## 3 Results and Discussion
### Results of the Optimisation of the CPM Mechanism Links
#### 3.3.2 Results of Optimising Link 4 of the CPM Main Positioner  
The same methodology was used to optimise link 4 using Generative Design techniques as was used to generate the structures for link 3. The mass of link 4 before optimisation after inflicting AL 6061 material was 0.89385 kg. Strength tests in the Creo Parametric programme showed that the von Mises stress for primary link 4 was 255.53 MPa, and displacement was 5.87 mm. The high value of displacement analogous to link 3 is due to the failure to take into account the stiffness of the shaft connecting links 3 to 4, which in a real-world solution provides adequate stiffness to the connection in kinematic pair 3-4. The above results will be the baseline to which we will refer to the results obtained from the new structures generated. The results of the optimisation of link 4 of the positioner mechanism are summarised in Tables 7-9. The results distinguish between the generated structures by the material used. The number of finite elements used in the numerical study was 23,011. A single finite element had a size of 0.003353 m. When using the AL 6061 material, the most favourable result was obtained after optimising the Generative Design at a limit volume of 30%. The final object \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Parameter** & **Limit Volume 20\%** & **Limit Volume 30\%** & **Limit Volume 40\%** & **Limit Volume 50\%** \\ \hline Starting mass, [kg] & & 2.35 & & \\ Valid value, [\%] & 14.2 & 25.1 & 36.5 & 49.3 \\ \hline \multicolumn{5}{c}{Parameters of link 4 after Generative Design optimisation} \\ \hline Displacement, [mm] & 4.0465 & 4.049 & 2.245 & 1.44 \\ Von Mises Stress, [MPa] & 318.18 & 201.21 & 202.60 & 203.03 \\ Final mass, [kg] & 0.3330 & 0.5900 & 0.8570 & 1.1550 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Results of Generative Design optimisation of link 4—material AL 6061. \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Parameter** & **Limit Volume 20\%** & **Limit Volume 30\%** & **Limit Volume 40\%** & **Limit Volume 50\%** \\ \hline Starting mass, [kg] & & 1.561 & \\ Valid value, [\%] & 14.2 & 25.3 & 35.9 & 49.2 \\ \hline \multicolumn{5}{c}{Parameters of link 4 after Generative Design optimisation} \\ \hline Displacement, [mm] & 4.4611 & 5.14 & 3.24 & 2.21 \\ Von Mises Stress, [MPa] & 240.42 & 201.80 & 202.49 & 202.97 \\ Final mass, [kg] & 0.2210 & 0.3950 & 0.5600 & 0.7690 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Results of Generative Design optimisation of link 4—material MG-AL-ZN ALLOY. mass was 0.59 kg. A better displacement value was also obtained relative to the original design, as it was 4.049 mm, relative to the original 5.87 mm. The von Mises stress for the tested structure was 201.21 MPa, giving a reduction from its initial pre-optimisation value of 255.53 MPa. An even greater reduction in mass is obtained for a limit volume value of 20%, although in this case, the von Mises stress after testing was as high as 318.18 MPa, despite a similar displacement value to the optimisation at a limit volume of 30%; hence, this result was rejected. Results above the 30% volume limit were discarded due to the mass of the objects obtained, which would not translate into a reduction in the value of the actuator torques in the CPM positioner design studied. When MG-AL-ZN ALLOY material was used to generate the structures, the most favourable result was obtained after optimisation at a limit volume of 50%. Although the mass of the object was not significantly reduced compared to the original solution, at 0.7690 kg (0.12458 kg less than the original), this solution was selected for its lowest displacement parameter value of 2.21 mm. It is worth noting that the von Mises stress values do not differ significantly when different volume limits are chosen. Thus, the factor of choosing the best solution mainly concerned the lowest mass, with a minimum displacement value.