Harmonic Drive gears are used for more than four decades for space applications. They provide low or zero backlash in combination with excellent precision. The large gear ratio enables the use of a small actuator motor (low mass and low power consumption) to move large components like solar panels.
Today, Harmonic Drive® gears are mainly used in liquid lubricated condition in order to satisfy the operational requirements. This limits their use to only "ambient" temperature in space, as greases bear the risk of outgassing. This leads to loss of lubrication, but also to contamination of sensible surfaces (optical components). This may even lead to loss of a full mission, e.g. in earth observation.
To serve the needs of space industry, the development targets of HARMADES are threefold:
- to reduce size (increase torque density),
- to implement surface treatments to improve load bearing capacity and life time of solid lubrication, and
- to setup testing capacities for the whole extreme temperature range.
These targets are transferred to the three main development activities of the proposed project: design of a new gear towards smaller size "14-160" (HDAG,D) increasing the torque density by a factor of 2,5, develop a surface treatment that increases the load bearing capacity especially of the gear teeth (AAC, HMW) and to design a test device that enables in future to characterise those gears in the whole temperature range (AAC).
Finally, all improvements shall be implemented to gears of these new size being tested under thermal vacuum. Being successful in those three actions, would give the technological basis to push Europe up to worldwide leadership in solid lubricated strain wave gears.
Those objectives are very demanding, without having a final solution on the table. Hence, to achieve this high impact, high risk has to be accounted. The confidence of the project consortium is based on step-by-step-successes in the recent past on selected topics: within EU-harmLES the feasibility of a solid lubrication in such gears in size "20-100" was shown with reasonable life times. A novel composite coating based on MoS2 was developed (and will be used for the current project as it is).
Results indicate that surface treatments improve lifetime and/or load bearing capacity. An optimisation of surface treatments for such components was started in the NISSCO-project: the basic process parameters could be identified, but development ended on sample level only.
The ability to improve performance by design was demonstrated in harmLES: the re-design of the gear by HDAG led to an increase of lifetimes under solid lubrication from a few hundred output revolutions to more than 20.000 (not yet including surface treatments). AAC is already running devices to test Harmonic Drive(R) gears under thermal vacuum. Based on that experiences, concepts to solve the problems of testing at extreme temperatures can be regarded as feasible.
Those recent stepwise successes underline the confidence that the ambiguous technical targets can be achieved, bearing in mind that the risk is high. Running this project in German-Austrian-cooperation offers the most highest synergies as the targets are closely related. On the other hand, the exploitation can be clearly outlined for each country.
HARMADES also will join the results of all previous development projects into this new gear, making those public funds become beneficial to the employees.
Aerospace & Advanced Composites GmbH
Härterei Michael Welser GmbH (HMW)
Aerospace & Advanced Composites GmbH
Dr. Andreas Merstallinger
Viktor Kaplan Straße 2 F
A-2700 Wiener Neustadt