Supports – Resilient support – Including additional energy absorbing means – e.g. – fluid or...
Reexamination Certificate
2000-01-05
2001-12-04
Ramirez, Ramon O. (Department: 3632)
Supports
Resilient support
Including additional energy absorbing means, e.g., fluid or...
C052S167400, C052S167500, C248S603000, C248S636000, C248S638000, C248S663000
Reexamination Certificate
active
06325351
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to kinematic couplings, particularly to a kinematic coupling for precision instruments, and more particularly to a highly damped kinematic coupling for precision instruments which utilizes three ball-cone constraints each combined with a released flexural degree of freedom and which include constrained-layer damping.
Load-sensitive apparatus, such as the projection optics system for extreme ultraviolet lithography (EUVL) requires precise alignment of the reflective optics within the structural housing. It is critical that the housing be isolated from variable loads that could change the optical alignment. Such loads could arise from being mounted to other structures in an overconstrained manner. Each constraint of the six rigid-body degrees of freedom may be achieved approximately with a kinematic coupling. Kinematic couplings have long been used for the purpose of repeatable location and minimal influence to the supported object. Friction present in the contacting surfaces of a typical kinematic coupling, for example, a three-vee coupling, introduces small but uncertain forces that distort the object being supported. In addition, the typical kinematic coupling provides very little damping at low excitation levels.
The present invention provides the same kinematics as the three-vee coupling by using three ball-cone constraints each combined with a released flexural degree of freedom. This three ball-cone arrangement enables higher load capacity and stiffness, but can also significantly reduce the friction level in proportion to the ball radius divided by the distance between the ball and the hinge axis. The coupling of this invention also utilizes blade flexures which reduce somewhat the stiffness of the coupling and provides an ideal location to apply constrained-layer damping, which includes a viscoelastic layer and a constraining layer on opposite sides of the two blade flexures of the coupling. Constrained-layer damping has been previously utilized as a damping treatment across flexures of kinematic couplings, see “Highly-Damped Exactly-Constrained Mounting Of An X-Ray Telescope,” P. S. Wilke et al., SPIE, Vol. 2445, Passive Damping, March 1995. It is reasonable to achieve one to two orders of magnitude reduction in the vibrational amplitude with the coupling arrangement of the present invention.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved kinematic coupling arrangement.
A further object of the invention is to provide a highly damped kinematic coupling for precision instruments.
A further object of the invention is to provide a kinematic coupling using ball-cone constraints and constrained-layer damping.
Another object of the invention is to provide a kinematic coupling using three ball-cone constraints each combined with a released flexural degree of freedom.
Another object of the invention is to provide a kinematic coupling using ball-cone constraints having blade flexures to which a constrained layer damping treatment is applied.
Another object of the invention is to provide a coupling using ball-cone constraints which include damped blade flexures on each side of which is mounted a viscoelastic layer and a constraining layer to provide dampening of the coupling.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves a highly damped flexure mechanism utilizes three identical damped flexures to kinematically support a load-sensitive apparatus, such as the projection optics system of an EUVL system. The invention is a highly damped kinematic coupling utilizing three ball-cone constraints, each using blade flexures to which is applied constrained-layer damping. The ball-cone constraints enable higher load capacity and stiffness, while significantly reducing the friction level. The friction level is reduced in proportion to the ball radius divided by the distance between the ball and the hinge axis. The constrained-layer damping achieves one to two orders of magnitude reduction in the vibration amplitude. While this invention has particular application as a support for the projection optics system of the EUVL, it may be used in other optical and precision systems requiring an exact-constraint mount that adds significant damping to the system.
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T.A. Decker et al.; “Highly-damped exactly-constrained mounting of an x-ray telescope”; SPIE vol. 2445, Mar. 1995.
Hale, Layton C. “Principles and Techniques for Designing Precision Machines” Doctor of Philosophy Thesis, Massachusetts, Institute of Technology, Feb. 1999.
Hale Layton C.
Jensen Steven A.
Carnahan L. E.
Le Tan
Ramirez Ramon O.
The Regents of the University of California
Thompson Alan H.
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