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Data analysis in chatter suppression

Data analysis in chatter suppression

Traditionally, solutions to monitor and diagnose chatter required the use of large equipment and specialised staff, resulting in high costs.

The use of state-of-the-art data analysis technology makes it possible to develop user-friendly portable devices that record vibrations on machines and to process the information to identify the causes and provide adequate solutions.

Industrial companies increasingly require accurate, more economical and efficient equipment to produce parts to high quality standards; to achieve this goal it is of key importance to reduce machine chatter to a minimum.Chatter is one of the main problems in industry and has a significant impact on productivity levels caused by undesired behaviour of equipment that reduces the lifespan of both machines and tools. Until now, the use of large equipment and highly specialised staff was required for diagnosing the cause of chatter and developing solutions for its suppression, resulting in high costs.Data analysis and the use of cutting-edge technologies provide comprehensive and innovative solutions to a recurrent problem that poses a major burden on productivity.

Designing new platforms with a high potential for data acquisition and computation and which in turn are easy to use, is an effective approach to tackle problems arising from chatter. These are technologies for acquisition and processing of signals and that measure and analyse dynamic behaviour of machine tools, a key sector in industrial production and one of the epicentres of economic development in the Basque Country.Moreover, devices based on data analysis technologies also produce more intuitive and easy-to-use designs to allow operation of such devices even without much technical knowledge.

IK4-IDEKO's contributionThe technological centre IK4-IDEKO, leader in advanced manufacturing technology, has over 20 years experience in designing solutions to provide an effective response to chatter and has succeeded in identifying the key areas of analysis aimed at improving the dynamic behaviour of machines.Experts from the Elgoibar-based centre have managed to identify eight areas of diagnosis related to chatter generation on which to focus to improve efficiency of the equipment with an in-house developed portable device that records and processes vibrations on machines to diagnose their potential problems. IK4-IDEKO's knowledge and experience of the latest technologies applied in manufacturing have resulted in the design of a platform that quickly and efficiently tackles this widespread problem on machines with rotary motion.This ik-DAS development has eight different operating modules that adapt to the required functions and analyses the signal frequency and natural frequency of key components such as gears, bearings, drives and structural parts of the machinery.

The 8 vibration diagnosis and analysis areas are:

1. Signal acquisition and frequency analysis

This is a general application which collects and performs a frequency analysis of any signal obtained with a sensor to subsequently analyse possible chatter. It is possible to record patterns which serve as a reference for later check-ups and to observe the degradation of a system by means of comparison, so it really works as a predictive tool.  It can be used for analysis of the condition of a system and for monitoring through comparison with a stable condition.

2. Analysis of natural frequencies

Application to obtain natural frequencies and FRFs. In order to obtain this type of frequencies, it is only necessary to place an accelerometer on the part to analyse and to hit it (stimulus) lightly with any item. If you wish to obtain FRFs, apart from an accelerometer, a specially calibrated hammer is required to obtain the impulse response. FRFs are especially useful to obtain more information such as the rigidity of the system. Obtaining a natural frequency can be done quickly and easily.

3. Analysis of gears and bearings

Acquiring a signal with an accelerometer and knowledge of the characteristics of the items to analyse used to generate a model (number of balls, diameter, number of teeth ...), allow to check the status of the items and identify the sources of vibration problems. This function is especially useful in maintenance to facilitate an early prediction of problems.

4. Machine balancing

Dynamic and static balancing can be performed automatically with different procedures: the 4-run method with an accelerometer, and phase plane method with an accelerometer and a tachometer - indicating what compensation mass is required and where it should be placed, in diameter and angle, to balance rotating items on a machine. It is also interesting to monitor the imbalance of the machine on-line to check if possible misalignments caused by heating of the equipment are responsible for this imbalance.Static balancing should be used for large parts, inside the clamping area (chuck or table) using telemetry (wireless system, for example wifi). The above method would serve to find out whether the part is placed correctly on the machine in terms of weight distribution.

5. Oscilloscope

The purpose is to represent any electrical signal taken from a system that may be subject to change over time. For example, to obtain machine consumption over time, with the help of a wattmeter.

6.- Low frequency Data Logger

It is useful to have the option to simultaneously record data over time from multiple channels. Temperature is a variable that serves as an example; up to 5 temperature sensors may be used to record its variation over time. This information would help determine the stabilisation time of the machine. Very useful to obtain the first correct part in any manufacturing process.

7. Measuring Run-Up

With the help of an accelerometer, this application generates an online representation of the reaction of the resonance frequencies running at critical speeds. Thus a chart with the characteristics of the vibrations at different speeds is obtained. Behavioural observation allows to determine the critical (problematic) rotation speeds of a system.

8.- Monitoring of severity

This application in conjunction with an accelerometer serves to continuously observe on-line the vibration level of a turning motor. According to the chosen ISO standard, previously modelled, and with the signal already acquired, it can be shown in a graph whether the vibration level is optimal, normal, high or unacceptable. To that purpose, the measurement is performed by comparing the signals obtained with the standards for standardised elements (motors). Also, it is possible to create one's own company standards. This application is particularly useful for assemblers and maintenance personnel.