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.

Novel Concept for Electro-Hydrostatic Actuators for Motion Control of Hydraulic Manipulators

Self-contained hydraulic cylinders have gained popularity in the recent years but have not been implemented for high power articulated hydraulic manipulators. This paper presents a novel concept for an electro-hydrostatic actuator applicable to large hydraulic manipulators. The actuator is designed and analyzed to comply with requirements such as load holding, overload handling, and differential flow compensation. The system is analyzed during four quadrant operation to investigate energy efficiency and regenerative capabilities. Numerical simulation is carried out using path control and 2DOF anti-swing of a hydraulic crane as a load case to illustrate a real world scenario. A comparison with traditional valve-controlled actuators is conducted, showing significantly improved efficiency and with similar dynamic response, as well as the possibility for regenerating energy.

Development of a redundant anthropomorphic hydraulically actuated manipulator with a roll-pitch-yaw spherical wrist

The demand for redundant hydraulic manipulators that can implement complex heavy-duty tasks in unstructured areas is increasing; however, current manipulator layouts that remarkably differ from human arms make intuitive kinematic operation challenging to achieve. This study proposes a seven-degree-of-freedom (7-DOF) redundant anthropomorphic hydraulically actuated manipulator with a novel roll-pitch-yaw spherical wrist. A hybrid series-parallel mechanism is presented to achieve the spherical wrist design, which consists of two parallel linear hydraulic cylinders to drive the yaw/pitch 2-DOF wrist plate connected serially to the roll structure. Designed as a 1RPRRR-1SPU mechanism (“R”, “P”, “S”, and “U” denote revolute, prismatic, spherical, and universal joints, respectively; the underlined letter indicates the active joint), the 2-DOF parallel structure is partially decoupled to obtain simple forward/inverse kinematic solutions in which a closed-loop subchain “RPRR” is included. The 7-DOF manipulator is then designed, and its third joint axis goes through the spherical center to obtain closed-form inverse kinematic computation. The analytical inverse kinematic solution is drawn by constructing self-motion manifolds. Finally, a physical prototype is developed, and the kinematic analysis is validated via numerical simulation and test results.

Valve Deadzone/Backlash Compensation for Lifting Motion Control of Hydraulic Manipulators

In this paper, a novel nonlinear model and high-precision lifting motion control method of a hydraulic manipulator driven by a proportional valve are presented, with consideration of severe system nonlinearities, various uncertainties as well as valve backlash/deadzone input nonlinearities. To accomplish this mission, based on the independent valve orifice throttling process, a new comprehensive pressure-flow model is proposed to uniformly indicate both the backlash and deadzone effects on the flow characteristics. Furthermore, in the manipulator lifting dynamics, considering mechanism nonlinearity and utilizing a smooth LuGre friction model to describe the friction dynamics, a nonlinear state-space mathematical model of hydraulic manipulation system is then established. To suppress the adverse effects of severe nonlinearities and uncertainties in the system, a high precision adaptive robust control method is proposed via backstepping, in which a projection-type adaptive law in combination with a robust feedback term is conducted to attenuate various uncertainties and disturbances. Lyapunov stability analysis demonstrates that the proposed control scheme can acquire transient and steady-state close-loop stability, and the excellent tracking performance of the designed control law is verified by comparative simulation results.

Investigation of Structure of Technology Cycle Time of Hydraulic Manipulators in the Process of Loading Forwarders with Logs

In the practice of using cut-to-length technology, hydraulic manipulators are widely used. Understanding manipulator cycle is important for improving existing logging technologies and developing new machine designs. The paper analyzes structure of technological cycle and operating time of manipulator in the process of loading forwarder on skid trails. Twenty-one loading processes were investigated. In the structure of technological cycle, the following elements were considered: empty movements, loaded movements, movements of manipulator links when performing operations inside load space of forwarder and special techniques such as re-grabbing logs and pulling of an incompletely closed log grip through the logs when the ends of the grabbed logs tilt and abut against the ground used during loading movement. Statistical processing of data showed that median values of samples consisting of time intervals of empty movements are in trange from 3.8 to 6 seconds, the median of samples of loaded movements is 6–16 seconds and median of samples of a pair of movements 5–9 seconds. With a 95% degree of probability, under the studied production conditions, the time of one loaded movement falls within the range of 4–14 seconds; one empty movement – in the range of 3–7 seconds. Total time of empty movements takes a share from 20 to 45% of the total loading time (on average 30%), the total time of loading movements is from 51 to 72% (on average 63%), the time of operations inside the load space is from 0 to 18% (on average 7%). Time of loaded movements, including use of special techniques, is from 13% to 64% of total time of loaded movements (or 10–53% of total number of loaded movements). The time, consisting of a pair of movements: empty and loaded, is somewhat influenced by forwarder size. Duration of one loaded movement is significantly affected by use of special techniques by the operator. Number and duration of loaded movements with these techniques is significantly influenced by: average size of loaded assortments and number of assortments carried in the grapple during one loaded movement. No significant influence of average size of assortments, number of assortments in grapple and size of the machine on empty movements was found. However, some influence on empty movements of number of loaded movements performed from one forwarder parking lot was observed. Duration and frequency of operations within the load space are weakly correlated with the size of assortments and forwarder size.

ASSESSMENT OF THE STATUS OF THE MODERN PARK OF DOMESTIC AND FOREIGN FOREST TRANSPORT VEHICLES

The article presents the results of the analysis of information on the manufacturers of timber road transport available on the world market. The features of the used timber haulers are described, their layout diagrams are given. The characteristic features of the existing timber trucks and trailers for them are considered. Possible layout diagrams of timber-carrying road trains, as well as the features of the placement of hydraulic manipulators on them are presented.