2 - feedback2 filled

2 - feedback2 filled - ME 575 Handouts Disk Drive Head...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ME 575 Handouts Disk Drive Head Positioning Objective: to precisely locate the head over the disk Options: 1) Open-loop control (without feedback) 2) Closed-loop control (with feedback) School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 1 Open-Loop Control Desired Track Position Controller Motor Voltage C Motor G School of Mechanical Engineering Purdue University Actual Head Position ME575 Session 2 - Feedback 2 1 ME 575 Handouts Open-Loop Control (with Disturbance) Desired Track Position Controller Voltage Disturbance Motor Voltage ++ C Motor Actual Head Position G School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 3 Introduce Feedback R(s) Controller + − C D(s) ++ Plant Y(s) G + + N(s) R(s): reference input signal for desired action D(s): disturbance signal acting on plant N(s): noise signal corrupting the measurement School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 4 2 ME 575 Handouts Closed-Loop Feedback Control R(s) Controller + − C D(s) ++ Plant G Y(s) + + N(s) Y (s) = CG G CG R (s) + D (s) − N(s) 1 + CG 1 + CG 1 + CG School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 5 Closed-Loop Feedback Control • Every transfer function between any one input and one output has the same denominator but different numerators. • The controller C affects inputs R and N in a similar way, but affects input D differently. School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 6 3 ME 575 Handouts Closed-Loop Control Requirements • YR → R ⇒ YR ( s ) = CG R (s) 1 + CG • YD → 0 ⇒ YD ( s ) = G D (s) 1 + CG • YN → 0 ⇒ YN ( s ) = − CG N(s) 1 + CG School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 7 Summary of Feedback Control • The use of feedback provides a mechanism to compensate for disturbances. • High-gain feedback essentially approximates plant inversion (the essence of control). • High-gain proportional control provides good reference tracking and disturbance rejection, but aggravates noise rejection. • How can we reconcile this apparent contradiction? School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 8 4 ME 575 Handouts Frequency Domain Design Assume the reference trajectory is primarily specified at low frequencies and the noise is primarily at high frequencies. Phase (deg); Magnitude (dB) 50 0 -50 -100 -150 -90 -135 -180 -225 -270 -2 10 10 -1 0 10 Frequency (rad/sec) 10 1 10 School of Mechanical Engineering Purdue University 2 ME575 Session 2 - Feedback 9 What about non-unity feedback? R(s) Pre-filter GR Controller + − C D(s) ++ Sensor GS School of Mechanical Engineering Purdue University Plant G Y(s) + + N(s) ME575 Session 2 - Feedback 10 5 ME 575 Handouts Non-unity feedback R(s) Pre-filter GR GS Controller + CGS − D(s) ++ Plant G Y(s) + + N(s) Y (s) = HC′G G C′G R (s) + D (s) − N(s) 1 + C′G 1 + C′G 1 + C′G School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 11 Combine Feedback with Feedforward GF R(s) D(s) C + ++ + Plant + − G Y(s) + + N(s) School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 12 6 ME 575 Handouts Disturbance Feedforward D(s) GD R(s) Controller ++ + − C Plant ++ G Y(s) + + N(s) School of Mechanical Engineering Purdue University ME575 Session 2 - Feedback 13 7 ...
View Full Document

This note was uploaded on 12/09/2011 for the course ME 575 taught by Professor Meckl during the Fall '10 term at Purdue.

Ask a homework question - tutors are online