Long-Travel 3-PRR Parallel Platform Based on Biomimetic Variable-Diameter Helical Flexible Hinges.

Technological advancements across various sectors are driving a growing demand for large-scale three-degree-of-freedom micro-nano positioning platforms, with substantial pressure to reduce footprints while enhancing motion range and accuracy. This study proposes a three-prismatic-revolute-revolute (3-PRR) parallel mechanism based on biomimetic variable-diameter helical flexible hinges. The resulting platform achieves high-precision planar motion along the X- and Y-axes, a centimeter-level translation range, and a rotational range of 35° around the Z-axis by integrating six variable-diameter flexible helical hinges that serve as rotational joints when actuated by three miniature linear servo drives. The drives are directly connected to the moving platform, thereby enhancing the compactness of the system. A kinematic model of the motion platform was established, and the accuracy and effectiveness of the forward and inverse kinematic solutions were validated using finite element analysis. Finally, a prototype of the 3-PRR parallel platform was fabricated, and its kinematic performance was experimentally verified visually for improved endpoint displacement detection. The assessment results revealed a maximum displacement error of 9.5% and confirmed that, judging by its favorable workspace-to-footprint ratio, the final system is significantly more compact than those reported in the literature.

Design of a locust leg-like compliant constant-force mechanism supporting large-scale damage-free manipulation.

Precision manipulation is plays an increasingly crucial role in bioengineering fields such as cell injection. Due to the specificity of the operational process, which is highly susceptible and damageable by the actuated force, millimeter-level nondestructive operations are gaining more and more attention. With this, a symmetrical compliant constant-force mechanism (CCFM) is developed to provide stable and large motion stroke for damage-free precision manipulation in this paper. The mechanism design is inspired by the legs of the locust, which flexes and folds when the locust jumps. In terms of structure design, double biomimetic diamond beams are used to generate positive and negative stiffness. A crossbeam is added to the internal diamond mechanism, which flexes during movement to provide negative stiffness, while the external diamond mechanism without additional constraint provides positive stiffness. The theoretical model of this CCFM is established to analyze its force-displacement relationship, which is verified by performing finite element analysis simulations and experimental studies. Meanwhile, a parametric study is conducted to investigate the influence of the dominant design variable of the CCFM. Finally, the test results show that the CCFM can generate motion range up to 5 mm with a constant output force ∼15.2 N. The developed CCFM has potential applications in the field of manipulation techniques of cell engineering and robotics in the future.

Design and Testing of a Novel Nested, Compliant, Constant-Force Mechanism with Millimeter-Scale Strokes.

This paper presents a novel nested, compliant, constant-force mechanism (CFM) that generates millimeter-scale manipulation stroke. The nested structure is utilized to improve the overall compactness of the CFM. A combination strategy of positive and negative stiffness is induced to generate constant force with a millimeter-level range. In particular, bi-stable beams are used as the negative stiffness part, and V-shaped beams are selected as the positive stiffness part, and they are constructed into the nested structures. With this, a design concept of the CFM is first proposed. From this, an analytical model of the CFM was developed based on the pseudo-rigid body method (PRBM) and chain beam constraint model (CBCM), which was verified by conducting a simulation study with nonlinear finite-element analysis (FEA). Meanwhile, a parametric study was conducted to investigate the influence of the dominant design variable on the CFM performance. To demonstrate the performance of the CFM, a prototype was fabricated by wire cutting. The experimental results revealed that the proposed CFM owns a good constant-force property. This configuration of CFM provides new ideas for the design of millimeter-scale, constant-force, micro/nano, and hard-surface manipulation systems.

Design and modeling of a piezo-driven three-dimensional bridge-type amplification mechanism with input/output guiding constraint.

Owing to the limited stroke of piezo stacks, compliant amplification mechanisms are widely employed to magnify the displacement of piezoelectric actuators for emerging applications in precision engineering. In this study, a three-dimensional (3D) bridge-type amplification mechanism composed of two serially connected bridge-type amplifiers with a novel constraint form has been developed. The parallel guiding beams mounted at the input and output ends significantly increase the lateral stiffness and minimize parasitic displacements for higher accuracy. Furthermore, a new theoretical model is established to predict the magnification behavior of the 3D amplifier that takes into account the displacement loss caused by the coupling of the two bridge-type amplifiers. The accuracy of this model and the mechanical performance of the developed amplifier are verified by conducting finite element simulations and experimental studies on the manufactured prototypes.

Long stroke displacement measurement with reduced coupling error supporting high precision control of a beam flexure-based micro-stage.

This paper presents a novel beam flexure-based X-Y-θ micro-stage integrated with a laser interferometric type displacement measurement approach for reducing the measurement error induced by the rotational motion and cross-axis load effect. Aiming at achieving high-precision real-time control of the proposed system, an active disturbance rejection controller is developed such that the inevitable parasitic and coupling errors can be treated as disturbances and actively compensated by using the extended state observer. Finally, the verification experiments are deployed on the fabricated prototype, where the results indicate that the proposed approach achieves excellent performance in terms of motion accuracy and disturbance rejections.

A PC-PU nanoparticle/PU/decellularized scaffold composite vascular patch: Synergistically optimized overall performance promotes endothelialization.

Composite vascular patches have gained increasingly attention due to the limited availability of autologous patches (vascular graft materials made from the blood vessels of the same recipient), the lack of growth capability of nonautologous patches (vascular graft materials made from the blood vessels of a different donor) and the disadvantages of synthetic patches. In this study, we report a highly biocompatible phosphatidylcholine-polyurethane nanoparticle/polyurethane/decellularized scaffold composite vascular patch (PCVP). It was fabricated by a facile method - cosedimentation. Its in vitro blood and cell compatibility including hemolysis, plasma recalcification time, coagulation time, platelet adhesion and cytotoxicity was evaluated. The surface modified with phosphatidylcholine-polyurethane (PC-PU) nanoparticles exhibited the improved anticoagulation activity. The in vivo performance of the PCVP was investigated in a mouse model. The nanopatterned surface that resembled the concave-convex structure of the luminal surface of native blood vessels enhanced cell attachment, proliferation, migration and differentiation. The decellularized scaffold had the mechanical property similar to that of the targeted blood vessels, which could withstand in vivo dynamic blood pressure. The overall performance of the PCVP was synergistically optimized by each layer of the multilayer design. The patched artery remained patent and the formation of endothelial tissue - endothelialization was achieved 30days after the in vivo implantation in a mouse model.