motors080904

motors080904 - Motors and Position Determination...

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Motors and Position Determination Motors and Position Determination L17 6.111 Fall 2003 – Introductory Digital Systems Laboratory
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x Controlling Position Controlling Position ± Feedback is used to control position. ² Measure the position, subtract a function of it from the desired position and then use this resulting signal to drive the system towards the desired position. This is negative feedback. ² The natural frequencies of the feedback system are the “zeros” of 1 + G(s)H(s). z The total system is unstable if these “zeros” are in the right half plane (RHP). With 180 degrees phase shift, “negative” feedback becomes “positive” feedback. z So we want these “zeros” to be in the left half plane (LHP). z Putting an integrator into H(s) drives steady state error to zero. z But high order systems are more likely to have RHP zeros. z Time delay and high gain lead to RHP zeros. H(s) G(s) + + y Y(s) H(s) = X(s) 1 + G(s) H(s) L17 6.111 Fall 2003 – Introductory Digital Systems Laboratory
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Servos Servos ± We can control parts of the servo, but the system dynamics is often a part we can’t control. ² The system dynamics results from masses. springs, losses, etc. ± Likely, we will implement servos as digital systems. ² Digital systems are more flexible to design. z They are more repeatable; they are not subject to gain drift. z We can use as many bits as we like so we can keep the computation noise small. ² Digital systems can have significant delays. z These delays are sometimes fixed, but are sometimes stochastic. Position + + x y Output Position G(s) C(s) A(s) Measurement System Dynamics Controls Likely boundary of Desired digital system L17 6.111 Fall 2003 – Introductory Digital Systems Laboratory
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Analog Position Measurements Analog Position Measurements Voltage is proportional to position.
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This note was uploaded on 07/21/2009 for the course EECS 6.111 taught by Professor Prof.ananthachandrakasan during the Spring '04 term at MIT.

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motors080904 - Motors and Position Determination...

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