Machine element or mechanism – Mechanical movements – Reciprocating or oscillating to or from alternating rotary
Reexamination Certificate
1999-12-01
2001-07-31
Green, Maryann (Department: 3682)
Machine element or mechanism
Mechanical movements
Reciprocating or oscillating to or from alternating rotary
C074S441000, C359S391000
Reexamination Certificate
active
06267021
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention resides in the field of adjustable work piece mounting devices for optical components and more particularly relates to motor driven precise positioning stages having anti-backlash components.
2. Description of the Prior Art
A precision positioning stage of the type relating to the invention is disclosed in U.S. Pat. Nos. 4,652,095 and 5,077,620 issued to the applicant. The device described therein employs an adhesive assembly concept for a stage utilizing two end plates having grooves for receiving a pair of rails and a work table slideably disposed between the plates.
The U.S. Pat. No. 5,077,620 is an improvement over U.S. Pat. No. 4,652,095 in that it provides an electrical motor, gear system, and encoder mounted on an additional plate also disposed between the rails and wherein the motor is operationally connected to the work table by, for example, a threaded rod working in conjunction with an anti-backlash device having engaging threads such that the table is precisely moved by actuation of the motor.
Although the device of U.S. Pat. No. 5,077,620 is capable of quite accurate control of the positioning, stability and movement of the work table, any imperfection of the threaded interconnection of the work table and the table drive mechanism, particularly deviations in thread diameters, clearance, alignment, etc. and undesired clearance between the male and female threads will detract from that accurate control. Modern miniature components and parts often require tolerances which are difficult or impossible to meet with constructions such as that of U.S. Pat. No. 5,077,620.
Backlash is an inevitable byproduct of imperfect fabrication techniques and allowable tolerances. It is the amount by which the space between threads exceeds the width of the engaging threads and generally tends to substantially effect the engaging threads and associated components upon reversal of gear rotation. As is appreciated by those of ordinary skill in the art, any reduction in backlash between threads, especially in the art of micro adjustable tools, amounts to a considerable increase in the precision with which associated components of the apparatus may be positioned.
Precise measurement to achieve the above described positioning entails paying particular attention to the alignment and precision of the engaging and moving parts, in particular between engaging threads. Elimination of backlash between threads is of considerable importance in the reduction of error in precise positioning.
Accordingly, it is an object of the present invention to overcome many or all of the thread related limitations of the prior art.
SUMMARY OF THE INVENTION
The invention may be summarized as an improvement in a work piece positioning stage of the type described above to provide a degree of precision and miniaturization not heretofore obtainable in that the travel of the work piece table is precisely performed and duplicated via the particularly accurate engagement between the threaded rod and an anti-backlash device attached to the table.
According to the invention there is provided an anti-backlash device defining a longitudinal axis and comprising at least three elongate spring members spaced apart about said axis and supported at opposed ends by first and second longitudinally spaced member supports, each spring member being fast with a threaded portion, the threaded portions being spaced apart about said axis to form an interrupted thread biased by the spring members for zero clearance engagement with a mating thread.
Also according to the invention there is provided in an optical positioning stage having a workpiece mounting table slideably disposed on rails, a motor assembly drivingly connected to a threaded rod wherein rotation of said motor affects lateral movement of said table along the rails; an anti-backlash device comprising, a tubular member having a first end and a second end separated by a plurality of resilient bridges, extending between said first and second ends, separated by a like plurality of slots also extending between said first and second ends, the first and second ends having an outer diameter to facilitate a press fit engagement within a bore in said table and the resilient bridges having an incurvate compressive bias providing a variable diameter decreasing to a central portion of the tubular member; the bridges together define, on an inner surface thereof, an interrupted female thread, for a biased, resilient engagement with the threaded rod to effectuate a resiliently biased substantially zero clearance engagement of the female thread with the thread of the rod.
REFERENCES:
patent: 2090337 (1937-08-01), Stoll
patent: 4002083 (1977-01-01), Glicken
patent: 4210033 (1980-07-01), Erikson et al.
patent: 4593572 (1986-06-01), Linley, Jr.
patent: 4652095 (1987-03-01), Mauro
patent: 5077620 (1991-12-01), Mauro
Davis & Bujold P.L.L.C.
Green Maryann
Joyce William C
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