IB Computer Science Control Systems
Distributed computing
A distributed system is made up of separate autonomous computers that communicate and coordinate their actions using messages such that they appear to the user to be a single integrated computing facility. • An example is a distributed database, which doesn't reside on one computer but is housed on several computers which update each other asynchronously.
Describe the importance of feedback in a control system.
A feedback system is the foundation of control system analysis and design as it maintains a prescribed relationship between one system variable to another by measuring the actual output with the desired output response of the system.
Examples
Automatic doors • Heating systems • Taxi meters • Elevators • Washing machines Process control • Device drivers • Domestic robots • GPS systems • Traffic lights
Comparision
Centralised One component with non- autonomous parts • Component shared by users all the Kme • All resources accessible • Software runs in a single process • Single Point of control • Single Point of failure Distributed • MulKple autonomous components • Components are not shared by all users • Resources may not be accessible • Software runs in concurrent processes on different processors • Multiple Points of control • Multiple Points of failure
Draw a diagram of open loop system
Desired output response -- actuating device --process --- Output
Draw a diagram of a closed loop system.
Desired output response -- comparision -- Controller -- Process --- Output
Microprocessor
Essentially it is a small CPU with a program written into its ROM • It is often part of an embedded system (a dedicated, single- purpose computer system forming part of a larger mechanical device)
Domestic Robots
Examples Vacuum cleaners • Lawn mowers • Pool cleaners • Security patrollers Inputs • Vacuum cleaners, lawn mowers and pool cleaners all sense the perimeter of the area in which they are to work. They do this with a combination of cameras and pressure sensors. • Security robots also detect movement and/or heat. Processing • Domestic robots build a map of their surroundings from their sensory input. They use this information to decide where to move and how to act. Outputs • Motors controls wheels and cleaning/mowing equipment. • Security robots can also take video of suspicious activity or alert a human.
Hardware associated with control system
Input - Sensors - AD Converters • Processing - Microcontroller/Microprocessor • Output - Actuators - Transducers - Fan, sprinkler, alarm, etc
Automatic doors
Inputs Optical motion sensors emit infrared or microwave radiation and detect it rebounding off an approaching person. The amount of radiation detected is converted to a digital value by an AD converter. Processing • If the value corresponding to the amount of radiation reflected back into the sensor exceeds some pre-set threshold, a command is issued by the microcontroller to open the doors. Outputs • Motors attached either to a hydraulic arm, belt or cable pull or slide the doors open. After some pre-set delay, the doors close again.
Heating Systems
Inputs Temperature sensors detect ambient temperature and convert the analog data into digital so that it can be interpreted by the microcontroller. (There are lots of ways to measure temperature but a common one is a thermistor, whose resistance changes with temperature.) Processing • If the temperature value is above or below some pre-set threshold, then a signal is sent to the appropriate temperature control device. Outputs • Turning a fan on/off • Turning a heater on/off • Turning an air conditioner on/off • Opening/closing windows
Device Drivers
Inputs: Requests issued by the operating system or application software Processing • Translation of the request into low-level instructions understood by the hardware Outputs • The hardware reacts appropriately
Washing Machines
Inputs: The programme number is entered by the user through buttons • The amount of water in the drum is detected by a pressure sensor beneath the drum (AD conversion) Processing: • The microcontroller responds to the programme choice by activating the appropriate cycle • When the amount of water reaches a pre-set level, the microcontroller issues a command to shut off the water supply Outputs: • The water supply is turned on when a cycle begins and shut off when it reaches the correct level • The drum turns according to the cycle chosen
Elevators
Inputs: Passengers press buttons to call the elevator. • Passengers press buttons to tell the elevator where to go. • A load sensor converts the current weight of the occupants of the elevator, converts it to a digital value using an AD converter, and sends this value to the microcontroller. Processing: • The microcontroller calculates where to go and in what order according to three pieces of information: - Where passengers are waking - Where passengers want to go - Where the elevator is currently • If the load value exceeds a pre-set threshold, the microcontroller produces some sort of appropriate output. Outputs: • The elevator is moved using either a hydraulic ram or a steel rope on a motor-driven pulley. • The doors are opened using cables on a motorized pulley that slide the doors on rollers. • A warning or alarm may sound in the event of excessive load, and the elevator may cease to function until the load is reduced.
Taxi meter
Inputs: Sensors attached to the transmission of the car measure the distance travelled. This is converted into a digital value by an AD converter. • A timer measures the journey time elapsed. Processing: • If the taxi travels a preset distance, then an amount is added to the fare total. • If the taxi waits for a preset period, then an amount is added to the fare total. • In practice, the microcontroller will use some algorithm to determine, from the combination of distance travelled and time elapsed, when to increase the fare total. Outputs • An amount is added to the fare total and a small digital display shows the running total.
GPS
Inputs: High-frequency, low-power radio waves are sent to and received from at least three geostationary satellites. Processing • The amount of time taken for the signal to come back from each satellite allows the handheld unit to calculate its own position. Outputs • The basic information provided by a GPS is your location, but some can also calculate speed and journey duration, together with a route travelled.
Define a control system
Interconnection of components forming a system configuration that will provide a desired system response.
Processing
The microcontroller or CPU makes a decision on the basis of the data input. If some threshold is reached, then some action is taken.
Output
The system affects the outside world in some way, e.g. turning on a heater, moving a robot arm, adjusting the speed of a motor. The generic term for the mechanism by which a control system acts on its environment is an actuator.
Process Control (Generic)
The system gathers data about the current state of the system from sensors that convert analog data to digital data so that it can be read and understood by the CPU or microcontroller (AD conversion). • Examples are heat, light, pressure, gas concentrations, movement, distance, pH, salinity, saturation, etc. Processing • The microcontroller compares the current state information with pre- programmed thresholds and acts accordingly. • For example if it is too cold, then a heater is turned on, if it movement is detected, an alarm goes off, etc. Outputs • The digital signal from the microcontroller causes some effect in the physical world through an actuator (digital-to-analog or DA conversion). The effect of the actuator is to regulate the state of the system.
Traffic Lights
There are different types of traffic lights, some for traffic only, some for pedestrians to cross. Inputs • A button is pressed by a pedestrian when they want to cross the road. • Some traffic lights can sense when a car is walking. • Some traffic lights can be overridden by humans who are watching the traffic through cameras. • Some traffic lights just work on timers. Processing • The system receives a signal from its sensory input requesting that it initiate its sequence. The system calculates how long since it last changed. If this time was sufficiently long ago, it initiates its sequence. Outputs • The lights change according to a pre-set sequence. • A sound alerts visually-impaired pedestrians.
Outline the role of smaller systems within a large control system.
These systems are able to find a bug much more quickly and fix it since it is a condensed module.
Discuss how closed loop systems can also be called intelligent systems.
They are intelligent because they are able to take feedback and do something with it.
Explain negative feedback control.
When some function of the output of a system, process, or mechanism is recorded and is then used as a new input for the system and is "fed back in" to change the new output. So the output is effecting the input, that then creates a new output.
Microcontroller
• A microcontroller is made up of a microprocessor (the CPU), plus some ROM and RAM, plus I/O ports, all integrated into a single chip. The role of a microcontroller is to make decisions about how a system is to behave based on the inputs it receives and the logic that is programmed into it. • Microcontrollers are found in all of the examples in this topic. They are responsible for the processing part of the control system.
Feedback
-Feedback occurs when a system changes the value that it senses. For example, a central heating system senses temperature but also changes the temperature. • The aim of a feedback system is to keep some value, e.g. temperature, within some range.
Discuss the social impact and ethical consideration of the following control systems:
-Tagging prisoners - They will be allowed to be "free" but they are being treated as animals. -Surveillance round the clock - People would act more obediently in public, but this invades privacy. -CCTV - People will act more obediently in public but this invades privacy.
Outline disadvantages of computerized control systems even though they can be run 24x7 .
-There is a very high cost for these systems -The system would not work if there is a power cut -Needs to be monitored 24/7 as well
Inputs
Sensors capture analog data, such as temperature, pressure, light. This is converted to digital by a AD (analog-to-digital) converter, so that it can be processed by a computer.
List examples of intelligent systems.
Siri Google Talk IBM Watson Automated Phone Calls?
Social and Ethical issues of embedded systems
Taggingprisoners - ☺ Fewer parole violations - ☹ Invasion of privacy • SurveillanceandCCTV - ☺ Reduction in crime - ☺ Invasion of privacy - ☹ InformtiKon can be misused (e.g. blackmail, discriminaKon, markeKng) • Safetysystems - ☺ Greater levels of safety - ☹ Overreliance - ☹ Threat from hackers
List 5 sensors and state two applications of each.
Temperature Sensor - Can be used in an air conditioner or computer fan Pressure Sensor - Can be used for 3D Touch or opening garage door Motion Sensor - Can be used for automatic doors or speedometer Photo resistor - Can be used for automatic street lights or backup generators Sound Sensor - Can be used for voice recognition or reciter
