JPH0610504Y2 - Photo detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a photodetection device for detecting translucency of an object to be detected by making a light emitting element and a light receiving element face each other with an object to be detected therebetween.

<Prior Art> As a device of this type, a video tape recorder (VT
A tape end detection device in R) is known. That is, in this type of VTR, transparent leader tape portions are provided at both ends of the magnetic tape housed in the cassette, and a light emitting or light receiving element inserted in the cassette,
The end of the tape is detected by providing a light-receiving or light-emitting element facing the magnetic tape via the opening of the cassette and detecting the light passing through the leader tape section by the light-receiving element.

<Problems to be Solved by the Invention> However, since the photosensitive element used as the light receiving element responds to any light, when external light leaks into the VTR and the photosensitive element is irradiated for a predetermined time or longer. Is also determined to be the end of the tape. Therefore, in a VTR configured to stop the tape running when the tape end is detected, the tape running is stopped when the malfunction occurs due to the external light during recording or reproduction. Therefore, when designing the VTR, it is necessary to design in consideration of the blocking of the external light, or to arrange the light receiving element at a position where the external light is not received, and there is a problem that the degree of freedom in design is reduced.

Further, in the tape end detecting device of the VTR, particularly rapid detection is required. For example, when winding the tape at high speed, the tape stops when the end of the tape is detected, but if it takes time to detect the end of the tape, the tape will be completely wound on one reel. , Because the tape will be heavily loaded.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a photodetector capable of quickly and accurately detecting the translucency of an object to be detected without malfunction due to external light.

<Means for Solving the Problems> For such a purpose, the photo-detecting device according to the present invention is a light-receiving element that faces a light-emitting element and the light-emitting element with the object to be detected interposed therebetween and is capable of always outputting a light-receiving result. And a first read command for instructing to read the light reception result output from the light receiving element, a light emission start command for instructing to start light emission of the light emitting element after issuing the first read command, and this light emission. After issuing a start command, a second read command for instructing the reading of the light reception result output from the light receiving element, and a light emission end for instructing the light emission end of the light emitting element after issuing the second read command A control means for issuing a command, and a detection means for detecting translucency of the object to be detected based on the output of the light receiving element obtained in response to the first and second read commands by the control means, The control means is the first 1 read command, light emission start command, second read command and light emission end command are repeatedly issued, and from the generation timing of the first read command issued via the light emission start command to the generation timing of the second read command. Is set to be shorter than the period from the generation timing of the second read command issued via the light emission end command to the generation timing of the first read command.

<Operation> In the above-described configuration, when the light receiving element receives the light obtained from the light emitting element through the detected body, the output signal from the light receiving element is not obtained at the first timing,
On the other hand, when external light is received by the light receiving element, there is output from the light receiving element even at the first timing, so that it is possible to distinguish between them. In addition, in the light receiving element, the response of the light emission is generally faster than the response of the light emission end. Therefore, by setting the period from the first timing to the second timing to be shorter, more rapid detection can be performed.

<Embodiment> FIGS. 1 and 2 are views for explaining an embodiment of the present invention. FIG. 1 is a block diagram, FIG. 2 is a flow chart, and FIG. 3 is a timing chart.

In FIG. 1, 1 is a light emitting diode, which is a light emitting element,
2 is a driving circuit for intermittently driving the light emitting diode 1;
Is a photo diode which is a light receiving element, 4 is a waveform shaping circuit, 5 is a microcomputer which performs pulse generation for driving the light emitting element and processing of signals, and 6 is a magnetic tape which is an object to be detected.

Next, in the configuration shown in FIG. 1, the processing of the microcomputer 5 will be described according to the flow chart of FIG. When the light receiving signal is fetched in the process 11, since the light emitting diode 1 is in the off state, the information indicating the presence or absence of external light is obtained from the photo diode 3 to the microcomputer 5 via the waveform shaping circuit 4. Next, in process 12, a light emission start command is issued to the drive circuit 2 and the light emitting diode 1 is turned on. Then, when the light reception signal is fetched again in the process 13, since the light emitting diode 1 is in a lighting state, the light transmittance of the detected object 4 is obtained from the photodiode 3 to the waveform shaping circuit 4 to the microcomputer 5. To be In process 14, the drive circuit is instructed to turn off the light emitting diode 1. After that, the signal from the photodiode 3 falls while the microcomputer 5 is performing other processing.

As described above, the signal detected immediately before the light emission of the light emitting diode 3 is constant regardless of whether or not the magnetic tape 4 is at the end, and at this timing, the information "incident light present" is obtained from the photodiode 3. In this case, it can be determined that this is due to external light, and the information “incident light present” detected at the timing after light emission is not used as “tape end” information. That is, the tape end is determined only when the information “no incident light” is obtained at the timing immediately before the light emission and the information “incident light is present” at the timing immediately after the light emission.

FIG. 3 (A) shows a driving pulse of the light emitting diode 1,
FIG. 3B shows the photodiode 3 obtained in response to this.
The output signal of is shown. As shown in the figure, the output signal of the photodiode 3 has a steeper characteristic at the rising edge than at the falling edge.
Therefore, as shown in FIG. 3A, the output signal of the photodiode 3 is read by the microcomputer 5 at the timing immediately before and after the start of the generation, that is, the reading timing when the light is not emitted (first timing) and the reading timing when the light is emitted. Timing (second
From the second timing to the first timing.
By setting the period shorter than the period up to the timing, it becomes possible to detect the end of the tape in an extremely short time.

In the device as described above, even when external light is incident on the photodiode 3, the tape end can be detected reliably without being erroneously determined as the tape end. Further, since the output signal from the photodiode is taken into the microcomputer 5 at the timing immediately before and after the light emission of the light emitting diode 1 is started, the tape end can be detected extremely quickly.

<Effect of the Invention> As described above, according to the present invention, it is possible to obtain the photodetector capable of detecting the translucency of the object to be detected quickly and reliably.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of a tape end detecting device as an embodiment of the present invention, FIG. 2 is a flow chart for explaining the operation of the microcomputer of FIG. 1, and FIG. 3 is each part of FIG. It is a timing chart explaining the operation of. 1 ... Light emitting diode as light emitting element 3 ... Photo diode as light receiving element 5 ... Micro computer 6 ... Magnetic tape as object to be detected

Claims (1)

[Scope of utility model registration request] 1. A light-emitting element, a light-receiving element that faces the light-emitting element with an object to be detected sandwiched therebetween, and is always capable of outputting a light-receiving result, and a first instruction for reading a light-receiving result output from the light-receiving element. Read command, and a light emission start command for issuing a light emission start command to the light emitting element after issuing the first read command, and a light reception result output from the light receiving element after issuing the light emission start command. And a control unit for issuing a second read command for issuing a second read command, and a light emission end command for instructing the end of light emission of the light emitting element after issuing the second read command, and the first and second A detection means for detecting the translucency of the object to be detected based on the output of the light receiving element obtained in response to a read command, wherein the control means includes the first read command, the light emission start command, and the second read command. Read command and light emission end command Is repeatedly issued, and the first is issued via the light emission start command.
Is shorter than the period from the generation timing of the second read command issued via the light emission end command to the generation timing of the first read command. A photodetector characterized by being set so that