Due to time constraints (project duration only 15 months), it was decided to test smaller ball screws because smaller dimensions mean a lower maximum load and also a shorter lifetime. This also ensured that the demonstration was financially economical, as compared to larger ball screws, there are lower costs both for the purchase of the ball screws themselves and for the design and construction of the demonstrator, which can be sized for the lower load. After consultation with the manufacturer, KSK Precise Motion, Inc., a 20 mm diameter ball screw was selected. At the same time, a load cycle was designed by the manufacturer. For an axial load force of 4000 N, 1000 rpm, and a symmetrical test cycle, a lifetime of approximately 720 h was calculated. The test cycle was programmed according to the manufacturer's design. First, the ball screw under test is loaded with torque from the servomotor, with the braking servomotor holding the ball screw nuts in the same position. Once the desired load is achieved, the braking servomotor adjusts the braking torque so that the connecting plate will move to the other side of the demonstrator at the given acceleration and speed. Here, the orientation of the load torque is changed on the drive motor (e.g. from 3.185 Nm to - 3.185 Nm), and when this is reached, the braking motor is used to perform a backward movement.

As already mentioned, at the end of the service life, the nut loses tension and backlash occurs. The nut preload cannot be measured directly - when converting the preload force to pressure in the spacer ring, the pressure value was found to be too small and not within the measurable range of any sensors (e.g. strain gauges). However, the preload is related to the ball screw stiffness, which can be measured indirectly, as well as the clearance (or positioning accuracy). Based on previous experience, it was decided to use primarily vibration analysis, supplemented by information from temperature sensors and motors (torque). Ultrasonic sensors are currently a less explored area and were only developed during the project. Conversely, microphones were not used at all, as they work on the same principle as vibration analysis (sound is vibration in the air), but due to the high environmental disturbance, they will warn of impending end-of-life much later. Tribometers were not used because of the complexity of measurement and evaluation - the ball screws were lubricated with grease, not oil. Although the number of sensors used is high (11 sensors in total), in practice this number is not necessary. When monitoring the lifetime of a ball screw in real operation, it is sufficient to use two accelerometers in the radial direction, measuring in mutually perpendicular directions (similar to those on the demonstrator ball screw nut). The other accelerometers on the bearing houses were used as additional measurements in a case bearing degradation and failure occurred. In that case, the largest increase in vibration will be on these accelerometers. Capacitive position sensors are not needed in actual operation, because with predictive maintenance algorithms, we will be able to determine the condition of the ball screw using vibration. There is no need for temperature sensors because, as we already know, deterioration of the CS will be reflected in the vibration signal long before the temperature increase that occurs at the very end of the lifetime