DRIVE MECHANISM HAVING A PRESSURE MEMBER

Abstract: A driving mechanism having a driving shaft (3), which is rotatable about a first axis (5) and on which a pressure member (17) is located engaging with a first roller segment (29) a fixed support (19) and with a second roller segment (33) an adjustment member (25), which can be coupled to a load (23) displaceable parallel to a second axis (21). The driving mechanism is particularly suitable for comparatively small and accurate displacements of a load, such as, for example, a mask table in an opto-lithographic apparatus.

Description: The invention relates to a drive mechanism having a driving shaft which is rotatable about a first axis and to which a pressure member is connected engaging an adjustment member, which is displaceable in translation along a second axis at right angles to the first axis, and wherein the adjustment member and the pressure member are relatively rolled off, said pressure member engaging at least at a first contact point a fixedly arranged support at the area of a first roller segment and at least at a second contact point the adjustement member at the area of a second roller segment located opposite to the first roller segment. In a driving mechanism of the kind mentioned in the opening paragraph (from "Machinery", Vol. 56, Sept. 1949, pp. 193-194) the driving shaft has mounted thereon a cam body with parallel guide rails for relative displacement of a cam-shaped bar. The presence of guide rails for the cam-shaped bar means play, friction and a relatively low stiffness. The invention has for its object to provide a driving mechanism, in which the said disadvantages are avoided. The driving mechanism according to the invention is for this purpose characterized in that the driving shaft and the pressure member constitute an unitary, integrated one-piece driven structure of which the pressure member acts as a cam between the fixedly arranged support and the adjustment member. A further embodiment of the driving mechanism according to the invention, in which a resetting force for the adjustment member is obtained in a simple manner, is characterized in that the adjustment member is tiltable about an second axis parallel to the first axis. A still further embodiment of the driving mechanism in which the so-called Hertzian stresses in the pressure member remain comparatively low, is characterized in that the first and the second roller segment, viewed in a plane transverse to the first axis, partly coincide with a cross-section of a first and a second circular cylinder having the same diameter and a first and second generatrix respectively, coinciding with a first and a second contact line parallel to the first axis between the first and second roller segment and the support and the adjustment member respectively, in a central position of the pressure member. A further embodiment of the driving mechanism, in which a comparatively small angular rotation of the pressure member about the first axis leads to a comparatively large displacement of the adjustment member, is characterized in that the first generatrix coincides at the area of the first contact line with the first axis in the central position of the pressure member. A still further embodiment of the driving mechanism having a simple stroke limitation of the pressure member and a very small eccentricity without self-braking occurring in the case of contamination and/or wear is further characterized in that the pressure member has a parallellogram-shaped cross-section in a plane transverse to the first axis, the first roller segment being located at the area of one of the angular points of the said cross-section and the second roller segment being located opposite to the first roller segment at the area of a further angular point of the parallellogram-shaped cross-section. A further embodiment of the driving mechanism with a substantially linear relation between the rotation of the driving shaft and the translation of the adjustment member is characterized in that with a relative position of the pressure member and the adjusment member in which a first bisectrix plane of the first roller segment and a second bisectrix plane of the second roller segment are parallel to the direction of translation, the sum of the values of the distance between a first cylinder axis of the first circular cylinder and a second cylinder axis of the second circular cylinder projected onto the direction of translation and of the diameter of the circular cylinder is larger than the diameter of the two circular cylinders. It should be noted that a driving mechanism is known from German patent DE-C-454399 wherein roller members are described which have been locked up in a sleeve of the driving shaft between two cam-shaped bodies. The rotatable and translatable roller members introduce play, friction and a relatively low stiffness. The invention will be described more fully with reference to the drawing, in which: Figure 1 shows diagrammatically in side elevation a first particular embodiment of the driving mechanism, Figure 2 is a longitudinal sectional view of the driving mechanism shown in Figure 1, Figure 3 is a plan view of the driving mechanism shown in Figure 1, Figure 4 shows on an enlarged scale a cross-section taken on the line IV-IV in Figure 3, Figure 5 shows diagrammatically in side elevation a second embodiment of the driving mechanism, Figure 6 shows diagrammatically in side elevation a third embodiment of the driving mechanism. The particular embodiment of the driving mechanism in the central position shown in Figures 1, 2, 3 and 4 has a driving shaft 3, which is coupled to an electric motor 1 and is rotatable about a first axis 5. The electric motor 1 is coupled to the driving shaft 3 via a delaying transmission 7 and a flexible bellows coupling 9. The assembly of the electric motor 1 and the transmission 7 is supported in a housing 11. The electric motor 1 is covered by a hood 13, which is secured to the housing 11. The driving shaft 3 is freely rotatable in a ball-bearing 15, which is mounted in the housing 11 and serves not for supporting the driving shaft 3, but for limiting any radial displacements of the driving shaft 3. The driving shaft 3 is therefore rotatable with a given radial clearance (0.1 mm) within the ball-bearing 15. At the end remote from the electric motor 1 the driving shaft 3 has a pressure member 17, which is integral therewith and engages by one side a fixedly arranged support 19, which is secured by means of a bolt 20 (cf. Figure 4) to the housing 11, this pressure member exerting on an opposite side a pressure force directed parallel to a second axis 21 on a load 23. It should be noted that the pressure member 17 can exert in a more or less direct manner a pressure force on the load 23. In the embodiments of the driving mechanism shown in the Figures and described hereinafter, a pressure force is always concerned which is exerted via an adjustment member 25 and a coupling member 27 on the load 23. As appears from Figure 1, the pressure member 17 has a first roller segment 29 (partly indicated in dotted lines), which engages the support 19 at the area of a contact line 31 coinciding with the first axis 5 and a second roller segment 33 (partly indicated in dotted lines) engaging the adjustment member 25 at the area of a contact line 35. The contact lines 31 and 35 constitute the generatrices of a first circular cylinder 37 and a second circular cylinder 39, respectively. Both circular cylinders are indicated in Figure 1 in dotted lines. Due to the fact that the contact points of the pressure member 17 on the support 19 and the adjustment member 25 are formed by a line or are strip-shaped, the elastic deformation of the pressure member 17, the support 19 and the adjustment member 25 caused by the pressure forces can remain comparatively small. In the position of the pressure member 17 shown in Figure 1, a first bisectrix plane 41 of the first roller segment 29 and a second bisectrix plane 43 of the second roller segment 33 extend in a plane at right angles to the plane of the drawing parallel to the second axis 21. The pressure member 17 is parallelogram-shaped, the roller segment 21 being located at the area of one of the angular points of the parallelogram and the roller segment 33 being located at the area of an angular point situated diagonally opposite thereto. The distance between a first cylinder axis 45 of the first circular cylinder 37 and a second cylinder axis 47 of the second circular cylinder 39 projected onto the direction of translation of the load 23 (coinciding with the second axis 21 in the position shown in Figure 1) is equal to S and the distance between the contact lines 31 and 35 projected onto the direction of translation of the load 23 is equal to S + D, where D is the diameter of the circular cylinders. The adjustment member 25 engages the coupling member 27 at the area of a contact point 49 located on the instantaneous tilting axis of the adjustment member 25 at right angles to the plane of the drawing. The part of the adjustment member 25 facing the coupling member 27 has the form of a semi-sphere with a radius R. It is assumed that a resetting force is exerted on the load 23, for example by a spring. The load 23 may be an object table supported by blade springs. The driving mechanism described above is intended for a maximum angular rotation α of the driving shaft 3 about the first axis 5. In the extreme angular positions of the driving shaft 3, the parallelogram sides of the pressure member 17 form a stroke limitation for the driving shaft 3. As a result, the maximum translation distance from the load 23 is therefore also determined. The driving mechanism shown in Figure 1 has the advantage that by means of the adjustment member 25 tiltable about the axis passing through the contact point 49 a resetting force is obtained which sets the adjustment member to the central position shown in Figure 1, in which an equilibrium of forces prevails. Due to the distance S between the cylinder axes 45 and 47 in the central position of the pressure member 17, a tiltable adjustment member 25 also affords the advantage of a substantially linear relation between the angular rotation of the driving shaft 3 and the translation of the load 23. Such a linear relation permits of obtaining a comparatively simple control loop with proportional linear control members. The positioning accuracy of the load 23 is thus considerably increased. In the present case, with an angular rotation of ± 0.1 radians of the driving shaft 3 a translation of the load 23 of about 120 µm ± 00.2 µm can be obtained. As appears from Figure 4, in a particular embodiment of the driving mechanism, an adjustment member 25 is used having a hat-shaped tiltable holder 51 provided with a conical edge 53 engaged on one side by a ball 55. The ball 55 engages by its other side a roller surface 57 of the coupling member 27. Such a radial clearance in the form of a wedge is present between the holder 51 and a sleeve 59 surrouding it that the holder 51 can be tilted with respect to the sleeve 59. The coupling member 27 is provided with a shoulder 61, behind which is hooked an edge 63 of the sleeve 59. The sleeve 59 has an annular flange 65, which engages one of the end faces of a helical spring 67. The helical spring 67 engages by its other end face an annular supporting surface 69 of the housing 11. Due to the pressure force of the pre-stressed spring 67, any clearance in the driving train constituted by the pressure member 17, the holder 51, the ball 55 and the coupling member 27 is prevented. In the driving mechanism free of clearance, upon rotation of the driving shaft 3, the first roller segment 29 accurately rolls off over the fixedly arranged support 19 and the second roller segment 33 accurately rolls off over the adjustment member 25. In the second embodiment of the driving mechanism according to the invention, shown in the central position in Figure 5, reference numerals corresponding to those in Figures 1 to 4 are used as far as possible. The pressure member 17 is shown in Figure 5 in the so-called central position for comparison with Figure 1. It is clear that the distance between the contact lines 31 and 35 projected onto the second axis 21 or the direction of translation of the adjustment member 25 is equal to the diameter D of the circular cylinders 37 and 39. This results in that no substantially linear relation exists between the angular rotation of the driving shaft 3 and the translation distance from the load 23. In a large number of applications, however, this is not objectionable. The principle of the reaction force of the fixedly arranged support occurring at the area at which the force is transferred also applies to this case. The combination of the adjustment member 25 and the coupling member 27 is constructed as shown in Figure 4 and is therefore shown only diagrammatically. The third embodiment of the driving mechanism in the central position shown in Figure 6 is also provided with reference numerals corresponding to those of the preceding Figures. The adjustment member 25 comprises a block 71 engaging on one side along the contact line 35 the pressure member 17 and on the other side balls 73 enclosed in compartments of a usual bearing ring 75. The balls 73 further engage the coupling member 27. By means of springs 77, the required resetting force of the adjustment member 25 constituted by the block 71, the balls 73 and the bearing ring 75 is obtained. The bearing ring 75 is displaced at half the speed of the block 71. The pressure member 17 can be provided with parallelogram sides having a comparatively large radius of curvature. Thus, the advantage is obtained of a weakened impact near the end of the stroke of the pressure member 17. Although in the foregoing use has always been made of a line contact between the pressure member 17 and the support 19 and the adjustment member 25, respectively, a point contact or a collection of point contacts is also possible. It is only essential that the cooperating surfaces of the pressure member 17, of the support 19 and of the adjustment member 25 can roll off over each other. Therefore, it is possible to transfer the roller segments 29 and 33 to the support 19 and the adjustment member 25, while the pressure member 17 is given a rectangular cross-section, which engages curved surfaces of the support 19 and the adjustment member 25 at the area of the long side of the rectangle. The axis of rotation 5 need not necessarily pass through the point of engagement of the roller segment 29 with the support 19, although it is thus prevented in a simple manner that slip occurs between the support 19 and the pressure member 17. In the three embodiments described, the second axis 21 is perpendicular not only to the first axis 5 (perpendicular crossing), but also to the facing surfaces of the support 19 and of the adjustment member 25. It is possible that the second axis 21 and the direction of translation of the load 23 enclose an angle with the said surfaces of the support and of the adjustment member. The admissible angle depends upon the required load of the drive and the friction coefficients of the cooperating materials. In general, an angle is preferred which is smaller than 0.1 radians. With the driving mechanisms described, a construction is obtained which ― when compared with eccentric mechanisms ― has an extremely small eccentricity without a self-braking effect occurring. This is even the case if dust is present on the cooperating surfaces, for example due to wear. The construction is compact and has a comparatively small mass inertia. Due to the fact that the force is transferred in the plane of the reaction forces of the support, a very rigid construction is obtained. The cooperating surfaces of the support, the pressure member and the adjustment member can be provided with guides with roller balls or roller cylinders. With a number of applications, the larger dimensions of such a construction are not objectionable. The driving mechanisms described above have a construction in which the journalling of the shaft 3 is no longer determinative of the rigidity of the drive. In this respect, the driving shaft and the pressure member are consequently effectively decoupled. The driving mechanisms described are particularly suitable for driving mask tables in opto-lithographic apparatuses used in the manufacture of integrated circuits. Displacements in the so-called submicron range are possible with the driving mechanism inter alia due to the very high rigidity and the very low friction in the construction.

Claims: 1. A driving mechanism having a driving shaft which is rotatable about a first axis and to which a pressure member is connected engaging an adjustment member, which is displaceable in translation along a second axis at right angles to the first axis, and wherein the adjustment member and the pressure member are relatively rolled off, said pressure member engaging at least at a first contact point a fixedly arranged support at the area of a first roller segment and at least at a second contact point the adjustment member at the area of a second roller segment located opposite to the first roller segment, characterized in that the driving shaft and the pressure member constitute an unitary, integrated one-piece driven structure of which the pressure member acts as a cam between the fixedly arranged support and the adjustment member. 2. A driving mechanism as claimed in Claim 1, characterized in that the adjustment member is tiltable about a second axis parallel to the first axis. 3. A driving mechanism as claimed in Claim 1, characterized in that the adjustment member is displaceable in a direction at right angles to the first and second axis. 4. A driving mechanism as claimed in Claim 1, characterized in that the first and the second roller segment, viewed in a plane transverse to the first axis, partly coincide with a cross-section of a first and a second circular cylinder having the same diameter and a first and second generatrix respectively, coinciding with a first and a second contact line parallel to the first axis between the first and second roller segment and the support and the adjustment member respectively, in a central position of the pressure member. 5. A driving mechanism as claimed in Claim 4, characterized in that the first generatrix coincides at the area of the first contact line with the first axis in the central position of the pressure member. 6. A driving mechanism as claimed in Claim 1, characterized in that the pressure member has a parallellogram-shaped cross-section in a plane transverse to the first axis, the first roller segment being located at the area of one of the angular points of the said cross-section and the second roller segment being located opposite to the first roller segment at the area of a further angular point of the parallellogram-shaped cross-section. 7. A driving mechanism as claimed in Claims 4 and 6, characterized in that with a relative position of the pressure member and the adjustment member in which a first bisectrix plane of the first roller segment and a second bisectrix plane of the second roller segment are parallel to the direction of translation, the sum of the values of the distance between a first cylinder axis of the first circular cylinder and a second cylinder axis of the second circular cylinder projected onto the direction of translation and of the diameter of the circular cylinder is larger than the diameter of the two circular cylinders. 8. A driving mechanism as claimed in Claim 2, characterized in that the adjustment member comprises a tiltable holder having a conical edge engaged by a ball on one side, the holder and the ball engaging resiliently the pressure member and a roller surface of a coupling member, respectively. 9. Optolithographic apparatus which is provided with a driving mechanism as claimed in one or more of the preceding claims.

Inventors: BUIS, EDWIN JOHAN
Applicants: ASM LITHOGRAPHY B.V.
Application year: 1988
Main classification: F16H25
IPC codes: F16H25, F16H21, G03F7, H01L21, F16H37