Luciano Luporini Menegaldo

Individual-specific muscle maximum force estimation using ultrasound for ankle joint torque prediction using an EMG-driven Hill-type model

EMG-driven models can be used to estimate muscle force in biomechanical systems. Collected and processed EMG readings are used as the input of a dynamic system, which is integrated numerically. This approach requires the definition of a reasonably large set of parameters. Some of these vary widely among subjects, and slight inaccuracies in such parameters can lead to large model output errors. One of these parameters is the maximum voluntary contraction force (F(om)). This paper proposes an approach to find F(om) by estimating muscle physiological cross-sectional area (PCSA) using ultrasound (US), which is multiplied by a realistic value of maximum muscle specific tension. Ultrasound is used to measure muscle thickness, which allows for the determination of muscle volume through regression equations. Soleus, gastrocnemius medialis and gastrocnemius lateralis PCSAs are estimated using published volume proportions among leg muscles, which also requires measurements of muscle fiber length and pennation angle by US. F(om) obtained by this approach and from data widely cited in the literature was used to comparatively test a Hill-type EMG-driven model of the ankle joint. The model uses 3 EMGs (Soleus, gastrocnemius medialis and gastrocnemius lateralis) as inputs with joint torque as the output. The EMG signals were obtained in a series of experiments carried out with 8 adult male subjects, who performed an isometric contraction protocol consisting of 10s step contractions at 20% and 60% of the maximum voluntary contraction level. Isometric torque was simultaneously collected using a dynamometer. A statistically significant reduction in the root mean square error was observed when US-obtained F(om) was used, as compared to F(om) from the literature.

Development and Navigation of a Mobile Robot for Floating Production Storage and Offloading Ship Hull Inspection

This paper describes the current development status of a mobile robot designed to inspect the outer surface of large oil ship hulls and floating production storage and offloading platforms. These vessels require a detailed inspection program, using several nondestructive testing techniques. A robotic crawler designed to perform such inspections is presented here. Locomotion over the hull is provided through magnetic tracks, and the system is controlled by two networked PCs and a set of custom hardware devices to drive motors, video cameras, ultrasound, inertial platform, and other devices. Navigation algorithm uses an extended-Kalman-filter (EKF) sensor-fusion formulation, integrating odometry and inertial sensors. It was shown that the inertial navigation errors can be decreased by selecting appropriate Q and R matrices in the EKF formulation.

SIRUS: A mobile robot for Floating Production Storage and Offloading (FPSO) ship hull inspection

This paper describes the current development status of a mobile robot designed to inspect the outer surface of large oil ship hulls and floating production storage offloading (FPSO) platforms. These are usually former oil tanker ships, especially adapted to work as an oil offshore platform. Several mechanisms of corrosion are present in such structures, worsen by the abnormal static operation regime of the vessel and other causes. This situation requires a detailed program of inspection, using several non destructive detection (NDT) techniques, operated manually. Here, a robotic crawler designed to perform such inspections is presented. Locomotion over the hull is provided trough a pair or DC-motor propelled magnetic tracks, while the system is controlled by two networked PCs and a set of custom hardware to drive the motors, video cameras, ultrasound (US), inertial platform and other devices. Navigation is provided by a extended Kalman filter sensor fusion formulation, integrating hodometry and inertial sensors. The current version of the prototype is able to perform ultrasound thickness measurements in the dry part of the hull.

Kinematical modeling and optimal design of a biped robot joint parallel linkage

This paper shows the design and analysis of a parallel three-dimensional linkage, conceived to work as the ankle and hip joints of an anthropometric biped robot. This kind of mechanism architecture provides low-weight, highly stable assemblies, and allows the use of actuator synergies. On the other hand, the mechanical transmission ratio is not usually favorable, and a non-linear kinematic model has to be derived and solved. The mechanism proposed here is driven by two rotational servo-actuators, and allows the joint to follow a specified angular trajectory determined by the gait pattern. Namely, the joint linkage can generate dorsi/plantar flexion and inversion/eversion of the ankle, and hip flexion/extension and adduction/abduction movements. Several approaches to the direct and inverse kinematical modeling of the linkage are presented and compared, regarding their accuracy and computational cost, where the last performance parameter is closely related to on-line computer implementing of the controller. Strategies to fit current gait angular amplitudes into the linkage workspace, as well as singularity analysis, are discussed. An optimization method was applied to find some geometrical design parameters of the linkage that minimizes a cost function. This function is the mean transmission ratio between the motor inputs and the joint output torques over a predefined dominion. The minimization is constrained to a minimum workspace area value and to minimum and maximum values of the design parameters. Several design solutions were generated. The chosen was one where the workspace is compatible to the gait amplitude requirements and that exhibits the lowest cost function. A biped robot using the linkage geometry designed in this paper has been built and tested with real human gait data acquired in a gait lab. Keywords: Parallel linkage, mechanisms, gait analysis, biped robot, optimal design

EMGD-FE: an open source graphical user interface for estimating isometric muscle forces in the lower limb using an EMG-driven model

BackgroundThis paper describes the “EMG Driven Force Estimator (EMGD-FE)”, a Matlab® graphical user interface (GUI) application that estimates skeletal muscle forces from electromyography (EMG) signals. Muscle forces are obtained by numerically integrating a system of ordinary differential equations (ODEs) that simulates Hill-type muscle dynamics and that utilises EMG signals as input. In the current version, the GUI can estimate the forces of lower limb muscles executing isometric contractions. Muscles from other parts of the body can be tested as well, although no default values for model parameters are provided. To achieve accurate evaluations, EMG collection is performed simultaneously with torque measurement from a dynamometer. The computer application guides the user, step-by-step, to pre-process the raw EMG signals, create inputs for the muscle model, numerically integrate the ODEs and analyse the results.ResultsAn example of the application’s functions is presented using the quadriceps femoris muscle. Individual muscle force estimations for the four components as well the knee isometric torque are shown.ConclusionsThe proposed GUI can estimate individual muscle forces from EMG signals of skeletal muscles. The estimation accuracy depends on several factors, including signal collection and modelling hypothesis issues.

Variations in the spatial distribution of the amplitude of surface electromyograms are unlikely explained by changes in the length of medial gastrocnemius fibres with knee joint angle.

This study investigates whether knee position affects the amplitude distribution of surface electromyogram (EMG) in the medial gastrocnemius (MG) muscle. Of further concern is understanding whether knee-induced changes in EMG amplitude distribution are associated with regional changes in MG fibre length. Fifteen surface EMGs were acquired proximo-distally from the MG muscle while 22 (13 male) healthy participants (age range: 23–47 years) exerted isometric plantar flexion at 60% of their maximal effort, with knee fully extended and at 90 degrees flexion. The number of channels providing EMGs with greatest amplitude, their relative proximo-distal position and the EMG amplitude averaged over channels were considered to characterise changes in myoelectric activity with knee position. From ultrasound images, collected at rest, fibre length, pennation angle and fat thickness were computed for MG proximo-distal regions. Surface EMGs detected with knee flexed were on average five times smaller than those collected during knee extended. However, during knee flexed, relatively larger EMGs were detected by a dramatically greater number of channels, centred at the MG more proximal regions. Variation in knee position at rest did not affect the proximo-distal values obtained for MG fibre length, pennation angle and fat thickness. Our main findings revealed that, with knee flexion: i) there is a redistribution of activity within the whole MG muscle; ii) EMGs detected locally unlikely suffice to characterise the changes in the neural drive to MG during isometric contractions at knee fully extended and 90 degrees flexed positions; iii) sources other than fibre length may substantially contribute to determining the net, MG activation.

Time Domain Simulation of a Target Tracking System with Backlash Compensation

This paper presents a model of a target tracking system assembled in a moving body. The system is modeled in time domain as a nonlinear system, which includes dry friction, backlash in gear transmission, control input tensions saturation, and armature current saturation. Time delays usually present in digital controllers are also included, and independent control channels are used for each motor. Their inputs are the targets angular errors with respect to the system axial axis and the outputs are control tensions for the motors. Since backlash in gear transmission may reduce the systems accuracy, its effects should be compensated. For that, backlash compensation blocks are added in the controllers. Each section of this paper contains a literature survey of recent works dealing with the issues discussed in this article.

In vivo passive mechanical properties estimation of Achilles tendon using ultrasound

A methodology is proposed for estimating Achilles tendon tangent modulus in vivo, to account for its large deformations and non-linear behavior. True stress is found dividing the axial force by the tendon true cross-sectional area (CSA), whose shrinking caused by axial tension is estimated with Poisson׳s coefficient. The true strain is calculated as the integral of incremental deformations along the tendon length change. Triceps surae tendon CSA and ankle moment arm, with the foot at relaxed equilibrium position, are estimated from subject-personalized data. Healthy males (N=19) volunteered for the study. The test consisted of passive ankle mobilization at the dynamometer with 5°/s velocity, from 30° of plantar flexion to the limit of dorsiflexion. Ultrasound was used to track myotendinous junction (MTJ) and tendon elongation, with the probe oriented over the medial gastrocnemius. Non-linear tendon stiffness pattern was observed during the joint range of motion, reaching 200N/mm peaks for the subjects with greater amplitudes of maximum dorsiflexion. The maximum values of modulus of elasticity, calculated from usual engineering stress and strain, (188.56±99.19MPa) were smaller than those reported in the literature for active maximum voluntary contractions tests. Maximum values for tangent modulus from true stress and strain were 312.38±171.95MPa. Such differences are likely to increase in large deformations.

Hand prosthesis prototype controlled by EMG and vibrotactile force feedback

In the last 30 years very innovative prosthetic hands have been developed. Nevertheless, most of prosthetic hands are basically simple grippers with one or two degrees of freedom (DOFs) providing low functionality. Efforts have been made to improve the performance of devices so that they are as similar as possible with the human hand by exploring recent progresses in mechatronics technology. A major challenge in the development of prosthetic hands with a greater number of DOFs and, consequently, better functionality is to unite the entire system in a compact and lightweight design, besides provide some sensorial information to the amputee. The goal of this work is to develop a prosthesis concept which brings several advantages such as: lightweight, low energy consumption, reduction in volume, simple control and flexibility. In addition, the system is able to provide prehension force feedback. The mechanical design of a finger is described, which composes an artificial hand prototype of two active fingers, with three DOFs each one, and a static thumb. A force sensor provides feedback to the user through mechanical vibrations, ensuring greater safety to grasp an object. Also, a myoelectric control is implemented such that amputees are able to control their artificial limbs in a more natural way.

Reconstruction of Riser Profiles by an Underwater Robot Using Inertial Navigation

This paper proposes a kinematic model and an inertial localization system architecture for a riser inspecting robot. The robot scrolls outside the catenary riser, used for underwater petroleum exploration, and is designed to perform several nondestructive tests. It can also be used to reconstruct the riser profile. Here, a realistic simulation model of robot kinematics and its environment is proposed, using different sources of data: oil platform characteristics, riser static configuration, sea currents and waves, vortex-induced vibrations, and instrumentation model. A dynamic finite element model of the riser generates a nominal riser profile. When the robot kinematic model virtually scrolls the simulated riser profile, a robot kinematic pattern is calculated. This pattern feeds error models of a strapdown inertial measurement unit (IMU) and of a depth sensor. A Kalman filter fuses the simulated accelerometers data with simulated external measurements. Along the riser vertical part, the estimated localization error between the simulated nominal and Kalman filter reconstructed robot paths was about 2 m. When the robot model approaches the seabed it assumes a more horizontal trajectory and the localization error increases significantly.