JP2982912B2 - Sensitivity adjustment volume of object detection sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a sensitivity adjusting volume of a photoelectric switch, a proximity switch, and the like.

[0002]

2. Description of the Related Art For example, in a reflection type photoelectric switch, a malfunction due to a non-detection object behind a detection object is prevented.
Sensitivity adjustment is indispensable in order to detect a delicate difference in reflectance, and sensitivity adjustment is also necessary in a transmission type photoelectric switch in order to detect delicate transmittance.
Therefore, this sensitivity adjustment has been conventionally performed with a volume.

As a problem to be solved in the sensitivity adjustment volume, there is a problem that the linearity is improved to facilitate the volume adjustment operation. However, when a certain level of light is emitted from the light projector in the photoelectric switch, the following exponential relationship exists between the distance L from the light projector to the light receiver and the light reception amount V of the light reaching the light receiver. . V = KL ^-2 K: coefficient determined by the characteristics of the photoelectric switch

On the other hand, in a reflection type photoelectric switch, light emitted from a projector is reflected by an object located at an arbitrary distance L and reaches a light receiving unit. The amount V is equal to 0, and the maximum amount of received light is not L = 0, but requires a specific distance. Therefore, assuming that this distance is a, the above equation becomes as follows. V = K (L + a) ^{-2 In} any case, the amount of light that reaches the light receiver changes as an exponential function of the distance between the photoelectric switch and the detection object. FIG.
Is a “distance-light receiving level characteristic” of a general reflection type photoelectric switch, and the interval indicated by a corresponds to the above-mentioned specific distance.

Next, FIG. 10 shows a block diagram of a light receiving circuit of a conventional photoelectric switch. Reference numeral 1 denotes a light receiving circuit, 2 denotes an amplifier circuit, 3 denotes a sensitivity adjustment volume, 4 denotes an amplifier circuit, and 5 denotes an input signal. Judge whether the level has been exceeded and turn it ON / OFF
A comparator circuit for outputting a signal, 6 a waveform shaping circuit,
7 is an output circuit. In this circuit, the sensitivity adjustment uses the volume 3 as an attenuator for the received light signal. Since this volume is a general variable resistor, its characteristics are shown in FIG.
1 is a B characteristic showing a linear change with respect to the rotation angle θ. Therefore, since the light receiving level is proportional to the rotation angle of the volume 3, the change in the operating distance with respect to the rotation angle of the volume 3 inherits the character of the equation as it is and has a characteristic that changes exponentially. FIG. 12 shows the characteristics.

On the other hand, the comparator circuit 5 is generally provided with a hysteresis with a constant voltage width in order to prevent chattering at the time of output. This hysteresis is the hysteresis of the photoelectric switch (distance shift between the switch-on timing and the switch-off timing). The smaller the hysteresis is, the more surely the change in the amount of light can be detected. In particular, when the distance to the detection object is short, the magnitude of the hysteresis directly reflects on the detection accuracy of the photoelectric switch. Furthermore, using an AC amplifier with a high gain can increase the operating distance as a photoelectric switch, and it is best to satisfy both of them.

[0007]

In the prior art described above, first, the output characteristic with respect to the rotation angle of the volume shows an exponential function as it is, so that it is difficult to adjust the sensitivity. That is, in a portion where the rotation angle of the volume is small, the change of the operating distance with respect to the angle is large, and the sensitivity adjustment requires an extremely specialized technique. Attempts have been made to combine fixed resistors in order to solve this problem, but at present there has not been a fundamental improvement.

On the other hand, with respect to the problems of improvement of hysteresis and high gain, the conventional technique has a fatal defect. That is, if high gain amplification is performed, the noise component superimposed on the detection signal in the light receiving circuit and the amplifier circuit preceding the comparator circuit 5 is equally amplified, so that the amplified noise component becomes the hysteresis voltage of the comparator. The closer it is, the greater the risk of chattering. This is inconsistent with providing hysteresis to the operation area of the comparator to prevent chattering. Therefore, an attempt to reduce the hysteresis has the contradictory result that the gain must be suppressed.

As described above, since the user of the photoelectric switch must adjust the sensitivity at the time of installation, it is very troublesome. Even if the adjustment procedure and the graph are specified in the manual at the time of shipment, the adjustment can be performed in the same manner. In some cases, this was not possible, causing trouble between the user and the manufacturer.

The present invention is intended to solve these conventional problems, and can improve the linearity of the sensitivity adjustment volume to facilitate the adjustment operation, and can provide a high gain with a small hysteresis. It is an object to provide a sensitivity adjustment volume.

[0011]

In order to achieve the above-mentioned object, according to the present invention, a detection signal is amplified, and the amplified signal is input to a comparator having a constant reference potential and hysteresis via a variable resistor. In the sensor, means for applying a DC potential to one side of the variable resistor together with the input of the amplified signal was used.

[0012]

The variable resistor functions as a sensitivity adjustment volume, which acts to adjust the gain of the detection signal. Means for further applying a DC potential to one side means that a preset fixed DC potential is further added to the potential of the amplified signal, which has the effect of linearly correcting the distance characteristic of the amplified signal. In addition to this, it also has the effect of suppressing the ratio of noise components contained in the amplified signal. Therefore, the function of linearity of sensitivity adjustment, suppression of hysteresis, and high gain can be obtained by this DC potential.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram of a sensitivity adjustment volume improved this time.
Is an amplifying circuit, 3 is a sensitivity adjusting volume constituted by a variable resistor, 4 is an amplifying circuit, 5 is a comparator circuit which determines whether an input signal has exceeded a predetermined level, and outputs an ON / OFF signal, and 6 is a waveform. A shaping circuit, 7 is an output circuit, and 8 is a resistor for correcting a defect in the sensitivity adjustment volume 3. FIG. 2 shows these as a circuit diagram. In this circuit, the light receiving circuit 1 is constituted by the photodiode PD and the resistor R1. The operational amplifier IC1 constitutes an amplifier circuit 2 together with the resistors R2 and R3 and the capacitor C2. VR is a sensitivity adjustment volume, and R4 is the resistance 8 shown in FIG. Has given a rank. IC2
Is a comparator, a threshold value which is a reference voltage is determined by the resistors R5 and R6, and a hysteresis is given to the comparator IC2 by the resistor R7, and these constitute the comparator circuit 5 of FIG.
It should be noted that the waveform shaping circuit 6 and the output circuit 7 in FIG. 1 employ the same circuits and functions as those in the related art, so they are omitted, and it is easier to explain the amplifier circuit 4 simply by considering it as a gain. Omitted.

In the circuit shown in FIG. 2, the signal level output from the amplifier circuit 2 is Va for explanation, the DC potential given to the sensitivity adjustment volume VR is Vd, and the sliding terminal VR ₂ of the sensitivity adjustment volume VR is used. DC potential of vd, resistance R5
- the threshold potential of the comparator IC2 given in R6 Vp, the signal level input to the comparator IC2 through sliding pin VR ₂ of the sensitivity adjuster VR and va, if Shimese the input-output relationship, as follows Can be expressed.

First, the input potential of the comparator IC2 is v
When the input potential becomes equal to or higher than Vp, the comparator IC2 outputs an ON output. Therefore, Vp = va + vd to indicate the reference level. ...... formula then with the rotation angle of the sensitivity adjuster VR theta, a theta = 1 when rotated to the fixed terminal VR ₃ of the maximum side and a and theta = 0 when in the fixed terminal VR ₁ side of the minimum side, The above va
And vd are given by the following equations. va = Va × θ vd = Vd × θ Expression: Accordingly, the expression becomes Vp = θ (Va + Vd). Expression ## EQU2 ## This expression is modified to obtain Va = (Vp−Vd · θ) / θ Expression Since the operating distance L is related to the equation, Va = K / (L + a) ² ... Then, when L is obtained by the equation and the equation, the following equation is obtained: L = K ′ ｛θ / (Vp−Vd · θ)｝ ^1/2 −a Equation The relational expression of the operating distance L is obtained.

The comparator IC2 determines that va = 0.
3, a constant is set so that Vp = 1, a = 0.
When the maximum sensitivity (θ = 1) when set to 15 is obtained by a calculation value, the following is obtained. Since K 'is a proportional coefficient, K' = 1 is set for ease of explanation. First, when vd is obtained, vd = 0.7 from the equation. Next, Vd = 0.7 is obtained by substituting each numerical value into the equation. Subsequently, these values were substituted into the equation to obtain the distance L for an arbitrary rotation angle θ of the sensitivity adjustment volume VR, as shown in Table 1. Further, the graph shown with A in FIG. 3 shows a graph in which the operating distance L = 1 is maximized.

On the other hand, if a relational expression similar to the above expression is obtained in a conventional circuit for comparison with the circuit of the present invention, since Vd = 0, L = K ′ (θ / Vp) ^1/2 −a Is shown. Table 2 shows the operating distance with respect to the rotation angle θ under the above-mentioned numerical values. If this is shown in FIG. 3, the curve shown by B is obtained.

Here, when comparing the present embodiment with the conventional example, the operating distance conventionally changes exponentially with respect to the rotation angle of the sensitivity adjustment volume, whereas the present embodiment shows a more linear change. You are. Further, FIG. 4 shows “rotation angle θ-operating distance characteristic” when the circuit of the present invention and the conventional example are actually applied. Among them, the curve C is for the circuit of the present invention, and the curve D is for the conventional example. As is clear from FIG. 4, in the conventional product, the adjustment is very difficult because the operating distance changes abruptly in a portion where the rotation angle θ is small. Because it changes, the adjustment is very easy.

Next, the relationship between the hysteresis and the gain in the hysteresis of the comparator, which is the second problem to be solved, will be described below. FIG. 5 shows the operation characteristics of the comparator provided with hysteresis. In the figure, a waveform E is a light receiving signal given to the input part of the comparator, and a waveform F is an output signal of the comparator. Here, assuming that the hysteresis voltage is Vh, as shown by the relationship between the waveforms E and F, va = Vp
When −vd, the comparator is turned on, and va = Vp−v
At d-Vh, the comparator is turned off. Since the hysteresis voltage Vh is constant with respect to the threshold voltage Vp, the electrical hysteresis at this time is: hysteresis (%) = Vh / va × 100 where va is a formula and a formula Va = Vp−Vd
.Theta., And when this is substituted into the equation, it can be expressed by the following equation: Hysteresis (%) = Vh / (Vp-Vd..theta.). Times.100. Therefore, according to this equation, the hysteresis is the largest when the sensitivity adjustment volume VR is θ = 1, and the hysteresis becomes smaller as θ = 0 approaches.
FIG. 6 shows this characteristic.

By the way, since Vd = 0 in the prior art, the hysteresis is expressed as follows based on the equation: hysteresis (%) = Vh / Vp × 100, and a constant value regardless of the rotation angle of the sensitivity adjustment volume VR. become.

Therefore, the circuit of the present invention has a feature that the hysteresis can be changed depending on the rotation angle of the sensitivity adjustment volume. That is, from this fact, in the circuit of the present invention, the hysteresis becomes smaller as the rotation angle is reduced and the detection distance is shortened, and the detection accuracy is increased. Will not be improved at all.

As described above, in an actual circuit, some noise components are superimposed on the signal level Va.
In FIG. 5, the comparator IC when the noise component is ignored
FIG. 7 shows the ideal waveform of FIG.
As shown in FIG. Here, assuming that the signal level Va is Vn and the noise voltage included in va is vn, the hysteresis voltage when noise is considered is reduced by the noise voltage. Therefore, the equation is as follows: Hysteresis (%) = (Vh−Vn .Theta.) / (Vp-Vd..theta.). Times.100. Here, Vh = 0.02, Vn = 0.
When the noise component at the maximum sensitivity (θ = 1) is set to 70% of the hysteresis voltage as in 014, the equation is as follows: Hysteresis (%) = (0.02−0.014 · θ) / (Vp−Vd · θ) × 100 Will be shown. At this time, Vp and Vd were set to appropriate values, and the response to the rotation angle of the sensitivity adjustment volume VR was determined, as shown in Table 3. Here, Vd = 0
The case corresponds to the conventional circuit.

As is clear from Table 3, in the conventional example, when the rotation angle is the maximum, the operation is the same as in other cases. However, if the rotation angle θ is reduced, the hysteresis increases. Therefore, if the conventional example is used in a range where the rotation angle is small, there is a characteristic that the detection accuracy is reduced. Therefore, the hysteresis voltage Vh may be reduced in order to reduce the hysteresis of the conventional example. However, as Vh approaches vn, the chance of chattering in the comparator output increases. Therefore, in order to reduce Vh in order to reduce the hysteresis, an alternative option has been urged to reduce the absolute value of the noise component vn included in the signal level Va at the expense of the gain of the amplifier circuit. In the circuit of the present invention, as shown in Table 3, the change in the hysteresis with respect to the rotation angle θ is small, and in particular, Vp
= 1 and Vd = 0.7, the hysteresis became constant at 2%. This means that the detection accuracy is constant regardless of how the detectable distance is changed by operating the sensitivity adjustment volume VR. FIG. 8 shows the “operating distance-hysteresis characteristic” of the conventional example and the present invention.

Although the present embodiment has been described mainly on the premise that a reflection type photoelectric switch is used, the present invention is not limited to this, and a detection means having an exponential relationship between a detection distance and a detection signal level is used. Then, for example, the same applies to a transmission type photoelectric switch or a proximity switch. Also,
Even if the power supply is in the opposite phase to the description of this embodiment,
Only the phase of the output waveform is reversed, and there is no change in the function and effect of the circuit itself.

[0025]

According to the present invention, the sensitivity is adjusted by using only the variable resistor, but the DC potential is further added to one side of the variable resistor. Therefore, the DC potential is added to the potential of the amplified signal. Will be applied to one side of the variable resistor. Therefore, in the low potential portion of the amplified signal having exponential characteristics, the ratio of the DC potential is particularly large, so that the correction width is increased, and the exponential curve with a sharp rise is corrected to have a more linear characteristic. I was able to.
As a result, in the present invention, since the rotation angle and the detection distance of the sensitivity adjustment volume are linearly displaced, the adjustment work is greatly facilitated.

Further, since the DC potential which is a non-noise component is added to the amplified signal including the noise component, the noise component of the signal input to the comparator can be remarkably suppressed as compared with the related art. Therefore, even when high-gain amplification is performed, the possibility of chattering due to noise can be extremely reduced. In addition, the hysteresis can be kept constant irrespective of the rotation angle of the sensitivity adjustment volume by setting the circuit constant to an appropriate value while maintaining high gain, so that it is not affected by the length of the detection distance. An extremely reliable circuit capable of maintaining the detection accuracy could be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of a circuit of the present invention.

FIG. 2 is a circuit diagram of the circuit of the present invention.

FIG. 3 is a graph showing a rotation angle-distance characteristic between the circuit of the present invention and a conventional example.

FIG. 4 is a graph showing rotation angle-operating distance characteristics of the circuit of the present invention and a conventional example.

FIG. 5 is a waveform chart showing input / output characteristics of a comparator.

FIG. 6 is a graph showing a rotation angle-hysteresis characteristic of the circuit of the present invention.

FIG. 7 is a waveform diagram showing input / output characteristics including a noise component of a comparator.

FIG. 8 is a graph showing operating distance-hysteresis characteristics of the circuit of the present invention and a conventional example.

FIG. 9 is a graph showing a distance-light receiving level characteristic of a reflection type photoelectric switch.

FIG. 10 is a block diagram showing a conventional example.

FIG. 11 is a graph showing a rotation angle-resistance value characteristic of the sensitivity adjustment volume itself.

FIG. 12 is a graph showing rotation-movement distance characteristics of sensitivity adjustment according to a conventional example.

[Table 1] What represents the distance to a specific rotation angle of the sensitivity adjustment volume of the present invention,

[Table 2] A representation of the distance to a specific rotation angle of the sensitivity adjustment volume of the conventional example,

[Table 3] This shows the hysteresis of the sensitivity adjustment volume with respect to a specific rotation angle.

Claims (1)

(57) [Claims] 1. An object detection sensor for amplifying a detection signal and inputting the amplified signal to a comparator having a constant reference potential and hysteresis via a variable resistor. A sensitivity adjustment volume of an object detection sensor to which a DC potential is applied.