2.2. Approach

Fig. 4 shows the 3D model of the conceived platform, able to be assembled on the guillotine structure, which allows giving a real vision about what can be expected and embodies a good way to detect issues to be improved. The platform consists of a frame held by four pneumatic cylinders, in which a guidance system enables the structure to move up and down, as well as to lean, but always without performing horizontal movements that would result in hitting the guillotine's main frame.

The main goal of this device is to be compatible with the new guillotines in production and with most of the guillotines already on the market, allowing to easily adapt this device to   them.

2.3. Methodology

2.3.1. Dynamic holder

The dynamic holder will support the cut strip during the cutting process and the first design was a simple plate provided with reinforcement in the middle and square pipes on the top, but this structure showed to be very heavy to handle in maintenance operations and cylinders check, requiring the removal of the whole holding system for repairing and checking tasks (Fig. 5a). The modular  chassis includes two removable plates around the central one (Fig. 5b), gaining access to the cylinders and decreasing the structure's weight, thus facilitating the assembly and maintenance procedures. The removable plates fastening system is constituted by countersunk bolts and nuts. As the space between holder and ground in the holder rest position has restricted access, the nuts were welded to facilitate the cover removal operation.

2.3.2. Guiding system

Firstly, it is necessary to explain why this system needs a guide. In Fig. 6 it is pointed out with green arrows the intended freedom degrees, while the red crosses indicate the restricted movements promoted by the guiding system.

The first developed design is shown in Fig. 7 and the working principle was based on two sets of two positioning bearings at each side of the holder. Bearing A limits the horizontal movements while bearing B keeps the holding system in the correct vertical   path.

Hence, at this stage the system needs to be improved because it is really hard to fabricate and the final cost will be higher than desired. The design was rethought and now it will consist of applying a central guide below the holder, using a rod end bearing to keep the holding system in the correct position, giving as well the necessary freedom to the system tilting movement. The rod end bearing allows the inclina- tion during the cutting process and rotation to extract the strip or keep the holding system in the rest position. A weak point of this new system is related to the square shaft and bushing responsible for the vertical movement, which are difficult to manufacture. Thus, the square shaft

Fig. 1. Guillotine cutting process scheme[18].

Fig. 2. Typical defects on guillotine cutting process [19]. Guillotine cutting process [19].

and bushing were replaced by a linear guide. This change makes this system completely standard and the final result is an easy to manu- facture system in which all the components can be easily replaced Fig. 8

.

2.3.3. Drive system

The driving system is one of the most important parts of this project because it represents the biggest associated cost. Thus, to choose the correct one it is necessary to focus on the required    positions:

2.3.3.1. Upper position.  In this position the dynamic holding  system is at the same level as the guillotine table, ensuring the horizontal plate position and the correct measurement of the strip to be cut, using the back gauge system. After positioning, the hold down jacks immobilize the plate, and the back gauge automatically retreats 100 mm, preventing the stress generated by the  contact  between  strip  and back gauge during the cutting  process.