A Pneumatic Flexible Linear Actuator Inspired by Snake Swallowing

In the previous study, a flexible pneumatic linear stepping actuator (PLSA) that can perform a long stroke motion with large force was developed. In this study, a novel PLSA that can push or pull the rod continuously while changing the direction of pushing / pulling force was developed. The control system that consists of an embedded controller with Bluetooth communication unit and on/off valves was also developed. It can be confirmed that the PLSA can realize continuous pushing / pulling motion of the rod while the bending direction of the rod is changing according to the transmitted code through Bluetooth. Also, the tested PLSA can realize pushing / pulling motion while the bending direction of the rod is changed. As a result, it can be confirmed that the tested PLSA is valid to be used as a home healthcare supporting device to give passive exercise for upper limbs while grasping the rod end by hand.

This paper presents the detailed analysis of a pneumatic clutch actuator with an artificial intelligence control algorithm. The low cost of pneumatic actuator makes it an advantage in automotive applications, but fast and precise control is difficult on account of its time-varying and nonlinear character. In order to achieve good performance and save cost, the development of a fast, accurate, and inexpensive automatic pneumatic actuator clutch system for a single-axle parallel hybrid electrical is important. Targeted for the working principle of electric-drive automated mechanical transmission parallel hybrid system for shifting and clutch dynamic control during operation mode switch course, the design adopts single neuron-adaptive PID-based clutch operation process, proposed the clutch actuator piston non-contact cylinder lock control method to overcome time-varying and nonlinear characteristics’ impact present in the pneumatic actuator closed-loop control, and through the effective control of segment displacement self-diagnosis during the clutch operation process, performs variable clutch control and improve the actuator fault tolerance. Experiments show that the proposed control algorithm is feasible, which has effectively reduced the torque shock and clutch friction work during clutch engaging process.

Pneumatic actuators are fast becoming a key instrument where cost, safety or pollution is a concern. They can be of linear or rotary type, depending on the motion they produce. Linear pneumatic actuator is also commonly known as pneumatic cylinder because it usually consists of a piston housed in a hollow cylinder. In this study, the feasibility of PID control for a double-acting cylinder actuated by McKibben muscles (DACAM) had been investigated. Due to the nonlinearity and hysteresis properties of the muscle, separate controllers for forward actuation and reverse actuation had been used. Result shows that when given a staircase input, the feedback system gave an average response of 4.28 s rise time, 6.06 s settling time, 0.01% overshoot and 0.01% steady-state error for forward actuation and 8.25 s fall time, 9.28 s settling time, 2.86% overshoot and 2.86% steady-state error for reverse actuation. The evidence from this study suggests that position control of a DACAM using PI control is possible. An implication of this is the possibility of developing a small, lightweight and simple pneumatic cylinder using McKibben muscles.

Soft pneumatic actuator with an embedded flexible polymeric piezoelectric membrane for sensing bending deformation

Fabric-based pneumatic actuators (FPAs) are extensively employed in the design of lightweight and compliant soft wearable assistive gloves. However, conventional FPAs typically exhibit limited output force, thereby restricting the applications of such gloves. This paper presents the development of a novel honeycomb pneumatic actuator (HPA) constructed using flexible thermoplastic polyurethane (TPU) coating through hot pressing or ultrasonic welding techniques. Compared to the previously utilized double-layer fabric-based pneumatic actuators (DLFPAs), the HPAs yields a remarkable 862% increase in end output force. It can produce a tip force of 13.57 N at a pressure of 150 kPa. The integration of HPAs onto a soft pneumatic glove enables the facilitation of various activities of daily living. A series of trials involving nine patients were conducted to assess the effectiveness of the soft glove. The experimental results indicate that when assisted by the glove, the patients' finger metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints achieved angles of 87.67 ± 19.27° and 64.2 ± 30.66°, respectively. Additionally, the average fingertip force reached 10.16 ± 4.24 N, the average grip force reached 26.04 ± 15.08 N, and the completion rate of daily functions for the patients increased from 39% to 76%. These outcomes demonstrate that the soft glove effectively aids in finger movements and significantly enhances the patients' daily functioning.

Printed silicone pneumatic actuators for soft robotics

This paper presents the development of a mathematical model for a robot with a Cartesian structure, commonly used in industrial and automation systems due to its simplicity, accuracy, and ease of control. The robot's mechanical design is based on three linear, orthogonal axes (X, Y, and Z), allowing straightforward positioning in three-dimensional space. The study focuses on the formulation of the kinematic and dynamic models necessary for precise control and trajectory planning. The dynamic model is derived using Newton-Euler methodology. Special attention is given to the structural configuration and the movement constraints imposed by the linear pneumatic actuators (three rodless cylinders, one cylinder with a piston rod on one side and a gripper). The resulting model provides a clear mathematical framework for understanding the behaviour of the Cartesian robot under various operating conditions. This work lays the foundation for future implementation of control algorithms and integration into automated systems, and it serves as a reference for the design and analysis of similar robotic platforms.

Most current pneumatic actuators, whether they have a single inflation chamber or multiple inflation chambers, are driven by a single air source, limiting their ability to complete precise and targeted manipulation. This paper describes a flexible pneumatic actuator with a three-chamber structure to mimic the motion of a human finger. Each chamber, which mimics the finger joint, is independently driven by a pressurized air source, making the finger flexible enough to grasp an object according to its shape. To achieve a more extensive deformation with lower pressure, the finite element method (FEM) was used to optimize and determine the structural parameters of the actuator. Actuators, both with and without fiber-reinforcement, were experimentally investigated to determine the bending performance of the artificial finger when pressurized individually or simultaneously. A three-finger gripper fabricated based on the multi-jointed pneumatic actuator successfully grasps various objects with higher contact area compared to previous designs, which achieves more stable grasping. The current actuator is flexible and stable enough to be used for a wide range of objects with different dimensions, shapes, and textures by controlling the various chambers.

A cyber-secure and flexible actuator is essential for cyber-physical-human systems. The use of wireless communication in such systems improves their usability but adds cybersecurity risks. This study proposes a cyber-secure flexible antagonistic pneumatic artificial muscle (PAM) actuator system. The proposed PAM actuator system has an encrypted proportional-integral controller and a real-time detector for cyberattacks. The controller is concealed in the encrypted control fashion using a homomorphic encryption scheme with security parameter 64 bit, and the control signal is computed over a cipher space. The detector has a threshold to detect significant changes in control inputs caused by cyberattacks such as signal injection and parameter falsification. The experimental results demonstrate that the proposed PAM actuator system achieves the desired control performance and improves the reliability of control operations under cyberattacks. The main contribution of this study is the first implementation of an encrypted controller for a pneumatic actuator to develop a secure PAM actuator with real-time detection of cyberattacks. The results of this study contribute to the future development of safe remote systems that interact with humans in the medical and industrial fields.

As the number of patients with amputations increases, research on assistive devices such as prosthetic limbs is actively being conducted. However, the development of assistive devices for patients with partial amputations is insufficient. In this study, we developed a finger prosthesis for patients with partial amputations. The design and mathematical modeling of the prosthesis are briefly presented. A pneumatic actuator, based on the McKibben muscle design, was employed to drive the finger prosthesis. We characterized the relationship between the actuator’s force and axial length changes with varying pressure. An empirical model derived from conventional mathematical modeling of force and axis length changes was proposed and compared with experimental data, and the error was measured to be between about 3% and 13%. In order to control the actuator using an electromyography (EMG) signal, an electrode was attached to the user’s finger flexors. The EMG signal was measured in relation to the actual gripping force and was provided with visual feedback, and the magnitude of the signal was evaluated using root mean square (RMS). Depending on the evaluated EMG signal magnitude, the pressure of the actuator was continuously adjusted. The pneumatic pressure was adjusted between 100 kPa and 250 kPa, and the gripping force of the finger prosthesis ranged from about 0.7 N to 6.5 N. The stiffness of the prosthesis can be varied using the SMA spring. The SMA spring is switched to a fully austenite state at 50 °C through PID control, and when the finger prosthesis is bent to a 90° angle, it can provide approximately 1.2 N of assistance force. Finally, the functional evaluation of the finger prosthesis was performed through a pinch grip test of eight movements.

While linear actuators have many applications, the majority of them are rigid and straight, limiting their applications and the work environment. This article presents a novel design for an electromagnetic flexible linear actuator (FLA) that can overcome such restrictions, as well as a computationally efficient model that predicts the output force based on the input current and the actuator shape. The FLA design is of a 3D-printable stator, easy-to-manufacture, and assemble with off-the-shelf components, modular, scalable, and easy to maintain. It can bend and take any arbitrary shape with reasonable curvature based on the dimensions of the motor. This facilitates the integration of the FLA in industry. The presented novel mathematical model fills the gap in the research area of the nonstraight actuator models. The model is derived by decomposing the actuator into noncoaxial coils and magnets. Through cascading the forces generated between each coil and the magnets, the output force of the actuator is calculated. The output of the model is validated experimentally by comparing its results to the actuator's force at different bending angles, planar, and in 3D space.

Soft robots in technology makes rapid development in the field of robotics, so that robots are widely used in all aspects of life. This paper proposed a bionic elephant trunk structure of pneumatic actuator (SPA). To solve the insufficient tip force and bending angle of SPA, mathematical model and Finite Element Analysis (FEA) are used to determine the optimal parameters of the SPA. Based on optimized SPAs, robots for multidisciplinary applications are developed. These applications include soft gripper with high gripping force of up to 480 N, a quadruped soft robot capable of adapting complex amphibious environments, and a robot designed to assist with sign language communication. These demonstrate the versatility of soft robots in addressing challenges across various domains, such as healthcare, human-machine interaction, and environmental exploration.

A novel pneumatic soft linear actuator Fiber-reinforced Origamic Robotic Actuator (FORA) is proposed with significant improvements on the popular McKibben-type actuators, offering nearly doubled motion range, substantially improved force profile, and significantly lower actuation pressure. The desirable feature set is made possible by a novel soft origamic chamber that expands radially while contracts axially when pressurized. Combining this new origamic chamber with a reinforcing fiber mesh, FORA generates very high traction force (over 150N) and very large contractile motion (over 50%) at very low input pressure (100 kPa). We developed quasi-static analytical models both to characterize the motion and forces and as guidelines for actuator design. Fabrication of FORA mostly involves consumer-grade three-dimensional (3D) printing. We provide a detailed list of materials and dimensions. Fabricated FORAs were tested on a dedicated platform against commercially available pneumatic artificial muscles from Shadow and Festo to showcase its superior performances and validate the analytical models with very good agreements. Finally, a robotic joint was developed driven by two antagonistic FORAs, to showcase the benefits of the performance improvements. With its simple structure, fully characterized mechanism, easy fabrication procedure, and highly desirable performance, FORA could be easily customized to application requirements and fabricated by anyone with access to a 3D printer. This will pave the way to the wider adaptation and application of soft robotic systems.

Pneumatic linear peristaltic actuators can offer some potential advantages when compared with conventional ones. The low cost, virtually unlimited stroke and easy implementation of curved motion profiles are among those benefits. On the downside, these actuators suffer high mechanical stress that can lead to short service life and increased leakage among chambers during the actuator lifetime. One way to cope with this problem is to impose the force—instead of the displacement—between rollers, as this has been shown to improve the endurance of the hose while reducing leakage during the actuator lifetime. This paper presents closed control loop results using such a setup. Previous studies with linear peristaltic actuators have revealed that, although it is possible to reach zero steady state error to constant references with closed loop control, the dynamic response obtained is very slow. This paper is mainly focused on this topic, namely on the development of several control laws to improve the dynamic performance of the system while avoiding limit cycles. The new developed control law leads to an average time of 1.67 s to reach a 0.1 mm error band in an experiment consisting of a series of 16 steps ranging from 0.02 to 0.32 m in amplitude.

This design activity is an innovative method of rapid assembly system for folding chairs. The research methods used in this study included literature analysis, TRIZ the method, human factors engineering (HFE), universal design, and IPA. First, the design of the folding chair and the layout of the literature related to the chair are analyzed. The contradiction matrix was used in the TRIZ method to find the principle of invention and analyze it, to provide a reference for the innovative design of folding chairs, and then use the relevant literature on materials to help design and select materials quickly. Next, the chair is assembled and unfolded and universal design is applied to design it into an acceptable product, causing it to be more popular. The human–machine interaction with HFE makes the design of rapid assembly and the design of folding chairs faster and safer. Finally, the IPA method is used to understand the subjective feelings of customers on the products of this research and the satisfaction and importance are used as the basis for evaluation; a two-dimensional matrix graph is drawn. After drawing a simulation using drawing software, it is compared with the traditional folding chair and the research results are as follows: (1) Quick unfolding function: use the pull ring upwards and it naturally unfolds downwards by gravity. (2) Quick folding and storage function: use the foot pedal, single-foot operation, and the folding chair can be quickly stored. (3) Rapid transportation and unfolding function: The chair back can be connected with other chair backs and has the functions of quick unfolding and quick storage, so as to realize the quick placement of the folding chair. This design activity realizes the preliminary design concept and design simulation of the product design through a systematic and innovative method. Through this design activity, we can understand the problems existing in product improvement before product development, so as to conduct market research and production cost assessment in the actual mass production later, and further reduce the cost of product design improvement.