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Experimental analysis of Type II singularities and assembly change points in a 3UPS+RPU parallel robot

MECHANISM AND MACHINE THEORY 2021年 158卷 104242-104242页

作者： Pulloquinga, Jose L. Mata, Vicente Valera, Angel Zamora-Ortiz, Pau Diaz-Rodriguez, Miguel Zambrano, Ivan Univ Politecn Valencia Dept Ingn Sistemas & Automat Inst Automat & Informat Ind Camino Vera S-N Valencia Spain Univ Politecn Valencia Dept Ingn Mecan & Mat Ctr Invest Ingn Mecan Camino Vera S-N Valencia Spain Univ Los Andes Nucleo Hechicera Dept Tecnol & Diseno Fac Ingn Merida 5101 Venezuela Escuela Politec Nacl Dept Ingn Mecan Fac Ingn Mecan E11-253 Quito Ecuador

parallel robots (PRs) have singular configurations where the robot gains at least one degree-of-freedom and loses control. Theoretically, such singularity occurs when the Forward Jacobian-Matrix determinant becomes zero (Type II). However, actual PRs could lose control owing to Type II singularities for determinant values near zero, but not zero, because manufacturing tolerances introduce errors that are complex to model due to their low repeatability. Thus, using an actual 3UPS + RPU PR, this paper presents three contributions: i) a proximity detection index for Type II singularities based on the angle between two Output Twist Screws. The index can identify which kinematic chains contribute to the singularity. ii) an experimental benchmark to study Type II singularities. iii) PR configurations where the proposed index is zero and the Forward Jacobian determinant is not. In this last configuration, the findings show that the actual robot is unable to handle external actions applied to the PR. (C) 2021 Elsevier Ltd. All rights reserved.

关键词： Singular configuration parallel robot Virtual power Screw theory Assembly modes

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Modeling, identification and minimum length integral sliding mode control of a 3-DOF cartesian parallel robot by considering virtual flexible links

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MECHANISM AND MACHINE THEORY 2021年 157卷 104183-104183页

作者： Beiranvand, Arman Kalhor, Ahmad Masouleh, Mehdi Tale Univ Tehran Sch Elect & Comp Engn Human & Robot Interact Lab Tehran Iran

This article presents a method for modeling the dynamics and minimum vibration controller design of a 3-DOF parallel mechanism, the so-called Tripteron. The proposed comprehensive dynamic model consists of the dynamic model of the prismatic actuators, variable friction in them, and dynamics of flexibility in the limbs which caused vibration of the robot's end-effector by considering a spring-damper element for each link based on the Tripteron structure. Then the identification procedure is carried out by collecting practical data from the robot. In order to design the oscillation damping controller, the Minimum Length Integral Sliding Mode Controller(MLISMC) is proposed in which the Phase Trajectory Length(PTL) approach is applied to ISMC for proper placement of closed-loop poles of the identified system. The foregoing method is based on numerical calculations to minimize the end-effector vibrations along the point-to-point control. Simulation and experimental results reveal that the PTL of the system have been reduced about 95% in simulation and 30% in the experimental test. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： parallel robot Flexible link Feed drive Identification Minimum vibration Integral sliding mode control

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Par4 parallel robot Trajectory Tracking Control Based on DMR-GWO2 and Fuzzy Predictive

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INTERNATIONAL JOURNAL OF COMPUTATIONAL INTELLIGENCE SYSTEMS 2021年第1期14卷 1597-1606页

作者： Zhang, Xiaoqing Ming, Zhengfeng Xianyang Normal Univ Sch Phys & Elect Engn 43 Wenlin Rd Xianyang 712000 Shaanxi Peoples R China Xidian Univ Sch Mechanoelect Engn 2 South Taibai Rd Xian 710000 Shaanxi Peoples R China

A dynamic Grey Wolf Optimizer (GWO) is proposed, noted as DGWO2, and a novel dynamic improved GWO algorithm is obtained after transferring the mutation operator and the eliminating-reconstructing mechanism to the DGWO2, noted as DMR-GWO2. A Type-2 fuzzy predictive compensation PID trajectory tracking controller based on the DMR-GWO2 is proposed to attain the tracking targets for the trajectory control of Par4 parallel robot. In the trajectory tracking controller, the DMR-GWO2 is designed for optimizing the Type-2 fuzzy logic controller which is in parallel with the PID controller to speed up the response of the parallel robot and to get the high adaptive capacity of the whole system. One input of the Type-2 fuzzy logic controller is the tracking error, while the other input is the sum of the derivative of the tracking error and the change rate of the expected angle. Finally, the experiments verify the effectiveness of the designed trajectory tracking controller and the tracking errors are small. (C) 2021 The Authors. Published by Atlantis Press B.V.

关键词： parallel robot Trajectory tracking control Type-2 fuzzy predictive compensation controller Grey wolf optimizer

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Trajectory tracking with collision avoidance for a parallel robot with flexible links

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CONTROL ENGINEERING PRACTICE 2021年 111卷 104788-104788页

作者： Morlock, Merlin Bajrami, Valmir Seifried, Robert Hamburg Univ Technol TUHH Inst Mech & Ocean Engn Eissendorfer Str 42 D-21073 Hamburg Germany

End-effector trajectory tracking of a highly flexible three-link parallel robot is combined with collision avoidance in real-time. Typical real-time collision avoidance algorithms issue commands on actuator level which can cause large oscillations within flexible robots. Thus, the needed evasive motion at the points which are about to collide is used to adapt the desired end-effector trajectory of the underactuated system, even for actuator limits and points other than the end-effector. In contrast to existing real-time collision avoidance concepts, which are essentially completely based on rigid models, a dynamic flexible model inversion is then used for tracking. Thereby, output redefinition leads to a minimum phase system. The presented computationally efficient concepts, being actuator limit and obstacle collision avoidance, use sigmoid functions providing smooth trajectories. The former calculates a braking factor for the end-effector when an actuator approaches its limit. The latter avoids external dynamic obstacles based on repulsive vectors. Experiments validate both concepts with a flexible model inversion which clearly outperforms the classical rigid body approach.

关键词： Collision avoidance Flexible robot parallel robot Underactuated robot

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Robust Impedance Control for a Five-Bar parallel robot Based on Uncertainty Estimation

Robust Impedance Control for a Five-Bar Parallel Robot Based...

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International Symposium on Autonomous Systems (ISAS)

作者： Cheng, Jie Zhang, Xuexin Sun, Tairen Yang, Hongjun Jiangsu Univ Sch Elect & Informat Engn Zhenjiang Jiangsu Peoples R China Chinese Acad Sci Inst Automat Beijing Peoples R China

ISBN: (纸本)9781665418829

We proposes a disturbance-observer-based robust impedance control strategy for a five-bar structured robot with a lumped uncertainty composed of the friction force and the system disturbances. Through a constructed reference trajectory, we transform the impedance control design into a impedance trajectory tracking problem. A disturbance observer is designed to approximate the lumped uncertainty without assuming the time derivative of friction forces being bounded prior to control implementation. Then, based on the uncertainty estimation, the robust impedance controller is designed with an interaction control term to enhance transient control performances. We validate the stability of the designed impedance controller and illustrate its effectiveness by simulation results.

关键词： parallel robot Impedance control Disturbance observer Uncertainty and disturbance estimation

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Using a Development Platform with an STM32 Processor to Prototype an Inexpensive 4-DoF Delta parallel robot

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SENSORS 2021年第23期21卷 7962-7962页

作者： Laski, Pawel Andrzej Smykowski, Mateusz Kielce Univ Technol Fac Mechatron & Machine Design Dept Automat & Robot Aleja Tysiaclecia Panstwa Polskiego 7 PL-25314 Kielce Poland

This article presents a construction prototype of a delta 4-DoF (Degree of Freedom) parallel robot. The structure of kinematic chain was described and the problem of inverse kinematic was formulated and solved. The author also proposed a concept of a control system. The dynamics of the control object were specified, a decision upon the controller and its settings was made, as well as simulation control studies of manipulator drive were conducted. The article contains a description of prepared applications and procedures as well as the research results of the manipulator.

关键词： STM32 processor parallel robot 4-DoF rapid control prototyping

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Intrinsically compliant parallel robot for fractured femur reduction: Mechanism optimization and control

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robotICS AND AUTONOMOUS SYSTEMS 2021年 141卷 103787-103787页

作者： Jamwal, Prashant K. Hussain, Shahid Ghayesh, Mergen H. Nazarbayev Univ Dept Elect & Comp Engn Astana 010000 Kazakhstan Univ Canberra Human Centred Technol Res Ctr Canberra ACT 2617 Australia Univ Adelaide Sch Mech Engn Adelaide SA Australia

A robotic system for the reduction of fractured femur bone is proposed in this research to help orthopedics during the labor intensive bone reduction procedures and also save them from radiation stimulated environment. Fractured femur reduction is a good candidate for robotics application owing to its elongated anatomy and strong counteracting forces from surrounding muscles. However, the robot forces should be compliant, and motions need to be accurate. Aiming to achieve these two conflicting objective, a parallel robot actuated by six intrinsically compliant actuators is being proposed here. After an initial design analysis, three performance metrics, namely, the conditioning index, actuator force index and interaction compliance index were identified and formulated. An evolutionary algorithm SPEA2 was employed to simultaneously optimize these objectives by varying the key robot design variables. Subsequent to the optimization, an optimal robot design is obtained which provides the best trade-off between the performance measures. Initial proof of concept experiments were carried out whereby the robot was tested for trajectory following accuracies while maneuvering the moving platform about the three axes. A fuzzy based closed loop feedback controller was implemented on the robot. Excellent trajectory tracking results were observed in response to the sinusoidal inputs. (C) 2021 Elsevier B.V. All rights reserved.

关键词： Femur Fracture reduction parallel robot Compliant actuation robot control Optimization

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Dynamic Visual Servoing of A 6-RSS parallel robot Based on Optical CMM

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JOURNAL OF INTELLIGENT & robotIC SYSTEMS 2021年第2期102卷 40-40页

作者： Li, Pengcheng Shu, Tingting Xie, Wen-Fang Tian, Wei Nanjing Univ Aeronaut & Astronaut Coll Mech & Elect Engn 29 Yudao St Nanjing 210016 Peoples R China Concordia Univ Dept Mech Ind Aerosp Engn 1455 De Maisonneuve Blvd W Montreal PQ H3G 1M8 Canada

The parallel robots exhibit some outstanding properties on the repeatability, stiffness and force-to-weight ratio compared with serial robots. 6-DOF parallel robots have been utilized in various applications and the research on control design has attracted the attentions of researchers. However, the current Cartesian space path tracking performance of the parallel robots cannot meet the growing requirements from industry. In this paper, a dynamic sliding mode control (DSMC) scheme combined with the position-based visual servoing (PBVS) method is proposed to improve the tracking performance of the 6-Revolute-Spherical-Spherical (6-RSS) parallel robot based on the measurements from the optical coordinate measuring machine (CMM) sensor. By employing the CMM sensor, the pose of the parallel robot in Cartesian space can be estimated and incorporated in a closed-loop visual servoing control scheme in real time. The stability of the proposed DSMC has been proved by using Lyapunov theorem. The real-time experiment tests on a 6-RSS parallel robot demonstrate that the complex 6-dimension trajectory tracking can be achieved with high-accuracy. Compared with the classical kinematic level controllers, the proposed DSMC exhibits the superiority in terms of tracking performance and robustness.

关键词： Visual servoing Sliding mode control parallel robot Optical CMM Path tracking Industrial robot

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Design of target trajectories for the detection of joint clearances in parallel robot based on the actuation torque measurement

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MECHANISM AND MACHINE THEORY 2021年 155卷 104081-104081页

作者： Ohno, Masumi Takeda, Yukio Tokyo Inst Technol Dept Mech Engn Meguro Ku 2-12-1 Ookayama Tokyo 1528552 Japan

This paper proposed a design method of trajectories for detecting the excessive clearances of passive joints in a DELTA robot on the basis of the phenomenon that the actuation torque waveform fluctuates due to the collision between joint elements. We introduced "Joint Impact Index," as an index to evaluate the magnitude of actuation torque fluctuation due to the collision at the passive joints with clearances. In order to simplify the problem of the clearance detection, this paper proposed to use a trajectory specially designed for the detection of each joint's clearance, called "target trajectory". For the design of the target trajectory, objective functions were defined based on the Joint Impact Index. Target trajectories obtained by solving the multi-objective optimization problem were applied to an industrial robot, and experiments were conducted. The relation between the detection performance in the experiments and the distribution of Joint Impact Index for the designed target trajectories was investigated and the effectiveness of the proposed method was discussed. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： parallel robot Failure detection Clearance joint Trajectory design Joint Impact Index

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Real-time trajectory tracking control of a parallel robot with flexible links

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MECHANISM AND MACHINE THEORY 2021年 158卷 104220-104220页

作者： Morlock, Merlin Meyer, Niklas Pick, Marc-Andre Seifried, Robert Hamburg Univ Technol TUHH Inst Mech & Ocean Engn Eissendorfer Str 42 D-21073 Hamburg Germany

Real-time end-effector trajectory tracking is applied to a newly developed parallel robotic system with two highly flexible links. In contrast to previous works, which are typically based on offline precalculations or rigid model inversion, a dynamic flexible multibody model is inverted online. As the underactuated system is non-minimum phase, the inverse model needs to be rendered stable for real-time integration. Therefore, three approaches are developed for the considered robot. Firstly, output redefinition is applied by directly weighting the elastic deformations and rotations of the links. Secondly, a small counter weight is attached at an advantageous location on the robot having only a minor influence on the eigenfrequencies. Lastly, the rotational degree of freedom of the end-effector is used to stabilize the internal dynamics of the inverse model with a small motion of a rotary motor. The concepts and real-time applicability are validated within experiments which extends the related literature being highly based on theoretical investigations. The experimental end-effector tracking performance based on the three minimum phase approaches is close to the desired trajectory and clearly outperforms classical rigid body inversion. (C) 2020 Elsevier Ltd. All rights reserved.

关键词： Flexible links Underactuated robot parallel robot Model inversion Internal dynamics Real-time control

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