Cascaded Position Control Research Articles

Design and Analysis of a Clutched Parallel Elastic Actuator

Various actuator topologies are discussed for the purpose of powering periodic processes and particularly walking robots. The Clutched Parallel Elastic Actuator (CPEA) is proposed to reduce the energy consumption of active exoskeletons. A nonlinear model of the CPEA is presented in addition to the mechanical design. The CPEA prototype is operated with a passive load on the walking trajectory of the hip joint. The actuator is controlled with a cascaded position control and a superimposed Iterative Learning Controller (ILC). The controller was chosen to ensure comparability between active and deactivated spring operation. The application of the CPEA has the potential to increase efficiency in the design of exoskeletons.

Novel Design and Position Control Strategy of a Soft Robot Arm

This article presents a novel design of a continuum arm, which has the ability to extend and bend efficiently. Numerous designs and experiments have been done to different dimensions on both types of McKibben pneumatic muscle actuators (PMA) in order to study their performances. The contraction and extension behaviour have been illustrated with single contractor actuators and single extensor actuators, respectively. The tensile force for the contractor actuator and the compressive force for the extensor PMA are thoroughly explained and compared. Furthermore, the bending behaviour has been explained for a single extensor PMA, multi extensor actuators and multi contractor actuators. A two-section continuum arm has been implemented from both types of actuators to achieve multiple operations. Then, a novel construction is proposed to achieve efficient bending behaviour of a single contraction PMA. This novel design of a bending-actuator has been used to modify the presented continuum arm. Two different position control strategies are presented, arising from the results of the modified soft robot arm experiment. A cascaded position control is applied to control the position of the end effector of the soft arm at no load by efficiently controlling the pressure of all the actuators in the continuum arm. A new algorithm is then proposed by distributing the x, y and z-axis to the actuators and applying an effective closed-loop position control to the proposed arm at different load conditions.

Data‐based cascade control of permanent magnet synchronous motor with industrial robot application

The industrial robot is typically actuated by a permanent magnet synchronous motor (PMSM). In manufacturing applications, the position control performance of the PMSM actuation systems will directly affect the efficiency and precision of the industrial robot. This study proposes a cascade control method to achieve accurate position profile-tracking for a field-bus industrial robot. The proposed method is a data-based method, which implies that only process data is directly used for the controller design without system model information. The cascade position controller optimisation problem is formulated using the collected data from the plant to be controlled. Then, a multiple degrees-of-freedom solution is designed to obtain the optimal control parameters for all actuation PMSM systems. The effectiveness and robustness of the proposed method are demonstrated using an experimental example implemented on the developed field-bus industrial robot.

PASSIVITY BASED ON ENERGY TANK FOR CARTESIAN IMPEDANCE CONTROL OF DLR SPACE ROBOTS WITH FLOATING BASE AND ELASTIC JOINTS

This paper presents a control structure for orbital servicing mission of CEASAR robotic arm developed by German Aerospace Center (DLR). In order to reduce mass the CEASAR arm is equipped with Harmonic-Drives with high ratio which unfortunately lead to high joint elasticity and high motor friction and have to be considered in controller design for successful manipulator in-orbit operations. Therefore, in this control structure, for high tracking control a cascaded position controller based on state feedback control structure with observer-based friction compensation and for safe interaction control with the environment a Cartesian impedance controller is used. The proposed control methods are very efficient and practicable. Furthermore, they are very robust with dynamic parameter uncertainties, coupling dynamics, and can simultaneously provide good results in term of the position accuracy and dynamic behavior. Simulation results validate practical efficiency of the controllers.

Novel soft bending actuator-based power augmentation hand exoskeleton controlled by human intention

This article presents the development of a soft material power augmentation wearable robot using novel bending soft artificial muscles. This soft exoskeleton was developed as a human hand power augmentation system for healthy or partially hand disabled individuals. The proposed prototype serves healthy manual workers by decreasing the muscular effort needed for grasping objects. Furthermore, it is a power augmentation wearable robot for partially hand disabled or post-stroke patients, supporting and augmenting the fingers’ grasping force with minimum muscular effort in most everyday activities. This wearable robot can fit any adult hand size without the need for any mechanical system changes or calibration. Novel bending soft actuators are developed to actuate this power augmentation device. The performance of these actuators has been experimentally assessed. A geometrical kinematic analysis and mathematical output force model have been developed for the novel actuators. The performance of this mathematical model has been proven experimentally with promising results. The control system of this exoskeleton is created by hybridization between cascaded position and force closed-loop intelligent controllers. The cascaded position controller is designed for the bending actuators to follow the fingers in their bending movements. The force controller is developed to control the grasping force augmentation. The operation of the control system with the exoskeleton has been experimentally validated. EMG signals were monitored during the experiments to determine that the proposed exoskeleton system decreased the muscular efforts of the wearer.

A Geometric Pulling Force Controller for Aerial Robotic Workers

The aim of this article is to establish a geometric, pulling force control scheme in order to enable the concept of Aerial Robotic Workers (ARWs), where the capabilities of the Unmanned Aerial Vehicles (UAVs) are enhanced by aerial manipulators in order to exert known pulling forces on the environment, with characteristic applications such as levers actuation, debris removal and safety assessments. The proposed novel approach consists of interfacing a cascaded position control scheme with a manipulation framework in such a way that the UAV, together with the manipulator are being controlled in a complete system The validity of the proposed scheme as well as the ability of the UAV to track a desired pulling force is validated through a real-world experiment.

Improved Controller Performance for Electromechanical Axes

The cascaded position control structure is state of the art in modern production machines and machine tools. Since an adequate controller performance of the electromechanical axes is still a key aspect for a resource efficient and high-quality production, this topic is addressed by the paper. An overall approach/framework to monitor and ensure an improved controller performance over time, comprising five tangible approaches is presented. All methodologies were developed in the department for control and feedback control technologies of the Technische Universitaet Chemnitz. They will be demonstrated and also be discussed based on experimental results.

One Nonlinear PID Control to Improve the Control Performance of a Manipulator Actuated by a Pneumatic Muscle Actuator

Braided pneumatic muscle actuator shows highly nonlinear properties between displacements and forces, which are caused by nonlinearity of pneumatic system and nonlinearity of its geometric construction. In this paper, a new model based on Bouc-Wen differential equation is proposed to describe the hysteretic behavior caused by its structure. The hysteretic loop between contractile force and displacement is dissolved into linear component and hysteretic component. Relationship between pressure within muscle actuator and parameters of the proposed model is discussed. A single degree of freedom manipulator actuated by PMA is designed. On the basis of the proposed model, a novel cascade position controller is designed. Single neuron adaptive PID algorithm is adopted to cope with the nonlinearity and model uncertainties of the manipulator. The outer loop of the controller is to handle position tracking problem and the inner loop is to control pressure. The controller is applied to the manipulator and experiments are conducted. Results demonstrate the effectiveness of the proposed controller.

Identification of Parametric Models and Controller Design for Cascaded Position Control

AbstractThe standard in industrial motion controllers comprises today a cascaded system of position loop, velocity loop and current loop. Each controller has to be designed according to its subordinated system behavior. The paper presents a method for the identification of plant parameters in the time domain. The approach is based on the auto relay feedback experiment by Åström/ Hägglund and a modified technique of gradual pole compensation. In addition to a theoretical description, the implementation as an automatic application in the motion control system SIMOTION is shown. Finally, the velocity controller and the position controller are adjusted according to the identified systems. Furthermore, the identification results as well as the achievable controller performance on a test rig will be presented.

A novel robust position estimator for self-sensing magnetic levitation systems based on least squares identification

In this work a novel method is introduced for the estimation of the position of a self-sensing magnetic levitation system, based on a least squares identification strategy. In the first step, a detailed mathematical model of the magnetic levitation system is derived and the properties of this system are analyzed for the case of a pulse-width modulated control. Based on this model, an estimation algorithm for the inductance of the magnetic levitation system is introduced. In classical position estimation schemes known form the literature large estimation errors are typically induced by a deviation of the electric resistance from its nominal value or by a fast motion of the levitated object. In this work it is shown that these errors can be exactly compensated by means of a suitable estimation strategy. Furthermore, it is outlined that the chosen structure of the estimation scheme allows for a very efficient implementation in real-time hardware. Afterwards, the design of a cascaded position controller for the magnetic levitation system is briefly summarized. Finally, the excellent quality and the high robustness of the proposed position estimator is demonstrated by means of simulation studies and measurement results on a test bench.

Flexible forming with hexapods

The work presented in this paper provides the basis for an extension of conventional orbital forming to a new, flexible forming process. A hydraulically actuated hexapod is used to move a swage in order to extrude a work piece towards a desired shape. This paper presents an analytical model of the actuators and the dynamics of the hexapod. This model is used for developing a cascaded position control law, and for developing a simulation environment representing the machine and the work piece in an entire forming process loop. The design of the machine is briefly introduced and results of position control are presented.

Hybrid Controller for Adaptive Link Control of Industrial Robots

This paper presents a new adaptation mechanism for a cascaded position controller. The cascaded position controller consists of P.I.D. controllers the parameters of which are changed by a fuzzy logic adaptation mechanism. The proposed fuzzy logic adaptation mechanism is tested using the six-degree-of-freedom-robot RV 15, manufactured by Reis Robotics. Using the fuzzy logic adaptation mechanism, the cartesian position error of the tool center point can be significantly reduced by 50 %. Another enhancement of the dynamic behaviour, which can be achieved by the fuzzy logic adaptation mechanism, is to lessen the influence of different loads on the cartesian position error.