JPH10141924A - Laser measuring method using knife-edge method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the surface of a die, etc., containing a part having such a surface shape that is difficult to be measured by an auto-focus method. SOLUTION: In an auto-focus measuring method in which the surface shape of an object to be measured is measured by irradiating the object with laser light and detecting an auto-focusing position, the part to be measured of the object is covered with fine power of a ceramic, etc., before measurement. At the time of measuring the surface shape of the part to be measured, the fine power of the ceramic, etc., is mixed in volatile oil and the surface to be measure is covered with the mixture by sprayed the mixture upon the surface with an air gun 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the shape of an object using laser light, and more particularly to a laser measurement method using a knife edge method.

[0002]

2. Description of the Related Art As a method of measuring the surface shape and surface properties of an object to be measured, there is a measuring method by an autofocus method.
In the autofocus method, measurement is performed by irradiating the surface of the measured object with laser light, detecting reflected light from the measured object, and controlling the servo to automatically adjust the measured object to the focal point position. It is. The knife edge method is also a method of detecting and measuring the deviation of the object to be measured from the focal position, and has a feature that extremely high-precision measurement is possible.

FIG. 3 shows a principle diagram of a measuring method by the knife edge method. In the knife edge method, a laser beam is irradiated on the object 10 through the objective lens 8, and the reflected light from the object 10 is cut in half by the knife edge 12 behind the objective lens 8. Reference numeral 14 denotes a sensor that detects light focused by the objective lens 8. FIG. 3A shows the measured object 10.
3 is a state where it is farther from the focus position, and FIG. 3C is a state where it is closer than the focus position.

Assuming that sensors A and B are arranged with the optical axis interposed therebetween, in the case of FIG. 3 (b), light is evenly applied to the sensors A and B, whereas in the case of FIG. 3A, a lot of light hits the sensor B side, and in the case of FIG. 3C, a lot of light hits the sensor A side. In the knife-edge method, by comparing the light amounts corresponding to the sensors A and B, it is possible to determine on which side of the focus position the object under test 10 is located, and use a servo mechanism or the like so that the sensors A and B are evenly irradiated with light. You can move the system to autofocus. Then, the shape of the measured object can be measured from the movement amount of the measurement system.

[0005]

By the way, in the laser measuring method by the knife edge method, an object to be measured is irradiated with a laser beam, and the measurement is performed by using the reflected light from the surface of the object to be measured. Measurement accuracy is affected by surface conditions. In other words, there is no problem if the reflected light from the measured object is easily detected on the measuring system side when the measured object is irradiated with laser light, but the part to be measured is reflected on the inclined surface toward the measuring system side. If the light is not reflected, the amount of light to be detected is insufficient and auto focus cannot be performed.
There is a problem that measurement becomes impossible.

[0006] For example, machining marks are formed on the finished surface of a mold obtained by cutting with a ball end mill. When measuring a mold surface having such machining marks, the machining is performed together with the angle of the measurement site. The direction of the streak greatly affects the measurement accuracy. FIG. 2A shows a case where laser light is irradiated from a direction parallel to the processing streak, and FIG. 2B shows a case where laser light is irradiated from a direction perpendicular to the processing streak. In each case, the measurement site is inclined with respect to the optical axis, and the case shown in Fig. 2 (a) indicates that the light reflected on the measurement surface is almost totally reflected on the opposite side to the measurement system and is not reflected on the measurement system. 2 (b) shows that the reflected light is reflected toward the measurement system. Since almost no irregular reflection occurs on the mold surface, measurement is impossible in the case of the arrangement shown in FIG.

According to the present invention, as in the case of measuring a mold surface on which such processing streaks are formed, light is not reflected on the measuring system depending on the type and surface condition of the object to be measured, and high-precision measurement can be performed. It is an object of the present invention to provide a laser measurement method by the knife edge method that can reliably measure a surface state even in a difficult case.

[0008]

The present invention has the following arrangement to achieve the above object. That is, in a laser measurement method of irradiating a laser beam to an object to be measured and measuring a surface shape of the object to be measured from an autofocus position, measurement is performed by previously covering a measurement target portion of the object to be measured with fine powder such as ceramics. It is characterized by performing. In addition, the present invention is characterized in that fine particles of ceramics or the like are mixed with the volatile oil and sprayed on the measurement target portion using an air gun, thereby covering the measurement target portion with the ceramic fine powder.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below. The laser measurement method according to the knife edge method according to the present invention is to coat the surface of the part to be measured with the object to be measured with fine powder of ceramics or the like in order to prevent the measurement from being impossible due to the properties of the measurement part of the measurement target. ,
In a normal measurement method, even when the reflected light does not enter the measurement system and measurement becomes impossible, the reflected light is always incident on the measurement system so that the measurement can be performed.

[0010] Fine powder of ceramics or the like covering the measurement surface of the object to be measured is used to generate light reflected by the measurement system in the irradiated laser light. In the embodiment, a powder having a particle diameter of 1 μm or less is used as the ceramic fine powder, the ceramic fine powder is mixed with the volatile oil, and the surface to be measured is sprayed to the surface of the object to be measured with an air gun to cover the measurement surface with the ceramic fine powder.

FIG. 1 shows a state in which fine powder of ceramics is sprayed on the surface of the object 10 to be measured. 12 is an air gun,
14 is a nozzle. The air gun 12 is attached to the tip of one axis of a controller having three axes (XYZ) of control axes, and sets application conditions so that the air gun 12 can be uniformly applied to the measurement object. When applying the ceramic fine powder, the air gun 12 is moved along the shape of the measured surface of the measured object 10 as shown in FIG.

In this embodiment, the nozzle diameter of the air gun is adjusted in the range of 0.2 mm to 0.4 mm according to the particle size of the powder used. The ceramic used was a powder of Si ₃ N ₄ . Powders having a particle size of 0.23 to 1.10 μm were mixed and used. The air pressure was adjusted in the range of 0.1 to 4 kgf / cm ² depending on the type, particle size and coating thickness of the powder. If the thickness of the ceramic fine powder applied to the surface of the device under test 10 is as thin as possible, the surface properties of the device under test 10 can be accurately measured. According to the above method, the coating thickness of the ceramic covering the surface to be measured could be reduced to about 2 μm.

With respect to the mold having processing marks as shown in FIG. 2, the measurement surface can be inclined with respect to the optical axis when the ceramic fine powder is applied and when the ceramic fine powder is not applied. The results of examining the range of various inclination angles are shown below. The measurement was performed on dies having different surface roughness in order to examine the relationship with the surface roughness of the die surface. The measurement results are shown for a case where the laser beam is incident substantially parallel to the processing streak and a case where the laser light is incident substantially perpendicular to the processing streak. The inclination angle of the mold surface indicated by α in FIG. 2 refers to the angle formed between the optical axis and the normal to the surface to be measured when the optical axis is in the vertical direction.

[0014] Table 1 shows the results of examining whether or not the measurement can be performed by inclining the mold surface with respect to the optical axis with respect to the mold surface on which the ceramic fine powder is not applied. This is a case where the laser beam is directed in a direction substantially perpendicular to the processing streak (FIG. 2B).

[0015]

[Table 1]

In the table, the mark あ っ た indicates that measurement was possible, the mark 測定 indicates that measurement was difficult, and the mark × indicates that measurement was impossible. From the above results, it can be seen that, for example, in the case of 0.8 μm Rmax, it is easy to measure up to an inclination angle of 20 °, but it becomes difficult to measure at an angle of 25 ° or more, and it becomes impossible to measure at an angle of 35 ° or more. The surface roughness is 12.5μ
When m Rmax was about 25 μm Rmax, it was easy to measure up to a tilt angle of about 45 degrees.

Table 2 shows the results of a test in which the laser beam was directed in a direction substantially parallel to the processing streak (FIG. 2A) on the mold surface on which the ceramic fine powder was not applied.

[0018]

[Table 2]

According to this test, for example, 0.8 μm R
In the case of max, measurement becomes difficult at an inclination angle of 5 degrees, and an inclination angle of
Measurement became impossible at more than the degree. Further, the surface roughness is 12.5
Even in the case of about .mu.m Rmax and about 25 .mu.m Rmax, measurement became difficult at an inclination angle of about 5 degrees. It can be seen that when laser light is incident parallel to the processing streak, autofocus becomes difficult due to total reflection on the mold surface, and measurement becomes difficult.

Table 3 shows the results obtained by applying fine ceramic powder to the mold surface and irradiating the measurement surface with laser light to change the inclination angle to determine whether or not measurement is possible. The results are shown for the case where the laser beam is incident perpendicular to the processing streak and the case where the laser beam is incident parallel to the processing streak. The surface roughness of the mold surface used in this test was 4 μm Rmax.

[0021]

[Table 3]

As shown in Table 3, when the mold surface is coated with the fine powder of ceramics, the laser beam is incident perpendicularly to the processing streak and the laser beam is incident parallel to the processing streak. Measurement is possible up to a tilt angle of 60 degrees, and a tilt angle of 65 degrees.
It became impossible to measure in degrees. In this way, the method of coating the mold surface with ceramic fine powder enables autofocus regardless of the direction of the processing streak, etc., and is applied to a measurement object that is easily totally reflected such as the mold surface. Very effective. The reason that the measurable range can be expanded by coating the measurement target with ceramic fine powder in this way is because the ceramic fine powder is spherical and there is always a plane perpendicular to the incident light. This is because reflected light can be returned to the measurement system.

In the method according to the present embodiment using the fine powder of ceramics, it is possible to perform autofocus by using the reflected light from the fine powder. Therefore, the reflected light is returned not only to the fine powder but also to the measuring system. The material is not limited as long as the material can be used. For example, fine powder using a plastic material, metal fine powder, or the like can be used. Since the plastic fine powder has flexibility, there is an advantage that the action of damaging the object to be measured is smaller than when using ceramic fine powder when applied to the surface of the object to be measured. In addition, as the fine powder used for measuring the surface properties, a spherical powder having a diameter of about 1 μm can be suitably used.

In the above embodiment, the test was performed with the mold surface having the processing streak as the measurement object. However, the measurement object is not limited to the mold surface, and the laser light is totally reflected similarly to the mold surface. It is also possible to apply the same method to an easy measurement object by coating the same with fine powder of ceramics. Also, when the measurement surface of the object to be measured is covered with fine powder of ceramics or the like, since the shape of the measurement surface is reliably reflected, measurement is performed with the fine powder of ceramic covered.
It is possible to reliably measure the surface state of the object to be measured.

[0025]

According to the laser measuring method by the knife edge method according to the present invention, it is possible to easily measure an inclined surface or the like, which is difficult to measure by a normal measuring method, and to measure the object to which the laser measuring method can be applied. Range can be expanded. In addition, it is easy to measure an object to be measured, which has been difficult to measure in the past, and this has a remarkable effect such as enabling more accurate measurement.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing a state in which fine ceramic powder is sprayed on a surface to be measured.

FIG. 2 is an explanatory view showing a positional relationship between a processing streak on a mold surface and a laser beam.

FIG. 3 is an explanatory diagram showing a laser measurement method using a knife edge method.

[Explanation of symbols]

 10 Mold 12 Air gun 14 Nozzle

Continued on the front page (71) Applicant 392036072 Nippon Digitech Co., Ltd. 143 Zenchoji-cho, Ayakoji-dori Muromachi west of Shimogyo-ku, Kyoto-shi, Kyoto (71) Applicant 394023414 Graphic Products Co., Ltd. 2-17-22 Takada, Toshima-ku, Tokyo No. (72) Inventor Yoshiaki Kakino 256-5 Iwakura Hanazonocho, Sakyo-ku, Kyoto-shi, Kyoto (72) Inventor Atsushi Matsubara 43 Petit Maison 101, 43, Kamigamo Minami-Oji-cho, Kita-ku, Kyoto-shi, Kyoto (72) Inventor Igao Yamaji Shiga 465-5 Go-Sanjo-cho, Hikone-shi, Japan (72) Inventor Tomohiko Kawai 143 Zenchoji-cho, Ayakoji-dori Muromachi, Shimogyo-ku, Kyoto-shi, Kyoto Japan Digitech Co., Ltd.

Claims (2)

[Claims] 1. A laser measuring method for irradiating a laser beam to a measurement object, detecting an auto-focus position and measuring a surface shape of the measurement object, comprising: A laser measurement method characterized by performing measurement by coating with a laser. 2. A ceramic fine powder is mixed with a volatile oil,
The laser measurement method according to claim 1, wherein the measurement target portion is coated with fine powder such as ceramics by spraying the measurement target portion with an air gun.