Roberto de Souza Baptista

Disturbance rejection in a fixed wing UAV using nonlinear H ∞ state feedback

This paper presents a nonlinear H∞ controller for the rejection of input disturbances in a fixed wing UAV. The proposed controller acts in all states of a complete nonlinear dynamic model. Simulation results show that the aircraft is successfully maintained in the desired stable condition after two different disturbances: a finite pulse and noise.

Split and merge algorithm for identification of Piecewise Affine systems

This paper adresses the identification of a class of hybrid dynamical systems which can be represented by a Piecewise Affine Autoregressive Exogenous (PWARX) model. These systems are composed of an usually unknown number of ARX sub-models, each of which corresponds to a polyhedral region of the regression space. It is proposed a Split and Merge clustering algorithm, used under a clustering based identification framework, to estimate the correct number of sub-models. The main advantages of this clustering algorithm is that it requires no initialization and there is only one tuning parameter to be adjusted. The resulting identification procedure is applied in a practical example in the identification of a DC motor with dead zone and saturation.

Design of variable-damping control for prosthetic knee based on a simulated biped

This paper presents the development of a variable-damping controller for a prosthetic knee using a simulated biped in a virtual environment before real tests are conducted on humans. The simulated biped incorporates several features of human walking, such as functional morphology, exploitation of inherent dynamics, hierarchical control network, combination of feed-forward and feedback controllers and phase-dependent modulation. Based on this virtual model of human walking, we have studied biomechanical aspects of the knee joint during walking. Observing the damping profile developed by the simulated biped throughout a gait cycle, we designed a controller for the knee joint. This controller has been evaluated on a modified version of the simulated biped, in which the model of a real prosthetic leg was incorporated. Results of such experiments for walking on flat and rough terrains have provided satisfactory outputs, including improved robustness.

Automatic Human Movement Assessment With Switching Linear Dynamic System: Motion Segmentation and Motor Performance

Performance assessment of human movement is critical in diagnosis and motor-control rehabilitation. Recent developments in portable sensor technology enable clinicians to measure spatiotemporal aspects to aid in the neurological assessment. However, the extraction of quantitative information from such measurements is usually done manually through visual inspection. This paper presents a novel framework for automatic human movement assessment that executes segmentation and motor performance parameter extraction in time-series of measurements from a sequence of human movements. We use the elements of a Switching Linear Dynamic System model as building blocks to translate formal definitions and procedures from human movement analysis. Our approach provides a method for users with no expertise in signal processing to create models for movements using labeled dataset and later use it for automatic assessment. We validated our framework on preliminary tests involving six healthy adult subjects that executed common movements in functional tests and rehabilitation exercise sessions, such as sit-to-stand and lateral elevation of the arms and five elderly subjects, two of which with limited mobility, that executed the sit-to-stand movement. The proposed method worked on random motion sequences for the dual purpose of movement segmentation (accuracy of 72%–100%) and motor performance assessment (mean error of 0%–12%).

Electrical stimulation to reduce the overload in upper limbs during sitting pivot transfer in paraplegic: a preliminary study

Transfer is a key ability and allows greater interact with the environment and social participation. Conversely, paraplegics have great risk of pain and injury in the upper limbs due to joint overloads during activities of daily living, like transfer. The main goal of this study is to verify if the use of functional electrical stimulation (FES) in the lower limbs of paraplegic individuals can assist the sitting pivot transfer (SPT). The secondary objective is to verify if there is a greater participation of the lower limbs during lift pivot phase. A preliminary study was done with one complete paraplegic individual. Temporal parameters were calculated and a kinetic assessment was done during the SPT. The preliminary results showed the feasibility of FES for assisting the SPT.

Methodology for automatic movement cycle extraction using Switching Linear Dynamic System

Human motion assessment is key for motor-control rehabilitation. Using standardized definitions and spatiotemporal features - usually presented as a movement cycle diagram- specialists can associate kinematic measures to progress in rehabilitation therapy or motor impairment due to trauma or disease. Although devices for capturing human motion today are cheap and widespread, the automatic interpretation of kinematic data for rehabilitation is still poor in terms of quantitative performance evaluation. In this paper we present an automatic approach to extract spatiotemporal features from kinematic data and present it as a cycle diagram. This is done by translating standard definitions from human movement analysis into mathematical elements of a Switching Linear Dynamic System model. The result is a straight-forward procedure to learn a tracking model from a sample execution. This model is robust when used to automatically extract the movement cycle diagram of the same motion (the Sit-Stand-Sit, as an example) executed in different subject-specific manner such as his own motion speed.

A Comparison of a Passive and Variable-Damping Controlled Leg Prosthesis in a Simulated Environment

This paper presents two control methods for a leg prosthesis: a passive based and a variable-damping based. First, the concept of the mechanical design for the leg prosthesis is described. A simulated environment is used to compare the two control methods. The joint setup and its control scheme, in which a passive or a variable-damping control can be easily implemented, are introduced for the prosthetic leg in the simulated environment. Intelligent prosthesis require a specific adjustment for each gait phase based on kinematic events of knee and ankle joints along a gait cycle. A feasible damping profile is generated based on kinematic and dynamical data of the knee joint along a gait cycle. This data set was extracted from a simulated biped which is 1.8m in height and 76 kg in weight with 21 degrees of freedom during normal walking. The data show that the damping profile is critical between the toe-off and heel contact events. Tests using the simulated biped with the passive and the variabledamping controlled leg prosthesis during walking enables the comparison of both control approaches.