Product description
2
Product description
2. System overview
A small deflection of the stylus tip produces a force which is applied via the stylus
module and kinematic coupling to the strain sensing structure housed in the probe
body. Electronic processing, based on a customised mixed signal integrated circuit
and hybrid microcircuit construction contained within the probe, converts the sensor
responses to a current proportional to strain. The probe output requires only two wires
for transmission to the PI 200 interface, enabling the TP200 to use the existing M8
mounting connector system fitted to a wide range of probe heads and extension bars.
In the PI 200 interface, the probe current is compared with pre-set reference levels
to determine the status of the probe, which may be armed (seated) or triggered. The
probe status (SYNC) and the trigger confirmation (HALT) signals are asserted when the
appropriate conditions are met.
At power-up, or when a probe is first connected, the PI 200 recognises whether
the probe is a kinematic switching probe (TP20/TP6/TP2 type) or a TP200, and
automatically selects the appropriate operating mode.
When using the SCR200 change rack to perform automatic stylus changing, the PI 200
inhibits probe triggers and resets the TP200 probe sensor to account for the loading
effects of the new stylus assembly on the strain sensors. Collision damage is prevented
by an overtravel mechanism and a limit switch in the base of the SCR200. A small
displacement will cause the PI 200 to assert the SYNC, HALT and STOP signals to
stop CMM motion.
2.2 Probe status signal (SYNC)
SYNC is the real time PICS trigger signal used to trigger recording of the machine scale
coordinates when taking a gauge point. SYNC may also initiate the process of stopping
and reversing CMM motion (sometimes called ‘back-off’) to the pre-hit point.
When the stylus contacts the workpiece, a change of strain occurs in the sensing
structure, causing the probe current to increase. SYNC is asserted when the probe
current exceeds the trigger reference level. When the stylus backs off from the
workpiece, the probe current will fall below the trigger reference level and SYNC will be
cleared to the armed state.
