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This paper aims to develop a robust decomposed system control (RDSC) strategy under input constraints for an electro‐mechanical linear actuator (EMLA) facing model uncertainty and external disturbances. At first, a state‐space model of a complex multi‐stage gearbox EMLA system, driven by a permanent magnet synchronous motor (PMSM), is developed, and the non‐ideal characteristics of the ball screw are presented through the model. The result is a four‐order nonlinear strict‐feedback form (NSFF) system decomposed into three subsystems. As the paper's main result, a novel RDSC strategy with uniform exponential stability for controlling subsystem states is presented. This developed controller avoids the "explosion of complexity" problem associated with backstepping by treating the time derivative of the virtual control input as an uncertain system term. The proposed method, despite assuming load disturbances and input constraints with arbitrary bounds, offers a straightforward control approach for a broader range of applications. Further, the controller's performance is evaluated by simulating two distinct duty cycles, each representing different levels of demand on the actuator facing load disturbances near the rated motor performance. [ABSTRACT FROM AUTHOR]

A vision-based guidance methodology is proposed for precise positioning of the tool center point (TCP) of heavy-duty, long-reach (HDLR) manipulators. HDLR manipulators are non-rigid structures with many nonlinearities. Therefore, conventional rigid-body–based modeling and control methods issue challenges for accurate TCP positioning. To compensate for these errors, we compute the pose error between the TCP and an object of interest (OOI) directly in the camera frame, while using motion-based local calibration to find the extrinsic sensor-to-robot correspondence. The proposed pipeline for local calibration is twofold: first, the detected tool is oriented perpendicularly with respect to the OOI. Second, range adjustment is performed in the local planar plane by exploiting the visual measurements. Two methods for adjusting the range were examined: a line equation–based method and a trajectory matching–based method. Real-time experiments were conducted using a HDLR manipulator with a 5 m reach, and visual fiducial markers were used as detectable objects for the visual sensor. The experimental results demonstrated that the proposed methodology can provide sub-centimeter positioning accuracy, which is very challenging to achieve with HDLR manipulators due to their characteristic uncertainties. [ABSTRACT FROM AUTHOR]

The bulldozer is a mobile earthmoving machine with a differentially steered mobile base and an onboard manipulator used for soil cutting and transportation. Grading the ground to match a desired contour is an end-effector path-following task, with required joint rates dependent on mobile base motion. The offline planning of travel velocity profiles that respect the available hydraulic flowrate limits is difficult due to uncertainties in the machine–soil interactions. Hence, we propose a flow-bounded velocity controller enabling accurate automatic grading with online velocity scaling. The capacity of hydrostatic transmission and manipulator actuators, as well as the desired velocity, are considered when deciding the commanded velocity reference for the mobile base. Our dynamic simulation results show that, with the proposed controller, a desired ground profile is cut accurately when the machine operates at its performance limits. Comparison to constant velocity driving shows that errors in blade positioning are reduced dramatically. Constant velocity selected to keep the flow within limits results in longer completion times compared to our solution, making it more time optimal. Furthermore, the rpm of the diesel engine can be reduced to save fuel without compromising control performance. [ABSTRACT FROM AUTHOR]

This study designs a high-precision bilateral teleoperation control for a dissimilar master–slave system. The proposed nonlinear control design takes advantage of a novel subsystem-dynamics-based control method that allows designing of individual (decentralized) model-based controllers for the manipulators locally at the subsystem level. Very importantly, a dynamic model of the human operator is incorporated into the control of the master manipulator. The individual controllers for the dissimilar master and slave manipulators are connected in a specific communication channel for the bilateral teleoperation to function. Stability of the overall control design is rigorously guaranteed with arbitrary time delays. Novel features of this study include the completely force-sensor-less design for the teleoperation system with a solution for a uniquely introduced computational algebraic loop, a method of estimating the exogenous operating force of an operator and the use of a commercial haptic manipulator. Most importantly, we conduct experiments on a dissimilar system in two degrees of freedom (DOFs). As an illustration of the performance of the proposed system, a force scaling factor of up to 800 and position scaling factor of up to 4 was used in the experiments. The experimental results show an exceptional tracking performance, verifying the real-world performance of the proposed concept. [ABSTRACT FROM AUTHOR]

Series elastic actuators (SEAs) have become a common actuation method in torque-controlled electric lightweight arm applications that physically interact with the environment in assembly tasks. Compared to traditional actuators, SEAs can provide high force fidelity, shock tolerance, and force sensing for interaction control. Considering inherent system dynamics and the variable stiffness of the fluid, the control design for hydraulic SEAs (HSEAs) that lead into fifth-order system is a challenging task. As a novelty, a full state feedback controller design for the developed fifth-order HSEA system is presented to serve as an inner-loop controller to handle highly nonlinear dynamics behavior. In addition, as an outer-loop impedance controller for HSEAs in heavy-duty applications, the position-based impedance controller is designed to handle control of the HSEA system during the contact motion. Experimental results with a one-degree-of-freedom real-size experimental setup with a payload of 200 kilos demonstrates the effectiveness of the proposed HSEA control methods both in the free-space motion and in a contact impedance motion. [ABSTRACT FROM AUTHOR]

The Compact Linear Collider (CLIC) is a study of a 3 TeV linear electron–positron (e+e−) accelerator and is a successor candidate for CERN's Large Hadron Collider. The CLIC luminosity target is 5.9 × 1034 cm−2 s−1, which causes unprecedented pre-alignment requirements of its main linear accelerator (main linac). Along the 50 km long tunnel, the main components of any 200 m long section have to be positioned within 10 µm from a straight reference line. The pre-alignment challenge has been studied at CERN since the 1990s, and the main technical challenges have been solved. This article summarizes the positioning strategy and presents it to an audience outside the particle accelerator community. The methods can be of interest especially in the field of large-scale metrology. The positioning strategy consists of several steps or subsystems. The development of a straight reference line over tens of kilometers allows absolute positioning of accelerator components, while a process called fiducialization defines component reference axes with regard to alignment targets. Emphasis is on a support pre-alignment network that acts as a link between the straight reference line and fiducialization. The subsystems and remaining challenges in their development are presented. The chosen strategy's potential is demonstrated experimentally by building a short test setup. [ABSTRACT FROM AUTHOR]

Crushing of blasted ore is an essential phase in extraction of valuable minerals in mining industry. It is typically performed in multiple stages with each stage producing finer fragmentation. Performance and throughput of the first stage of crushing is highly dependent on the size distribution of the blasted ore. In the crushing plant, a metal grate prevents oversized boulders from getting into the crusher jaws, and a human‐controlled hydraulic manipulator equipped with a rock hammer is required to break oversized boulders and ensure continuous material flow. This secondary breaking task is event‐based in the sense that ore trucks deliver boulders at irregular intervals, thus requiring constant human supervision to ensure continuous material flow and prevent blockages. To automatize such breaking tasks, an intelligent robotic control system along with a visual perception system (VPS) is essential. In this manuscript, we propose an autonomous breaker system that includes a VPS capable of detecting multiple irregularly shaped rocks, a robotic control system featuring a decision‐making mechanism for determining the breaking order when dealing with multiple rocks, and a comprehensive manipulator control system. We present a proof of concept for an autonomous robotic boulder breaking system, which consists of a stereo‐camera‐based VPS and an industrial rock‐breaking manipulator robotized with our retrofitted system design. The experiments in this study were conducted in a real‐world setup, and the results were evaluated based on the success rates of breaking. The experiments yielded an average success rate of 34% and a break pace of 3.3 attempts per minute. [ABSTRACT FROM AUTHOR]

A gravity-referenced joint angle estimation, which acts in joint space, is proposed for multiple-degree-of-freedom hydraulic manipulators. As a novelty, the estimation pairs up inertial units across a section of an open kinematic chain. In this way, the three-axis linear accelerometers and the three-axis rate gyros provide a drift-free solution for observing the motion state of a rotary joint connecting two links without relying on the full forward kinematics. For a low-noise, low-delay estimate, the linear accelerations acting on the paired inertial units are modeled and robustly combined with the principles of complementary and Kalman filtering. In pick-and-place experiments with a serial-link manipulator on a multiton, off-road forestry vehicle, joint angle sensing error of less than ±1° was achieved in spite of the dynamic interaction between the vehicle base and the terrain. Furthermore, the kinematic modeling’s ability to compensate for the nonplanar, coupled 3-D linkage motion is studied for one- and two-axis rate measurements along with Cartesian path tracking. This gives new insights from the typical planar kinematic models and heavy-duty control viewpoints. [ABSTRACT FROM PUBLISHER]

This paper proposes, for the first time without using any linearization or order reduction, an adaptive and model-based discharge pressure control design for the variable displacement axial piston pumps (VDAPPs), whose dynamical behaviors are highly nonlinear and can be described by a fourth-order differential equation. The rigorous stability proof, with an asymptotic convergence, is given for the entire system. In the proposed novel controller design method, the specifically designed stabilizing terms constitute an essential core to cancel out all the stability-preventing terms. The experimental results reveal that rapid parameter adaptation significantly improves the feedback signal tracking precision compared to a known-parameter controller design. In the comparative experiments, the adaptive controller design demonstrates the state-of-the-art discharge pressure control performance, enabling a possibility for energy consumption reductions in hydraulic systems driven with VDAPP. [ABSTRACT FROM AUTHOR]

This paper addresses the energy-inefficiency problem of four-degrees-of-freedom (4-DOF) hydraulic manipulators through redundancy resolution in robotic closed-loop controlled applications. Because conventional methods typically are local and have poor performance for resolving redundancy with respect to minimum hydraulic energy consumption, global energy-optimal redundancy resolution is proposed at the valve-controlled actuator and hydraulic power system interaction level. The energy consumption of the widely popular valve-controlled load-sensing (LS) and constant-pressure (CP) systems is effectively minimised through cost functions formulated in a discrete-time dynamic programming (DP) approach with minimum state representation. A prescribed end-effector path and important actuator constraints at the position, velocity and acceleration levels are also satisfied in the solution. Extensive field experiments performed on a forestry hydraulic manipulator demonstrate the performance of the proposed solution. Approximately 15–30% greater hydraulic energy consumption was observed with the conventional methods in the LS and CP systems. These results encourage energy-optimal redundancy resolution in future robotic applications of hydraulic manipulators. [ABSTRACT FROM AUTHOR]

This paper presents the recent advancements in the control of multiple-degree-of-freedom hydraulic robotic manipulators. A literature review is performed on their control, covering both free-space and constrained motions of serial and parallel manipulators. Stability-guaranteed control system design is the primary requirement for all control systems. Thus, this paper pays special attention to such systems. An objective evaluation of the effectiveness of different methods and the state of the art in a given field is one of the cornerstones of scientific research and progress. For this purpose, the maximum position tracking error |e|max and a performance indicator $\rho$  (the ratio of |e|max with respect to the maximum velocity) are used to evaluate and benchmark different free-space control methods in the literature. These indicators showed that stability-guaranteed nonlinear model based control designs have resulted in the most advanced control performance. In addition to stable closed-loop control, lack of energy efficiency is another significant challenge in hydraulic robotic systems. This paper pays special attention to these challenges in hydraulic robotic systems and discusses their reciprocal contradiction. Potential solutions to improve the system energy efficiency without control performance deterioration are discussed. Finally, for hydraulic robotic systems, open problems are defined and future trends are projected. [ABSTRACT FROM PUBLISHER]

In challenging robotic tasks, high-bandwidth closed-loop control performance of the system is required for successful task completion. One of the most critical factors inhibiting the wide-spread use of closed-loop contact control applications has been the control system stability problems. To prevent unstable system behavior, the need for rigorously addressed manipulator dynamics is substantial. This is because the contact dynamics between a manipulator and its environment can be drastic. In this paper, a novel Cartesian space impedance control method is proposed for hydraulic robotic manipulators. To address the highly nonlinear dynamic behavior of the hydraulic manipulator, the system control is designed according to the subsystem-dynamics-based virtual decomposition control (VDC) approach. The unique features of VDC (virtual power flow and virtual stability) are used to analyze the interaction dynamics between the manipulator and the environment. Based on the desired impedance parameters and stability analysis, an explicit method to design the control gains for the proposed impedance control law is developed. The \boldsymbol L_2  and \boldsymbol L_\infty stability is guaranteed in both free-space motions and constrained motions. Experimental results demonstrate that the hydraulic robotic manipulator is capable of adjusting its dynamic behavior accurately in relation to the imposed target impedance behavior. This provides compliant system behavior, which is needed in many dynamically challenging robotic tasks. [ABSTRACT FROM PUBLISHER]

A gravity-referenced joint angle estimation approach is proposed for multiple-degree-of-freedom hydraulic manipulators. The approach is built solely upon easy-to-install linear accelerometers and angular rate gyroscopes to avoid physical contact to rotary joint mechanisms and the use of in-axis sensors. As a significant novelty, a comprehensive kinematics model for linear accelerations acting on the accelerometers during motion is associated with the well-known principles of complementary sensor fusion for the first time, which provides a practical solution for using the force of gravity as an angular reference while in fast motion. In experiments with a serial-link manipulator of a multiton off-road forestry vehicle, gyro-aided sensor fusion employing the kinematics model achieved a joint angle sensing error of less than $\pm$1 $^\circ$, which translated to a centimeter end-effector positioning accuracy. This can be considered a significant result in view of the vibrations oscillating through the manipulator structure, coupled linear accelerations of linkage motion, and nonstatic interaction between the vehicle base and the terrain. [ABSTRACT FROM PUBLISHER]