chatter reduction through active vibration damping - iit … dynamics/ppt/dr... · chatter...

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Chatter reduction through active vibration damping

Abhijit Ganguli

Department of Civil Engineering, IIT Delhi

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Motivation of the work:

• To demonstrate active damping as a chatter control strategy

Organization of the presentation •  Introduction •  Regenerative chatter in turning

•  Regenerative chatter in milling

•  Active control of chatter

•  Experimental investigations

Realization of Demonstrator for chatter in turning

Realization of Demonstrator for chatter in milling

Application of active damping

•  Conclusion

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Applications of machining- •  Aircraft & Automobile industries •  All kinds basic metallic components & parts •  High precision tiny equipments

Introduction

Typical machining operations

Workpiece

Tool

Turning

Milling

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Chatter Marks Problem affecting machining:

Machine tool chatter instability

Broken tools

Effects of chatter

•  Low precision and low surface quality •  Damage to tool or workpiece system •  Low efficiency •  Rising costs

Requirement for the machined end product

•  High quality of surface finish

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Organization of the presentation

•  Introduction

•  Regenerative chatter in turning




Realization of demonstrator for chatter in turning



•  Conclusion

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The regeneration process

T = 60/N = Period of one revolution

Dynamic Chip Thickness

Oscillation during previous pass Oscillation during

current pass

Cutting Force Cutting Constant

Axial width of cut

Chip Thickness

Kcut

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Feedback Loop Model for chatter in turning (Merrit 1965)

Stable

Marginally Stable

Unstable

Machine vibration

Dynamic chip thickness

Cutting stiffness

Cutting force

Machine tool transfer function

Time delay

+

+

+ _ y(s) Kcut G(s)

Feed

Structural Dynamics

Cutting Process

Displacement Forces

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Solve characteristic equation

1 + (1 - e-sT ) Kcut G(s) = 0

Pade Approximation

Methods of stability analysis •  Time domain simulations •  Root Locus Method

Outline of Root Locus Method •  Choose spindle speed i.e., T •  Solve characteristic equation with increasing Kcut •  Identify the value of Kcut for which at least a couple of conjugate roots lie on the imaginary axis

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Spindle speed

Kcu

t / k

Unstable

Stable

The Traditional Stability Lobe Diagram

Parameters governing regenerative instability:

•  Spindle Speed •  Kcut

Delay

Structural Mode

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•  Introduction








•  Conclusion

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Δx = x – x(t – T); Δy = y – y(t – T) T = tooth passing period = (Period

of rotation/number of teeth)

Regenerative chatter in milling

Periodic Regenerative Forces

Regenerative Displacements

Cutting forces

Axial width of cut

Cutting Constant

Periodic feed

forces

Governing equation: Linear DDE with periodic coefficients

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Complexities of milling chatter •  Existence of tooth passing frequency harmonics (Nm/60) •  Multiple mechanisms of chatter

•  Stability limits dependent on the kind of milling operation, direction of feed etc.

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Flip Bifurcation

Hopf Bifurcation

Characteristics of chatter frequencies in milling •  Harmonics of tooth passing frequency

•  Hopf Bifurcation : Basic chatter frequency close to structural modal frequency

•  Flip Bifucation : Chatter frequencies located at odd multiples of one half of tooth passing frequency

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Observation •  Hopf Bifurcation in low stability regions •  Flip Bifurcation in certain parts of high stability regions

Downmilling

Downmilling

Upmilling

Stability lobes in milling

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•  Introduction








•  Conclusion

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Active control of chatter

•  Online control of spindle speed •  Application of damping

Spindle speed

Kcu

t / k

Unstable

Stable

High stability Region (control spindle speed)

Augment damping

H(s)

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Active Damping

Colocated actuator/sensor

Alternating poles & zeros

Actuator

sens

or Control laws with

guaranteed stability

Source – Vibration Control of Active Structures- An Introduction André Preumont

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How does active damping work?

Enhanced modal damping

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Demonstration of enhanced damping effect

Stability enhancement more pronounced

Damping Coefficient Feedback

gain

Chatter Frequency

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Effect of Active Damping of both directions (Numerical Simulation)

•  Enhancement of stability more pronounced in low stability regions

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•  Introduction








•  Conclusion

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Motivation •  To investigate active damping as a chatter control strategy

Difficulties in real machining •  Perform numerous cutting tests •  Chatter needs to be actually triggered •  Life of the machine endangered •  Repeatibility of results

Intermediate Platform

A laboratory demonstrator

Technological advances •  Chatter model well developed •  Advances in signal processing technologies

Potentials •  Realistic simulation of regenerative chatter •  Repeatability •  Platform for active damping

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Conceptual model of a mechatronic simulator (Hardware in the Loop concept)

Basic parameters governing regenerative instability: Tooth passing period (Spindle speed) •  Kcut •  Angle of entry & angle of exit (Type of milling)

User defined

Experimental stability Analysis •  Choose cutting conditions •  Increase Kcut step wise •  Monitor displacements •  Store Kcut value at instability

Structural Dynamics

Cutting Process

Displacement Forces

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The Chatter Demonstrator for 1 DOF turning

Structural Dynamics

Software Layer

Hardware Layer

Cutting process

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Comparison between Experimental & Numerical Simulations

Stability Lobe Diagram

Chatter Frequency Diagram

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•  Introduction








•  Conclusion

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Demonstrator for milling

Cutting process simulation

Voice coil Actuators (electro- magnetic)

Displacement signal

DSP

Cutting force signals

Cutting Conditions

Monitor Displacements

x y

z

Manufacturer: Micromega Dynamics

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Experimental and numerical stability lobe diagrams

Upmilling

Downmilling

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•  Introduction








•  Conclusion

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Application of active damping (Direct acceleration feedback)

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Effect of active damping (Experimental)

Bending X 2.1 % 6.7 % 8.2 %

Bending Y 2.7 % 4.5 % 5.8 %

Uncontrolled Damped 1 Damped 2

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Source: Soraluce & Micromega Dynamics

Application of active damping on an industrial setup

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Application of active damping on an industrial setup

Source: Huller-Hille & Micromega Dynamics

Active Mass Damper

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Conclusions

•  Phenomenon of regenerative chatter investigated

•  Laboratory mechatronic setups realized

•  Demonstrators simulate regenerative chatter realistically

•  Active damping as chatter reduction strategy demonstrated

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Acknowledgements

•  Prof. André Preumont

•  Drs. M . Horodinca, I. Romanescu, A. Deraemaeker

•  All members of the ASL team

• The SMARTOOL Consortium

• The European commission

•  Micromega Dynamics

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Thank you

chatter reduction through active vibration damping - iit … dynamics/ppt/dr... · chatter...

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