240 vibration until the powder has moved from the Drill to CHIMRA. Once inside CHIMRA, powder moves  using Arm repositioning and CHIMRA vibration until the pos e in Figure 5b is achieved. In this pose, the  powder is above the 150-µm sieve. CHIMRA vibrati on operates until all particles smaller than 150 µm  have passed through the sieve. Arm repositioning and CHIMRA vibration is again used to move the  sieved particles into the portioning chamber and to create the 45-65 mm3 portion. The Arm moves  CHIMRA to the position in Figure 5c above one of the SAM inlets. The Inlet Cover door opens, the  CHIMRA portion door opens, and vibration moves the portion into the funnel. CHIMRA can create and  deliver additional portions to either SAM or Chemin . If none are desired by either instrument, the Arm  moves CHIMRA away and the Inlet Cover door closes. At  this point a number of different choices are  available. The Arm can move CHIMRA into a position where it can be opened up and viewed by the  Rover cameras. The remaining sub-150 µm particles can be placed on the Observation Tray for viewing  by the APXS or MAHLI or all the remaining mate rial can be discarded onto the ground. After CHIMRA  uses vibration and thwacking to clean itself, it  is ready to process a different sample. 

Fault Tolerance   As described in the previous sections, the 17 actuated degrees-of-freedom in  the SA/SPaH subsystem  are arranged to provide the required functionalit y and create the 5 minimum sample paths needed to  support the scientific investigation targeted at the acquisition and analysis  of rocks and regolith. A mix of  hardware redundancy and functional redundancy is used wi th the components of the sample paths to  ensure that in the event of a failure , some of the sample paths remain intact. In addition to the hardware  components of the SA/SPaH subsystem (Arm, Drill, CHIMR A, Inlet Covers), consideration must be given  to the science instruments the SA/SPaH feeds with sample (SAM, Chemin), and the motor drivers.   The Arm is critical to all aspects of the sampling functionality and all 5 sample paths because it positions  and manipulates all the Turret-mounted tools. The failure of any Arm joint severely degrades the  subsystem functionality and leaves none of the 5 sample  paths viable. Therefore the approach here is to  provide hardware redundancy, particularly in the electr ical circuits required for Arm use. The Avionics  subsystem provides the capability to  operate 8 actuators simultaneously across all the Rover functionality  (32 actuators total, 17 in the SA/SPaH). Multiplexing of the motor drivers provides the needed operations. Due to the importance of the Arm functionality, the multiplex table has a backup driver available if a  primary driver for an Arm joints fails. These redundant drivers for each Arm joint are carried in separate  cable paths in both the round wire and the flex cabl e out to each Arm actuator. Moreover these are  carried through multiple lines in the flex cable so in the event of a problem in one of the lines, a degraded torque capability would be available. The windings of the motor are not fully redundant but again these elements are created by multiple physical wires terminated at multiple pins so a degraded torque capability would be available in the event of a problem. Each Arm actuator has a power-off brake that is  mechanically engaged when non-powered to lock the motor ro tor, preventing rotation. A brake solenoid is  energized to release the motor. The brakes have redundant coils, each capable of releasing the brake,  energized by separate brake drivers and separately cabled. All actuator s with brakes on the Rover are  configured with redundant solenoids. The mechanica l components of each Arm actuator such as  bearings, gears, and shafts are not redundant. The life requi rement for the Arm joints is not very large:  6000 output cycles or less, depending on the joint. Ensu ring a reliable design is done through life testing  of a qualification unit.  Instead of using a hardware redundancy approach, t he Drill and CHIMRA taken together are designed to  have functional redundancy in the overall ability to ac quire, process, and deliver samples to the SAM and  Chemin instruments. Multiple sample paths from ac quisition to depositing into Instrument Inlets exist and  while all paths are not equally important to the science investigation, all provi de useful science. Figure 8  illustrates the Drill, CHIMRA, and Inlet Cover functions comprising each of the 5 sample paths and the required degrees-of-freedom to perform each function. Except for CHIMRA Vibe, the failure of a single  actuated degree-of-freedom can cause the loss of a function and the loss of one or more sample paths but other sample paths remain viable. Due to its importance in all the CHIMRA functionality, CHIMRA  

NASA/CP-2010-216272