Neural-Network Application for Mechanical Variables Estimation of a Two-Mass Drive System

This paper deals with the application of neural networks (NNs) to the mechanical state estimation of the drive system with elastic joint. The torsional vibrations of the two-mass system are damped using the control structure with additional feedbacks from the torsional torque and the load-side speed. These feedbacks signals are obtained using NN estimators. The learning procedure of the NNs is described, and the influence of the input vector size to the accuracy of the state-variable estimation is investigated. The neural estimators of the torsional torque and the load machine speed are tested with open-loop and closed-loop control structures. The simulation results are confirmed by laboratory experiments     

Performance Improvement of Industrial Drives With Mechanical Elasticity Using Nonlinear Adaptive Kalman Filter

This paper deals with the application of the adaptive control structure for torsional vibration suppression in the drive system with an elastic coupling. The proportional-integral speed controller and gain factors of two additional feedback loops, from the shaft torque and load side speed, are tuned on-line according to the changeable load side inertia. This parameter, as well as other mechanical variables of the drive system (load side speed, torsional and load torques), are estimated with the use of the developed nonlinear extended Kalman filter (NEKF). The initial values of the Kalman filter covariance matrices are set using the genetic algorithm. Then, to ensure the smallest state and parameter estimation errors, the on-line adaptation law for the chosen element of the state covariance matrix of the NEKF is proposed. The described control strategy is tested in an open and a closed-loop control structure. The simulation results are confirmed by laboratory experiments.     

High-performance adaptive robust control with balanced torque allocation for the over-actuated cutter-head driving system in tunnel boring machine

The tunnel boring machine(TBM) is a kind of large-scale underground equipment for the tunnel and subway excavations. The cutter-head driving system is one of the key components in hard rock TBM, which is driven by multiple motors to provide enough torque during the excavation. Synchronizing motions of the multiple driving motors and balancing the driving torques are two essential control issues to be addressed of cutter-head driving system. However, the existing synchronization control approaches usually focus on the pure motion synchronization of the multiple driving motors only. These methods will lead to the phenomena of uneven driving torques even when their motions are quite well synchronized, and may result in the shaft broken accident. Instead in this paper, an adaptive robust control law integrated with torque allocation technique scheme is proposed that achieves not only better motion synchronization of the driving motors but also simultaneous regulation of driving torques. Namely, the adaptive robust control (ARC) is introduced to deal with the negative effects from uncertainties and variable load acting on the cutter-head. And a torque allocation algorithm is proposed to distribute the driving torque of each motor evenly. Comparative simulations are carried out to verify the excellent performance of the proposed scheme.     

Multimotor electronic line shafts for rotary offset printingpresses: a revolution in printing machine techniques

In rotary offset printing presses, mechanical line shafts are being replaced by electronic shafts which consist of synchronized position and speed-controlled AC motors driving the complete printing units or single printing cylinders. The dynamic stiffness of the multimotor system to satisfy the requirements of high printing accuracy can be achieved by high-dynamic, cascaded current, speed and position control of the the drives, which can be combined with disturbance observers in critical cases, or by direct drive technology     

Kalman filter and LQ based speed controller for torsional vibrationsuppression in a 2-mass motor drive system

In this paper, a high-performance speed control for torsional vibration suppression in a 2-mass motor drive system, like a rolling mill which has a long shaft and large loadside mass or a robot arm which has flexible coupling, was studied. The speed control method which has better control response than a typical one in command following, torsional vibration suppression, disturbance rejection, and robustness to parameter variation, was proposed. The performance of command following, torsional vibration suppression, and robustness to parameter variation was satisfied by using a Kalman filter and LQ based speed control with an integrator. Also, disturbance rejection performance was improved through load torque compensation. Through various experiments of a real 22 kW field oriented controlled AC motor drive system having 2-mass mechanical system, the characteristics of the proposed speed controller and typical PI speed controller were compared and analyzed     

Torsional Vibration Assessment Using Induction Machine Electromagnetic Torque Estimation

Mechanical anomalies such as load troubles, great torque dynamic variations, and torsional oscillations result in the shaft fatigue of electrical machine and other mechanical parts such as bearings and gearboxes. Particularly, the torsional vibration may attain a significant level at resonant frequencies which damage or cause additional lifetime consumption of mechanical parts. In this way, this paper proposes a noninvasive technique through the electromagnetic torque estimation of driving induction machine as a mean of mechanical torsional stresses monitoring. The lubrication loss is considered as a gear failure to demonstrate its influence on the vibration and on the electromagnetic estimated torque signatures. Then, it is shown that the information in the electromagnetic torque can be decomposed into high- and low-frequency bandwidths which are associated to induction machine and gearbox mechanical-related frequencies, respectively. A setup based on a 5.5-kW three-phase squirrel-cage induction motor connected to a 4-kW wound-rotor induction generator via a one-stage gearbox has been used to validate the proposed method in both stationary and nonstationary conditions.     

Measurement and control of torque ripple-induced frame torsional vibration in a surface mount permanent magnet machine

A sensor to measure the stator torsional vibration due to torque ripple produced by a surface mount permanent magnet machine is first described. The sensor is relatively inexpensive and is straight forward to incorporate into a drive system. Experiments are performed to validate that the voltage produced by the sensor is linearly related to torque ripple amplitude. Closed-loop controllers are then described that adjust the stator current harmonics applied to the machine to achieve a commanded average torque while mitigating measured torsional vibration. Simulation and experimental results are used to demonstrate the effectiveness of the control techniques.     

Utilization of a piezoelectric polymer to sense harmonics of electromagnetic torque

In this paper, the use of a piezoelectric polymer material to measure the harmonics of electromagnetic torque produced by a permanent magnet synchronous machine is described. The advantages of the polymer include low cost, durability, and flexibility. In addition, wide-bandwidth sensors are relatively easy to design and couple to drive system hardware for harmonic evaluation or to use in feedback-based control. To illustrate the use of the polymer, the electrical and mechanical properties of three sensors are described. The results of time-domain simulation and hardware experiments are used to validate that the voltage obtained from the sensors is linearly related to the torque ripple produced by the machine.     

Force oscillations in contact motion of industrial robots: anexperimental investigation

Describes the results of research on the oscillatory behavior that has been systematically experienced in the force measured during contact motion of an industrial robot. Two phenomena have been found to be mainly responsible for it, namely, the arm structural elasticity due to the torsional flexibility of the joints and the torque ripple of the brushless motors. The structural elasticity is characterized by a resonance frequency which varies with the arm configuration, while the torque ripple has harmonics of frequency proportional to the motor velocity. Most severe oscillations, and even loss of the contact, arise when the resonance and ripple frequency values come closer or match, so that elasticity and ripple excite each other     

Sensorless load angle control for two-phase hybrid stepper motors

The widely used full-step open-loop stepping motor drive algorithms are characterised by a low torque/power ratio, large torque ripple and resonance problems. In order to use stepping motors in more demanding applications, closed-loop control is needed. In this paper, a previously described load angle estimation algorithm, solely based on voltage and current measurements, is used to provide the necessary feedback without using a mechanical position sensor. This paper introduces a novel closed-loop load angle controller which optimises the current level based on the estimated load angle. This approach is challenging as the current - load angle dynamics are highly nonlinear. However, in this research a linear model is proposed and used to tune a PI load angle controller. The controller reduces the current level to obtain the optimal load angle but does not change the way stepping-motor are driven by step command pulses. This results in a broad industrial employability of these algorithms. The proposed sensorless controller is validated trough both simulations and measurements.     

Independent field-oriented control of two split-phase induction motors from a single six-phase inverter

Split-phase (six-phase) induction motor stator windings consist of two sets of three phase windings, which are spatially phase separated by 30 electrical degrees. Due to mutual cancellation of the air gap flux for all the 6n/spl plusmn/1 (n=1,3,5...) order harmonic voltages, called zero sequence components, large harmonic currents are generated in the stator phases. Only the 12n/spl plusmn/1 (n=0,1,2,3...)-order harmonic voltage components contribute toward the air gap flux and electromagnetic torque production in the machine. In this paper, a novel scheme is proposed where two six-phase induction motors are connected in series with proper phase sequence so that the zero sequence component voltages of one machine act as torque and flux producing components for the other. Thus, the two six-phase motors can be independently controlled from a single six-phase inverter. A vector control scheme for the dual motor drive is developed and experimentally verified in this paper.     

双电动机拖动系统调速装置控制方式的选择

介绍了在铸造吊主起升机构上使用变频器驱动的双电动机拖动系统在运行中存在的问题,通过对比分析,经速度环带转矩差补偿的主从控制方式在非刚性连接的双电动机拖动系统中的应用效果优于传统主从控制方式。     

A novel bearingless interior permanent magnet slice motor driven blood pump

A 2-pole bearingless interior permanent magnet (IPM) motor with slice rotor configuration is presented in this paper. A novel IPM rotor is designed considering direct and indirect operational specifications such as force constant, torque constant, axial/radial stiffness and cogging torque. Cogging torque and its resulting vibrations affect motor and levitation operation significantly. Hence, various rotor configurations are simulated using the finite element method to develop a topology that minimizes these phenomena. The final topology is tested for closed-loop levitation and speed control. The motor is also tested for its intended application as a blood pump. A mock circulatory loop is developed to measure the performance of the pump. The simulation results, experimental control system performance and pump performance results are shown and explained in the paper.     

Damping a hybrid stepping motor with estimated position and velocity

It is well known that microstepping reduces the resonance behavior of stepping motors since the rotor moves in a sequence of very small steps. However, the under-damped nature of the motor does not change. In this paper, a scheme that uses microstepping and closed loop position control to stabilize and reduce resonance damping of the motor is proposed. The motor currents are controlled in a frame rotating synchronously with the excitation frequency. The d-axis current provides the torque to oppose the external load, and the q-axis current provides the transient torque to damp the motor. The motor velocity and position are estimated via an observer that tracks the angle of the motor back EMF voltage. The response of the closed loop system is independent of the external load level. Both simulation and experimental results have shown that the proposed control scheme is very effective in damping out the resonance of microstepping-controlled motors.     

A torque estimator using online tuning grey fuzzy PID for applications to torque-sensorless control of DC motors

DC motors are used indispensably in industrial applications because they provide such advantages as small size, high speed, low construction cost, and safe operation. A major area of research in DC motors is to determine a better method to measure the torque of motor shaft. The traditional way to measure the mechanical torque of a rotating shaft is attachment a torque transducer in the transmission system between the driving motor and the load. However, this technique requires additional parts for the transmission system, which makes the design more complicated, time consuming, costly in construction, and in many cases impossible to achieve.The purpose of this paper is to present a new method for estimating the load torque of a DC motor shaft by using a novel modelling method based on an adaptive control technique, named as online tuning grey fuzzy PID (OTGFPID). A test rig using a DC motor is setup to investigate the torque behaviour as well as to evaluate the developed estimator. Firstly, mathematical model is developed for the motor. Secondly, the experimental speed-torque data and the optimized motor model is used to optimize the torque estimator. Then the optimized estimator is used to estimate accurately the load torque. Finally, the capability of the optimized torque estimator has been validated with the practical experiments in comparison with a typical estimation method.     

Theoretical modelling and experimental identification of nonlinear torsional behaviour in harmonic drives

The demand for accurate and reliable positioning in industrial applications, especially in robotics and high-precusion machines, has led to the increased use of harmonic drives. The unique performance features of harmonic drives, such as high reduction ratio and high torque capacity in a compact geometry, justify their widespread application. However, nonlinear torsional compliance and friction are the most fundamental problems in these components, manifesting themselves as a combination of stiffening spring together with hysteresis at reversal points. Accurate modelling of the static and dynamic behaviour is expected to improve the performance of the system.This paper offers a model for torsional compliance of harmonic drives. A statistical measure of variation is defined, by which the reliability of the estimated parameters for different operating conditions, as well as the accuracy and integrity of the proposed model, are quantified. The model performance is assessed by simulation to verify the experimental results.Two test setups have been developed and built, which are employed to evaluate experimentally the behaviour of the system. Each setup comprises a different type of harmonic drive, namely the high load torque and the low load torque harmonic drive. The results show an accurate match between the simulation torque obtained from the identified model and the measured torque from the experiment, which indicates the reliability of the proposed model.     

Novel switching techniques for reducing the speed ripple of AC drives with direct torque control

The main theme of this paper is to present novel switching techniques, which insert zero-voltage vectors and/or more nonzero-voltage vectors to the conventional switching table, for AC drives with direct torque control. For the same sampling frequency of a drive controller, the proposed techniques are quite effective in reducing the torque pulsation and the speed ripples of the motors, as demonstrated in several experimental results. Moreover, the experimental confirmations have been made not only on an induction machine but also on a permanent-magnet synchronous machine.     

Minimum torque ripple, maximum efficiency excitation of brushlesspermanent magnet motors

Permanent magnet motors are usually driven in one of two ways. Sinusoidal currents are applied when the motor has a sinusoidal back EMF, and rectangular currents are applied when the back EMF has a trapezoidal shape. If implemented perfectly, each of these drive schemes is capable of producing ripple-free torque, which is desirable in many applications. However, in reality, permanent magnet motors never exhibit perfectly sinusoidal or trapezoidal back EMFs. Moreover, the power electronics used to drive the motor often has limitations that keep it from producing the required current waveform, especially as speed or load torque increases. In addition to these limitations, a permanent magnet motor often exhibits parasitic cogging torque that directly contributes to torque ripple. This work explores the relationships between motor current and back EMF, and identifies minimum torque ripple, maximum efficiency current excitations that can be implemented with finite bandwidth power electronics (current controlled VSI)     

Probabilistic voltage harmonic analysis of direct torque controlled induction motor drives

In high frequency motor-drives such as direct torque controlled (DTC) induction motor drives, the motor harmonic loss, and electromagnetic interference are largely affected by the spectrum of the motor input voltage. Nonlinear elements in the control loop of DTC drive make harmonic analysis of the drive very complex compared to classical pulsewidth modulated controlled drives. In this paper, a probabilistic method to study the harmonic contents of voltage in DTC of induction motors is presented. The DTC voltage chain is simulated with a random process. Then, the autocorrelation function of voltage vectors is calculated and its power spectrum density is obtained. The effect of flux and torque hysteresis controller bands, machine parameters, and inverter dc-link voltage on the motor voltage spectrum is investigated. Major harmonics in the DTC voltage spectrum are specified and their behaviors are described. Simulation and experimental results are presented to justify the theoretical analysis.