An extended DMP framework for robot learning and improving variable stiffness manipulation

2019 ◽  
Vol 40 (1) ◽  
pp. 85-94
Author(s):  
Feifei Bian ◽  
Danmei Ren ◽  
Ruifeng Li ◽  
Peidong Liang ◽  
Ke Wang ◽  
...  
Keyword(s):  
Design Methodology ◽  
Variable Stiffness ◽  
Admittance Control ◽  
End Effector ◽  
Content Type ◽  
Human Dose ◽  
Robot Cooperation ◽  
Electromyographic Signals ◽  
Reference Trajectories ◽  
Teaching By Demonstration

Purpose The purpose of this paper is to present a method which enables a robot to learn both motion skills and stiffness profiles from humans through kinesthetic human-robot cooperation. Design Methodology Approach Admittance control is applied to allow robot-compliant behaviors when following the reference trajectories. By extending the dynamical movement primitives (DMP) model, a new concept of DMP and stiffness primitives is introduced to encode a kinesthetic demonstration as a combination of trajectories and stiffness profiles, which are subsequently transferred to the robot. Electromyographic signals are extracted from a human’s upper limbs to obtain target stiffness profiles. By monitoring vibrations of the end-effector velocities, a stability observer is developed. The virtual damping coefficient of admittance controller is adjusted accordingly to eliminate the vibrations. Findings The performance of the proposed methods is evaluated experimentally. The result shows that the robot can perform tasks in a variable stiffness mode as like the human dose in the teaching phase. Originality Value DMP has been widely used as a teaching by demonstration method to represent movements of humans and robots. The proposed method extends the DMP framework to allow a robot to learn not only motion skills but also stiffness profiles. Additionally, the authors proposed a stability observer to eliminate vibrations when the robot is disturbed by environment.

Technology jump in the industry: human–robot cooperation in production

2020 ◽  
Vol 47 (5) ◽  
pp. 757-775
Author(s):  
Zoltan Dobra ◽  
Krishna S. Dhir
Keyword(s):  
Design Methodology ◽  
Manufacturing Industry ◽  
Current Status ◽  
Robot System ◽  
Content Type ◽  
New Directions ◽  
Academic Publications ◽  
Robot Cooperation ◽  
Human Robot Collaboration ◽  
Practical Implications

Purpose Recent years have seen a technological change, Industry 4.0, in the manufacturing industry. Human–robot cooperation, a new application, is increasing and facilitating collaboration without fences, cages or any kind of separation. The purpose of the paper is to review mainstream academic publications to evaluate the current status of human–robot cooperation and identify potential areas of further research. Design/methodology/approach A systematic literature review is offered that searches, appraises, synthetizes and analyses relevant works. Findings The authors report the prevailing status of human–robot collaboration, human factors, complexity/ programming, safety, collision avoidance, instructing the robot system and other aspects of human–robot collaboration. Practical implications This paper identifies new directions and potential research in practice of human–robot collaboration, such as measuring the degree of collaboration, integrating human–robot cooperation into teamwork theories, effective functional relocation of the robot and product design for human robot collaboration. Originality/value This paper will be useful for three cohorts of readers, namely, the manufacturers who require a baseline for development and deployment of robots; users of robots-seeking manufacturing advantage and researchers looking for new directions for further exploration of human–machine collaboration.

Robot compliant catching by Maxwell model based Cartesian admittance control

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Le Fu ◽  
Jie Zhao
Keyword(s):  
Control Method ◽  
Maxwell Model ◽  
Admittance Control ◽  
End Effector ◽  
Content Type ◽  
Model Based ◽  
Time Optimal ◽  
Voigt Model ◽  
Optimal Movement ◽  
The Impact

Purpose Admittance control is a typical complaint control methodology. Traditionally, admittance control systems are based on a dynamical relationship described by Voigt model. By contrast, after changing connection of spring and damper, Maxwell model produces different dynamics and has shown better impact absorption performance. This paper aims to design a novel compliant control method based on Maxwell model and implement it in a robot catching scenario. Design/methodology/approach To achieve this goal, this paper proposed a Maxwell model based admittance control scheme. Considering several motion stages involved in one catching attempt, the following approaches are adopted. First, Kalman filter is used to process the position data stream acquired from motion capture system and predict the subsequent object flying trajectory. Then, a linear segments with parabolic blends reaching motion is generated to achieve time-optimal movement under kinematic and joint inherent constraints. After robot reached the desired catching point, the proposed Maxwell model based admittance controller performs such as a cushion to moderate the impact between robot end-effector and flying object. Findings This paper has experimentally demonstrated the feasibility and effectiveness of the proposed method. Compared with typical Voigt model based compliant catching, less object bounding away from end-effector happens and the success rate of catching has been improved. Originality/value The authors proposed a novel Maxwell model based admittance control method and demonstrated its effectiveness in a robot catching scenario. The author’s approach may inspire other related researchers and has great potential of practical usage in a widespread of robot applications.

Trajectory evaluation for manipulators with motion and sensor uncertainties

2017 ◽  
Vol 44 (5) ◽  
pp. 658-670 ◽  
Author(s):  
Ruolong Qi ◽  
Weijia Zhou ◽  
Wang Tiejun
Keyword(s):  
Design Methodology ◽  
Prior Probability ◽  
Probability Distributions ◽  
Space Station ◽  
Linear Quadratic Regulator ◽  
Goal Area ◽  
Linear Quadratic ◽  
End Effector ◽  
Content Type ◽  
Entire Trajectory

Purpose Uncertainty can arise for a manipulator because its motion can deviate unpredictably from the assumed dynamical model and because sensors might provide information regarding the system state that is imperfect because of noise and imprecise measurement. This paper aims to propose a method to estimate the probable error ranges of the entire trajectory for a manipulator with motion and sensor uncertainties. The aims are to evaluate whether a manipulator can safely avoid all obstacles under uncertain conditions and to determine the probability that the end effector arrives at its goal area. Design/methodology/approach An effective, analytical method is presented to evaluate the trajectory error correctly, and a motion plan was executed using Gaussian models by considering sensor and motion uncertainties. The method used an integrated algorithm that combined a Gaussian error model with an extended Kalman filter and a linear–quadratic regulator. Iterative linearization of the nonlinear dynamics was used around every section of the trajectory to derive all of the prior probability distributions before execution. Findings Simulation and experimental results indicate that the proposed trajectory planning method based on the motion and sensor uncertainties is indeed highly convenient and efficient. Originality/value The proposed approach is applicable to manipulators with motion and sensor uncertainties. It helps determine the error distribution of the predefined trajectory. Based on the evaluation results, the most appropriate trajectory can be selected among many predefined trajectories according to the error ranges and the probability of arriving at the goal area. The method has been successfully applied to a manipulator operating on the Chinese Space Station.

Automatic stepping for circumferential splice drilling in aircraft fuselage assembly

2016 ◽  
Vol 43 (2) ◽  
pp. 144-152
Author(s):  
Weidong Zhu ◽  
Along Zhang ◽  
Biao Mei ◽  
Yinglin Ke
Keyword(s):  
Design Methodology ◽  
Detection Method ◽  
High Accuracy ◽  
Drilling Machine ◽  
End Effector ◽  
Content Type ◽  
Aircraft Fuselage ◽  
Position Detection ◽  
Suppression Method ◽  
Practical Implications

Purpose – A large number of fastener holes have to be drilled with high quality in the circumferential splice region during the assembly of aircraft fuselage. The purpose of this paper is to design an automatic stepping mechanism for a circumferential splice drilling machine, to meet the requirements of large workspace and high accuracy in drilling at the same time. Design/methodology/approach – A docking position detection method based on magnetic proximity sensors is proposed for the positioning of the arc-shaped rail with respect to the circumferential rails, which significantly improves the accuracy and reliability of automatic stepping. The slipping phenomenon of the end-effector is analyzed, and the optimized counter weights are used to eliminate the slipping and improve the working stability of the stepping mechanism. Findings – An automatic stepping mechanism is developed for the circumferential splice drilling machine, which comprises the docking position detection method and the elimination/suppression method of the end-effector’s slipping. Practical implications – The proposed automatic stepping mechanism has been integrated into the circumferential splice drilling machine for the fuselage assembly in an aircraft company in China. Originality/value – An automatic stepping scheme for the circumferential splice drilling machine is proposed, which enhances the efficiency in circumferential splice drilling in aircraft fuselage assembly.

A new variable stiffness robot joint

2015 ◽  
Vol 42 (4) ◽  
pp. 371-378 ◽  
Author(s):  
Yong Tao ◽  
Tianmiao Wang ◽  
Yunqing Wang ◽  
Long Guo ◽  
Hegen Xiong ◽  
...  
Keyword(s):  
Design Methodology ◽  
Dynamic Stiffness ◽  
Variable Stiffness ◽  
System Behavior ◽  
Pivot Point ◽  
Content Type ◽  
Wide Range ◽  
Variable Stiffness Actuators ◽  
Stiffness Adjustment ◽  
Elastic Elements

Purpose – This study aims to propose a new variable stiffness robot joint (VSR-joint) for operating safely. More and more variable stiffness actuators are being designed and implemented because of their ability to minimize large forces due to shocks, to safely interact with the user and their ability to store and release energy in passive elastic elements. Design/methodology/approach – The design of VSR-joint is compact and integrated highly and the operating is simply. The mechanics, the principle of operation and the model of the VSR-joint are proposed. The principle of operation of VSR-joint is based on a lever arm mechanism with a continuously regulated pivot point. The VSR-joint features a highly dynamic stiffness adjustment along with a mechanically programmable system behavior. This allows an easy adaption to a big variety of tasks. Findings – Preliminary results are presented to demonstrate the fast stiffness regulation response and the wide range of stiffness achieved by the proposed VSR-joint design. Originality/value – In this paper, a new variable stiffness joint is proposed through changing the cantilever arm to change the performance of the elastic element, which is compact, small size and simple adjustment.

Dynamical system based variable admittance control for physical human-robot interaction

2020 ◽  
Vol 47 (4) ◽  
pp. 623-635
Author(s):  
Feifei Bian ◽  
Danmei Ren ◽  
Ruifeng Li ◽  
Peidong Liang ◽  
Ke Wang ◽  
...  
Keyword(s):  
Dynamical System ◽  
Human Robot Interaction ◽  
Contact Forces ◽  
Robot Motion ◽  
Admittance Control ◽  
Robot Interaction ◽  
Content Type ◽  
Impedance Characteristics ◽  
Task Requirements ◽  
Reference Trajectories

Purpose The purpose of this paper is to enable robots to intelligently adapt their damping characteristics and motions in a reactive fashion toward human inputs and task requirements during physical human–robot interaction. Design/methodology/approach This paper exploits a combination of the dynamical system and the admittance model to create robot behaviors. The reference trajectories are generated by dynamical systems while the admittance control enables robots to compliantly follow the reference trajectories. To determine how control is divided between the two models, a collaborative arbitration algorithm is presented to change their contributions to the robot motion based on the contact forces. In addition, the authors investigate to model the robot’s impedance characteristics as a function of the task requirements and build a novel artificial damping field (ADF) to represent the virtual damping at arbitrary robot states. Findings The authors evaluate their methods through experiments on an UR10 robot. The result shows promising performances for the robot to achieve complex tasks in collaboration with human partners. Originality/value The proposed method extends the dynamical system approach with an admittance control law to allow a robot motion being adjusted in real time. Besides, the authors propose a novel ADF method to model the robot’s impedance characteristics as a function of the task requirements.

Development of ground experiment system for space end-effector capturing the floating target in 3-dimensional space

2015 ◽  
Vol 42 (4) ◽  
pp. 347-358 ◽  
Author(s):  
Haitao Yang ◽  
Zongwu Xie ◽  
Kui Sun ◽  
Xiaoyu Zhao ◽  
Minghe Jin ◽  
...  
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Admittance Control ◽  
End Effector ◽  
Content Type ◽  
Experiment System ◽  
Ground Experiment ◽  
Motion State ◽  
Basic Functions ◽  
Three Dimensional Space

Purpose – The purpose of this paper is to develop a set of ground experiment system to verify the basic functions of space effector and the capturing reliability of space end-effector for the free-floating target payload in the three-dimensional space. The development of ground experiment system for space end-effector is essential and significant, because it costs too much to launch a space robot or other spacecraft and carry out operation tasks in space. Owing to the negligible gravity in space, which is different from that in the ground environment, ground experiment system for space end-effector should have the capability of verifying the basic functions of space effector and the reliability of space end-effector in capturing the free-floating target payload in space. Design/methodology/approach – The ground experiment system for space end-effector mainly adopts the hybrid simulation method, which includes the real hardware experiment and software simulation. To emulate the micro-gravity environment, the contact dynamics simulator is applied to emulating the motion state of the free-floating target payload, while the admittance control is used to realize the “soft” capturing of space end-effector to simulate the real situation in space. Findings – With the gravity compensation, the influence of gravity is almost eliminated and the results meet the requirements of the experiment. In the ground experiment, the admittance control is effective and the actual motion state of space end-effector capturing the target in space can be simulated. The experiment results show that space end-effector can capture the free-floating target payload successfully and hopefully have the ability to capture a free-floating target in space. Originality/value – The system can verify space end-effector capturing the free-floating target payload in three-dimensional space and imitate the motion of space end-effector capturing the free-floating target in space. The system can also be modified and improved for application in the verification of space robot capturing and docking the target, which is valuable for the ground verification of space applications.

ARES, a variable stiffness actuator with embedded force sensor for the ATLAS exoskeleton

2014 ◽  
Vol 41 (6) ◽  
pp. 518-526 ◽  
Author(s):  
M. Cestari ◽  
D. Sanz-Merodio ◽  
J.C. Arevalo ◽  
E. Garcia
Keyword(s):  
Design Methodology ◽  
Variable Stiffness ◽  
Force Sensor ◽  
Content Type ◽  
Torque Measurements ◽  
Variable Stiffness Actuator ◽  
Compact Design ◽  
Intrinsic Dynamic

Purpose – The purpose of this study is to present a variable stiffness actuator, one of whose main features is that the compliant elements simultaneously allow measuring of the torque exerted by the joint. Conceived as a force-controlled actuator, this actuator with Adjustable Rigidity and Embedded Sensor (ARES) is intended to be implemented in the knee of the ATLAS exoskeleton for children to allow the exploitation of the intrinsic dynamic during the locomotion cycle. Design/methodology/approach – A set of simulations were performed to evaluate the behavior of the actuator mechanism and a prototype of the variable impedance actuator was incorporated into the exoskeleton’s knee and evaluations of the torque measurements capabilities along with the rigidity adjustments were made. Findings – Mass and inertia of the actuator are minimized by the compact design and the utilization of the different component for more than one utility. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected. Originality/value – In the actuator, the compliant elements simultaneously allow measuring of the torque exerted by the join. By a proper match of the compliance of the joint and the performed task, good torque measurements can be achieved and no bandwidth saturation is expected.

New mechanism for press-fit processes: preliminary analysis

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Lorenzo Fiorineschi ◽  
Luca Pugi ◽  
Federico Rotini
Keyword(s):  
Load Distribution ◽  
Preliminary Analysis ◽  
Design Methodology ◽  
Research Work ◽  
Structural Elements ◽  
End Effector ◽  
Content Type ◽  
Press Fit ◽  
Comprehensive Evaluations ◽  
Technology Processes

Purpose The purpose of this paper is to present an alternative solution for press-fit technology processes, which could improve the precision of the positioning movements and the stiffness of the structural elements. Design/methodology/approach A concept is presented and the related kinematics is described. Then, preliminary embodiment evaluations have been performed in terms of kinematics, force control and load distribution on the main structural elements. Findings Thanks to the additional leg, the proposed solution allows a preload that is capable of compensating the backlash of joints. The particular structure with four extendible legs and eight cardan joints ensures the parallelism between the ground and the plate holding the end effector, without any need of additional controls. However, it implies that the legs are not subjected to pure tension–compression stresses. Research limitations/implications This work is focused on the conceptual phase of the design process, with only preliminary embodiment analysis that paves the way for subsequent and more detailed design steps. Especially concerning the actual stiffness of the system, comprehensive evaluations could be performed only after the identification of the particular parts/devices used to implement the main functional elements. Originality/value To the best of the authors’ knowledge, this is the first research work that comprehensively describes and analyzes the considered kinematics, within a real industrial application context.

Wrinkle and boundary detection of fiber products in robotic composites manufacturing

2019 ◽  
Vol 40 (2) ◽  
pp. 283-291
Author(s):  
Kashish Gupta ◽  
Marian Körber ◽  
Abtin Djavadifar ◽  
Florian Krebs ◽  
Homayoun Najjaran
Keyword(s):  
Production Process ◽  
Design Methodology ◽  
Laboratory Experiments ◽  
Applied Research ◽  
Boundary Edge ◽  
End Effector ◽  
Content Type ◽  
Composites Manufacturing ◽  
Processing Solution ◽  
Process Material

Purpose The paper aims to focus on a vision-based approach to advance the automated process of the manufacturing of an Airbus A350’s pressure bulkhead. The setup enables automated deformation and draping of a fiber textile on a form-variable end-effector. Design/methodology/approach The proposed method uses the information of infrared (IR) and color-based images in Red, Green and Blue (RGB) representative format, as well as depth measurements to identify the wrinkles and boundary edge of semi-finished dry fiber products on the double-curved surface of a flexible modular gripper used for laying the fabric. The technique implements a simple and practical image processing solution using a sequence of pixel-wise binary masks on an industrial scale setup; it bridges the gap between laboratory experiments and real-world execution, thereby demonstrating practical and applied research. Findings The efficacy of the technique is demonstrated via experiments in the presented work. The two objectives as follows boundary edge detection and wrinkle detection are accomplished in real time in an industrial setup. Originality/value During the draping process, tensions developed in the fibers of the textile cause wrinkles on the surface, which are highly detrimental to the production process, material quality and strength. The proposed method automates the identification and detection of the wrinkles and the textile on the gripper surface. The proposed work aids in alleviating the problems caused by these wrinkles and helps in quality control in the production process.

Sign in / Sign up

Export Citation Format

Share Document