Order-reduced-model based integral sliding mode control of a heavy-duty hydraulic manipulator with disturbances estimation

A sliding mode control method is adapted to the trajectory tracking and positioning control of a heavy-duty hydraulic manipulator in this article, which shows high performance with the drive of hydraulic proportional valve. The dynamic model of the system is established, the complexity of which is reduced based on the singular perturbation theory to simplify the analysis and the online calculation of the control variable. The extended state observer is developed in the control loop to estimate the real-time disturbances including the parameter uncertainties and load changes of the system. The integral sliding mode control law is designed combining the extended state observer, and the stability of the system is proved theoretically. The experimental results on a heavy-duty hydraulic manipulator show that the proposed control method has high dynamic tracking performance and positioning accuracy, and the proposed extended state observer can effectively resist disturbances.

Real-Time Flow Optimization of Hydraulic Manipulator with One Degree of Redundancy Considering Joint Limit Constraint

Due to the complexity in unstructured environments (e.g., rescue response and forestry logging), more hydraulic manipulators are equipped with one redundant joint to improve their motion flexibility. In addition to considering joint limit constraint and maneuverability optimization like electrically driven manipulators, hydraulic manipulators can optimize flow consumption consider flow optimization aiming at energy saving and flow anti-saturation for redundancy resolution, since multiple joints are supplied by one pump. Therefore, this paper proposes a redundancy resolution method combining the gradient projection method with a weighted Jacobian matrix (GPM-WJM) for real-time flow optimization of the hydraulic manipulator with one degree of redundancy considering joint limit constraint. Its solution consists of two parts: a special solution (the weighted least-norm solution) and a general solution (the projection of the optimization index in the null space of the weighted task Jacobian matrix). Simulations are carried out to verify its effectiveness. The simulation result shows that GPM-WJM can meet the constraints of joint limit without affecting the tool center point (TCP) trajectory and utilize the remaining redundancy to optimize the flow consumption and manipulability in real-time, which can reduce average system flow by 10.45%. Compared with the gradient projection method (GPM) for flow optimization, GPM-WJM can reduce the maximum acceleration when avoiding the joint limits by 80% at the cost of slightly weakening the flow optimization effect, which is beneficial to improve the accuracy of the manipulator in practice.

Composite Adaptive Dynamic Surface Control for a Multi-DOF Hydraulic Manipulator With Disturbance Observer

This paper presents an adaptive dynamic surface control strategy based on composite adaptive method for a multi-DOF hydraulic manipulator with the unknown disturbance and uncertainties. The manipulator is driven by multiple hydraulic actuators so that the system can have the advantages of the hydraulic system such as the high-power density. Dynamic characteristics of the hydraulic system have a non-negligible impact on the performance of the manipulator. Considering the hydraulic actuator dynamics, the mathematical model of the hydraulic manipulator is derived at first. The dynamic model is high nonlinear, and has unmatched and matched disturbances and parameter uncertainties such as the mass and length of each articulated arm and the elastic modulus of hydraulic oil. Then, a composite adaptive control law is designed to estimate the uncertain parameters of the hydraulic manipulator, and a disturbance observer is explored to compensate the unknown disturbances without acceleration measurement that generally introduces the high noise into the system. Besides, the dynamic surface controller is proposed to account for the system nonlinearity and stabilize the closed-loop system. Finally, comparative experiments of the position tracking of the hydraulic manipulator are performed to verify the effectiveness of the proposed control strategy.

IMPROVEMENT OF THE ENERGY RECOVERY SYSTEM OF A TIMBER TRACTOR WITH A LUMBER TRUCK

The place of road transport in logging production has been considered. The main advantages of using timber tractors with timber drags in comparison with other layout schemes of timber road trains have been described. Conse-quences of dynamic loads acting on the pivot of the turning bunk of a timber-carrying area from frequent braking of a timber tractor with a timber drag have been given. Based on the analysis of scientific works of foreign scientists, the promising direction of research in the field of recuperation of various types of energy in road transport is substantiated, which makes it possible to reduce dynamic loads during braking in the pivot pin and at the same time accumulate, with subsequent useful use, energy unproductively dissipated into the surrounding space from the energy forces of the trailer with a pack of whips. The design of the main manufacturers of platforms for timber haulers with timber drags has been described. The requirements for timber haulers with timber drags operated on public roads have been considered. The main forces acting on the links of a timber tractor with a timber drag during braking have been analyzed. Diagrams of the mutual positions of a timber tractor with a timber drag when moving along a timber road on the rise, downhill and turn have been given. The analysis of the dependences of the forces arising in the pivot of the swivel bunk of a timber platform during the movement of a timber tractor with a timber drag on the turning radius and speed of movement has been carried out. A promising design of a recuperative bolster device for a timber haulage site has been proposed. It enables to accumulate hydraulic energy during frequent braking of a timber tractor with a timber drag, followed by its use in the process of loading and unloading timber by a hydraulic manipulator

An Adaptive Robust Controller for Hydraulic Robotic Manipulators with a Flow-Mapping Compensator

Proportional directional control valves have flexible control functions for the control of various hydraulic manipulators. It is foreseeable that the application of proportional directional control valves will be further expanded. However, due to its own structure, its important parameter, flow gain, is complex, and it has a complex functional relationship with valve opening and temperature. The variable flow gain reduces the performance of a strictly derived nonlinear controller. Therefore, it is necessary to consider the nonlinearity of flow gain in the controller design. In order to solve the above problems, this paper proposes an adaptive robust controller for a hydraulic manipulator with a flow-mapping compensator, which takes into account the nonlinear flow gain and improves the performance of the nonlinear controller. First, we established an adaptive robust controller of the hydraulic manipulator to obtain the load flow of the control input valve. Then, the function of flow gain, input voltage, and temperature are calibrated offline using cubic polynomial, and the flow-mapping compensator is obtained. Finally, we calculate the input voltage based on the flow-mapping compensator and load flow. The flow-mapping compensator further reduces the uncertainty of the model and improves the robustness of the system. By using the proposed controller, the control accuracy of the hydraulic manipulator is significantly improved.

Robust Controller for Pursuing Trajectory and Force Estimations of a Bilateral Tele-Operated Hydraulic Manipulator

In hazardous/emergency situations, public safety is of the utmost concern. In areas where human access is not possible or is restricted due to hazardous situations, a system or robot that can be distantly controlled is mandatory. There are many applications in which force cannot be applied directly while using physical sensors. Therefore, in this research, a robust controller for pursuing trajectory and force estimations while deprived of any signals or sensors for bilateral tele-operation of a hydraulic manipulator is suggested to handle these hazardous, emergency circumstances. A terminal sliding control with a sliding perturbation observer (TSMCSPO) is considered as the robust controller for a coupled leader and hydraulic follower system. The ultimate use of this controller is as a sliding perturbation observer (SPO) that can estimate the reaction force without any physical force sensors. Robust and perfect position tracking is attained with terminal sliding mode control (TSMC) in addition to control of the hydraulic follower manipulator. The force estimation and pursuing trajectory for the leader–follower system is built upon a bilateral tele-operation control approach. The difference between the reaction forces (caused by the remote environment) and the operating forces (applied by the human operator) required the involvement of an impedance model. The impedance model is implemented in the leader manipulator to provide human operators with an actual sense of the reaction force while the manipulator connects with the remote environment. A camera is used to ensure the safety of the workplace through visual feedback. The experimental results showed that the controller was robust at pursuing trajectory and force estimations for the bilateral tele-operation control of a hydraulic manipulator.