A Bidirectional Fabric-based Pneumatic Actuator for the Infant Shoulder: Design and Comparative Kinematic Analysis

Abstract

This paper focuses on the design and systematic evaluation of fabric-based, bellow-type soft pneumatic actuators to assist with flexion and extension of the elbow, intended for use in infant wearable devices. Initially, the performance of a range of actuator variants was explored via simulation. The actuator variants were parameterized based on the shape, number, and size of the cells present. Subsequently, viable actuator variants identified from the simulations were fabricated and underwent further testing on a physical model based on an infant's body anthropometrics. The performance of these variants was evaluated based on kinematic analyses using metrics including movement smoothness, path length, and elbow joint angle. Internal pressure of the actuators was also attained. Taken together, results reported herein provide valuable insights about the suitability of several actuator designs to serve as components for pediatric wearable assistive devices.

Closed-loop Position Control of a Pediatric Soft Robotic Wearable Device for Upper Extremity Assistance

“…4) placed at a distance from the mannequin. 2 The actuators are anchored on the mannequin via velcro straps at places that minimize motion restrictions as per our previous works [17], [23], [28]. 3 The mannequin is designed and fabricated in-house based on average 12-month-old infant anthropometrics [32], [33]; the upper arm has a length of l a = 0.14 m. The joints and upper-arm and forearm are 3D-printed.…”

“…In fact, the currently limited F/E motion range can be readily rectified by fabricating and employing actuators that integrate a large number of pouches, and is part of ongoing work. Fabricating different actuator designs of distinct length and number of pouches to extend or reduce the range of motion can be done quickly and in a costeffective manner [23]. As far as the AB/AD range of motion is concerned, this was deemed satisfactory.…”

“…4 Shoulder AB/AD motion (angle θ 1 ) employs a recent design that has been extensively tested and validated in our previous work (Fig. 3 a) [23], but a new actuator for shoulder F/E motion (angle θ 2 ) was developed herein (Fig. 3 b).…”

“…Given a higher-level controller (e.g., admittance force control) yielding desired trajectories (e.g., as seen in other soft wearable assistive devices [26]), a low-level controller operating at the pneumatic-system level needs to ensure the desired trajectory is achieved. In our past work we have developed feedforward [17], [27] as well as setpoint [28] and learning-based feedback [29] controllers for soft pneumatic actuators used in various iterations of our wearable device prototypes [17], [23]. Feedback controllers can help make the device more responsive, while tracking desired setpoints is a key function on its own, e.g., to counter gravity at the shoulder joint [3].…”

“…Soft wearable assistive devices, in particular, can afford a wide variety of methods for actuation, sensing and control, which in many cases are intertwined with each other and can be adjusted to meet the characteristics of the infant population. Actuation methods can utilize 3D-printing [13]- [15], casting [16]- [18] or fabric [19]- [23] to improve strength [2], [24] and minimize fatigue [4], [21]. Several of the current actuator designs employed in wearable devices are pneumatic-based (as in this work too), in an effort to facilitate motion while providing comfort and safety with minimal constraints on the arms [25].…”