Motor Bearing Fault Diagnosis in an Industrial Robot Under Complex Variable Speed Conditions

Motor bearing is the key vulnerable part of the servo motor in an industrial robot, which is always arranged at the joint that is the main load area. In the movement process of the robot, motor bearing bears a great impact due to the frequent movement of joints, which is easily damaged. The fault characteristic information of a bearing in these complex conditions shows strong non-stationary features. Early non-stationary fault signals are often weak and submerged in background noise. The non-stationary signal processing method using computed order analysis and the weak signal enhancement method using adaptive stochastic resonance both show good performances for the above problems. Inspired by these, a hybrid diagnosis strategy for motor bearing under these speed conditions is proposed. Firstly, the non-stationary fault signals of the motor bearing are transformed into stationary angular signals via computed order analysis. Then, the fault modes are identified via resonance demodulation and variational mode decomposition in the order spectrum. Finally, adaptive stochastic resonance is used to extract the fault features reflecting the bearing operation state. Two types of typical speed conditions are considered, which is representative at the joint. Numerical simulation analysis and experiments verify the effectiveness of the diagnosis method.