JP2011209034A - Measurement method by laser displacement gauge, and circuit for controlling the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simply and accurately inspect a surface condition of a target of measurement by means of a laser displacement gauge, without presetting measurement information.SOLUTION: There are disclosed a measurement method by a laser displacement gauge for inspecting the surface condition of a target 1 of measurement includes steps of placing the laser displacement gauge 3 on a moving stage 4, in a Z-direction having a linear encoder 5 mounted; and moving the moving stage 4 in the Z-direction via the linear encoder 5 so that the voltage output at a position level of d/2 in a length measuring range d is always 0 V so that the distance D between the surface of the target 1 and the laser displacement gauge 3 is kept constant. A circuit for controlling the method is also disclosed.

Description

  The present invention relates to a laser displacement meter for inspecting the surface condition of a certain sample.

For example, in order to measure the height unevenness at 0.1 mm formed on the surface of a lens with high curvature, an interferometer has been used in the past, but a laser displacement meter is used because it is extremely expensive. It is becoming. Laser displacement meters are used for inspection of the surface condition of many industrial products because of their advantages such as high measurement resolution and non-contact.

As is well known, a laser displacement meter measures a length by scanning a laser beam from a semiconductor laser on a measurement object and measuring the intensity of the reflected beam as a voltage value with a light receiving element. Depending on the displacement meter, if the length measurement resolution is to be obtained high, the side length range is narrowed, and if the side length range is to be widened, the side length resolution is lowered.

That is, in some apparatus A, the side length range is ± 0.3 mm, but the length measurement resolution is required to 0.01 μm, whereas in some apparatus B, the side length range is ± 5.3 mm, but the length measurement resolution is However, it cannot be measured when the thickness of the measured object exceeds the lateral length range.

FIG. 1 is an extreme representation of the convex portion 2 on the surface of the measuring object 1, and the distance D from the laser displacement meter 3 to the measuring object 1 is fixed. In the state of FIG. The laser beam is reflected at the level a position. The measurement range d of the laser displacement meter 3 here is from level a to level b, and the form of level a can be measured.

However, from the state of FIG. 1A, an XY stage (not shown) on which the measurement object 1 is mounted is operated to scan in the X direction, for example, and when the state of FIG. The range of height (thickness) exceeding b cannot be measured because it is outside the measurement range d.

Therefore, conventionally, a means has been adopted in which the laser displacement meter 3 is mounted on a movable stage 4 that can move in the Z direction to compensate for the length measurement range. That is, in FIG. 2A, since the distance D from the laser displacement meter 3 to the measurement object 1 is fixed, the level a position of the measurement object 1 can be measured. Then, when the measuring object 1 is scanned in the X direction and is in the state of FIG. 2B and faces the convex portion 2, first, the level a ′ of the upper position is temporarily set and the position of the level a is measured. Then, the movable stage 4 is raised by an interval from level a to level a ′, and the measurement range d of the laser displacement meter 3 here is set from level a ′ to level b ′ and measured.

However, with this means, the shape of the convex portion 2 on the surface of the measurement object 1 has to be examined in advance, so that it is extremely inefficient in terms of setting measurement information and measuring.

Japanese Patent Laid-Open No. 10-318703 JP 2006-138673 A

  In the description of FIG. 2 in the invention “dimension measuring apparatus” of Patent Document 1, a non-contact measuring means is disclosed using a laser displacement meter, but the problem clarified in FIG. 1 described above has been solved. Absent.

  In addition, the invention “surface shape measuring method and measuring system” of Patent Document 2 is a configuration for measuring and comparing the surface shape of an object to be measured before and after the occurrence of unevenness, and is clarified in FIG. 2 described above. There are similar disadvantages as inconveniences.

  Therefore, the present invention has been invented to eliminate the above-mentioned drawbacks, disadvantages, and dissatisfactions of the prior art, and uses a laser displacement meter to easily and accurately measure an object without setting measurement information in advance. It is intended to be able to inspect the surface condition of the.

In order to solve the above-described problems, the present invention provides a measurement method using a laser displacement meter that inspects the surface state of a measurement object. The laser displacement meter is mounted on a moving stage in the Z direction on which a linear encoder is mounted, and a length measurement is performed. The distance between the surface of the object to be measured and the laser displacement meter is fixed by moving the moving stage in the Z direction via a linear encoder so that the voltage output at the position d / 2 in the range d is always 0V. It is characterized by maintaining to.

  In addition, the control circuit of the measuring method using the laser displacement meter according to the present invention includes an input unit to which a voltage output of a ± 10 V laser displacement meter is input, and a signal from this input unit is converted into a positive and negative two-pole signal. A linear encoder using two signals: a comparison unit to be generated, an AD conversion unit that generates a signal from the input unit as a 0 V neighborhood signal, and a comparison signal from the comparison unit and a neighborhood signal from the AD conversion unit And a control unit that controls the movement of the stage in the Z direction.

The laser displacement meter outputs a voltage of −10 V to +10 V depending on the detection distance. This range corresponds to the measurement range d, and the voltage output at the position level of d / 2 is 0V. Therefore, if the value of the linear encoder is controlled as displacement information so that the movement of the moving stage in the Z direction is always 0 V, the distance between the surface of the object to be measured and the laser displacement meter can always be kept constant. Therefore, length measurement is possible without being influenced by the value of the length measurement range of each laser displacement meter.

  The linearity of the positional voltage information of the laser displacement meter is high and extremely accurate near 0V, but is low and inaccurate near -10V and + 10V. In this respect, in the present invention, a linear encoder having a high linearity, for example, 0.1 μm is used as a position voltage information source and is used in the vicinity of 0 V where the linearity of the laser displacement meter is high.

  Even if a laser displacement meter with a low side length resolution, for example, a product with a side length resolution of 1 μm is used, only one point passes 0 V, so that the present invention can measure with a resolution of 0.1 μm. There are many excellent effects.

It is explanatory drawing which shows an example of the measuring method by the conventional laser displacement meter. It is explanatory drawing which similarly shows an example of the measuring method by the conventional laser displacement meter. It is explanatory drawing which shows an example of the measuring method by the laser displacement meter concerning this invention. It is a graph which shows the change of the voltage within a measurement range. It is a circuit diagram of the measuring method by the laser displacement meter concerning this invention.

The laser displacement meter 3 is mounted on a Z-direction moving stage 4 on which a linear encoder 5 is mounted, and the measurement object 1 is mounted on an XY stage (not shown), and is fixed from the laser displacement meter 3 to the measurement object 1. The distance D thus set is set so that the laser beam is reflected at the level a position which is the surface of the measurement object 1 in FIG. In this case, the measurement range d of the laser displacement meter 3 is from level a to level b, and the voltage output at the position level d / 2 of the measurement range d is 0V.

  In this state, the XY stage is operated to scan in the X direction, and when the convex portion 2 on the surface of the measurement object 1 is irradiated with the laser beam (FIG. 3B), the linear measurement range d through the linear encoder 5 is obtained. The distance D between the surface of the measuring object 1 and the laser displacement meter 3 is controlled by controlling the motor controller of the moving stage 4 so that the voltage output at the position level of d / 2 becomes 0V, and moving the moving stage 4 in the Z direction. Is kept constant.

  FIG. 5 is a circuit diagram for achieving the present invention. When the voltage output of the laser displacement meter 3 of ± 10 V is input to the input unit 6, the comparison unit 7 generates a positive and negative bipolar signal. The AD conversion unit 8 generates a 0V neighborhood signal. Then, the control unit 9 controls the movement of the stage 4 in the Z direction via the linear encoder 5 using the comparison signal and the proximity signal.

  FIG. 4 shows the change in voltage within the measurement range. The linearity is unstable in the vicinity of −10 V and +10 V, and the linear voltage is in the vicinity of 0 V, and the position voltage information of the laser displacement meter 3 is Even in that case, the vicinity of ± 2 V is desirable. However, as described above, no error occurs as long as the measurement is performed at only one point passing 0V.

DESCRIPTION OF SYMBOLS 1 Measuring object 2 Convex part 3 Laser displacement meter 4 Z direction moving stage 5 Linear encoder 6 Input part 7 Comparison part 8 AD conversion part 9 Control part

Claims (2)

  A measurement method using a laser displacement meter that inspects the surface state of a measurement object (1), wherein the laser displacement meter (3) is mounted on a moving stage (4) in the Z direction on which a linear encoder (5) is mounted, By moving the moving stage (4) in the Z direction via the linear encoder (5) so that the voltage output at the position of d / 2 in the measuring range d is always 0 V, the measured object (1) A measurement method using a laser displacement meter, wherein a distance D between the surface and the laser displacement meter (3) is maintained constant. The input part (6) to which the voltage output of the laser displacement meter (3) of ± 10 V is inputted, and the signal from the input part (6) is converted into a positive and negative bipolar signal. A comparison unit (7) to be generated, an AD conversion unit (8) that generates a signal from the input unit (6) as a signal near 0 V, a comparison signal from the comparison unit (7), and the AD conversion unit (8) And a control unit (9) for controlling the movement of the stage (4) in the Z direction via the linear encoder (5) using two signals of the vicinity signal of and a measurement by a laser displacement meter Method control circuit.

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