## 2 Materials and Methods
### The Principle of Sampling Working Lubricants for Contamination Analysis Purposes  
In order to obtain relevant information about the condition and quality of the lubricant, it is essential to ensure proper sampling. The validity and accuracy of the tribotechnical analysis results are directly dependent on the quality of the sample collected. A sample can only be obtained by following basic sampling principles, and the sample intended for tribotechnical diagnostics must meet the following requirements:  
* The lubricant sample must be taken from a representative part of the robotic system, specifically, from each gear mechanism (joint), with the sample being taken from the individual positions on the test rig in this case.
* The lubricant sampling is performed at low speeds of the gear reducer and under operational temperature conditions to ensure sufficient homogeneity of the sample.
* During sampling, it is crucial to prevent contamination of the lubricant by any foreign substances or impurities.
* The sample must always be taken from the same location and in the same manner to ensure the repeatability and comparability of the analysis results.
* Care must be taken to maintain the cleanliness of the surrounding area of the sampling point in order to eliminate the risk of secondary contamination of the sample.  
Contaminants in the form of mechanical particles or resinous components tend to settle and form sediments. In the case of improper sampling procedures, a non-homogeneous sample may be obtained, which does not represent the actual condition of the lubricant in the gear mechanism. For the purposes of our analysis, a portable analytical kit designed for lubricant sampling was used.  
The portable analytical kit developed is designed for on-site lubricant condition monitoring, enabling rapid and reliable detection of contamination levels. Key features include the following:  
* Compact design, suitable for industrial environments and easy handling during field sampling.
* Multi-parameter sensing capability, allowing for simultaneous measurement of contamination particles, viscosity, and temperature of the lubricant.
* Integration of optical and electronic sensors, providing real-time data on particle counts and fluid cleanliness according to ISO 4406 standards.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Type of System/Application** & **Recommended Cleanliness Class** \\
**Environment/Components Used** & **According to ISO 4406** \\ \hline Pumps/drives & \\  • Axial piston pumps & 18/16/13 \\  • Radial piston pumps & 19/17/13 \\  • Gear pumps & 20/18/15 \\  • Vane pumps & 19/17/14 \\ \hline Valves & \\  • Direct acting valves & 20/18/15 \\  • Pressure relief valves & 19/17/14 \\  • Flow control valves & 19/17/14 \\  • Safety valves & 20/18/15 \\  • Proportional valves & 18/16/13 \\  • Servo-driven valves & 16/14/11 \\ \hline \hline \end{tabular}
\end{table}
Table 2: _Cont._User-friendly interface with automated data acquisition and wireless data transmission to a central monitoring system.
* Low power consumption and rechargeable battery, ensuring extended operation times without frequent recharging.
* Modular design, allowing for customization and future expansion with additional sensing modules tailored to specific lubrication conditions.
* This device supports proactive maintenance by enabling immediate detection of lubricant degradation or contamination, reducing downtime and preventing damage to gear components.