Smart ArM: a customizable and versatile robotic arm prosthesis platform for Cybathlon and research

Abstract

Background: In the last decade, notable progress in mechatronics paved the way for a new generation of arm prostheses, expanding motor capabilities thanks to their multiple active joints. Yet, the design of control schemes for these advanced devices still poses a challenge, especially with the limited availability of command signals for higher levels of arm impairment. When addressing this challenge, current commercial devices lack versatility and customizing options to be employed as test-beds for developing novel control schemes. As a consequence, researchers resort to using lab-specific experimental apparatuses on which to deploy their innovations, such as virtual reality setups or mock prosthetic devices worn by unimpaired participants.

Methods: To meet this need for a test-bed, we developed the Smart Arm platform, a human-like, multi-articulated robotic arm that can be worn as a trans-humeral arm prosthesis. The design process followed three principles: provide a reprogrammable embedded system allowing in-depth customization of control schemes, favor easy-to-buy parts rather than custom-made components, and guarantee compatibility with industrial standards in prosthetics.

Results: The Smart ArM platform includes motorized elbow and wrist joints while being compatible with commercial prosthetic hands. Its software and electronic architecture can be easily adapted to build devices with a wide variety of sensors and actuators. This platform was employed in several experiments studying arm prosthesis control and sensory feedback. We also report our participation in Cybathlon, where our pilot with forearm agenesia successfully drives the Smart Arm prosthesis to perform activities of daily living requiring both strength and dexterity.

Conclusion: These application scenarios illustrate the versatility and adaptability of the proposed platform, for research purposes as well as outside the lab. The Smart Arm platform offers a test-bed for experimenting with prosthetic control laws and command signals, suitable for running tests in lifelike settings where impaired participants wear it as a prosthetic device. In this way, we aim at bridging a critical gap in the field of upper limb prosthetics: the need for realistic, ecological test conditions to assess the actual benefit of a technological innovation for the end-users.

Keywords: Arm prosthesis; Cybathlon; Rehabilitation engineering; Research test-bed; Robotic arm.

Fig. 1

The Smart ArM prosthesis in its current iteration, fitted with a Taska prosthetic hand

Fig. 2

Close-up picture of the prosthesis’s forearm, with upper shell open. LED light-emitting diode, NGIMU new generation inertial measurement unit (from x-IO Technologies)

Fig. 3

Diagram of connections between the components of the platform in its current iteration. I2C Inter-Integrated Circuit, MQTT message queuing telemetry transport (obsolete meaning), SPI Serial Peripheral Interface, UART universal asynchronous receiver-transmitter, USB Universal Serial Bus, WLAN wireless local area network

Fig. 4

Examples of peripheral devices compatible with the Smart Arm platform

Fig. 5

Disassembled view of the prosthesis’s essential electronic components

Fig. 6

A, B Close-up pictures of the elbow actuation unit, before and after attaching the socket and forearm, respectively. C Computer-aided design (CAD) view of the elbow actuation. unit

Fig. 7

A Close-up picture of the wrist assembly, including the control panel and LED strip described in Section "User interface". B CAD view of the wrist assembly, without the control panel

Fig. 8

Four-layer structure of the embedded system’s software stack. The Web browser interface, shown in dotted lines, is described in Section "Wireless communication"

Fig. 9

Screen capture of the dynamic HTML interface in operation

Fig. 10

Examples of tasks in Cybathlon’s ARM race. A Carrying bottles (weights ranging from 100 g to 1.6 kg). B Stacking cups (photograph ©Pierre Kitmacher, Sorbonne Université). C “Clean Sweep” i.e. small object manipulation

Fig. 11

Early prototype of the Smart Arm prosthesis driven with phantom limb motion [45]

Fig. 12

Early prototype of the Smart Arm prosthesis driven with a movement-based control while fitted to a conventional trans-humeral socket (A) or an osseo-integrated implant (B) [47]

Fig. 13

Smart Arm prosthesis fitted with an i-Limb Quantum hand and driven with 2-DoF CCC (wrist and elbow) [32]

Fig. 14

Experimental setup for testing vibro-tactile proprioceptive feedback with an early version of the Smart Arm platform. [48]

Fig. 15

Taska hand equipped with force sensors and rotary encoder [49]

Fig. 16

Experimental setup for evaluating a pattern-recognition-based control of a prosthetic hand and wrist [50]