waashk/dblp huggingface dataset:
powered ankle--foot prosthesis improves walking metabolic economy. at moderate to fast walking speeds, the human ankle provides net positive work at high-mechanical-power output to propel the body upward and forward during the stance period. on the contrary, conventional ankle-foot prostheses exhibit a passive-elastic response during stance, and consequently, cannot provide net work. clinical studies indicate that transtibial amputees using conventional prostheses have higher gait metabolic rates than normal. researcher s believe that the main cause for these higher rates is due to the inability of conventional prostheses to provide sufficient positive power at terminal stance in the trailing leg to limit heel strike losses of the adjacent leading leg. in this investigation, we evaluate the hypothesis that a powered ankle-foot prosthesis, capable of providing human-like ankle work and power during stance, can decrease the metabolic cost of transport (cot) compared to a conventional passive-elastic prosthesis. to test the hypothesis, a powered prosthesis is built that comprises a unidirectional spring, configured in parallel with a force-controllable actuator with series elasticity. the prosthesis is shown to deliver the high mechanical power and net positive work observed in normal human walking. the rate of oxygen consumption and carbon dioxide production is measured as a determinant of metabolic rate on three unilateral transtibial amputees walking at self-selected speeds. we find that the powered prosthesis decreases the amputee's metabolic cot on average by 14% compared to the conventional passive-elastic prostheses evaluated (flex-foot ceterus® and freedom innovations sierra), even thuugh the powered system is over twofold heavier than the conventional devices. these results highlight the clinical importance of prosthetic interventions that closely mimic the mass distribution, kinetics, and kinematics of the missing limb.
a passive 2-dof walker: hunting for gaits using virtual holonomic constraints. a planar compass-like biped on a shallow slope is one of the simplest models of a passive walker. it is a 2-degree-of-freedom (dof) impulsive mechanical system that is known to possess periodic solutions reminiscent of human walking. finding such solutions is a challenging computational task that has attractedmany researchers who are motivated by various aspects of passive and active dynamic walking. we propose a new approach to find stable as well as unstable hybrid limit cycles without integrating the full set of differential equations and, at the same time, without approximating the dynamics. the procedure exploits a time-independent representation of a possible periodic solution via a virtual holonomic constraint. the description of the limit cycle obtained in this way is useful for the analysis and characterization of passive gaits as well as for design of regulators to achieve gaits with the smallest required control efforts. some insights into the notion of hybrid zero dynamics, which are related to such a description, are presented as well.
geometrical optimization of parallel mechanisms based on natural frequency evaluation: application to a spherical mechanism for future space applications. this paper presents an optimization procedure conceived to design parallel mechanisms (pms) with legs of constant and/or variable length connected, at their endpoints, to a fixed base and a movable platform through universal and spherical joints, respectively. in the proposed procedure, the first natural frequency of the mechanism is the objective function to be maximized. the optimization problem is formulated by using dimensionless variables in order to identify the optimal geometry independently of mechanism size, platform density, and leg cross-sectional area and material. as a case study, the procedure is employed to find the optimal geometry of a 2-dof spherical pm to be used as an orienting device in future space missions.
a foldable 3-dof parallel mechanism with application to a flat-panel tv mounting device. this paper deals with a new 3-degree-of-freedom (dof) parallel mechanism for a flat-panel tv mounting device with two rotations and one translation. the most important operational requirements of this device are that it should support the heavy weight of the flat-panel tv and should be foldable to save space between the flat panel and the wall. an asymmetric parallel structure that has three kinematic chains with internal four-bar linkage is proposed to meet such requirements. kinematic modeling was performed along with actuator sizing. finally, the mechanism was developed and tested to show its effectiveness as a flat-panel tv mounting device.
online segmentation and clustering from continuous observation of whole body motions. this paper describes a novel approach for incremental learning of human motion pattern primitives through online observation of human motion. the observed time series data stream is first stochastically segmented into potential motion primitive segments, based on the assumption that data belonging to the same motion primitive will have the same underlying distribution. the motion segments are then abstracted into a stochastic model representation and automatically clustered and organized. as new motion patterns are observed, they are incrementally grouped together into a tree structure, based on their relative distance in the model space. the tree leaves, which represent the most specialized learned motion primitives, are then passed back to the segmentation algorithm so that as the number of known motion primitives increases, the accuracy of the segmentation can also be improved. the combined algorithm is tested on a sequence of continuous human motion data that are obtained through motion capture, and demonstrates the performance of the proposed approach.
case studies of musculoskeletal-simulation-based rehabilitation program evaluation. variability in motor rehabilitation program outcomes can be attributed not only to individual components (human patient/rehabilitation equipment) but also to their system-level interactions. thus, effective deployment of a rehabilitation program depends upon: 1) suitable therapist selection of user-device ergonomics; 2) adjustable device settings; and 3) exercise regimen parameters; to achieve desired system-levelmotor performance. in this paper, we discuss aspects of creation of a virtual design environment, leveraging tools from musculoskeletal analysis, optimization, and simulation-based design, to permit therapists to rapidly evaluate and systematically customize rehabilitation programs. specifically, this framework is intended to facilitate 1) parametric study of ergonomic/device/regimen settings on musculoskeletal performance; 2) use of design tools such as optimization for decision support in arriving at the best program; and 3) scaffolded examination of linkage between form and function by iterative what-if type of analyses. we use two case studies (bicep-curling and motor rehabilitative driving) to highlight benefits of such simulation-based rehabilitation program evaluation.
parallel mechanisms with bifurcation of schoenflies motion. type synthesis of lower mobility parallel mechanisms (pms) has attracted extensive attention in research community of robotics over the last seven years. one important trend in this area is to synthesize pms with prespecified motion properties. this paper focuses on the type synthesis of a special family of pms whose moving platform can undergo a bifurcation of schoenflies motion. first, bifurcation of schoenfties motion in pms is interpreted in terms of displacement group theory and the basic limb bond {x(y)} {r(n, x)} is identified. further, the geometric condition for constructing a pm with bifurcation of schoenflies motion is presented. the kinematic equivalence between {x(y)} {r(n,x)} and {x(y)} {x(x)} is proven. four subcategories of irreducible representation of the product {x(y)} {x(x)} are proposed and the limb chains that produce the desired limb bond are synthesized. finally, the partitioned mobility of pms with bifurcation of schoenflies motion and its effect on actuation selection are discussed.
swing-up control of the pendubot: an impulse-momentum approach. the standard control problem of the pendubot refers to the task of stabilizing its equilibrium configuration with the highest potential energy. linearization of the dynamics of the pendubot about this equilibrium results in a completely controllable system and allows a linear controller to be designed for local asymptotic stability. for the underactuated pendubot, the important task is, therefore, to design a controller that will swing up both links and bring the configuration variables of the system within the region of attraction of the desired equilibrium. this paper provides a new method for swing-up control based on a series of rest-to-rest maneuvers of the first link about its vertically upright configuration. the rest-to-rest maneuvers are designed such that each maneuver results in a net gain in energy of the second link. this results in swing-up of the second link and the pendubot configuration reaching the region of attraction of the desired equilibrium. a four-step algorithm is provided for swing-up control followed by stabilization. simulation results are presented to demonstrate the efficacy of the approach.
needle insertion parameter optimization for brachytherapy. this paper presents a new needle path planning method for the insertion of rigid needles into deformable tissue. the needle insertion point, needle heading, and needle depth are optimized by minimizing the distance between a rigid needle and a number of targets in the tissue. the optimization method is based on iterative simulations performed using a tissue finite element model. at each iteration, the best 3-d line fitted to the displaced targets in the deformed tissue is used as a candidate for a new insertion line. first, this method is implemented in a prostate brachytherapy simulator under different boundary conditions tominimize the targeting error. it is shown that the optimization method converges in a few iterations and decreases the seed misplacement error to less than the needle diameter. second, the efficacy of the optimization algorithm is verified by optimizing the insertion parameters for a brachytherapy needle before insertion into a prostate tissue phantom. the elastic properties of the phantom and the needle-tissue interaction parameters were identified in an independent experiment. the optimization algorithm is effective in decreasing the targeting error.
boundary condition relaxation method for stepwise pedipulation planning of biped robots. a completely stepwise online pedipulation planning method is proposed. it is an analytical approach based on the general solution of the equation of motion of an approximate dynamical biped model whose mass is concentrated at the center of mass. a physically feasible referential trajectory with a constraint about the reaction force taken into account is planned only in one interval by relaxing the boundary condition, namely, by admitting a certain level of error between the desired and actually reached states, and discontinuity of zero-moment point at each end of the interval. it potentially creates responsivemotions that require strong instantaneous acceleration. a semiautomatic continual pedipulation planning method is also presented. it generates a referential trajectory of the whole body only from the next desired foot placement. the validity of the proposed method is ensured through experiments with a small anthropomorphic robot.
a nonlinear set membership approach for the localization and map building of underwater robots. this paper proposes a set membership method based on interval analysis to solve the simultaneous localization and map building (slam) problem. the principle of the approach is to cast the slam problem into a constraint satisfaction problem for which interval propagation algorithms are particularly powerful. the resulting propagation method is illustrated on the localization and map building of an actual underwater robot.
reactive path planning in a dynamic environment. this paper deals with the problem of path planning in a dynamic environment, where the workspace is cluttered with unpredictably moving objects. the concept of the virtual plane is introduced and used to create reactive kinematic-based navigation laws. a virtual plane is an invertible transformation equivalent to the workspace, which is constructed by using a local observer. this results in important simplifications of the collision detection process. based on the virtual plane, it is possible to determine the intervals of the linear velocity and the paths that lead to collisions with moving obstacles and then derive a dynamic window for the velocity and the orientation to navigate the robot safely. the speed of the robot and the orientation angle are controlled independently using simple collision cones and collision windows constructed from the virtual plane. the robot's path is controlled using kinematic-based navigation laws that depend on navigation parameters. these parameters are tuned in real time to adjust the path of the robot. simulation is used to illustrate collision detection and path planning.
estimation of terrain forces and parameters for rigid-wheeled vehicles. this paper provides a methodology for the estimation of resistance, thrust, and resistive torques on each wheel of a rigid-wheeled vehicle generated at the vehicle-terrain interface, and from these forces and moments, a methodology to estimate terrain parameters is presented. terrain force estimation, which is independent of a terrain model, can infer the ability to accelerate, climb, or tow a load independent of the underlying terrain properties. when a terrain model is available, parameters of that model, such as soil cohesion, friction angle, maximum normal stress, and stress distribution parameters, are determined from estimated vehicle-terrain forces using a multiple-model estimation approach, providing parameters that relate to accepted mobility metrics. the methodology requires a standard proprioceptive sensor suite--accelerometers, rate gyros,wheel speeds, motor torques, and ground speed. sinkage sensors are not required. simulation results demonstrate efficacy of the method on three terrains spanning a range of soil cohesions reported in the literature.
visual servo control achieving nanometer resolution in x - y - z. this paperpresents a three-axis vision motion sensor and its applications to visual servo control. the vision sensor is integrated with a three-axis piezo stage to form a visual servo control system that achieves nanometer resolution in all three x- y-z motion axes. motion measurement is achieved using a single interferometer-equipped optical microscope. a real-time imageprocessing algorithm that processes interference fringe patterns and that achieves nanometer out-of-plane resolution is presented. furthermore, a feedback-control scheme is introduced to control the sensor plane using an objective-z-positioner to enable automatic tracking of moving objects. it expands the out-of-plane measurement range of the vision sensor beyond its inherent depth of field of several micrometers to 100 µm and beyond. an integrated visual servo system is implemented and experimental results are shown.
a highly backdrivable, lightweight knee actuator for investigating gait in stroke. many of those who survive a stroke develop a gait disability known as stiff-knee gait (skg). characterized by reduced knee flexion angle during swing, people with skg walk with poor energy efficiency and asymmetry due to the compensatory mechanisms required to clear the foot. previous modeling studies have shown that knee flexion activity directly before the foot leaves the ground, and this should result in improved knee flexion angle during swing the goal of this research is to physically test this hypothesis using robotic intervention. we developed a device that is capable of assisting knee flexion torque before swing but feels imperceptible (transparent) for the rest of the gait cycle. this device uses sheathed bowden cable to control the deflection of a compliant torsional spring in a configuration known as a series elastic remote knee aquator (serka). in this investigation, we describe the design and evaluation of serka, which includes a pilot experiment on stroke subjects. serka could supply a substantial torque (12 n-m) in less than 20 ms, with a maximum torque of 41 n-m. the device resisted knee flexion imperceptibly when desired, at less than 1 n-m rms torque during normal gait. with the remote location of the actuator, the user experiences a mass of only 1-2 kg on the knee. we found that the device was capable of increasing both peak knee flexion angle and velocity during gait in stroke subjects. thus, the serka is a valid experimental device that selectively alters knee kinetics and kinematics in gait after stroke.
motion synchronization control of distributed multisubsystems with invariant local natural dynamics. this paper addresses a new control strategy for synchronizing two or more distributed and interconnected dynamic systems having communication time delays. the proposed strategy that uses the smith predictor principle and delay information not only achieves synchronization but also preserves the natural local dynamics of each subsystem without being affected by the feedback nature of control. the proposed synchronization scheme is generalized to cases that deal with an arbitrary number of heterogeneous interconnected systems through dynamic scaling of input under a ring-type network configuration. in addition, possibility of applying the proposed scheme to nonlinear systems is discussed. simulation and experimental tests are conducted to validate theoretical results.
emg-based control of a robot arm using low-dimensional embeddings. as robots come closer to humans, an efficient human-robot-control interface is an utmost necessity. in this paper, electromyographic (emg) signals from muscles of the human upper limb are used as the control interface between the user and a robot arm. a mathematical model is trained to decode upper limb motion from emg recordings, using a dimensionality-reduction technique that represents muscle synergies and motion primitives. it is shown that a 2-d embedding of muscle activations can be decoded to a continuous profile of arm motion representation in the 3-d cartesian space, embedded in a 2-d space. the system is used for the continuous control of a robot arm, using only emg signals from the upper limb. the accuracy of the method is assessed through real-time experiments, including random arm motions.
autonomous robotic pick-and-place of microobjects. this paper presents a robotic system that is capable of both picking up and releasing microobjects with high accuracy, reliability, and speed. due to force-scaling laws, large adhesion forces at the microscale make rapid, accurate release of microobjects a long-standing challenge in micromanipulation, thus representing a hurdle toward automated robotic pick-and-place of micrometer-sized objects. the system employs a novel microelectromechanical systems (mems) microgripper with a controllable plunging structure to impact amicroobject that gains sufficient momentum to overcome adhesion forces. the performance was experimentally quantified through the manipulation of 7.5-10.9 µm borosilicate glass spheres in an ambient environment. experimental results demonstrate that the system, for the first time, achieves a 100% success rate in release (which is based on 700 trials) and a release accuracy of 0.45±0.24 µm. high-speed, automated microrobotic pick-and-place was realized by visually recognizing the microgripper and microspheres, by visually detecting the contact of the microgripper with the substrate, and by vision-based control. example patterns were constructed through automated microrobotic pick-and-place of microspheres, achieving a speed of 6 s/sphere, which is an order of magnitude faster than the highest speed that has been reported in the literature.
a darboux-frame-based formulation of spin-rolling motion of rigid objects with point contact. this paper investigates the kinematics of spin-rolling motion of rigid objects. this paper does not consider slipping but applies a darboux frame to develop kinematics of spin-rolling motion, which occurs in a nonholonomic system. a new formulation of spin-rolling motion of the moving object is derived in terms of contravariant vectors, rolling velocity, and geometric invariants, including normal curvature, geodesic curvature, and geodesic torsion of the respective contact curve. the equation is represented with geometric invariants. it can be readily generalized to suit both arbitrary parametric surface and contact trajectory and can be differentiated to any order. effect of the relative curvatures and torsion on spin-rolling kinematics is explicitly presented. the translation velocity of an arbitrary point on the moving object is also derived based on the darboux frame.
kinematic-sensitivity indices for dimensionally nonhomogeneous jacobian matrices. numerous performance indices have been proposed to compare robot architectures based on their kinematic properties. however, none of these indices seems to draw a consensus among the robotics community. the most notorious indices, which aremanipulability and dexterity, still entail some drawbacks, which are mainly due to the impossibility to define a single invariant metric for the special euclidean group. the natural consequence is to use two distinct metrics, i.e., one for rotations and one for point displacements, as has already been proposed by other researchers. this is the approach used in this paper, where we define the maximum rotation sensitivity and the maximum point-displacement sensitivity. these two indices provide tight upper bounds to the end-effector rotation and point-displacement sensitivity under a unit-magnitude array of actuated-joint displacements. therefore, their meaning is thought to be clear and definite to the designer of a robotic manipulator. furthermore, methods for the computation of the proposed indices are devised, some of their properties are established and interpreted in the context of robotic manipulator design, and an example is provided.
consequences of geometric imperfections for the control of redundantly actuated parallel manipulators. actuation redundancy increases and homogenizes the kinematic dexterity and stiffness as well as the force distribution among the actuators of parallel-kinematics machines (pkms). it also allows for internal prestresses within the pkm without affecting the environment that can potentially be used to account for secondary tasks, such as active stiffness and backlash-avoiding control. however, in the presence of geometric uncertainties, this feature can become a serious problem, since then, control forces may be annihilated, or even some of the intentional prestress components may interfere with the environment. while model uncertainties can generally be tackled with robust-control concepts, actuation redundancy of pkm impedes the use of established robust-control schemes. the effect of such uncertainties and the applicability of standard model-based control schemes are analyzed in this paper. it is shown that geometric uncertainties lead to parasitic perturbation forces that cannot be compensated by adjustment of the controls. an amended version of the augmented pd and computed torque-control scheme is proposed that does not suffer from such effects.