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Tubular linear motor drives all-in-one positioning axis

01 October, 2005

Tubular linear motor drives all-in-one positioning axis

Festo has developed a linear positioning system which, it claims, offers the benefits of linear-motor technology in a novel form that is easy to apply and delivers superior performance. The HME system integrates an innovative three-phase linear servo motor with a precision guide assembly and a displacement encoder.

The complete system (shown above) consists of just two elements - the handling axis, and a programmable controller incorporating the necessary power electronics.

Unlike rival linear-motor-based actuators, the heavy-duty guide is said to ensure consistent performance throughout its stroke, without needing any extra mechanical components. The guide, which is designed to provide smooth, backlash-free operation, can accommodate up to 50Nm of torque and 500N of cantilever force on its yoke plate, without affecting performance.

Festo asserts that these figures are "completely outside the domain of conventional linear motor axes," which would need complicated integration with sophisticated guidance systems to approach this level of load tolerance.

The patented linear servo motor that drives the axis has a novel tubular construction and uses high flux-density radial magnets, and a special coil-winding technology to shrink the cross-sectional area dramatically. It is said to be much smaller than conventional linear motors and to provide uniform performance throughout its travel, unlike most other linear machines whose characteristics change as their magnets move, making them difficult to tune. Because the motor has no external magnets, it can be used in applications such as machine tools, where there may be metallic swarf.

The HME axes are available in two thrust forces - 40N nominal 160N peak, and 85N nominal, 220N peak - with stroke lengths from 100-400mm. The axes can move at up to 3m/s, and a repeatable positioning accuracy of ±0.03mm is promised.

The axes can be used in thrust, speed or position control modes. The matching SFC-LAC positioning controllers are sealed to IP54 and can be sited next to the axis or in a control cabinet. A single cable carries all drive and encoder signals and the only item needed to complete an installation is a 48V DC power supply.

The controller is configured using menu-driven PC software. Because the software is aware of the HME`s mechanical and electrical characteristics, almost no system tuning is needed. The controller can store up to 31 travel profiles, and can operate in response to external signals fed via its I/O interface or a fieldbus.

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