Abstract
4SPRR-SPR parallel robot is a novel closed-loop mechanism. The research of kinematics is the basis of real-time and robust robot control. This paper aims to proposing a method to address a surrogate model of forward kinematics for PMs (Parallel Mechanisms). Herein, the forward kinematics model is derived by training the VQTAM (Vector-Quantified Temporal Associative Memory) network, which originates from a SOM (Self-Organized Mapping). During the processes of training, testing and estimating this neural network, the priority K-means tree search algorithm is utilized, thus improving the training efficacy. Furthermore, LLR (Local Linear Regression), LWR (Local Weighted Linear Regression) and LLE (Local Linear Embedding) algorithms are respectively combined with VQTAM to get three improvement algorithms, aiming to further optimize the prediction accuracy of the networks. To speed up solving the least squared equation in the three algorithms, SVD (Singular Value Decomposition) is introduced. Finally, Data from inverse kinematics by geometric method is obtained, which is for constructing and validating the VQTAM neural network. Results show that the prediction effect of LLE algorithm is better than others, which could be a potential surrogate model to estimate the output of forward kinematics.
Highlights
Parallel robots offer noticeable advantages in machining applications, especially in the field of heavy equipment manufacture, due to their high rigid-weight ratio and load capacity
The machine tool industry has discovered the potential advantages of PMs and many parallel machine tools have been developed based on either the 6-DOF parallel mechanisms or 5-DOF PMs.[1]
Stewart introduced a 6-DOF PM, which is popularly known as Stewart platform.[2]
Summary
Parallel robots offer noticeable advantages in machining applications, especially in the field of heavy equipment manufacture, due to their high rigid-weight ratio and load capacity. Parallel robots or PMs with 5 or 6 DOF are often used as motion simulators and crane devices. Stewart introduced a 6-DOF PM, which is popularly known as Stewart platform.[2] It is commonly used in flight or driving simulators, vibration isolation platform, space docking mechanisms, and space telescope.[3,4] Hereafter the lower-mobility (2-5 DOFs) PMs have emerged and have become popular owing to their simple structure, low kinematic coupling, low cost and convenient control.[5,6,7] Xie et al.,[5] Huang et al.[6] and Joshi et al.[7] studied the type synthesis for different types of lower-mobility PM.
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