Developing a Novel Prosthetic Hand with Wireless Wearable Sensor Technology Based on User Perspectives: A Pilot Study

Abstract

Myoelectric hands are beneficial tools in the daily activities of people with upper-limb deficiencies. Because traditional myoelectric hands rely on detecting muscle activity in residual limbs, they are not suitable for individuals with short stumps or paralyzed limbs. Therefore, we developed a novel electric prosthetic hand that functions without myoelectricity, utilizing wearable wireless sensor technology for control. As a preliminary evaluation, our prototype hand with wireless button sensors was compared with a conventional myoelectric hand (Ottobock). Ten healthy therapists were enrolled in this study. The hands were fixed to their forearms, myoelectric hand muscle activity sensors were attached to the wrist extensor and flexor muscles, and wireless button sensors for the prostheses were attached to each user's trunk. Clinical evaluations were performed using the Simple Test for Evaluating Hand Function and the Action Research Arm Test. The fatigue degree was evaluated using the modified Borg scale before and after the tests. While no statistically significant differences were observed between the two hands across the tests, the change in the Borg scale was notably smaller for our prosthetic hand (p = 0.045). Compared with the Ottobock hand, the proposed hand prosthesis has potential for widespread applications in people with upper-limb deficiencies.

Keywords: electric prosthetic hand; prosthetic hand user perspective; three-dimensional printer; upper-limb deficiency; wireless wearable sensors.

Figure 1

Novel wireless prosthetic hand. The proposed hand is constructed predominantly from nylon resin and shaped using a three-dimensional (3D) printer, with stainless steel employed for the joints to enhance durability. It contains two linear actuators within its structure that control the flexion and extension of each finger, from the index to the little finger, via fishing lines. Externally, stainless-steel mechanisms facilitate the radial-palmar abduction and adduction movements of the thumb.

Figure 2

Schematic of our novel wireless prosthetic hand.

Figure 3

Photograph showing all the systems designed and tested in this study.

Figure 4

Schematic of the wireless receiver circuit. The wireless transmitter circuit on the left side and a schematic of the wireless receiver circuit on the right side. In the wireless transmitter circuit, the 5 V battery directly supplies 5 V to the Arduino NANO compatible, and the dropout 3.3 V is supplied to the nRF24L01 via a low-loss 3-terminal regulator TA48M033F. While the green button is pressed, ADC4 goes low, and the hand can be operated to open. On the other hand, while the red button is pressed, ADC3 goes low, and the hand can be operated to close. If both are pressed or neither is pressed, the hand stops. In the wireless receiver circuit, the voltage from the 5 V battery is converted to a safe 5 V isolated from the battery via a DC/DC converter SUCS30505C, and then the dropped 3.3 V is supplied to the nRF24L01 via a three-terminal regulator TA48M033F. The voltage of the 5 V battery is boosted to the required 12 V via the DC/DC converter SUCS100512C, and then the 12 V is used to drive two linear actuators PQ12-100-12-P through two motor drivers IC TB6648KQ.

Figure 5

Prosthetic simulator hands. Two prosthetic simulators were developed to compare both hands. The body of the simulators was made of fiber-reinforced plastic (FRP), where acrylic resin was infiltrated into nylon, cotton, and carbon fiber layers. (a) Ottobock hand (8E38 = 6 DMC plus, Ottobock, Germany) with the simulator. The simulator was made of FRP and leather belts such that it could fit the user’s forearm while using the Ottobock hand. It also had a special battery for use with only the Ottobock myoelectric hand. Non-slip finger sacs were worn on the fingers. (b) Our novel hand and wrist component for cosmetic hands (10V39 and 10A30, Ottobock, Germany) with the simulator hand. The simulator was also made of FRP and leather belts such that it could fit the user’s forearm while using the Ottobock hand. Non-slip finger sacs were worn on the fingers.

Figure 6

Wireless sensor with control buttons. (a) Photograph showing the two buttons outside the plastic container. (b) A participant, who is in the middle of the STEF test using the novel hand, places the control button box on the left trunk while the novel hand is worn on the right forearm. The green button is a trigger for four-finger flexion; the red is for extension.

Figure 7

Ottobock wrist part in our prosthetic simulator hand. Ottobock wrist parts (10V39 and 10A30) for a cosmetic hand (in a blue square) are used for our novel hand.