Development of artificial hand using pneumatic artificial muscle

Pneumatic artificial muscles (PAMs) are soft actuators that generate tension via contraction when supplied with compressed air. Although PAMs have been widely used in robots mimicking endoskeletal organisms, recent advancements in millimeter-scale thin PAMs have enabled a more precise replication of complex musculoskeletal systems. In contrast, exoskeletal organisms, such as crustaceans and insects actuate their joints using pennate muscles embedded within their exoskeletons. However, integrating actuators into the exoskeletons of exoskeletal-inspired robots is challenging owing to spatial constraints. Consequently, wire and servo-driven mechanisms are predominantly employed, and studies on exoskeletal robots incorporating the muscle-apodeme structures of exoskeletal organisms remain largely unexplored. To address this gap, this paper presents the development of a crab-inspired robotic walking leg featuring an exoskeletal structure with embedded pneumatic artificial pennate muscles, modeled after the muscle-apodeme structures of snow crabs. The experimental evaluations demonstrated that the robot successfully performed joint opening and closing motions, achieving a range of motion comparable to that of a snow crab.

Pneumatic artificial muscles are a class of pneumatically driven actuators that are remarkable for their simplicity, lightweight, high stroke, and high force. The McKibben artificial muscle, which is a type of pneumatic artificial muscle, is composed of an elastomeric bladder, a braided mesh sleeve, and two end fittings. Gaylord first developed an analysis of the McKibben artificial muscle based on the conservation of energy principle. The Gaylord model predicts block force but fails to accurately capture actuation force versus contraction ratio behavior. To address this lack, a non-linear quasi-static model is developed based on finite strain theory. The internal stresses in the bladder are determined by treating it as a cylinder subjected to applied internal pressure and a prescribed kinematic constraint of the outer surface. Subsequently, the force balance approach is applied to derive the equilibrium equations in both the axial and circumferential directions. Finally, the closed-form pneumatic artificial muscle quasi-static actuator force is obtained. The analysis was experimentally validated using actuation force versus contraction ratio test data at a series of discrete inflation pressures for two different pneumatic artificial muscles: a large pneumatic artificial muscle ( L = 128.5 mm, B = 7.85 mm, with a latex bladder) and a miniature pneumatic artificial muscle ( L = 43.9 mm, B = 2.3 mm, with a V330 elastomeric bladder).

Recently, the demand for wearable apparatus for supporting human movement in the medical and welfare fields increases with low birthrate and aging of society in many countries. In these apparatus, a pneumatic artificial muscle like a McKibben artificial muscle is highly expected as the actuator because of its high power, light weight and flexibility. But the conventional displacement sensors are not suitable for controlling the pneumatic artificial muscle, because, compared with the artificial muscle, the sensors are expensive and rigid. Additionally they are incorporated in the system separately from the artificial muscle generally. In order to solve the problem, in this study, conductive fibers are utilized as the displacement sensor for the pneumatic artificial muscle by replacing the fiber component of the artificial muscle. This paper describes the basic design of a smart pneumatic artificial muscle integrating the conductive fibers as the sensor. Additionally results of basic characteristics of the smart pneumatic artificial muscle are shown experimentally.

Shortage of labor and increased work of young people are causing problems in terms of care and welfare of a growing proportion of elderly people. This is a looming social problem because people of advanced ages are increasing. Necessary in the fields of care and welfare, pneumatic artificial muscles in actuators of robots are being examined. Pneumatic artificial muscles have a high output per unit of weight, and they are soft, similarly to human muscles. However, in previous research of robots using pneumatic artificial muscles, rigid sensors were often installed at joints and other locations due to the robots’ structures. Therefore, we developed a smart actuator that integrates a bending sensor that functions as a human muscle spindle; it can be externally attached to the pneumatic artificial muscle. This paper reports a smart artificial muscle actuator that can sense contraction, which can be applied to developed self-monitoring and robot posture control.

Both pneumatic artificial muscles and additive manufacturing have attracted great attention with the development of the robotics industry. In this paper, the authors report on the design, fabrication, and experiments of a 3D printable origami vacuum-driven pneumatic artificial muscle with a simple, low-cost, and easily replicable structure. The proposed artificial muscle requires low vacuum pressure and can achieve a 62% contraction ratio due to the origami structure. The structure is printed by the soft TPE material with a small volume and enhanced by thin inner support rings, which prompt the entire folding process can be finished within 0.18 s without radial expansion or contraction. It processes a low self-weight of 15 g and can lift up a 3 kg load that is 200 times its self-weight. A prototype is built based on the proposed fabrication method, on which the validation experiments are conducted. The experimental results prove the satisfied capabilities of the proposed artificial muscle. Since the chamber can be easily printed by a commercial 3D printer with a single nozzle in a single step and the inner support rings are easy to be assembled, everyone can build the artificial muscle following the rapid prototype methods introduced in this paper with a 3D printer.

As full-scale pneumatic artificial muscles (PAMs) are already known for their high workto-mass and force-to-volume ratios, research has been undertaken toward miniaturizing this actuator technology in order to develop small-scale PAMs that can be contained within the palm of a robotic hand to effect the desired movement of the robotic fingers. The first step in implementing these small-scale PAMs in a functional robotic manipulator was to design and characterize the miniature actuator. To that end, this paper presents the manufacturing process, experimental characterization, and analytical modeling of PAMs with millimeterscale diameters. First, a fabrication method was developed to consistently deliver low-cost, high-performance, miniature PAMs using commercially available materials. The quasi-static behavior of these PAMs was determined through experimentation on a single actuator with an active length of 39.16 mm (1.54 in) and a diameter of 4.13 mm (0.1625 in). Testing revealed the PAM’s full evolution of force with displacement over a broad spectrum of operating pressures, as well as the blocked force and free contraction capabilities at each pressure. This study also explores the nature of stress-softening in the PAM bladder, characterizing the change in actuator performance with increased use. Furthermore, this work compares the data from these experiments to two previously developed models for fullscale PAMs. With the inclusion of correction terms to account for physical phenomena encountered during testing, comparison between the models and the experimental results indicates that the improved models can accurately predict the behavior of these miniature PAMs below 4% contraction.

Bipedal robotic leg kinematics and dynamics are a key component in designing biomimetic humanoid robots. This work describes the process of designing artificial muscle attachment locations of the legs of a bipedal robot utilizing pneumatic artificial muscles (PAMs). PAMs offer similar force and activation times to real muscles, while being lightweight and low power. However, not all properties are identical, and substituting artificial muscles in with the same attachment locations results in different torque profiles about each joint. This work analyzes muscle length, moment arm, and isometric force of muscles over a range of different joint configurations, based on muscle attachment and wrapping points of the Gait2392 model in OpenSim. These parameters are then used to find joint torques produced by each muscle. This process is repeated for a model of the robot actuated by PAMs. Joint torques for individual muscles and groups of muscles are then compared between the models. Results indicate that several muscles torque profiles in the robot model closely match that of the human model, however, many muscles fall far short of the human capabilities. Where appropriate, additional results demonstrate how muscle attachment locations on the robot have been modified to better match the torque capabilities demonstrated by the OpenSim model. Matlab tools created for this project will facilitate further design refinement before implementation on the robot.

This paper presents compliance characteristics of antagonistic actuation by the pair of Mckibben pneumatic artificial muscles and force tracking using a sliding control scheme for safe human-robot interaction. The variable stiffness capability of artificial muscles was investigated carefully by resilience tests from a biased initial position and impact tests based on an intended collision between a stationary object and a rotating linkage actuated by pneumatic artificial muscles. Considering the frequency response analysis of a whole pneumatic circuit for artificial muscles, a sliding control system was designed to control contacting force between a linkage actuated by artificial muscles and a rigid environment. Experimental results showed that the proposed force control scheme gave better tracking performance under model uncertainties due to air flow than the conventional PID controller whose feedback gains were well-tuned experimentally.

A mechanical model for McKibben pneumatic artificial muscles based on limiting chain extensibility and 3D application of the network alteration theories

McKibben artificial muscle realizing variable contraction characteristics using helical shape-memory polymer fibers

Compared with pneumatic artificial muscles (PAMs), water hydraulic artificial muscles (WHAMs) have the advantages of high force/weight ratio, high stiffness, rapid response speed, large operating pressure range, low working noise, etc. Although the physical models of PAMs have been widely studied, the model of WHAMs still need to be researched for the different structure parameters and work conditions between PAMs and WHAMs. Therefore, the geometry and the material properties need to be considered in models, including the wall thickness of rubber tube, the geometry of ends, the elastic force of rubber tube, the elongation of fibers, and the friction among fiber strands. WHAMs with different wall thickness and fiber materials were manufactured, and static characteristic experiments were performed when the actuator is static and fixed on both ends, which reflects the relationship between contraction force and pressure under the different contraction ratio. The deviations between theoretical values and experimental results were analyzed to investigate the effect of each physical factor on the modified physical model accuracy at different operating pressures. The results show the relative error of the modified physical model was 7.1% and the relative error of the ideal model was 17.4%. When contraction ratio is below 10% and operating pressure is 4 MPa, the wall thickness of rubber tube was the strongest factor on the accuracy of modified model. When the WHAM contraction ratio from 3% to 20%, the relative error between the modified physical model and the experimental data was within ±10%. Considering the various physical factors, the accuracy of the modified physical model of WHAM is improved, which lays a foundation of non-linear control of the high-strength, tightly fiber-braided and thick-walled WHAMs.

There is a long history demonstrating humans’ tendency to create artificial copies of living creatures. For moving machines called robots, actuators play a key role in developing human-like movements. Among different types of actuation, PAMs (pneumatic artificial muscles) are known as the most similar ones to biological muscles. In addition to similarities in force generation mechanism (tension based), the well-accepted argumentation from Klute et al., states that the PAM force-length (f l ) behavior is close to biological muscles, while the force-velocity (f v ) pattern is different. Using the multiplicative formulation of the pressure (as an activation term), f l and f v beside an additive passive parallel elastic element, we present a new model of PAM. This muscle-based model can predict PAM dynamic behaviors with high precision. With a second experiment on a two-segmented leg, the proposed model is verified to predict the generated forces of PAMs in an antagonistic arrangement. Such a dynamic muscle-like model of artificial muscles can be used for the design and control of legged robots to generate robust, efficient and versatile gaits.

Describes a method and a process for developing a soft artificial hand similar to a real human hand and its small-size soft actuator. For the soft actuator, we took a pneumatic artificial muscle and succeeded in reducing it to a diameter of 3.5 mm. The pneumatic artificial muscle allows the artificial hand not only to move softly and powerfully by pneumatic power but also works as a sensor. As a frame for the artificial hand, we used the skeleton model of human hand in order to make the hand similar to real human hand in structure as well as motion.

Pneumatic artificial muscles (PAMs) are inherently compliant and relatively safe. They are widely used in applications where human beings and robots interact closely, such as service robots or medical robots. However, PAMs are constrained by bulky pumps and valve control systems, limiting their mobility, portability, and practical applications. In this research, a novel type of artificial muscle, namely Twisting Tube Artificial Muscle (TTAM), is presented. In a TTAM design, fluid (pressurized air in this research) is contained inside an elastic tube (constrained by a braiding). By twisting the tube from one end, the fluid inside the twisted part will be extruded to the untwisted part, resulting in a pressure increase inside the untwisted part. Both the twisted and untwisted parts will thus contract. Modeling and experimental characterization of the TTAM are conducted. In an experimental test at 100 kPa initial air pressure, after a 6π twisting angle, the internal pressure of a prototype TTAM is increased to 219 kPa, and the largest contraction force of the TTAM was up to 200 N. A novel antagonistic robotic joint actuated by two TTAMs is developed as a sample application.

Ankle–Foot injuries are amongst the most common injuries of the lower limb and almost 25,000 people experience ankle injuries each day due to vigorous activities. Traditionally, ankle injuries are rehabilitated via physiotherapy using simple equipment like elastic bands and rollers, requiring intensive efforts of therapists and patients. Currently, Stewart platform rehabilitation devices are actuated by various methods including double acting pneumatic cylinder, hydraulic, electric motor and shape memory alloy. The limitation of using these actuation methods is that it provides lower range of motions and requires higher maintenances. A less known type is Pneumatic Artificial Muscles (PAMs). PAMs are operated by pneumatic pressure and are contractible naturally upon inflation. The objective of this study is to fabricate Stewart platform using Pneumatic Artificial Muscle, to analyze the range of motion produce by various diameter of the PAMs. The diameters of PAM used were 8, 10 and 12 mm. It was observed that Stewart Platform actuated by PAM of diameter of 12 mm produced maximum platform angle of 31.73°, whereas PAM with the diameter of 10 and 8 mm produced maximum platform angle of 28.62° and 25.31°, respectively.KeywordsPneumatic Artificial MuscleStewart PlatformRange of motion (ROM)