Quality assurance with vibration measurements

Quality assurance of harvesters

Usually, a device starts making noises or shaking once some rotating or moving part of it is worn out. Vibration measurement may reveal an incipient failure and need for servicing before the planned annual maintenance. This allows the failure to be accessed before the device starts to malfunction, ceases to function altogether or even breaks down more seriously.

Vibration is not as straight-forward to be measured as temperature, as vibrations come in various forms. Within vibration measurements, all products are in effect unique measurement targets within vibration measurements. The machines have usually got several actuators. So also several measuring points are needed. Possibly exceptional phenomena can be noticed by monitoring the signal alterations within the vibration measurements.

Vibration measurement system improves the quality assurance within the assembly of Sampo-Rosenlew harvesters. Faulty parts are exposed at the factory, before delivering the harvester to the customer. This avoids the need for warranty repairs during the most urgent time, when the harvesters are at work in the field. Harvesters are tested at the factory after their assembly. Each harvester is run within the hall from half an hour to an hour. This ensures that everything functions correctly and that there are for instance no leakages. At the same time, all controls and settings of the harvester are inspected.

Sampo-Rosenlew wanted to test whether vibration measurements could be used for detecting possibly faulty parts during the test run phase. Sensors were attached into four parts, usually close to some shaft bearing. Using frequency spectrums calculated from the measurements it is easy to see within which frequencies the vibrations appear. The vibrations are often multiples of the engine’s RPM value. In order to get comparable results, the test runs are always carried out using constant RPMs.

The system has been in operation for several years. Enough material has been accumulated to see what is normal and what kind of exceptions there may occur. The computer software used in the analysis automatically alarms if vibration exists within unexpected frequency range; or if the existing vibration within a particular frequency range is clearly exceptionally intense. Vibration frequency spectrums are saved into the system, together with all other harvester-specific material. The material can easily be found afterwards, in case there is need to compare the current status with the status right after assembly.

Etteplan defined the correct analysing methods for Sampo-Rosenlew, delivered the necessary hardware and software and trained their personnel. Today, the assurance is done by company’s own personnel. Each harvester coming out from the assembly line is tested and measured using this system.

Building a measurement system calls for experience

Correct accelerometers need to be selected for each system, as their qualities have significant impacts on the test results. The selection depends on the estimated intensity and frequency range of the vibration. The price of the accelerometers is also affected by their accuracy, performance and resilience for environmental conditions. This may prove to be essential, if accelerometers are to be needed in large quantities. It is important to remember that monitoring based on vibration measurements cannot be bought from a shop as a package wrapped inside cellophane. You see, there are no two similar objects for it, and each project needs to be implemented individually. A vibration measurement system can be fully exploited only after collecting sufficient amount of data. Comprehensive material shows us normal value ranges and enables definition of alarm limits.

Anyone interested in measuring vibration can easily start doing it with National Instruments equipment. A high-quality vibration sensor by Piezotronics, combined with an NI9234 measurement module is a good package, and high-performance NI Sound&Vibration toolkit software provides you with everything needed for carrying out the measurements and analysing the results (image below).

Huge amounts of measurement data can easily obtained. Fortunately, a Sound&Vibration toolkit provides excellent tools for analyzing the data. In the beginning, it is essential to find the frequency ranges which contain the interesting phenomena in as large amplitude deviations as possible. However, this is just where the actual work begins. ”Usually, our goal is to automatically detect the essential phenomena in the vibration measurements. Developing reliable automation requires good source data, development of algorithms and lots of testing”, says Jouko Perkkiö, SW designer behind the algorithms. ”Especially, detecting various phenomena taking place in the time domain may be very difficult”, Perkkiö continues.

The person carrying out the measurements needs to choose the place for the sensor. He/she needs also to take care of fastening the sensor in a way adequate for requirements set by the amplitude and frequency of the vibration. Also desired measurement conditions need to be created, which usually means running the machine or device in a comparable way.