JP2008286598A - Wavelength estimation method of tracking laser interferometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate the wavelength of measurement light of a tracking laser interferometer in a simple composition without performing measurement of an outside environment such as temperature. <P>SOLUTION: The tracking interferometer for outputting a counted value in response to the increase and decrease of a distance between a reference point 12 in a body 10 and a recursive reflector 32 includes: providing the recursive reflector 32 on a head 52 on a coordinate measurement device 40 having a deformation direction of one axis or more capable of reading deformation with a scale 50 provided along the direction of the deformation; outputting a measured position by the scale 50 and the counted value corresponding to the reference point 12 and the recursive reflector 32 by deforming the head 52 at a plurality of positions; allying to substitute the measured positions at the plurality of the positions and the counted values in a relative equation determined by the measured positions, the counted values, the reference point 12, the wavelength of the measurement light, and an initial offset distance being a distance from the initial position of the recursive reflector 32 to the reference point 12; and estimating the wavelength by solving a simultaneous equation being the relative equation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wavelength estimation method for a tracking laser interferometer, and in particular, a recursive reflector for reflecting incident measurement light back to the incident direction, means for emitting measurement light, and the recursive reflection A light receiving means for receiving the return light reflected back from the body, a main body having an emission direction control means for controlling the emission direction of the measurement light so that the distance between the optical axes of the measurement light and the return light is always constant, When the wavelength of the measurement light is unknown, which is suitable for using a tracking laser interferometer that outputs a count value according to an increase or decrease in the distance between the reference point in the main body and the retroreflector The present invention relates to a wavelength estimation method for a tracking laser interferometer that enables estimation of the wavelength of measurement light when the refractive index of air changes depending on the external environment.

  In general, a tracking laser interferometer is a device mainly used for measuring (indication) error caused by a motion error of a three-dimensional measuring machine. This is to control the emission direction of the laser beam, which is the measurement light, to track the retroreflector (also referred to as a retroreflector) attached to the measurement object, and to determine the distance to the retroreflector by laser interference. It measures with high accuracy. Such measurement is performed as one process of the manufacturing process of the three-dimensional measuring machine, and distortion of the measurement space can be measured with respect to an unknown reference such as a scale of a coordinate measuring device including the three-dimensional measuring machine.

  Hereinafter, a tracking laser interferometer represented by Patent Document 1 and having the above application will be described with reference to the schematic configuration diagram of FIG.

  The tracking laser interferometer includes a main body 10, a control device 28, and a retroreflector 32 attached to the measurement target 30. The main body 10 includes a light emitting portion (not shown) that is a means for emitting the measurement light 14 from the reference point 12, a light receiver 20 that is a light receiving means including the first and second light receiving elements 22 and 24, and And a biaxial rotation mechanism 26 serving as an emission direction control means.

  The light emitting unit emits the measurement light 14 by directing a part of the laser beam toward the recursive reflector 32 using a half mirror or the like. The other part of the laser beam is incident on the first light receiving element 22 as reference light for distance measurement.

  The light receiver 20 includes a first light receiving element 22 used for measuring the distance from the reference point 12 in the main body 10 to the retroreflector 32 fixed to the measurement object 30, and the retroreflector. The second light receiving element 24 is used for tracking control of the 32 displacements. The first light receiving element 22 receives light that is reflected by the retroreflector 32 and returns (hereinafter referred to as return light) and the above-described reference light, and outputs the received light signal to the control device 28. . On the other hand, the second light receiving element 24 receives the optical axis of the measurement light 14 and the optical axis of the return light, and outputs a signal about the amount of deviation between the two optical axes to the control device 28.

  The biaxial rotating mechanism 26 is composed of biaxial rotating mechanisms that are orthogonal to each other. In this case, the common center position of the two axes is used as the reference point 12. In order to prevent the measurement of the distance by the first light receiving element 22 from being interrupted, the deviation amount between the two optical axes sent from the second light receiving element 24 is always kept constant by the biaxial rotating mechanism 26. It is.

  The control device 28 obtains a count value based on a signal input from the first light receiving element 22. Here, the count value is obtained by counting the number of bright and dark waves of the interference light caused by the displacement according to the increase or decrease of the distance from the initial position of the recursive reflector 32 to the destination. That is, it is a value obtained by an incremental measurement. Further, the control device 28 controls the biaxial rotation mechanism 26 so that the emission direction of the measurement light 14 is directed toward the recursive reflector 32 based on the signal input from the second light receiving element 24.

  In the retroreflector 32, the optical axes of the incident light and the reflected light are parallel, and the optical axis of the incident light and the reflected light with respect to the center of the retroreflector 32 is a point object. It is an optical element. Therefore, the retroreflector 32 has a function of reflecting the incident measurement light 14 back in the incident direction. When the measurement light 14 is incident on a position away from the center of the retroreflector 32, the positions of the optical axes of the measurement light 14 and the return light are different. The amount of deviation of the optical axis will be observed.

  Note that the count value represents only the displacement from the initial position of the recursive reflector 32 as described above, and does not represent the distance between the reference point 12 and the position of the recursive reflector 32. Therefore, in order to obtain the distance between the reference point 12 and the position of the recursive reflector 32, the distance between the reference point 12 and the initial position of the recursive reflector 32 (hereinafter referred to as the initial offset distance), the recursive reflector It is necessary to add the distance obtained from the measurement value obtained by 32 movements.

  With such a configuration and function, a count value corresponding to the distance observed by the first light receiving element 22 is output as a measurement value of the tracking laser interferometer. Therefore, in general, a plurality of tracking laser interferometers are combined to measure the distance to the retroreflector 32 at the same time, and the three-dimensional coordinates of the retroreflector 32 are identified by the principle of three-side surveying.

Japanese Patent No. 2603429

  However, when the external environment such as temperature changes, the optical refractive index in the measurement optical path is greatly affected. When the refractive index changes, the wavelength of the measurement light 14 changes. In this case, measurement is performed using the “wrong wavelength”, and the count value is dragged by the “wrong wavelength” and is distorted. In other words, the situation is equivalent to the fact that the physical difference (scale) is stretched or shrunk, and the measurement value is stretched or shrunk from the true length, and the count value is measured. Therefore, in order to perform high-precision measurement, it is necessary to accurately grasp the change factors of the external environment. However, an expensive device is required for the measurement, and the burden on the cost is very large.

  However, even if an expensive device is purchased and the wavelength is corrected by observing and measuring the surrounding environment, if the measurement distance becomes long, minute errors that could not be corrected accumulate and the error becomes large. Also, there may be a case where an accurate refractive index cannot be estimated for some reason.

  In some cases, the wavelength is unknown from the beginning, and in that case, there is a problem that the wavelength needs to be estimated.

  The present invention has been made to solve the above-described conventional problems, and enables the wavelength of the measurement light of the tracking laser interferometer to be estimated with a simple configuration without measuring the external environment such as temperature. .

  The present invention relates to a retroreflector for reflecting incident measurement light and returning it to the incident direction, means for emitting the measurement light, and light receiving means for receiving the return light reflected and returned by the retroreflector. And a main body having an emission direction control means for controlling the emission direction of the measurement light so that the distance between the optical axes of the measurement light and the return light is always constant, and the reference point in the main body and the recursive reflection In a tracking type laser interferometer that outputs a count value according to an increase / decrease of a distance from a body, the recursive reflector has a displacement direction of one axis or more that allows displacement to be read with a scale provided along the displacement direction. Provided on a head on a coordinate measuring device having a plurality of positions, and outputting a measurement position by the scale and a count value corresponding to a distance between the reference point and the recursive reflector, Measurement position, count value, and reference And the measurement position and the count value at a plurality of positions are substituted into the relational expression determined by the wavelength of the measurement light and the initial offset distance that is the distance from the initial position of the recursive reflector to the reference point, The problem is solved by estimating the wavelength by solving the simultaneous equations which are the simultaneous relational expressions. This is because when a tracking laser interferometer is used to observe a motion error of a coordinate measuring device, if an incorrect wavelength is used as described above, the observed error is enlarged or reduced accordingly. Resulting in. In this case, the correct wavelength value must be obtained by some method, corrected, and corrected to the correct scale (object difference). In the present invention, this is performed using the scale mounted on the coordinate measuring apparatus. It is.

  The main body can be provided on a surface plate of a coordinate measuring device.

  In addition, the simultaneous equations include a relational expression that the distance obtained by adding the initial offset distance to the product of the count value and the wavelength is equal to the distance obtained from the reference point and the measurement position, and is determined for each measurement position. The relational expressions can be made simultaneous.

  The reference point can be provided on the axis when the displacement direction of the moving body of the coordinate measuring apparatus is one axis, and within a plane constituted by the two axes when the displacement direction is two axes. .

  According to the present invention, it is possible to estimate the wavelength of measurement light of a tracking laser interferometer by combining a coordinate measuring device having a scale with a conventional tracking laser interferometer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 2 is a schematic configuration diagram for wavelength estimation of the tracking laser interferometer according to the present embodiment.

  The present embodiment includes a conventional tracking laser interferometer having a main body 10 and a retroreflector 32, and a coordinate measuring device 40. As shown in FIG. 2, the main body 10 of the tracking type laser interferometer is installed on a surface plate 42 of a coordinate measuring device 40, and the recursive reflector 32 is attached to a head 52.

  The coordinate measuring device 40 may be, for example, a three-dimensional measuring machine, and has a head 52 on a portal frame 44 provided on a surface plate 42, and a probe on the head 52 allows the measurement object to be measured. A three-dimensional shape is measured. The gate-shaped frame 44 includes a pair of columns 46 rising from the surface plate 42 and a beam 48 spanned between the pair of columns 46. The column 46 supports the beam 48, and the head 52 is movable along the beam 48 in the left-right direction (x-axis direction) in the figure. Although not shown in the drawing, the head 52 can move in the vertical direction (z-axis direction) in the drawing with respect to the beam 48. Further, since the column 46 can move the surface plate 42 in the front-rear direction (y-axis direction) in the figure, the head 52 can also move in the y-axis direction.

  A high-precision scale 50 and a temperature sensor 60 are attached to the beam 48. The moving distance of the head 52 in the x-axis direction can be read with the scale 50, and the temperature sensor 60 detects and corrects the external environment temperature at the time of measurement, thereby correcting the temperature change of the beam 48, the scale 50, and the air. It is possible to eliminate errors caused by expansion and contraction. A similar configuration is also provided in other movement directions, and it is possible to read the movement distance with high accuracy in the z-axis and y-axis directions.

  The tracking laser interferometer is the same as that shown in FIG.

  Next, the principle of wavelength estimation will be described below.

  The coordinate measuring device 40 has a motion error caused by its straight running performance and the tilt during the motion of the mechanism constituting each axis. Therefore, a motion error occurs at each movement position in the measurement space. In order to observe this motion error, a tracking laser interferometer is generally used. However, the scale 50 used in the coordinate measuring apparatus 40 is originally highly accurate, further temperature-corrected and the like, and the error is not so large even in a relatively wide range. Here, when the scale 50 is mounted on the coordinate measuring device 40, the Abbe error due to the above-described motion error or the like occurs, and the position of the retroreflector 32 attached to the head 52 on the coordinate measuring device 40 is measured by the scale 50. It will shift from the position. However, this Abbe error occurs as unevenness of the scale 50 in a narrow range of the measurement space, but it can be considered that the average of the errors is almost zero in a relatively wide measurement space. Based on this idea, the tracking type laser interferometer is inversely calibrated with the reading position of the scale 50 as a reference without fixing the wavelength value, so that unreasonable distortion is not generated in the measured value. Therefore, it is possible to estimate the wavelength of the tracking laser interferometer by measuring the coordinates of a plurality of positions over the entire measurement space using both the coordinate measuring device 40 and the tracking laser interferometer and processing the result. Is possible.

  A specific estimation method will be described with reference to FIG. Although the schematic shapes of the main body 10 and the retroreflector 32 of the tracking laser interferometer are different from those in FIG. 2, they are simplified for the sake of illustration and have the same functions.

  The recursive reflector 32 is attached to the probe position on the head 52 of the coordinate measuring device 40 as a coordinate measuring device 40, and the main body 10 of the tracking type laser interferometer is installed on the surface plate 42 of the three-dimensional measuring device 40. Measure in

  Here, the reference point 12 in the main body 10 is (x0, y0, z0), and the position measured by the scale 50 is the position of the i-th recursive reflector 32 among a plurality of measurement times ( xi, yi, zi), the wavelength of the measurement light 14 to be estimated is λ, the count value of the tracking laser interferometer at the position of the i-th recursive reflector 32 is ni, and the initial offset distance is f. Then, the relational expression of Expression (1) is derived.

((xi-x0) ² + (yi-y0) ² + (zi-z0) ² ) ^1/2 = f + ni * λ (1)

  Here, (xi, yi, zi) and ni are obtained by measurement, but (x0, y0, z0), λ, and f are unknown. The values on both sides represent the distance between the reference point 12 and the position of the i-th recursive reflector 32.

  Then, by performing coordinate measurement and count value measurement a plurality of times in a sufficiently wide range of the measurement space, the equation (1) corresponding to the number of times of measurement is established, and by solving them as simultaneous equations, (x0, y0, z0), λ, and f can be estimated.

  The simultaneous equations can be solved using a general nonlinear least square method. For example, Gauss-Newton method, Marquardt method, hybrid method, and the like can be used. It is also possible to solve by the linear least square method by squaring both sides of the equation (1). For example, you may apply a solving method that establishes a normal equation such as Cholesky method or eigenvalue decomposition method, or you may use a solution by direct decomposition of Jacobian such as Gram-Schmidt method, Householder method, singular value decomposition method, etc. .

  Therefore, based on the above-described principle, the wavelength λ of the measurement light 14 can be accurately estimated with a very simple configuration, and high-accuracy measurement using a tracking laser interferometer is possible.

  At the same time, since it is not necessary to measure the external environment such as temperature for correcting the air refractive index, it is possible to significantly reduce the cost for expensive equipment.

  It is also possible to further improve the wavelength estimation accuracy by measuring a block gauge or the like separately set as a national standard and calibrating the expansion and contraction of the measurement space.

  As described above, in the present embodiment, the measurement space is three-dimensional, but the same wavelength estimation is possible in a two-dimensional or one-dimensional space. In this case, however, the reference point 12 of the tracking laser interferometer is measured in the same space as the measurement space. That is, in the two-dimensional case, the reference point 12 is included in the xy plane that is the measurement plane as shown in FIG. 4, and in the one-dimensional case, the reference point on the x-axis is shown in FIG. 12 need to be included. In this case, since the installation position of the main body 10 of the tracking type laser interferometer is limited, it takes time for installation, but a coordinate measuring device capable of measuring a three-dimensional space is not necessarily required. Wavelength estimation is possible with a simple device. At the same time, the number of measurement points can be reduced, and simultaneous equations can be easily solved.

  Although this embodiment assumes that the wavelength of the measurement light changes in the external environment, it is clear that the wavelength can be estimated by applying the present invention even when the wavelength is unknown. It is.

  Needless to say, the present invention is not limited to the case where the wavelength is unknown or the case of estimating the wavelength of measurement light that changes due to a change in the external environment, but can also be applied to periodic calibration of a tracking laser interferometer.

Schematic configuration diagram of a conventional tracking laser interferometer Schematic configuration diagram showing an embodiment of the present invention Schematic showing the arrangement of the main body of the tracking laser interferometer and the retroreflector in the same three-dimensional measurement space Schematic showing the arrangement of the tracking laser interferometer body and recursive reflector in a two-dimensional measurement space Schematic showing the arrangement of the tracking laser interferometer body and recursive reflector in a one-dimensional measurement space

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Main body 12 ... Reference point 14 ... Measuring light 20 ... Light receiver 26 ... Biaxial rotating mechanism 28 ... Control device 30 ... Measurement object 32 ... Recursive reflector 40 ... Coordinate measuring device 42 ... Surface plate 44 ... Portal-shaped Frame 46 ... Column 48 ... Beam 50 ... Scale 52 ... Head 60 ... Temperature sensor

Claims (4)

A recursive reflector for reflecting incident measurement light and returning it to the incident direction;
Means for emitting measurement light, light receiving means for receiving return light reflected and returned by the recursive reflector, and measuring light emission direction so that the distance between the optical axes of the measurement light and return light is always constant. A main body having emission direction control means for controlling,
In a tracking laser interferometer that outputs a count value according to an increase or decrease in the distance between a reference point in the main body and a retroreflector,
The recursive reflector is provided on a head on a coordinate measuring apparatus having a displacement direction of one axis or more that allows displacement to be read by a scale provided along the direction of displacement,
Displace the head to a plurality of positions, and output a measurement position by the scale and a count value according to the distance between the reference point and the recursive reflector,
The measurement at a plurality of positions is a relational expression determined by the measurement position, the count value, the reference point, the wavelength of the measurement light, and the initial offset distance that is the distance from the initial position of the recursive reflector to the reference point. Substituting position and count value,
A wavelength estimation method for a tracking laser interferometer, wherein the wavelength is estimated by solving simultaneous equations which are the simultaneous relational expressions.   2. The wavelength estimation method for a tracking laser interferometer according to claim 1, wherein the main body is provided on a surface plate of a coordinate measuring apparatus. The simultaneous equations comprise a relational expression that the distance obtained by adding the initial offset distance to the product of the count value and the wavelength is equal to the distance obtained from the reference point and the measurement position,
3. The tracking type laser interferometer wavelength estimation method according to claim 1, wherein the relational expression determined for each measurement position is made simultaneous.   The reference point is provided on the axis when the displacement direction of the moving body of the coordinate measuring apparatus is one axis, and within a plane constituted by the two axes when the displacement direction is two axes. The wavelength estimation method of the tracking type laser interferometer according to any one of claims 1 to 3.

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