Robot control
Inverse dynamics
Definition
Inverse dynamics calculates the joint forces or torques required for specified joint positions, velocities, and accelerations under a dynamics model. The result also depends on gravity and specified external loading.
Also known as: Robot inverse dynamics
Updated
From desired motion to actuator effort
A robot following a trajectory needs forces that accelerate its links and account for gravity and motion-dependent effects. Inverse dynamics calculates those model-based efforts from a desired motion state.
Modern Robotics presents the recursive Newton-Euler method for an open chain. A forward pass calculates link velocities and accelerations. A backward pass propagates the required wrenches toward the base and extracts the joint efforts.
External loading belongs in the problem
Holding an object or pushing on the environment changes the forces the robot must supply. The reference algorithm therefore includes an end-effector wrench as an input alongside the joint motion and gravity.
These calculations need inertial properties as well as link geometry. A forward-kinematics model alone cannot predict the required torque.
A model prediction is not perfect tracking
The calculated effort is useful for feedforward torque control, but it is only as complete as the dynamics model. The forward-dynamics lesson shows how omitted friction changes simulated behavior.
Inverse kinematics instead solves for joint positions from a target pose. Forward dynamics reverses the dynamics question by predicting acceleration from applied effort.
Sources
Related terms
Forward dynamics
Forward dynamics predicts a robot's acceleration from its current configuration, velocity, applied joint forces or torques, and external forces. It uses the robot's mass, inertia, and other modeled dynamic properties.
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.
Inverse kinematics
Inverse kinematics finds joint positions that produce a desired robot end-effector position, orientation, or other geometric task. A target can have multiple solutions, no solution, or a continuous family of solutions.