scholarly journals Contact force controlled robotic polishing for complex PMMA parts with an active end-effector

2021 ◽  
Vol 1 (1) ◽  
pp. 71-80
Author(s):  
Yang YU ◽  
Ruoqi WANG ◽  
Yingpeng WANG ◽  
Yuwen SUN
Keyword(s):  
Contact Force ◽  
End Effector

scholarly journals Imitation learning-based framework for learning 6-D linear compliant motions

2021 ◽  
Author(s):  
Markku Suomalainen ◽  
Fares J. Abu-dakka ◽  
Ville Kyrki
Keyword(s):  
Contact Force ◽  
Free Space ◽  
Prior Information ◽  
Goal Area ◽  
Imitation Learning ◽  
Learning From Demonstration ◽  
End Effector ◽  
Localization Accuracy ◽  
Novel Method ◽  
Contact Tasks

AbstractWe present a novel method for learning from demonstration 6-D tasks that can be modeled as a sequence of linear motions and compliances. The focus of this paper is the learning of a single linear primitive, many of which can be sequenced to perform more complex tasks. The presented method learns from demonstrations how to take advantage of mechanical gradients in in-contact tasks, such as assembly, both for translations and rotations, without any prior information. The method assumes there exists a desired linear direction in 6-D which, if followed by the manipulator, leads the robot’s end-effector to the goal area shown in the demonstration, either in free space or by leveraging contact through compliance. First, demonstrations are gathered where the teacher explicitly shows the robot how the mechanical gradients can be used as guidance towards the goal. From the demonstrations, a set of directions is computed which would result in the observed motion at each timestep during a demonstration of a single primitive. By observing which direction is included in all these sets, we find a single desired direction which can reproduce the demonstrated motion. Finding the number of compliant axes and their directions in both rotation and translation is based on the assumption that in the presence of a desired direction of motion, all other observed motion is caused by the contact force of the environment, signalling the need for compliance. We evaluate the method on a KUKA LWR4+ robot with test setups imitating typical tasks where a human would use compliance to cope with positional uncertainty. Results show that the method can successfully learn and reproduce compliant motions by taking advantage of the geometry of the task, therefore reducing the need for localization accuracy.

Force Analysis and Modelling of Soft Actuators for Catheter Robots

2016 ◽  
Author(s):  
Mark Gilbertson ◽  
Darrin Beekman ◽  
Biswaranjan Mohanty ◽  
Saeed Hashemi ◽  
Sangyoon Lee ◽  
...  
Keyword(s):  
Contact Force ◽  
Force Control ◽  
Loading Condition ◽  
System Model ◽  
Experimental Result ◽  
End Effector ◽  
Actuator System ◽  
Soft Actuators ◽  
Non Linear System

Soft robotic actuators may provide the means to develop a soft robotic catheter, enabling safer and more effective transcatheter procedures. In many clinical applications, device contact force affects the quality of diagnostic or the degree of therapy delivered. Therefore precise end effector force control will be a requirement for the soft robotic catheter. In this study a bending soft actuator system was fabricated, and the relationship between volume input and end effector contact force is examined. Static and dynamic system identification were conducted under two different loading conditions loosely related to actuation in a blood vessel. The experimental data from these tests led to the creation of a non-linear system model. A reduced term model was developed using a Root Mean Square Error (RMSE) method in order to observe the importance of system dynamics and nonlinearities. A different system model was designed for each loading condition. These two reduced models matched with experimental result, but differed in model terms and parameters, suggesting that either loading condition identification or end effector closed-loop sensing will be needed for accurate contact force control of a soft robotic actuator in an intravascular environment.

scholarly journals ASSESSMENT OF APPLE DAMAGE CAUSED BY A FLEXIBLE END-EFFECTOR

2020 ◽  
pp. 309-317
Author(s):  
LingXin Bu ◽  
ChengKun Chen ◽  
GuangRui Hu ◽  
JianGuo Zhou ◽  
Adilet Sugirbay ◽  
...  
Keyword(s):  
Contact Force ◽  
Mechanical Damage ◽  
Von Mises Stress ◽  
End Effector ◽  
Damage Degree ◽  
Interaction Control ◽  
Fin Ray ◽  
Von Mises ◽  
Non Destructive ◽  
Maximum Contact

In recent years, apple harvesters have become a research hotspot. Interaction control between the robot end-effector and the fruit is crucial to reduce mechanical damage to the fruit and achieve high picking performance. In this article, the damage degree was also quantified using a damage factor based on the damage plasticity model. A flexible three-finger end-effector was designed based on the Fin-Ray effect, and finite element models were established in ABAQUS to simulate the cortex damage during grasping. The results showed that the maximum von Mises stress was 0.159 MPa for the apple skin, 0.082 MPa for the cortex, and 4.178 N for the contact force, respectively. The result of the verification test showed that the maximum contact force was 4.572 N, and the relative error between the simulation and experimental results was 8.62%. Simulation and verification tests showed that the flexible three-finger end-effector achieved non-destructive grasping of apples.

scholarly journals PD-Impedance Combined Control Strategy for Capture Operations Using a 3-DOF Space Manipulator with a Compliant End-Effector

Sensors ◽  
2020 ◽  
Vol 20 (23) ◽  
pp. 6739
Author(s):  
Guohua Kang ◽  
Qi Zhang ◽  
Jiaqi Wu ◽  
Han Zhang
Keyword(s):  
Contact Force ◽  
Relative Velocity ◽  
Control Algorithm ◽  
Time Interval ◽  
Reference Trajectory ◽  
Space Manipulator ◽  
End Effector ◽  
Combined Control ◽  
The Impact ◽  
Target Spacecraft

The contact force/torque between the end-effector of the space manipulator and the target spacecraft will reduce the efficiency and safety of the capture task. A capture strategy using PD-impedance combined control algorithm is proposed to achieve compliant contact between the chaser and target spacecraft. In order to absorb the impact energy, a spring-damper system is designed at the end-effector, and the corresponding dynamics model is established by Lagrange’s equation. Then a PD-impedance control algorithm based on steady-state force tracking error is proposed. Using this method, a compliant contact between the chaser and target spacecraft is realized while considering the dynamic coupling of the system. Finally, the general equation of the reference trajectory of the manipulator end-effector is derived according to the relative velocity and impact direction. The performance of the proposed capture strategy is studied by a co-simulation of MSC Adams and MATLAB Simulink in this paper. The results show that the contact plane at the end-effector of the manipulator can decelerate and detumble the target spacecraft. Besides, the contact force, relative velocity, and angular velocity all decrease to zero gradually, and the final stable state can be maintained for a prescribed time interval.

Decentralized adaptive compliance control of robot manipulators

Robotica ◽  
1995 ◽  
Vol 13 (5) ◽  
pp. 485-498 ◽  
Author(s):  
R. Colbaugh ◽  
K. Glass
Keyword(s):  
Contact Force ◽  
Robot Manipulators ◽  
Adaptive Controller ◽  
Control Input ◽  
End Effector ◽  
Joint Torques ◽  
Control Approach ◽  
Dynamic Relationship ◽  
Position Controller ◽  
Parameter Values

SummaryThis paper presents two adaptive schemes for controlling the end-effector compliance of robot manipulators. Each controller possesses a decentralized structure, in which the control input for each configuration degree-offreedom (DOF) is computed based on information concerning only that DOF. The first scheme is developed using an adaptive impedance control approach and consists of two subsystems: a simple “filter” which modifies the end-effector position trajectory based on the sensed contact force and the desired dynamic relationship between the position and force, and an adaptive controller that produces the joint torques required to track this modified trajectory. The second compliant motion control strategy is an adaptive admittance controller for position-controlled manipulators. In this scheme a desired contact force is specified and then position setpoints for the “inner-loop” position controller are generated which ensure that this desired force is achieved. The proposed controllers are extremely simple computationally, do not require knowledge of the manipulator dynamic model or parameter values of the manipulator or the environment, and are implemented in decentralized form.

Contact Force Control Between Robotic End-Effector and Environmrnt

2012 ◽  
Vol 15 (1) ◽  
pp. 16-21
Author(s):  
Shiuh-Jer Huang ◽  
Chiao-Kuen Yui ◽  
Jang-Yann Lin
Keyword(s):  
Contact Force ◽  
Force Control ◽  
End Effector ◽  
Contact Force Control

Contact force control and vibration suppression in robotic polishing with a smart end effector

2019 ◽  
Vol 57 ◽  
pp. 391-403 ◽  
Author(s):  
Fan Chen ◽  
Huan Zhao ◽  
Dingwei Li ◽  
Lin Chen ◽  
Chao Tan ◽  
...  
Keyword(s):  
Contact Force ◽  
Force Control ◽  
Vibration Suppression ◽  
End Effector ◽  
Contact Force Control

Unknown External Force Estimation and Collision Detection for a Cooperative Robot

Robotica ◽  
2019 ◽  
Vol 38 (9) ◽  
pp. 1665-1681 ◽  
Author(s):  
Shirin Yousefizadeh ◽  
Thomas Bak
Keyword(s):  
Contact Force ◽  
Joint Space ◽  
Estimation Methods ◽  
Control Force ◽  
Task Space ◽  
Force Estimation ◽  
End Effector ◽  
User Input ◽  
Safety Issues ◽  
External Forces

SUMMARYIn human–robot cooperative industrial manipulators, safety issues are crucial. To control force safely, contact force information is necessary. Since force/torque sensors are expensive and hard to integrate into the robot design, estimation methods are used to estimate external forces. In this paper, the goal is to estimate external forces acting on the end-effector of the robot. The forces at the task space affect the joint space torques. Therefore, by employing an observer to estimate the torques, the task space forces can be obtained. To accomplish this, loadcells are employed to compute the net torques at the joints. The considered observers are extended Kalman filter (EKF) and nonlinear disturbance observer (NDOB). Utilizing the computed torque obtained based on the loadcells measurements and the observer, the estimates of external torques applied on the robot end-effector can be achieved. Moreover, to improve the degree of safety, an algorithm is proposed to distinguish between intentional contact force from an operator and accidental collisions. The proposed algorithms are demonstrated on a robot, namely WallMoBot, which is designed to help the operator to install heavy glass panels. Simulation results and preliminary experimental results are presented to demonstrate the effectiveness of the proposed methods in estimating the joint space torques generated by the external forces applied to the WallMoBot end-effector and to distinguish between the user-input force and accidental collisions.

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