Publications by authors named "Thomas Sugar"

16 Publications

  • Page 1 of 1

Design, Development, and Control of a Fabric-Based Soft Ankle Module to Mimic Human Ankle Stiffness.

IEEE Int Conf Rehabil Robot 2019 06;2019:886-891

This paper investigates the design of a robotic fabric-based, soft ankle module capable of generating 50% of the human ankle stiffness, in plantarflexion and dorsiflexion for walking. Kinematics, dynamics, and anatomy of the human ankle joint are studied to set the functional requirements of the module. The design of the compliant and lightweight soft ankle module uses fabric-based inflatable actuator arrays for actuation. Models for the human ankle stiffness, as well as a data-driven model of soft ankle module is presented. A high-level stiffness controller utilizing the human ankle and soft ankle model with a low-level pressure controller is implemented. We demonstrate the ability to closely follow the ankle stiffness trajectory using soft ankle module.
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http://dx.doi.org/10.1109/ICORR.2019.8779495DOI Listing
June 2019

Anticipatory muscle responses in transitions from rigid to compliant surfaces: towards smart ankle-foot prostheses.

IEEE Int Conf Rehabil Robot 2019 06;2019:880-885

Locomotion is paramount in enabling human beings to effectively respond in space and time to meet different needs. There are 2 million Americans living with an amputation and the majority of those amputations are of the lower limbs. Although current powered prostheses can accommodate walking, and in some cases running, basic functions like hiking or walking on various non-rigid or dynamic terrains are requirements that have yet to be met. This paper focuses on the mechanisms involved during human locomotion, while transitioning from rigid to compliant surfaces such as from pavement to sand, grass or granular media. Utilizing a unique tool, the Variable Stiffness Treadmill (VST), as the platform for human locomotion, rigid to compliant surface transitions are simulated. The analysis of muscular activation during the transition from rigid to compliant surfaces reveals specific anticipatory muscle activation that precedes stepping on the compliant surface. These results are novel and important since the evoked activation changes can be used for altering the powered prosthesis control parameters to adapt to the new surface, and therefore result in significantly increased robustness for smart powered lower limb prostheses.
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http://dx.doi.org/10.1109/ICORR.2019.8779403DOI Listing
June 2019

A powered prosthetic ankle joint for walking and running.

Biomed Eng Online 2016 Dec 19;15(Suppl 3):141. Epub 2016 Dec 19.

Lauflabor Locomotion Laboratory, Institute of Sports Science, TU Darmstadt, Magdalenenstraße 27, 64289, Darmstadt, Germany.

Background: Current prosthetic ankle joints are designed either for walking or for running. In order to mimic the capabilities of an able-bodied, a powered prosthetic ankle for walking and running was designed. A powered system has the potential to reduce the limitations in range of motion and positive work output of passive walking and running feet.

Methods: To perform the experiments a controller capable of transitions between standing, walking, and running with speed adaptations was developed. In the first case study the system was mounted on an ankle bypass in parallel with the foot of a non-amputee subject. By this method the functionality of hardware and controller was proven.

Results: The Walk-Run ankle was capable of mimicking desired torque and angle trajectories in walking and running up to 2.6 m/s. At 4 m/s running, ankle angle could be matched while ankle torque could not. Limited ankle output power resulting from a suboptimal spring stiffness value was identified as a main reason.

Conclusions: Further studies have to show to what extent the findings can be transferred to amputees.
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http://dx.doi.org/10.1186/s12938-016-0286-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5249039PMC
December 2016

Optical angular constancy is maintained as a navigational control strategy when pursuing robots moving along complex pathways.

J Vis 2015 Mar 24;15(3). Epub 2015 Mar 24.

The Polytechnic School, Ira A. Fulton Schools of Engineering, Arizona State University, Mesa, AZ, USA.

The optical navigational control strategy used to intercept moving targets was explored using a real-world object that travels along complex, evasive pathways. Fielders ran across a gymnasium attempting to catch a moving robot that varied in speed and direction, while ongoing position was measured using an infrared motion-capture system. Fielder running paths were compared with the predictions of three lateral control models, each based on maintaining a particular optical angle relative to the robotic target: (a) constant alignment angle (CAA), (b) constant eccentricity angle (CEA), and (c) linear optical trajectory (LOT). Findings reveal that running pathways were most consistent with maintenance of LOT and least consistent with CEA. This supports that fielders use the same optical control strategy of maintaining angular constancy using a LOT when navigating toward targets moving along complex pathways as when intercepting simple ballistic trajectories. In those cases in which a target dramatically deviates from its optical path, fielders appear to simply reset LOT parameters using a new constant angle value. Maintenance of such optical angular constancy has now been shown to work well with ballistic, complex, and evasive moving targets, confirming the LOT strategy as a robust, general-purpose optical control mechanism for navigating to intercept catchable targets, both airborne and ground based.
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http://dx.doi.org/10.1167/15.3.16DOI Listing
March 2015

Navigational strategy used to intercept fly balls under real-world conditions with moving visual background fields.

Atten Percept Psychophys 2015 Feb;77(2):613-25

Department of Psychology and Institute for Mind and Biology, The University of Chicago, Chicago, IL, USA,

This study explored the navigational strategy used to intercept fly balls in a real-world environment under conditions with moving visual background fields. Fielders ran across a gymnasium attempting to catch fly balls that varied in distance and direction. During each trial, the launched balls traveled in front of a moving background texture that was projected onto an entire wall of a gymnasium. The background texture consisted of a field of random dots that moved together, at a constant speed and direction that varied between trials. The fielder route deviation was defined as the signed area swept out between the actual running path and a straight-line path to the destination, and these route deviation values were compared as a function of the background motion conditions. The findings confirmed that the moving visual background fields systematically altered the fielder running paths, which curved more forward and then to the side when the background gradient moved laterally with the ball, and curved more to the side and then forward when the background gradient moved opposite the ball. Fielder running paths deviated systematically, in a manner consistent with the use of a geometric optical control strategy that helps guide real-world perception-action tasks of interception, such as catching balls.
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http://dx.doi.org/10.3758/s13414-014-0797-xDOI Listing
February 2015

Gaze anticipation during human locomotion.

Exp Brain Res 2012 Nov 12;223(1):65-78. Epub 2012 Sep 12.

LPPA, UMR7152, CNRS-Collège de France, 11, Place Marcelin Berthelot, 75005, Paris, France.

During locomotion, a top-down organization has been previously demonstrated with the head as a stabilized platform and gaze anticipating the horizontal direction of the trajectory. However, the quantitative assessment of the anticipatory sequence from gaze to trajectory and body segments has not been documented. The present paper provides a detailed investigation into the spatial and temporal anticipatory relationships among the direction of gaze and body segments during locomotion. Participants had to walk along several mentally simulated complex trajectories, without any visual cues indicating the trajectory to follow. The trajectory shapes were presented to the participants on a sheet of paper. Our study includes an analysis of the relationships between horizontal gaze anticipatory behavior direction and the upcoming changes in the trajectory. Our findings confirm the following: 1) The hierarchical ordered organization of gaze and body segment orientations during complex trajectories and free locomotion. Gaze direction anticipates the head orientation, and head orientation anticipates reorientation of the other body segments. 2) The influence of the curvature of the trajectory and constraints of the tasks on the temporal and spatial relationships between gaze and the body segments: Increased curvature resulted in increased time and spatial anticipation. 3) A different sequence of gaze movements at inflection points where gaze plans a much later segment of the trajectory.
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http://dx.doi.org/10.1007/s00221-012-3241-2DOI Listing
November 2012

Stroke Survivors' Gait Adaptations to a Powered Ankle Foot Orthosis.

Adv Robot 2011 Jan;25(15):1879-1901

Washington University; Saint Louis, Missouri 63130.

Background And Purpose: Stroke is the leading cause of long term disability in the United States, and for many it causes loss of gait function. The purpose of this research is to examine stroke survivors' gait adaptations to training on the Powered Ankle Foot Orthosis (PAFO). Of particular interest is the stroke survivors' ability to learn how to store and release energy properly while using the device. The PAFO utilizes robotic tendon technology and supports motion with a single degree of freedom, ankle rotation in the sagittal plane. This actuator comprises a motor and series spring. The user interacts with the output side of the spring while the robot controls the input side of the spring such that typical able body ankle moments would be generated, assuming able body ankle kinematics are seen at the output side of the spring.

Methods: Three individuals post-stroke participated in a three week training protocol. Outcome measures (temporal, kinematic, and kinetic) were derived from robot sensors and recorded for every step. These data are used to evaluate each stroke survivor's adaptations to robotic gait assistance. The robot was worn only on the paretic ankle. For validation of the kinematic results, motion capture data were collected on the third subject.

Results: All subjects showed increased cadence, ankle range of motion, and power generation capabilities. Additionally, all subjects were able to achieve a larger power output than power input from the robot. Motion capture data collected from subject three validated the robot sensor kinematic data on the affected side, but also demonstrated an unexpected gait adaptation on the unaffected ankle.

Conclusions: Sensors on the gait assisting robot provide large volumes of valuable information on how gait parameters change over time. We have developed key gait evaluation metrics based on the available robot sensor information that may be useful to future researchers. All subjects adapted their gait to the robotic assistance, and many of their key metrics moved closer to typical able body values. This suggests that each subject learned to utilize the assistive moments generated by the robot, despite having no predefined ankle trajectory input from the robot. The security of being harnessed on the treadmill led to more dramatic and favorable results.
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http://dx.doi.org/10.1163/016918611X588907DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4203663PMC
January 2011

Evidence for axis-aligned motion bias: football axis-trajectory misalignment causes systematic error in projected final destinations of thrown American footballs.

Perception 2009 ;38(3):399-410

Department of Psychology, Arizona State University, Tempe, AZ 85287-1104, USA.

The axis-aligned motion (AAM) bias is the tendency of observers to assume that symmetric moving objects maintain axis-trajectory alignment and to bias their judgments of trajectory toward the axis when they are misaligned. We tested whether humans exhibit an AAM bias in a realistic, cue-rich, 3-D setting by examining the impact of axis-trajectory misalignment on estimates of final destinations of thrown American footballs. In experiments 1 and 2 we show that observers are significantly worse in judging destinations of footballs than those of volleyballs and basketballs. This difference in performance is due to the deviation of the football's axis from trajectory in flight, as shown by the correspondence of participants' lateral judgment error and the football's lateral axial deviation from trajectory, which was predicted by passer handedness. Nearly all animals exhibit bilateral symmetry and maintain axis-trajectory alignment during locomotion, and we argue that the AAM bias is complementary mental attunement to the natural regularity of this axis-aligned motion. Furthermore, this bias is also a prototypical example of a perceptual regularity that is a mixed blessing-advantageous in perceptual judgment tasks of axis trajectory-aligned moving entities like most living creatures, and disadvantageous in tasks demanding judgments of axis-trajectory-misaligned moving objects which are typically artifacts.
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http://dx.doi.org/10.1068/p6114DOI Listing
January 2010

Evidence for a generic interceptive strategy.

Percept Psychophys 2008 Jan;70(1):145-57

Department of Psychology, Ohio State University, Mansfield, Ohio 44906, USA.

In the present work, we first clarify a more precise definition of instantaneous optical angles in control tasks such as interception. We then test how well two interceptive strategies that have been proposed for catching fly balls account for human Frisbee-catching behavior. The first strategy is to maintain the ball's image along a linear optical trajectory (LOT). The second is to keep vertical optical ball velocity decreasing while maintaining constant lateral optical velocity. We found that an LOT accounted for an average of over 96% of the variance in optical Frisbee movement, while maintenance of vertical and lateral optical velocities was random. This work confirms a common interception strategy used across interceptive tasks, extending to complex target trajectories.
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http://dx.doi.org/10.3758/pp.70.1.145DOI Listing
January 2008

Robotic modeling of mobile ball-catching as a tool for understanding biological interceptive behavior.

Behav Brain Sci 2001 Dec;24(6):1078-1080

Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85287 http://www.eas.asu.edu/~tsugar.

We support Webb's insights into the potential benefits of using robotic modeling to better understand biological behavior. We defend the major points put forward by Webb by presenting a specific case study in which robotic modeling of mobile ball catching has helped refine and clarify aspects of our understanding of biological interceptive behavior.
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http://dx.doi.org/10.1017/S0140525X01530125DOI Listing
December 2001

Design and control of RUPERT: a device for robotic upper extremity repetitive therapy.

IEEE Trans Neural Syst Rehabil Eng 2007 Sep;15(3):336-46

Department of Engineering, Arizona State University, Mesa, AZ 85287, USA.

The structural design, control system, and integrated biofeedback for a wearable exoskeletal robot for upper extremity stroke rehabilitation are presented. Assisted with clinical evaluation, designers, engineers, and scientists have built a device for robotic assisted upper extremity repetitive therapy (RUPERT). Intense, repetitive physical rehabilitation has been shown to be beneficial overcoming upper extremity deficits, but the therapy is labor intensive and expensive and difficult to evaluate quantitatively and objectively. The RUPERT is developed to provide a low cost, safe and easy-to-use, robotic-device to assist the patient and therapist to achieve more systematic therapy at home or in the clinic. The RUPERT has four actuated degrees-of-freedom driven by compliant and safe pneumatic muscles (PMs) on the shoulder, elbow, and wrist. They are programmed to actuate the device to extend the arm and move the arm in 3-D space. It is very important to note that gravity is not compensated and the daily tasks are practiced in a natural setting. Because the device is wearable and lightweight to increase portability, it can be worn standing or sitting providing therapy tasks that better mimic activities of daily living. The sensors feed back position and force information for quantitative evaluation of task performance. The device can also provide real-time, objective assessment of functional improvement. We have tested the device on stroke survivors performing two critical activities of daily living (ADL): reaching out and self feeding. The future improvement of the device involves increased degrees-of-freedom and interactive control to adapt to a user's physical conditions.
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http://dx.doi.org/10.1109/TNSRE.2007.903903DOI Listing
September 2007

A unified fielder theory for interception of moving objects either above or below the horizon.

Psychon Bull Rev 2006 Oct;13(5):908-17

Department of Engineering, Arizona State University, Mesa 85212-0180, USA.

A unified fielder theory is presented that explains how humans navigate to intercept targets that approach from either above or below the horizon. Despite vastly different physical forces affecting airborne and ground-based moving targets, a common set of invariant perception-action principles appears to guide pursuers. When intercepting airborne projectiles, fielders keep the target image rising at a constant optical speed in a vertical image plane and moving in a constantoptical direction in an image plane that remains perpendicular to gaze direction. We confirm that fielders use the same strategies to intercept grounders. Fielders maintained a cotangent of gaze angle that decreases linearly with time (accounting for 98.7% of variance in ball speed) and a linear optical trajectory along an image plane that remains perpendicular to gaze direction (accounting for 98.2% of variance in ball position). The universality of maintaining optical speed and direction for both airborne and ground-based targets supports the theory that these mechanisms are domain independent.
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http://dx.doi.org/10.3758/bf03194018DOI Listing
October 2006

Spring over muscle (SOM) actuator for rehabilitation devices.

Conf Proc IEEE Eng Med Biol Soc 2004;2004:2726-9

Dept. of Mech. & Aerosp. Eng., Arizona State Univ., Tempe, AZ, USA.

For people affected by stroke, frequent physical therapy has been shown to be an effective form of rehabilitation. To this goal, several home therapy devices have been developed. Many of these devices may benefit from the use of a bidirectional pneumatic muscle actuator. This work presents the concept and design of the double-acting, compliant, spring over muscle (SOM) actuator. The principle design uses a spring in parallel with a pneumatic muscle actuator. This concept is economical, and easily scalable. Additionally, a design proposal for an ankle rehabilitation device, which incorporates the SOM actuator, is discussed.
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http://dx.doi.org/10.1109/IEMBS.2004.1403781DOI Listing
June 2007

An efficient robotic tendon for gait assistance.

J Biomech Eng 2006 Oct;128(5):788-91

Departments of Mechanical and Aerospace Engineering, and Industrial Design, Arizona State University, Tempe, AZ 85287-6106, USA.

A robotic tendon is a spring based, linear actuator in which the stiffness of the spring is crucial for its successful use in a lightweight, energy efficient, powered ankle orthosis. Like its human analog, the robotic tendon uses its inherent elastic nature to reduce both peak power and energy requirements for its motor. In the ideal example, peak power required of the motor for ankle gait is reduced from 250 W to just 77 W. In addition, ideal energy requirements are reduced from nearly 36 J to just 21 J. Using this approach, an initial prototype has provided 100% of the power and energy necessary for ankle gait in a compact 0.95 kg package, seven times less than an equivalent motor/gearbox system.
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http://dx.doi.org/10.1115/1.2264391DOI Listing
October 2006

Design of a robotic gait trainer using spring over muscle actuators for ankle stroke rehabilitation.

J Biomech Eng 2005 Nov;127(6):1009-13

Human/Machine Integration Laboratory, Arizona State University, Tempe, AZ 85287, USA.

Repetitive task training is an effective form of rehabilitation for people suffering from debilitating injuries of stroke. We present the design and working concept of a robotic gait trainer (RGT), an ankle rehabilitation device for assisting stroke patients during gait. Structurally based on a tripod mechanism, the device is a parallel robot that incorporates two pneumatically powered, double-acting, compliant, spring over muscle actuators as actuation links which move the ankle in dorsiflex ion/plantarflexion and inversion/eversion. A unique feature in the tripod design is that the human anatomy is part of the robot, the first fixed link being the patient's leg. The kinematics and workspace of the tripod device have been analyzed determining its range of motion. Experimental gait data from an able-bodied person wearing the working RGT prototype are presented.
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http://dx.doi.org/10.1115/1.2049333DOI Listing
November 2005

The Galileo bias: a naive conceptual belief that influences people's perceptions and performance in a ball-dropping task.

J Exp Psychol Learn Mem Cogn 2005 Jul;31(4):643-53

Department of Psychology, Arizona State University, Box 871104, Tempe, AZ 85287, USA.

This research introduces a new naive physics belief, the Galileo bias, whereby people ignore air resistance and falsely believe that all objects fall at the same rate. Survey results revealed that this bias is held by many and is surprisingly strongest for those with formal physics instruction. In 2 experiments, 98 participants dropped ball pairs varying in volume and/or mass from a height of 10 m, with the goal of both balls hitting the ground simultaneously. The majority of participants in both experiments adopted a single strategy consistent with the Galileo bias, showing no improvement across trials. Yet, for participants reporting intentions of dropping both balls at the same time, the differences between release points were significantly greater than 0 ms. These findings support separate but interacting cognition and perception-action systems.
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http://dx.doi.org/10.1037/0278-7393.31.4.643DOI Listing
July 2005
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