## 3 Application of the Design Approach to the Definition of the Innovative Test Rig
### Design of the General System ('Test Rig')
#### 3.2.1 Conceptualization of the Mechanism(s) for Operating the System (\(\rightarrow\) Step 1.c)
Moreover, in some of these solutions (Figure 12) there is also an additional link (AD), namely the 'platform support-frame', which is an intermediate structure supporting both semi-platforms and responsible for their global inclination. The additional links of Figure 13 which form an articulated parallelogram have been introduced to have a link (BD) connected to the same revolute pair of link BC (the upper semi-platform) and to keep the horizontal position at every inclination of AB, thus constituting a close reference for the inclination of BC. In schemes 2L.b-e, 3L.b-f, 4L.b-f there is at least one component that is controlled in its inclination and one (or none) supported only in a single point. By referring to the schematics of beams, the so-called 'unsupported length' is equal to a semi-platform length in scheme 2L.b, 4L.b, 4L.e-f, but can reach the entire extension of the platform as the sum of the two semi-platforms' lengths (2L.c-e, 3L.c-f), or it can be equal to the additional component length (3L.b, 3L.e, 3L.f) or articulated parallelogram side (4L.c-f). In particular, in schemes 2L.b, 2L.e, 3L.b, 3L.e-f, 4L.b, and 4L.e-f there are components that behave like a cantilever beam. Therefore, all these solutions are more likely to suffer from problems of elastic oscillations and perhaps even resonance caused by the vehicle travelling on the semi-platforms, as described by different Euler buckling modes. For the described reasons, solutions acting on the position of the end points of the links (2L.a, 3L.a, 4L.a) should be preferred. Figure 11: Side schemes of the platform (the \(y\)-axis is vertical) with different possibilities for operating a system with two links. Red straight vectors represent a control of the position of a point (or a control of the relative distance of a point from a reference); blue curved vectors represent a control of the angular between two links (segments AB and BC represent the semi-platforms in all the schemes). Note that in the pictures **2L.a, 2L.b, 2L.c,** and **2L.d** the distances of the points (B and/or C) are typically taken from the ground, but alternatives are possible: e.g., from a vertical reference, as represented within brackets in pictures **2L.a, 2L.c,** and **2L.d. ** Scheme 2L.e represents a situation in which the configuration of the platform is controlled by acting directly on the links inclination. In schemes 2L.a, 2L.d and 4L.a-f, if the two semi-platforms have to be inclined whilst remaining aligned, points A, B, and C should be aligned. This means that both the actuators (whichever they are) have to be operated simultaneously and with proper synchronization. This adds a further (mechanical) complication to the operation of the platform, underlining also that the dofs of global inclination and angulation are not fully independent, and that the actuator controlling the position of B acts on the inclination of both semi-platforms. According to the general design principles enunciated before (functional analysis and functional decomposition), it is convenient to keep the functions of overall inclination and angulation of the two semi-platforms separate, opting for a solution that provides for a separate actuation systems. Indeed, the scheme 3L.a does not suffer from the alignment problems of AB and BC thanks to the presence of the support frame AD. The schemes of Figures 11 and 12 have another problem: if the inclination of the lower semi-platform AB (or rather, the vertical position of B) is changed, the inclination of the upper semi-platform BC is also changed. Given the impossibility of independently controlling the inclination of the two semi-platforms with these schemes except by applying more complex schemes (e.g., using an articulated parallelogram as in Figure 13), and considering the advantages of the support frame with the aim of avoiding too much long 'unsupported length', and not increasing the complexity of the linkage, scheme 3L.a should be considered as the most suitable.