JPH04313021A - Optical beam sensor - Google Patents

Abstract

PURPOSE:To prevent the occurrence of such a case that the object detecting output signal of an optical beam sensor is not fixed to a unique value near a point where optical beams are intercepted due to the vibration, etc., of the object when the object is detected by means of the sensor and, at the same time, to freely set the range. CONSTITUTION:Two optical beams (a) and (b) are prepared and a circuit is configured in such a way that the presence of an object is not decided even when the first optical beam is intercepted, but decided when both optical beams (a) and (b) are intercepted. When the object is removed, the presence of the object is decided even when the first optical beams is passed through, but the absence of the object is decided only when both beams (a) and (b) are passed through. In addition, the circuit configuration is set to a fail-safe state.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particularly fail-safe light beam sensor in which the light beam sensor transmitted between a projector and a receiver is interrupted by an object.

0002

2. Description of the Related Art A light beam sensor in which a light beam transmitted between a light emitter and a light receiver is blocked by an object has a structure shown in FIG. 6, for example. In the figure, 1 is the emitter, 2 is the receiver, φ
1 is the transmitting directional characteristic, φ2 is the receiving directional characteristic, and φ1 and φ2
The product (φ1×φ2) gives the directivity characteristics of the transmitted and received waves. Since the wavelength of an optical beam sensor is shorter than that of a sound wave or an electromagnetic wave, the directivity characteristics of the transmitted and received waves tend to become sharp. For this reason, in Figure 6, the center axis (dotted chain line) of the transducer (emitter/receiver)
When the distance y is taken in the direction perpendicular to the central axis with A small change Δy in the width y causes a change in the detected/non-sensed output signal. Figure 7
The received light level in FIG. 6 is taken as the voltage V on the vertical axis, and
The horizontal axis is the position of interruption by an object that is sufficiently large compared to the beam width (y=0 on the central axis). The reception level V0 when the beam is not interrupted is when the object is on the central axis (
y=0), the reception level is normally V0/2. The reception level V1 is the threshold for light beam interruption by an object.
If the position of the object at this time is y1, then in the case of a light beam with a sharp directivity characteristic of transmitting and receiving waves φ1×φ2, there is a drawback that a slight variation Δy of the object can cause discrimination between blocking and non-blocking by the object. Ta.

0003

[Problems to be Solved by the Invention] Conventionally, as a method of compensating for this drawback, a method of providing hysteresis (making the identification level for blocking and the threshold level for non-blocking different from each other) in the threshold value V1 for the reception level V has been proposed. However, no matter how large the hysteresis is provided for the reception level threshold V1, in an optical beam sensor where ΔV/Δy is large, the hysteresis width obtained as the change Δy in position y will actually be small. It happened.

0004

[Means for Solving the Problems] Therefore, in the present invention, a plurality of light beams with sharp directional characteristics are provided, the light beams are made into alternating current, and the light reception levels are added. and,
This addition output is generated using a self-holding circuit using a fail-safe comparator that does not generate an output signal in the event of a failure.
The structure is such that different light beams are used to identify whether the light beam is blocked or not.

[0005]

[Operation] According to the above configuration, the position where the light beam is blocked or not blocked by an object can be set to an arbitrary width using a light beam with sharp directional characteristics, and the circuit constituting the light beam sensor can be In the event of a failure, the output signal is equivalent to when no light beam is received (fail-safe output signal)
can be obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an embodiment of the structure of the present invention. In the figure, 11 and 12 are light projecting elements (electricity-to-light conversion elements), and 5 is an AC signal generator for exciting the light projecting elements 11 and 12. Reference numeral 12 constitutes two projectors (corresponding to the projector 1 in FIG. 6) that generate light beams a and b, respectively. 21 and 22 are light receivers that receive the light beams a and b, respectively; 3 is an adder circuit that adds the output signals of the light receivers 21 and 22; and 4 is a level that performs threshold calculation on the output signal e of the adder circuit. In a self-holding circuit using a comparator, the present invention uses a fail-safe window comparator as a level comparator.

FIGS. 2 and 3 show the optical receivers 21 and 2 shown in FIG.
2 and a method of configuring an adder circuit that adds these output signals. 2 and 3, 210 and 220 are light receiving elements, 8 is an analog amplifier, 9 is a rectifier circuit that rectifies the alternating current component of the analog amplifier 8, 10 and 100 are light receiving elements 210,
An amplifier circuit 220 generates the light reception signal as a switch output signal, and 13 and 130 are rectifier circuits that rectify the output signals of the amplifier circuits 10 and 100. analog amplifier 8 and rectifier circuit 9, and amplifier circuits 10 and 100 and rectifier circuit 13,
Reference numeral 130 indicates an example of a specific circuit configuration of the adder circuit 3 in FIG.

In FIG. 1, light beams a and b are received by photoreceivers 21 and 22 as alternating current light. In FIG. 2, 210, 220
indicates the case of a light receiving element, and light beams a and b are ON at the same time.
/OFF (that is, the light emitting elements 11 and 12 are ON at the same time)
), the light is received by the light receiving elements 210 and 220 at the same time. Therefore, in the analog amplifier 8, when the AC signal is received by both of the light receiving elements 210 and 220, twice as much output signal e is generated in the rectifier circuit 9 as compared to when the AC signal is received by only one of the light receiving elements 210 and 220. Also, in the case of Figure 3,
The output signals of the amplifier circuits 10, 100 are switch signals (saturated AC signals), while the output signals of the rectifier circuits 13, 130 are added to produce the output e.

Next, the sets of light emitting/receiving elements 11, 21 and 12, 2
2 are arranged at different positions in space, for example two beams are transmitted in parallel. Therefore, for example, if we consider the output signal e of the adder circuit when an object larger than the width of beams a and b and the distance between them blocks the light beams a and b at right angles, then both beams a and b are received. The output level (denoted as Ve2) when
Power level when only beam a or b is interrupted (
If the output level when both beams a and b are cut off (let it be Ve1) is a logic value 0, then the logic level that gives the respective logic values 2, 1, and 0 is For, Ve2 > Ve1 > Ve0
holds true.

In FIG. 1, the self-holding circuit 4 is composed of a fail-safe two-input window comparator. A fail-safe two-input window comparator is known, for example, from Patent Publication No. 60-68719. Figure 8 shows a fail-safe two-input window.
A configuration diagram of the comparator is shown, and the general configuration and operation will be described as follows.

In FIG. 8, terminals T1 and T2 are DC input terminals, E is a power supply input terminal, and transistors Q1 to Q
7 constitutes an amplifier circuit with transistors connected in series, and the next input voltages Vi1, Vi2 (
The terminal T1 side input is set as Vi1, and the T2 side is set as Vi2)
This is an oscillation circuit in which the output signal of the transistor Q7 is fed back to the base of the transistor Q1 via the resistor R6 to generate feedback oscillation. That is, this oscillation condition is given as the input voltage Vi1 (=Vi2) as follows. (R1 +R2 +R3)E/R3<
Vi1 (=Vi2)<(R4 +R5)E/R5
Here, approximately (R1 +R2 +R3)E/R3 gives the lower limit value of oscillation, and approximately (R4 +R5)E/R5 gives the upper limit value of oscillation.

[0012] Furthermore, if a breakage or short-circuit failure occurs in the resistor constituting the circuit in FIG. It has a fail-safe characteristic of not generating an output signal (OUT). Furthermore, it has an AND function that oscillates only when an input voltage that satisfies the above formula is applied to the two input terminals. When configuring a self-holding circuit using the threshold value calculation element shown in FIG. 8, an alternating current (oscillation) output signal may be rectified and fed back to one of the input terminals.

In FIG. 1, 41 is a comparator AND circuit (window comparator) based on FIG. 8, 42 is a rectifier circuit for rectifying this AC signal, and C is a feedback circuit provided to configure a self-holding circuit. A circuit 43 is a rectifier circuit separate from the rectifier circuit 42 for rectifying the output signal of the window comparator 41. D is a diode inserted to prevent the feedback signal for self-holding from returning to the input side.

Next, the operation of FIG. 1 will be explained using FIG. 4. The logical values 2, 1, generated as the output signal e of the adder circuit 3
For logic level 0, window comparator 4
1 input terminal T1 (the input terminal on the side with feedback, i.e.
The lower threshold of the trigger input terminal of the self-holding circuit is
It is set to e2 between logic levels Ve2 and Ve1, and the lower threshold of input terminal T2 (reset side input terminal of the self-holding circuit) is set between logic levels Ve1 and Ve0.
(zero level), it is set to e1. therefore,
The self-holding circuit 4 starts from a state in which both the light beams a and b are blocked, and only when one of the light beams is sequentially received and then both are received (that is, the output signal e of the adder circuit exceeds the threshold value e2). Then, the output signal of the self-holding circuit is self-held even if one of the light beams is interrupted, and the output signal disappears only when both of the light beams are interrupted. That is, for example, if an obstacle blocks the light beams a and b at right angles, the output signal of the self-holding circuit will disappear when both beams are blocked, and even if the obstacle returns, both beams will be received. The output signal of the self-holding circuit will not be generated unless it returns to that point.

Here, the output signal of the self-holding circuit is generated/
Extinction means hysteresis in the detection space determined by the arrangement (interval) of the light beams, and the width of this hysteresis is the width of the light beam a
, b. In addition, the floodlight 11,
12 and the light receivers 21 and 22, it is obvious that the same effect will be obtained even if the light transmitting element or the light receiving element is provided with a fiber for transmitting light. Furthermore, the reason why alternating current light is used as the light beam is to prevent an output signal from being generated when a fixed failure occurs in the amplifier circuit constituting the light receiver, and is a known method. Furthermore, when three optical beam sensors are arranged in a row, an optical sensor with the same effect can be constructed by appropriately determining the trigger level and reset level of the self-holding circuit for the summed output of the output signals of the three optical receivers. is clear.

FIG. 5 shows another embodiment of the self-holding circuit 4 using the window comparator of FIG. 4 in the same figure
11, the threshold values of the two input terminals are both input level e=
Window comparator set to e2, 411R
412 is a rectifier circuit for rectifying the output signal of the window comparator 411, the output signal of the window comparator 411 (that is, the output signal of the rectifier circuit 411R) is used as a trigger input signal, and the lower limit is set to the input signal e=e1. A window in which a threshold value is set and this input signal e≦e1 is used as a reset signal. In the comparator, 42',
43' is a rectifier circuit that rectifies the output of the window comparator 412, and C' is the window comparator 412.
This is a feedback circuit to make the circuit a self-holding circuit. In the circuit shown in the figure, when the input signal e rises and exceeds e2, the window
The comparator 411 oscillates, and this output signal causes the window comparator 412 to self-hold, causing the output (OUT
) occurs. Next, when the input signal e decreases to e=e1 or less, the output signal of the window comparator 412 disappears.

[0017]

[Effects of the Invention] As explained above, according to the present invention,
By adding the output signals of two light beams placed in space,
The level of this output signal was verified using a fail-safe self-holding circuit that uses a reset signal when one light reception signal is generated and a trigger signal when both light reception signals are generated. A large hysteresis width could be obtained, and this hysteresis width could be changed by changing the arrangement of the light beams.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment according to the present invention, FIG. 2 is a block diagram showing an embodiment of the adder circuit in the embodiment of FIG. 1, and FIG. 3 is a block diagram showing another embodiment of the adder circuit in the embodiment of FIG. Block diagram, FIG. 4 is a diagram for explaining the operation of the adder circuit in the embodiment of FIG. 1, FIG. 5 is another embodiment of the self-holding circuit, and FIG. 6 is a block diagram of a light beam sensor based on the prior art. 7 is a diagram showing the characteristics of FIG. 6, and FIG. 8 is a circuit diagram of a two-input window comparator.

[Explanation of symbols]

a, b
light beam, 1,

Floodlights 11, 12
Light projecting element 2, 21, 2
2
Light receivers 210, 220
Light receiving element 3

Addition circuit, 4
Fail-safe self-holding circuit 5
AC signal generator 8
Analog amplifiers 9, 13, 130, 42, 43
Rectifier circuit 411R, 42', 43'
Rectifier circuit 10, 100
amplifier 41,
411, 412
window comparator

Claims (1)

[Claims] 1. A plurality of light emitters and receivers arranged in parallel, an adder circuit that adds output signals of the light receivers, and a logic on the high side of the output signal of the adder circuit that corresponds to the output signal of the light receivers. A light beam sensor consisting of a self-holding circuit that uses a level as a trigger input signal and a lower logic level as a reset signal.