Biomechatronics lecture 3

Biomechatronics

Bart Koopman

lower extremity orthotics and prosthetics

Biomechatronics

Plant: Skeletal system,

external load

Actuator:muscles

Sensors: physiological

sensory system

intention

Plant: Orthosis

Prosthesis

Actuator:motor

Sensors: artificial

Artificial

Physiological

Controller:artificial

Controller:CNS

Prosthetics and Orthotics

Prosthesis:• Replacement of body

parts and/or functions

Orthosis:• Support of body functions

Short history: amputation and prosthesiology

• 1000 bC: Rig-Veda (sanskriet)• 400 bC: Hippocrates• 300 bC: eldest prosthesis

Amputation in middle ages

H. Von Gerßdorf, 1517, Feldtbuch der Wundarztney

Armprosthesis

Götz von Berlichingen, Landshut1504

Ambroise Paré (1510-1590)

Prosthesis of Paré

Dominique Jean Larrey (1766-1843)

Modern amputation techniques

Orthotics

Functions:• Support• Redressing• Stabilization (immobilization)• Cosmetic

Control orthosis

Plant: Skeletal system,

external load

Actuator:muscle

Controller:Central Nervous

system (CNS)

Sensors: physiological

sensory system

intentionActiv-ation force Movement

Orthosis

Muscle control

motor unit

fiber

fiber

fiber

fiber

fiber

motor unit

mor

phol

ogy r11

r12

Muscle 1

motor unit

fiber

fiber

fiber

fiber

fiber

motor unit

mor

phol

ogy

r2

Muscle 2

Joint 1

Joint 2+

+

Mj1,pass

Seg

men

ts m

odel

Mj2,pass

347106104

Normal control

r11

r12

r2

knee joint

Hip joint+

+

Mj1,pass

Mj2,pass

Muscle 1

Muscle 2

Mechanical properties

Segments model

Hip angle

Knee angle

External loads

Sensor dynamics

control orthosis

r11

r12

r2

Knee joint

Hip joint+

+

Mj1,pass

Mj2,pass

Muscle 1

Muscle 2

Mechanical properties

Segments model

Hip angle

Knee angle

Orthosis

External loads

Skeletal systemMuscles

Phys. Sensors

CNS

OrthosisProsthesis

MotorArt. Controller

Art. Sensors

Example

UTX-swing orthosis• Knee Ankle Foot Orthosis for

paralyzed knee muscles• controller allows flexion during

swing and locking during stance

Old KAFO UTX-swing

Leg orthoses

Prosthetics

Functions:• Support• Cosmetic

TF-prosthesis:• modular• 1,5 – 4 kg• 3 – 30 k€

Amputations in NL

Amputation causes

Normal control

r11

r12

r2

knee joint

Hip joint+

+

Mj1,pass

Mj2,pass

Muscle 1

Muscle 2

Mechanical properties

Segments model

Hip angle

Knee angle

External loads

Sensor dynamics

control prosthesis

r2 Hip joint+

Mj2,pass

Muscle 2

Mechanical properties

Segments model

Hip angle

Knee angleProsthesis

External loads

Sensor dynamics

control prosthesis

Mechanical properties

Segments model

Hip torque

Knee angleProsthesis

External loads

Sensor dynamics

Hip angle

Prostetic knee design

4-axial knee: • Improve local stability• Improve controllability• No actuation!

Inverted knee design

Posterior view

Model predictions: • increased push-off time• increased velocity

Regular vs. inverse knee

Post. Ant.

polar curve

inverted knee

-0,50

0,00

0,50

1,00

1,50

0 5 10 15 20 25 30 35

Knee Angle [deg]

dM/dϕ stable

regular 4-axial knee

-2,00

-1,50

-1,00

-0,50

0,000 5 10 15 20 25 30 35

Knee Angle [deg]

dM/dϕ instable

Experimental results

Skeletal systemMuscles

Phys. Sensors

CNS

OrthosisProsthesis

MotorArt. Controller

Art. Sensors

Example

EMG-activated prostheses• lower extremities: controlled damping,

no motor, artificial sensors• upper extremities: myo-electric arm

prosthesis, motor, no artificial sensors

Skeletal systemMuscles

Phys. Sensors

CNS

OrthosisProsthesis

MotorArt. Controller

Art. Sensors

Example

Skeletal systemMuscles

Phys. Sensors

CNS

OrthosisProsthesis

MotorArt. Controller

Art. Sensors

Example

Otto Bock C-leg

Prosthetic foot design

passive mechanism: • damping 10 J• energy storing??• No actuation!

Concepts of gait

• Walking is:– preventing to fall– cyclical movement with left/right foot placements in

front of the other supporting body weight

• The purpose of bipedal walking is to maximize the double support time while maintaining the forward velocity.

• Stability is maintained by balancing the trunk through coordinated actions of joints.

Double support phase

Stilt walking

Pelvic tilt: ±35°

Stilt walking + feet

Pelvic tilt: ±15°

Stilt walking + feet + knees

Pelvic tilt: ±0°

Normal walking(feet, knees, ankles, pelvic rotation)

Pelvic tilt: free

Why is d.s. phase important ?

• Largest ground reaction forces

• largest muscle forces• almost all mechanical

work• stable position

slow walking

00,20,40,60,8

11,21,4

0 20 40 60 80 100

time [% stride]

reac

tion

forc

e [-]

right left total

other phases are more or less ballisticMaximize double support time !

Prosthetic / orthotic gait

Walking without knee function would result in…

• Reduced velocity• Reduced double support time• Reduced step length• Increased pelvic tilt

Balancing mechanism

• direct ground reaction force (push against large mass of trunk)

• trunk will rotate (a little)• requires coordinated

joint actions

Balancing mechanism

Trunk movement in walking

Fast walking

Normal walking

Walking with large steps