JPS6241384Y2 - - Google Patents

Description

[Detailed description of the invention] The invention relates to an automatic stop circuit for magnetic tape.
For example, the present invention relates to a magnetic tape automatic stop circuit for detecting the end of a tape in a cassette for a video tape recorder and driving an automatic stop solenoid to unload the tape.

Generally, as a means for detecting the tape end of this type of magnetic tape, a transparent leader tape is connected to the beginning and end of the magnetic tape, the passage of the leader tape is detected by a photocoupler, and the photocoupler's photocoupler is used. A device is known in which the end of the magnetic tape is detected by the conduction of a transistor.

However, the length of the leader tape is set long due to manufacturing reasons, and it reaches from the take-up reel to the supply reel during loading, so both the photocoupler at the start of winding and the photocoupler at the end of winding operate for detection. However, there was a drawback that loading was stopped undesirably, resulting in a situation similar to when the end of the tape was detected at the start.

Conventionally, in order to prevent such an erroneous tape stop operation at the start, the length of the leader tape and the time it takes for the leader tape to pass between the photo couplers (4.7 seconds) are considered to prevent the tape from erroneously stopping. Although an automatic magnetic tape stop circuit (see Figure 2) has been devised to prevent this, in other words, if the time it takes for the leader tape to pass between the photocouplers is not flat, 4.7 seconds, in such a conventional circuit, Therefore, if the length of the leader tape is longer than a predetermined length or shorter than a predetermined length, there is a problem that the device may be stopped erroneously at the time of starting.

The configuration, operation, and drawbacks of this conventional circuit will be explained in more detail with reference to FIG.

In the figure, 40 is a first photocoupler consisting of a light emitting diode 41 and a phototransistor 42;
This first photocoupler 40 is provided on the supply reel (rewind reel) side and detects the end of the tape at the end of feeding.

43 is a second photocoupler consisting of a light emitting diode 44 and a phototransistor 45;
A photocoupler 43 is provided on the take-up reel side and detects the end of the tape at the end of rewinding.

The collector electrodes of the phototransistors 42 and 45 are connected to a NAND circuit 46 and a NOR circuit 47, respectively, and inverters 48 and 49 and diodes 50 and 51 are connected to the output stages of the NAND circuit 46 and NOR circuit 47, respectively. A CR time constant circuit 54 consisting of a resistor 52 and a capacitor 53 is interposed between the NOR circuit 47 and the inverter 49. Further, a transistor 55 is connected to the front stage of the inverter 48. This transistor 55 short-circuits the output of the NAND circuit 46 to ground using the output of the NOR circuit 47.

Reference numeral 56 denotes an automatic stop solenoid, and the solenoid 56 automatically stops the magnetic tape through an automatic stop mechanism (not shown).
An output transistor 57 is connected between the solenoid 56 and ground, and a pre-transistor 58 is provided in front of the output transistor 57 to turn the transistor 57 on and off.

In addition, in FIG. 2, 59 to 67 are resistors, and 6
8 is a capacitor, 69 is a diode, 70 is a memory switch, 71 is a counter switch, 72
73 is a rewind switch, and 73 is a DC power input terminal.

In the conventional circuit shown in FIG. 2, the operation at the start when the length of the leader tape is a predetermined length will be described. At the start, the leader tape straddles both the first and second photo couplers 40, 44. Therefore, these photo couplers 4
Both phototransistors 42,4 in 0,44
5 is turned on, and both points A and B are at the "0" level, and a "1" signal is output to the output of the NAND circuit 46, and a "1" signal is also output to the output of the NOR circuit 47. The transistor 55 is turned on by the “1” signal from the output stage of the circuit 47, and the NAND circuit 4
Short-circuit the "1" signal, which is the output of 6, to ground.
Therefore, the previous stage signal of the inverter 48 becomes "0", and this "0" signal is inverted by the inverter 48 to become a "1" signal.

In addition, the output stage of the inverter 49 maintains the "1" level due to the action of the CR time constant circuit 54 until 4.7 seconds have elapsed from the start point.
The point becomes a "1" level, and transistors 58 and 5
Since both terminals 7 and 8 are non-conductive, it is possible to prevent the tape from erroneously stopping when starting. However, this only works if the leader tape passes between the photocouplers in 4.7 seconds flat. If the length of the leader tape differs from the specified length, an erroneous stop will occur as described below.

That is, if the leader tape is shorter than the predetermined length, the first photocoupler 40 is turned off at a time less than 4.7 seconds from the start time, or in extreme cases at the start time. When the first photocoupler 40 is turned off and the phototransistor 42 in the first photocoupler 40 becomes non-conductive, the point A becomes the "1" level. At this time, a leader tape is interposed in the second photocoupler 43, and since the phototransistor 45 in the second photocoupler 43 is conductive, the point B is at the "0" level.

The “1” signal and “0” signal are connected to the NAND circuit 46.
The NAND circuit 46 logically outputs a "1" signal. At this time, since the "0" signal is output to the output stage of the NAND circuit 47 and the transistor 55 is non-conductive, the "1" signal appearing at the output stage of the NAND circuit 46 is directly transmitted to the inverter 48. applied.

This "1" signal is inverted by the inverter 48 to become a "0" signal, and as a result, the level at point C becomes "0" level, so the front transistor 58 becomes conductive, and then the output transistor 57 becomes conductive. Conduct.

When the transistor 57 becomes conductive, a DC power is applied to the automatic stop solenoid 56, and the running of the magnetic tape is automatically stopped. In other words, if the leader tape is shorter than a predetermined length, an erroneous stop operation will occur at the time of start, and loading will be stopped undesirably.

Furthermore, if the leader tape is longer than the predetermined length, even if 4.7 seconds have already elapsed from the start time, the leader tape will be positioned at one photocoupler 43 and the other photocoupler 43 will be positioned.
Since the magnetic tape is located at point C and the tape arrangement is the same as at the start when the leader tape is too short, the level at point C is "0".
level, and the automatic stop solenoid 56 is activated to automatically stop the running of the magnetic tape unnecessarily.

In this way, in the conventional circuit shown in Fig. 2,
Regardless of whether the length of the leader tape is greater than or equal to a predetermined length, there is a drawback that an erroneous stop operation occurs at the start, and there is a defect that the leader tape does not operate normally unless the length and passing time of the leader tape are strictly set and controlled.

The present invention overcomes these conventional drawbacks and can detect the end of the tape and automatically stop the tape at the end of fast-forward playback or recording, that is, at the end of feeding and rewinding. An object of the present invention is to provide an automatic stop circuit for a magnetic tape, which can smoothly load a magnetic tape without causing an erroneous stop operation at the time of start, regardless of the length of the magnetic tape.

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

FIG. 1 is an electric circuit diagram showing an automatic stop circuit for magnetic tape according to the present invention, in which 1 is a bistable multivibrator circuit (hereinafter simply referred to as a bistable circuit); includes a first CR time constant circuit 2, a first transistor 3, a second CR time constant circuit 4, and a second transistor 5.

The first CR time constant circuit 2 includes two resistors 6 and 7.
and a capacitor 8. Further, the second CR time constant circuit 4 is composed of two resistors 9 and 10 and a capacitor 11.

Reference numeral 12 designates a first photocoupler on the supply reel side. This first photocoupler 12 is composed of a light emitting diode 13 and a phototransistor 14, and the collector of the phototransistor 14 is connected to the emitter of the first transistor 3. A photocoupler 12 detects the end of the tape at the end of feeding.

15 is a second photocoupler on the take-up reel side, and this second photocoupler 15 is composed of a light emitting diode 16 and a phototransistor 17, and the collector of the phototransistor 17 is connected to the emitter of the second transistor 5. Second
A photocoupler 15 detects the end of the tape at the end of rewinding.

18 is a select switch, and this select switch 18 is a switch that is switched in conjunction with a feed operation push button and a rewind operation push button (not shown).
That is, this select switch 18 has a common terminal 18c, a feeding side terminal 18f, and a rewinding side terminal 1.
8r, and when the rewind operation push button (not shown) is turned on, the switching terminal 18b is switched to the rewind side terminal 1.
When touching 8r and performing other operations, such as playback, recording,
The switching terminal 1 is used during recording and fast forwarding operations.
8b comes into contact with the feeding side terminal 18f.

Here, the rewind side terminal 18r of the select switch 18 is connected between the resistors 6 and 7 of the first CR time constant circuit 2, and the feed side terminal 18f is connected to the second CR time constant circuit 4. Resistance 9, 10
It is connected in between.

Further, the common terminal 18c of the select switch 18 is connected to the front transistor 20 through a resistor 19.
is connected to the base electrode of

This front transistor 20 is of an npn type and is provided in the front stage of the output transistor 21, and the collector electrode of the transistor 20 is connected to the base electrode of the transistor 21.

Further, the output transistor 21 is of an NPN type that controls the energization of the automatic stop solenoid 22, and is configured to operate the automatic stop solenoid 22 when the transistor 21 is conductive to automatically stop the running of the magnetic tape. are doing.

23 to 25 are resistors, 26 is a diode, 27 is a memory switch, 28 is a counter switch, and one of the resistors 23 to 25 is a resistor 2.
4 is a time constant control resistor connected in parallel with the resistor 6 or 9 in either of the time constant circuits 2 or 4 when the select switch 18 is switched; The constant is configured to be smaller than the time constant on the non-selected side.

The present invention is constructed as described above, and its operation will be explained below.

First, the operation will be described using a fast forward operation as an example. During such an operation, the switching terminal 18b of the select switch 18 is in contact with the feeding side terminal 18f as shown in FIG.

At the start, the transparent leader tape extends from the first photocoupler 12 on the supply reel side to the second photocoupler 15 on the take-up reel side, so that the light beams from the light emitting diodes 13 and 16 are both connected to the phototransistors 14 and 17. and each of these phototransistors 14,1
7 are both conductive, the respective emitter electrodes of the transistors 3 and 5 in the bistable circuit 1 are connected to ground through the phototransistors 14 and 17, respectively, and the bistable circuit 1 is completely formed.

Here, the first transistor 3 is biased by the time constant of the first CR time constant circuit 2, and the second
The transistor 5 is biased by the time constant of the second CR time constant circuit 4, and the time constant control resistor 24
Because of the parallel connection, the time constant of the second CR time constant circuit 4 is smaller than that of the other time constant circuits 2, so the second transistor 5 always becomes conductive first.

When the second transistor 5 becomes conductive, the point A goes to the "0" level and the point B goes to the "0" level due to their interaction.
level, and point C becomes level "1" again.

This "1" level signal at point C is applied to the base electrode of the front transistor 20 via the select switch 18 and the resistor 19, so that the transistor 20 becomes conductive. As a result, the bias voltage of the output transistor 21 is short-circuited to the ground, so that the output transistor 21 does not become conductive, and the automatic stop solenoid 22 is maintained in a state where the power supply to the automatic stop solenoid 22 is slightly cut off.

Therefore, under such conditions, the loading of the magnetic tape will not be interrupted undesirably.

When the magnetic tape is smoothly loaded in this manner, the leader tape passes between the light emitting diode 13 and the phototransistor 14 of the first photocoupler 12 as the leader tape advances; The light emitting diode 1
An opaque magnetic tape is located between the first transistor 3 and the phototransistor 14, and this magnetic tape blocks light from the light emitting diode 13, so the phototransistor 14 becomes non-conductive and the emitter electrode of the first transistor 3 The conduction between the emitter electrode and the ground is briefly broken, and the emitter electrode becomes open.

When the emitter electrode of the first transistor 3 becomes open, the level at point C becomes the "1" level as a matter of course, and the "1" level signal at point C is sent to the select switch 18 in the same manner as described above.
and is applied to the base electrode of the front transistor 20 via the resistor 19, and as a result, the transistor 20 maintains conduction, the output transistor 21 maintains the non-conduction state, and the automatic stop solenoid 22
will not operate unnecessarily.

Therefore, even under such conditions, the magnetic tape can be loaded smoothly without undesirably interrupting the running of the magnetic tape.

As the magnetic tape continues to run in this manner, the leader tape passes between the light emitting diode 16 and the phototransistor 17 of the second photocoupler 15. A magnetic tape is positioned, and the light emitting diode 1 is connected by this magnetic tape.
Since the light from the second transistor 6 is blocked, the phototransistor 17 becomes non-conductive, and the conduction between the emitter electrode of the second transistor 5 and the ground is briefly interrupted, and the emitter electrode becomes open.

Since the point C is at the "1" level at this point as well, the automatic stop solenoid 22 does not operate unnecessarily in the same manner as described above, and the magnetic tape is loaded smoothly.

Further, at the same time that the emitter electrode of the second transistor 5 becomes open, the point A goes to the "1" level, and the point B also goes to the "1" level, biasing the first transistor 3.

Although the first transistor 3 is biased in this way, the emitter electrode of the first transistor 3 is open, so that the transistor 3 is not conducting at this point.

In this way, the magnetic tape is loaded continuously and smoothly, and when it reaches the end of the tape on the feeding side and the transparent leader tape is placed between the light emitting diode 13 and phototransistor 14 of the first photocoupler 12, it emits light. After passing through the leader tape, the light beam from diode 13 reaches phototransistor 14, causing phototransistor 14 to conduct.

When the transistor 14 becomes conductive, the first transistor 3 in the bistable circuit 1 becomes conductive, and the potential at point C becomes the "0" level, lowering the base potential of the front transistor 20 via the select switch 18. , makes the transistor 20 non-conductive.

When this transistor 20 becomes non-conductive, the base potential of the output transistor 21 becomes high, so that the transistor 21 becomes conductive. As a result, DC power is applied to the automatic stop solenoid 22, which operates and automatically stops the running of the tape at the end of the tape at the end of feeding via an automatic stop mechanism (not shown). It is.

Next, the operation during rewinding will be described. During such an operation, the switching terminal 18b of the select switch 18 is in contact with the rewinding side terminal 18r.

At the start, the transparent leader tape is attached to the second photocoupler 1 on the take-up reel side.
5 to the first photocoupler 12 on the supply reel side
Since the light emitting diodes 16 and 13 are
The light from both phototransistors 17 and 14
, and each of these phototransistors 17,
Since both phototransistors 17 and 14 are conductive, the emitter electrodes of the transistors 5 and 3 in the bistable circuit 1 are connected to ground via the phototransistors 17 and 14, respectively, and the bistable circuit 1 is completely formed.

Here, the first transistor 3 is biased by the time constant of the first CR time constant circuit 2, and the second
The transistor 5 is biased by the time constant of the second CR time constant circuit 4, but since the time constant control resistor 24 is connected in parallel to the resistor 6, the time constant of the first CR time constant circuit 2 is biased. Since the time constant of the first transistor 3 is smaller than that of the time constant circuit 4, the first transistor 3 always becomes conductive first.

When the second transistor 3 becomes conductive, the point C goes to the "0" level and the point D goes to the "0" level due to their interaction.
level, and the A point becomes "1" level again.

The "1" level signal at point A is applied to the base electrode of the front transistor 20 via the select switch 18 and the resistor 19, so that the transistor 20 becomes conductive. As a result, the bias voltage of the output transistor 21 is short-circuited to ground, and the output transistor 21 does not become conductive, maintaining the state in which the automatic stop solenoid 22 is not energized.

Therefore, under such conditions, the loading of the magnetic tape will not be interrupted undesirably.

When the magnetic tape is smoothly loaded in this way, the leader tape passes between the light emitting diode 16 and the phototransistor 17 of the second photocoupler 15 as the leader tape advances; The light emitting diode 1
An opaque magnetic tape is located between the second transistor 6 and the phototransistor 17, and this magnetic tape blocks light from the light emitting diode 16, so the phototransistor 17 becomes non-conductive and the emitter electrode of the second transistor 5 The conduction between the emitter electrode and the ground is briefly broken, and the emitter electrode becomes open.

When the emitter electrode of the second transistor 5 becomes open, the level at point A naturally becomes the "1" level, and this "1" level signal at point A is applied to the select switch 18 in the same manner as described above.
and is applied to the base electrode of the front transistor 20 via the resistor 19, and as a result, the transistor 20 maintains conduction, the output transistor 21 maintains the non-conduction state, and the automatic stop solenoid 22
will not operate unnecessarily.

Therefore, even under such conditions, the magnetic tape can be loaded smoothly without undesirably interrupting the running of the magnetic tape.

As the magnetic tape continues to run in this manner, the leader tape passes between the light emitting diode 13 and the phototransistor 14 of the first photocoupler 12, and there is an opaque layer between the light emitting diode 13 and the phototransistor 14. A magnetic tape is positioned, and the light emitting diode 1 is connected by this magnetic tape.
Since the light from the first transistor 3 is blocked, the phototransistor 14 becomes non-conductive, and the conduction between the emitter electrode of the first transistor 3 and the ground is briefly broken, and the emitter electrode becomes open.

Since the point A is at the "1" level at this point as well, the automatic stop solenoid 22 does not operate unnecessarily in the same manner as described above, and the magnetic tape is loaded smoothly.

Also, at the same time that the emitter electrode of the first transistor 3 becomes open, the point C becomes "1".
At the same time, the second point also becomes the "1" level, biasing the second transistor 5.

Although the second transistor 5 is biased in this way, the emitter electrode of the second transistor 5 is open, so that the second transistor 5 is not conducting at this point.

In this way, the magnetic tape is loaded continuously and smoothly until it reaches the end of the tape on the rewinding side.
Light emitting diode 16 of the second photocoupler 15
When a transparent leader tape is placed between the light emitting diode 16 and the phototransistor 17, the light beam from the light emitting diode 16 passes through the leader tape and reaches the phototransistor 17, making the phototransistor 17 conductive.

When the transistor 17 becomes conductive, the second transistor 5 in the bistable circuit 1 becomes conductive, and the potential at point A becomes the "0" level, lowering the base potential of the front transistor 20 via the select switch 18. , makes the transistor 20 non-conductive.

When this transistor 20 becomes non-conductive, the base potential of the output transistor 21 becomes high, so that the transistor 21 becomes conductive. As a result, DC power is applied to the automatic stop solenoid 22, which operates and automatically stops the tape at the end of the tape at the end of rewinding via an automatic stop mechanism (not shown). It is.

As described in detail above, the present invention includes a bistable multivibrator circuit 1 including a first CR time constant circuit 2 and a first transistor 3, a second CR time constant circuit 4 and a second transistor 5, and the first transistor 3 and ground, the first photocoupler 12 on the supply reel side is connected between the second transistor 5
A second photocoupler 15 on the take-up reel side is interposed between the terminal and ground, and a select switch 18 is provided which switches in conjunction with the feeding operation and the rewinding operation, and the rewinding side terminal 18r of the switch 18 is provided. resistors 6 and 7 of the 1st CR time constant circuit 2
In between, the feeding side terminal 18f is connected between the resistors 9 and 10 of the second CR time constant circuit 4, respectively, and a pre-transistor 20 is provided at the front stage of the output transistor 21 that controls the energization of the automatic stop solenoid 22. The base electrode of this front transistor 20 is connected to the common terminal 18c of the select switch 18, and a time constant control resistor 24 is provided, which is connected in parallel with the resistor in any of the time constant circuits when the select switch 18 is switched. Since the time constant on the side selected by the select switch 18 is smaller than the time constant on the side not selected, the end of the tape is detected at the end of feeding and at the end of rewinding. Not only can the magnetic tape be stopped automatically, but also the loading can be carried out smoothly without causing an erroneous stop operation at the time of start, regardless of the length of the leader tape.

[Brief explanation of the drawing]

FIG. 1 is an electric circuit diagram showing a magnetic tape automatic stop circuit according to the present invention, and FIG. 2 is an electric circuit diagram showing a conventional automatic stop circuit. 1...2 stable multivibrator circuit, 2...
1st CR time constant circuit, 3...1st transistor, 4
...Second CR time constant circuit, 5...Second transistor, 6, 7...Resistor, 9,10...Resistor, 12...
...First photocoupler, 15...Second photocoupler, 18...Select switch, 18r...Rewinding side terminal, 18f...Feeding side terminal, 18c...Common terminal, 20...Front transistor, 21...
Output transistor, 22... automatic stop solenoid, 24... time constant control resistor.

Claims (1)

[Scope of utility model registration request] First CR time constant circuit 2 and first transistor 3
and the second CR time constant circuit 4 and the second transistor 5
A bistable multivibrator circuit 1 is provided including a first photocoupler 12 on the supply reel side between the first transistor 3 and the ground, and a second photocoupler 12 on the supply reel side.
A second photocoupler 15 on the take-up reel side is interposed between the transistor 5 and the ground, and a select switch 18 that is switched in conjunction with the feeding operation and rewinding operation is provided, and the rewind side of the switch 18 is provided. The terminal 18r is connected between the resistors 6 and 7 of the first CR time constant circuit 2, and the feed side terminal 18f is connected between the resistors 6 and 7 of the first CR time constant circuit 2.
A pre-transistor 20 is provided at the front stage of the output transistor 21 which is connected between the resistors 9 and 10 of the 2CR time constant circuit 4 and further controls the energization of the automatic stop solenoid 22, and the base electrode of the pre-transistor 20 is connected to the selector. While connecting to the common terminal 18c of the switch 18, the select switch 1
8, a time constant control resistor 24 is provided which is connected in parallel with the resistor in one of the time constant circuits, and the time constant on the side selected by the select switch 18 is compared with the time constant on the side not selected. An automatic magnetic tape stop circuit characterized by a small size.