Tuomo Lindh

Diagnosis tool for motor condition monitoring

In the modern industrial environment there is increasing demand for automatic condition monitoring. With reliable condition monitoring, faults such as mechanical motor failures could be identified in their early stages and further damage to the system could be prevented. Successful monitoring is a complex and application-specific problem, but a generic tool would be useful in preliminary analysis of new signals and in verification of known theories. A generic condition diagnosis tool is introduced in this paper. The tool is based on discriminative energy functions which reveal discriminative frequency-domain regions where failures can be identified. The tool was applied to induction motor bearing fault detection and succeeded in finding characteristic frequencies which allow accurate detection of bearing faults.

A new approach to data transmission between an electric motor and an inverter

In electrical drives data transmission between a motor and an inverter is required due to sensors, installed at the motor, that are used in the motor diagnostics or controlling. Generally, the data transmission is carried out using additionally installed cabling, such as, twisted pairs. In this article a new method is proposed that provides an Ethernet based communication link between the electric motor and the inverter. The method uses a motor feeder cable as a media and power line communications (PLC) as a communication method. Laboratory measurements with the method are carried out and the results of the measurements are analyzed

Applicability of ZigBee technology to electric motor rotor measurements

The purpose of this work is to determine the applicability of the ZigBee technology to electric motor rotor measurements. Requirements for data transmission, electrical structure and powering of a sensor are discussed. A prototype wireless ZigBee-based torque sensor is built and tested. The results of the tests are analyzed

Chatter Detection in Turning Processes Using Coherence of Acceleration and Audio Signals

Chatter is an unfavorable phenomenon in turning operation causing poor surface quality. Active chatter elimination methods require the chatter to be detected before the control reacts. In this paper, a chatter detection method based on a coherence function of the acceleration of the tool in the x direction and an audio signal is proposed. The method was experimentally tested on longitudinal turning of a stock bar and facing of a hollow bar. The results show that the proposed method detects the chatter in an early stage and allows correcting control actions before the chatter influences the surface quality of the workpiece. The method is applicable both to facing and longitudinal turning.

Design considerations for current transformer based energy harvesting for electronics attached to electric motor

Energy harvesting or scavenging from environment is being researched intensively. The main motivation of the research is to develop a maintenance free energy source for ubiquitous electronics, such as wireless sensors or sensor networks. The on-line condition monitoring of electric motors requires also sensors that are installed at the motor. In this case, the energy required by sensors could be harvested from a magnetic field. In this article, current transformer based energy harvesting is considered. A switch-mode power supply utilizing current transformer is designed. It is tested in laboratory with the mains supply and variable speed drive. According to the tests carried out, the current transformer based power sources are a feasible alternative to supply the electronics attached to an electric motor.

Bearing damage detection based on statistical discrimination of stator current

In this study, a method is presented for discriminating stator current signals from two classes, motors in normal condition and ones with a bearing failure. The study has two main objectives, to verify the former results on the bearing fault detection based on the stator current, and to show the applicability of the proposed method for the diagnosis based on frequency content. The method is based on statistical analysis of Gabor filter responses. In the empirical part of this study where the method is applied to the real measurements, the results indicate that it is not possible to detect a bearing fault if the internal radial clearance of the bearing is not adequate.

Online Estimation of Linear Tooth Belt Drive System Parameters

Many control schemes rely on an analytical model of the servomechanism to be controlled, and hence, accurate knowledge about the position- and time-dependent parameter variability becomes crucial in many contexts, such as robust control methods. Although a properly designed robust controller can cope with a large parameter variation, real-time identification of the system parameter behavior could lead to several advantages by means of monitoring the varying dynamics, e.g., the predetermined uncertainty region around the nominal value. This paper addresses issues in online parameter estimation of a linear tooth belt drive with a limited stroke. Particular attention is paid to detecting the position-dependent changes in the system dynamics by using recursive least squares algorithm and exciting the system in different cart positions in order to identify the varying dynamics. The algorithm used is based on an indirect output-error identification scheme. The experimentally estimated parameters are compared with the corresponding two-mass model parameters. The results show an acceptable agreement and demonstrate the feasibility of the estimation method to estimate the parameters of a closed-loop controlled servomechanism with a limited stroke and time-varying parameters.

Estimation of the data transfer requirements of vibration and temperature measurements in induction motor condition monitoring

Continuous condition monitoring requires data transmission from the sensors to a higher level where the analyses and decisions are made. In this paper, the amounts of data produced by vibration and temperature measurements of the condition monitoring of induction machines are estimated. The effect of communication protocols to the data transmission capacity requirements is analysed

Online Identification of a Mechanical System in Frequency Domain Using Sliding DFT

A proper real-time system identification method is of great importance in order to acquire an analytical model that sufficiently represents the characteristics of the monitored system. While the use of different time-domain online identification techniques has been widely recognized as a powerful approach to system diagnostics, the frequency-domain identification techniques have primarily been considered for offline commissioning purposes. This paper addresses issues in the online frequency-domain identification of a mechanical system with varying dynamics; particular attention is paid to detect the changes in the system dynamics. A closed-loop online identification method is presented that is based on a sliding discrete Fourier transform at a selected set of frequencies. The method is experimentally validated by a closed-loop controlled servomechanism with a limited stroke and time-varying parameters.

Simulation model for input impedance of low voltage electric motor at frequency band 10 kHz-30 MHz

This paper concentrates on the input impedance of a low voltage electric motor at high signal frequencies. A series of impedance measurements is carried out for a group of induction motors. The measurements are analyzed and a simple measurement based model for the input impedance of the electric motor is formed. In addition, the effect of the rotor on the input impedance is researched. Finally, the effect of impedance mismatch at the interface of the motor and the cable is briefly analyzed.