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Mechanically Programming the Cross-Sectional Shape of Soft Growing Robotic Structures for Patient Transfer

O. Godson Osele, Kentaro Barhydt, Teagan Sullivan, H. Harry Asada, Allison M. Okamura

TL;DR

This work introduces a method to mechanically program the cross-sectional shape of soft everting robots by bonding flexible strips to constrain radial expansion, enabling a wide yet thin, flat cross-section while preserving multi-axis bending. An analytical model links design specifications $(H_s, H_c, w)$ to fabrication parameters $(S_c, S_s, L)$ under constant-curvature and coradial assumptions, and is validated against experiments. A full soft growing robotic sling is demonstrated for bed-to-chair patient transfer, implementing eversion, deflation to a sheet, and automatic removal, with an ergonomic index used to assess patient comfort. The results show accurate cross-section prediction ($A_{measured}/A_{model}\approx 0.99$) and practical transfer performance with a single caregiver, highlighting the approach's potential to reduce manual handling risk in caregiving settings.

Abstract

Pneumatic soft everting robotic structures have the potential to facilitate human transfer tasks due to their ability to grow underneath humans without sliding friction and their utility as a flexible sling when deflated. Tubular structures naturally yield circular cross-sections when inflated, whereas a robotic sling must be both thin enough to grow between them and their resting surface and wide enough to cradle the human. Recent works have achieved flattened cross-sections by including rigid components into the structure, but this reduces conformability to the human. We present a method of mechanically programming the cross-section of soft everting robotic structures using flexible strips that constrain radial expansion between points along the outer membrane. Our method enables simultaneously wide and thin profiles while maintaining the full multi-axis flexibility of traditional slings. We develop and validate a model relating the geometric design specifications to the fabrication parameters, and experimentally characterize their effects on growth rate. Finally, we prototype a soft growing robotic sling system and demonstrate its use for assisting a single caregiver in bed-to-chair patient transfer.

Mechanically Programming the Cross-Sectional Shape of Soft Growing Robotic Structures for Patient Transfer

TL;DR

This work introduces a method to mechanically program the cross-sectional shape of soft everting robots by bonding flexible strips to constrain radial expansion, enabling a wide yet thin, flat cross-section while preserving multi-axis bending. An analytical model links design specifications to fabrication parameters under constant-curvature and coradial assumptions, and is validated against experiments. A full soft growing robotic sling is demonstrated for bed-to-chair patient transfer, implementing eversion, deflation to a sheet, and automatic removal, with an ergonomic index used to assess patient comfort. The results show accurate cross-section prediction () and practical transfer performance with a single caregiver, highlighting the approach's potential to reduce manual handling risk in caregiving settings.

Abstract

Pneumatic soft everting robotic structures have the potential to facilitate human transfer tasks due to their ability to grow underneath humans without sliding friction and their utility as a flexible sling when deflated. Tubular structures naturally yield circular cross-sections when inflated, whereas a robotic sling must be both thin enough to grow between them and their resting surface and wide enough to cradle the human. Recent works have achieved flattened cross-sections by including rigid components into the structure, but this reduces conformability to the human. We present a method of mechanically programming the cross-section of soft everting robotic structures using flexible strips that constrain radial expansion between points along the outer membrane. Our method enables simultaneously wide and thin profiles while maintaining the full multi-axis flexibility of traditional slings. We develop and validate a model relating the geometric design specifications to the fabrication parameters, and experimentally characterize their effects on growth rate. Finally, we prototype a soft growing robotic sling system and demonstrate its use for assisting a single caregiver in bed-to-chair patient transfer.
Paper Structure (20 sections, 24 equations, 5 figures)

This paper contains 20 sections, 24 equations, 5 figures.

Table of Contents

  1. INTRODUCTION
  2. DESIGN
  3. Principles
  4. Eversion
  5. Restricting radial expansion
  6. Implementation and Fabrication
  7. Fabricating the robot body
  8. Creating strong attachments
  9. Wide base
  10. MODELING
  11. Problem Definition and Assumptions
  12. Simplifying Geometric Principles
  13. Curved segment parametrization
  14. Arcs of center channel are coradial
  15. Cross-Section Geometry Model
  16. ...and 5 more sections

Figures (5)

  • Figure 1: Soft growing robotic sling prototype with a flattened inflated cross-section. (a) and (b) show the sling growing out of a wide base and grown to its full length, respectively. (c) shows the wide base with the sling fully retracted and placed under the head of a human, (d) shows the sling fully grown and deflated under the human with its ends attached to a Hoyer lift device via cables, and (e) shows the human lifted by the sling connected to a Hoyer lift.
  • Figure 2: (a) Constraining strips pulls points along the outer membrane inward to flatten the cross-section. (b) Full design of the soft growing robotic sling system, including the robotic sling with flattened cross-section, a wide motorized base to accommodate the flattened cross-section, and loops to attach to Hoyer lift cables. (c) Sequence over which the robotic sling with constraining fabric strips everts. (d) Sequence of robotic sling growing between the human body and its resting surface.
  • Figure 3: Geometry of robotic sling cross section. (a) Full cross section geometry. (b) Free-body diagram of differential segment of curved section. (c) Side channel geometry. (d) Center channel geometry without aligned arc centers. (e) Center channel geometry with aligned arc centers.
  • Figure 4: (a) Geometry model cross-section shape prediction vs. experimentally measured prototype shape. Measurement to model area ratios ($A_{measured}:A_{model}$) ranged from 0.98 to 0.99. (b) Growth rates of prototypes with different fabrication parameter values driven at constant pressure. (c) The effects of fabrication parameters on user comfort.
  • Figure 5: Patient transfer demonstrations. (a-b) With the soft growing robotic sling system placed under the participant's head, the robotic sling grows underneath the participant's body. (c-d) Participant is lifted from the bed with the deflated robotic sling using a Hoyer lift. (e) Hoyer lift is maneuvered by the caregiver to transfer the participant to a chair. (f) Participant is transferred back to lay in the bed. (g) Robotic sling automatically retracts itself from under the participant. (h) The system, including the wide base, is manually removed from under the participant's head.