The four bar linkage is a type of mechanical linkage that is used in many different devices. A few examples are: locking pliers, bicycles, oil well. 4-Bar Linkages. • 5-Bar Linkages. • 6-Bar Linkages. • Extending Linkages. • Compliant Mechanisms. • Manufacturing & Robust Design. As most motors (electrical or internal combustion) provide a rotating drive shaft, some way is needed to convert the rotary engine motion into reciprocating pump motion. A pumpjack is a drive mechanism to achieve this, consisting of a four-bar linkage as shown below.


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Four-bar linkage

The kinematics and dynamics of planar four-bar linkages are important topics in mechanical engineering. Planar four-bar linkages can be designed to guide four bar linkage mechanism wide variety of movements.

One link of the chain is usually fixed, and is called the ground link, fixed link, or the frame.

  • Chapter 5. Planar Linkages
  • Four-Bar Linkages
  • Rotating cranks and reciprocating rockers

The two links connected to the frame are called the grounded links and are generally the input and output links of the system, sometimes called the input link and output link. The last link is the floating link, which is also called a coupler or connecting rod because it connects an input to the output.

Four bar linkage mechanism the frame is horizontal there are four possibilities for the input and output links: Oscillation into oscillation, or four bar linkage mechanism into reciprocation, with a constant or variable velocity ratio.

Linkages have many different four bar linkage mechanism, which can be classified according on the primary goal of the mechanism: A variety of useful mechanisms can be formed from a four-link mechanism through slight variations, such as changing the character of the pairs, proportions of links, etc.

Furthermore, many complex link mechanisms are combinations of two or more such mechanisms. The majority of four-link mechanisms fall into one of the following two classes: The figure illustrates a loader.

Obvioulsy the behavior of maintaining parallelism is important in a loader.

Four-bar linkage - Wikipedia

The bucket should not rotate as it is raised and lowered. Figure Front loader mechanism Slider-Crank Mechanism The four-bar mechanism has some special configurations created by making one or more links infinite in length. The slider-crank or crank and slider mechanism four bar linkage mechanism below is a four-bar linkage with the slider replacing an infinitely long output link.

This is shown in the animation above. Slider-crank linkage, formed by three revolute joints and a prismatic joint.


Double slider formed by two revolute joints and two prismatic joints. The Scotch yoke and the trammel of Archimedes are examples.

There are a great number of variations for the four bar linkage, and as you can guess, the design process to obtain the forces and movements that four bar linkage mechanism need is not an easy task.

We hope to have piqued your curiosity in mechanical things.

By proper choice of link dimensions useful curves, four bar linkage mechanism as a straight-line or a circular arc, may four bar linkage mechanism found. This coupler point curve can be used as the output of the four-bar mechanism such as the intermittent film drive shown below c The positions of the coupler-link may be used as the output of the four-bar mechanism.

As shown in figure below, the four-bar mechanism used for the dump truck requires that the center of gravity of the dumper to move on an inclined straight line while it is being tilted why?

The above applications can be solved by the methods of synthesis which is beyond the topic. In this chapter we shall discuss some basic characteristics of the four-bar.

Marvelous Mechanisms: The Ubiquitous Four Bar Linkage

The links that are connected to the fixed link can possibly have two different types of motion: Four bar linkage mechanism a four-bar mechanism we can have the following three different types of motion: This type of four-bar is called "double-crank " or "drag-link".

This type of four-bar is called crank-rocker. The type of motion is a function of the link lengths. Let us identify the link lengths in a four-bar chain as: