High Power Optical System—Renishaw

Modern Machine Shop, March, 2001 by Elizabeth M. Gruber

The company brings CMM levels of probing performance and tenfold probe life to industry's largest machine tools with its MP700E high power optical system. The system combines the sub-micron repeatability of the MP700 with a 12-m (39.3 ft.) transmission range and 360-degree signal coverage from any spindle orientation. The high power system allows operators of very large, five-axis machine tools to verify critical features in process, achieve tighter tolerances for more precise fits and perform final inspection while the part is still on the machine tool.

The extended-range system uses a high power infrared transmitter, modified optical receiver and machine interface with a high speed digital switch. Strain gage trigger design minimizes pre-travel variation and its effects on probing precision to provide CMM-like precision--unidirectional repeatability of 0.000010" (0.25 micron) with a 2" (50-mm) stylus. Solid-state construction increases probe life tenfold, while strain gauge sensors deliver low trigger force and a uniform 3D triggering pattern. This is said to allow faster probing on complex parts while eliminating the programmer's requirement to compensate for characteristics that can affect probing precision.

A multi-channel digital filter recognizes and ignores unintended triggers resulting from machine vibration and high acceleration/deceleration forces. This makes the MP700E particularly suited to high speed and high power machining centers, such as those used in the aerospace and off-road equipment industries.

The system is designed for applications requiring extended range transmission up to 12 m, environments that are not conducive to the use of RF transmission or tilt-spindle applications, which position the probe at complex vectors that can result in loss of an optical signal.

CNC probing can make it viable to do final inspection and "buy off" of finished parts by the machine tool to reduce in-process time. This eliminates the delays, difficulties and costs of transporting and fixturing large parts for post-process inspection. In-process probing provides a form of closed-loop process control that can enable machining centers to achieve accuracies comparable to boring mills and other high precision machines.