# 3D Printed Robotic Hand with Piezoresistive Touch Capability
## 1 Introduction  
The development of prosthetic systems that not only prioritize superior mechanical functionality, such as more complete movement of the mechanical hand with a wider range of finger movement and a greater degree of freedom, but also focus on the sensory aspect is still very limited and in dire need of further research. Focusing on the above aspects, this work proposes the design of a low-cost sensory glove system that complements the functionality of a 3D-printed mechanical robotic hand [1; 2; 3]. The choice of 3D printing as a method for manufacturing prostheses allowed for a more controlled production process with cost reduction, maintaining the quality of each individual part and allowing for a wider range of choices in terms of the types of raw materials used [4; 5; 6; 7]. The raw materials were selected according to the requirements of parts and the type of function the parts would perform, for example, since the robotic hand has a greater need for resistance regarding mechanical strength than the forearm, these two structures were made with different polymers. Polylatic acid (PLA) was the main material used for the hand parts due to its superior mechanical properties after printing: a tensile yield strength of \(\approx\)51 MPa, a tensile modulus of \(\approx\)2.3 GPa, a flexural strength of \(\approx\)83 MPa and a flexural modulus of \(\approx\)3.1 GPa [8]. As the forearm is in direct contact with the user's body and is not subject to the same mechanical stress as the hand, polyethylene terephthalate (PETG) was chosen for its manufacture, as it is biocompatible and can also withstand some mechanical stress: \(\approx\)47 MPa tensile yield strength, \(\approx\)1.5 GPa tensile modulus and 5.1% elongation at yield point [9]. For the sensory glove system, it was decided to separate the prosthetic and sensory systems, as many patients who tried sensory prototypes could not fully adapt to them. Furthermore, only one type of somatosensory sensation (touch) was studied and/or produced, as the addition of other parameters, such as temperature and proprioception, would result in greater complexity without adequately addressing each parameter individually. Asan example of a multi-layered system, [PERSON] et al. [10] developed a multi-sensory glove where, in addition to temperature and humidity, touch measurements using piezoresistive sensors were considered to deepen the information about objects held by the sensory system. The data produced by this system were more complete because it simultaneously reduced the sensing area and evenly distributed the sensors, focusing on very small areas of the palm rather than the main touch areas, and also placed the temperature and humidity sensors in more central areas of the palm of the prosthetic hand, excluding the fingers. While the use of sensors offers a wider range of applications in health monitoring and human-machine interaction, it also has some drawbacks. The type of mounting has a major impact on quality and aesthetics, and the connections between the processing units and the sensors lead to complications if the wire paths are not well designed [11; 12]. However, the use of sensors allows systems to achieve high performance, functionality, lower cost and greater accessibility compared to fiber-based solutions. Although these types of solutions are easier to integrate and address electrically, they suffer from limited performance and, more importantly, are more difficult to access (in terms of market and cost terms) and replace if damaged [11; 12]. The type of sensor used and the method of measurement are key issues. Several investigations have used piezoresistive and piezoelectric effects, or both, as the basis for operation. Detection systems based on the piezoelectric effect use mechanical deformation to produce an electrical signal that varies proportionally with the amount of strain [13].