Understanding Dynamics for Production Control through Vibration Testing on Vacuum Cleaner Motors

Long service life and acoustics are quality criteria which are vital to consumers, especially in daily-use household appliances. All vacuum cleaner motors by Vorwerk are subject to final testing during production for this reason. The test is performed by utilizing three laser vibrometers, which calculate the vibrations at three characteristic locations.

A PASS/FAIL decision is made based on a comparison between measured spectra and reference spectra. To gather viable results in production and to reduce false rejects, it is crucial to locate suitable measurement points. The motors which have already been optimized in the development phase concerning their vibration behavior are measured using a 3D Scanning Vibrometer to optimize the testing process.

Figure 1. Operational deflection shape.

Figure 2. RoboVib^® Test Station.

The measuring system establishes and visualizes the operational deflection shape (Fig. 1). The suitable test points can then be identified based on this. It was decided that a series of nine motors would be measured to take into account variations between motors.

The RoboVib^® Structural Test Station (Fig. 2) seemed to be especially well-suited for this task since the vibration profile was to be established around the whole periphery in addition to the axial direction on the motor’s front side.

As the motors are geometrically identical, the robot program, geometry, and other settings only need to be adjusted once so all of the motors can be tested with the same settings. This results in low cost and high reproducibility in particular (Fig. 3). Vorwerk can now define suitable measurement points for the 100% final testing of motors by using this measurement data.

Measurement Sequence

A robot program is defined after assembly and positioning of the motors that are inserted in a mounting. This program includes several robot positions, from which it is possible to reach all surfaces or points to be measured using the vibrometer lasers (Fig. 4). The mounting was designed so that a quick changeover and identical positioning was possible, as numerous motors were going to be measured sequentially.

Figure 3. Vibration measurement on a vacuum cleaner motor.

Figure 4. Measurement beam of the laser vibrometer.

The geometry of the motor is measured at the designated measurement points once the robot program is defined. To accomplish this, the robot moves to each measuring position. To attain high accuracy with this relatively small measurement object (80 mm diameter), the function "VideoTriangulation^®" is utilized.

This function is employed to optimize geometric measurement and beam superposition. The laser positions on the measurement object are optimized so that all three of the laser beams are perfectly superimposed before the measurement begins at the first scanning point. The 3D coordinates are then established using triangulation and updated in the geometry.

The vibration measurement results in addition to the geometry are available for all measured points after scanning the surface from each robot position. The geometry data are then imported for each of the other motors.

Clear Increase in Efficiency

As the measurement is so easily repeatable, it was possible to completely measure 12 motors within three days instead of the planned series of 9 motors. Without robot support, high-resolution measurement during the development phase would have taken a full two days for one motor alone, including the preparation work. In this instance, RoboVib^® supplied a clear increase in inefficiency.

By utilizing this measurement data, Vorwerk can now establish suitable measurement points for the complete final testing of motors. As discussed, Vorwerk’s quality control test stands also employ laser vibrometers so that the motors may be inspected and classified in a contact-free way.

Summary

To undertake a meaningful 100% check of vibration parameters, it is crucial to possess precise knowledge of the overall vibration behavior of a component and any error indicators in the vibration spectrum.

The contact-free measurement approach outlined in this article is extremely efficient, both for the test stand and for the identification of measurement points. Taking into consideration the scatter, the qualification of a series of parts is particularly time-efficient when utilizing the automated RoboVib^® technique and can be attained with high reproducibility.

The system is required to undergo just one learning procedure to supply high-resolution operating vibration shapes for the entire series. The result of the process is high-quality vacuum cleaner motors and so many satisfied customers.

This information has been sourced, reviewed and adapted from materials provided by Polytec.

For more information on this source, please visit Polytec.