## 4 Experiments
### Pick-and-Place Experiment  
A pick-and-place experiment was conducted to investigate the stability and operability of the prosthetic hand. The hand was controlled through electromyography (EMG) signals acquired from an able-bodied male adult [26; 27; 28]. The experimental equipment included a socket for the subject to wear the hand, a microcomputer for recognizing the EMG signal and controlling the motors, a glove for covering the hand, myoelectric sensors, batteries, and the prosthetic hand, as illustrated in Figure 16. The prosthetic hand was attached to the right forearm of the subject by means of the socket. Moreover, to investigate the performance of the prosthetic hand, the same experiments were conducted using previously designed hands [29]. Three types of previous prosthetic hands exist, as follows. (1) Joint fixed type--two motors are adopted, where motor 1 is connected to the MP joint for flexion and extension of the four fingers, and motor 2 is for adduction and abduction of the thumb. The remaining PIP, DIP, MP, and IP joints are unmovable and fixed at certain preset angles (shown in Figure 17). (2) Adaptive linkage type--two motors are adopted, as in the case of the first hand type, but the PIP and DIP joints can be driven to flex or extend passively by the MP joint, which can adapt to the shape of the object being grasped. A soft structure such as a sponge block is provided at each fingertip (shown in Figure 18). (3) Stable linkage type--this type is nearly the same as the adaptive type, but only the PIP joint can be passively driven by the MP joint, and the DIP joint is fixed at a preset angle, which can provide a certain trajectory of the finger joints in grasping (shown in Figure 19). Before the pick-and-place experiment, the motion performance of these previous hands was also tested to verify how many types of motion can be achieved by these hands based on the Cutkosky taxonomy. The same motor controller as the one used in the grasp motion verification experiment was used to control each hand to perform the grasp tasks. Tables 4-6 listed the achievable motions of each hand. Figure 16: Experimental devices. Figure 17: Joint fixed type: the assembled hand, parts of the four fingers, and thumb. Figure 18: Adaptive linkage type: the assembled hand, part of the thumb, and tendon-driven mechanism of the four fingers. Figure 19: Stable linkage type: the assembled hand, part of the thumb, and tendon-driven mechanism of the four fingers. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{1}{c}{} & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Achievable motion types (stable linkage type). \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{1}{c}{} & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Achievable motion types (adaptive linkage type). In order to compare the grasp performance of the proposed hand and previously designed hands, the same experiments were conducted. As illustrated in Figure 20, several objects of daily use were selected for this experiment. Table 7 lists the weight, shape, and size parameters of the experimental objects. The subject was required to perform certain tasks. Firstly, mark two \(15\times 15\) mm square markers on a table at an interval of 300 mm. Secondly, for each object, control the prosthetic hand to pick up the object from one marker area and place it in the other repeatedly within 30 s. If the object was not dropped while moving it, it was recorded as one successful task. Figure 21 illustrates two successful tasks during the experimental process.