Various types of soft actuators have been developed for application in wearable movement-assist devices or soft robots. The authors have developed a straight-fiber-reinforced pneumatic rubber artificial muscle (SF-ARM). The SFARM is composed of rubber that is reinforced with fibers aligned only in the axial direction. When air pressure is applied to the SF-ARM, the reinforced fibers limit the rubber expansion to the radial direction so that the muscle contracts in the axial direction. The SF-ARM contracts by 38% at maximum, and this contraction rate exceeds the contraction rate of the McKibben artificial muscle. However, the SF-ARM is not well-suited for practical use because the strain on the SF-ARM while it is actuated is large which can cause fatigue failure of the rubber. This study focuses on suppressing the growth of cracks using strain-induced crystallization of the natural rubber, to prolong the lifetime of the SF-ARM. Natural rubbers form a crystalline layer in the direction perpendicular to the direction of stretching. This crystal layer effectively suppresses the growth of cracks in the SF-ARM when under strain. Deliberately developing a crystal layer should extend the lifetime of the SF-ARM. First, this study confirmed the formation of a crystal layer under extension of natural rubber (NR) and styrene butadiene rubber (SBR) using wide-angle X-ray diffraction measurements. Next, the strain concentration near the crack was analyzed using finite element method simulations. Finally, fatigue-life tests were conducted with SF-ARMs made of NR and SBR.
A dielectric elastomer actuator (DEA) is a soft actuator with low manufacturing cost and high energy efficiency. The structure of a DEA consists of a dielectric material interlayered with elastic electrodes, and DEA expands when an electric field is applied. The degree of freedom of movement of the DEA can be increased by devising the electrode arrangement in DEA. The performance of DEA is determined by permittivity, Young's modulus, and applicable electric field. Material properties including hysteresis loss are also important when a DEA is used as a sensor or high precision actuator. Generally, silicon and acrylic rubbers are used as the dielectric layer. This study focused on the use of a slidering material (SRM) as a more suitable dielectric for DEA than silicone and acrylic rubbers in terms of its dielectric constant and hysteresis loss. In a previous study, a DEA was developed using SRM as a dielectric, and the image correlation method (ICM) was applied to measure the strain distributions in a two-dimensional plane and the basic characteristics of DEA with one pair of electrodes. Here, the strain distribution was measured when the electrodes of the DEA were segmented into several pairs as the next step in the investigation of its basic characteristics. Patterns of electrode arrangements and the amount of DEA prestretching were changed, and strain distribution was measured using ICM.
A sensor-actuator coupled device was developed using solid polymer electrolyte membrane (SPM) as an active tracheal
tube for ventilator. Active tracheal tube is a novel type of tube for ventilator that removes patient's phlegm
automatically upon sensing the narrowing of trachea by phlegm. This type of active tube is extremely useful in clinical
settings as currently the sole measure to remove phlegm from patient's tube is to do it manually by a nurse every few
As SPM works both as a sensor and an actuator, an effective compact device was developed. SPM based
sensor-actuator coupled device was fabricated with modified gold plating method. Prepared SPM was fixed as an array
on a plastic pipe of diameter 22 mm and was connected to a ventilator circuit and driven by a ventilator with a volume
control ventilation (VCV) mode. SPM was connected both to a sensing unit and an actuation unit.
Generated voltage developed by the membrane with the setting of the maximum pressure from 5 cmH<sub>2</sub>O to 20 cmH<sub>2</sub>O
was in order of several hundred &mgr;V. SPM sensor demonstrated a biphasic response to the ventilator flow. The sensor
data showed nearly linearly proportional voltage development to the intra-tracheal pressure.
The sensed signal was filtered and digitized with an A/D converting unit on a PC board. A real time operating program
was used to detect the sensed signal that indicates the narrowing of trachea. The program then activated a driving
signal to control the actuation of the membrane. The signal was sent to a D/A converting unit. The output of the D/A
unit was sent to an amplifier and the galvanostat unit which drives the membrane with constant current regardless of the
change in the load.
It was demonstrated that the sensor-actuator unit detects the narrowing of trachea within several hundreds milli-seconds
and responds by actuating the same membrane with the driving voltage of 3-4 V and driving current of several hundred
milli-ampere for each membrane. SPM array actuated the obstructing material of 2 g to expel from the trachea tube.
Also, a theoretical model of the propagating wave generated by SPM was examined.
This paper describes experimental comparison between a conventional McKibben type artificial muscle
and a straight fibers type artificial muscle developed by the authors. A wearable device and a rehabilitation
robot which assists a human muscle should have characteristics similar to those of human muscle. In
addition, because the wearable device and the rehabilitation robot should be light, an actuator with a high
power/weight ratio is needed. At present, the McKibben type is widely used as an artificial muscle, but in
fact its physical model is highly nonlinear. Further, the heat and mechanical loss of this actuator are large
because of the friction caused by the expansion and contraction of the sleeve. Therefore, the authors have
developed an artificial muscle tube in which high strength glass fibers have been built into the tube made
from natural latex rubber.
As results, experimental results demonstrated that the developed artificial muscle is more effective
regarding its fundamental characteristics than that of the McKibben type; the straight fibers types of
artificial muscle have more contraction ratio and power, longer lifetime than the McKibben types. And it
has almost same characteristics of human muscle for isotonic and isometric that evaluate it dynamically.
Solid polymer electrolyte membrane (SPM) acts not only as an actuator but as a small, voltage generating, and fast response sensor. Sensing characteristics of SPM as applied to a flow sensor for a ventilator was studied. SPM was prepared by chemically plating with gold on the surface of Nafion membrane. A new technique using Nafion R-1100 resin was applied to fabricate SPM with an arbitrary thickness between 200-1000 μm. Flow sensing unit and signal amplifier was constructed to measure the induced voltage by bending SPM with air-flow from the ventilator. Induced voltage by SPM ranged 1-100 μV over a ventilator air-flow range of 20-100 L/min. SPM sensor showed linear increase of induced voltage by the increase of flow. This relationship was tested over a range of SPM thickness, length and width. The result was compared with an electro-mechanical coupling model of SPM transducer: data showed consistent result on the relation between the induced voltage and membrane length and thickness while a discrepancy was observed in the relation of membrane width and induced voltage. The result, however, was consistent with the assumption of capacitive component model.