A flexure based 3-DOF micro positioner

Report
MSc presentation · R.H.S. Bruinen
Supervisor · Prof. ir. R. H. Munnig Schmidt
Daily supervisor · P. Estevez Castillo MSc
Design and analysis of
a flexure based 3-DOF micro positioner
DCMM
Content
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Introduction
Conceptual design
Stiffness analysis
Results and conclusions
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Introduction
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Introduction / Application
Sources: apple.com, shavers.co.uk, delfly.nl
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Introduction / Haptic teleoperation
Gripper
User
Command
Micropositioner robot
Haptic interface
Force & vision
feedback
Sources: micropositioners.net, mekabot.com
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Introduction / My project
Allow 3D translations, constrain rotations
Specifications
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Workspace 20x20x20mm
MIM (minimum incremental motion) 0,2µm
Natural frequency > 100Hz
Micropositioner robot
Actuator forces < 1N
Velocity 0.1 m/s
Acceleration 1.5 m/s2
…
Source: micropositioners.net
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Conceptual design
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Conceptual design / Serial or parallel
Serial
Parallel
Low moving mass
High stiffness
Small workspace
Sources: xyz-stage.com, pi.com
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Conceptual design / Parallel mechanisms
Adept
Tripteron
Quattro
Sources: robot.gmc.ulaval.ca, motionsystemdesign.com
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Conceptual design / Bearings or flexures
Bearings
Flexures
No dry friction
Short range
Sources: rchellevoet.nl , flexpivots.com
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Conceptual design / Architecture
Mechanism
Legs
Joints
Beams
1 DOF
2 DOF
3 DOF
Sources: kxcad.net, hephaist.co.jp
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Conceptual design / Architecture
Design options from literature
e.g. Jin and Zhao “New kinematic structures for 2-, 3-, 4-, and 5-DOF parallel manipulator designs”
1 DOF joints
Examples:
Selected:
High stiffness
Cartesian
Modified
U* design
mechanism
Delta
Source: Jin and Zhao “New kinematic structures…”, Gosselin “Compact dynamic models…”
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Conceptual design / Geometry
Main design variables
• Upper leg angle
90°
• Lower leg angle
90°
• Line of actuation
in line with upper leg
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Conceptual design / Joints
Flexure requirements
• Low pivot stiffness  Large workspace
• High off-axis stiffness  High resonances & precision
Notch
Intersecting cross
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3-leaf
14
Stiffness analysis
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Stiffness analysis / Introduction
Dimensioning
Stiffness
Mechanism performance
• Mechanism size
• Workspace
• Joint length, width
and thickness
• MIM
Stick-slip
F
• Resonances
Case 1: Actuation force
Case 2: Interaction force
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Stiffness analysis / Introduction
Dimensioning
Stiffness
Mechanism performance
• Mechanism size
• Workspace
• Joint length, width
and thickness
• Resonances
• MIM
Existing literature
Howell and Midha “A Method for the Design of Compliant
Mechanisms With Small-Length Flexural Pivots”
- 1 DOF joint
- No parallel mechanisms
Pham and Chen “Stiffness modeling of flexure parallel mechanism”
- Theoretical approach
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Stiffness analysis / Introduction
Dimensioning
Stiffness
Mechanism performance
• Mechanism size
• Workspace
• Joint length, width
and thickness
• Resonances
• MIM
Stiffness analysis
Joints
Legs
Mechanism
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Stiffness analysis / Joints
Leaf
Joint
Bending:
Stiffness around pivot axis
Stiffness around off-axis
Compression:
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Stiffness analysis / Legs
Example: Translation, X direction
θ = M·Cp = F·ll·Cp
Cp = joint compliance around pivot axis
Δx = θ·ll = Fx·ll2·Cp
Case 1: Actuation force
Case 2: Interaction force
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Stiffness analysis / Mechanism
Case 1: Actuation force
Case 2: Interaction force
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Stiffness analysis / Mechanism transformation
Transform to horizontal-vertical coordinate system
with Euler rotations
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Stiffness analysis / Dimensioning
Dimensioning
Stiffness
Mechanism performance
• Mechanism size 16cm
• Workspace
• Joint length
length,8mm,
widthwidth
and 10mm
and
thickness 0.15mm
thickness
18x18x18 mm3
20x20x20 mm3
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• Resonances 240 Hz
100 Hz
++
• Stick-slip
200 nm
++
75 nm
Stiffness analysis
Joints
Legs
Mechanism
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Results and conclusions
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Results
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Designed a flexure based 3 DOF micropositioner
Developed stiffness analysis method for flexure parallel mechanisms
‘Second International Symposium on Compliant Mechanisms’
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Submitted a paper
Created 3D print
Presentation and demonstration
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Conclusions
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The stiffness analysis
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Addition to existing literature
Tool for the design of flexure parallel mechanisms
More insight into the mechanism
The final design
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High precision performance with a large workspace
Use in industry or research
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Design and analysis of
a flexure based 3-DOF micro positioner
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Mechanism specifications
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Conceptual design / Actuators and sensors
Selected actuator: Lorentz motor
• No friction, no backlash
• No added stiffness in system
Selected sensor: optical encoder
• Sufficient range and resolution
• Affordable
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Stiffness analysis / Legs
Example: Translation, X direction
M=Fx·ll
θ=M·Cp
Δx2 = θ1·ll
Δx3 = Fx·ll2·Cp
CxI = ll2·Cp
Case I
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Stiffness analysis / Mechanism performance
Workspace
Stick-slip
Resonances
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