Precision workpiece positioning device

Geometrical instruments – Distance measuring – Scale reading position sensor

Reexamination Certificate

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Details

C033S702000, C033S645000

Reexamination Certificate

active

06260285

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to high precision workpiece positioning equipment and, more particularly, to equipment for precisely positioning workpieces in a vertical direction.
2. Description of the Related Art
There are many devices intended to provide physical placement of objects along and around multiple axes. However, with modem advances in technology, the need to precisely position workpieces, such as during manufacturing and testing procedures, has become more prevalent. For example, often, mechanical, optical, electronic, genetic, medical and chemical disciplines require exact placement of various components combined with an ability to manipulate the object in one or more dimensions. Possibly one of the more prominent needs is in the optical world of precision optics, lasers, lenses, and fiber optics. Other needs include micromachining and semiconductor device inspection.
Conventional methods include a series of adjustable leadscrews which are attached to a working platform or table at one end and some suitable base on the other. Each axis may then be manipulated by turning a micrometer type positioner a prescribed amount which, in turn, moves the working platform or table to the desired position relative to its base or some other reference such as an optical axis. However, these types of devices are inherently less precise than the precision required by today's technology.
Other conventional workpiece positioning devices are known to include two wedge-shaped members wherein a first wedge is driven by a leadscrew and is caused to engage the surface of a second wedge connected to the working platform. Thus, as the surfaces of the two wedges and the first wedge is driven forward and backward, the working platform is raised and lowered accordingly. However, conventional wedge-drive workpiece positioning devices exhibit limited ability to precisely position the workpiece, due to the tolerances in the angle, accumulation of manufacturing tolerances and smoothness of the contact surfaces of the opposing wedges.
Another problem with conventional wedge drive designs is a loss of accuracy associated with inadequate stability of the working platform as it is driven along the vertical axis, due, in large part, to the horizontal component of the force exerted by the wedge drive on an elevator component which supports and lifts the working platform. Conventional wedge drive positioning systems typically feature widely spaced cross roller guides which have a certain level of geometry error in the guide planes due to manufacturability. Since there are 3×2 surface planes involved, such widely spaced locating surfaces cannot be machined to the exceedingly close tolerances required to achieve the accuracies obtainable with the present invention. The design of the present invention reduces to 2 planes at close proximity.
What is clearly needed is a workpiece positioning device which overcomes the accuracy problems associated with prior art devices and is capable of positioning workpieces with a high degree of precision to meet the needs of present day technology.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a positioning device which is configured to permit positioning of workpieces in a vertical direction with higher precision than existing vertical positioning devices.
In one embodiment of the present invention a workpiece positioning device includes a frame; an elevator assembly mounted on the frame for motion along a z-axis; an inclined plane assembly attached to the elevator assembly; and a drive assembly mounted on the frame and configured to cause the elevator assembly to move along the z-axis, the drive assembly including a slide member and a bearing positioned in a first end portion of the slide member (which is formed in the shape of a wedge) to contact the inclined plane assembly. The drive assembly further includes a leadscrew for driving the slide member toward and away from the inclined plane assembly. The bearing is positioned in the first end portion of the slide member such that a portion of a circumference of the bearing protrudes from a surface of the first end portion of the slide member such that the bearing contacts the inclined plane assembly at a single point to cause the elevator assembly to move along a z-axis as the slide member is driven toward and away from the inclined plane assembly.
The elevator assembly includes a platform for supporting a workpiece, and at least one set of guides positioned on either side of the elevator assembly for maintaining the elevator assembly in alignment with the z-axis. An encoder may be mounted adjacent to the elevator assembly for measuring a displacement of the elevator assembly along the z-axis.
An angle formed between the inclined plane assembly and the frame is preferably 26 degrees, and the drive assembly, inclined plane assembly and elevator assembly are configured to cause displacement of a workpiece in increments of about ten nanometers.
A method of positioning a workpiece is also provided which includes the steps of mounting an elevator assembly on a frame; supporting a workpiece on a platform on the elevator assembly; attaching an inclined plane assembly to the elevator assembly; and driving a drive assembly toward and away from the elevator assembly to cause the elevator assembly to move a desired distance along a z-axis via a single point of contact between the drive assembly and the inclined plane assembly. The method of positioning a workpiece may further include the step of measuring the displacement of the elevator assembly along the z-axis via an encoder mounted on the elevator assembly. The driving step preferably includes driving the elevator assembly along the z-axis in increments of about ten nanometers.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments, which is to be read in connection with the accompanying drawings.


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patent: 5768798 (1998-06-01), Takahashi et al.
patent: 6058618 (2000-05-01), Hemmelgarn et al.

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