Abstract
Ball screw mechanisms are commonly designed and adopted to work for a high number of cycles, so that one of their most relevant characteristics is mechanical endurance. State-of-art experimental setups designed to characterize these mechanisms under operational load conditions require a layout able to withstand high loads and a relevant power to actuate the ball screw, therefore, being rather complex and expensive. To overcome these issues, this paper proposes an innovative test bench exploiting the recirculating power principle, designed for testing a ball screw under operational loads. It enables (at the same time) a reduction of loads on the test rig frame and a reduction of the mechanical power required to actuate the screw. The concept and the design of the proposed test bench are presented, as well as a simplified model to calculate the motor torque and the forces transmitted at the supports. An experimental setup is then realized and tested under actual loads for endurance tests. The results show that the use of the recirculating principle is promising to realize a test rig for endurance tests on a ball screw, thanks to the effectiveness of the solution and the simplicity of the realization of the system even under heavy loads. Among all the measuring instruments adopted (accelerometers, strain gauges, thermocouples and laser sensors for distance measurement on the test bench), the adoption of accelerometers on the nuts seems to be the most promising for condition monitoring, allowing to detect an incipient fault before a macroscopic failure of the ball screw system occurs.
Highlights
Ball screw mechanisms are widely used in a large number of applications in which high precision linear movements are required
To overcome the critical aspects highlighted in the previously mentioned test rigs, this paper proposes an innovative device with low mechanical power required to actuate the ball screw, enabling the reduction of the loads on the test rig frame at the same time
A 25-mm diameter ball screw is used in the prototyping phase for design convenience, even if the peculiarities of the described layout make it suitable for endurance tests of large size ball screws
Summary
Ball screw mechanisms are widely used in a large number of applications in which high precision linear movements are required They are commonly designed and adopted to work for a high number of cycles, so that one of their most relevant required characteristics is the endurance capability. The experimental investigation of ball screw behavior under operating conditions, and in particular the interaction between ball screw and nut, is significantly difficult since ball screws are closed systems. For this reason, several mathematical models have been developed in the course of time to better understand the mechanics of the above-mentioned items and to develop some tools able to quantify the parameters representing the system behavior. Levit [1,2] discussed the design rules and the calculations for assessing static load, fatigue life and axial rigidity of a ball screw, creating a reference frame for all the following developments
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