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Close Up: Renishaw's Fast Scanning

"Renishaw" has pretty much become synonymous with probes for coordinate measuring machines (CMMs). Renishaw Inc. (Hoffman Estates, IL; www.renishaw.com) is nothing else if not an advanced technology company, so its engineers have developed a five-axis scanning system, the Renscan5, and the associated REVO, an infinite-positioning two-axis head.

"Renishaw" has pretty much become synonymous with probes for coordinate measuring machines (CMMs). Renishaw Inc. (Hoffman Estates, IL; www.renishaw.com) is nothing else if not an advanced technology company, so its engineers have developed a five-axis scanning system, the Renscan5, and the associated REVO, an infinite-positioning two-axis head. Think of this as the Renishaw probe you're familiar with brought up to heightened levels. If you know nothing else about this new gear, know this: It offers CMM scanning speeds of up to 500 mm/sec., which is said to be on the order of 20 times more than what is conventionally obtaining by scanning. OK, one more thing, too: it provides 10X data point acquisition.

One of the problems with conventional high-speed scanning on CMMs is that dynamic deflections occur during acceleration and deceleration of the machine structure. So one of the things the Renscan5 system does is to minimize the moves of the overall machine structure and to increase the use of the two-axis head for the stylus motion, such that they're able to obtain as many as 4,000 points per second on a surface. Essentially, the CMM moves the head into place, and then the REVO makes the high-speed moves. This permits the CMM to move at a slower pace than that which could cause the dynamic deflection. 

A concept behind this new tech is that it allows manufacturers to measure all parts being produced rather than simply sampling. What's more, given the rate, it is possible to check every feature on said part, not just the size and position. In one application, the system is used to measure 12 valve seats in a cylinder head; 36 scans are made on the valve guides (three scans per guide). The before: three-axis scanning at a rate of 15 mm/sec. The after: scanning at rates of 400 mm/sec. and 50 mm/sec. Before: 29 minutes and 13 seconds. After: 3 minutes, 42 seconds. In another application, it is used on an automatic transmission valve body, checking 12 6-mm diameter holes, six 5-mm diameter holes, 25 points on the gasket face, 45 spool bores, a three-shot scan on the gasket face, and six points on the spool face. This is accomplished via REVO scanning in 7 minutes, 5 seconds, versus 18 minutes, 5 seconds for the three-axis scanning approach.

The REVO head uses air bearings and brushless motors. The reach ranges from 250 mm to 500 mm. One of the ways that accuracy is assured is through the laser that shoots down the length of the stylus to the probe tip and then back. The amount of tip deflection is thereby known by the system. The length of the stylus is such that it can measure inside bores as well as on surfaces or in gasket cutouts. Stylus calibration is performed on a sphere, which is fairly conventional. What's interesting is that the head can subsequently be used in any angular position without addition calibration. The Renishaw UCC2 CMM controller contains the Renscan5 system software. Several CMM manufacturers make machines that can utilize this system.

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