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.
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 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.
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.
Most existing formation control approaches assume that accurate global or local position measurements of the robots are directly available, without giving details about how to obtain these ...measurements, or only providing Kalman filter-type estimators to get them without considering effects of the estimation on the closed-loop system stability. Hence, developing formation controllers with position estimators that can guarantee overall closed-loop system stability becomes highly desirable. This technical note presents a new formation tracking controller for the nonholonomic mobile robots without using direct position measurements. To deal with the absence of accurate position measurements, feedback information from a perspective camera, the odometry and Attitude and Heading Reference System (AHRS) sensors is used to design an observer to provide online estimates of the relative position of the follower with respect to the leader. Using Lyapunov stability analysis, we show that the combined observer-controller closed-loop system is stable, and both the formation tracking errors and the relative position estimation errors asymptotically converge to zero. The performance of the proposed scheme is illustrated through experimental results.
In this paper, the task-space cooperative tracking control problem of networked robotic manipulators without task-space velocity measurements is addressed. To overcome the problem without task-space ...velocity measurements, a novel task-space position observer is designed to update the estimated task-space position and to simultaneously provide the estimated task-space velocity, based on which an adaptive cooperative tracking controller without task-space velocity measurements is presented by introducing new estimated task-space reference velocity and acceleration. Furthermore, adaptive laws are provided to cope with uncertain kinematics and dynamics and rigorous stability analysis is given to show asymptotical convergence of the task-space tracking and synchronization errors in the presence of communication delays under strongly connected directed graphs. Simulation results are given to demonstrate the performance of the proposed approach.
This paper presents a novel scheme for image-based visual servoing (IBVS) of a robot manipulator by considering robot dynamics without using joint velocity measurements in the presence of ...constraints, uncalibrated camera intrinsic and extrinsic parameters and unknown feature position parameters. An approach to design model predictive control (MPC) method based on identification algorithm and sliding mode observer has been proposed. Based on the MPC method, the IBVS tasks can be considered as a nonlinear optimization problem while the constraints due to the visibility constraint and the torque constraint can be explicitly taken into account. By using the depth-independent interaction matrix framework, the identification algorithm can be used to update the unknown parameters and the prediction model. In addition, many existing controllers require the joint velocity measurements which can be contaminated by noises, thus resulting in the IBVS performance degradation. To overcome the problem without joint velocity measurements, the sliding mode observer is designed to estimate the joint velocities of the IBVS system. The simulation results for both eye-in-hand and eye-to-hand camera configurations are presented to verify the effectiveness of the proposed control method.
The task-space tracking control of robots without the exact knowledge of kinematics and dynamics has been studied before with the assumption that the joint velocities are available for controller ...designs. However, the velocity measurements can be contaminated by noises, thereby resulting in poor system performance, or even leading to instability problems. Therefore, in this paper, we propose a new tracking controller for robots in the task space without the use of both task-space and joint-space-velocity measurements, under the condition that both the robot kinematics and dynamics are unknown. To overcome these incapacities without the velocity measurements, we introduce the well-known sliding-observer-design techniques to estimate the joint velocities for the purpose of our controller design. Our main concern, i.e., the stability analysis of our controller design incorporated with the siding observer, is presented with the help of Lyapunov-analysis methodology and the sliding-patch concept. Simulation results are presented to show the performance of our controller-observer designs.
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