JPH0216433Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tape end detection device for a cassette tape recorder or the like.

In a tape recorder, when the tape stops running for some reason during a recording/reproducing operation or during tape rewinding, fast forwarding, etc., it is necessary to immediately stop the tape drive mechanism.

In order to do this automatically, a device is required to monitor the running state of the tape while the tape drive mechanism is operating and detect when it has stopped; however, in general, when the tape drive mechanism is operating, Since the running of the tape almost always stops when the tape reaches its end, such a detection device is called a tape end detection device.

The method that has been widely used in the past for this tape end detection device is to provide means for generating pulses in accordance with the rotation of the reel around which the tape is wound, and when the period of the pulses thereby reaches a predetermined value or more, An example of a method for determining that the tape has stopped running is shown in FIG.

In Figure 1, 1 is a pulse generation circuit that generates pulses as the reel table rotates, 2, 3, and 7 are resistors, 4 and 8 are capacitors, 5 and 6 are diodes, and 9 is a tape end detection circuit. .

The pulse generating circuit 1 includes a reed switch that is opened and closed by a permanent magnet attached to the shaft of the reel stand, and each time the permanent magnet rotates together with the reel stand, the reed switch operates and generates a pulse signal.

The diode 5 functions to discharge the charge in the capacitor 4 when the pulse signal from the pulse generating circuit 1 becomes a low level (hereinafter referred to as "L").

Similarly, the diode 6 functions to charge the capacitor 8 when the pulse signal becomes high level (hereinafter referred to as "H").

The tape end detection circuit 9 monitors the terminal voltage of the capacitor 8, and operates to stop the tape drive mechanism when this voltage falls below a predetermined threshold voltage νs.

Next, the operation of this device will be explained using the waveform diagram shown in FIG.

In FIG. 2, waveforms a and b represent the pulse signal a and the terminal voltage b of the capacitor 8 in FIG. 1, respectively.

While the magnetic tape is running, a pulse signal a is output from the pulse generation circuit 1 in accordance with the rotation of the reel stand, and the capacitor 4 is charged via the resistor 2 by the "L" and "H" levels of the pulse signal a. Since a discharge current flows, as a result, the terminal voltage of the capacitor 8 becomes the second
The waveform will look like waveform b in the figure. That is, pulse generation circuit 1
When the output signal (waveform a) is "H", the current charges the capacitor 8 via the resistor 2, the capacitor 4, and the diode 6, and the terminal voltage b of the capacitor 8 increases.
increases from ν _L to ν _H . Conversely, when waveform a is "L", the charge charged in capacitor 4 is discharged by resistor 3 and diode 5, and the charge charged in capacitor 8 is discharged by resistor 7, so the voltage between the terminals of capacitor 8 is It decreases from V _H to V _L. While the reel stand is rotating, charging and discharging are repeated as described above, and the terminal voltage b of the capacitor 8 is ν _L
~ _νH is maintained, and the tape end is not detected.
Next, when the end of the tape is reached and the tape stops running, the rotation of the reel stand also stops, and as a result, the pulse signal a no longer appears at the output of the pulse generating circuit 1. Therefore, the electric charge charged in the capacitor 8 continues to be discharged by the resistor 7, and the terminal voltage b of the capacitor 8 decreases, and when the threshold voltage _Vs at the input of the tape end detection circuit 9 is divided, the voltage at the terminal voltage b of the capacitor 8 decreases. is activated, autostop is activated, and the tape drive mechanism is stopped.

As described above, in the conventional technology, since the capacitor 8 is charged with the "H" signal of the pulse signal a and discharged with the "L" signal, the charging/discharging period of the capacitor 8 and the pulse period of the pulse generation circuit 1 are the same. It's getting old.
Therefore, even when the rotation speed of the reel stand becomes relatively slow even though the tape is running normally, such as near the end of the tape during recording or playback, this can be prevented from being mistakenly detected as the end of the tape. Therefore, it was necessary to select the threshold voltage Vs of the tape end detection circuit 9 to be relatively low so that it does not respond even if the period of the pulse signal a becomes considerably long.

Therefore, in the conventional example shown in FIG. 1, the period from when the tape actually stops running until it is detected by the tape end detection circuit 9 is relatively long, and the tape drive mechanism stops. The disadvantage was that it took a long time to complete the process, and during that time it placed a heavy burden on the tape and drive mechanism.

In particular, when a Hall element is used in place of a reed switch as the pulse generation circuit 1, or in a so-called half-speed tape recorder in which the tape running speed is halved in order to lengthen the recording time, the period of the pulse signal a from the pulse generation circuit 1 is The disadvantage was that the speed was twice that of a reed switch or a tape recorder with a normal tape speed, and the time required for auto-stop to function was also twice as high, placing an even greater burden on the tape and drive mechanism.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, and to detect the stoppage of tape running with a relatively short delay even when the period of the pulse signal obtained as the reel base rotates becomes quite long. The purpose of the present invention is to provide a possible tape end detection device.

In order to achieve this purpose, the present invention obtains a trigger pulse signal from both the rising and falling edges of a pulse signal taken out in accordance with the rotation of the reel stand of a tape recorder, and uses this trigger pulse signal to The feature is that the end is detected.

Embodiments of the tape end detection device according to the present invention will be described below with reference to the drawings.

FIG. 3 shows an embodiment of the present invention, in which the pulse generation circuit 1, capacitor 8, and tape end detection circuit 9 are the same as in the conventional example shown in FIG.

In the figure, 11, 14, and 15 are resistors, 12 is a capacitor, and 13 is an exclusive OR circuit (hereinafter referred to as EX
-OR circuit), 16 is a transistor, 17
is an inverter.

The resistor 11 and the capacitor 12 form an integrating circuit, which integrates the pulse signal a and connects it to the EX-OR circuit 13.
supply to one side.

The EX-OR circuit 13 generates a trigger pulse signal e by performing an exclusive OR operation on the pulse signal a and a signal d obtained by integrating the signal a.

The transistor 16 is made conductive by the trigger pulse signal e, and performs a switching operation to discharge the charge stored in the capacitor 8.

Resistor 14 forms a charging circuit for capacitor 8.

The inverter 17 functions to invert the output from "H" to "L" when the terminal voltage f of the capacitor 8 exceeds a predetermined threshold level Vs.

The tape end detection circuit 9 functions to operate an auto-stop when the output of the inverter 17 becomes "L".

Next, the operation of this embodiment will be explained with reference to the waveform diagram in FIG.

When a pulse signal a is generated from the pulse generation circuit 1 due to the rotation of the reel stand, this pulse signal a flows to the capacitor 12 via the resistor 11, and since the capacitor 12 is repeatedly charged and discharged, its terminal voltage b
The rising and falling portions of pulse signal a are blunted, resulting in a signal as shown by waveform b. and,
Since the input of the EX-OR circuit 13 is supplied with the pulse signal a and the signal of waveform b, the result is
-As is clear from the waveform diagram in FIG. 4, the output of the OR circuit 13 has both inputs at the same level, that is, "L",
“L” or “H”, “L” when it becomes “H”
It is an output, and becomes an "H" output only when the input is at the opposite level, that is, "L" and "H". Therefore, this output becomes as shown by the waveform c, and both the rising and falling edges of the pulse signal a from the pulse generating circuit 1 become a short trigger pulse signal c. This trigger pulse signal c is input to the base of the transistor 16 via the resistor 15.

The collector of the transistor 16 is connected to the power supply via the resistor 14, but the emitter is grounded, so it is normally off and turns on only when the trigger pulse signal c is supplied. Therefore, when there is no trigger pulse signal c and the transistor 16 is off, a charging current flows into the capacitor 8 from the power supply through the resistor 14, and the terminal voltage d increases.
Trigger pulse signal c is input to the base of transistor 16, and only when transistor 16 is turned on, the charge in capacitor 8 is discharged and terminal voltage d drops. Therefore, while the tape is running and the reel stand is rotating, the pulse signal a is generated at a predetermined synchronization, so the capacitor 8 is repeatedly charged and discharged.
The terminal voltage d maintains a voltage between 0 and _VH . When the end of the tape is reached, the reel stand stops rotating.
Since the pulse signal a is no longer output from the pulse generating circuit 1, the trigger pulse signal c also disappears, and the charge in the capacitor 8 is no longer discharged. Therefore, current flows into the capacitor 8 from the power supply through the resistor 14 and charging continues, and the terminal voltage d of the capacitor 8 increases.
increases towards the supply voltage. The moment the terminal voltage d of the capacitor 8 exceeds the threshold level Vs of the input of the inverter 17 on the way to reaching the power supply voltage, the output of the inverter 17 is reversed from "H" to "L".

When the output of the inverter 17 is inverted to "L", the tape end detection circuit 9 operates to stop the tape drive mechanism and activate the auto-stop.

Therefore, in this embodiment, since the charging/discharging period of the capacitor 8 is half the period of the pulse signal a from the pulse generating circuit 1, the rotational speed of the reel stand is considerably reduced when the tape is running normally. Even if the tape stops running, the time from when the tape stops running until it is detected is short, and there is no risk of damage to the tape or drive mechanism due to the long time it takes for the autostop to work.

Therefore, if a method using a magnet and a Hall element is used instead of the conventional method using a magnet and reed switch as the pulse generation circuit 1 for detecting the rotation of the reel stand, in order to shorten the tape end detection time, For example, a method of increasing the number of magnetic poles of a magnet is known, but according to the embodiment of the present invention, since the charging/discharging cycle of the capacitor 8 is half of the pulse signal a, the number of magnetic poles of the magnet can be doubled. The same effect can be obtained as in the case where the present invention is used, and even when applied to a tape end detection device such as a half-speed tape recorder, sufficiently satisfactory operation can be expected.

Additionally, most half-speed tape recorders are of the two-speed switching type so that they can be used at both normal tape speed and half-speed; If the tape end switching device is switched between the conventional one shown in FIG. 1 and the one of the present invention, a constant detection time can be maintained at all times, and accurate auto-stop operation can be expected.

In the embodiment shown in FIG. 3, an integrating circuit consisting of a resistor 11 and a capacitor 12 and an EX-OR circuit 13 are used to obtain the trigger pulse signal c from both the rising and falling portions of the pulse signal a. However, this is just an example, and it goes without saying that any configuration having equivalent functionality can be adopted. However, the embodiment shown in FIG. 3 has the advantage that it can be constructed relatively easily and can be implemented at low cost.

As explained above, according to the present invention, the detection time can be halved without changing the pulse generation circuit that generates pulse signals in accordance with the rotation of the reel stand, so the auto-stop system can eliminate the drawbacks of the conventional technology. A tape end detection device that takes a short time to operate and does not damage the tape or drive mechanism can be provided at low cost.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example of a tape end detection device, Fig. 2 is a waveform diagram for explaining its operation, and Fig. 3 is a circuit diagram showing a conventional example of a tape end detection device.
The figure is a circuit diagram showing one embodiment of the tape end detection device according to the present invention, and FIG. 4 is a waveform diagram for explaining its operation. 1...Pulse generation circuit, 8...Capacitor charged and discharged by trigger pulse, 9...Tape end detection circuit, 12...Capacitor for integration, 13
...Exclusive OR circuit, 16...Switching transistor, 17...Inverter.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) In a tape end detection device for a tape recorder that detects the stoppage of a reel stand based on a pulse signal generated as the reel stand rotates,
a trigger pulse signal generation circuit that receives the pulse signal as input and generates a trigger pulse signal at both the rising and falling portions of the pulse signal; a transistor that receives the trigger pulse signal as input and becomes conductive in accordance with the trigger pulse signal; A capacitor that discharges a charge when the transistor is conductive and charges when it is non-conductive, and a charging voltage of the capacitor is increased in a predetermined manner based on the stoppage of generation of the pulse signal and the trigger pulse signal when the rotation of the reel stand is stopped. 1. A tape end detection circuit comprising: a threshold detection circuit that generates an output signal when the level of . (2) In claim 1 of the utility model registration claim, the trigger pulse signal generating circuit has one input of the trigger pulse signal and the other input thereof is supplied with the pulse signal via an integrating circuit. A tape end detection device comprising an OR circuit.