JPH038498B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape recording and reproducing apparatus used in a VTR or the like, which is equipped with a correction circuit that corrects the detected voltage by compensating for a drift appearing in the detected voltage of a tension detector that detects tape tension.

Figure 1 shows a known cassette type helical scan type.
The tape running system and tape tension servo loop of a VTR are schematically shown.

During normal recording and playback, the tape 4 unwound from the supply reel 2 of the cassette 1 advances in the direction of arrow a, passes through a guide pin, and is wound around the circumferential surface of a drum 7 to which a rotating head (not shown) is attached. Furthermore, it is wound onto a take-up reel 3 via a capstan 5, a pinch roller 6, and a guide pin. Note that the reels 2 and 3 are driven by reel motors 8 and 9. A tension detector 10 is provided near the tape exit of the cassette 1, and a comparator 11 compares the detected voltage _e1 with the tension target value voltage Vref. By controlling the motor 8 based on the comparison output, the tape tension in the tape running system is controlled to a predetermined magnitude.

The tension detector used in such a tension servo has a detector 10a biased in the projecting direction by a spring, and the displacement when the detector 10a is pushed by tape tension against the biasing force of the spring. The amount is C _d S,
It is configured to detect with a magnetically sensitive element or the like to obtain a voltage value corresponding to the tension. In such a tension detector, a drift may occur in the detected voltage.

Drift is a phenomenon in which the detected voltage gradually fluctuates due to factors such as, for example, when the tension detector is placed under high or low temperatures for a long time, or due to changes over time.
If there is such a drift in the detection voltage, a non-negligible error will occur when converting a minute displacement of the detector 10a due to a minute change in tension into a voltage. In addition, if the drift is large and the tape is pulled out by threading the VTR, stable tension cannot be applied to the tape, which may damage the tape or make the tape run unstable. There is a problem in that it causes various troubles. Although tension detectors that use a differential transformer have been known as tension detectors with low drift and good stability in displacement-voltage conversion, they are very expensive and require a heavy movable core. The resonant frequency is low, so the servo loop gain cannot be set high. Furthermore, since a high-frequency oscillator is used, and the lead source through which the high-frequency current flows is routed inside the VTR, handling is inconvenient, as it is necessary to consider the effect on other circuits.

The present invention has been made in view of the above problems, and an embodiment in which the present invention is applied to the VTR shown in FIG. 1 will be described below with reference to FIG. 2.

As mentioned above, the drift of the tension detector is caused by changes over time or by being placed under high or low temperatures for a long period of time, and drift does not normally occur during short-term use. Therefore, drift becomes a problem when the device is used again after a long period of use, and the detection voltage must be readjusted at that time. Therefore, in this embodiment, before using the VTR, correction is performed to bring the drift of the detection voltage _e1 of the tension detector 10 within a predetermined range, for example, within a range of ±20 mV. The correction is
This is performed when the VTR is in an unthreaded state (the tape 4 is not pulled out from the cassette 1), that is, the tape 4 is not in contact with the detector 10a of the tension detector 10. Therefore, in this state, the detector 10 detects zero tension, and if the correct detection voltage _e1 at this time is zero, if there is a drift, _e1 will move in the positive or negative direction around the zero potential. Change. This is corrected to keep it within ±20mV.

The circuit shown in FIG. 2 is configured to obtain a corrected detection voltage e ₂ at the output terminal 13 when the detection voltage e ₁ including the drift obtained from the detector 10 is applied to the input terminal 12. This voltage e ₂ is applied to, for example, the comparator 11 in FIG.
Compared to Vref.

The detection voltage e ₁ is applied to the positive terminal of a differential amplifier 18 made up of resistors R ₁ to R ₄ and an operational amplifier. The output voltage _e5 of the up-down counter 21 is applied to the negative terminal of the differential amplifier 18.
Since R ₁ to _{R 4} are selected to have equal resistance values, the output of this differential amplifier 18 is e ₂ =e ₁ −e ₅ . This e ₂ is applied to the output terminal 13 and to the negative terminals of comparators 19 and 20 via a low-pass filter 28 formed by capacitors C ₁ and R ₁₇ , respectively. A voltage e 3 obtained by dividing the power supply voltage +Vcc by R ₅ and R ₆ is applied to the positive terminal of the comparator 19, and a voltage e ₃ obtained by dividing the power supply voltage +Vcc by R 5 and R 6 is applied to the positive terminal of the comparator 20.
A voltage _e4 , which is V _EE divided by R ₈ and R ₉ , is applied. These e ₃ and e ₄ are minute values, e.g. e ₃ = +20mV ₁ e ₄
= −20mV. Further, R ₇ and R ₁₀ are for feeding back a part of the outputs of the comparators 19 and 20 to give the outputs hysteresis characteristics, so that the comparators 19 and 20 operate as window comparators. The hysteresis characteristic of this window comparator prevents malfunctions due to noise. The low-pass filter 28 is used to smooth out ripples in _e2 caused by vibrations of the VTR. Comparator 1
9, when e ₂ exceeds e ₃ , that is, exceeds +20 mV, the output is reversed from "H" (high level) to "L" (low level). When e ₂ exceeds e ₄ , that is, exceeds -20 mV, the output of the comparator 20 is inverted from "H" to "L". Comparator 19
The output of the comparator 20 and the output obtained by inverting the output of the comparator 20 by the inverter 22 are applied to the gate 23. Therefore, when e ₂ exceeds the range of e ₃ to _{e 4} , the output of this gate 23 becomes "H" and opens the gate 24 of the next stage. This gate 24 is the input terminal 15
The clock pulse CK applied to the counter 21 is passed through the gate 25 and supplied to the counter 21. Further, a signal UNTH which becomes "H" when the VTR is in the unthreaded state is applied to the input terminal 14, and this signal UNTH is inverted by the inverter 26 to open the gate 25. Therefore the clock pulse
CK is not supplied to the counter 21 except when the VTR is in an unthreaded state. The counter 21 counts the clock CK, and the direction of this count is determined by the output of the inverter 22. That is, when the output of the inverter 22 is "H", the count is up, and when the output is "L", the count is down. The output voltages of the Q ₁ to _{Q 4} terminals of the counter 21 are added together via R ₁₁ to R ₁₄ and R ₁₅ to become e ₅ .
The resistance values of R ₁₁ to _{R 14} are R ₁₁ = 8R ₁₄ , R ₁₂ = 4R ₁₄ , R ₁₃
=2R ₁₄ is selected. Therefore, in the case of count-up, _e5 increases in steps every time the clock CK is counted, and in the case of countdown, _e5 decreases in steps.

According to the above configuration, when e ₂ exceeds e ₅ , the count is up, and when e ₂ is lower than e ₄ , the count is down. Note that the output of the inverter 22 is also "H" when it is in the range of e ₃ to _{e 4} , but in this case, the output of the gate 23 is "L" and the gate 24 is closed, so the clock pulse CK is not applied and the count is stopped. No action is taken. According to the above count up
When e ₅ increases, e ₂ decreases due to the relationship e ₂ = e ₁ − e ₅ .
When e ₂ falls within the range of e ₃ to _{e 4} , the comparator 19 is inverted and the counting operation is stopped. Also, when e ₅ falls due to the above countdown, e ₂ rises, and when it enters the range of e ₃ to e ₄ , comparator 2
0 is inverted and counting is stopped. As described above, even if there is a drift in _e1 , it can be corrected to a negligible magnitude.

Note that the counter 21 is preset by a pulse P applied to the terminal 17 when the VTR is powered on. This preset is applied to the J ₁ to J ₂ terminals.
This is done with a preset value of ``1000'' by adding V _EE and +V _cc to the _J4 terminal. When performing correction, it is unknown whether the drift value will be positive or negative, so if the value is preset to approximately zero potential at the start of counting, correction can be performed in the shortest possible time.

If the drift greatly exceeds the range of e ₃ to _{e 4} , even if the counter 21 becomes "0000" or "1111", e ₂ cannot be placed within the above range, and the counter 21 will overflow. This causes an oscillation state in which the count is counted again. In this case, the detector 10 cannot be used and tension servo cannot be applied. At this time, if you thread the VTR and pull out the tape, the tension will not be applied stably.
It causes various troubles. Therefore, in this embodiment, the output of the gate 23 and the signal UNTH are applied to the gate 27. Then, when the output of the gate 23 is "H", that is, the drift is outside the range of _e3 to _e4 , a threading inhibition signal TH/DIS of the "L" level is obtained at the output terminal 16, and this signal TH/DIS is output at the output terminal 16.
The operation of the threading motor is stopped by the DIS.

As explained above, according to the present invention, there is provided a tension detector that detects the tension of the tape, a detection circuit that detects whether the detection output of the tension detector is within a predetermined range, and the tension detector that detects the tension of the tape. When the detection circuit detects that the detection output is not within the predetermined range in an unthreading state where the tape is not stored in the device, the detection output is brought within the predetermined range. the tape is applied to the tension detector until the detection circuit detects that the detection output is within the predetermined range in the unthreading state; A threading prohibition circuit is provided which outputs a threading prohibition signal that prohibits the threading operation caused by threading, so it is possible to detect whether or not the detection output of the tension detector is within a predetermined range in the unthreaded state, and to prevent drift, etc. If it is outside the specified range, the correction circuit will make a correction, and
It is possible to provide a tape recording and reproducing apparatus in which the threading operation is controlled not to be performed until the detection output falls within a predetermined range, and the threading operation is performed after the correction of the detection output is completed. In addition, since the output voltage of the tension detector in the state of zero tension is corrected to the magnitude within a predetermined range, it is possible to use a normal tension detector without using an expensive tension detector using a differential transformer. It is possible to detect minute tension fluctuations. Furthermore, when used for tension servo, the resonant frequency of the servo loop can be raised to increase the loop gain, so the servo operation can be performed stably and the tension can be stably maintained at a predetermined value.

[Brief explanation of the drawing]

FIG. 1 is a schematic plan view of a tape running system of a VTR to which the present invention is applicable and a schematic block diagram of a tension servo loop, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In addition, in the symbols used in the drawings, 10
...Tension detector, 19,20...Comparator,
21...Counter, 22...Inverter, 23,
24, 26, 27... are gates.

Claims (1)

[Claims] 1. A tension detector that detects the tension of the tape; a detection circuit that detects whether the detection output of the tension detector is within a predetermined range; When the detection circuit detects that the detection output is not within the predetermined range in an unprecedented unthreading state, correction is performed to bring the detection output within the predetermined range. a correction circuit for performing a threading operation in which the tape is applied to the tension detector until the detection circuit detects that the detection output is within the predetermined range in the unthreading state; 1. A tape recording and reproducing device comprising: a threading prohibition circuit that outputs a threading prohibition signal.