Machine Design

Linear-motion systems for heavy automation and pick and place

There are a wide variety of linearmotion systems available for heavy automation and pick-andplace applications, though most use one of two load-bearing technologies: wheels and recirculating-ball bearings.

Beam sections can be joined to build long runs.

Cap wipers on guide wheels let the systems work in dirty environments.

This XZ gantry incorporates a rack drive in the slide, eliminating the need for a separate rack. The Z axis telescopes, useful when overhead height is limited.

Which technology makes sense depends on many factors, including the operating environment, ease of installation, maintenance, and cost.

Certain cutting applications, for example, produce debris that can foul up many recirculating-ball systems and cause them to prematurely fail, particularly when they aren't properly maintained. Guide wheels, in contrast, can be fitted with cap wipers that continuously lubricate the wheels for life and help keep debris away.

Applications with long runs can be a challenge, especially for recirculating-ball-bearing types. Installation and adjustment of such systems may take several hours because, to work properly, the guides must mount flat within tight tolerances. In contrast, wheel-type linear-motion systems, such as the Hepco Heavy Duty Series, better tolerate installations with slightly relaxed tolerances.

HDS uses a rigid aluminum beam to which a system of components attaches, in 22 different positions and in dozens of combinations. Aluminum-alloy beams have a lower overall installed cost compared with steel sections. And they are amply rigid and accurate for heavy pickand-place jobs.

HDS Series vee slides and beams come in two grades: precision ground for higher tolerances, and commercial grade for cost-sensitive applications where accuracy is not as critical. The steel slides easily fit to the aluminum beams, simplifying installation and maintenance of long runs. Slides and beams come in two standard sizes, plus a compact version, in single lengths to 4 m. Longer runs are possible by joining individual sections. A double-edge slide gives built-in parallelism, while a singleedge model saves space.

Wheels come standard with doublerow ball bearings. Optional four-needle roller bearings handle high loads (to 40 kN) and high-accuracy applications. Linear speeds exceeding 10 m/sec are possible. Wheel-based linear guides work in any plane and are significantly quieter in operation than recirculating-ballbearing types.

Systems may incorporate a rack and pinion or belt drive. Belts run through the hollow beam, while the beam itself permits attachment of motors and pulleys.

The aluminum beams can build high-load XYZ and XZ gantry systems. For example, a 300 X 200 mm beam, which is typically used as the X axis, accommodates bearing sizes to 128 mm and handles loads to 12,000 lb. A 220 X 130-mm HDCB beam works for lighter loads. The HDCB permits mounting on all four corners, and can be used as either a single-axis or twostage telescopic axis.

HDS systems can ship as assembled units (including drive transmissions), which lowers installation costs.

Bishop-Wisecarver Corp., (888) 580-8272,

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