# Numerical Analysis of the Kinematic Accuracy of the Hermetic Harmonic Drive in Space Vehicles
###### Abstract  
The unfriendly-for-humans environment of space causes automatic or remotely controlled vehicles and devices to be used for its research. In robot and manipulator control systems, and also in mechanisms adjusting antennas and photovoltaic panels, the hermetic harmonic drive can be used. A special advantage of this type of gear is the ability to transfer power to an isolated space separated by physical barriers from external influences. Therefore, the purpose was to design gears that will allow achieving the highest kinematic precision for control systems by simultaneously maintaining their hermetics. The article presented an analysis of the kinematic accuracy of harmonic hermetic drives powered by four different types of wave generators. The generators used differed in construction but also caused other deformations of the flexspline. The calculation of angular displacement was prepared in the computer program Abaqus. The simulations were performed on virtual models of a complete harmonic hermetic drive using the finite element method (FEM). The results from the analysis allow the most favorable solution to be applied to the Mars rover drive or spacecraft control system. It was determined for which of the wave generators the kinematic accuracy is the highest and how high the backlash exists for the reversing rotation. Finally, the proposed design will allow one to increase the accuracy of the working movements and control of space vehicles while ensuring a minimal influence of the external ambient. harmonic drive; angular displacement; backlash; kinematic accuracy; Mars rover; MES; mechanical engineering +
Footnote †: journal: _Applied Sciences_  
The characteristic feature of the harmonic drive is a way of transferring motion to the passive element (2) as a result of the cycle deformation of the flexspline (1) by the wave generator (3). The flexspline, while the harmonic drive is working, is deformed by the generator in the radial direction by its relative rotational motion. The flexspline has an outer toothed wheel rim with which the internally toothed circular spline meshes. The number of flexspline teeth is lower than the number of circular spline teeth; hence, outside the meshing area, the teeth of both circulars pass each other. These harmonic drives can have generators with different shapes, methods of operation, and numbers of waves of deformation on the circuit of flexspline, which also influences its complexity. A large number of construction solutions are also in operation. New types of harmonic drives are still being researched, and they have applications in new, previously unprecedented areas of life. Often, the emergence of new design solutions is related to the requirements and expectations of the environment. The need for harmonic drive-in isolation from the space of the engine forced an uprising for a new type of harmonic drive-in--the hermetic variant. The hermetic harmonic drive has this unique feature that allows handover to an insulated space separated from the ambient by a partition. Moreover, it is the possible opposite solution, in which the engine is closed in a sealed casing and torque is passed to the outer just by hermetic harmonic drive. The applied type of generator can directly impact the form of flexspline and the kinematic accuracy of the entire drive. The selection of the appropriate type of generator is not simple because access is not always available to special gears or advanced technology that allows cam machining. In the article, there was also the possibility of the execution of the elements of harmonic drive by using incremental methods such as 3D printing. This possibility is analyzed for the production and reproduction of elements of harmonic drive in outer space. These harmonic drives, thanks to high kinematic accuracy, can be used in control systems of transmitting antennas or in the drives of vehicles on colonized planets. Figure 1: Schematic of the hermetic harmonic drive: 1—circular spline, 2—flexpline, 3—wave generator, 4—hermetic partition.