Experimental study of force control based on intelligent prediction algorithm in open architecture robot system

This paper presents the formulation of an impedance controller for regulating the contact force with the environment. To achieve an accurate force tracking control, uncertainties in both robot dynamics and the environment require to be addressed. As part of the framework of the proposed force tracking formulation, a neural network is introduced at the desired trajectory to compensate for all uncertainties in an on-line manner. Compensation at the input trajectory leads to a remarkable structural advantage in that no modifications of the internal force controllers are required. Minimizing the objective function of the training signal for a neural network satisfies the desired force tracking performance. A neural network actually compensates for uncertainties at the input trajectory level in an on-line fashion. Simulation results confirm the position and force tracking abilities of a robot manipulator.

This chapter presents a virtual environment implementation for embedded design, simulation, and conception of supervision and control systems for mobile robots, which are capable of operating and adapting to different environments and conditions. The purpose of this virtual system is to facilitate the development of embedded architecture systems, emphasizing the implementation of tools that allow the simulation of the kinematic, dynamic, and control conditions, in real time monitoring of all important system points. To achieve this, an open control architecture is proposed, integrating the two main techniques of robotic control implementation at the hardware level: systems microprocessors and reconfigurable hardware devices. The utilization of a hierarchic and open architecture, distributing the diverse actions of control in increasing levels of complexity and the use of resources of reconfigurable computation are made in a virtual simulator for mobile robots. The validation of this environment is made in a nonholonomic mobile robot and in a wheelchair; both of them used an embedded control rapid prototyping technique for the best navigation strategy implementation. After being tested and validated in the simulator, the control system is programmed in the control board memory of the mobile robot or wheelchair. Thus, the use of time and material is optimized, first validating the entire model virtually and then operating the physical implementation of the navigation system.

Currently, an increasing number of robotic manipulators are discarded on the factory floor, because they are classified as unserviceable equipment, while still being able to be re-used. This problem occurs due to the fact that robot manufacturers use fully closed architecture control to their hardware and software systems. Thus, there is no interchangeability between the control cabinets and the programming languages used to generate kinematics, which make the repairs, modifications and implementations to system more expensive, due to these processes being dependent of each manufacturer. Therefore this paper proposes a methodology for the implementation of remanufacturing industrial robotic manipulators. In this methodology electronic components and electromechanical robot original can be re-used and its control systems are adapted to new technologies, using a fully open control architecture. Thus, the hardware devices are interchangeable with other processes and the programming language is not proprietary and can be modified or replaced by another.

As the industrial robot manipulators are widely used in various industrial fields, the limitation of traditional closed architectures for robot control systems becomes increasingly evident. It is almost impossible to modify the planning algorithms, the robot model, or the type of servo amplifier block. In this paper, an open architecture of robot control system is presented. It allows users to change the hardware architecture of the control system, e.g. change the geometric parameters of robots, the number/type of axes, and the servo amplifier block. It allows users to modify both the motion and interfacing software, e.g., modify/replace motion planning/control algorithms or change the human-machine interface to make it friendlier. In most traditional robot control systems, it is not provided to plan velocity profile on-line, which becomes essential in some applications. An on-line velocity filter with the function of look-ahead is thus proposed and implemented. It is integrated in the open-architecture robot control system, which provides users great flexibility to plan the motion on-line. Furthermore, the velocity look-ahead function guarantees the motion accuracy by imposing limits on velocity. Experiments validated the proposed velocity filter and the control system.

Many current robotic applications are limited by the industry state of art of the manipulators control algorithms. The inclusion of force and vision feedbacks, the possibility of cooperation between two or more manipulators, the control of robots with irregular topology will certainly enlarge the industrial robotics applications. The development of control algorithms to this end brings the necessity of using open-architecture controllers. Generally the robotic controllers are developed for position control, without accomplishing integrally the requirements of tasks in which interactions with the environment occur. Therefore, this is currently one of the main research areas in robotics, e.g., in (Abele et al., 2007) is presented the identification of characteristics to an industrial robot to execute machining applications. To consider this interaction the robot controller has to give priority to the force control time response, because in the instant of end-effectors contact with the surface, several forces act on the system. Depending on the speeds and the accelerations involved in the process, damages or errors can occur. To avoid these effects, compliances are inserted in tool or in surface of operation. A new reference model for a control system functional architecture applied to openarchitecture robot controllers is presented. Where, this model is applied for integrally development of a five-layer based open-architecture robotic controller for interaction tasks, which uses parallel and distributed processing techniques, avoiding the necessity of compliance in system, allowing a real-time processing of the application and the total control of information. This architecture provides flexibility, the knowledge of all the control structures and allows the user to modify all controller layers. The used controller conception aims to fulfill with the following requirements: high capacity of processing, low cost, connectivity with other systems, availability for the remote access, easiness of maintenance, flexibility in the implementation, integration with a personal computer and programming in high level. 5

In this paper, we propose an adaptive nonlinear strategy for the motion and force control of manipulators with flexible joints. Our approach provides force control when in contact and robust motion control in its absence, all without the need for a control switch. This self-tuning behaviour for mixed contact/non-contact scenarios results from a unified formulation of force and motion control, with an integral transpose-based inverse kinematics core and adaptive update laws to cope with the manipulator flexibility and the contact stiffnesses. The global boundedness of all signals and the asymptotic stability of this controller are guaranteed via Lyapunov analysis. Finally, we validate its applicability experimentally by using low-cost hardware in a realistic mixed-contact scenario, demonstrating low computational demand.

This paper presents the feasibility study of an adaptive impedance force control application to deburring/milling process. The proposed control regulates desired force on nonhomogeneous workpiece in regardless of unknown location and stiffness of the workpiece. The adaptive technique of minimizing the force error between the desired and the actual force is used to compensate for uncertainties in unknown workpiece. Effect of selecting the impedance damping gain with different workpiece stiffness on force tracking is analytically determined. Analyzing the stability of the proposed adaptive force control yields the bound of the adaptive gain for stability. Simulation studies of deburring/milling process show the excellent force tracking and confirm stability bound for stable force tracking.

This paper addresses the problem of steady-state position and force tracking in bilateral teleoperation. Passivity-based control schemes for bilateral teleoperation provide robust stability against network delays in the feedback loop and velocity tracking, but do not guarantee steady-state position and force tracking in general. Position drift due to data loss and offset of initial conditions is a well-known problem in such systems. In this paper, we introduce a new architecture, which builds upon the traditional passivity-based configuration by using additional position control on both the master and slave robots, to solve the steady-state position and force-tracking problem. Lyapunov stability methods are used to establish the range of the position control gains on the master and slave sides. Experimental results using a single-degree-of-freedom master/slave system are presented, showing the performance of the resulting system

2 - Preliminary simulation of intelligent force control

This paper describes the application of a closed-loop inverse kinematics algorithm to kinematic control of a robot manipulator. The scheme is formulated at the second-order level, i.e., in terms of velocity and acceleration variables, so as to allow the use of joint space computed torque control. A damped least-squares inverse of the Jacobian is used to ensure feasible joint motion in the neighborhood of kinematic singularities. The theoretical analysis of algorithm convergence is performed on the basis of a Lyapunov argument. The results of experiments on a six-joint industrial robot with open control architecture are presented.

In a parallel development to traditional rigid rehabilitation robotic systems, cable-driven systems are becoming popular. The robowalk expander product uses passive elastic bands in the training of the lower limbs. However, a well-controlled assistance or resistance is desirable for effective walking relearning and muscle training. To achieve well-controlled force during locomotion training with the robowalk expander, we replaced the elastic bands with actuator-driven cables and implemented force control algorithms for regulation of cable tensions. The aim of this work was to develop an active cable-driven robotic system, and to evaluate force control strategies for walking rehabilitation using frequency-domain analysis. The system parameters were determined through experiment-assisted simulation. Then force-feedback lead controllers were developed for static force tracking, and velocity-feedforward lead compensators were implemented to reduce velocity-related disturbances during walking. The technical evaluation of the active cable-driven robotic system showed that force-feedback lead controllers produced satisfactory force tracking in the static tests with a mean error of 5.5%, but in the dynamic tests, a mean error of 13.2% was observed. Further implementation of the velocity-feedforward lead compensators reduced the force tracking error to 9% in dynamic tests. With the combined control algorithms, the active cable-driven robotic system produced constant force within the four cables during walking on the treadmill, with a mean force-tracking error of 10.3%. This study demonstrates that the force control algorithms are technically feasible. The active cable-driven, force-controlled robotic system has the potential to produce user-defined assistance or resistance in rehabilitation and fitness training.

Virtual environments are often used in pre-wearing training and assessment of prosthetic control abilities. Here, we developed a virtual prosthetic hand training platform for evaluation of closed-loop control of grasp force. Biorealistic controllers emulated a pair of antagonistic muscles that actuated the thumb and index fingers of the hand. Surface electromyographic (sEMG) signals from a pair of antagonistic residual muscles drove the biorealistic controllers. Tactile forces from fingertip sensors were conveyed to amputees through evoked tactile sensations (ETS) elicited at the projected finger map (PFM) areas of the stump. A forearm amputee subject participated in force tracking or holding tasks using the virtual hand with residual muscle EMGs, or the contralateral intact hand. Root-mean-square error (RMSE) was used as outcome measure of motor performance. Results in this subject showed that the biorealistic controller enabled the virtual hand to track and maintain grasping forces. The best performance in both tasks was achieved by the contralateral intact hand with visual feedback. The roles of visual or tactile feedback in force tracking or maintaining were also assessed with the virtual hand. For force holding task, hybrid tactile and visual feedback with biorealistic control had a better performance than single visual or tactile feedback in terms of RMSE, success rate, and force variability. While in the force pursuing task, tactile feedback did not seem to add visual feedback in following the target force. The study suggests that training may be required for a novel virtual hand user to perceive and integrate multiple modalities of feedback information, so as to optimize the closed-loop control ability.

This article presents the contact force control approach for a quad-rotor system to perform tasks of interacting with the environment. The hovering capability of the quad-rotor system allows the force in the altitude direction to be regulated by realizing the impedance function. To obtain the better force control performance, inherent and external disturbances to the quad-rotor system are suppressed by designing the acceleration-based disturbance observer (AbDOB). Force tracking impedance control is applied to regulate the contact force to the environment. Simulation studies of force tracking control for changing a light bulb on the ceiling are performed to evaluate the feasibility of the proposed force control task for a quad-rotor system.

Measurement and evaluation of produced energy by thermoelectric generator in vehicle

It is widely believed that effective water resource management can optimize the scheduling of water supply plans, which is essential for sustainable development. The core of management is to accurately predict future water consumption. However, existing studies generally face two challenges. First, a reliable bottom platform for the support of online data integration is absent. In addition, multisource factors that primarily affect water consumption are neglected when modeling. To solve the above problems, this paper proposes a data-driven peer-to-peer blockchain framework to predict water consumption. Fundamentally, it utilizes a blockchain system with a peer-to-peer network to serve as the decision support platform hardware. On this basis, an intelligent prediction algorithm that combines the grey model and long short-term memory model is developed to drive the hardware infrastructure. After that, the performance of the proposed method is evaluated by carrying out experiments on a real-world dataset, and three typical approaches are selected for comparison. The experimental results show that the proposal exceeds general prediction models by approximately 8%.