Vito R. Gervasi

Additive fabrication of custom pedorthoses for clubfoot correction

Purpose – The purpose of this paper is to determine the most‐practical means of transforming computer‐aided‐design models of custom clubfoot pedorthoses into functional pedorthoses for testing on patients in a clinical trial.Design/methodology/approach – The materials used in conventional orthosis fabrication are not yet available for solid free‐form fabrication; therefore, to fabricate the pedorthoses, several approaches were considered, including direct manufacturing, additive‐based moulding, laser cutting of foam and combinations of several of these approaches.Findings – The chosen approach of additively manufacturing the custom hard shell, and moulding the polyurethane‐foam insert, resulted in accurate, durable and effective pedorthoses that fit well, and could be adjusted as needed. The pedorthoses that were produced are currently being tested on the respective patients for their improvement in mobility and degree of clubfoot correction, and will continue through early 2010.Practical implications – A...

Design, Additive Manufacture, and Control of a Pneumatic MR-Compatible Needle Driver

This paper reports the design, modeling, and control of an MR-compatible actuation unit comprising pneumatic stepper mechanisms. One helix-shaped bellows and one toroid-shaped bellows were designed to actuate in pure rotation and pure translation, respectively. The actuation unit is a 2-degree-of-freedom (DOF) needle driver that translates and rotates the base of one tube of a steerable needle like a concentric tube robot. For safety, mechanical stops limit needle motion to maximum unplanned step sizes of 0.5 mm and 0.5°. Additively manufactured by selective laser sintering, the flexible fluidic actuating (FFA) mechanism achieves 2-DOF motion as a monolithic, compact, and hermetically sealed device. A second novel contribution is substep control for precise translations and rotations less than full-step increments; steady-state errors of 0.013 mm and 0.018° were achieved. The linear FFA produced peak forces of 33 and -26.5 N for needle insertion and retraction, respectively. The rotary FFA produced bidirectional peak torques of 68 N·mm. With the FFAs in full motion in a 3-T scanner, no loss in signal-to-noise ratio of MR images observed.

Design and Precision Control of an MR-Compatible Flexible Fluidic Actuator

Magnetic resonance imaging (MRI) offers many benefits to image-guided interventions, including excellent soft tissue distinction, little to no repositioning of the patient, and zero radiation exposure. The closed, narrow bore of a high field MRI scanner limits clinician access to the patient, such that an MR-compatible robot is essentially required for many potential interventions. A robotic system of this kind could additionally provide the clinician increased accuracy and more degrees of freedom within the minimally invasive context. Fluid power is an excellent type of actuation to use inside the MRI scanner, as such actuators can be designed free of magnetic and electrical components. However, there are no fluid power actuators readily available that are suitable for use in the operating room. This paper reports a compact, intrinsically safe, sterilizable fluid power actuator. Using additive manufacturing processes, the actuator was printed in a single build. Thus, it is composed of several integrated parts in a compact design. Employing an inchworm-like behavior, the linear actuator can advance or retract a needle or mechanism rod in discrete steps; thus the device is intrinsically safe. The actuator is fluid agnostic, but a pneumatic prototype is presented here with initial testing results. For the pneumatic case, sub-step positioning control has been tested using a nonlinear, modelbased controller, and the mean steady-state error was 0.025 mm. Thus this type of actuator appears to be promising solution for use in MRI-guided interventions.

Geometry and procedure for benchmarking SFF and hybrid fabrication process resolution

Purpose – The purpose of this paper is to share with the solid freeform fabrication community a new procedure and benchmark geometries for evaluating SFF process capabilities. The procedure evaluates the range capability of various SFF and SFF‐based hybrid processes in producing rod and hole elements.Design/methodology/approach – By following the procedure and using the appropriate combination of benchmark parts the user can determine the minimal rod and hole size capabilities of an SFF or SFF‐based process. Benchmark parts are designed to capture feature size limitations, build angle problems, and aspect ratio capabilities.Findings – The geometries and procedure were found to work for evaluating simple rod and hole elements resulting from SFF‐based processes.Research limitations/implications – Future work could address slot and wall features using a similar procedure. Mechanical properties and performance of resulting parts are not within the scope of this procedure.Practical implications – The procedure...