Ask engineers what kind of improvements they want from motion products and you'll likely get a quick response of “smaller, better, cheaper.” And in linear motion components, that's exactly what's happening. “The need for power density is resulting in the downsizing of linear motion systems,” says Jim Marek, director of engineering for Danaher Motion's Thomson division. And the need to keep cost and design complexity in check has pushed many users into modular components they can drop into their machinery designs, according to Marek. Medical equipment in particular is driving the push into smaller sizes that don't scrimp on accuracy and repeatability. “We are continuing to develop smaller and smaller precision products for medical and lab automation systems,” says Kevin Gingerich, marketing director for Bosch Rexroth's linear motion products. Here's a look a three examples of linear motion products that have a smaller package, performance improvements or more modularity.
Positioning Slides Go Modular
The new MicroStage MS46 Positioning Slides from Danaher Motion's Thomson group feature a modular design that lets users easily configure slide lengths and choose between three linear actuation methods — pre-loaded ballscrew, lead screw and belt-drive. Made from aluminum, MS46 slides offer strokes to 1,634 mm and load capacities to 330N. Jim Marek, Thomson's director of engineering, says one ideal application for this lightweight system is the carried axis in a multi-axis assembly. “They can help minimize the moving system mass,” he says, noting the product has handled light to medium loads in factory automation, semiconductor and life-science applications. The MS46's ballscrew versions are available with leads of 5 and 10 mm. Lead screw versions feature 3-, 10- and 25-mm leads. Belt-drive models allow twice the slide length compared with the ballscrew and lead screw versions and support Micron NemaTrue 23 gearbox ratios of 3:1, 5:1 and 10:1.
Pitch, Roll and Yaw Free
The latest linear guide system from Bosch Rexroth — the High-precision Ball Rail System — tackles the pitch, roll and yaw deviations rooted in ball recirculation. “There is virtually no deviation in the x, y or z directions, which results in extremely smooth motion,” says Kevin Gingerich, marketing director for the company's linear motion products. The secret to the system's steadiness is a new bearing raceway geometry optimized to minimize ball pulsations and reduce contact between the runner block and guideway bolts. The company offers the new guide system in standard DIN accuracies. The new system handles the same dynamic loads as Bosch Rexroth's standard products and is available in sizes from 15 to 45, with or without ball-chain technology. Dynamic loads on a size 45, for example, are up to 68 kN. Single-piece rail lengths up to 6m are available. Target applications include precise motion systems, including medical and semiconductor equipment. “We see the high-precision ball rail systems replacing air bearings in less demanding applications,” Gingerich says.
Precision Modules Shrink
Bosch Rexroth has shrunk the size of its PSK Precision Modules, offering a 40-mm wide x 20-mm high model called the PSK 40. Previously, the smallest size was 50-mm wide. The PSK 40 has a positioning repeatability spec of 0.005 mm and incorporates a 6 mm-diameter ball screw with options for 1- or 2-mm lead. The company manufactures the ball screw to Class 7 with a preloaded ball nut for the sake of positioning accuracy and stiffness. Maximum speed is 375 mm/s — about twice what you would commonly find for units this size, according to Rexroth's Kevin Gingerich. And with lengths up to 350 mm, the PSK 40 reduces the need to upsize to larger modules as longer stroke requirements. The PSK 40's ball tracks for the linear guide system are machined into the precision steel base, which includes a machined reference edge. The steel base also provides rigidity, making the PSK 40 well-suited for small, multi-axis systems. Gingerich reports, early uses for the PSK 40 include medical liquid dispensing and semiconductor applications.