# Spindle Bearing Preload Control Using NI MyRIO
## 6 MyRIO Application
As can be easily seen, a different value of the preload of its bearings may  
Figure 4: Diagram of the bearing arrangement of the model spindle with a vibration exciter: 1—GW-V20 type exciter from Data Physics Corporation (San Jose, CA, USA), 2—equivalent mass, 3—front support, 4—piezo actuators (three pieces) type PSt 150/40/10 from Piezomechanik GmbH (Munich, Germany), 5—rear support, F—preload force from the piezo actuators. be required for one machine spindle at a given moment of operation, hence the need for systems thanks to which this tension can be changed. During the design of the control application, the author assumed that the change in the initial voltage would be directly proportional to the amplitude of the front spindle tip vibrations. It was subjected to continuous monitoring using a non-contact distance sensor (IPPT PAN Warsaw design [20]). The sensor was attached to the base of the test stand between the substitute mass (grinding wheel) and the front bearing support. It measured the vibration movement of the shaft in the direction of the exciter. This arrangement allowed for free change of substitute masses and direct examination of the vibration movement of the spindle. The only disadvantage of this solution was that the sensor was placed 40 mm from the shaft end, which meant that the measured amplitude value could be slightly smaller than the amplitude of the substitute mass. However, this sensor arrangement was chosen deliberately because the substitute mass to which the exciter generating vibrations was attached was mounted on an additional bearing type 61903 from FAG. This bearing ensured free rotation of the shaft when the substitute mass did not rotate. However, it could also introduce disturbances in the vibration movement, which is why, in the author's opinion, measuring the vibration amplitude directly on the shaft is much more reliable. A diagram of the measurement system is shown in Figure 5.  
Active adjustment of the bearing preload from the software side was developed using the MyRIO 1900 device from National Instruments. A control and measurement application for the entire spindle system was developed in the LabVIEW program. The inputs of the measuring system were fed signals of the relative displacement of the bearing raceways and the signal of the amplitude of vibrations of the front spindle tip. The output of the system was used as a control signal for three piezo actuators that set the preload of the bearing system. Using the PID controller, this voltage was adjusted to the current operating conditions of the spindle system. The assumption was that when the system operates at the set rotational speed and the amplitude of vibrations of the spindle tip does not exceed 10 \(\upmu\)m, the control system does not take any action. When the threshold value is exceeded, the controller is to reduce the value of the vibration amplitude to below 10 \(\upmu\)m in the shortest possible time. Figure 6 shows a diagram of the connection of the test stand. Figure 5: Schematic diagram of forced vibration measurement using active preload regulation: 1—GW-V20 exciter from Data Physics Corporation (San Jose, CA, USA), 2—equivalent mass, 3—tested spindle, 4—non-contact displacement sensor (designed by IPPT PAN Warsaw [20]). The excitation through the exciter was selected in such a way that during 120 s the spindle system was excited by a random signal with an increasing excitation frequency in the range of 150-450 Hz. Based on model tests, it is known that for different equivalent masses there was a different natural vibration frequency. For such a selected excitation range, in each case the system worked temporarily with the resonance frequency. The application in the LabVIEW program is shown in Figure 7. It provided real-time monitoring of the relative position of the bearing raceways (1, 2, 6) and the vibration amplitude of the front spindle tip (7). It allowed for setting (3) and displaying (4) the selected spindle speed, and saving measurement results (5), by specifying the file saving path (9).