PSI - Issue 42

Taško Maneski et al. / Procedia Structural Integrity 42 (2022) 1503–1511 T. Maneski at al/ Structural Integrity Procedia 00 (2019) 000 – 000

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1. Introduction Robots are used in numerous mechanical systems, primarily for high-precision tasks and in intensive production. Today, there are a wide range of robots of diverse powers and dimensions for various purposes, and these machines periodically repeat very complex movements [1]. Industrial robots are frequently used in painting processes. For this, extremely precisely planned robot movements with kinematic modeling and programming of the robotic arm are required [2]. Painting and lacquering processes are necessary in almost all factories that produce vehicles like airplanes, trains, and cars, furniture, and various other products; a standard painting robot is shown in Figure 1 [3]. Painting and lacquering processes can be very dangerous for human workers because the easily flammable air in paint shops is polluted with toxic, often carcinogenic compounds. Compared with using human labor, the application of automation in jobs of this type also contributes to better efficiency of production, higher quality workmanship, and significant material savings.

Figure 1. Painting robots

Figure 2. Support structure in the fender paint shop

Systems to monitor and maintain industrial robots must be implemented to achieve maximum reliability and usability of these machines. 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 [4]. Vibrodiagnostics is also a very important analytical tool for the operation of rotary machines [5]. In vibration analysis, the relevant parameters of vibration spectra in the time and frequency domains are defined and measured. In doing so, all regulations applied by the industry regarding the definition of vibration levels for the safe operation of any machine must always be observed. The regulations applicable to vibration analysis performed by industrial robots are defined by ISO 10816 (2372) Vibration Severity Standards [6]. These standards provide guidelines for estimating vibration strengths in machines operating in the range from 10 Hz to 200 Hz. Examples of these types of machines are small electric motors, pumps, compressors, and fans, which are all components of automatic painting and lacquering assemblies. The connection of these machines with the base, ie the support structure, is also very important. Vibrodiagnostics is very widespread because it is not invasive, it requires little investment, and it reliably detects and diagnoses faults. In [7], the basics of vibrodiagnostics are presented, and the basic parameters that are monitored according to the widely accepted ISO 10816 standard are defined. In this paper, the process of diagnosing the condition of the support structure that carries robots for painting and lacquering automobile fenders in the company Magneti Marelli, Serbia, is presented. The support structure in one part of the paint shop, where only fender painting occurs, is shown in Figure 2. The support structure consists of two parts. The first part is the main support structure with vertical columns and rotating bars (global construction), while the second part is the carriage substructure for supporting the robot (local construction). Painting robots are located under the central area of the support structure, while the fenders move along the edges of the support structure. The robots are supported on their undersides, and the schematic appearance of this assembly is shown in Figure 3. In the paint shop, the motion reducer in the gear-box of a fender painting robot failed. To determine the cause of the failure, relatively extensive theoretical and experimental analyses were undertaken, which included the following steps: static calculations to detect deformations in the support structure; dynamic calculations to determine the main forms of oscillation; determination of the gain of function in the frequency domain, i.e., determination of