Meaning
Mounting mechanisms that constrain exactly six degrees of freedom without over-constraint provide highly repeatable positioning for optical and electronic assemblies. A classic kinematic mount uses three spheres that rest in a groove, a slot, and a flat plate. This layout prevents internal stress build-up when temperature changes occur.
Degrees of Freedom
Mechanical constraints are distributed such that each mating surface pair restricts specific directions of movement. The total number of points of contact must equal the six degrees of freedom of a free body. Extra contacts create over-constraint, which can warp high-precision mirrors.
Under-constraint allows unwanted movement during transport.
Thermal Isolation
Thermal expansion differences between the optic bracket and the housing are accommodated without bending the optical elements. When the temperature fluctuates, the spheres slide along their mating grooves to release the expansion stress. This feature is essential in laser assemblies where sub-micron alignment must be maintained across a wide operating range.
Repeatability Performance
Sub-micron precision is achieved because the mechanical parts always settle back into the same geometric positions. The surfaces must be kept clean and hard to prevent micro-brinelling and wear. Lubrication is sometimes avoided because it can attract dust and degrade positioning accuracy.
Precision systems often use hardened steel or ceramic components to ensure that the interface remains undamaged over thousands of cycles. A consistent preload force is required to hold the parts together against external vibration. If the preload is too low, the connection may separate under shock loads.
