Guilherme Aramizo Ribeiro

Design and Evaluation of a 2-DOF Instrumented Platform for Estimation of the Ankle Mechanical Impedance in the Sagittal and Frontal Planes

This paper describes the fabrication and initial evaluation of a vibrating platform with two degrees of freedom (DOF) to estimate the human ankles mechanical impedance in two DOFs; namely dorsiflexion-plantarflexion (DP) and inversion-eversion (IE). The device consists of an actuation and a force plate module. The actuation module generates torque perturbations up to 168 N·m in DP and 26 N·m in IE in the force plate module using Bowden cables. This provides a low-profile system that can be installed in a walkway. The frame of the force plate module rotates in two DOFs, applying torque perturbations to the human ankle in DP and IE. The ankles rotations are measured using a motion capture camera system. The analytical and numerical approaches for estimation of the ankles torques, rotations, and impedances are presented. A system validation using a mockup was conducted to verify the systems ability to estimate the impedance of a physical system in two DOFs. The developed system was capable of identifying the mockups physical properties up to 15 Hz. The mockups impedance magnitude at 0.9 Hz using a stochastic identification method was shown to be within 1.68% and 0.54% of the mockups stiffness in DP and IE, respectively.

Instrumented Walkway for Estimation of the Ankle Impedance in Dorsiflexion-Plantarflexion and Inversion-Eversion During Standing and Walking

This paper describes in detail the fabrication of an instrumented walkway for estimation of the ankle mechanical impedance in both dorsiflexion-plantarflexion (DP) and in inversion-eversion (IE) directions during walking in arbitrary directions and standing. The platform consists of two linear actuators, each capable of generating ±351.3 N peak force that are mechanically coupled to a force plate using Bowden cables. The applied forces cause the force plate to rotate in two degrees of freedom (DOF) and transfer torques to the human ankle to generate DP and IE rotations. The relative rotational motion of the foot with respect to the shin is recorded using a motion capture camera system while the forces applied to the foot are measured with the force plate, from which the torques applied to the ankle are calculated. The analytical methods required for the estimation of the ankle torques, rotations, and impedances are presented. To validate the system, a mockup with known stiffness was used, and it was shown that the developed system was capable of properly estimating the stiffness of the mockup in two DOF with less than 5% error. Also, a preliminary experiment with a human subject in standing position was performed, and the estimated quasi-static impedance of the ankle was estimated at 319 Nm/rad in DP and 119 Nm/rad in IE.Copyright

Design and Preliminary Evaluation of a Two DOFs Cable-Driven Ankle–Foot Prosthesis with Active Dorsiflexion–Plantarflexion and Inversion–Eversion

This paper describes the design of an ankle–foot robotic prosthesis controllable in the sagittal and frontal planes. The prosthesis was designed to meet the mechanical characteristics of the human ankle including power, range of motion, and weight. To transfer the power from the motors and gearboxes to the ankle–foot mechanism, a Bowden cable system was used. The Bowden cable allows for optimal placement of the motors and gearboxes in order to improve gait biomechanics such as the metabolic energy cost and gait asymmetry during locomotion. Additionally, it allows flexibility in the customization of the device to amputees with different residual limb sizes. To control the prosthesis, impedance controllers in both sagittal and frontal planes were developed. The impedance controllers used torque feedback from strain gages installed on the foot. Preliminary evaluation was performed to verify the capability of the prosthesis to track the kinematics of the human ankle in two degrees of freedom (DOFs), the mechanical efficiency of the Bowden cable transmission, and the ability of the prosthesis to modulate the impedance of the ankle. Moreover, the system was characterized by describing the relationship between the stiffness of the impedance controllers to the actual stiffness of the ankle. Efficiency estimation showed 85.4% efficiency in the Bowden cable transmission. The prosthesis was capable of properly mimicking human ankle kinematics and changing its mechanical impedance in two DOFs in real time with a range of stiffness sufficient for normal human walking. In dorsiflexion–plantarflexion (DP), the stiffness ranged from 0 to 236 Nm/rad and in inversion–eversion (IE), the stiffness ranged from 1 to 33 Nm/rad.

A multi-level motion controller for low-cost Underwater Gliders

An underwater glider named ROUGHIE (Research Oriented Underwater Glider for Hands-on Investigative Engineering) is designed and manufactured to provide a test platform and framework for experimental underwater automation. This paper presents an efficient multi-level motion controller that can be used to enhance underwater glider control systems or easily modified for additional sensing, computing, or other requirements for advanced automation design testing. The ultimate goal is to have a fleet of modular and inexpensive test platforms for addressing the issues that currently limit the use of autonomous underwater vehicles (AUVs). Producing a low-cost vehicle with maneuvering capabilities and a straightforward expansion path will permit easy experimentation and testing of different approaches to improve underwater automation.

GUPPIE, underwater 3D printed robot a game changer in control design education

This paper presents innovative strategies to teach control and robotic concepts. These strategies include: 1) a real world focus on social/environmental contexts that are meaningful and “make a difference”; 2) continuous design potential and engagement through use of a platform that integrates design with engineering; 3) mission-based versus application-based approaches, where meaningful application justifies the process; and 4) hands-on, inquiry-based problem-solving. For this purpose a Glider for Underwater Problem-solving and Promotion of Interest in Engineering or “GUPPIE” platform and its simulator were utilized. GUPPIE is easy and inexpensive to manufacture, with readily available lightweight and durable components. It is also modular to accommodate a variety of learning activities. This paper describes how GUPPIE and its interdisciplinary nature was used as a pedagogical platform for teaching core control concepts for different age groups. The activities are designed to attract the interest of students as early as middle school and sustain their interest through college. The game changing aspect of this approach is scaffolded learning and the fact that the students will work with the same platform while progressing through the concepts.

Mechanical Impedance of the Non-loaded Lower Leg with Relaxed Muscles in the Transverse Plane.

This paper describes the protocols and results of the experiments for the estimation of the mechanical impedance of the humans’ lower leg in the External–Internal direction in the transverse plane under non-load bearing condition and with relaxed muscles. The objectives of the estimation of the lower leg’s mechanical impedance are to facilitate the design of passive and active prostheses with mechanical characteristics similar to the humans’ lower leg, and to define a reference that can be compared to the values from the patients suffering from spasticity. The experiments were performed with 10 unimpaired male subjects using a lower extremity rehabilitation robot (Anklebot, Interactive Motion Technologies, Inc.) capable of applying torque perturbations to the foot. The subjects were in a seated position, and the Anklebot recorded the applied torques and the resulting angular movement of the lower leg. In this configuration, the recorded dynamics are due mainly to the rotations of the ankle’s talocrural and the subtalar joints, and any contribution of the tibiofibular joints and knee joint. The dynamic mechanical impedance of the lower leg was estimated in the frequency domain with an average coherence of 0.92 within the frequency range of 0–30 Hz, showing a linear correlation between the displacement and the torques within this frequency range under the conditions of the experiment. The mean magnitude of the stiffness of the lower leg (the impedance magnitude averaged in the range of 0–1 Hz) was determined as 4.9 ± 0.74 Nm/rad. The direct estimation of the quasi-static stiffness of the lower leg results in the mean value of 5.8 ± 0.81 Nm/rad. An analysis of variance shows that the estimated values for the stiffness from the two experiments are not statistically different.

Time-varying human ankle impedance in the sagittal and frontal planes during stance phase of walking

This paper, for the first time, describes the estimation of the time-varying impedance of the human ankle in the sagittal (SP) and frontal (FP) planes during the stance phase of walking. The result of this work is aimed to provide design parameters for the development of 2-DOF powered ankle-foot prostheses capable of mimicking the time-varying impedance of the human ankle. Sixteen axes of rotations combining different amounts of SP and FP rotations were studied. For each axis, positive and negative rotations were considered separately. Four unimpaired male subjects walked on an instrumented vibrating platform that applied combined torque perturbations in the SP and FP simultaneously, while the ankle angles and torques were recorded. Based on the recorded data, the ankle impedance was estimated with a time resolution of 20 ms from 7% to 93% of the stance length (SL). The ankle stiffness and damping showed great variability through the SL and across axes of rotation. The maximum stiffness was 4.7±0.5 Nm/rad/kg at 0.21 s of the SL when the ankle rotated at an axis 22.5° from the SP combining Dorsiflexion (D) and Inversion (I). The minimum stiffness was 1.4±0.6 Nm/rad/kg at 0.05 s of the SL at an axis 45° from the SP combining D and Eversion (E). The maximum damping was 0.09±0.02 Nms/rad/kg at 0.21 s of the SL combining D and I at an axis 25° from the SP. The minimum was 0.02±0.01 Nms/rad/kg at 0.05 s of the SL combining P and I at an axis 45° from the SP.

Correlation Between Ankle Impedance and EMG Signals

The correlation of the lower-leg muscle contraction to the ankle impedance of unimpaired subjects is studied. Each subject participated in 5 experimental trials, each with a different co-contraction level: 0%, 10%, 20%, 30%, and 40% of their maximum voluntary contraction (MVC). A linear model is developed to relate the muscle contraction and the ankle impedance. Next, an ANOVA test is used to verify the significance of the parameters. Low correlation is found on the inversion-eversion degree-of-freedom of the ankle, suggesting non-linear models might be more effective in describing this relationship.

Validation of an Instrumented Walkway Designed for Estimation of the Ankle Impedance in Sagittal and Frontal Planes

Recently, the authors designed and fabricated an Instrumented Walkway for the estimation of the ankle mechanical impedance in the sagittal and frontal planes during walking in arbitrary directions [1]. It consists of a powered platform; therefore, the users do not need to wear or carry any measurement device or actuation system other than reflective markers used to record the ankle kinematics with a motion capture camera system. This paper describes the continuous development of the Instrumented Walkway and presents an experimental preliminary validation of its capability to estimate the impedance of a system with time-varying dynamics. To validate the system, a mockup with mechanical characteristics similar to a human lower-leg and controllable time-varying stiffness was used. The stiffness of the mockup was estimated with fixed and time-varying stiffness. With fixed stiffness, a stochastic system identification method was used to estimate the mockup’s impedance. When the mockup presented a timevarying stiffness, a second order parametric model was used. The RMS error between the two methods was 2.81 Nm/rad (maximum 4.12 Nm/rad and minimum of -3.41 Nm/rad). The results show that the proposed approach can estimate the stiffness of systems with time-varying dynamics or static dynamics with similar accuracy. Since the setup was already validated for systems with time-invariant dynamics, it concluded the system’s applicability for time-varying systems such as the human ankle-foot during the stance phase. INTRODUCTION The estimation of the mechanical impedance of the human ankle has been the focus of research since it provides insight on the mechanical properties of the ankle and how it interacts with the environment. The ankle is the first major joint to interact with the ground during walking and it plays a major role in propulsion and stability, while generating torques and angles in all anatomical planes. The impedance of the ankle continually changes during walking to accomplish its task, and the way it changes depends on the type of gait. The impedance of a system correlates the output torque due to an input disturbance, and for a second order system, it is a function of the system’s mass, damping, and inertia. The human ankle is capable of impedance modulation by muscle contraction of the muscles involved on its operation. Impedance controllers are often used in prosthesis, as it allows the device to mimic the mechanical properties of the human limb. For an ankle-foot prosthesis, the quasi-static impedance of the ankle in the sagittal plane has been used [2-4]; however, for proper control of the prosthesis, there is strong evidence that time-varying and task-dependent impedance modulation of the ankle is necessary [5, 6]. Activities of daily living (ADLs) include gait scenarios that require significant modulation of the ankle impedance in all anatomical planes, mainly in Inversion-Eversion (IE) and DorsiflexionPlantarflexion (DP) [5, 6]. These activities include but are not limited to turning, traversing slopes, and adapting to uneven Proceedings of the ASME 2016 Dynamic Systems and Control Conference DSCC2016 October 12-14, 2016, Minneapolis, Minnesota, USA