A Stiffness-Adjustable Hyperredundant Manipulator Using a Variable Neutral-Line Mechanism for Minimally Invasive Surgery

In robotic single-port surgery, it is desirable for a manipulator to exhibit the property of variable stiffness. Small-port incisions may require both high flexibility of the manipulator for safety purposes, as well as high structural stiffness for operational precision and high payload capability. This paper presents a new hyperredundant tubular manipulator with a variable neutral-line mechanisms and adjustable stiffness. A unique asymmetric arrangement of the tendons and the links realizes both articulation of the manipulator and continuous stiffness modulation. This asymmetric motion of the manipulator is compensated by a novel actuation mechanism without affecting its structural stiffness. The paper describes the basic mechanics of the variable neutral-line manipulator, and its stiffness characteristics. Simulation and experimental results verify the performance of the proposed mechanism.Samsung Advanced Institute of Technolog

Design and analysis of a wire-driven flexible manipulator for bronchoscopic interventions

Bronchoscopic interventions are widely performed for the diagnosis and treatment of lung diseases. However, for most endobronchial devices, the lack of a bendable tip restricts their access ability to get into distal bronchi with complex bifurcations. This paper presents the design of a new wire-driven continuum manipulator to help guide these devices. The proposed manipulator is built by assembling miniaturized blocks that are featured with interlocking circular joints. It has the capability of maintaining its integrity when the lengths of actuation wires change due to the shaft flex. It allows the existence of a relatively large central cavity to pass through other instruments and enables two rotational degrees of freedom. All these features make it suitable for procedures where tubular anatomies are involved and the flexible shafts have to be considerably bent in usage, just like bronchoscopic interventions. A kinematic model is built to estimate the relationship between the translations of actuation wires and the manipulator tip position. A scale-up model is produced for evaluation experiments and the results validate the performance of the proposed mechanism

Rolling-joint design optimization for tendon driven snake-like surgical robots

The use of snake-like robots for surgery is a popular choice for intra-luminal procedures. In practice, the requirements for strength, flexibility and accuracy are difficult to be satisfied simultaneously. This paper presents a computational approach for optimizing the design of a snake-like robot using serial rolling-joints and tendons as the base architecture. The method optimizes the design in terms of joint angle range and tendon placement to prevent the tendons and joints from colliding during bending motion. The resulting optimized joints were manufactured using 3D printing. The robot was characterized in terms of workspace, dexterity, precision and manipulation forces. The results show a repeatability as low as 0.9mm and manipulation forces of up to 5.6N

Granular Jamming as Controllable Stiffness Mechanism for Endoscopic and Catheter Applications

Context During minimally invasive procedures, most of the devices (endoscopes, catheters, guidewires, etc.) need to be sufficiently flexible to avoid damaging patient tissues or causing pain, but have to be stiff enough to transmit force for support or for puncture. In the case of vascular stenosis, the guidewire has to be flexible to reach the stenosis (through the blood vessels), but it requires a rigid support to pass through the occlusion for treatment, to avoid buckling or deformation due to the force application. In order to solve this duality on the rigidity, controllable stiffness mechanisms can be used. Various mechanisms to control the stiffness can be found in the literature [1]. One of the promising solutions to achieve this objective is based on granular material jamming [2]. This research aims at studying the scaling laws of such solutions for miniaturized applications (with diameters below 3mm), the mechanical rules of design and the optimization based on the stiffness performances. Granular jamming The granular jamming is based on the locking of granular material. In this study, a flexible membrane is filled with a granular material (glass beads). When the pressure difference between outside and inside the membrane is low, the grains are free to move with respect to each other. In this configuration, the system is very flexible. Once the difference of pressure is increased, the grains are locked to each other due to the inter-grain friction. In this configuration, the system is more rigid. It is possible to adjust the stiffness of the device by controlling the pressure difference across the membrane. Materials and methods In this work, the performances of the stiffness change thanks to the granular jamming are quantified by mechanical testing. On the one hand, three point bending and cantilever beam tests are performed to quantify the flexural stiffness EI (product of the Young Modulus, E, and the second moment of area, I) of the solutions. Various granular materials and diameters of the samples are studied. On the other hand, triaxial compression tests are performed to observe the influence of the pressure difference on the rigidity obtained via granular jamming, using different granular materials. Results and discussion The tests described previously provide information on the performances of the granular jamming solution as well as an indication of the most important parameters to optimize. An optimal size of grains is highlighted by the results of these mechanical tests. The results of the triaxial compression tests show that the pressure difference is the most important parameter influencing the Young Modulus. The bending tests show that the second moment of area greatly impacts this stiffness. Removing the influence of the geometry, the equivalent Young Modulus is positively influenced for smaller diameters which is promising for the applications targeted in this work. Some of these results, as well as pictures and conclusions are illustrated in the poster file available in the following link : https://dipot.ulb.ac.be/dspace/bitstream/2013/239703/3/20161125PosterNCBMElblanc.pdf. One of the perspectives of this work is to develop a model for linking the results obtained from the different mechanical tests and to observe the optimization of the grains (shape and size) and cross-section of the samples with respect to the change of stiffness obtained. Further studies on stimulation method and on materials should be performed. References - [1] Kuder, I. K. et Al., ?Variable stiffness material and structural concepts for morphing applications?, Progress in Aerospace Sciences, pp.33-55, 2013. - [2] Loeve, A. J. et Al., ?Vacuum packed particles as flexible endoscope guides with controllable rigidity?, Granular Matter, pp. 543-554, 2010

Design of a Variable Stiffness Passive Layer Jamming Structure for Anthropomorphic Robotic Finger Applications

Soft robots can effectively mimic human hand interface characteristics and facilitate collaborative operations with humans in a safe manner. This dissertation research concerns the design and fabrication of a low cost variable stiffness structure for applications in compliant robotic fingers. A conceptual design of a compact multi-layer structure is proposed for realizing variable stiffness, when applied to underactuated fingers of an anthropomorphic robotic hand. The proposed design comprises thin material layers with clearance that permits a progressive hardening feature while grasping and added design flexibility and tuning of the fingers’ compliance. The design permits stiffness variations in a passive manner in the soft contact regions. The design is realized to ensure ease of scalability and cost-effective fabrication by the ’Additive Manufacturing (AM)’/3D-printing technology. Both the multi-layer structures and the fingers could be fabricated as a single entity, and from a single base material with relatively low elastic modulus. The proposed design also exhibits finite degrees-of-freedom representative of the human finger - The feasibility of the design and its manufacturability are verified through prototype fabrication using a readily available 3D-printing material, namely; 'Thermoplastic PolyUrethane (TPU)' with Young’s Modulus of 25MPa. The chosen material permitted low stiffness of the multi-layer structure in the contact interface under relatively small deformations, while ensuring sufficient rigidity on the non-contact regions of the finger. A finite element (FE) model is formulated considering 3D tetrahedral elements and a nodal-normal contact detection method together with the augmented Lagrange formulation. The model is analyzed to determine the force-displacement characteristics of the structure subject to linearly increasing compressive load, under the assumption of low interface friction. A simplified analytical model of the multi-layer structure is also formulated considering essential boundary and support conditions for each individual layer. The model revealed progressive hardening characteristics of the multilayer structure during compression due to sequential jamming of individual layers. The force-displacement characteristics of the design could thus be varied by varying the multi-layer structure parameters, such as number of layers, thickness of individual layers, material properties, and clearance between the successive layers. It is shown that the simplified analytical model could provide reasonably good estimate of the force-deflection properties of the structure in a computationally efficient manner. The analytical model is subsequently used to investigate the influences of variations in the multilayer structure parameters in a computationally efficient manner. It is shown that the proposed design offers superior tuning flexibility to realize desired force-displacement characteristics of the structure for developing scalable anthropomorphic robotic fingers of a compliant robotic hand, in addition to the cost-effective manufacturability

Snake Robots for Surgical Applications: A Review

Although substantial advancements have been achieved in robot-assisted surgery, the blueprint to existing snake robotics predominantly focuses on the preliminary structural design, control, and human–robot interfaces, with features which have not been particularly explored in the literature. This paper aims to conduct a review of planning and operation concepts of hyper-redundant serpentine robots for surgical use, as well as any future challenges and solutions for better manipulation. Current researchers in the field of the manufacture and navigation of snake robots have faced issues, such as a low dexterity of the end-effectors around delicate organs, state estimation and the lack of depth perception on two-dimensional screens. A wide range of robots have been analysed, such as the i2Snake robot, inspiring the use of force and position feedback, visual servoing and augmented reality (AR). We present the types of actuation methods, robot kinematics, dynamics, sensing, and prospects of AR integration in snake robots, whilst addressing their shortcomings to facilitate the surgeon’s task. For a smoother gait control, validation and optimization algorithms such as deep learning databases are examined to mitigate redundancy in module linkage backlash and accidental self-collision. In essence, we aim to provide an outlook on robot configurations during motion by enhancing their material compositions within anatomical biocompatibility standards

Hybrid Compliant Musculoskeletal System for Fast Actuation in Robots

A nature-inspired musculoskeletal system is designed and developed to examine the principle of nonlinear elastic energy storage–release for robotic applications. The musculoskeletal system architecture consists of elastically rigid segments and hyperelastic soft materials to emulate rigid–soft interactions in limbless vertebrates. The objectives are to (i) improve the energy efficiency of actuation beyond that of current pure soft actuators while (ii) producing a high range of motion similar to that of soft robots but with structural stability. This paper proposes a musculoskeletal design that takes advantage of structural segmentation to increase the system’s degrees of freedom, which enhances the range of motion. Our findings show that rigid–soft interactions provide a remarkable increase in energy storage and release and, thus, an increase in the undulation speed. The energy efficiency achieved is approximately 68% for bending the musculoskeletal system from the straight configuration, compared to 2.5–30% efficiency in purely soft actuators. The hybrid compliance of the musculoskeletal system under investigation shows promise for alleviating the need for actuators at each joint in a robot.</p