JP2013181817A - Surface shape measurement method and instrument thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and instrument capable of measuring a surface shape while holding contact force in a constant state by adjusting the contact force between a sensor contact part and a measurement object in measurement of the surface shape of a minute object using a contact type displacement sensor or the like.SOLUTION: A measuring instrument 11 scans a surface of an object 22 to be measured while bringing a tip of a stylus 20 into contact with the surface, and acquires a surface shape of the object 22 to be measured by measuring displacement of the stylus 20 at that time. Then, the contact force between the stylus 20 and the object 22 to be measured during measurement is adjusted by a counterbalance, and the surface shape of the object 22 to be measured is accurately measured and evaluated while maintaining a state where the contact force is extremely reduced.

Description

  The present invention relates to a measuring method and apparatus for maintaining a constant contact force by reducing a load applied to an object to be measured by a stylus in surface shape measurement using a contact-type displacement sensor. It can be applied not only to three-dimensional precision shape measuring machines, but also to on-machine shape measuring instruments mounted on machine tools.

  Surface shapes that have been subjected to precision machining in precision molds, optical instruments, and the like are important factors that determine their performance, and shape measurement is indispensable for evaluating machining accuracy and ensuring performance.

  Conventionally, a contact-type shape measuring machine or a stylus-type shape measuring machine using a stylus having a sharp tip has been used for surface shape measurement. In a conventional contact-type shape measuring device and stylus-type roughness meter, the stylus is scanned over the measurement object while maintaining contact between the stylus tip and the surface of the measurement object, and the stylus displacement at that time Is measured by the sensor, and the surface shape of the object to be measured is measured.

  In the conventional contact-type shape measuring machine and stylus-type roughness meter, when measuring the surface shape, the contact between the stylus tip and the surface of the object to be measured is the stylus's own weight (for example, Patent Document 1). ). However, in maintaining the contact state with the object to be measured by the stylus's own weight, the load applied to the object to be measured depends on the stylus mass, and it is difficult to adjust the contact force.

  In the conventional contact-type shape measuring machine and the stylus-type roughness meter, the contact between the stylus tip and the measurement surface is maintained using a load applied by a spring (for example, Non-Patent Document 1). In these devices, one end of the stylus is fixed by a spring so that a load is applied to the stylus and brought into contact with the surface to be measured, and the contact force can be adjusted by changing the spring constant. However, in the stylus that maintains the contact state with the object to be measured by the spring, the contact force increases with an increase in the displacement of the stylus, so that deformation or damage of the object to be measured becomes a problem.

  In the shape measurement using the conventional contact type shape measuring machine and stylus type roughness meter, the stylus is held by the slide bearing and the tip is inclined from the vertical direction as a method of reducing the contact force applied to the measurement object. Has been proposed (see, for example, Non-Patent Document 2). By tilting the stylus, the gravitational load applied to the object to be measured can be reduced. However, since the contact force applied to the object to be measured changes depending on the angle at which the stylus is inclined, it is difficult to keep the contact force constant.

  Further, in the conventional contact type shape measuring machine and stylus type roughness meter, a magnetic bearing using a stylus bias coil is used as a method for reducing the load on the surface of the object to be measured and keeping the contact force constant. (For example, Non-Patent Document 3) and a method for holding by vacuum suction (for example, see Non-Patent Document 4). These can detect a very weak contact force by holding the stylus by magnetic force or vacuum suction. However, the configuration of these stylus holding mechanisms is complicated and large, and it is difficult to mount on a processing machine and perform on-machine measurement.

  In addition, in the conventional contact-type shape measuring machine and stylus type roughness meter, when the shape measuring machine is mounted on the processing machine and the measurement object is measured on the machine, the spatial constraints on the processing machine. Therefore, it is desirable that measurement can be performed with the tip of the stylus inclined not only in the vertical direction but also at an arbitrary angle.

JP 2005-147746 A

KW Lee, YJ Noh, W. Gao, Y. Arai, Y. Shimizu, K. Tanaka, M. Fukuta, and Y. Kai: Experimental investigation of an air-bearing displacement sensor for on-machine surface form measurement of micro- structures, Int. J. Precis. Eng. Manuf., Vol. 12, pp. 671-678, 2011. P. A. McKeown, W. J. Wills-Moren, and R. F. Read: In-Situ Metrology and Machine Based Interferometry for Shape Determination, Proc.SPIE, Vol. 802, 1987. H. Shinno, H. Yoshioka, T. Gokan, and H. Sawano: A newly developed three-dimensional profile scanner with nanometer spatial resolution, CIRP Annals -Manufacturing Technology, Vol. 59, pp. 525-528, 2010. Oswart Horikawa, Koji Sato, Akira Shimokawabe: Journal-type active bearing (2nd report) -Examination of shape characteristics and absolute rotational motion accuracy-, Journal of Japan Society for Precision Engineering, Vol. 58, pp. 1047-1052, 1992.

  Therefore, in the present invention, by holding the stylus with a counterweight, the contact force between the object to be measured and the tip of the stylus is reduced, and a surface shape measurement method that keeps the contact force constant regardless of the displacement of the stylus is realized. To do. Moreover, the apparatus of the structure which can maintain the contact force with to-be-measured object constant irrespective of the inclination from the perpendicular direction of a stylus is provided.

  According to the present invention, a surface shape measuring method using a contact sensor, which is a shape measuring device including a stylus used for measuring a surface shape, a counterweight and a sensor for measuring displacement, is obtained. The stylus is fixed to one end of the shaft, and the other end of the shaft is connected to a counterweight by a wire and supported through a fixed pulley. The mass of the counterweight is set equal to or slightly lighter than the mass of the shaft. Since the shaft is supported by the counterweight, the contact force applied to the surface of the object to be measured is reduced as compared with the case where the stylus is in contact with the vertical direction. The contact state between the stylus tip and the object to be measured is maintained by the difference in mass between the stylus and the shaft and the counterweight. The mass of the counterweight is slightly smaller than that of the shaft on which the stylus is attached, so that the tip of the stylus is kept in contact with the surface to be measured by the gravity load of the shaft itself attached with the stylus. While maintaining the contact state between the stylus and the object to be measured, the surface shape is measured by scanning the surface of the object to be measured in the horizontal direction and measuring the displacement of the stylus with a sensor.

  In addition, according to the present invention, there is provided a shape measuring apparatus that is a surface shape measuring method using a contact sensor, and includes a stylus held by an air bearing. The shaft to which the stylus is fixed is held by an air bearing, and the shaft can move in the casing without being affected by friction due to contact with the casing. Since this shaft floats in the casing by the compressed air of the air bearing, even if the shaft is inclined, a non-contact state can be maintained between the shaft and the casing. Therefore, even when the stylus is tilted, the stylus can be displaced without being affected by the friction between the shaft and the casing. Can be measured.

  Furthermore, according to the present invention, there is provided a method for measuring a surface shape using a contact sensor, wherein the displacement of the stylus is measured by a non-contact displacement sensor such as an optical linear encoder, so that the stylus and the shaft can be measured. It is possible to obtain a shape measuring apparatus characterized in that the stylus displacement can be measured without interfering with the moving displacement.

  According to the present invention, by controlling the contact force between the stylus and the object to be measured to be constant, the load applied to the object to be measured by the stylus tip can be reduced, and there is no damage or deformation of the stylus and the object to be measured. The effect that the three-dimensional surface of the surface of the measuring object can be measured using the stylus displacement detected by the displacement sensor using the optical linear encoder is obtained.

Schematic of the adjustment method and apparatus of stylus contact force using the counterweight concerning this invention. 1 is a schematic view of a surface shape measuring apparatus according to the present invention. The schematic diagram showing the structure of a counterweight. The figure which displayed the relationship between the amount of axial movements of a stylus, and contact force. The figure which displayed the shape measured from the displacement of the stylus.

  An embodiment according to the present invention will be described in detail with reference to FIGS. FIG. 1 shows a schematic diagram of a method and apparatus for adjusting the contact force of a stylus according to the present invention. The stylus 20 is fixed to one end of a shaft 21, and the other end of the shaft 21 is connected to a counterweight 29 by a wire 25. The mass of the counterweight 29 is set equal to or slightly less than the total mass of the stylus 20 and the shaft 21. A wire 25 between the shaft 21 and the counterweight 29 is suspended from the fixed pulley 23. The stylus 20 is kept in contact with the surface of the measurement object 22 by its own weight. In the present invention, since the weight of the stylus 20 and the shaft 21 is supported by the counterweight 29, the contact force applied to the object to be measured by the stylus can be reduced. Further, since the stylus is held by the counterweight 29 via the wire 25, the contact force does not change due to the displacement unlike the spring, and the contact applied to the object to be measured by the stylus regardless of the displacement in the Z direction. The force can be constant.

  FIG. 2 is a schematic view of the surface shape measuring apparatus 11 according to the present invention. The stylus 20 is fixed to one end of the shaft 21, and the tip of the stylus 20 is also brought into contact with the surface of the measurement object 22. The stylus 20, the shaft 21 and the air bearing 27 shown in FIG. 10 are mounted on the tilt stage 33. The shaft 21 is connected to the counterweight 12 by the wire 25 through the fixed pulley 23 and the fixed pulley 36. The shaft 21 is held by a shaft holding air bearing 27 fixed inside the shaft casing 26. The shaft 21 can be moved in the long axis direction without being affected by friction by being held by the air bearing. A load is applied to the tip of the stylus 20, and the shaft 21 moves in the long axis direction. The movement displacement of the shaft 21 is measured by an optical linear encoder 28.

  A shaft holding casing 26 containing the stylus 20 and the shaft 21 is attached to the tilt stage 33. As a result, the tip of the stylus can be inclined at an arbitrary angle with respect to the Z direction, and the tip of the stylus 20 is brought into contact with the surface of the object 22 to be measured not only in the vertical direction but also from the oblique direction. It can be measured. The fixed pulley 23 is mounted on an inclined stage, and holds the position of the wire 25 so that the central axis of the shaft 21 and the wire 25 are always arranged in a straight line.

  From here, a description will be given of a method for adjusting the contact force between the stylus 20 and the object 22 to be measured. The contact force at the tip of the stylus 20 can be adjusted by the difference between the total mass of the stylus 20 and the shaft 21 and the mass of the counterweight 12. FIG. 3 shows details of the configuration of the counterweight 12. The counterweight 12 includes a counterweight shaft 33 and an adjustment weight 34. One end of the counterweight shaft 33 is connected to the shaft 21 by a wire 25. Also, the inside of the counterweight shaft 33 has a hollow structure, and the total mass of the counterweight can be adjusted by adding an adjustment weight 36 inside. The counterweight shaft 34 is also held by a counterweight-holding air bearing 33 fixed in the counterweight portion casing 37 to prevent the counterweight from swinging and to be smoothly displaced in the Z direction. .

  In a state where the mass of the counterweight is adjusted and the contact force between the tip of the stylus 20 and the measurement target 22 is adjusted, the measurement target 22 is moved in the X and Y directions by the XYZ axis positioning stage 30. The surface shape is precisely measured by measuring the movement displacement of the shaft 21 at that time by the optical linear encoder 28 accommodated in the shaft holding casing.

  The load applied to the non-measurement object 22 by the stylus 20 is measured by the load cell 31 mounted on the XYZ axis positioning stage. FIG. 4 shows the load measured using the load cell 31 when a displacement is applied in the Z-axis direction using the XYZ-axis positioning stage. The tip of the stylus is arranged perpendicular to the XY plane. It can be seen that even when a displacement in the Z direction is applied, the load applied to the load cell 31 is maintained substantially constant without increasing due to the displacement as in the case of a spring. The arrows in FIG. 4 indicate the measurement range of the stylus of the present invention, and it is possible to keep the contact force substantially constant in the range of the stylus displacement from the contact with the object to be measured to 1.5 mm. Show. However, the contact force varies depending on the displacement of the stylus in the Z direction and the number of measurements, and further improvement is necessary to keep the contact force constant.

  FIG. 5 shows the result of measuring the shape with a stylus using the contact force adjusting method of the present invention. In FIG. 5, the surface shape was measured with a stylus using a steel ball having a diameter of 4.7 mm as an object to be measured. The stylus was arranged perpendicular to the Z direction, and the displacement of the stylus in the Z direction when the object to be measured was translated in the Y-axis direction while being in contact with the surface of the steel ball was measured with a linear encoder. In FIG. 5, the measurement result of the stylus displacement shows repeatability when the Y-direction displacement of the stage is 1.75 mm, that is, near the apex of the steel ball, but the measurement result of the stylus displacement varies as the distance from the apex is increased. Can be seen. This variation in the measurement position needs to be improved in the future.

  By using the present invention, it is possible to observe the surface shape of the processing surface on the precision processing machine on the spot and feed back the measured processing shape information to the processing machine to correct the shape in real time. Therefore, it is possible to improve the precision and reproducibility of microfabrication.

10 Outline of Adjustment Method of Contact Force by Counterweight in the Present Invention 11 Configuration of Measuring Machine Used for Measuring Surface Shape in the Present Invention 12 Counterweight 20 Stylus 21 Shaft 22 Measurement Object 23 Constant Pulley 24 Constant Pulley 25 Wire 26 Shaft Holding casing 27 Shaft holding air bearing 28 Optical linear encoder 29 Balance weight 30 XYZ-axis positioning stage 31 Load cell 32 Coarse movement Z-axis stage 33 Inclination stage 34 Balanced weight shaft 35 Balanced weight holding air bearing 36 For adjustment Weight 37 Balanced weight part casing

Claims (3)

  A method for measuring the surface shape of a structure that has undergone ultra-precise machining using a contact-type profilometer, comprising a stylus that contacts the surface of the object to be measured, and a counterweight for adjusting the contact force of the stylus The mass of the stylus and the counterweight is approximately the same, these are connected via a fixed pulley, and the contact force due to the gravity load of the stylus applied to the object to be measured causes the mass of the counterweight to be equal to or slightly the same as the stylus part. A surface shape measuring method characterized in that it can be reduced by adjusting it to a small value.   A method for measuring the surface shape of structures that have been precision processed in the production of precision molds, optical instruments, etc., where the stylus is attached to a shaft supported by an air bearing, and the tip of the stylus contacts the object to be measured In a state where the state is maintained, by scanning in the horizontal direction and measuring the displacement of the shaft in which the stylus is fixed at this time using a non-contact type displacement measuring sensor such as an optical linear encoder, 2. A surface shape measuring apparatus for carrying out the measuring method according to claim 1, wherein the shape of the surface of the object to be measured is measured.   The surface shape measuring apparatus according to claim 2, wherein the stylus held by the air bearing is held by a counterweight, so that the contact force is kept constant regardless of the displacement and inclination of the stylus.

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