JPH026503Y2 - - Google Patents

Description

[Detailed Description of the Invention] Object of the Invention The present invention relates to a tape end detection device, and particularly to a detection device that uses reflected light or transmitted light on a tape surface.

Purpose of the invention The purpose of the invention is to optically detect the difference in reflectance or transmittance between the magnetic material part of the magnetic tape and the splicing tape part, and to detect the end of the tape by using a flashing light as the detection light source in the device. An object of the present invention is to provide a tape end detection device that can distinguish between external light and detection light, prevent erroneous detection, and reliably detect a tape end.

Prior Art and Its Disadvantages Conventionally, there has been a so-called auto-reverse type tape recorder that uses both sides of a magnetic tape continuously with almost no interruption in recording or playback. In a tape recorder like this one, which detects the end of the tape and reverses the running direction of the magnetic tape, recording or playback cannot be performed while the leader tape section passes the magnetic head, and continuous recording or playback cannot be performed. Playback could not be performed. For this reason, auto-reverse tape recorders are required to detect the edge of the magnetic material and immediately reverse the running direction of the magnetic tape so that continuous recording or playback can be performed. Ta.

FIG. 1 is a diagram showing the structure near the end of a tape such as a cassette tape. In the figure, A is a magnetic material coating part (hereinafter simply referred to as a magnetic material part), C is a leader tape part, and B is a splicing tape part pasted to connect the magnetic material part A and the leader tape part C.

Conventional detection devices that detect the end of the magnetic material part of such a tape shine light from a light source onto the surface of the running tape, detect the reflected light, and then compare it with a fixed reference voltage. Tape ends have been detected by detecting changes in reflectance at the splicing tape portion.

However, with such conventional detection devices, the reflectance of splicing tape varies depending on each tape manufacturer and individual tape, so the intensity of reflected light that can be compared with the standard voltage value is not always accurate. Therefore, there was a drawback that detection of the signal at the end of the magnetic body part failed. Furthermore, the cassette tape loading section of some recording and reproducing apparatuses is exposed to external light, and in such cases there is a drawback that the end of the tape may be erroneously detected due to the influence of this external light.

Summary of the invention In order to eliminate the above-mentioned drawbacks and achieve the purpose, the present invention reflects or transmits flashing light on the tape surface, and detects the reflected or transmitted flashing light with a light-receiving element to generate a detection signal. A first operational amplifier is provided for extracting a signal of a predetermined polarity corresponding to the detection signal for a predetermined period by comparing the integrated signal and the signal of the detection signal passed through the resistor. a variable resistor to which a signal obtained by negatively rectifying and integrating the output signal of the first operational amplifier that passes through and is fed back to the input terminal, a signal that has passed through the resistor, and a feedback output signal of the first operational amplifier are supplied. A second operational amplifier is provided that extracts a pulse signal of a predetermined polarity corresponding to the detection signal for a predetermined period by comparing the signal taken out from the sliding terminal that divides the resistance value so that the resistance value on the input side is small. ,
The tape end is detected using the output signal of the second operational amplifier.

Embodiment of the invention An embodiment of the invention will be described below with reference to the drawings.

FIG. 2 shows a circuit diagram of the tape end detection device according to the present invention. In the figure, 1 is an oscillator, which is connected to the base of an NPN transistor X ₁ via a resistor R ₁ . The collector of the transistor _X1 is connected via a resistor _R2 to the cathode of a light emitting diode _D1 serving as a light source, while its emitter is grounded. The anode of the light emitting diode D ₁ is connected to the collector of the phototransistor X ₂ and also to the power supply terminal 2 . The emitter of phototransistor X ₂ is grounded via resistor R ₄ and connected to the non-inverting input terminal of operational amplifier OP ₁ via capacitor C ₃ and resistor R ₅ in series. The connection point between the capacitor C ₃ and the resistor R ₅ is connected to the power supply terminal 2 via the resistor R ₃ and also to the volume VR ₁
and grounded via resistor _R7 . Note that the resistors R ₃ and R ₇ are resistors for setting the bias of the operational amplifier OP ₁ , respectively. resistance
The connection point between _R5 and the non-inverting input terminal of operational amplifier _OP1 is grounded via capacitor _C1 . The other fixed terminal of volume VR ₁ is operational amplifier OP ₁
The sliding terminal is connected to the inverting input terminal of the volume VR ₂ and the operational amplifier.
Connected to the inverting input terminal of OP ₁ . operational amplifier
The output terminal of OP ₁ is connected to the non-inverting input terminal of operational amplifier OP ₂ via a diode D ₁ and a resistor R ₆ in series. The connection point between this resistor R ₆ and the non-inverting input terminal of the operational amplifier OP ₂ is grounded via a capacitor C ₂ . On the other hand, the sliding terminal of volume VR ₂ is connected to the inverting input terminal of operational amplifier OP ₂ ,
Its other fixed terminal is a diode D ₂ and a resistor
Connected to the connection point with R ₆ . The output of operational amplifier OP ₂ is connected to output terminal 3.

Next, the operation of the above-mentioned constituent circuit will be explained.

In the same figure, the third
A pulse with a constant oscillation frequency (signal waveform a) as shown in Figure A is applied to the base of the NPN transistor _X1 via the resistor _R1 . As a result, the transistor X ₁ is turned on during the pulse width period when the output pulse of the oscillator 1 is at a high level, and the collector current is caused to flow through the light emitting diode D ₁ and the resistor R ₂ in series with the current supplied from the power supply terminal 2. flowing,
Light up the light emitting diode _D1 . Thereafter, the transistor _X1 is turned off until the next pulse comes in, so that no current flows through the light emitting diode _D1 either, causing the light emitting diode _D1 to turn off. Then,
The light emitting diode _D1 will flash at a constant frequency.

The light emitted from the light emitting diode _D1 is irradiated onto the surface of the tape, and the reflected light is detected by the phototransistor _{X2 .} Output signals are obtained at both ends.

The DC component of this output signal is cut off by capacitor _C3 , and then integrated (averaged) by an integrating circuit consisting of resistor _R5 and capacitor _C1 , and then supplied to the non-inverting input terminal of operational amplifier _OP1. Meanwhile, this output signal is fed via the volume VR ₁ to the inverting input terminal of the operational amplifier OP ₁ . At this time, the reflectance of the light emitted from the light emitting diode _D1 changes in the process of moving from the magnetic body part A to the splicing tape part B near the end of the tape as shown in FIG. 3. signal waveform b
This appears as a change in the peak value as shown in the figure. However, the signal input to the non-inverting input terminal of operational amplifier OP ₁ is integrated (averaged) to form a signal waveform c as shown in Figure 3C. Tracking changes in light reflectance is delayed. Therefore, the operational amplifier OP ₁ converts the signal output therefrom into the signal input to the inverting input terminal with reference to the potential of the signal {signal waveform c in FIG. 3C} input to the non-inverting input terminal. The signal waveform b} in FIG. 3B is taken out in an inverted form, and this output signal is rectified on the negative side by a diode _D2 , thereby obtaining a signal waveform d as shown in FIG. 3D. And part of this signal is the volume
It passes through VR ₂ and is fed back to the inverting input terminal of operational amplifier OP ₁ . Additionally, resistor R ₆ and capacitor
The signal is again integrated (averaged) by the integrating circuit constituted by _C2 , resulting in a signal waveform e as shown in FIG. 3E, which is supplied to the non-inverting input terminal of the operational amplifier _OP2 .

On the other hand, a signal taken out from the sliding terminal of the volume VR ₁ is supplied to one fixed terminal of the volume VR ₂ . This signal, together with the feedback signal described above, increases the resistance value (r ₁ + r ₂ ) of the volume VR ₂ by r ₁ < r ₂
It is taken out from the sliding terminal that divides into
As shown in FIG. 3F, a portion where the peak value is higher than the average level (a portion where the reflectance has changed) is made into a low signal waveform f, and is supplied to the inverting input terminal of the operational amplifier _OP1 .

As described above, the signals supplied to each input terminal of the operational amplifier OP ₂ are compared by the operational amplifier OP ₂ (which operates as a comparator) and output to the output terminal 3 thereof. That is, only when the level of the signal {signal waveform f in FIG. 3F} supplied to the inverting input terminal is lower than the level of the signal {signal waveform e in FIG. 3E} supplied to the non-inverting input terminal, The operational amplifier _OP2 operates and outputs a signal waveform g as shown in FIG. 3G.

Therefore, when the reflectance of the emitted light changes in the magnetic body part A and the splicing tape part B near the tape end, such a continuous pulse train {signal waveform g in FIG. 3 G} can be obtained. Can be done.

Then, by appropriately counting the number of pulses of this output pulse signal using, for example, a counting circuit (not shown) and checking that the number of pulses exceeds a preset certain number, it is possible to reliably detect that the reflectance has changed. The end of the tape can be detected.

Effects of the invention The tape end detection device of the present invention reliably detects changes in reflectance or transmittance in the magnetic material portion and splicing tape portion near the tape end, and the continuation thereof, and further detects the tape end. By using a blinking light source as the light source for detection, it is distinguished from external light, its influence is eliminated, and erroneous detection is prevented, so that the tape end can be detected reliably.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the structure near the end of a tape such as a cassette tape, Fig. 2 is a circuit diagram of an embodiment of the tape end detection device of the present invention, and Figs. 3A to 3G.
2 is a signal waveform diagram of each part of the circuit of FIG. 2. FIG. 1... Oscillator _{, 2... Power supply terminal, 3... Output terminal, R1, R2, R3, R4, R5 , R6 , R7 ... Resistor} ,
C ₁ , C ₂ ... Capacitor, X ₁ ... NPN transistor, X ₂ ... Photo transistor, D ₁ ... Light emitting diode, D ₂ ... Diode, VR ₁ , VR ₂ ...
Volume, OP ₁ , OP ₂ ...Operation amplifier.

Claims (1)

[Scope of utility model registration request] The detection signal is obtained by reflecting or transmitting the flashing light on the tape surface and comparing the signal obtained by integrating the detection signal obtained by detecting the reflected or transmitted flashing light with a light receiving element and the signal obtained by passing the detection signal through the resistor. A first step for extracting a signal of a predetermined polarity corresponding to a predetermined period of time.
an operational amplifier, further comprising a signal obtained by negatively rectifying and integrating an output signal of the first operational amplifier, in which a part of the signal passes through a variable resistor and is fed back to the input terminal, and a signal that passes through the resistor. and a signal taken out from a sliding terminal that divides the resistance value of the variable resistor to which the feedback output signal of the first operational amplifier is supplied so that the resistance value on the input side becomes small. a second operational amplifier for extracting a corresponding pulse signal of a predetermined polarity for a predetermined period;
A tape end detection device configured to detect a tape end using an output signal of the second operational amplifier.