Torben Ole Andersen

Development of a high-performance magnetic gear

This paper presents calculation and measurement results of a high-performance permanent-magnetic gear. The analyzed permanent-magnetic gear has a gear ratio of 5.5 and is able to deliver 27 N/spl middot/m. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analyzed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 N/spl middot/m reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears has shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally, it is concluded that the results in this paper may help to initiate a shift from mechanical gears to magnetic gears.

Development of a high performance magnetic gear

This paper presents calculation and measurement results of a high-performance permanent-magnetic gear. The analyzed permanent-magnetic gear has a gear ratio of 5.5 and is able to deliver 27 N/spl middot/m. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analyzed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 N/spl middot/m reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears has shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally, it is concluded that the results in this paper may help to initiate a shift from mechanical gears to magnetic gears.This paper presents calculation and measurement results of a high performance permanent magnetic gear. The analysed permanent magnetic gear has a gear ratio of 5.5 and is able to deliver 27 Nm. The analysis has shown that special attention needs to be paid to the system where the gear is to be installed because of a low natural torsion spring constant. The analysed gear was also constructed in practice in order to validate the analysis and predict the efficiency. The measured torque from the magnetic gear was only 16 Nm reduced by the large end-effects. A systematic analysis of the loss components in the magnetic gear is also performed in order to figure out why the efficiency for the actual construction was only 81%. A large magnetic loss component originated in the bearings, where an unplanned extra bearing was necessary due to mechanical problems. Without the losses of magnetic origin in the bearings and less end-effects caused by relatively short stack, an impressive efficiency estimated at 96% can be obtained. Comparison with classical mechanical gears have shown that the magnetic gear has a better efficiency and a comparable torque per volume density. Finally it is concluded that the result in this paper may help to initiate a shift from mechanical gears to magnetic gears.

Two dimensional model of a permanent magnet spur gear

This paper extends an analysis method developed for a radial magnetized spur gear. The extension describes how a parallel magnetized spur gear can be modeled analytically. The analytical method for a parallel magnetized gear is verified with the finite element method, which showed good agreements. The results with the parallel magnetized are also compared with results from the previous developed analytical method for radial magnetized gear, and the parallel magnetized version turned out to give a better performance. A test model was also built to verify the theoretical calculations.

Modelling of a special class of spherical parallel manipulators with euler parameters

A method of workspace modelling for spherical parallel manipulators (SPMs) of symmetrical architecture is developed by virtue of Euler parameters in the paper. The adoption of Euler parameters in the expression of spatial rotations of SPMs helps not only to eliminate the possible singularity in the rotation matrix, but also to formulate all equations in polynomials, which are more easily manipulated. Moreover, a homogeneous workspace can be obtained with Euler parameters for the SPMs, which facilitates the evaluation of dexterity. In this work, the problem of workspace modelling and analysis is formulated in terms of Euler parameters. An equation dealing with boundary surfaces is derived and branches of boundary surface are identified. Evaluation of dexterity is explored to quantitatively describe the capability of a manipulator to attain orientations. The singularity identification is also addressed. Examples are included to demonstrate the application of the proposed method.

Analysis of discrete pressure level systems for Wave Energy Converters

Within the research field of harvesting the energy of ocean waves, fluid power has been identified as a crucial technology in the Power Take-Off (PTO) design, due to the high torque densities required in Wave Energy Converters (WECs). The PTO is the technology converting the captured wave motion into electricity. However, conventional fluid power systems are characterized by offering poor efficiencies, rendering current PTO designs inefficient. This paper investigates the feasibility of a fluid power system based on implementing the force control of hydraulic cylinders by switching between a few fixed system pressures. The proposed design is optimized at multiple levels, as evaluating the feasibility of a solution highly depends on finding the optimum trade-off between e.g. harvested wave energy and losses in the PTO system.

Robust Non-Chattering Observer Based Sliding Control Concept for Electro-Hydraulic Drives

Abstract This paper presents an observer-based sliding mode control concept with chattering reduction, generally applicable for position tracking control of electro-hydraulic valve-cylinder drives (VCDs). The proposed control concept requires only common data sheet information and no knowledge on load characteristics. Furthermore the proposed scheme only employ ***piston-and valve spool positions- and pressure feedback, commonly available in industry. The main target is to overcome problems with linear controllers deteriorating performance due to the inherent nonlinear nature of such systems, without requiring extensive knowledge on system parameters nor advanced control theory. In order to accomplish this task, an integral sliding mode controller designed for the control derivative employing state observation is proposed, based on a generalized reduced order model structure of a VCD with unmatched valve flow- and cylinder asymmetries. It is shown that limited attention can be given to bounds on parameter estimates, that chattering is reduced and the number of tuning parameters is reduced to the level seen in conventional PID schemes. Furthermore, simulation results demonstrate a high level of robustness when subjected to strong perturbations in supply pressure and coulomb friction force, and that tracking accuracy may be reduced to the level of noise. Furthermore, the proposed controller tolerates significant noise levels, while still remaining stable and accurate.

Design of energy efficient SMISMO-ELS control strategies

Traditionally mechanical linked meter-in and meterout spool valves are used for velocity control of hydraulic differential cylinders. However with the demand for energy efficient systems the individual meter-in and meter-out valves draws massive attention. This paper propose an energy efficient actuator control and combines this with energy efficient system control. Finally energy neutral performance improvments are suggested for the subjacent actuator in an ELS system.

Comparison of Methods for Modeling a Hydraulic Loader Crane With Flexible Translational Links

When modeling flexible robots and structures for control purposes, most often the assumed modes (AMs) method is used to describe the deformation in combination with a floating reference frame formulation. This typically has the benefit of obtaining a low-order, but accurate model of the flexible structure, if the number of modes and AMs are properly chosen. The basis for using this method is, however, that the vibrations (deflections) are time and position independent, i.e., the expression is separable in space and time. This holds for the classic Euler–Bernoulli beam equation, but essentially does not hold for translational links. Hence, special care has to be taken when including flexible translational links. In the current paper, different methods for modeling a hydraulic loader crane with a telescopic arm are investigated and compared using both the finite segment (FS) and AMs method. The translational links are approximated by a single beam, respectively, multiple beam elements, with both one and two modes and using different mode shapes. The models are all validated against experimental data and the comparison is made for different operating scenarios. Based on the results, it is found that in most cases a single beam, low mode order approximation is sufficient to accurately model the mechanical structure and this yields similar results as the FS method.

Optimum design of seat region in valves suitable for digital displacement machines

Digital displacement fluid power is an upcoming technology setting new standards for the achievable efficiency in variable displacement fluid power pumps and motors. In the present work, an annular seat valve suitable for use in digital displacement units is considered, and the valve geometry is optimised considering both the mechanical strength during pressure loading and fluid flow restriction in the open valve state. Material stresses are modelled using finite element (FE) analysis including non-linear material behaviour, contact elements and fluid pressure penetrating load, closely reflecting the actual load of the seat valve connected to a fluid pressure chamber. Valve pressure losses are modelled using computational fluid dynamics (CFD). On basis of an overall physical size requirement and material specification, optimum valve geometry and stroke length are given as function of a defined normalised flow coefficient directly related to the machine efficiency.

On Application of Second Order Sliding Mode Control to Electro-Hydraulic Systems

This paper discusses the application of second order mode controls to hydraulic valve-cylinder drives with a special focus on the limitations resulting from nonlinear dynamic effects in flow control valves. Second order sliding mode algorithms appear highly attractive in the successive implementation of sliding mode control, achieving continuous control inputs, while maintaining the main properties of sliding modes. Under certain model assumptions, some of these controllers may even be applied as output feedback controllers. However, intrinsic nonlinear dynamic effects of hydraulic valves such as slew rates and time delays arising in the amplification stages, limits the applicability of such methods, and may lead to partial losses of robustness and limit cycles. These properties are analyzed and experimentally verified, and compensation methods are proposed. The application of the second order sliding algorithm known as the super twisting controller is considered for output feedback control and compared with conventional first order sliding mode control. The controllers under consideration are applied for position tracking control of a hydraulic valve-cylinder drive exhibiting strong variations in inertia- and gravitational loads. Results demonstrate that the super twisting algorithm may be successfully applied for output feedback control of hydraulic valve-cylinder drives, with modifications guaranteeing robust control performance in a small vicinity of the control target.© 2014 ASME