Path Curvature in Workspace and in Joint Space: Evidence for Coexisting Coordinative Rules in Aiming

In this study we tried to establish whether point-to-point aiming movements are planned in workspace, joint space, or both. Eight right-handed subjects performed horizontal, vertical, and diagonal aiming movements on a transversal plane. Movements were performed at several speeds. Curvature variations of the hand and corresponding joint-space paths were investigated as a function of position, direction, and speed. Straightness of hand paths predominated for vertical movements but was systematically violated for horizontal and top-right to bottom-left movements. Furthermore, the hand-path curvature of the latter movements increased with speed. Joint-space paths showed more deviation from a straight line than hand paths except for top-left to bottom-right movements in which the paths were equally curved. A comparison of normalized path curvatures at the hand and joint level indicated that in aiming, the coordinative rule of straight-line production seems to apply to both workspace and joint-space planning. The present findings confirm Kawato's (1996) views that optimization processes operate concurrently at the two control levels of arm-trajectory formation under study.

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Development of Point-to-Point Path Control in Actuator Space for Hydraulic Knuckle Boom Crane

Actuators ◽

10.3390/act9020027 ◽

2020 ◽

Vol 9 (2) ◽

pp. 27

Author(s):

Konrad Johan Jensen ◽

Morten Kjeld Ebbesen ◽

Michael Rygaard Hansen

Keyword(s):

Feedback Linearization ◽

Control Algorithm ◽

Joint Space ◽

Path Control ◽

Straight Line ◽

Starting Point ◽

Novel Method ◽

Point To Point ◽

Almost All ◽

Boom Crane

This paper presents a novel method for point-to-point path control for a hydraulic knuckle boom crane. The developed path control algorithm differs from previous solutions by operating in the actuator space instead of the joint space or Cartesian space of the crane. By operating in actuator space, almost all the parameters and constraints of the system become either linear or constant, which greatly reduces the complexity of both the control algorithm and path generator. For a given starting point and endpoint, the motion for each actuator is minimized compared to other methods. This ensures that any change in direction of motion is avoided, thereby greatly minimizing fatigue, jerky motion, and energy consumption. However, where other methods may move the tool-point in a straight line from start to end, the method in actuator space will not. In addition, when working in actuator space in combination with pressure-compensated control valves, there is no need for linearization of the system or feedback linearization due to the linear relationship between the control signal and the actuator velocities. The proposed solution has been tested on a physical system and shows good setpoint tracking and minimal oscillations.

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On indirect Methods of acquiring Knowledge - The Method of History. - The First Table of Mortality

The Assurance Magazine ◽

10.1017/s2046164x00054740 ◽

1851 ◽

Vol 1 (1) ◽

pp. 40-46

Author(s):

Edwin James Farren

Keyword(s):

Real Line ◽

English Language ◽

The Other ◽

Adult Student ◽

Indirect Methods ◽

The Real ◽

Straight Line ◽

Point To Point ◽

The One

The term scholar, as current in the English language, has two extreme acceptations, tyro and proficient; or what the later Greeks fancifully termed the alpha and omega of acquirement. If we attempt to trace the steps by which even the adult student of any especial branch of professional or literary knowledge has fairly passed the boundary defined by the one meaning in passing on to that position denoted by the other, it will commonly be found, that in place of that lucid order, that straight line from point to point, which theory and resolve generally premise, the real order of acquirement has been desultory—the real line of progression, circuitous and uncertain.

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Regions of Feasible Point-to-Point Trajectories in the Cartesian Workspace of Fully-Parallel Manipulators

Volume 1: 25th Design Automation Conference ◽

10.1115/detc99/dac-8645 ◽

1999 ◽

Author(s):

Damien Chablat ◽

Philippe Wenger

Keyword(s):

Parallel Manipulator ◽

Cartesian Product ◽

Parallel Manipulators ◽

Joint Space ◽

Inverse Kinematic ◽

Connected Components ◽

Feasible Point ◽

Cartesian Space ◽

Point Trajectories ◽

Point To Point

Abstract The goal of this paper is to define the n-connected regions in the Cartesian workspace of fully-parallel manipulators, i.e. the maximal regions where it is possible to execute point-to-point motions. The manipulators considered in this study may have multiple direct and inverse kinematic solutions. The N-connected regions are characterized by projection, onto the Cartesian workspace, of the connected components of the reachable configuration space defined in the Cartesian product of the Cartesian space by the joint space. Generalized octree models are used for the construction of all spaces. This study is illustrated with a simple planar fully-parallel manipulator.

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Highly Directive Biconic Antennas Embedded in a Dielectric

Applied Sciences ◽

10.3390/app10248828 ◽

2020 ◽

Vol 10 (24) ◽

pp. 8828

Author(s):

Alessandro Chiolerio ◽

Lorenzo Diazzi ◽

Daniele Funaro

Keyword(s):

Power Transmission ◽

Dielectric Material ◽

Communication Channels ◽

Extended Model ◽

Wireless Power ◽

Speed Of Light ◽

Straight Line ◽

Electromagnetic Signals ◽

Point To Point ◽

Wave Phenomena

Designing antennas suitable for generating highly directive electromagnetic signals has become a fundamental task. This is particularly relevant for the development of efficient and sustainable point-to-point communication channels, and for energy transfer. Indeed, these are nowadays expanding areas of research. In order to deal with said particular wave phenomena, an extension of the electrodynamics equations is taken into account, where exact solitonic type solutions are admitted. These waves may have compact support and travel along a straight line, without dissipation, at the speed of light. The result suggests the design of biconic type antennas having specific properties that are numerically examined in this paper. The cones, supplied with an oscillating source, are embedded in a dielectric material of suitable shape, with the purpose of driving the signal in the proper direction. The computations based on the extended model are aimed toward simulating the possibility of generating peculiar wave behaviors, in view of practical implementations in the framework of point-to-point communications or wireless power transmission.

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A unified framework for coordinated multi-arm motion planning

The International Journal of Robotics Research ◽

10.1177/0278364918765952 ◽

2018 ◽

Vol 37 (10) ◽

pp. 1205-1232 ◽

Cited By ~ 7

Author(s):

Seyed Sina Mirrazavi Salehian ◽

Nadia Figueroa ◽

Aude Billard

Keyword(s):

Moving Objects ◽

Control Strategies ◽

Dynamic Control ◽

Joint Space ◽

Quadratic Program ◽

Task Space ◽

Unified Framework ◽

External Variable ◽

Arm Motion ◽

Point To Point

Coordination is essential in the design of dynamic control strategies for multi-arm robotic systems. Given the complexity of the task and dexterity of the system, coordination constraints can emerge from different levels of planning and control. Primarily, one must consider task-space coordination, where the robots must coordinate with each other, with an object or with a target of interest. Coordination is also necessary in joint space, as the robots should avoid self-collisions at any time. We provide such joint-space coordination by introducing a centralized inverse kinematics (IK) solver under self-collision avoidance constraints, formulated as a quadratic program and solved in real-time. The space of free motion is modeled through a sparse non-linear kernel classification method in a data-driven learning approach. Moreover, we provide multi-arm task-space coordination for both synchronous or asynchronous behaviors. We define a synchronous behavior as that in which the robot arms must coordinate with each other and with a moving object such that they reach for it in synchrony. In contrast, an asynchronous behavior allows for each robot to perform independent point-to-point reaching motions. To transition smoothly from asynchronous to synchronous behaviors and vice versa, we introduce the notion of synchronization allocation. We show how this allocation can be controlled through an external variable, such as the location of the object to be manipulated. Both behaviors and their synchronization allocation are encoded in a single dynamical system. We validate our framework on a dual-arm robotic system and demonstrate that the robots can re-synchronize and adapt the motion of each arm while avoiding self-collision within milliseconds. The speed of control is exploited to intercept fast moving objects whose motion cannot be predicted accurately.

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Sensorimotor adaptation of point-to-point arm movements after spaceflight: the role of internal representation of gravity force in trajectory planning

Journal of Neurophysiology ◽

10.1152/jn.00081.2011 ◽

2011 ◽

Vol 106 (2) ◽

pp. 620-629 ◽

Cited By ~ 24

Author(s):

Jérémie Gaveau ◽

Christos Paizis ◽

Bastien Berret ◽

Thierry Pozzo ◽

Charalambos Papaxanthis

Keyword(s):

Central Nervous System ◽

Nervous System ◽

Arm Movements ◽

The Body ◽

Sensorimotor Adaptation ◽

Subjective Feeling ◽

Gravity Level ◽

The Central Nervous System ◽

Path Curvature ◽

Point To Point

After an exposure to weightlessness, the central nervous system operates under new dynamic and sensory contexts. To find optimal solutions for rapid adaptation, cosmonauts have to decide whether parameters from the world or their body have changed and to estimate their properties. Here, we investigated sensorimotor adaptation after a spaceflight of 10 days. Five cosmonauts performed forward point-to-point arm movements in the sagittal plane 40 days before and 24 and 72 h after the spaceflight. We found that, whereas the shape of hand velocity profiles remained unaffected after the spaceflight, hand path curvature significantly increased 1 day after landing and returned to the preflight level on the third day. Control experiments, carried out by 10 subjects under normal gravity conditions, showed that loading the arm with varying loads (from 0.3 to 1.350 kg) did not affect path curvature. Therefore, changes in path curvature after spaceflight cannot be the outcome of a control process based on the subjective feeling that arm inertia was increased. By performing optimal control simulations, we found that arm kinematics after exposure to microgravity corresponded to a planning process that overestimated the gravity level and optimized movements in a hypergravity environment (∼1.4 g). With time and practice, the sensorimotor system was recalibrated to Earth's gravity conditions, and cosmonauts progressively generated accurate estimations of the body state, gravity level, and sensory consequences of the motor commands (72 h). These observations provide novel insights into how the central nervous system evaluates body (inertia) and environmental (gravity) states during sensorimotor adaptation of point-to-point arm movements after an exposure to weightlessness.

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Kinematics and control of frog hindlimb movements

Journal of Neurophysiology ◽

10.1152/jn.1991.65.3.547 ◽

1991 ◽

Vol 65 (3) ◽

pp. 547-562 ◽

Cited By ~ 61

Author(s):

D. J. Ostry ◽

A. G. Feldman ◽

J. R. Flanagan

Keyword(s):

Nervous System ◽

High Speed ◽

Imaging System ◽

Maximum Velocity ◽

Joint Space ◽

Motion Path ◽

Three Dimension ◽

Joint Angles ◽

Joint Configuration ◽

Straight Line

1. The determinants of the motion path of the hindlimb were explored in both intact and spinal frogs. In the spinal preparations the kinematic properties of withdrawal and crossed-extension reflexes were studied. In the intact frog the kinematics of withdrawal and swimming movements were examined. Frog hindlimb paths were described in joint angle (intrinsic) coordinates rather than limb endpoint (extrinsic) coordinates. 2. To study withdrawal and crossed-extension reflexes, the initial angles at the hip, knee, and ankle were varied. Withdrawal and crossed extension were recorded in three dimension (3-D) with the use of an infra-red spatial imaging system. Swimming movements against currents of different speeds were obtained with high-speed film. 3. Three strategies were considered related to the form of the hypothesized equilibrium paths specified by the nervous system: all trajectories lie on a single line in angular coordinates; all trajectories are directed toward a common final position; and all trajectories have the same direction independent of initial joint configuration. 4. Joint space paths in withdrawal were found to be straight and parallel independent of the initial joint configuration. The hip and knee were found to start simultaneously and in 75% of the conditions tested to reach maximum velocity simultaneously. Hip-knee maximum velocity ratios were similar in magnitude over differences in initial joint angles. This is consistent with the observation of parallel paths and supports the view that the nervous system specifies a single direction for equilibrium trajectories. 5. Straight line paths with slopes similar to those observed in withdrawal in the spinal preparation were found in swimming movements in the intact frog. Straight line paths in joint space are consistent with the idea that swimming and withdrawal are organized and controlled in a joint-level coordinate system. The similarities observed between spinal and intact preparations suggest that a common set of constructive elements underlies these behaviors. 6. Path curvature was introduced when joint limits were approached toward the end of the movement. Depending on the initial joint angles, the joint movements ended at different times. When initial joint angles were unequal, joints moving from smaller initial angles reached their functional limits earlier and stopped first. 7. In withdrawal and crossed extension in the spinal frog, velocity profiles at a given joint were similar over the initial portion of the curve for movements of different amplitude. This is consistent with the idea that withdrawal and crossed-extension movements of different amplitude are produced by a constant rate of shift of the equilibrium position.

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Lower bounds for point-to-point wandering exponents in Euclidean first-passage percolation

Journal of Applied Probability ◽

10.1017/s0021900200018222 ◽

2000 ◽

Vol 37 (04) ◽

pp. 1061-1073

Author(s):

C. Douglas Howard

Keyword(s):

Lower Bounds ◽

Upper Bound ◽

Line Segment ◽

Passage Time ◽

Straight Line Segment ◽

First Passage Percolation ◽

First Passage ◽

Straight Line ◽

Point To Point

In first-passage percolation models, the passage time T(0,L) from the origin to a point L is expected to exhibit deviations of order |L|χ from its mean, while minimizing paths are expected to exhibit fluctuations of order |L|ξ away from the straight line segment . Here, for Euclidean models in dimension d, we establish the lower bounds ξ ≥ 1/(d+1) and χ ≥(1-(d-1)ξ)/2. Combining this latter bound with the known upper bound ξ ≤ 3/4 yields that χ ≥ 1/8 for d=2.

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Postural Control of Three-Dimensional Prehension Movements

Journal of Neurophysiology ◽

10.1152/jn.1997.77.1.452 ◽

1997 ◽

Vol 77 (1) ◽

pp. 452-464 ◽

Cited By ~ 74

Author(s):

Michel Desmurget ◽

Claude Prablanc

Keyword(s):

Postural Control ◽

Upper Limb ◽

Three Dimensional ◽

Joint Space ◽

Object Orientation ◽

Task Space ◽

Movement Onset ◽

Dynamic Level ◽

Prehension Movements ◽

Path Curvature

Desmurget, Michel and Claude Prablanc. Postural control of three-dimensional prehension movements. J. Neurophysiol. 77: 452–464, 1997. This experiment was carried out to test the hypothesis that three-dimensional upper limb movements could be initiated and controlled in the joint space via a mechanism comparing an estimate of the current postural state of the upper arm with a target value determined by one specific inverse static transform converting the coordinates of the object into a set of arm, forearm, and wrist angles. This hypothesis involves two main predictions: 1) despite joint redundancy, the posture reached by the upper limb should be invariant for a given context; and 2) a movement programmed in joint space should exhibit invariant characteristics of the joint covariation pattern as well as a corresponding variable hand path curvature in the task space. To test these predictions, we examined prehension movements toward a cylindrical object presented at a fixed spatial location and at various orientations without vision of the moving limb. Once presented, the object orientation was either kept constant (unperturbed trials) or suddenly modified at movement onset (perturbed trials). Three-dimensional movement trajectories were analyzed in both joint and task spaces. For the unperturbed trials, the task space analysis showed a variable hand path curvature depending on object orientation. The joint space analysis showed that the seven final angles characterizing the upper limb posture at hand-to-object contact varied monotonically with object orientation. At a dynamic level, movement onset and end were nearly identical for all joints. Moreover, for all joints having a monotonic variation, maximum velocity occurred almost simultaneously. For the elbow, the only joint presenting a reversal, the reversal was synchronized with the time to peak velocity of the other joint angles. For the perturbed trials, a smooth and complete compensation of the movement trajectory was observed in the task space. At a static level the upper limb final posture was identical to that obtained when the object was initially presented at the orientation following the perturbation. This result was particularly remarkable considering the large set of comfortable postures allowed by joint redundancy. At a dynamic level, the joints' covariation pattern was updated to reach the new target posture. The initial synergies were not disrupted by the perturbation, but smoothly modified, the different joints' movements ending nearly at the same time. Taken together, these results support the hypothesis that prehension movements are initiated and controlled in the joint space on the basis of a joint angular error vector rather than a spatial error vector.

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