Fault Prediction For ATC Of A Disc-type Tool Changer Of Machining Center

The overall level of Computer Numerical Control(CNC) system, as the basis ofequipment manufacturing industry, determines one country’s manufacturing competitiveness.As one of the important indices for evaluation of CNC machine tool performance, reliabilityhas received the widespread attention. Though domestic machine tool industry developsrapidly, most of high-end CNC machine tools are imported. The main reasons are that, withlow reliability, MTBF of domestic CNC machine cannot reach the level of same kind CNCmachine tools from foreign companies. One of the important measures to improvingreliability of CNC machine tools is to enhance reliability of key functional units of CNCmachine tools, thus, it’s urgent to improve the key functional units of CNC.Much more attention is paid on ATC system of machining center, as one of the keyfunctional units of CNC, for its high fault occurrence rate, long maintenance cycle andexpensive maintenance costs. In this paper, based on the domestic ATC system of machiningcenter, set up reliability test bed for ATC system of machine center, and establish conditionmonitoring and fault prediction system for this reliability test bed. In addition, put forwardone method for fault prediction by analyzing peak characteristics of vibration signal, carryout experimental tests of several knife handle rivets by a case of rivet loosening fault, buildmathematical model of prediction threshold in this fault mode and it’s verified by tests, anddemonstrates that the fault prediction method is feasible.In this paper, the main research tasks are as follows:(1) Project design for reliability test bed of disc tool change system:Design the whole control system and establish upper and lower computer, electriccontrol system and software control scheme.(2) Project design for condition monitoring and fault prediction system of conditionmonitoring and fault prediction system: Based on the fault of disc tool change system happened in factory and laboratory, chooseseveral sensors specifically and establish PC, electric control system, software control anddata collection scheme.(3) Design for lower computer control system:Based on PLC, the function of normal operation of test bed and alarm of warning deviceare achieved. Firstly, design the main control circuit and the auxiliary one and design circuitof electrical components, temperature sensor, vibration sensor, data acquisition card andprogrammable controller. Then, select PLC and design its input and output circuits. Inaddition, compile PLC program. Thus, the lower computer control system is obtained.(4) Design for PC control system:PC control system includes program for normal operation of test bed and for real-timedata acquisition and condition monitoring, achieved mainly by Visual Basic interfaceprogram controlling PLC and data acquisition card.(5) Establish fault prediction threshold:Single variable method is used to carry out approximate fault experiment. Collectexperimental data, fit mathematical function between vibration signal amplitude peak andloose rivet quality and carry out experimental tests by this function. The function is:Y=-0.111X2+0.151X+51.28, and the failure warning threshold is51.28±1.3. The test showsthat fault prediction for rivet looseness fault by vibration signal is feasible.