Hand Prototype Research Articles

A mortise-tenon inspired variable stiffness finger for multi-mode grasping

Variable stiffness soft robots feature low stiffness during deformation and high stiffness during operation, making them versatile for various tasks. In this study, we propose a mortise-tenon inspired variable stiffness mechanism (VSM) capable of continuously regulating the structural stiffness within a wide range. The relationship between the structural stiffness of the VSM and the pneumatic pressure applied to a driving airbag was theoretically modeled and experimentally verified. A soft-rigid hybrid finger, integrating soft actuators and the VSM, was developed to explore its deformation capabilities through numerical simulations and experimental tests. Furthermore, a four-fingered hand prototype was assembled, and its grasping performance was systematically evaluated. The results demonstrated that the four-fingered hand could actively switch grasping modes by leveraging the variable stiffness of the VSM, exhibiting exceptional adaptability to various shapes and loads. The variable stiffness mechanism proposed in this study provides new technological support for the design of reprogrammable stiffness soft robots, significantly enhancing their adaptability.

Soft pneumatic actuators for pushing fingers into extension

BackgroundCompliant pneumatic actuators possess many characteristics that are desirable for wearable robotic systems. These actuators can be lightweight, integrated with clothing, and accommodate uncontrolled degrees of freedom. These attributes are especially desirable for hand exoskeletons, where the soft actuator can conform to the highly variable digit shape. In particular, locating the pneumatic actuator on the palmar side of the digit may have benefits for assisting finger extension and resisting unwanted finger flexion, but this configuration requires suppleness to allow digit flexion while retaining sufficient stiffness to assist extension.MethodsTo meet these needs, we designed an actuator consisting of a hollow chamber long enough to span the joints of each digit while sufficiently narrow not to inhibit finger adduction. We explored the geometrical design parameter space for this chamber in terms of shape, dimensions, and wall thickness. After fabricating an elastomer-based prototype for each actuator design, we measured active extension force and passive resistance to bending for each chamber using a mechanical jig. We also created a finite element model for each chamber to enable estimation of the impact of chamber deformation, caused by joint rotation, on airflow through the chamber. Finally, we created a prototype hand exoskeleton with the chamber parameters yielding the best outcomes.ResultsA rectangular cross-sectional area was preferable to a semi-obround shape for the chamber; wall thickness also impacted performance. Extension joint torque reached 0.33 N-m at a low chamber pressure of 48.3 kPa. The finite element model confirmed that airflow for the rectangular chamber remained high despite deformation resulting from joint rotation. The hand exoskeleton created with the rectangular chambers enabled rapid movement, with a cycle time of 1.1 s for voluntary flexion followed by actuated extension.ConclusionsThe developed soft actuators are feasible for use in promoting finger extension from the palmar side of the hand. This placement utilizes pushing rather than pulling for digit extension, which is more comfortable and safer. The small chamber volumes allow rapid filling and evacuation to facilitate relatively high frequency finger movements.

A tendon-driven actuator with cantilever initiated variable stiffness used for robotic fingers

Variable stiffness actuators (VSAs) have emerged as a key actuation technology known for their bionic performance and task adaptability. However, current VSAs often exhibit relatively large sizes, making them possible for use in robotic arms and legs but less convenient for integrations into robotic hands. This paper introduces a compact design of a tendon-driven variable stiffness actuator (TVSA) based on an adjustable cantilever mechanism, which can be embedded into a robotic finger. This implementation endows the robotic finger with the independent regulation of joint position and stiffness. A concise and computationally efficient stiffness mapping model from the TVSA to the finger joints is then established, providing a theoretical foundation for the stiffness regulation of the tendon-driven fingers. A prototype of a robotic hand equipped with the presented TVSA demonstrates safe interactions with various objects of diverse shapes, weights and stiffness.

Anthropomorphic Robotic Hand Prosthesis Developed for Children.

The use of both hands is a common practice in everyday life. The capacity to interact with the environment is largely dependent on the ability to use both hands. A thorough review of the current state of the art reveals that commercially available prosthetic hands designed for children are very different in functionality from those developed for adults, primarily due to prosthetic hands for adults featuring a greater number of actuated joints. Many times, patients stop using their prosthetic device because they feel that it does not fit well in terms of shape and size. With the idea of solving these problems, the design of HandBot-Kid has been developed with the anthropomorphic qualities of a child between the ages of eight and twelve in mind. Fitting the features of this age range, the robotic hand has a length of 16 cm, width of 7 cm, thickness of 3.6 cm, and weight of 328 g. The prosthesis is equipped with a total of fifteen degrees of freedom (DOF), with three DOFs allocated to each finger. The concept of design for manufacturing and assembly (DFMA) has been integrated into the development process, enabling the number of parts to be optimized in order to reduce the production time and cost. The utilization of 3D printing technology in conjunction with aluminum machining enabled the manufacturing process of the robotic hand prototype to be streamlined. The flexion-extension movement of each finger exhibits a trajectory that is highly similar to that of a real human finger. The four-bar mechanism integrated into the finger design achieves a mechanical advantage (MA) of 40.33% and a fingertip pressure force of 10.23 N. Finally, HandBot-Kid was subjected to a series of studies and taxonomical tests, including Cutkosky (16 points) and Kapandji (4 points) score tests, and the functional results were compared with some commercial solutions for children mentioned in the state of the art.

Developing a Novel Prosthetic Hand with Wireless Wearable Sensor Technology Based on User Perspectives: A Pilot Study.

Myoelectric hands are beneficial tools in the daily activities of people with upper-limb deficiencies. Because traditional myoelectric hands rely on detecting muscle activity in residual limbs, they are not suitable for individuals with short stumps or paralyzed limbs. Therefore, we developed a novel electric prosthetic hand that functions without myoelectricity, utilizing wearable wireless sensor technology for control. As a preliminary evaluation, our prototype hand with wireless button sensors was compared with a conventional myoelectric hand (Ottobock). Ten healthy therapists were enrolled in this study. The hands were fixed to their forearms, myoelectric hand muscle activity sensors were attached to the wrist extensor and flexor muscles, and wireless button sensors for the prostheses were attached to each user's trunk. Clinical evaluations were performed using the Simple Test for Evaluating Hand Function and the Action Research Arm Test. The fatigue degree was evaluated using the modified Borg scale before and after the tests. While no statistically significant differences were observed between the two hands across the tests, the change in the Borg scale was notably smaller for our prosthetic hand (p = 0.045). Compared with the Ottobock hand, the proposed hand prosthesis has potential for widespread applications in people with upper-limb deficiencies.

Innovative strain measuring device with flex sensor for twisted and coiled actuator and dexterous hand application

The displacement of twisted and coiled polymer (TCP) actuators, a key physical characteristic, can be measured using a lightweight method, thereby improving the TCP responses and applications in the robot control. This work presents a strain measurement device based on the flex sensor and the hinge links applied in the displacement measuring of the TCP. The bent angle from the sensor affixed to the hinge is converted to the displacement value of the TCP based on the angle-strain model. Compared to the laser sensor, the calculated displacement of the device shows a good tracking effect within the 95 % confidence interval. In the dexterous hand prototype, finger trajectory and joint angles are smoother under a PID controller compared to a non-PID controller, demonstrating the effectiveness of feedback control involving displacement and tension. Finally, the device can cover an extensive range of TCP strains and be applied in more TCP-driven bionic robots.

Additive manufacturing of hydrogel-based lunar regolith pastes: A pathway toward in-situ resource utilization and in-space manufacturing

Additive Manufacturing (AM), combined with efficient in-situ resource utilization, has the potential to enable sustained presence on the Moon through in-situ production and replacement of construction blocks, engineered parts, and devices in the lunar terrain. As an initial step toward realizing this vision, this work proposes a new material formulation utilizing lunar regolith simulants (LHS-1), water, and a hydrophilic hydrogel-forming polymer (Pluronic F127) to produce a hydrogel-based lunar regolith paste suitable for material extrusion AM. This formulation enables the use of water as another potential lunar in-situ resource for the first time in the literature, considering the recent confirmation of large quantities of water-ice in the shadowed craters around the lunar poles and the presence of water on the sunlit surface of the Moon. To systematically investigate the viability of the proposed hydrogel-based lunar regolith material feedstock and the application of material extrusion AM, this work introduces a three-stage design of experiment (DOE) framework to achieve two fundamental objectives. First, the viable range of lunar regolith simulant in the hydrogel-based material formulation is identified using a categorical quality evaluation of single and multi-layer material depositions. Second, the material printability window is established in terms of printing speed and extrusion rate for different viable material compositions through hierarchically designed experiments. The observed porosity of the sintered parts decreased with increasing regolith content in the material composition, while the density and compressive strength increased with higher regolith content. For material compositions consisting of 25–40 vol% regolith simulants, the observed porosity of the sintered parts decreased from 6.4 to 2.18 %, their density increased from 0.78 to 0.89 g/cm3, and their average compressive strength ranged between 0.68 and 1.32 MPa. Finally, the printability of the material was demonstrated by producing various prototype hand tools and lab-scale construction blocks with varying geometrical complexities. This work represents a crucial step toward in situ resource utilization and sustainable in-space manufacturing, sets the stage for future investigations, and the introduced DOE driven framework offers a pathway toward systematically identifying the optimal material compositions and the corresponding process parameters to enable high-quality prints.

Grasping characteristics of SMA bionic flexible dexterous hand

In order to achieve the mechanical performance of grasping objects with SMA bionic flexible hands, a tendon finite element modeling method is proposed in this article to meet the mechanical requirements of the tendon being subjected to only axial forces and not radial forces. By using finite element dynamic simulation and experimental testing methods, the mechanical characteristics of the SMA bionic hands during the grasping process are analyzed and validated. A finite element dynamic simulation model of the SMA bionic hand grasping process is established to study the overall stress characteristics and contact forces of each phalanx, revealing the grasping characteristics of the bionic hand under SMA driving conditions. By creating a physical prototype of the SMA bionic hand, grasping of different objects is achieved. The results show that the stress in the grasping state of the bionic hand does not exceed 21 MPa, the sum of contact forces is 22 N, the theoretical grasping force is 13 N, and the prototype can grasp objects within a diameter range of 70 mm.

Compact water pump and its application to self-contained soft robot hand for vegetable factory

As the number of agricultural workers is decreasing, there are a lot of demands on the robotics automation of agricultural tasks, including the automation of repacking and shipping in vegetable factories. A soft robot hand is suitable for such tasks because of its less damaging to vegetables and adaptability to variety in size and weight of vegetables. However, most of soft robotic hands are actuated by the air pressure, and the output force is not sufficient for heavy vegetables that are often dealt with in a vegetable factory. To solve this problem, we developed a prototype of a hydraulic soft robot hand in our previous research. Selecting an oil as the hydraulic source, the prototype was actuated by a compact built-in pump, we showed that the prototype could hold 2 or cabbage with pressure control. In this paper, we develop a compact water pump that can generate maximum , and update the prototype selecting the water as the hydraulic source. We experimentally show that the soft hand can grasp and hold a cabbages, assuming a real situation in a vegetable factory.

Prototype of robotic hand using two-fingered hand and rubber sheet for gripping nonuniform shaped objects

Prototype of robotic hand using two-fingered hand and rubber sheet for gripping nonuniform shaped objects

Simplified Configuration Design of Anthropomorphic Hand Imitating Specific Human Hand Grasps

How to design an anthropomorphic hand imitating specific human hand grasps with as few actuators as possible is still a challenge. This letter presents a method for obtaining a simplified configuration of anthropomorphic hand imitating specific human hand grasps based on the motion analyses of the human hand. A participation matrix which characterizes a human hand grasp on joint motion level is constructed according to the motion participation of each finger joint. By adding all participation matrices of expected human hand grasps together a total participation matrix can be derived, and through mathematical processing a simplified anthropomorphic hand configuration can be obtained. Following the proposed method, a simplified anthropomorphic hand configuration that imitates six basic human hand grasps was obtained. A series of grasp experiments with the anthropomorphic hand prototype were conducted to validate the grasping capability as well as the proposed simplified configuration design method. This method can help to obtain a reasonably simplified configuration of an anthropomorphic hand when expected human hand grasps are definite.

Design and Building of a Multi-finger Robotic Hand Prototype for Grip Control

Design and Building of a Multi-finger Robotic Hand Prototype for Grip Control

Development of a Novel Biomimetic Mechanical Hand Based on Physical Characteristics of Apples

For the purpose of minimizing the damage to apples during the operation of an apple-picking robot, improving the stability of an apple-harvesting mechanical hand and reducing the use and operation cost of the robot, a novel biomimetic apple mechanical hand based on negative pressure air suction is purposely designed based on the physical characteristics of apples by imitating octopus predation. The mechanical hand has four suction cups evenly distributed in the hand, which produce concave deformation under negative vacuum pressure to fit the apple surface and adsorb the apple; the fruit stalk is separated by wrist rotation and dragging in a compound way to complete the picking operation. This paper firstly determines the key parameters of the mechanical hand based on the characteristics of silicone material and the three growth postures of apples, tries to make a physical prototype of the mechanical hand and conducts relevant performance tests on the picking platform built in the laboratory to explore the best combination of parameters and further optimize the manipulator. The results show that the success rate of the biomimetic nondestructive apple picker with the best combination of parameters is 100%, 76% and 68% for three different apple-growth postures and the operation is smooth, reliable, safe and non-invasive.

A Biomimetic Soft‐Rigid Hybrid Finger with Autonomous Lateral Stiffness Enhancement

The application of soft robotics improves the compliance of robotic fingers, which, however, usually loses sufficient stiffness. Here, a biomimetic soft‐rigid hybrid (BSH) finger that can achieve both inherent compliance and autonomous lateral stiffness enhancement is proposed. Driven by pneumatic artificial muscles, the proposed two‐joined BSH finger can produce two flexion degrees of freedom (DOFs) and one lateral DOF motion. Imitating the human finger anatomy, the BSH finger is designed with elliptical bony ridges and eccentrically arranged ligaments. By leveraging the contact interference of the ridges and tensioning of the ligaments, the lateral stiffness of the BSH finger can be autonomously enhanced through finger flexion. During its natural stage, the lateral stiffness is relatively low to ensure mobility and compliance, while in its flexion stage, its lateral stiffness can increase to resist lateral deflection and high payload. To further investigate the advantages of the design, four BSH fingers are assembled into a robotic hand prototype with three grasping types including enveloping grasp, precise pinch, and power grasp. Experimental results demonstrate that the robotic hand prototype is capable of grasping various objects with a wide range of diameters, lengths, thicknesses, and weights, which will verify the effectiveness of the design methodology.

In-Hand Manipulation Inspired by Diabolo Juggling

This letter discusses in-hand manipulation inspired by diabolo juggling. Continuous rotational manipulation using the vibration of a flexible belt attached to the hand is proposed. This method is highly adaptable, enabling the hand to manipulate various types of objects, without requiring complex sensing or control, or a complex mechanism. First, a simplified analytical model composed of a flexible belt and a cylindrical object is introduced. Based on periodic input to the two endpoints of the belt, continuous rotation based on slipping of the object is theoretically discussed. Then, via numerical examples, it is shown that the average angular velocity of the object can be controlled. Finally, the proposed method is experimentally validated using a prototype hand. It is shown that the stable holding and continuous rotation of the object are easily achieved. The versatility of the method is demonstrated through experiments using objects with various shapes, sizes, and masses.

Robot Operating System controlled anthropomorphic robot hand

This paper presents a new design of a dexterous robot hand by incorporating human hand factors. The robotic hand is a Robot Operating System (ROS) controlled standalone unit that can perform key tasks and work independently. Hardware such as actuators, electronics, sensors, pulleys etc. are embedded within or on the hand itself. Raspberry Pi, a single board computer which runs ROS and is used to control the hand movements as well as process the sensor signals is placed outside of the hand. It supports peripheral devices such as screen display, keyboard and mouse. The hand prototype is designed in Solid Works and 3D printed/built using aluminum sheet. The prototype is similar to the human hand in terms of shape and possesses key functionalities and abilities of the human hand, especially to imitate key movements of the human hand and be as dexterous as possible whilst keeping a low cost. Other important factors considered while prototyping the model were that the hand should be reliable, have a durable const­­ruction, and should be built using widely available off-the-shelf components and an open-source software. Though the prototype hand only has 6 degrees-of-freedom (DOF) compared to the 22 DOF of the human hand, it is able to perform most grasps effectively. The proposed model will allow other researchers to build similar robotic hands and perform specialized research.

Electromagnetic Switching Multiple Grasping Modes Robot Hand

Giving robot hands more powerful functions has always been one of the goals pursued by scholars in this field. In this paper, an electromagnetic switching multiple grasping modes robot hand (ESMGM hand) is proposed, which integrates three typical grasping modes and therefore has versatile usage and improved performance. The switchable CPS mechanism developed in this paper integrated the parallel grasping and coupled grasping modes, which are incompatible with each other, through ingenious design. The partial effective transmission mechanism guarantees the fusion and connection to self-adaptive grasping mode from both parallel grasping mode and coupled grasping mode. Based on the above two essential mechanisms, the specific structure of the ESMGM robot hand is designed. Theoretical analyses for the kinematic and grasping forces are performed, and the results show that the ESMGM hand not only has multiple grasping functions but also has the characteristics of equitable grasping motions, adequate grasping forces, and stable grasping effects. To further verify the performance of the ESMGM hand, the prototype of the ESMGM hand is manufactured, and grasping experiments are performed. The grasping forces distribution results are consistent with the theoretical analysis results. The general grasping experiments also illustrate that the ESMGM hand has the features of fast electromagnetic switching speed, good adaptability, high stability, fast response, and broad application prospects.

Antagonistic Control of a Cable-Driven Prosthetic Hand with Neuromorphic Model of Muscle Reflex.

In this paper, a novel prototype of a cable-driven prosthetic hand with biorealisitic muscle property was developed. A pair of antagonistic muscles controlled the flexion and extension of the prosthetic index finger. Biorealistic properties of muscle were emulated using a neuromorphic model of muscle reflex in real time. The model output was coupled to a servo motor that tracked the computed muscle force. The servo motor was able to track model output within a frequency range from 0 to 8.29 (Hz) with a phase shift from 2 to 205 (deg). Surface electromyography signals collected from the amputee's forearm were used as α commands to drive the muscle model. With this prototype system, we evaluated its characteristics for force and stiffness control. Results of the force variability test showed that the standard deviation of fingertip force was linear to the mean fingertip force, indicating that force variability was proportional to the background force. At different levels of antagonistic co-contraction, the index finger and muscles displayed different levels of stiffness corresponding to the degree of co-activation. This prototype system showed the similar compliant behaviors of human limbs actuated with biological muscles. In further studies, this prototype system would be thoroughly evaluated for its biorealistic properties, and integrated with sensors to investigate feedback strategies of various sensory information for individuals with amputation. Clinical Relevance- This article established an antagonistic control of a cable-driven prosthetic hand with biorealistic properties of muscle reflex for application to individuals with amputation.

Development and Evaluation of a Passive Multiloop Wearable Hand Device for Natural Motion

Abstract This article describes the development and evaluation of our passively actuated closed-loop articulated wearable (CLAW) that uses a common slider to passively drive its exo-fingers for use in physical training of people with limited hand mobility. Our design approach utilizes physiological tasks for dimensional synthesis and yields a variety of design candidates that fulfill the desired fingertip precision grasping trajectory. Once it is ensured that the synthesized fingertip motion is close to the physiological fingertip grasping trajectories, performance assessment criteria related to user–device interference and natural joint angle movement are taken into account. After the most preferred design for each finger is chosen, minor modifications are made related to substituting the backbone chain with the wearer’s limb to provide the skeletal structure for the customized passive device. Subsequently, we evaluate it for natural joint motion based on a novel design candidate assessment method. A hand prototype is printed, and its preliminary performance regarding natural joint motion, wearability, and scalability are assessed. The pilot experimental test on a range of healthy subjects with different hand/finger sizes shows that the CLAW hand is easy to operate and guides the user’s fingers without causing any discomfort. It also ensures both precision and power grasping in a natural manner. This study establishes the importance of incorporating novel design candidate assessment techniques, based on human finger kinematic models, on a conceptual design level that can assist in finding design candidates for natural joint motion coordination.

A humanoid robotic hand capable of internal assembly and measurement in spacesuit gloves

PurposeTo identify the dexterity of spacesuit gloves, they need to undergo bending tests in the development process. The ideal way is to place a humanoid robotic hand into the spacesuit glove, mimicking the motions of a human hand and measuring the bending angle/force of the spacesuit glove. However, traditional robotic hands are too large to enter the narrow inner space of the spacesuit glove and perform measurements. This paper aims to design a humanoid robot hand that can wear spacesuit gloves and perform measurements.Design/methodology/approachThe proposed humanoid robotic hand is composed of five modular fingers and a parallel wrist driven by electrical linear motors. The fingers and wrist can be delivered into the spacesuit glove separately and then assembled inside. A mathematical model of the robotic hand is formulated by using the geometric constraints and principle of virtual work to analyze the kinematics and statics of the robotic hand. This model allows for estimating the bending angle and output force/torque of the robotic hand through the displacement and force of the linear motors.FindingsA prototype of the robotic hand, as well as its testing benches, was constructed to validate the presented methods. The experimental results show that the whole robotic hand can be transported to and assembled in a spacesuit glove to measure the motion characteristics of the glove.Originality/valueThe proposed humanoid robotic hand provides a new method for wearing and measuring the spacesuit glove. It can also be used to other gloves for special protective suits that have highly restricted internal space.