# Spindle Bearing Preload Control Using NI MyRIO
## 6 MyRIO Application  
One of the most important elements of an efficient system using an active bearing support, apart from the correct mechanical and structural solution, is the appropriate selection and development of a control system. In this article, the author presents a new version of the control system used for data recording, generating the forcing signal and controlling the active support. The entire algorithm is based on the MyRIO 1900 platform from National Instruments. This system is described by the manufacturer as a system for learning and implementing various projects. It is equipped with 40 bilateral digital inputs/outputs, 10 analog inputs, six analog outputs, LED diodes, a built-in accelerometer, an FPGA system, and a dual-core ARM Cortex-A9 processor (ARM Limited, Cambridge, UK). It can be programmed using LabVIEW or C (v.18 or higher). All the system parameters can be found in the manufacturer's documentation [19]. The following principle was assumed during the design of the control system. Piezo actuators are designed to change or correct the preload of the bearings in the spindle system in real time so as to significantly change the stiffness of the system. This stiffness has a direct effect on the natural frequency of the spindle shaft vibrations. The current relative displacement of the bearing raceways in the active support as well as the vibration amplitude of the front end of the spindle will be provided as an input signal. Knowing the characteristics of the bearings used, the level of their preload can be determined based on the relative displacement of the bearing raceways. At the same time, it should be remembered that this procedure is burdened with several important issues that require a broader explanation. The model spindle is built from a shaft supported on single B7206-CT-PS4-UM bearings from FAG [18]. These bearings are arranged in an \"O\" configuration, which means that when the initial tension is exerted in one bearing (force F, Figure 4), it is automatically transferred to the other bearing, causing the same initial tension value in it. The bearing method for the described structure, together with the vibration exciter connection diagram, is shown in Figure 4.  
During the operation of such a system, e.g., due to changes in the operating temperature of the spindle, and mainly of the shaft itself (thermal expansion phenomenon), the initially set value of the preload changes, which changes the properties of the entire spindle. The full range of the preload of the bearings used in the spindle is in the range from 60 to 430 N (from light to heavy preload). By changing the value of preload, we significantly influence the change in the value of the natural vibration frequency of the system. Based on model tests using three different grinding-wheel models, it is known that the first three natural frequencies of the system are in the frequency range from 196 Hz to 2191 Hz. It should be remembered that the variable stiffness of the bearing supports can actively influence mainly the first form of the natural vibration of the system. The results presented in the article were developed for a numerical model with an average value of the preload of the bearings. For his own needs, the author also conducted tests for other values of the preload, but did not include them in the publication. This type of research with a different value of the preload bearing gave slightly different values of the frequency and amplitude of natural vibrations. Hence, the practical research used the excitation area of the tested system in the range of 150-450 Hz. This is mainly related to the change in the spindle stiffness. The higher the preload force, the higher the frequency of the natural vibrations of the system and vice versa. A lower preload force gives lower resistance to movement and allows to limit temperature gradients on the bearings, especially at high rotational speeds.