Determining the cause of incorrect work of bumper paint robot reducer

Abstract

Industrial robots are used for high-precision tasks and in intensive production. One of the most reliable methods for monitoring robots’ work is vibrodiagnostics, which provides recommendations and maintenance procedures, and also serves as a reliable diagnostic method for determining the causes of industrial robot failures. Connection of robot and the supporting structure is very important and it affects on dynamic behavior of the robot. This paper presents the process of diagnosing dynamic condition of the structure with painting robots, after the failure of the robot motion reducer. To analyze the causes of the failure, a numerical-experimental analysis was performed, which included: static calculation, dynamic calculation, determining transfer function in frequency domain and reinforcement factors and measuring accelerations. Supporting structure has very low eigen-frequencies (3,5 to 9.5 Hz), it cannot accept inertial forces and large deformations and resonant behavior occur. Using FEM analysis is shown that the behavior of the structure is unfavorable because 20 eigen-oscillations had a frequency less than 17 Hz, and all are located in the robots’ working space. Determination of the transfer functions showed that the dynamic gain factor in all three directions of the excitation force is extremely large, while the corresponding frequencies are 5 ÷ 20 Hz. As a part of the experimental analysis, accelerations and displacements at the robots’ locations were measured. Accelerations exceed the standard acceptable limit. It was determined that the main problem was the rigidity of the supporting structure and maintenance omissions observed during the visual inspection. Only a partial and relatively quick repair was done on the structure, and it significantly decreased displacements of most critical zones (robots).