Abstract:
A multi-axis optical projector comprises an optical yoke having two spaced-apart primary objective lenses and optical paths for transmitting either backlight or front light from light sources to a target object disposed between the primary objective lenses and from the target object to a secondary objective lens focussing on an eyepiece which may be a video camera. The projector is used, for example in a tool presetting or tool measuring system, for viewing of a specimen, such as a cutting tool, to measure tool profile and to identify tool surface defects such as cracks, chips, wear patterns and coating abnormalities.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a multi-axis optical projector comprising an optical yoke for use, for example in a tool presetting or tool measuring system, for viewing of a specimen, such as a cutting tool, to measure tool profiles and to identify tool surface defects such as cracks, chips, wear patterns and coating abnormalities. 
     Optical comparators are often used in conjunction with tool presetting apparatus. Such prior art devices permit viewing of a specimen in silhouette (backlighting). When viewing a curved surface, a comparator can be expected to create a &#34;fuzzy&#34; image. This is because of parallax: the specimen usually is illuminated broadly on both sides of the focal point due to the usual low quality (normally plano-convex) lenses employed in a separate, discrete lamp house. The target is flood-lit both before and after the functional focal plane of the objective lens. 
     The traditional approach to determining edge position and tool size with presetting fixtures has been to make use of electromechanical touch probes or single view optical projectors. The latter method offers the advantage of non-contact dimensional determination for cutting tools such as those composed of polycrystalline diamond or other brittle materials. However, with current optical projectors, only a backlighted image is available for viewing a specimen. The prior art is devoid of optical arrangements employing a microscope or macro-capable telescope with dual, selectable objective lens systems providing for both backlighting and front lighting so that both tool measurement and surface integrity can be determined. 
     Moreover, current optical projectors used in conjunction with tool presetting applications inherently bias the presetting machine to either a right or left hand tool setting orientation. 
     SUMMARY OF THE INVENTION 
     In contrast to prior art optical comparators, the present invention provides means to illuminate a target zone with an intense light source at or near infinite distance, thereby eliminating the fuzziness encountered with use of prior art devices. The object to be viewed is placed between two alternative objective lenses disposed at 180° from each other, and providing for both front and backlighting. This permits, not only profile measurements, but also accurate surface inspection of specimens such as tools for checking for flaws which are difficult or impossible to detect with only a backlighted image. The overall arrangement of lenses, mirrors and prisms in accordance with the invention allows an operator an additional viewing perspective, permits viewing of tools possessing &#34;handedness&#34; (clockwise or counter-clockwise rotation during cutting operations), and, with re-direction of the image path, achieves a non-biased tool-setting orientation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of an optical yoke in accordance with the present invention in a left hand tool viewing position. 
     FIG. 2 is a front elevational view of the yoke of FIG. 1. 
     FIG. 3 is a top plan view of an optical yoke in accordance with the present invention in a right hand tool viewing position. 
     FIG. 4 is a front elevational view of the yoke of FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In FIG. 1, the numeral 1 refers generally to an optical yoke comprising a cross-piece 2 and legs 3 and 4. At the free end of the legs 3 and 4 are mounted primary achromatic objective lenses 6 and 7 respectively. These lenses are adjustable, for focussing, and are equidistant from a point &#34;O&#34; representing disposition of a object to be viewed. 
     A mirror 8 is disposed at the outer corner of the juncture of the cross-piece 2 and the leg 3, and a pair of mirrors 9, 11, functioning in the nature of a prism, are disposed at the outer corner of the junction of the cross-piece 2 and the leg 4. A mirror 5 is disposed at the outer corner of the free end of leg 4 and a mirror 10 is disposed at the outer corner of the free end of leg 3. 
     As more clearly shown in FIG. 2, a number of optical elements are mounted on a selector slide, generally denoted by the numeral 12, which in turn is reciprocally movably mounted on the cross-piece 2. A selector knob 13 is affixed to the slide 12 and serves as a handle for manually moving the slide 12 in a desired direction. 
     The optical elements mounted on slide 12 comprise a first beam splitter 14, a pentaprism 16, a mirror 17 and a second beam splitter 18. 
     Also mounted on the yoke cross-piece are a first light source 19 and a second light source 21. Each light source can serve as a source of backlighting or front lighting. For right hand tool viewing, the first light source is selected for front lighting, with the first beam splitter under the light source, and the second light source is selected for backlighting with the slide-mounted mirror under the light source. For left hand tool viewing the second light source is selected for front lighting, with the second beam splitter under the light source, and the first light source is selected for backlighting, with the pentaprism under the light source. 
     A housing 22 is mounted on cross-piece 2 and accommodates a video camera 23 having an adjustable adaptor 24 for focussing and is attached by a lock ring 26 to a camera tube 27. Mounted within the camera tube 27 is an achromatic secondary or eyepiece lens 28 fixed in a stationary mount 29. 
     The lens 28 focuses an image &#34;I&#34; on a charge couple device (&#34;CCD&#34;) array (not shown) of the video camera 23. In the device as illustrated, the image &#34;I&#34; is inverted and reversed. The image is re-erected by the video camera. 
     FIGS. 1 and 2 show the optical yoke in a left hand tool viewing position, whereas FIGS. 3 and 4, depicting the same apparatus with the same elements identified by the same numerals as FIGS. 1 and 2, shows the apparatus in a right hand tool viewing position. 
     In the different positions of FIGS. 2 and 4, the direction of the frontlight path is denoted by the letter &#34;A,&#34; the direction of the backlight path is denoted by the letter &#34;B,&#34; and the direction of the image path is denoted by the letter &#34;C.&#34; 
     It is seen (FIGS. 1 and 3) that the primary objective lenses 6 and 7 are arranged 180° apart and are focussed on opposite sides of a target object &#34;O&#34; located centrally between these lenses. This permits viewing tools possessing left or right handedness, without bias. This arrangement of lenses, mirrors and prisms also permits viewing of a specimen or group of specimens through a single eyepiece (or camera) with multiple, selectable objective lens sets, so that multiple perspective views are possible. 
     As shown in the drawings, two alternative optical viewing paths are provided. These alternate paths are identified as left and right hand viewing. The provision of two available light sources permits front illumination in addition to backlighting (viewing of an object in silhouette) as is commonly done with prior art optical comparators. The arrangement of the invention thus provides four primary viewing modes: left hand viewing with backlight or front light source, and right hand viewing with backlight or front light source, as well as mixed illumination. 
     Selection of the primary objective lens elements to be used is accomplished by moving the optical elements placed in the light path between the objective lenses 6 or 7 and the eyepiece lens sets. In the embodiment shown in the FIGURES, this is done manually by moving selector slide 12 by means of knob 13. Switching also may be done by using a galvanometer-mounted optical element arrangement to permit automated selection of objective or interleaving of frames in which, for example, opposite sides of a two-dimensional object can be alternately viewed, or interval-timed images can be obtained showing movement of the object or scene viewed, e.g. in space-surveillance applications. Such an arrangement, in which views can be obtained from two or more viewpoints without the need for a moving camera, may be especially desirable for video camera data acquisition for digitizing and analysis. A typical example of interleaved frames would be edge-finding without strobe light sources. 
     The optical yoke system herein shown and described preferably uses an objective lens-to-target distance of one focal length. Since focal length is defined a the distance required for parallel light waves from an infinitely distant source to be focussed, it follows that the unerected image travels as an infinitely distant object, and the light path distances from either side of the optical yoke are not critical for imaging. In the backlighting or silhouette mode, the light focus is critical in order to minimize distortion. Here also the distance from the target object to the primary objective lens preferably is one focal length. 
     In use of the present invention as shown, the image of the target object is erected at actual size on the CCD array of the video camera. Magnification occurs during presentation of this information on an attached monitor. Degree of magnification or reduction can be provided by changing lenses and/or distance from the objective lens to the target object. Formulae for calculating such options are well known to those familiar with the art. 
     The arrangement of optical elements shown presents a frontal view through both light paths, with the object image focussed on the CCD array of the video camera. By rearranging the optical elements, it is possible to obtain an erect image through one light path and an inverted image through the other light path. Such an arrangement is appropriate for optical overlay applications.