Reducing CMM Scanning Time

New high speed scanning technology meets manufacturer needs for both faster throughput and more data points

March 9, 2009

A new high speed scanning system for coordinate measuring machines is achieving tremendous productivity gains. Manufacturers have retrofitted existing CMMs with the new Renscan5 system and infinite positioning REVO head from Renishaw and applied the system to speeding inspection on some of their more complex and time-consuming parts.

A new high speed scanning system for coordinate measuring machines is achieving tremendous productivity gains. Manufacturers have retrofitted existing CMMs with the new Renscan5 system and infinite positioning REVO head from Renishaw and applied the system to speeding inspection on some of their more complex and time-consuming parts.

Following are results that they've realized, compared to previous practice:

• Three-axis axis scanning 15 mm/s—29 min. 13 sec.
• REVO scanning 400 mm/s for valve seats and 50 mm/s for valve guide bores—3 min. 42 sec.

"These developments are revolutionizing measurement throughput," said Paul Gane, Renishaw Canada's CMM product manager. "Besides major reductions in cycle times, Renscan5 and REVO make it possible to obtain far greater data point coverage. REVO's low-mass, low-inertia design allows ultra-high-speed data capture - up to 4,000 points a second compared to 200 to 300 data points for conventional scanning."

The agility and point-taking productivity of the Renscan5/REVO dynamic measurement system is stimulating the creativity of metrology professionals, added Gane.

Helical scanning, for example, can greatly speed the measurement of bores, while generating thousands of data points to determine roundness, concentricity or taper.

In comparative testing, he noted, Renscan5 reduced form measurement scanning of a cylinder bore from 90 seconds to just 2.5, enabling all cylinders of a V-8 engine block to be scanned in less time than a single cylinder by conventional methods.

A leading automobile manufacturer, he said, is applying the system's massive data capture capabilities to measure engines for wear analysis and deviations of the cylindricity of each cylinder in its spatial orientation. Wear is portrayed in visual graphics similar to a thermal scan.

"Faster inspection is especially vital on large, complex, high-value parts with many critical features," said Gane. "CMM inspection can be a major bottleneck to efforts to speed throughput and gain lean efficiencies. Form measurement of complex parts and critical geometries for functional fits can demand many thousands of data points. Needing to produce and document parts to ever-higher precision, ever-tighter tolerances, manufacturers are looking to CMM speed for a solution."

As a practical matter, conventional three-axis CMMs scan at rates of five to 15 mm/sec in order to hold accuracy, said Gane. This is to avoid high acc/dec rates and rapid axis changes that can induce inertia errors, causing deterioration in measurement accuracy.

"CMM inspection has been stuck in that time warp for over two decades," he added.

Created under Renishaw's longest and largest development program, Renscan5 blows away the speed limits, he said. The Renscan5 enabling technology encompasses a range of breakthrough five-axis scanning products that measure at up to 500mm and 4,000 data points per second, while virtually eliminating the measurement errors normally associated with existing three-axis scanning systems.

A 3D measuring device in its own right, the REVO head features two rotary axes - one in vertical plane, one in horizontal - to give infinite rotation and positioning capability. The REVO measuring head performs synchronized Y- and Z-axis motion to quickly follow changes in part geometry during inspection routines, avoiding the dynamic errors caused when moving the larger mass of a CMM structure. Where X-axis motion is required for the probing routine, Renscan5 moves the CMM at a constant velocity along a constant vector as measurements are being taken, removing the acceleration/deceleration inertia errors incurred in conventional scanning.