For parallel robots with two rotations and one translation, a great design challenge is to achieve high orientation capability while eliminating undesired parasitic motion. To cope with it, this study proposes and dev...
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For parallel robots with two rotations and one translation, a great design challenge is to achieve high orientation capability while eliminating undesired parasitic motion. To cope with it, this study proposes and develops a slider-crank-inspired parallel robot. This novel mechanism follows a seven-stage evolutionary process originally from planar slider-crank mechanisms, sticking to three major design principles (symmetrical design, actuation redundancy, and articulated moving platform). Several slider-crank mechanisms with a centric layout are adopted to obtain zero crank angle and are arranged symmetrically and redundantly, which brings a large orientation workspace without singularity and high-quality transmission performance. By using an articulated platform, the adopted centric slider-crank mechanisms share one common rotation center to eliminate parasitic motion. Furthermore, all the kinematic pairs are single-degree-of-freedom joints-except for four active prismatic joints, the remains are revolute joints-that can reduce interference. Theoretical and experimental results lead to several major conclusions: 1) the built robot exhibits an outstanding orientation capability, capable of tilting up to 70 degrees in all directions;2) the articulated moving platform can rotate exclusively about one point, demonstrating zero parasitic motion;and 3) the robot possesses simple forward and decoupled kinematics, partially attributed to the simplicity of slider-crank mechanisms.
This article presents the synthesis, control and experimental validation of a backdrivable three-degree-of- freedom translational mini robot used to control the interaction between a robot and a machined part during f...
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This article presents the synthesis, control and experimental validation of a backdrivable three-degree-of- freedom translational mini robot used to control the interaction between a robot and a machined part during finishing tasks, such as polishing, sanding and deburring without requiring the use of a force/torque sensor. The mini robot acts as an active contact flange, allowing an industrial robot (the macro robot) to adapt to a part using an impedance control algorithm. Firstly, different three-degree-of-freedom parallel robot architectures are compared and the most suitable architecture is selected. Geometrical properties are chosen for the robot and the physical capabilities of the architecture are predicted to ensure that the design criteria are satisfied. An impedance control algorithm is then developed for the mini robot. The macro-mini system is formed by installing the mini robot on a gantry robot. Sanding tests are carried out in order to validate the performance of the system and the mini robot is compared to other contact flanges already available on the market. Finally, a method allowing the determination of the magnitude of the friction forces in the mini robot is presented and a preliminary friction compensation algorithm is developed. As opposed to existing tools, the novel mini robot proposed in this work is based on a compact parallel architecture, which makes it possible to ensure the backdrivability of the system in three directions. An impedance control algorithm can therefore be implemented thereby providing stability even with stiff environments and eliminating the need for a force/torque sensor.
This paper proposes a hybrid parallel robot for friction stir welding(FSW), and carries out a systematic kinematic analysis and reachable workspace analysis of this parallel robot. A gapcontaining ball-hinge model is ...
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This paper proposes a hybrid parallel robot for friction stir welding(FSW), and carries out a systematic kinematic analysis and reachable workspace analysis of this parallel robot. A gapcontaining ball-hinge model is introduced to establish the dynamics of the FSW parallel robot by combining the different welding stages of FSW, solving the driving force of each strut chain under a typical trajectory and inversely solving the motion trajectory by forward dynamics. Joint Reflected Inertia (JRI) and Coefficient of Variation of Joint Space Inertia (CVI) are introduced to analyze the dynamics performance of the FSW parallel robot. The results show that when the FSW parallel robot is under a large expansion and contraction amount and a large turning angle, which leads to the deterioration of the inertia and acceleration performance between the robot's struts, resulting in the precision being affected, the FSW should be kept operating under smaller values of the JRI and the CVI, to ensure the efficient and precise execution of the complex tasks.
The planar parallel robots are widely employed in industrial applications due to simple geometry, few linkage interferences, and a large, reachable workspace. The symmetric geometry can bring significant convenience t...
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The planar parallel robots are widely employed in industrial applications due to simple geometry, few linkage interferences, and a large, reachable workspace. The symmetric geometry can bring significant convenience to parallel robots. The complexity of the mathematic models can be simplified since only one calculation method can be proposed to deal with various kinematic limbs in a parallel manipulator. The symmetric geometry can ease the assembly and maintenance procedures due to the modular design of linkages/joints. A novel 2-translation and 1-rotation (2T1R) parallel robot with symmetric geometry is proposed in this research. There is one closed loop in each kinematic limb, and 18 revolute joints are applied in its planar structure. Both the inverse and direct kinematic models are explored. The first-order relationship between robot inputs and outputs are constructed. Various singularity configurations are obtained based on the Jacobian matrix. The reachable workspace is resolved by the discrete spatial searching methodology, followed by the impacts originating from various linkages. The dexterity analysis of the parallel robot is conducted.
The paper presents a novel modular parallel robot for pancreatic surgery and its higher-order kinematics derived based on various formalisms. The classical vector, homogeneous transformation matrices and dual quaterni...
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The paper presents a novel modular parallel robot for pancreatic surgery and its higher-order kinematics derived based on various formalisms. The classical vector, homogeneous transformation matrices and dual quaternion approaches are studied for the kinematic functions using both classical differentiation and multidual algebra. The algorithms for inverse kinematics for all three studied formalisms are presented for both differentiation and multidual algebra approaches. Furthermore, these algorithms are compared based on numerical stability, execution times and number and type of mathematical functions and operators contained in each algorithm. A statistical analysis shows that there is significant improvement in execution time for the algorithms implemented using multidual algebra, while the numerical stability is appropriate for all algorithms derived based on differentiation and multidual algebra. While the implementation of the kinematic algorithms using multidual algebra shows positive results when benchmarked on a standard PC, further work is required to evaluate the multidual algorithms on hardware/software used for the modular parallel robot command and control.
Energy efficiency is a challenging and relevant research field in modern manufacturing industries, where robotic systems play an essential role in the automation of several industrial operations. In this paper, we pre...
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Energy efficiency is a challenging and relevant research field in modern manufacturing industries, where robotic systems play an essential role in the automation of several industrial operations. In this paper, we present an approach for the energy-efficiency optimization of a 3-DOF parallel robot. The proposed strategy leverages the task placement, the execution time, and the length of the robot lower arms to minimize the energy consumption for the execution of a predefined high-speed pick-and-place operation. To evaluate the actuators energy consumption, the kinematic, dynamic and electro-mechanic mathematical models, as well as an equivalent multibody model, of the parallel robot are implemented. The results of extensive numerical simulations show that the proposed strategy provides notable improvements in the energy efficiency of the parallel robot, with respect to alternative approaches. Starting from a pick-and-place task with optimal task placement with a consumption of 38.2 J (with a cycle time of 0.4 s), the energy expenditure can be reduced to 3.75 J (with a cycle time of 1.86 s), with a reduction percentage of 90.2%, by additionally optimizing the execution time, and the length of the robot lower arms. These results lead to a reduction from 5733 J/min (for 150 cycles/min) to 121 J/min (for 32 cycles/min), allowing to choose the best trade-off between robot productivity and consumed energy.
The 6-prismatic-spherical-universal (6-PSU) parallel robot is useful for high-accuracy positioning, where the motors are installed on the robot base and the moving parts of the robot have low inertia. A highly accurat...
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The 6-prismatic-spherical-universal (6-PSU) parallel robot is useful for high-accuracy positioning, where the motors are installed on the robot base and the moving parts of the robot have low inertia. A highly accurate kinematic model of the robot is fundamental for the control. The joint clearances of all limbs often exist and have a significant influence on kinematic model accuracy. In this study, an actuation acceleration information-based kinematic modeling and identification method for a 6-PSU parallel robot with joint clearances is proposed. The direction of the joint clearance is related to the direction of the force acted on the joint, which is determined by the acceleration of the prismatic actuator. The existence of joint clearances is equivalent to the link length change. The joint clearances are identified from the experiments and compensated. Simulations and experiments show that the proposed method is effective and improves the accuracy of the kinematic model.
An elaborated bimanual 4-degrees-of-freedom (DOF) parallel robot is designed with large translational workspace, light moving mass and direct-drive actuation. The transient response greatly affects the throughput when...
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An elaborated bimanual 4-degrees-of-freedom (DOF) parallel robot is designed with large translational workspace, light moving mass and direct-drive actuation. The transient response greatly affects the throughput when using this robot for high-speed pick-and-place applications. However, this cannot be properly taken care by existing black-box model-based control schemes. Meanwhile, it is tedious to derive its dynamic model analytically and such a model is inapplicable for the real-time control. In this work, a gray-box-model-based control structure is proposed, with the retained inertial dynamics are directly derived by the principle of virtual work and the other parts are estimated by adaptive neural networks. This ensures calculation efficiency and integrity of the dynamics. Moreover, a prescribed performance function is constructed to ensure the specified tracking requirements both in transient and steady states. On the basis, the robust integral of signum of error term is incorporated to compensate the structural and unstructural uncertainties, which further improves the robustness during high-frequency motion. Comparative real-time experiments have been performed on the actual robot with attainment of the predefined performance and higher tracking accuracy.
Considering the flexibility of the transmission shaft system, this paper presents an approach for mechanical resonance suppression of the high-speed parallel robot based on fractional order disturbance observer. First...
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Considering the flexibility of the transmission shaft system, this paper presents an approach for mechanical resonance suppression of the high-speed parallel robot based on fractional order disturbance observer. First, in order to evaluate mechanical resonance, a decoupled mechatronic dynamics model is built. Based on the proposed decoupled dynamics model, the mechanical resonance under different influence factors is analyzed. Then, based on the three closed-loop control structure of servo system, a model-based parameter tuning method is adopted in the controller parameter tuning. Finally, inspired by the traditional disturbance observer, a fractional order disturbance observer is established by introducing a fractional order filter. Results show that due to the flexibility of the transmission shaft system, under the combined action of mechanical disturbance torque and electromagnetic driving torque, the joint transmission system will generate mechanical resonance phenomena. Therefore, this paper proposes a method for the mechanical resonance suppression of the high-speed parallel robot based on the fractional order disturbance observer. And the proposed method can be applied to other mechatronic device including flexible transmission shaft system.
The trajectory tracking control of parallel robots is challenging due to their complicated dynamics and kinematics. This paper proposes a position -based visual servoing (PBVS) approach for a 6-Revolute-SphericalSpher...
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The trajectory tracking control of parallel robots is challenging due to their complicated dynamics and kinematics. This paper proposes a position -based visual servoing (PBVS) approach for a 6-Revolute-SphericalSpherical (6-RSS) parallel robot using adaptive sliding mode control in Cartesian space. A photogrammetry sensor C -Track 780 in the eye -to -hand configuration is adopted to measure the real-time pose of the robot end -effector, which can avoid the calculation of robot forward kinematics and provide more flexibility for controller design. An adaptive Kalman filter is utilized to deal with uncertain noises in visual measurements to increase the pose estimation accuracy. A sliding mode controller with strong robustness is designed to cope with system uncertainties, and a radial basis function (RBF) neural network is incorporated to realize the auto -tuning of the control gains, which make the robot effectively track different trajectories with time -varying conditions in real applications. Based on Lyapunov theorem, the stability analysis of the controller has been done. Experiments have been conducted to validate the effectiveness of the proposed strategy and illustrate the of the controller.
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