A soft manipulator usually has infinite joints. The infinite DOFs of a soft manipulator make it impossible to build the mechanical model like traditional rigid manipulator. The dynamic model based on ...circular arcs assumption, proposed by previous literature, does not take torsion into consideration. The introduction of torsion to piecewise constant curvature assumption could improve accuracy for 3-D motion, but it still cannot deal with problems with normal strain and viscidity of soft material, especially when the Young's Modulus is small. In this paper, by combining the geometrically exact Cosserat rod theory and Kelvin model, a new mechanical model for a silicone rubber soft manipulator is proposed. Two vectors, curvature vector and strain vector, are used to depict the bending and torsion effect, and normal strain. Both 2-D and 3-D experiments are performed to verify the mechanical model.
Soft robots are more safe than rigid robots in tasks with environmental interactions. To implement the interaction control for soft robots, this article proposes a hybrid vision force controller. The ...control law is based on a deformation model, which describes the deformation and the configuration of the soft robot under the effect of gravity and force applied on the tip. To control the motion of the tip, the Jacobian of soft robots is calculated to describe the actual relationship between actuation and tip motion. Then, the vision and force feedback are used to implement visual servo in motion-free space and force control in motion-constraint space. The stability of the controller is verified both theoretically and experimentally.
It is unavoidable for a soft manipulator to interact with environments during some tasks. These interactions may affect the soft manipulator and make the kinematic model different from the one in ...free space, e.g., the soft manipulator's effective length and the target positions might change. In order to apply the soft manipulator to constrained environments, an adaptive visual servo controller based on piecewise-constant curvature kinematic, without knowing the true values of the manipulator's length and the target positions, is proposed in this paper. Experimental results in the free space, constrained environment, and the gravity-influenced environment, demonstrate the convergence of the image errors under the proposed controller.
The shape of soft a manipulator cannot be sensed by the operator directly, when applied to rescue of mine disaster, science exploration, or minimally invasive surgery due to the narrow and closed ...environment. Shape information is sometimes important for the soft manipulator to be controlled. In order to deal with the problem of shape sensing, a shape sensing algorithm and sensor network based on Fiber Bragg Gratings (FBGs) are introduced in this paper. The shape sensing algorithm is based on piecewise constant curvature and torsion assumption, and can translate the curvature and torsion measured by sensor network into global positions and orientations of nodes. Three-dimensional experiments show that the algorithm introduced in this paper can achieve high accuracy for 3-D shapes.
In this paper, an image-based visual servoing control law is proposed for a quadrotor unmanned aerial vehicle using an on-board monocular camera and an inertial measurement unit sensor. Based on the ...perspective projection model, suitable image features are defined on a rotated image plane called virtual image plane, thus a decoupled image feature dynamics is achieved. Then, a translational velocity observer is presented using these image features. The image feature dynamics and quadrotor dynamics are combined to derive a nonlinear controller. The controller is based on backstepping technique to account for the underactuation of the quadrotor. The image-based visual servoing controller only needs three point features, which make it useable in general environment. The closed-loop system is proved globally asymptotic stable by means of Lyapunov analysis. Computer simulations that regulate a quadrotor to a desired position with respect to (w.r.t.) four points lying on a horizontal plane and three points lying on a full rotated slope are conducted separately. Smooth and efficient trajectories are obtained both in virtual image plane and Cartesian space. Finally, experimental tests including pushing and pulling the visual target are conducted to verify the validity and robustness of the proposed controller. The proposed control law regulates the quadrotor to a desired position, defined by desired image, from an unknown initial position, which can be used in monitoring, landing, and other applications.
This paper studies the visibility problem in the visual servoing control of quadrotor unmanned aerial vehicles (UAVs). Visual servoing is a useful technique for the inspection, positioning, landing, ...and tracking of quadrotor UAVs. However, one prerequisite in previous research works is that the visual target stays inside the field of view of the camera for all time. While lose sight of the visual target will result in fatal failure of the task, how to guarantee this prerequisite is often overlooked. In this paper, we aim to achieve reliable visual servoing by deriving a provable solution to guarantee visibility in quadrotor visual serving control. The main idea is to ensure the forward invariance of a set using control barrier functions. The set is constructed as the visible set, which specifies the upper bound of the distance between the center of the image plane and the coordinates of visual features in the image plane. Then, the visibility constraint is developed based on control barrier function. The original control inputs are minimally modified to satisfy the visibility constraint, thus preserving visibility. Finally, some simulations and experimental results are presented to validate this method.
Robotics has aroused huge attention since the 1950s. Irrespective of the uniqueness that industrial applications exhibit, conventional rigid robots have displayed noticeable limitations, particularly ...in safe cooperation as well as with environmental adaption. Accordingly, scientists have shifted their focus on soft robotics to apply this type of robots more effectively in unstructured environments. For decades, they have been committed to exploring sub-fields of soft robotics (e.g., cutting-edge techniques in design and fabrication, accurate modeling, as well as advanced control algorithms). Although scientists have made many different efforts, they share the common goal of enhancing applicability. The presented paper aims to brief the progress of soft robotic research for readers interested in this field, and clarify how an appropriate control algorithm can be produced for soft robots with specific morphologies. This paper, instead of enumerating existing modeling or control methods of a certain soft robot prototype, interprets for the relationship between morphology and morphology-dependent motion strategy, attempts to delve into the common issues in a particular class of soft robots, and elucidates a generic solution to enhance their performance.
This paper focuses on the problem of vision-based leader-follower formation control of mobile robots. The proposed adaptive controller only requires the image information from an uncalibrated ...perspective camera mounted at any position and orientation (attitude) on the follower robot. Furthermore, the approach does not depend on the relative position measurement and communication between the leader and follower. First, a new real-time observer is developed to estimate the unknown intrinsic and extrinsic camera parameters as well as the unknown coefficients of the plane where the feature point moves relative to the camera frame. Second, the Lyapunov method is employed to prove the stability of the closed-loop system, where it is shown that convergence of the image error is guaranteed. Finally, the performance of the approach is demonstrated through physical experiments and experimental results.
Emerging role of MRI in radiation therapy Chandarana, Hersh; Wang, Hesheng; Tijssen, R.H.N. ...
Journal of magnetic resonance imaging,
December 2018, Volume:
48, Issue:
6
Journal Article
Peer reviewed
Open access
Advances in multimodality imaging, providing accurate information of the irradiated target volume and the adjacent critical structures or organs at risk (OAR), has made significant improvements in ...delivery of the external beam radiation dose. Radiation therapy conventionally has used computed tomography (CT) imaging for treatment planning and dose delivery. However, magnetic resonance imaging (MRI) provides unique advantages: added contrast information that can improve segmentation of the areas of interest, motion information that can help to better target and deliver radiation therapy, and posttreatment outcome analysis to better understand the biologic effect of radiation. To take advantage of these and other potential advantages of MRI in radiation therapy, radiologists and MRI physicists will need to understand the current radiation therapy workflow and speak the same language as our radiation therapy colleagues. This review article highlights the emerging role of MRI in radiation dose planning and delivery, but more so for MR‐only treatment planning and delivery. Some of the areas of interest and challenges in implementing MRI in radiation therapy workflow are also briefly discussed.
Level of Evidence: 5
Technical Efficacy: Stage 5
J. Magn. Reson. Imaging 2018;48:1468–1478
In this paper, the uncalibrated image-based trajectory tracking control problem of wheeled mobile robots will be studied. The motion of the wheeled mobile robot can be observed using an uncalibrated ...fixed camera on the ceiling. Different from traditional vision-based control strategies of wheeled mobile robots in the fixed camera configuration, the camera image plane is not required to be parallel to the motion plane of the wheeled mobile robots and the camera can be placed at a general position. To guarantee that the wheeled mobile robot can efficiently track its desired trajectory, which is specified by the desired image trajectory of a feature point at the forward axis of the wheeled mobile robot, we will propose a new adaptive image-based trajectory tracking control approach without the exact knowledge of the camera intrinsic and extrinsic parameters and the position parameter of the feature point. To eliminate the nonlinear dependence on the unknown parameters from the closed-loop system, a depth-independent image Jacobian matrix framework for the wheeled mobile robots will be developed such that unknown parameters in the closed-loop system can be linearly parameterized. In this way, adaptive laws can be designed to estimate the unknown parameters online, and the depth information of the feature point can be allowed to be time varying in this case. The Lyapunov stability analysis will also be performed to show asymptotical convergence of image position and velocity tracking errors of the wheeled mobile robot. The simulation results based on a two-wheeled mobile robot will be given in this paper to illustrate the performance of the proposed approach as well. The experimental results based on a real wheeled mobile robot will also be provided to validate the proposed approach.
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