scholarly journals Learning to Control Arm Stiffness Under Static Conditions

2004 ◽  
Vol 92 (6) ◽  
pp. 3344-3350 ◽  
Author(s):  
Mohammad Darainy ◽  
Nicole Malfait ◽  
Paul L. Gribble ◽  
Farzad Towhidkhah ◽  
David J. Ostry
Keyword(s):  
Impedance Control ◽  
Arm Movement ◽  
Realistic Model ◽  
Impedance Change ◽  
Robotic Device ◽  
Lateral Direction ◽  
Maximum Stiffness ◽  
Asymmetric Pattern ◽  
Static Conditions ◽  
Endpoint Stiffness

We used a robotic device to test the idea that impedance control involves a process of learning or adaptation that is acquired over time and permits the voluntary control of the pattern of stiffness at the hand. The tests were conducted in statics. Subjects were trained over the course of 3 successive days to resist the effects of one of three different kinds of mechanical loads: single axis loads acting in the lateral direction, single axis loads acting in the forward/backward direction, and isotropic loads that perturbed the limb in eight directions about a circle. We found that subjects in contact with single axis loads voluntarily modified their hand stiffness orientation such that changes to the direction of maximum stiffness mirrored the direction of applied load. In the case of isotropic loads, a uniform increase in endpoint stiffness was observed. Using a physiologically realistic model of two-joint arm movement, the experimentally determined pattern of impedance change could be replicated by assuming that coactivation of elbow and double joint muscles was independent of coactivation of muscles at the shoulder. Moreover, using this pattern of coactivation control we were able to replicate an asymmetric pattern of rotation of the stiffness ellipse that was observed empirically. These findings are consistent with the idea that arm stiffness is controlled through the use of at least two independent co-contraction commands.

scholarly journals Endoscopic endonasal transsphenoidal surgery using the iArmS operation support robot: initial experience in 43 patients

2017 ◽  
Vol 42 (5) ◽  
pp. E10 ◽  
Author(s):  
Toshihiro Ogiwara ◽  
Tetsuya Goto ◽  
Alhusain Nagm ◽  
Kazuhiro Hongo
Keyword(s):  
Pituitary Adenoma ◽  
Transsphenoidal Surgery ◽  
Arm Movement ◽  
Clinical Results ◽  
Initial Experience ◽  
Robotic Device ◽  
Endoscopic Endonasal ◽  
Arm Support ◽  
Study Population ◽  
Endoscopic Endonasal Transsphenoidal Surgery

ObjectiveThe intelligent arm-support system, iArmS, which follows the surgeon’s arm and automatically fixes it at an adequate position, was developed as an operation support robot. iArmS was designed to support the surgeon’s forearm to prevent hand trembling and to alleviate fatigue during surgery with a microscope. In this study, the authors report on application of this robotic device to endoscopic endonasal transsphenoidal surgery (ETSS) and evaluate their initial experiences.MethodsThe study population consisted of 43 patients: 29 with pituitary adenoma, 3 with meningioma, 3 with Rathke’s cleft cyst, 2 with craniopharyngioma, 2 with chordoma, and 4 with other conditions. All patients underwent surgery via the endonasal transsphenoidal approach using a rigid endoscope. During the nasal and sphenoid phases, iArmS was used to support the surgeon’s nondominant arm, which held the endoscope. The details of the iArmS and clinical results were collected.Results iArmS followed the surgeon’s arm movement automatically. It reduced the surgeon’s fatigue and stabilized the surgeon’s hand during ETSS. Shaking of the video image decreased due to the steadying of the surgeon’s scope-holding hand with iArmS. There were no complications related to use of the device.ConclusionsThe intelligent armrest, iArmS, seems to be safe and effective during ETSS. iArmS is helpful for improving the precision and safety not only for microscopic neurosurgery, but also for ETSS. Ongoing advances in robotics ensure the continued evolution of neurosurgery.

scholarly journals Voluntary Control of Human Jaw Stiffness

2005 ◽  
Vol 94 (3) ◽  
pp. 2207-2217 ◽  
Author(s):  
Douglas M. Shiller ◽  
Guillaume Houle ◽  
David J. Ostry
Keyword(s):  
Nervous System ◽  
Arm Movement ◽  
Vertical Axis ◽  
Voluntary Control ◽  
Robotic Device ◽  
Movement Accuracy ◽  
Human Arm ◽  
Applied Forces ◽  
Stiffness Control

Recent studies of human arm movement have suggested that the control of stiffness may be important both for maintaining stability and for achieving differences in movement accuracy. In the present study, we have examined the voluntary control of postural stiffness in 3D in the human jaw. The goal is to address the possible role of stiffness control in both stabilizing the jaw and in achieving the differential precision requirements of speech sounds. We previously showed that patterns of kinematic variability in speech are systematically related to the stiffness of the jaw. If the nervous system uses stiffness control as a means to regulate kinematic variation in speech, it should also be possible to show that subjects can voluntarily modify jaw stiffness. Using a robotic device, a series of force pulses was applied to the jaw to elicit changes in stiffness to resist displacement. Three orthogonal directions and three magnitudes of forces were tested. In all conditions, subjects increased the magnitude of jaw stiffness to resist the effects of the applied forces. Apart from the horizontal direction, greater increases in stiffness were observed when larger forces were applied. Moreover, subjects differentially increased jaw stiffness along a vertical axis to counteract disturbances in this direction. The observed changes in the magnitude of stiffness in different directions suggest an ability to control the pattern of stiffness of the jaw. The results are interpreted as evidence that jaw stiffness can be adjusted voluntarily, and thus may play a role in stabilizing the jaw and in controlling movement variation in the orofacial system.

Relations between Attentional and Intentional Neural Systems

1995 ◽  
Vol 81 (3) ◽  
pp. 947-951 ◽  
Author(s):  
Gianpaolo Basso ◽  
Paolo Nichelli
Keyword(s):  
Visual Field ◽  
Cerebral Hemisphere ◽  
Arm Movement ◽  
Neural Systems ◽  
Right Visual Field ◽  
Contralateral Hemisphere ◽  
Lateral Direction ◽  
Response Latencies ◽  
Rightward Movement ◽  
The Right

This study explored whether preparing an arm movement influences detection of a visual stimulus We cued subjects to respond with either a rightward or a leftward movement to the appearance of a stimulus located either in the centre, in the left, or in the right visual field. Programming a movement toward a lateral direction enhanced visual attention at that side. Rightward movements were associated with an attentional cost only for responses to a central location, while leftward movements slowed response latencies to both central and right-sided stimuli. We hypothesized that programming a rightward movement depends on the activation of intentional centers in either cerebral hemisphere. On the contrary, leftward movements might be only driven by the contralateral hemisphere.

Sensitivity Analysis of Dynamics System in the Upper Limb Movement Control

2012 ◽  
Author(s):  
Kai Chen ◽  
Richard A. Foulds
Keyword(s):  
Sensitivity Analysis ◽  
Upper Limb ◽  
Impedance Control ◽  
Muscle Length ◽  
Movement Control ◽  
Arm Movement ◽  
Human Movement ◽  
Limb Movement ◽  
Feedback Information ◽  
Analysis Of Dynamics

The dependence of muscle force on muscle length gives rise to a “spring–like” behavior which has been shown to play an important role during human movement. Neville Hogan (Hogan, 1985) proposed a mathematical model in terms of impedance control of arm movement. Discussing this work, Dr. Hogan admits that it can not effectively model all aspects of the performance of the system. He said “Controlling the complete dynamic behavior of the limb may be beyond the capacity of the central nervous system. If the disturbance is sufficiently abrupt, then, because of the inevitable transmission delays, continuous intervention based on neural feedback information will not be a feasible method of modulating these quantities.”. However, the model proposed in this study, accomplished most the work which Hogan believed was not feasible. In order to validate the result of proposed model, this study perform sensitivity analysis between the results produced by the dynamics system and the results measured, the comparison showed the difference between these two results were less than 10%, which strongly support the idea that proposed dynamic model can accurately reflect dynamics system in the upper limb movement control.

scholarly journals Effects of Human Arm Impedance on Dynamics Learning and Generalization

2009 ◽  
Vol 101 (6) ◽  
pp. 3158-3168 ◽  
Author(s):  
Mohammad Darainy ◽  
Andrew A. G. Mattar ◽  
David J. Ostry
Keyword(s):  
Motor Learning ◽  
Force Field ◽  
Strong Correlation ◽  
Transfer Of Learning ◽  
Kinematic Error ◽  
Robotic Device ◽  
Human Arm ◽  
Applied Forces ◽  
Static Conditions ◽  
Dynamic Perturbation

Previous studies have demonstrated anisotropic patterns of hand impedance under static conditions and during movement. Here we show that the pattern of kinematic error observed in studies of dynamics learning is associated with this anisotropic impedance pattern. We also show that the magnitude of kinematic error associated with this anisotropy dictates the amount of motor learning and, consequently, the extent to which dynamics learning generalizes. Subjects were trained to reach to visual targets while holding a robotic device that applied forces during movement. On infrequent trials, the load was removed and the resulting kinematic error was measured. We found a strong correlation between the pattern of kinematic error and the anisotropic pattern of hand stiffness. In a second experiment subjects were trained under force-field conditions to move in two directions: one in which the dynamic perturbation was in the direction of maximum arm impedance and the associated kinematic error was low and another in which the perturbation was in the direction of low impedance where kinematic error was high. Generalization of learning was assessed in a reference direction that lay intermediate to the two training directions. We found that transfer of learning was greater when training occurred in the direction associated with the larger kinematic error. This suggests that the anisotropic patterns of impedance and kinematic error determine the magnitude of dynamics learning and the extent to which it generalizes.

scholarly journals Control of Hand Impedance Under Static Conditions and During Reaching Movement

2007 ◽  
Vol 97 (4) ◽  
pp. 2676-2685 ◽  
Author(s):  
Mohammad Darainy ◽  
Farzad Towhidkhah ◽  
David J. Ostry
Keyword(s):  
Muscle Activation ◽  
Impedance Control ◽  
Longitudinal Direction ◽  
Movement Direction ◽  
Reference Trajectory ◽  
Reaching Movement ◽  
Counterclockwise Rotation ◽  
Modeling Studies ◽  
Environmental Instability ◽  
Static Conditions

It is known that humans can modify the impedance of the musculoskeletal periphery, but the extent of this modification is uncertain. Previous studies on impedance control under static conditions indicate a limited ability to modify impedance, whereas studies of impedance control during reaching in unstable environments suggest a greater range of impedance modification. As a first step in accounting for this difference, we quantified the extent to which stiffness changes from posture to movement even when there are no destabilizing forces. Hand stiffness was estimated under static conditions and at the same position during both longitudinal (near to far) and lateral movements using a position-servo technique. A new method was developed to predict the hand “reference” trajectory for purposes of estimating stiffness. For movements in a longitudinal direction, there was considerable counterclockwise rotation of the hand stiffness ellipse relative to stiffness under static conditions. In contrast, a small counterclockwise rotation was observed during lateral movement. In the modeling studies, even when we used the same modeled cocontraction level during posture and movement, we found that there was a substantial difference in the orientation of the stiffness ellipse, comparable with that observed empirically. Indeed, the main determinant of the orientation of the ellipse in our modeling studies was the movement direction and the muscle activation associated with movement. Changes in the cocontraction level and the balance of cocontraction had smaller effects. Thus even when there is no environmental instability, the orientation of stiffness ellipse changes during movement in a manner that varies with movement direction.

Impedance Control Balances Stability With Metabolically Costly Muscle Activation

2004 ◽  
Vol 92 (5) ◽  
pp. 3097-3105 ◽  
Author(s):  
David W. Franklin ◽  
Udell So ◽  
Mitsuo Kawato ◽  
Theodore E. Milner
Keyword(s):  
Force Field ◽  
Muscle Activation ◽  
Force Fields ◽  
Impedance Control ◽  
Reaching Movements ◽  
The Novel ◽  
Minimum Level ◽  
Stable Direction ◽  
Endpoint Stiffness ◽  
Unstable Dynamics

Humans are able to stabilize their movements in environments with unstable dynamics by selectively modifying arm impedance independently of force and torque. We further investigated adaptation to unstable dynamics to determine whether the CNS maintains a constant overall level of stability as the instability of the environmental dynamics is varied. Subjects performed reaching movements in unstable force fields of varying strength, generated by a robotic manipulator. Although the force fields disrupted the initial movements, subjects were able to adapt to the novel dynamics and learned to produce straight trajectories. After adaptation, the endpoint stiffness of the arm was measured at the midpoint of the movement. The stiffness had been selectively modified in the direction of the instability. The stiffness in the stable direction was relatively unchanged from that measured during movements in a null force field prior to exposure to the unstable force field. This impedance modification was achieved without changes in force and torque. The overall stiffness of the arm and environment in the direction of instability was adapted to the force field strength such that it remained equivalent to that of the null force field. This suggests that the CNS attempts both to maintain a minimum level of stability and minimize energy expenditure.

On the influence of specimen thickness in TEM images of super-conducting vortices

1996 ◽  
Vol 54 ◽  
pp. 724-725
Author(s):  
J. Bonevich ◽  
D. Capacci ◽  
G. Pozzi ◽  
K. Harada ◽  
H. Kasai ◽  
...  
Keyword(s):  
Flux Line ◽  
Analytical Form ◽  
Realistic Model ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Flux Tubes ◽  
Analytical Expression ◽  
Flux Lines ◽  
Normal Core ◽  
Two Parameters

The successful observation of superconducting flux lines (fluxons) in thin specimens both in conventional and high Tc superconductors by means of Lorentz and electron holography methods has presented several problems concerning the interpretation of the experimental results. The first approach has been to model the fluxon as a bundle of flux tubes perpendicular to the specimen surface (for which the electron optical phase shift has been found in analytical form) with a magnetic flux distribution given by the London model, which corresponds to a flux line having an infinitely small normal core. In addition to being described by an analytical expression, this model has the advantage that a single parameter, the London penetration depth, completely characterizes the superconducting fluxon. The obtained results have shown that the most relevant features of the experimental data are well interpreted by this model. However, Clem has proposed another more realistic model for the fluxon core that removes the unphysical limitation of the infinitely small normal core and has the advantage of being described by an analytical expression depending on two parameters (the coherence length and the London depth).

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