# 3D Printed Robotic Hand with Piezoresistive Touch Capability
## 4 Robotic Hand Sensing  
### Description of the Materials/Hardware  
Following the same methodology as the instrumentation, the sensory system was implemented with a focus on cost reduction while maintaining the performance of the system. It was also important that the sensory system was removable and independent of the limb instrumentation, so that the end user could decide whether to include it or  
Figure 4: Illustration of an instrumented robotic hand: (**A**) servomotors (A1 and A2) and power cable (F); (**B**) potentiometers (B1 and B2), _Arduino UNO_ (C), capacitor (D) and breadboard (E).  
make the robotic hand even more economical. A breathable polyester-based glove with a polyurethane coating on the palm and fingertips was used as the basis for the sensory system. The proposed system consisted of sixteen piezoresistive sensors attached to the glove in certain key areas of interest (Figure 5), allowing more accurate detection of the prosthetic hand's interactions with objects and the measurement of forces and their locations.  
The piezoresistive sensors used were force resistive sensors (_FRS_) from the 400 series, model _FRS402_, shown in Figure 6, a device based on a thick polytetrafluoroethylene (PTF) polymer film that exhibits a decrease in electrical resistance when a force is applied to its active surface. It has a circular detection area of 1.27 cm, an overall length of 6.0325 cm and a width of 1.905 cm. This type of sensor has a suitable sensitivity range (100 g to 10 kg) and measuring range (12.7 mm) [20]. Its morphology made it easy to install in the glove, as the strip fixed in the measurement area allowed a simplified connection between the sensor and the _Arduino_. The FSR402 sensor has been used in similar research to measure forces in a variety of applications [21; 22]. According to [10], this type of sensor is suitable for detecting pressure differences on prosthetic surfaces.  
Due to the large number of sensors used in the assembly of the sensory glove, the processing unit had to provide a large number of simultaneous analogue read inputs. This led to the choice of the Arduino Mega2560, which has a total of sixteen analogue inputs.  
The design of the glove's instrumentation again took a simplified approach, using the _Arduino Mega2560_ (5 V) as the power supply controller, unlike the mechanical system instrumentation which was powered directly, reducing signal interference to the sensors. Following the manufacturer's assembly guidelines, each sensor was assembled using a current div  
Figure 5: Representation of: (**A**) prosthetic hand; (**B**) locations where the sixteen piezoresistive sensors were placed.  
Figure 6: Illustration of the FRS402 piezoresistive sensor used.  
### Description of the Materials/Hardware  
Due to the large number of sensors used, the programming of the system was carefully considered, as the _Arduino Mega2560_ only had one analogue-to-digital converter (ADC), which allowed only one reading and one input each time the system was used. To overcome this limitation, a simple toggle function was implemented to make the sensors work one at a time by selecting the number that identifies each sensor and its specific position (Figure 8). In this way, the difference between simultaneous or individual functionality of the sensors did not have a major impact on the final results.