Optical scanning measurement of dimensions with a double-concave mirror

• US 5,742,068 A
• Filed: 11/08/1995
• Issued: 04/21/1998
• Est. Priority Date: 05/13/1993
• Status: Expired due to Term

• Current Assignee: Cargoscan A/S
• Original Assignee: Cargoscan A/S
• Inventors: Slettemoen, Gudmunn, L.o slashed.ken, Morten, Dybdahl, Stig, Holte, Stian, S.o slashed.rensen, Einar, Staver, Arild
• Primary Examiner(s): Westin, Edward P.
• Assistant Examiner(s): PYO, KEVIN K
• Application Number:
  US08/545,801
• Time in Patent Office: 895 Days
• Field of Search: 250/559.19, 250/559.24, 250/559.26, 250/559.38, 250/236, 356/356, 356/379, 356/380
• US Class Current: 250/559.19
• CPC Class Codes: G01B 11/00 Measuring arrangements characterised by the use of optical techniques
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G02B 26/12 using multifaceted mirrors
• CPC Class Codes: G02B 5/09 Multifaceted or polygonal mirrors , e.g. polygonal scanning mirrors; Fresnel mirrors

Abstract

An apparatus (5) for measuring the dimensions of an object (1) where a measuring carriage (6) moves the object at a distance thereabove. A polygonal mirror unit (32) receives laser light (16) and reflects it in a fan-shaped form toward a stationary angled mirror unit (37, 38) which directs the light towards a double-curved stationary mirror unit (39) which reflects the beam onto the object. Mirrors (40) of the polygonal unit are adjustable.

Claims

1. An apparatus for measuring the distance to one or more areas of an object in order to determine one or more dimensions of the object, comprising means for directing a light beam towards the object, means for registering the light beams that are reflected from the object, means for calculating the time it takes for the beams to travel to and from the object, and means for causing the light beam to sweep across the object perpendicular in relation to a fixed reference plane during the entire sweeping operation, and with relative movement between the apparatus and the object which is to be measured, said light which is reflected by the object returning back to the light registration means via said light beam sweeping means, and said light beam sweeping means including a stationary mirror which is arced in its longitudinal direction, and also rotatable mirror means, comprising

a first mirror,

a second, plane mirror,

a third plane mirror which forms and angle of 90°

with the second mirror,

said rotatable mirror means being made of a rotating polygonal mirror unit having a rotor means, in that the light beam which is emitted from a light generator has a path of movement via the first mirror, thence via the polygonal mirror unit, thence towards the second mirror, thence to the third mirror, thence to the stationary mirror, thence towards the object, the light beam reflected from the object having a path of movement back to the light registration means via the stationary mirror, said third and second mirrors, and the polygonal mirror unit, said stationary mirror in the longitudinal direction having an arced cross section so that the mirror forms a double concave mirror surface, the radius of curvature of the arc changing along the length of the stationary mirror and being greatest at the ends of said mirror.

2. An apparatus according to claim 1, wherein the rotating polygonal mirror unit is arranged at a distance above the stationary mirror.

3. An apparatus according to claim 1, wherein said second mirror (1) and the rotating polygonal mirror unit (2) are located on a first (1) level and said third mirror and said stationary mirror (2) are located on a second level.

4. An apparatus according to claim 2, wherein said second mirror (1) and the rotating polygonal mirror unit (2) are located on a first (1) level and said third mirror and said stationary mirror (2) are located on a second level.

5. An apparatus according to claim 1, wherein the double concave mirror surface spans over an arc that is less than 180°

.

6. An apparatus according to claim 1, wherein the pitch of the stationary mirror, comprising a distance between a chord drawn between the ends of the mirror and to the mid-point of the mirror is appreciably less than the smallest radius of curvature of the mirror by about 15-30% of said radius of curvature.

7. An apparatus according to claim 1, wherein at one end of the stationary mirror a fifth mirror is positioned which deflects received light beams from the light generator along the path of movement of the apparatus in the direction of a reference plate having areas of different reflective properties, and which is securely fixed to one end of the rail system along which a carriage for the apparatus can move, the time it takes the light beam to travel from said reference plate to the light registration means being a function of the position of the apparatus/carriage relative to the rail system.

8. Art apparatus according to claim 1, wherein the rotatable mirror means being a rotating polygonal mirror unit with individually adjustable mirrors.

9. An apparatus according to claim 8, wherein each mirror along a first edge thereof is mounted in a respective receiving groove on said rotor means, said groove having its axis located transverse to the axis of rotation of said rotor means, and wherein each said mirror along a second edge thereof parallel to said first edge is adjustably attached to said rotor means by means of a spring element in the form of a metal plate, said spring element being adjustable by means of a screw/nut connection which is attached to said rotor means at one end and at the other end engages said spring element, said spring element having its bending curvature changed upon adjustment of said screw/nut connection to cause said mirror to be moved correspondingly in a direction towards or away from a mid point of said polygonal mirror unit.

10. An apparatus according to claim 9, wherein said metal plate has a first portion extending over said second edge and engaging a front face of said mirror and a second portion in the form of two punched-out tongues having the free ends thereof bearing against a rear face portion of said mirror.

11. An apparatus for measuring the distance to one or more areas of an object in order to determine one or more dimensions of the object, comprising means for directing a light beam towards the object, means for registering the light beams that are reflected from the object, means for calculating the time the beams take to travel to and from the object, and means for causing the light beam to sweep over the object perpendicular in relation to a fixed reference plane during the entire sweeping operation, and with relative movement between the apparatus and the object which is to be measured, the light that is reflected by the object returning to the light registration means via said light beam sweeping means, and said light beam sweeping means comprising a stationary mirror which is arced over the length thereof, and means causing the light beam to move over the stationary mirror, wherein the stationary mirror has an arced cross-section in its longitudinal direction such that the mirror forms a double concave mirror surface, and wherein the radius of curvature of the arc changes along the length of the stationary mirror, and is greatest at the ends of said mirror.

12. An apparatus according to claim 11, wherein the double concave mirror surface spans over an arc that is less than 180°

.

13. An apparatus according to claim 11, wherein the pitch of the stationary mirror, comprising a distance between a chord drawn between the ends of the mirror and to the mid-point of the mirror is appreciably less than the smallest radius of curvature of the mirror by about 15-30% of said radius of curvature.

14. An apparatus according to claim 13, wherein the pitch of the stationary mirror, comprising a distance between a chord drawn between the ends of the mirror and to the mid-point of the mirror is appreciably less than the smallest radius of curvature of the mirror by about 15-30% of said radius of curvature.

15. An apparatus according to claim 11, wherein at one end of the stationary mirror a fifth mirror is positioned which deflects received light beams from the light generator along the path of movement of the apparatus in the direction of a reference plate having areas of different reflective properties, and which is securely fixed to one end of the rail system along which a carriage for the apparatus can move, the time it takes the light beam to travel from said reference plate to the light registration means being a function of the position of the apparatus/carriage relative to the rail system.

16. An apparatus for measuring the distance to one or more areas of an object in order to determine one or more dimensions of the object, comprising means for directing a light beam towards the object, means for registering the light beams that are reflected from the object, means for calculating the time it takes for the beams to travel to and from the object, and means for causing the light beam to sweep across the object perpendicular in relation to a fixed reference plane during the entire sweeping operation, and with relative movement between the apparatus and the object which is to be measured, said light which is reflected by the object returning back to the light registration means via said light beam sweeping means, and said light beam sweeping means including a stationary mirror which is arced in its longitudinal direction, and means causing the light beam to move over the stationary mirror, wherein the stationary mirror in the longitudinal direction has an arced cross section so that the mirror forms a double concave mirror surface, the radius of curvature of the arc changing along the length of the stationary mirror and being greatest at the ends of said mirror, and wherein said means for moving the light beam is a rotating polygonal mirror unit.

17. An apparatus according to claim 16, wherein the double concave mirror surface spans over an arc that is less than 180°

.

18. An apparatus according to claim 16, further comprising a first mirror, a second plane mirror, a third plane mirror which forms an angle of 90°

with the second mirror, the light beam which is emitted from a light generator having a path of movement via the first mirror, thence via the polygonal mirror unit, thence towards the second mirror, thence to the third mirror, thence to the stationary mirror, thence towards the object, the light beam reflected from the object having a path of movement back to the light registration means via the stationary mirror, said third and second mirrors, and the polygonal mirror unit.

19. An apparatus according to claim 16, wherein the rotating polygonal mirror unit is arranged at a distance above the stationary mirror.

20. An apparatus according to claim 18, wherein said, second mirror and the rotating polygonal mirror unit are located on a first (1) level and said third mirror and said stationary (2) mirror are located on a second level.

21. An apparatus according to claim 19, wherein said second mirror and the rotating polygonal mirror unit are located on a first level and said third mirror and said stationary mirror are located on a second level.

22. An apparatus according to claim 16, wherein the distance between a chord drawn between the ends of the stationary mirror and to the mid-point of the stationary mirror, which corresponds to the pitch of the stationary mirror, is appreciably less than the smallest radius of curvature of said stationary mirror and on the order of approximately 15-30% of said radius of curvature.

23. An apparatus according to claim 16, wherein at one end of the stationary mirror a fifth mirror is positioned which deflects received light beams from the light emitter along the path of movement of the apparatus in the direction of a reference plate having areas of different reflective properties, and which is securely fixed to one end of the rail system along which a carriage for the apparatus can move, the time it takes the light beam to travel from said reference plate to the light registration means being a function of the position of the apparatus/carriage relative to the rail system.

24. An apparatus according to claim 16, wherein the rotating polygonal mirror unit has individually adjustable mirrors.

25. An apparatus according to claim 24, wherein each mirror along a first edge thereof is mounted about an axis located transverse to the axis of rotation of said polygonal mirror unit, and wherein each said mirror along a second edge thereof parallel to said first edge is adjustably attached to a rotor means of said polygonal mirror unit by means of an adjustable spring element.

26. An apparatus according to claim 25, wherein a the spring element is adjustable by means of screw/nut connection which is attached to said rotor means at one end and at the other end engages said spring element, said spring element having its bending curvature changed upon adjustment of said screw/nut connection to cause said mirror to be moved correspondingly in a direction towards or away from a midpoint of said polygonal mirror unit.