Resource-efficient ball screw by adaptive lubrication

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In period 1 of the sub-project of the Priority Program 1551 it was illustrated, that the achievable lifetime and thus the resource efficiency of ball screws can be significantly increased by an adaptive lubrication, for constant operating conditions. Current results suggest that lifetime increases of 50% and more are possible. However, the operation of ball screws in industrial practice is characterized by periods of thermal and tribological changes because of varying conditions. This also leads to a change of ball screw friction torque and temperature, which were taken as indicators for a demand of lubricant in period 1. Due to the interaction of these effects, the exclusive monitoring of these command variables for an adaptive lubrication during operation with dynamically changing operating parameters is not sufficient.The aim of the second period of the project is now to enable an adaptive lubrication and the increase of lifetime, which was already proven for static operating conditions, in the case of dynamically changing operating conditions, too.The approach for this is the enhancement of the lubrication algorithm from period 1. Core of the algorithm is the ball screw friction model. This will be enhanced in the following period of the project, to enable the consideration of the superimposed effects on the ball screw`s friction torque and the temperature associated with the dynamic conditions. As input to the enhanced ball screw friction-model a database is used in which the actual and previous values of revolution, load and temperature were recorded and stored lifelong. The output variables of the enhanced friction model are the expected friction torque and temperature.In the enhanced lubrication algorithm the decision on a possible lubrication process is carried out in two steps. In the first step the measured values are compared to the calculated values by the enhanced friction-model. In case of excessive measured values in the second step of the algorithm the decision will be taken based on the ball screw lubrication documentation. In the documentation all previous lubrication processes were logged with information regarding time and quantity.The result of the project is an enhanced lubrication algorithm that allows an adaptive lubrication of ball screws in the case of dynamically modified operating parameters and thus the resource efficiency of ball screws is increased because of a significantly longer lifetime and a decrease in the average lubricant demand and lower power consumption of the electric drives by reduced friction.