JPH0476587B2 - - Google Patents

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. If the value is exceeded,
The present invention relates to a distance setting photoelectric switch that outputs a detection signal.

[Conventional technology]

The following types of conventional distance setting photoelectric switches have been used. As shown in FIG. 5, 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 focused as a light receiving point on the light receiving element 5 using the light receiving lens 4. image. When the measuring object 3 changes its position in the figure and moves from a to b to c, this light receiving point moves on the light receiving element 5 from a' to b' to c' accordingly. 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.

As the light receiving element 5, a PSD (Position Sensitive Device), which is a one-dimensional position detection element, is generally often used. Then, two types of output current i ₁ ,
i ₂ is output from this light receiving element 5, and these are input to a subtracter 9 and an adder 10, respectively, and (v ₁ −
v ₂ ), (v ₁ + v ₂ ) output. Thereafter, it is converted into a (v ₁ −v ₂ )/(v ₁ +v ₂ ) output by the divider 11, thereby obtaining a voltage value according to the distance to the measurement object 3 regardless of the amount of received light. be able to.

The relationship between the output voltage of the divider 11 and the distance to the object to be measured 3 is a proportional relationship 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 11. Therefore, after the divider 11, a comparator 12 ( By providing a threshold setting circuit 13 (see FIG. 5), it is possible to determine whether the object to be measured 3 is closer or farther than a certain set distance x. If the threshold value y is set according to
By setting new thresholds for either or both of the distances, a detection signal is output when the object approaches too much or when it moves too far away.

[Problem that the invention seeks to solve]

However, the conventional photoelectric switch for distance setting when the divider 11 is used has the following problems. The divider 11 has various drawbacks such as poor temperature characteristics, narrow dynamic range, slow response speed, and poor linearity. Therefore, the use of the divider 11 has a great effect on the distance measurement accuracy, and there is a problem that the photoelectric switch for distance setting as a whole cannot obtain a measurement accuracy higher than that obtained by the divider 11. It was hot.

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, to form an image of the reflected light onto a light receiving element using an imaging means, and to form a light beam on the light receiving element in accordance with the imaging position. the first and second obtained from
In a distance setting photoelectric switch that measures the distance to the object to be measured based on the output of the sensor and outputs a detection signal when this measured value exceeds a set threshold, one output of the light receiving element is a non-inverting amplifying circuit for amplifying, an inverting amplifying circuit for amplifying the other output of the light receiving element, and a slider for dividing a resistor, the output of the non-inverting amplifying circuit being connected to one end of the resistor; A variable resistor having the output of the inverting amplifier circuit connected to the other end, and a slider output of the variable resistor connected to one input terminal, and compared with a threshold value connected to the other input terminal. and a comparison circuit that outputs the comparison result as a detection signal.

[Effect]

Since this invention employs the above-mentioned means, a reference position is set by sliding a variable resistance slider, and detection is performed when the object to be measured moves toward or away from the reference position. A 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. As shown in FIG. 2, a light beam emitted from a light projecting element 1 forms a light spot projected onto a measurement object 3 by a light projecting lens 2. As shown in FIG. 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 to b to c in the figure, this light receiving point moves from a' to b' to c' accordingly.
This light receiving element 5 uses a PSD.

As shown in Fig. 1, when the measurement object 3 is at position a (see Fig. 2), its light receiving point a' is
In the figure, it is located at the lower part of PSD5. As mentioned above, when the measurement object 3 moves from the above position to c via b, the light receiving point changes accordingly.
Place a'→b'→c' on the PSD5 at the same time and move upward.

In this case, when the measurement object 3 is at position a, the currents i ₁ and i ₂ (i ₁ is
In the diagram of PSD5, the current output from the upper end,
i ₂ is the current output from the lower end), where l ₁ is the distance from the lower end to the light receiving point a' in the diagram of the PSD5, and l ₂ is the distance from the upper end to the light receiving point a', i ₁ : The relationship is i ₂ = l ₁ : l ₂ .

The output current i ₁ of this PSD5 is the non-inverting amplifier circuit A ₁
It is amplified by , and converted to voltage v ₁ . On the other hand, the output current i ₂ of the PSD 5 is amplified and inverted by the inverting amplifier circuit A ₂ and converted into a voltage −v ₂ . Between non-inverting amplifier circuit A ₁ and inverting amplifier circuit A ₂ ,
A variable resistor VR is connected. This variable resistance
The VR slider 6 is connected to the negative input terminal of the comparison circuit 7. The positive terminal of the comparison circuit 7 is grounded.

Next, the operation of the distance setting photoelectric switch having such a circuit configuration will be explained. As described above, the relationship between the light receiving point on the PSD 5 and the output current of the PSD 5 is i ₁ :i ₂ =l ₁ :l ₂ . Therefore, the relationship between the voltages v ₁ and −v ₂ applied across the variable resistor VR and the light receiving point on the PSD 5 is v ₁ :v ₂ =l ₁ :l ₂ . Also, these voltages v ₁ , −v ₂ and the distance l ₁
The relationship is a straight line that slopes upward to the right as shown in FIG. Therefore, in the relationship between the position on the variable resistor VR and this distance _l1 , the straight line 8 indicating zero potential slopes downward to the right as shown in FIG.

From the above, the zero potential point on the variable resistor VR is determined by the resistance value from the end of the variable resistor VR on the non-inverting amplifier circuit A ₁ side to the slider ₆ as shown in FIG. If the resistance value from the end of the variable resistor VR on the inverting amplifier circuit A ₂ side to the slider 6 is R ₂ , it exists at a position where R ₁ :R ₂ =l ₁ :l ₂ . Therefore, by sliding the slider 6, when R ₁ /R ₂ changes from large to small or from small to large with respect to l ₁ /l ₂ , both inputs of the comparator circuit 7 match and are detected. Output a signal.

Therefore, by selecting the position of the slider 6 so that R ₁ /R ₂ =l ₁ /l ₂ , the measurement target 3
A detection signal is output when the object moves away from or approaches position a with reference to position a (see FIG. 1). When outputting a detection signal using another position of the measurement object 3 as a reference, slide the slider 6 so that the negative input of the comparator circuit 7 becomes zero V when it reaches the position. You just have to choose.

In this embodiment, the slider 6 is connected to the comparator circuit 7.
Although it is connected to the negative input terminal of , it may be connected to the positive terminal. With this switch, both when approaching and when moving away,
It can be configured to output a detection signal. That is, when the slider 6 is connected to the negative input terminal of the comparison circuit 7 as in this embodiment, a detection signal is output when the measurement object 3 moves away from the reference position a. If you set it up, if you connect it in reverse, a
A detection signal is output when approaching from the position.

In addition, in this embodiment, the non-inverting amplifier circuit
Although only one set of A ₁ , inverting amplifier circuit A ₂ , variable resistor VR, and comparison circuit 7 is installed, two or more sets may be installed. In this way, the comparison circuit 7
It is now possible to output a detection signal both when approaching and leaving the reference position without switching between positive and negative inputs.Alternatively, multiple reference positions can be set, allowing extremely detailed detection. It becomes possible.

Furthermore, in this embodiment, the light receiving element 5
Although a PSD is used, the present invention is not limited to this, and the same effect can be obtained by using, for example, a two-part photodiode instead.

〔Effect of the invention〕

As is clear from the above explanation, this invention
Since the distance setting photoelectric switch is configured without using a divider, it is possible to calculate the temperature characteristics and linearity of the distance setting photoelectric switch based on the state of the measurement object approaching or moving away from the reference position due to the displacement of the measurement object. Detection is possible without any damage, over a wide dynamic range, and with 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 explanation of the drawing]

Fig. 1 is a simplified circuit diagram of the photoelectric switch for distance setting according to the present invention, Fig. 2 is a diagram explaining the principle of this photoelectric switch, and Fig. 3 is a diagram showing the light receiving point on the light receiving element of this photoelectric switch and the variable resistor. FIG. 4 is a correlation diagram of the applied voltage, FIG. 4 is a correlation diagram of the light receiving point on the light receiving element and the position on the variable resistor, FIG. 5 is a block diagram of a conventional distance setting photoelectric switch, and FIG. 6 is a diagram of this 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. 1... Light projecting element, 2... Light projecting lens, 3... Measurement object, 4... Light receiving lens, 5... Light receiving element,
6...Slider, 7...Comparison circuit, _A1 ...Non-inverting amplifier circuit, _A2 ...Inverting amplifier circuit, VR...Variable resistor.

Claims (1)

[Scope of Claims] 1. A light beam is projected onto an object to be measured, the reflected light is imaged on a light receiving element by an imaging means, and the first and second light beams obtained from the light receiving element correspond to the imaging position. In a distance setting photoelectric switch that measures the distance to the object to be measured using a second output and outputs a detection signal when this measured value exceeds a set threshold, one of the light receiving elements a non-inverting amplifier circuit that amplifies the output; an inverting amplifier circuit that amplifies the other output of the light receiving element; and a slider that divides a resistor, the output of the non-inverting amplifier circuit being connected to one end of the resistor. a variable resistor, the other end of which is connected to the output of the inverting amplifier circuit, and a slider output of the variable resistor connected to one input terminal, and a threshold value connected to the other input terminal. A photoelectric switch for distance setting, comprising: a comparison circuit that compares and outputs the comparison result as 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.