Multi-Point Orientation Control of Discretely-Magnetized Continuum Manipulators

In the past decade, remote actuation through magnetic fields has been used for position and orientation control of continuum manipulators (CMs) with a single magnet at the distal tip. By leveraging multiple points of actuation along the length of the CM it is possible to achieve increasingly complex shapes, which could be of interest in complex navigation tasks, for example, in minimally invasive surgery. In this study we present an approach for multi-point orientation control of discretely magnetized CMs. The approach is demonstrated with a manipulator that contains two permanent magnets, which are each actuated inside a non-homogeneous magnetic field. We formulate an accurate field model that conforms to Maxwell's equations and apply this to the available actuation system. Furthermore, Cosserat rod theory is used to model the manipulator deformation under external wrenches, and is utilized to numerically compute a Jacobian necessary to calculate the actuation inputs. During experiments, a stereo vision setup is used for manipulator shape feedback. Target orientations are manually provided as input to show independent orientation control of the two permanent magnets. Additionally, simulations with an extended virtual clone of the electromagnetic system are performed to show the capability of achieving more complex manipulator shapes. In both scenarios, it is observed that the algorithm is able to independently control the orientation of two interconnected magnets in a non-uniform magnetic field

Tandem actuation of legged locomotion and grasping manipulation in soft robots using magnetic fields

Untethered soft robots have the potential to impact a variety of applications, particularly if they are capable of controllable locomotion and dexterous manipulation. Magnetic fields can provide humansafe, contactless actuation, opening the gates to applications in confined spaces - for example, in minimally invasive surgery. To translate these concepts into reality, soft robots are being developed with different capabilities, such as functional components to achieve motion and object manipulation. This paper investigates the tandem actuation of two separate functions (locomotion and grasping) through multi-legged soft robots with grippers, actuated by magnetic fields. The locomotion and grasping functions are activated separately by exploiting the difference in the response of the soft robots to the magnitude, frequency and direction of the actuating magnetic field. Two robots capable of performing controllable straight and turning motions are demonstrated: a millipede-inspired robot with legs moving in a rhythmic pattern, and a hexapod robot with six magnetic legs following an alternating tripod gait. Two types of grippers are developed: one inspired by prehensile tails and another similar to flowers or jellyfish. The various components are fabricated using a composite of silicone rubber with magnetic powder, and analyzed using quasi-static models and experimental results. Fully untethered locomotion of the robots and independent gripper actuation are illustrated through experiments. The maneuverability of the robots is proven through teleoperated steering experiments where the robots navigate through the workspace while avoiding obstacles. The ability of the robots to manipulate objects by operating in tandem with the grippers is demonstrated through multiple experiments, including pick-and-place tasks where the robots grasp and release cargo at specific locations when triggered using magnetic fields. (C) 2020 The Authors. Published by Elsevier Ltd

A Snake-Inspired Multi-Segmented Magnetic Soft Robot Towards Medical Applications

Magnetically-actuated soft robots have potential for medical application but require further innovation on functionality and biocompatibility. In this letter, a multi-segmented snake-inspired soft robot with dissolvable and hiocompatible segments is designed. The actuation response under external magnetic field is investigated through simulations and experiments. A dissolve-controllable mixture of gelatin, glycerol and water (GGW) in a mass ratio of 1:5:6 is used to form the structure of the robot. The dissolution of GGW in water and mucus is tested. Magnetic cubes made of silicone rubber mixed with ferromagnetic particles are used to achieve snake-like motion under the influence of a rotating magnetic field. The motion of the robot is tested under different magnitudes and frequencies of the magnetic field. The ability of the robot to navigate obstacles, move over ground and under water as well as on the oil-coated surface, dissolve and release a drug is demonstrated through experiments. The combination of multi-segmented design and biocompatible and dissolvable materials illustrates the potential of such robots for medical applications

Surgical Applications of Compliant Mechanisms:A Review

Current surgical devices are mostly rigid and are made of stiff materials, even though their predominant use is on soft and wet tissues. With the emergence of compliant mechanisms (CMs), surgical tools can be designed to be flexible and made using soft materials. CMs offer many advantages such as monolithic fabrication, high precision, no wear, no friction, and no need for lubrication. It is therefore beneficial to consolidate the developments in this field and point to challenges ahead. With this objective, in this article, we review the application of CMs to surgical interventions. The scope of the review covers five aspects that are important in the development of surgical devices: (i) conceptual design and synthesis, (ii) analysis, (iii) materials, (iv) maim facturing, and (v) actuation. Furthermore, the surgical applications of CMs are assessed by classification into five major groups, namely, (i) grasping and cutting, (ii) reachability and steerability, (iii) transmission, (iv) sensing, and (v) implants and deployable devices. The scope and prospects of surgical devices using CMs are also discussed

A Monolithic Compliant Continuum Manipulator:A Proof-of-Concept Study

Continuum robots have the potential to form an effective interface between the patient and surgeon in minimally invasive procedures. Magnetic actuation has the potential for accurate catheter steering, reducing tissue trauma and decreasing radiation exposure. In this paper, a new design of a monolithic metallic compliant continuum manipulator is presented, with flexures for precise motion. Contactless actuation is achieved using time-varying magnetic fields generated by an array of electromagnetic coils. The motion of the manipulator under magnetic actuation for planar deflection is studied. The mean errors of the theoretical model compared to experiments over three designs are found to be 1.9 mm and 5.1degrees in estimating the in-plane position and orientation of the tip of the manipulator, respectively and 1.2 mm for the whole shape of the manipulator. Maneuverability of the manipulator is demonstrated by steering it along a path of known curvature and also through a gelatin phantom which is visualized in real time using ultrasound imaging, substantiating its application as a steerable surgical manipulator

Dynamic modeling of soft continuum manipulators using lie group variational integration

This paper presents the derivation and experimental validation of algorithms for modeling and estimation of soft continuum manipulators using Lie group variational integration. Existing approaches are generally limited to static and quasi-static analyses, and are not sufficiently validated for dynamic motion. However, in several applications, models need to consider the dynamical behavior of the continuum manipulators. The proposed modeling and estimation formulation is obtained from a discrete variational principle, and therefore grants outstanding conservation properties to the continuum mechanical model. The main contribution of this article is the experimental validation of the dynamic model of soft continuum manipulators, including external torques and forces (e.g., generated by magnetic fields, friction, and the gravity), by carrying out different experiments with metal rods and polymer-based soft rods. To consider dissipative forces in the validation process, distributed estimation filters are proposed. The experimental and numerical tests also illustrate the algorithm's performance on a magnetically-actuated soft continuum manipulator. The model demonstrates good agreement with dynamic experiments in estimating the tip position of a Polydimethylsiloxane (PDMS) rod. The experimental results show an average absolute error and maximum error in tip position estimation of 0.13 mm and 0.58 mm, respectively, for a manipulator length of 60.55 mm

Locally Addressable Energy Efficient Actuation of Magnetic Soft Actuator Array Systems

Advances in magnetoresponsive composites and (electro-)magnetic actuators have led to development of magnetic soft machines (MSMs) as building blocks for small-scale robotic devices. Near-field MSMs offer energy efficiency and compactness by bringing the field source and effectors in close proximity. Current challenges of near-field MSM are limited programmability of effector motion, dimensionality, ability to perform collaborative tasks, and structural flexibility. Herein, a new class of near-field MSMs is demonstrated that combines microscale thickness flexible planar coils with magnetoresponsive polymer effectors. Ultrathin manufacturing and magnetic programming of effectors is used to tailor their response to the nonhomogeneous near-field distribution on the coil surface. The MSMs are demonstrated to lift, tilt, pull, or grasp in close proximity to each other. These ultrathin (80 µm) and lightweight (100 gm−2) MSMs can operate at high frequency (25 Hz) and low energy consumption (0.5 W), required for the use of MSMs in portable electronics.</p

A Versatile 3R Pseudo-Rigid-Body Model for Initially Curved and Straight Compliant Beams of Uniform Cross section

Rigid-body discretization of continuum elements was developed as a method for simplifying the kinematics of otherwise complex systems. Recent work on pseudo-rigid-body (PRB) models for compliant mechanisms has opened up the possibility of using similar concepts for synthesis and design, while incorporating various types of flexible elements within the same framework. In this paper, an idea for combining initially curved and straight beams within planar compliant mechanisms is developed to create a set of equations that can be used to analyze various designs and topologies. A PRB model with three revolute joints is derived to approximate the behavior of initially curved compliant beams, while treating straight beams as a special case (zero curvature). The optimized model parameter values are tabled for a range of arc angles. The general kinematic and static equations for a single-loop mechanism are shown, with an example to illustrate accuracy for shape and displacement. Finally, this framework is used for the design of a compliant constant force mechanism to illustrate its application, and comparisons with finite element analysis (FEA) are provided for validation