# Brake Torque Sensor Calibration Device
## 4 Calibration Equipment Models
### Design with a Calibration Wheel  
In previous designs, errors introduced by friction from rolling bearings, problematic settings of the measuring assembly, and relatively complex construction affected the calibration process; thus, it was necessary to eliminate these influencing factors. For this reason, a design solution was proposed, where a set of calibrated weights was used as a standard and the occurrence of rolling bearings was removed. This design, which is shown in Figure 8, minimized the influence of external factors affecting the calibration results and simplified the construction of the entire device, which resulted in a reduction of the total weight. Significant advantages include easy handling, good securing of the position of the calibration device on the measuring device, and reliable clamping of the sensor in this calibration device. The advantage of this device is that it can be used for all torque sensors used in the measuring laboratory. By using a calibration wheel with a given radius, it was ensured that after the steel strip with the weight carriers was established, the system was able to stabilize itself in an equilibrium position. This calibration device works on the principle of creating a moment of force according to the following relationship:  
\[M=F\cdot r=m\cdot g\cdot r \tag{9}\]  
where  
\(M\) denotes the force moment [Nm]. \(F\) denotes the force induced by the calibration weight [N]. \(r\) denotes the length of the arm on which the force F acts [m]. \(m\) denotes the weight of the weight [kg]. \(g\) denotes the local gravity acceleration [m/s\({}^{2}\)]. Figure 7: Design of the calibration device with weight carriers. The calibration device with a calibration wheel works on the principle of creating a torque \(M\) [Nm]. A force \(F\) [N] acts on the calibration wheel with the radius \(r\) [m] representing the arm. This force F is induced using a set of calibration weights m, whose value is recalculated and determined in newtons based on the local gravity acceleration \(g\) [m/s\({}^{2}\)]. The force, \(F\), induced by means of weights, acts on the arm (radius of the calibration wheel) and creates the required torque, which is necessary for the calibration of the torque sensors. The device is designed in such a way that it is possible to induce a moment of force in both the right and left directions of rotation. When designing the selected device, its load during operation was also taken into account. For this reason, the steel strip was determined as the weakest member of the system. This strip serves as a connecting member between the calibration wheel and the weight carriers and also as a holder for the weight carriers themselves. From this point of view, it was necessary to verify this steel strip for its maximum load. Verification was performed on a Zwick/Roell Z030 test rig. The condition for compliance was that the used steel strip with a thickness of \(h=0.07\) mm could withstand a load of at least \(F=80\) N. After the test was completed, it was found that the beginning of the deformation occurred at a force of \(F=362.3\) N, which in the case of the calibration device is satisfactory. Even a certain degree of oversizing was achieved. Based on a comparison of the advantages and disadvantages with the previous three proposals of calibration devices, which are listed in Table 4, variant 4 (with a calibration wheel) was shown to be the most suitable solution; therefore, the next part of this paper is devoted to its use for the calibration of the torque sensor. \begin{table}
\begin{tabular}{l l l} \hline
**Variant of Calibration Device** & **Advantages** & **Disadvantages** \\ \hline \hline
1. Threaded rod & The possibility of simple clamping on the measuring table. & More time-consuming setting of the torque value using a threaded rod and it was problematic to set the torque sensor with the standard on one axis. Bearings that would cause resistance during calibration. \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparison of designed calibration devices.