Hybrid Serial-parallel Manipulator Research Articles

Dynamics and control of a 7-DOF hybrid manipulator for capturing a non-cooperative target in space

This paper proposes a 7-DOF hybrid serial-parallel manipulator for capturing a non-cooperative target in space and discusses its dynamics and control. The hybrid manipulator is connected in a series by a 3-DOF parallel part with 1-PU&2-PUS configurations and a 4-DOF serial part with a 4R configuration. First, the UP-RRRR equivalent serial mechanism is presented for the kinematic analysis of the hybrid manipulator. Utilizing the Newton-Euler method, the dynamic model of the equivalent serial mechanism is derived in a recursive form. Then the dynamic equations of the parallel part in recursive form are also developed using the Newton-Euler method. Based on the complete dynamic model, we propose a control scheme for a hybrid robot to capture a non-cooperative target in a zero-gravity environment, including three modules: admittance control, motion estimation of the target satellite, and feedforward of the reaction forces. Finally, experimental results of full physical experiments based on air-bearing testbeds confirm the validity of the proposed control scheme for the hybrid robot to capture a non-cooperative target in space.

Analysis and Optimization of a Spatial Parallel Mechanism for a New 5-DOF Hybrid Serial-Parallel Manipulator

Hybrid manipulators have potentially application in machining industries and attract extensive attention from many researchers on the basis of high stiffness and high dexterity. Therefore, in order to expand the application prospects of hybrid manipulator, a novel 5-degree-of-freedom (DOF) hybrid serial-parallel manipulator (HSPM) is proposed. Firstly, the design plan of this manipulator is introduced. Secondly, the analysis of this manipulator is carried out in detail, including kinematics analysis, statics analysis, and workspace analysis. Especially, an amplitude equivalent method of disposing the over-constrained force/couple to the non-overconstrained force/couple is used in the statics analysis. Then, three performance indices are used to optimize the PM. Two of them have been widely used, and the third one is a new index which considers the characteristics of the actuated force. Based on the performance indices, the performance atlas is drawn and the optimal design of the PM is investigated. In order to satisfy the anticipant kinetic characteristics of the PM, the verification of the optimized physical dimension is done and the workspace based on the optimized physical dimension is carried out. This paper will lay good theoretical foundations for application of this novel HSPM and also can be applied to other hybrid manipulators.

Design of a novel 5-DOF hybrid serial-parallel manipulator and theoretical analysis of its parallel part

Abstract Parallel mechanisms (PMs) with two rotational degrees-of-freedom (DOF) and one translational DOF (2R1T) have gained much attention, in view of their good comprehensive performance in the field of machine tools. In this paper, a novel 2R1T 2UPU/SP PM is presented, and a 5-DOF hybrid serial-parallel manipulator is constructed on the basis of this novel PM. First, to better understand typical 2R1T PMs, a type synthesis method in virtue of the inner properties of PMs are investigated; in particular, the construction principles for the 2UPU/SP PM are introduced. Second, as the 2UPU/SP PM belongs to an over-constrained 2R1T PM, the constraint force and torque generated on the moving platform (MP) are analyzed in detail, and the rotational axes of the 2UPU/SP PM are obtained. Third, the kinematics of the 2UPU/SP PM are studied systematically, including position, velocity and acceleration analysis; based on the kinematic model, an inverse dynamic model is established using the virtual work principle method. The analysis of this PM shows that its kinematic and dynamic models are quite simple. To confirm the correctness of the kinematic and dynamic models, numerical simulations are performed. Next, the workspace is drawn using MATLAB and CAD softwares, which makes it possible to visualize it fully. Finally, the dimensional synthesis on the basis of the motion/force transmissibility is analyzed and relatively optimized physical dimensions are obtained. This study will enhance the research applications of PM and establish good theoretical foundations for the application of this novel manipulator.

Kinematics, dynamics and stiffness analysis of a novel 3-DOF kinematically/actuation redundant planar parallel mechanism

A novel 5-degree-of-freedom (DOF) hybrid serial-parallel manipulator is introduced, and the prototype of its parallel part has been manufactured for pratical testing purpose. The parallel part is a 3-DOF metamorphic planar parallel mechanism (PM) with two different types of configuration: actuation redundancy and kinematic redundancy. First, to establish the inverse dynamic model of the 3-DOF planar PM, its kinematics are studied systematically, including mobility, position, velocity, acceleration, singularity and workspace analysis. Second, an inverse dynamic model of the kinematically redundant planar PM is established by using the virtual work principle method. The actuation forces of the kinematically redundant planar PM are obtained, and the internal forces acting on revolute joints are also obtained by means of separated model blocks. Then, the stiffness matrix is obtained easily by means of the same method used in the dynamics modeling. Finally, kinematics, dynamic numerical simulations considering actuation forces and joint force trends are performed, and the stiffness distributions with contour atlases are also given. The results show the correct of the theoretical kinematic and dynamic models and give reference to know the stiffness performances. A systematic and comprehensive analysis of mentioned planar PM shows that the kinematics of this manipulator with a high degree of modularity are quite simple. And the metamorphic characteristics of kinematic redundancy and actuation redundancy are believed to be able to enhance the research applications of the robot. This research will lay good theoretical foundations for application of this novel manipulator.

Type synthesis of the 2R1T parallel mechanism with two continuous rotational axes and study on the principle of its motion decoupling

The two-rotational-degrees-of-freedom and one-translational-degree-of-freedom (2R1T) parallel mechanism (PM) with two continuous rotational axes (CRAs) has a simple kinematic model, and it is therefore easy to implement trajectory planning, parameter calibration, and motion control. However, no systematic analysis on the structural constraints of the 2R1T-PM with two CRAs has been performed. Furthermore, there are few types of 2R1T-PM with two CRAs. Firstly, combining the theories of screw theory and space geometry, we explore the spatial geometrical relationships of the constraint forces supplied by the branches that give the 2R1T-PM two CRAs. Then, type synthesis of the 2R1T-PM with two CRAs is carried out based on the constraint forces meeting special arrangements. In addition, based on the positional relationship between the actuation force and the rotational axe, we analyze the decoupling principle between two rotational degrees of freedom for the 2R1T-PM, and put forward the criteria for distinguishing whether the two rotational degrees of freedom are partially decoupled or completely decoupled. At last, aiming at the different spatial arrangements of the two CRAs for the 2R1T-PM, we propose different configuration modes to construct 5-DOF hybrid serial-parallel manipulator, and get a 5-DOF hybrid serial-parallel manipulator on the basis of one 2R1T-PM.

Position Analysis of a Hybrid Serial-Parallel Manipulator in Immersion Lithography

This paper proposes a novel hybrid serial-parallel mechanism with 6 degrees of freedom. The new mechanism combines two different parallel modules in a serial form. 3-P̲(PH) parallel module is architecture of 3 degrees of freedom based on higher joints and specializes in describing two planes’ relative pose. 3-P̲SP parallel module is typical architecture which has been widely investigated in recent researches. In this paper, the direct-inverse position problems of the 3-P̲SP parallel module in the couple mixed-type mode are analyzed in detail, and the solutions are obtained in an analytical form. Furthermore, the solutions for the direct and inverse position problems of the novel hybrid serial-parallel mechanism are also derived and obtained in the analytical form. The proposed hybrid serial-parallel mechanism is applied to regulate the immersion hood’s pose in an immersion lithography system. Through measuring and regulating the pose of the immersion hood with respect to the wafer surface simultaneously, the immersion hood can track the wafer surface’s pose in real-time and the gap status is stabilized. This is another exploration to hybrid serial-parallel mechanism’s application.

Kinematic analysis of a hybrid serial-parallel manipulator

The kinematic analysis of a new type hybrid serial-parallel manipulator is presented. This manipulator is based on two kinds of 3-UPU parallel mechanisms (PM). Each 3-UPU possesses one platform, one base and three limbs, and hence has 3 degrees of freedom (DOF). Each limb comprises of universal (U), prismatic (P), and universal (U) joints in series. Therefore the hybrid manipulator has totally 6 degrees of freedom and has also an elegant structure. The moving platform (mid platform) of the first PM moves with pure translation with respect to the fixed base and the moving platform (end platform) in the second PM only changes its orientation with respect to the mid platform. In this paper, closed-form kinematic solutions are obtained for this type of mechanism and related theoretical results have been verified numerically.

Design and analysis of a hybrid serial-parallel manipulator

This work presents a novel design of a hybrid serial–parallel Stewart like mechanism (HS-PM). This design presents a compromise between high rigidity of fully parallel manipulators and extended workspace of serial manipulators. This mechanism is made of a base and two platforms in series. The first platform, called the mid platform is linked to the base by three legs in parallel. Its motion is restricted to only three translations using three successive prismatic joints linking the mid platform to the base. The second platform, called the top platform, has a spherical joint with the mid platform and three legs in parallel are used to impart the relative motion between these two platforms. Therefore, the top platform has 6 degrees of freedom with respect to the base. The nature of this design presents several advantages. Firstly, a closed-form solution is obtained for this type of mechanism allowing the determination of all possible solutions of the forward analysis problem. This characteristic is a great help in investigating the capabilities of this type of platforms and it is a valuable tool for the engineer to derive its controller. It is also shown that for the lower platform, formed by the base and the mid platform, a maximum of two solutions exist, whereas eight solutions were found for the upper platform, which is made from the mid platform and the top platform. This second result confirms the numerical solution of the upper platform found in recent literature. Secondly, this design presents the particularity of having the size of the orientation workspace independent of the position of the top platform, unlike the fully parallel mechanisms. This characteristic is achieved by separating the actuators responsible for each type of motion. Indeed, the three legs of the lower platform are responsible of the linear displacement of the top platform, whereas the three legs of the upper platform cause the change of orientation of the top platform. Finally, a numerical example is treated to demonstrate our analysis and to determine the range of permissible extension of the legs.