Hexapod Precision Positioning Systems Provide Motion In 6 Degrees Of Freedom

Hexapod positioning systems (Stewart- Gough platforms) for precision micro-positioning applications became first commercially available in the 1990. Todays electromechanical and piezoelectric hexapods are now mainstream and provide many advantages over to serial kinematics electromechanical and hydraulic parallel positioning positioning systems.

Hexapod positioners are used as surgical robots and for single mode fiber alignment applications. They are key components for all modern astronomical telescopes.

A hexapod, is mostly designed as a six-legged parallel mechanism structure with 6 actuators between two platforms. The precision actuators move in parallel (parallel kinematics). Computer controlled motion of all actuators enables motion in any degree of freedom (3 linear directions x, y, z (lateral, longitudinal and vertical), and the three rotation directions (pitch, roll and yaw).

There are fixed strut length and variable strut length hexapod designs available.
Fiixed-strut-length designs can use 6 linear motors to move the basis of each joint up and down, or move in plane.

Benefits of Hexapods vs Stacked Traditional Precision Positioners
Parallel-kinematic mechanism (PKM) motion control systems have a number of advantages over standard serial kinematic (stacked) positioning systems.

Higher Stiffness
In a hexapod, all actuators act directly on the same moving platform, with the same dynamic characteristics for the six axes. Because each actuator basically only has one degree of freedom, (unlike a serial stack of stages, where imperfections bearings in each axis contribute to crosstalk and runout), accumulation of off-axis errors is much less of a concern for hexapod designs. Due to the high stiffness flexing and bending errors are not an issue.

Faster
Because of the lower moving mass positioning can be performed with faster settling times than with conventional, stacked stage systems.

No Moving Cables
In such systems, runout, guiding errors, and the friction and inertia of moving cables all accumulate to limit accuracy and repeatabilityproblems which do not affect parallel kinematic systems like the Hexapod.

Fixed Virtual Pivot Point
For optics and other alignment tasks, it is important to be able to define a fixed pivot point. The more sophisticated Hexapod vector controller allows choosing any point in space as the pivot point for the rotation axes by software command. The pivot point remains fixed relative to the platform.

No Cumulative Errors In serial stacked precision positioning systems, the bottom stage supports its own moving platform plus all stages above it and wobble and guiding errors of each axis accumulate. With a hexapod all actuators work parallel and their bearings are constricted to one degree of freedom.

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Hexapods

Hexapod positioning systems (Stewart- Gough platforms) for precision micro-positioning applications became first commercially available in the 1990. Todays electromechanical and piezoelectric hexapods are now mainstream and provide many advantages over to serial kinematics electromechanical and hydraulic parallel positioning positioning systems.

Article Originally Published On: http://www.articlesnatch.com

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