59 Testing and Lessons learned  

Due to the challenging manufacturing tolerances and constraints, the integration of PSDDS mechanism  had to be shortly postponed, this leading to not being able to complete the full testing program in time for  the submission of this paper.  However, the three major sub- systems of the PSDDS  previously discussed  in this paper  are also present in the PSHS which has already successfully completed the qualification  campaign. Test results and lessons learned of the PSHS are fully valid also for PSDDS and are  presented in this paper, together with test results already provided by t he ongoing PSDDS qualification  campaign. The full PSDDS test results will be presented in the  oral presentation at the AMS 2016.  

Pre-torque Device  PSDDS and PSHS are using the same pre- torque device. They are identical .   During this test, the positioning performance of the PSHS has been determined  with an external absolute   encoder, which can measure the correct position of the PSHS movable part at any time with reference to  the fixed part of the housing.  This measurement has been performed under ambient condition (20°C and  1bar absolute air pressure) and Mars -like conditions  (-60°C and 7 mbar absolute CO 2 atmosphere) . For  the evaluation of the positioning performance,  the following parameter s are important:   • Hard- Stop accuracy :  o Describes the positioning uncertainty introduced by the Hard- Stop parts when they become in  contact.   o Depends strongly on how the Hard- Stop is achieved and on the switch -off criteria of the motor  current when the Hard- Stop is reached.   • Mechanism Play:   o Is the distance the motor has to run until the end- shaft moves again after a direction change ?  • Repeatability:   o Is the spread of the reached positions when the mechanism is operated multiple times in the  same conditions?   • Relative accuracy:   o Is the accuracy that can be achieved when the mechanism is moved from one point to  another?   • Absolute accuracy:   o Is the  distance between the actual position and the position measured by the mechanism’s  sensor?   During the first positioning accuracy tests, a relatively high deviation from the required absolute accuracy  was found. After several measurement series,  it became obvious  that the measured deviation was  completely static and thus reproducible.  In consequence,  it was easy to compensate this deviation with a  compensation curve that  has been implemented into the control electronic s. The fact that the position  tolerances of the teeth in the internal ring gear has the same value as the distance between max and min value of the compensation curve suggests that the  observed inaccuracy is solely a result  of the  manufacturing tolerances of th is (last)  gear stage.    The results show that all accuracy requirements (resolution 20 µm, absolute accuracy 100 µm) are   fulfilled under an ambient as well as a Mars -like e nvironment.  

Bearing Concept:   PSHS and PSD DS are using the same kind of wire  race bearing. The only difference is that the bearing in  the PDDS has a diameter of 110 mm and the PSHS has a diameter of 70 mm. Since the distance  between the balls is the same in both systems, the amount of balls in the PSDDS is higher.