![Strandbeest-Animation-rgb-100ms](https://upload.wikimedia.org/wikipedia/commons/c/c2/Strandbeest-Animation-rgb-100ms.gif)
A leg mechanism (walking mechanism) is a
mechanical system
A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
designed to provide a propulsive force by intermittent frictional contact with the ground. This is in contrast with
wheels
A wheel is a circular component that is intended to rotate on an axle bearing. The wheel is one of the key components of the wheel and axle which is one of the six simple machines. Wheels, in conjunction with axles, allow heavy objects to be ...
or
continuous track
Continuous track is a system of vehicle propulsion used in tracked vehicles, running on a continuous band of treads or track plates driven by two or more wheels. The large surface area of the tracks distributes the weight of the vehicle b ...
s which are intended to maintain continuous frictional contact with the ground. Mechanical legs are
linkages that can have one or more actuators, and can perform simple planar or complex motion. Compared to a wheel, a leg mechanism is potentially better fitted to uneven terrain, as it can step over obstacles.
An early design for a leg mechanism called the ''Plantigrade Machine'' by
Pafnuty Chebyshev
Pafnuty Lvovich Chebyshev ( rus, Пафну́тий Льво́вич Чебышёв, p=pɐfˈnutʲɪj ˈlʲvovʲɪtɕ tɕɪbɨˈʂof) ( – ) was a Russian mathematician and considered to be the founding father of Russian mathematics.
Chebyshe ...
was shown at the
Exposition Universelle (1878)
The third Paris World's Fair, called an Exposition Universelle in French, was held from 1 May to 10 November 1878. It celebrated the recovery of France after the 1870–71 Franco-Prussian War.
Construction
The buildings and the fairgroun ...
. The original engravings for this leg mechanism are available. The design of the leg mechanism for the Ohio State Adaptive Suspension Vehicle (ASV) is presented in the 1988 book ''Machines that Walk''. In 1996, W-B. Shieh presented a design methodology for leg mechanisms.
The artwork of
Theo Jansen
Theodorus Gerardus Jozef Jansen (; born 14 March 1948) is a Dutch artist. In 1990, he began building large mechanisms out of PVC that are able to move on their own and, collectively, are titled ''Strandbeest''. The kinetic sculptures appear to ...
, see
Jansen's linkage, has been particularly inspiring for the design of leg mechanisms, as well as the
Klann patent, which is the basis for the leg mechanism of the
Mondo Spider.
Design goals
* horizontal speed as constant as possible while touching the ground (support phase)
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* while the foot is not touching the ground, it should move as fast as possible
* constant torque/force input (or at least no extreme spikes/changes)
* stride height (enough for clearance, not too much to conserve energy)
* the foot has to touch the ground for at least half of the cycle for a two/four leg mechanism or respectively, a third of the cycle for a three/six leg mechanism
* minimized moving mass
* vertical center of mass always inside the base of support
* the speed of each leg or group of legs should be separately controllable for steering
* the leg mechanism should allow forward and backward walking
Another design goal can be, that stride height and length etc. can be controlled by the operator. This can relatively easily be achieved with a hydraulic leg mechanism, but is not practicable with a crank-based leg mechanism.
The optimization has to be done for the whole vehicle – ideally the force/torque variation during a rotation should cancel each other out.
History
Richard Lovell Edgeworth
Richard Lovell Edgeworth (31 May 1744 – 13 June 1817) was an Anglo-Irish politician, writer and inventor.
Biography
Edgeworth was born in Pierrepont Street, Bath, England, son of Richard Edgeworth senior, and great-grandson of Sir Sal ...
tried in 1770 to construct a machine he called a "Wooden Horse", but was not successful.
Patents
Patents for leg mechanism designs range from rotating cranks to four-bar and six-bar linkages. See for example the following patents:
U.S. Patent No. 469,169 Figure Toy, F. O. Norton (1892)
U.S. Patent No. 1,146,700, Animated Toy, A. Gund (1915)
A leg mechanism formed by an inverted slider-crank.
U.S. Patent No. 1,363,460, Walking Toy, J. A. Ekelund (1920)
A leg mechanism formed by a rotating crank with extensions that contact the ground.
U.S. Patent No. 1,576,956, Quadruped Walking Mechanism, E. Dunshee (1926)
A four-bar leg mechanism that shows the coupler curve forms the foot trajectory.
U.S. Patent No. 1,803,197, Walking Toy, P. C. Marie (1931)
Another rotating crank leg mechanism.
U.S. Patent No. 1,819,029, Mechanical Toy Horse, J. St. C. King (1931)
A crank-rocker leg mechanism with a one-way friction mechanisms in the foot.
U.S. Patent No. 2,591,469, Animated Mechanical Toy, H. Saito (1952)
An inverted slider crank mechanism for the front foot and crank-rocker for the back foot.
U.S. Patent No. 4095661, Walking Work Vehicle, J. R. Sturges (1978)
A lambda mechanism combined with a parallelogram linkage to form a translating leg that follows the coupler curve.
U.S. Patent No. 6,260,862, Walking Device, J. C. Klann (2001)
The coupler curve of a four-bar linkage guides the lower link of an RR serial chain to form a leg mechanism, known as the Klann linkage
The Klann linkage is a planar mechanism designed to simulate the gait of legged animal and function as a wheel replacement, a leg mechanism. The linkage consists of the frame, a crank, two grounded rockers, and two couplers all connected by ...
.
U.S. Patent No. 6,481,513, Single Actuator per Leg Robotic Hexapod, M. Buehler et al. (2002)
A leg mechanism that consists of a single rotating crank.
U.S. Patent No. 6,488,560, Walking Apparatus, Y. Nishikawa (2002)
Another rotating crank leg mechanism.
Gallery
Stationary
File:Strandbeest-Walking-Animation.gif, Jansen linkage
File:F4-motion.gif, Klann linkage
The Klann linkage is a planar mechanism designed to simulate the gait of legged animal and function as a wheel replacement, a leg mechanism. The linkage consists of the frame, a crank, two grounded rockers, and two couplers all connected by ...
File:Leg mechanism.gif, Eight-bar leg mechanism
File:Tokyo Institute of Technology leg mechanism.gif, Tokyo Institute of Technology walking chair
File:LegMechanism2DOF.gif, 2 DOF pantograph leg mechanism
File:RPRPR leg mechanism.gif, 2 DOF leg mechanism of the RPRPR type.
File:Strandbeest--Full-Walking-Animation.gif, Strandbeest (applied Jansen linkage)
File:Ghassaei Linkage four legs.gif, Ghassaei Linkage
File:Tchebyshevs plantigrade machine.gif, Tchebyshevs plantigrade machine
File:TrotBot without Heel Linkage.gif, TrotBot Linkage (without heel linkage)
File:TrotBot - 1 Corner of 12 Leg Robot.gif, TrotBot Linkage Speed Variability as Ground Height Changes
File:Strider Linkage - 1 Corner of 12 Leg Robot.gif, Strider Linkage Speed Variability as Ground Height Changes
File:Strider Linkage Animated.gif, Strider Linkage
File:Strandbeest, TrotBot, Strider, Klann Linkages.gif, Foot-Paths of Strandbeest, TrotBot, Strider and Klann Linkages
Walking
Complex mechanism
Shown above are only planar mechanisms, but there are also more complex mechanisms:
File:Lauron4c 2009 FZI Karlsruhe.jpg
File:Legged robot.jpg
File:Sechsbeiniger Laufroboter LAURON aus dem Jahr 1995 im Deutschen Museum in München entwickelt vom Forschungszentrum Informatik, Karlsruhe.jpg
See also
* Hexapod (robotics)
''A six-legged walking robot should not be confused with a Stewart platform, a kind of parallel manipulator used in robotics applications''.
A hexapod robot is a mechanical vehicle that walks on six legs. Since a robot can be statically stabl ...
* Jansen's linkage
* Kinematics
Kinematics is a subfield of physics, developed in classical mechanics, that describes the Motion (physics), motion of points, Physical object, bodies (objects), and systems of bodies (groups of objects) without considering the forces that cause ...
* Kinematic pair
In classical mechanics, a kinematic pair is a connection between two physical objects that imposes constraints on their relative movement (kinematics). German engineer Franz Reuleaux introduced the kinematic pair as a new approach to the study o ...
s
* Klann linkage
The Klann linkage is a planar mechanism designed to simulate the gait of legged animal and function as a wheel replacement, a leg mechanism. The linkage consists of the frame, a crank, two grounded rockers, and two couplers all connected by ...
* Chebyshev's Lambda Mechanism
* Linkage (mechanical)
A mechanical linkage is an assembly of systems connected to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing i ...
* Machine
A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
* Mecha
In science fiction, or mechs are giant robots or machines controlled by people, typically depicted as humanoid walking vehicles. The term was first used in Japanese (language), Japanese after shortening the English loanword or , but the mean ...
* Mobile robot
A mobile robot is an automatic machine that is capable of locomotion.Hu, J.; Bhowmick, P.; Lanzon, A.,Group Coordinated Control of Networked Mobile Robots with Applications to Object Transportation IEEE Transactions on Vehicular Technology, 2021 ...
References
External links
*{{Commonscatinline
Linkages (mechanical)