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.