47 research outputs found
Dynamic modelling and visco-elastic parameter identification of a fibre-reinforced soft fluidic elastomer manipulator
A dynamic model of a soft fibre-reinforced fluidic elastomer is presented and experimentally verified, which
can be used for model-based controller design. Due to the
inherent visco-(hyper)elastic characteristics and nonlinear timedependent behaviour of soft fluidic elastomer robots, analytic
dynamic modelling is challenging. The fibre reinforced noninflatable soft fluidic elastomer robot used in this paper can produce both planar and spatial movements. Dynamic equations
are developed for both cases. Parameters, related to the viscoelastic behaviour of the robot during elongation and bending
motion, are identified experimentally and incorporated into
our model. The modified dynamic model is then validated in
experiments comparing the time responses of the physical robot
with the corresponding outputs of the simulation model. The
results validate the accuracy of the proposed dynamic model
Real-Time Pose Esti ation and Obstacle Avoidance for Multi-segment Continuum Manipulator in Dynamic Environments
In this paper, we present a novel pose estimation and obstacle avoidance approach for tendon-driven multi-segment continuum manipulators moving in dynamic environments. A novel multi-stage implementation of an Extended Kalman Filter is used to estimate the pose of every point along the manipulator's body using only the position information of each segment tip. Combined with a potential field, the overall algorithm will guide the manipulator tip to a desired target location and, at the same time, keep the manipulator body safe from collisions with obstacles. The results show that the approach works well in a real-time simulation environment that contains moving obstacles in the vicinity of the manipulator
Control Design for Interval Type-2 Fuzzy Systems Under Imperfect Premise Matching
Abstract—This paper focuses on designing interval type-2 (IT2)
control for nonlinear systems subject to parameter uncertainties.
To facilitate the stability analysis and control synthesis, an IT2 TS
fuzzy model is employed to represent the dynamics of nonlinear
systems of which the parameter uncertainties are captured by
IT2 membership functions characterized by the lower and upper
membership functions. A novel IT2 fuzzy controller is proposed
to perform the control process, where the membership functions
and number of rules can be freely chosen and different from
those of the IT2 T-S fuzzy model. Consequently, the IT2 fuzzymodel-
based (FMB) control system is with imperfectly matched
membership functions, which hinders the stability analysis. To
relax the stability analysis for this class of IT2 FMB control
systems, the information of footprint of uncertainties, and the
lower and upper membership functions are taken into account
for the stability analysis. Based on the Lyapunov stability theory,
some stability conditions in terms of linear matrix inequalities
are obtained to determine the system stability and achieve the
control design. Finally, simulation and experimental examples
are provided to demonstrate the effectiveness and the merit of
the proposed approach
Open-loop position control in collaborative, modular Variable-Stiffness-Link (VSL) robots
— Collaborative robots (cobots) open up new avenues
in the fields of industrial robotics and physical Human-Robot
Interaction (pHRI) as they are suitable to work in close approximation and in collaboration with humans. The integration
and control of variable stiffness elements allow inherently safe
interaction. Apart from notable work on Variable Stiffness
Actuators, the concept of Variable-Stiffness-Link (VSL) manipulators promises safety improvements in cases of unintentional
physical collisions. However, position control of these type of
robotic manipulators is challenging for critical task-oriented
motions (e.g., pick and place). Hence, the study of open-loop
position control for VSL robots is crucial to achieve high
levels of safety, accuracy and hardware cost-efficiency in pHRI
applications. In this paper, we propose a hybrid, learning based
kinematic modelling approach to improve the performance
of traditional open-loop position controllers for a modular,
collaborative VSL robot. We show that our approach improves
the performance of traditional open-loop position controllers
for robots with VSL and compensates for position errors, in
particular, for lower stiffness values inside the links: Using
our upgraded and modular robot, two experiments have been
carried out to evaluate the behaviour of the robot during taskoriented motions. Results show that traditional model-based
kinematics are not able to accurately control the position
of the end-effector: the position error increases with higher
loads and lower pressures inside the VSLs. On the other
hand, we demonstrate that, using our approach, the VSL robot
can outperform the position control compared to a robotic
manipulator with 3D printed rigid links
Actuation and stiffening in fluid-driven soft robots using low-melting-point material
Soft material robots offer a number of advantages
over traditional rigid robots in applications including humanrobot
interaction, rehabilitation and surgery. These robots can
navigate around obstacles, elongate, squeeze through narrow
openings or be squeezed - and they are considered to be
inherently safe. The ability to stiffen compliant soft actuators
has been achieved by embedding various mechanisms that are
generally decoupled from the actuation principle. Miniaturisation
becomes challenging due to space limitations which can
in turn result in diminution of stiffening effects. Here, we
propose to hydraulically actuate soft manipulators with lowmelting-
point material and, at the same time, be able to switch
between a soft and stiff state. Instead of allocating an additional
stiffening chamber within the soft robot, one chamber only is
used for actuation and stiffening. Low Melting Point Alloy is
integrated into the actuation chamber of a single-compartment
soft robotic manipulator and the interfaced robotic syringe
pump. Temperature change is enabled through embedded
nichrome wires. Our experimental results show higher stiffness
factors, from 9-12 opposing the motion of curvature, than
those previously found for jamming mechanisms incorporated
in separate additional chambers, in the range of 2-8 for the
same motion
Real-time pose estimation and obstacle avoidance for multi-segment continuum manipulator in dynamic environments
In this paper, we present a novel pose estimation and obstacle avoidance approach for tendon-driven multi-segment continuum manipulators moving in dynamic environments. A novel multi-stage implementation of an Extended Kalman Filter is used to estimate the pose of every point along the manipulator's body using only the position information of each segment tip. Combined with a potential field, the overall algorithm will guide the manipulator tip to a desired target location and, at the same time, keep the manipulator body safe from collisions with obstacles. The results show that the approach works well in a real-time simulation environment that contains moving obstacles in the vicinity of the manipulator
Variable Stiffness Link (VSL): Toward inherently safe robotic manipulators
© 2017 IEEE. Nowadays, the field of industrial robotics focuses particularly on collaborative robots that are able to work closely together with a human worker in an inherently safe way. To detect and prevent harmful collisions, a number of solutions both from the actuation and sensing sides have been suggested. However, due to the rigid body structures of the majority of systems, the risk of harmful collisions with human operators in a collaborative environment remains. In this paper, we propose a novel concept for a collaborative robot made of Variable Stiffness Links (VSLs). The idea is to use a combination of silicone based structures and fabric materials to create stiffness-controllable links that are pneumatically actuated. According to the application, it is possible to change the stiffness of the links by varying the value of pressure inside their structure. Moreover, the pressure readings from the pressure sensors inside the regulators can be utilised to detect collisions between the manipulator body and a human worker, for instance. A set of experiments are performed with the aim to assess the performance of the VSL when embedded in a robotic manipulator. The effects of different loads and pressures on the workspace of the manipulator are evaluated together with the efficiency of the collision detection control system and hardware
Highly dexterous 2-module soft robot for intra-organ navigation in minimally invasive surgery
Background: For some surgical interventions, like the Total Mesorectal Excision (TME), traditional laparoscopes lack the flexibility to safely maneuver and reach difficult surgical targets. This paper answers this need through designing, fabricating and modelling a highly dexterous 2-module soft robot for minimally invasive surgery (MIS). / Methods: A soft robotic approach is proposed that uses flexible fluidic actuators (FFAs) allowing highly dexterous and inherently safe navigation. Dexterity is provided by an optimized design of fluid chambers within the robot modules. Safe physical interaction is ensured by fabricating the entire structure by soft and compliant elastomers, resulting in a squeezable 2-module robot. An inner free lumen/chamber along the central axis serves as a guide of flexible endoscopic tools. A constant curvature based inverse kinematics model is also proposed, providing insight into the robot capabilities. / Results: Experimental tests in a surgical scenario using a cadaver model are reported, demonstrating the robot advantages over standard systems in a realistic MIS environment. / Conclusion: Simulations and experiments show the efficacy of the proposed soft robot
Affordable passive 3D-printed prosthesis for persons with partial hand amputation
Background and Aim:
Partial hand amputations are common in developing countries and have a negative impact on patients and their families’ quality of life. The uniqueness of each partial hand amputation, coupled with the relatively high costs of prostheses, makes it challenging to provide suitable prosthetic solutions in developing countries. Current solutions often have long lead times and require a high level of expertise to produce. The aim of this study was to design and develop an affordable patient-specific partial hand prosthesis for developing countries.
Technique:
The prosthesis was designed for a patient with transmetacarpal amputation (i.e. three amputated fingers and partial palm). The final design was passive, controlled by the contralateral hand, and utilized the advanced flexibility properties of thermoplastic polyurethane in a glove-like design that costs approximately 20 USD to fabricate. Quantitative and qualitative tests were conducted to assess performance of the device after the patient used the final design. A qualitative assessment was performed to gather the patient’s feedback following a series of tests of grasp taxonomy. A quantitative assessment was performed through a grasp and lift test to measure the prosthesis’ maximum load capacity.
Discussion:
This study showed that the prosthesis enhanced the patient’s manual handling capabilities, mainly in the form of grasp stability. The prosthesis was light weight and could be donned and doffed by the patient independently. Limitations include the need to use the contralateral hand to achieve grasping and low grasp strength.
Clinical relevance:
Persons with partial hand amputation in developing countries lack access to affordable functional prostheses, hindering their ability to participate in the community. 3D-printed prostheses can provide a low-cost solution that is adaptable to different amputation configurations