JP2733990B2 - Distance measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device that measures a distance between a device and an object in a non-contact manner using laser light.

[Conventional technology]

Conventionally, as a distance measuring device of this type, a distance to an object to be measured and a moving speed thereof are measured using a Doppler beat signal generated by a phase difference between an optical path of a reference light and an optical path to an object to be measured. There is a device, shown as a block diagram in FIG. In the figure, a laser beam from a semiconductor laser 1 driven and frequency-modulated by a triangular wave generator 21 is guided to a Michelson interferometer type optical system. After this laser light is split into two by the beam splitter 3,
One irradiates the object 4 to be measured at a distance l ₁ and the other irradiates a fixed mirror 6 at a distance l ₂ . The scattered light from the measuring object 4 is condensed by the fixed focus lens 35, passes through the beam splitter 3, and is superimposed on the photoelectric conversion element 8 together with the reflected light from the fixed mirror 6 and condensed. The output of the photoelectric conversion element 8 is input to a counter 23, which measures the period 1 / f _b of the beat signal (where f _b is the beat frequency). At this time, there is the following relationship between the frequency f _b and the optical path difference (l ₁ −l ₂ ).

Here, ν _m is the modulation frequency of the laser light, Δν is the modulation width of the laser light, and C is the speed of light.

From this equation (1), ν _m , △ ν, l ₂ is fixed, and the distance l ₁
And be previously obtained relation between the beat frequency f _b, it is possible to determine the distance l ₁ from the beat frequency f _b. The details are described in, for example, a paper by Kato et al., "FM Heterodyne Measurement Method of Distance and Speed Using Semiconductor Laser" (MW84-25, pp.73 et seq.).

[Problems to be solved by the invention]

In the above-described conventional distance measuring device, since the fixed lens 35 that collects the scattered light on the measuring object 4 has a fixed focal point, the distance measurement range is limited to the range of the focal depth unique to the lens. There is a disadvantage that the range that can be measured (dynamic range) is reduced.

An object of the present invention is to provide a distance measuring device that eliminates such disadvantages and extends the dynamic range of distance measurement.

[Means for solving the problem]

The configuration of the distance measuring device of the present invention, a coherent light generator that generates coherent light, a signal generator that modulates the frequency of light emitted from the coherent light generator,
A light splitting unit that splits the light emitted from the coherent light generator into two, a beam reflecting unit that reflects one of the lights split by the light splitting unit, and the other of the split lights. A variable focus lens for irradiating the object to be measured and condensing scattered light generated from the object to be measured; Photoelectric conversion means, a movement direction calculation means for calculating the movement direction of the object from the Doppler beat signal detected by the photoelectric conversion means, and a movement speed calculation means for calculating the movement speed of the object, A moving amount calculating unit that calculates a moving amount by integrating a moving speed obtained from the moving speed calculating unit; and a movement of the device under measurement calculated by the moving direction calculating unit and the moving amount calculating unit. An automatic focus control means for the focus to determine the change direction and variation of the focal length of the variable lens, changing its result the focal length in accordance with direction and amount of movement,
A distance calculating unit for calculating a distance from the Doppler beat signal, wherein the automatic focus control unit controls the focal length to extend a possible range (dynamic range) of the distance measurement.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a schematic block diagram showing one embodiment of the present invention. In the figure, a triangular wave generator is provided from a semiconductor laser 1.
By 21, the frequency-modulated laser light is guided to a Michelson interferometer type optical system. This laser light becomes parallel light by the collimator lens 2 and is split into two by the beam splitter 3, one of which is applied to the moving or stationary measurement object 4 separated by a distance l ₁ , and the other is applied to the distance l _The light is incident on the fixed mirror 6 separated by ₂ . The scattered light from the measurement object 4 is condensed by the zoom lens 5, and after being transmitted through the beam splitter 3, is superimposed and condensed on the light receiving surface of the photoelectric conversion element 8 by the lens 7 together with the reflected light from the fixed mirror 6. .

At this time, a Doppler beat signal as shown in the waveform diagram of FIG. 2 appears at the output of the photoelectric conversion element 8. As shown in FIG. 2, the Doppler beat signal frequency f _d2 generated by the Doppler beat signal frequency f _d1 and negative section T ₂ the magnitude of the slope of the triangular wave is modulated signal is generated at the positive period T ₁ is It differs according to the moving direction of the measuring object, and becomes as in the following equations.

i) When moving in the Z direction ii) When moving in the -Z direction, iii) When stationary f _d1 = f _d2 = f _b (6) where ν ₀ is the center frequency of the laser beam, Δν is the modulation width of the laser beam, ν _m is the modulation frequency of the laser beam, v is the moving speed of the measuring object, and θ is the angle between the Z axis and the moving direction of the measuring object.

The Doppler beat signal is input to the amplifier 9 and amplified, and the output is input to the high-pass filter 10. After removing the modulated wave component, the output is input to the frequency measuring unit 11.

The frequency measuring section 11 has a configuration as shown in the block diagram of FIG. 3, for example. In FIG. 3, a high-pass filter
The Doppler beat signal output from 10 is input to the counter 23, and after counting its period, the operation unit 24 calculates the reciprocal and converts it to its frequency. Changeover switch 25 is to select the従Gai buffer 26 and 27 to the synchronization signal output from the synchronization unit 22 is connected to the buffer 26 (a) side when the section T _1, when the interval T ₂ buffer 27 (b) Connected to the side. Therefore,
The buffer 26 stores the Doppler beat signal f _d1 interval T ₁ is, the Doppler beat signal f _d2 interval T ₂ is stored in the Ba'a 27.

The Doppler beat frequency measured by the frequency measuring unit 11 is output to the distance calculating unit 12, the moving speed calculating unit 13, and the moving direction calculating unit 14.

The distance calculator 12 has a configuration as shown in FIG. 4, for example. In FIG. 4, the buffer 26 has a Doppler beat frequency f
_d1 and the buffer 27 store the Doppler beat frequency f _d2 , and the beat frequency calculator 28
The average value f _b of _d1 and f _d2 is calculated from the following equation.

The distance conversion unit 29 substitutes f _b into a function F (f _b ) that represents the relationship between the frequency f _b and the distance l ₁ stored in advance in the function storage unit 30, calculates the distance l ₁ , Store to 31.

The moving speed calculator 13 has a configuration as shown in FIG. 5, for example. The speed calculation unit 32 compares the magnitude relationship between the beat frequencies f _d1 and f _d2 stored in the buffers 26 and 27 with the following equation, and stores the following flag in the flag buffer 34 based on the result.

i) When f _d1 > f _d2 : Flag 1, ii) When f _d1 <f _d2 : Flag-1 iii) When f _d1 = f _d2 : Flag 0 The movement amount calculation unit 36 is, for example, as shown in FIG. Such a configuration is adopted.
In FIG. 7, the integrator 37 is connected to the buffer 31 of the speed calculation unit 14.
Is integrated for a certain period of time, for example, the section 2T shown in FIG. 8 as an integration range, and the calculation result, that is, the movement amount Δl during the section 2T is output to the buffer 31. At this time, the value stored in the buffer 31 is updated in synchronization with the rise of the control signal shown in FIG.

The automatic focus control unit 15 determines the direction of change of the focal length of the zoom lens 5 and the amount of change Δf as described below, and changes the zoom lens according to the result. First, the change direction is determined according to the contents of the flag buffer of the movement direction calculation unit 14.
It is determined as follows.

i) In the case of the flag 1: the focal length of the lens is lengthened. ii) In the case of the flag -1: the focal length of the lens is shortened.

iii) When the flag is 0: No change is made.

Next, the change amount Δf is determined according to the magnitude of the movement amount Δl stored in the buffer of the movement amount calculation unit 36. that time,
For example, the conversion table of △ l and △ f is stored in the automatic focus control unit 15.
And may be determined with reference to it.

When an appropriate focal length at which the distance is possible is unknown, such as at the start of measurement, the signal light power from the measurement object 4 is changed while changing the focal length of the zoom lens 5 from the maximum to the minimum.
P _sig may be monitored, and the focal length may be roughly adjusted so that the optical power P _sig is maximized.

The ND filter control unit 16 monitors the signal light power P _sig and the reference light power P _ref by switching the shield plate 18, and adjusts the ND filter so that the power ratio P _sig / P _ref becomes an optimum value obtained in advance. The transmittance of the filter 17 is controlled. At this time, when the reflected light on the front and back surfaces of the ND filter 17 and the multiple reflected light on the front and back surfaces enter the light receiving surface of the photoelectric conversion element 8,
The correct beat frequency cannot be measured because the optical path length of the reference light changes. To avoid this effect, ND filter 17
Is inserted obliquely to the incident laser light to prevent the reflected light from entering the light receiving surface of the photoelectric conversion element 8. The display unit 19 may display the distance to the measurement target, the moving speed, the moving direction, the moving amount, and the like, and may output these measured values to an external device via the interface unit 20.

As described above, the case where the focal length of the zoom lens is changed using the moving direction and the moving amount of the measurement object has been described, but the moving direction calculating unit 14 and the moving amount calculating unit 36 are not provided, and the distance calculating unit is not provided. A similar function can be obtained by using only the distance obtained from 13.

〔The invention's effect〕

As described above, the present invention measures a moving direction, a moving speed, and a moving amount of a moving or stationary measuring object from a Doppler beat signal, and according to the measurement result, a focal length, a changing direction, and a changing direction of the zoom lens. By controlling the amount, there is an effect that the dynamic range of the distance measurement can be widened.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a distance measuring device according to the present invention, FIG. 2 is a waveform diagram of a modulation signal and a beat signal in FIG. 1, and FIG. 3 is a frequency measuring unit 11 in FIG. FIG. 4 is a block diagram of an example of the distance calculation unit 12 of FIG. 1, FIG. 5 is a block diagram of an example of the movement speed calculation unit 13 of FIG. 1, and FIG. FIG. 7 is a block diagram of an example of the movement amount calculation unit 36 of FIG. 1, FIG. 8 is a waveform diagram of a signal output from the synchronization unit 22 of FIG. FIG. 9 is a block diagram of an example of a conventional distance measuring device. 1 ... Semiconductor laser, 2 ... Collimator lens, 3 ...
Beam splitter, 4 ... measurement object, 5 ... zoom lens, 6 ... fixed mirror, 7 ... image forming lens, 8 ... photoelectric conversion element, 9 ... amplifier, 10 ... high-pass filter,
11: frequency measuring unit, 12: distance calculating unit, 13: moving speed calculating unit, 14: moving direction calculating unit, 15: automatic focus control unit, 16: ND filter control unit, 17: ND Filter, 18…
... Shield plate, 19 ... Display, 20 ... Interface, 21 ... Triangle wave generator, 22 ... Synchronizer, 23 ... Counter, 24 ... Calculator, 25 ... Switch, 26,27,31 ......
Buffer, 28: beat frequency calculation unit, 29: distance conversion unit, 30: function storage unit, 32: speed calculation unit, 33: comparison unit, 34: flag buffer, 35: fixed focus lens, 36
…… Moving amount calculator, 37 …… Integrator.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Nagamitsu Oki 5-33-1, Shiba, Minato-ku, Tokyo NEC Corporation (56) References JP-A-54-89780 (JP, A) IEICE Spring National Conference Lecture Paper Volume C-1] (63-3-15) IEICE, P. 309

Claims (2)

(57) [Claims] 1. A coherent light generator for generating coherent light, a signal generator for modulating the frequency of light emitted from the coherent light generator, and light emitted from the coherent light generator divided into two. A light splitting means, a beam reflecting means for reflecting one of the lights split by the light splitting means, and a scattered light emitted from the measured object by irradiating the other of the split lights to the measured object Variable focus lens for collecting light, photoelectric conversion means for photoelectrically converting light in which scattered light collected by the variable focus lens and light reflected by the beam reflecting means are superimposed, and detected by the photoelectric conversion means A moving direction calculating means for calculating a moving direction of the object to be measured from a Doppler beat signal, a moving speed calculating means for calculating a moving speed of the object to be measured, and the moving speed calculating means. Moving amount calculating means for calculating the moving amount by integrating the moving speed, and the focus of the variable focus lens according to the moving direction and moving amount of the object calculated by the moving direction calculating means and the moving amount calculating means. An automatic focus control unit for determining a direction and an amount of change in the distance, and as a result, a distance calculating unit for calculating a distance from the Doppler beat signal; and A distance measuring device characterized by extending the dynamic range of distance measurement by changing the distance. 2. A coherent light generator for generating coherent light, a signal generator for modulating the frequency of light emitted from the coherent light generator, and light emitted from the coherent light generator divided into two. A light splitting means, a beam reflecting means for reflecting one of the lights split by the light splitting means, and a scattered light emitted from the measured object by irradiating the other of the split lights to the measured object Variable focus lens for collecting light, photoelectric conversion means for photoelectrically converting light in which scattered light collected by the variable focus lens and light reflected by the beam reflecting means are superimposed, and detected by the photoelectric conversion means A moving direction calculating means for calculating a moving direction of the object to be measured from a Doppler beat signal, a moving speed calculating means for calculating a moving speed of the object to be measured, and the moving speed calculating means. Moving amount calculating means for calculating a moving amount by integrating moving speed, distance calculating means for calculating a distance from the Doppler beat signal, and a focal length of the focus variable lens using the distance calculated from the distance calculating means. And an automatic focus control means for variably controlling the distance, wherein the automatic focus control means changes the focal length, thereby expanding a dynamic range of the distance measurement.