Motion Control Components Keep Curiosity on the Go
- Thursday, 01 November 2012
PI Ceramic monolithic piezo actuators (PICMA) were put to use in the Chemistry and Mineralogy instrument (CheMin) on the Mars Science Laboratory rover, Curiosity. CheMin is an Xray diffraction-capable mineralogy instrument whose purpose is to determine if water was present in the formation of Martian rocks and soil.
A sample handling system is required to feed mineral powder samples through a funnel into the individual sample cells. The powder in the tunable sample cells must be shaken at variable amplitudes and frequencies in the range of 0.9 to 2.2 kHz to homogenize particle size or density segregations. The precisely controlled vibrations are generated by the PICMA multilayer piezo actuators. These ceramicencapsulated actuators emerged after rigorous tests by NASA’s Jet Propulsion Laboratory (JPL). Multiple samples passed 100 billion cycles of life testing with no failures, maintaining greater than 96% of their performance at the end of the test.
The PI miCos precision motorized positioning stage is used on Curiosity’s ChemCam (Chemistry and Camera instrument), which consists of a laserinduced breakdown spectrometer and a high-resolution imaging camera. ChemCam determines, through laserbased remote pre-testing, which rocks in the vicinity of the rover (distances up to 9 m) warrant a closer examination with in-situ instruments. The highpower laser beam evaporates the rock and the light emitted from the plasma is analyzed with the spectrometer (see photo below).
A specially modified and space-qualified MT-40 linear positioning stage focuses the analyzing system at the desired distance by translating the secondary mirror of the telescope. Due to violent shocks and vibration during launch and landing, every component in the stage, from the stepper motor to the crossed roller bearings and limit switches, had to be closely examined and optimized to eliminate the possibility of failure or performance loss. For fast and precise focusing, high resolution and linearity were required, and backlash had to be controlled tightly. Modeling and thermal compensation were used, as well as special vacuum-compatible lubricants for all moving parts.