FIELD OF THE INVENTION
This invention relates to supports, commonly called “dials”, for precisely indexing fixtures for workpieces in and out of processing stations, such as laser drilling stations, and more particularly to a dial support system which protects the dial against out-of-plane excursions while at the same time relaxing the performance specifications of the bearings associated with the dial indexing motor.
BACKGROUND OF THE INVENTION
It is known to use rotatable dials to index workpieces in and out of processing stations, such as laser drilling stations, where precise control over the location of the workpiece is required. The dial is typically circular and has a central, vertical axis of rotation, referred to as the “Z-axis”. A motor is mounted in a frame below the table for indexing the table on command. The frame typically includes a dimensionally stable surface underlying the table.
In conventional rotary indexers, the dial mass is supported by the indexer motor bearings. To protect the dial against out-of-plane excursions; large, expensive and highly precise indexer bearings are required as to minimize play in the thrust direction; i.e., along said axis of rotation, and in tipping or tilting as a result of radial play. In the case of large diameter dials; i.e., dials of one meter or more in diameter, expensive measures have been taken to prevent tipping or tilling when vertical forces are applied near the outer edge of the dial. The measures include increasing the size of the indexer thrust bearings and adding outrigger structures which engage the dial when in an indexing location. The larger thrust bearing add cost and the outriggers consume processing time and can cause positional errors.
SUMMARY OF THE INVENTION
The present invention provides for a high degree of stability and protection against out-of-plane excursions for indexable dials without the expense of larger indexer thrust and without the problems created by selectively engageable outriggers. In brief, the invention removes the task of supporting the dial mass from the indexer.
In general, this is accomplished first through the use of a flexure element mechanically interconnecting the motor and the dial, and second by an air bearing system supporting the dial. The flexure element is non-compliant in torsion while at the same time essentially decoupling the table from the indexer along the Z-axis. The air bearing system supports the dial mass and allows smaller, less expensive indexers to be used.
As hereinafter described, the air-bearing arrangement can take several forms and may incorporate vacuum preloading as well as partial integration into the dial structure. For a complete understanding of the invention, reference should be taken to the following description of illustrative embodiments thereof.
BRIEF SUMMARY OF THE DRAWINGS
The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views and wherein:
FIG. 1 is a perspective drawing of a laser drilling system incorporating the invention;
FIG. 2 is a perspective drawing of a first dial support system for the drilling system of FIG. 1;
FIG. 3 is a perspective drawing of the FIG. 2 apparatus from another angle;
FIG. 4 is a schematic cross-section of an alternative support system for the dial of FIG. 1;
FIG. 5 is a schematic cross-section of a second alternative support system;
FIG. 6 is a partial schematic side view of an exemplary air bearing installation; and
FIG. 7 is a partial schematic side view of an inverted dial embodiment.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
Referring to FIG. 1, there is shown a laser drilling system 10 comprising a frame 12 supporting a steel plate 14, the top surface of which is leveled. Supported above the plate 14 is an indexable dial 16 supported by a system of air bearings 28 hereinafter described. The indexable dial is designed to receive workpieces on fixtures 17 which allow the workpieces to be precisely positioned for processing steps such as laser drilling performed by a laser system 18 under the control of a real time computer 20. As soon as the indexer is on position, a command to verify alignment and laser that the part is given. A programming station 19 is provided. The balance of the system 10 comprises housings 22 for subsystems for providing power, temperature control, air processing and other needs for the laser drilling device 18. Details of such system components may be found in my co-pending application Ser. No. 12/394,966 filed Feb. 27, 2009 and assigned to Electro Scientific Industries, Inc.
Referring now to FIGS. 2, 3 and 6, a first support system for the dial 16 will be
described. The dial 16 is shown as circular and mounted for rotation about a vertical Z-axis by an indexing motor 24 which is secured to the frame 12. FIGS. 2 and 3 show the dial 16 supported by four equally circumferentially and radially spaced air bearings 28 which may be of a type available from New Way Air Bearings, contact telephone 610.494.6700. According to that company's product literature, the bearings 28 produce a fluid film achieved by supplying a flow of air under positive pressure through a porous carbon diffuser in the bearing. New Way Air Bearings are susceptible of use in a combination positive air flow/vacuum mode using both positive air pressure and vacuum ports to provide vacuum preloading, a feature which can be used to advantage in the present invention as it adds stiffness to the air bearings 28. FIG. 6 shows how the bearings 28 are mounted to plate 14 by means of a standoff 30 and a spherical joint 31 with a fine pitch thread. The standoff 30 is attached to the plate 14 and the joint is attached to the bearing 28.
FIGS. 2 and 3 show how the dial 16, which may be up to or in excess of one meter
in diameter, is mechanically interconnected to the output shaft of the motor 24 through a flexure member 26 which is a plate-like structure made of low carbon steel. The flexure member 26 has a substantially circular center section 42 directly attached to the output member of the motor 24 by two screws, and four flexure arms 44 which are attached by screws to the bottom of the dial 16 as shown in FIG. 2. The configuration of the flexure 26 is such as to be stiff in torsion; i.e., it transmits torque from the motor 24 to the dial 42 in a highly non-compliant way. However, the flexure arms 44 allow substantial compliance along the Z-axis so as to prevent excursions of the motor output shaft along the Z-axis from being transmitted to the dial 16. In short, the flexure 26 selectively decouples the dial 16 from the motor along the Z-axis.
As discussed above, the air bearings 28 lie approximately 12 to 15 inches radially outwardly from the center of the rotating structure shown in FIGS. 2 and 3 and thus provide substantial support for the dial 16 when supplied by positive pressure from a source (not shown). As also discussed above, the air bearings 28 may be operated in a dual mode by connecting to a vacuum source thereby to provide vacuum preloading which increases the stiffness of the air bearings and also permits rapid switching to a mode in which the vacuum preload dominates and effectively sucks the bottom surface of the table 16 onto the upper surface of the bearings 18 for positional stability during, for example, a laser drilling process. While four bearings are shown, it will be understood that a greater or lesser number may be used, three being the minimum in the case of discreet bearings.
Referring now to FIG. 4, a first alternative embodiment of the invention is shown. In FIG. 4, the motor shown at 24′ mechanically connected to the flexure 26 through a spacer 27. Flexure 26 has in turn the flexure arms 44 thereof fastened to the underside of the dial 16′. The dial is shown sitting closely adjacent to the top surface of the plate 14 which, as shown in FIG. 1, is supported by the frame 12. A vacuum and compressed air slip ring/manifold structure 46 provides compressed air to bearing inlets 36 which exit as orifices from the underside of the dial 16′ to provide the lifting aspects of the air bearing. Circular concavities 40 are milled into the underside of the dial 16′ and connected by lines 38 to a vacuum source through the slip ring manifold 46 to provide the vacuum preloading aspect described above. The positive air pressure to the lines 36 can be shut off, thus creating a vacuum which draws the underside of the dial 16′ to the top surface of the plate 14 as previously described.
The flexure 26 prevents Z-axis excursions from passing from the motor 24′ to the dial 16′ whereas the air bearings provided by positive lines 36 and vacuum preload lines 38 with cup-shaped recesses 40 maintains the stability of the dial 16′ during and between indexing operations. The flexure also allows the dial 16′ to drop down against the plate surface as described above.
FIG. 5 shows a stiff further embodiment of the invention in which the positive and negative air pressure conduits′3′6″and 38′, respectively, run through or under the plate 14′ rather than through the dial 16″, eliminating the need for the rotary coupling 46 to supply air to the dial 16″. In the FIG. 5 embodiment, compressed air flows via lines 36′ to orifices in the plate 14′ under dial 16″ while lines 38′ are attached to a vacuum source to draw a vacuum in milled concavities 42 in the plate 14′. Controls can be provided for regulating the positive and negative pressure flows independently of one another.
While the invention has been described with reference to several embodiments in which the dial overlies the bearings, it is within the scope of the invention to locate and size the vacuum system such that it holds the dial 16 against gravity, thus allowing parts to be processed in an inverted manner as desired. Such an embodiment is shown in FIG. 6 where the dial 16′″ is below the plate″. The air flow paths 36″ and 38″ are similar to those of FIG. 5 but suction via paths 38″ holds the dial 16′″ against gravity. The indexer is shown under the dial 16′″ but may also be above it.
Patent Application
20100310200
