Manufacturing of micro-robots by MEMS technology may cause large clearance at the joints – only one order of magnitude smaller, and even of the same order of magnitude, as the links themselves. Due to the clearances, the direct kinematic solutions are not discrete, but form a volume that is defined as the “clearance-space”. When clearances are large enough, two separate regions of the clearance-space may unite, causing a major failure as the forward kinematic might be shifted into a different unwanted solution. Moreover, static and dynamics calculations and behavior of MEMS mechanisms also need to be modified in order to account for the clearances and ambiguity caused by clearance.
Parallel mechanisms usually possess some direct kinematics solutions that are called assembly modes or postures. There are few methods to "move" from one assembly mode to another without crossing any structural singularity. One way of accomplishing this is by encircling a cusp point, which is a joint-space point where triple direct kinematics solutions merge. Another method is by crossing an inverse kinematics singularity on a path like a ramp, and a third method is by approaching a direct kinematics singularity and utilizing the clearance at the mechanism joints to jump to the neighboring mode. This third method is significant in micro-mechanisms, where clearances are relatively large, while the two first methods are relevant also to standard mechanisms in the macro world. Thorough understanding of these phenomena leads to better design and control of complex MEMS mechanisms.