Search

Soft actuators are gaining attention as flexible components for soft robotics. Responsive materials that respond to external stimuli such as light are often used as the driving part of the soft actuator. For example, thermoresponsive soft actuators are fabricated by bilayer polymer films of different thermal expansion coefficients. Heating of such bilayer polymer films by plasmon heating enables the soft actuators to be driven remotely by light. In the present study, we report the fabrication of plasmonic heating driven responsive soft actuators by using metal-organic framework (MOF) thin films as supports of plasmonic nanoparticles. The thin films of Cu2(bpydc)2 (bpydc = 2,2’-bipyridine-5,5’-dicarboxylate) of which metal ion adsorption capacity is high were fabricated on Cu2(bpdc)2 (bpdc = 4,4’-biphenyldicarboxylate) which grown on ceramics precursor, Cu(OH)2. The actuating was operated by plasmon heating of Ag nanoparticles contained in MOF thin films inserted in between the two polymers, PDMS (poly(dimethylsiloxane)) and PVDC (poly(vinylidene chloride)). Two polymers have different thermal expansion coefficient so that they work as soft actuators by plasmon heating. Such fabrication process of soft actuators would pave the way for development of advanced devices in the field of soft robotics. [ABSTRACT FROM AUTHOR]

Soft robotics technology has the potential for a wide range of applications; however, their implementation is hindered by the lack of accurate mathematical models and control methods. For example, a method to control multiple pneumatic inflatable actuators in turn by a passive mechanism has been proposed in a literature, but no mathematical model was presented to develop control laws for the system. This study proposes a mathematical model for the inflation characteristics of sequential soft actuators, and theoretical control law for passive sequential control of the inflation of multiple actuators by using flow resistors. The model is constructed from the physical requirements of the actuators based on fluid dynamics and thermodynamics. The study shows that the pressure change characteristics can be derived from the differential equations even for complex parallel and series circuits. The model mathematically represents the physical principle by which the actuators' inflation order depends on the relationship between changes in the input pressure and internal pressure with time. Experiments with real circuits of simple and complex layouts are presented. The actuators are inflated in sequence from a single air pressure source, and the mathematical model was able to describe the pressure and flow rate change characteristics at each point in the circuit.

Since abnormal posture of the trunk due to aging decreases walking ability, the use of a trunk device is required to maintain and improve posture. Wearable assistive devices for the purpose of extending healthy life expectancy must be lightweight, have a simple mechanism, and have a drive system that cooperates with human movements. In our previous study, we developed an adjustable stiffness mechanism to correct the posture of the trunk. In this study, we propose a rotation mechanism that can support trunk rotation during walking and posture correction. The mechanism is a simple structure consisting of a bearing mechanism to reduce rotational resistance and a plastic block connected to pneumatic soft actuator bellows. Using a pneumatic soft actuator provides high adaptability to sudden human movements. This paper explains the outline of the proposed mechanism and the mathematical model of the actuator, followed by a description of the rotational stiffness adjustment method to support trunk rotation movements. Finally, the validity of the proposed mechanism and the effectiveness of the stiffness adjustment method are described based on the results of evaluation experiments.

The objective of this study was to improve the utility of a shape-memory-alloy (SMA) knitted fabric actuator. To that end, we employed a double-sided knitting structure with excellent structural stability and high yarn density and fabricated samples with different total number of courses, wales, and diameters of SMA fibers. These samples were subjected to repeated heating tests during uniaxial elongation along the direction of the wale, and the generated contraction force was measured. Furthermore, by comparing the results of the measurements, the influence of each parameter on the contraction force was evaluated. By including the amount of deformation in the direction of the knitting fabric width and the bending rigidity of the yarn in our analysis, we were able to determine the trend followed by the contraction force generated by SMA double-sided knitted fabrics. The results of this study are expected to be applicable to the development of smart textile products. [ABSTRACT FROM AUTHOR]

In a power assist robot driven with an artificial muscle, an accurate artificial muscle model is required to design a robot. It is desirable that the model can be calculated without adjustment parameters based on the actual characteristics of the artificial muscle. The characteristics of various artificial muscles mounted on the robot must be actually measured to identify the adjustment parameters. The above explanation is the reason why the accurate artificial muscle model without adjustment parameters is required. The purpose of this study is to improve the accuracy of the artificial muscle model by modeling the hysteresis characteristics of the artificial muscle based on the parameters such as material properties and geometric conditions. In this paper, we propose the hysteresis characteristic model of McKibben type artificial rubber muscle focused on the end shape of the artificial muscle. It is considered that the hysteresis is caused by the shearing force between the rubber surface and the fiber sleeve at the muscle end owing to friction. In the proposed model, the hysteresis characteristic is modeled based on the physical properties and shape parameters of the artificial muscle. The accuracy of the proposed model is confirmed by comparing with the actual characteristics of artificial muscles made with the same dimensions as the model.

Kyphosis causes decline in respiratory and circulatory functions owing to compresses of internal organs. The purpose of this study is to develop a posture keep assist device. The device is constructed with multiple resin components and McKibben type artificial rubber muscle. This device at initial state has a flexibility because the resin components are separated. On the other hand, the resin component can be connected by pressurized artificial muscle. The shape of device in which all resin components are connected imitates spine-curve to fit human back. So, the proposed device can retain entire range of trunk. Target pressure to correct posture is determined from the mathematical model of artificial muscle. In this paper, the structure of device is described, and control method to retain posture based on artificial muscle model is discussed. Finally, effectiveness of the device is verified from experiments in which subject wears this device actually. We reveal correcting trunk posture by using the device from the results.

Soft actuators are attracting attention as safe driving sources suitable for robots coexisting in human living environment. As one of the promising actuators, a fishing line artificial muscle has been proposed. It is manufactured by twisting nylon fiber into coil shape. It expands and contracts in response to temperature change. By using conductive nylon fiber as a material or winding a nichrome wire, it is possible to drive electrically by Joule heating. The actuator is able to control by simple driving circuit and feedback control method; however, a squared nonlinearity due to Joule's law exists in response characteristics. In this research, we apply a linearizing compensation by PWM drive and simple feedback control with unti-windup method. The proposed method is investigated through experiments.

The purpose of this research is to clarify the contractile force mechanism of a shape memory alloy (SMA) knitted fabric actuator. We knitted SMA yarn with plain stitches. We then determined the limit up to which SMA plain knitted fabric can be uniaxially elongated and thereafter the original dimensions can be recovered through its repeated heating. Moreover, the temperature dependence of SMA plain knitted fabric in the case of contractile force is quantitatively evaluated experimentally by heating it and then measuring its tension after it is extended to a certain length and fixed at both ends. The results show that, in its wale direction, the maximum tension by heating exceeds the tension corresponding to the extension. Furthermore, it is confirmed that theoretical calculations for the tensile properties of the knitted fabric of spun yam and filament yarn can be applied to plain knitted fabric of SMA yarn. Using this theoretical calculation, and the flexural rigidity measured by KES system, it is clarified the contractile force of the SMA knitted fabric actuator is affected not only by contraction of SMA yarn but also an increase in its flexural rigidity. [ABSTRACT FROM AUTHOR]

The purpose of this research is to develop a smart textile actuator for clothes. We developed a soft actuator with shape memory alloy wire by using flat knitting technology. It is capable of generating a maximum force of 0.61 N/mm and a maximum contraction of 7.8% when used for compression stockings. It was possible to increase the compression pressure from 10 hPa to 30 hPa in approximately 10 s. We also developed a soft actuator prototype of a flat knitting actuator covered by silicone sheets for a power assist suit. It has a length of 100 mm, a width of 60 mm, and a thickness of 2.3 mm. This actuator is capable of generating a maximum force of 22.7 N, which is more than twice the tension when it is 100% stretched. The data show that the soft actuator can be used for a power assist suit to prevent lumbago. [ABSTRACT FROM AUTHOR]

An ionic polymer-metal composite (IPMC) actuator is an electric driven soft actuator. It is fabricated by chemically plating metal on both surface of an ion-exchange membrane. It is able to be activated by a simple driving circuit and low applied voltage (0.5-3 V). However, a precise control of the IPMC actuator is difficult because of individual difference and characteristics changes from environmental conditions. To solve this problem, we applied the stochastic ON/OFF controllers to the integrated IPMC actuator with parallel connections. The controller consists of a central controller and distributed controllers. The central controller broadcasts a control signal as an error signal to distributed controllers uniformly. The distributed controllers switch the ON/OFF states based on the broadcasted signal stochastically. The central controller dose not measure the states of each IPMC actuator, and the control signals is calculated by using the output signal of the integrated actuator and reference signal. The validity of the applied methods was investigated through numerical simulations and experiments of displacement control. The proposed method was demonstrated to be useful as in the case that some actuator elements fail.