What are the basic parts of a robot manipulator: links, joints, end effector and workspace?

In one line

A robot manipulator is a chain of rigid links connected by joints, starting at a fixed base and ending at an end effector that does the work.

Explained simply

Your arm is a good model: the shoulder is attached to your body (the base), the upper arm and forearm are links, the shoulder, elbow and wrist are joints, and your hand is the end effector. Everywhere your hand can reach is your workspace.

Technically, robot mechanics studies the geometry and motion of such kinematic chains. A serial manipulator is an open chain in which each joint connects two consecutive links.

How it works

1. Base: fixed link (link 0), usually bolted to the floor.
2. Links: rigid members between joints, numbered 1, 2, ... from the base.
3. Joints: each allows one relative motion. Revolute (R): rotation, variable is the joint angle \( \theta \). Prismatic (P): sliding, variable is the displacement d.
4. End effector: gripper, welding torch or spray gun at the last link.
5. Workspace: all points the end effector can reach.
6. Common configurations: Cartesian (PPP), cylindrical (RPP), spherical/polar (RRP), SCARA (RRP with parallel vertical axes), articulated (RRR, like a human arm).

Key formula

For a planar 2-link arm with lengths \( L_1, L_2 \) and full joint rotation, the workspace is an annulus with outer radius \( L_1 + L_2 \) and inner radius \( |L_1 - L_2| \) (m).

Quick example

A 2-link planar arm with \( L_1 = 1 \) m and \( L_2 = 0.5 \) m can reach any point between 0.5 m and 1.5 m from its base. A car-factory welding robot is usually articulated; a pick-and-place robot for electronics is often SCARA.

Common mistakes

• Counting the base as a moving link.
• Mixing up revolute and prismatic joint variables (angle vs distance).
• Thinking the workspace is a full circle of radius \( L_1 + L_2 \) when \( L_1 \neq L_2 \).

How MU asks it

A 3 to 4-mark theory part: 'Explain the basic components of a robot', 'Explain types of joints' or 'Classify robots by configuration'. Draw a simple 2-link arm with labelled base, links, joints and end effector; list joint types with symbols.