waashk/dblp huggingface dataset:
minimum-order kalman filter with vector selector for accurate estimation of human body orientation. this paper describes a new quaternion-based kalman filter (kf) for estimating human body orientation using an inertial/magnetic sensor. the proposed algorithm is comprised of a quaternion measurement step and a kf step that are connected in feedback relationship. this allows the algorithm to have a minimum-order structure (i.e., fourth order) that is computationally very efficient. furthermore, to offer more reliable information to the quaternion measurement step, a vector selector scheme is adopted, which effectively adds the gyro measurement to the so-called wahba's problem that conventionally uses only the accelerometer and magnetometer measurements. this protects the algorithm against undesirable conditions such as fast movements and temporary magnetic disturbances, enabling it to compute an accurate orientation estimate. due to the computational efficiency of the algorithm, it is suitable for real-time ambulatory human motion tracking applications that require multiple and untethered inertial/magnetic sensors with low-cost onboard processing.
an adaptive automated robotic task-practice system for rehabilitation of arm functions after stroke. we present a novel robotic task-practice system, i.e., adaptive and automatic presentation of tasks (adapt), which is designed to enhance the recovery of upper extremity functions in patients with stroke. we designed adapt in accordance with current training guidelines for stroke rehabilitation; adapt engages the patient intensively, actively, and adaptively in a variety of realistic functional tasks that require reaching and manipulation. a general-purpose robot simulates the dynamics of the functional tasks and presents these functional tasks to the patient. a novel tool-changing system enables adapt to automatically switch between the tools corresponding to the functional tasks. the control architecture of adapt is composed of three main components: a high-level task scheduler, a functional task model, and a low-level admittance controller. the high-level task scheduler adaptively selects the task to practice and sets the task difficulty based on the previous performance of the patients. the functional task model generates desired trajectories based on learned models of task dynamics. tasks dynamics are modeled with receptive field weighted regression (rfwr), such that the feel of the task tools is accurately modeled, and the task difficulty can be easily adjusted. the low-level admittance controller, which is also learned with rfwr, implements the selected task trajectory for robot-patient interaction. the results of a preliminary experiment with a healthy subject demonstrate the successful operation of adapt.
a reactive robotized interface for lower limb rehabilitation: clinical results. this paper presents clinical results from the use of monitor-nomad (monimad), which is a reactive robotized interface for lower limb rehabilitation of patients suffering from cerebellar disease. the first problem to be addressed is the postural analysis of sit-to-stand motion. experiments with healthy subjects were performed for this purpose. analysis of external forces shows that sit-to-stand transfer can be subdivided into several phases: preacceleration, acceleration, start rising, and rising. observation of center of pressure, ground forces, and horizontal components force on handles yields rules that identify the stability of the patient and adjust the robotic interface motion to the human voluntary movement. these rules are used in a fuzzy-based controller implementation. the controller is validated on experiments with diseased patients at bellan hospital, paris, france.
structural shakiness of nonoverconstrained translational parallel mechanisms with identical limbs. one important category of parallel mechanisms is the translational parallel mechanism (tpm). this paper focuses on the structural shakiness of the nonoverconstrained tpm. such a structural shakiness is due to the unavoidable lack of rigidity of the real bodies, which leads to uncheckable orientation changes ofthe moving platform of a tpm. using algebraic properties of displacement subsets and, especially, displacement lie subgroup theory, we show that the structural shakiness of the nonoverconstrained tpm is inherently determined by the structural type of its limb chains. a structural shakiness index (ssi) for a nonoverconstrained tpm is introduced. when the set of feasible displacements of the end body of a 5-degree-of.freedom (dofs) limb chain contains two infinities of parallel axes of rotation, we have ssi = 2; when the displacement set of the end body of a 5-dof limb chain contains only one infinity of parallel axes of rotation, we have ssi = 1. it is proven that nonoverconstained tpms constructed with limb chains with ssi = 1 are much less prone to orientation changes than those constructed with limb chains with ssi = 2. based on the ssi, we enumerate limh kinematic chains and construct 21 nonoverconstrained tpms with less shakiness.
asymptotically stable walking of a five-link underactuated 3-d bipedal robot. this paper presents three feedback controllers that achieve an asymptotically stable, periodic, and fast walking gait for a 3-d bipedal robot consisting of a torso, revolute knees, and passive (unactuated) point feet. the walking surface is assumed to be rigid and flat; the contact between the robot and the walking surface is assumed to inhibit yaw rotation. the studied robot has 8 dof in the single support phase and six actuators. in addition to the reduced number of actuators, the interest of studying robots with point feet is that the feedback control solution must explicitly account for the robot's natural dynamics in order to achieve balance while walking. we use an extension of the method of virtual constraints and hybrid zero dynamics (hzd), a very successful method for planar bipeds, in order to simultaneously compute a periodic orbit and an autonomous feedback controller that realizes the orbit, for a 3-d (spatial) bipedal walking robot. this method allows the computations for the controller design and the periodic orbit to be carried out on a 2-dof subsystem of the 8-dof robot model. the stability of the walking gait under closed-loop control is evaluated witt the linearization of the restricted poincare map of the hzd. most periodic walking gaits for this robot are unstable when the controlled outputs are selected to be the actuated coordinates. three strategies are explored to produce stable walking. the first strategy consists of imposing a stability condition during the search of a periodic gait by optimization. the second strategy uses an event-based controller to modify the eigenvalues of the (linearized) poincare map. in the third approach, the effect of output selection on the zero dynamics is discussed and a pertinent choice of outputs is proposed, leading to stabilization without the use of a supplemental event-based controller.
planar bipedal jumping gaits with stable landing. in this paper, landing stability of jumping gaits is studied for a four-link planar biped model. rotation of the foot during the landing phase leads to underactuation due to the passive degree of freedom at the toe, which results in nontrivial zero dynamics (zd). compliance between the foot and ground is modeled as a spring-damper system. rotation of the foot along with the compliance model introduces switching in the zd. the stability conditions for the "switching zd" and closed-loop dynamics (cld) are established. "critical potential index" and "critical kinetic index" are introduced as measures of the stability of the cld of the biped during landing. landing stability is achieved by utilizing the stability conditions. stable jumping motion is experimentally realized on a biped robot.
a linear relaxation technique for the position analysis of multiloop linkages. this paper presents a new method to isolate all configurations that a multiloop linkage can adopt. the problem is tackled by means of formulation and resolution techniques that fit particularly well together. the adopted formulation yields a system of simple equations (only containing linear, bilinear, and quadratic monomials, and trivial trigonometric terms for the helical pair only) whose structure is later exploited by a branch-and-prune method based on linear relaxations. the method is general, as it can be applied to linkages with single or multiple loops with arbitrary topology, involving lower pairs of any kind, and complete, as all possible solutions get accurately bounded, irrespective of whether the linkage is rigid or mobile.
self-aligning exoskeleton axes through decoupling of joint rotations and translations. to automatically align exoskeleton axes to human anatomical axes, we propose to decouple the joint rotations from the joint translations. decoupling can reduce setup times and painful misalignment forces, at the cost of increased mechanical complexity and movement inertia. the decoupling approach was applied to the dampace and limpact exoskeletons.
adaptive/robust control for time-delay teleoperation. the control of time-delay bilateral teleoperation systems involves a delicate tradeoff between the conflicting requirements of transparency and robust stability. the control design is complicated by latency in data communication between the master and slave sites as well as uncertainties in the dynamics of operator, master, slave, and environment. this paper proposes a systematic design procedure for improving teleoperation fidelity while maintaining its stability in the presence of dynamic uncertainty and a constant time delay. in a two-step control approach, first local lyapunov-based adaptive/nonlinear controllers are applied to linearize the system dynamics and eliminate dependency on the master and slave parameters. teleoperation coordination, subject to parametric uncertainty in the user and environment dynamics, is then achieved by formulating an i/o time-delay h∞ robust control synthesis that is solved via its decomposition to the so-called adobe problems. the transparency and robust stability properties of the proposed method is examined via numerical analysis, furthermore, the results are successfully validated in experiments.
robotic cell injection system with position and force control: toward automatic batch biomanipulation. biological cell injection is laborious work that requires lengthy training and suffers from a low success rate. in this paper, a robotic cell-injection system for automatic injection of batch-suspended cells is proposed. to facilitate the process, these suspended cells are held and fixed to a cell array by a specially designed cell-holding device, and injected one by one through an "outof-plane" cell-injection process. a micropipette equipped with a polyvinylidene fluoride microforce sensor to measure real-time injection force is integrated in the proposed system. through calibration, an empirical relationship between the cell-injection force and the desired injector pipette trajectory is obtained in advance. then, after decoupling the out-of-plane cell injection into a position control in the x-y horizontal plane and an impedance control in the z-axis, a position and force control algorithm is developed to control the injection pipette. the depth motion of the injector pipette, which cannot be observed by microscope, is indirectly controlled via the impedance control, and the desired force is determined from the online x-y position control and cell calibration results. finally, experimental results demonstrate the effectiveness of the proposed approach.
return maps, parameterization, and cycle-wise planning of yo-yo playing. this note presents a unified approach to nominal control generation and return map parameterization for yo-yo playing. the approach is based on choosing an intermediate state of the yo-yo as the parameter and formulating an optimization problem with appropriate boundary conditions that incorporate the corresponding parameter. by solving the optimization problems, both the return map and the nominal optimal control for the robot can be obtained. the return map is naturally parameterized with the intermediate state, which can be treated as a virtual control. the return map facilitates the application of standard analysis and design methods for discrete-time control systems. the approach is promising as it might be extended to control other cyclic dynamic systems.
sensorless position control using feedforward internal force for completely restrained parallel-wire-driven systems. generally, point-to-point control for a completely restrained (cr) parallel-wire-driven system requires a balancing internal force to prevent slackening of wires, along with a feedback term based on some displacement sensor. this paper specifically describes cr systems' internal force properties, then presents the possibility of motion convergence at a desired position when the internal force balancing at a position is given as sensorless feedforward input. subsequently, we use the property of internal force positively for sensorless position control. this positioning method is applicable for low-cost manipulation, which does not require high accuracy, and for emergency positioning of systems when sensors malfunction.
a new assessment of singularities of parallel kinematic chains. this paper presents a novel assessment of singularities of general parallel kinematic chains. hierarchical levels in which different critical phenomena originate are recognized. at each level, the causes of singular events are identified and interpreted, and on their basis, a comprehensive taxonomy is proposed. first, the unactuated kinematic chain is studied.the concepts of leg and passive-constraint singularities are described, and stationary and increased instantaneous mobility configurations are identified. then, a set of motorized joints is chosen. the effects of first-level singularities on the actuated chain are investigated, and further phenomena are identified, such as redundancy singularities and active-constraint singularities. the notions of reaction and action spaces are originally discussed. the consequences on the ability of the actuated chain to effectively govern its local and global freedoms are analyzed, and the complex interactions between the various singular events are studied. the instantaneous redundancy of actuators, which occur when these work either against each other or against joint constraints, is also evaluated. finally, when the input-output mechanism is considered, the events described at the previous stages are interpreted within the perspective of the machine's desired use.
using haptic feedback to improve grasp force control in multiple sclerosis patients. we describe a simple and low-cost system that can help multiple sclerosis (ms) patients with asymmetric impairment to exert better grasp force control in manipulation tasks. the approach consists of measuring force vectors at the fingertips of the impaired hand, computing the force imbalance among the fingers, and providing corresponding haptic signals to the fingers of the opposite hand. tests conducted on 24 ms patients indicated that for those with mild impairment, slightly better results were obtained with an "event-cue" feedback (ecf) that alerted them when the grasp forces were straying outside of a desirable range. for patients with more severe impairment, better results were obtained by providing a proportional signal, in which the frequency and duty cycle of vibration pulses were correlated directly with the magnitudes of the fingertip forces. post-test surveys of the patients also indicated that mildly impaired subjects preferred an eventcue feedback, and more severely impaired subjects preferred the proportional feedback.
optimal design of a 4-dof parallel manipulator: from academia to industry. this paper presents an optimal design of a parallel manipulator aiming to perform pick-and-place operations at high speed and high acceleration. after reviewing existing architectures of high-speed and high-acceleration parallel manipulators, a new design of a 4-dof parallel manipulator is presented, with an articulated traveling plate, which is free of internal singularities and is able to achieve high performances. the kinematic and simplified, but realistic, dynamic models are derived and validated on a manipulator prototype. experimental tests show that this design is able to perform beyond the high targets, i.e., it reaches a speed of 5.5 m/s and an acceleration of 165 m/s2. the experimental prototype was further optimized on the basis of kinematic and dynamic criteria. once the motors, gear ratio, and several link lengths are determined, a modified design of the articulated traveling plate is proposed in order to reach a better dynamic equilibrium among the four legs of the manipulator. the obtained design is the basis of a commercial product offering the shortest cycle times among all robots available in today's market.
description of instantaneous restriction space for multi-dofs bilateral teleoperation systems using position sensors in unstructured environments. this paper investigates a novel position-sensor-based force reflection framework for multi-degree-of-freedom (dof) bilateral teleoperation systems in unstructured environments. the conventional position-sensor-based force reflection method, which is known as position error feedback, may generate grossly inaccurate force reflection directions during collisions involving the slave manipulator links. the proposed restriction space projection framework calculates the instantaneous restriction space to provide the accurate force reflection, regardless of kinematic dissimilarity (kds) conditions of bilateral teleoperation systems. simulation results confirmed the validity of the proposed framework in a kds bilateral teleoperation system under various constraint conditions.
flow-through policies for hybrid controller synthesis applied to fully actuated systems. this paper addresses the coupled navigation and control problem for fully actuated dynamical systems operating in cluttered environments. the proposed method composes local feedback control policies to address the global problem in a formally correct manner. our contribution extends the method of sequential composition to a new class of flow-through policies, which are defined for an idealized point robot that is subject to bounds on velocity and acceleration. these policies, which are defined over convex polytopes, express natural behaviors and guarantee safe trajectories while respecting system constraints. this paper presents a constructive technique for building hybrid control systems with guaranteed transitions and stability properties. simulation results demonstrate policy-based decision making for various initial conditions.
mechanics of precurved-tube continuum robots. this paper presents a new class of thin, dexterous continuum robot, which we call active cannulas due to their potential medical applications. an active cannula is composed of telescoping, concentric, precurved superelastic tubes that can be axially translated and rotated at the base relative to one another. active cannulas derive bending not from tendon wires or other external mechanisn 15 but from elastic tube interaction in the backbone itself, permitting high dexterity and small size, and dexterity improves with miniaturization. they are designed to traverse narrow and winding environments without relying on "guiding" environmental reaction forces. these features seem ideal for a variety of applications where a very thin robot with tentacle-like dexterity is needed. in this paper, we apply beam mechanics to obtain a kinematic model of active cannula shape and describe design tools that result from them modeling process. after deriving general equations, we apply them to a simple three-link active cannula. experimental results illustrate the importance of including torsional effects and the ability of our model to predict energy bifurcation and active cannula shape.
design and analysis of a totally decoupled flexure-based xy parallel micromanipulator. in this paper, a concept of totally decoupling is proposed for the design of a flexure parallel micromanipulator with both input and output decoupling. based on flexure hinges, the design procedure for an xy totally decoupled parallel stage (tdps) is presented, which is featured with decoupled actuation and decoupled output motion as well. by employing (double) compound parallelogram flexures and a compact displacement amplifier, a class of novel xy tdps with simple and symmetric structures are enumerated, and one example is chosen for further analysis. the kinematic and dynamicmodeling of the manipulator are conducted by resorting to compliance and stiffness analysis based on the matrix method, which are validated by finite-element analysis (fea). in view of predefined performance constraints, the dimension optimization is carried out by means of particle swarm optimization, and a prototype of the optimized stage is fabricated for performance tests. both fea and experimental studies well validate the decoupling property of the xy stage that is expected to be adopted into micro-/nanoscale manipulations.
image-based visual servo control of the translation kinematics of a quadrotor aerial vehicle. in this paper, we investigate a range of image-based visual servo control algorithms for regulation of the position ofa quadrotor aerial vehicle. the most promising control algorithms have been successfully implemented on an autonomous aerial vehicle and demonstrate excellent performance.
stabilization of a hierarchical formation of unicycle robots with velocity and curvature constraints. the paper proposes a new geometric approach to the stabilization of a hierarchical formation of unicycle robots. hierarchical formations consist of elementary leader-follower units disposed on a rooted tree: each follower sees its relative leader as a fixed point in its own reference frame. robots' linear velocity and trajectory curvature are forced to satisfy some given bounds. the major contribution of the paper is to study the effect of these bounds on the admissible trajectories of the main leader. in particular, we provide recursive formulas for the maximum velocity and curvature allowed for the main leader, so that the robots can achieve the desired formation while respecting their input constraints. an original formation control law is proposed and the asymptotic stabilization is proved. simulation experiments illustrate the theory and show the effectiveness of the proposed designs.
3-d source seeking for underactuated vehicles without position measurement. our past work introduced source seeking methods for gps-denied autonomous vehicles using only local signal measurement and operating in two dimensions. in this paper, we extend these results to three dimensions. the 3-d extensions introduce many interesting challenges, including the choice of vehicle models in 3-d, sensov placement to allow probing-based gradient estimation of an unknown signal field in 3-d, the question of what type of pattern of vehicle motion can be produced in an underactuated 3-d vehicle to allow tuning by single-loop or multiloop extremum seeking, and the shape of attractors, which become very complex in 3-d. we present two control schemes that address these questions. the first scheme focuses on vehicles with a constant forward velocity and the ability to actuate pitch and yaw velocities. the second scheme employs vehicles with constant forward and pitch velocities and actuate only the roll velocity. our results include convergence analysis and simulation results.