PI is the leading manufacturer of Hexapod high-performance micro- and nanopositioning systems. These parallel-kinematics devices, in a number of different forms, are suitable for diverse applications, ranging from handling systems in electronics fabrication and tool control in precision machining, through medical technology, to optical systems like those found in space telescopes and satellite receiving antennas. Various models of the powerful parallel kinematic machines(PKM) can move masses of 50, 200 or even 1000 kilograms with micron accuracy as required in their respective applications.
These Hexapod systems are all built with six, high-resolution electro-mechanical or piezoelectric actuators all acting on a common platform. It is the familiar flight simulator design, but considerably more precise: in place of hydraulic cylinders, the Hexapods are driven by highly accurate, precision-controlled rotary or linear motors. Different drive principles are employed, depending on the application: Hexapods with NEXLINE® drives make for a positioning system which is not only vacuum compatible but also completely non-magnetic .
All PI Hexapod systems include a sophisticated, yet easy to use controller. The Hexapod controller allows the user to set a pivot point anywhere inside or outside the Hexapod working space, by a simple software command. This freely definable pivot point stays with the platform, no matter how it moves—an invaluable feature for example in optics applications. Moves are specified in Cartesian coordinates and the PC-based controller transforms them into the required motion-vectors for the individual actuator drives. The latest controller generation features flexible interfaces: highspeed RS-232, or TCP/IP interface for remote / network / Internet addressing.
Advantages of PKM:
- Low moved mass, lower inertia
- Better dynamic behaviour, shorter settling times
- Smaller package size
- Higher stiffness
- No accumulation of position errors, increased accuracy
- Freely definable pivot point
- Reduced runout errors
- No moving cables: better repeatability
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The ALMA project in the Atacama desert in Chile is to include up to 64 antennas interconnected to form an enormous radio telescope. PI Hexapod systems are used to position the secondary reflectors in the antennas. The M-850K systems, specially designed for outdoor operation in hostile conditions, can position loads of up to 75 kg (photo: Vertex Antennentechnik GmbH)
Stacked serial kinematics 6D system vs. Hexapod parallel kinematics system designs. Advantages such as compactness and minimized inertia (one platform for all six actuators) are easily seen. The reduced inertial mass makes for significantly faster response than with serial kinematics. Because there are no moving cables to cause friction, repeatability is improved also
This automated interferometric inspection system allows optical mold inserts to be checked directly while still on the production line. The hexapod is mounted "upside down" on a 20-millimeter-thick aluminum plate with the interferometer positioned in the central core of the hexapod, where it does interfere with the motion. Control is integrated into a MatLab program, which also handles the metrological image processing (photo: Physik Instrumente (PI) / Fraunhofer Institute for Production Technology IPT
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