Geometrical instruments – Gauge – Coordinate movable probe or machine
Reexamination Certificate
2000-10-11
2002-08-27
Fulton, Christopher W. (Department: 2859)
Geometrical instruments
Gauge
Coordinate movable probe or machine
C033S561000
Reexamination Certificate
active
06438856
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
This invention claims priority of a German filed patent application DE 199 49 044.9.
FIELD OF THE INVENTION
The invention concerns an apparatus for fine positioning of a component, and a coordinate measuring machine having an apparatus for fine positioning of a component.
BACKGROUND OF THE INVENTION
The article of C. Hoffrogge and H.-J. Rademacher entitled “A double parallel spring as precision guide system” [Eine Doppelparallelfeder als Präzisionsführung], PTB-Mitteilungen 2/73, pp. 79-82, describes an apparatus for fine positioning of a component having an integrally machined double parallel spring. The double parallel spring has a stationary frame and a movable center bar that is retained by multiple parallel springs. Energy transfer from a spindle drive arranged outside the double parallel spring to the center bar is accomplished by way of a coupling member and a wire cable. As a result, the overall system is very large. The double parallel spring described is provided in particular for operation in a horizontal position. Operation in a vertical position requires considerable additional design effort with regard to energy transfer, and the attachment of heavy and therefore also large compensation weights. The overall structure thereby becomes even larger and heavier. A displacement of the center bar with little tilting is possible only by way of a complicated distribution of the applied forces.
The present apparatus for fine positioning of a component is to be used in particular for fine positioning of an objective as it is focused in an ultrahighprecision coordinate measuring machine. A coordinate measuring machine of this kind has an X-Y measurement stage for receiving a substrate whose patterns are to be measured with nanometer precision. The objective with the subsequent imaging optical system is arranged above the X-Y measurement stage. After each change in measurement stage position, e.g. after moving to another pattern that is to be measured, refocusing by positioning of the objective is necessary, since even small irregularities in the measurement stage surface, a minor wedge error in the substrate surface, and slight deflection of the substrate (usually mounted on three support points) will result in a vertical discrepancy in the focal position.
One known measurement method involves using the objective to scan (for example optically) a pattern that is to be measured, and then focusing. The position of the X-Y measurement stage is then measured interferometrically, and the position of the pattern in relation to a reference point is determined from the measurement stage position with nanometer accuracy. Pattern widths or pattern spacings, for example, can then be determined from multiple measurements.
At the desired accuracy, even small sources of error in the position determination must be detected and either eliminated or minimized in the instrument design. One such error source is tilting of the objective with respect to the optical axis of the coordinate measuring machine. This tilting occurs upon vertical movement of the objective during focusing, and results in a lateral offset of the objective axis on the substrate having the patterns to be measured. A pattern to be measured is therefore optically sensed by a tilted objective as being in a different, laterally offset position than it would be by an untilted objective. This discrepancy becomes a measurement error in the measurement result for the position determination of the pattern being measured.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to create an apparatus for fine positioning of a component which allows a precise rectilinear movement path for the component that deviates only extremely slightly from a reference axis.
This object is achieved with an apparatus for fine positioning of a component having a one-piece double parallel spring element having an axis of symmetry, including: i) an external stationary frame on whose inner side two holding elements are shaped at positions lying opposite one another about the axis of symmetry; ii) a movable center bar between the holding elements; iii) two movable side bars arranged on either side of the center bar; and iv) pairs of parallel connecting elements, arranged on either side of each holding element and equipped at the ends with bending points, the first connecting element being in each case joined to one side bar and one holding element, and the second connecting element being in each case joined to the side bar and the center bar. An elastic element is located between a holding element and one end of the center bar, and a fine adjustment element is arranged between one holding element and one end of the center bar. The dependent claims recite advantageous embodiments of the invention.
An apparatus according to the present invention for vertical fine positioning of a component has a double parallel spring element that is fabricated in one piece and is configured symmetrically with respect to an axis of symmetry. It comprises a stationary frame that is attached, for example, to a supporting part of a higher-order device. A movable center bar is arranged on the axis of symmetry in the center of the frame. The component to be positioned can be attached to the center bar. Two side bars are movably arranged inside the frame on either side of the center bar.
Two parallel, straight connecting elements are arranged in the region of the ends of each side bar. Bending points in the form of leaf springs are configured at the ends of each connecting element. The first of the two parallel connecting elements creates, by way of the bending points shaped onto it, a movable connection between the side bar and the frame. The second parallel connecting element creates, by way of the bending points shaped onto it, a movable connection between the side bar and the center bar. The center bar is thereby movably connected, with four connecting elements, symmetrically to the two side bars.
The center bar is preloaded in the direction of the frame by way of a spring. The center bar must not touch the frame, since any such contact would cause internal distortion of the double parallel spring element. This would disadvantageously change the bending characteristics of the bending points, and move the center bar out of its movement direction lying strictly parallel to the axis of symmetry. The spring can be configured, for example, as a compression spring or as a tension spring.
Arranged between one end of the center bar and the frame is a fine adjustment element with which the center bar can be adjusted in tilt-free fashion in its longitudinal direction against the spring force of the compression spring. If the adjustment travel of the fine adjustment element is to be not only adjustable but also controllable, it is advantageous to connect the adjustment element to a high-resolution length measurement system for measuring its instantaneous setting. The measured values of the length measurement system are conveyed as the controlled variable to the input of an electronic control system whose output signals control the settings of the fine adjustment element.
A fine adjustment screw, which is driven in either manual or motorized fashion, can be used as the fine adjustment element. In a particularly advantageous embodiment, the fine adjustment element is configured as a piezoelement whose length changes as a function of the magnitude of an applied voltage.
In the apparatus according to the present invention, the configuration of the double parallel spring element is of particular importance. For example, the double parallel spring element must be shaped as a single piece from one plate. The plate must be sufficiently thick that the bending points are configured as wide leaf springs. This is the only way to prevent tilting of the center bar with respect to the axis of symmetry, and to make the double parallel spring element sufficiently stable, in particular in a vertical arrangement. In addition, the plate must
Crowell & Moring LLP
Fulton Christopher W.
Leica Microsystems Wetzlar GmbH
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