Coordinate systems used in robot programming

The position of the robot tool can be described in several frames. The controller converts between them using kinematics.

Coordinate system	Origin and axes	Typical use
Joint (axis)	Each joint angle or displacement (θ₁ to θ₆)	Moving a single axis, reaching a configuration, avoiding singularities
World / global	Fixed point in the cell, usually on the floor	Coordinating several robots and equipment
Base	Fixed to the robot base	Default Cartesian jogging
Tool	Origin at the tool centre point (TCP); moves with the tool	Moving along the tool direction, e.g. drilling or welding
User / work-object	Defined on a fixture or workpiece	Reusing a program when the fixture moves

Arm geometries and their coordinates

Cartesian (x, y, z), cylindrical (r, θ, z), spherical (r, θ, φ) and articulated (joint angles).

Why it matters

A taught point is stored relative to a frame. If the frame is shifted (for example a moved fixture), all related points move with it without reteaching.

Exam tip

Draw base, world, tool and work-object frames on one sketch with the axes labelled.