JP2005351863A - Measurement method of surface shape - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make measurements of surface shapes with higher accuracy, by avoiding reduction of measurement accuracy affected from undulation and bending of a linear guide, as well as vertical motions during transit time of a sliding block moving along this linear guide, in a technique for measuring the surface of measured things, such as lapping surface plate with high accuracy by moving contact-type or noncontact-type length sensors along the surface of measured bodies. <P>SOLUTION: An oppositely placed image 7 and one side of an imager system 6, such as cameras are arranged at a fixed position, while another side is forced to move along the surface of measured bodies 2. During this movement, by obtaining the image 7 as plurality of image information with the imager system 6; and by assessing displacement of the reference point in these images at accuracy below pixel unit of the image information concerned, the surface shape of the measured bodies can be measured as a reference with respect to the image or the imager system arranged at the fixed position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for measuring the surface shape of an object to be measured by moving a contact type or non-contact type length sensor along the surface of the object to be measured. For example, the present invention relates to a lapping surface plate or a polishing plate. More particularly, the present invention relates to a measurement method suitable for high-precision measurement of the shape of a large-diameter surface plate or a long flat surface.

  Conventional surface shape measurement is performed by a method of scanning the surface of an object to be measured with a contact or non-contact sensor mounted on a slider that moves along a linear guide. (For example, Patent Document 1). In this method, since the shape of the surface is measured with reference to the slider that moves the sensor, the movement accuracy of the slider has an influence on the measurement accuracy. Therefore, the measurement result of the surface shape of the object to be measured includes a slider movement error.

  However, in measuring the surface shape of a lapping surface plate or the like, measurement with accuracy exceeding the parallelism of the linear guide itself is required. In addition, when measuring the surface shape of a large-diameter lap surface plate, high-precision measurement is difficult due to the influence of linear guide bending and deflection. Patent Document 2 discloses a mechanism for moving a measuring device for measuring the reference surface in parallel with the measurement surface based on a wire or thin plate having a small cross-sectional area, distance information to the measurement surface or the reference surface, and calculation. There has been proposed a method for obtaining the flatness and the surface shape by using the amount of deflection by the weight of the reference surface obtained by the above and the amount of horizontal movement with respect to the measurement surface.

On the other hand, it is conceivable to perform high-precision measurement of the surface of the surface plate by correcting the vertical position of the sensor due to the waviness or deflection of the linear guide with reference to laser light projected in parallel with the linear guide. In this case, a signal processing method is required that can measure the displacement of the laser light receiving element due to the swell or deflection of the linear guide with high resolution on the basis of the height of the laser light. However, this method is difficult to realize in the array signal processing in which the analysis is performed based on the reception phase difference because the speed of the laser light is extremely high.
JP 2001-41732 A Japanese Patent Laid-Open No. 2003-322520

  As described above, in the conventional technology, the influence of the movement accuracy of the length sensor that measures the shape of the surface of the object to be measured cannot be ignored, and the displacement of the sensor when moving along the linear guide affects the measurement accuracy. It has become an obstacle to high-precision measurement.

  The present invention avoids a decrease in measurement accuracy due to the influence of waviness and deflection of the linear guide and the vertical movement during the movement of the slider that moves along the linear guide, and can perform more accurate surface shape measurement. The task is to obtain a measurement method.

  In the present invention, one of the facing image 7 and the camera or other image acquisition device 6 is set at a non-moving position, and the other is moved along the surface of the object 2 to be measured. By acquiring the image 7 as a plurality of pieces of image information and evaluating the change in the position of the reference point in these images with an accuracy equal to or less than the pixel unit of the image information, the image or the image acquisition device installed at the fixed position is used as a reference. Measure the surface shape of the measured object.

  In general, a contact type or non-contact type length sensor 5 or 16 that measures the surface of an object to be measured is mounted on a slider 4 that is guided and moved by a linear guide 3. Preferably, a fixed image 7 is installed on the extension of the moving direction of the slider 4, a camera 6 is attached to the contact sensor or slider, and a plurality of pieces of image information are acquired by photographing the fixed image 7 with the camera 6. Thus, the reference point 13a in the image is calculated with an accuracy of a pixel unit or less. By acquiring image information each time the positions of the sensors 5 and 16 are changed along the linear guide 3, a change in the position of the reference point 13a among a plurality of pieces of image information is caused by a change in the surface shape of the object to be measured or the slider. It becomes equal to the straight line error, and high-precision surface shape measurement or correction becomes possible.

  The installation positions of the camera and the image may be reversed. That is, the image 7 may be provided on the probe 5 or the slider 4 serving as a length sensor, and the camera 6 may be installed at a fixed position that is not affected by the movement of the slider.

  As can be understood from the above, in the surface shape measuring method according to the invention of claim 1 of the present application that solves the above-described problem, one of the facing image 7 and the image acquisition device 6 is installed at a fixed position, and the other is fixed. The probe is mounted on a probe 5 mounted on a slider 4 that moves along a plane or straight line that is substantially parallel to the surface of the object 2 to be measured, and the tip of the probe is placed on the surface of the object to be measured at a plurality of positions as the slider moves. The amount of deviation between the pieces of image information of the plurality of images acquired by the image acquisition device in the contact state is detected.

  Further, the surface shape measuring method according to the second aspect of the present invention is such that the shape of the surface is measured by the length sensors 5 and 16 mounted on the slider 4 that moves along a plane or straight line substantially parallel to the surface of the object 2 to be measured. In the surface shape measurement method for measuring the image, one of the facing image 7 and the image acquisition device 6 is installed at a stationary position and the other is installed on the slider, and the image acquisition device acquires the images at a plurality of positions as the slider moves. The measurement value of the length sensor is corrected by detecting a shift between the plurality of images.

  According to the present invention, it is possible to provide a surface shape measuring device that is not affected by the movement accuracy of the slider 4. Conventionally, the focus has been on increasing the movement accuracy of the slider 4, but in the present invention, since the movement accuracy of the slider 4 is not affected, the movement accuracy of the slider 4 can be reduced even when manufacturing the apparatus. Since it is not necessary to consider so much, by adopting the method of the present invention, an inexpensive and highly accurate surface shape measuring device can be provided.

  FIG. 1 schematically shows a first embodiment of the present invention, in which 1 is a measuring table, 2 is a lapping surface plate (object to be measured) placed on the measuring table 1, and 3 is a lapping surface plate 2. 4 is a slider that moves along the linear guide 3, and 5 is a probe (length sensor) that is supported by the slider 4 so as to be movable up and down and whose tip is in contact with the upper surface of the lap platen. ), 6 is a camera mounted on the probe 5 with the front of the slider 4 in the moving direction, and 7 is a non-moving image installed at a fixed position in front of the camera 6.

Next, a method for measuring the surface shape of the surface plate 2 using the apparatus shown in FIG. 1 will be described.
(1) A camera 6 serving as an image acquisition device captures a fixed-position screen or object serving as a non-moving image 7 while the probe 5 moves in the guide direction.
(2) The coordinates of a specific point serving as a measurement base point in the image captured by the camera 6 are calculated by an image processing algorithm.
(3) The procedures (1) and (2) are repeated every time the slider 4 moves at a predetermined interval.
(4) Regarding the coordinates of the measurement base point of (2) obtained by the image processing, the change in the coordinates of the measurement base point accompanying the movement of the probe 5 in the guide direction is equal to the vertical displacement of the probe 5, and therefore The change becomes the surface shape of the surface plate 2.

As the image processing algorithm used in the above (2), known image processing algorithms such as normalized correlation and incremental code correlation can be used. The inventor of the present application used the straight line intersection image as the immovable image and the Hough transform as the image processing algorithm to test the measurement accuracy of the surface shape by the method of the present invention. The test method will be described below with reference to FIG.
(1) A screen in which a fine moving base 12 capable of accurately measuring the amount of movement with a micrometer 11 is installed in front of the camera base 10 and two straight lines 13 that obliquely intersect the surface of the fine moving base facing the camera base 10 are drawn. 7 is pasted.
(2) The camera 6 is mounted on the camera base 10 toward the fine movement base 12, the screen 7 is photographed by the camera 6, and the obtained image data is taken into the personal computer 15.
(3) The coordinates of the intersection 13a in the image are calculated by the personal computer 15 using the Hough transform from the captured image.
(4) The fine moving base 12 is moved by a predetermined amount, the screen 7 is captured again by the camera 6, and the image is taken into the personal computer 15.
(5) The captured image is analyzed by the Hough transform, and the relationship between the amount of movement (μm) of the fine movement table and the amount of movement (pixel) of the intersection in the image is obtained.

  It was confirmed by the image analysis using the Hough transform that the amount of movement of the intersection 13a of the image can be measured with 0.1 pixel accuracy. When an element of 4 million pixels is used as an image sensor of a camera, the minimum resolution is 2.5 μm. Furthermore, by using known sub-pixel image processing as high-precision image processing, it is possible to further enlarge the pixel by about 20 times. By using this, measurement accuracy of the order of 0.1 μm can be obtained.

  In FIG. 1, a camera 6 is attached to a probe 5 mounted on a slider 4, and a non-moving image 7 is taken with this camera. Since this method directly measures the movement of the probe 5 that moves up and down according to the surface shape of the surface plate 2, as described above, the coordinate change of the measured intersection 13a becomes the measured value of the surface of the surface plate 2 as it is. The same applies when the camera 6 and the image 7 are reversed, that is, when the image 7 is attached to the probe 5 and the camera 6 is set at a fixed position.

  On the other hand, when the camera or the image is attached to the slider, the surface plate surface is measured with high accuracy by correcting the measurement value of the length sensor with the image shift amount detected by the method of the present invention. When a non-contact type sensor is used as the length sensor, there is no member that moves up and down following the shape of the surface of the surface plate, so this correction method is used.

  FIG. 3 is a diagram showing an example in which the moving image 7 is attached to the slider 4 using the immobile camera 6 and the moving image 7.

Next, a method for measuring the surface shape of the surface plate 2 with the apparatus shown in FIG. 3 will be described.
(1) The moving image 7 attached to the slider 4 is picked up by the stationary camera 6 as the slider 4 moves in the guide direction. At the same time, the measurement value of the length sensor 16 is read.
(2) The coordinates of a specific point serving as a measurement base point in the digital image captured by the stationary camera 6 are calculated by an image processing algorithm.
(3) The procedures (1) and (2) are repeated every time the slider 4 moves at a predetermined interval.
(4) The value obtained by correcting the measurement value of the length sensor 16 accompanying the movement of the slider 4 in the guide direction by the change in the coordinates of the measurement base point (2) at the time of the measurement is the surface shape of the surface plate 2. Become.

  In the case of the configuration in which the camera 6 and the image 7 in FIG. I do.

The figure which shows 1st Embodiment Figure showing a measurement accuracy confirmation test and an example of the image used for this The figure which shows 2nd Embodiment

Explanation of symbols

2 Object 3 Linear guide 4 Slider 5 Probe (contact type length sensor)
6 Camera 7 Image
15 Personal computer (image processing device)
16 Non-contact type length sensor

Claims (2)

  One of the opposing image (7) and image acquisition device (6) is placed at a fixed position, and the other is mounted on a slider (4) that moves along a plane or straight line that is substantially parallel to the surface of the object to be measured (2). The image information of the plurality of images acquired by the image acquisition device in a state where the tip of the probe is in contact with the surface of the object to be measured at a plurality of positions accompanying the movement of the slider. A surface shape measurement method that detects the amount of mutual displacement.   In the surface shape measurement method that measures the shape of the surface with a length sensor (5, 16) mounted on a slider (4) that moves along a plane or straight line that is substantially parallel to the surface of the object to be measured (2), One of the image (7) and the image acquisition device (6) to be installed is set at a non-moving position and the other is set to the slider, and a plurality of the images acquired by the image acquisition device at a plurality of positions accompanying the movement of the slider A surface shape measurement method comprising correcting a measurement value of the length sensor by detecting a shift between images.

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