EVALUATION OF JOINT LOADS
IN PUSHING / PULLING
ATTENDANT-PROPELLED WHEELCHAIRS
DURING FORWARD WALKING ON
UPWARD AND DOWNWARD SLOPES
Tatsuto Suzuki, Maizuru National College of Technology, Japan
Hironobu Uchiyama, Kansai University, Japan
Catherine Holloway, University College London, UK
Nick Tyler, University College London, UK
Background
The pushing and pulling cart are
well met tasks in daily life.
Typical pushing and pulling wheel carts
- Attendant propelled wheelchair (80kg)
- Shopping cart (30kg)
- Baby pushchair (25kg)
- Medical stretcher (140kg)
- Trolley aboard aircraft (85kg)
- Industrial cart (up to 400kg)
Workload factors
Provided capability
by person
Attendant
- Push/pull performance
- Age
- Gender
Required capability
by wheelchair and environments
Wheelchair
- Weight
- Rolling resistance
- Dimensions
Environment
- longitudinal and cross slopes
- Kerbs
- Gaps
- Roughness of road surfaces
Problems
1. Pushing/pulling is very hard task
2. Pushing/pulling is a known risk factor
for musculoskeletal disorders
(Back pain, joint strain, sprains)
3. Cause of musculoskeletal disorders
- Peak and cumulative forces
- duration and repetition,
- Continuous tense non-neutral posture
Objectives
1. How hard are pushing/pulling tasks?
-> How large is the required capability in power?
2. How to adapt push/pull style against the
increase of load?
-> How to change push/pull posture?
3. How hard are shoulder and elbow?
-> How large are the joint torque in shoulder
and elbow?
Methodology
1. Change slope angles
Longitudinal slope angle:+00, +6.5%, +9%, and 12%
2. Change the weight of a wheelchair
Wheelchair weight: 36Kg + 00, 20, 40, and 60kg
3. Subjects
Ablebodied five patiripants
Average age: 33years old
Longitudinal slopes
UCL Pamela platform
- Each plate size: 1200 x 1200mm
- Maximum height difference: 300mm
- Slope conditions: 0%, 6.5%, 9.0%, 12%
12%
0%
9.0%
6.5%
Attendant propelled wheelchair
Force measurement:
6-axis load cell at both grips
Velocity measurement:
Rotary encoder at both wheels
Main specifications
Wheelchair weight: 36kg
Grip height: 0.95m
Additional weight:
+00, +20, +40, +60kg
Joint position measurement
Two dimensional measurement
- One camera and reflective markers
- Marker tracking software
Joint torque calculation
Figure 1 (a) Experimental system with seven link model to analyse joint torques.
(b) Each link difinition in multibody dynamics
Joint torque calculation
M iq˙˙i - Fqi li = gi
System mass matrix: Mi = diag [mi, mi, μi ]
System state vector: qi = [xi, yi, ϕi ]
External force vector: gi = [gexi, geyi - mig, geni ]
Jacobian matrix:
Φqi = [1 0; 0 1; -(yPa-yi) (xPa - xi ) ]
Reaction force vector by constraint: λi = [λxi, λyi ]
The external force vector gi was described next equation.
gexi = fxi - λx(i-1)
geyi = fyi - λy(i-1)
(2)
geni = τa – τb + (rPb - ri ) x [gxi, gyi ]T
where, the subscript i of each variables is link number.
Change of push/pull force and velocity
Figure 2 Averaged propelling forces and wheelchair velocities in ascending and
descending under four weight and slope conditions.
Change of push/pull force and velocity
Heavy load
Light load
Heavy load
Figure 2 Averaged propelling forces and wheelchair velocities in ascending and
descending under four weight and slope conditions.
Push/pull power
Push/pull power
Heavy load
Light load
Heavy load
Posture in push/pull
(a)
(b)
(c)
Figure 3 The difference of propelling postures during stance phase.(participant
one) (a) Propelling at a level. (b) Ascend propelling at +9.0%. (c) Descent propelling
at -9.0%. Each first frame is the beginning of the stance phase, and last frame is the
end of the phase. The time interval between two frames is 25% of the phase. All
weight conditions are W = 60kg.
Posture in push/pull
Lean forward
Light push
(a)
Lean Backward
Heavy push
Heavy pull
(b)
(c)
Figure 3 The difference of propelling postures during stance phase.(participant
one) (a) Propelling at a level. (b) Ascend propelling at +9.0%. (c) Descent propelling
at -9.0%. Each first frame is the beginning of the stance phase, and last frame is the
end of the phase. The time interval between two frames is 25% of the phase. All
weight conditions are W = 60kg.
Joint angle in shoulder and elbow
Figure 4 Averaged shoulder and elbow angle during stance phase. The joint angles
were measured based on the medical definition.
Joint angle in shoulder and elbow
Extension
with the increase of load
Flexion
with the increase of load
Figure 4 Averaged shoulder and elbow angle during stance phase. The joint angles
were measured based on the medical definition.
Joint torque in shoulder and elbow
Figure 5 Averaged shoulder and elbow torque during stance phase. The
calculation was carried out with the model in Figure 1.
Joint torque in shoulder and elbow
Push: Shoulder torque increased
Push: Low shoulder torque
Large pull torque
Elbow torque increased
Figure 5 Averaged shoulder and elbow torque during stance phase. The
calculation was carried out with the model in Figure 1.
Discussions
1. Maximum workload at push/pull
around 60W
- The same as electric bulbs!
- Over 60W in required capability is quite hard
to push/pull
Discussions
2. Posture Change with the increase of load
- lean forward (Push)
- lean backward (Pull)
- Need to keep balance to apply push/pull force
3. Joint torque in shoulder and elbow
- Shoulder in push is harder than in pull
- Elbow in pull is harder than in push
- Elbow in pull on 12% slope is quite hard
Future works
1. Calculate joint power
2. Assisting system for attendants!