New Designs of Stage Mirrors for Highest Precision Positioning and Measuring Machines

Ultra high precision positioning and measuring machines have to face the demand for increasing moving and measuring volumes while reaching accuracy in the nanometer range. For three dimensional measuring systems with the required accuracy a setup of three fixed laser interferometers and a moving mirror with three planes are in use in most cases. The mirror carries the measuring object relatively to the static tool. A metrology frame is used to obtain an invariable relative position of the tool and interferometers relative to one another. Beside the interferometers themselves all elements in the measurement loop have to be designed carefully. Limiting factors for dynamic and metrological properties of the machines are stiffness, thermal stability and long term stability. Also the optical quality of the measuring mirror has a direct influence. Existing mirrors have several disadvantages which reduce the possible machine accuracy. Therefore new designs are necessary. The paper presents novel designs of measuring mirrors and frames utilizing consequently design principles and virtual prototyping.