Abstract
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.
Highlights
Since the appearance of parallel mechanisms (PMs), PMs have been studied widely, mainly because of PMs owning the characteristics of compact structure, high stiffness, and high load capacity compared with serial mechanisms [1, 2]
The 2RPU/UPR PM is a new 2R1T PM with two continuous rotational axis (CRA), so it is easier to implement trajectory planning, parameter calibration, and motion control, compared with the general 2R1T PMs. (2) The structure of this machine is described in detail and the kinematics, statics and workspace are all analyzed, which help us to better understanding the structural characteristics and is convenient to optimal design
(3) A modified discretization method is used to reveal the workspace of the PM which could incidentally solve the volume of the workspace
Summary
Since the appearance of parallel mechanisms (PMs), PMs have been studied widely, mainly because of PMs owning the characteristics of compact structure, high stiffness, and high load capacity compared with serial mechanisms [1, 2]. In order to measure the global behavior of the motion/force transmission over the whole workspace, the first one of the three indices is the global transmission index (GTI). If the transmission angle μ is equal to 0 or 180°, the mechanism is in the “dead point” where the mechanism has the self-jamming characteristic. It is a kind of singularity for the PM which leads to loss of controllability and change of internal DOF. As the 2RPU/UPR PM can be divided into two planar mechanisms, it is logical to optimize this PM by transmission angle index.
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