Desired Velocity Vector Research Articles

Independent Control Strategy of Multiple Magnetic Flexible Millirobots for Position Control and Path Following

Magnetically actuated small-scale robots have great potential for numerous applications in remote, confined, or enclosed environments. Multiple small-scale robots enable cooperation and increase the operating efficiency. However, independent control of multiple magnetic small-scale robots is a great challenge, because the robots receive identical control inputs from the same external magnetic field. In this article, we propose a novel strategy of completely decoupled independent control of magnetically actuated flexible swimming millirobots. A flexible millirobot shows a crawling motion on a flat plane within an oscillating magnetic field. Millirobots with different magnetization directions have the same velocity response curve to the oscillating magnetic field but with a difference of phase. We designed and fabricated a group of up to four heterogeneous millirobots with identical geometries and different magnetization directions. According to their velocity response curves, an optimal direction of oscillating magnetic field is calculated to induce a desired velocity vector for the millirobot group, one of which is nonzero and the others are approximately zero. The strategy is verified by experiments of independent position control of up to four millirobots and independent path following control of up to three millirobots with small errors. We further expect that with this independent control strategy, the millirobots will be able to cooperate to finish complicated tasks.

Broadcast Guidance of Multi-Agent Systems

We consider the emergent behavior of a group of mobile agents guided by an exogenous broadcast signal. The agents’ dynamics is modelled by single integrators and they are assumed oblivious to their own position, however they share a common orientation (i.e. they have compasses). The broadcast control, a desired velocity vector, is detected by arbitrary subgroups of agents,that upon receipt of the guidance signal become "ad-hoc" leaders. The control signal and the set of leaders are assumed to be constant over some considerable intervals in time. A system without "ad-hoc" leaders is referred to as autonomous. The autonomous rule of motion is identical for all agents and is a gathering process ensuring a cohesive group. The agents that become leaders upon receipt of the exogenous control add the detected broadcast velocity to the velocity vector dictated by the autonomous rule of motion. This paradigm was considered in conjunction with several models of cohesive dynamics, linear and non-linear, with fixed inter-agent interaction topology, as well as systems with neighborhood based topology determined by the inter-agent distances. The autonomous dynamics of the models considered provides cohesion to the swarm, while, upon detection of a broadcast velocity vector, the leaders guide the group of agents in the direction of the control. For each local cohesion interaction model we analyse the effect of the broadcast velocity and of the set of leaders on the emergent behavior of the system. We show that in all cases considered the swarm moves in the direction of the broadcast velocity signal with speed set by the number of agents receiving the control and in a constellation determined by the model and the subset of "ad-hoc" leaders. All results are illustrated by simulations.

Adaptive Fuzzy Velocity Field Control for Navigation of Nonholonomic Mobile Robots

This paper presents a novel contour tracking scheme based on a well-posed kinematic representation of differential-driven nonholonomic mobile robots. Firstly, a fuzzy aggregation of spatial sets in cluttered environments allows designing a velocity field to encode the desired velocity vector pointing to the target (the contour). Thus, the resultant smooth trajectory avoids obstacles by combining spatially distributed velocity fields that enable the robot navigation. Finally, the universal approximation property of fuzzy systems facilitates the design of an adaptive PI-like controller, whose closed-loop stability leads to the precise tracking of the velocity field. The results of the performed numerical simulations illustrate the reliability of the proposed scheme.

A Vector Potential Function-Based Collision Avoidance Control for Differential-Steered Robots

A collision avoidance control that tracks a vector potential field-based velocity plan of a differential-steered robot is designed. Vector potential function (VPF) is a type of potential function used for motion planning. The plan resulted by the VPF is the desired velocity vector of the robot on all points in collision-free space. The problem to address in this paper is velocity tracking control in the environment of a circular obstacle. A controller is designed to track the VPF-based velocity plan. A concept of collision cone will be used to evaluate the ability of the controller to avoid collision between the robot and the obstacle. The stability of the controller is verified by using the Lyapunov stability analysis. Simulations of the controller’s performance are presented.

A Hybrid Switched Reactive-Based Visual Servo Control of 5-DOF Robot Manipulators for Pick-and-Place Tasks

This paper addresses the problem of visual servo control for a five-degree-of-freedom robot manipulator to perform pick-and-place tasks. A new hybrid switched reactive-based visual servo control structure, inspired from a sensing-and-reaction behavior without the inverse interaction matrix computing, is proposed to handle this problem efficiently. The proposed structure is similar to the logic-based approaches, but the requirements of the fuzzy modeling and/or the fuzzy-rule base learning are omitted. To achieve this, a novel hardware-aware reactive function approach is presented to directly map an image position error vector to a desired end-effector velocity vector under the consideration of hardware limitations. This approach helps to simplify the implementation of visual servo systems with improved reliability. Moreover, the proposed control system is a hybrid switching controller consisting of both image-based and position-based reactive planning schemes, which allows improving the robustness and effectiveness of the visual servo system. Experimental results validate the performance of the proposed visual servo control method in a realistic scenario setting.

Control of underactuated mechanical systems via passive velocity field control: Application to snakeboard and 3D rigid body

In this paper we consider the application of a new formulation of passive velocity field control (PVFC) to the control problem of a class of underactuated mechanical systems (UAMS). In our previous report synthesizing the desired velocity vector fields for PVFC by the decoupling vector fields, we were able to prove that control torques may be successfully obtained and the solvability of the synthesizing problem of PVFC for the UAMS may be guaranteed. We newly develop this control design methodology and propose an explicit feedback solution to the control problems of the UAMS, such as snakeboard, underactuated 3D rigid bodies. Several simulations show the validity of the proposed control methodology.

Control of a class of underactuated mechanical systems

In this paper a new control methodology for underactuated mechanical systems is proposed. The basic idea of this method is to combine passive velocity field control with decoupling vector field. In order that the underactuated mechanical systems can be stabilized at the desired position after settling on the desired velocity vector field, novel control strategies are proposed. Proposed control strategies are applied to the underactuated planar three-link manipulator and underactuated planar body. Simulations demonstrate the usefulness and effectiveness of the proposed control methodology.

Adaptive Modular Vector Field Control for Robot Contact Tasks in Uncertain Environments

We propose adaptive modular vector field control (AMVFC) for a robot manipulator to interact with uncertain environmental geometric constraints. Starting from an uncertain geometric model of the environment, we first parameterize the desired velocity vector field of the robot using the weighted combination of a set of basis vector fields. Then, to overcome the influence of environmental model uncertainty, we add force feedback to adjust robot dynamics and the weight parameters of the desired velocity field for the robot to approach the real environment. Simulation of a robot interacting with uncertain circles and an ellipse demonstrates the effectiveness of our approach.

ON MANIPULATOR CONTROL VIA VELOCITY FIELDS

This paper addresses the control of robotic manipulators using the velocity field approach. Instead of the usual specification in motion robot control via desired position trajectories depending on time, the specification in the velocity field control formulation is given through a desired velocity vector field as a function of actual position regardless of time. This approach is useful for control following task. This paper presents two controllers to solve the velocity field control formulation in task space. Experiments using these controllers on a two degrees–of–freedom direct–drive arm illustrate the feasibility of the proposed approach.

Hybrid Control of a Flexible Manipulator Reducing Interferences between Position and Force responses.

A hybrid control method for a flexible manipulator based on an angular velocity control is presented, which is applicable to curved constraint surfaces. The error of contact force is converted into a velocity vector according to the force/velocity conversion law which consideres both force respose characteristics and variational angular velocity with respect to normal direction of the surface. The velocity vector which is tangent to the constraint surface is calculated using the velocity control law. The desired velocity vector is obtained as a sum of the above two velocity vectors, and is converted into angular velocity vectors. A vibration control law is proposed to reduce overshoot of end point velocity response. The desired angular velocity vector is obtained as a sum of the above angular velocity vector and vibration control term. Motion and force controls without calculating inverse dynamics is performed using DC motors whose desired values are equal to the above desired angular velocity vectors. Computer simulations and experimental analyses are carried out to clarify the validity of the proposed method.

Motion and Force Controls of Dual Flexible Manipulators with Velocity-Controlled DC Motors. 1st Report. Coordinative Control in Free Space.

A simple method is presented for controlling the motion and gripping force in dual flexible manipulators without calculating inverse dynamics. The gripping force is converted into a velocity vector according to the proposed force/velocity conversion law considering the flexibility of the manipulator. The velocity vector of contact point is calculated from the velocity of the object. The desired velocity vector is obtained as a sum of the above two velocity vectors, and is converted into angular velocity vector considering defectional velocity of the flexible links. The desired angular velocity vector is obtained as a sum of the above angular velocity vector and strain feedback term. Coordinative control is performed using DC motors whose desired values are equal to the above desired angular velocity vector. The characteristics of gripping force response of control system is also considered. Computer simulations and experimental analyses are carried out to clarify the validity of the proposed method.

Motion and Force Control of a Flexible Manipulator with Velocity Controlled DC Motors.

This paper presents a simple method for controlling both the motion and contact force of a flexible manipulator without calculating inverse dynamics. The contact force is converted into a velocity vector according to the proposed force/velocity conversion law considering the flexibility of the manipulator. The velocity vector which is tangent to the constraint surface is calculated using velocity control law. The desired velocity vector is obtained as a sum of the above two velocity vectors, and is converted into angular velocity vectors considering deflectional velocity of the flexible links. The desired angular velocity vector is obtained as a sum of the above angular velocity vector and strain feedback term. Motion and force control is performed using DC motors whose desired values are the above desired angular velocity vectors. Computer simulations and experimental analyses are carried out to clarify the validity of the proposed method.

Motion and Force Control of a Manipulator using a Task Coordinates Servo. Suggestion of Control Law and Analysis of Stability.

This paper presents a simple hybrid method for controlling both the motion and contact force of a manipulator without calculating inverse dynamics. The contact force is converted into a velocity vector according to the force/velocity conversion law. The velocity vector which is tangent to the constraint surface is calculated by the velocity servo. The desired velocity vecotor is obtained as a sum of the above two velocity vectors. The desired axial velocity vector is calculated from the desired velocity vector using inverse Jacobian matrix. Motion and force control is performed using DC motors whose desired values are the above desired axial velocity vector. The stability of the motion control system is also considered.

Collision Avoidance among Movile Robots Mobing on the Route Crossing and Joining

The problem of collision avoidance among mobile robots moving along crossing and joining paths is formulated as a motion planning problem in terms of the velocity vector modification. In this paper, a local approach based on a nonlinear programming is applied to solve this problem. Here, the velocity vector constraint for robots are set up using the relative position and velocity information of neighboring robots. The desired velocity vector, which enables robots to navigate without collision, is given as the optimal solution of objective function under this velocity vector constraint. This method is implemented using both experimental robots system and computer simulated one. From the results, it is shown that the experimental robots achieves acceptable performance both in case of crossing and joinig. The feasibility and effectiveness of our method are also discussed through the simulation results.

Collision Avoidance among Multiple Mobile Robots

This paper presents a local approach for real-time collision avoidance among autonomous mobile robots based on non-linear programming. Here, we consider multiple mobile robots travelling to their own destinations in a two-dimensional workspace, e. g., automated guided vehicles in a factory shop. Each robot is assumed to have its identical area and limited sensing area represented by closed circles. In this approach, a distance function between neighbouring two robots is introduced to set up the velocity vector constraint for robots. The desired velocity vector, which enables a robot to navigate without collision by following it, is given as the optimal solution of the objective function under this velocity vector constraint. Our method is implemented using the computer simulated robots. The feasibility and effectiveness of our method are also discussed through the simulation results.