physics

Six-bar linkage

Six-bar linkage is a physics topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Six-bar linkage rather than just read about it. In short: 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.

Key takeaways

Six-bar linkage belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Six-bar linkage to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Six-bar linkage from memory before moving on to harder problems.

Reference excerpt

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. In general, each joint of a linkage connects two links, and a binary link supports two joints. If we consider a hexagon constructed from six binary links with six of the seven joints forming its vertices, then the seventh joint can be added to connect two sides of the hexagon to form a six-bar linkage with two ternary links connected by one joint. This type of six-bar linkage is said to have the Watt topology. A six-bar linkage can also be constructed by first assembling five binary links into a pentagon, which uses five of the seven joints, and then completing the linkage by adding a binary link that connects two sides of the pentagon. This again creates two ternary links that are now separated by one or more binary links. This type of six-bar linkage is said to have the Stephenson topology. The Klann linkage has the Stephenson topology.

Watt six-bar linkage Watt's parallel motion generator consists of the four-bar linkage that has a coupler curve that traces an approximately straight line trajectory, combined with a parallelogram linkage that copies this straight line movement to a desired location. This configuration of six bars and seven joints has two four-bar loops.

Stephenson six-bar linkage The six-bars and seven joints of the Stephenson linkage comprise one four-bar loop and one five-bar loop. It has two ternary links that are separated by a binary link. This means the two ternary links are not connected to each other by a joint as in the case of the Watt topology. The Stephenson has three forms depending on the link that is selected as the frame, which are denoted Stephenson I, II and III.

See also Mechanism (engineering) Linkage (mechanical) Five-bar linkage

References

External links A six-bar straight-line linkage in the collection of Reuleaux models at Cornell University Mechanism animations including the Klann linkage Example of a six-bar function generator that compute the angle for a given range. Animations of six-bar linkage for a bicycle suspension. A variety of six-bar linkage designs. Lecture on the design of six-bar and eight-bar linkages Article about patents and six-bar linkages

Illustrations

Worked examples

Example 1 — a first encounter with Six-bar linkage

Start with the simplest possible case. Write down what Six-bar linkage claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Six-bar linkage before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Six-bar linkage ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Six-bar linkage

In research: Six-bar linkage appears in physics research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Six-bar linkage in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Six-bar linkage is common in secondary-school and first-year university syllabi. It links to neighbouring topics Linkages (mechanical), so understanding it makes those chapters shorter.
In everyday life: Look for Six-bar linkage outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Six-bar linkage in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Six-bar linkage means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Six-bar linkage out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Six-bar linkage in simple terms?

Why does Six-bar linkage matter?

Because it connects several physics ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Six-bar linkage?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Six-bar linkage.