A stewart platform is a parallel manipulator device that is used for positioning and motion control. The device consists of two plates joined by six adjustable legs that allow it to be precisely adjusted and controlled. Although originally used to test tires, the stewart platform soon found applications in the aerospace, automotive, and machining industries. It is perhaps best known for its use in providing the precise movement required of flight simulators.
The base plate of a stewart device is the only part of the device that is not adjustable. It is usually bolted to the floor or some other stable surface. Six legs attach the base plate to the adjustable upper plate. Both ends of the legs are connected using universal joints that allow for a wide range of motion. Each of the legs has a cylinder joint so that the leg can telescope out or collapse down as needed.
Due to the six-leg design, the stewart platform is sometimes called a hexapod. The term can be used to describe any six-legged device. The stewart platform is also classified as a parallel manipulator, meaning that the legs of the platform are attached to only the base and upper plate but not to each other. By contrast, a serial manipulator uses a series of rigid structures connected by joints. The manipulation of one of these rigid sections directly affects the positioning of the sections after it.
Parallel manipulators demonstrate several advantages over serial manipulators. For example, a parallel manipulator can be controlled more precisely because errors are contained to a single leg. With a serial manipulator, an error in the movement of one of the rigid structures is amplified in each of the structures that follows. Parallel manipulators are also able to handle much larger and heavier work loads and have a better strength-to-mass ratio than serial manipulators.
The device that would become the stewart platform was first designed by V. Eric Gough of the United Kingdom in 1954. Gough was working as an engineer at the Dunlop Tyres Factory in Birmingham, England when he built an early version of the stewart platform to be used in the testing of tires. Just over a decade later, D. Stewart presented a paper to the UK Institution of Mechanical Engineers proposing an adjustable platform to be used in flight simulators. This is how the device got its name, though some engineers refer to it as a Gough-stewart platform in deference to its original inventor.
