JPS60174905A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to measure a distance with high resolving power by a miniaturized light wt. distance measuring apparatus, by excluding the relation of the spot size of laser beam at an irradiation position and a distance to be measured from proportional relation. CONSTITUTION:The spot size D of laser beam is constant regardless of a distance. Herein, the intensity distribution of speckle by diffused beam from the irradiation point of laser beam is at first detected by a beam detector 6 (a unidimensional photodiode array is used). A speckle average paricle size DSP becomes large with the increase of a distance L0 to be measured. That is, by using parallel beam, the particle size DSP can have the proportional relation with the distance L0. Next, the particle size DSP is calculated from the self-correlation of the speckle intensity distribution obtained by the beam detector 6 and, as the width of correlation at a point lowered by a certain value from the peak value of the calculated correlation function, the distance DSP is calculated. Therefore, the operation content of an operation apparatus 7 is constituted of three stages, that is, correlation operation, peak value detection and correration calculation.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a device for remotely measuring distance to an object. In particular, the present invention relates to a device for remotely measuring distance to an object. In particular, it uses laser speckles and is a compact and lightweight distance measurement device that can be mounted on a robot or the like. Regarding equipment.

[Background of the invention]

Conventionally, distance measuring devices that use laser light... (1)
A device that measures the time from laser irradiation to reflection.

(2) One that uses the interference effect between irradiated laser light and reflected light.

(3) The angle formed by the irradiated light and reflected light, and the position where the irradiated light is generated
- Triangulation method that calculates the distance to the object from the distance to the detection point.

There is.

Method (1) is effective when the distance is large because the speed of light is high. However, since the time from laser emission to reflected light detection is short, high-speed switching is required, making the device large and complicated.

Method (2) is a method that is sensitive to changes in distance on the order of the wavelength of the laser beam (contrary to υ). Therefore, it requires complex adjustments such as preventing vibrations in the optical system. Also, it modulates the intensity of the laser beam. There is also a method to remove interference between modulation frequencies, but in addition to requiring an operation to select the modulation frequency depending on the distance, the light reflectance of the object becomes a problem.Method (3): However, there are significant practical limitations.

(As a variation of the υ method, there is also an ultrasonic radar distance measurement method that uses ultrasonic waves instead of laser light. This method cannot be used to measure small objects because the ultrasonic waves cannot be made into a spatially focused narrow beam. Distance measurement becomes impossible. (3)
As a modification of this method, a method of scanning an infrared beam and measuring distance based on the presence or absence of reflected light from an object to be measured has been put into practical use with autofocus cameras, etc. This method does not improve the resolution, and in order to increase the resolution, the length between the beam emission point and the detection point must be increased, which increases the size of the apparatus.

[Purpose of the invention]

The present invention has been made for the purpose of solving the problems of the prior art described above. In other words, it is an object of the present invention to provide a distance measuring device that is small, lightweight, and has high resolution.

[Summary of the invention]

An outline of the present invention will be explained below. When a laser beam is irradiated onto an object to be measured, the light diffused from the irradiation point interferes with each other.
Forms a pattern with spatial light intensity. This pattern is called a speckle pattern. A speckle pattern occurs when the roughness of the surface of the object to be measured at the laser beam irradiation point is greater than the laser beam wavelength.◎This condition is.

holds true in most cases, except when the object is not an interface, and there is no need to perform any processing on the object to be measured.O Observing the one-dimensional intensity distribution of the laser speckle pattern, we can see that We get a distribution like this.

The average spatial wavelength of the distribution as shown in Figure 1 (hereinafter referred to as
When we subtract the speckle average grain size), we get the following formula.

Here, Dsp; speckle average particle diameter λ; laser light wavelength Lo; distance to be measured D; laser light spot size at the irradiation position K; For a laser beam, K=2, a value that depends on the beam shape and intensity distribution. K, λ, and D are quantities that can be determined in advance. -Lo can be calculated backwards by detecting Dsp. In the present invention, Lo can be measured by removing the relationship between D and Lo from the proportional relationship. Furthermore, we will improve the method of calculating D s p and speed it up to construct a practical device.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 2 is a diagram showing a first embodiment of the present invention.

1 indicates the surface of the object to be measured, and distance measurement to 1 is the object of the present invention. A laser beam is emitted from a laser generator 2, and a parallel beam 5 is obtained by a collimator 4.
Irradiate to 1. At this time, the spot size D of the laser beam is constant regardless of the distance. Speckle intensity distribution due to diffused light from the laser beam irradiation point.
It is detected by a photodetector 6. 6, a one-dimensional 7-otodiode array was used. The third example of the intensity distribution detected by a sensor with a pitch of 25 μm and a number of diodes of 256 @
As shown in the figure. Distance. It can be seen that the average speckle particle size increases as the value increases. The relationship between average particle diameter D [IP and distance is expressed by the following formula since D is constant regardless of distance in this example.

DIlP = K' ・Lo (21 In other words, by making it a parallel beam, it can be set as a constant, and therefore the speckle average grain size can be made to have a proportional relationship with Lo. 7 is the speckle average Particle size D
Details of the calculation contents of 07, which is the calculation device that calculates sp, will be described later. 7, the arithmetic unit 8 performs the operation of dividing a known constant by '. Two cabinets, 8
・Lo −Da p/K' (3J is calculated, and the distance Lo from the director 6 to the laser irradiation point housing above 1 is
The charge fcLo to be calculated is displayed on the display device 9.

Next, the calculation for calculating 1 Lee-Dsp with 2 calculations of 7 will be described. In this example, the calculation of Ds+p is calculated from the autocross correlation 271 of the speckle intensity distribution obtained in step 6.The width of the correlation at a point that is 2 values lower than the peak value of the correlation function obtained in step 6 is taken as 1.Average grain size. Calculate Dsp. For this reason,
The calculation content in step 7 consists of three steps: correlation calculation, peak value detection, and correlation part calculation.

n from one end of the photodiode array (total number N)
O autocorrelation R(k
) is demaru. Figure 4 is a diagram showing an example of 0k=
The correlation is maximum at 0. Find the value of k at the point where the correlation decreases from the maximum value to the set value.

If the value of k at this time is k[IP, then Dsp is.

Dsp = 2Xksp X P (5). Here, it is the diode pitch width of the PH7 Otodiode array. The point at which the correlation drops from the maximum value differs depending on the shape of the beam2.For example, in a square or circular beam with constant intensity, it is 1/2 of the correlation peak.In this way, the laser beam shape is set in advance. By doing this, the above 1 (set value for determining lIP is determined.This ksP
Then, calculate the DSF according to equation (5). By the above operations, DI! Although it is possible to calculate P, it is advisable to use a computer such as a microcomputer as the specific configuration of the device 7. A processing flowchart of the computer is shown in FIG. In step 701, an intensity distribution signal of a speckle pattern is obtained from the detector 6, and in step 702, an autocorrelation calculation is performed. Set the setting value in advance to ・R(
0) - That is, - Multiply the peak value of the correlation calculation result, k at the point where the result intersects R(k), that is, claim
03).

D s pt is derived from ksP according to equation (5) (704).

The DSP takes advantage of this calculation. From this Dsp, Lo is calculated according to equation (3) as described above, but this calculation may also be included in the computer.

As described above, the distance Lo k can be calculated from the speckle average grain size using the method shown in this example. FIG. 6 shows an example of actual measurement results. The results of observing changes in DIIP by changing Lo' show a proportional relationship between LO and Dsp. Lo can be calculated from the reversed D s P, and the effectiveness of the present invention is clear.

FIG. 7 shows a second embodiment of the present invention. In this embodiment, instead of the parallel laser beam used in the first embodiment, a beam having a large distance tl and a beam spot having a small size is used.

In FIG. 6, 2.6.7.9 are the same as in the first embodiment. 8' differs from the first embodiment in its processing method, which will be described later.The difference from the first embodiment is that lenses 41 and 42i are used instead of 4, and the nine beams 5' are narrowed down to 1. The point is to irradiate the target.

Furthermore, the positions 42 and 6 are brought close to each other. 42,6 to 1
The distance Lo will be determined. Assuming that the distance et to the point where 5' is converged and becomes a dot, the spot diameter d of the beam on 1 is 0 d=(1--)D (6). Here, D indicates the spot diameter on 42, and is a value that can be determined in advance. Moreover, t is also a value that was roughly measured. Substituting equation (6) into equation (1) and rearranging it.

becomes. (Comparing the method with Equation (1), it can be seen that Equation (7) is multiplied by Equation (1) IcI/(I Lo/A). If we measure a distance closer than the point that would otherwise be narrowed down, then 1/ (i - Lo/j ) > i.In other words, the change in DIIP for a certain change in Lo is expressed by the equation (7) from the equation (1). This means that the sensitivity to distance measurement is improved, which is the greatest feature of this embodiment. Above, we have specifically described the differences in the structure of this embodiment from the first embodiment. Next, we will explain how to calculate DIIP.
The method for calculating Lo will be described.

The calculation of D s p is the same as in the first embodiment, and the processing content is shown in the flowchart of FIG. The calculation of LO is
This embodiment differs from the first embodiment, and this difference will be described below. Obtain ・ from equation (7). The arithmetic unit 8' calculates the equation (8). That is, Lo is calculated from the known values t, λ, and DIIP obtained as the result of the calculation of 7 according to equation (8).

Specifically, the calculation is performed by a computer, but the flowchart thereof is omitted since it is simple.

It is also possible to include 8' in 7 and use the same computer. As described above, in this embodiment, the sensitivity of distance measurement is increased by controlling the laser beam to be focused.

FIG. 8 is a diagram showing a third embodiment of the present invention. This embodiment is characterized in that a variable focus lens mechanism 43 is used in place of the lenses 41 and 42 of the second embodiment, so that the method of converging the laser beam can be arbitrarily changed. In Figure 8, 2,6.8'.

9 is the same as in the second embodiment. Reference numeral 43 denotes a lens mechanism that can electrically vary the focal length, such as used in a camera zoom mechanism, and its lens position signal is also transmitted to the computer 7'. The process 7' is the same as 7 in the second embodiment.
In addition to the above processing, a determination as to whether the DIIP is within a certain setting range, and a lens movement operation process when the DIIP is not within a certain setting range are added. In other words, the processing contents of step 7' are as shown in FIG. Processes 701, 702, 703, 704 are the fifth
As in the figure, 710, 711, 712, and 713 are the parts added for this embodiment. D in processing up to 704
Although the value of sp is frozen, the magnitude relationship between this DgpK and preset pMax and DMln is compared.

This corresponds to processing 710 and 712. 0Dsp is l)
If it is between Max and ])Mln, the process ends. D
gp > ]) Max, the lens 43 is moved in the direction of increasing the focal length, and the process of increasing the Dsp is started again. Dsp can be reduced by moving the lens in a direction that increases the focal length. Also, Dsp
< I) When Min, move the lens in the opposite direction and perform the same process. By performing this elaborate operation and processing, 1ffD+, p is l) Max and DMln (falls between 0.]) Max and DMITl can be selected by (1) in equation (7).
/ILaI3). As t approaches LO, the value of (, 1/1-LaI4) increases. That is,
The change in Dsp with respect to the change in Lo is large, and the sensitivity is improved. However, when −Lo and L are equal, D g p
becomes infinite, which is impractical. DMax is determined by converting the size of 6 and Dspk, ])Max/ , Dg
p; Set at approximately 0.9. , [)Min is :()M
The requested D sp is a value slightly smaller than ax.
The same process as step 8' in the second embodiment is performed to convert Lo.

As described above, in this embodiment, by changing the focal length, D+++'l'' is changed.Distance measurement is performed at a location where there is a large change with respect to LO, that is, where the sensitivity to Lo is large.

The fourth embodiment has the same device configuration as the third embodiment, but differs in part of the process 7'. In this embodiment, Lo is converted by subtracting t at which the requested D s p becomes a preset value. In the process of 7′,
Set Dyax = DMln. As a result, Ds
p = DMix, and t at this time can be determined. At this stage, Lo can be calculated using equation (8). However, in equation (8), ・D, DgpK, and λ are known, so t is set in advance.

It is advantageous from the viewpoint of shortening the calculation time to store a correspondence table between 0 and 1 in the storage device of the arithmetic unit and calculate Lo k from this correspondence table. This reduces calculation time and makes it possible to measure distances at points with high sensitivity to changes in distance.

FIG. 10 is a diagram showing a fifth embodiment of the present invention. 1
9 to 9 are the same as those in the first embodiment. ◎10 is a frequency analysis device and 11 is an arithmetic device. In this embodiment, D 8 P is determined by frequency analysis of the speckle intensity distribution detected by the detector 6, and Lo is converted from this.

Consider the case where the intensity distribution of speckles detected in step 6 is frequency analyzed. Assuming that beam 5 is a square beam with constant intensity and XD, the frequency component of the intensity distribution is: (9) where δ(f): delta function f; spatial frequency (when DBP-f≦2) 10(Dsp- When f≧2) [I]: Laser light intensity. The ten analysis result examples are as shown in the eleventh example. There are three ways to set up DBP:

(1) A method of solving the equation with A (f) at two frequencies.

(2) Intensity at the point f=0 (D'ap/2) 2
D].

(3) Maximum spatial frequency f, I, -x = Dsp/2
k method.

Dsp can be calculated from the 10 analysis results using any method, or 1 or multiple methods may be used in combination. In step 11, any of the above three methods or a plurality of methods are calculated, and the processing flowchart is shown in FIG. The analysis result is obtained from 10 (101). Method(
1) is to reduce the inclination. This is the value at two frequencies, A'(f r ), A (fz,)
Solve the simultaneous equations from . The result is . This calculation is performed at 102. Method (2) is the value at the point r=0, that is, the value can be claimed.

Since A (0) = (Dsp/2)2[I], Ds, = z can be claimed by a weak 7 stone copy αυ (103), (The method of 31 is 10
Find the point fMax where the frequency analysis result of is O.

From this, it can be claimed as ・DsF=2・f Max Q3 (104). The processing method for determining D sp ' from the frequency analysis results has been described above.

Any of the above three methods may be used, or processing such as averaging the results of multiple methods may be used. In this example, a square beam was described in detail, but a circular beam or a beam with an intensity Dl also for non-constant Gaussian beams
IP calculations are possible.

FIG. 13 is a diagram showing a sixth embodiment of the present invention. This embodiment is characterized in that an average frequency calculator 12 is used instead of the frequency analysis of the fifth embodiment. In FIG. 13, 1 to 9 are the same as in the previous embodiment. The average frequency computing unit 12 is a known one that is composed of a filter, an effective value computing element, and a dividing element. The average frequencies A and F are
If the output waveform from 6 is a composite wave of a certain frequency component v(f), it can be found at the 0th floor. For a square beam with constant intensity.

Therefore, formula a9 is. From now on, set A, F to 12, DlIP, D
sp = 1/6π・(A, F) It can be calculated using α9. D who obtained the output of 12 and was able to divide the equation 05)
The arithmetic unit 13 converts 8F to LO. The contents of the calculation in step 13 are the division of the Q51 formula and the conversion to Lo. Since these are the matters described in the previous embodiment, detailed explanation will be omitted. This embodiment is similar to the fifth embodiment in that it focuses on frequency information, but differs in that Dsp is calculated using the average frequency.

In the seventh embodiment, instead of using a photodiode array as the detector 6, a single photodetecting element is used to scan the space to obtain the spatial intensity distribution of speckles. The method of converting -Dir and Lo' from the intensity distribution thus obtained is the same as in Examples 1 to 7.

The eighth embodiment is characterized in that, as shown in FIG. 14, an optical filter 14 and an optical amplifier 15 are provided in front of the detector 6 to allow only the irradiated laser beam to pass through. 6 and subsequent steps are the same as in the previous embodiment. By using 14, measurements can be made even in a white light environment, for example. 15 is a microchannel plate or the like, which enables detection of even a weak speckle pattern. 15 is
By changing the applied low pressure, the light amplification level can be changed and the speckle intensity can be controlled to be optimal.

The ninth embodiment is the same as the embodiments described above except that it includes a shutter 16 for turning on and off the laser beam, and a control device 17 for the shutter. Furthermore, a subtractor 18 was provided, and 16 was turned on, that is, from the speckle pattern when the laser beam was emitted, 16 was turned off. Perform an operation to subtract the background light when there is no laser light. 18 onwards are the same as in the previous embodiment. By the subtraction processing in step 18, background light included in the speckle pattern can be completely removed, making it possible to improve measurement accuracy.

The 16th factor is a diagram showing a 10th embodiment of the present invention.

This embodiment is characterized by a structure in which a rotatable mirror 19 is provided and the irradiation direction of the laser beam 5 can be changed arbitrarily. 19 is controlled by the 2 control device 20, and at the same time, 6 is controlled so that the VC detection surface always faces the irradiation direction. Processing after step 6 is the same as in the previous embodiment. In this embodiment, it is possible to easily change the irradiation point of the laser beam and measure the distance to any position.

〔Effect of the invention〕

As described above, according to the present invention, the distance to a point irradiated with laser light can be measured remotely using a small, lightweight device with a simple optical system. Therefore, it is possible to install it on a robot, etc., and it also has the effect of making it possible to recognize delicate objects.

[Brief explanation of drawings]

Figure 1 is a waveform diagram of the intensity distribution of the speckle pattern.
The figure is an explanatory diagram showing the first embodiment of the present invention, and FIG.
In this example, the waveform diagram of the actual measurement of the intensity distribution of the speckle pattern is shown. FIG. , FIG. 5 is a processing flowchart for adjusting the DSP, and FIG. 6 is a diagram of the measurement results in the embodiment of Toi 1.
Figure 7. FIG. 8 shows the second embodiment of the present invention. 9 is a flowchart of the process of the third embodiment, FIG. 10 is an explanatory diagram of the fifth embodiment of the present invention, and FIG. 11 is an explanatory diagram of the fifth embodiment. A diagram showing an example of the wave number analysis result of the famous station, FIG. 12 is a processing flowchart for setting the DSP regarding the fifth embodiment, and FIG. 13 is an explanatory diagram showing the sixth embodiment of the present invention. 1st
Figure 4. 15 and 16 respectively show the 8th and 9th parts of the present invention.
．． It is an explanatory view showing a 10th example. 1... Object to be measured, 2... Laser generator, 6
...Photodetector・7.7'...Arithmetic unit, 8.8'・
... Arithmetic unit, 9... Display device, 10... Frequency analysis result, 11... Arithmetic device, 13... Arithmetic unit, 14.
...Optical filter, 15... Optical amplifier, 16...
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Claims (1)

[Claims] 1. means for detecting the spatial intensity distribution of laser speckles; means for calculating the self-phase opening of the detected intensity distribution;
The present invention is characterized by comprising means for calculating the average speckle particle size from a position where the autocorrelation calculation result is a preset value, and means for calculating the distance from the claimed average speckle particle size to the laser irradiation point. Distance measuring device.