JPS62147384A - Laser distance measuring instrument - Google Patents

Abstract

PURPOSE:To enable a distance to be measured with a high accuracy by inputting the output of first and second photosensors to an arithmetic control unit and slidingly controlling a condenser lens so that calculated values obtained from the output of the photosensors become prescribed values determined in advance. CONSTITUTION:A condenser lens 10 collects a laser beam from a semiconductor laser 1 and irradiates the beam onto an object 11 to be measured. On the other hand, a measuring optical system 20 overlaps reflected beam from the object 11 to be measured and that from a reference reflector 17 to generate a measuring beat wave and a reference optical system 21 overlaps laser beams reflected from reference reflectors 24 and 26 to generate a reference beat wave. An arithmetic sequence unit 15 calculates and measures a distance to the object 11 to be measured from the ratio between the numbers of the measuring waves and the reference waves generated by the optical systems 20 and 21, respectively, and the known distances to the reflectors. The output of a photosensor 50 disposed inside the focus of a lens 46 and the output of another photosensor 51 disposed outside the focus of a lens 47 are inputted to the unit 15 and the condenser lens 10 is controlled by driving means 55 so that a calculated value obtained from the output of the photosensors has a prescribed one.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a laser 4111 distance device using a laser beam.

"Prior Art" Conventionally, various methods have already been proposed for laser Xll distance devices that use laser beams. At the same time, the frequency of the laser beam is modulated to generate a total of Δ]1 beat wave in the superimposed reflected light, and the measured beat wave is A device is known in which the distance to the object to be measured is measured by measuring the distance.

However, when calculating the distance to the measured object by measuring the above-mentioned beat wave, it is necessary to use the amount of frequency deviation as a known quantity, which has unstable factors due to temperature changes, etc. , large measurement errors could occur.

Therefore, the present applicant has proposed that by providing a reference optical system for obtaining a reference beat wave for reference in the measurement optical system for obtaining the above-mentioned measurement beat wave, the above-mentioned measured object can be measured without being influenced by the value of the frequency deviation amount. We have proposed a laser distance measuring device that can calculate and measure the distance to objects (patent application filed in 1983).
No. 0-64311).

According to the distance measuring device proposed by the present applicant, the distance to the object to be measured can be calculated using the calculation method 'A' without being influenced by the value of the frequency deviation amount.
Therefore, the M1 distance can be reliably measured without causing a large measurement error. Furthermore, when irradiating a laser beam onto a wavemeter 71111 object, even if the object to be measured is shifted from the focus position of the condensing lens, the S/N ratio of the signal will decrease, but basically as long as a beat wave can be obtained. has the advantage that it does not adversely affect the calculated measurement value and does not require much attention to the focus of the condenser lens.

"Problems to be Solved by the Invention" However, the wavemeter at++ object deviates greatly from the focal position of the condensing lens, and the irradiation area of the laser beam becomes large.
In addition, when the object to be measured is tilted, there is a problem that it is unclear which point of the irradiation area was measured.

"Means for Solving the Problems" In view of such circumstances, the present invention provides the above-mentioned laser distance measuring device, which includes a laser oscillator capable of modulating one oscillation frequency and a laser beam emitted from the laser oscillator. A measurement beat is created by superimposing the condensing lens that emits light onto the object to be measured, the reflected light reflected from the object to be measured, and the reflected light reflected from a reference reflector placed a predetermined distance apart. A measurement optical system that generates waves and a laser beam from the laser oscillator are reflected by a first reference reflector and a second reference reflector, which are respectively provided at a predetermined distance apart, and are superimposed to generate a reference beat. A reference optical system that generates a wave, and a measurement beat wave and a reference beat wave generated by the measurement optical system and the reference optical system, measure the wave number ratio thereof, and calculate the ratio of both wave numbers and the known value up to the reflector. A calculation system OI that calculates the distance from the distance to the object to be measured.
a driving means for moving the condensing lens forward and backward along the optical axis of the laser beam, and condensing the reflected light reflected and branched from the object to be measured, respectively. A first lens, a second lens, a first photosensor placed inside the focal point of the first lens, and a second photosensor placed outside the focal point of the second lens, The output of the sensor and the output of the second photosensor are input to the calculation control device, and the condenser lens is controlled to advance or retreat so that the calculated value obtained from each output becomes a predetermined value. It is.

"Operation" According to such a configuration, it is possible to position the object to be measured at the focal position of the focusing lens by controlling the movement of the focusing lens. The irradiation area can be kept small and the resolution in the direction perpendicular to the optical axis can be increased.

Embodiment The present invention will be described below with reference to the illustrated embodiment. In FIG. 1, a semiconductor laser l receives a DC drive TL and current through a modulation circuit 2 and oscillates a single mode laser beam.
Moreover, the oscillation frequency can be modulated in accordance with the magnitude of the drive current controlled by the modulation circuit 2.

The laser beam emitted from the semiconductor laser 1 is turned into a parallel beam by the collimating lens 3, and further includes a polarizing beam splitter 4, a wavelength plate 5, a beam splitter 6,
Polarizing beam splitter 7, beam splitter 8. A radio wave plate 9 and a condensing lens 10 consisting of a concave lens or a convex lens
The light passes through and is irradiated onto the object to be measured 11 having a rough surface.

The light reflected by the object to be measured 11 is reflected by the polarizing beam splitter 7, passes through the analyzer 12 and the convex lens 13, and is received by a photosensor 14 such as a photodiode. 14 signals are input to an arithmetic and control unit 15 including a microcomputer.

At the same time, a part of the laser beam emitted from the semiconductor laser l is reflected by the polarizing beam splitter 7 and transmitted through the electromagnetic wave plate IB, and then separated from the polarizing beam splitter 7 by a predetermined distance L1. The reflected light reflected by the reference reflector 17 passes through the polarizing beam splitter 7 and is superimposed on the reflected light from the object to be measured 11. The light passes through the analyzer 12 and the convex lens 13, is received by the photosensor 14, and is input to the arithmetic and control unit 15.

Therefore, since the two reflected light signals introduced to the arithmetic and control device 15 have a time d difference due to the optical path difference between the two, specifically, the distance #L1 between the polarizing beam splitter 7 and the reference reflector 17, Polarizing beam splitter 7 and object to be measured 1
A phase difference occurs due to a time delay corresponding to a distance twice as large as the distance L2 between L2 and L2.

In this state, the modulation circuit 2 controls the magnitude of the driving current supplied to the semiconductor laser l, and as shown in FIG. 2, a modulation current having a linear waveform is applied to the semiconductor laser l to oscillate the When the frequency is linearly modulated in the same way as the modulation current, the above phase difference changes in response to changes in the frequency of the laser beam, generating a measurement beat wave, and the wave number of the measurement beat wave is determined by the above calculation. Measured by the control device 15.

Next, in addition to the measurement optical system 20 that obtains the measurement beat wave,
Reference optical system 2 to obtain a reference beat wave for further reference
In this reference optical system 21, the laser beam from the semiconductor laser 1 is split by the beam splitter 6.

After a part of the branched laser beam is transmitted through the polarizing beam splitter 22 and the radio wave plate 23, a first reference reflector such as a mirror or prism is spaced a predetermined distance from the polarizing beam splitter 22. 24, and the remainder of the laser beam is reflected by the polarizing beam splitter 22 and transmitted through the electromagnetic wave plate 25, after which it is irradiated with a mirror or prism or the like spaced a predetermined distance 2 from the polarizing beam splitter 22. Second reference reflector 26
is irradiated. Note that the polarizing beam splitter 2
The respective distances gI of the first reference reflector 24 and the second reference reflector 26 with respect to 2 are different.

The reflected light reflected by the first reference reflector 24 is reflected by the polarizing beam splitter 22, transmitted through the analyzer 27 and the convex lens 28, received by the photosensor 29, and reflected by the second reference reflector 26. The reflected light passes through the polarizing beam splitter 22, is superimposed on the reflected light from the first reference reflector 24, passes through the convex lens 28, and is received by the photosensor 28.

The signal from the photosensor 28 is then introduced into the arithmetic and control unit 15, and the wave number of the reference beat wave is calculated.

Therefore, when a modulated current having a linear waveform is applied to the semiconductor laser 1 by the modulation circuit 2, the arithmetic and control unit 15 receives the measurement beat wave from the measurement optical system 20, and the reference optical system 21 receives the measurement beat wave. Each beat wave will be input.

However, in this embodiment, the arithmetic and control unit 15 modulates the frequency of the laser beam for a predetermined period of time via the modulation circuit 2.
Specifically, the integer wave of the measurement beat signal is modulated by the time required to count a predetermined number. Therefore, if the distance L2 to the object 11 to be measured differs, the frequency of the measurement beat signal differs, so the frequency of the measurement beat signal differs. Time is the distance f
Although it differs depending on liI L 2, in any case, the wave number of the total Jllll beat waves for an unknown predetermined time is predetermined to be constant.

On the other hand, the arithmetic and control unit ξ15 starts counting the wave number of the reference beat signal at the same time as it starts counting the wave number of the measurement beat signal, and after counting a predetermined number of integer waves of the measurement beat signal, that is, for an unknown predetermined time. After , stop counting the number of reference beat waves. Since the wave number of this reference beat signal is usually not an integer, the arithmetic and control unit 15 is designed to be able to measure the wave number of the reference beat signal down to the decimal point.

In this way, if the wave number of the measurement beat signal and the wave number of the reference beat signal for the unknown predetermined time, and therefore the ratio of both wave numbers, can be obtained, even if the predetermined time is unknown, the distance L2 to the object to be measured 11 can be obtained. can be calculated.

That is, the time difference between the reflected lights superimposed in the measurement optical system 20 is τ, and the difference between the pressures fa L2 and Ll is R.
1 If the speed of light is C, then the time difference is expressed by the following formula: It will be done.

Nb=δ・τ ・・・・・・・・・(2
) Therefore, the following equation is obtained from equations (1) and (2).

R=clINb/(2δ) ・・・・・・・・・(
3) Similarly, the wave number Nr of the reference beat wave is expressed by the following equation.

Rr=c*Nr/(2δ) ・・・・・・・・・(4
) However, Rr is the difference between the distance intersection 1 and the distance intersection 2 between the first reference reflector 24 and the second reference reflector 26 of the reference optical system 21, and this difference is of course known.

From the above equations (3) and (4), R=Rr・Nb
/Nr - (5) is obtained, and from this equation, if the ratio between the wave number Nb of the measured beat signal and the wave number Nr of the reference beat signal is obtained, as mentioned above, there is an unstable element due to temperature changes etc. It is clear that the distance L2 to the object to be measured 11 can be calculated without using the value of the frequency deviation amount δ.

Next, Figure 3 shows 1. This is a block diagram showing a specific configuration of a circuit that measures the ratio between the wave number Nb of the measurement beat signal and the wave number Nr of the reference beat signal in the arithmetic and control device 15.
In this circuit, the measurement beat signal and the reference beat signal from each photo sensor 14.29 are respectively input to the waveform shaping circuit 30.31 and waveform-shaped, and the waveform-shaped signal is converted into an integer waveform in each beat wave. are respectively input to integer wave counters 32 and 33 that count the number of .

An integer wave setter 34 is connected to the integer wave counter 32 to which the measurement beat signal is input.
When the number of integer waves of the measurement beat signal counted by 2, that is, the wave number of the measurement beat wave, reaches the setting value preset by the integer wave setter 34, this integer wave counter 32 causes the integer wave counter 33 of the reference system to stop counting. A command signal 35 is output, whereby the integer wave counter 33 stops counting the number of integer waves of the reference beat signal.

At this time, since the integer wave counter 33 can only count the wave number of the reference beat wave an integer number of times, a clock generator 36 is provided to measure the wave number below the decimal point. This clock generator 36 generates a clock at a frequency much higher than the frequency of the reference beat wave, and the clock counter 37 is configured to be able to count the clock.

The integer wave counter 33 outputs a reset signal 38 to the clock counter 37 to reset the clock counter 37 every time it counts an integer wave of the reference beat wave. When the integer wave counter 32 of the measurement system outputs a count stop command signal 35, the clock counter 37 inputs it and stops counting. It counts the number of waves corresponding to the wave number below the decimal point.

The distance to each of the reference reflectors 24 and 28 is always constant, and therefore the frequency of the beat signal does not change. Therefore, the count number of the clock counter 37 for one cycle of the reference beat signal is fixed in advance. The count number of one cycle and the above count stop command signal 3
The wave number of the reference beat signal can be obtained below the decimal point from the count counted by the lock counter 37 when 5 is output.

The arithmetic circuit 39 thus calculates the wave number below the decimal point, and inputs the signals from the integer wave counter 33 and the integer wave setter 34 to determine the distance L2 to the object to be measured 11.
is calculated and displayed on the display 40. At this time,
The wave number of the calculated reference beat wave may be displayed on the display 40 down to the decimal point.

However, in FIG. 1, after the reflected light from the object to be measured 11 is reflected by the beam splitter 8,
The light is split into two by the beam splitter 45, transmitted through a lens 48.47 and a pinhole 48.49, and received by a photosensor 50.51. The pair of photosensors 50 and 51 are configured such that one first photosensor 50 is placed inside the focal point of one first lens 46 and the other second The photosensors 51 are arranged outside the focal point of the other second lens 47, and signals from each photosensor 50, 51 are input to the arithmetic and control device 15.

The beam splitter 8, % wavelength plate 9, condenser lens 10
, beam splitter 45, lens 48.47, pinhole 48.49, and photosensor 50.51 are provided on a moving frame 52, and a screw shaft 53 screwed into this moving frame 52 and a servo motor 54 rotating it. The movable frame 52 is moved by a driving means 55 composed of
By moving forward and backward, the condenser lens 10 can be moved forward and backward along the optical axis of the laser beam.

As described above, the first photosensor 50 is placed inside the focal point of the first lens 46, and the second photosensor 51 is placed inside the focal point of the first lens 46.
Since they are each placed outside the focal point of the lens 47,
The condensing lens lO is moved in one direction via the moving frame 52,
For example, if the object to be measured 11 is moved in a direction, the first photosensor 50 will be moved in a direction out of focus, and the second photosensor 51 will be moved in a direction in which it is in focus. Therefore, the amount of light received by the first photosensor 50 decreases, and the amount of light received by the second photosensor 51 increases.

As a result, as shown in FIG. 4, the outputs of each photosensor 50, 51 are out of phase with each other as the distance 81 between the condenser lens 10 and the object to be measured 11 is changed. will be obtained. and both photosensors 5
It is set so that when the outputs of 0.51 and 0.51 match (point f in FIG. 4), the object to be measured 11 is located at the focal position of the condenser lens 10.

Next, in FIG. 5, each of the above photosensors 50, 51
The signals are input to the subtracter 62 and adder 83 via bypass filters 80.81, respectively, and the outputs A and H of each photosensor 50.51 are subtracted (A
-B) and addition (A+B). Then, from the outputs obtained by the subtracter 62 and adder 63, a divider 64 calculates the value (AB)/(A+B).

(A-B)/(A +
The value of B) is obtained as the curve shown in FIG. 6, and when the value becomes zero, the object to be measured 11 is located on the focal position of the condenser lens 10. Then, the arithmetic and control unit 15 determines the moving direction of the condensing lens 10 depending on whether the value is positive or negative, and drives the condensing lens 10 via the driving means 55 so that the value becomes zero. It is designed to control the position of.

In addition, in the above embodiment, the wave number of the measured beat signal and the wave number of the reference beat signal are directly measured to find the ratio of the two, but the frequency of the measured beat signal and the frequency of the reference beat signal can be adjusted as appropriate. The ratio of the wave number of the total ΔIII beat signal and the wave number of the reference beat signal may be determined indirectly from the ratio of the image frequencies by measuring with a frequency measuring device.

"Effects of the Invention" As described above, according to the present invention, all wavemeter objects can be positioned at the focal position of the condensing lens, so the irradiation area of the laser beam on the object to be measured can be kept small. The effect is that the resolution in the direction perpendicular to the optical axis is increased and distance measurement can be performed with even higher accuracy.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram for explaining the current waveform applied to the semiconductor laser 1,
3 is a block diagram showing a part of the arithmetic and control unit 15 shown in FIG. 1, FIG. 4 is a characteristic diagram showing each output of the first photosensor 50 and the second photosensor 51, and FIG. FIG. 6 is a circuit diagram showing another part of the arithmetic and control unit 15 shown in the figure, and FIG. 6 is a diagram showing calculation results obtained from the output of FIG. 4. 1... Semiconductor laser lO... Condensing lens 11
...Measurement object 14.28...Photo sensor 15...Arithmetic control device 17...Reference reflector 20...Measurement optical system 21...Reference optical system 2
4... First reference reflector 26... Second reference reflector 46... Second lens 50... First photosensor 51... vj2 photosensor 55...
... Drive means 62 ... Subtractor 63 ... Adder 84 ... Multiplier '12 diagram

Claims (1)

[Claims] A laser oscillator whose oscillation frequency can be modulated, a condensing lens that focuses the laser beam emitted from the laser oscillator and irradiates it onto an object to be measured, and a condensing lens that focuses the laser beam emitted from the laser oscillator and irradiates it onto the object to be measured, and a laser beam that is reflected from the object to be measured at a predetermined distance. a measurement optical system that generates a measurement beat wave by superimposing the reflected light reflected from a reference reflector provided at a distance; and a first laser beam provided at a predetermined distance apart from each other by a predetermined distance from the laser beam from the laser oscillator. a reference optical system that generates a reference beat wave by reflecting the waves with a reference reflector and a second reference reflector and superimposing them; and a measurement beat wave and a reference beat wave generated by the measurement optical system and the reference optical system. and an arithmetic and control device that measures the ratio of their wave numbers and calculates the distance to the object to be measured from the ratio of both wave numbers and the known distance to the reflector. a driving means for moving the condensing lens forward and backward along the optical axis of the laser beam; a first lens and a second lens that respectively condense reflected light reflected and branched from the object to be measured; and the first lens. a first photosensor placed inside the focal point of the second lens; and a second photosensor placed outside the focal point of the second lens;
The output of the photosensor and the output of the second photosensor are input to the arithmetic and control device, and the condensing lens is controlled to advance or retreat so that the calculated value obtained from each output becomes a predetermined value. Laser distance measuring device.