Docstoc

User Centered Design of a Wheelc

Document Sample
User Centered Design of a Wheelc Powered By Docstoc
					               User Centered Design of a Wheelchair-Anchored Safety Restraint
                        Linda van Roosmalen PhD and Jason Sellers BS
                     Department of Rehabilitation Science and Technology
                         University of Pittsburgh, Pittsburgh, PA, USA
ABSTRACT
   Wheelchair users with limited upper extremity function have difficulty in using belt and buckle
type safety restraints when they ride motor vehicles while seated in their wheelchairs. A
wheelchair-anchored pelvic-belt restraint with a user-friendly buckle mechanism was designed to
enable independent occupant restraint use by individuals with reduced upper extremity function.
Design criteria included usability and robustness during daily use as well as compliance with
ANSI/RESNA WC19 (WC19). An early prototype of the design was mounted onto a manual
wheelchair and evaluated by individuals with limited upper extremity function. The final design
was optimized based on user input and a solid model of the design was evaluated using Finite
Element Analysis (FEA).
Key words: wheelchair, transportation, restraint, safety, usability, independence, buckle


BACKGROUND
    Wheelchair users often use their wheelchairs as motor vehicle seats when riding as a passenger
or driver in a motor vehicle. The use of wheelchair tiedowns and occupant restraint systems
(WTORS) provide wheelchair occupants with crash protection during motor vehicle travel.
Wheelchair tiedowns limit wheelchair movement and upper torso and pelvic safety restraints
prevent wheelchair occupants from sliding forward from their wheelchairs and/or being ejected
from their wheelchair seat.
    A study conducted by Van Roosmalen, et al. shows that wheelchair-anchored occupant
restraints are a feasible solution to improve wheelchair transportation safety, and suggests that
further development of wheelchair-anchored pelvic belts in conjunction with improved belt fit and
usage would be beneficial to the safety and independence of wheelchair users [1]. Attaching the
pelvic-belt portion of the occupant restraint system to the wheelchair is the first step to improved
independence and safety of individuals riding in vehicles. However, results from a study conducted
among wheelchair users indicate that typical buckle and latch plate-style belt restraints are difficult
to use independently by individuals with limited upper extremity function [2] (Figure 1).
    This study proposes a solution to the (user) problems that exist with buckle mechanisms on
occupant restraints. In addition a pelvic safety restraint design is proposed to connect with a vehicle
anchored shoulder belt, to provide optimal belt fit and comfort to potential users and to not cause
user injury during a motor vehicle incident or accident.




Figure 1: Photo of typical automotive seatbelt buckle, with push-button receptacle and latch plate.
STUDY AIMS
    The aim of this study is to design and evaluate a wheelchair-anchored pelvic belt for use by
wheelchair users with limited upper-extremity function. The pelvic belt should also provide for
attachment of an upper torso belt by means of a standard pin connector to comprise a three-point
belt restraint system. It should also be designed so as to not interfere with the wheelchair user’s
activities of daily living (e.g. transfers, postural support use, reaching) and must be cost effective
and aesthetically pleasing to potential users.
DESIGN METHOD
    Results from a usability study formed the basis for the design of the improved pelvic-belt
restraint [2]. Suggestions to improve pelvic belt usability of existing buckle and latch-plate
included the following:
    - Place buckle within reach
    - Place latch plate within reach
    - Fixate buckle receptacle during connecting
    - Make it easier to release latch plate from buckle receptacle
    - Reduce release spring force on buckle
    - Make it easier to connect latch plate with buckle
    - Make latch-plate grabbing and belt tensioning easier
    - Integrate pelvic belt with postural support system
    - Provide ability to snug the belt
    - Have less tension on belt when performing belt-donning
    Several pelvic belt restraint ideas were generated and the most promising was built into a test
prototype and evaluated by potential wheelchair users with a range of upper-extremity limitations
(Figure 2). Individuals were asked to buckle up and release the prototype pelvic belt several times.
Based on this preliminary user study several design changes were made to the pelvic restraint
components to improve its usability.




       Grasp hook                 Rotary buckle

                       Latch plate            Stiff mount
Figure 2: First prototype of the rotary buckle mechanism with latch plate.
    An improved pelvic restraint concept was developed using Solid Works. FEA using COSMOS
was used to evaluate the strength of various key components during impact loading. A load of 3000
lbs was used for the FEA and represents the load that can act onto a wheelchair-anchored pelvic
belt and vehicle-anchored upper-torso belt during a 20-g/30-mph sled impact with a manual
wheelchair occupied by a 50th percentile Hybrid III Anthropomorphic Test Device [3].


DESIGN SOLUTION
    Figure 3 shows the assembly of the improved pelvic restraint when attached to the rear
securement points on a manual wheelchair. The rear securement points were slightly modified and
re-evaluated for their use as pelvic-belt anchor points. The wheelchair and use of a wheelchair-
anchored pelvic belt was previously evaluated during a 20-g/30-mph sled impact test.
    Wheelchair occupants strive for independence, and a restraint device that is simple to operate,
preferably with one hand, is a must. This means that the restraint must be able to be buckled and
unbuckled with one hand using minimal effort. The push-button mechanism present on common
buckle designs can only be activated by fingers or knuckles. A rotational buckle mechanism gives
the user the choice to disengage with the use of the fingers, the palm of the hand, or even the distal
forearm. The rotary buckle knob has rather smooth and rounded edges so that clothing or other
items cannot hook onto the buckle and inadvertently open it. However, it does have three edges to
allow a hand to create enough moment to release the buckle (Figure 4).




Figure 3: Drawing of prototype pelvic restraint assembly attached to the securement point of a
WC19-compliant manual wheelchair.
Figure 4: Rotary buckle with several funneled slots to allow for latch plate misalignment.


     Subjects had difficulty aiming the latch plate into the buckle slot. Funneled slots in the rotary
buckle design make it easier to connect and release the latch plate by allowing the latch plate to
enter and exit under different angles (Figure 4). Individuals from the user study also had difficulty
grasping and holding a flat metal latch plate. They often used the little latch hole of the plate to pull
with one finger. However, this hole is fairly narrow and sharp at the edges and is not always present
on latch plates. Therefore, to make the latch plate easier to reach, grab, and hold onto, a flexible
grasp hook was designed to fit over the latch plate (Figure 5). This way, the user can grab, pull, and
guide the latch plate into the rotary buckle. The latch plate is attached to webbing which is housed
in a wheelchair-mounted retractor that provides automatic adjustability of the pelvic belt. To make
it easy for individuals who have use of only one hand to connect the latch plate with the buckle,
the buckle mechanism is fixed onto a stiff curved rod that goes around the user’s abdomen. The
length of the rod can easily be altered by a caregiver to adjust the buckle properly for each adult
wheelchair user (Figure 6). The adjuster attaches with a bolt connection to the rear securement
points of the wheelchair.




Figure 5: Grab hook that slides over latch plate attached to belt webbing.
Figure 6: Drawing of buckle adjuster mechanism attached to the wheelchair’s rear securement
point.

    When the rotary buckle, the mount, and adjuster components were quasi-statically loaded to
3000 lb (1500 lb times a with safety factor of 2.0), COSMOS results indicate that the material
stresses stayed below the yield strength, and system components showed no points of failure or
excessive deformation during loading (see Figure 7).




Figure 7: FEA results for the adjuster (Al7176) and the rotary buckle and latch component when
loaded at 3000 lb.


CONCLUSIONS AND FUTURE STEPS
    An easy-to-use rotary-style pelvic belt restraint system was designed to attach to the securement
points of a crashworthy manual wheelchair frame. Early user evaluations show that a rotary buckle
is easier to connect and release independently than a push-style buckle, and a hook on the latch
plate side of the seat belt can assist users during the latching process. FEA results of the pelvic
restraint show that it can withstand the loading up to 3000 lb. Future considerations include a user
study to evaluate the torque required to release the rotary buckle and to look at overall product
usability and comfort during normal use of the device. The prototype pelvic belt restraint design
needs to be evaluated under dynamic loading conditions. Since this restraint was designed to attach
to the rear securement points of a wheelchair, it can easily be placed on other type wheelchairs that
comply with WC19.
    The study focus was only on the pelvic belt of the occupant restraint system. However, to
safely restrain a wheelchair occupant during transportation in motor vehicles, a vehicle-anchored
shoulder belt needs to be used and connected (currently by pin-bushing) to the pelvic belt near the
hip of the user. The ease of use and safety of the standard pin-bushing connector on the pelvic
restraint design needs further investigation.

REFERENCES
1. Van Roosmalen, L., Bertocci, G. E., Ha, D. and Karg, P. (2002). Wheelchair integrated occupant
restraints: feasibility in frontal impact. Medical Engineering & Physics 23(10): 685-698.
2. Van Roosmalen, L., Reed, M., Bertocci, G. E. Pilot Study of Safety Belt Usability For Vehicle
Occupants Seated In Wheelchairs. Assistive Technology Journal 17(1), 2006.
3. American National Standards Institute (ANSI)/Rehabilitation Engineering Society of North
America (RESNA), (1998). WC/Vol. 1-Section 19: Wheelchairs used as seats in motor vehicles.
ANSI/RESNA.


ACKNOWLEDGEMENTS
    This project was funded by the Rehabilitation Engineering Research Center on Wheelchair
Transportation Safety, Grant #H133E010302 from the National Institute on Disability and
Rehabilitation Research, U.S. Department of Education. We thank IMMI (J. Chinni) and the VA-
HERL (J. Puhlman) for their assistance with prototyping and Sunrise Medical for donating a
manual wheelchair. Opinions are those of the authors only and do not necessarily reflect those of
the funding agency.

Linda van Roosmalen, University of Pittsburgh, Department of Rehabilitation Science and
Technology, Suite 1311, 2310 Jane St, Pittsburgh, PA 15203, 412-586-6911, Lvanroos@pitt.edu

				
DOCUMENT INFO