Motion control

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This is about the general industrial term. For the usage in film, see Motion control photography

Motion control is a sub-field of automation, in which the position and/or velocity of machines are controlled using some type of device such as a hydraulic pump, linear actuator, or an electric motor, generally a servo. Motion control is an important part of robotics and CNC machine tools, however it is more complex than in the use of specialized machines, where the kinematics are usually simpler. The latter is often called General Motion Control (GMC). Motion control is widely used in the packaging, printing, textile and assembly industries.

The basic architecture of a motion control system contains:

  • A motion controller to generate the set points (the desired output) and close the position feedback loop. Many controllers also internally close a velocity loop.
  • A drive or amplifier to transform the control signal (often desired velocity or torque signal) from the motion controller into a higher power electrical current or voltage. Newer "intelligent" drives can close the position and velocity loops internally, resulting it much more accurate control.
  • An actuator such as a hydraulic pump, air cylinder, linear actuator, or electric motor for output motion.
  • A feedback sensor such as an optical encoder, resolver or hall effect device to return the position of the actuator to the motion controller in order to close the position control loop.
  • Mechanical components to transform the motion of the actuator into the desired motion, including: gears, shafting, ball screw, belts, linkages, and linear and rotational bearings.

Common control functions include:

  • Velocity control.
  • Position (point-to-point) control. There are several methods for computing a motion trajectory. These are often based on the velocity profiles of a move such as a triangular profile, trapezoidal profile, or an S-curve.
  • Electronic gearing (or cam profiling). The position of a slave axis is mathematically linked to the position of a master axis. A good example of this would be in a system where two rotating drums turn at a given ration to each other. A more advanced case of electronic gearing is electronic camming. With E-camming, a slave axis follows a profile that is a function of the master position. This profile need not be linear, but it must be a function.

[edit] See also

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