Inspection Device for Measuring a Geometric Dimension of a Part

1. Field of the Invention

This invention relates to inspection devices and, more particularly, to an inspection device which utilizes dual radiation detectors to identify a geometric dimension of a part.

2. Description of the Related Art

Lasers have been known and used for measuring the geometric dimensions of a part. Such techniques as shown in FIG. 1 involve positioning a part in the path of a single laser beam 99 thereby obstructing a portion of the beam. The magnitude of radiation present in unobstructed portions 100, 102 then falls incident upon a singular measuring device which converts the magnitude of radiation present in portions 100, 102 to a voltage value which is proportional to a respective physical dimension. Such a technique is not capable of discerning the concentricity of a part as the effective axis 108 of the part may shift (i.e., a non concentric part) in the beam without affecting the total magnitude of radiation which is incident on the measuring device.

Techniques shown in FIG. 2 have been developed which utilize two non-parallel, preferably co-planar laser beams 200 and 210 and two light measuring devices (not shown) to monitor the magnitude of light present in unobstructed portions 202, 212. The part 203 is positioned in the non-parallel beams so that a first portion incident on part 203 is obstructed; whereas a second portion remains unobstructed. By positioning each laser to produce non-parallel paths through the part, any off-axis dimensional characteristic of the part may be detected as a change in magnitude of radiation present in unobstructed portions 202, 212. Co-planar laser beams are necessary to ensure that each beam is incident at the same cross-section of the part. A non-planar analysis performed by non-planar beams will not produce an accurate measure of the part cross section. Two lasers, two detectors and substantial space is required to accommodate such dual non-parallel laser inspection devices. Therefore, there is a need to reduce the number of lasers and provide a package efficient inspection device. In addition, the dual laser systems are typically mounted on a planar structural member in attempt to produce co-planar laser beams. Such a mechanical attempt to achieve co-planar beams is very complex and sensitive to physical disturbance resulting in an expensive and unreliable solution. Therefore, there is a need to provide a low cost and reliable inspection device which is capable of inspecting the cross-section of a part using a single laser beam.

The present invention utilizes a laser for producing a beam of radiation which is then refined in cross sectional dimension by use of plano-cylindrical lenses. The refined beam of radiation falls incident on a part to be measured. The unobstructed portions of the beam are then redirected by a pair of reflective surfaces producing non-parallel radiating beams; each beam comprises of the unobstructed portion of radiation which has passed radially opposed halves of the part. The magnitude of radiation present in each non-parallel radiating beam is then measured. The magnitude of radiation measured is proportional to a dimensional measurement.

These and other aspects of the present invention will become more readily apparent by reference to the following detailed description of the embodiments as shown in the drawings.

FIG. 1 is a side view of a part in a radiation beam used in a first prior art device;

FIG. 2 is a cross-sectional view of a part in a second prior art device which uses two non-parallel laser beams;

FIG. 3 is a partial schematic shown in side view of the present invention;

FIG. 4 is a plan view taken along 4--4 of FIG. 3;

FIG. 5 is an end view of the present invention taken along 5--5 of FIG. 3;

FIG. 6 is a cross sectional view of the present invention taken along 6--6 of FIG. 5;

FIG. 7 is a cross-section taken at line 7--7 of FIG. 3;

FIG. 8 is a distribution of energy magnitude taken along the Y axis of FIG. 7;

FIG. 9 is an electrical schematic which may be used to process an output of the present invention; and

FIG. 10 is a voltage signal which is produced by the present invention used to inspect various parts.

The present invention, as shown in FIG. 3, 4 and 5, includes a radiation source provided by a line generating laser 300 producing a laser beam 302 characterized by a beam width of 0.8 mm and a height characterized by radiation emanating at an included angle of 60 degrees from the point source.

The beam 302 as shown in cross-section in FIG. 7, features a distribution of energy as shown in FIG. 8. Planocylindrical lens 304 truncates the lower magnitude energy portion outside dimension 304d by means of its dimension and position in beam 302. Lens 304 is positioned such that the axis of radius of the lens is oriented perpendicular to the beam line and the curved surface of lens 304 faces away from laser 300 producing a beam of constant height.

Plano-cylindric lens 306 is positioned such that the axis of radius is in-line with the constant height of the beam and the curved surface is oriented toward laser 300. Lens 304 produces a beam of constant height and lens 306 focuses the beam to a focal point 310 shown in FIG. 4 which forms a line 310' in FIG. 3.

Precision measurement of a dimensional characteristic is achieved by minimizing the laser beam width and positioning the part at the point of minimum beam width. Such may be achieved by using optical devices which produce a focal line at which the part is positioned for measurement.

A part 308 positioned in beam 312 at or near focal point 310 will obstruct a portion of beam 312. The unobstructed portions 312A, 312B passing opposed radial sides represent the dimensional characteristics of part 308. Next, the unobstructed portions 312A and 312B of beam 312 are redirected by reflective surfaces 314, 314' defined on prism 316 into two non-parallel radiating beams 318, 318'.

Plano-cylindrical lenses 320, 320' focus beams 318, 318' to a beam height dimension -b- which is smaller than the dimension of sensing elements 324, 324' of the photo detectors 322, 322'0 as shown in FIGS. 3 and 6. Plano-cylindrical lens 320, 320' are oriented with the curved surfaces toward the direction from which radiating beams 316, 316' originate.

Lens 326, 326' are negative concave lenses which widens beam 316, 316' preferably to a which is beam width dimension -a- greater than the respective dimensions of sensing elements 324, 324' of photo detectors 322, 322'. In this manner, the resolution of the present invention is enhanced; that is, all beam length information is captured. The beam height is representative of the measured part dimension whereas the beam width contains no information and in fact can cause inaccuracy of measurement. By using a sensing elements 324, 324' which offers a smaller dimension than the corresponding incident beam widths, any fringing effect is eliminated and a more accurate measurement can be performed.

FIG. 9 illustrates the electrical circuitry in simplified form which allows one to practice the present invention. Photo diode 322 is shown connected to circuit 328 which includes resistor 330 and voltage source 332. A voltage measuring device may be used to convert information in beams 318, 318' to a voltage which is representative of the radial dimension of part 308.

FIG. 10 illustrates graphically the various voltage values that will be produced when parts of various radial dimensions are measured; Vo will be produced if no part is present in the laser beam; Vc will be produced if a part of the correct radial dimension is being tested, and Vr will be produced if a part having radial dimensions greater than the correct radial dimension is being tested. Such a feature may be used to sort parts. Techniques to move part 308 axially while measuring the geometric dimensions of part 308 will provide a complete analysis of part 308.

Comparisons of the collected geometric dimensions can be performed to determine if part 308 satisfies predetermined criteria. In addition, part 308 may be rotated about its axis to perform an analysis of the concentricity of the part. Rotation will also assist in identification of defects which may not extend over 180 degrees of the part surface.

One skilled in the art will readily recognize that certain specific details shown in the foregoing specification and drawings are exemplary in nature and subject to modification without departing from the teachings of the disclosure. Various modifications of the invention discussed in the foregoing description will become apparent to those skilled in the art. All such variations that basically rely on the teachings through which the invention has advanced the art are properly considered within the spirit and scope of the invention.