2.3.3.2. Intermediate position. Starting the cut, a command is given for the cylinders to recede from the platform edge at the right position, resulting in the holder's tilt. Thousandths of a second later, the same order  is  given  to  the  cylinders  at  the  opposite  side.  The   cylinders

movement coordination is crucial in order to keep the holding system close to the strip cut point at each   moment.

2.3.3.3. Discharge position. After the strip has been cut, the two inner cylinders are driven to give as much tilt as possible, leading to the strip discharge operation.

2.3.3.4. Rest position. This position corresponds to the final stage of the cycle, being used as well when the sheet thickness exceeds 5 mm, since the pneumatic components are only designed to handle the structure and plates up to 5 mm thickness. It was considered necessary to implement a structure that allows optimizing the unit, making possible the cut for thicknesses higher than 5 mm. Therefore, it was decided to include two longitudinal reinforcements that absorb the impact loads of the strips exceeding 5 mm thickness dropping on the holder. Other established requirements are related to the very confined space to place the pneumatic cylinders and that components price should be as low as possible. After a long and careful market survey, the best options found are presented as  follows.

Fig. 3. Traditional defect (a) and high stress concentration (red zone) (b) (For interpretation of the references to color in this figure, the reader is referred to the web version of this article).

Fig. 4. Isometric view (a) and exploded view (b) of preliminary holder version.

2.3.4. Option 1 – conventional cylinders

These cylinders present as advantage the high perpendicular resistance to the axis loads, adjustable pneumatic damping and can be easily found in the market. However, to use this solution it is necessary to use a “Multi-Position Kit”. This kit will dock the two cylinders coaxially, allowing four possible positions: a fall-back position and three forward positions, as shown in Fig. 9. The great advantage of these cylinders is their  price.

2.3.5. Option 2 - servo-pneumatic  cylinders

This option satisfies the largest number of requirements initially drawn for this project. These cylinders have the particularity to ensure greater positioning accuracy and enable stopping in several positions along its path, contrary to conventional cylinders, which only allow the retreat and forward positions. These are standard cylinders with a positioning control, Fig. 10, which let a position accuracy of around   ±

0.2 mm [24], thus ensuring the exact positioning of the holder at the desired position. The position versatility that these cylinders can offer, allows an exact following of the holding system during cutting process independently of cutting angle and this is undoubtedly a huge advantage. However, this system has a drawback: their high acquisition cost. Therefore, solutions must be found that could meet the needs, taking into account the system and budgeting   constraints.

Regarding these two driving system possibilities, it is possible to have at least two different manufacturing options. Figs. 11 and 12 presents the general view of the different driving systems. Due to the longest length of the servo cylinders, their assembly needs to respect the maximum length available. Thus, their position had to be con- veniently studied to get the cylinder's holders into the space available (Fig.  11).  The  conventional  cylinders  have  a  lower  length,  allowing