The programme looks at the theoretical background behind the glass cutter design at Pilkington Brothers Ltd.
|Module code and title:
|T391, Control engineering
|First transmission date:
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|Chris Dillon; John Monk; Ted Wilson
|BBC Open University
|Control system; Glass cutter; Pilkingtons
|John Monk (v/o) introduces the programme. Film shots of the glass cutter and its transducers at Pilkington Brothers Ltd. Monk interviews Ted Wilson (Pilkington Control Engineer) about the glass cutter control system. Wilson lists the original specifications for the cutter, explains how a cut is made by the machine, and why a feedback control system is necessary in this process. The interview continues. Wilson discusses the constraints on the transient response of the system and their implication for the control system. Finally Wilson explains what mathematics were used in the design of the cutter control system. Chris Dillon, with a model of the Pilkington glass cutter, briefly explains how it works. He goes on to list the parameters of such a control system and then examines its block diagram. Monk looks at Bode diagrams which have plotted on them results of frequency response experiments conducted by Pilkington engineers. He then overlays well known curves which closely match the experimental curves and derives a fourth order model for the system's motor/cutter, function for this is captioned. The transfer Chris Dillon adds the fourth order model of the motor/cutter to the block diagram of the system as a whole. He then adds a proportional controller to the block diagram and explains why. To check the response of the system to a proportional controller, Dillon experiments with a working model of the glass cutter which he operates with proportional gain only. John Monk, using a sketched graph and computer graphics, plots the root locus for this control system on the axes of sigma and omega. He explains how the root locus is used to determine how fast the transient response of the glass cutter can be. Monk goes on, using a still computer plot and a computer animation, to explain how a better transient response can be achieved by adding a zero to the sigma axis. Chris Dillon explains how these ideas can be implemented in a practical control system by using a velocity feedback technique. Shots of a block diagram of the control system as he talks. Then, using a working model of a glass cutter, Dillon tests his ideas in practice. John Monk, using computer animations, explains how the root locus can be used to determine if the fastest possible response is being generated by the system. Chris Dillon discusses the importance of being able to provide information on steady state behaviour as well as best dynamic performance. He uses a model of the glass cutter and a block diagram to help make his points. Dillon goes on to discuss what he means by velocity feed forward and how this affects steady state performance of the system. He then demonstrates with a model. Dillon sums up the programme.
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