devices: case study of pneumatic actuator A. Ortlieb, J. Olivier, M. - - PowerPoint PPT Presentation

Series elastic actuation for assistive orthotic devices: case study of pneumatic actuator

• A. Ortlieb, J. Olivier, M. Bouri and H. Bleuler

08.07.2015

Context: walking assistive devices

Who Why How Assist/mobilize/correct lower body motions Elderly Stroke patients Paraplegics Neuro-muscular disorders Safety (prevent falls) Health (provide (natural) motion) Autonomy (through mobility) Stabilize upper body

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SEA : series elastic actuator

 1997 MIT patent (G. Pratt, M. Williamson): Elastic actuator for precise force control  2012 GM patent: Rotary SEA Motor Spring Force Reduction Position

UT-SEA actuator RoboKnee from Yobotics inc LOPES, Twente university

A Novel Compact Torsional Spring for Series Elastic Actuators for Assistive Wearable Robots, Carpino et al. 2012

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SEA advantages

 Precise force control  Bio-inspired (muscle-tendon)  Adapted to locomotion  Reduction in peak power, energy required, force  User friendly (compliant)

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A Comparison of Parallel- and Series Elastic Elements in an actuator for Mimicking Human Ankle Joint in Walking and Running, Grimmer et al. 2012

Actuators properties regarding walking activity of the ankle joint

Goal and motivations

 Evaluation of pneumatic cylinders as candidate to SEA for assistive

• rthotic devices

Motivations

 Pneumatic cylinders are compact double-SEA  Elastic behavior is “imposed” : P V = n R T

Chamber 1 Chamber 2

Compressible gas

Force Displacement

Dilated gas Compressed gas ∆𝒚

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Material

Double acting pneumatic cylinder Bore Ø50mm

Frame 100 mm Output lever

400 mm height 120 mm width

120°

Axis for encoder

Pressure sensors

Sensors

• 1x Encoder for output angle
• 2x pressure sensors for output force

Properties

• Max torque: 50-60 Nm [@ 4bar]
• Weight: 2.4 kg

5/3 Distributor Proportionnal electrovalves

Source 4 [bar] Sink 1 [bar] Sink 1 [bar]

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Experiment

 Factors

 Pressure at rest P0 [1 to to 4 bar bar]  Position at rest α0 [1/4 to to 3/4 of

• f cylin

cylinder len ength]  Torque output ΓM [0 to to 20 Nm]

 Response

 Displacement Δα

 Design of experiment

 Parametric model  Box-Behnken design  Forward selection and backward elimination (optimization of final model)

M P1, V1 P2, V2 P1’, V1’ P2’, V2’ 𝜷 𝟏 𝒚 𝟏 ∆𝒚 ∆𝜷 𝚫 𝑵

 

   

       

2 2 m n m m mn

• ut

b P

𝑄0

Γ𝑁

𝛽0

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at rest loaded

Results

Γ

𝑝𝑣𝑢 (Nm)

𝑄 0 = 1 bar 𝑄 0 = 2 bar 𝑄 0 = 3 bar 𝑄 0 = 4 bar

 Backward elimination

 R2 = 0.998               

2 21 2 02 11

P b P b P b cst

• ut

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 Forward selection

 R2 = 0.988             

3 03 2 02 01

P b P b P b cst

• ut

Walking curves from measurement of D. Winter, 1984

Torque (Nm) Angular position (deg)

flexion extension flexion extension dorsiflexion plantar flexion

HIP KNEE ANKLE

Swing phase Stance phase

60 80 20 15 5 50 10 60 20 160 20 20

Application to human locomotion (1)

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Walking curves from measurement of S. Ounpuu, 1994

Torque (Nm) Angular position (deg)

flexion extension flexion extension dorsiflexion plantar flexion

HIP KNEE ANKLE

Swing phase Stance phase

80 60 30 30 50 70 40 130 20 20

Application to human locomotion (2)

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Application to human locomotion (3)

• W. Stance 1
• W. Stance 1
• W. Stance 1
• O. Stance 1
• O. Stance 1
• O. Stance 1
• W. Stance 2
• O. Stance 2
• W. Swing
• W. Swing
• W. Swing
• O. Swing
• O. Swing
• O. Swing

P=1 bar P=2 bar P=3 bar P=4 bar P=5 bar 1 2 3 4 5 6 7

Hip Knee Ankle Stiffness [Nm/deg]

Joints vs pneumatic SEA stiffness 11

Conclusions

 Pneumatic cylinders are (pros)

 Able to reproduce human joints behavior (during walking)  Simple double-SEA  Can be downsized using higher pressure  Different mode (active, damping, passive)

 Pneumatic cylinders have/are (cons)

 Bulky/heavy power source (tank or pump+battery)  Noisy due to air flow  Dry friction (rod)

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Further study

 Evaluation of impedance control with pneumatic actuator  Application to locomotion and evaluation

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Series elastic actuation for assistive orthotic devices: case study of pneumatic actuator

• A. Ortlieb, J. Olivier, M. Bouri and H. Bleuler

Questions ?