While the use of SMA-actuated devices continues to grow in many industries, current device limitations pose a challenge to successful adoption for certain classes of applications. SMA-actuated devices typically demonstrate motion with non-constant velocity due to the non-linear thermo-mechanically coupled behavior of SMA material transformation, and motion sensitivity to external factors such as voltage and load. This variation in motion can lead to the perception of poor device quality, limiting SMA-actuated devices to applications hidden from the sight of the product user, or requiring them to be augmented with higher cost controls to improve the motion quality. Therefore, a need exists for simple, passive, low-cost device technologies that enable the designer to prescribe desired motion characteristics with relative insensitivity to fluctuation in operating conditions. This paper presents a Damper Controlled Switch (DCS) mechanism that delivers constant velocity and relative insensitivity to operating conditions when combined with a standard SMA wire actuator. The DCS includes a damper that acts against a spring to open a switch when the velocity exceeds a tunable threshold. To validate the ability of the DCS to provide the desired motion quality, experiments were conducted comparing the normal motion of the SMA actuator to the motion produced when the same actuator was fitted with a DCS prototype. The addition of the DCS produced nearly constant actuator velocity, performing significantly better than the SMA actuator alone. The tunability of the DCS was demonstrated producing a wide range of attainable constant velocities. Finally, a set of experiments explored the DCS’s sensitivity to voltage and load, indicating a low sensitivity to a wide range of operating parameters for which the operating limits were identified. The DCS represents a simple, compact technology based on passive, low-cost components, providing a very practical solution that will enable integration of SMA-actuated devices into a broader class of applications.
Short Bowel Syndrome (SBS) is medical condition characterized by insufficient small intestine length, leading to
improper nutrient absorption and significant mortality rates. The complications of current treatment methods have
encouraged the development of a novel treatment method based on mechanotransduction, the process through which
mechanical tensile loading induces longitudinal growth of intestine. Animal based studies with simple extension devices
have demonstrated the potential of the treatment to grow healthy bowel, but an implantable device suitable for clinical
use remains undeveloped. This paper presents the development of an instrumented fully implantable bowel extender
based upon a shape memory alloy driven linear ratchet that can be controlled and monitored remotely. The overall
bowel extender system is described with respect to specifications for pig experimental tests. The functionality of the
mechanical and electrical subsystems of the device are detailed and experimentally validated on the bench top, in
segments of living bowel tissue removed from a pig, and in cadaveric pigs. Mechanical loading characteristics and safe
load limits on bowel tissue are identified. Results from these experiments establish the readiness of the device to be
tested in living pigs, enabling studies to move one step closer to clinical studies.