Smart Soft Composite Research Articles

Sensitivity analysis of a smart soft composite robotic finger design using geometrically nonlinear laminated composite finite beam elements

Soft robotics is an emerging research field that uses deformable materials to build compliant and adaptable systems, using simple integrated mechanisms, enabling biomimetic behavior. This paper presents a sensitivity analysis of a shape memory alloy (SMA)-driven smart soft composite (SSC) bending actuator that is used as an artificial finger in robots or prosthetics. This SSC structure is made of a flexible material, such as polydimethylsiloxane (PDMS), reinforced with some layers of glass fiber sheets, and actuated via SMA wires embedded in the flexible material. The SMA wires shrink when thermally activated, resulting in bending the three flexible hinges of the finger. Designing such smart soft structures involves optimizing large number of design parameters such as the flexible hinge length and thickness, the number of composite layers and their orientation, the number of SMA wires and their diameters. Hence an accurate and efficient computational tool is required to perform sensitivity analysis, and facilitate and accelerate the design process. The mathematical model should also account for geometric nonlinearity due to the large deformation and rotation of the structure in hand. A recently-developed accurate and efficient novel geometrically-nonlinear laminated composite beam finite element model is used in this work for analyzing the SSC robotic finger. The sensitivity analysis revealed that the effect of the flexible hinge thickness in the studied design is much more significant than the hinge length, and that the relationship between the fingertip rotation and the hinge thickness is nonlinear for the case of one glass fiber sheet and approaches linearity as the number of sheets increases to three.

Pulse width modulation as energy-saving strategy of shape memory alloy based smart soft composite actuator

This paper presents electrical power consumption decreased in actuating a shape memory alloy (SMA) based smart soft composite (SSC) actuator using pulse width modulation (PWM). A DC current input generator and a PWM signal generator were designed to apply inputs to SSCs. Experiments were carried out on two types of SSC: one conventional, using a single SMA wire, and the other using multiple wires. The blocking force was measured to analyze the performance of the SSC. The experiments demonstrated that the PWM signal was able to reduce the actuation energy while showing the same performance as an analog current input. These results suggest that a PWM signal could be an alternative candidate for the input paradigm for SSCs to reduce energy consumption, expanding the uses of SSC actuators in robotic applications.

Soft morphing hand driven by SMA tendon wire

Abstract Most existing approaches to developing robotic manipulators or artificial hands have used rigid components, with joints, linkages, gears, and motors. Rigid robotic systems can perform tasks with precise and articulated motion, but require complex integrated feedback-based control systems. Soft robotics is an emerging research field that uses deformable materials to build systems that are compliant and adaptable via simple integrated mechanisms, enabling biomimetic behavior with compact systems. Here, we report a novel tendon-driven bending actuator using smart soft composite (SSC) and shape memory alloy (SMA). First, an artificial finger was designed based on a SMA wire and a sliding mechanism, which mimics flexion of the human hand. This artificial finger has a soft hinge structure to enable the bending motion of the actuator. Experiments were conducted to evaluate the bending and load resistance of the artificial finger, and an optimal material composition was identified. The bending performance of the actuator was measured with various numbers of glass fiber sheets, and two-layered actuator showed the best performance in terms of the trade-off relationship between the bending capacity and the load holding capacity – bending angle of 305° with weight of 20 g and bending angle of 61° with weight of 60 g. Finally, a prototype robotic hand was then developed using four tendon-driven SSC fingers and a thumb, and grasping capabilities were demonstrated with various objects with diverse shapes.

Soft composite hinge actuator and application to compliant robotic gripper

Abstract This work introduces the design of a smart soft composite (SSC) hinge actuator capable of a pure bending motion concentrated on specific sections of the actuator. This actuator makes use of a shape memory alloy (SMA) wire in a polydimethylsiloxane (PDMS) matrix embedded with segmented rigid components. The bending deformation was accomplished by actuating the SMA wire embedded along the length of the matrix eccentrically from neutral surface. This study introduces the design and manufacturing method of the actuator and experimental results for the maximum bending curvature for different configurations of the actuator. A model was presented to calculate the maximum bending curvature and validated against the experimental data. Results show that a smaller flexible length ratio is better for obtaining a larger maximum bending curvature, and that for an actuator containing multiple hinges, the total length of the hinges is more important than the number of hinges in the actuator. Finally, a gripper consisting of three fingers was developed where each finger consists of a hinge actuator with two hinges. The fingers of the gripper have a working length of 90 mm and the gripper was evaluated by grabbing cylindrical objects with diameters ranging between 1 mm and 80 mm. Results show that the gripper has a good passively adaptive capability for grasping a large range of objects with different sizes by virtue of the properties of the hinge actuator. Afterwards, the pulling force through different grasps was tested and it was shown that the gripper is capable from transitioning directly from a power grasping to a fingertip grasp and that power grasping is better than the fingertip grasp.

35 Hz shape memory alloy actuator with bending-twisting mode.

Shape Memory Alloy (SMA) materials are widely used as an actuating source for bending actuators due to their high power density. However, due to the slow actuation speed of SMAs, there are limitations in their range of possible applications. This paper proposes a smart soft composite (SSC) actuator capable of fast bending actuation with large deformations. To increase the actuation speed of SMA actuator, multiple thin SMA wires are used to increase the heat dissipation for faster cooling. The actuation characteristics of the actuator at different frequencies are measured with different actuator lengths and results show that resonance can be used to realize large deformations up to 35 Hz. The actuation characteristics of the actuator can be modified by changing the design of the layered reinforcement structure embedded in the actuator, thus the natural frequency and length of an actuator can be optimized for a specific actuation speed. A model is used to compare with the experimental results of actuators with different layered reinforcement structure designs. Also, a bend-twist coupled motion using an anisotropic layered reinforcement structure at a speed of 10 Hz is also realized. By increasing their range of actuation characteristics, the proposed actuator extends the range of application of SMA bending actuators.

Shape memory alloy/glass fiber woven composite for soft morphing winglets of unmanned aerial vehicles

Morphing technology is inspired by biological motion for implementation in missions in a variety of areas without shape-change device. This study investigates the aerodynamic performance of a self-contained morphing winglet for an unmanned aerial vehicle (UAV) that mimics the wing-tip feathers of gliding birds. A smart soft composite (SSC), formed of shape memory alloy (SMA) wires and glass fibers within a soft polymeric matrix, was used to fabricate morphing winglets. Experiments were conducted with various diameters and numbers of embedded SMA wires, and numbers of the glass-fiber fabric lamina, which were compared with an analytical model. Morphing winglets were implemented at both wing tips of a WASP 4/7-scale UAV, and the aerodynamic characteristics were investigated using a wind tunnel testing with various attack angles. As results, when the morphing winglet was actuated, the lift-to-drag ratio increased by 5.8% compared with the flat wing geometry for attack angle greater than 5°.

지능형 연성 복합재 구동기 제작을 위한 3D 프린팅-캐스팅 복합 공정

Intricate deflection requires many conventional actuators (motors, pistons etc.), which can be financially and spatially wasteful. Novel smart soft composite (SSC) actuators have been suggested, but fabrication complexity restricts their widespread use as general-purpose actuators. In this study, a hybrid manufacturing process comprising 3-D printing and casting was developed for automated fabrication of SSC actuators with 200 µm precision, using a 3-D printer (3DISON, ROKIT), a simple polymer mixer, and a compressor controller. A method to improve precision is suggested, and the design compensates for deposition and backlash errors (maximum, 170 µm). A suitable flow rate and tool path are suggested for the polymer casting process. The equipment and process costs proposed here are lower than those of existing 3D printers for a multi-material deposition system and the technique has 200 µm precision, which is suitable for fabrication of SSC actuators.

Comparison of mold designs for SMA-based twisting soft actuator

The design of SMA-based soft actuators is often limited by the design of the molds used, and these limitations are even more pronounced for actuators with complex shape memory alloy (SMA) wire positioning such as SMA-based twisting soft actuators. This paper aims at developing new mold designs to enable new design possibilities for the fabrication of pure-twisting smart soft composite (SSC) actuators. The basic design of the actuator uses two SMA wires embedded in a polymeric matrix at opposite eccentricity and crossing the matrix in opposite directions. This positioning induces a twisting motion to the matrix during actuation, but current mold designs impose many limitations on the design of the actuator. In this work, two molds design strategies are proposed that enable three distinct approaches to improve the performance of this actuator: interference fit fastening molds and using intermediate elements to reorient the SMA wires. These solutions enable the design of I-shaped cross-sections, composite cross-sections and square-helix positioning of the SMA wires within the matrix. A base actuator size is used to compare the performance of the different strategies then three actuators using combined solutions are manufactured and tested. Results show that the improved mold design can significantly increase the performance of this type of actuator.

Fabrication of wrist-like SMA-based actuator by double smart soft composite casting

A new manufacturing method for smart soft composite (SSC) actuators that consists of double casting a SSC actuator to produce an actuator with non-linear shape memory alloy (SMA) wire positioning is proposed. This method is used to manufacture a tube-shaped SSC actuator in which the SMA wires follow the curvature of the tube and is capable of pure-twisting deformations while sustaining a cantilever load. The concept is tested by measuring the maximum twisting angle and a simple control method is proposed to control the twisting angle of the actuator. Then, a soft robotic wrist with a length of 18 cm is built, its load-carrying capability is tested by measuring the cantilever force required for deforming the actuator, and its load-carrying capability during actuation is tested by loading one end with different objects and actuating the actuator. This wrist actuator shows good repeatability, is capable of twisting deformations up to 25° while holding objects weighing 100 g, and can sustain loads above 2 N without undergoing buckling.

SMA-based smart soft composite structure capable of multiple modes of actuation

This paper introduces the design of a smart soft composite (SSC) actuator capable of multiple modes of actuation. This actuator combines four shape memory alloy (SMA) wires embedded in a soft matrix where one or two SMA wires can be activated to induce the actuator into either the bending mode, the twisting mode or the combined bending and twisting mode of actuation. Experimental results for actuators of different lengths were obtained for all modes of actuation and the actuator is capable of large deformations in all modes and directions of actuation. Then a simple FEA model was used to predict the range of deformation for different lengths in the different modes of actuation. This model is able to predict accurately the bending and twisting angles of the actuator for the different modes of actuation. The 120 mm actuator is capable of deformations up to approximately 160° in both the pure bending and pure twisting modes and of approximately 80° for both twisting and bending in the combined twisting and bending mode of actuation.

Smart Phone Robot Made of Smart Soft Composite (SSC)

Soft morphing robotics making use of smart material and based on biomimetic principles are capable of continuous locomotion in harmony with its environment. Since these robots do not use traditional mechanical components, they can be built to be light weight and capable of a diverse range of locomotion. This paper illustrates a flexible smart phone robot made of smart soft composite (SSC) with inchworm-like locomotion capable of two-way linear motion. Since rigid components are embedded within the robot, bending actuators with embedded rigid segments were investigated in order to obtain the maximum bending curvature. To verify the results, a simple mechanical model of this actuator was built and compared with experimental data. After that, the flexible robot was implemented as part of a smart phone robot where the rigid components of the phone were embedded within the matrix. Then, experiments were conducted to test the smart phone robot actuation force under different deflections to verify its load carrying capability. After that, the communication between the smart phone and robot controller was implemented and a corresponding phone application was developed. The locomotion of the smart phone robot actuated through an independent controller was also tested.

Smart soft composite actuator with shape retention capability using embedded fusible alloy structures

This work presents a new kind of shape memory alloy (SMA) based composite actuators that can retain its shape in multiple configurations without continuous energy consumption by changing locally between a high-stiffness and a low-stiffness state. This was accomplished by embedding fusible alloy (FA) material, Ni-chrome (Ni–Cr) wires and SMA wires in a smart soft composite (SSC) structure. The soft morphing capability of SMA-based SSC structures allows the actuator to produce a smooth continuous deformation. The stiffness variation of the actuator was accomplished by melting the embedded FA structures using Ni–Cr wires embedded in the FA structure. First, the design and manufacturing method of the actuator are described. Then, the stiffness of the structure in the low and high-stiffness states of the actuator were measured for different applied currents and heating durations of the FA structure and results show that the highest stiffness of the actuator is more than eight times that of its lowest stiffness. The different shape retention capability of the actuator were tested using actuators with one or two segments and these were compared with a numerical model.

Locomotion of inchworm-inspired robot made of smart soft composite (SSC)

A soft-bodied robot made of smart soft composite with inchworm-inspired locomotion capable of both two-way linear and turning movement has been proposed, developed, and tested. The robot was divided into three functional parts based on the different functions of the inchworm: the body, the back foot, and the front foot. Shape memory alloy wires were embedded longitudinally in a soft polymer to imitate the longitudinal muscle fibers that control the abdominal contractions of the inchworm during locomotion. Each foot of the robot has three segments with different friction coefficients to implement the anchor and sliding movement. Then, utilizing actuation patterns between the body and feet based on the looping gait, the robot achieves a biomimetic inchworm gait. Experiments were conducted to evaluate the robot’s locomotive performance for both linear locomotion and turning movement. Results show that the proposed robot’s stride length was nearly one third of its body length, with a maximum linear speed of 3.6 mm s−1, a linear locomotion efficiency of 96.4%, a maximum turning capability of 4.3 degrees per stride, and a turning locomotion efficiency of 39.7%.

Cross-shaped twisting structure using SMA-based smart soft composite

This paper introduces a novel geometry for a pure-twisting soft morphing actuator that improves the stability of the actuator and allows it to obtain a larger twisting angle. The smart soft composite (SSC) actuator uses pair of NiTi shape memory alloy (SMA) wires embedded in a cross-shaped polydimethylsiloxane (PDMS) matrix at constant and opposite eccentricity across the cross-section in opposite directions in order to produce a twisting motion. To evaluate the twisting performance of the cross-shaped actuator, specimens with rectangular cross-sections and cross-shaped cross-sections are made and their twist angles are measured and compared. Results show that the cross-shaped actuator is capable of a higher twisting rate by using a thinner flange due to a more stable twisting motion.

Woven type smart soft composite beam with in-plane shape retention

Shape memory alloy (SMA) wire embedded composites (SMAECs) are widely used as morphing structures in small-size and high-output systems. However, conventional SMAECs cannot keep deformed shapes without additional energy. In this paper, a new kind of smart structure named the woven type smart soft composite (SSC) beam is introduced, which is not only capable of morphing, but also maintaining its deformed shape without additional energy. The woven type SSC beam consists of two parts: woven wires and matrix. The selected woven wires are nitinol (Ni–Ti) SMA wires and glass fibers, while the matrix part is polydimethylsiloxane (PDMS). In order to evaluate the performance of the woven type SSC beam in areas such as in-plane deformation, blocking force and repeatability, a beam-shape specimen is prepared of size 100 mm (length) × 8 mm (width) ×3 mm (thickness). The fabricated SSC beam achieved 21 mm deformation and 16 mm shape retention. Blocking force was measured using a dynamometer, and was about 60 mN. In the repeatability test, it recovered almost the same position when its cooling time was 90 s more. Consequently, the woven type SSC beam can be applied to bio-mimicking, soft morphing actuators, consuming less energy than traditional SMAECs.

직조 형태의 지능형 연성 복합재료를 이용한 쉘 구동기의 제작

Smart material such as SMA (Shape Memory Alloy) has been studied in various ways because it can perform continuous, flexible, and complex actuation in simple structure. Smart soft composite (SSC) was developed to achieve large deformation of smart material. In this paper, a shell actuator using woven type SSC was developed to enhance stiffness of the structure while keeping its deformation capacity. The fabricated actuator consisted of a flexible polymer and woven structure which contains SMA wires and glass fibers. The actuator showed various actuation motions by controlling a pattern of applied electricity because the SMA wires are embedded in the structure as fibers. To verify the actuation ability, we measured its maximum end-edge bending angle, twisting angle, and actuating force, which were 103°, 10°, and 0.15 N, respectively.

A turtle-like swimming robot using a smart soft composite (SSC) structure

This paper describes the development of a biomimetic swimming robot based on the locomotion of a marine turtle. To realize the smooth, soft flapping motions of this type of turtle, a novel actuator was also developed, using a smart soft composite (SSC) structure that can generate bending and twisting motions in a simple, lightweight structure. The SSC structure is a composite consisting of an active component to generate the actuation force, a passive component to determine the twisting angle of the structure, and a matrix to combine the components. The motion of such a structure can be designed by specifying the angle between a filament of the scaffold structure and a shape-memory alloy (SMA) wire. The bending and twisting motion of the SSC structure is explained in terms of classical laminate theory, and cross-ply and angled-ply structures were fabricated to evaluate its motion. Finally, the turtle-like motion of a swimming robot was realized by employing a specially designed SSC structure. To mimic the posterior positive twisting angle of a turtle’s flipper during the upstroke, the SMA wire on the upper side was offset, and a positive ply-angled scaffold was used. Likewise, for the anterior negative twisting angle of the flipper during the downstroke, an offset SMA wire on the lower side and a positive ply-angled scaffold were also required. The fabricated flipper’s length is 64.3 mm and it realizes 55 mm bending and 24° twisting. The resulting robot achieved a swimming speed of 22.5 mm s−1.