## 4 Manufacturing of a Prototype and Preliminary System Testing  
Current additive manufacturing technologies allow for complex mechanisms to be tested before mass production--however, in some instances, they even allow for direct-to-customer-use manufacturing. For our designed mechanism, such a path was chosen, in that small batches could be produced and modified for specific needs in terms of the shapes of glasses frames. It is also important to note here that the current wide array of both materials, as well as composites, allow for the mechanism to be customized even further in terms of mechanical properties, look and feel, while taking into consideration that almost all of the changes to the material will, in some capacity, modify the way the mechanism transmits force and motion through elastic body transformation. To this end, several materials were considered, of course, principally taking into consideration the notion that they should be inherently chemically inert to external use with the person wearing the glasses and the support system. Using this as a starting point and after some tests and consideration, as presented in a previous study [1], a specific version of thermoplastic polyurethane was chosen [1], with some of the material's properties being density 1.18 g/cm\({}^{3}\), a Young modulus of 0.396 GPa and a yield strength of 65.85 MPa. While these parameters are specific to this material and do allow for the imposed travel of the mechanism's supports at approximately 30 mm at a 35 N-applied force on each end, further research has proven that such mechanical behaviour can also be obtained by using other materials, such as specific variants of Polylactic acid PLA. Also, some studies could be performed in order to determine to what extent, for this specific shape and purpose, slicing and FDM [37; 38; 39; 40; 41; 42] parameters influence compliant behaviour, as well as long term use of the system. Regarding FDM parameters, while a general-purpose FDM slicing software was used, specific parameters were tested in order to allow for the best results, both cosmetic and structural. Regarding the actual additive manufacturing system, a general-purpose desktop cartesian system was used, Prusa i3 model, capable of temperatures that are compatible with working with materials such as TPU or Nylon. It should be noted here that, since the material is flexible, a direct drive extruder is needed, with adjustments made to the pretensioning mechanism, specific to the elasticity of the material used. As for some of the specific parameters used during slicing, a low speed was selected (20 mm/s) for the infill, with an even lower speed of 15 mm/s for the outer walls. Infill was selected as full (100%), with a wall thickness of 0.8 mm, with bottom and top walls at a minimum of 1.2 mm. During  
Figure 6: A simulation of the operation of the compliant mechanism proposed for the optometric field. several tests performed, it was concluded that, in order to obtain the best results in both elasticity and overall mechanism usability, an infill of 100% should be used. There was also no advantage to be had by experimenting with other infill percentages since, with these current parameters, all of the requirements, such as shape and weight, were met. The physical model was tested on a wide array of shapes of glasses, with a height from approximately 27 mm up to 60 mm, with good results in terms of both ease in fixing the support and maintaining its position in use. The model was proven to allow for accurate measurements of previously specified parameters (see Figure 3). Also, the model proved to allow for movement on behalf of the patient, without disturbing the position of the device once it was fixed to the frames. During the tests, it was determined that, while certain rarer models of frames might pose an issue--such as extremely large or small models, as the ones encountered in use for children--the model could be easily modified to fit such situations.