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Soft robotic gripper with EMB3D printed soft fingers. (a) Three fingers comprise a soft gripper fixed to a robot arm. (b) Inflating the tip (left), base (center), or tip and base (right) actuator networks enable three modes of finger bending and (c) different grasps. (d) Schematics of the finger from side (top), top-down (middle), and bottom-up (bottom) views. Scale bars are 30 mm.
Source publication
Soft robotic grippers enable gentle, adaptive, and bioinspired manipulation that is simply not possible using traditional rigid robots. However, it has remained challenging to create multi-degree-of-freedom soft actuators with appropriate sensory capabilities for soft manipulators requiring greater dexterity and closed-loop control. In this work, w...
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... somatosensitive manipulation requires an integrated design and fabrication strategy that streamlines the production of soft actuators with discrete actuation modes and integrated sensors. Here, we use embedded 3D (EMB3D) printing [12]- [15] to rapidly create soft, sensorized FEAbased fingers with multiple actuation motifs for soft manipulators ( Fig. 1). As a demonstration, we print soft fingers with two discrete fluidic networks that allows for tip, base, and full-finger actuation (Fig. 1b) and multiple grasping motifs (Fig. 1c). Four soft resistive sensors -two curvature and two contact sensors -innervate each finger (Fig. ...
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... discrete actuation modes and integrated sensors. Here, we use embedded 3D (EMB3D) printing [12]- [15] to rapidly create soft, sensorized FEAbased fingers with multiple actuation motifs for soft manipulators ( Fig. 1). As a demonstration, we print soft fingers with two discrete fluidic networks that allows for tip, base, and full-finger actuation (Fig. 1b) and multiple grasping motifs (Fig. 1c). Four soft resistive sensors -two curvature and two contact sensors -innervate each finger (Fig. ...
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... sensors. Here, we use embedded 3D (EMB3D) printing [12]- [15] to rapidly create soft, sensorized FEAbased fingers with multiple actuation motifs for soft manipulators ( Fig. 1). As a demonstration, we print soft fingers with two discrete fluidic networks that allows for tip, base, and full-finger actuation (Fig. 1b) and multiple grasping motifs (Fig. 1c). Four soft resistive sensors -two curvature and two contact sensors -innervate each finger (Fig. ...
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... fingers with multiple actuation motifs for soft manipulators ( Fig. 1). As a demonstration, we print soft fingers with two discrete fluidic networks that allows for tip, base, and full-finger actuation (Fig. 1b) and multiple grasping motifs (Fig. 1c). Four soft resistive sensors -two curvature and two contact sensors -innervate each finger (Fig. ...
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... we designed a soft robotic gripper comprised of three FEA-based fingers possessing discrete actuation modes with soft proprioceptive and tactile sensors corresponding to each DOF in actuation. While our methods can be used to create actuators with an arbitrary number of free-form sensors and actuator networks, the devices presented in this work (Fig. 1d) have two FEA networks, a base and tip actuator network, that drive bending of the base and tip regions of the finger. The fingers' ionogel sensors, have a resistance, R S , given by R S = ρ * (l/A), where ρ is the resistivity of the ionogel ink, l is the length of the sensor, and A is the cross-sectional area of the sensor trace. As ...
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... is inflated. Short (S Contact,S ) and long contact (S Contact,L ) sensors beneath the fingertip provide tactile sensing when these features are compressed by contact pressures. S Contact,L is designed to indicate when contact has been made at the very tip of the finger, and S Contact,S provides feedback when contact is more proximal from the tip (Fig. 1d). Given their complex form and multi-material composition, we used EMB3D printing to fabricate our soft fingers. We print the soft sensors from an organic ionogel-based sensor ink to ensure stable, reliable perception with hysteresis-free conductivity. Finally, we designed new readout hardware for streamlined measurement of changes in ...
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... our gripper grabs with full-finger actuation, the fingers rarely hold objects right against both contact sensors. By contrast, good contact between the contact sensors and an object can occur with base-only actuation (Figs. 1c, 8ab), increasing both contact sensors' resistances. However, depending on how contact is made with an object, full actuation can generate sufficiently high contact forces to increase resistance of both contact sensors, even though the object is not pressing directly against both. To showcase the value of having discrete control over base ...
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... The choice of flexible tactile sensors is a viable option for measuring the firmness of the fruit. However, current tactile sensor technologies such as photoelectric [20], piezoresistance [21], capacitance [22,23], and liquid pressure [24,25] have limitations in accurately detecting fruit firmness due to their inability in precisely measuring fruit deformation. The GelSight sensor is a photometric stereo vision-based tactile sensor that can detect the 3D texture of a measured object's surface and its shape after compression and deformation. ...
Since fresh cherry tomatoes have a high likelihood of spoilage during post-harvest transport and storage, assessing the fruit grade based on its firmness or predicting its potential storage time becomes necessary. The study proposes a method for non-destructive fruit firmness detection using a photometric stereo vision-based tactile sensor. The tactile sensor can measure the three-dimensional deformation of cherry tomatoes by mapping between pixel color and surface normal using a gradient prediction network. The summation of the deformation heights measured by a tactile sensor pressing on the cherry tomatoes can accurately describe fruit firmness, which was also verified by a comparative experiment with the Texture Analyzer. To create a model of firmness variation over time, a group of tomatoes of the same variety and origin were measured for firmness at various storage dates following harvest in subsequent experiments. An experiment was conducted to measure and predict the variation in the firmness of cherry tomatoes using a tactile sensor. The results indicate that the firmness of cherry tomatoes decreases linearly over time under similar conditions. The relative prediction errors were found to be mostly within ± 15% and ± 25% during 1 and 2 weeks of storage, respectively. All findings indicate that the proposed method can effectively measure the firmness of cherry tomatoes and accurately predict their short-term variations.
Soft robots have revolutionized machine interactions with humans and the environment to enable safe operations. The fixed morphology of these soft robots dictates their mechanical performance, including strength and stiffness, which limits their task range and applications. Proposed here are modular, reconfigurable soft robots with the capabilities of changing their morphology and adjusting their stiffness to perform versatile object handling and planar or spatial operational tasks. The reconfiguration and tunable interconnectivity between the elemental soft, pneumatically driven actuation units is made possible through integrated permanent magnets with coils (PMC). The proposed concept of attaching/detaching actuators enables these robots to be easily rearranged in various configurations to change the morphology of the system. While the potential for these actuators allows for arbitrary reconfiguration through parallel or serial connection on their four sides, we demonstrate here a configuration called ManusBot. ManusBot is a hand-like structure with digits and palm capable of individual actuation. The capabilities of this system are demonstrated through specific examples of stiffness modulation, variable payload capacity, and structure forming for enhanced and versatile object manipulation and operations. The proposed modular, soft robotic system with interconnecting capabilities significantly expands the versatility of operational tasks as well as the adaptability of handling objects of various shapes, sizes, and weights using a single system.
Soft actuators are one of the primary and critical components of a soft robot. Soft robots demand dexterous, fast, and reversible soft actuators that must be able to contract, extend, bend, and/or twist with favorable performance while delivering sufficient output forces. Pneumatic soft actuators are one of the most used types of soft actuators for soft robotic systems since they can be designed with internal deformable hollow chambers that dictate a desired output motion and can be directly fabricated using various additive manufacturing techniques. Pneumatic soft actuators based on a volumetric expansion and contraction are two main classes that include positive pressure soft actuators requiring compressed air to be activated or inflated upon their actuation and negative pressure soft actuators requiring a vacuum source for actuation. This chapter presents four-dimensional (4D)-printed pneumatic soft actuators that are fabricated directly using various additive manufacturing techniques, including fused deposition modeling (FDM), stereolithography (SLA), digital light processing (DLP), selective laser sintering (SLS), material jetting (MJ), and rapid liquid printing (RLP), to generate a useful mechanical output for a purpose and function they are designed and fabricated for. The actuators are presented in terms of their types, modeling, materials, fabrication, sensing, control, capabilities, and applications in diverse soft robotic systems. A discussion is provided on the presented 4D-printable soft actuators along with a list of what is needed to develop robust and functional soft pneumatic actuators for soft robots. This chapter emphasizes the importance of implementing a top-down approach to stimulate more interaction between materials scientists and robotic researchers so that three-dimensional (3D)- and 4D-printable soft materials that meet the function and application requirements of a robotic system are developed to fully exploit such synthesized materials by roboticists and use them in practical robotic systems and devices.
Soft actuators are compliant structures that are generally made of elastomers and generates large deformation. The behavior of these structures cannot be estimated accurately using infinitesimal strain theories. The objective of soft robotics applications is the controlled large deformation of these structures. In this article, we propose an analytical model for a pneu-net soft actuator. The model is based on the Euler–Bernoulli finite strain hyperelastic thin cantilever beam theory. The deformation of the air chambers is modeled using finite strain membrane theory. The analytical model is developed for two different states of the actuator: 1) free space; and 2) when the actuator was subjected to tip contact. The proposed theoretical model predicts the deformation and force characteristics of the actuator for the grasping state. The theoretical formulation of the developed model is different from previously developed infinitesimal strain models for the actuator, as it considers the axial stretch and forces applied to the actuator. In addition, it can be theoretically implemented on similar structured actuators for various applications. The theoretically calculated deformation and force characteristics of different actuators are compared with the finite element (FE) model and experimental characteristics. The results suggest that the proposed model can predict the actuator deformation and force characteristics as accurately as the FE model, but the computation time of the proposed model is less than 1% that of the FE model. The proposed model is further implemented on a three-finger gripper to predict the air pressure required for a stable grasp of different objects and is validated experimentally.
Soft robots built with active soft materials have been increasingly attractive. Despite tremendous efforts in soft sensors and actuators, it remains extremely challenging to construct intelligent soft materials that simultaneously actuate and sense their own motions, resembling living organisms’ neuromuscular behaviors. This work presents a soft robotic strategy that couples actuation and strain-sensing into a single homogeneous material, composed of an interpenetrating double-network of a nanostructured thermo-responsive hydrogel poly(N-isopropylacrylamide) (PNIPAAm) and a light-absorbing, electrically conductive polymer polypyrrole (PPy). This design grants the material both photo/thermal-responsiveness and piezoresistive-responsiveness, enabling remotely-triggered actuation and local strain-sensing. This self-sensing actuating soft material demonstrated ultra-high stretchability (210%) and large volume shrinkage (70%) rapidly upon irradiation or heating (13%/°C, 6-time faster than conventional PNIPAAm). The significant deswelling of the hydrogel network induces densification of percolation in the PPy network, leading to a drastic conductivity change upon locomotion with a gauge factor of 1.0. The material demonstrated a variety of precise and remotely-driven photo-responsive locomotion such as signal-tracking, bending, weightlifting, object grasping and transporting, while simultaneously monitoring these motions itself via real-time resistance change. The multifunctional sensory actuatable materials may lead to the next-generation soft robots of higher levels of autonomy and complexity with self-diagnostic feedback control.
Additive manufacturing, or more commonly known as 3D printing, has been at the forefront of manufacturing research for the past couple decades. Many advances have occurred in the basic printing techniques, materials, and post-processing schemes. In recent years, there have been many critical developments in the field 3D printing, such as the development of volumetric 3D printing to increase the printing speed, composite 3D printing to create piezoelectric devices, and hydrogel structures highly similar to blood vessels. The spectrum of materials that can be printed has also increased, allowing researchers to print a variety of materials including live cells, modulus changing polymers and even spacecraft-grade metals.
