Mechanism (engineering)

A mechanism is a tool that helps things move.

It takes a push or a pull and turns it into a new move.

Many parts work together to do this job.

Some parts are called links. These are the solid pieces. Other parts are called joints. Joints let the links move.

A car has a steering mechanism. A watch has a winding mechanism. Even a robot arm is a mechanism. These tools make work happen in a special way.

A mechanism is a device that changes movement. It takes an input force and turns it into a new output.

Most mechanisms are parts of a larger machine. A car has a steering mechanism. A watch has a winding mechanism.

Mechanisms use parts called links. These links are solid bodies. To study them, we treat them as rigid. This means the links do not bend or change shape.

Links are joined by parts called kinematic pairs. We often call these joints.

There are different kinds of joints. A lower pair has surface contact. A revolute pair is a hinged joint. It lets parts rotate. A prismatic joint is a slider. It lets parts slide in a line.

Higher pairs only touch at a point or a line. A cam and follower is a higher pair. The cam is the driving part. The follower is the part that is moved.

These parts work together to move in a set way.

A mechanism is a device that changes movement. It takes an input force and turns it into a new output.

Most mechanisms are parts of a larger machine. A car has a steering mechanism. A watch has a winding mechanism. A set of many mechanisms working together is called a machine. Mechanisms manage power to achieve a specific set of forces and movement. This makes them very important for how our world works.

To understand how they work, we look at links and joints. Links are the solid parts of the mechanism. Engineers model them as rigid bodies. This means the links do not bend or change shape when they move.

The links are joined by kinematic pairs, which are also called joints. These joints control how the links move against each other. They can limit movement to a single point or a single line.

There are two main types of joints. A lower pair has surface contact between the parts. A revolute pair is a hinged joint that allows rotation.

A prismatic joint is a slider that allows one part to slide. A spherical joint, or ball joint, allows movement in three ways. A higher pair only touches at a point or a line. For example, a cam and follower is a higher pair. The cam is the driving part that moves the follower.

Scientists have studied these ideas for a long time. Long ago, people saw machines as simple tools like levers or pulleys.

In the 1800s, a German scientist named Franz Reuleaux changed how we think about them. He focused on the links and the joints that connect them. He defined a machine as a combination of bodies that use nature's forces to do work. This helped engineers design much more complex systems.

Mechanisms can move in many different ways. Planar mechanisms move in a flat plane. Spherical mechanisms move around a fixed center point, like a robotic wrist.

Spatial mechanisms can move through three-dimensional space.

You can see these ideas in things like robot arms or even walking machines. Some special linkages, like the Jansen linkage, even help machines move like they are walking.

In engineering, a mechanism is a device that transforms input forces and movement into a specific set of output forces and movement. While we often use the word "machine" to describe a complete device, a mechanism is usually just one part of a larger mechanical system. For example, a car contains a steering mechanism, and a wristwatch contains a winding mechanism. When multiple mechanisms work together, they form a machine. A mechanism essentially manages power to achieve a desired physical result.

To study how these devices work, engineers use a model consisting of links and kinematic pairs. Links are the individual components, which are modeled as rigid bodies. This means that the distances between points on a link do not change during movement; the link does not flex. Kinematic pairs, also called joints, are the connections between these links. These joints provide ideal constraints that dictate how the links can move relative to one another.

Kinematic pairs are categorized into two main types: lower pairs and higher pairs. A lower pair is an ideal joint characterized by surface contact between the two elements. Examples include the revolute pair, which is a hinged joint that allows rotation, and the prismatic joint, which acts as a slider. Other lower pairs include cylindrical joints, which combine rotation and sliding, and spherical joints, also known as ball joints. A screw joint is another lower pair, but it has only one degree of freedom because its sliding and rotational motions are linked by a helix angle.

In contrast, a higher pair involves contact at only a single line or a single point. A common example is the cam and follower mechanism. In this setup, a driving link called the cam makes direct contact with a driven link called the follower. The specific shape of the cam determines the movement of the follower. Another example of a higher pair is the contact between the meshing teeth of two gears.

Historically, the study of mechanisms has evolved significantly. From the time of Archimedes through the Renaissance, people viewed mechanisms as combinations of simple machines like levers, pulleys, and screws. However, the German scientist Franz Reuleaux changed this perspective in the late 1800s. He focused on the relationship between links and their joints. Reuleaux defined a machine as a combination of resistant bodies arranged to compel the mechanical forces of nature to do work through determinate motion.

Mechanisms are also classified by the type of space in which they move. Planar mechanisms are constrained so that all movement occurs within a single plane. These can be analyzed using plane geometry and are often represented by a skeleton-like kinematic diagram. Spherical mechanisms, such as a gimbaled gyroscope or a robotic wrist, move around a fixed center point. Finally, spatial mechanisms allow a body to move through general three-dimensional space.

Examples of spatial mechanisms include robot arms, humanoid robotic systems, and the Stewart platform.

Linkages are a specific type of mechanism made of a collection of links connected by joints. One of the most useful examples is the planar four-bar linkage. There are many specialized linkages, such as Watt's linkage, which helps generate an approximate straight line. This was vital for the early steam engine and is still used in vehicle suspensions. More recent inventions include the Klann and Jansen linkages, which are designed to create walking movements.

Modern engineering also utilizes compliant mechanisms. Unlike traditional mechanisms that use rigid bodies, these consist of rigid bodies connected by flexible or "compliant" elements. These systems offer several advantages, such as a reduced part count and lower maintenance. Because they do not rely on traditional joints, they do not require lubrication and experience less mechanical wear. They also eliminate "slop," which is the unwanted parasitic motion caused by gaps between moving parts.