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Owing to the integrated muscular, ligamentous and skeletal structures and coupled degrees of freedom (DoFs), it is a long-term challenge in the field of robotics to design an anthropomorphic hand that mimics the biological structures and dexterous motions of human hands. In this paper, we present pneumatical, multi-material 3D-printed, modularized...
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... hand may introduce difficulties in design, fabrication and control [30]. In this section, we decouple the mobility of human hand into 11 DoFs and employ the modularized RFiSFAs to construct the 2-DoF flexion finger and the 3-DoF thumb. Note that index, middle, ring and little fingers share the same finger type, i.e., the 2-DoF flexion finger. Fig. 8(a) illustrates the 2-DoF flexion finger consisting of two serially linked 7-bellow RFiSFAs. These two RFiSFAs are responsible for flexion motions at MCP joint and PIP joint, respectively. MCP joint and PIP joint are underactuated with an internal air channel and hence only one air inlet is reserved for tube connection. The distal ...
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... motions at MCP joint and PIP joint, respectively. MCP joint and PIP joint are underactuated with an internal air channel and hence only one air inlet is reserved for tube connection. The distal interphalangeal (DIP) joint is passive and integrated with the fingertip, which is designed as an interactive flexible interface with the environment. Fig. 8(b) illustrates the 3-DoF thumb consisting of two parallel 10-bellow RFiSFAs and two serial 7-bellow RFiSFAs. It performs circumduction, adduction and flexion motions from the proximal end to the distal end. Firstly, two parallel 10-bellow RFiSFAs form the circumduction unit which is fixed on the palm skeleton with an incidence angle of ...
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... The rigid opaque resin (Vero series, Vero PureWhite TM ) and the Agilus30 (Shore hardness = 30A, a polyjet rubber-like material) were selected to effectively distinguish the rigid facets (white) from the flexible creases (black) [36]. Their fundamental mechanical properties can be found in [61] and on stratasys.com. ...
Kresling origami is a topic that is constantly being researched, especially when it comes to the cylindrical mechanisms made up of special quadrilateral units. It’s also fascinating that the conical mechanisms based on the Kresling pattern are gaining more attention lately. However, designing conical mechanisms with stable behavior and solving the stress concentration in crease areas for practical engineering applications remains less researched. Therefore, this study considers quadrilateral unit cells as the research object, designs a conical origami tube (COT), and establishes a theoretical model with five variables to systematically investigate the COT. Based on this, the design domain related to the design variables is proposed, and the COT is analyzed in three cases. We further explored the influence of η (conical degree) on the COT. In addition, this study implements a cutting design on each crease vertex to reduce the impact of stress concentration on the nonlinear response through finite element shell models and uniaxial compression experiments. The findings of this study reveal that the setting of η and the crease-cutting design have a remarkable impact on the mechanical properties and stability behavior.
... The embedding of the sensor by FFF can be seen in Figure 1A, and a hypothetical example of a sensor embedded in a soft robotic gripper arm gripping a strawberry is shown in Figure 1B. AM also introduces the possibility to easily manipulate compliance by fabricating multi-material and meta-material components or by integrating other features such as self-healing in the structure [2,25,31,32]. NinjaTek Eel [33] is a commercially available TPU 3D-printing filament with carbon additives, resulting in both conductive and flexible properties [34]. The material can be integrated in the component to create integrated PCBs and three-dimensional meshes of flexible conductive wires. ...
... Printed sensors have been used to measure strain, tactility, pressure, stress, displacement, acceleration, magnetic fields, temperature, and humidity [39][40][41][42]. FFF offers the possibility to print flexible sensors integrated into soft robots using multi-material printing, although previous studies have shown the AM also introduces the possibility to easily manipulate compliance by fabricating multi-material and meta-material components or by integrating other features such as self-healing in the structure [2,25,31,32]. NinjaTek Eel [33] is a commercially available TPU 3D-printing filament with carbon additives, resulting in both conductive and flexible properties [34]. The material can be integrated in the component to create integrated PCBs and three-dimensional meshes of flexible conductive wires. ...
Additive manufacturing (AM) offers new possibilities in soft robotics as materials can easily be combined in multi-material designs. Proper sensing is essential for the soft actuators to interact with the surroundings successfully. By fabricating sensors through AM, sensors can be embedded directly into the components during manufacturing. This paper investigates NinjaTek Eels electrical resistance response to strain and the feasibility of using the material to create strain sensors. Strain sensors were 3D-printed out of NinjaTek Eel, a soft conductive TPU, and was tested during cyclic loading. A custom resistance-strain test rig was developed for measuring sensor behavior. The rig was calibrated for electric resistance, able to measure electric resistance as a function of strain. A parabolic response curve was observed during cyclic loading, which led to ambiguous readings. A 10-specimen validation test was conducted, evaluating the statistical variation for the first 100 loading cycles. The validation test showed that the sensor is capable of accurate and predictable readings during single load cases and cyclic loading, with the overall root mean square error being 66.9 Ω. Combining two sensors of different cross-sections gave promising results in terms of calibrating. By monitoring load cycles and strain rates, calibration can also be achieved by machine learning models by the microcontroller used to extract data. The presented work in this article explores the potential of using conductive TPUs as sensors embedded in products such as soft robotics, life monitoring of products with structural, and digital twins for live product to user feedback.
... Reproduced with permission. [112] Copyright 2023, Elsevier. e) A bio-inspired joint that mimics the anatomy of a human hand with 3D-printed bone structures and rubber ligaments. ...
... Reproduced with permission. [112] Copyright 2023, IEEE. e) An articulated robotic hand with soft sensing chambers and tendons printed in a single print job. ...
In this article, 3D‐printed anthropomorphic hands for prosthetic or robotic applications are reviewed as 3D printing has transformed manufacturing by enabling the creation of intricate structures layer by layer, offering design freedom and efficiency. This review categorizes 3D‐printed anthropomorphic hands based on actuation, transmission, joint, and functional features like sensing and grasp patterns. It also assesses the level of anthropomorphism and validation methods by presenting criteria in prosthetic and robotic applications. Then, the article discusses 3D printing technologies in their usage and types, highlighting the advantages of multi‐material capabilities and integration of different hand components. Future directions on structural components, anthropomorphism, validation, and use of 3D printing are discussed, focusing on trends that only 3D printing technology can achieve in anthropomorphic hand development.
... A series of SPAs with specific deformation modes including elongation/contraction, bending, and twisting are proposed, such as fiber-reinforced actuators [6], [7], [8], [9], pneumatic networks (PneuNets) actuators [10], [11], bellow actuators [12], [13], [14], [15], and pouch actuators [16], [17], and they are further integrated into grippers and manipulators to execute grasp or manipulation tasks. However, the single motion mode by these actuators is insufficient for achieving complex tasks in different working scenarios, limiting their application in manipulation. ...
Soft pneumatic actuators (SPAs), due to their compliance and adaptiveness, are promising solutions for manipulation. However, most SPAs have only simple motion modes and cannot perform the compound motion required for complex manipulation. In this work, we propose a parallel-chamber actuator capable of multidirectional compound bending, short for CBPCA, to provide compound motion. The key component of the actuator is the specially trimmed fishbone-like strain-limiting layer. By differentially limiting the strain on the CBPCA surface, the layer induces the main bending while allowing lateral bending to enable multidirectional compound bending of CBPCA. Further, the layer is designable to tune the motion and mechanical properties of CBPCA. We develop a kinematic model based on constant curvature assumptions to analyze and forecast the motion of CBPCA. Further, we characterize the manipulation-related indicators of the CBPCA, including workspace, passive stiffness, and blocked force. The proposed CBPCA can achieve a wide-range kite-shaped spatial workspace with a motion range of 80.5
$\%$
and 76.9
$\%$
actuator length in main and lateral bending directions, respectively. To verify the manipulation capability of the CBPCA, we developed two typical forms of manipulators: a four-finger gripper and a three-finger anthropomorphic hand to conduct experiments. The results show that the CBPCA performs effectively in dexterous manipulation where basic motion primitives and complex manipulation in activities of daily living, such as setting workpieces and installing bulbs, are well-completed.
... Compliant mechanisms offer benefits such as bi-directional force generation, compactness, lack of lubrication requirements, and absence of backlash. These approaches often involve additive manufacturing or 3D printing for components, typically combined with elastic elements like spring steel [17,18,42] or are fabricated entirely using 3D printing [43,44]. The latter, however, is more common in the design of robotic fingers, and has not been as widely implemented in the hand exoskeleton space. ...
Hand exoskeletons are potential solutions for enhancing upper extremity function after stroke, yet achieving intuitive control remains challenging. We recently showed that isometric grip force tracking is preserved after stroke, providing a possible control source for a hand exoskeleton. In this study, we developed a hand exoskeleton with a soft compliant mechanism and novel force control strategy that leverages isometric grip force control of digits 3–5 to control an index–thumb pinch grip. We first present characterization of the compliant mechanisms output impedance (34.77 N/m), and output force (2.3 ± 0.57 N). We then present results of a study that assessed the intuitiveness of the strategy during a grip–lift–move task in ten unimpaired individuals. From four unimpaired individuals we also gathered user preferences on force sensitivity and operating mode, where in one mode flexion force from digits 3–5 caused index finger closing, while in the other mode it caused index finger opening. The strategy proved intuitive, improving movement frequency on the grip–lift–move task by 30%. Users preferred greater force sensitivity and using flexion force from digits 3–5 to drive index finger extension. The force control strategy incorporated into the exoskeleton shows promise warranting further investigation in neurologically impaired participants.
... Digital fabrication can involve direct or indirect approaches. Threedimensional printing effectively realizes soft actuators and glove components [67][68][69]. ...
Stroke, the third leading cause of global disability, poses significant challenges to healthcare systems worldwide. Addressing the restoration of impaired hand functions is crucial, especially amid healthcare workforce shortages. While robotic-assisted therapy shows promise, cost and healthcare community concerns hinder the adoption of hand exoskeletons. However, recent advancements in soft robotics and digital fabrication, particularly 3D printing, have sparked renewed interest in this area. This review article offers a thorough exploration of the current landscape of soft hand exoskeletons, emphasizing recent advancements and alternative designs. It surveys previous reviews in the field and examines relevant aspects of hand anatomy pertinent to wearable rehabilitation devices. Furthermore, the article investigates the design requirements for soft hand exoskeletons and provides a detailed review of various soft exoskeleton gloves, categorized based on their design principles. The discussion encompasses simulation-supported methods, affordability considerations, and future research directions. This review aims to benefit researchers, clinicians, and stakeholders by disseminating the latest advances in soft hand exoskeleton technology, ultimately enhancing stroke rehabilitation outcomes and patient care.
... Other variable stiffness methodologies include interference-based methods [98], motor-based methods [99], variable modulus-based methods [100], electromagnetic field-based methods [101], and phase change material-based methods [102]. Examples of stiffness-based methods to adjust grasping and manipulation performance are presented in Figure 3. Rigid−flexible integration configuration [33], (b), integration of shape memory polymer for variable stiffness [103] (c), particle jamming method for two fingered−gripper (d), particle jamming method for three−fingered gripper [96]. ...
... Moreover, current rigid-soft coupling gripper designs often feature complex and bulky structures, which substantially limit their compliance. Furthermore, high stability is imperative for robotic grippers, as soft robotic grippers frequently undergo deformation [33], (b), integration of shape memory polymer for variable stiffness [103] (c), particle jamming method for two fingered−gripper (d), particle jamming method for three−fingered gripper [96]. ...
Humans possess dexterous hands that surpass those of other animals, enabling them to perform intricate, complex movements. Soft hands, known for their inherent flexibility, aim to replicate the functionality of human hands. This article provides an overview of the development processes and key directions in soft hand evolution. Starting from basic multi-finger grippers, these hands have made significant advancements in the field of robotics. By mimicking the shape, structure, and functionality of human hands, soft hands can partially replicate human-like movements, offering adaptability and operability during grasping tasks. In addition to mimicking human hand structure, advancements in flexible sensor technology enable soft hands to exhibit touch and perceptual capabilities similar to humans, enhancing their performance in complex tasks. Furthermore, integrating machine learning techniques has significantly promoted the advancement of soft hands, making it possible for them to intelligently adapt to a variety of environments and tasks. It is anticipated that these soft hands, designed to mimic human dexterity, will become a focal point in robotic hand development. They hold significant application potential for industrial flexible gripping solutions, medical rehabilitation, household services, and other domains, offering broad market prospects.
... And on the controls side, a concept called "synergies" has been studied in the context of achieving dexterous and efficient movements. [76,110,111] Synergies provide coordinated patterns of joint movements that allow the hand to perform grasping and manipulation tasks effectively. Since the underactuated design allows for shared mechanical elements, and since synergies give a simplified variable of motion, researchers have connected the two concepts closely to improve robotic hands' capabilities [20,112]. ...
The development of robotic hands that can replicate the complex
movements and dexterity of the human hand has been a longstanding challenge for
scientists and engineers. A human hand is capable of not only delicate operation but
also crushing with power. For performing tasks alongside and in place of humans, an
anthropomorphic manipulator design is considered the most advanced implementation,
because it is able to follow humans’ examples and use tools designed for people. In
this article, we explore the journey from human hands to robot hands, tracing the
historical advancements and current state-of-the-art in hand manipulator development.
We begin by investigating the anatomy and function of the human hand, highlighting
the bone-tendon-muscle structure, skin properties, and motion mechanisms. We then
delve into the field of robotic hand development, focusing on highly anthropomorphic
designs. Finally, we identify the requirements and directions for achieving the next
level of robotic hand technology.
... Some works like [10][11][12] also develop different actuators applied in dexterous thumb joints. Meanwhile, our group [13][14][15] develop several different types of soft actuators that can be applied to soft prosthetic hands. Overall, to realize the motion of thumb, current prototypes generally adopt silicon-rubber-based soft actuators. ...
Although various advanced anthropomorphic hands have been proposed, the design and fabrication of thumb joints to achieve dexterity function in a limited space is still a great challenge. To promote the dexterity of the anthropomorphic thumb joints in the cramped space of the palm, we present a fabric-based flexible actuator used for thumb joints to realize two degrees of freedom (DOFs): circumduction and adduction. First, we introduce the design concept inspired by muscle groups of the human palm. A kind of pneumatic small-scale actuators that relies on fabric-crease to produce deformation is proposed. Then the properties of flexible lightweight actuators are characterized. The actuators just need ± 10 kPa pressure to realize a flexion range of 90°. Finally, we modularly assemble the actuators to construct a compact two DOFs thumb joints. Experimental results show that the applied fabric-based thumb joints can achieve dexterous manipulation like sliding the smartphone screen.KeywordsFabric-based flexible actuatorSoft
anthropomorphic handsthumb jointsBio-inspired designSmall-scaleDexterous manipulation
... In order to make the manipulator not only flexible but also with sufficient stiffness and output force, researchers have combined rigid structures and flexible materials in robotic hand designs [15], [16]. For example, Hashemi et al. [15] embedded rigid structures into a fiber-reinforced bending soft robotic finger and Zhang et al. [16] designed a soft finger that has a bioinspired hybrid structure integrating a pneumatic bellows chamber and joint skeletons. ...
... In order to make the manipulator not only flexible but also with sufficient stiffness and output force, researchers have combined rigid structures and flexible materials in robotic hand designs [15], [16]. For example, Hashemi et al. [15] embedded rigid structures into a fiber-reinforced bending soft robotic finger and Zhang et al. [16] designed a soft finger that has a bioinspired hybrid structure integrating a pneumatic bellows chamber and joint skeletons. Nevertheless, the extension motion of most soft pneumatic hands, including the above-mentioned robotic hands with rigid-soft hybrid structures, relies on the resilience of the material or structure itself, even though the bi-directional actuation, namely finger flexion and extension, is critical to the robot's ability to perform the task. ...
... Most existing soft robotic hands rely only on the resilience of the material or structure to assist the finger extension motion, increasing the time required to finish the grasping motion [15], [16]. We claim that the proposed robotic hand enables higher motion speed through the proposed bidirectional pneumatic actuation. ...
Anthropomorphic robotic hands are seeking to achieve key features such as multi-degree-of-freedom motion ability, bi-directional actuation, high adaptability, and sufficient stiffness. In this research, we propose a 10 active degrees-of-freedom anthropomorphic robotic hand with a soft-rigid hybrid structure and positive-negative pneumatic actuation. The fingers of the hand utilize pneumatic actuators composed of soft bellows to actuate a rigid skeleton for bending motion with unidirectional, stretchable nylon elastic fabric as a strain limiting layer. The positive-negative pneumatic actuation mimics the flexors and extensors of the human hand to implement bi-directional finger actuation. We present a prototype implementation of this robotic hand and provide a preliminary evaluation. The experimental results show that the combined positive-negative pneumatic actuation can extend the workspace of the finger and increase the finger stiffness compared to using only positive pneumatic actuation. The proposed robotic hand has good comprehensive
performance (generated a blocking force of 7.5 N, scored 7 in the Kapandji test, achieved 32 of the 33 grasp postures from the Feix taxonomy, and could implement 5 human grasping strategies) compared to other robotic hands in literatures.
