JPS6313140B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention performs differential detection using two reflective photoelectric detectors that can obtain an output voltage proportional to the amount of reflected light over a wide range of glossiness and color. The present invention relates to the constructed differential photoelectric detection device.

The differential detection method uses a comparative calculation function to cancel out error-causing factors such as noise and drift in characteristics due to temperature changes, so it has been commonly used for various types of detection in order to achieve stability.

In Figure 1, photoelectric detector Ph ₁ detects the mark M on sheet X ₁ flowing in the direction of arrow a, and the other photoelectric detector Ph ₂ monitors only the base G of sheet X ₁ . be. Here, x, y, and z each indicate a fixed location on the sheet _X1 . When photoelectric detector Ph ₁ detects mark M, the amount of light incident on photoelectric detector Ph ₁ changes, so photoelectric detector Ph ₂
A difference is generated between the output level of
The output is now coming out.

In such detection, there may be cases where it is desired to use several colors or different gloss levels for the mark M and to discriminate based on the respective color signals. In this case, the necessary conditions are that it is possible to distinguish between the amount of light reflected from the base and the amount of light reflected from various marks, that the output voltage difference can be taken over a wide range of colors, and that the rod can be changed easily. The detection function is not affected even if the color or gloss of the base changes.

Conventionally, as a method that can meet such requests,
Photoelectric detectors use light bulbs as light sources, but they are easily affected by ambient light, and special considerations have been taken to avoid this ambient light when used in the field. Further, it is difficult to detect a weak change in the amount of received light because it is affected by ambient light.

To improve this, a photoelectric switch that modulates and drives a light emitting diode is used as a detector.
It is conceivable to have a large tolerance for disturbance light. However, in this case, since the light intensity of the light emitting diode is extremely small, the amplification degree of the amplifier on the light receiving side of the detector must be increased. Therefore, when an object with a high reflectance enters the field of view of the detector, the intensifier becomes saturated and cannot track it, resulting in a detection range that is narrow relative to color and glossiness. Become.

This invention has a wide detection range, has a large tolerance for disturbance light, and is therefore capable of reliably responding to even weak changes in the amount of light received. The photoelectric detection device disclosed in Sho 53-12697 (Japanese Patent Publication No. Sho 61-59445) is configured as a reflection type photoelectric detection device and is used as photoelectric detectors Ph ₁ and Ph ₂ as shown in Figure 1. be.

The photoelectric detector of the patent application modulates and drives a light emitting diode, but instead of amplifying and detecting the absolute value of an electric signal corresponding to the amount of received modulated light and outputting it, the photoelectric detector of the patent application modulates and drives a light emitting diode. The electrical signal corresponding to the modulated light is amplified by a variable gain amplifier, the DC signal obtained by detecting it is compared with a reference voltage, the difference is amplified, and this is used as the variable gain amplifier. This is designed to feed back to the amplifier and also output it. Therefore, in order to detect weak amounts of received light, the variable gain amplifier does not become saturated even if the amplification rate is increased, and the amount of change can be detected analogously in response to wide changes in the amount of received light. It is output as a voltage level.

That is, when the block diagram of the electric circuit of these photoelectric detectors Ph ₁ and Ph ₂ is shown in FIG. 2, 1 is a light emitting element such as a light emitting diode, 2 is its driving device, 3 is a light receiving element such as a photodiode, and 4 is a light emitting element such as a light emitting diode. 5 is a variable gain amplifier, 5 is a detector, 6 is an error amplifier, 7 is a constant voltage generator, and 8 is an inverter.

The outputs of these two photodetectors Ph ₁ and Ph ₂ are input to a comparison calculation function U as shown in detail in FIG. That is, in this figure, the sensitivity adjuster 9 adjusts the level of the output signal A of the photoelectric detector Ph ₁ , and the sensitivity adjuster 9 adjusts the level of the output signal A of the photoelectric detector Ph 1.
It is possible to make the output signal B of Ph ₂ larger in advance and adjust it using the sensitivity adjuster 9 so that C=B. The subtracter 10 has a reference level S by the reference level setter 11, and the signals C and B
With reference to the signal B of the photoelectric detector Ph ₂ ,
Perform subtraction of (B-C)+S. That is, if C<B, a signal D that changes to the positive side with respect to the reference level S is output, and if C=B, the signal D=S, and if C>B, a signal that changes to the negative side with respect to the reference level S. Output D. The comparator 12 is set to an on/off level in advance by a hysteresis setting device 13 (the width of the on/off level corresponds to hysteresis).
A signal F is set, a change in the input signal D is compared with the signal F, and a binary signal E is output based on the magnitude relative to the signal F. In response to changes in signal E, signal F of hysteresis setter 13 is alternately set to on level (UTL) and off level (LTL). Note that the level and width of the hysteresis setting in the hysteresis setting device 13 can be freely changed depending on the detected object _X1 . Relay 14 can be turned on and off by signal E to drive a desired load.

4a and 4b are operation waveform diagrams of the circuit of FIG. 3, and FIG. 4b shows a case where the object to be detected in FIG. 4a changes. In this way, due to changes in _the detected object, _the output signals A,
Although B also changes, it is clear from the figure that it does not affect the detection function.

In addition, in Fig. 4a, the signal A changes in the negative direction due to the detection of the mark M, but the
In the combination of and mark M, the signal A may change in the positive direction, and in this case, the output of the photoelectric detector Ph ₁ is the output shown in the above-mentioned Fig. 2,
By selecting one of the outputs, it is possible to perform detection using the same comparison calculation function U (shown in the third diagram).

If the outputs of the two photoelectric detectors Ph ₁ and Ph ₂ are input to the comparison calculation function U in this way, the base _G and mark M on the sheet
It can fully respond to optical changes in detection targets such as
It is also possible to respond to a slight difference in the amount of light received by the two opposing photoelectric detectors Ph ₁ and Ph ₂ . Therefore, the differential photoelectric detection device of the present invention can reliably read color signals such as various marks on a sheet over a wide range.

[Brief explanation of the drawing]

Figure 1 is a perspective view illustrating the photoelectric detector portion of a differential photoelectric detection device, Figure 2 is a block diagram of the circuit of the photoelectric detector used in this invention, and Figure 3 is a diagram of the photoelectric detector used in this invention. A block diagram of the comparison arithmetic function circuit, FIGS. 4a and 4b are operational waveform diagrams of the circuit of FIG. 3. X ₁ ... Sheet, M ... Mark, Ph ₁ , Ph ₂ ...
Photoelectric detector, G...base, U...comparison calculation function.

Claims (1)

[Claims] 1 The electrical signal corresponding to the received modulated light is amplified by a variable gain amplifier, the DC signal obtained by detecting it is compared with a reference voltage, the difference is amplified, and this is Two photoelectric detectors that provide feedback to and output from the variable gain amplifier are installed in parallel to the object to be detected, their respective outputs are compared and calculated, and the difference is compared with a reference value. ,
A differential photoelectric detection device characterized in that a detection signal is output when the value is higher than the reference value.