Design of a Soft Robotic Elbow Sleeve with Passive and Intent-Controlled Actuation

Tze Hui Koh, Nicholas Cheng, Hong Kai Yap, Chen-Hua Yeow, Tze Hui Koh, Nicholas Cheng, Hong Kai Yap, Chen-Hua Yeow

Abstract

The provision of continuous passive, and intent-based assisted movements for neuromuscular training can be incorporated into a robotic elbow sleeve. The objective of this study is to propose the design and test the functionality of a soft robotic elbow sleeve in assisting flexion and extension of the elbow, both passively and using intent-based motion reinforcement. First, the elbow sleeve was developed, using elastomeric and fabric-based pneumatic actuators, which are soft and lightweight, in order to address issues of non-portability and poor alignment with joints that conventional robotic rehabilitation devices are faced with. Second, the control system was developed to allow for: (i) continuous passive actuation, in which the actuators will be activated in cycles, alternating between flexion and extension; and (ii) an intent-based actuation, in which user intent is detected by surface electromyography (sEMG) sensors attached to the biceps and triceps, and passed through a logic sequence to allow for flexion or extension of the elbow. Using this setup, the elbow sleeve was tested on six healthy subjects to assess the functionality of the device, in terms of the range of motion afforded by the device while in the continuous passive actuation. The results showed that the elbow sleeve is capable of achieving approximately 50% of the full range of motion of the elbow joint among all subjects. Next, further experiments were conducted to test the efficacy of the intent-based actuation on these healthy subjects. The results showed that all subjects were capable of achieving electromyography (EMG) control of the elbow sleeve. These preliminary results show that the elbow sleeve is capable of carrying out continuous passive and intent-based assisted movements. Further investigation of the clinical implementation of the elbow sleeve for the neuromuscular training of neurologically-impaired persons, such as stroke survivors, is needed.

Keywords: assistive; elbow; electromyography-driven; rehabilitation; robotic; soft-robotic; stroke; wearable.

Figures

Figure 1
Figure 1
Soft robotic elbow sleeve for stroke rehabilitation. (A) Illustration of the soft robotic sleeve. (B) Schematic of the constraining layer for the flexion actuator. (C) Fully assembled system.
Figure 2
Figure 2
Arm configurations during the use of the soft robotic elbow sleeve. (A) Flexed configuration. (B) Extended configuration.
Figure 3
Figure 3
Key stages of actuator fabrication. (A) Molding of the actuator's elastomeric body (Dragon Skin 20) using a 3D-printed mold (ABS). (B) Application of a thin elastomeric layer (Dragon skin 20) together with strain limiting layer (Nylon). (C) Winding of a monofilament thread (Nylon) in a double-helical pattern to provide radial reinforcement.
Figure 4
Figure 4
Illustrating the effect of wrapping Nylon around the flexion actuator to acquire a desired angular configuration. (A) An unconstrained elastomeric actuator in flexed formation, with the yellow curve indicating a rounded curvature upon air pressure input. (B) A fabric constrained elastomeric actuator upon pressurization, with the yellow lines indicating the angular curvature achieved.
Figure 5
Figure 5
Illustrating the two configurations of the extension actuator, with and without air pressurization. (A) The deflated nylon ripstop actuator in flexed configuration, which allows conformation to the flexion actuator. (B) The inflated nylon ripstop actuator in extended configuration, which acts as a rigid beam and resists bending deformation.
Figure 6
Figure 6
Experimental platforms for the characterization of the actuators. (A) Flexion actuator experimental platform. (B) Extension actuator experimental platform.
Figure 7
Figure 7
Flowchart of the logic scheme used to detect user intent and control flexion and extension of the soft robotic elbow sleeve.
Figure 8
Figure 8
The positions used in the range of motion study. (A) Vertical position of the elbow (in flexed configuration). (B) Horizontal position of the elbow (in flexed configuration). (C) Extended elbow configuration, which serves as the starting point for the trials.
Figure 9
Figure 9
Marker positions for real-time tracking of segment coordinates.
Figure 10
Figure 10
Graphs showing the relationship between force and pressure for the actuators. (A) Graph of tip force vs. pressure of flexion actuator. (B) Graph of resistive force vs. pressure of extension actuator.
Figure 11
Figure 11
Graph showing the functionality of the PID control of pressure within the actuators.
Figure 12
Figure 12
Graphs of angle achieved during exercise cycle (with shaded area depicting standard deviation) of a single subject for each sub-experiment. (A) Active vertical sub-experiment. (B) Passive vertical sub-experiment. (C) Active horizontal sub-experiment. (D) Passive horizontal sub-experiment.
Figure 13
Figure 13
Graph showing the angle of the elbow over the exercise cycle corresponding to the captured surface EMG signals over time from the biceps and triceps, in cyclic flexion and extension.

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