David P. VanSickle

Performance of selected lightweight wheelchairs on ANSI/RESNA tests

OBJECTIVE This study provides data for clinicians and wheelchair users to compare the durability, stability, and cost effectiveness of three different lightweight wheelchair models: the Everest & Jennings EZ Lite, the Invacare Rolls 2000, and the Quickie Designs Breezy. A second objective was to compare the results from this study to those published for ultralight and institutional depot wheelchairs. DESIGN Randomized standards testing of three wheelchair models from each manufacturer (nine wheelchairs total). RESULTS There were no significant differences (p > .05) in fatigue life, life-cycle cost, or static stability between the three models of lightweight wheelchairs (ie, EZ Lite, Rolls 2000, or Breezy). There were, however, significant differences (p < .05) in fatigue life among the lightweight wheelchairs of this study and the published results for ultralight rehabilitation wheelchairs and for depot wheelchairs. The lightweight wheelchairs had an average fatigue life greater than the depot wheelchairs but less than the rehabilitation wheelchairs. A depot-type wheelchair was defined as a manual wheelchair designed for hospital or institutional use. At lightweight wheelchair was defined as a manual wheelchair with minimal adjustments designed for individual or institutional use. An ultralight rehabilitation wheelchair was defined as a manual wheelchair designed for an individuals use as a long-term mobility aid. CONCLUSION The three models of lightweight wheelchairs tested are substantially similar and their fatigue lives are significantly (p < .05) lower than rehabilitation wheelchairs. Ultralight rehabilitation wheelchairs are the most cost effective over the life of the wheelchair, costing 3.4 times less (dollars per life cycle) than depot wheelchairs, and 2.3 times less (dollars per life cycle) than the lightweight wheelchairs tested in this study.

Road loads acting on manual wheelchairs

A barrier to performing more in-depth analyzes during the wheelchair design process is a lack of dynamic reaction force and moment data, and the instrumentation to collect this data. Instrumentation was developed to collect the dynamic force and moment data. New data collections methodologies and analysis techniques were implemented to facilitate computer-aided-engineering for wheelchair designs. Data were collected during standardized wheelchair fatigue tests, while driving over a simulated road course within a laboratory, and while driving in the community. Seventeen subjects participated in this study. Based upon the three test conditions, a pseudo-statistical distribution of the force and moment data at both a caster and rear wheel was developed. The key parameters describing the distribution and the extremums of the data (minima and maxima) were compared using analysis of variance. The results showed that the force and moment distributions and extreme values were similar for the both sets of human trials (i.e., simulated road course and field trials). However, the standardized testing (i.e., wheelchair fatigue testing) differed from both human trials. The force/moment data gathered during this study are suitable for inputs in finite element analysis and dynamic modeling. Our results suggest that the fatigue tests should be modified to change the magnitude and increase the frequency of the forces and moments imparted on the wheelchair. The data reported from this study can be used to improve wheelchair standards and to facilitate computer-aided-engineer in wheelchair design.

Projection of the point of force application onto a palmar plane of the hand during wheelchair propulsion

The objective of this study was to develop and test a method for projecting the pushrim point of force application (PFA) onto a palmar plane model of the hand. Repetitive wheelchair use often leads to hand and wrist pain or injury. The manner by which the hands grasp the pushrim and how the forces and moments applied to the pushrim are directed may contribute to the high incidence of pain and injury. The projections of the PFA onto the palmar surface model of the hand reside primarily within zone II. These results are in agreement with previous studies which have assumed the PFA to be coincident with one of the metacarpophalangeal (MP) joints. However, the results from three subjects show different PFA patterns within the palmar surface of the hand which can be related to each subjects propulsion pattern, and the PFA is not focused at a single MP joint. Projection of the world coordinates of the four hand marker system onto the palmar plane show the resolution to be within 3 mm, or one half the diameter of the passive reflective markers. The errors in the planar model assumption were greatest for the second and fifth MP markers. This was expected because as the hand grasp changes these markers do not remain coplanar. The results of this study indicate that new knowledge about how forces are applied by the hand onto the pushrim can be obtained using this method. This technical note provides insight into understanding the details within the kinetics of wheelchair propulsion and describes a technique for estimation of the PFA on the palmar surface of the hand. This technical note provides initial results from three different wheelchair users.

A method for analyzing center of pressure during manual wheelchair propulsion

Little published information is available on joint kinetics during wheelchair propulsion. This is partially due to the lack of appropriate instrumentation and techniques. Biomechanical-mechanical techniques may be developed to assist in the amelioration of upper extremity pain among wheelchair users, Elbow, wrist, and hand pain have been reported to exist among 16, 13, and 11% of manual wheelchair users, respectively. This paper focuses on methods for determining the location of the pushrim center of pressure during wheelchair propulsion. Wheelchair propulsion is accomplished by bilateral simultaneous repetitive motion of the upper extremities. The pushrim is grasped or struck and pushed downward and forward, in turn, rotating the wheels. During the propulsive phase, the hand is capable of exerting a three-dimensional moment against the pushrim. The moments and forces exerted on the pushrim were measured by a specialized wheelchair wheel, the SMART/sup wheel/. The center of pressure (COP) for the upper extremities is found in three planes parallel to the frontal, sagittal, and transverse anatomical planes, This calculation of the COP is analogous to the calculation of the COP for lower extremity gait analysis using a force plate. One difference is that the hand has the ability to pull on the pushrim and, therefore, the upper extremity COP does not necessarily reside within the projection of the hand. Another difference is that with a force plate, there is only one plane of interest (the plane of the force plate), and three are used for the complete analysis of the upper extremity. Kinetic data were collected using the SMART/sup Wheel/ from three subjects who are wheelchair users. Kinematic data were also collected concurrently using a PEEKS video analysis system. Graphs of the COP from the sagittal plane show great variability, which is probably due to the low medial-lateral forces exerted against the pushrim. Frontal COP graphs show less variability and indicate that with these three subjects the line of action for the anterior-posterior force component is located between 10 and 15 cm lateral to the pushrim and a variable distance above or below the location of the 2nd metacarpal-phalangeal joint. Future studies with more subjects may show force offset to be a modality in the cause of carpal-tunnel syndrome.

Uncertainty analysis for wheelchair propulsion dynamics

Wheelchair propulsion kinetic measurements require the use of custom pushrim force/moment measuring instruments which are not currently commercially available. With the ability to measure pushrim forces and moments has come the development of several dynamic metrics derived for analyzing key aspects of wheelchair propulsion. This paper presents several of the equations used to calculate or derive the primary variables used in the study of wheelchair propulsion biomechanics. The uncertainties for these variables were derived, and then numerically calculated for a current version of the SMARTWheel. The uncertainty results indicate that the SMARTWheel provides data which has better than 5 to 10% uncertainty, depending upon the variable concerned, at the maximum, and during most of the propulsion phase the uncertainty is considerably smaller (i.e., approximately 1%). The uncertainty analysis provides a more complete picture of the attainable accuracy of the SMARTWheel and of the degree of confidence with which the data can be recorded. The derivations and results indicate where improvements in measurement of wheelchair propulsion biomechanical variables are likely to originate. The most efficient approach is to address those variables in the design of the system which make the greatest contribution to the uncertainty. Future research will focus on the point of force application and examination of nonlinear effects.

A unified method for calculating the center of pressure during wheelchair propulsion

AbstractThe measurement of the center of pressure (COP) has been and continues to be a successful tool for gait analysis. The definition of a similar COP for wheelchair propulsion, however, is not straightforward. Previously, a COP definition similar to that used in force plate analysis had been proposed. Unfortunately, this solution has the disadvantage of requiring a separate COP definition for each plane of analysis. A definition of the generalized center of pressure (GCOP) which is consistent in all planes of analysis is derived here. This definition is based on the placement of a force-moment system, equivalent to the force-moment system at the hub, on a line in space where the moment vector (wrench moment) is parallel to the force vector. The parallel force-moment system is then intersected with three planes defined by anatomical landmarks on the hand. Data were collected using eight subjects at propulsion speeds of 1.34 m/s and 2.24 m/s (1.34 m/s only for subject 1, 0.894 m/s and 1.79 m/s for subject 8). Each subject propelled a wheelchair instrumented with a SMARTWheel. A PEAK 5 video system was used to determine the position of anatomical markers attached to each subject’s upper extremity. The GCOP in the transverse plane of the wrist formed clusters for all subject’s except subject 2 at 1.34 m/s. The clustering of the GCOP indicates that the line of action for the force applied by the hand is approximately perpendicular to the transverse plane through the wrist. When comparing the magnitude of the moment vector part of the wrench with the moment of the force vector of the wrench about the hub, the wrench moment is approximately an order of magnitude smaller. This indicates that the role of the wrist for wheelchair propulsion is primarily to stabilize the force applied by the arm and shoulder.

Determination of wheelchair dynamic load data for use with finite element analysis

A methodology is introduced for the experimental determination of the dynamic loads which act on a wheelchair. A box frame wheelchair and a cantilever frame wheelchair were tested on an ANSI/RESNA curb-drop tester [1]. The accelerations of an ANSI/RESNA test dummy [1] were recorded with an array of 12 accelerometers mounted as four three-axis groups. Signal averaging was used to produce a composite dynamic load history. The dynamic loads were calculated from the acceleration data and the inertia of the test dummy using software written by the authors. These loads were imported into a finite element program (ALGOR) [5], [6] as load cases. A prototype carbon fiber design was then optimized through design and analysis iterations. The results of the acceleration data indicate that the curb-drop test produces an asymmetric loading scheme. One of the rear wheels hits the ground before the other, placing most of the dynamic load on one side of the wheelchair. The favored side appears to be fixed at the time of setup. Preliminary results are given for the design of a modular carbon fiber wheelchair using the finite element (FE) method. These results indicate, however, that the use of a static factor of safety is, in most cases, inadequate for the dynamic loads present in the curb-drop test.

Wheelchair virtual joystick interface

Video games can be used as a motivational tool to promote exercise among individuals with disabilities. The velocity of the wheels of a stationary wheelchair is used as a control interface for video games. This interface is implemented with an entirely digital system. An MC68HC11A1 microcontroller is used to perform quadrature on the input of two optical encoders and dynamically adjust two X9C104P digital potentiometers. The result is a virtual joystick which is controlled by the speed and direction of the wheelchair wheel rotation. This system can be mounted to any personal computer game port and used for virtual reality applications as well as games.

Whole body dampening properties of a wheelchair rider

A model is developed to simulate the whole body dampening properties of a wheelchair rider. This model is based on a 4 pole, 2 zero, transfer function. The order of the model was determined by finding an inflection in the model order verses correlation curves. The model produced correlation between predicted accelerations at the riders head and actual accelerations at the riders head which averaged 0.84. The poles were found to be located in consistent positions within the unit circle. This transfer function can now be used for the purpose of correlating rider comfort with transmitted and absorbed accelerations without the need for mounting accelerometers on the individual and for quantitatively comparing wheelchair designs.<<ETX>>

SMART/sup HUB/ and SMART/sup CASTOR/: force and moment sensing wheelchair wheels

The SMART/sup HUB/ and SMART/sup CASTOR/ are two new strain-gage based sensors designed to measure the reaction forces and moments at the rear axle and castor spindle, respectively. Both are five degree-of-freedom sensors, which measure all three force components and the two moment components perpendicular to the axes of rotation. These sensors will be used to improve wheelchair designs by allowing advanced engineering techniques such as finite element analysis to be applied with greater confidence. Both sensors are highly linear. When calibrated the lowest correlation coefficient was 0.9965 (N=21) and the cross-axes sensitivity was always less than 5%. Preliminary data are presented for two wheelchair users propelling over an indoor course and a non-wheelchair user traversing an outdoor course. The indoor data was transferred from a microcontroller-based signal conditioning board to a host PC through a high-speed serial port. For the outdoor data, the microcontroller was programmed to sample the data and to generate a histogram of force and moment frequencies, which was subsequently downloaded.