Controls

Big Idea Control theory deals with the behavior of dynamic systems. The desired output of a system is called the reference. When one or more output variables of a system need to follow a certain reference over time, a controller manipulates the inputs to a system to obtain the desired effect on the output of the system.

Purpose of Lesson Students will understand that controls are mechanisms or activities that use information to cause a system to change.

Learning Objectives Identify and describe selected principles of design applied in technological design. Analyze an automated technological system using a graphic organizer. Construct a simple control mechanism. Describe controls as mechanisms or activities that use information to cause a system to change. Explain the role of feedback, or the use of information about an output of a system to regulate the inputs to a system. Design, fabricate, and test a feedback-controlled system.

Working in pairs, write down the answers to the following questions. What is meant by the term “automated?” From your experience, what are some devices or systems that are automated?

Answers “automated” -The art of making processes or machines self-acting or self-moving. The use of automatic machinery in manufacturing and data processing, so that entire procedures can be automatically controlled with minimal or no human intervention. Examples - Coffee makers, clock radios, cruise control, robots, etc.

What comes to your mind as you read this quote? “If every instrument could accomplish its own work, obeying or anticipating the will of others... if the shuttle could weave, and the pick touch the lyre, without a hand to guide them; chief workmen would not need servants...” (Aristotle)

Think about what each part of the feedback control system does and how the parts are related.

Analysis of an Automated Technological System Cruise Control on an Automobile

Assignment Students will research and then analyze a system of your choice and share ideas on what each part of the feedback control system does and how the parts are related. Use handout to analyze- Student Resource You will present annotated diagram to the class

Exploration Read about “Cornelius Drebbel’s Thermostat” See (Student Resource 3.3.2)

automobile thermostat The thermostat’s main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator. At low temperatures, the outlet to the radiator is completely blocked—all of the coolant is recirculated back through the engine.

Automobile Thermostat Once the temperature of the coolant rises to between 180º and 195º F (82º-91º C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200º to 218º F (93º-103º C), the thermostat is open all the way.

Mechanical Clock - Video In mechanical clocks, an escapement device is used as a feed back regulator that controls the speed. Consider a mechanical clock powered by a falling weight being acted on by the force of gravity. Energy is transmitted through a set of gears using the force of gravity

Clock In such a clock, the gears spin uncontrollably unless a control mechanism is applied at the other end of the gear train. The control mechanism consists of an oscillating device that prevents the gear train from rotating, except at specific intervals, when it releases one tooth of the last gear in the train.

Clock By controlling the rate of rotation of the gears, it is possible to use this device to measure time by incorporating an indicator and a scale at the end of the shaft of one of the gears. The oscillating device is called an escapement mechanism.

Controls Controls are mechanisms or activities that use information to cause a system to change. Controls do not always succeed or work perfectly. Control systems were first developed over two thousand years ago.

Water Clock The first feedback control device on record is thought to be the ancient water clock of Ktesibios in Alexandria Egypt around the third century B.C.

Water Clock It kept time by regulating the water level in a vessel and, therefore, the water flow from that vessel. Was a successful device, as water clocks of similar design were still being made in Baghdad when the Mongols captured the city in 1258 A.D. Automatic devices have been used over the centuries to accomplish useful tasks or simply to just entertain.

Automata = Open loop Control The latter includes the “automata,” popular in Europe in the 17th and 18th centuries, featuring dancing figures that would repeat the same task over and over again; these “automata” are examples of open-loop control.

Closed Loop – Automatic Control Device Milestones among feedback, or “closed-loop” automatic control devices, include the temperature regulator of a furnace attributed to Drebbel, circa 1620, and the centrifugal flyball governor used for regulating the speed of steam engines by James Watt in 1788.

Governors In his 1868 paper “On Governors,” J. C. Maxwell was able to explain instabilities exhibited by the flyball governor using differential equations to describe the control system. This demonstrated the importance and useful- ness of mathematical models and methods. signaled the beginning of mathematical control and systems theory.

Maxwell’s Analysis Elements of control theory had appeared earlier but not as dramatically and convincingly as in Maxwell’s analysis. Control theory made significant strides in the next 100 years New mathematical techniques made it possible to control, more accurately, signifincantly more complex systems than the original flyball governor.

Optimal Control developments in optimal control in the 1950s and 1960s, followed by progress in adaptive and optimal control methods in the 1970s and 1980s. Control Methodology have made the following advancements possible ▫space travel ▫communication satellites ▫safer and more efficient aircraft ▫ cleaner auto engines, cleaner and more efficient chemical processes

Review Concepts Understanding the role of feedback, or the use of information about an output of a system to regulate the inputs to a system, is important in being able to determine how controls work in various kinds of systems. The stability of a technological system is influenced by all of the components in the system, especially those in the feedback loop.

Review Concepts Research and development is a specific problem- solving approach that is used intensively in business and industry to prepare devices and systems for the marketplace. Management is the process of planning, organizing, and controlling work. New technologies create new processes.

Review Concepts In engineering and mathematics, control theory deals with the behavior of dynamic systems. The desired output of a system is called the reference. When one or more output variables of a system need to follow a certain reference over time, a controller manipulates the inputs to a system to obtain the desired effect on the output of the system.

Extension Water Clock Copyright Vernon MacMillan

Water Clock Students will read more about water clocks in A Walk Through Time, The Evolution of Time Measurement Through the Age. As you read write down the answers to the following questions on the next slide.

Questions What are the parts of a water clock? What is a water clock designed to do? What advantage does a water clock have over other devices such as sundials? What is the largest problem associated with water clocks?

Extension Assignment Students, working in teams of two, will address the following problem. Design, fabricate, and test a feedback- controlled system (a water clock). Design Brief Student Resource