JPS617487A - Optical object detector - Google Patents

Abstract

PURPOSE:To prevent the difference of the installation place of an alarm or the disorder of detection sensitivity due to a secular change, by performing detection operation by comparing the reference voltage based on reflected light at a usual time and the detection signal at this point of time. CONSTITUTION:Light irradiated from a light emitting element LD is reflected from the object in a monitor space and the reflected light is received by a light receiving element PD. Therefore, when the object does not move at a usual time, a constant pulse signal is detected at a constant cycle. The pulse signal is amplified to a proper magnitude by an amplifying circuit 1 and outputted to a reference voltage generation circuit 3 and a comparing circuit 4. The reference voltage generation circuit 3 froms reference voltage based on the average peak value obtained by averaging peak values of the pulse signal of the amplifying circuit 1 plural times. The pulse peak voltage of the amplifying circuit 1 is compared with reference voltage by the comparing circuit 4 and, when deflection extends over a definite extent or more, a detection signal is outputted.

Description

[Detailed Description of the Invention] "Industrial Application Field" This invention is a light beam system that irradiates a monitoring space with a light beam (generally near-infrared light) and detects theft or the passage of a person from changes in the light reflected by objects. O regarding object detectors: "Prior art" As described in Japanese Patent Application Laid-open No. 55-105795, a light source of an alarm emits a light beam into a monitoring space, and changes in the reflected light are used to detect theft and people. In a light beam alarm that detects passage, there is a signal processing circuit that outputs a detection signal when the light reflected by an object increases or decreases. This outputs a detection signal when the signal voltage based on the reflected light falls below the upper limit value.

``Problems to be Solved by the Invention'' In the signal processing circuit of a conventional optical beam alarm, the reflected light during normal operation is affected by the installation location of the alarm and changes over time. Therefore, the detection sensitivity may vary due to differences in the location of the equipment or due to aging. Further, the upper and lower limit values are easily affected by temperature and affect detection sensitivity.

This invention eliminates this drawback.

``Means for Solving the Problems'' This invention generates a reference voltage from a detection signal based on reflected light during normal times, compares this reference voltage with the current detection signal, and detects a deviation of more than a certain level. It is designed to perform a detection operation when it is recognized.

Further, the gain of the amplifier circuit or the light path section is controlled based on the reference voltage, thereby achieving more stable monitoring operation.

``Operation'' This invention allows comparison of changes in reflected light based on a reference voltage that hardly changes when the change in reflected light is relatively short (about 10 seconds), as well as the gain of an amplifier circuit and the light emission. Since the detection sensitivity is controlled, fluctuations in detection sensitivity can be extremely reduced.

"Example" Embodiments of this invention will be described based on FIGS. 1 to 3.

FIG. 1 shows an example of a block diagram of the optical object detector of the invention, which includes a light emitting element LD that irradiates a monitoring space with a light beam, and a light emitting element drive circuit 2 that drives this light emitting element LD in a pulsed manner. , a light receiving element FD that receives reflected light reflected from objects in the monitoring space, an amplifier circuit 1 that amplifies the detection signal of this light receiving element FD, and a time constant of about 100 seconds.
a reference voltage generation circuit 3 that follows the output voltage of the amplifier circuit 1 in a relaxed manner and supplies a reference voltage; and a comparison circuit 4 that is compared with this reference voltage and detects an increase of more than a predetermined value or a decrease of more than a predetermined value of the current output voltage. , and an output circuit 5 that outputs an object detection signal based on the output of the comparison circuit 4.

To explain the operation of the optical object detector of the present invention configured as described above, first, all or part of each circuit that processes reflected light signals is synchronized with the light emitting element drive circuit 2. Assume that it works. The light emitting element LD is driven in a pulsed manner by the light emitting element driving circuit 2, and intermittently irradiates the monitoring space with a light beam. The irradiated light beam is reflected by objects in the monitoring space, and this reflected light is captured by the light receiving element PD. Therefore, when an object moves frequently during normal times, a constant pulse signal is detected at a constant cycle. This pulse signal is amplified to an appropriate size by an amplifier circuit 1 and then sent to a reference voltage generating circuit 3.
and output to the comparison circuit 4, respectively. The reference voltage generation circuit 3 is composed of a peak hold circuit, a delay circuit (time constant circuit) having an integral characteristic, etc., and generates a reference voltage based on the average of multiple peak values of the pulse signal of the amplifier circuit 1.

Therefore, although this reference voltage fluctuates due to differences in installation locations and changes over time, it does not fluctuate due to changes in reflected light within a relatively short period of time.

The pulse peak voltage of the amplifier circuit 1 and the reference voltage are connected to the comparator circuit 4.
can be compared, and a detection signal is output if the deviation exceeds a certain value. Therefore, a detection signal is output when the peak value of the pulse voltage increases or decreases by more than a predetermined value compared to the reference voltage due to the movement of the object. The output circuit 5 performs signal processing to improve reliability based on the detection signal, and outputs a signal for driving a load such as an alarm or a display.

Generally, reflected light varies greatly depending on the surrounding conditions in which the detector is installed. Therefore, if the gain of the amplifier circuit 1 is kept constant, this output signal may become extremely small or reach a saturated state. In order to prevent this, the gain of the amplifier circuit 1 or the light emitting element drive circuit 2 is controlled based on the reference voltage of the reference voltage generation circuit 30, and the magnitude of the output signal based on the reflected light in normal conditions is kept within a predetermined range. can be adjusted to Note that this function is performed by the comparator circuit 4, and is not particularly necessary depending on the selection of the amplifier circuit 1.

FIG. 2 shows an embodiment of the reference voltage generation circuit 3 and comparison circuit 4 of this detector, and FIG. be. In FIG. 2, comparator circuit 4 includes diodes D1. D2.
A series circuit consisting of a resistor R1 and a diode D1. D2.
variable resistors VR11VR2, which are connected in parallel with each other, and two Oka comparators A1. It is composed of A2. The reference voltage generation circuit 3 is composed of a peak hold circuit including a diode D3 and a capacitor C4, and a delay circuit 31 (time constant circuit) having integral characteristics.

The reference voltage generation circuit 3 receives the pulse peak voltage vP1 which is also output from the amplifier circuit 1 through a diode D3 and a capacitor C.
Hold the light weight peak voltage at 1. This holding voltage is passed through a time constant circuit 31 to obtain a reference voltage v1.

The comparator circuit 4 will be explained with reference to FIG.
□, D2. A resistor ⇠□ is also applied to a series circuit consisting of. The variable resistor ■VR2 determines the upper and lower limit dark values and is used for sensitivity adjustment. Each variable resistor V 1. (2) The terminals from the slider of R2 are inputted to one input of the comparators A and A2, respectively, and the reference voltage v1 is inputted to the other inputs of the comparators A and A2, respectively. Comparator A1 detects a decrease in the signal and comparator A2 detects an increase in the signal. When the reflected light changes, the pulse peak voltage VP of the amplifier circuit 1 changes.

also changes as shown in FIG. That's right, comparator A.
1+A2 input voltage vP2. vP3 is a diode D□.

Due to the characteristics of D2, it changes in parallel with the output voltage vp. Now, assume that the reference voltage V□ is on line A.

Here, if the voltage vp changes in a relatively short time (compared to the time constant of the reference voltage generation circuit 3) and increases on the line B-ij, the reference voltage V1 remains unchanged and the voltage VP3 changes from this reference voltage v1. exceed. The output of comparator A2 changes from high to low, detecting a constant increase. When the cut voltage VP drops to line C, the voltage vP2 becomes lower than the reference voltage v1. Comparator A1 changes from high to low and detects a constant decrease. This comparator circuit 4 has a voltage v related to the reflected light.
P1 and diode D1. Due to the characteristics of D2, the voltage VP2.
Since VP3 changes in parallel, there is no fluctuation in the upper and lower thresholds, and sensitivity deviations are less likely to occur. In addition, the diode D1. D
If a constant voltage greater than 2 is required, diodes are connected in series, such as Zener diodes.

"Effects of the Invention" As explained above, the optical object detector of the present invention has extremely stable monitoring operation because the sensitivity does not change due to differences in ambient conditions at different installation locations or changes over time. can be done. Also, since the upper and lower limit values are constant, the variable resistance V1. It is possible to make the vi bow a fixed resistance and not have to adjust it.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the invention, Fig. 2 (d
FIG. 3 is a circuit block diagram of an embodiment of the comparison circuit and reference voltage generation circuit of the present invention, and is a characteristic diagram for explaining the operation of the comparison circuit shown in FIG. 2.

Claims (1)

[Scope of Claims] 1. A light emitting element that irradiates a monitoring space with a light beam, a light emitting element drive circuit that drives the light emitting element, a light receiving element that detects the reflected light of the light beam from an object, and detection of the light receiving element. In an optical object detector that is composed of a signal processing circuit that processes signals and detects theft or the passage of a person based on fluctuations in the reflected light, the signal processing circuit detects a signal based on the magnitude of the reflected light during normal times. a reference voltage generation circuit that determines a reference voltage based on the reference voltage; an amplifier circuit that amplifies the detection signal of the light receiving element; and a comparison circuit that compares the reference voltage with the output voltage of the amplifier circuit, and outputs a detection signal when the output voltage deviates by more than a predetermined value. It consists of a comparison circuit that outputs, and the reflected light increases by a predetermined amount compared to normal times.
Alternatively, a light beam type object detector is characterized in that a detection operation is performed when a phenomenon in which the decrease exceeds a predetermined value is detected. 2. The optical object detector according to claim 1, wherein the reference voltage generation circuit is comprised of a peak hold circuit and a time constant circuit. 3. Claims in which the comparison circuit comprises a series circuit consisting of two constant voltage elements and a resistor that determine the upper and lower limit voltages, and two comparators to which the upper and lower limit voltages are respectively input. The optical object detector according to item 1. 4. The optical object detector according to claim 1, wherein the gain of the amplifier circuit or the light emitting element drive circuit is controlled based on the reference voltage of the reference voltage generation circuit.