JPH01206212A - Measuring apparatus of distance - Google Patents

Abstract

PURPOSE:To detect the position of an object accurately from a position signal detecting means, by maintaining the sum of light signals of diffuse reflection lights at a fixed value substantially. CONSTITUTION:A projecting element 1 is driven intermittently by a projection pulse signal whose output increases gradually, and thereby parallel light beams are applied from a projecting unit to a detection region. If a reflection light is obtained from an object in the direction region, a received light signal can be obtained at any position of a position detecting element 6. Then light signals at opposite ends thereof are added up by an addition means 11, and an addition value obtained thereby is compared by a comparison means 21 having a prescribed threshold level. When a comparison output exceeds a certain value, the drive of the projecting element 1 is maintained for a period of the projection pulse signal at the level of this signal at that time point. The reflected light is made to be fixed substantially, and the position of the object is detected on the basis of an output distribution of the position detecting element 6 at that time.

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a distance measuring device that optically accurately measures the distance to a detection target using a triangulation method, and particularly to a distance measuring device that optically accurately measures the distance to a detection target using a triangulation method. This invention relates to a distance measuring device.

[Prior art]

Conventionally, as shown in, for example, Japanese Patent Laid-Open No. 57-44809, a distance measuring device using trigonometry as shown in FIG. 4 has been used as a device for detecting the distance to an object.

In this device, light from a light emitting element 1 such as a light emitting diode is irradiated in the direction in which the distance is to be detected using a converging lens 2 as a parallel light beam 3, and an object located a predetermined distance away from the lens 2 is irradiated. A condenser lens 5 receives reflected light from the condenser lens 4, and a position detection element (PSD; position sensitive device) 6 is provided behind the condenser lens 5, which provides different current outputs to both ends based on the irradiation position of the light. Then, when the object 4 is at a position a predetermined distance away from the front surface of the lens 2, this light beam 3
When the light is blocked, the diffusely reflected light is focused by the condenser lens 5 and irradiated onto the position detection element 6. Therefore, the position of the reflected light irradiated onto the position detection element 6 changes depending on the distance from the lens 2 to the detection target object 4. A bias power supply 7 is connected to the position detection element 6, and provides two different analog current outputs to the outside from both ends depending on the position of light irradiation, and each output is sent to an I/V converter 8.9.
given to. The I/V converter 8.9 converts the current output from the position detection element 6 into a voltage signal and supplies it to the subtraction circuit 10 and the addition circuit 11. And the division circuit 12 is the subtraction circuit 10
．． By dividing the output of the adder circuit 11, the signal is normalized and output as a signal corresponding to the light receiving position, regardless of the total amount of light received. The output is given to a comparator circuit 13, for example. Comparison circuit 13 detects a signal exceeding a predetermined threshold level and supplies it to signal processing circuit 14 . Further, the light emitting element 1 is pulse-lit by the output of the pulse oscillation circuit 15 via the light emitting element drive circuit 16, and the output of the pulse oscillation circuit 15 is transmitted to the signal processing circuit 14.

The signal processing circuit 14 outputs the detection signal to the outside via the output circuit 17 when the detection signal is applied during the pulse oscillation period.

[Problem to be solved by the invention]

However, in such a conventional distance measuring device, the outputs of the addition circuit and the subtraction circuit are divided by a division circuit to obtain a position detection signal.

Therefore, there is a drawback that the error varies greatly depending on the light amount level. That is, if the light intensity level is sufficiently large, an accurate position detection signal can be obtained, but if the light intensity entering the position detection element 6 is low, the position signal will change significantly due to a slight variation in the output difference of the I/V converter 8.9. That will happen. Therefore, there is a drawback that measurement accuracy varies depending on the amount of light.

Furthermore, since the level fluctuation of the input to the divider circuit is large, there is a problem that errors are likely to occur unless a divider circuit with a wide dynamic range and a fast response speed is used.

The present invention was made in view of the problems of conventional distance measuring devices, and by maintaining the amount of light received by the position detection element at a constant level, it is possible to achieve accurate distance measurement without requiring high-speed response from the dividing circuit. The technical problem is to be able to detect the position of an object based on the output distribution of a position detection element.

[Structure and effects of the invention]

(Means for Solving the Problems) The present invention includes a light projecting section that has a light projecting element and irradiates a parallel light beam toward a detection area, and a parallel light beam that intersects at a certain angle from the optical axis of the light projecting section. a light receiving section having a position detection element disposed in the object, which receives the diffusely reflected light from the object, and provides different current outputs to both ends of the light receiving section depending on the irradiation position;
A distance measuring device that detects the distance to an object based on the light receiving position of a position detection element, as shown in FIG. 1, includes an addition means for adding optical signals obtained at both ends of the position detection element; Comparison means for comparing the output of a light projection control means for holding the pulse signal at that level; and a position signal detection means for outputting the position to the object based on the distribution of the output of the optical signal obtained at both ends of the position detection element by giving it to a division circuit. It is characterized by comprising the following.

(Function) According to the present invention having such features, the light projecting element is intermittently driven by a light projecting pulse signal whose output gradually increases, and a parallel light beam is irradiated from the light projecting section onto the detection area. ing. If reflected light is obtained from an object in the detection area, a light reception signal can be obtained at any position of the position detection element.
The optical signals at both ends are added by an adding means, and the added value is compared by a comparing means having a predetermined threshold level. When the comparison output exceeds a certain value, the driving of the light emitting element is maintained at the level of the light emitting pulse signal at that time for the period. Then, the position of the object is detected based on the output distribution of the position detection element at that time, with the reflected light being kept almost constant.

(Effects of the Invention) Therefore, according to the present invention, the sum of the optical signals of the diffusely reflected light can be kept at a substantially constant value, and the position of the object can be detected by the position signal detection means. At that time, the output ratio at both ends of the position detection element is given to the division circuit for division, but since the emitted light pulse is held at a predetermined level and that level is held until the end of the cycle, the division circuit The input does not change significantly. Therefore, the divider circuit is not required to have a wide dynamic range or high-speed response, and even if a normal divider circuit is used, it is possible to obtain a highly accurate position detection signal.

[Explanation of Examples]

FIG. 1 is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present invention, and the same parts as in the conventional example are indicated using the same symbols. Now, in this embodiment, the light beam 3 is radiated in the direction in which the distance is to be detected, and a condenser lens 5 is arranged at a predetermined distance from the condenser lens 2 to receive the reflected light. A one-dimensional position detection element 6, which is the same as the conventional example, is provided behind it. A bias power source 7 is connected to the center of the position detection element 6 as in the conventional example, and provides two different analog current outputs to terminals at both ends corresponding to the position of light irradiation. The current output of each position detection element 6 is applied to an I/V converter 8.9. I/V
The converters 8 and 9 convert the current output obtained from both ends of the position detection element 6 into a voltage signal, and provide the respective outputs to a subtraction circuit 10 and an addition circuit 11 serving as addition means. Addition circuit 11
The output of the subtraction circuit 10 is applied to a division circuit 2o, and the subtraction output is divided by the addition output. The output is then given to the comparator circuit 13. A predetermined level Vrefl set by the user within the distance measurement range is set in the comparator circuit 13, and if a signal exceeding that level is provided, an object detection signal is provided to the signal processing circuit 14.

Further, the output of the adder circuit 11 is given to a comparison circuit 21 which is a comparison means. The comparison circuit 21 has a predetermined threshold value Vref2 set therein, and provides a comparison output to the light projection control circuit 22 when the input signal exceeds this level. Further, the distance measuring device of this embodiment has an oscillation circuit 23 that generates a square wave signal at predetermined intervals, and its output is given to the signal processing circuit 14 and the light projection control circuit 22. Light projection control circuit 2
2 is the oscillation circuit 2 until a signal is given from the comparison circuit 21.
3 is applied to the light emitting element drive circuit 16 as a signal that gradually increases at predetermined intervals, and constitutes a light emitting control means that maintains the output level when the comparison output is provided. The light projecting element drive circuit 16 drives the light projecting element 1 intermittently, similar to the conventional example described above. Light emitter drive circuit 16. The light projecting element 1 and the focusing lens 2 constitute a light projecting section that irradiates a parallel light beam toward a detection area. The signal processing circuit 14 includes a gate circuit 14a that inputs the square wave signal of the oscillation circuit 23 as a gate signal and the output of the comparison circuit 13, an integration circuit 14b that integrates the output of the gate circuit 14a with a predetermined time constant, and a gate circuit 14b that integrates the output of the gate circuit 14a with a predetermined time constant. It has a comparison circuit 14c that performs discrimination based on a threshold level Vref3, and provides an object detection signal to the output circuit 17 when a signal is obtained from the comparison circuit 13 a plurality of times in succession.

The output circuit 17 outputs to the outside as an output signal such as a relay contact output or an open collector output.

Here, the subtraction circuit 10 and the division circuit 20 are connected to the position detection element 6.
The position signal detecting means 24 outputs the position to the object based on the output distribution.

Next, the light projection control circuit 229, oscillation circuit 23, and its peripheral circuits will be explained in more detail with reference to FIG. In this figure, the oscillation circuit 23 includes an operational amplifier 31 and a transistor T.
ri is a square wave generation circuit that generates a square wave signal, and its output is transmitted to the transistors Tr2.ri of the light projection control circuit 22. Given to the base of T r3. Also, the comparison output of the comparison circuit 21 is connected to the OR circuit 32 and the inverter 33.
is applied to the set input terminal of the RS flip-flop 34 via the RS flip-flop 34. The RS flip-flop 34 is reset by the falling edge of the square wave signal and holds the comparison output for that period, and its Q output is given to the OR circuit 32. The output of the OR circuit 32 is connected to the base of a transistor Tr4 connected in parallel with the transistor Tr2. Transistor Tr2. Tr4 controls a transistor Tr5 connected to the power supply side. The transistor Tr5 is controlled in parallel to the capacitor C1, and its collector terminal is grounded via a constant current source 35. And the terminal voltage of capacitor C1 is voltage follower 3
6, and its output is connected to the input terminal of transistor Tr6.
is connected to capacitor C2 via. The voltage follower 36 gradually charges the capacitor C2 to obtain a transmission pulse signal having a waveform in which the rate of change gradually increases every cycle, and the terminal output of the capacitor C2 is sent to the light emitting element drive circuit 16. Given. The light emitting element drive circuit 16 includes a voltage follower 37 and a transistor Tr7, and drives the light emitting element 1, for example, a light emitting diode, with a light emitting pulse signal.

Next, the operation of this embodiment will be explained with reference to waveform diagrams. FIG. 3(a) shows the oscillation output of the oscillation circuit 23 (collector output of the transistor Tri), and this signal causes the transistor Tr2 to operate at, for example, times t, ~h, and ta.
Off during ~t6-・-・-, t, ~L*, tb~t
It turns on during 7. When the transistor Tr2 is off, the transistor Tr5 is also off at the same time, so the constant current source 35 charges the capacitor C1. Therefore, the terminal voltage of the capacitor CI decreases after the time jlt tt, tt, as shown in FIG. 3 (bl).

When there is no object in front of the distance measuring device of this embodiment, the transistor Tr2 is off during the period t, .about.1. ．． Figure 2 (b) between 14 and t b-...
The terminal voltage of the capacitor C1 decreases as shown by the broken line. If the charging time constant is set to a sufficiently large value, a substantially linear triangular wave signal can be obtained as shown in the figure. This signal is applied to the capacitor C2 via the voltage follower 36 and the transistor Tr6, and the capacitor C2 is charged. Therefore capacitor C2
The terminal voltage at time t+ is as shown by the broken line in FIG.
, ti, L+ . . . , the rate of increase gradually increases. Therefore, the light emitting element drive circuit 1
6, a light projection pulse signal as shown by the broken line in FIG. 3(d) is obtained, and the light projection element 1 is energized. When the object 4 is present in a predetermined detection area on the light beam 3 as shown in FIG. A signal is given. At that time, the current obtained across the position detection element 6 is I/
Since the voltage signals are converted into voltage signals by the V converter 8.9 and added by the adder circuit 11, the light reception signal shown in FIG. 3(e) is obtained from the adder circuit 11. This signal is discriminated by a threshold value V ref2 set in the comparison circuit 21, and when it exceeds this level, the flip-flop 34 of the light projection control circuit 22 is inverted. Therefore, as shown in FIG. 3 (ff) and (g), a Q output is obtained from the flip-flop 34 when the threshold value Vref2 is exceeded. This flip-flop 34 is connected to the rise time t3 of the output of the oscillation circuit 23. t6
Since it is reset at ...-, the times t and t3.
Time t2 to t3 between t4 and 16------. The rHJ level is maintained from time t4 to time t. Then, the time tt, t when the flip-flop 34 is set
Since the transistor Tr4 is turned on via the OR circuit 32 at s, charging is stopped even when the capacitor C1 is being charged.

Therefore, the terminal voltage of the capacitor C1 has the waveform shown by the solid line in FIG. 3(C), and correspondingly, the terminal voltage of the capacitor C2 also has the waveform shown by the solid line in FIG. 3(C). Therefore, as shown by the solid line in FIG. 3(d), the actual light emitting pulse signal is generated from the time from when the comparison circuit 21 gives the comparison output to the end of its transmission cycle, that is, the time from 2 to 1. , 1. ~t6-・
A certain level will be maintained between .... Therefore, since the input level of the position detection element 6 is also constant, in this embodiment, the division circuit 20 has the input voltages t2~t, ts~t6---
An addition output and a subtraction output that do not change by the amount of ----- are respectively given. Since the input of the divider circuit 20 does not fluctuate in this way, there is no need to use a divider circuit with fast response, and since the addition output is almost constant, a normal divider circuit can be used without requiring a wide dynamic range. An accurate position signal up to the object can be obtained from the division circuit 20. The output of the division circuit 20 is given to the comparison circuit 13, and if it exceeds the threshold value Vrefl, it can be determined whether the object is located within a predetermined range.

The output of the comparison circuit 13 is then given to the signal processing circuit 14, and the gate circuit 14a of the signal processing circuit 14 determines whether the output of the comparison circuit 13 can be obtained. If a comparison signal is obtained within this range, the integration circuit 14b
When input is given to , its output increases. Therefore, the comparison circuit 13 is
Only when the output of is transmitted to the integrating circuit 14b, the threshold level Vref3 of the comparing circuit 14c is reached and an object detection signal can be output. and the time 1 when each cycle ends. , 1. ... Since the transistor Tr3 becomes conductive, the capacitor C2 can be discharged.

Now, if the amount of light received from the object 4 is large, the light emission pulse will be maintained for a short time after the start of light emission, and if the object is far away or the diffuse reflected light obtained from the object is small due to its surface condition, , the light emission level is fixed after a long period of time after the start of light emission.

Further, when the amount of light is extremely small and the current output obtained at both ends of the position detection element 6 is low, the transmission pulse is not stopped and only the division process is performed by the division circuit 20 and the position signal of the object is output.

In this embodiment, the flip-flop 34 is set by the output of the comparator circuit 21, and charging of the capacitor C1 during that period is stopped to maintain the level of the light emitting pulse. This is because if the transistor Tr4 is directly controlled by the output of the comparator circuit 21, the light reception level becomes less than Vref2, the comparison output falls, and light emission starts again. Therefore, once light projection is stopped within each cycle, a constant light projection level is maintained until the end of that cycle.

In addition, in this embodiment, a capacitor is charged at each light emitting period to form a triangular wave, and by charging the capacitor based on the triangular wave, a parabolic wave is created in which the voltage increases in proportion to the square of time at each start of a light emitting pulse. Although a triangular wave may be used directly as a light projection pulse signal, it is also possible to use an exponential waveform as a light projection pulse signal.

Further, in this embodiment, the subtraction circuit 1 is used as the position signal detection means 24.
0 and the division circuit 20 are used to calculate the ratio between the addition output and the subtraction output in the division circuit 20 and use it as a position signal, but the two I/V conversion outputs obtained from both ends of the position sensing element 6 are directly sent to the division circuit 20. It is also possible to obtain a position signal based on the output ratio. It is also possible to obtain a position signal by performing division between the adder circuit and the output of one of the I/■ converters, for example, the output of the I/V converter 9.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a distance measuring device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the detailed configuration of the light projection control circuit and its peripheral circuits of this embodiment, and FIG. FIG. 4 is a waveform diagram showing waveforms of various parts of this embodiment, and a block diagram showing an example of a conventional distance measuring device. 1.--Light emitter 2.5...-Lens 6
−・−−1−−Position detection element 8.9・−・−・−1
/V converter 10...-- Subtraction circuit 11.
・−1−−−Addition circuit 12°20−−−・Division circuit 13.21−−−Comparison circuit 14−−−・Signal processing circuit 16−−−・−Light emitting element drive circuit 22-------・Light projection control circuit 23...
-Oscillation circuit 24-...-Position signal detection means Tr
l~Tr 1-----One transistor C1, C
2---Capacitor patent applicant Tateishi Electric Co., Ltd. agent Patent attorney Yoshiki Okamoto (and one other person)

Claims (1)

[Claims] (1) A light projecting section that has a light projecting element and irradiates a parallel light beam toward a detection area, and a light projecting section that is arranged so as to intersect at a certain angle from the optical axis of the light projecting section, and that is arranged to intersect at a certain angle from the optical axis of the light projecting section, and to diffuse light from an object. a light receiving section having a position detecting element that receives reflected light and gives different current outputs at both ends depending on the irradiation position, and detects the distance to an object based on the light receiving position of the position detecting element. The apparatus comprises: an adding means for adding optical signals obtained at both ends of the position detection element; a comparison means for comparing the output of the adding means with a predetermined threshold level; and a light emitting pulse signal whose output gradually increases. a light emitting control means that generates a light emitting pulse signal at a predetermined period and holds a light emitting pulse signal at that level when a signal exceeding a predetermined threshold level is obtained from the comparing means; A distance measuring device comprising: a position signal detecting means for outputting a position to an object based on the distribution of an optical signal by applying the output of the optical signal to a division circuit.