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George W. Woodruff School of Mechanical Engineering
George W. Woodruff School of Mechanical Engineering
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ItemMechanical performance characterization of manual wheelchairs using robotic wheelchair operator with intermittent torque-based propulsion(Georgia Institute of Technology, 2020-12-06) Misch, Jacob P.The current manual wheelchair design process lacks consistent and objective connection to performance-based metrics. The goal of this research was to empirically assess over-ground manual wheelchair performances and identify important design trade-offs through the use of a robotic apparatus with a novel cyclic propulsion control method. This research had four specific aims: 1) to design, implement, and validate torque-based propulsion to emulate the intermittent human propulsion cycle with an existing robotic wheelchair tester, 2) to investigate the influence of incremental mass additions to the wheelchair frame on over-ground propulsion characteristics, 3) to demonstrably improve the performance of a representative high-strength lightweight wheelchair by leveraging existing component-level test results, and 4) to characterize the mechanical performances of representative folding and rigid ultra-lightweight wheelchair frames. The outcomes of this research include an objective, repeatable, and validated test method to assess over-ground performances of manual wheelchairs in realistic contexts of use, as well as insight on the mechanics of the system that were previously under-studied or confounded by variabilities within human subject testing. Controlled propulsion tests are used to identify differences between wheelchair configurations. The outcome variable of propulsion cost represents the energetic requirements of propelling each chair a given distance and has direct relevance to manufacturers, clinicians, and wheelchair users alike. Ultimately, these outcomes will inform clinicians and manufacturers about how configuration choices influence propulsive efforts, which can be used in turn to improve their classification techniques and existing design processes. This knowledge will additionally empower wheelchair users to make informed choices during the wheelchair selection process based on objective mechanical performance metrics.
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ItemDevelopment of component and system level test methods to characterize manual wheelchair propulsion cost(Georgia Institute of Technology, 2017-11-10) Huang, MorrisThe current approach to manual wheelchair design lacks a sound and objective connection to metrics for wheelchair performance. The objective of this research was three-fold: 1) to characterize the inertial and resistive properties of different wheelchair components and configurations, 2) to characterize the systems-level wheelchair propulsion cost, and 3) to model wheelchair propulsion cost as a function of measured component and configuration properties. Scientific tools developed include 1) a series of instruments and methodologies to evaluate the rotational inertia, rolling resistance, and scrub torque of wheelchair casters and drive wheels on various surface types, and 2) a wheelchair-propelling robot capable of measuring propulsion cost across a collection of maneuvers representative of everyday wheelchair mobility. This suite of tools were used to demonstrate the variance manifested in the resistive properties of 8 casters and 4 drive wheels, and the impact/tradeoffs of these components (as well as mass and weight distribution) on system-level wheelchair propulsion cost. Coupling these findings with a theoretical framework describing wheelchair dynamics resulted in two empirical models linking system propulsion cost to component resistive properties. The outcomes of this research empower clinicians and users to make more informed wheelchair selections, as well as offer manufacturers a basis by which to optimize their wheelchair designs.
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ItemDesign and analysis of an inertial properties measurement device for manual wheelchairs(Georgia Institute of Technology, 2010-07-07) Eicholtz, Matthew R.The dynamics of rigid body motion are dependent on the inertial properties of the body - that is, the mass and moment of inertia. For complex systems, it may be necessary to derive these results empirically. Such is the case for manual wheelchairs, which can be modeled as a rigid body frame connected to four wheels. While 3D modeling software is capable of estimating inertial parameters, modeling inaccuracies and ill-defined material properties may introduce significant errors in this estimation technique and necessitate experimental measurements. To that end, this thesis discusses the design of a device called the iMachine that empirically determines the mass, location of the center of mass, and moment of inertia about the vertical (yaw) axis passing through the center of mass of the wheelchair. The iMachine is a spring-loaded rotating platform that freely oscillates about an axis passing through its center due to an initial angular velocity. The mass and location of the center of mass can be determined using a static analysis of a triangular configuration of load cells. An optical encoder records the dynamic angular displacement of the platform, and the natural frequency of free vibration is calculated using several techniques. Finally, the moment of inertia is determined from the natural frequency of the system. In this thesis, test results are presented for the calibration of the load cells and spring rate. In addition, objects with known mass properties were tested and comparisons are made between the analytical and empirical inertia results. In general, the mass measurement of the test object had greater than 99% accuracy. The average relative error for the x and y-coordinates of the center of mass was 0.891% and 1.99%, respectively. For the moment of inertia, a relationship was established between relative error and the ratio of the test object inertia to the inertia of the system. The results suggest that 95% accuracy can be achieved if the test object accounts for at least 25% of the total inertia of the system. Finally, the moment of inertia of a manual wheelchair is determined using the device (I = 1.213 kg-m²), and conclusions are made regarding the reliability and validity of results. The results of this project will feed into energy calculations for the Anatomical Model Propulsion System (AMPS), a wheelchair-propelling robot used to measure the mechanical efficiency of manual wheelchairs.
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ItemTweel (TM) technology tires for wheelchairs and instrumentation for measuring everyday wheeled mobility(Georgia Institute of Technology, 2007-04-04) Meruani, AzeemThis thesis is focused on two aspects related to wheeled mobility: 1) Evaluating the impact of a new tire design on powered mobility, and 2) Instrumentation that permits better monitoring and assessment of wheeled mobility in everyday use. The Tweel technology tires developed by Michelin USA are comprised of an outer polyurethane ring supported by polyurethane fins instead of metal spokes, which allow the tire to deflect under pressure. As a wheelchair tire they offer a potential breakthrough as they have deflection properties similar to a pneumatic tire while maintaining the low maintenance of a solid foam-core tire. A study was conducted to compare the Tweel technology tires to standard solid foam-core tires for vibration transmission, traction and overall life span. The Tweel technology tires failed produce any significant difference in vibration transmitted to the user compared to solid foam-core tires. Additionally, the Tweel technology tires showed significant signs of deterioration after a month long field trial, thus indicating a short life span. However, Tweel technology tires provided better traction on both dry and wet concrete. Overall, Tweel technology tires have to be re-engineered to provide better damping properties, leading to lower vibrational levels transmitted to the user. The second section this thesis addressed the need to develop a methodology of measuring mobility in everyday usage. This section is part of a greater ongoing research project at CATEA (Center for Assistive Technology and Environmental Access) aimed at understanding everyday wheelchair usage. Methodology was developed to measure bouts of mobility that characterize wheelchair usage; which includes the number of starts, stops, turns and distance traveled through the day. Three different technologies which included, Accelerometer unit on the rim of the drive wheel, Gyro-Accelerometer unit on the frame of the chair and Reed switches, were tested. Testing included various criteria for accuracy, durability and compatibility for measuring bouts of everyday wheeled mobility. Although a single technology could not be used to measure all aspects of mobility, the Accelerometer unit on the rim met the design criteria for measuring starts stops and distance, while the Gyro-Accelerometer unit met the requirements for measuring turns.
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ItemDesign of Wheelchair Seating Systems for Users with High-Tone Extensor Thrust(Georgia Institute of Technology, 2006-05-22) Kitchen, James PatrickHigh-tone extensor thrust is common to those with cerebral palsy and those suffering spinal cord injuries. It is a muscle-control phenomenon that causes the body to straighten spastically. One goal of this thesis is to design a dynamic seating system that moves with respect to the wheelchair frame, allowing the seat to move with the user during an extensor thrust and reduce forces. One unique challenge is that the seat needs to remain rigid during normal functional activities and only become dynamic when an involuntary thrust is detected. A second goal of this thesis is to design a control scheme that is able to differentiate between these two types of motion. These design goals are initially investigated with a hinged-seatback system, instrumented with sensors to allow for the detection of thrusts and to actively control seating components. A full seating system is then built to allow for full-body extensor thrusts, involving the seatback, seat bottom, and leg rest of the wheelchair. This system is analyzed for effectiveness of reducing forces on the body during an extensor thrust. Another serious problem for this segment of the population is pressure ulcers. These are caused by prolonged pressure on the skin from weight-bearing bony prominences. Various seating system configurations are known to help with pressure relief. The three standard configurations for a chair are tilt, recline, and standing. The final goal of this thesis is to measure and compare the effectiveness of these three methods for their ability to relieve pressure on the seat bottom. To accomplish this, a powered wheelchair with built-in capabilities for recline and standing is mounted to a tilting mechanism. Test subjects are used to experimentally compare the effectiveness of each method for pressure reduction using pressure mats on all weight-bearing surfaces. A 2D model is also developed and validated with the experimental results.