JPH0367563B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention provides a method in which a plurality of light emitting and light receiving elements each have one
This invention relates to a photoelectric object detection device that detects objects one by one in pairs.

<Summary of the Invention> When switching a corresponding pair of light-emitting element and light-receiving element in a time division manner, the light-emitting element is brought into an active state after a predetermined period of time delay than the light-receiving element, whereby one amplifier circuit When amplifying and sampling the amplified data in time series, avoid the influence of unnecessary noise generated when switching light receiving elements.

<Background of the Invention> For example, in detecting the size of a document, a light emitting part and a light receiving part are provided, a plurality of light emitting elements and light receiving elements constituting the light emitting part and the light receiving part are arranged at predetermined positions, and they are time-divided. It has been proposed that a single amplification circuit amplifies the information in time series by operating the sensor to identify and detect the object to be detected (in the above example, the size of the document is detected).

According to the above, there is only one amplifier circuit, and when signal processing is performed by a microcomputer or the like, there is an advantage that the circuit configuration can be extremely simple.

<Problems to be Solved by the Invention> By the way, when sampling the amplified signal of the output of the light receiving element after time-divisionally switching the light emitting element and the light receiving element, unnecessary noise is generated when switching the light receiving element due to the internal capacitance of the light receiving element. There was a risk of misjudges occurring in the sampling of the amplified signal.

An object of the present invention is to provide an optical object detection device that prevents such misjudges.

<Means for Solving the Problems> When switching a corresponding pair of light emitting element and light receiving element in a time-division manner, a switching means is provided which puts the light emitting element into an operating state with a predetermined time delay from the light receiving element.

<Function> As described above, the light receiving element becomes operational after the unnecessary noise generated when switching the light emitting element has sufficiently subsided, so that it is not affected by unnecessary noise during sampling, and misjudges can be prevented. Also,
Another advantage is that the light emitting element has a short operating period, long life, and low power consumption.

<Embodiment> FIG. 1 shows a circuit configuration diagram in an embodiment of the present invention, and FIG. 2 shows the operation timing of each part.

As the elements constituting the light emitting part and the light receiving part, an example is shown here in which three pairs of light emitting elements 1 and light receiving elements 2 are arranged at predetermined positions. Note that the light emitting elements 1a, 1
It is assumed that b and 1c detect the object 3 in correspondence with the light receiving elements 2a, 2b and 2c, respectively.

A first switching circuit 5 connected to the microcomputer 4 is connected to each light emitting element 1a, 1b, 1c and drives them in a time division manner, and a second switching circuit 6 is connected to each light receiving element 2a, 2b, 2c. These are time-divisionally driven. The light receiving element output derived from the second switching circuit 6 is inputted to an amplifier 8 via a filter 7, whereby the light receiving element output is amplified and then inputted to the microcomputer 4. The filter 7 is provided to remove optical noise from the output of the light receiving element.

Light receiving elements 2a, 2b, 2c and light emitting element 1a,
The driving timing of 1b and 1c is as shown in FIG.
a, light receiving element 2b, light emitting element 1b, light receiving element 2c
and each pair of light emitting elements 1c are sequentially switched to the active state. Note that the light receiving element 2
The light emitting elements a, 2b and 2c are switched earlier than the light emitting elements 1a, 1b and 1c in time division driving. That is, the light emitting elements 1a, 1b, 1c are switched to the operating state with a predetermined delay from each of the light receiving elements 2a, 2b, 2c.

As shown in the output waveform of the amplifier 7 in FIG. 2, unnecessary noise is a signal generated in synchronization with the rising edge of the drive timing of each light receiving element 2a, 2b, 2c. That is, when the light receiving elements 2a, 2b, 2c are activated, an unnecessary pulse appears in the output of the amplifier 8 due to the internal capacitance of each light receiving element 2a, 2b, 2c. This unnecessary pulse falls according to the time constant of the filter 7. Light emitting elements 1a, 1b, 1
c becomes active when the above-mentioned unnecessary pulse has sufficiently fallen.

In the microcomputer 4, each light emitting element 1a, 1
The signal from the amplifier 7 is sampled during the period when b and 1c are active, the influence of unnecessary noise is removed, and the presence or absence of the object 3 can be accurately determined. More preferably, as shown in the figure, each light emitting element 1
It is possible to remove the influence of noise to a greater extent by sampling at the end of the period in which a, 1b, and 1c are active.

By the way, if they become active at the same time, unnecessary noise will be added to the photodetector output and the peak value will become high.
The fall is delayed, and the influence of unnecessary noise remains during sampling.

Furthermore, according to this example, the light emitting elements 1a, 1
This has the advantage that the operating period of the light emitting elements 1a, 1b, 1c can be shortened, the lifespan of the light emitting elements 1a, 1b, 1c can be extended by short-time driving, and power consumption can also be reduced.

<Effects of the Invention> As described above, according to the present invention, it is possible to provide a photoelectric object detection device that is time-division-based and unaffected by unnecessary noise and is useful and has high practical value.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
FIG. 2 is an operation timing chart of each part. 1a, 1b, 1c...Light emitting element, 2a, 2b, 2
c... Light receiving element, 3... Object, 4... Microcomputer, 5... First switching circuit, 6... Second switching circuit, 7... Filter, 8... Amplifier.

Claims (1)

[Claims] 1. A plurality of light emitting elements and light receiving elements constituting a light emitting part and a light receiving part are arranged at predetermined positions, and the corresponding 1
The paired light emitting element and light receiving element are sequentially switched in a time-division manner, amplified in time series by one amplifier circuit, and the amplified light receiving element output is sampled to detect the presence or absence of an object at each predetermined position. The photoelectronic device is characterized in that, when switching the corresponding pair of light-emitting element and light-receiving element in a time-divisional manner, switching means is provided for setting the light-emitting element into an operating state with a predetermined time delay from the light-receiving element. type object detection device.