Design and evaluation of a novel variable stiffness spherical joint with application to MR-compatible robot design (original) (raw)
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Experiments on a variable stiffness tensegrity mechanism for an MR-compatible needle holder
2015
In this paper, we present the design of a novel MR-compatible needle holder with variable stiffness and a first experimental evaluation of its ability to be controlled in position and stiffness. The device should be able to control both the orientation and the angular stiffness of the needle around the insertion point within the MR-environment. To do so, our design is based on tensegrity mechanisms, a class of prestressed mechanisms that exhibit interesting properties for our context since they are compact, lightweight and remotely controllable. An experimental setup is developed. The position and stiffness control on one degree of freedom is then performed using an open loop control strategy. Encouraging results are finally presented as well as future works to be carried out.
Modeling of a Cable-Based Revolute Joint Using Biphasic Media Variable Stiffness Actuation
2019 Third IEEE International Conference on Robotic Computing (IRC)
In recent times, safe interactions between humans and robots are required for innumerable tasks and environments. This safety can be achieved using compliance design and control of mechanisms. Cable-driven mechanisms are used when applications need to have light structures, meaning that their actuators must be relocated to ground and forces are transferred along tensioned cables. This paper presents a compliant cable-driven revolute joint using biphasic media variable stiffness actuators. Actuator's stiffness is controlled by changing pressure of control fluid into distribution lines. The used control fluid is biphasic, composed of separated gas and liquid fractions with predefined ratio. The mathematical model of the actuator is presented along with its position and stiffness model-based control, then, equations relating to the dynamics of the mechanism are provided with a joint stiffness and orientation controller. Results from simulations are discussed.
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 two degree-of-freedom 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 degrees. Additively manufactured by selective laser sintering, the flexible fluidic actuating (FFA) mechanism achieves two degree-of-freedom motion as a monolithic, compact, and hermetically-sealed device. A second novel contribution is sub-step control for precise translations and rotations less than full step increments; steady-state errors of 0.013 mm and 0.018 degrees were achieved. The linear FFA produced peak forces of 33 N and -26.5 N for needle insertion and retraction, respectively. The rotary FFA produced bidirectional peak torques of 68 N-mm. With the FFA's in full motion in a 3T scanner, no loss in signal-to-noise ratio of MR images observed.
Compliant Actuation in New Robotic Applications
This paper gives an overview of different robotic applications based on two compliant actuator technologies developed within the Robotics & Multibody Mechanics Research Group at Vrije Universiteit Brussel: the Pleated Pneumatic Artificial Muscle (PPAM) and the Mechanically Adaptable Compliance and Controllable Equilibrium Position Actuator (MACCEPA). Both actuators have built-in intrinsic compliance, which makes for two control parameters to be set, namely the equilibrium position of the actuated joint and the equivalent torsion spring stiffness. The increase of control complexity is countered by the added value of adaptable compliance. Compliant actuation, as opposed to conventional, stiff actuators like electrical drives, is currently growing in importance and has applications in a variety of robotic technologies where accurate trajectory tracking is not prevalent: bipedal walking robots, assistive technology, rehabilitation training. The current status of our research projects in compliant actuation and their future perspectives are presented.
Design of a robot joint with variable stiffness
2008 IEEE International Conference on Robotics and Automation, 2008
A robot joint with a variable stiffness unit is presented. The variable stiffness unit (VSU) is composed of a motor, two rings that consist of arc-shaped magnets separated by spacers, and a linear guide to change the cross-sectional area of the two rings. Angular displacement between two rings causes the magnets to generate torque, which acts as a nonlinear spring. The stiffness of the joint is varied via changing the overlapping area of the magnets. The VS J exhibits nearly zero stiffness, which enables robot manipulator to be harmless to humans at a wide range of operating speed. Connected to a joint motor in series, the stiffness by the VSU and the position of the joint are controlled independently by two motors. The torque generated by the magnets is analyzed. Using dynamics of the joint, feedback linearization method is adopted to control the VSJ. In addition to feedback linearization, an integral controller is augmented in order to reduce the effect of model uncertainty and di...
Frontiers in Robotics and AI, 2021
Living beings modulate the impedance of their joints to interact proficiently, robustly, and safely with the environment. These observations inspired the design of soft articulated robots with the development of Variable Impedance and Variable Stiffness Actuators. However, designing them remains a challenging task due to their mechanical complexity, encumbrance, and weight, but also due to the different specifications that the wide range of applications requires. For instance, as prostheses or parts of humanoid systems, there is currently a need for multi-degree-of-freedom joints that have abilities similar to those of human articulations. Toward this goal, we propose a new compact and configurable design for a two-degree-of-freedom variable stiffness joint that can match the passive behavior of a human wrist and ankle. Using only three motors, this joint can control its equilibrium orientation around two perpendicular axes and its overall stiffness as a one-dimensional parameter, l...
Toward a Variable Stiffness Surgical Manipulator Based on Fiber Jamming Transition
Frontiers in Robotics and AI
Soft robots have proved to represent a new frontier for the development of intelligent machines able to show new capabilities that can complement those currently performed by robots based on rigid materials. One of the main application areas where this shift is promising an impact is minimally invasive surgery. In previous works, the STFF-FLOP soft manipulator has been introduced as a new concept of using soft materials to develop endoscopic tools. In this paper, we present a novel kind of stiffening system based on fiber jamming transition that can be embedded in the manipulator to widen its applicability by increasing its stability and with the possibility to produce and transmit higher forces. The STIFF-FLOP original module has been redesigned in two new versions to incorporate the variable stiffness mechanism. The two designs have been evaluated in terms of dexterity and variable stiffness capability and, despite a general optimization rule did not clearly emerge, the study confirmed that fiber jamming transition can be considered an effective technological approach for obtaining variable stiffness in slender soft structures.
Opportunities and Challenges in MR-Compatible Robotics
IEEE Engineering in Medicine and Biology Magazine, 2008
This article gives an overview of the opportunities offered by a novel technique, the components of MR-compatible robotic systems, the history of MR-compatible robotics, and the main challenges and directions for future developments. Robotic interfaces can dynamically interact with humans performing movements and can be used to study neuromuscular adaptation. A haptic interface that could be used in conjunction with fMRI would enable neuroscientists to view and investigate the brain mechanisms involved in human motor control and related dysfunctions. This could become a critical tool in neuroscience and rehabilitation. It is concluded that with all robotic systems for medical applications, the community needs to demonstrate the ability of such systems in assisting surgeons and augmenting their performance.
The case for MR‐compatible robotics: a review of the state of the art
… journal of medical …, 2008
Background The numerous imaging capabilities of magnetic resonance imaging (MRI) coupled with its lack of ionizing radiation has made it a desirable modality for real-time guidance of interventional procedures. The combination of these abilities with the advantages granted by robotic systems to perform accurate and precise positioning of tools has driven the recent development of MR-compatible interventional and assistive devices. Methods The challenges in this field are presented, including the selection of suitable materials, actuators and sensors in the intense magnetic fields of the MR environment. Results Only a small number of developed systems have made it to the clinical level (only two have become commercial ventures), showing that the field has not yet reached maturity. Conclusions A brief overview of the current state of the art is given, along with a description of the main opportunities, possibilities and challenges that the future will bring to this exciting and promising field.
Workshop on Soft and stiffness-controllable robots for MIS
This workshop aims to bring together medical experts active in the field of minimally invasive surgery and roboticists creating and studying soft and stiffness controllable robot devices. We will explore the synergies that will arise from robotic surgeons cooperating with such modern robots to conduct advanced surgical interventions previously not possible.