Article positioner and method
BACKGROUND OF THE INVENTION 
     The present invention relates to article positioners in general and, more particularly, to an X, Y, Z and θ article positioner that utilizes a plurality of sliding wedges to mutually independent movement in one or more orthogonally related directions. 
     The use of wedges to position an article is known in the art. See: U.S. Pat. No. 1,218,771, &#34;Mechanical Movement&#34;, issued Mar. 13, 1917; U.S. Pat. No. 3,266,329, &#34;Mechanical Movement&#34;, issued Aug. 16, 1966; and, U.S. Pat. No. 4,213,509, &#34;Hydrostatic Setting Apparatus For Support Of Loads&#34;, issued July 22, 1980. 
     Article positioners per se are used in a variety of industries. For example, in the semiconductor industry X, Y, Z and θ &#34;tables&#34; are employed to position a semiconductor wafer with respect to the testing head of a wafer prober. The semiconductor wafer is positioned in X, Y and θ and then moved in the Z axis to contact the wafer prober. After testing, the wafer is moved in the opposite direction along the Z axis and then positionally adjusted with respect to a new test point in X, Y and θ orientation. In this example, the Z axis movement is significantly less than movement in the X and Y axes. Not only is the Z axis movement smaller, but the positional resolution constraint is significantly tighter. Furthermore, it is important to have the table relatively stiff in the Z axis as opposed to the X and Y axes. 
     It is accordingly a general object of the present invention to provide an improved X, Y, Z and θ article positioner. 
     It is a specific object of the invention to provide an article positioner that employs a plurality of sliding wedges to achieve mutually independent movement in at least two orthogonally related axes. 
     It is a further object of the invention to provide an article positioner that is relatively stiff in one axis as compared to the stiffness in the other axes of movement. 
     It is a feature of the invention that the article positioner provides greater travel in the X direction as compared to a conventional article positioner having a similar &#34;footprint&#34;. 
     It is another feature of the invention that the article positioner provides greater X speed and greater X acceleration when compared to traditional article positioners. 
     It is still a further feature of the invention that stiffness in the Z direction is significantly increased together with increased resolution in the Z direction. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The article positioner and method utilize three independently driven wedges that are slidably mounted in superposed relation with respect to each other. The relative movement of the wedges provides a single axis or combinational axes movement to position a workpiece in X, Y and Z with rotational movement of the three wedges as an entity providing θ axis positioning. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the invention described above will best be understood from a detailed description of a preferred embodiment, selected for purposes of illustration, and shown in the accompanying drawings in which: 
     FIG. 1 is a diagrammatic view showing three slidable wedges and the geometric relationships required to produce movement in the X and Z directions; 
     FIGS. 2A through 2C are similar diagrammatic views showing the three wedges in a neutral position in FIG. 2A, the movement of the upper and middle wedges to produce a pure X movement in FIG. 2B and movement of the upper and middle wedges to produce a pure Z movement in FIG. 2C; 
     FIG. 3 is a simplified view in front elevation showing the ball mounting of the lowermost wedge; 
     FIG. 4 is a rear perspective view of the article positioner of the present invention showing the wedges positioned for a pure -X movement; 
     FIG. 5 is a view in side elevation showing the article positioner of the present invention with the three wedges in a &#34;neutral&#34; position; 
     FIG. 6 is a view in side elevation showing the position of the wedges for a pure +X movement; and, 
     FIG. 7 is another view in side elevation showing the position of the wedges to produce a pure +Z. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to the drawings, and particularly to FIG. 1, there is shown in diagrammatic form the general case for the X and Z axis movement of three wedges 10, 12 and 14. The three wedges are shown in superposed relation and will be referred to hereinafter as the lower wedge 10, middle wedge 12 and upper wedge 14. The use of the terms &#34;lower&#34;, &#34;middle&#34; and &#34;upper&#34; are used only for convenience in describing the relationships of the three wedges and it should be understood that the three wedges can be orientated in any direction with respect to a gravity vector. 
     FIGS. 2A through 2C illustrate in diagrammatic form the movements obtained by moving the middle and upper wedges 12 and 14, respectively. The neutral positions for the wedges is depicted in FIG. 2A. FIG. 2B illustrates the movements required to achieve a &#34;pure&#34; movement in the X direction. The wedge configuration in FIG. 2B utilizes two degrees of freedom to obtain X and Z motion. The motion of the middle wedge 12 with respect to the bottom wedge 10 can be considered (X+Z). Similarly, the motion of the upper stage 14 with respect to the middle stage 12 (in the same direction) can be considered as (X-Z). Thus, to obtain pure X movement, equal distance moves are made along both axes in the same direction. In other words, (X+Z)+(X-Z)=2X. Similarly, to obtain a &#34;pure&#34; Z movement as illustrated in FIG. 2C, the middle and upper wedges 12 and 14, respectively, are moved by the same amount, i.e., distance, but in opposite directions. Thus, (X+Z)-(X-Z)=2Z. 
     Referring now to FIGS. 3 through 7, there is shown an article positioner constructed in accordance with the present invention and indicated generally by the reference numeral 16. In this embodiment, two axes are utilized, one inclined at 13° and one inclined at -13°. Using the &#34;general case&#34; formula set forth in FIG. 1, α=β=13° and, therefore: ##EQU1## 
     Looking at FIGS. 3 and 4, the article positioner 16 is shown in front view in FIG. 3 and in a perspective, rear view in FIG. 4. The lower wedge 10 is mounted for sliding movement with respect to a Y axis base plate 18 by means of a linear bearing indicated generally by the reference numeral 20. The linear bearing 20 comprises four linear bearing tracks 22a, 22b, 22c and 22d. A variety of commercially available antifriction guideways can be used for the linear bearing 20. For example, the linear bearings manufactured by Schneeberger are suitable for use in the article positioner 16. 
     Sliding movement of the lower wedge 10 along the longitudinal, i.e. the Y axis, of the Y axis baseplate 18 is accomplished by means of a lead screw 24 that is driven by a stepper motor 26 mounted on the Y axis baseplate 18. The same linear bearing, lead screw and stepper motor arrangement is used to mount and drive the middle wedge 12 with respect to the lower wedge 10 and the upper wedge 14 with respect to the middle wedge 12. For simplicity, the same reference numerals have been used to indicate the same components with respect to both the middle and upper wedges. 
     The upper wedge 14 has a three point plate stage mounting system comprising adjustable mounts 28 that support a workpiece support plate 30 upon which is located a workpiece 32. The adjustable mounts 28 permit leveling of the workpiece support plate 30 with respect to a reference plane (not shown). 
     The entire assembly of the wedges, motors and workpiece support plate is mounted for θ axis rotation by means of a θ axis ball mount indicated generally by the reference numeral 34. The ball mount permits rotation about the θ axis which is normal to θ axis baseplate 36. Rotation of the article positioner about the θ axis is provided by a motor drive (not shown). 
     Looking now at FIGS. 5, 6 and 7, FIG. 5 shows the position of the lower, middle and upper wedges in the &#34;neutral&#34; position. Movement of both the middle and upper wedges 12 and 14, respectively, at the same rate and in the same direction and by the same amount accomplishes a &#34;pure&#34; movement along the X axis. FIG. 6 depicts &#34;pure&#34; X movement in the +X direction, while FIG. 4 shows the same &#34;pure&#34; X movement, but in the -X direction. If both the middle and upper wedges are moved at the same rate and by the same amount, but in opposite directions, as shown in FIG. 7, &#34;pure&#34; Z movement is obtained, in this case &#34;pure&#34; Z movement in the +Z direction. 
     Having described in detail a preferred embodiment of my invention, it will now be apparent to those skilled in the art that numerous modifications can be made therein without departing from the scope of the invention as defined in the following claims. For example, although reference has been made to movement in only the X and Z directions, comparable movement can be achieved in all three axes, i.e., X, Y and Z, using my sliding wedge concept.