Optical scanning apparatus for detecting faults on a surface

• US 4,924,086 A
• Filed: 10/28/1988
• Issued: 05/08/1990
• Est. Priority Date: 11/05/1987
• Status: Expired due to Fees

• Current Assignee: Erwin SICK GmbH Optik-Elektronik
• Original Assignee: Erwin SICK GmbH Optik-Elektronik
• Inventors: Weber, Klaus
• Primary Examiner(s): Westin, Edward P.
• Application Number:
  US07/264,230
• Time in Patent Office: 557 Days
• Field of Search: 250/235, 250/236, 250/563, 250/572, 350/6.8, 356/430, 356/431, 356/237, 356/238
• US Class Current: 250/235
• CPC Class Codes: G01N 21/8901 Optical details; Scanning details per se G02B
• CPC Class Codes: G02B 17/0642 off-axis or unobscured systems in which not all of the mirrors share a common axis of rotational symmetry, e.g. at least one of the mirrors is warped, tilted or decentered with respect to the other elements
• CPC Class Codes: G02B 26/10 Scanning systems

Abstract

An optical scanning apparatus for plane surfaces (13) having a laser light source (20), a light deflecting means (16) illuminated by the laser beam, a telecentric image forming element (15) and a light receiving means. Parallel to the scanning line (11) generated by the light deflecting means (16) and the telecentric image forming element (15) there is arranged, at the angle of regular reflection, an image forming retroreflector (12; 38,39) which forms an image of the light bead running along the scanning line (11) on itself.

Claims

1. Optical scanning apparatus for flat surfaces comprising:

a laser light source;

a periodic light deflecting means illuminated by a laser beam;

a telecentric optical scanning system for directing the laser beam, periodically swept over a specific angular range by the light deflecting means in the form of a scanning beam displaced parallel to itself at an angle of incidence other than zero towards the flat surface where a light bead arises which periodically scans the flat surface along a scanning line;

a light receiving means for receiving the light reflected from the region of the scanning line on the surface; and

an image forming retroreflector disposed at an angle of regular reflection and forming an image of the light bead running along the scanning line, the image being formed adjacent the light bead.

2. Optical scanning apparatus in accordance with claim 1, wherein said image forming retroreflector comprises a right cylindrical mirror having substantially the length of the scanning line disposed at the angle of reflection of the scanning beam, an imaginary central cylindrical axis of the scanning beam extending parallel to the scanning line such that the imaginary central cylinder axis lies adjacent the scanning line on the surface.

3. Optical scanning apparatus in accordance with claim 1, wherein said image forming retroreflector comprises a spherical lens strip having substantially the length of the scanning line disposed at the angle of reflection of the scanning beam parallel to the scanning line and spaced from the scanning line by a distance equivalent to its focal length, said apparatus including a further lens strip extending parallel to the first lens strip disposed at the distance of its focal length from the focal plane of the first lens strip remote from the scanning line in such a way that it receives the reflected light emerging from the scanning line;

and wherein a plane strip mirror is disposed behind the further lens strip perpendicular to the optical axis at a distance equal to the focal length of the further lens strip.

4. Optical scanning apparatus in accordance with claim 1, wherein said image forming retroreflector comprises a spherically concave mirror strip having substantially the length of the scanning line disposed at the angle of reflection of the scanning beam parallel to the scanning line and spaced from the scanning line by a distance equal to its focal length;

wherein a focal plane of the concave mirror strip is displaced by a slight tilting of the concave mirror strip about its longitudinal axis, and further comprising a plane deflecting mirror strip disposed in the light reflected therefrom, onto a side of the concave mirror strip remote from the scanning line; and

a further lens strip extending parallel to the first concave mirror strip disposed at a distance equal to its focal length, from the focal plane of the first concave mirror strip remote from the scanning line in such a way that it receives the reflected light emerging from the scanning line; and

wherein a plane strip mirror is disposed behind the further lens strip, with the plane strip mirror being perpendicular to the optical axis and spaced behind the further lens strip by a distance equal to the focal length of the lens strip.

5. Optical scanning apparatus in accordance with claim 1, wherein said image forming retroreflector comprises a spherical concave mirror strip having substantially the length of the scanning line disposed at the angle of reflection of the scanning beam parallel to the scanning line at a distance from the scanning line equal to its focal length;

and further comprising a triple mirror which receives the reflected light coming from the scanning line disposed in the focal plane of the concave mirror strip positioned remote from the scanning line due to slight tilting of the concave mirror about its longitudinal axis and due to a deflecting mirror strip arranged in the light reflected by the concave mirror strip.

6. Apparatus in accordance with claim 1, wherein said light receiving means comprises a photoreceiver arrangement and a partly permeable mirror disposed in a beam path between the telecentric optical scanning system and the light deflecting means and deflecting the light it receives from the surface to said photoreceiver arrangement.

7. Apparatus in accordance with claim 1, wherein the imaginary central cylindrical axis is arranged at a relatively small distance from the scanning line and parallel to the scanning line on the material surface.

8. Apparatus in accordance with claim 7, wherein the relatively small distance amounts to 5 to 10 mm.

9. Apparatus in accordance with claim 1, wherein the front focal point of the image forming retroreflector is spaced millimeters from the scanning line.

10. Apparatus in accordance with claim 1, wherein said light receiving means comprises a photoreceiver arrangement and a deflecting mirror disposed in a received beam path apart from the transmitted light beam adjacent to the light deflecting means and directs the light it receives from the surface to said photoreceiver arrangement.

11. Apparatus in accordance with claim 6, wherein the photoreceiver arrangement comprises a linear photoreceiver array extending perpendicular to the direction of the scanning line.

12. Apparatus in accordance with claim 10, wherein the photoreceiver arrangement comprises a linear photoreceiver array extending perpendicular to the direction of the scanning line.