Touch Hand 4.5: low-cost additive manufacturing prosthetic hand participated in Cybathlon 2020 ARM discipline

Abstract

Background: The Touch Hand 4.5 is a highly customisable prosthetic hand, which features an optimised modular design of the Touch Hand 4. The Touch Hand team has developed a low-cost prosthetic hand, which has been built using an additive manufacturing process. The functionality and features are discussed that are crucial for amputees.

Methods: This paper documents the design and integration of the Touch Hand 4.5 to be used in the Cybathlon 2020 event as well as the development of the mechanical structure of the hand, socket, electronics and control system utilized. The Touch Hand 4.5 was designed and continuously optimized, with the goal to achieve the tasks in the Cybathlon 2020 event.

Results: The performance and functionality of the Touch Hand 4.5 was tested on a global scale at the Cybathlon 2020. The device and technology were evaluated against the leading prosthetics and prototypes from around the world. A series of everyday tasks, as set by the Cybathlon event, were performed to determine the capabilities of the device, with the pinch grip, full grip, half grip, and a thumb grip. The Touch Hand team was the only team to complete the Haptic Box task in all three races, which comprised of the identification of objects without the aid of visual input or perception, with a duration between 100 and 120 s. The Breakfast task entailed completing a series of everyday breakfast tasks, such as cutting a loaf of bread, lighting a candle, opening a sugar packet, opening a plastic bottle and a jar, as well as opening a tin can with a can opener. This task was only completed in Race 3, with a duration of 132 s, due to a faulty equipment that was supplied.

Conclusion: The first contribution that was achieved was the design and development of an additive manufactured hand and socket, considering the socket to have comfort, breathability and decreased irritability. The second contribution was the design optimisation with the linear actuator integration, for a multi-grip hand, which allowed for the pinch grip, full grip, half grip, and a thumb grip. Slippage prevention with grip force control system integration was also implemented.

Trial registration number: Ethical clearance certificate HCC/0161/011.

Keywords: Additive manufacturing; Cybathlon; Low cost; Prosthetic hand; Touch Hand.

Fig. 1

The Touch Hand 4 prototype

Fig. 2:

3D CAD model representing the index finger before and after the redesign

Fig. 3:

3D CAD model representing the ring finger complex before and after the redesign

Fig. 4:

3D CAD model representing the palm structure before and after the redesign

Fig. 5

The intermediate assembly of the components, excluding the thumb

Fig. 6

Two images on left shows the original actuation position, two images on right shows the improved actuation position

Fig. 7

Positioning of linear actuator on the palm structure

Fig. 8:

3D printed model showing the positioning of the linear actuator

Fig. 9

Silicone covers for the thumb, index and ring finger respectively

Fig. 10

The snap fit clip clipped into the socket collar

Fig. 11

Construction of the 3D printed socket structure

Fig. 12

Block Diagram representing the electronics system of the Touch Hand

Fig. 13

Code flow diagram for the control system of the Touch Hand 4.5

Fig. 14

Touch Hand 4.5 demonstrating the pinch grip

Fig. 15

Full grip demonstrated by the pilot using Touch Hand 4.5

Fig. 16

Pilot demonstrating the half grip using the Touch Hand 4.5

Fig. 17

Pilot using the thumb grip to complete different tasks in the Cybathlon 2020 event

Fig. 18

Graph showing the time taken for each of the participating teams to complete the Breakfast task in all three races

Fig. 19

Graph showing the time taken for each team to complete the haptic box task in each race