Robot control
Visual servoing
Definition
Visual servoing uses visual measurements inside a feedback loop to control robot motion. The controller updates movement to reduce an error defined from image features or visually estimated pose.
Also known as: Visual servo control
Updated
Vision stays in the feedback loop
A robot can repeatedly observe a target and adjust its motion as the observed error changes. This is different from taking one image, planning once, and then executing without visual correction. Chaumette and Hutchinson's tutorial develops the control formulation for this closed-loop use of visual information.
For example, a wrist camera can guide a gripper toward an object by aligning selected visual features with their desired positions.
Image-based and position-based control
Image-based visual servoing defines its error directly from image features. Position-based visual servoing uses visual data to estimate a three-dimensional pose and controls an error in that space. The tutorial compares the two approaches and their stability and performance characteristics.
Geometry and visibility constrain performance
The relationship between camera motion and image-feature motion enters the control law. Calibration, feature depth, and the current configuration affect this relationship. Features can also leave the camera's field of view during movement. A visually decreasing error is therefore not enough to establish collision-free motion or joint-limit compliance. Those constraints need to be addressed by the larger robot-control system.
Sources
Related terms
Pose estimation
Pose estimation determines the position and orientation of an object or robot relative to a reference frame. For a rigid body in three-dimensional space, a full pose has three translational and three rotational degrees of freedom.
Robot Jacobian
A robot Jacobian is a configuration-dependent matrix that maps joint velocities to a chosen task velocity, often an end-effector twist. It describes the local relationship between joint motion and task motion.
Robotic manipulation
Robotic manipulation is the use of a robot to change an object's position, orientation, or state through physical interaction. It includes grasping and moving objects as well as actions such as pushing or carrying them without a grasp.