JPH0545587U - Light type detector - Google Patents

Abstract

(57) [Summary] [Objective] The optimum light-receiving sensitivity according to the installation distance between the light-emitter and light-receiver is obtained by automatic adjustment, and stable detection operation is obtained. [Structure] The voltage dividing resistance of the input of the amplifier is controlled by the parallel output corresponding to each bit of the digital signal according to the signal level after amplification inside the light receiver, and the level of the light reception signal is automatically fixed to a predetermined value. The signal level storage means and the reset switch are provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an improvement of a photodetector of a light beam type detection device, which is composed of a projector that emits pulse-modulated light and a photoreceiver that receives the pulse-modulated light.

[0002]

[Prior Art]

 In this type of detector, the sender and receiver are installed at a specified distance, and the intensity of the pulse-modulated light that reaches the receiver from the sender depends on weather conditions such as rain and fog, and the pulse-modulation of the device. Considering the attenuation due to dirt on the window that allows light to pass through, this value has a margin. For example, even in the case of a device that warns a distance of 100 m, it is general that the detection signal is not emitted even if the light reception signal level on the light receiver side is attenuated to 1/100 of the maximum value. Since this type of device is sometimes installed at a distance shorter than a predetermined warning distance, it is controlled using an automatic gain control circuit (AGC) in order to prevent the received light level from rising more than necessary. It was With this light level adjustment using AGC, even if the detected object cuts off the pulse-modulated light, the pulse-modulated light on the receiver side will not be completely zero due to the slight wraparound of the light due to reflection from the ground. , A certain time constant was used, and signal processing was performed so that a detection output was obtained when the light reception level suddenly decreased.

[0003]

[Problems to be solved by the device]

 With the conventional received light level control method, when the object is installed at a distance shorter than the specified warning distance, the passage of the detected object can be detected, but when this object stops between the sender and the receiver, the received light level remains as little as possible. Then, after a certain period of time, the level automatically increased, and the detection output threshold was exceeded, and there was the inconvenience of becoming a warning state (the same state as when there are no light-shielding objects).

[0004]

[Means for Solving the Problems]

 A signal level adjusting means with a voltage dividing resistor is provided between the light receiving element and the amplifying part that follows, and one of the voltage dividing resistors is a variable resistor, and the signal level is adjusted by changing this. However, instead of this variable resistor, multiple fixed resistors connected in parallel are used, and the same result as adjusting the variable resistor by selecting these and causing current to flow can be obtained. Obtainable. Focusing on this point, the present invention connects the parallel digital signal output means controlled by the CPU to the other end of the group of resistors connected in parallel, and outputs the digital signal according to the received light signal level after amplification. At each bit output, a current is selectively passed through these resistors to control the input signal of the amplifier, and as a result, the signal level after amplification is kept constant.

[0005]

【Example】

 FIG. 1 is a block diagram showing the construction of a light beam type detection device of the present invention. The pulse-modulated light P emitted from the projector T toward the light receiver is collected by the optical system (not shown) such as a parabolic reflector in the photodiode 1 arranged at the focal point and converted into an electric signal. It is sent to the signal level adjusting means 2. The signal whose level has been adjusted here is amplified by the amplifying unit 3, becomes a DC signal by the DC signal converting unit 4, and is sent to the output unit 10 at the subsequent stage. The output unit 10 compares the signal level with a reference value, and when a signal lower than the reference value is received, the signal is sent to the outside as an output signal.

The signal from the DC signal conversion unit 4 is sent to the output unit 10 and also to the A / D conversion unit 5 where it is converted into a digital signal. The digital signal output means 8 outputs a plurality of outputs corresponding to the states of the respective bits of the digital signal. With this output, the voltage dividing resistors R1 to R6 of the signal level adjusting means 2 are respectively connected to the ground level of the circuit, and the size of the input signal of the amplifying section 3 is determined by the combined resistance of R1 to R6 and the voltage dividing ratio of R0. It In this embodiment, the upper 6 bits of the 8-bit digital signal are used. The signal level storage means 9 stores the adjusted signal level. The switch 7 operates in response to the attachment / detachment of the cover of the light receiver to give a reset signal to the CPU 6 which controls the movements of the A / D conversion means 5, the digital signal output means 8 and the signal level storage means 9. .. In the parallel resonant circuit formed by C and L in the signal level adjusting means 2, the output voltage of the light receiving element reaches a saturation state when strong disturbance light such as sunlight enters the light receiving element 1. The resonance frequency is tuned to the modulation frequency of the pulse-modulated light P coming from the projector.

In the above configuration, the process of adjusting the signal level will be described in more detail according to the procedure for installing the projector T and the photoreceiver. The projector T and the light receiver, which are installed at a predetermined distance, adjust the orientation of the internal optical system (optical axis adjustment), and are set so that the light receiving level becomes the maximum value. At this time, the projector T and the cover of the photoreceiver are removed, and the switch 7 provided in the photoreceiver main body operates together with the removal of this cover, and the amplification section inside the photoreceiver has the maximum amplification degree. When the cover is attached after the optical axis adjustment, the switch 7 is inverted and the reset signal is input to the CPU 6. Here, the CPU 6 controls the digital signal output means 8 to output an output according to the A / D conversion means 5, the voltage dividing resistance of the signal level adjusting means 2 changes, and the output signal after amplification is preset. It will be adjusted until it reaches the specified value. After the signal level stabilizes at a predetermined value, this level is stored in the signal level storage means 9.

Even if the power supply is stopped in this state, if a battery for holding the memory is provided inside, it can be automatically set to the state before the power failure when the power supply is restarted. The state after this setting is maintained until the switch 7 is actuated, that is, until the cover of the light receiver is removed. Therefore, even when used at a distance shorter than the predetermined warning distance, the gain is fixed to the optimum sensitivity margin at that distance, so it is possible to reliably detect even under all light-shielding conditions. .. The light receiving level to be set and the resistance values of R0 and R1 to R6 are determined by conditions such as the maximum installation distance of the light beam type detector. The procedure for adjusting the signal level is executed by the control program of the CPU 6.

[0009]

[Effect of the device]

 In the light beam type detection device of the present invention, the optimum light receiving level is automatically set only by adjusting the optical axes of the sender and the receiver and attaching the cover. The adjusted light-receiving level is such that the pulse-modulated light incident on the light receiver due to the reflection on the ground does not cause a warning condition. became. It is a digital signal that corresponds to the output after amplification and is finely controlled with a resolution that corresponds to the number of bits, so it is possible to set an accurate level that does not change over time. Also, once set, the state can be stored, so there is no need to readjust in case of a power failure. As described above, according to the present invention, a stable beam-type detection device can be obtained by receiving the pulse-modulated light with a high margin and removing the conventional defects caused by the pulse-modulated light that is incident at an unnecessarily high level.

[Brief description of drawings]

FIG. 1 is a block diagram of a light beam type detection device of the present invention.

[Explanation of symbols]

 1 Photodiode 2 Signal level adjusting means 3 Amplifying section 4 DC signal converting section 5 A / D converting means 6 CPU 7 switch 8 Digital signal outputting means 9 Signal level storing means 10 Output section T Projector

Claims (1)

[Scope of utility model registration request] Receiving light from a light-type detector that consists of a projector that emits pulse-modulated light and a light receiver that receives this pulse-modulated light. In the device, the light receiving element, the signal level adjusting means by the voltage dividing resistor, the amplifying section, the DC signal converting section, and the output section are connected in this order, and the signal from the DC signal converting section is converted into a digital value. A / D conversion means, a digital signal output means for outputting the digital value in parallel, a storage means for storing the digital value, and an electronic control means for controlling each of these means are provided. One of the voltage dividing resistors is composed of a plurality of resistors connected in parallel, one end of the plurality of resistors is connected to the digital signal output means, depending on the signal level obtained from the DC signal converter. Controlling the ratio of the resistors is always light type detecting device, characterized in that where the structure signal of a constant value is sent to the output unit.