Optimal Design and Tracking Control of a Superelastic Flexure Hinge Based 3-PRR Compliant Parallel Manipulator

Miao Yang,Wei Dong,Chi Zhang,Guilin Yang

doi:10.1109/access.2019.2954842

Abstract

A major obstacle that restricts the application of notched flexure hinge based compliant mechanism is its limited motion range. This paper presents the optimal design and tracking control of a superelastic flexure hinge based 3-PRR compliant parallel manipulator (CPM) to achieve high precision planar motion within centimeter's translation range and up to 10 degrees' rotational range. Firstly, a novel asymmetric ellipse-parabola (AEP) notch shape is proposed, and the geometric parameters of the AEP superelastic flexure hinge are acquired via multi-objective optimization to obtain desirable transmission performance. Secondly, a nominal inverse kinematic model of the CPM is established, and the dimension parameters of the 3-PRR manipulator are synthesized to maximize the dexterity of the CPM over the regular workspace. Thereafter, a disturbance observer based inverse kinematic control scheme (DOB-IKM) is proposed to suppress the model mismatches and external disturbances of the 3-PRR CPM, where the unmodeled factors of the system are approximated through an online learning radical basis function neural network (RBFNN) and the external disturbances of the CPM is observed and compensated by a disturbance observer (DOB). Finally, a prototype of the 3-PRR CPM is manufactured, and experimental tests show the effectiveness of the proposed control scheme and the superiority of the 3-PRR CPM.

Highlights

Flexure hinges always serve as passive rotational joints in compliant parallel manipulator (CPM) to transmit motion and force continuously
The performance indices of an elliptic superelastic flexure hinge with the same notch length and minimum thickness of the optimized flexure hinge are presented in Table 1, which can be regarded as a special case of the asymmetric ellipse-parabola (AEP) flexure hinge, i.e., λ = 0.5, e1 = 1.563, φt1 = −π/2, e2 = 1.563, and φt2 = −π
This paper presents a superelastic flexure hinge based planar 3-PRR CPM which is capable of achieving high precision with large regular workspace

Summary

Introduction

Flexure hinges always serve as passive rotational joints in CPMs to transmit motion and force continuously. The notched flexure hinge is the most frequently used flexure hinge for it’s structure and high transmission precision. The motion ranges of conventional notched flexure hinge. Based CPMs are mainly within micron scales due to the stress concentration at the outer edge of the flexure hinges’ thinnest section [5], which severely restricts the application of CPMs. With the development of modern precision engineering, CPMs with centimeter motion range are highly demanded in biomedical sciences and optical engineering, such as, scanning probe microscopy, lithography, and cell micromanipulation [6], [7]. A promising way to enlarge the motion range of notched flexure hinge based CPMs is to improve the deformability of the material which used to fabricate the flexure hinges. Shape memory alloy (SMA) may be the best candidate because of the superelasticity, whose maximum recoverable strain is about 6% [8], while the maximum recoverable strain of most metal materials is only 0.2-0.8% [9]

Methods

Results

Conclusion