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Joints: These are the connections between the links that allow relative motion. In planar mechanisms, the most
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common joints are:
Revolute Joint: Allows two links to rotate relative to each other, like a hinge.
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Prismatic Joint: Allows two links to slide relative to each other along a straight line.
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Frame: One of the links is a fixed link, called the Frame, to which all the other links are connected. This provides a
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stable reference point for the entire mechanism’s motion.
Characteristics of Planar Mechanisms

1. Two-Dimensional Motion: All points on the mechanism move within or parallel to the same plane. This simplifies the
mathematical analysis from three dimensions to two, primarily using coordinate geometry.
2. Links and Joints: Like a robotic arm, a planar mechanism consists of rigid links connected by joints. The most
common joints are:
Pin Joints (Revolute Joints): Allow rotation in the plane, like a hinge.
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Slider Joints (Prismatic Joints): Allow linear motion (sliding) in the plane, like a piston moving in a cylinder.
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3. Kinematic Analysis: The behaviour of a planar mechanism can be fully described by its kinematics—the study of
its motion (position, velocity, and acceleration) without considering the forces involved. This is significantly easier to
perform for planar systems than for three-dimensional systems.
4. Degrees of Freedom: The degrees of freedom of a planar mechanism refer to the number of independent variables
needed to completely define its position. For a mechanism with one input motion (like a crank), the degrees of
freedom are typically one.

Robots are Already Helping Doctors Save Lives
Medical robotics is one of the most inspiring applications of AI and robotics. The Da Vinci
Surgical System, for example, allows surgeons to operate with robotic arms that moves more
BRAINY precisely than a human hand. These systems can perform minimally invasive surgeries, reducing
FACT
recovery time and risk for patients. Robots are also used in telemedicine, where doctors in one
country can operate on a patient in another, thanks to robotic precision and fast internet
connectivity. It’s science fiction becoming everyday healthcare reality.

Real-Life Examples of Planar Mechanisms

Planar mechanisms are everywhere around us, demonstrating their practicality and effectiveness in solving specific
mechanical problems.
Windshield Wipers

Mechanism: A classic example is the windshield wiper mechanism in a car. It uses a motor to drive a crank (a
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rotating link). This crank is connected to a series of other links that translate its continuous rotational motion into the
back-and-forth oscillating motion of the wiper blade across the windshield.
How it Works: The motor rotates in a circle, but the linkage system ensures that the wiper blade moves in a controlled
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arc, covering the windshield efficiently. The entire system operates in a single plane, the surface of the windshield.

Scissors
Mechanism: A pair of scissors is a simple two-link planar mechanism. Each blade is a link, and they are connected
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by a single revolute joint (the pivot point).
u How it Works: When you apply force to the handles, the blades rotate around the pivot in a single plane to cut paper
or cloth. The motion is entirely restricted to the plane of the scissors.

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Mechanical System