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Control Theory in Industry, Robotics and Infrastructure. Lachlan Blackhall and Tyler Summers. Motivating Example. You walk into your classroom and turn your air conditioning on to a temperature of 24 degrees. - PowerPoint PPT Presentation
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Control Theory in Industry, Robotics and
InfrastructureLachlan Blackhall and Tyler Summers
Motivating Example
• You walk into your classroom and turn your air conditioning on to a temperature of 24 degrees.
• The air conditioner turns on until the internal thermostat registers that the air temperature is 24 degrees then shuts off the air conditioner until the temperature rises again.
• A simple controller is responsible for keeping you cool!
Systems Modelling
Control Components
• A system
– Possibly a mathematical model of that system.
• A control goal
• A sensor to observe the system
• An actuator to influence the system
• A control algorithm that tells the actuator how to behave based on the observations of the sensor.
• A computer or analog circuit to link it together.
Differential Equations
• Control is primarily concerned with systems that can be written as differential equations.
• Almost everything can be written in this form so control really applies to any physical systems.
• It all started with trying to apply external control to simple differential equations.
Industrial Applications
• Control emerged as a way to automate:– Manufacturing– Assembly– Processing and Refinement
• Has since been used successfully in additional areas:– Robotics– Infrastructure
Revisiting our Example
• The thermostat is one of the simplest controllers you can create.
• This type of controller is known as a bang-bang controller.
• A bang–bang controller (on–off controller) is a feedback controller that switches abruptly between two states.
Bang-Bang Control
• They are routinely used to control a plant that accepts a binary input, for example a heater or air conditioner.
• Bang–bang controls are actually optimal controls in some cases, although they are also often implemented because of simplicity or convenience.
PID Control
• PID stands for proportional–integral–derivative.
• PID is a generic control loop feedback mechanism used in industrial control systems.
• The control signal has three components based on the error between the observed operation and the nominal set point:– A proportional component– An integral component– A derivative component
PID Control (cont.)
• Some history– Developed in the late 1800s– Initially trialled as a way to control US Navy
ship steering.– Can be implemented mechanically, using
analog electronics and now using digital electronics like FPGAs
– Most commonly implemented in industry these days using programmable logic controllers.
PID Control (cont.)
used with permission from http://commons.wikimedia.org/wiki/File:PID.svg
PID Control (cont.)
• Heuristically:– P depends on the present error– I on the accumulation of past errors– D is a prediction of future errors, based on
the current rate of change.
• The weighted sum of these three actions is used to adjust the process via a control element or actuator.
PID Control (cont.)
• In the absence of knowledge of the underlying process, a PID controller is the best controller.
• The response of the controller can be described in terms of the responsiveness of the controller to an error, the degree to which the controller overshoots the set-point and the degree of system oscillation.
• Note that the use of the PID algorithm for control does not guarantee optimal control of the system or system stability.
PID Control (cont.)
• Some applications may require using only one or two actions to provide the appropriate system control.
• This is achieved by setting the other parameters to zero.
• A PID controller will be called a PI, PD, P or I controller in the absence of the respective control actions.
• http://www.youtube.com/watch?v=ALVo4aJpcF0 – P vs PID Control
Demonstration
• LEGO Mindstorms Line Following Robot – Bang-Bang vs P Controller
• LEGO Mindstorms Segway Robot – PID Control
Applications of PID
• Assembly
• Robotics
• SCADA
• Building Control
Assembly
• PID Controllers are vitally important to robots used for automated assembly.
• Precision control was the technological breakthrough that allowed robotic assembly to become so commonplace.
• Demonstrations:– http://www.youtube.com/watch?v=HPpTK2ezxL0
- 1936 Car Assembly Footage– http://www.youtube.com/watch?v=-_SxW_7v9is –
BMW Assembly Plant Footage
Robotics
• Beyond assembly industrial robots can perform a great many tasks including:– Welding– painting,– pick and place (such as packaging,
palletizing and SMT)– product inspection, and testing
• There are lots of other robots out there using PID control.
Robotics (cont.)
• Demonstrations:– http://www.youtube.com/watch?
v=Fxzh3pFr3Gs - Catching balls and darts (Lund)
– http://www.youtube.com/watch?v=SOESSCXGhFo – ABB Challenge
– http://www.youtube.com/watch?v=R8UeT9r4cmg - ASIMO
– http://www.youtube.com/watch?v=cNZPRsrwumQ – BIG DOG
SCADA
• How do you control a number of systems, and a number of controllers that are possibly spread out on a factory floor or over a large geographic footprint?
SCADA
• SCADA (supervisory control and data acquisition) are industrial control systems (ICS) that monitor and control industrial, infrastructure, or facility-based processes.
• Industrial processes include:– Manufacturing / production / assembly– Power generation, transmission and distribution– Wastewater collection and treatment– Oil and gas pipelines and refineries
SCADA (cont.)
SCADA (cont.)
• A SCADA system usually consists of the following subsystems:– A human–machine interface or HMI– A supervisory (computer) system, gathering (acquiring) data
on the process and sending commands (control) to the process.
– Remote terminal units (RTUs) connecting to sensors in the process, converting sensor signals to digital data and sending digital data to the supervisory system.
– Programmable logic controller (PLCs) for implementing PID control through actuators.
– Communication infrastructure connecting the supervisory system to the remote terminal units.
SCADA (cont.)
• Demonstration Videos– http://www.youtube.com/watch?
v=ZSFdOjxB-1I – http://www.youtube.com/watch?
v=rj44AkHmVCo&feature=watch_response_rev
Building Control
• Modern buildings have a variety of control systems:– HVAC– Energy– Security– Structural stability
• http://www.youtube.com/watch?v=gCuPx9shWT0 - Siemens Future Buildings
Group Task
• Forms groups of 8-10.
• Briefly discuss:– Areas where you think control could or
should be used in your society.– Are there systems in your society that
could be controlled that are currently not?
• Present to the group.