A variable reluctance stepping microdynamometer

A magnetic variable reluctance stepping micromotor fabricated using LIGA processing is described which is integrated with an external planar coupled gear train and electromagnetic brake. Variable mechanical loading of the micromotor through the electrically controlled brake allows dynamometry measurements to be performed. All components are fabricated from electroplated 78 Permalloy. A planar gear coupling is achieved by using involute gear teeth as the salient elements in the rotor. The rotor used for testing has a pitch radius near 500 μm with 180 μm thickness and is complemented with a stator which provides for a step rotation of 2.4°. Coil windings are implemented with assembled spring clip coil forms with 400 turns of 50 AWG magnet wire. Improved coil efficiency is responsible for decreasing the minimum power required for rotor rotation to 52 micro Watts. Maximum speeds near 8000 rpm are achieved although stepping action is affected by stepping instabilities which are a function of excitation magnitude and frequency. Calibration of the electromagnetic brake is accomplished with static beam bending measurements and indicates a maximum peripheral rotor output force of 0.6 milliNewton corresponding to an output torque near 0.3 microNewton-meter. Dynamometry measurements indicate a maximum mechanical power output of 20 microWatts. This work was supported in part by the National Science Foundation under grant #ECS-9116566 and additionally by ARPA-DALP contract ONR N00014-93-1-0911. Beamline support at the Synchrotron Radiation Center in Madison, WI was provided by P. Mangat and was funded under the HI-MEMS Alliance TRP/ARPA Technology Development Agreement contract MDA972-94-3-0043. The Synchrotron Radiation Center is supported by the National Science Foundation under grant number DMR-88-21625. Work at Sandia National Laboratories is supported by the United States Department of Energy under contract DE-AC04-94AL85000.     

CADSTEP: Computer-aided design of variable reluctance stepping motors

This paper describes a computer program package, called CADSTEP, for designing variable reluctance stepping motors. The performance specifications like stepping angle, stepping rate, output torque, number of phases, switching sequence, and saturation flux density, etc. form the inputs to the program. The program computes and prints out the dimensions of the motor from which manufacturing drawings may be prepared and the motor manufactured. The program is based on the step-by-step design procedure which in turn, has evolved from the general theory of variable reluctance stepping motors. This is the first time that such computer aided design program for VR stepping motors is being reported. The flow-chart for the program is given.     

Design and simulation of an asymmetric variable reluctance stepping millimotor

A pancake-shaped step motor, which has a geometry with an axial dimension that is much smaller than the radius, was designed and built using a combination of conventional and LIGA-based fabrication methods. Preliminary open loop dynamic testing indicated that the motor rotated normally as designed, but some abnormal phenomena were also observed at certain input frequencies. A simple model was developed to simulate the dynamic behavior of the rotor. The simulation results match the trend of abnormal behavior observed in the test. They indicate that a reliable open-loop operation is feasible for a wide range of operating frequencies.We would like to acknowledge the fabrication, testing, and other assistance of A. A. Jojola, V. E. Lucero, B. G. Carlen, T. R. Christenson, W. D. Bonivert, M. A. Bankert, J. T. Hachman, D. R. Boehme, A. M. Morales and J. M. Hruby. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Dept. of Energy under Contract DE-AC04-94AL85000.     

A planar variable reluctance magnetic micromotor with fullyintegrated stator and coils

A fully functional electrically excited planar variable reluctance magnetic micromotor has been demonstrated on a silicon wafer. The motor uses a micromachined nickel-iron rotor and a fully integrated stator, in which a toroidal-meander type integrated inductive component is used for flux generations. To reduce the magnetic reluctance in the stator, a modified stator geometry was adopted which removes the yoke used in a conventional magnetic variable reluctance motor. Using polyimide as both an integral structural material as well as an electroplating mold, a 40-μm-thick nickel-iron rotor 500 μm in diameter was microassembled onto a fully integrated nickel-iron stator 120 μm in thickness. When 500 mA of current was applied to each stator, 12° of rotation (1 stroke in this motor) was observed. By applying three phase 200-mA current pulses to the stators, rotation of the rotor was observed. The speed and direction of the rotation could be adjusted by changing the frequency and phase firing order of the power supply, respectively. Continuous rotor rotation was observed at speeds up to 500 rpm; this speed limitation was solely due to the limitation of the maximum frequency of the controller used. The micromotor could be reproducibly started, stopped, reversed, and continuously rotated. The predicted torque for the fabricated micromotor at 500-mA driving current was calculated to be 3.3 nN-m     

Static and dynamic sliding mode control of variable reluctance motors

In this paper, static and a dynamic sliding mode control schemes are proposed for the speed control of a variable reluctance motor (VRM). The proposed controllers guarantee the asymptotic regulation of the speed of the motor to its desired value. Simulation results of the proposed controllers are given to illustrate the developed theory. In addition, the robustness of the proposed sliding mode controllers to changes in the parameters of the motor and to load disturbances is validated through simulation studies.     

Feedback linearizing and sliding mode control of a variable reluctance motor

Direct-drive connection of electric motors represents a suitable solution to friction and backlash problems introduced by mechanical reduction gears. Variable reluctance (VR) are a special type of switched reluctance motors whose construction is well suited for direct-drive connection. Although these motors are traditionally conceived as stepper motors, continuous motion can be obtained by implementing suitable closed-loop control in the drive. The authors' main aim is to design a high-performance robust controller for a VR motor intended for velocity trajectory tracking in robotics applications where continuous motion is required. A cascade controller structure (velocity-torque) is considered. In the design of the torque controller, both feedback linearizing and sliding mode techniques are considered. Feedback linearization performs slightly better in the ideal case, but under more realistic operating conditions the sliding mode controller demonstrates comparable or even better performance. A very simple but extremely robust velocity controller is designed using a dynamic sliding mode approach, ensuring robustness to large variations of load torque and inertia, typical of direct-drive robotics applications. A simulation experiment of the overall controller with the motor connected to a single link robotic arm shows very good tracking properties as well as insensitivity to large variations of load torque and inertia.     

A novel reluctance actuator employing an embedded ferromagnetic foil

In this paper we present a reluctance actuator which contains laser cut ferromagnetic structures for flux guidance made of Mumetal foil. By means of analytic calculations and numeric simulations it is shown that much higher magnetic forces are achievable by using the Mumetal foil compared to electroplated ferromagnetic alloys like nickel–iron. Furthermore, the processing of such foils and the integration of foil structures into the actuator are described.     

步进式加热炉步进装置的电气控制

加热炉在轧钢生产线中广泛应用,它是轧钢工艺的前部工序。步进装置的控制是加热炉电气控制中最为重要的一环。文章以北方某钢厂的2300mm热连轧生产线的节能型组合蓄热步进梁式板坯加热炉改造工程为例,阐述如何更为有效的对步进装置进行控制以满足高产、优质、低耗、节能和无公害及生产操作自动化程度高的工艺要求。     

A note on a norm-preserving continuous Galerkin time stepping scheme

In this note we shall devise a variable-order continuous Galerkin time stepping method which is especially geared towards norm-preserving dynamical systems. In addition, we will provide an a posteriori estimate for the \(L^\infty \)-error.     

一种开关磁阻电动机功率变换器故障诊断方法

针对现有开关磁阻电动机功率变换器故障诊断方法存在可靠性不高等问题,提出了一种新型的功率管故障诊断方法。该方法以不对称半桥型功率变换器主电路为研究对象,以常见的功率管开路和短路2种故障情况为诊断对象,通过比较母线电流估算值和实测值来判断故障,结合故障相绕组电流实现故障相的识别,必要时通过中断测试来确定故障点。选取电动机空载、低速度和高速度运行等较难实现故障诊断的工况进行了试验分析,结果表明,该方法均能完成故障类型的定性及故障点的准确定位。     

Extra stepping stone for testing

As the relatively young profession of software testing graduallymatures, certification is changing to keep up. ISEB has justupdated the content and structure of its practitioner leveland added a stepping stone to reach that standard, as HelenBoddy reports.     

Applications of the closed-loop stepping motor

This paper describes a bang-bang controller which, with a particular novel scheme of discrete-state variable instrumentation, operates the stepping motor as a digital servo. The near time-optimal servomechanism is designed on a second-order basis, and the rather coarse staircase approximation of the switching curve yields good results. All control circuits have been implemented with integrated circuit components. The entire package has been product tested in the field.     

Feedback linearizing control of switched reluctance motors

Motivated by technological advances in power electronics and signal processing, and by the interest in using direct drives for robot manipulators, we investigate the control problem of high-performance drives for switched reluctance motors (SRM's). SRM's are quite simple, low cost, and reliable motors as compared to the widely used dc motors. However, the SRM presents a coupled nonlinear multivariable control structure which calls for complex nonlinear control design in order to achieve high dynamic performances. We first develop a detailed nonlinear model which matches experimental data and establish an electronic commutation strategy. Then, on the basis of recent nonlinear control techniques, we design a state feedback control algorithm which compensates for all the nonlinearities and decouples the effect of stator phase currents in the torque production. The position dependent logic of the electronic commutator assigns control authority to one phase, which controls the motion, while the remaining phase currents are forced to decay to zero. Simulations for a direct drive, single link manipulator with the SRM are reported, which show the control performance of the algorithm we propose in nominal conditions and test its robustness versus the most critical parameter uncertainties of payload mass and stator resistance.     

A multiple electrostatic electrodes torsion micromirror device with linear stepping angle effect

Torsion micromirror devices that can achieve linear stepping angle effects play an important role in optical MEMS applications. However, traditional torsion micromirror devices driven by a single electrostatic electrode have difficulty meeting this requirement due to their nonlinear angle-voltage transfer characteristics. In this regard, the concept of a multiple-electrodecontrolled micromirror is proposed to eliminate this drawback. Through this novel design, linear stepping angles can be easily achieved by a set of linearly varied or constantly applied voltages. A simple mathematical model has been developed to predict the angle-voltage transfer characteristics of the proposed device and has been simulated with finite element simulations. The corresponding control strategies of this device, named the linear control strategy and the digital control strategy, are also proposed in this paper. The Cronos/MEMSCAP Multi-User MEMS Process (MUMPs) was used in conjunction with flip-chip bonding technology to fabricate the proposed torsion micromirror device. Experimental data indicates that the relative stepping angle error, between the fabricated device and the mathematical model, are within 5%.     

步进电机控制系统

步进电机是一种将脉冲信号转换为相应角位移的执行元件。它广泛应用于单片机控制系统。本文主要介绍了采用单片机80C196KC根据1－5V的控制信号来控制步进电机转角的一种方法，包括其硬件设计和软件设计。     

Self-sensing for electromagnetic actuators. Part I: A coupled reluctance network model approach

A self-sensing arrangement in active magnetic bearings (AMBs) comprises a single electromagnetic transducer to realize the actuation and sensing functions concurrently. Minimizing the number of sensing devices and associated interfacing directly reduces possible failure points, system costs, and system complexity. Currently, self-sensing performance is degraded due to problems such as magnetic cross-coupling, eddy currents, saturation, and high losses. This first paper in a two part series presents an integrated model for self-sensing of an 8-pole heteropolar magnetic bearing. The proposed self-sensing approach addresses mechanisms that contribute to modelling error and uncertainty by using several techniques in an integrated structure. A coupled reluctance network model (RNM) is developed which models the coil impedance at the switching frequency. The accuracy of the model is improved by incorporating terms for air gap fringing, complex permeability, and magnetic material nonlinearity. The RNM is verified and refined through a process of iteration using finite element method (FEM) results and experimental AMB measurements. The results demonstrate that a RNM with only 40 nodes can achieve high levels of accuracy when compared to an 80 000 node FEM analysis.In Part II of the series, the refined RNM is incorporated into a multiple input multiple output (MIMO) parameter estimation self-sensing scheme.     

A variable compliance, soft gripper

Autonomous grasping is an important but challenging task and has therefore been intensively addressed by the robotics community. One of the important issues is the ability of the grasping device to accommodate varying object shapes in order to form a stable, multi-point grasp. Particularly in the human environment, where robots are faced with a vast set of objects varying in shape and size, a versatile grasping device is highly desirable. Solutions to this problem have often involved discrete continuum structures that typically comprise of compliant sections interconnected with mechanically rigid parts. Such devices require a more complex control and planning of the grasping action than intrinsically compliant structures which passively adapt to complex shapes objects. In this paper, we present a low-cost, soft cable-driven gripper, featuring no stiff sections, which is able to adapt to a wide range of objects due to its entirely soft structure. Its versatility is demonstrated in several experiments. In addition, we also show how its compliance can be passively varied to ensure a compliant but also stable and safe grasp.     

A variable step-size affine projection algorithm

In this paper, we propose a new time-varying step-size for the affine projection (AP) algorithm based on the minimization of the mean-square error (MSE) at each time instant. The step-size is dependent on accessible quantities and, therefore, does not need approximation. In addition, we show how the new step-size control equations can be incorporated into the fast AP (FAP) algorithm leading to a reduced complexity implementation of the proposed algorithm. The algorithm improved performance characteristics are verified by simulation experiments.     

Computers are stepping stones to improved imaging

Never before has the radiology industry embraced the computer with such enthusiasm. Graphics supercomputers as well as UNIX- and RISC-based computing platforms are turning up in every digital imaging modality and especially in systems designed to enhance and transmit images, says author Greg Freiherr on assignment for Computers in Healthcare at the Radiological Society of North America conference in Chicago.