Defective sensors: Finding the cause with the MSR165 acceleration data logger
Author: Fabian Acklin, TSH-1 Saddle Stitcher Technology, Mechanical Engineer Müller Martini Druckverarbeitungs-Systeme AG
During the product development of a new saddle stitcher for magazines, Muller Martini, a globally active company in the field of print finishing machines, discovered that sensors were failing. Small MSR acceleration data loggers were used to track down the cause of the fault.
The faulty components in the three-knife trimmer for the new saddle stitcher were edge sensors that detect the position of the products immediately before the cut. They had previously worked faultlessly, but had now failed during the test phase at the customer's premises. Analysis of the defective sensors revealed mechanical damage in the sensor element.
Vibrations were suspected to be the cause of the damage. However, as there were many different possible causes for this problem due to the very dynamic movement sequences in the machine, ways were sought to record the vibrations present at the sensor. The aim of the measurements was to determine the possible sources of the faults as precisely as possible in order to draw the right conclusions. The measures implemented were also to be quickly checked for their effectiveness.
After a brief internet search, online configuration on the MSR website and a telephone conversation with the consultant there, the miniature data logger from the MSR165 series was defined as a suitable measuring device.
Troubleshooting: miniature data logger for shock and vibration
The MSR165 data logger for shock and vibration is capable of performing 1600 measurements per second for up to five years. Its core sensor element is a high-resolution 3-axis digital accelerometer. It is ideal for vibration measurements and shock monitoring, for example for transportation monitoring, fault diagnosis and load tests.
Shock monitoring is possible with the MSR165 up to ±15 g or ±200 g, 32 measured values are recorded before the event. The logger's memory capacity of over two million measured values is sufficient to record over 10,000 shocks - even over very long periods of time if necessary. Using a microSD card, the capacity can even be increased to over 1 billion measured values (10,000,000 shocks). All data can be quickly transferred to a computer via USB or microSD card. The MSR165 comes with PC software for configuring and evaluating the data as well as the MSR ShockViewer software. The powerful evaluation software is used for advanced analysis and graphical display of the data recorded in shock mode as well as automatic report generation.
Measurements and results of the tests
The data logger was attached to the affected sensor of the new machine using double-sided adhesive tape (Fig. 2). During operation, accelerations of up to 218 g were measured in the x-axis (Fig. 3). In comparative measurements with the data logger on the old machine (Fig. 4), the results showed acceleration of only around 35 g (Fig. 5). This explains why the sensors on the new machine were damaged.
By switching off individual subsystems, it was quickly established that the massive accelerations were caused by the pneumatic stops. These stops were now analyzed in more detail and all differences were listed.
Figure 2
Figure 3
Figure 4
Picture 5
The cause of the fault was quickly eliminated
The hose length between the valve and the stop made the difference. With the same hose length as on the old machine, the accelerations are now again of a comparable order of magnitude. At the same time, the sensor manufacturer optimized the sensor for the relatively high accelerations that were still present. Since then, no sensor has failed.
Conclusion
The cause of the sensor failure on the new machine could not have been found within one working day without the data loggers. This shows that these loggers are an optimal and, above all, time-saving aid for fault diagnosis in the event of mechanical problems with shocks, vibrations and accelerations on machine elements.