Machine dynamics: High acceleration, high accuracy and a low vibration level to maximize throughput, yield and resolution

 

 

High acceleration, high accuracy and a low vibration level to maximize throughput, yield and resolution; many of the designed machines at NTS are based on optimizing and controlling the machine dynamics. Once the key requirements have been discussed, the engineers at NTS will generate conceptual designs. The use of high-level dynamic analysis makes it possible to compare these (low-detailed) conceptual designs effectively with minimal effort. The focus will be on performance, but also cost-price and lead time will be taken into account. In a trade-off meeting, together with the customer, one or two conceptual designs will be chosen, based on these focus points and the key requirements. The design(s) will be elaborated; critical purchase parts will be added, resulting in a 3D model that can be used in a more detailed dynamical analysis. When the design is meeting the requirements, the final details will be added and drawing are made. After assembly of the first system, the last step is to proof the performance. NTS has the right tools and experience in verification of machine dynamics.

 

 

“If you can’t measure it, you can’t make it”

- Philip Rosing, System Lead Engineer

 

Download our whitepaper "Dynamic system architecture for Nearfield’s Quadra"

NTS supported Nearfield Instruments with developments for their launching platform for high throughput scanning probe microscopy, the Quadra. The assignment was to contribute to some critical modules in the Quadra architecture phase, together with other suppliers, to turn Nearfield’s proof of principle into an industrial system that can runs autonomously in a semiconductor fab. In this whitepaper, we discuss the dynamical architecture of the system to enable both high throughput and very low noise measurements to measure the smallest details with the AFMs.

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Model based design

In the early stage of designing dynamic machines, it is needed to get an indication for the parameters dominating the dynamical performance; weight, rigidity and disturbance forces.

NTS has developed tooling that links multiple commercially available programs used for dynamical analysis.  This tooling makes it possible to simulate dynamic behaviour swiftly and accurately. The start will be a rigid-body model; mechanical layout, actuators, sensors and control strategies can be changed to see the effect of different component (positions) and control strategies. Vibration sources like floor vibrations (and also measured vibrations) can be used as input to test the design’s performance of noise suppression. Damping (including constraint layer damping) can be simulated to increase noise suppression even more.

The output of the model will be the input for the mechanical design and the choice of critical purchase parts like linear guiding, actuator, motion controller and sensor.

Detailed analysis

With the results of the high-level simulations the mechanical design can begin. The search for purchase parts can start; in NTS’s extended list of suppliers the best matching parts, preferably off-the-shelf, will be selected. For design parts that need special attention with respect to rigidity, strength or stability, early involvement of our production sites for frames, cabinets or granite will lead to lower costs and better manufacturability. The Mechanical Designers will be accompanied by a FEA Specialist to support calculations on rigidity and strength. A first FEA simulation can be executed as soon as all critical (purchase and design) parts are known and designed. When the mechanical design meets the required rigidity and mass, a dynamical FEA model can be made. This model will replace (parts of) the rigid-body model used in the high-level simulation and will improve the accuracy of the dynamic model. Performance or disturbances of critical purchase parts can also be updated since the they are known in the design. The result is an accurate model that mitigates the risk that performance is not met.

Verification techniques

Once the first system has been assembled and commissioned it is time to proof the performance. For some systems the use of internal sensors is sufficient but for others external measurement equipment is needed. How to measure has been discussed during the creation of the conceptual design. If needed, accessibility or an interface for external measurement equipment has been integrated in the design. At NTS, we have many years of experience in verification measurements. Modal-analysis methods will be used when mode-shapes of mechanical assemblies need to be verified, we can perform position accuracy and repeatability measurements using a laser-interferometer. When high-speed dynamics need to be measured a laser-vibrometer will be used. After verification, our customer will know exactly what the performance is.

 

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