## 1 Introduction
very expensive and usually require special training and occupy a large part of the clinic for use. One such system is the highly capable ZEISS i.Terminal 2 [5]. An important aspect in choosing the technology used is also the ease with which the mechanism can be manufactured, without the need for specialized training and in proximity to the field of operation (optometry). It is also important to consider the biocompatibility of the materials used, as this mechanism will be used in the immediate vicinity of patients, it is desirable that it does not affect their health in any way. One last important aspect is the possibility of recycling these devices. Choosing a metal or composite material will make it difficult to recycle the material to produce other devices [6]. Starting from the conditions listed above, several more variants of materials and manufacturing technologies have been considered. These include:  
* Plastic injection--the first of the technologies considered has the disadvantage of the very high initial cost (mould cost), as well as the difficulties encountered in case of modification to the initial model [7; 8; 9; 10]
* This technological process can only be considered if it is desired to produce a very large number of components, without changing their shape [7; 8; 9; 10]. * Selective laser sintering--this technology allows rapid modification of the model used, is compatible with elastic materials, but the prohibitive costs and special conditions of use make it unsuitable for the requested model [11; 12; 13; 14]. * Stereolithography--this technology has several advantages, such as the relatively low price of the equipment and ease of use, while disadvantages include the high cost of the polymer and the fact that it requires ventilation installation [15; 16; 17; 18]. * Thermoplastic extrusion--FDM technology allows the realization of prototypes in a very short time, from a very wide range of materials that have a low price and are affordable [19; 20; 21; 22]. The wide spread of this technology has allowed for the very rapid development of both commercial solutions for depositing plastic in layers and materials. FDM technology involves the deposition of a continuous flow of material in the form of a heated filament to obtain geometric shapes, under the control of a computer system. Deposition usually occurs on the x and y axes (plane) with the increment of the Z axis after complete deposition of the material on the current layer. The thermoplastic materials used are part of an extraordinarily wide range and include Polylactic acid PLA, Acrylonitrile Butadiene Styrene ABS, Thermoplastic Polyurethane TPU, Nylon, Polyethylene terephthalate glycol PETG, and other variations of them or composite materials. Among the presented solutions, the FDM technology corresponds in terms of cost and quality for the execution of the compliant mechanism [23]. The materials used to make the mechanism were chosen based on the mechanical characteristics, availability, and cost price: PLA, ABS and TPU. The shape of the mechanism was determined after multiple experiments over several iterations and using the pros and cons of current marked solutions. Regarding the size and stroke of the mechanism, they were determined by measuring the lowest and highest frame sizes usually encountered in the industry. Furthermore, a key determining factor of the size was the industry standards in terms of lens size before it is cut to fit the frames (between 60-70 mm). Along with this, the shape allows for easy dimensioning up or down, with regards to using FDM technology. The shape and usability cases for the device were based on tens of years of experience in the field of optometry. For the shape and requirements for the system, feedback received from users who have employed similar systems for a number of years was considered.