Electro-hydraulic Manipulator Research Articles

Actuation of an electrohydraulic manipulator with a novel feedforward compensation scheme and PID feedback in servo-proportional valves

Achieving good tracking control beyond 0.1Hz by electrohydraulic manipulators still remains challenging due to the coupling of nonlinear actuation dynamics and multiple actuations. A novel order-separated feedforward, or FF, model has been proposed for estimating the major part of the commands of servo-proportional valves for metering their ports to monitor oil flow in the paired cylinders. Motion studies have been executed in serial manipulation mode by using such control to two valves and in serial–parallel mode to eight valves. Oil leakage and cylinder friction have been included as lower-order effects for the narrow radial clearance and near-zero lap in the valves each paired with a low-friction cylinder. Other assumptions of negligible inertia and suspended weight under the pistons have been validated by a numerical exercise. A PID feedback has been added during real-time tracking by an FFPID controller. Reciprocating and circular motion demands in the serial mode and heave tracking in serial–parallel mode, all in a vertical plane, have been executed. More precise and smoother tracking has been achieved up to 1Hz in the serial mode mostly with lower expense of energy than a conventional PID-alone controller. Results indicate FF guidance to mitigate oscillations occasionally apparent in PID-only case due to either hunting among multiple solutions or gain sensitivity of the nonlinear system. Good heave tracking has been obtained up to 0.2Hz. Substantial disturbance rejection capability of the controller has been demonstrated against tension arising from the connecting oil hoses. A potential use of the FF model in diagnosing emerging valve or cylinder fault with their aging has also been explained.

Tracking error constraint-based adaptive dynamic surface control of electro-hydraulic manipulator system

Tracking error constraint-based adaptive dynamic surface control of electro-hydraulic manipulator system

Non‐linear optimal control for multi‐DOF electro‐hydraulic robotic manipulators

A non-linear optimal (H-infinity) control approach is proposed for the dynamic model of multi-degree-of-freedom (DOF) electro-hydraulic robotic manipulators. Control of electro-hydraulic manipulators is a non-trivial problem because of their non-linear and multi-variable dynamics. In this study, the considered robotic system consists of a multi-link robotic manipulator that receives actuation from rotary electro-hydraulic drives. The article's approach relies first on approximate linearisation of the state-space model of the electro-hydraulic manipulator, according to first-order Taylor series expansion and the computation of the related Jacobian matrices. For the approximately linearised model of the manipulator, a stabilising H-infinity feedback controller is designed. To compute the controller's gains, an algebraic Riccati equation is solved at each time-step of the control algorithm. The global stability properties of the control scheme are proven through Lyapunov analysis. The proposed control method retains the advantages of typical optimal control, i.e. fast and accurate tracking of the reference setpoints under moderate variations of the control inputs.

Adaptive Backstepping Sliding Mode Control Based RBFNN for a Hydraulic Manipulator Including Actuator Dynamics

In this paper, an adaptive robust control is investigated in order to deal with the unmatched and matched uncertainties in the manipulator dynamics and the actuator dynamics, respectively. Because these uncertainties usually include smooth and unsmooth functions, two adaptive mechanisms were investigated. First, an adaptive mechanism based on radial basis function neural network (RBFNN) was used to estimate the smooth functions. Based on the Taylor series expansion, adaptive laws derive for not only the weighting vector of the RBFNN, but also for the means and standard derivatives of the RBFs. The second one was the adaptive robust laws, which is designed to estimate the boundary of the unsmooth function. The robust gains will increase when the sliding variable leave the predefined region. Conversely, they will significantly decrease when the variable approaches the region. So, when these adaptive mechanisms are derived with the backstepping technique and sliding mode control, the proposed controller will compensate the uncertainties to improve the accuracy. In order to prove stability and robustness of the controlled system, the Lyapunov approach, based on backstepping technique, was used. Some simulation and experimental results of the proposed methodology in the electrohydraulic manipulator were presented and compared to other control to show the effectiveness of the proposed control.

Electrohydraulic Robotic Manipulator With Multiple Instruments for Minimally Invasive Surgery1

Electrohydraulic Robotic Manipulator With Multiple Instruments for Minimally Invasive Surgery1

Automated Identification of a Mechatronic System Model Using Genetic Programming and Bond Graphs

Modeling, identification (experimental modeling), and design of dynamic systems and the associated problem of controller design are common problems in the field of mechatronics. A typical mechatronic problem entails finding the best topology as well as parameter values of the desired solution. In view of dynamic interactions in a mechatronic system, which involves more than one domain, it is desirable to use concurrent and integrated methodology in the solution. The powerful search ability of genetic programming (GP) along with the domain independence and the open architecture of bond graph (BG) modeling can be integrated to develop an evolutionary mechatronic tool for identification of a complex mechatronic system. This paper extends this integrated approach to nonlinear mechatronic problems and develops a software tool for this purpose. It is illustrated how the developed technique and the corresponding software tool can be used in the automated synthesis and identification of a nonlinear mechatronic system. The performance of the software tool is validated by applying it to a nonlinear electrohydraulic manipulator, which falls into the class of multidomain systems. The results obtained from the application are quite encouraging, and form a rationale for the extension of the tool for concurrent and optimal design of mechatronic systems.

Integrated Direct/Indirect Adaptive Robust Control of Hydraulic Manipulators With Valve Deadband

In this paper, an integrated direct indirect adaptive robust control (DIARC) algorithm is proposed for an electro-hydraulic manipulator with unknown valve deadband to improve the achievable output-tracking performance. The controller design for such a system is nontrivial due to various factors, such as nonsmooth static and Coulomb friction model uncertainties arising from the use of a simplified proportional-flow-valve model, and other unknown disturbances present in the system. Furthermore, when an unknown input-valve deadband is present, the controller performance can deteriorate if it is not taken care of explicitly. This paper recognizes the fact that though unknown valve deadband nonlinearity is not globally linearly parameterizable, it can still be linearly parameterized during most of the working ranges. Hence, by using an indirect estimation algorithm with online condition monitoring, accurate estimates of the unknown deadband parameters are obtained for an improved control performance. Comparative experimental results for motion control of an electro-hydraulic manipulator with two different valves having deadband illustrate the effectiveness of the proposed algorithm.

A System Framework With Online Monitoring and Evaluation for Design Evolution of Engineering Systems

This paper presents a methodology for the design evolution of engineering systems, with a mechatronic emphasis. The developed approach specifically integrates machine health monitoring and an expert system and carries out the design evolution of a multidomain dynamic system using bond graph modeling and genetic programming. The evolution of a bond graph model of a mechatronic system through genetic programming enables the exploration of the design space, thereby generating a global optimum design solution in an automated manner. Domain knowledge and expertise are used to control the design exploration and to restrict it only to a meaningful design space. As an illustrative example, the developed methodology is applied to redesign the electrohydraulic manipulator of an existing industrial fish processing machine.

Design of a robust force control system for an automatic live-line maintenance robot using a force disturbance observer

Uninterrupted power supply has become indispensable during the maintenance task of high-voltage live lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and needs skilled workers. Therefore it is necessary to realize an autonomous robot system using an electrohydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and high power/mass density. Meanwhile an electrohydraulic manipulator using hydraulic actuators has many non-linear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. Therefore it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of an automatic live-line maintenance robot used in the real maintenance task of an active electric line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust force disturbance observer is designed using this information in an H∞ framework and implemented on two different set-ups. Experimental results show that highly robust force tracking by the automatic live-line maintenance robot could be achieved even if the stiffness of environment and the shape of wall change.

Design of a robust force control system for an automatic live-line maintenance robot using a force disturbance observer

Uninterrupted power supply has become indispensable during the maintenance task of high-voltage live lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and needs skilled workers. Therefore it is necessary to realize an autonomous robot system using an electrohydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and high power/mass density. Meanwhile an electrohydraulic manipulator using hydraulic actuators has many non-linear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. Therefore it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of an automatic live-line maintenance robot used in the real maintenance task of an active electric line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust force disturbance observer is designed using this information in an H∞ framework and implemented on two different set-ups. Experimental results show that highly robust force tracking by the automatic live-line maintenance robot could be achieved even if the stiffness of environment and the shape of wall change.

6축 전기 유압 매니퓰레이터의 컴플라이언스 제어

An electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is quite difficult to obtain stable control performance. We have applied a disturbance estimation and compensation type robust control to all the axes in a 6-link electro-hydraulic manipulator. It was confirmed that the performance of trajectory tracking and attitude regulating was greatly improved by the disturbance observer. For autonomous assembly tasks, it is said that compliance control is one of the most popular methods in contact task. We have proposed a compliance control based on the position control by a disturbance observer for our manipulator system. To realize more stable contact work, the states in the compliance loop are feedbacked, where not only displacement but also the velocity and acceleration are considered. We have also applied this compliance control to the Peg-in-Hole insertion task and proposed new methods of (1)rotating of the end-effector periodically in order to reduce the friction force, (2)random searching for the center of a hole and (3)trajectory modification to reduce the impact force. As a result of these new methods, it could be experimentally confirmed that the Peg-in-Hole insertion task with a clearance of 0.007 [mm] could be achieved.

Design and experimental evaluation of a robust force controller for a 6-link electro-hydraulic manipulator via h∞ control theory

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today’s highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulators because hydraulic manipulators have the advantage of electric insulation and power/mass density. Meanwhile an electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of a 6-link electro-hydraulic manipulator system used in the real maintenance task of active electric lines is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust disturbance observers for force control are designed using this information in an H∞ framework, and implemented on the two different setups. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved even if the stiffness of environment and the shape of wall change.

On modeling, identification, and control of a heavy-duty electrohydraulic harvester manipulator

Focuses on modeling, parameter estimation, and control for a heavy-duty electrohydraulic manipulator of a harvester machine. The linear-graph method is implemented in deriving mathematical models for the swing, boom and stick subsystems. Actuation dynamics are subsequently integrated with manipulator dynamics to result in a complete machine model. Identification procedures employed in estimating physical parameters are discussed in detail and key parameter results supplied. Model validation studies show good agreement between model predictions and experiments. A Cartesian controller for the motion of the manipulator end-point is described and response results are presented. It is shown that the obtained response is very good for the purposes of this harvester machine, resulting in very small relative tracking errors.

다층 뉴럴네트워크를 이용한 애자 스탠드에서의 볼트 구멍의 중심위치 인식

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today's highly information-oriented society and increasing demand of electric utilities. The maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system. In order to realize these tasks autonomously, the three dimensional position of target object such as electric line and the stand of insulator must be recognized accurately and rapidly. The approaching of an insulator and the wrenching of a nut task is selected as the typical task of the maintenance of active electric power distribution lines in this paper. Image recognition by multilayer neural network and optimal target position calculation method are newly proposed in order to recognize the center 3 dimensional position of the bolt hole in the stand of insulator. By the proposed image recognition method, it is proved that the center 3 dimensional position of the bolt hole can be recognized rapidly and accurately without regard to the pose of the stand of insulator. Finally the approaching and wrenching task is automatically realized using 6-link electro-hydraulic manipulators.

Robust Force Control of a 6-Link Electro-Hydraulic Manipulator

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today's highly information-oriented society and increasing demand of electric utilities. This maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulator because hydraulic manipulators have the advantage of electric insulation and power/mass density. Meanwhile an electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is relatively difficult to realize not only stable contact work but also accurate force control for the autonomous assembly tasks using hydraulic manipulators. In this paper, the robust force control of a 6-link electro-hydraulic manipulator system used in the real maintenance task of active electic line is examined in detail. A nominal model for the system is obtained from experimental frequency responses of the system, and the deviation of the manipulator system from the nominal model is derived by a multiplicative uncertainty. Robust disturbance observers for force control are designed using this information in an H∞ framework, and implemented on the two different setups. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved even if the stiffness of environment and the shape of wall change.

Application of Discrete Event Control to the Insertion Task of Electric Line Using 6-Link Electro-Hydraulic Manipulators with Dual Arm.

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today's highly information-oriented society and increasing demand of electric utilities. The maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulator because hydraulic manipulators have the advantage of electric insulation. Meanwhile it is relatively difficult to realize autonomous assembly tasks particularly in the case of manipulating flexible objects such as electric lines. In this report, a discrete event control system is introduced for automatic assembly task of electric lines into sleeves as one of a typical task of active electric power lines. In the implementation of a discrete event control system, LVQNN (learning vector quantization neural network) is applied to the insertion task of electric lines to sleeves. In order to apply these proposed control system to the unknown environment, virtual learning data for LVQNN was generated by fuzzy inference. By the experimental results of two types of electric lines and sleeves, these proposed discrete event control and neural network learning algorithm are confirmed very effective to the insertion tasks of electric lines to sleeves as a typical task of active electric power maintenance tasks.

Automatic assembly task of electric line using 6-link electro-hydraulic manipulators

Uninterrupted power supply has become indispensable during the maintenance task of active electric power lines as a result of today’s highly information-oriented society and increasing demand of electric utilities. The maintenance task has the risk of electric shock and the danger of falling from high place. Therefore it is necessary to realize an autonomous robot system using electro-hydraulic manipulator because hydraulic manipulators have the advantage of electric insulation. Meanwhile it is relatively difficult to realize autonomous assembly tasks particularly in the case of manipulating flexible objects such as electric lines. In this report, a discrete event control system is introduced for automatic assembly task of electric lines into sleeves as one of the typical task of active electric power lines. In the implementation of a discrete event control system, LVQNN (linear vector quantization neural network) is applied to the insertion task of electric lines to sleeves. In order to apply these proposed control system to the unknown environment, virtual learning data for LVQNN is generated by fuzzy inference. By the experimental results of two types of electric lines and sleeves, these proposed discrete event control and neural network learning algorithm are confirmed very effective to the insertion tasks of electric lines to sleeves as a typical task of active electric power maintenance tasks.

Two-degree-of-freedom Control with Parallel Feedforward Compensators

An electro-hydraulic manipulator with hydraulic actuators has many nonlinear elements, and its parameter fl uctuations are greater than those of an electrically driven manipulator. So it is quite difficult to obtain good robust control performance. In this paper, we propose a two-degree-of-freedom control method with parallel feedforward compensators (PFC). The PFC plays a most important role in the stability of a proposed control system. Through the experimental results applied to a six-link electro-hydraulic serial manipulator, it is shown that the stability and therobustness against disturbances are improved by using the proposed control method. As the results of our previous papers, it was shown that the control method using disturbance observer designed by making use of H-infinity control theory is the most suitable among other robust control methods. Through the comparisons with the results of the disturbance observer, it is ascertained that the proposed control method is also suitable for the control as well as the disturbance observer above mentioned. We examined and established the design criterion of control system using the proposed method. The optimal parameters of the controller can be easily determined by using the design algorithm proposed here. The effectiveness of this proposed control method is verified through experiments of the six-link electro-hydraulic serial manipulator.

한쌍의 6축 전기유압 매니퓰레이터를 이용한 힘 제어 (너트의 장착 및 체결 작업에의 응용)

An electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements, and its parameter fluctuations are greater than those of an electrically driven manipulator. So it is relatively difficult to realize not only stable contact work but also accurate force control for the automatic assembly tasks using hydraulic manipulators. In this manuscript, we applied a compliance control, which is based on the position control by a disturbance observer for our manipulator system. A reference trajectory modification method is proposed in order to achieve accurate force control even though the stiffness and the position of the environment change. Experimental results show that highly robust force tracking by a 6-link electro-hydraulic manipulator could be achieved under various environment conditions. The proposed force control algorithm is applied to the approaching of bolt and the wrenching of nut tasks as one typical task in the maintenance work of live power electric line and is experimentally confirmed very effective for the task.

Coordinative Control of 6-Link Electro-Hydraulic Manipulators with Dual Arm. Application of a Discrete Event Control to the Insertion Task of Electric Lines into Sleeves.

To supply electric power uninteruptedly during the maintenance task of live power electric line, it is necessary to realize an autonomous control of 6-link electro-hydraulic manipulator for the safe maintenance task. However electro-hydraulic manipulator using hydraulic actuators has many nonlinear elements and its parameter fluctuations are greater than those of an electrically driven manipulator. Therefore it is relatively difficult to realize autonomous assembly tasks particularly in the case of manipulating flexible objects. In this report, a discrete event control system is introduced for the assembly task of electric lines into sleeves as a typical task of live power electric lines. In the implemetation of a discrete event control system, a novel learning vector quantization neural network is proposed and applied to the insertion task. To apply the proposed discrete event control system to the electric lines and sleeves which are not used in the neural network learning, lerning data have been generated by using the fuzzy inference. By the experimental results of 2 types of electric lines and sleeves, the proposed discrete event control algorithm and neural network learning using the generation of learning data by the fuzzy inference are comfirmed very effective to the complex task such as the insertion of electric lines to sleeves.