# CHARMIE: A Collaborative Healthcare and Home Service and Assistant Robot for Elderly Care
## 2 Materials and Methods
### System and Hardware
#### 2.1.3 Robotic Arm  
The arm's design objective was to develop an affordable, lightweight component with a human-like design. The initial design demonstrates an autonomous robotic manipulator with four degrees of freedom, named the Robotic Arm for Collaboration with Humans in Industrial Environment (RACHIE) [39]. This robot's primary goal was to perform a simplified service pick and place task with human interaction to sort cans according to their colour and shape. By simplifying some of the tasks that generic service robots must perform, it allowed the development of a robotic arm that fulfilled all of the objectives previously stated. However, this manipulator did not provide the degrees of freedom necessary for some generic service robot tasks' complexity. The desired solution, to also comply with the anthropomorphic objective, should present similarities to a shoulder, elbow and hand redundant manipulator [40]. The solution implemented in CHARMIE is based on the InMoov arm [41], initially designed by [PERSON]. InMoov consists of the first Open Source 3D printed life-size robot. The main differences between the original InMoov arm and CHARMIE's arm reside on the bicep and shoulder. The whole arm is printable on a 12 \(\times\) 12 \(\times\) 12 cm 3D, and its PLA parts weigh around 1.414 kg, with the actuators weighing around 0.766 kg. The whole weight of the arm is approximately 2.2 kg. From shoulder to the hand, the arm measures 75 cm and can lift a maximum load of around 400 g.  
This arm can be divided into three main parts: (i) hand and forearm; (ii) bicep; and (iii) shoulder. Most generic service robots with robotic manipulators tend to use grippers to simplify this task. However, the anthropomorphic hand presents more DOFs that allow the robot to best use the hand according to the object, providing greater dexterity capability [42; 43]. The hand is composed of five fingers, similar to a human hand, to provide different ways to pick up various objects. Each finger has a different number of joints, as can be seen in Figure 5a. The thumb has two DOF, the index and middle finger have three DOF, and the ring and little finger have four DOF. Each finger has one actuator (servo motor) that moves all DOF of the respective finger. The movement is based on a pulley mechanism, similar to tendons, where the motors are located in the robot's forearm, as shown in Figure 5b with fishing line tendons leading to the fingers. So, regarding kinematic architecture, this is an underactuated hand since, in total, it has seventeen DOF, but only five actuators. The wrist has one servo motor responsible for rotating the hand. The bicep has two servo motors, one responsible for lifting and lowering the forearm, and the second responsible for rotating the bicep and the forearm. The shoulder has two individual DOF for moving the whole arm parallel to the robot body and lifting the whole arm perpendicular to the body. In total, as shown in Figure 5c this redundant manipulator has 22 DOF with 10 actuators, which define the movement of the arm. The Denavit-Hartenberg parameters for the arm are described in the Table 1. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(\theta\) **(deg)** & **d (mm)** & **1 (mm)** & \(\alpha\) **(deg)** \\ \hline \(\theta_{1}\) & 0.00 & 40.02 & \(-90.0\) \\ \(\theta_{2}+90\) & 66.10 & 0.00 & 90.0 \\ \(\theta_{3}+90\) & 287.83 & 31.04 & 90.0 \\ \(\theta_{4}-26.6\) & 0.00 & 0.00 & \(-90.0\) \\ \(\theta_{5}\) & 283.03 & 59.74 & 0.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Denavit-Hartenberg from [PERSON]’s robot arm. Figure 5: **(a)** An assembly of a finger, with three degrees of freedom but only one actuator, using fishing line as tendons. From top to bottom, the finger starts closed and opens until it is fully stretched. **(b)** The interior of the forearm has five servos actuators that individually control each finger. **(c)** The complete assembly of [PERSON]’s arm.