Graham Mackrell, managing director Harmonic Drive, explains why its strain wave gears have been the top choice in space for over forty years.
Anything that goes into space is seen as the pinnacle of human creation. Astronauts are highly trained and are at the peak of physical fitness, space shuttles are crafted by large teams of expert engineers and all the technology used is so high-tech it’s as if it belongs to science fiction.
Many decades ago, the first Harmonic Drive gears were sent into space during the Apollo 15 mission. Even from the beginnings of the space race, the expectations for the technology used were high. The equipment used in space had to be reliable, compact and lightweight and given the increasing demands on equipment in today’s space missions, it must also now be highly accurate with zero backlash and have high torque capacity.
When aerospace engineers were recently designing a new space rover, they looked to Harmonic Drive gears for reliability. Due to the obvious difficulties of performing repairs in space, a high mean time between equipment failures is a high priority. Harmonic Drive products achieve this by prioritising quality throughout the entire design and manufacturing process.
It is vital that aerospace gears are thoroughly tested before they are sent to customers, ensuring that they always receive a quality product. At Harmonic Drive, we test products using finite element method (FEM) testing. This process simulates real world physics to ensure that the product is capable of surviving in space. For example, structural testing is carried out to ensure the product is robust and the space rover travelling over rough terrain will not damage the actuators used in the wheels. Thermodynamic properties are also important as aerospace gears are often exposed to both extremes of the temperature range, which are tested in the initial design process.
Also considered in the design process is the part count of the aerospace gears. Harmonic uses a low part count which means that they are maintenance free. In addition, there is a lower chance of components failing giving the gears a high Mean Time Between Failure (MTBF). This also contributes to the compactness and light weight of the gears, a feature essential in space.
Another key feature for aerospace gears is high torque capacity and zero backlash. This is essential for systems which communicate the location of the rover to the control room. If traditional, high backlash gears were to be used, the system would misreport the rover’s location. This would cause problems when the rover is used to survey uncharted areas of planets and could lead to inaccurate mapping. Due to the emphasis on high precision with Harmonic Drive gears, this problem can be avoided.
The numerous quality processes that Harmonic Drive undertakes have led to recognition from a number of accrediting bodies. Harmonic Drive products are AS9100 certified, a specific aerospace standard for the design, manufacture and sale of precision gear reducers, servo-actuators and electro-mechanical positioning systems.
To be the pinnacle of global technology, there are no shortcuts. Components used in aerospace technology must be subject to vigorous testing in order to be reliable, safe and have a long product life.