The term hexapod is derived from the Greek word for six legs, and has been adapted to a variety of different meanings.
Insects and walking robots
In the animal kingdom, the hexapod describes insects and a few other related miniature six-legged groups.
In the world of mechanical engineering, hexapod again has two different meanings. There are hexapod positioning platforms and hexapod walking robots, modeled after the way insects move.
Stewart Gough Platforms
Hexapod positioning platforms (often also called Stewart platform or Stewart Gough platform) have had a significant impact on the advancement of various industries. These positioning platforms are called parallel kinematic machines or direct kinematic robots because all the actuators operate directly on a platform in parallel. Many different hexapod platform designs exist today, but the first one was devised by Eric Gough, an engineer involved in automotive tire testing. Developed the high load hexapod 6-axis positioning platform to apply loads to your tires in all 6 degrees of freedom, that is, all 3 linear movements (XYZ) and all 3 rotations, around X, Y, and Z (also called pitch, roll and yaw).
Hexapods are best known for flight simulators and driving simulators, where huge hydraulic actuators provide high forces and fast movement. In fact, in 1965, an article published by D. Stewart in the UK described the idea of using a 6 degrees of freedom motion platform for flight simulators. This is how the Stewart platform got its name from him.
High precision hexapod platforms
At the other end of the spectrum are ultra-high-precision hexapod positioners with electromagnetic and piezoelectric drives for applications such as fiber optic alignment, nanotechnology, and computer-aided surgery. Here precision down to the submicron and even nanometer realm is required. Control of a Hexapod needs a fast processor to provide the necessary coordinate transformations and 6-D vector motions. Usually every movement, even a simple linear movement in a straight line, involves all 6 actuators. This can be a challenge in controller and mechanical design.
Series and parallel kinematics
On the other hand, hexapods have many advantages over conventional multi-axis positioning systems (serial kinematics or stacked axes). Hexapods are lighter, stiffer, and have less inertia than these traditional positioning systems. The lower inertia allows much higher dynamics, quicker acceleration and start/stop behaviour. Hexapods and parallel kinematics are even used in CNC precision machining centers and also in pick and place robots due to their fast response.
More hexapod applications
Large astronomical telescopes mainly use hexapod jigs to align the optics and mirrors. The small footprint, high rigidity, and large central opening play a key role here. Motorized and automated fiber positioners also benefit from hexapod principles. With full degrees of freedom and a freely programmable pivot point, fiber tip rotations can be executed around the waist of the bundle, and even fiber bundles can be aligned quickly and efficiently.
In vacuum applications, space is often at a premium and smaller is better when it comes to installing a positioning system inside a vacuum chamber. Here, the compact vacuum hexapod design offers further advantages. Since the cables are not connected to individual sliding and rotary shafts, as with stacked locators, there are no issues with hitting obstacles and the bending forces or torque exerted by rigid vacuum cables do not adversely affect accuracy. of the positioning system.
While hexapod precision positioning systems won’t replace all traditional multi-axis positioners anytime soon, the variety of options that are available today—mechanical configurations, advanced controllers, and software simulation tools to help with design and installation) will facilitate movement. -System design engineers to think outside the box/traditional stack.