Supports – Machinery support – Movable machine
Reexamination Certificate
1999-03-31
2001-06-19
Ramirez, Ramon O. (Department: 3632)
Supports
Machinery support
Movable machine
C248S664000, C359S822000, C384S220000, C384S581000
Reexamination Certificate
active
06247676
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of rotatable positioning devices and particularly relates to devices for retaining optical components which are designed for rotation through a limited arc at an extremely fine degree of resolution, particularly those stages designed to rotate polarizing prisms, and most particularly to rotary stages which utilize cylindrical bearings formed from materials having a spring constant effective to insure lateral stability without experiencing irreversible deformation.
BACKGROUND OF THE INVENTION
Opto-mechanical devices are precision instruments useful for controlling the path along which light travels. This path is subject to six independently controlled constraints. A beam of light may travel on a particular path defined by specifying X, Y and Z coordinates. This beam of light is further defined in terms of its rotation about these same axes. This rotation about the X, Y and Z axes is referred to as roll, pitch and yaw respectively. The ability to accurately detect these parameters with a high degree of resolution is required for a variety of applications. For example, detection of a particular species of organic compound, e.g. those having dextrorotatory or levorotatory characteristics requires the ability to measure the rotation of light about an axis as it passes through a solution containing the compound being investigated. This same inventor, in U.S. Pat. No. 5,822,067, Oct. 13, 1998, the contents of which are herein incorporated by reference, describes an optical detection system for use in measuring optical activity within a sample as it flows through a detector consisting of a laser diode with a beam shaping means, a polarizing prism, a flow cell, and a means for attenuating laser fluctuation effects from the sensed signal. In order to control the rotation of the polarizing prism with a high degree of precision, it is known to utilize micro-precision rotation stages.
Micro-precision rotation stages suitable for such applications are available from a variety of manufacturers. Among these are the Melles Griot company, which markets a variety of stages having multiple drive knobs for vernier scale adjustment and operation at resolutions from 5 arc min to 18 arc sec. Another type of rotation stage is available from the Newport Corporation, which manufactures a broad variety of both manual and motorized rotary stages. The Newport devices provide rotary stages having a center aperture which permits the mounting and adjustment of rotating components in light transmissive applications. The Newport rotary stages provide preloaded bearings which are placed in precision-ground races. These stages provide resolution in the range of 4 arc sec-30 arc min.
The Aerotech Corp. manufactures a rotary stage with a clear aperture, marketed under the name ARS301, which utilizes a “sub-arc” second resolution drive mechanism, capable of achieving a 0.1 arc sec resolution. The rotating portion is supported by ball bearings and rotation is effected by manipulation of a steel spring which is placed circumferentially about the rotating portion and is extended or retracted via a finely-threaded adjustment screw.
The problem with these prior art devices is that the use of ball bearings fails to provide a system which accurately and repeatably translates the minute angular excursions of the rotary stage into true linear movement. The bearings are not perfectly round, and they are not being utilized in a manner consistent with their intended function. If a bearing and race combination is included, e.g in a wheel and axle assembly, the bearings make many complete revolutions per minute as they reduce the frictional forces which would otherwise hamper the wheel's rotation. In such an environment, minute inconsistencies in the bearings are of no real consequence. In environments such as that of the instant application, the bearings do not revolve, rather they are moved back and forth over a very small portion of their circumference, on the order of 5-10 degrees. In this type of an environment, inconsistencies in the “roundness” of the bearings result in a substantial reduction in the repeatable resolution which can be attained with such devices.
As an alternative to the use of ball bearings in limited movement applications, another type of flexural joint is available from the C-Flex Bearing Co. Both the C-Flex joint and a similar device available from the Lucas Aerospace Power Transmission Corp. are low hysteresis, frictionless joints designed to provide accurate linear movement in limited rotation environments. The design of these joints, do not, however, provide a clear central aperture, and therefore would not be useful for mounting of light transmissive devices such as polarizing prisms.
Thus, what is lacking in the art, is a rotary positioning device having a clear aperture for inclusion of light transmissive optical equipment which is capable of positioning such equipment for precise and reproducible rotation at resolutions finer than 0.1 arc seconds.
SUMMARY OF THE INVENTION
The present invention provides a rotary positioning apparatus having a clear central aperture and enhanced resolution and stability. The apparatus is especially useful for positioning optical devices, for example polarizing prisms, or any similar optical device through which light is transmitted and which requires precise rotation thereof. It is extremely important, when positioning a device such as a polarizing prism, that the plane in which the prism rotates is maintained perpendicular to the path of the light beam. Prior art rotary positioning stages allowed for rotation of such a device about an axis with up to about 0.1 arc second resolution, however the lateral stability along the axis of rotation denigrated the efficacy of these devices. The present invention provides a rotary positioning apparatus which includes a mounting device that may be affixed to a work surface, for example, a laboratory bench or the like. The mounting device is formed with a generally cylindrical aperture of a particular diameter, and is constructed so that it will accept a circular retention ring, having a smaller diameter, that is positioned within the device and in coaxial alignment therewith. In the annular space between the mounting device and retention ring, a plurality of cylindrically shaped bearing members are symmetrically positioned in corresponding machined areas and are in flexural engagement with the mounting device and retention ring. The bearing members are formed from a material having a spring constant value effective for maintaining lateral stability without experiencing irreversible deformation. In a preferred embodiment, the bearing members are formed from a beryllium-copper alloy or from an elastomeric material. This arrangement creates a rotational flexural joint having a useful range of rotation of up to about 4 degrees, subsequent to pre-loading. The apparatus further includes a rotation means in mechanical engagement with said retention ring and extending perpendicularly to the axis thereof. In a preferred embodiment, the rotation means is formed as an upstanding member attached to the outer periphery of the retention ring and fixed within a plane perpendicular to the axis of rotation. In use, the apparatus may be initially pre-loaded by applying a force to the rotation means so as to rotate the retention ring up to about 5 degrees. This pre-loading step increases the forces of flexural engagement between the parts of the device thereby enhancing the degree of axial and lateral stability which is achieved and the concomitant attainable resolution. Subsequent application of force to said rotation means results in reproducible rotation of said retention ring with a degree of resolution of at least about 0.035 arc seconds, which represents almost a three-fold improvement over prior art devices.
Accordingly, it is an objective of the instant invention to disclose a rotary positioning device displaying a repeatable resolution of at least about 0.035 arc seconds.
McHale & Slavin
Ramirez Ramon O.
Szumny Jon
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