JPH04319608A - Method and apparatus for measuring degree of straightness and displacement within plane by light beam - Google Patents

Abstract

PURPOSE:To measure the degree of straightness and the displacement within a plane highly precisely by using a laser light as a straight-line reference. CONSTITUTION:A laser light is divided into two parallel laser lights 208 and 209 being symmetric in dimensions with the direction of a directional change. The axis of symmetry of these two laser lights being used as a straight-line reference, adjustment is made by an optical system 203 so that the optical paths of the two laser lights be equal. The lights are made to enter two position detectors 205 and 206 fixed to a substance 204 to be measured and signals from these position detectors are computed.

Description

Detailed Description of the Invention [0001] [Industrial Application Field] The present invention uses a laser beam as a straight line reference to determine the straightness (the amount by which a straight part or stroke of a machine deviates from a true straight line). The present invention relates to a method and apparatus for measuring in-plane displacement (displacement in a plane perpendicular to a laser beam) with high precision. 2. Description of the Related Art Measuring the straightness of a laser beam using a semiconductor position detector has been widely put into practical use because a straight line reference of tens of meters or more can be easily set anywhere. However, in reality, the direction of the laser beam itself, which should be a straight line reference, changes irregularly due to thermal deformation of the laser beam generator, so highly accurate measurements cannot be expected. Conventionally, in order to solve this problem, the laser beam was divided into two beams, one of which was used as a straight line reference to measure the straightness, and the other one was used to measure the change in direction of the laser beam itself. A method of correcting the straightness measurement results has been proposed, and an example thereof is shown in FIG. In FIG. 6, a laser beam emitted from a laser beam generator 102 fixed on a table 101 is split into two parallel laser beams 105 and 106 by a half mirror 103 and a mirror 104. Further, a first semiconductor position detector 108 is fixed to the object to be measured 107, and a second semiconductor position detector 110 is fixed to the table 109, which is integrally structured with the table 101 and is located near the end of the movement stroke of the object to be measured. has been done. The object to be measured 107 moves in the direction of arrow A, and its straightness is different from that of the laser beam 105.
This measurement result includes an error due to a change in the direction of the laser beam. On the other hand, the laser beam 106 and the second semiconductor position detector 11
Since the change in the direction of the laser beam can be measured by 0, the error caused by the change in the direction of the laser can be corrected from the measurement result of the straightness. 111 is an arithmetic circuit. [0003] Furthermore, Japanese Patent Laid-Open No. 103362/1983 discloses that the light generated from the light beam generator is split into two by a prism.
Split the book into parallel light, receive one light on the reference plane,
A straightness measuring instrument is described in which the other light is received on a measurement surface, the difference between the signals obtained at each light receiving section is determined, and disturbances are removed. JP-A-60-203804 discloses a laser beam generator that generates two parallel laser beams from near one stroke end of a machine whose straightness is to be measured, and a laser beam generator which generates two parallel laser beams from near one stroke end of a machine whose straightness is to be measured. Consisting of a first detector that is provided and receives one of the lights, and a second detector that is provided near the other stroke end of the machine and receives the other light,
A straightness measuring device is described in which the two-dimensional position of a laser beam spot is detected by first and second detectors, and straightness is measured based on the outputs of these detectors. Further, Japanese Patent Application Laid-Open No. 63-95302 describes a pattern detection device that performs positioning in a semiconductor exposure device using laser light. [0004] In the conventional apparatus shown in FIG. 6, the relative positional relationship between the table 101 and the table 109 is not strictly accurate due to temperature changes and external vibrations of the entire apparatus. Since it is always changing, it is not possible to know only the direction change of the laser beam 106 from the output of the second semiconductor position detector 110. Therefore, it is impossible to completely correct the influence of the change in direction of the laser beam included in the straightness measurement results. This effect becomes more noticeable as the motion stroke of the object to be measured increases, and the straightness measurement accuracy deteriorates. [0005] Also, Japanese Patent Application Laid-Open No. 50-103362,
All of the straightness measuring devices described in Japanese Patent Application Laid-Open No. 60-203804 split a laser beam into two or more beams, use one of them as a straight line reference, measure the straightness of the object to be measured, and Measure pointing stability using a book,
By correcting the former with the latter, correct straightness is attempted. Therefore, as in the case of FIG. 6, there is a problem in that the accuracy of measuring straightness is low. Furthermore, the device described in Japanese Unexamined Patent Publication No. 63-95302 relates to a device for detecting pattern position, and has a different purpose and configuration from that for measuring straightness. The present invention has been made in view of the above points, and is an immobile device constructed using an optical system that can, in principle, cancel the influence of changes in the direction of laser light caused by thermal deformation of the laser light generating device. By using the straight line criterion of
It is an object of the present invention to provide a method and apparatus that can measure the straightness, in-plane change, etc. of an object that moves with a long stroke with high accuracy compared to conventional techniques. Means and Effects for Solving the Problems In order to achieve the above object, a method for measuring straightness and in-plane displacement using a light beam according to the present invention will be explained with reference to FIGS. 1 to 5. Then, the following processes (a) to (c), namely (a) the process of dividing the laser beam 207 into two parallel laser beams 208 and 209 whose direction and magnitude are symmetrical; ,(
b) The two position detectors 2 fixed to the object to be measured 204 are adjusted so that the optical path lengths of the two laser beams are equal, using the symmetry axis of the two divided laser beams as a linear reference.
05 and 206, and (c) a process of calculating signals from the two position detectors. In the method of the present invention, since the two signals obtained from the two position detectors correspond to the two-dimensional position of the laser beam incident on each position detector, by calculating the two signals, the laser beam It is possible to measure straightness and in-plane displacement by utilizing the straightness of the laser beam and, in principle, without being affected by changes in the direction of the laser beam. [0007] The straightness and straightness of the light beam of the present invention are
The in-plane displacement measuring device will be described with reference to FIGS. 1 to 5. It includes a laser beam generator 202 that generates a laser beam that serves as a linear reference, and a laser beam that generates a laser beam with a direction change direction and magnitude. an optical system 203 that divides into two symmetrical parallel laser beams 208 and 209 and adjusts the optical path lengths of the two laser beams to be equal; and a light receiving surface on which each of the two laser beams enters. two position detectors 205 and 206 fixed to the object to be measured 204, and an arithmetic circuit 21 for calculating outputs from the two position detectors.
It is characterized by including 0 and . As the position detector, for example, a semiconductor position detector, a 4-segment photosensor, a PSD (position detection element), etc. are used. The direction of the laser beam emitted from the laser beam generator 202 is constantly changing due to thermal deformation of the device 202, etc., but there are two laser beams 208 whose direction and magnitude of this change are symmetrical. , 209 are fixed. Therefore, the present invention uses the above-mentioned axis of symmetry as a linear reference, thereby making use of the straightness of the laser beam and making it possible to measure the straightness without being affected by changes in the direction of the laser beam. The laser beam emitted from the laser beam generator 202 is divided into two laser beams 208 and 209 whose direction change and magnitude are symmetrical. Two semiconductor position detectors 205 and 206 are fixed to an object to be measured 204 whose straightness of linear motion is to be measured. The above two laser beams are incident on these two semiconductor position detectors, and signals S1,
S2 is output respectively. Average value of these two signals A=
(S1+S2)/2 represents the position of the symmetry axis of the two laser beams. Therefore, by detecting the change in the average value A, the symmetry axis of the two laser beams is used as a straight line reference, and as a result, straightness measurement can be performed that is completely unaffected by changes in the direction of the laser beams. DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However, unless there is a specific description, the shapes of the components described in this embodiment, their relative positions, etc. are not intended to limit the scope of the present invention to these, but are merely illustrative examples. It's nothing more than that. As shown in FIG. 1, a table 201 includes a laser beam generator 202, a laser beam 207 emitted from the laser beam generator 202, and two parallel laser beams 208, 209.
The object to be measured 204 whose straightness of motion in the direction of arrow B is to be measured is provided with an optical system 203 that divides the
semiconductor position detectors 205, 206 are fixed. The arithmetic circuit 210 includes semiconductor position detectors 205 and 206.
The average value A of the outputs S1 and S2 is output. Optical system 2
03 has at least the following three functions. The first is the function of splitting the laser beam 207 into two nearly parallel laser beams 208 and 209, and the second is a symmetrical direction change in the two laser beams 208 and 209 when a direction change occurs in the laser beam 207. The third function is to equalize the optical path lengths L from when the laser beams 208 and 209 are emitted from the laser beam generator 202 until they are incident on the semiconductor position detectors 205 and 206, respectively. FIG. 2 shows an example of the optical system 203, and FIG.
shows another example of the optical system 203 configured with a prism 211. In FIG. 2, a laser beam 207 is converted into two laser beams 208 and 209 by a half mirror 301.
It is divided into The laser beam 208 further passes through a mirror 30.
2, 303 and is reflected by the semiconductor position detector 205
(See Figure 1). The laser beam 209 is adjusted by mirrors 304 and 305 so that it is substantially parallel to the laser beam 208 and has the same optical path length, and then is emitted toward the semiconductor position detector 206 (see FIG. 1). Here, when the laser beam 207 changes direction by an angle θ, the laser beams 208 and 209 change direction symmetrically to each other, and as shown in FIG.
As shown in , the position changes of the laser beams on the semiconductor position detectors 205 and 206 are -Lθ and Lθ, respectively, and the change in the signal from the semiconductor position detectors 205 and 206 corresponding to these position changes ΔS1=- nLθ, ΔS2=
nLθ=−ΔS1 (n is a coefficient representing the relationship between the incident position of the laser beam and the output of the semiconductor position detector) is output. Therefore, the change in the output of the arithmetic circuit 210 becomes ΔA=0. Furthermore, as shown in FIG. 5, when the straightness error X of the object to be measured 204 is added, the change in the output from the arithmetic circuit 210 becomes ΔA=nX, and is completely unaffected by the direction change θ of the laser beam. , it is possible to obtain a signal representing only straightness. Although FIGS. 1, 2, 4, and 5 illustrate straightness measurement in a plane in order to facilitate explanation of the principle of the present invention, this principle also applies to straightness measurement in space. Needless to say. Further, as described above, the optical system 203 can also be configured with a prism. [0011] Since the present invention is constructed as described above, it produces the following effects. (1) Since changes in the direction of the laser beam are theoretically canceled by optical means, it is possible to set an immovable straight line standard, making it easier to measure straightness and in-plane changes compared to conventional methods. It is possible to significantly improve accuracy. (2) According to the present invention, since it is completely unaffected by changes in the direction of the laser beam, it is possible to measure the straightness of a linear motion of several tens of meters or more with high accuracy on the order of submicrons. (3) Since one laser beam is divided into two parallel laser beams and their symmetry axes are used as a straight line reference, there is no effect of pointing stability as in the prior art. By using two position detectors, measurements can be carried out quickly and continuously.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of equipment layout showing an embodiment of a straightness/in-plane displacement measuring device using a light beam according to the present invention.

FIG. 2 is an explanatory diagram showing an example of an optical system used in the present invention.

FIG. 3 is an explanatory diagram showing an example in which an optical system for spatially applying the present invention is configured using a prism.

FIG. 4 is an explanatory diagram showing a state in which the direction of laser light has changed in FIG. 1;

FIG. 5 is an explanatory diagram showing a state in which the direction of the laser beam changes in FIG. 1, and the object to be measured further becomes out of straightness.

FIG. 6 is an explanatory diagram showing an example of a conventional straightness measuring device.

[Explanation of symbols]

101 Table 102 Laser light generator 103 Half mirror 104 Mirror 105 Laser light 106 Laser light 107 Object to be measured 108 First position detector 109 Table 110 Second position detector 111 Arithmetic circuit 201 Table 202 Laser light generator 203 Optical system 204 Object to be measured 205 Position detector 206 Position detector 207 Laser light 208 Laser light 209 Laser light 210 Arithmetic circuit 211 Prism 301 Half mirror 302 Mirror 303 Mirror 304 Mirror 305 Mirror

Claims (2)

[Claims] Claim 1: Processes (a) to (c) below, namely (a) converting the laser beam (207) into two parallel laser beams (208) whose direction and magnitude are symmetrical;
, (209) The process of dividing into (209), (b) the divided 2
Using the axis of symmetry of the laser beam of the book as a straight line reference, adjust the optical path length of the two laser beams to be equal, and adjust the optical path length of the two laser beams to be equal.
4), two position detectors (205) and (20
6) A method for measuring straightness and in-plane displacement using a light beam, comprising the steps of: (c) calculating signals from the two position detectors. 2. A laser beam generator (202) that generates a laser beam serving as a straight line reference;
an optical system (208) and (209) that adjusts the optical path lengths of the two laser beams to be equal;
3), two position detectors (205) and (206) fixed to the object to be measured (204), each having a light-receiving surface on which the two laser beams are incident, and the two position detectors (206); an arithmetic circuit (210) for calculating the output from the device;
A device for measuring straightness and in-plane displacement using a light beam, characterized by including the following.