System architecture and modularity decisions are inherent to preliminary concept design. Prior modularity research has considered minimizing interactions between modules and increasing the commonality among modular product variants. Effective approaches include function structure partitioning guidelines, affinity analysis or matrix clustering algorithms. We consider here designs with field constraints, such as situations when elements cannot be placed in certain regions such as a high temperature field, a high pressure field, a high magnetic field, etc. which place constraints on modularity choices. Practical design guidelines are developed here for modularity considering field constraints. Two types of guidelines are proposed, field separation and concept generation. The field separation guidelines propose zonal boundaries within which a system modules need be confined. The concept generation guidelines propose how to violate the field constraints through new concepts. Moving functionality from one side of a field boundary to the other is nontrivial and involves new concept generation for the modules to function at the higher or lower field values. The guidelines are defined and illustrated via multiple common examples as well as two extended case studies. We demonstrate the approach using field boundaries on an electric motor controller and on a medical contrast injector, and also use of fields to generated novel concepts. The guidelines support for modularity concept and embodiment decisions.

Increase in the interaction forces/torques at the exoskeleton-human connection due to kinematic mismatches may consequently result in the user discomfort and/or lower performance of the exoskeleton. The stiffness of the exoskeleton-human connection elements plays a key role in this issue. The purpose of this study is to assess the effects of the exoskeleton-human connection stiffness on the user comfort and limb tracking error during normal gait. A biomechanical model of the leg was built and connected to a model of an exoskeleton by elastic connections whose stiffness tensors were identified experimentally for one study participant. The effects of the connection stiffness on the gait performance was investigated using two indices: discomfort index, DI, and tracking error (i.e., the difference between the human joint angle and that of the exoskeleton), TEI. DI was calculated based on the mechanical energy stored in the elastic connections elements. Although increase of the stiffness magnitude in every direction results in DI growth, the torsional stiffness of the shank connection was found to be the most sensitive for DI. TEI, on the other hand, showed both increasing and decreasing trends with the stiffness increase in different directions. It was found that there are optimal values for some connection stiffness elements, especially shank connection, possibly due to intricacy of the knee joint, that would improve both DI and TEI. For instance, decrease of the torsional and mediolateral shank connection stiffness improved DI and TEI by an average of about 50%.

The simultaneous control of force and motion is important in everyday activities when humans interact with objects. While many studies have analyzed the control of movement within a perturbing force field, few have investigated its dual aspects of controlling a contact force in nonisometric conditions. The mechanism by which the central nervous system controls forces during movements is still unclear, and it can be elucidated by estimating the mechanical properties of the arm during tasks with concurrent motion and contact force goals. We investigate how arm mechanics change when a force control task is accomplished during low-frequency positional perturbations of the arm. Contrary to many force regulation algorithms implemented in robotics, where contact impedance is decreased to reduce force fluctuations in response to position disturbances, we observed a steady increase of arm endpoint stiffness as the task progressed. Based on this evidence, we propose a theoretical framework suggesting that an internal model of the perturbing trajectory is formed. We observed that force regulation in the presence of predictable positional disturbances is implemented using a position control strategy together with the modulation of the endpoint stiffness magnitude, where the direction of the endpoint stiffness ellipse's major axis is oriented toward the desired force.

This paper describes the design and control of a novel hand exoskeleton. A subcategory of upper extremity exoskeletons, hand exoskeletons have promising applications in healthcare services, industrial workplaces, virtual reality, and military. Although much progress has been made in this field, most of the existing systems are position controlled and face several design challenges, including achieving minimal size and weight, difficulty enforcing natural grasping motions, exerting sufficient grip strength, ensuring the safety of the users hand, and maintaining overall user friendliness. To address these issues, this paper proposes a novel, slim, lightweight linkage mechanism design for a hand exoskeleton with a force control paradigm enabled via a compact series elastic actuator. A detailed design overview of the proposed mechanism is provided, along with kinematic and static analyses. To validate the overall proposed hand exoskeleton system, a fully integrated prototype is developed and tested in a series of experimental trials.

In this paper, we investigated the effects of herringbone riblets, a type of bio-inspired micro-scale surface patterns, on the pressure losses and flow turning angles in a linear cascade over a range of low Reynolds numbers from 0.50×10 5 to 1.50×10 5 and at three different angles of attack. Our experiments showed that despite the micro-scale size of herringbone riblets they produced a significant reduction in pressure loss coefficient and a substantial increase in flow turning angle except at the low end of Reynolds numbers tested. In comparison to the baseline case without riblets, the highest reduction in mean pressure loss achieved was 36.4% which was accompanied by an increase of average turning angle of 4.1°. It was observed that the loss reduction is associated with a reduction in the maximum pressure loss at lower angles of attack and a narrower wake zone at higher angles of attack as a result of suppression of flow separation on the blade suction surface. It was also noted that such a significant improvement in performance was accompanied by the appearance of a serrated wake structure in the contours of pressure loss coefficient. The improvement in blade performance was attributed to the secondary flow motion produced by herringbone riblets which energises the boundary layer. Overall, this work has produced convincing experimental evidence that herringbone riblets can be used as passive flow control devices for reducing flow separation in compressors at low Reynolds numbers.

Humans are daily presented with tasks that they complete with little effort or even consideration of the planning that goes into the movement. Movements such as manual manipulation tasks are completed with ease, even though the complexities and years of learned behavior are largely hidden from the person. Digital human modeling (DHM) and specifically optimization-based posture and motion prediction methodologies have employed numerical methods in order to simulate/predict/analyze human movements. However, these movements are heavily constrained such that the planning of the motion/posture is explicitly provided in the formulation of the problem. This paper presents the addition of cognitive principles into the optimization-based posture and motion prediction formulations. The simulation/prediction of manual manipulation tasks is considered such that a single formulation can accomplish multiple tasks. It adopts a theory from cognitive psychology referred to as the end-state comfort effect in order to derive general constraints for the prediction of the initial and final posture states that frame the movement related to the manual manipulation task. It considers multiple tasks from the literature that have been heavily studied through experimentation in order to evaluate the efficacy of the formulation. The results show strong correlation with observations reported in the literature.

Achieving coordinated motion between transfemoral amputee patients and powered prosthetic joints is of paramount importance for powered prostheses control. In this article, we propose employing an algebraic curve representation of nominal human walking data for a powered knee prosthesis controller design. The proposed algebraic curve representation encodes the desired holonomic relationship between the human and the powered prosthetic joints with no dependence on joint velocities. For an impedance model of the knee joint motion driven by the hip angle signal, we create a continuum of equilibria along the gait cycle using a variable impedance scheme. Our variable impedance-based control law, which is designed using the parameter-dependent Lyapunov function framework, realizes the coordinated hip-knee motion with a family of spring and damper behaviors that continuously change along the human-inspired algebraic curve. In order to accommodate variability in the user's hip motion, we propose a computationally efficient radial projection-based algorithm onto the human-inspired algebraic curve in the hip-knee plane.

Postural stability is important in everyday life as falls can cause severe injuries. Risk of injuries is higher in the elderly whose balance is often impaired. Modeling postural stability and the parameters that govern it is important to understand the balance mechanism and allow for the development of fall prevention strategies. Several mathematical models have been proposed to represent postural stability of bipeds. These models differ on the number of degrees-of-freedom (DOF) of the skeletal structure, force generation function for the muscle models, and capability to change their behavior as a function of the task. This work proposes a nonlinear model that captures fall recovery using a hip–ankle strategy. The muscle actuation is modeled as a third-order Poynting–Thomson's (PT) mechanical system where muscles and tendons are represented as lumped parameters actuating the aforementioned joints. Both a regression technique and a Kalman Filter (KF) are used to estimate the muscle–tendon parameters of the model. With a good model, the direct estimation of these parameters would allow clinicians to improve postural stability in the elderly, monitor the deterioration of the physical condition in individuals affected by neuro-degenerative diseases, and develop rehabilitation appropriate processes.

Ultrasound guidance is used for a variety of surgical needle insertion procedures, but there is currently no standard for the teaching of ultrasound skills. Recently, computer ultrasound simulation has been introduced as an alternative teaching method to traditional manikin and cadaver training because of its ability to provide diverse scenario training, quantitative feedback, and objective assessment. Current computer ultrasound training simulation is limited in its ability to image tissue deformation caused by needle insertions, even though tissue deformation identification is a critical skill in performing an ultrasound-guided needle insertion. To fill this need for improved simulation, a novel method of simulating ultrasound tissue–needle deformation is proposed and evaluated. First, a cadaver study is conducted to obtain ultrasound video of a peripheral nerve block. Then, optical flow analysis is conducted on this video to characterize the tissue movement due to the needle insertion. Tissue movement is characterized into three zones of motion: tissue near the needle being pulled, and zones above and below the needle where the tissue rolls. The rolling zones were centered 1.34 mm above and below the needle and 4.53 mm behind the needle. Using this characterization, a vector field is generated mimicking these zones. This vector field is then applied to an ultrasound image using inverse mapping to simulate tissue movement. The resulting simulation can be processed at 3.1 frames per second. This methodology can be applied through future optimized graphical processing to allow for accurate real time needle tissue simulation.

This paper presents a semi-adaptive closed-loop control approach to autonomous infusion of medications exhibiting significant transport delay in clinical effects. The basic idea of the approach is to enable stable adaptive control of medication infusion by (1) incorporating transport delay explicitly into control design by way of a Padé approximation while (2) facilitating linear parameterization of control design model by desensitization of nonlinearly parameterized cooperativity constant associated with pharmacodynamics (PD). A novel dynamic dose–response model for control design is presented, in which the cooperativity constant exerts zero influence on the model output in the steady-state. Then, an adaptive pole placement control (APPC) technique was employed to fulfill adaptive control design in the presence of nonminimum phase dynamics associated with the Padé approximation of transport delay. The controller was evaluated in silico using a case study of regulating a cardiovascular variable with a sedative under a wide range of transport delay and pharmacological profiles. The results suggest that adaptation of transport delay and pharmacological characteristics may be beneficial in achieving consistent and robust regulation of medication-elicited clinical effects.

Study of human upright posture (UP) stability is of great relevance to fall prevention and rehabilitation, especially for those with balance deficits for whom a balance board (BB) is a widely used mechanism to improve balance. The stability of the human-BB system has been widely investigated from a dynamical system point of view. However, most studies assume small disturbances, which allow to linearize the nonlinear human-BB dynamical system, neglecting the effect of the nonlinear terms on the stability. Such assumption has been useful to simplify the system and use bifurcation analyses to determine local dynamic stability properties. However, dynamic stability analysis results through such linearization of the system have not been verified. Moreover, bifurcation analyses cannot provide insight on dynamical behaviors for different points within the stable and unstable regions. In this study, we numerically solve the nonlinear delay differential equation that describes the human-BB dynamics for a range of selected parameters (proprioceptive feedback and time-delays). The resulting solutions in time domain are used to verify the stability properties given by the bifurcation analyses and to compare different dynamical behaviors within the regions. Results show that the selected bifurcation parameters have significant impacts not only on UP stability but also on the amplitude, frequency, and increasing or decaying rate of the resulting trajectory solutions.

During percutaneous coronary interventions (PCI), a guidewire is used as an initial way of accessing a specific vasculature. There are varieties of guidewires on the market and choosing an appropriate one for each case is critical for a safe and successful intervention. The main objective of this study is to predict the behavior of the guidewire and its performance in a vasculature prior to the procedure. Therefore, we evaluate the effectiveness of different mechanical properties of the guidewire on its behavior. A two-dimensional (2D) model has been developed in which a guidewire is considered as a set of small rigid segments connected to each other by revolute joints. These joints have two degrees-of-freedom to allow rotation. Linear torsional springs and dampers are applied in each joint to account for the elastic properties of the guidewire; the elastic properties have been measured for two commercially available guidewires (Hi-Torque Balance Middleweight Universal II—Abbot and Amplatz Super Stiff—Boston Scientific) and these are used in the model. Only translational motion has been applied to the guidewires and the effect of bending stiffness of the guidewire and also friction between guidewire and vasculature on its behavior are investigated. The results are validated with actual movement of the guidewires in a simple phantom model. Behavior of a guidewire in a vasculature was predicted using the developed model. The results of both simulation and experiment show that the behavior of a guidewire is influenced by its mechanical properties and by the friction between the guidewire and vasculature. This study is the first step to develop a complete model, which can predict the behavior of a guidewire inside the vasculature. We compared the tip trajectory for two commercial guidewires in one vasculature geometry. In future, this kind of knowledge might support not only the interventionist in choosing the best suitable guidewire for a procedure but also the designer to optimize new instrument to have the desired behavior.

Computational modeling of cardiac function has gradually progressed during the past four decades and now beginning to translate toward clinical use as a noninvasive mean of optimizing cardiac treatment options. Recent experimental findings and numerical investigations have suggested an important role of mechanical and intrinsic properties of cardiac tissues in overall electromechanical dynamics of the heart. The inertial effects, which were usually neglected in earlier computational studies, have now been found to alter cardiac dynamics through stretch activated channels (SAC) and can lead to cardiac disorders under specific set of physiological conditions. Considering possible role of inertia in cardiac dynamics, we have modeled electromechanical activity of the heart with inertia terms for computing pressure volume relation and action potentials over a complete cardiac cycle. To this end, we use the continuum balance laws to capture physiological function of the human left ventricle (LV) on an idealized geometry and solve the resulting equations using a python-based finite element platform. For the same set of pressure boundary conditions, the finite element models for quasi-static (less inertia) and dynamic (with inertia terms) formulation yielded a difference of 4.2% end diastolic volume (EDV), 3.1% ejection fraction, and variations in fiber strain pattern. The mechano-electric transduction channels sensitive to small mechanical perturbations in combination with changes in electrical conductivity due to deformation caused quantitative variations over cardiac electrical activity up to 2.75–5% reduction in action potential duration (APD) at 50% repolarization (APD50) and 3.5–5.75% reduction at 90% repolarization (APD90). Catering the effect of inertia can help the research community to improve future computational models in investigating the electromechanics of the heart.

This work deals with the dynamics of the human knee during vertical jump exercise. The focus is on the joint forces necessary to produce the jump and to dissipate energy during landing. A two-dimensional (2D) sagittal plane, inverse dynamics human leg model is developed. This model uses data from a motion capture system and force plates in order to predict knee and hip joint forces during the vertical jump exercise. The model consists of three bony structures femur, tibia, and patella, ligament structures to include both cruciate and collateral ligaments, and knee joint muscles. The inverse dynamics model is solved using optimization in order to predict joint forces during this exercise. matlab software package is used for the optimization computations. Results are compared with data available in the literature. This work provides insight regarding contact forces and ligaments forces, muscle forces, and knee and hip contact forces in the vertical jump exercise.

Tissue freezing has significant applications in cryopreservation and cryosurgery processes. The freezing rate is an important factor during the cryopreservation process. To improve and make an accurate estimation of the freezing rate, radiation heat transfer plays a major role. To analyze in details, a two-dimensional coupled conduction–radiation model is developed. The tissue is frozen from the left side while the other sides are at the initial temperature. Finite volume method (FVM) is used to discretize both the radiative transfer equation (RTE) and energy equation. The algebraic equation after discretization is solved by the tri-diagonal matrix algorithm. The radiative heat flux is calculated by solving the RTE. The energy equation provides the temperature field. The enthalpy-porosity method is used to update the liquid volume fraction and thus the freezing front is captured. A linearization technique is proposed to linearize the radiative source term in the energy equation to avoid chances of divergence of the solution. The present model is first validated with the results of the existing literature and a good agreement is found. The effects of different parameters such as conduction–radiation parameter, scattering albedo, extinction coefficient and Stefan number on the prediction of temperature field, and the position of the freezing front are studied in details. It is found that a decrease in the values of conduction–radiation parameter, scattering albedo, and increase in the values of extinction coefficient and Stefan number cause more radiative heat loss. Hence, the freezing rate is improved and more frozen region is observed.

The characteristics of anisotropic material, finite deformation, and lubrication in biological system diminish the friction and wear between soft tissues with relative motion. In this research, the lubrication between pleura surfaces in relative motion is analyzed by soft elastohydrodynamic lubrication (soft-EHL) line contact with an equivalent model. The model is a soft, transversely isotropic (TI) elastic strip with finite thickness sliding under a rigid sinusoidal surface, which is used to simulate the surface irregularities, with lubricant in between. The material nonlinearity and the curvature effects due to finite deformation, which are significant in soft-EHL, are considered in the present study. The pressure distribution, film thickness, von Mises stress, and material deformation are analyzed and discussed under various combinations of elastic moduli and Poisson's ratios for the transversely isotropic models. The simulation results reveal that the soft-EHL modeling fit actual result better than the traditional EHL (t-EHL) modeling. The Poisson's ratio ν p = 0.1 and ν pz = 0.49 situation will have more gentle stress distribution. The present soft-EHL solver can be used to realize some desired stress distributions and to identify the mechanical properties bio-materials under the aids of experiments.

A robotic finger-actuated by novel artificial muscles known as Twisted and Coiled Polymer (TCP) muscles has been proposed as an inexpensive, yet high-performance component of a robotic hand in recent years. In this paper, the Euler-Lagrangian method coupled with an electro-thermo-mechanical model-based transfer function was used for the analysis of finger joints in the hand. Experiments were performed at three power magnitudes provided to the TCP muscles and the output angular displacements of the index finger subtended corresponding to the power levels were measured. The measured input and output parameters were used for system identification. To elucidate how the new artificial muscle influence the finger motion, two types of numerical simulations were performed: Force Input Simulation (FIS) using measured force as input and Power Input Simulation (PIS) using measured electrical power as input. Results were quantified statistically, and the simulated data were compared with the experimental results. Sensitivity analysis was also presented to understand the effect of the mechanical properties on the system. This model will help in understanding the effect of the TCP muscles and other similar smart actuators on the dynamics of the robotic finger.

In this paper, we develop an analytical framework for designing the locomotion of mobile robots with a circular core and equispaced diametral legs, each having a radial translational degree of freedom. The mechanism has resemblance with certain cellular locomotions. The robot travels by radial actuation of the legs in a sequential and synchronized manner. Two elementary regimes of motion are first designed using the geometry and degrees of freedom of the mechanism. Overall motion of the robot is generated by repeated switching between the two regimes. The paper addresses both kinematics and kinetics of the mechanism, enabling the prediction of trajectories, and computation of constraint as well as actuation forces. Simulation results are provided in support of the theory developed.

X-ray computed tomography (XCT) is a promising non-destructive evaluation technique for additively manufactured (AM) parts with complex shapes. Industrial XCT scanning is a relatively new development, and XCT has several acquisition parameters a user can change for a scan whose effects are not fully understood. An artifact incorporating simulated defects of different sizes was produced using laser powder bed fusion (LPBF) AM. The influence of six XCT acquisition parameters was investigated experimentally based on a fractional factorial designed experiment. Twenty experimental runs were performed. The noise level of the XCT images was affected by the acquisition parameters, and the importance of the acquisition parameters was ranked. The measurement results were further analyzed to understand the probability of detection (POD) of the simulated defects. The POD determination process is detailed, including estimation of the POD confidence limit curve using a bootstrap method. The results are interpreted in the context of the AM process and XCT acquisition parameters.