JP2000266852A - Distance-measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a constant accuracy whether a measurement distance is large or small and speed up measurement. SOLUTION: A distance-measuring apparatus 1 which outputs object distance data by measuring a time from a projection time point to a reception time point of a pulse light has a plurality of light sources for projecting pulse lights of mutually different wavelengths, an optical member 13 for making optical axes of pulse lights projected from the plurality of light sources agree with each other, a light-splitting means for separating received pulse lights, and a plurality of photoelectric conversion devices corresponding one by one to the separated pulse lights. The plurality of light sources are made to emit and project light at the same time or sequentially with mutually different output intensities. The reception time point is detected on the basis of an output signal of a largest peak value in an appropriate range among output signals of the plurality of photoelectric conversion devices.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring apparatus for measuring the round trip propagation time of light to an object reflecting light as distance information.

[0002]

2. Description of the Related Art A so-called flight time (TOF: ti) from transmission of a light pulse to reception of a pulse reflected by an object and returned.
By measuring the me of flight, the distance between the objectives can be determined by applying a known light propagation velocity. This method has been applied in various fields such as civil engineering and astronomy. In principle, the closer the pulse width is to zero, the higher the measurement accuracy is. However, in practice, the pulse width is equal to or larger than a value determined by constraints such as light source response and reception sensitivity. In a general distance measuring device, the pulse width is 50 to 1 with a resolution of about several cm.
The value is about 00 ns, and the waveform is a single peak.

[0003] The closer the object that reflects the pulsed light, the greater the amount of received light, and the better the SN ratio of photoelectric conversion. However, if the object is too close, the photoelectric conversion signal will be saturated, and it will not be possible to accurately specify the light receiving point. Therefore, conventionally, in order to extend a measurement range in which a photoelectric conversion signal of an appropriate level can be obtained, an apparatus for simultaneously projecting a plurality of laser beams having different intensities with slightly shifted optical axes has been proposed (Japanese Patent No. 2765291). issue). The proposed device is
The plurality of laser beams reflected back from the outside are distinguished by using the shift of their optical axes, and are converted into electric signals using a plurality of light receiving elements.

[0004]

In the conventional apparatus, since the optical axes of a plurality of pulsed lights having different intensities are different, a slight difference occurs in the measurement result depending on which pulsed light is used for the measurement. There was a problem. In order to eliminate this difference, it is necessary to perform a plurality of projections by slightly changing the projection angle, which increases the time required for measurement. In particular, when measuring the shape of an object by projecting in a plurality of directions, the control of changing (scanning) the projection angle becomes complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to secure a constant accuracy regardless of the magnitude of the measurement distance and to speed up the measurement.

[0006]

In the present invention, a plurality of pulsed lights having different intensities and wavelengths are projected. By performing projections with different intensities, the distance range over which an appropriate non-saturated received signal can be obtained is expanded as compared with the case of performing projection with a single intensity. Further, by performing projections with different wavelengths, even if the optical paths of a plurality of pulsed lights are made to coincide, it is possible to perform photoelectric conversion while distinguishing each pulsed light by spectroscopy.
If the optical paths are the same, the result will be the same regardless of which pulsed light is used for the measurement.

According to a first aspect of the present invention, there is provided an apparatus comprising: a light projecting means for projecting a pulse light to the outside; and a light receiving means for receiving the pulse light reflected outside and performing photoelectric conversion, and projecting the pulse light. A distance measuring device for measuring a time from a time point to a light receiving time point and outputting inter-object distance data, wherein the light projecting means includes a plurality of light sources that emit pulsed light beams having different wavelengths, and each of the plurality of light sources. An optical member that matches the optical axis of the pulsed light emitted from the light source, the light receiving unit is a spectral unit that separates the pulsed light emitted from each of the plurality of light sources, and each of the separated pulsed light. And a plurality of photoelectric conversion devices corresponding one by one,
The plurality of light sources emit light simultaneously or sequentially at different output intensities and perform projection, and among the output signals of the plurality of photoelectric conversion devices, the peak value is used to determine the light receiving time based on the largest output signal within an appropriate range. It is to detect.

The distance measuring apparatus according to a second aspect of the present invention projects the pulse light a plurality of times by changing the direction or position of the optical axis thereof,
The object distance data for a plurality of times is output as shape data.

[0009]

FIG. 1 is an overall configuration diagram of a distance measuring apparatus according to the present invention. The distance measuring device 1 includes a transmission optical system 10 as a light projecting unit, a reception optical system 20 as a light receiving unit, a reception processing circuit 30, a controller 40, a clock generator 45,
And an output port 46. Transmission optical system 1
0 includes two light emitting units 11 and 12 and an optical path unifying unit 13 for matching the optical axes of the pulsed lights P1 and P2 emitted from the two light emitting units 11 and 12, respectively. Pulse light P1, P of pulse width
Inject 2 to the outside. The pulse lights P1 and P2 emitted at the time point tp0 are reflected by the object Q, return to the distance measuring device 1, and received by the receiving optical system 20 at the time point tp1. The receiving optical system 20 receives a signal (photoelectric conversion signal) S2 corresponding to the amount of received light.
0 to the reception processing circuit 30, and the reception processing circuit 30 outputs data D30 indicating the time point tp1 based on the reception signal S20.
Generate The time from the time point tp0 to the time point tp1 is obtained as a light propagation time (time required for a round trip of the distance L) Ta,
Further, the controller 40 is in charge of calculating the distance L by applying a known light propagation speed (3 × 10 ⁸ m / s). The calculated distance L is transferred as measurement data DL from the output port 46 to another device (display, computer, etc.).

FIG. 2 is a block diagram of a transmission optical system, and FIG. 3 is a time chart of a projection operation. The light emitting unit 11 includes a light source (semiconductor laser) 111 for emitting laser light, a driver 112 for light emission, a pulse circuit 113 for defining a light emission time,
And a light projecting lens (collimator lens) 114. Similarly, the light emitting unit 12 includes a light source 121, a driver 122,
It comprises a pulse circuit 123 and a lens 124. However, in the present embodiment, the emission wavelength λ2 of the light source 121 is selected to be different from the emission wavelength λ1 of the light source 111 (λ1 ≠ λ2).

A projection timing signal S1 is supplied from the controller 40 to the light emitting units 11 and 12. The pulse circuits 113 and 123 output pulse signals SP1 and SP2 having a predetermined width in response to the rises t1, t2, t3,... Of the projection timing signal S1. When the pulse signal SP1 is active, a predetermined drive current is supplied from the driver 112 to the light source 111, and the light source 111 emits light. Similarly, when the pulse signal SP2 is active, the driver 12
A predetermined drive current is supplied to the light source 121 from
21 emits light. At this time, the intensity (peak value of the light emission distribution) Pp1 of the pulse light P1 emitted from the light source 111 and the light source 1
Light emission is controlled so that the intensity Pp2 of the pulse light P2 emitted from the light emitting device 21 is different. In this example, Pp1> Pp2. For example, Pp1 is set to about 1.5 to 2 times Pp2.
The pulse lights P1 and P2 emitted at the same time are
After that, it goes to the object Q through the same optical path.

The above-mentioned time point tp0 may be a time point when a predetermined time has elapsed from the rising edge of the projection timing signal S1 (estimated peak time of light emission intensity), or may be set by peak detection of light emission intensity. Good.

FIG. 4 is a diagram showing a specific example of the optical path unifying unit. By combining the prisms 131, 132, and 133 as shown, the optical axis of the light collimated by the collimator lens 114 and the optical axis of the light collimated by the collimator lens 124 can be matched. Prism 1
31 is provided for adjusting the optical path length.

FIG. 5 is a block diagram of the receiving optical system. The receiving optical system 20 includes two light receiving elements (for example, photodiodes) 21 and 22, light receiving drivers 23 and 24, amplifiers 25 and 26 for converting a photocurrent into a voltage, a light receiving lens 27, and an optical path branching unit. Consists of 28. Amplifier 25, 26
Are output to the subsequent stage as a reception signal S20. The optical path branching unit 28 disperses the received light condensed by the lens 27 and outputs the pulse light P1 having the wavelength λ1
And the pulse light P2 having the wavelength λ2 is guided to the light receiving element 22.

FIG. 6 is a diagram showing a specific example of the optical path branching unit. The function of the optical path branching unit 28 can be realized by a dichroic prism including a multilayer reflective film 281 having a predetermined characteristic and a pair of triangular prisms 282 and 283 sandwiching the multilayer reflective film 281.

FIG. 7 is a block diagram of the reception processing circuit, and FIG. 8 is a conceptual diagram of the center of gravity calculation. The reception processing circuit 30 includes a signal selector 31, an A / D converter 32, a memory 33, and a center-of-gravity calculation circuit. Pulsed light P1, P with different intensities
One of the received signals S25 and S26 obtained by photoelectrically converting each of the two is selected by the signal selector 31 and sent to the A / D converter 32. The A / D converter 32 samples and holds and quantizes the input signal at a timing synchronized with the clock from the clock generator 45. The output of the A / D converter 32 is stored in the memory 33 in time series, and then sent to the center-of-gravity calculation circuit 34. The center-of-gravity calculating circuit 34 is provided for specifying the light receiving time point tp1 in a time unit shorter than the clock cycle and improving the measurement accuracy, and calculates the time center of gravity ip expressed by the following equation as data D30.

[0017]

(Equation 1)

As shown in FIG. 8, the time centroid ip is a predetermined number n obtained by periodically sampling the amount of received pulsed light.
(N = 30 in the figure) is the barycenter on the time axis in the distribution of the received light data, and corresponds to the peak time when the amount of received light is maximum.

FIG. 9 is a diagram for explaining the operation of the signal selector. The signal selector 31 detects the reception signals S25, S
26 peak values Vp1 and Vp2 are detected, and the peak value Vp
1, Vp2 and a threshold value Vmax are compared. As shown in FIG. 9A, when Vp1 <Vmax (that is, at the time of long-distance measurement), the reception signal S25 that is less affected by noise than the reception signal S26 is selected as an output. When Vp1> Vmax as shown in FIG. 9B (that is, when the light receiving element 21 is saturated at the time of the short distance measurement), the reception signal S25 is received.
Select Regardless of either the center-of-gravity calculation or the peak detection, if the received signal is saturated, the reception time point tp1 cannot be specified accurately.

In the above embodiment, an example is described in which a prism is used for unifying the optical path and branching the optical path. However, a star coupler of an optical fiber may be used. The number of light sources is not limited to two, but three
The use of more than two light sources enables a wider range of measurement. A three-dimensional shape can be measured by providing a scanning mechanism for changing the projection angle or moving the projection start point in parallel, and performing scanning in two directions.

[0021]

According to the first or second aspect of the present invention,
Irrespective of the magnitude of the measurement distance, it is possible to secure a certain accuracy and to speed up the measurement.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a distance measuring apparatus according to the present invention.

FIG. 2 is a block diagram of a transmission optical system.

FIG. 3 is a time chart of a projection operation.

FIG. 4 is a diagram illustrating a specific example of an optical path unifying unit.

FIG. 5 is a block diagram of a receiving optical system.

FIG. 6 is a diagram illustrating a specific example of an optical path branching unit.

FIG. 7 is a block diagram of a reception processing circuit.

FIG. 8 is a conceptual diagram of the center of gravity calculation.

FIG. 9 is a diagram for explaining the operation of the signal selector.

[Explanation of symbols]

 Reference Signs List 1 distance measuring device P1, P2 pulsed light 10 transmission optical system (light emitting means) 20 receiving optical system (light receiving means) tp0 time (projection time) tp1 time (light reception time) Ta light propagation time (time) DL distance data (objective) Distance data) 111, 121 Light source 13 Optical path unifying unit (optical member) 40 Controller (projection control unit) 28 Optical path branching unit (spectral unit) λ1, λ2 Emission wavelength 21, 22, Light receiving element (photoelectric conversion device)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Manami Tsukusako 2-3-1-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Fumiya Yagi, Chuo-ku, Osaka-shi, Osaka 2nd-13-13 Azuchicho Osaka International Building Minolta Co., Ltd. (72) Inventor Eiichi Ede 2-3-113 Azuchicho Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Co., Ltd. (72) Inventor Kondo Takashi Takashi 2-3-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka F-term in Osaka International Building Minolta Co., Ltd. 2F065 AA06 DD03 FF31 GG04 JJ05 LL04 LL46 2F112 AD01 5J084 AA05 AD01 BA03 BA12 BA19 BA36 BA38 BB02 BB04 BB11 BB24 CA57 CA61 CA70 DA09 EA04

Claims (2)

[Claims] A light projecting means for projecting the pulse light to the outside; and a light receiving means for receiving the pulse light reflected outside and performing photoelectric conversion, and a time period from the time when the pulse light is projected to the time when the pulse light is received. A distance measuring device that outputs inter-object distance data by measuring the plurality of light sources, wherein the light projecting unit emits a plurality of light sources that emit pulse light having different wavelengths from each other, and the pulse light emitted from each of the plurality of light sources. An optical member for aligning optical axes, wherein the light receiving unit is configured to separate pulse light emitted from each of the plurality of light sources, and a plurality of light receiving units corresponding to each of the separated pulse light. The plurality of light sources are simultaneously or sequentially emitted with different output intensities and project, and among the output signals of the plurality of photoelectric conversion devices, the peak value is the most within an appropriate range. Distance measuring apparatus and detects the reception time on the basis of hearing output signal. 2. The distance measuring apparatus according to claim 1, wherein the pulse light is projected a plurality of times while changing the direction or position of the optical axis thereof, and the distance data for a plurality of times is output as shape data.