Multiaxis Loading Device for Reliability Tests of Machine Tools

Reliability of machine tools is critical to high- efficiency manufacturing, and the failure data of feeding systems are requisite to analyze the reliability. This paper presents a multiaxis loading device (MLD) to simulate loading condition of an operating feeding system of a machine tool in a real machining process; this could cause breakdowns of the system and collect failure data. The MLD was developed based on a six-degree-of-freedom (6-DOF) parallel mechanism, and its prototype was presented. Its kinematics was analyzed, and dynamic equations were established based on the principle of virtual work. A fuzzy proportional-integral-derivative controller was designed to build an explicit force control system, whose proportional and integral gain can be adjusted according to the errors between reference and actual forces; and a force and a velocity feedforward were integrated to improve the performance of the control system. Loading experiments were conducted on an experimental platform to validate the loading capacity of the MLD; the spindle of the platform was set to be stationary and driven to perform feeding motions with different dimensions. Results of the experiment with the stationary spindle indicate that the MLD can simultaneously provide a 3-DOF force and a 3-DOF moment with acceptable errors. Experiments with moving spindle illustrate that the MLD accomplished tracking a spindle that is executing a 3-DOF trajectory-unknown feeding motion and adding 3-DOF forces on the feeding system through the spindle. The actual output multiaxis forces have little hysteresis and errors less than 10%. Compared with the long-term machining to load the feeding system in traditional reliability tests of machine tools, the proposed MLD provides an efficient method to simulate the loading condition of the system with reduced testing costs.