Leg mechanism

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Theo Jansen's Strandbeest, a group of planar walking mechanisms. Strandbeest-Animation-rgb-100ms.gif
Theo Jansen's Strandbeest, a group of planar walking mechanisms.

A leg mechanism (walking mechanism) is a mechanical system designed to provide a propulsive force by intermittent frictional contact with the ground. This is in contrast with wheels or continuous tracks 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. [1]

Contents

An early design for a leg mechanism called the Plantigrade Machine by Pafnuty Chebyshev was shown at the Exposition Universelle (1878). The original engravings for this leg mechanism are available. [2] The design of the leg mechanism for the Ohio State Adaptive Suspension Vehicle (ASV) is presented in the 1988 book Machines that Walk. [3] In 1996, W-B. Shieh presented a design methodology for leg mechanisms. [4]

The artwork of Theo Jansen, [5] 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

Another design goal can be, that stride height and length etc. can be controlled by the operator. [6] This can relatively easily be achieved with a hydraulic leg mechanism, but is not practicable with a crank-based leg mechanism. [6]

The optimization has to be done for the whole vehicle – ideally the force/torque variation during a rotation should cancel each other out. [1]

History

Richard Lovell Edgeworth tried in 1770 to construct a machine he called a "Wooden Horse", but was not successful. [7] [8]

Patents

Patents for leg mechanism designs range from rotating cranks to four-bar and six-bar linkages. [9] See for example the following patents:

Stationary

Walking

*4 legs6 legs
Strandbeest Strandbeest walking with four legs.gif Strandbeest walking with six legs.gif
Ghassaei Ghassaei Beest Walking Paths traced.gif Ghassaei Beest walking with six legs.gif
Klann linkage 1 Klann Linkage Walking with four legs.gif Klann Linkage six legs.gif
Klann linkage 2 Klann Linkage Walking with four legs - alternative measures.gif
Plantigrade Mechanism Plantigrade walking 4 legs.gif
Trotbot [16] Trotbot-Walking.gif
TrotBot with 6 Legs Moving.gif
Strider Linkage [15]
Strider Linkage Robot.gif
Strider Prototype, 4 legs/side
Strider Linkage in Motion.gif

Complex mechanism

Shown above are only planar mechanisms, but there are also more complex mechanisms:

See also

Related Research Articles

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A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecules, such as molecular machines. Machines can be driven by animals and people, by natural forces such as wind and water, and by chemical, thermal, or electrical power, and include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. They can also include computers and sensors that monitor performance and plan movement, often called mechanical systems.

<span class="mw-page-title-main">Parallel motion linkage</span> Six-bar straight-line mechanism

In kinematics, the parallel motion linkage is a six-bar mechanical linkage invented by the Scottish engineer James Watt in 1784 for the double-acting Watt steam engine. It allows a rod moving practically straight up and down to transmit motion to a beam moving in an arc, without putting significant sideways strain on the rod.

<span class="mw-page-title-main">Four-bar linkage</span> Mechanical linkage consisting of four links connected by joints in a loop

In the study of mechanisms, a four-bar linkage, also called a four-bar, is the simplest closed-chain movable linkage. It consists of four bodies, called bars or links, connected in a loop by four joints. Generally, the joints are configured so the links move in parallel planes, and the assembly is called a planar four-bar linkage. Spherical and spatial four-bar linkages also exist and are used in practice.

<span class="mw-page-title-main">Linkage (mechanical)</span> Assembly of systems connected to manage forces and movement

A mechanical linkage is an assembly of systems connected so as 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 ideal movement, pure rotation or sliding for example, and are called joints. A linkage modeled as a network of rigid links and ideal joints is called a kinematic chain.

<span class="mw-page-title-main">Theo Jansen</span> Dutch artist (born 1948)

Theodorus Gerardus Jozef Jansen 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 walk. His animated works are intended to be a fusion of art and engineering. He has said that "The walls between art and engineering exist only in our minds." Some of his creations are reported to incorporate primitive logic gates for collision detection with obstacles such as the sea.

<span class="mw-page-title-main">Chebyshev lambda linkage</span> Four-bar straight-line mechanism

In kinematics, the Chebyshev Lambda Linkage is a four-bar linkage that converts rotational motion to approximate straight-line motion with approximate constant velocity. It is so-named because it looks like a lowercase Greek letter lambda (λ). The precise design trades off straightness, lack of acceleration, and the proportion of the driving rotation that is spent in the linear portion of the full curve.

<span class="mw-page-title-main">Kinematic chain</span> Mathematical model for a mechanical system

In mechanical engineering, a kinematic chain is an assembly of rigid bodies connected by joints to provide constrained motion that is the mathematical model for a mechanical system. As the word chain suggests, the rigid bodies, or links, are constrained by their connections to other links. An example is the simple open chain formed by links connected in series, like the usual chain, which is the kinematic model for a typical robot manipulator.

<span class="mw-page-title-main">Legged robot</span> Type of mobile robot

Legged robots are a type of mobile robot which use articulated limbs, such as leg mechanisms, to provide locomotion. They are more versatile than wheeled robots and can traverse many different terrains, though these advantages require increased complexity and power consumption. Legged robots often imitate legged animals, such as humans or insects, in an example of biomimicry.

<span class="mw-page-title-main">Straight-line mechanism</span> Mechanisms generating real or approximate straight line motion

A straight-line mechanism is a mechanism that converts any type of rotary or angular motion to perfect or near-perfect straight-line motion, or vice versa. Straight-line motion is linear motion of definite length or "stroke", every forward stroke being followed by a return stroke, giving reciprocating motion. The first such mechanism, patented in 1784 by James Watt, produced approximate straight-line motion, referred to by Watt as parallel motion.

<span class="mw-page-title-main">Sarrus linkage</span> Six-bar straight-line mechanism

The Sarrus linkage, invented in 1853 by Pierre Frédéric Sarrus, is a mechanical linkage to convert a limited circular motion to a linear motion or vice versa without reference guideways. It is a spatial six-bar linkage (6R) with two groups of three parallel adjacent joint-axes.

<span class="mw-page-title-main">Mondo spider</span> Walking machine

The Mondo Spider is a ride-on walking machine propelled via eight steel legs in a walking motion utilizing the Klann Linkage.

<span class="mw-page-title-main">Klann linkage</span> Planar mechanism designed to simulate the gait of legged animals

The Klannlinkage 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 pivot joints. It was developed by Joe Klann in 1994 as an expansion of Burmester curves which are used to develop four-bar double-rocker linkages such as harbor crane booms. It is categorized as a modified Stephenson type III kinematic chain.

<span class="mw-page-title-main">Mechanism (engineering)</span> Device which converts input forces and motion to output forces and motion

In engineering, a mechanism is a device that transforms input forces and movement into a desired set of output forces and movement. Mechanisms generally consist of moving components which may include Gears and gear trains; Belts and chain drives; cams and followers; Linkages; Friction devices, such as brakes or clutches; Structural components such as a frame, fasteners, bearings, springs, or lubricants; Various machine elements, such as splines, pins, or keys.

<span class="mw-page-title-main">Jansen's linkage</span> Planar leg mechanism

Jansen's linkage is a planar leg mechanism designed by the kinetic sculptor Theo Jansen to generate a smooth walking motion. Jansen has used his mechanism in a variety of kinetic sculptures which are known as Strandbeesten. Jansen's linkage bears artistic as well as mechanical merit for its simulation of organic walking motion using a simple rotary input. These leg mechanisms have applications in mobile robotics and in gait analysis.

<span class="mw-page-title-main">Six-bar linkage</span> 1-DoF mechanism with 6 links and 7 joints

In mechanics, a six-bar linkage is a mechanism with one degree of freedom that is constructed from six links and seven joints. An example is the Klann linkage used to drive the legs of a walking machine.

<span class="mw-page-title-main">Slider crank chain inversion</span>

Slider-crank chain inversion arises when the connecting rod, or coupler, of a slider-crank linkage becomes the ground link, so the slider is connected directly to the crank. This inverted slider-crank is the form of a slider-crank linkage that is often used to actuate a hinged joint in construction equipment like a crane or backhoe, as well as to open and close a swinging gate or door.

<span class="mw-page-title-main">Eight-bar linkage</span> 1-DoF mechanism made from 8 links and 10 joints

In kinematics, an eight-bar linkage is a mechanism with one degree of freedom that is constructed from eight links and ten joints. These linkages are rare compared to four-bar and six-bar linkages, but two well-known examples are the Peaucellier linkage and the linkage designed by Theo Jansen for his walking machines.

<span class="mw-page-title-main">Quick return mechanism</span> Mechanism to produce a reciprocating motion with different speeds in opposing directions

A quick return mechanism is an apparatus to produce a reciprocating motion in which the time taken for travel in return stroke is less than in the forward stroke. It is driven by a circular motion source and uses a system of links with three turning pairs and a sliding pair. A quick-return mechanism is a subclass of a slider-crank linkage, with an offset crank.

In mechanical engineering, kinematic synthesis determines the size and configuration of mechanisms that shape the flow of power through a mechanical system, or machine, to achieve a desired performance. The word synthesis refers to combining parts to form a whole. Hartenberg and Denavit describe kinematic synthesis as

...it is design, the creation of something new. Kinematically, it is the conversion of a motion idea into hardware.

<span class="mw-page-title-main">Five-bar linkage</span> 2-DoF mechanism with 5 links and 5 joints

In kinematics, a five-bar linkage is a mechanism with two degrees of freedom that is constructed from five links that are connected together in a closed chain. All links are connected to each other by five joints in series forming a loop. One of the links is the ground or base. This configuration is also called a pantograph, however, it is not to be confused with the parallelogram-copying linkage pantograph.

References

  1. 1 2 3 4 5 6 Ghassaei, Amanda (20 April 2011). The Design and Optimization of a Crank-Based Leg Mechanism (PDF) (Thesis). Pomona College. Archived (PDF) from the original on 29 October 2013. Retrieved 27 July 2016.
  2. P. L. Tchebyshev. Plantigrade Machine Engraving. stored in the Musée des arts et métiers du Conservatoire national des arts et métiers Paris, France CNAM 10475-0000.
  3. S. M. Song and K. J. Waldron (November 1988). Machines that Walk: The Adaptive Suspension Vehicle. The MIT Press. ISBN   9780262192743.
  4. W. B. Shieh (1996). Design and Optimization of Planar Leg Mechanisms Featuring Symmetrical Foot-Point Paths (Thesis). PhD Dissertation, The University of Maryland.
  5. Theo Jansen. Strangdbeest.
  6. 1 2 3 4 5 Shigley, Joseph E. (September 1960). The Mechanics of Walking Vehicles: A Feasibility Study (PDF) (Report). University of Michigan Department of Mechanical Engineering. Archived from the original (PDF) on 4 March 2016. Retrieved 27 July 2016. Alt URL
  7. Giesbrecht, Daniel (8 April 2010). Design and optimization of a one-degree-of-freedom eight-bar leg mechanism for a walking machine (Thesis). University of Manitoba. hdl:1993/3922.
  8. Uglow, Jenny (2002). The Lunar Men: Five Friends Whose Curiosity Changed the World . New York, New York: Farrar, Straus and Giroux. ISBN   0-374-19440-8 . Retrieved 27 July 2016.
  9. J. Michael McCarthy (March 2019). Kinematic Synthesis of Mechanisms: a project based approach. MDA Press.
  10. Simionescu, P.A.; Tempea, I. (20–24 June 1999). Kinematic and kinetostatic simulation of a leg mechanism (PDF). 10th World Congress on the Theory of Machines and Mechanisms. Oulu, Finland. pp. 572–577. Retrieved 27 July 2016.
  11. Funabashi, H.; Takeda, Y.; Kawabuchi, I.; Higuchi, M. (20–24 June 1999). Development of a walking chair with a self-attitude-adjusting mechanism for stable walking on uneven terrain. 10th World Congress on the Theory of Machines and Mechanisms. Oulu, Finland. pp. 1164–1169.
  12. "Plantigrade machine — Mechanisms by P. L. Tchebyshev".
  13. Vagle, Wade. "TrotBot Linkage Plans". DIYwalkers.
  14. 1 2 "Shigley's Study Applied". DIYwalkers.
  15. 1 2 Vagle, Wade. "Strider Linkage Plans". DIYwalkers.
  16. "TrotBot".