A hexapod is a special form of parallel kinematics machine that has six legs of variable length. The typical construction of the hexapod enables mobility in all six degrees of freedom (three translational and three rotary ). Due to the parallel arrangement of the drives, hexapods have a better ratio of payload to dead weight compared to serial robots.
Until a few years ago, it was believed that the concept of the hexapod was first introduced by D. Stewart in 1965. This is where the common name Stewart platform comes from . Another publication on the subject is much older and comes from Eric Gough , which is why the Hexapod is now also referred to as the Stewart / Gough platform . Eric Gough is said to have built the first hexapod back in the 1950s. Another name related to the development of the hexapod is Klaus Cappel , who built his first hexapod in 1962.
Hexapods are regularly used in various configurations for special purposes:
- Actuator drive for driving and flight simulators
- Mounting of telescopes, see hexapod telescope
- in robotics
- in medical technology, see Taylor Spatial Frame
- As a basic element in machine tools (see section on parallel kinematics), especially when machining complex geometries and free-form surfaces
The high dynamics and the simple statics of hexapods is an ideal construction, especially for motion simulations.
Use in a flight simulator
Because of the special kinematics (parallel kinematics ), the construction principle of hexapods is fundamentally very interesting for use in robots or special industrial robots and machine tools . Such systems are available from many manufacturers and in basic research for over 20 years. To date, however, there has been no significant use in production, which is traditionally dominated by machines with serial kinematics. The following are special advantages and disadvantages:
|High dynamics and low moving masses. This results in high accelerations and top speeds (rapid traverse) and a correspondingly faster workpiece processing or manipulation.|
|Positioning accuracy is fundamentally better with parallel kinematics, since position errors of the axes do not add up - as with serial kinematics - but are only partially included in the overall movement.|
|High mobility. The degree of freedom of the tool or the tool holder reaches almost spherical 5-sided. However, traditional machines with serial kinematics today achieve a comparably high degree of freedom with the simultaneous use of swiveling tool heads and rotating clamping tables.|
|Due to the spatial spanning of the hexapod design, use in robots results in very limited mobility between and especially in other machines (e.g. removal of a forged workpiece ) compared to the most common design as a multi-jointed, single arm (e.g. KUKA robot ) from a press ). For the same reason, a hexapod design in machine tools requires a considerably larger installation area (cost factor).|
|Higher control effort (software & hardware) due to the more complex kinematics (6 always simultaneously active feed assemblies ).|
|The lower mass of the construction results in a significantly higher susceptibility to vibrations , which is generally very undesirable, especially when machining ( roughness ).|
|Construction-related sensitivity or a correspondingly high level of wear and tear on the usually very expensive feed assemblies, since hydraulic cylinders or ball screw spindles are not suitable for all forces acting on them due to the construction of hexapods.|
|Higher thermal load on the measuring systems, which in a construction with serial kinematics are usually protected, hidden outside the work area, in or behind the guides. In the case of hexapods, a corresponding protective construction would be too expensive or it would negate the advantages of the hexapod construction (high dynamics, high mobility).|
- VE Gough, SG Whitehall: Universal Tire Test Machine. In: G. Eley (Ed.): Ninth international automobile technical congress, 1962. Proceeding. International Federation of Automobile Engineers 'and Technicians' Associations. Institution of Mechanical Engineers, London 1962, pp. 117–137, iri.upc.edu (PDF; 3.3 MB)
- Jean-Pierre Merlet: Parallel Robots. Kluwer Academic Publishers, Boston MA 2000, ISBN 0-7923-6308-6 ( Solid Mechanics and its Applications 74).
- D. Stewart: A Platform with Six Degrees of Freedom. In: Proceedings of the Institution of Mechanical Engineers. Vol 180, Pt 1, No 15 1965/66, pp. 371–386, iri.upc.edu (PDF; 5 MB)
- Reimund Neugebauer : Parallel kinematic machines: design, construction, application . Springer, Berlin 2005, ISBN 978-3-540-20991-1 .
- Homemade hexapod (MPG video; 2.03 MB)
- Comprehensive overview of the different variants of the parallel kinematics
- Free Hexapod project ( Memento from July 28, 2014 in the Internet Archive ) at the Laboratory for Micro Enterprise
- Hexapod for micropositioning by SYMETRIE - France Cairo University
- Free software CNC for hexapods, including calibration. License: GPL
- Treatise on the Hexapod University of Cairo
- Pneumatics based Stewart Platform ( Memento from July 23, 2011 in the Internet Archive ) (PDF; 8.28 MB) Diploma thesis