JPH07107482B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to improvement of a distance measuring device using a one-dimensional scanning light receiving array such as a CCD or BBD, and more specifically, improvement of distance measuring accuracy. The present invention relates to a distance measuring device having a circuit configuration that enables the above.

(B) Conventional technology Conventionally, an object to be measured is irradiated with beam light, reflected light from the object to be measured is received by a light receiving element, the light reception signal of this light receiving element is arithmetically processed, and the triangulation method is applied to the object to be measured. As a distance measuring device for measuring the distance of an object, a device to which a one-dimensional scanning type light receiving array such as CCD or BBD is applied (for example, refer to Japanese Patent Laid-Open No. 57-211008) or a semiconductor optical position detecting element (PSD) A device to which is applied (for example, JP-A-57-44809 and JP-A-5-4809).
No. 7-175904) is known.

An example of a conventional distance measuring device to which a one-dimensional scanning light receiving array is applied will be described with reference to FIGS. 3 and 4. Reference numeral 22 denotes a light projecting means, which includes a light projecting element 24 such as an LED and the light projecting means 24.
It is composed of a lens 25 for irradiating the object to be measured 38 with the above light as a beam.

A part of the reflected light from the surface of the object to be measured 38 is transmitted through the lens 27, narrowed down, and received on the CCD 28. The light-receiving signal of the CCD 28 is amplified by the amplifier circuit 29 and then input to the comparator 30 and converted into a pulse train. This pulse train is further counted by the counters 32 and 33, and the distance of the DUT 38 is calculated based on the count result. The clock pulse from the oscillator 37 is input to the CCD 28 and the counters 32 and 33.

The processing of the received light signal of the CCD 28 will be described in more detail.
The received light signal of 28 is a mountain-shaped signal as shown in FIG.
The comparator 30 has a threshold value Th and converts this received light signal into a pulse train as shown in FIG. Counter 31
4 counts N ₁ timing and the counter 32 counts N ₂ timing (counts the number of clock pulses). Each pulse of the pulse train corresponds to each pixel in the light receiving state of the CCD 28.

The arithmetic circuit 36 calculates the arithmetic mean N _P of the timings N ₁ and N ₂ [=
(N ₁ + N ₂ ) / 2] is calculated. The pixel of the CCD 28 corresponding to this timing N _P is located at the center of the reflected light. Further, the arithmetic circuit 36 determines a triangle formed by the light beams of the lenses 25 and 27 and the light projecting device 22 based on the position of this pixel on the CCD 28, and obtains the distance of the DUT 38.

FIG. 5 is a block diagram showing an example of processing of another CCD light receiving signal. The light reception signal of the CCD 48 is amplified by the amplification circuit 49, and then the light reception signal of each pixel is sequentially held by the sample hold circuit 50. This held light reception signal is
The analog / digital (A / D) converter 51 converts the signal into a digital signal, which is input to the signal processing circuit 52. Signal processing circuit
52 is a device that processes these digital signals to determine what constitutes a peak, and applies the trigonometric method from the pixel position of the CCD 48 corresponding to that peak to measure the distance to the DUT. Is. As in the previous case, the CCD 48, the sale hold circuit 50, the A / D converter 51, and the signal processing circuit 52 are
A clock pulse from the oscillator 53 is input.

(C) Problems to be Solved by the Invention In the case of the distance measuring device shown in FIG. 3, there is no problem if the received light signal of the CCD 28 is symmetrical as shown in FIG. However, due to the coma aberration of lens 27,
The light receiving signal of the CCD 28 becomes asymmetrical as shown by the solid line in FIG. 6 (note that the light receiving signal of each pixel is shown by the envelope in FIG. 6). Therefore, there is a problem that the value of N _P and the actual peak position P do not match and an error occurs in the distance measurement, and in order to correct this, the arithmetic circuit becomes complicated.

On the other hand, in the case of the distance measuring device shown in FIG.
Since the D converter 51 is used, there is a problem that the frequency of the clock pulse cannot be increased and the response is slow. Further, as shown by the broken line in FIG. 6, when the received light signal of the CCD 48 is saturated, it becomes difficult to determine the peak, and there is a problem that the distance measurement accuracy is reduced.

On the other hand, in the distance measuring device using the PSD, since the PSD light receiving signal is an analog signal, there is a problem that an error occurs in the distance measurement due to the temperature characteristic of the PSD itself and the drift of the light receiving signal processing circuit. .

The present invention has been made in view of the above, and an object thereof is to provide a distance measuring device having a simple circuit configuration, high distance measuring accuracy, and excellent responsiveness.

(D) Means for Solving the Problems The configuration of the distance measuring device of the present invention will be described with reference to FIG. 1 corresponding to the embodiment, and the one-dimensional scanning light receiving array 8 will be described.
And a light projecting means 2 for projecting the light beam B onto the object to be measured 18,
An optical system 7 for narrowing down the reflected light R of the beam light B on the object to be measured 18 and causing each pixel of the one-dimensional scanning light receiving array 8 to receive the light.
At least a first comparator 10 and a second comparator 11 for converting a light receiving signal of the one-dimensional scanning light receiving array 8 into a pulse train and having different thresholds L ₁ and L ₂ , respectively, and these comparators.
Start timing T ₁ , T _{3 of} pulse train output from 10 and 11
And a plurality of counters 12, 13, 14, 15 for respectively counting the end timings T ₂ , T ₄ , and a coordinate system (T, L) having coordinates of the level L of the light receiving signal of the one-dimensional scanning light receiving array 8 and the timing T. ) Peaks the T coordinate of the intersection of the line connecting points (T ₁ , L ₁ ) and (T ₃ , L ₂ ) and the line connecting points (T ₂ , L ₁ ) and (T ₄ , L ₂ ). The corresponding timing T _P , the light receiving position of the one-dimensional scanning type light receiving array 8 is obtained from the peak corresponding timing T _P, and the arithmetic circuit 16 for calculating the distance to the object to be measured 18 by the trigonometric method and the one-dimensional scanning It comprises a mold light receiving array 8 and a synchronizing signal generating circuit 17 for sending synchronizing signals to the counters 12, 13, 14, 15.

(E) Action In the distance measuring device of the present invention, the one-dimensional scanning light receiving array is used to receive the reflected light from the object to be measured, and the light receiving signal is digitally processed. There is no risk of measurement errors due to drift of the signal processing circuit.

Further, the distance measuring device of the present invention will be described with reference to FIG. 2 corresponding to the embodiment. In the coordinate system (T, L),
The envelope of the received light signal of the one-dimensional scanning light receiving array 8 is the second
It is represented by curve C in the figure. When this curve C is cut by two threshold values L ₁ and L ₂ , a straight line l ₁ connecting points (T ₁ , L ₁ ) and (T ₃ , L ₂ ) and a point (T ₂ , L _{2 1} ), a straight line l ₂ connecting (T ₄ , L ₂ )
The T _P of intersection (T _P, L _P) and, even if the curve C is asymmetrical, substantially coincides with the peak P of the curve C. Therefore, if this T _P is set as the peak corresponding timing, it becomes possible to measure the distance with higher accuracy than in the past.

These points (T ₁ , L ₁ ), (T ₃ , L ₂ ), (T ₂ , L ₁ ), (T ₄ ,
The determination of L ₂ ) and T _P can be obtained by at least two comparators, a plurality of counters, and an arithmetic circuit as described above, and the circuit configuration of the distance measuring device can be simplified.

Further, in the distance measuring device of the present invention, the processing time can be shortened without the need to convert the light receiving signal of each pixel of the one-dimensional scanning optical array into a digital signal.

(F) Embodiment One embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram illustrating an optical system and a circuit configuration of a distance measuring device according to an embodiment. 2 is a light projecting means for projecting the spot beam light B onto the object to be measured 18. The light projecting means 2 comprises a light projecting element 3 including a light emitting diode, a drive circuit 4 for driving the light projecting element 3, and a lens 5 for converting the light from the light projecting element 3 into spot beam light B. ing. The design of the light projecting means such as a laser diode or a gas laser light source can be appropriately changed.

A lens (optical system) 7 is provided adjacent to the lens 5. The lens 7 focuses the reflected light R from the object to be measured 18 so that each pixel of a CCD (one-dimensional scanning light receiving array) 8 receives the light. That is, a spot image of light on the object to be measured 18 is formed on the CCD 8. A pinhole may be used instead of the lens 7, and the design can be changed as appropriate.

The light reception signal of the CCD 8 is amplified by the amplifier circuit 9 and then input to the comparators (comparators) 10 and 11, respectively. The comparator 10 converts the light receiving signal of the CCD 8 into a pulse train by the threshold value L ₁ (see also FIG. 2). On the other hand, the comparator 11 converts the light receiving signal of the CCD 8 into a pulse train by the threshold value L ₂ (> L ₁ ).

The output pulse train of the comparator 10 is input to the counters 12 and 13. Further, the output pulse train of the comparator 11 is input to the counters 14 and 15. These counters 12, 13, 1
Oscillator (synchronous signal generation circuit) for 4, 15 and CCD8
The clock pulse from is input.

The count results of the counters 12, 13, 14, and 15 are calculated by the arithmetic circuit.
Entered in 16. In the arithmetic circuit 16, the arithmetic processing described later is performed, and the distance of the object to be measured is calculated and output.

Next, the operation of the distance measuring apparatus of this embodiment will be described.

The object to be measured 18 has a spot beam light B from the light projecting means 2.
Is being projected. The reflected light R from the object to be measured 18 is focused by the lens 7 and received on the CCD 8. The light receiving signal of the CCD 8 is represented by a curve C in the orthogonal coordinate system (T, L) of the timing T and the light receiving signal level L as shown in FIG. This curve C is the envelope of the light receiving signal of each pixel of the CCD 8, and in this case, it has a bilaterally asymmetric shape due to the coma aberration of the lens 7.

The comparator 10 converts the light receiving signal of the CCD 8 into a pulse train by the threshold value L ₁ . The envelope of this pulse train is shown in FIG. 2, but it is of course composed of pulses corresponding to individual pixels (having a light-receiving signal level of a threshold value L ₁ or more). Similarly, the comparator 11 also converts the light receiving signal of the CCD 8 into a pulse train. Since the threshold L ₂ is larger than the threshold L ₁ , the pulse train of the comparator 11 has a shorter length than the pulse train of the comparator 10.

The counter 12 is the start timing T ₁ of the pulse train of the comparator 10, and the counter 13 is the end timing of the pulse train.
Count T ₂ . On the other hand, the counters 14 and 15 respectively count the starting timing T ₃ and the ending timing T ₄ of the pulse train of the comparator 11. In addition, the beginning and end are
This is a concept for identifying one end and the other end of the pulse train.

Counting results on counters 12, 13, 14, 15 T ₁ , T ₂ , T ₃ ,
_Four points are defined in the Cartesian coordinate system (T, L) by T ₄ and the thresholds L ₁ , L ₂ of the comparators 10, 11. That is, the points (T ₁ , L ₁ ), (T ₃ , L ₂ ), (T ₂ , L ₁ ),
(T ₄ , L ₂ ). Point _{(T 1, L 1),} (T 3, L 2) straight lines l ₁ connecting point _{(T 2, L 1),} (T 4, L 2) the intersection of the straight line l ₂ connecting (T _P, L T _{P of P} ) is the peak corresponding timing.

The straight line l ₁ is L = aT + b (1a) It is expressed by. On the other hand, the straight line l ₂ is L = cT + d (2a) It is represented by. Peaking Timing T _P is It is represented by.

The arithmetic circuit 16 is input from the counters 12, 13, 14, and 15.
Based on T ₁ , T ₂ , T ₃ , T ₄ and preset L ₁ and L ₂ , the peaks are calculated from the above formulas (1b), (1c), (2b), (2c) and (3). Calculate the corresponding timing T _P.

Further, the arithmetic circuit 16 obtains the light receiving spot center position on the CCD 8 from the peak corresponding timing T _P. The peak-corresponding timing T _P substantially coincides with the peak P of the curve C even when the received light signal of the CCD 8 has the asymmetrical curve C. Of course, when the curve C is symmetrical, the peak-corresponding timing T _P coincides with the peak P of the curve C. Therefore, the light receiving position on the CCD 8 can be obtained more accurately than before. Even when the CCD 8 received light signal is saturated as shown by the broken line C'in FIG.
T _P can be calculated, can be determined accurately receiving position.

The arithmetic circuit 16 outputs the spot beam light B from the light receiving position,
A trigonal system composed of the lens 5 and the lens 7 is determined, the distance of the DUT 18 is calculated, and this is output.

Although two comparators are used in the above embodiment, three or more comparators having different thresholds may be used. In this case, it is advisable to calculate the peak-corresponding timing T _P by counting the output pulse trains of the comparator having the highest threshold value and the comparator having the lowest threshold value with which the output pulse train is obtained. This is because the greater the difference between the thresholds of the two comparators, the closer the obtained peak corresponding timing T _P can be to the peak _P of the received light signal.

(G) Effects of the Invention As described above, the distance measuring device of the present invention has an advantage that the peak of the light receiving signal of the one-dimensional scanning light receiving array can be accurately obtained and the accuracy of distance measurement can be improved. ing. Further, it is not necessary to digitally change the received light signals of each pixel of the one-dimensional scanning type light receiving array one by one and process the received light signals, which is advantageous in that the response can be made excellent. further,
It also has an advantage that the circuit configuration can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an optical system and a circuit configuration of a distance measuring device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operation of the distance measuring device, and FIG. FIG. 4 is a block diagram for explaining an optical system and a circuit configuration of a conventional distance measuring device, FIG. 4 is a diagram for explaining the operation of the conventional distance measuring device, and FIG. 5 is a diagram of another conventional distance measuring device. FIG. 6 is a block diagram for explaining the circuit configuration, and FIG. 6 is a diagram for explaining the problems of the conventional distance measuring device. 2: Light emitting means, 7: Optical system, 8: CCD, 10/11: Comparator 12, 13/14/15: Counter, 16: Arithmetic circuit, 17: Oscillator, 18: Object to be measured, B: Spot beam light ， R: Reflected light.

Claims (1)

[Claims] 1. A one-dimensional scanning type light receiving array, a light projecting means for projecting a beam of light onto an object to be measured, and a reflected light of the beam light on the object to be measured being narrowed down. An optical system for allowing each pixel to receive light, and at least a first comparator and a second comparator having different threshold values L ₁ and L ₂ for converting the light receiving signal of the one-dimensional scanning light receiving array into a pulse train, , The start timings T ₁ and T ₃ and the end timing T _{2 of} the pulse trains output from the first and second comparators,
A plurality of counters for respectively calculating T ₄ , points (T ₁ , L ₁ ) and (T in the coordinate system (T, L) whose coordinates are the level L of the light receiving signal of the one-dimensional scanning light receiving array and the timing T. _3, L ₂₎ and a straight line connecting, the point (T _2, L ₁₎ and (T _4, L ₂₎ peaks corresponding to T coordinates of intersection of the straight line connecting the timing T _P, than this peak corresponding timing T _P An arithmetic circuit for obtaining the light receiving position of the one-dimensional scanning light receiving array and calculating the distance to the object to be measured by trigonometric calculation; and a synchronization signal for sending a synchronization signal to the one-dimensional scanning light receiving array and the counter. A distance measuring device comprising a generating circuit.