Shape Memory Alloy Coil Actuators Research Articles

A Wearable Skin-Stretching Tactile Interface for Human–Robot and Human–Human Communication

Currently, the majority of wearable robotic haptic feedback devices rely on vibrations for relaying sensory information to the user. While this can be very effective, vibration as a physical stimulation is limited in modality and is uncommon in the natural world. In many cases, for human–robot and human–human interaction, a more natural, affective tactile interaction is needed to provide comfortable and varied stimuli. In this letter, we present the super-cutaneous wearable electrical empathic stimulator (SCWEES), a tactile device that gently stretches and squeezes the surface of the skin. Our hypothesis is that this device can create a pleasant, unobtrusive sensation that can be used to mediate social interactions or to deliver subtle alerts. We describe the design of the SCWEES, a lightweight 3D-printed semi-flexible structure that attaches to the skin at two points and actuates via two shape-memory alloy coil actuators. We evaluate the SCWEES through a range of human interaction experiments: stimulation strength and pleasantness, contraction and extension, and the conveyance of non-disruptive notifications. Quantitative and qualitative results show that the SCWEES generates a pleasant sensation, can convey useful information in human–machine interactions, and delivers affective stimulation that is less disruptive than conventional vibratory tactile stimulation when the user is engaged in a task.

Design of Shape Memory Alloy Coil Spring Actuator for Improving Performance in Cyclic Actuation

Performance of the shape memory alloy (SMA) coil spring actuator in cyclic actuation as an artificial muscle is strongly related to the mechanical design of the coil geometry. This paper proposes a practical design method for improving the frequency and efficiency of the SMA coil spring actuator; by designing the SMA coil spring to have large index (coil diameter/wire diameter) and pitch angle (LIP), cooling characteristics can be improved (increasing the actuation frequency) and large deformation can be obtained. The LIP design process is based on the two-state static model that describes the displacement-force relationship of the SMA coil spring in two states—a fully austenite phase and a fully martensite phase. The design process gives accurate design parameters of the SMA coil spring actuator that satisfy the required stroke and force. The model of the fully martensite phase of the SMA coil that includes the stress-induced detwinning enables the use of maximum shear strain of the SMA. The design method reduces the mass of an SMA without changing the stroke and increase the power density and efficiency. The cyclic actuation experiments demonstrate that the LIP design doubles the maximum frequency of SMA coil actuator with one-sixth the mass of the non-LIP design.

Optimizing POF/PCF based optical switch for indoor LAN

For indoor local area network (LAN) the Polymer optical fiber (POF) is mostly appropriate, because of its large core diameter and flexible material. A 1×2 optical switch for indoor LAN using POF and a shape memory alloy (SMA) coil actuator with magnetic latches was successfully fabricated and tested. To achieve switching by the movement of a POF, large displacement is necessary because the core diameter is large (e.g., 0.486mm). A SMA coil actuator is used for large displacement and a magnetic latching system is used for fixing the position of the shifted POF. The insertion loss is 0.40 to 0.50dB and crosstalk is more than 50dB without index-matching oil. Switching speed is less than 1s at a driving current of 80mA. A cycling test was performed 1.4 million times. Polymer clad fiber optical (PCF) switch also fabricated and tasted.

形状記憶合金を用いた能動屈曲電子内視鏡

Bending motions of the tip of a conventional endoscope are controlled from outside the body by wire traction. A shaft of an endoscope should be relatively hard to avoid buckling by wire traction. Therefore, precise operation of the endoscope is difficult in complex shape areas such as the intestine. Furthermore, patients suffer pain during a procedure with an endoscope. An active bending electric endoscope using shape memory alloy (SMA) actuators has been developed. A CCD camera (410,000 pixels) is mounted at the end of the endoscope and the tip has an omni-directional bending mechanism using three SMA coil actuators. The SMA coil actuators contract by supplying electrical current and bend the endoscope. The external diameter of the fabricated endoscope is 5.5 mm. The maximum bending angle of the fabricated endoscope is 90° (Curvature radius: 29 mm). The observation of the inside of a blood vessel model by the CCD imager of a fabricated endoscope was confirmed. The active bending shaft of the fabricated endoscope, which is realized using SMA coil actuators instead of wire traction, is soft. Therefore, using this endoscope, it may be possible to perform precise observations and treatment of deep areas of the human body.

Design and characteristics of large displacement optical fiber switch

Plastic optical fiber (POF) is suitable for indoor local area network (LAN), for example, in-home or office networks, because of its flexibility and its ease of connection due to its relatively large core diameter. A 1/spl times/2 optical switch for indoor LAN using POF and a shape memory alloy (SMA) coil actuator with magnetic latches was successfully fabricated and tested. In this paper, the design concept and the characteristics of this switch are described. To achieve switching by the movement of a POF, large displacement is necessary because the core diameter is large (e.g., 0.486 mm). A SMA coil actuator is used for large displacement and a magnetic latching system is employed for fixing the position of the shifted POF. For this design, the insertion loss is 0.40 to 0.50 dB and crosstalk is more than -50 dB without index-matching oil. Switching speed is less than 0.5 s at a driving current of 80 mA. A cycling test was performed 1.4 million times at room temperature. Another optical fiber switch was fabricated and successfully actuated using plastic clad fiber (PCF). PCF also has a large core diameter (e.g., 0.20 mm) and optical switches using PCF will be useful for short distance networks between buildings.

Dynamic Braille display using SMA coil actuator and magnetic latch

Braille points are varied arrangements of raised dots representing characters which are identified by touch by visually impaired people. A dynamic Braille display which presents Braille points by the up-and-down movement of pins using shape memory alloy (SMA) coil actuators and a magnetic latch has been developed. When the SMA coil actuator is heated by the flow of an electrical current, the compressed SMA extends, causing the pins to move up or down. The magnetic latch mechanism keeps the pins in an up or down state and solves the problem of heat storage and power consumption of the SMA actuator. Six Braille points (2 × 3) represent one character, the distances between the points being 2–3 mm. In order to fabricate a dense array of the SMA-actuated dynamic pins, Ni electroplating is utilized for batch forming of electrical connections between the SMA coil and the electrode on printed circuit boards. Displacement and latching power of each fabricated pin are sufficient for dynamic Braille. Sixteen pins representing two characters and two cursors are modularized to realize a line of dynamic Braille characters by lining up the modules. A control circuit and a driving circuit are mounted on each module to reduce the number of lead wires.