Motion control
Encyclopedia
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.
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:
Automation
Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...
, 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
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
, generally a servo
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
. Motion control is an important part of robotics
Robotics
Robotics is the branch of technology that deals with the design, construction, operation, structural disposition, manufacture and application of robots...
and CNC machine tools, however it is more complex than in the use of specialized machines, where the kinematics
Kinematics
Kinematics is the branch of classical mechanics that describes the motion of bodies and systems without consideration of the forces that cause the motion....
are usually simpler. The latter is often called General Motion Control
General Motion Control
General motion control is a sub-field of motion control, 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...
(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 feedbackFeedbackFeedback describes the situation when output from an event or phenomenon in the past will influence an occurrence or occurrences of the same Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or...
loop.
- A drive or amplifierAmplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
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 actuatorActuatorAn actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...
such as a hydraulic pump, air cylinder, linear actuator, or electric motor for output motion. - One or more feedback sensors such as optical encodersRotary encoderA rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code. The output of incremental encoders provides information about the motion of the shaft which is typically further processed...
, resolversResolver (electrical)A resolver is a type of rotary electrical transformer used for measuring degrees of rotation. It is considered an analog device, and has a digital counterpart, the rotary encoder.-Description:...
or Hall effectHall effectThe Hall effect is the production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current...
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: gearGearA gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine....
s, shafting, ball screwBall screwA ball screw is a mechanical linear actuator that translates rotational motion to linear motion with little friction. A threaded shaft provides a helical raceway for ball bearings which act as a precision screw. As well as being able to apply or withstand high thrust loads, they can do so with...
, beltsBelt (mechanical)A belt is a loop of flexible material used to link two or more rotating shafts mechanically. Belts may be used as a source of motion, to transmit power efficiently, or to track relative movement. Belts are looped over pulleys. In a two pulley system, the belt can either drive the pulleys in the...
, linkagesLinkage (mechanical)A mechanical linkage is an assembly of bodies connected together to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for...
, and linear and rotational bearingsBearing (mechanical)A bearing is a device to allow constrained relative motion between two or more parts, typically rotation or linear movement. Bearings may be classified broadly according to the motions they allow and according to their principle of operation as well as by the directions of applied loads they can...
.
The interface between the motion controller and drives it controls is very critical when coordinated motion is required, as it must provide tight synchronization
Synchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
. 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
SERCOS interface
- Introduction :In the field of Industrial Control Systems, the interfacing of various control components must provide a means to coordinate the signals and commands sent between control modules...
in 1991 which is now enhanced to SERCOS III
SERCOS III
sercos III is the third generation of the sercos interface, a globally standardized open digital interface for the communication between industrial controls, motion devices, and input/output devices . sercos III merges the hard real-time aspects of the sercos interface with Ethernet. It is based...
. Later interfaces capable of motion control include Profinet IRT, Ethernet Powerlink
Ethernet Powerlink
Ethernet Powerlink is a deterministic real-time protocol for standard Ethernet. It is an open protocol managed by the Ethernet POWERLINK Standardization Group...
, and EtherCAT
EtherCAT
EtherCAT - Ethernet for Control Automation Technology - is an open high performance Ethernet-based fieldbus system. The development goal of EtherCAT was to apply Ethernet to automation applications which require short data update times with low communication jitter and low hardware costs.-...
.
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 functionFunction (mathematics)In mathematics, a function associates one quantity, the argument of the function, also known as the input, with another quantity, the value of the function, also known as the output. A function assigns exactly one output to each input. The argument and the value may be real numbers, but they can...
.
See also
- Match movingMatch movingIn cinematography, match moving is a visual-effects, cinematic techniques that allows the insertion of computer graphics into live-action footage with correct position, scale, orientation, and motion relative to the photographed objects in the shot...
, for motion tracking in computer-generated imageryComputer-generated imageryComputer-generated imagery is the application of the field of computer graphics or, more specifically, 3D computer graphics to special effects in art, video games, films, television programs, commercials, simulators and simulation generally, and printed media... - MechatronicsMechatronicsMechatronics is the combination of mechanical engineering, electronic engineering, computer engineering, software engineering, control engineering, and systems design engineering in order to design, and manufacture useful products. Mechatronics is a multidisciplinary field of engineering, that is...
, the science of computer-controlled smart motion devices - Control systemControl systemA control system is a device, or set of devices to manage, command, direct or regulate the behavior of other devices or system.There are two common classes of control systems, with many variations and combinations: logic or sequential controls, and feedback or linear controls...
- PID controllerPID controllerA proportional–integral–derivative controller is a generic control loop feedback mechanism widely used in industrial control systems – a PID is the most commonly used feedback controller. A PID controller calculates an "error" value as the difference between a measured process variable and a...
, proportional-integral-derivative controller - Slewing
- Motion ControllerMotion ControllerA motion controller controls the motion of some object. Frequently motion controllers are implemented using digital computers, but motion controllers can also be implemented with only analog components as well.-Implementation:...
- PneumaticsPneumaticsPneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...