微纳操作系统是精密操作、精密加工领域重要组成部分。微纳操作系统的载物平台负责放置样品和大行程搬运样品，需要大行程、高精度的定位。宏微结合的方法能弥补精密定位平台行程不足的缺点，而并联机构能实现高精度定位，因此采用3PRR(3自由度，每条支链包括一个移动副(P)驱动和两个转动副(R))并联平台作为扫描电子显微镜(Scanning electron microscopy, SEM)环境下的宏微结合精密平台中的宏动部分。为了实现大行程、高精度定位，需要分析机构工作空间与奇异性分布。通过推导3PRR运动学方程，求得机构雅可比矩阵，研究雅可比矩阵特性，求得3PRR并联平台非奇异工作空间分布，把机构雅可比矩阵特性与奇异分布引入控制范畴，提出两种奇异区域规避控制策略与一种奇异位型逃逸控制策略。对机构如何规避奇异区域与进入奇异位型后如何快速逃逸提供了理论指导，仿真分析表明，提出的策略对机构精密定位与可控性提供了保障。
莫嘉嗣
,
张宪民
,
邱志成
,
魏骏杨
. SEM环境下3PRR并联平台奇异区域规避与逃逸控制策略[J]. 机械工程学报, 2015
, 51(23)
: 1
-11
.
DOI: 10.3901/JME.2015.23.001
Micro-nano operating system is an important part in the field of precision operation and machining. The sample stage of the micro-nano operating system is used to place and move samples at large-scale stroke; therefore the sample stage needs to possess the features of large stroke and high precision positioning. Macro-micro combination method can make up the stroke deficiency of the precision positioning platform, whereas parallel mechanism can realize high precision positioning. Hence, under the environment of the scanning electron microscopy (SEM), the 3PRR parallel positioning stage, which has 3 degrees of freedom and whose chains each consist of a prismatic joint and two revolute joints, is adopted to constitute the macro-movement part of the macro-micro combination precision positioning platform. In order to achieve the large stroke and high precision positioning, the workspace and singularity distribution of the 3PRR require to be analyzed. The Jacobi matrix is obtained by calculating the kinematics equation. And after the analysis of the characteristics of the Jacobi matrix, the nonsingular workspace distribution of the 3PRR stage is acquired. Then, based on the characteristics of the Jacobi matrix and the singular workspace distribution, two control strategies are presented for avoiding singular area, and one control strategy for escaping the singular position. The corresponding theory of the strategies is provided. The simulation and analytic results show that these strategies can ensure the precision positioning and controllability of the mechanism.
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