Swivel Angle Research Articles

Comparison of Advanced Multivariable Control Techniques for Axial-Piston Pump

This article is devoted to a comparison of two advanced control techniques applied to the same plant. The plant is a certain type of axial-piston pump. A linear-quadratic (LQR) controller and an H-infinity (H∞) controller were synthesized to regulate the displacement volume of the pump. The classical solution to such a problem is to use a hydro-mechanical controller (by pressure, flow rate, or power) but, in the available sources, there are solutions that implement proportional-integral-derivative (PID), LQR, model predictive control (MPC), etc. Unlike a classical solution, in our case, the hydro-mechanical controller is replaced by an electro-hydraulic proportional valve, which receives a reference signal from an industrial microcontroller. It is used as the actuator of the pump swash plate. The pump swash plate swivel angle determines the displacement volume, respectively, and the flow rate of the pump. The microcontroller is capable of embedding various control algorithms with different structures and complexities. The developed LQR and H∞ controllers are compared in the simulation and real experiment conditions. For this purpose, the authors have developed a laboratory experimental test bench, enabling a real-time function of the control system via USB/CAN communication. Both controllers are compared under different pump loading modes. Also, this paper contributes an uncertain model of an axial-piston pump with proportional valve control that is obtained from experimental data. Based on this model, the robust stability of the closed-loop system is investigated by comparing the structure of a singular value (μ). The investigations show that both control systems achieved robust stability. Moreover, they can tolerate up to four times larger uncertainties than modeled ones. The system with the H∞ controller attenuates approximately at least 30 times the disturbances with frequency up to 1 rad/s while the system with the LQR controller attenuates at least 10 times the same disturbances.

Effect of changing the acquisition trajectory of the 3D C-arm (CBCT) on image quality in spine surgery: experimental study using an artificial bone model

BackgroundIntraoperative 3D imaging using cone-beam CT (CBCT) provides improved assessment of implant position and reduction in spine surgery, is used for navigated surgical techniques, and therefore leads to improved quality of care. However, in some cases the image quality is not sufficient to correctly assess pedicle screw position and reduction, especially due to metal artifacts. The aim of this study was to investigate whether changing the acquisition trajectory of the CBCT in relation to the pedicle screw position during dorsal instrumentation of the spine can reduce metal artifacts and consequently improve image quality as well as clinical assessability on the artificial bone model.MethodsAn artificial bone model was instrumented with pedicle screws in the thoracic and lumbar spine region (Th10 to L5). Then, the acquisition trajectory of the CBCT (Cios Spin, Siemens, Germany) to the pedicle screws was systematically changed in 5° steps in angulation (− 30° to + 30°) and swivel (− 30° to + 30°). Subsequently, radiological evaluation was performed by three blinded, qualified raters on image quality using 9 questions (including anatomical structures, implant position, appearance of artifacts) with a score (1–5 points). For statistical evaluation, the image quality of the different acquisition trajectories was compared to the standard acquisition trajectory and checked for significant differences.ResultsThe angulated acquisition trajectory increased the score for subjective image quality (p < 0.001) as well as the clinical assessability of pedicle screw position (p < 0.001) highly significant with particularly strong effects on subjective image quality in the vertebral pedicle region (d = 1.06). Swivel of the acquisition trajectory significantly improved all queried domains of subjective image quality (p < 0.001) as well as clinical assessability of pedicle screw position (p < 0.001). The data show that maximizing the angulation or swivel angle toward 30° provides the best tested subjective image quality.SummaryAngulation and swivel of the acquisition trajectory result in a clinically relevant improvement in image quality in intraoperative 3D imaging (CBCT) during dorsal instrumentation of the spine.

A Robust Visual Servoing Controller for Anthropomorphic Manipulators With Field-of-View Constraints and Swivel-Angle Motion: Overcoming System Uncertainty and Improving Control Performance

Human–robot collaboration has attracted significant attention in the industry due to the flexibility of humans and the accuracy of robots. Humanoid control of anthropomorphic robotic arms combined with visual servoing will enhance the intelligence of industrial robots. However, the robotic manipulator will introduce psychological discomfort to nearby humans, and the loss of visual features will induce visual servoing task failure. Aiming at these problems, this article proposes a humanoid control method based on visual servoing by utilizing the swivel angle derived from the human arm to realize the human-like behavior of anthropomorphic robot manipulators. To advance the visual servoing control performance, a function constraint is designed with the barrier Lyapunov function (BLF) to ensure that image features stay within the field of view (FoV). The sliding mode control (SMC) is combined with image-based visual servoing (IBVS) to dispose of the uncertainties of a seven-degree-of-freedom (7-DoF) redundant robot manipulator. The proposed algorithm is substantiated through comparison experiments based on the Sawyer robot and constructed visual servoing physical platform.

Influence of Rheological Properties of Lithium Greases on Operating Behavior in Oscillating Rolling Bearings at a Small Swivel Angle

In this study, the behavior of greases during oscillating bearing operation with a small oscillation angle and high frequency was investigated. This mode of operation entails demands on the lubrication system that differ significantly from those for continuously rotating bearings. In order to determine the variables influencing the suitability of a lubricating grease for small angle oscillating operation, the grease samples were examined with particular regard to their rheological properties. The focus of this investigation was to find a relationship between the rheological parameters and the real behavior in the bearing. Therefore, rheological and physical parameters, which influence the long-term structural changes and lubrication conditions, were identified. For this purpose, the viscosity was measured over a wide shear-rate range. The storage and loss modulus, the work of deformation, and the adhesion force jump are also determined. Afterward, rotational transient flow measurements were performed. These allowed us to analyze the development of the shear stress over time, at a constant shear rate, and to examine the internal friction behavior by evaluating the energy density. Subsequently, grease-lubricated four-point bearings were used in component tests, while the frictional torque was measured. These bearings operated in oscillating motion. Moreover, the yield point of mechanically aged greases was measured and compared with that of fresh greases to examine the influence of the oscillating operation on the lubricant condition. Finally, correlations between grease composition, rheological measurements, and component tests were investigated. Thereby, parameters influencing the frictional behavior of greases in rolling bearings during oscillating operation at small swivel angles were identified.

Electric thruster configuration design optimization for geostationary satellites with robotic manipulators

This paper proposes a novel electric thruster configuration design optimization scheme to implement efficient station-keeping operations for geostationary satellites. In this work, the electric thrusters are equipped with 4-DOF robotic manipulators to provide flexible control thrust in space, which consumes much less propellant than the conventional station-keeping process using fixed-position electric thrusters. To effectively determine the firing right ascensions and firing durations of each electric thruster during the station-keeping process, a novel station-keeping control strategy is developed in view of the low-thrust feature of electric thrusters and the flexible pointing capacity of robotic manipulators. A low-thrust station-keeping period includes one two-day orbit determination period and six two-day control periods, where the initial orbital elements are determined in the orbit determination period, and the electric thrusters fire to compensate the perturbations in the control periods. Based on the control strategy, the electric thruster configuration design optimization problem is formulated to minimize the total propellant consumption via optimizing the robotic manipulator joint swivel angles and firing durations simultaneously, subject to several practical engineering constraints including the station-keeping accuracy, angular momentum dumping, collision between electric thruster and solar array, and electric thruster plume. Finally, the proposed electric thruster configuration design optimization scheme is applied to real-world station-keeping problems. The simulation results show that the geostationary satellites can be successfully maintained in an assigned station-keeping window using the robotic manipulators based low-thrust station-keeping control strategy. Moreover, the optimized electric thruster configuration with robotic manipulators can save 31.58% propellant consumption compared with that of the conventional configuration owing to the favorable flexibility of control thrust, which demonstrates the effectiveness and practicality of this work.

Transport control of a swivel crane based on a highly versatile vibration suppression trajectory

In this study, methods for automatically controlling load transportation by a swivel crane with high speed and suppressed swing motion of suspended load are proposed. First, highly versatile trajectories for each of swivel and straight transport of load are proposed on the basis of a linearized and simplified analytical model and the optimal control theory. The proposed method has the versatility that it can be applied even with different swivel radii and swivel angles. The effectiveness and limitations of the proposed methods are shown with computer simulations and experiments with a laboratory model. Next, we propose a new method that expands the proposed method and uses the measurement data of the swing information of the load. It is shown that by using this method, even if the load swings at the start of transport, it is possible to suppress the swing of the load at the target point of transport.

Muscle-Effort-Minimization-Inspired Kinematic Redundancy Resolution for Replicating Natural Posture of Human Arm.

Replicating natural postures of human arms is essential to generate human-like behaviors in robotic applications for humans nearby. However, how to realize this requirement in interactive scenarios remains a challenge due to the kinematic redundancy and unknown postural control strategy of human arms. Inspired by the physiological characteristics that the musculoskeletal system is coordinated to minimize muscle effort in human behaviors, this paper aims to address the issue by solving a muscle effort minimization problem. It adopts a high-fidelity human arm musculoskeletal model (HAMM) and considers the implicit constraint (desired hand pose) and the inequality constraints (range of joint motion). The constrained minimization is in general nonconvex, consequently sensitive to initial guesses in iterative procedures. So, it is impracticable to solve it directly with existing gradient-based deterministic approaches or standard evolutionary algorithms. As the main contribution, a hybrid inverse kinematics algorithm was proposed for the HAMM with 7 independent and 13 mimic joints to obtain the feasible arm postures satisfying the minimization constraints. Using the arm swivel angle that parametrizes the kinematic redundancy of the HAMM, geometrically equidistant initial guess candidates can be generated over the 1-dimension feasible posture manifold. As another contribution, we present a two-phase global minimization algorithm to handle the nonconvexity of the constrained minimization. It consists of a local-search phase on the null-space of the geometric Jacobian matrix and a global-search phase with an initial guess resampling strategy. The proposed approach was validated by replicating the natural arm postures of 5 right-handed subjects in daily tasks.

Overcoming Kinematic Singularities for Motion Control in a Caster Wheeled Omnidirectional Robot

Omnidirectional planar robots are common these days due to their high mobility, for example in human–robot interactions. The motion of such mechanisms is based on specially designed wheels, which may vary when different terrains are considered. The usage of actuated caster wheels (ACW) may enable the usage of regular wheels. Yet, it is known that an ACW robot with three actuated wheels needs to overcome kinematic singularities. This paper introduces the kinematic model for an ACW omni robot. We present a novel method to overcome the kinematic singularities of the mechanism’s Jacobian matrix by performing the time propagation in the mechanism’s configuration space. We show how the implementation of this method enables the estimation of caster wheels’ swivel angles by tracking the plate’s velocity. We present the mechanism’s kinematics and trajectory tracking in real-world experimentation using a novel robot design.

Inducing Human Motor Adaptation Without Explicit Error Feedback: A Motor Cost Approach.

Recent studies have shown that motor adaptation is an optimisation process on both kinematic error and effort. This work aims to induce a motor adaption in an experimental setup solely relying on the effort without any explicit kinematic error. In this experiment, the intervention space and adaptation space are decoupled: while the force field only applies to the hand linear velocity, the adaptation is expected to happen in the arm joint null space (i.e. the swivel angle). The primary hypothesis is that such an effort-based force field can induce a movement pattern change in an indirect manner. Secondarily, assuming that this adaptation may be further promoted through subtle prompts to explore the cost space, a variation of the approach with a progressive goal is also tested. Twenty naive subjects were allocated into two groups with slightly different implementations of the force field: one with a Constant Goal (CG) and another one with a Progressively changing Goal (PG). Subjects were asked to perform reaching tasks while attached to a 3D manipulandum. During the intervention, the device applied a resistive viscous force at the subject's hand as a function of the subject's swivel angle to encourage an increase of the latter. Significant increases of the swivel angle of 4.9° and 6.3° were observed for the CG and the PG groups respectively. This result confirms the feasibility of inducing motor adaptation in the redundant joint space by providing a task space intervention without explicit error feedback.

Motion Planning of Upper-Limb Exoskeleton Robots: A Review

(1) Background: Motion planning is an important part of exoskeleton control that improves the wearer’s safety and comfort. However, its usage introduces the problem of trajectory planning. The objective of trajectory planning is to generate the reference input for the motion-control system. This review explores the methods of trajectory planning for exoskeleton control. In order to reduce the number of surveyed papers, this review focuses on the upper limbs, which require refined three-dimensional motion planning. (2) Methods: A systematic search covering the last 20 years was conducted in Ei Compendex, Inspect-IET, Web of Science, PubMed, ProQuest, and Science-Direct. The search strategy was to use and combine terms “trajectory planning”, “upper limb”, and ”exoskeleton” as high-level keywords. “Trajectory planning” and “motion planning” were also combined with the following keywords: “rehabilitation”, “humanlike motion“, “upper extremity“, “inverse kinematic“, and “learning machine “. (3) Results: A total of 67 relevant papers were discovered. Results were then classified into two main categories of methods to plan trajectory: (i) Approaches based on Cartesian motion planning, and inverse kinematics using polynomial-interpolation or optimization-based methods such as minimum-jerk, minimum-torque-change, and inertia-like models; and (ii) approaches based on “learning by demonstration” using machine-learning techniques such as supervised learning based on neural networks, and learning methods based on hidden Markov models, Gaussian mixture models, and dynamic motion primitives. (4) Conclusions: Various methods have been proposed to plan the trajectories for upper-limb exoskeleton robots, but most of them plan the trajectory offline. The review approach is general and could be extended to lower limbs. Trajectory planning has the advantage of extending the applicability of therapy robots to home usage (assistive exoskeletons); it also makes it possible to mitigate the shortages of medical caregivers and therapists, and therapy costs. In this paper, we also discuss challenges associated with trajectory planning: kinematic redundancy and incompatibility, and the trajectory-optimization problem. Commonly, methods based on the computation of swivel angles and other methods rely on the relationship (e.g., coordinated or synergistic) between the degrees of freedom used to resolve kinematic redundancy for exoskeletons. Moreover, two general solutions, namely, the self-tracing configuration of the joint axis and the alignment-free configuration of the joint axis, which add the appropriate number of extra degrees of freedom to the mechanism, were employed to improve the kinematic incompatibility between human and exoskeleton. Future work will focus on online trajectory planning and optimal control. This will be done because very few online methods were found in the scope of this study.

Constrained real-time control of hydromechanical powertrains – methodology and practical application

Axial piston motors and pumps are core components in many hydromechanical systems as for instance the powertrain of wheel loader vehicles. The optimal performance of the individual components as well as the entire powertrain requires a fast and exact control of both the motor’s swivel angle as well as the pressure difference over the pump by means of the currently available information and despite their respective a-priori unknown reference signal generated by the driver with a joystick or gas pedal operation. Therefore, it is essential that the swivel angle and pressure controllers fully exploit the possible dynamics and the constrained resources of the nonlinear swivel angle displacement and the pressure adjustment system, respectively. In this work, a flatness-based feedforward control strategy for the motor’s swivel angle as well as a flatness-based tracking two-degree-of-freedom controller for the pump pressure are proposed. For the realization of the flat feedforward and the tracking controller, a constrained online trajectory generation by means of a nonlinear (switched) state variable filter is designed for each. Therefore, both controllers are capable of considering the relevant state and input constraints in real-time and without relying on an online optimization. The proposed control algorithms are both discussed and their performance is illustrated with measurement data from a wheel loader vehicle.

A novel method for closed-loop topology modification of helical gears using internal-meshing gear honing

The internal-meshing honing process allows excellent machining efficiency for the tooth crowning of helical gears. A gear with double-crowned tooth flanks is better than that with longitudinal-crowned tooth flanks because the tooth edge contact is prevented and the contact load distribution is improved more effectively. This study proposes a numerical approach for the closed-loop topology modification on cylindrical gears that have double-crowned and anti-twist tooth flanks for a CNC internal-meshing gear honing machine. Additional motions are added in forms of polynomials to three machine axes, including the radial feed of honing wheel, the swivel angle of honing wheel and the rotational angle of work gear. A sensitivity matrix combined with the Levenberg-Marquardt (LM) algorithm is employed to obtain the polynomial coefficients of additional motions for desired tooth surfaces. The amount of crowning on the work gear tooth surface can be specified using the proposed method. The results in the presented numerical examples verify the advantages of the proposed method.

Teeth interference in harmonic drives intended for heavy engineering

Based on geometric studies and force analysis of a heavy harmonic gearing and through application of the elasticity theory methods, motions of the deformed gearing from the theoretically preset positioning have been ascertained. A fundamental design feature of the heavy harmonic drive consists in a disk wave generator which permits to provide additional deformations of the flexible gear due to incomplete contact between the disks and the flexible wheel. The scale factor along with the small tooth module between 1.5 and 2 mm of the wave-type reducers and heavy loads imposed on the flexible gear increase its deformations and intensify formation of interference between the teeth. The above circumstances drastically reduce load-carrying capacities of the harmonic drives and actually restrict them due to the carrying capacity of a flexible bearing. The results obtained provide both qualitative and quantitative characteristics of the teeth interference depending on the wave generator swivel angle φ at various values of the transmitted torque between 0 and 5·105 kNm.

Kinematic Redundancy Analysis during Goal-Directed Motion for Trajectory Planning of an Upper-Limb Exoskeleton Robot.

The kinematic redundancy of human arm imposes challenges on joint space trajectory planning for upper-limb rehabilitation robot. This paper aims to investigate normal motion patterns in reaching and reach-to-grasp movements, and obtain the unique solution in joint space for a five-DOF exoskeleton. Firstly, a six-camera optical motion tracking system was used to capture participants' arm motion during goal-directed reaching or reach-to-grasp movements. Secondly, statistical analysis was executed to explore the characteristics of swivel angle, which revealed that the swivel angle can be approximated to the mean value (155° ± 5°) in resolving the arm redundancy problem. Thirdly, combined with the minimum-jerk trajectory of end-effector, the generated joint trajectory complied well with the joint trajectory captured in healthy humans. Consequently, the obtained results facilitate a new way for three-dimensional trajectory planning of the exoskeleton robot. Further, adaptive assist-as-needed control of the exoskeleton robot can be implemented based on the optimal reference trajectory, with aims to provide assistance according to the patient's performance, and in turn promote neural plasticity.

Experimental Study on the Width of the Reasonable Segment Pillar of the Extremely Soft Coal Seam in the Deep Mine

Various dynamic disasters will happen in the extremely soft coal seam mining process of Gob-side entry in the deep mine, including large deformation of roadways, rock burst, gas unusual, floor water invasion, spontaneous combustion of coal seam and so on. Therefore, a reasonable segment pillar will not only avoid the dynamic disasters in the excavating process, but also improve the resource utilization. Taking the goaf working face of extremely soft coal seam in the deep mine in one particular mine of Shandong Province as the engineering example, this paper first analyzes optional locations of the gob-side entry, finding that the gob-side entry should be located in the low stress block and it’s the most favorable to keep small pillars and goafs isolated. Then, it is found that small surrounding rock deformation of gob-side entry takes place in the driving process through the numerical simulation, and the deformation will increase with the increasing width of the chain pillar. The surrounding rock deformation of gob-side entry increases in the stoping stage. Small width of the chain pillar will easily result in the instability of the roadway. As the swivel angle of the basic roof increases, the surrounding rock deformation of gob-side entry will accordingly increase. Finally, the numerical calculation and on-spot mine pressure monitoring illustrate that the width of the segment pillar in the gob-side entry should be 5–7 m, with 6 m the best.

Closed-loop cortical control of virtual reach and posture using Cartesian and joint velocity commands

Objective. Brain–computer interfaces (BCIs) are a promising technology for the restoration of function to people with paralysis, especially for controlling coordinated reaching. Typical BCI studies decode Cartesian endpoint velocities as commands, but human arm movements might be better controlled in a joint-based coordinate frame, which may match underlying movement encoding in the motor cortex. A better understanding of BCI controlled reaching by people with paralysis may lead to performance improvements in brain-controlled assistive devices. Approach. Two intracortical BCI participants in the BrainGate2 pilot clinical trial performed a visual 3D endpoint virtual reality reaching task using two decoders: Cartesian and joint velocity. Task performance metrics (i.e. success rate and path efficiency) and single feature and population tuning were compared across the two decoder conditions. The participants also demonstrated the first BCI control of a fourth dimension of reaching, the arm’s swivel angle, in a 4D posture matching task. Main results. Both users achieved significantly higher success rates using Cartesian velocity control, and joint controlled trajectories were more variable and significantly more curved. Neural tuning analyses showed that most single feature activity was best described by a Cartesian kinematic encoding model, and population analyses revealed only slight differences in aggregate activity between the decoder conditions. Simulations of a BCI user reproduced trajectory features seen during closed-loop joint control when assuming only Cartesian-tuned features passed through a joint decoder. With minimal training, both participants controlled the virtual arm’s swivel angle to complete a 4D posture matching task, and achieved significantly higher success using a Cartesian + swivel velocity decoder compared to a joint velocity decoder. Significance. These results suggest that Cartesian velocity command interfaces may provide better BCI control of arm movements than other kinematic variables, even in 4D posture tasks with swivel angle targets.

Constrained real-time swivel angle control for hydraulic axial piston motors

Axial piston motors are core components in many hydro-mechanical systems as e.g. the powertrain of wheel loader vehicles. The optimal performance of the motor as well as the powertrain requires a fast and exact control of the motor’s swivel angle according to the a-priori unknown reference signal which is e.g. generated by the driver with a joystick or gas pedal operation. Therefore, it is essential that the swivel angle controller fully exploits the possible dynamics and the constrained resources of the nonlinear swivel angle adjustment system. In this work, a novel flatness-based feedforward control strategy for the swivel angle is presented, which is capable of considering the relevant state and input constraints in real-time, i.e. only by means of the currently available information and without relying on an online optimization. The proposed swivel angle controller is finally demonstrated and discussed with the results of both a simulation study and measurement data from a wheel loader vehicle.

PENGARUH TWIST ANGLE BLADE TURBIN SAVONIUS BERPENGARAH ALIRAN APLIKASI PADA TURBIN AIR

Water turbine is one of the mechanical equipment that functions to generateenergy into mechanical energy. There are types of water turbines one of which isthe Savonius water turbine. Savonius water turbines have the advantage of otherturbines, namely installation in rivers that do not damage the environment, areable to work and do not require special maintenance as well as providingweaknesses that can affect the positive force and the negative force on the rotor isstill small. This turbine has never been widespread. To make this turbine it ispossible to conduct research to improve its performance, especially in the turbinerotor. In these words we will try the rattan turbine by varying the blade's turningangle from 00, 30o, 60o, 90o and 120o and adding ½ and ¼ opening flow guides.Based on the results of the research that we have done, we can say the differencein blade angle and flow guide to turbine performance. The variation of twist angleand flow controller that provides the most appropriate turbine performance is a90o swivel with turbine flow guide openings ¼. At the swivel angle 120o the waveguide is not as wide.

Online human-like redundancy optimization for tele-operated anthropomorphic manipulators

Robot human-like behavior can enhance the performance of human–robot cooperation with prominently improved natural interaction. This also holds for redundant robots with an anthropomorphic kinematics. In this article, we translated human ability of managing redundancy to control a seven degrees of freedom anthropomorphic robot arm (LWR4+, KUKA, Germany) during tele-operated tasks. We implemented a nonlinear regression method—based on neural networks—between the human arm elbow swivel angle and the hand target pose to achieve an anthropomorphic arm posture during tele-operation tasks. The method was assessed in simulation and experiments were performed with virtual reality tracking tasks in a lab environment. The results showed that the robot achieves a human-like arm posture during tele-operation, and the subjects prefer to work with the biologically inspired robot. The proposed method can be applied in control of anthropomorphic robot manipulators for tele-operated collaborative tasks, such as in factories or in operating rooms.

Dual lead-crowning for helical gears with long face width on a CNC internal gear honing machine

Gear tooth surfaces are usually crowned to meet various needs, including enhanced of the load capacity, avoidance of edge contact and longer service life. However, the traditional single lead-crowning method is less adequate for a long face-width helical gear meshing with two gears simultaneously. This study proposes a novel method for dual lead-crowning for helical gears with long face-widths using a CNC internal gear honing machine. The anti-twist tooth modification is carried out by controlling the swivel angle and the rotation angle of work gear. Dual lead-crowning with different crowning amounts for different tooth proportions, anti-twist tooth modification and tooth contact analysis (TCA) are presented in the numerical examples to demonstrate the validity and advantages of the proposed method.