of a cassette type VTR. The following description will be made with reference to FIG. 1. 10 indicates a tape cassette, and 1 indicates its magnetic tape. 5
T and 5S are take-up and supply reel shafts of the VTR, and are adapted to engage with the take-up and supply reels 14T and 14S of the tape cassette 10. Reference numerals 6T and 6S are take-up and supply reel motors that directly drive the take-up and supply reel shafts 5T and 5S. In this case, the connection between the motor shaft and the reel shaft is such that there is no play in transmitting the driving force, and it may be a direct connection or a connection via a gear device. Reference numeral 4 denotes a tape guide drum, on which a pair of rotating magnetic heads (not shown) are provided. and magnetic tape 1
The tape is wound around the tape guide drum 4 at an angle of about 180 degrees, and the video signal is recorded by the rotating magnetic head so as to form a recording track diagonal to the longitudinal direction. It is meant to be played. 2 is a capstan, and 3 is a pinch roller. Further, 9T and 9S are take-up side and supply side tape tension detectors, which are provided between the take-up side reel shaft 5T and the tape guide drum 4 and between the supply side reel shaft 5S and the tape guide drum 4, respectively. ing. These tape tension detectors 9T and 9S are
It consists of a tension arm and means for converting its angle into an electrical signal. 8T and 8S are amplifiers that amplify the tape tension detection outputs from the tape tension detectors on the winding side and the supply side.

11T and 11S are winding side and supply side servo circuits. The winding side servo circuit 11T is a winding side tension error detection circuit 15T in the forward constant speed running mode, and a winding side tension error detection circuit 16 in the reverse direction constant speed running mode.
T, from the winding-side tension error detection circuit 17T in the tape running stop mode, the tension error detection circuit 18 in the rewinding running mode, the winding-side rotation error detection circuit 13T, the winding-side rotation detector 12T, and the motor drive amplifier 7T. It is configured.

The supply side servo circuit 11S includes a supply side tension error detection circuit 15S in the forward direction constant speed running mode, a supply side tension error detection circuit 16S in the reverse direction constant speed running mode, and a supply side tension error detection circuit 1 in the tape running stop mode.
7S, Tension error detection circuit 1 in fast forward running mode
9, a supply side rotation error detection circuit 13S, a supply side rotation detector 12S, and a motor drive amplifier 7S.

It should be noted that the magnetic tape 1 can be used not only in the forward constant speed running mode and the reverse direction constant speed running mode described above, but also in the fast forward running mode and the rewinding running mode.
is wound around the tape guide drum 4 and made to run.

In forward and reverse constant speed driving modes,
The torques of the take-up reel motors 6T and 6S are simultaneously controlled so that the tension of the magnetic tape 1 is constant. In addition, in the fast-forward running mode, the take-up reel motor 6T is controlled to have a constant rotation speed, and the supply reel motor 6S is controlled to rotate the magnetic tape 1.
The torque is controlled so that the tape tension is constant. In the rewind running mode, the supply reel motor 6S is controlled to have a constant rotational speed, and the torque of the take-up reel motor 6T is controlled so that the tension of the magnetic tape 1 is constant.

The output of the tape tension detector 9T on the winding side is sent to the amplifier 8.
The signal is supplied to detection circuits 15T, 16T, 17T and 19 through T. Further, the output of the tape tension detector 9S on the supply side is sent to the detection circuit 1 through the amplifier 8S.
5S, 16S, 17S and 18.

The error detection outputs of the detection circuits 15T, 16T, 17T, and 18 are supplied to the take-up reel motor 6T through the amplifier 7T. Detection circuit 15S, 16
The outputs of S, 17S and 19 are supplied to the supply reel motor 6S through an amplifier 7S. The rotation of the take-up side reel motor 6T is detected by the take-up side rotation detector 12T.
The detected output is supplied to the take-up side rotation error detection circuit 13T, and the detected output is supplied to the take-up side reel motor 6T through the amplifier 7T. The rotation of the supply side reel motor 6S is detected by the supply side rotation detector 12S, the detection output is supplied to the supply side rotation error detection circuit 13S, and the detection output is transmitted to the motor 6 through the amplifier 7S.
Supplied to S.

Tension error detection circuits 15T, 16T, 17T, 18, 15 each having an input terminal t ₁ and an output terminal t ₂
S, 16S, 17, and 19 are for controlling the torque of the reel motor so that the tension of the magnetic tape 1 is constant, but since the method of control differs depending on the tape running mode, it is necessary to change the circuit constant or supply. Circuits with different voltages are provided for each tape running mode. The configurations of the winding-side and supply-side rotational error detection circuits 13T and 13S are conventionally known, so further explanation will be omitted and reference will be made to FIG. 2 for the specific configuration of the tension error detection circuit described above. I will explain.

In FIG. 2, 21 is a phase compensation circuit, to which a tape tension detection signal from an input terminal _t1 is supplied through a changeover switch _SW1 . The phase compensation circuit 21 is composed of resistors 22 and 23 and a capacitor 24 with a large capacity, and is a kind of low-pass filter. The time constant is selected to an appropriate value depending on each detection circuit shown in FIG.

25 is a level comparator which connects the output of the phase compensation circuit 21 and the reference voltage source 3 for setting tape tension.
0 is compared with a reference voltage, and the comparison output is outputted to the output terminal _t2 through the changeover switch _SW2 . The level comparator 25 includes an operational amplifier 26 and negative feedback resistors 27 and 28. The output of the phase compensation circuit 21 is supplied to the inverting input terminal of the operational amplifier 26 through a resistor 27. In addition, resistor 2
8 is connected between the output terminal and the inverting input terminal of the operational amplifier 26.

The tape tension setting reference voltage source 34 is composed of a potentiometer 31 connected between positive and negative DC power supplies +B and -B, and a series circuit of resistors 32 and 33 that voltage divides the output of its movable contact. , the output of the midpoint between the resistors 32 and 33 is the operational amplifier 26.
The signal is supplied to the non-inverting input terminal of the circuit.

35 is an initial value voltage generation source for the phase compensation circuit 21, and is constituted by a potentiometer 36 connected between positive and negative DC power supplies +B and -B.
The output from the movable contact is supplied to the output end of the phase compensation circuit 21 through the changeover switch _SW3 .

Note that the switches SW ₁ , SW ₂ and SW ₃ are configured to be switched in conjunction with each other. When the detection circuit is in operation, switches SW ₁ and SW ₂ are both on and switch SW ₃ is off, and when the detection circuit is in non-operation, both switches SW ₁ and SW ₂ are off and switch SW ₃ is off. is turned on.

When this detection circuit is operating normally, the phase compensation circuit 21 normally compensates the phase of the tape tension detection output and supplies it to the level comparator 25, but when the detection circuit is not operating, an initial value voltage is generated. The voltage from the source 35 is applied to the capacitor 24 through the resistor 23, and the voltage at the output end of the phase compensation circuit 21 is set to a voltage determined by the initial value voltage of the initial value voltage generation source 35.

Therefore, the detection circuit operates and the changeover switch _SW1 ,
A predetermined voltage is obtained at the level comparator 25 even at the first moment when SW ₂ is turned on at the same time. Incidentally, if there is no initial value voltage generation source 35, the switch will not work.
The time required for the capacitor 24 to be charged by the tape tension detection output after SW ₁ is turned on means that a normal tension error detection output cannot be obtained from the output terminal _t2 , and the tape tension by the reel motor is If the control is disturbed and the tape tension becomes excessive,
The tape may become loose.

Note that this initial value voltage is determined as follows. The initial value voltage is set so that the torque of the reel motor on the winding operation side becomes large, and the torque of the reel motor on the supplying operation side becomes small.

FIG. 3 shows the frequency characteristics of the gain of the tension servo loop for the above-mentioned reel motor. Note that the broken line shows the characteristics when the phase compensation circuit 21 is not provided, and the solid line shows the characteristics when the phase compensation circuit 21 is provided. It should be noted that in the solid curve, there is a slightly raised curved portion at a portion slightly smaller than 10 Hz, but this is a mechanical resonance portion of the tape running system.

Next, another example of the tension error detection circuit will be described with reference to FIG. 4, but parts corresponding to those in FIG. 2 will be denoted by the same reference numerals and redundant explanation will be omitted. In this example, the second
This is a case where the adjustment of the tape tension setting reference voltage source 30 and the initial value voltage generation source 35 in the figure are integrated. The configuration of the tape tension setting reference voltage source 30 is the same as that shown in FIG. and a movable contact, and the midpoint of the connection is supplied to the output end of the phase compensation circuit 21 through a changeover switch _SW3 . In addition, the negative side DC voltage source -
The resistance value of the resistor 38 on the B side is, for example, about 100 kΩ.
The resistance value of the other resistor 39 is approximately 1 kΩ. With this configuration, the reference voltage for tape tension setting and the initial value voltage can be adjusted simultaneously by simply adjusting the potentiometer 31. In this case, the tape tension setting reference voltage and the initial value voltage are set to be different from each other.

According to the present invention described above, since an initial value voltage generation source is provided that applies an initial value voltage to the phase compensation circuit when the tape tension detection signal is not supplied to the phase compensation circuit, it is possible to change the tape running mode. Thus, it is possible to obtain a servo circuit for a reel motor that can normally control tape tension even at certain times. Therefore, there is no risk of damaging the tape or the tape running system.

Note that the present invention is applicable not only to VTRs but also to audio tape recorders and the like.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of a part of the circuit shown in FIG. 1, FIG. 3 is a characteristic curve diagram, and FIG. FIG. 2 is a circuit diagram showing another specific example similar to FIG. 2; 1 is a magnetic tape, 4 is a tape guide drum, 5T
and 5S are the take-up side and supply side reel shafts, 6
T and 6S are the reel motors on the winding side and supply side, respectively;
9T and 9S are tape tension detectors on the winding side and supply side respectively, 10 is a tape cassette, 11T and 11S
are the take-up side and supply side servo circuits, 15T, 1, respectively.
5S, 16T, 16S, 17T, 17S, 18 and 19 are tension error detection circuits, 21 is a phase compensation circuit, 22 and 23 are resistors, 24 is a capacitor,
25 is a level comparator, 30 is a reference voltage source for setting tape tension, and 35 is an initial value voltage generation source.

Claims (1)

[Claims] 1. A phase compensation circuit to which a tape tension detection signal is supplied, and a level comparator to which the output of the phase compensation circuit and a reference voltage for setting tape tension are supplied and compared, and controls the reel motor based on the comparison output; A servo circuit for a reel motor, comprising: an initial value voltage generation source that applies an initial value voltage to the phase compensation circuit when a tape tension detection signal is not supplied to the phase compensation circuit.