HARMLES · Dry lubricated Harmonic Drives for space applications

On spacecrafts reduction of mass and power consumption are a major issue. On the other hand, in case of mechanisms for Solar Arrays or antennas big masses have to be moved and kept in position for long times. Harmonic Drives would fulfil the requirements: high gear ratios enable the use of small actuator motors (low mass and power), they provide high stiffness and high precision even at very low speeds.However, the use is presently limited by the need of grease lubrication. This is linked with risk of outgassing, contamination of other parts and limits the usage in temperatures approx. -50°C to +70°C. The use of solid lubricants typically for bearings may extremely widen the usage to at least -170°C to 300°C.First trials to apply these technologies for space use based on commercial available coatings (partially used in space bearings) did not lead to success, due to the strongly differing mechanical and contact situation in the Harmonic Drive.Therefore, project HarmLES will focus on the development of solid lubricant coatings for Harmonic Drives in space. This is seen as an integrated approach between gear design and material adaptation and the application of a suitable coating. It will start with a promising composite coating which has already been tested in space. On the other hand, a huge variety of coatings are available that claim “self-lubricating”, they will be benchmarked for their applicability in space. Besides space related lab-testing, application testing will ensure the proper feedback. The overall, tribosystem will be re-considered on bases of FEM-simulations and alternative material solutions.An end-user group consisting of several industrial end-users from space will be involved to recommend the research path by defining requirements for later applications. The consortium is small, but it covers the major players and reflects existing expertise in this field to perform the project successfully.