Types of interpolation for robot motion control

Type	Principle	Tool path	Typical commands	Use
Joint (point-to-point)	All joints move at the same time from start to end angles and finish together; each follows its own profile	Unpredictable curve in space	VAL: MOVE; RAPID: MoveJ; FANUC: J	Fast moves in free space, approach to a pick point
Linear (straight line)	The tool centre point moves on a straight line; joint angles are recalculated at each step by inverse kinematics	Straight line	VAL: MOVES; RAPID: MoveL; FANUC: L	Welding seams, gluing, insertion
Circular	An arc is defined by three points (start, via, end) and the TCP follows the circle	Arc or circle	RAPID: MoveC; FANUC: C	Circular welds, dispensing around a hole

Velocity profiles

Most controllers use a trapezoidal profile (accelerate, cruise, decelerate). Smoother systems use S-curve profiles to reduce jerk.

Comparison

• Joint interpolation is quickest and avoids singularities, but the path is not a straight line.
• Linear and circular interpolation give a controlled path but need more computation and can pass near singularities.

Exam tip

A three-row table with VAL and RAPID command examples is enough for full marks.