Optical measuring system

• US 4,204,772 A
• Filed: 09/25/1078
• Issued: 05/27/1980
• Est. Priority Date: 09/25/1978
• Status: Expired due to Term

• Current Assignee: Recognition Systems Inc
• Original Assignee: Recognition Systems Inc
• Inventors: Balasubramanian, N.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): Rosenberger, R. A.
• Application Number:
  US05/945,628
• Time in Patent Office: 329,328 Days
• Field of Search: 356/1, 356/3, 356/4, 356/16, 356/372, 356/373, 356/375, 356/376, 356/381
• US Class Current: 356/602
• CPC Class Codes: G01B 11/026 by measuring distance between sensor and object G01B11/0608 takes precedence
• CPC Class Codes: G01C 3/24 using a parallactic triangle with fixed angles and a base of variable length in the observation station, e.g. in the instrument

Abstract

A non-contacting optical probe incorporates an optical system designed to measure distances between various surfaces which may be internal or external such as exists in molds and the like. A collimated light beam is passed off-center through a first lens and focused to a first point on a first surface coplanar with the focal plane of the lens. When the distance between the first surface and the optical probe carrying the collimated beam changes so that a second surface is presented, this second surface is no longer in the focal plane with the result that a laterally displaced image of the point of interception of the collimated beam with the point of the intersection of the optical axis of the system occurs. This lateral displacement is imaged back through the optical system to a sensing surface. The primary focusing lens is then physically shifted along its optical axis to bring the focal plane into coplanar relationship with the second surface, the amount of lens movement being readily determined when the laterally displaced image point on the sensor surface is brought into coincidence with the center optical axis of the lens system on the sensor surface. The distance through which the lens is physically moved then corresponds precisely to the distance between the first and second surfaces.

Claims

1. An optical method of measuring the distance between first and second surfaces with an optical system including the steps of:

(a) passing a collimated light beam through a first lens having a focal plane coinciding with said first surface in a direction parallel to and displaced from the optical axis of said first lens so that said collimated beam is focused to a first point coinciding with the point of intersection of the optical axis of said first lens in said focal plane;

(b) re-imaging light from said first point passing back along the optical axis and through said first lens with a second lens onto a sensor surface, said collimated light beam, first and second lens and sensor surface constituting part of said optical system;

(c) effecting relative movement between said optical system and said second surface to position said second surface to intercept said collimated beam at a second point, said second point being laterally displaced from the point of intersection of the optical axis with said second surface by an amount directly proportional to the distance of said second surface from the focal plane of said first lens;

(d) re-imaging light from said second point passing back through said first lens with said second lens onto said sensor surface, the image of said second point on said sensor surface being laterally displaced from the position occupied by the image of the first point on said sensor surface; and

(e) moving said first lens along its optical axis relative to said second surface until the second point image on said sensor surface reaches the position that the first point image on said sensor surface occupied thereby positioning the focal plane of said first lens in a position coplanar with said second surface, the physical distance over which said first lens is moved indicating the distance between said first and second surfaces.

2. The method of claim 1, including the step of generating said collimated light beam with a laser, the diameter of said collimated beam being less than 1/4 the diameter of said first lens.

3. An optical apparatus for measuring the distance between first and second surfaces, including, in combination:

(a) a first lens positioned so that its focal plane coincides with said first surface;

(b) a source of collimated light positioned to direct a collimated beam through said first lens in a direction parallel to and displaced from the optical axis of said first lens so that said collimated beam is focused to a first point on said first surface coinciding with the point of intersection of said optical axis of said first lens with said focal plane;

(c) a second lens positioned on the optical axis of said first lens for receiving light from said first point passing back along said optical axis through said first lens;

(d) a light sensor means having a sensing surface positioned to receive the image of said first point formed by said second lens, said collimated beam intersecting said second surface at a second point laterally displaced from the point of intersection of said optical axis with said second surface, the re-imaged second point on said sensor surface being laterally displaced from the position occupied by the image of the first point on said surface; and

(e) means for physically moving said first lens along its said optical axis to thereby move the position of the focal plane of said first lens, whereby said focal plane can be repositioned into coplanar relationship with said second surface, the second point image on said sensor surface coinciding with the position occupied by the first point image on said sensor surface when said focal plane is coplanar with said second surface, the physical distance through which said first lens is moved by said means corresponding to the distance between said first and second surfaces.

4. An apparatus according to claim 3, in which said source of collimated light comprises a laser, the diameter of said collimated beam being less than 1/4 the diameter of said first lens.

5. An apparatus according to claim 3, in which said light sensor includes means for providing a signal constituting a function of the lateral displacement between said first point image and said second point image on said sensor surface, said means for moving said first lens including servo means responsive to said signal so that a continuous automatic positioning of said first lens is effected in accord with varying distances between said first and second surfaces.

6. An apparatus according to claim 5, in which said apparatus includes an elongated probe coaxial with said optical axis and a 45°

angled mirror at the end of said probe for directing said collimated beam at right angles to the axis of the probe whereby the internal relief of a surface surrounding the end portion of said probe can be continuously read out by rotating said probe about its axis.