Designing Monolithic Titanium Bipod Flexures for Cryogenic Optomechanical Subsystems
Monolithic Ti-6Al-4V ELI bipod flexures isolate cryogenic optical mirrors from thermal deformation when precision wire EDM recast layers are chemically removed.
Parasitic Stiffness
Meaning
Unintended mechanical resistance that occurs in directions other than the primary axis of motion. parasitic stiffness arises in flexures or mechanisms when the geometry of the part causes a cross-coupling of forces. This resistance can degrade the precision of a positioning stage by increasing the motor power required to achieve a move.
Coupling Effect
Displacement in one degree of freedom leads to an increase in the torque required for motion in another. In a flexure hinge, parasitic stiffness appears as a restoring force that opposes the intended rotation. This effect is often non linear and depends on the total angle of deflection of the mechanism.
Design Mitigation
Symmetrical arrangements of flexure elements can cancel out the most severe cross-coupling terms. Engineers reduce parasitic stiffness by optimizing the blade thickness and the geometry of the pivots. Analytical models help predict the magnitude of these unwanted forces before the prototype is manufactured.
The choice of material also plays a role, as high modulus alloys can worsen the stiffness if the dimensions are not scaled correctly. Precision is maintained through careful geometry.
Control Influence
Feedback loops in a control system must compensate for the non linear forces generated by the mechanism.