JPS6227688A - Photoelectric switch for setting distance - Google Patents

Abstract

PURPOSE:To output a detection signal when a measuring object is displaced to approach a reference position or to be spaced apart therefrom, by setting a reference position by appropriately selecting the resistance value of the variable resistor of one amplifying circuit of a light receiving element. CONSTITUTION:The laser beam from a light emitting element forms a beam spot on a measuring object 3 by a beam projecting lens 2. This beam spot is formed into an image on a beam receiving element 5 as a beam receiving point by a beam receiving lens 4. This beam receiving point moves to a direction a' b' c' when the object 3 moves to a direction a b c. When the object 3 is present at the position (a), the relation of i1:i2=l1:l2 is formed between the output currents i1, i2 of the element 5 and the distances l1, l2 up to the beam receiving point. The current i1 is inputted to the negative terminal of an operational amplifier OP2 fed back by a variable resistor VR2 and the current i2 is similarly inputted to the negative terminal of an operational amplifier OP1 by a resistor R1. Because the currents i1, i2 and the distances l1, l2 take proportional relation, when the value of the resistor VR2 is set to form R1:VR2=l1:l2, a detection signal is outputted from a comparing circuit 6 when the object 3 is spaced apart from the reference position (a) or approach said position (a).

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention projects a light beam onto an object to be measured, uses the reflected light to measure the distance to the object, and uses this measured value as a set threshold. The present invention relates to a distance setting photoelectric switch that outputs a detection signal when a distance value is exceeded.

[Conventional technology]

The following types of conventional distance setting photoelectric switches have been used. As shown in FIG. 4, a light spot is formed on the measurement object 3 by the light projecting element 1 and the light projecting lens 2, and this light spot is imaged as a light receiving point on the light receiving element 5 using the light receiving lens 4. . When the measuring object 3 changes its position in the figure and moves from a → b → C, this light receiving point is
Accordingly, the light receiving element 5 is moved a' - bb' - c'.
and move. That is, the distance to the measurement object 3 is determined not by a change in the amount of light received, but by knowing the position of the light receiving point on the light receiving element 5.

This light receiving element 5 includes P which is a -dimensional position detecting element.
S D (Position 5 sensitive D
evice) is commonly used. Then, two types of output currents i5 and 12 are output from this light receiving element 5,
These are input to a subtracter 12 and an adder 13, respectively,
(v+vz), converted to (Vl+V2) output. After this, the divider 14 calculates (Vl - V2) /
By being converted to (Vl +vz) output,
A voltage value corresponding to the distance to the measurement target 3 can be obtained regardless of the amount of received light.

The relationship between the output voltage of the divider 14 and the distance to the object to be measured 3 is proportional as shown in FIG.

The distances a, b, and c to the measurement object 3 are determined corresponding to the outputs a'', b'', and C'' of the divider 14. Therefore,
By providing a comparator 15 after the divider 14, it is possible to determine whether the object to be measured 3 is closer or farther than a certain set distance X.

That is, in the same figure, if the threshold value y is set by the threshold value setting circuit 16, it is possible to determine whether the measuring object 3 is far or near based on the set distance X. By setting a new threshold value for the object, a detection signal is output when the object gets too close or too far away.

[Problem that the invention seeks to solve]

However, the conventional photoelectric switch for distance setting when the divider 14 is used has the following problems. The divider 14 has various drawbacks such as poor temperature characteristics, narrow range, slow response speed, and poor linearity.

Therefore, the use of the divider 14 has a large effect on the distance measurement accuracy, and there is a problem that it is not possible to obtain a measurement accuracy higher than that obtained by the divider 14 as a whole for the photoelectric switch for distance setting. .

This invention was made in view of the above problems, and it is possible to measure the distance to the object to be measured without using a divider, and when this measured value exceeds a set threshold, a detection signal is generated. The purpose of this invention is to provide a photoelectric switch for distance setting that outputs .

[Means for solving problems]

A specific means for solving the above problem is to project a light beam onto the object to be measured, use an imaging means to form an image of this reflected light onto a light receiving element, and use the output of the light receiving element to create a connection between the object and the object to be measured. In a distance setting photoelectric switch that measures a distance and outputs a detection signal when the measured value exceeds a set threshold, a first one that amplifies the output of one of the light receiving elements at a constant amplification factor. an amplifier circuit; a second amplifier circuit that amplifies the other output of the light receiving element by varying an amplification factor;
The present invention further includes a comparison circuit that compares the outputs of the two amplifier circuits and outputs a detection signal.

[For production]

Since this invention employs the above-mentioned means, the reference position is set by selecting the resistance value of the variable resistor of the second amplifier circuit, and the object to be measured is displaced to approach or move away from the reference position. When this occurs, a detection signal is output.

〔Example〕

The distance setting photoelectric switch according to the present invention will be explained in detail below. Note that the same parts as those in the prior art are given the same symbols.

First, a first example will be described. As shown in FIG. 1, a light beam emitted from a light projecting element 1 is projected onto a measuring object 3 by a light projecting lens 2 to form a light spot. This light spot is imaged as a light-receiving spot on the light-receiving element 5 using the light-receiving lens 4. When the object to be measured moves from a-h l)-h (in the figure), this light-receiving point changes from a° to b accordingly.

-11('). This light receiving element 5 uses a PSD.

As shown in Fig. 2, when the measurement object 3 is at position a (see Fig. 1), its light receiving point a' is P in the figure.
Located on the right side of SD5. As described above, when the measurement object 3 moves from the position b to C, the light-receiving point moves on the PSD 5 from a to b to C to the left in the figure.

In this case, when the measurement object 3 is at position a, the current i1. output from the PSD 5. i2 (i, is P
In Figure 2 of SD5, the current output from the right end is 1
2 is the current output from the left end), if in Figure 2 of the PSD5, the distance from the left end to the light receiving point a'' is 11, and the distance from the right end to the light receiving point a' is 12, then i,: iz =], : The relationship is 1□.

The output current iI of this PSD5 is, as shown in FIG.
It is input to the negative terminal of the operational amplifier OP2, which is subjected to negative feedback by the gain adjustment variable resistor VRz. The positive terminal of this operational amplifier OP2 is grounded. On the other hand, the output current 12 of the PSD5 is input to the negative terminal of the operational amplifier OP1, which is negatively fed back by the resistor R8.The positive terminal of the operational amplifier OPI is also grounded.The operational amplifier OPI
The output of the operational amplifier OP2 is input to the negative terminal of the comparison circuit 6, and the output of the operational amplifier OP2 is input to the positive terminal of the comparison circuit 6.

In this case, the voltage V(+) on the positive terminal side of the comparator circuit 6 is y (+)=i, VRz, while the voltage V(~) on the negative terminal side is v (-) −i2 RI. The comparator circuit 6 inverts its output when the positive and negative input voltages match. In addition, as mentioned above, since il : iz = 11 : l□, by setting the value of variable resistor ■R2 so that RI : VRz = 1+ : lz, the measurement object 3 can be placed at position a. (See FIG. 1), a detection signal is output when the object moves away from this position a. When outputting a detection signal based on another position of the measurement object 3, the variable resistor VR of the operational amplifier OP2 is used as in the above case.
, may be changed so that the positive and negative inputs of the comparator circuit 6 match when the position is reached.

In this first embodiment, the second amplifier circuit is configured by the operational amplifier OP2 and the variable resistor VR2, but it may of course be configured by an operational amplifier and a variable attenuator that are negatively fed back by a resistor.

Furthermore, in this first embodiment, the operational amplifier OPI
Although the output of the operational amplifier OP2 is input to the negative terminal of the comparison circuit 6 and the output of the operational amplifier OP2 is input to the positive terminal of the comparison circuit 6, they may be connected in the opposite manner. By this switching, the detection signal can be outputted both when the object approaches and when the object moves away from the object. That is, when the input terminal of the comparison circuit 6 is connected as in this embodiment, a detection signal is output when the measurement object 3 moves away from the position a. Therefore, if the connection is reversed, a detection signal will be output when approaching from position a. In addition, it is an operational amplifier.

By adding a comparison circuit, etc., it is possible to output a detection signal both when approaching and leaving the reference position without switching between positive and negative inputs of the comparison circuit 6. Multiple settings can be made, allowing extremely detailed detection.

Next, a second example will be described. This example is
In the first embodiment described above, the measurement object 3 (first
The purpose of this invention is to solve the difficulty in setting the resistance value of the variable resistor VR, since the correlation between the distance from the light receiving element 5 (see figure) and the position of the light receiving point of the light receiving element 5 is not linear.

As shown in FIG. 3, a current 12 generated from the light receiving element (PSD) 5 is converted into a voltage by a current-voltage conversion circuit 7a. This output voltage is input to an adder 9 after being amplified by an amplifier 8a. On the other hand, the current il of the light receiving element 5 is
After being converted into voltage by the current-voltage conversion circuit 7b, 2
It is divided into

One of them is amplified by an amplifier 8b and input to the adder 9. The other signal is amplified by the amplifier 8c and input to the variable attenuator 10. The output of the adder 9 is input to the negative terminal of the comparator 11, and the output of the variable attenuator 1o is input to the positive terminal of the comparator 11. Since the comparator 11 outputs a detection signal when both human forces match, by varying the amount of attenuation of the variable attenuator 10, various reference positions, which are the positions of the measurement object 3 from which the detection signal is output, can be selected. Note that this second
In the embodiment, the current-voltage conversion circuit 7a and the amplifier 8a constitute a first amplifier circuit, the current-voltage conversion circuit 7b, amplifiers 8b and 8c, and the variable attenuator 10 constitute a second amplifier circuit, Adder 9 and comparator 11
A comparison circuit is constructed.

With such a configuration, by selecting the amplification factors of the amplifiers 8a and 8b so that the correlation between the distance to the measurement object 3 and the light receiving point on the light receiving element 5 is linear, the variable attenuator 10 The correlation between the amount of attenuation and the reference position becomes linear, making it easy to set the amount of attenuation.

In these embodiments, a PSD is used as the light receiving element 5, but the present invention is not limited to this. For example, the same effect can be obtained even if a two-split photodiode is used instead.

〔Effect of the invention〕

As is clear from the above description, the distance setting photoelectric switch of the present invention is constructed without using a divider, so that the state of the object to be measured approaching or moving away from the reference position is determined by the displacement of the object. , without impairing the temperature characteristics and linearity of the photoelectric switch for distance setting (also, it can detect over a wide range and with a fast response speed.

Moreover, since the circuit configuration is simple, the number of parts is small, and therefore the manufacturing process can be simplified and the cost can be reduced.

[Brief Description of the Drawings] Fig. 1 is a simplified circuit diagram of the first embodiment of the distance setting photoelectric switch according to the present invention, and Fig. 2 shows the function of the light receiving element used in this distance setting photoelectric switch. 3 is a simplified circuit diagram of the second embodiment of this distance setting photoelectric switch, FIG. 4 is a block diagram of a conventional distance setting photoelectric switch, and FIG. 5 is a simplified circuit diagram of the second embodiment of this distance setting photoelectric switch. FIG. 3 is a correlation diagram between the distance between the switch and the object to be measured and the output of the divider.

Claims (2)

[Claims] (1) A light beam is projected onto the object to be measured, the reflected light is imaged onto a light receiving element by an imaging means, the distance to the object to be measured is measured based on the output of this light receiving element, and this measured value is set. A distance setting photoelectric switch that outputs a detection signal when a detected threshold value is exceeded, the distance setting photoelectric switch includes: a first amplification circuit that amplifies the output of one of the light receiving elements at a constant amplification factor; A photoelectric switch for distance setting, comprising: a second amplifier circuit that amplifies the output by varying an amplification factor; and a comparison circuit that compares the outputs of the two amplifier circuits and outputs a detection signal. (2) The distance setting photoelectric switch according to claim 1, wherein the light receiving element is a one-dimensional position detecting element.