## 4 Prototype for Experimental Evaluation
### Conceptual Design  
The essential concept of the prototype is based on a mold/die clamping mechanism with adjustable mechanical error(s), and whose operating performance can be detected by installed sensors. Figure 10 shows the computer-aided design (CAD) model of the conceptual design results, in which, the prototype used for mechanical error detection mainly consists of a nine-link type mold/die clamping mechanism driven by a ballscrew linear table. The theoretical geometric parameters of the mold/die clamping mechanism are identical to those for the presented case study (as listed in Table 1), which are approximately one-third sizes of the clamping system of a real die casting machine. Hence, the mold/die clamping mechanism shown in Figure 10 is designed as a desktop hardware model. The ballscrew linear table, instead of a hydraulic cylinder, is thus alternatively applied to drive the mold/die clamping mechanism because of its high positional precision. It can also be noted in Figure 10a that one of the link members in the mold/die clamping mechanism, i.e., link 8 referring to Figures 4 and 5, is a so-called \"length adjustable link member\" used for adjusting the mechanical error \(\Delta\)r\({}_{8}\) (i.e., the length error of link 8). Figure 11 shows the explosive view of the CAD model of the length adjustable link member, in which, this link member mainly consists of a left-half sub member, a right-half sub member, and a compound screw. Two clamping shaft collars attached to each sub member are used to clamp two attached linear shafts, respectively. The compound screw with both left and right hand threads is assembled between the left-half and right-half sub members to form  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**IT Grade** & \(\delta\mathbf{L_{\text{wor}}}\) **(mm)** & \(\delta\mathbf{L_{\text{rss}}}\) **(mm)** \\ \hline
6 & 0.089 & 0.062 \\
7 & 0.142 & 0.099 \\
8 & 0.218 & 0.153 \\
9 & 0.352 & 0.246 \\
10 & 0.566 & 0.396 \\
11 & 0.890 & 0.623 \\
12 & 1.416 & 0.991 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Values of the evaluation indices at the toggle position with respect to the specified ISO tolerance grades.  
Figure 9: Variation trends of the evaluation indices at the toggle position with respect to the specified ISO tolerance grades.  
two helical pairs, respectively. The rotational axis of the compound screw is parallel to the two linear shafts. When the compound screw is driven (while the clamping shaft collars are loosened), the two sub members will move together along the rotational axis of the screw in opposite directions, and the length (i.e., the mechanical error) of this link member can thus be fine adjusted. When the mechanical error is fine adjusted to a preferred magnitude, the clamping shaft collars are then fastened to fix the length of this link member. Through such a design concept, a mold/die clamping mechanism with adjustable mechanical error(s) can be realized.  
Subsequently, in order to quantitatively detect the operating performance of the mold/die clamping mechanism, two sensors are installed in the prototype, as illustrated in Figure 10b. An optical linear encoder is installed between the output link (the moving platen) and the base plate (of the frame) of the mechanism, which is used to detect the resultant output position caused by mechanical errors. Further, a load cell is installed between the input link of the mechanism and the moving stage of the ballscrew linear table, which is used to detect the required input force for driving the entire mechanism. Therefore, the quantitative influence of mechanical errors on the operating performance of a mold/die clamping mechanism could be evaluated through the presented prototype.  
Figure 10: The CAD model of the conceptual design of the prototype used for mechanical error detection: (**a**) perspective view and (**b**) front view.