Shape sensing of medical continuum robots is important both for closed-loop control as well as for enabling the clinician to visualize the robot inside the body. There is a need for inexpensive, but accurate shape sensing technologies. This paper proposes the use of magnetic ball chains as a means of generating shape-specific magnetic fields that can be detected by an external array of Hall effect sensors. Such a ball chain, encased in a flexible polymer sleeve, could be inserted inside the lumen of any continuum robot to provide real-time shape feedback. The sleeve could be removed, as needed, during the procedure to enable use of the entire lumen. To investigate this approach, a shape-sensing model for a steerable catheter tip is derived and an observability and sensitivity analysis are presented. Experiments show maximum estimation errors of 7.1% and mean of 2.9% of the tip position with respect to total length.

This paper introduces a novel class of hyperredun-dant robots comprised of chains of permanently magnetized spheres enclosed in a cylindrical polymer skin. With their shape controlled using an externally-applied magnetic field, the spherical joints of these robots enable them to bend to very small radii of curvature. These robots can be used as steerable tips for endoluminal instruments. A kinematic model is derived based on minimizing magnetic and elastic potential energy. Simulation is used to demonstrate the enhanced steerability of these robots in comparison to magnetic soft continuum robots designed using either distributed or lumped magnetic material. Experiments are included to validate the model and to demonstrate the steering capability of ball chain robots in bifurcating channels.

A hybrid continuum robot design is introduced that combines a proximal tendon-actuated section with a distal telescoping section comprised of permanent-magnet spheres actuated using an external magnet. While, individually, each section can approach a point in its workspace from one or at most several orientations, the two-section combination possesses a dexterous workspace. The paper describes kinematic modeling of the hybrid design and provides a description of the dexterous workspace. We present experimental validation which shows that a simplified kinematic model produces tip position mean and maximum errors of 3% and 7% of total robot length, respectively.

Magnetically actuated robots have proven effective in several applications, specifically in medicine. However, generating high actuating fields with a high degree of manipulability is still a challenge, especially when the application needs a large workspace to suitably cover a patient. The presented work discusses a novel approach for the control of magnetic field and field gradients using two robotically actuated permanent magnets. In this case, permanent magnets—relative to coil-based systems—have the advantage of larger field density without energy consumption. We demonstrate that collaborative manipulation of the two permanent magnets can introduce up to three additional Degrees of Freedom (DOFs) when compared to single permanent magnet approaches (five DOFs). We characterized the dual-arm system through the measurement of the fields and gradients and show accurate open-loop control with a 13.5% mean error. We then demonstrate how the magnetic DOFs can be employed in magnetomechanical manipulation, by controlling and measuring the wrench on two orthogonal magnets within the workspace, observing a maximum crosstalk of 6.1% and a mean error of 11.1%.

Magnetically actuated soft robots have recently been identified for application in medicine, due to their potential to perform minimally invasive exploration of human cavities. Magnetic solutions permit further miniaturization when compared to other actuation techniques, without loss in functionalities. Our long-term goal is to propose a novel actuation method for magnetically actuated soft robots, based on dual-arm collaborative magnetic manipulation. A fundamental step in this direction is to show that this actuation method is capable of controlling up to 8 coincident, independent Degrees of Freedom (DOFs). In present paper, we prove this concept by measuring the independent wrench components on a second pair of static permanent magnets, by means of a high resolution 6-axis load cell. The experiments show dominant activation of the desired DOFs, with mean cross-activation error of the undesired DOFs ranging from 2% to 10%.

In the present paper we discuss a novel dynamic controller for Cable Driven Parallel Robots, based on the Backstepping technique. The main challenge in controlling these robots, is expressing the dynamic equilibrium with respect to the joint variables. This drawback makes the definition of closed-loop controllers more challenging, in comparison with their serial counterparts. The problem is tackled by considering redundant dynamics, expressed in both task and joints space and solved through the method of quasi-velocity. We propose the usage of the observer linearization to estimate the end effector pose and stiffness, by just measuring the motor position, velocity and torque. These variables are used in the feedback loop to control the pose of the end effector. A 3-tendon planar platform is used for the experimental analysis.