JPH0445137Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a tape end detection mechanism used in video tape recorders (VTRs) and the like.

(b) Conventional technology In a VTR, the means for detecting the end of a magnetic tape and stopping the rotation of the reel stand when the end is reached to stop the tape from running is such that more tension than necessary is applied to the magnetic tape at the end. It is essential to prevent this. An example of this tape end detection mechanism is disclosed in Japanese Utility Model Application No. 59-34291.

In the prior art, the first output and the first
a control signal generating means for generating a second output with a delayed output; and a control signal generating means that is in a light emitting state when the second output is generated.
It is placed opposite the LED across the running path of the magnetic tape with transparent tape attached to the end.
When a phototransistor enters the detection mode when a first output and a second output are generated, and when a first detection output corresponding to the first output exists in the light reception output of the phototransistor (when there is an influence of ambient light), prevents the second detection output corresponding to the second output from being derived as a tape end output, and prevents the second detection output from being derived as the tape end output when the first detection output does not exist (when there is no influence of ambient light). By including the determination means that allows the output to be output as a tape end output, it is possible to prevent false detection of the tape end due to the influence of ambient light before the tape end is reached.

(c) Problems to be solved by the invention According to the above-mentioned prior art, a light receiving element such as a phototransistor driven by the first output and the second output, shown in an equivalent circuit, consists of a resistor with extremely high impedance and a capacitor. is equivalent to connecting switches in parallel. Therefore, when such a light-receiving element is driven intermittently, there is a possibility that current may momentarily flow through the capacitor even when the switch is OFF, that is, when no light is being received. Despite the absence of light, the first detection output corresponding to the first output is obtained by the phototransistor, which may prevent the second detection output from being derived as the tape end output.

(d) Means for solving the problem The present invention is a tape end detection mechanism.
A control signal generating means for generating an output and a second output that is delayed with the first output, a light emitting means that becomes a light emitting state when the second output is generated, and a running path of a magnetic tape having a transparent tape connected to the end thereof. a light-receiving means disposed opposite the light-emitting means, a first holding means for holding the output of the light-receiving means at a first timing during the delay period, and a second holding means for holding the output of the light-receiving means at a first timing during the delay period; The present invention is characterized in that it comprises a second holding means for holding the output of the light receiving means at a timing of , and a determining means for determining that the tape is at the end based on the outputs of both the holding means.

(e) Effect Since the present invention is constructed as described above, false detection of the tape end caused by intermittent driving of the phototransistor can be prevented.

(F) Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a diagram showing the positional relationship among the cassette, light emitting means, and light receiving means of this embodiment. In Fig. 2, 2 is a cassette for storing a magnetic tape 1 with transparent tape continuous at the beginning and end, and has openings 2b on both sides and a round hole 2a in the center of the bottom. . When the cassette 2 is placed on the reel stand, an LED (light emitting means) 3 planted on the chassis protrudes into the inside of the cassette 2 from the round hole 2a, and a phototransistor (light receiving means) placed on the chassis also protrudes from the round hole 2a.
4, 4 face the openings 2b, 2b. Accordingly
The LED 3 and the phototransistors 4, 4 are placed at opposing positions across the running path of the magnetic tape 1.
Incidentally, reference numerals 5 and 5 indicate optical filters for reducing the influence of ambient light.

Next, a circuit block diagram of this embodiment will be explained with reference to FIG. Reference numeral 9 denotes an oscillator 6 that emits pulses at a constant period, a frequency divider circuit 7 that divides the output of the oscillator 6 and generates a first output, and a frequency divider circuit 7 that is connected to the output terminal of the frequency divider circuit 7 and outputs the first output for a constant period. This control signal generating means is composed of a delay circuit 8 that generates a delayed second output. The delay circuit 8 is connected via a resistor to the base of an NPN type transistor 10 whose emitter is grounded and whose collector side is connected to the power line (+B) and an LED 3, and the second output emitted from the delay circuit 8. LED3 only when the
is configured so that it is in a light emitting state.

A phototransistor 4 placed opposite the LED 3 across the running path of the magnetic tape 1 has a collector connected to a power supply line (+B) and an emitter connected to ground via a resistor 12, respectively.

Reference numerals 13 and 14 designate first and second counters which use the output of the oscillator 6 as a clock input and are reset at the rising edge of the output (first output) of the frequency divider circuit 7. The first counter 13 outputs a count pulse at an arbitrary timing (first timing) during the delay period by the delay circuit 8, and the second counter 14 outputs a count pulse at an arbitrary timing during the second output generation period. The count number is set in advance so that the count pulse is output at (second timing).

15 is the emitter side of the phototransistor 4;
That is, the first latch circuit is connected to point g and uses the output of the first counter 13 as a timing pulse to hold the voltage level at point g at that time.
Together with the counter 13, it constitutes a first holding means 21. Similarly, 16 is a second latch circuit that is connected to point g and holds the voltage level at point g using the output of the second counter 14 as a timing pulse, and together with the second counter 14 constitutes a second holding means 22. . The first latch circuit 15 and the second latch circuit 16 are connected to the input side of a first AND gate 18 via an inverter 17, and the output of the first AND gate 18 is connected to the input side of the first AND gate 18 together with the output of the second counter 14.
It serves as an input to the 2AND gate 19. Said No.
The output of the 2AND gate 19 is configured to be delivered to the output terminal j as a tape end detection output.
The inverter 17, the first and second AND gates 1
8 and 19 constitute a determining means 20.

Next, the operation of this embodiment will be explained with reference to FIG. In addition, a, b, c... in Fig. 3 are the first
The waveforms are shown at points a, b, c, etc. in the figure.

The oscillator 6 always emits pulses at a constant period as shown in a, and in response to this, the frequency divider circuit 7 divides the frequency by a preset ratio as shown in b.
Derive the output. Furthermore, in response to this, the delay circuit 8 delays the first output by a preset delay amount such as c, and outputs the delayed output as a second output. The first counter 13 issues a count pulse at a first timing during the delay period, as indicated by e, and the second counter 14 issues a count pulse at a second timing, indicated as f, during the second output generation period.

In the case of the region I, which is not at the tape end and is not affected by disturbance light, the light from the LED 3 is blocked by the magnetic tape 1, and the disturbance light level is L level as shown in d, so the phototransistor 4 does not receive any light. Therefore, the non-conducting state is maintained, and the g-point voltage becomes L level. Therefore, this g-point voltage is latched at the first timing and the second timing.
The outputs of latch circuits 15 and 16 are both low as h and i.
level, and the first and second AND gates 18 and 19
The output becomes L level, and the tape end detection output at output end j becomes L level.

In an area other than the tape end where there is an influence of ambient light, the phototransistor 4 is conductive in order to receive the ambient light at the level shown in d, and the voltage at point g is always H.
level. The outputs obtained by latching this g-point voltage at the first and second timings both become H level,
Since the output of the first latch circuit 15 is inverted to L level by the inverter 17, the outputs of the first and second AND gates 18 and 19 are both L level and the tape end detection output is maintained at L level.

Next, when the end of the tape is reached and there is no influence of ambient light, the phototransistor 4 becomes conductive only when the LED 3 is in a light emitting state. Therefore, the g-point voltage is
You will get the same output. Therefore, the latch output in the first latch circuit 15 at the first timing is L level, and the latch output in the second latch circuit 16 is at the L level.
The latch output at the timing becomes H level.
Therefore, the output of the first AND gate 18 goes to H level.
An output equal to the output of the second counter 14 is obtained from the second AND gate 19, which is delivered to the output end j as a tape end detection pulse, and the tape running is stopped by a control means (not shown).

In addition, in cases other than the above-mentioned three areas, that is, when the tape end is reached and there is an influence of ambient light, another auto-stop mechanism such as a reel rotation detection mechanism is operated. Furthermore, it goes without saying that this embodiment also includes a case where the control signal generating means 9, the first and second holding means, and the discriminating means 20 are configured by software using a microcomputer.

(g) Effects of the invention As described above, according to the invention, even if the tape is affected by strong disturbance light before reaching the tape end, there is no risk of accidentally emitting a tape end detection pulse and stopping tape running. Furthermore, since the light receiving means is always in the light reception detection mode, false detection due to the characteristics of the light receiving element itself is prevented, and this has extremely high practical value.

[Brief explanation of drawings]

All drawings relate to embodiments of the present invention, and Figure 1 is
FIG. 2 is a circuit block diagram, and FIG. 3 is a timing chart. 1...magnetic tape, 2...cassette, 3...
LED (light emitting means), 4...phototransistor (light receiving means), 9...control signal generating means, 20...discriminating means, 21...first holding means, 22...second holding means.

Claims (1)

[Claims for Utility Model Registration] A cassette in which a transparent tape is arranged at the end of the magnetic tape; a control signal generating means for generating a first output and a second output delayed from the first output; and when the second output is generated. a light-emitting means that is in a light-emitting state; a light-receiving means disposed opposite to the light-emitting means across a tape running path; and a first holding device that holds the output of the light-receiving means at a first timing during the delay period. means; second holding means for holding the output of the light receiving means at a second timing during the second output generation period; and the first holding means holding the non-operating output of the light receiving means; A tape end detection mechanism, comprising: a determination means for determining that the tape is at the end when the second holding means holds the operation output.