Torque Feed-forward

The torqueTorque is the tendency of a force to rotate an object about an axis. Just as a force is a push or a pull, a torque can be thought of as a twist feed-forwardThis describes an element or pathway within a control system which passes a controlling signal from a source in the control system's external environment, often a command signal from an external operator, to a load elsewhere in its external environment tells the controller what forces is required to move the axis in an arbitrary trajectory.

Here are the major features of torque feed-forward:

• TorqueTorque is the tendency of a force to rotate an object about an axis. Just as a force is a push or a pull, a torque can be thought of as a twist feed-forward results in virtually instantaneous response of the system.
• Feedback control loops (using PID"Proportional-Integral-Derivative" A PID controller is a generic control-loop feedback mechanism widely used in industrial control systems. An "error" occurs when an event or a disturbance triggers off a change in the process variable. A PID controller attempts to correct the error between a measured process variable and a desired setpoint by calculating and then outputting a corrective action that can adjust the process accordingly loop or similar) take a finite amount of time before reacting.
• Torque feed-forward relies on an imperfect model of the system. This means that the feed-forwards need help from the feedback control loop in order to get accurate motion.
• Torque feed-forward can make the bulk of the move very quickly, while the feedback control loops correct the small errors that remain. As a result, a faster settling time can be achieved than if torque feed-forward was not used.
• There is a common misconception that torque feed-forward is similar to control loops and result in instability. Torque feed-forward is open loopA positioning technique, typically utilizing stepper motors, in which the controller issues a sequence of commands to the motor without an absolute means of detecting if the move has been made. When the load and move velocity and acceleration are appropriately defined, open loop positioning is capable of extended operation without losing steps., so it cannot suffer from closed loopThe use of feedback devices (encoders, resolvers, interferometers, etc.) to allow a motor to position a user payload accurately. instability.
• Torque feed-forward is typically less sensitive to being misadjusted than closed loop parameters.
• Feedback control systems can be excited into instability by grossly misadjusted torque feed-forward. However, the amount of misadjustment in the torque feed-forward necessary to cause such instability is very rare.