A Stewart platform is a type of
parallel manipulator
A parallel manipulator is a mechanical system that uses several computer-controlled serial chains to support a single platform, or end-effector. Perhaps, the best known parallel manipulator is formed from six linear actuators that support a mov ...
that has six
prismatic actuators, commonly
hydraulic jack
A jack is a mechanical lifting device used to apply great forces or lift heavy loads. A mechanical jack employs a screw thread for lifting heavy equipment. A hydraulic jack uses hydraulic power. The most common form is a car jack, floor jack o ...
s or electric
linear actuator
A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as d ...
s, attached in pairs to three positions on the platform's baseplate, crossing over to three mounting points on a top plate. All 12 connections are made via
universal joints. Devices placed on the top plate can be moved in the
six degrees of freedom in which it is possible for a freely-suspended body to move: three linear movements x, y, z (lateral, longitudinal, and vertical), and the three rotations (pitch, roll, and yaw).
Stewart platforms are known by various other names. In many applications, including in flight simulators, it is commonly referred to as a motion base. It is sometimes called a ''six-axis platform'' or ''6-DoF platform'' because of its possible motions and, because the motions are produced by a combination of movements of multiple actuators, it may be referred to as a ''synergistic motion platform'', due to the synergy (mutual interaction) between the way that the actuators are programmed. Because the device has six actuators, it is often called a ''hexapod'' (six legs) in common usage, a name which was originally
trademarked by
Geodetic Technology for Stewart platforms used in
machine tools.
History
This specialised six-jack layout was first used by
V E (Eric) Gough of the
UK and was operational in 1954,
the design later being publicised in a 1965 paper by D Stewart to the UK
Institution of Mechanical Engineers.
In 1962, prior to the publication of Stewart's paper, American engineer
Klaus Cappel
Klaus is a German, Dutch and Scandinavian given name and surname. It originated as a short form of Nikolaus, a German form of the Greek given name Nicholas.
Notable persons whose family name is Klaus
*Billy Klaus (1928–2006), American baseba ...
independently developed the same hexapod. Klaus patented his design and licensed it to the first flight simulator companies, and built the first commercial octahedral hexapod motion simulators.
Although the title ''Stewart platform'' is commonly used, some have posited that ''Gough–Stewart platform'' is a more appropriate name because the original Stewart platform had a slightly different design, while others argue that the contributions of all three engineers should be recognized.
Actuation
Linear actuation
In industrial applications, linear hydraulic actuators are typically used for their simple and unique
inverse kinematics closed form solution and their good strength and acceleration.
Rotary actuation
For prototyping and low budget applications, typically rotary servo motors are used. A unique closed form solution for the
inverse kinematics of rotary actuators also exists, as shown by Robert Eisele
Applications
Stewart platforms have applications in flight simulators, machine tool technology,
animatronics
Animatronics refers to mechatronic puppets. They are a modern variant of the automaton and are often used for the portrayal of characters in films and in theme park attractions.
It is a multidisciplinary field integrating puppetry, anatomy a ...
, crane technology, underwater research, simulation of earthquakes, air-to-sea rescue,
mechanical bull
A mechanical bull, also known as a bucking machine, is a device that replicates the sensation of riding a bucking animal, such as a rodeo bull or horse popularized by Sherwood Cryer. It is usually powered by a variable-speed electric motor. Pa ...
s, satellite dish positioning, the
Hexapod-Telescope
The Hexapod-Telescope (HPT) is a telescope located at Cerro Armazones Observatory in northern Chile. The Ritchey-Chrétien reflecting telescope is notable for the design of the telescope mount. Instead of the typical mounting where the telesco ...
, robotics, and orthopedic surgery.
Flight simulation
The Stewart platform design is extensively used in
flight simulators, particularly in the
full flight simulator
Full flight simulator (FFS) is a term used by national (civil) aviation authorities (NAA) for a high technical level of flight simulator. Such authorities include the Federal Aviation Administration (FAA) in the United States and the European Avia ...
which requires all 6 degrees of freedom. This application was developed by
Redifon, whose simulators featuring it became available for the Boeing 707, Douglas DC-8,
Sud Aviation Caravelle,
Canadair CL-44
The Canadair CL-44 was a Canadian turboprop airliner and cargo aircraft based on the Bristol Britannia that was developed and produced by Canadair in the late 1950s and early 1960s. Although innovative, only a small number of the aircraft we ...
,
Boeing 727
The Boeing 727 is an American narrow-body airliner that was developed and produced by Boeing Commercial Airplanes.
After the heavy 707 quad-jet was introduced in 1958, Boeing addressed the demand for shorter flight lengths from smaller airpor ...
, Comet,
Vickers Viscount
The Vickers Viscount is a British medium-range turboprop airliner first flown in 1948 by Vickers-Armstrongs. A design requirement from the Brabazon Committee, it entered service in 1953 and was the first turboprop-powered airliner.
The Vis ...
,
Vickers Vanguard
The Vickers Vanguard was a short/medium-range turboprop airliner designed and produced by the British aircraft manufacturer Vickers-Armstrongs.
The Vanguard was developed during the mid-to-late 1950s in response to a specification issued by ...
,
Convair CV 990,
Lockheed C-130 Hercules,
Vickers VC10
The Vickers VC10 is a mid-sized, narrow-body long-range British jet airliner designed and built by Vickers-Armstrongs (Aircraft) Ltd and first flown at Brooklands, Surrey, in 1962. The airliner was designed to operate on long-distance route ...
, and
Fokker F-27
The Fokker F27 Friendship is a turboprop airliner developed and manufactured by the Dutch aircraft manufacturer Fokker. It is the most numerous post-war aircraft manufactured in the Netherlands; the F27 was also one of the most successful Europ ...
by 1962.
In this role, the payload is a replica cockpit and a visual display system, normally of several channels, for showing the outside-world visual scene to the aircraft crew that are being trained.
Similar platforms are used in
driving simulators, typically mounted on large
X-Y table {{Unreferenced, date=May 2009
X-Y tables, also known as cross working tables or coordinate tables, help provide horizontal motion for automated machinery such as assembly robots in manufacturing facilities. Robotic arms and other automated machiner ...
s to simulate short term acceleration. Long term acceleration can be simulated by tilting the platform, and an active research area is how to mix the two.
Robocrane
James S. Albus of the
National Institute of Standards and Technology (NIST) developed the
Robocrane, where the platform hangs from six cables instead of being supported by six jacks.
LIDS
The
Low Impact Docking System developed by NASA uses a Stewart platform to manipulate space vehicles during the docking process.
CAREN
The Computer Assisted Rehabilitation Environment developed by Motek Medical uses a Stewart platform coupled with virtual reality to do advanced biomechanical and clinical research.
Taylor Spatial Frame
Dr. J. Charles Taylor used the Stewart platform to develop the
Taylor Spatial Frame
The Taylor Spatial Frame (TSF) is an external fixator used by paediatric and orthopaedic surgeons to treat complex fractures and bone deformities. The medical device shares a number of components and features of the Ilizarov apparatus. The Taylo ...
, an
external fixator
External fixation is a surgical treatment wherein rods are screwed into bone and exit the body to be attached to a stabilizing structure on the outside of the body. It is an alternative to internal fixation, where the components used to provide ...
used in
orthopedic surgery for the correction of bone deformities and treatment of complex fractures.
Mechanical testing
*First application: Eric Gough was an automotive engineer and worked at
Fort Dunlop
Fort Dunlop (), is the common name of the original tyre factory and main office of Dunlop Rubber in the Erdington district of Birmingham, England. It was established in 1917, and by 1954 the entire factory area employed 10,000 workers. At one ...
, the
Dunlop Tyres
Dunlop Tyres is a brand of tyres which is managed by different companies around the world. It was founded by pneumatic tyre pioneer John Boyd Dunlop in Dublin, Ireland, in 1890.
The brand is operated by Goodyear in North America (passenger c ...
factory in
Birmingham
Birmingham ( ) is a city and metropolitan borough in the metropolitan county of West Midlands in England. It is the second-largest city in the United Kingdom with a population of 1.145 million in the city proper, 2.92 million in the West ...
, England. He developed his "Universal Tyre-Testing Machine" (also called the "Universal Rig") in the 1950s and his platform was operational by 1954.
The rig was able to mechanically test tyres under combined loads. Dr. Gough died in 1972 but his testing rig continued to be used up until the late 1980s when the factory was closed down and then demolished. His rig was saved and transported to the
Science Museum, London storage facility at Wroughton near Swindon.
*Recent applications: the rebirth of interest for a mechanical testing machine based on Gough-Stewart platform occurred in the mid '90s. They are often biomedical applications (for example spinal study) because of the complexity and large amplitude of the motions needed to reproduce human or animal behaviour. Such requirements are also encountered in the civil engineering field for seism simulation. Controlled by a full-field kinematic measurement algorithm, such machines can also be used to study complex phenomena on stiff specimens (for example the curved propagation of a crack through a concrete block
) that need high load capacities and displacement accuracy.
Motion compensation
The
Ampelmann system is a motion-compensated gangway using a Stewart platform. This allows access from a moving
platform supply vessel
A platform supply vessel (PSV) is a ship specially designed to supply offshore oil and gas platforms. These ships range from in length and accomplish a variety of tasks. The primary function for most of these vessels is logistic support and tr ...
to
offshore constructions even in high wave conditions.
See also
*
Acceleration onset cueing
Acceleration onset cueing is a term for the cueing principle used by a simulator motion platform.
Motion platforms used in "Level D" Full flight simulators (FFS) and equivalent military simulators have six jacks that can move the replica cock ...
*
Actuator
An actuator is a component of a machine that is responsible for moving and controlling a mechanism or system, for example by opening a valve. In simple terms, it is a "mover".
An actuator requires a control device (controlled by control signal) an ...
*
Linear actuator
A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer peripherals such as d ...
*
Parallel manipulator
A parallel manipulator is a mechanical system that uses several computer-controlled serial chains to support a single platform, or end-effector. Perhaps, the best known parallel manipulator is formed from six linear actuators that support a mov ...
*
Robot kinematics
In robotics, robot kinematics applies geometry to the study of the movement of multi-degree of freedom kinematic chains that form the structure of robotic systems. The emphasis on geometry means that the links of the robot are modeled as rig ...
References
Further reading
*Bonev, I.A.,
The True Origins of Parallel Robots, ParalleMIC online review
External links
{{Commons category, Hexapods
Picture of the NIST/Ingersoll prototype octahedral hexapodHexapod Structures for SurgeryHexapod for Astronomy
Mechanisms (engineering)
Parallel robots
1954 in robotics