Method and device for measuring height of object whose surface has irregular reflectance

• US 5,392,110 A
• Filed: 04/16/1993
• Issued: 02/21/1995
• Est. Priority Date: 04/22/1992
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kinoshita, Masao, Yojima, Masayuki
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US08/048,998
• Time in Patent Office: 676 Days
• Field of Search: 250/214 B, 250/214 C, 356/1, 356/4, 356/376, 356/375
• US Class Current: 356/3.04
• CPC Class Codes: G01B 11/0608 Height gauges

Abstract

In a signal processing circuit, a height arithmetic circuit obtains a measured value of a height of an object by using the principle of triangulation from a second light receiving signal which is transmitted from a second photodetector of position detecting type thereto. An error arithmetic circuit acquires a measurement error by using the principle of triangulation from a first light receiving signal which is transmitted from a first photodetector of position detecting type thereto. A correction circuit calculates a correct height of the object by subtracting an output signal of the error arithmetic circuit from an output signal of the height arithmetic circuit.

Claims

1. A method of measuring a height of a surface of an object having a non-uniform reflectivity, said method comprising:

a first step of projecting a laser beam vertically to the surface,

a second step of calculating a measurement error of the surface height caused by the non-uniform reflectivity of the surface, said measurement error being calculated responsive to a first reflected light of the laser beam reflected vertically from the surface,

a third step of receiving a second reflected light of the laser beam reflected from the surface in a direction which is different from the vertical direction, and calculating a measured value of the surface height responsive to the second reflected light, and

a fourth step of correcting the value measured in step three by compensating the measured value for the measurement error calculated in step two.

2. A method as claimed in claim 1, wherein the second step includes steps of;

condensing the first reflected light and focusing it to form a first light spot on a light receiving surface of a first photodetector means of a position detector type,

calculating a position of an intensity centroid of the first spot on the light receiving surface of the first photodetector means, and

computing the measurement error in response to a deviation of the position of the intensity centroid from position of the center of the first light spot,

the third step includes steps of;

condensing the second reflected light and focusing it to form a second light spot on a light receiving surface of a second photodetector means of a position detector type,

calculating a position of an intensity centroid of the second light spot on the light receiving surface of the second photodetector means, and

computing the measured value in response to a deviation of the position of the intensity centroid of the second light spot from a predetermined reference position corresponding to a reference height of the surface in accordance with the triangulation method.

3. A method of measuring a height of a surface of an object having a non-uniform reflectivity, said method comprising;

a first step of projecting a laser beam vertically to the surface,

a second step of calculating a measurement error of the surface height caused by the non-uniform reflectivity of the surface, said measurement error being calculated in response to a first reflected light of the laser beam reflected vertically from the surface,

a third step of receiving a second reflected light of the laser beam reflected from the surface in a direction which is different from the vertical direction, and calculating a measured value of the surface height in response to the second reflected light,

a fourth step of comparing the measurement error with a predetermined fixed value, and

a fifth step of outputting the measured value as a surface height only when the absolute value of the measurement error is smaller than the fixed value.

4. A method as claimed in claim 3, wherein the second step includes steps of:

condensing the first reflected light and focusing it to form a light spot on a two-sectional light receiving surface of a two-sectional photodetector means, and

calculating the measurement error from a difference between outputs of the two sections of two-sectional light receiving surface.

5. An apparatus for measuring a height of a surface of an object having a non-uniform reflectivity, said apparatus comprising:

a measuring board for mounting the object,

floodlight optical means for projecting a laser beam of a given diameter vertically to the surface of the object,

first light condensing means for condensing a first reflected light of the laser beam vertically reflected from the surface so that the first reflected light is focused to form a first light spot,

first photodetector means disposed at a position on which the first light spot is focused for detecting a first deviation of an intensity centroid of the first light spot due to the non-uniform reflectivity of the surface from a position at the center of the first light spot,

second light condensing means for condensing a second reflected light of the laser beam reflected from the surface in a direction which is different from the vertical direction so that the second reflected light is focused to form a second light spot,

second photodetection means disposed at a position on which the second light spot is focused for detecting a second deviation of a position of the intensity centroid of the second light spot from predetermined reference position corresponding to a reference height of the surface,

height arithmetic means for calculating a measured value of a surface height of the object in according with the triangulation method from the second deviation detected by the second photodetection means,

measurement error arithmetic means for calculating a measurement error of the surface height accordance with the triangulation method from the first deviation detected by the first photodetection means, and

correcting means for correcting the measured value by compensating measured value for the measurement error.

6. An apparatus for measuring a height of a surface of an object having a non-uniform reflectivity, said apparatus comprising;

a measuring board for mounting the object,

floodlight optical means for projecting a laser beam of a given diameter vertically to the surface of the object,

first light condensing means for condensing a first reflected light of the laser beam vertically reflected from the surface so that the first reflected light is focused to form a first light spot,

first photodetector means with a two-sectional light receiving surface mounted at a position on which the first light spot is focused for producing a difference between outputs of the two sections of the two-sectional light receiving surface,

second light condensing means for condensing a second reflected light of the laser beam reflected from the surface in a direction which is different from the vertical direction so that the second reflected light is focused to form a second light spot,

second photodetection means disposed at a position on which the second light spot is focused for detecting a deviation of a position of the intensity centroid of the second light spot from a predetermined reference position corresponding to a reference height of the surface,

height arithmetic means for calculating a measured value of a surface height of the object in according with the triangulation method from the deviation detected by the second photodetection means,

comparing means for comparing the difference produced by the first photodetector means with a predetermined fixed value, and

output means for outputting the measured value calculated by the height arithmetic means only when the difference is smaller than the fixed value.