252 In order to create sample flow within its internal passageways, the CHIMRA is vibrated as a whole with a  dynamic level of 4-10 G’s while it is reoriented with  respect to gravity by the Robotic Arm. The dynamic  environment is generated by a mechanism that couples  the speed of a spinning eccentric mass with the  natural frequency of the structure supporting CHIMRA fr om the turret. This allows the 8-kg CHIMRA to be  shaken with a relatively small input force of 150 N. Internal geometric one-w ay valves (Figure 6) and  chamber sizing is used to prevent migration of sample within CHIMRA into unwanted compartments. A combination of dilution cleaning, using chemica lly understood sample to flush CHIMRA, and forced  ejection of clogged particles is used to internally clean CHIMRA between sample processing tasks. Both the 150-micron and 1-millimeter sieves are attached to thwacker mechanisms: a mousetrap mechanism that slams the sieve and frame against a hardstop in order to induce a dynamic impact pulse that ejects clogged particles from the sieve and jo lts other internal clogs free.     CHIMRA is composed of four distinct mechanisms , each driven by an actuator: the primary thwack  mechanism (PTM), the secondary thwack mechanism (STM), the portion actuator, and the vibration mechanism. Each of the thwack mechanisms performs multiple functions, making configuration of CHIMRA in the required volume achievable by mini mizing the number of required actuators. Each  actuator in CHIMRA was configured to be supported by a central core struct ure. This is in contrast to the  style of a robotic arm configuration where actuators are supported serially off one another. With a central  core configuration, each actuator is only required to move the structure associated with its function. This reduces the output gearbox requirements of a given actuator, lowering the mass and volume required of  that device.    The method of creating a sample portion had to both accurately generate a small volume of sample and be robust to the pres ence of sub-millimeter particle dust. To remove any possibility of an active portion  mechanism becoming mechanically clogged or ja mmed, a passive method of portioning was  implemented. Both the 150-micron and 1-millimeter po rtion chambers contain an open-ended cylinder, or  sample tube, that is sized to fill with a specific volume when material is vibrated into it. After bulk sample is brought to the portioning chambers, dynamic ex citation and specific rotation of CHIMRA allows  gravitational forces to help fill the sample tube,  remove excess sample above the tube and eject the  sample contained in the cylinder from CHIMRA. The inter nal geometry that facilitat es these actions in the  150 micron portion chamber is illustrated in Figure 7. Once the sample tube is filled, additional vibration  levels off the tube and motivates the excess sample to an overflow chamber. The correct portion size is  now held in the portion tube while the excess samp le is prevented from exiting CHIMRA with the  delivered portion. The portion actuator then opens a door at the base of the sample tube and vibration  motivates the sample to fall out. After the existing portion is delivered, a new portion can be created by using a 360-degree rotation of the turret to bring th e sample in the overflow chamber back above the  portion tube. The inclusion of a dedicated portion ac tuator helps guarantee the ejected sample is less  than 150 micron. This is because prior to exiting t he sample tube, particles must first pass through the  150-micron screen. A detailed study was conducted on the optimal portion tube geometry to ensure that a  consistent portion size is reliably generated and a favorable particle-to-tube-diameter aspect ratio is  maintained, thereby minimizing the likelihood of inte rnal arching or tube clo gging. The passive method  employed by CHIMRA for generating a 150-micron portion provides a consistent portion size without  requiring mechanical components that would likel y jam when manipulating fine dust particles.   A combination of geometry and internal featur es allowed a second portioning mechanism to be  seamlessly integrated into existing CHIMRA featur es; this novel configuration removes the need for an  additional actuator but sacrifices some portion size consistency. Figure 8 illustrates the features of the  scoop and 1-millimeter thwack arm that allow for portion generation. Bulk sample is first sorted by both a four millimeter grate and a 1-millimeter sieve before it is passed through a one-way valve into the 1 millimeter portioning chamber. The purpose of the four millimeter grate is not to sort the sample, but  instead to provide structur al protection for the fragile 0.05-mm thick,  1-millimeter sieve, in order to ensure  that it is not punctured when the scoop is full and closed.     NASA/CP-2010-216272