Design principles of the SP25M system
The SP25M design features an optical transducer sensor system which is located within the SP25M probe body. The design also features a spring pivoting motion system which is located within the SM25 scanning modules.
Two infrared light emitting diodes (IREDs) mounted in the SP25M probe body project invisible infrared beams on to two mirrors mounted on the pivoting motion structure within the SM25 scanning module. The mirrors reflect the beam back to the SP25M probe body where their change in position is detected by two position sensitive devices (PSDs) when the stylus is deflected. The PSDs provide signal outputs in the three probe axes; P, Q and R.
NOTE: The SP25M probe system does not have a fixed rate, gain or resolution and the P, Q and R probe axis outputs are non-linear and non-orthogonal. These outputs are converted to X, Y and Z signals by the calibration routine. Renishaw offer support and advice on scanning calibration algorithms suited to SP25M.
The SM25 scanning modules are designed to provide an optimised level of accuracy and contact force over a specified stylus range. This minimises the reduction in performance seen in other types of scanning probes as the stylus length increases.