Robot control
Joint-space control
Definition
Joint-space control expresses a robot's motion targets and tracking errors in joint coordinates, such as joint angles or linear displacements. It regulates those coordinates rather than defining the primary motion error directly at the end-effector.
Also known as: Joint space control
Updated
Track a posture or joint trajectory
An arm controller can compare desired shoulder and elbow angles with measured angles, then command motion that reduces the differences. The targets may be a fixed posture or a sequence of joint positions over time.
Modern Robotics develops this idea using a joint-position error and a velocity command. Feedback corrects deviations that simply replaying a planned command would leave unresolved.
Coordinates and actuator commands are different choices
“Joint-space” identifies how the motion objective is expressed. It does not require one particular actuator interface. A controller may request joint velocities from lower-level loops, or calculate forces and torques using robot dynamics.
The control-system overview shows motion feedback feeding a controller that requests joint torques. Torque control describes regulating actuator effort, so it is not a synonym for joint-space control.
Compare with an end-effector objective
Task-space control expresses the motion error in variables such as hand position and orientation. The task-space control lesson converts a desired hand velocity into joint velocities through a robot Jacobian.
Both approaches ultimately move joints. The distinction is where the primary motion error is defined; joint limits and actuator limits still need explicit handling.
Sources
Related terms
Joint
A joint is a connection between robot links that constrains their permitted relative motion. Its kinematic type determines which rotations or translations the connected links can make relative to one another.
PID control
PID control is feedback control that combines terms proportional to the current error, the accumulated error, and the rate of change of error. These terms determine the command sent to the controlled system.
Torque control
Torque control regulates the turning effort delivered by an actuator or robot joint. It provides an actuation interface from which motion, force, and impedance controllers can produce the joint torques their tasks require.
Operational-space control
Operational-space control formulates a robot’s motion and force behavior in task coordinates, such as the position and orientation of its hand, while accounting for the robot’s dynamics. Secondary joint objectives can be coordinated with the primary task.