Machine Design

Short stretch over long runs

Billed as an "endless" linear module, the HLE-Z Series unit from Parker Hannifin Corp.'s Daedal Div., Irwin, Pa., guides, transports, or positions payloads over long travel distances while maintaining high dynamic performance and repeatability.

The drive module employs a unique rack-and-pinion-style system. Here, the teeth of an inverted timing belt mesh with an aluminum gear rack, forming an interlocked "tractor-tread" style drive. Lateral deflection rollers pretension the system to remove backlash, and "hold down" rollers assure that a full series of teeth always remain in mesh. The reinforced polymer timing belt and aluminum rack combination provides a safe, quiet running, and clean linear drive without lubrication.

This drive is said to offer all the advantages of a conventional rack and pinion drive but without many of the drawbacks. For instance, the fully engaged teeth provide better traction with less backlash than the limited tooth mesh of a typical rack and pinion, claims the company. The HLE-Z is said to outperform conventional timing belt and pulley drives over long travels because it uses the same short timing belt regardless of travel length. This minimizes the effects of belt stretch and tension. The new design provides high accelerations and velocities, and allows for several carriages to be independently positioned on a single unit.

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