SLAK Completely Supports Sit to Stand*
Allan J. Veale, Kyrian Staman, and Herman van der Kooij
Abstract— Current soft actuators are favorable for wearable
applications because of their intrinsic safety [1] and ergonomic
comfort [2]. However, they cannot provide the torque to
completely support everyday movements such as sit to stand
[3]. High torques, sometimes sufficient for complete support,
are important for people with complete spinal cord injuries,
rehabilitation of stiff joints, and protecting workers in
danger-ous environments from injury.
This talk reports the design and preliminary results on a
simple high torque actuator, the pleated pneumatic interference
actuator (PPIA), that is used in a sit to stand (STS) orthosis
(Fig. 1), the soft lifting assistor for the knee (SLAK). PPIAs
are based on Nesler et al.’s [4] PIA and made from fabric
reinforced rubber bladders. In our previous work [5], the
constraints required to laterally stabilize the single PPIA behind
the leg limited its range of motion (ROM) well below that
required for STS. The 1.35 kg SLAK eliminates the lateral
constraints. Instead, it has three parallel PPIAs made of sealed
firehose lengths inserted into a 1000D Cordura fabric sleeve.
At 320 kPa the SLAK was shown to completely support
standing over 94 % of the STS motion (Fig. 2), a very significant
improvement over the 67 % of the STS motion of our previous
design [5]. The SLAK does so with a torque of 3.8 Nm at 7.9 °
increasing parabolically to 320 Nm at 82 ° knee flexion.
When worn, the SLAK generates a torque over the knee’s
complete ROM, even providing a torque to support the knee
in full extension. However, this is not reflected in the data due
to the shifting of the SLAK on the smooth test leg, particularly
at low flexion angles. At these angles the significant shear
component generated by the PPIA’s torque caused the two
ends of the PPIA to move away from each other, misaligning
it completely away from the knee joint and preventing it from
applying measurable torque. Future work will resolve this
problem, and characterize the power and speed performance
of the SLAK.
R
EFERENCES[1] R. Van Ham, T. G. Sugar, B. Vanderborght, K. W. Hollander, and D. Lefeber, “Compliant actuator designs: Review of actuators with passive adjustable compliance/controllable stiffness for robotic appli-cations,” IEEE Robot. Autom. Mag., vol. 16, no. 3, pp. 81–94, 2009. [2] M. Wehner, B. Quinlivan, P. M. Aubin, E. Martinez-Villalpando,
M. Baumann, L. Stirling, K. Holt, R. Wood, and C. Walsh, “A lightweight soft exosuit for gait assistance,” in IEEE Int. Conf. Robot. Autom., May 6–10, 2013, pp. 3362–9.
[3] J. Chung, R. Heimgartner, C. T. O’Neill, N. S. Phipps, and C. J. Walsh, “ExoBoot, a soft inflatable robotic boot to assist ankle during walking: Design, characterization and preliminary tests,” in IEEE Int. Conf. Biomed. Robot. Biomechatron., Enschede, Netherlands, August 26–9, 2018, pp. 509–16.
[4] C. R. Nesler, T. A. Swift, and E. J. Rouse, “Initial design and experimental evaluation of a pneumatic interference actuator,” Soft Robotics, vol. 5, no. 2, pp. 138–48, 2018.
*This work is supported by the Netherlands Organization for Scientific Research (NWO), project number 14429.
Authors are with the Department of Biomechanical Engineering, Faculty of Engineering Technology, University of Twente, 7500 AE Enschede, The Netherlands (email:
a.j.veale@utwente.nl
)Pleat constraint Pleat Air in/out Flexible tube Valley fold Mountain fold (a) P θ
τ
(b)Fig. 1: The SLAK (a), and operation of the PPIA (b).
Inflation of a flexible pleated tube generates a torque τ
dependent on its flexion angle θ and pressure P .
Fig. 2: Sit to stand (STS) knee extension torque-angle data
[6], [7], [8] for an 80 kg person, the maximum torque of
Chung et al.’s ExoBoot [3], the torque produced by the
SLAK (n = 6 experiments), and the torque produced by
the previous PPIA orthosis [5]
[5] A. J. Veale, K. Staman, and H. van der Kooij, “Realizing soft high torque actuators for complete assistance wearable robots,” in Int. Symp. Wearable Robotics, Pisa, Italy, October 16–20, 2018, pp. 39–43. [6] M. K. Y. Mak, O. Levin, J. Mizrahi, and C. W. Y. Hui-Chan, “Joint
torques during sit-to-stand in healthy subjects and people with parkin-sons disease,” Clin. Biomech., vol. 18, no. 3, pp. 197–206, 2003. [7] Y.-C. Pai and M. W. Rogers, “Speed variation and resultant joint torques
during sit-to-stand,” Arch. Phys. Med. Rehabil., vol. 72, no. 11, pp. 881– 5, 1991.
[8] M. E. Roebroeck, C. A. M. Doorenbosch, J. Harlaar, R. Jacobs, and G. J. Lankhorst, “Biomechanics and muscular activity during sit-to-stand transfer,” Clin. Biomech., vol. 9, no. 4, pp. 235–44, 1994.
