Abstract
A 3-PRR (three links with each link consisting of a prismatic pair and two rotating pairs) parallel platform was designed for application in a vacuum environment. To meet the requirement of high tracking accuracy of the 3-PRR parallel platform, a full closed-loop control precision tracking system with laser displacement sensors and linear grating encoders was analysed and implemented. Equally-spaced laser displacement sensors and linear grating encoders were adopted not only for measurement but also for feedback control. A feed-forward control method was applied for comparison before conducting the closed-loop feedback control experiments. The closed-loop control experiments were conducted by adopting the PI (proportion and integration) feedback control and RBF (radial basis function) neural network control algorithms. The experimental results demonstrate that the feed-forward control, PI feedback control, and RBF neural-network control algorithms all have a better control effect than that of semi-closed-loop control, which proves the validity of the designed full closed-loop control system based on the combination of laser displacement sensors and linear grating encoders.
Highlights
Precision positioning systems increasingly require a high positioning accuracy and a large travel range [1,2], and play an important role in the fields of planar manipulations, industrial robots, measurement systems, and so on [3,4,5]
(three degrees of freedom with each branch consisting of three rotating pairs) and 3-PRR planar parallel mechanisms [7]
The precision encoders for full closed-loop control is illustrated in detail, and demonstrates high measurement tracking system with three -spaced laser displacement sensors and linear grating encoders accuracy
Summary
Precision positioning systems increasingly require a high positioning accuracy and a large travel range [1,2], and play an important role in the fields of planar manipulations, industrial robots, measurement systems, and so on [3,4,5]. Three capacitance sensors were installed at the end of a planar three-degrees-of-freedom (3-DOF) nano-positioning platform to realize feedback control, and the trajectory tracking accuracy of the mechanism was improved by using the traditional PID (proportion, integration, and differentiation) control algorithm [18]. The above analysis shows that few people are designing and investigating a full closed-loop control 3-PRR precision tracking system with laser displacement sensors and neural-network-based control algorithms. The precision encoders for full closed-loop control is illustrated in detail, and demonstrates high measurement tracking system with three -spaced laser displacement sensors and linear grating encoders accuracy. The six-degrees-of-freedom motion of more complicated mechanisms can be measured by studies of semi-closed-loop control, feed-forward control, PI feedback control, and RBF more -spaced laser displacement sensors in combination. Based on the combination of laser displacement sensors and linear grating encoders
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