JPH03296609A - Measuring apparatus of shape of object - Google Patents

Abstract

PURPOSE:To obtain analog information of an incident light by providing means for switching the ratio of the photodetecting level an the electric output signal level (photodetecting sensitivity) to a plurality of ranges. CONSTITUTION:Optical axes of a high sensitivity channel TV camera 12, a low sensitivity channel TV camera 22 are fixed parallel to each other. A translucent mirror 10 and a total reflection mirror 20 are set 45 deg. to the axes. An incident light 1 is divided into a transmitting light 11 sent straight by the mirror 10 and a reflecting light 2 reflected at right angles to the transmitting light 11. The transmitting light 11 enters the camera 12. Meanwhile, the reflecting light 2 is reflected by the mirror 20 and input as a reflecting light 21 to the camera 22. The camera 22 is provided with an extinction plate 27 with a transmission loss which is set so that the photodetecting sensitivity be a predetermined value at a predetermined wavelength. Video outputs 13, 23 from the cameras 12, 22 are converted to digital signals 15, 25 by respective A/D converters 14, 24. The information is accumulated in image memories 16, 26 of each channel and taken into a processing circuit 30.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a method for determining the shape of an object by irradiating the object with a laser beam and processing the image signal obtained by receiving the reflected light with a photoelectric conversion device. The present invention relates to an object shape measuring device for recognition or measurement.

[Prior Art] In order to recognize or measure the shape of an object, it is necessary to receive reflected light from the object and convert it into an electrical signal for processing by a computer.

As this light receiving device, a television camera has conventionally been widely used. For reflected light from an object, there are two methods: use normal natural light or indoor lighting without using a special light source, and two methods: use a light source such as a laser beam to direct light with specified characteristics such as wavelength and waveform to the object. There is a method of irradiation. In the latter case, (1) light of a specific wavelength can be used (2)
It is possible to change the intensity of the light irradiating an object with a specific bang or modulate it with a specific cycle. (3) It has the advantage of being able to irradiate an object with point-like or linear light from a specific direction, and is used to measure the distance to an object and the shape of the object based on the principle of triangulation. However, since this method receives the reflected light on the object surface as the signal light, the scattered reflected light is weak for the measurement target where the reflection coefficient of the object surface is large, and therefore the signal light level is low. Under a geometrical situation in which the specularly reflected light directly enters the light receiving device, the signal light level becomes very high.

FIG. 5 shows the input/output characteristics of a typical CCD television camera. The input is the incident exposure amount (the intensity of the incident light is integrated over the period during which the signal light is incident), and the output is an electrical video signal. According to the NTSC standard, the saturation level of the video output is 0.7v, and this is usually expressed in units of 100 (IR
E).

When the incident light becomes very strong, smear 102 occurs in a solid-state imaging device such as a CCD. This is a type of noise, and is a phenomenon in which bright lines appear in the vertical direction (direction perpendicular to the horizontal scanning of the television). On a normal TV screen, this is just a problem when viewing images, but when using a TV camera as an input device for image information, the smear
If 02 occurs, the information regarding the pixels on that bright line will be lost, which is fatal. Therefore, the incident exposure must always be below the level I smext at which smear appears on the screen.

When using a television camera as an image information input device,
Since it is common to digitize analog video signals in order to perform image signal processing, such a situation will be assumed below. If the number of bits of the A/D converter used now is N, the lowest video signal level S win is Sm1n
=100/2'IRE.

When using a television camera as an input device for image information, the required input information is 0. If it is a binary value of 1, that is, information about the intensity of light can be ignored, then the maximum dynamic range that can be used by the television camera is MAXDR.
is the incident exposure amount for the lowest video signal level 101,
In other words, a weak signal below this level is considered to be 0.
If man, MAXDR= 20 log (I
smest / I win).

On the other hand, if information about the intensity of light, that is, analog information, is required, the incident exposure must be used at a saturation exposure I sat or less, so the dynamic range DR is
is DR-201og (Isat/lm1n).

In a device that measures the shape of an object using the principle of triangulation by irradiating a laser beam onto an object and detecting the scattered reflected light from the object, the light reception signal is, in principle, a binary signal corresponding to the presence or absence of light. That's fine. That is, in principle, such a device can provide a dynamic range up to the above-mentioned MAXDR. However, in actual shape measurement, the output signal of a TV camera contains a lot of noise, so information about the level of the video signal is used to thin lines, extract contours,
Processing such as removal of unnecessary signals is performed, and for this purpose, not only binary information but also some kind of analog information regarding the signal level is required.

Therefore, in actual equipment, the dynamic range is
Therefore, the entire wide area up to MAXDR could not be used effectively.

An example of a commercially available television camera has a MAXDR of approximately 90 dB, but a DR of only 35 dB.

[Problems to be Solved by the Invention] The present invention allows the incident exposure amount up to the smear generation level of the image sensor used, even when analog image input information regarding the level of the incident exposure amount is required. The object of the present invention is to provide an object shape measuring device that can significantly improve the effective dynamic range.

Measures for Solving Problem c] In order to effectively utilize the high light-receiving sensitivity of the image sensor, effectively use the wide incident exposure range that leads to the occurrence of smear, and further obtain analog information of the incident exposure level, A means for realizing a plurality of sensitivity states is provided inside an imaging device or a light source driving device, and a set of image input information is acquired in each light reception state, and all of these input information are synthesized. This will solve the problem.

The principle of the present invention is shown in FIG. A high sensitivity state 103 is a state in which the original sensitivity of the image sensor (usually a CCD) used in this apparatus is used as is. Low sensitivity state 10
The sensitivity setting of 4 is such that when an input light level equal to the incident saturation exposure amount l5xtl in the high sensitivity state 103 is applied, the output level becomes 81n. At this time, if the incident saturation exposure amount 1s*t2 in the low sensitivity state 104 is greater than Ismext as shown in FIG. 6, the total dynamic range can be up to MAXDR. But if Itxt2<
If I smelr, the overall dynamic is DR-
201or (Isst 2/lm1n)<MAX
Becomes DR. In this case, if the dynamic range is
If you want to obtain up to XDR, it is necessary to add a third sensitivity state with lower sensitivity, but the principle is the same as in the case of 2 ranges. For simplicity, l5at2> I smea
The case of 2 ranges, r, will be explained.

[Example] Examples will be described below.

(1) Multi-output method The simplest way to realize the two-range method, which is the principle of the present invention, is to use separate image sensors or devices for the high-sensitivity range and the low-sensitivity range, and each image sensor or device This is a method of simultaneously obtaining independent video output from the

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> FIG. 1 is a first embodiment of the present invention, which shows the device configuration of a method in which two television cameras are used as a set.

In this embodiment, the optical axes of the television camera 12 for the high sensitivity channel and the television camera 22 for the low sensitivity channel are fixed in parallel, and the semi-transparent mirror 10 and the total reflection mirror 20 are set at an angle of 45° with respect to this optical axis. It is assumed that it is installed at an angle.

Incident light 1 becomes transmitted light 1 that travels straight through semi-transparent mirror 10
1 and reflected light 2 that is reflected in a direction perpendicular to it,
The transmitted light 11 enters the camera 12 in the sensitive channel. On the other hand, the reflected light 2 is further reflected in the direction of the reflected light 21 by the total reflection mirror 20 and enters the camera 22 of the low sensitivity channel, but this camera is set so that the light receiving sensitivity is a predetermined value at a predetermined wavelength. A light attenuating plate 27 having a transmission loss of 100% is attached. The operation of the lower side channels is the same, and the video output 13.
23 is converted into a digital signal 15.25 by each A/D converter 14.24, and the information is stored in the image memory 16.26 of each channel and taken into the processing circuit 30.

In this embodiment, the incident light 2 to the low sensitivity channel is reflected by the mirror 20.
However, the mirror 20 may be omitted and the camera 22 may be arranged at right angles to the camera 12.

<Example 2> In Example 1, two cameras were used as a set, but it is also possible to integrate the two cameras using a color camera or a specially designed camera described below. .

Color information is usually not required when measuring the shape of an object, so
High-resolution monochrome cameras are often used. However, it is conceivable to use a commercially available color television camera and use color information as range information. In a single-chip color television camera CCD, a color filter is arranged at each pixel. The color filter has three colors (not necessarily three primary colors) or four colors including white. In order to use a commercially available color television camera as a two-range system, the following conditions are required.

(i) The camera may be a single-panel, two-panel, or three-panel type, but the red, green, and blue color signals must be separated and can be taken out independently.

(ii) The level ratio of two different color signals (for example, red and blue) is sufficiently large with respect to the wavelength of the laser of the light source.

At present, it is not possible to select a combination of COD and laser that satisfies the second condition from commercially available products, but if a device that satisfies this condition becomes available in the future, it will be possible to construct a simple and compact device. I can do it.

Furthermore, it is technically easier to manufacture a special CCD for this purpose rather than to use a commercially available color COD than to manufacture a color CCD. For example, such a CCD may have a structure in which a striped light attenuation film is attached on pixel columns at odd addresses (or even addresses) in the vertical direction (vertical scanning direction). Information in a high sensitivity range can be output from a pixel row to which a light attenuation film is not attached, and information in a low sensitivity range can be output from a pixel row to which a light attenuation film is attached. Such a camera will be referred to as a multi-range camera.

FIG. 2 shows a second embodiment of the invention. This method uses the above-mentioned color camera or multi-range camera 32 to integrate the two cameras shown in FIG. 1, and is basically the same as that shown in FIG. 1.

The incident light 1 directly enters the camera 32 and produces two video outputs 13.
．． 23 is generated. Since the subsequent steps are exactly the same as in Example 1, the same symbols as in FIG. 1 are given, and the explanation will be omitted.

(II) Time-division system By switching the sensitivity of the television camera in a time-division manner,
It is possible to extract video signals for two ranges from one television camera. This requires real-time control of light-receiving sensitivity and synchronization of range switching.

First, control of light receiving sensitivity will be explained. There are the following methods to control the light receiving sensitivity.

(1) Control of accumulation time Some commercially available TV cameras have an electronic shutter function, and the accumulation time (integration time) of the incident light is determined by the shutter open time, and the light receiving sensitivity depends on the shutter open time. Proportional. However, electronic shutters have the inconvenience of being able to select only a unique value set in the camera, like the mechanical shutter time of a normal camera, and the minimum time of current commercially available products is up to 100 μs.

As described above, this method has low flexibility and is not practical, but if used in combination with other methods, it is useful for device configuration.

(2) Control of laser brightness By modulating the brightness of a laser serving as a light source, the light receiving sensitivity can be effectively changed. Although the brightness of a semiconductor laser can be changed by changing the drive current, it is not very practical because it cannot be made lower than the threshold current or the relationship between the brightness and the drive current is complicated. Therefore, the brightness modulation of the laser pulses the laser and its shock coefficient (du
t71xctot). In actual measurements, laser brightness has a linear relationship with impact coefficient.

Next, synchronization of range switching will be explained.

<Embodiment 3> The laser beam is normally mechanically scanned by a rotating mirror, but the range is switched every time the laser beam is scanned, and a high-sensitivity state and a low-sensitivity state are alternately realized. An example of this configuration is shown in FIG. (a) In the figure, the drive coil current I m1 of the rotating mirror 3
rror is a sawtooth wave as shown in FIG. 3B and is synchronized with the synchronization pulse 40. Further, the drive current I 1iset of the laser diode 5 is a rectangular pulse synchronized with the synchronization pulse 40, and its impact coefficient (dut7 tsio)
7 changes in a pulse-like manner in synchronization with the sawtooth wave of 11ittor as shown in figure (C). In other words, the brightness of the laser is high during the period when γ is high, and therefore the level of incident light 1 in figure (a) also changes. The image output 43 obtained during this period corresponds to the high-sensitivity channel in FIG. This corresponds to the second low sensitivity channel.

With this method, the information for one time of Example 1 can be obtained by two mechanical scans, so it takes twice as long to input the information as in Example 1. By sampling for , it is possible to obtain information about the same point on the target object in both ranges, so
There is no extra software burden when processing acquired image information.

(a) In the figure, the video output 43 of the television camera 42 is A/D
It is digitized by a converter 44 and separated into a high sensitivity channel and a low sensitivity channel by a switch 41 driven by a synchronization pulse 40. Since the subsequent steps are exactly the same as those in Example 1, the same symbols as in FIG. 1 are given, and the explanation will be omitted.

<Embodiment 4> The range is switched for each frame of the television, and an example of its configuration is shown in FIG. The same symbols are attached to the same components as in FIG. 3 above. The operation is similar to that shown in FIG. 3, but in the fourth embodiment, the synchronization pulse 40 is synchronized with the horizontal synchronization signal 50 taken out from the television camera 42, and the drive current I1xset of the laser diode 5 and the switch 41 are switched at the frame period. There is. In this method, the high-sensitivity and low-sensitivity sampling points are shifted by the angle that the mirror moves in 1/30 seconds, but this shift can be corrected using software. In this method, image information for one image is obtained in two frames, so the effective number of images per mechanical scan is halved (Example 5). The switching method is the same as the configuration shown in FIG. 4, except that the drive current 11aser of the laser diode 5 and the switch 41 are switched at the field cycle. In this method, the high-sensitivity and low-sensitivity sampling points are shifted by the angle that the mirror moves in 1/60 second, but this can be corrected by software processing similar to the fourth embodiment. In this method, the range is switched for each horizontal scanning line, so information for one line is obtained from two horizontal scanning lines, and the resolution in the vertical scanning direction is halved.

[Effects of the Invention] According to the present invention, analog information of incident light can be obtained by effectively utilizing the high light-receiving sensitivity of a solid-state image sensor, and by efficiently using a wide range of incident exposure amount until smear occurs. I can do it. Specifically, a dynamic range of 14 bits or more can be obtained using an ordinary commercially available television camera.

[Brief explanation of the drawing]

1 to 4 are diagrams showing the configurations of the first to fifth embodiments of the present invention, respectively. FIG. 6 is a diagram explaining the present invention in detail. DESCRIPTION OF SYMBOLS 1... Incident light, 2.21... Reflected light, 3... Rotating mirror 4... Rotating mirror drive coil, 5... Laser diode, 10... Semi-transparent mirror, 11... Transmitted light. 12.22...Camera, 13.23...Video output. 14.24.44...A/D converter, 15.25...
・Digital signal, 16.26...Image memory, 20
... Total reflection mirror, 27 ... Attenuating plate, 30 ... Processing circuit. 32...Color camera or multi-camera, 40...
- Synchronous pulse, 41... switch, 42... TV camera. 43...Video output

Claims (8)

[Claims] (1) In an object shape measuring device that measures the shape of an object by irradiating the object with a laser beam and receiving the reflected light from the object, the ratio of the received light level to the electrical output signal level (hereinafter referred to as light receiving sensitivity) is used. ) to a plurality of ranges. (2) A patent claim characterized in that two television cameras are used as a set, and one television camera is equipped with a dimmer having a predetermined transmission loss for the wavelength of laser light used as a light source. The object shape measuring device according to item 1. (3) Object shape measurement according to claim 1, characterized in that a two-dimensional light receiving sensor is used in which two or more types of pixels having different light receiving sensitivities are arranged with respect to the wavelength of a laser beam used as a light source. Device. (4) A two-dimensional light-receiving sensor is used in which pixels equipped with a light-attenuating film having a predetermined transmission loss for the wavelength of the laser light used as a light source and pixels without the light-attenuating film are arranged at predetermined positions. An object shape measuring device according to claim 1, characterized in that: (5) The object shape measuring device according to claim 1, further comprising a laser driver that changes the brightness of the laser beam in synchronization with an external signal. (6) The object shape measuring device according to claim 5, further comprising means for changing the brightness of the laser beam in synchronization with the mechanical scanning of the laser. (7) The object shape measuring device according to claim 5, further comprising means for changing the output of a laser beam used as a light source in synchronization with the frame period of a television. (8) The object shape measuring device according to claim 5, further comprising means for changing the output of a laser beam used as a light source in synchronization with the field period of a television.