sintonia manual kinetix6000
TRANSCRIPT
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Copyright 2008 Rockwell Automation, Inc. All rights reserved.
Manually Tuning a
Servo Axis in a Logix5000 Motion System
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Motion Applications Overview
High performance is required:
High speed
High accuracy Repeatability
System has been properly sized and applied:
Load to motor inertia ratio in acceptable range
Motion controller/drives can perform required tasks
Machine was properly built::
Compliance and machine resonance minimized
Quality gearboxes and actuators/guides chosen
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Copyright 2008 Rockwell Automation, Inc. All rights reserved. 4
Inertia
Inertia is important for the following reasons:
Effect on dither in steady state AND in motion
Effect on all other tuning calculations
As inertia increases, gains are increased (scaling)
Drive quantization increases
Causes high frequency noise/heat in kHz of drive update
Requires a notch filter, but doesnt eliminate (cascades) Compliance and backlash issues made worse by high inertia
Why does a high resolution encoder help?
Dither distance is reduced
More information comes back (higher BW) per drive update
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Copyright 2008 Rockwell Automation, Inc. All rights reserved. 5
Tuning Terminology
Loop Pgain can do most of the work, but not all
Use Integrals to help close the steady state error
Whether standing still or at constant speed Use velocity Igain if speed is crucial
Use position Igain if steady-state position is crucial
Use velocity Igain if path is important (this works)
Use Feed Forward values if following a path only Velocity(ff) for constant speed portion Acceleration(ff) for blending velocities
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Copyright 2008 Rockwell Automation, Inc. All rights reserved. 6
Tuning Terminology
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Tuning Terminology
Output filters High integral gains can lead to low speed instability
High derivative gains can lead to high speed instability
Torque offset Compensation for vertical applications.
Requires bi-directional tuning
Friction compensation Used when not coming into end point tolerance due to stiction
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Basic Servo Loop Diagram
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Ziegler-Nichols Method to Tune a Closed-Loop
Ziegler-Nichols method of tuning for a closed control loop Determines ultimate gain
Determines ulltimate period
Requires the following steps Create an instability on the control loop
Continue decreasing the gain until a stable response is reached (do not want thesystem to be completely damped)
Tip: ZieglerTip: Ziegler--Nichols method recommended for schemes based onNichols method recommended for schemes based onproportional control. The value of gain should be 1/2 to 1/3 theproportional control. The value of gain should be 1/2 to 1/3 the
ultimate gain to obtain 1/4 wave response curve.ultimate gain to obtain 1/4 wave response curve.
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Copyright 2008 Rockwell Automation, Inc. All rights reserved. 10
Over-damped
Ziegler-Nichols Method to Tune a Closed-Loop
Under-damped
Critically damped
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(3) Main Types of Motion Applications
Point
to Point
Pick-Place
Packaging
Cut to Length
Tracking
(Follower)
Winding
Flying Shear
Web
Constant
Speed
Conveyor
Line Shaft
Crank
Type 1 Type 2 Type 3
Tip:Tip: AutotuneAutotune works well if the inertia mismatch is less than 10:1. It isworks well if the inertia mismatch is less than 10:1. It isbest to manually tune when the inertia mismatch exceeds 10:1.best to manually tune when the inertia mismatch exceeds 10:1.
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Compliant Load Tuning Tips
For resonance below velocity loop bandwidth: Natural resonance of machine is within drives velocity BW
Must use BW reduction to detune (today), reduce Vel BW
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Additional Manual Tuning Tips
Start out with box settings
Use the RSLogix 5000 trend feature to monitor the motor position error.
Set the velocity and acceleration feedforward parameters to 100% in thegains tab.
Run the required motion profile.
If necessary, gradually increase the torque/force scaling value until the
position error becomes close to zero.
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Copyright 2008 Rockwell Automation, Inc. All rights reserved.