Could Chalk Hopping Be Caused by Reverse Chatter?

2018 ◽  
Author(s):  
John W. Sanders
Keyword(s):  
Control Algorithm ◽  
Human Hand ◽  
Related Phenomenon ◽  
Painlevé Paradox ◽  
Loss Of Contact ◽  
Subsequent Motion ◽  
Parameter Values ◽  
External Loads ◽  
Physical Manifestation ◽  
Two Bodies

Anyone who has ever used a chalkboard is probably familiar with the phenomenon of “chalk hopping,” where the chalk unexpectedly skips across the chalkboard, leaving a dotted line in its wake. Such behavior is ubiquitous to mechanical systems with moving parts in contact, where it is almost always undesirable. It is widely believed that hopping behavior is a physical manifestation of either the classical Painlevé paradox or a related phenomenon called dynamical jam. The present paper poses the question of whether chalk hopping might be caused by a different, and much more recently discovered, instability called “reverse chatter,” in which two bodies initially in sustained contact can lose contact through a sequence of impacts with increasing amplitude. Previous simulations of reverse chatter have considered only constant external loads, which do not adequately model the forces exerted on a piece of chalk. The current work presents simulation results for a model system in the presence of a control algorithm that mimics the human hand by attempting to keep the chalk in contact with the chalkboard. The simulations reveal that there exist physically realistic parameter values for which a loss of contact occurs that cannot be attributed to either the classical Painlevé paradox or dynamical jam, but which can only be attributed to reverse chatter. Furthermore, the subsequent motion of the system after losing contact is found to be strikingly similar to that of chalk hopping on a chalkboard, to a hitherto unparalleled degree. These results show that neither the classical Painlevé paradox nor dynamical jam is necessary for hopping behavior, and suggest that reverse chatter may be the most plausible explanation for chalk hopping.

scholarly journals Multidigit force control during unconstrained grasping in response to object perturbations

2017 ◽  
Vol 117 (5) ◽  
pp. 2025-2036 ◽  
Author(s):  
Abdeldjallil Naceri ◽  
Alessandro Moscatelli ◽  
Robert Haschke ◽  
Helge Ritter ◽  
Marco Santello ◽  
...  
Keyword(s):  
Nervous System ◽  
Control Algorithm ◽  
External Disturbance ◽  
Human Hand ◽  
Force Distribution ◽  
Robotic Hand ◽  
Robotic Grasping ◽  
Motor Synergies ◽  
Complex Anatomy ◽  
The Central Nervous System

Because of the complex anatomy of the human hand, in the absence of external constraints, a large number of postures and force combinations can be used to attain a stable grasp. Motor synergies provide a viable strategy to solve this problem of motor redundancy. In this study, we exploited the technical advantages of an innovative sensorized object to study unconstrained hand grasping within the theoretical framework of motor synergies. Participants were required to grasp, lift, and hold the sensorized object. During the holding phase, we repetitively applied external disturbance forces and torques and recorded the spatiotemporal distribution of grip forces produced by each digit. We found that the time to reach the maximum grip force during each perturbation was roughly equal across fingers, consistent with a synchronous, synergistic stiffening across digits. We further evaluated this hypothesis by comparing the force distribution of human grasping vs. robotic grasping, where the control strategy was set by the experimenter. We controlled the global hand stiffness of the robotic hand and found that this control algorithm produced a force pattern qualitatively similar to human grasping performance. Our results suggest that the nervous system uses a default whole hand synergistic control to maintain a stable grasp regardless of the number of digits involved in the task, their position on the objects, and the type and frequency of external perturbations. NEW & NOTEWORTHY We studied hand grasping using a sensorized object allowing unconstrained finger placement. During object perturbation, the time to reach the peak force was roughly equal across fingers, consistently with a synergistic stiffening across fingers. Force distribution of a robotic grasping hand, where the control algorithm is based on global hand stiffness, was qualitatively similar to human grasping. This suggests that the central nervous system uses a default whole hand synergistic control to maintain a stable grasp.

scholarly journals Validity of Mechanical advantage hypothesis of human grasping depends on the nature of task difficulty

2021 ◽  
Author(s):  
Banuvathy Rajakumar ◽  
Swarnab Dutta ◽  
Varadhan SKM
Keyword(s):  
Center Of Mass ◽  
Tangential Force ◽  
Contact Forces ◽  
Human Hand ◽  
Mechanical Advantage ◽  
Moment Arms ◽  
The Central Nervous System ◽  
Constant Magnitude ◽  
The Individual ◽  
External Loads

Abstract Successful object interaction during daily living involves maintaining the grasped object in a static equilibrium by properly arranging the fingertip contact forces. According to the mechanical advantage hypothesis, during supination or pronation torque production, fingers with longer moment arms would produce greater normal force than those with shorter moment arms. Previous studies have probed this hypothesis by investigating the force contributions of the individual fingers through systematic variations (or perturbations) of properties of the grasped handle. In the current study, we examined the applicability of this hypothesis in a paradigm wherein the thumb tangential force was constrained to a minimal constant magnitude. This was achieved by placing the thumb on a freely movable slider platform. The total mass of the handle was systematically varied by adding external loads directly below the center of mass of the handle. Our findings suggest that in the human hand, the central nervous system (CNS) adopts the principle of mechanical advantage depending on an abstract sense of challenge attached to the task situation.

scholarly journals A Static Control Algorithm for Adaptive Beam String Structures Based on Minimal Displacement

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Yanbin Shen ◽  
Huaqiang Cheng ◽  
Pengcheng Yang ◽  
Yaozhi Luo
Keyword(s):  
Control Algorithm ◽  
Simulated Annealing Algorithm ◽  
Control Process ◽  
Control Device ◽  
Linear Displacement ◽  
Smart Structure ◽  
Sensitivity Analysis Method ◽  
String Structure ◽  
Annealing Algorithm ◽  
External Loads

The beam string structure (BSS) is a type of prestressed structure and has been widely used in large span structures nowadays. The adaptive BSS is a typical smart structure that can optimize the working status itself by controlling the length of active struts via certain control device. The control device commonly consists of actuators in all struts and sensors on the beam. The key point of the control process is to determine the length adjustment values of actuators according to the data obtained by preinstalled sensors. In this paper, a static control algorithm for adaptive BSS has been presented for the adjustment solution. To begin with, an optimization model of adaptive BSS with multiple active struts is established, which uses a sensitivity analysis method. Next, a linear displacement control process is presented, and the adjustment values of struts are calculated by a simulated annealing algorithm. A nonlinear iteration procedure is used afterwards to calibrate the results of linear calculation. Finally, an example of adaptive BSS under different external loads is carried out to verify the feasibility and accuracy of the algorithm. And the results also show that the adaptive BSS has much better adaptivity and capability than the noncontrolled BSS.

Using a Virtual Reality-Based Night Drive Simulator as a Tool for the Virtual Prototyping of an Advanced Leveling Light System

2008 ◽  
Author(s):  
Jan Berssenbru¨gge ◽  
Sven Kreft ◽  
Ju¨rgen Gausemeier
Keyword(s):  
Vehicle Dynamics ◽  
Control Algorithm ◽  
Control Parameter ◽  
Driving Simulator ◽  
Virtual Prototyping ◽  
The Road ◽  
Virtual Test ◽  
Light System ◽  
Parameter Values ◽  
Real Test

Modern automobiles contain various mechatronical components to support the task of driving. To enhance driver vision and driving safety at night time, advanced lighting systems, such as a predictive advanced front lighting system (PAFS) enhance automotive lighting by swiveling the headlights horizontally into approaching curves on a winding road. In addition to this, basic leveling light systems tilt the headlights vertically, in order to adjust to the vehicle chassis pitch due to the vehicle load or suspension effects based on the vehicle dynamics from driving on a rough road. More advanced leveling systems even account for the vertical course of an undulating road using GPS-data to locate the vehicle’s position plus digital map data to predict the vertical course of the road in front of the vehicle. That way, the headlights follow the road curvature and illuminate the road ahead of the vehicle without glaring oncoming traffic. In order to design, evaluate, and optimize the control algorithm within the electronic control unit (ECU) of the leveling light system, various control parameter values need to be adjusted and fine-tuned to ensure an optimal response of the system to the current road scenario. For this task, numerous time-consuming and costly test drives at night are necessary. This paper proposes to use a Virtual Reality-based night driving simulator as tool to simulate and evaluate an advanced leveling light system. The PC-based night drive simulator visualizes the complex beam patterns of automotive headlights in high detail and in real-time. The user drives a simulated vehicle over a virtual test track at night, while the vehicle motion directly affects the lighting direction of headlights. Thus, the effect of the vehicle dynamics on the lighting can be evaluated directly in the simulator. The system is connected to the control algorithm of the advanced leveling light system, which controls the headlights tilting angle. This provides a close-to-reality simulation of the advanced leveling light system during a simulated drive at night. That way, within the virtual prototyping process of the advanced leveling light system, good combinations of control parameter values can be indentified, based on virtual test drives in the night driving simulator, and the number of real test drives can be reduced significantly. Promising combinations of the control parameter values then can be validated during a real test drive a night.

scholarly journals Prediction of Motion Intentions as a Novel Method of Upper Limb Rehabilitation Support

Sensors ◽  
2021 ◽  
Vol 21 (2) ◽  
pp. 410
Author(s):  
Bogusz Lewandowski ◽  
Sławomir Wudarczyk ◽  
Przemysław Sperzyński ◽  
Jacek Bałchanowski
Keyword(s):  
Upper Limb ◽  
Experimental Studies ◽  
Dynamic Parameter ◽  
Mechatronic System ◽  
Upper Limb Rehabilitation ◽  
Angular Velocities ◽  
Novel Method ◽  
Limb Rehabilitation ◽  
Parameter Values ◽  
External Loads

This article is devoted to the novel method of upper limb rehabilitation support using a dedicated mechatronic system. The mechatronic rehabilitation system’s main advantages are the repeatability of the process and the ability to measure key features and the progress of the therapy. In addition, the assisted therapy standard is the same for each patient. The new method proposed in this article is based on the prediction of the patient’s intentions, understood as the intentions to perform a movement that would be not normally possible due to the patient’s limited motor functions. Determining those intentions is realized based on a comparative analysis of measured kinematic (range of motion, angular velocities, and accelerations) and dynamic parameter values, as well as external loads resulting from the interaction of patients. Appropriate procedures were implemented in the control system, for which verification was conducted via experiments. The aim of the research in the article was to examine whether it is possible to sense the movement intentions of a patient during exercises, using only measured load parameters and kinematic parameters of the movement. In this study, the construction of a mechatronic system prototype equipped with sensory grip to measure the external loads, control algorithms, and the description of experimental studies were presented. The experimental studies of the mechanism were aimed at the verification of the proper operation of the system and were not a clinical trial.

Discrete Sliding Mode Controller Design Based on the Suboptimal LQR Approach

2003 ◽  
Author(s):  
Wen-Chun Yu ◽  
Gou-Jen Wang
Keyword(s):  
Control System ◽  
Sliding Mode Control ◽  
Performance Index ◽  
Control Algorithm ◽  
Position Control ◽  
Controller Design ◽  
Sliding Mode ◽  
Sliding Mode Controller ◽  
Control Loop ◽  
External Loads

A systematic and simple discrete sliding mode controller design scheme based on the suboptimal approach is presented. The behaviors of the control system can be determined through a preferred performance index. The AC servomotor position control is obtained using only the q-axis voltage control loop. The proposed method is simulated and experimented to verify the capability of this new sliding mode control algorithm. Properties such as easy implementation, fast resonse, and robust to external loads are demonstrated.

Robot Soft Grabbing with New Piezoresistive Tactile Sensor

2013 ◽  
Vol 744 ◽  
pp. 501-504 ◽  
Author(s):  
Jin Jun Chen ◽  
Ting Xiang
Keyword(s):  
Control Algorithm ◽  
Statistical Parameter ◽  
Control Program ◽  
Tactile Sensor ◽  
Visible Range ◽  
Human Hand ◽  
Active Perception ◽  
Tactile Sensors ◽  
Technology Application ◽  
And Control

A type of tactile sensors based on piezoresistive principle is designed for the robot grab force detection and control. According to human behaves and awareness, the robot grabbing control program imitate human hand grasp active perception and action mechanisms. With the tactile sensors, the slip and grasping process pressure signal is sampled and analysed by general time-domain statistical parameter, and a simpler control algorithm is researched. In the experiment the robot has accomplished soft grabbing by modeling human hand action and applied appropriate grabbing force on objects of different weights or material by means of the control algorithm. Experiments suggest that this sensor and action biomimetic process is suitable to be used in the tele-presence technology application in the case of the visible range or visual equipment aid especially.

scholarly journals Achieving Target Voriconazole Concentrations More Accurately in Children and Adolescents

2015 ◽  
Vol 59 (6) ◽  
pp. 3090-3097 ◽  
Author(s):  
Michael Neely ◽  
Ashley Margol ◽  
Xiaowei Fu ◽  
Michael van Guilder ◽  
David Bayard ◽  
...  
Keyword(s):  
Steady State ◽  
Trough Concentration ◽  
Population Model ◽  
Control Algorithm ◽  
Interquartile Range ◽  
Optimal Time ◽  
Therapeutic Drug ◽  
Multiple Model ◽  
Trough Concentrations ◽  
Parameter Values

ABSTRACTDespite the documented benefit of voriconazole therapeutic drug monitoring, nonlinear pharmacokinetics make the timing of steady-state trough sampling and appropriate dose adjustments unpredictable by conventional methods. We developed a nonparametric population model with data from 141 previously richly sampled children and adults. We then used it in our multiple-model Bayesian adaptive control algorithm to predict measured concentrations and doses in a separate cohort of 33 pediatric patients aged 8 months to 17 years who were receiving voriconazole and enrolled in a pharmacokinetic study. Using all available samples to estimate the individual Bayesian posterior parameter values, the median percent prediction bias relative to a measured target trough concentration in the patients was 1.1% (interquartile range, −17.1 to 10%). Compared to the actual dose that resulted in the target concentration, the percent bias of the predicted dose was −0.7% (interquartile range, −7 to 20%). Using only trough concentrations to generate the Bayesian posterior parameter values, the target bias was 6.4% (interquartile range, −1.4 to 14.7%;P= 0.16 versus the full posterior parameter value) and the dose bias was −6.7% (interquartile range, −18.7 to 2.4%;P= 0.15). Use of a sample collected at an optimal time of 4 h after a dose, in addition to the trough concentration, resulted in a nonsignificantly improved target bias of 3.8% (interquartile range, −13.1 to 18%;P= 0.32) and a dose bias of −3.5% (interquartile range, −18 to 14%;P= 0.33). With the nonparametric population model and trough concentrations, our control algorithm can accurately manage voriconazole therapy in children independently of steady-state conditions, and it is generalizable to any drug with a nonparametric pharmacokinetic model. (This study has been registered at ClinicalTrials.gov under registration no. NCT01976078.)

A Contact Force Model With Nonlinear Compliance and Residual Indentation1

2013 ◽  
Vol 81 (2) ◽  
Author(s):  
Xiaogang Xiong ◽  
Ryo Kikuuwe ◽  
Motoji Yamamoto
Keyword(s):  
Numerical Simulations ◽  
Contact Force ◽  
Relative Position ◽  
Biological Tissues ◽  
Force Model ◽  
Differential Algebraic Equation ◽  
Contact Force Model ◽  
Nonlinear Force ◽  
Loss Of Contact ◽  
Two Bodies

The contact between two bodies is a complicated phenomenon in which the force and the relative position have nonlinear relations. Empirical results in the literature show that, in some mechanical systems such as biological tissues, the relation between the contact force and the indentation is characterized by the following three features: (i) continuity of the force at the time of collision, (ii) a Hertz-like nonlinear force-indentation curve, and (iii) nonzero indentation at the time of loss of contact force. The conventional Hunt–Crossley (HC) model does not capture the feature (iii) as the model makes the contact force and the indentation reach zero simultaneously. This paper proposes a compliant contact model based on a differential-algebraic equation that satisfies all three features. The behaviors of the model and the effect of the parameters in the model are investigated through numerical simulations.

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