Motion control

Motion control is a sub-field of automation, in which the position 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, semiconductor production, and assembly industries.

Overview

The basic architecture of a motion control system contains:

• A motion controller to generate set points (the desired output or motion profile) and close a position or velocity feedback loop.^[1]

• A drive or amplifier to transform the control signal from the motion controller into a higher power electrical current or voltage that is presented to the actuator. Newer "intelligent" drives can close the position and velocity loops internally, resulting in much more accurate control.
• An actuator such as a hydraulic pump, air cylinder, linear actuator, or electric motor for output motion.
• One or more feedback sensors such as optical encoders, resolvers or Hall effect devices to return the position or velocity of the actuator to the motion controller in order to close the position or velocity control loops.
• 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.

The interface between the motion controller and drives it controls is very critical when coordinated motion is required, as it must provide tight synchronization. Historically the only open interface was an analog signal, until open interfaces were developed that satisfied the requirements of coordinated motion control, the first being SERCOS in 1991 which is now enhanced to SERCOS III. Later interfaces capable of motion control include Profinet IRT, Ethernet Powerlink, and EtherCAT.

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 profile.
• Pressure or Force control.
• 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 ratio to each other. A more advanced case of electronic gearing is electronic camming. With electronic camming, a slave axis follows a profile that is a function of the master position. This profile need not be salted, but it must be an animated function.

See also

• Match moving, for motion tracking in computer-generated imagery
• Mechatronics, the science of computer-controlled smart motion devices
• Control system
• PID controller, proportional-integral-derivative controller
• Slewing
• Motion Controller
• Pneumatics

References

• Tan K. K., T. H. Lee and S. Huang, Precision motion control: Design and implementation, 2nd ed., London, Springer, 2008.

External links

• Indexer information
• Trm Motion Controls