This article describes a novel and simple shaft actuated tip articulation (SATA) mechanism that allows arthroscopic instruments to articulate while remaining stiff. Since the SATA mechanism requires only independent rotation of two tubes for hinge articulation, cables, gears, or other internal components that are normally found in steerable endoscopic instruments become obsolete. The SATA mechanism was integrated in a new steerable cutter prototype and tested. Early user, mechanical strength and cadaver experiments were performed that indicate that this first prototype withstands an axial and sideways force of 100 N and 20 N, that trained users can (dis)assemble the instrument in less than 1.5 min and that a surgeon is able to reach all important locations on the menisci.
Advanced robotic hand prostheses are praised for their impressive robust and fine grasping capabilities generated from intricate systems. Nevertheless, a high demand remains for grasping mechanisms that are mechanically simple, lightweight, and cheap to produce, easy to assemble and low in maintenance costs. This paper presents the design of a partially compliant underactuated finger to demonstrate the feasibility of achieving these rigorous requirements. The conceptual topology of the three phalanx finger is selected based on competitive analysis. Employing Pseudo-Rigid Body Model and Finite Element Analysis, a genetic optimization problem is formulated to minimize bending stresses within compliant flexures. The result is a fully functional demonstrator capable of flexing 180° in finger rotation. The prototype is fabricated from flexible high strength nylon and requires no assembly steps beyond 3D printing. Experimental testing verifies the design method with an acceptable error of < 5%.
A novel fabrication process and design optimization method for a micro forceps is presented. This work is part of a larger research effort to design and fabricate nanoparticulate enabled surgical instruments. The micro forceps is a monolithic compliant mechanism that due to its two-dimensional design can be manufactured using the new fabrication process. The process begins with fabrication of an array of molds on refractory substrates using a modified UV lithography technique. In parallel, engineered ceramic nanocolloidal slurries are prepared for gel-casting into the molds. Mold infiltration takes place via a squeegee technique adapted from screen printing with excess slurry removed using an ethanol wipe. Finally, the photoresist molds are removed with a reactive ion etch (RIE) step, and ceramic parts sintered to full density. Employing this manufacturing technique for the compliant micro forceps design is advantageous because a large number of parts can be produced with a large aspect ratio (≥40:1), sharp edges (∼ 1 μm), and a resolution of 2 μm. Two optimization problems are formulated to determine the effect of dimensional parameters and material strength on the performance of the compliant micro forceps. First, performance is sensitive to small changes in the geometry, indicating that dimensions and shrinkage rates must be carefully controlled during processing. Second, performance can also be improved by using very large aspect ratios and/or improvements in material strength. A sample part manufactured using the new process is presented.
This paper describes a multidisciplinary project focused on developing design and fabrication methods for narrow-gauge compliant mechanisms expected to be useful in advanced minimally invasive surgery. In this paper, three aspects of the project are discussed: meso-scale fabrication, compliant mechanism design, and experimental determination of mechanical properties and forceps performance. The selected manufacturing method is a lost mold rapid infiltration forming process that is being developed at Penn State University. The process is capable of producing hundreds of freestanding metallic and ceramic parts with feature sizes ranging from sub-10 μm to approximately 300 μm. To fulfill surgical and manufacturing requirements, a contact-aided compliant mechanism design is proposed. A finite element analysis solution, used to evaluate large deformation and contact, is implemented into an optimization routine to maximize tool performance. A case study demonstrates the design and manufacturing processes for a 1 mm diameter austenitic (300 series) stainless steel forceps. Due to manufacturing variables that affect grain size and particle adhesion, the strength of the fabricated parts are expected to vary from the bulk material properties. Therefore, fabricated parts are experimentally tested to determine accurate material properties. Three point bend tests reveal yield strengths between 603 and 677 MPa. Results from the design optimization routine show that material strengths within this range require large instrument aspect ratios between 40 and 50 with anticipated blocked forces as high as 1.5 N. An initial prototype is assembled and tested to compare experimental and theoretical tool performance. Good agreement between the computational and experimental data confirms the efficacy of the processes used to develop a meso-scale contact-aided compliant forceps.
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