JP2007178309A - Noncontact displacement measuring device, its edge detection method and edge detection program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noncontact displacement measuring device capable of detecting the edge of a measuring object, even when the surface property of the measuring object is not fit to a detection probe. <P>SOLUTION: The measuring object 12 is irradiated with light from a light source, and reflected or transmitted light therefrom is received by a photodetector, and thereby the edge of the measuring object is detected based on an output from the photodetector and a prescribed threshold, while moving a laser probe 35 for detecting displacement of the measuring object 12 in the optical axis direction. Distance information (Z<SB>1</SB>, Z<SB>2</SB>, etc.) and surface property information (SNR<SB>1</SB>, SNR<SB>2</SB>, etc.) are acquired from an acquired output signal together with moved position information (X<SB>1</SB>, X<SB>2</SB>, etc.) (Y<SB>1</SB>, Y<SB>2</SB>, etc.), and the edge position is specified based on each information. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-contact displacement measuring apparatus that has a detection unit that receives reflected light from a measurement target and measures the displacement of the measurement target based on an output signal output from the detection unit, and more particularly to the measurement target. The present invention relates to an edge detection method and program for detecting the position of a target edge.

  When determining the position of a boundary (hereinafter referred to as an edge position) where unevenness exists on the measurement target, there is a technique for calculating the distance between the detector and the measurement target and detecting the edge position by the change in the distance. Various methods are used to calculate the distance in a non-contact manner using light. For example, the following two methods are also known.

  In the first method, the light of the point light source is converged and projected onto the object to be measured, and the relative position of the object to be measured with respect to the point light source is adjusted so that the image of the point light source is focused on the object to be measured. In this method, the position where adjustment is achieved and the focus is obtained is measured by a scale or the like.

  On the other hand, the second method is a method of measuring the distance of the measurement target without moving in the vertical direction with respect to the measurement target (Patent Document 1). For example, in the case of the apparatus disclosed in Patent Document 1, a laser beam is incident on a point to be measured, and a spherical wave returning from the point is converted into two wavefronts whose polarization directions are orthogonal to each other by a birefringent crystal. The phase is divided and a phase difference is generated between the two polarized lights. Thereafter, concentric interference fringes are generated by overlapping again through the analyzer. Since the period of the interference fringes generated at this time is determined by the height (scattering angle) of the object, the distance of the measurement target can be detected by frequency analysis of the interference fringes.

  As another method, white light including light of various wavelength components is converged and projected onto a measurement target via an optical system having axial chromatic aberration, and the reflected light is spectrally separated through a spatial filter. A device having a confocal optical system for receiving light by an optical device is known. The measurement principle of this distance detection is as follows. That is, since the optical system having axial chromatic aberration has a different refractive index depending on the wavelength, the imaging position of the light passing therethrough also differs. For this reason, for example, only a specific wavelength component in white light forms an image on the measurement target, passes through the spatial filter, and enters the spectroscope, and light of other wavelength components hardly enters the spectroscope. For this reason, the distance of the measurement object can be detected by analyzing the wavelength of the light transmitted through the spatial filter by the spectroscope.

When performing edge detection using a non-contact displacement measuring apparatus based on the second method and other methods, the measurement system 90 is moved in parallel with the measurement surface of the object 100 as shown in FIG. While measuring the reflected light from the object to be measured and measuring the positions (X ₁ , X ₂ ,..., X _N ), (Y ₁ , Y ₂ ,..., Y _N ) The distances (Z ₁ , Z ₂ ,..., Z _N ) with the measurement target 100 are calculated from the received light. Then, the positions (X ₁ , X ₂ ,..., X _N ), (Y ₁ , Y ₂ ,..., Y _N ) and the distances (Z ₁ , Z ₂ ,. Based on Z _N ), the edge position of the measurement target can be calculated.
JP-A-3-94288

  However, the conventional edge detection method described above has the first region 100a and the second region 100b with the edge 100c as a boundary as shown in FIG. 11A, and the surface properties (roughness, reflectance, etc.). ) Is constant in each region, and when measuring the object 100 to be measured, the surface properties are not suitable for distance detection, as shown in FIG. There is a problem that it is difficult to accurately determine the edge position due to noise included in the distance signal.

  Accordingly, the present invention provides a non-contact displacement measuring device capable of detecting an edge of a measurement target even when the surface property of the measurement target is not suitable for displacement detection, an edge detection method thereof, and a program thereof. With the goal.

  In order to achieve the above object, a non-contact displacement measuring apparatus according to the present invention includes a light source that irradiates light to a measurement target, and a light detection that receives reflected light that is emitted from the light source and reflected from the measurement target. A displacement calculating unit that calculates a displacement of the measurement target based on an output signal of the light detection unit and outputs a displacement signal indicating the calculated displacement, and a signal quality indicating a signal quality of the displacement signal A signal quality calculation unit that calculates and outputs a parameter; and an edge position determination unit that determines the position of the edge of the measurement target based on the signal quality parameter or the signal quality parameter and the displacement signal. And

  Further, the edge detection method of the non-contact displacement measuring apparatus according to the present invention includes a step of irradiating a measurement target with light and receiving reflected light from the measurement target with a light detection unit, and an output signal of the light detection unit Calculating the displacement of the surface of the object to be measured based on the output and outputting a displacement signal indicating the calculated displacement; calculating and outputting a signal quality parameter indicating the signal quality of the displacement signal; and Determining the position of the edge of the measurement object based on at least one of a signal quality parameter or the signal quality parameter and a light intensity signal indicating the light intensity of the reflected light.

  An edge detection program for a non-contact displacement measuring apparatus according to the present invention includes a step of irradiating a measurement target with light and receiving reflected light from the measurement target with a light detection unit, and an output signal of the light detection unit Calculating the displacement of the surface of the object to be measured based on the output and outputting a displacement signal indicating the calculated displacement; calculating and outputting a signal quality parameter indicating the signal quality of the displacement signal; and Determining the position of the edge of the object to be measured based on at least one of a signal quality parameter or the signal quality parameter and a light intensity signal indicating the light intensity of the reflected light. Features.

  According to the present invention, there is provided a non-contact displacement measuring device capable of accurately detecting an edge position of a measurement target even when the surface property of the measurement target is not suitable for displacement detection, and an edge detection method and program thereof Is possible.

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

  FIG. 1 is a perspective view showing the entire three-dimensional measuring apparatus having the function of the non-contact displacement measuring apparatus according to the present embodiment. The three-dimensional measuring apparatus includes a non-contact type three-dimensional measuring machine 1 and a computer system 2 that drives and controls the three-dimensional measuring machine 1 and executes necessary data processing.

  The three-dimensional measuring machine 1 is configured as follows. That is, a measurement table 13 on which the measurement target 12 is placed is mounted on the gantry 11, and this measurement table 13 is driven in the Y-axis direction by a Y-axis drive mechanism (not shown). Support arms 14 and 15 extending upward are fixed to the center of both side edges of the gantry 11, and an X-axis guide 16 is fixed so as to connect both upper ends of the support arms 14 and 15. An imaging unit 17 is supported on the X-axis guide 16. The imaging unit 17 is driven along the X-axis guide 16 by an X-axis drive mechanism (not shown).

  The inside of the imaging unit 17 is configured as shown in FIG. That is, the slider 31 is provided so as to be movable along the X-axis guide 16, and the Z-axis guide 32 is fixed to the slider 31 integrally. A support plate 33 is provided on the Z-axis guide 32 so as to be slidable in the Z-axis direction. The support plate 33 is provided with a CCD camera 34 serving as an imaging means for measuring an image and a laser serving as a non-contact displacement meter. A probe 35 is also provided. As a result, the CCD camera 34 and the laser probe 35 can move simultaneously in the three axial directions of X, Y, and Z while maintaining a fixed positional relationship.

  An illumination device 36 for illuminating the imaging range is added to the CCD camera 34. In order to confirm the measurement position of the laser probe 35 by the laser beam, a CCD camera 38 that images the periphery of the measurement position and an illumination device 39 for illuminating the measurement position of the laser probe 35 are located near the laser probe 35. And are provided. The laser probe 35 is supported by a vertical movement mechanism 40 for retracting the laser probe 35 when the imaging unit 17 is moved, and a rotation mechanism 41 for adapting the directivity of the laser beam to an optimum direction. .

  FIG. 3 is a diagram illustrating an example of the laser probe 35. The laser probe 35 includes a semiconductor laser 51 and a light amount control unit 51 a that controls the amount of light emitted from the semiconductor laser 51. The light emitted from the semiconductor laser 51 forms a light spot on the measurement unit of the workpiece 12 via the beam splitter 52, the quarter wavelength plate 53, and the objective lens 54. The light reflected from the measurement unit of the work 12 is reflected by the beam splitter 52 through the quarter wavelength plate 53, passes through the conoscope unit 55, and forms interference fringes on the CCD element of the CCD camera 56. The conoscope unit 55 includes an incident-side polarizer 55a, an output-side analyzer 55c, and a birefringent crystal 55b sandwiched therebetween. That is, the incident light is polarized by the polarizer 55a, and is split into two wavefronts orthogonal to the polarization direction by the birefringent crystal 55b, and a phase difference is generated between the two polarized light components. In between, a 90 ° phase shift is introduced. After that, concentric interference fringes are generated by overlapping again via the analyzer 55c. At this time, since the period of the generated interference fringe is determined by the height (scattering angle) of the object, it is possible to detect the displacement of the measurement target in the optical axis direction by analyzing the frequency of the interference fringe. it can. As described above, since the height information is included in the output of the laser probe, there is an advantage that information such as a cross-sectional shape and a surface property on the scanning surface can be obtained. In addition, edge detection by a laser probe has an advantage that it is faster than edge detection by an image measurement CCD camera.

  FIG. 4 is a block diagram of the entire apparatus showing the configurations of the coordinate measuring machine 1 and the computer system 2 in more detail. In the three-dimensional measuring machine 1, an image signal obtained by imaging the workpiece 12 by the CCD camera 34 for image measurement and the CCD camera 38 for confirming the measurement position of the laser probe 35 is supplied to the computer 21. One of these two types of images is selected by a selection circuit Sc described later and displayed on the CRT display 25. Illumination light necessary for imaging by the CCD cameras 34 and 38 is given by the illumination control units 74 and 75 controlling the illumination devices 36 and 39 based on the control of the computer 21. The displacement signal obtained from the laser probe 35 is temporarily stored in the second memory 83 via the A / D converter 76 and supplied to the computer 21. Then, the imaging unit 17 including these is driven in the XYZ axis direction by an XYZ axis driving unit 77 that operates based on the control of the computer 21. The position of the imaging unit 17 in the XYZ axis direction is detected by the XYZ axis encoder 78 and supplied to the computer 21. The light amount control unit 51 a that controls the amount of laser light emitted from the semiconductor laser 51 in the laser probe 35 executes control based on a control signal from the CPU 81.

  On the other hand, the computer 21 includes a CPU 81 that is the center of control, a first memory 82 connected to the CPU 81, a second memory 83, a program storage unit 84, a work memory 85, and interfaces 86, 87, and 89. In order to display the multi-value image data stored in the first memory 82 or the image signal supplied from the CCD camera 38 and the multi-value image data selected by the selection circuit Sc on the CRT display 25. Display control unit 88. The CPU 81 switches the selection circuit Sc between the image measurement mode and the laser measurement mode. The image based on the multi-value image data stored in the first memory 82 or the image based on the image signal supplied from the CCD camera 38 is displayed on the CRT display 25 by the display control operation of the display control unit 88.

  On the other hand, operator instruction information input from the keyboard 22, joystick 23 and mouse 24 is input to the CPU 81 via the interface 86. Further, the CPU 81 captures the displacement detected by the laser probe 35, XYZ coordinate information from the XYZ axis encoder 78, and the like. Based on the input information, the operator's instruction, the program stored in the program storage unit 83, and the table 84t, the CPU 81 performs stage movement by the XYZ axis driving unit 77, analysis of the image of the work 12, calculation processing of the measured value, Various processes such as a process for controlling the amount of laser light output from the semiconductor laser 51 are executed. The work memory 85 provides a work area for various processes of the CPU 81. The measured value is output to the printer 26 via the interface 87. The interface 89 is for converting CAD data of the work 12 provided by an external CAD system or the like (not shown) into a predetermined format and inputting it to the computer system 21.

  FIG. 5 is a functional block diagram of the three-dimensional measuring apparatus 1 realized by the CPU 81 and its peripheral devices. As shown in FIG. 5, the interference fringe acquisition unit 91 acquires interference fringes. That is, the interference fringe acquisition unit 91 acquires the interference fringe information while driving the laser probe 35 in the specified range of the measurement target 12 based on the operation of the keyboard 22, the mouse 24, and the like. The interference fringe information is stored in the second memory 83, and then read out by the interference fringe acquisition unit 91 and output to the frequency analysis unit 92. The frequency analysis unit 92 performs frequency analysis on the interference fringe information, and converts the frequency into an output signal having a specific intensity for each frequency. Based on this output signal, the distance calculation unit 93 calculates the distance (displacement) between the laser probe 35 and the measurement target 12 and outputs a distance (displacement) signal. Similarly, the signal quality calculation unit 94 calculates a quality of the distance signal, that is, a signal quality parameter indicating the reliability of measurement based on the obtained output signal. On the other hand, at the same time that the interference fringes are acquired by the interference fringe acquisition unit 91, the position information acquisition unit 95 acquires the position information of the laser probe 35 in the XY axis direction from the output of the XYZ encoder 78 when the interference fringes are acquired. The distance between the laser probe 35 and the measurement target 12, the signal quality parameter indicating the reliability of measurement, and the position information of the laser probe 35 when detecting them are associated with each other in the second memory 83 at any time. Stored. Based on this information, the edge position determination unit 96 differentiates the distance and signal quality parameter at each measurement position with respect to the measurement position, and detects the peak of the obtained signal as the edge position.

That is, the outline of the non-contact displacement measuring apparatus according to the present invention realized by the above-described configuration is as shown in FIG. 6 in which the measurement positions (X ₁ , X ₂ ,..., X _N ) and (Y ₁ , Y ₂ ,..., Y _N ), distances corresponding to these measurement positions (Z ₁ , Z ₂ ,..., Z _N ), and signal quality parameters (SNR ₁ , SNR ₂ ,..., SNR _N ) It is comprised so that calculation is possible.

  Next, an edge detection method of the non-contact displacement measuring device will be described with reference to FIGS. As shown in the flowchart of FIG. 7, first, the user designates a measurement range using the keyboard 22 and the mouse 24 (S1). When the designation is completed, the laser probe 35 is driven by the XYZ axis driving unit 77 (S2), and interference fringes due to the reflected light from the measurement target 12 are imaged (S3). Subsequently, frequency analysis is performed on the obtained interference fringes (S4).

  Next, the distance calculation unit 63 detects the frequency f1 of the signal P1 having the highest intensity from the acquired output signal as shown in FIG. 8, for example. Since the frequency f1 of the signal P1 correlates with the distance between the measurement object 12 and the laser probe 35, the distance calculation unit 93 calculates the distance Z based on the frequency f1 (S5).

  The signal quality calculation unit 94 calculates a signal quality parameter based on the obtained output signal (S5). For example, the signal quality parameter is calculated as an S / N ratio (SNR) of the distance signal P1 from an output signal having a specific intensity for each frequency as shown in FIG. That is, the signal intensity of the distance signal P1 having a peak at the frequency f1 is A1, and the average value of the integrated intensity of the entire output signal is A2. These intensity ratios (A1 / A2) become the S / N ratio (SNR). The obtained frequency f1 and intensity ratio (A1 / A2) are stored in the second memory 83. The numerator of the intensity ratio is not limited to the peak signal intensity A1, but may be the integrated intensity of the signal within a predetermined frequency range centered on the frequency f1. Further, the denominator of the intensity ratio is not limited to the average value A2 of the integrated intensity of the entire output signal, but may be the integrated intensity of the entire output signal.

  Subsequently, the CPU 81 determines whether or not the measurement in the range specified in S1 is finished (S6). If the measurement in the range designated in S1 is not completed (S6, No), the process moves to the next measurement location, returns to S2, and repeats the steps up to S5. On the other hand, if the measurement of the range specified in S1 is completed (S6, Yes), edge calculation based on the distance and the signal quality parameter (or the signal quality parameter alone) is executed (S7), and this control flow ends. To do.

  Next, with reference to FIG. 9, an example of edge detection using the distance and the signal quality parameter (SNR) obtained by executing the above S1 to S7 by edge detection by non-contact displacement measurement according to the present embodiment will be described. FIG. 9 shows an example in which the measurement is performed by scanning the laser probe 35 parallel to the measurement surface of the measurement target 12 and on a straight line in order to simplify the description. FIG. 9A is a diagram illustrating a cross section of the measurement target 12. Here, the measurement surface of the object 12 to be measured is divided into a first region 12a and a second region 12b having different reflectivities, with the edge 12c as a boundary, and the surfaces of both the regions 12a and 12b have minute heights. It is assumed that there is only a difference, and the first region 12a is a mirror surface and the second region 12b is a satin finish. In the non-contact displacement measuring apparatus according to the present embodiment, in the case of satin or resin molding, the SNR is output high, and in the case of a mirror or the like, the SNR is output low and a sufficient distance signal is obtained. Is not suitable. The reason for this is that the non-contact displacement meter according to the present embodiment is calibrated with respect to the state in which the diffusing surface is being measured. This is because it concentrates on one point of the CCD element of the camera 39 and the period of interference fringes cannot be specified. FIG. 9B shows a measurement target 12 shown in FIG. 9A and shows the distance Z at the measurement position X. FIG. 9B shows a differential value obtained by differentiating FIG. The figure shown is FIG.9 (c). Similarly, FIG. 9D is a diagram showing the signal quality parameter SNR at the measurement position X of the measurement target 12 shown in FIG. 9A, and the differential value obtained by differentiating FIG. 9D by the position. FIG. 9 (e) is a diagram showing.

  As described above, when the measurement surface of the measurement target 12 is not suitable for distance detection, the edge position is buried in noise as shown in FIG. Therefore, even if the edge position determination unit 96 calculates the differential value as shown in FIG. 9C, the peak indicating the edge is not detected.

  On the other hand, when the edge is calculated based on the signal quality parameter (SNR), the edge is not buried in noise, and can be easily determined as shown in FIG. If the differential value is calculated as shown in FIG. 9 (e), the peak corresponding to the edge can be easily determined.

  As described above, by using the non-contact displacement measuring apparatus of the present invention, it is possible to specify an edge from the displacement of the signal quality parameter even when the surface property of the measurement target is not suitable for detection. In addition, since two types of edge detection processing are output depending on the distance and the signal quality parameter, even if it is difficult to specify the edge by one of the output signals, the edge is detected by the other output signal. It is possible to specify.

  Although one embodiment of the present invention has been described above, the present invention is not limited to these embodiments, and various modifications, additions, substitutions, and the like are possible without departing from the spirit of the invention. For example, in the above-described embodiment, the edge position of the measurement target is determined based on the interference fringes formed through the conoscope. However, if the distance and the signal quality parameter can be calculated, the conoscope is not included. Any configuration may be used. Further, the signal quality parameter may be a light intensity signal of reflected light, in addition to the SNR.

It is a perspective view which shows the structure of the three-dimensional measuring apparatus which has a function of the non-contact displacement measuring apparatus which concerns on one Embodiment of this invention. It is a perspective view inside the imaging unit of the three-dimensional measuring apparatus of FIG. 1 which concerns on one Embodiment of this invention. It is a figure which shows the structure of the laser probe which has a function of the non-contact displacement measuring device which concerns on one Embodiment of this invention. It is a functional block diagram which shows the structure of the computer system which has a function of the non-contact displacement measuring device which concerns on one Embodiment of this invention. It is a functional block of CPU of the non-contact displacement measuring device concerning one embodiment of the present invention. It is a figure showing the outline of the non-contact displacement measuring device concerning one embodiment of the present invention. It is a flowchart figure which shows the operation | movement of edge detection of the non-contact displacement measuring device which concerns on one Embodiment of this invention. It is a figure which shows an example of the output signal measured by the non-contact displacement measuring device which concerns on one Embodiment of this invention. It is a figure which shows one example of a detection of the edge of the non-contact displacement measuring device which concerns on one Embodiment of this invention. It is a schematic diagram which shows operation | movement of the non-contact displacement measuring device which concerns on a prior art example. It is a figure which shows the example of a detection of the edge of the non-contact displacement measuring device which concerns on a prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Three-dimensional measuring machine, 2 ... Computer system, 11 ... Mount, 12 ... Workpiece, 13 ... Measurement table, 14, 15 ... Support arm, 16 ... X axis Guide, 17 ... Imaging unit, 21 ... Computer, 22 ... Keyboard, 23 ... Joystick box, 24 ... Mouse, 25 ... CRT display, 26 ... Printer, 34, 38 ... CCD camera, 35 ... Laser probe, 36, 39 ... Illumination device, 40 ... Vertical movement mechanism, 41 ... Rotation mechanism, 51 ... Semiconductor laser, 51a ... Light quantity control , 52... Beam splitter, 53... Quarter-wave plate, 54... Objective lens, 55... Conoscope unit, 56. 73 ... Selection circuit, 74, 75 ... illumination control unit, 76 ... A / D converter, 77 ... XYZ axis drive unit, 78 ... XYZ axis encoder, 81 ... CPU, 82 ... First memory, 83 ... Second memory, 84 ... Program storage unit, 85 ... Work memory, 86, 87, 89 ... Interface, Sc ... Selection circuit, 88 ... Display control 91: Interference fringe acquisition unit, 92 ... Frequency analysis unit, 93 ... Distance calculation unit, 94 ... Signal quality calculation unit, 95 ... Position information acquisition unit, 96 ... Edge Position determination unit.

Claims (5)

A light source for irradiating the object to be measured;
A light detector that receives reflected light emitted from the light source and reflected from the measurement target;
A displacement calculation unit that calculates a displacement of the measurement target based on an output signal of the light detection unit, and outputs a displacement signal indicating the calculated displacement;
A signal quality calculation unit that calculates and outputs a signal quality parameter indicating the signal quality of the displacement signal;
An non-contact displacement measuring apparatus comprising: an edge position determining unit that determines a position of an edge of the measurement target based on the signal quality parameter or the signal quality parameter and the displacement signal.   The non-contact displacement measuring apparatus according to claim 1, wherein the signal quality parameter is at least one of an S / N ratio of the displacement signal and a light intensity signal indicating a light intensity of the reflected light.   The non-contact displacement measuring apparatus according to claim 1, wherein the light detection unit includes a conoscope unit including a polarizer, an analyzer, and a birefringent crystal inserted between them. Irradiating the object to be measured with light and receiving the reflected light from the object to be measured by a light detection unit;
Calculating the displacement of the surface of the object to be measured based on the output signal of the light detection unit, and outputting a displacement signal indicating the calculated displacement;
Calculating and outputting a signal quality parameter indicating the signal quality of the displacement signal;
Determining the position of the edge of the object to be measured based on at least one of the signal quality parameter or the signal quality parameter and a light intensity signal indicating the light intensity of the reflected light. Edge detection method for measuring device. Irradiating the object to be measured with light and receiving the reflected light from the object to be measured by a light detection unit;
Calculating a displacement of the surface of the object to be measured based on an output signal of the light detection unit, and outputting a displacement signal indicating the calculated displacement;
Calculating and outputting a signal quality parameter indicating the signal quality of the displacement signal; and
Determining the position of the edge of the object to be measured based on at least one of the signal quality parameter or the signal quality parameter and a light intensity signal indicating the light intensity of the reflected light. An edge detection program for a non-contact displacement measuring device.

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