Combined rolling and plain bearings for rotary bearings and linear guides (EFB 10/108)

Combined rolling and plain bearings for rotary bearings and linear guides (EFB 10/108)

 

Motivation

The use of plain bearings in servo presses is critical. Servo presses are characterized by the controllability of the position and the speed of the ram. In the control system of the press, however, plain bearings act as dead time elements, and due to the undefined position of the bearing shaft in the bearing shell lead to uncertainties in the control system. In addition, the operating conditions for plain bearings as a pivot bearing, for example, during the pendulum stroke are extremely unfavorable. Frequent change of direction leads to the permanent collapse of the bearing lubricating film and thus to increased wear. Rolling bearings are not affected by these problems, but do not have the required load capacity and good damping characteristics of plain bearings. A possible approach to solve this problem, is the combination of rolling and plain bearings. In the range of lower load the rolling bearings take the load and prevent contact of the bearing shaft and the plain bearing bush. With increasing load, the rolling elements deform elastically, whereby an eccentricity of the bearing shaft is formed and the plain bearing begins to take the higher loads. Thus, this novel bearing element combines the positive properties of plain and rolling bearings.

Comparison of bearing behaviours
Figure 1: Comparison of bearing behaviours | Source: Scheitza, Matthias ; Schmitt, Sebastian O. ; Emde, Stefan : Potential and challenges of combined roller and plain bearings for servo presses. In: Advanced Materials Research, 769 pp. 285-292.
Combined roller and plain bearing
Figure 2: Combined roller and plain bearing

Aim

The aim of this project is to gain first insights into the properties of the new bearing elements. An important feature of the interpretation for use in presses is the bearing stiffness. Therefore a suitable test bench hast to be developed that allows to analyze the bearing under a defined test load and to take relevant measures.

Methodical approach

An Existing test bench is expanded to initiate an oscillating pivoting movement in the combined roller bearings with a defined swivel angle and regulated peripheral speed. The bearing is loaded in the test bench with a variable test load. Eddy current sensors, which are incorporated into the plain bearing component take the shaft to shift in the micron range. From the bearing displacement and the test force acting eventually the bearing stiffness can be determined.

Expanded testbench
Figure 3: Expanded testbench

Acknowledgment

The research project is funded by the German Federation of Industrial Research Associations (AiF).