l19 - 6.111 Lecture 19 Controlling Position Servomechanisms...

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6.111 Lecture # 19 Controlling Position Servomechanisms are of this form: Some General Features of Servos: They are feedback circuits± Natural frequencies are 'zeros' of 1+G(s)H(s)± System is unstable if these zeros are in the right half plane± 'Negative' feedback becomes positive with 180 degree phase shift± Putting an integrator into H(s) drives steady error to zero± But high order systems are more likely to have RHP zeros± Time delay and high gain lead to RHP zeros± 1 Digital Servos Major parts of the system are digital Digital systems are more flexible to design More repeatable (not subject to gain drift) Analog parts are important But in many cases can be avoided. .. But note that digital servos have fixed (or worse stochastic) time delays Position Measurement Voltage proportional to position Linear or rotary potentiometer Accuracy limited by that of potentiometer Accuracy limited by voltage source 3 4 2
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Two sinusoidal potentiometers V1 = V0 cos θ V2 = V0 sin θ This can be done magnetically too Sinusoidal coupling Requires complex analog detection Is called a Resolver These are still analog Accuracy limited Subject to drift Complex calculations Another Digital Method Low Resolution Absolute Sensor Digital Measurement of Position Sense light transmission Typically through a transparent sector Gives a reading over a range of positions May need a lot of sensors. .. 5
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This note was uploaded on 07/20/2009 for the course ELECTRICAL 6.111 taught by Professor Prof.dontroxel during the Fall '02 term at MIT.

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l19 - 6.111 Lecture 19 Controlling Position Servomechanisms...

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