LQG Controller Design Applied to a Pneumatic Stewart-Gough Platform

This paper is concerned with the practical application control of a pneumatically actuated Stewart-Gough platform with 6-degrees of freedom （6-DOF）. The control approach for motion control of the platform is presented using a modern control technique, namely, linear quadratic Gaussinn （LQG） with reference tracking. The LQG controller is the combination of a Kalman filter, i.e., a linear-quadratic estimator （LQE） with a linear-quadratic regulator （LQR）. The robustness of the control scheme is accessed under various load conditions, and the experimental results are shown.

Dynamic Analysis and Decoupling Control of Octo-pneumatic Actuator Vibration Isolation Platform

Control of a six-DOF vibration isolation platform is generally difficult which is due to the strong coupling among its input and output channels. The dynamic behavior and decoupling approach of a six-DOF vibration isolation platform with eight pneumatic actuators are investigated. Owing to the symmetric configuration design of the platform, the coupling among different channels is greatly weakened. When the payload＇s principal axes of inertia parallel to the platform＇s axes of symmetry and the payload＇s center of mass is at the extension line of the platform＇s central axis, the motion can be decomposed into two independent single-input single-output channels and two independent two-input two-output subsystems. The second-order subsystems are decoupled further with the simultaneous matrix diagonalization. Thus a decoupling control strategy is developed. Effectiveness of the decoupling approach is verified through experiments of the platform, and the experimental results show that vibrations of the platform are attenuated obviously owing to the active control.

Analysis of Power Matching on Energy Savings of a Pneumatic Rotary Actuator Servo-Control System

When saving energy in a pneumatic system,the problem of energy losses is usually solved by reducing the air supply pressure.The power-matching method is applied to optimize the air-supply pressure of the pneumatic system,and the energy-saving effect is verified by experiments.First,the experimental platform of a pneumatic rotary actuator servo-control system is built,and the mechanism of the valve-controlled cylinder system is analyzed.Then,the output power characteristics and load characteristics of the system are derived,and their characteristic curves are drawn.The employed air compressor is considered as a constant-pressure source of a quantitative pump,and the power characteristic of the system is matched.The power source characteristic curve should envelope the output characteristic curve and load characteristic curve.The minimum gas supply pressure obtained by power matching represents the optimal gas supply pressure.The comparative experiments under two different gas supply pressure conditions show that the system under the optimal gas supply pressure can greatly reduce energy losses.

STUDY ON THE CONTROL OF SINGLE PNEUMATIC MUSCLE ACTUATOR

The control of single pneumatic muscle actuator is studied, as one basic partof research on the parallel-robot arthrosis actuated by pneumatic muscle actuators. Experimentsshow that a self-modified fuzzy-PID controller is obviously effective for its position servo and asimple PID controller is good for its force track.

Study on Control of Pneumatic Selecting and Shifting Actuators Using Rapid Control Prototyping

A gearbox in-the-loop control platform using dSPACE real-time system is designed for the study on the control technology of pneumatic selecting and shifting actuators based on rapid control prototyping.The operational principle of such actuators was analyzed using dSPACE hardware and software,resulting in a better knowledge of the logical relationship among solenoid valves,gear positions of cylinders and system input/output.Based on these,a control model was developed under the Matlab/Simulink environment and rapidly improved to meet requirements through experiments.Relevant tests have shown that analysis efficiency on selecting and shifting actuators could be raised and development of control strategy facilitated.

Development of a Wearable Upper Limb Rehabilitation Robot Based on Reinforced Soft Pneumatic Actuators

Dyskinesia of the upper limbs caused by stroke,sports injury,or trafc accidents limits the ability to perform the activities of daily living.Besides the necessary medical treatment,correct and scientifc rehabilitation training for the injured joint is an important auxiliary means during the treatment of the efected upper limb.Conventional upperlimb rehabilitation robots have some disadvantages,such as a complex structure,poor compliance,high cost,and poor portability.In this study,a novel soft wearable upper limb rehabilitation robot(SWULRR)with reinforced soft pneumatic actuators(RSPAs)that can withstand high pressure and featuring excellent loading characteristics was developed.Driven by RSPAs,this portable SWULRR can perform rehabilitation training of the wrist and elbow joints.In this study,the kinematics of an SWULRR were analyzed,and the force and motion characteristics of RSPA were studied experimentally.The results provide a reference for the development and application of wearable upper limb rehabilitation robots.An experimental study on the rotation angle of the wrist and the pressure of the RSPA was conducted to test the efect of the rehabilitation training and verify the rationality of the theoretical model.The process of wrist rehabilitation training was tested and evaluated,indicating that SWULRR with RSPAs will enhance the fexibility,comfort,and safety of rehabilitation training.This work is expected to promote the development of wearable upper-limb rehabilitation robots based on modular reinforced soft pneumatic actuators.

Soft pneumatic actuators by digital light processing combined with injection-assisted post-curing

The soft robotics display huge advantages over their rigid counterparts when interacting with living organisms and fragile objects.As one of the most efficient actuators toward soft robotics,the soft pneumatic actuator(SPA)can produce large,complex responses with utilizing pressure as the only input source.In this work,a new approach that combines digital light processing(DLP)and injection-assisted post-curing is proposed to create SPAs that can realize different functionalities.To enable this,we develop a new class of photo-cross linked elastomers with tunable mechanical properties,good stretchability,and rapid curing speed.By carefully designing the geometry of the cavities embedded in the actuators,the resulting actuators can realize contracting,expanding,flapping,and twisting motions.In addition,we successfully fabricate a soft self-sensing bending actuator by injecting conductive liquids into the three-dimensional(3D)printed actuator,demonstrating that the present method has the potential to be used to manufacture intelligent soft robotic systems.

Position Control of Single Pneumatic Muscle Actuator

The PID, fuzzy, self-organized fuzzy and self-organized fuzzy-PID controllers are adopted in the position control of single pneumatic muscle actuator. Experiments show that the self-organized fuzzy-PID is obviously effective for the position control of single pneumatic muscle actuator, which can realize precision within 0.3 mm and withstand 18?N variable load plus about 36?N fixed load. It is relatively precise and robust.

Intelligent PID Control of Pneumatic Rotary Actuator Angle Servo-System

In order to solve the problems that make the orientation of pneumatic rotary actuator inaccurate, a newly intelligent PID control algorithm is proposed. Pneumatic rotary actuator angle servo-system uses electropneumatic proportional valve as control device, which changes the pressure of cavity and then pushes the actuator to revolve to the expected position. Using intelligent PID control algorithm, several special methods were put forward to overcome the connatural shortcomings of pneumatic system and make the rotary actuator track the expected value timely and accurately. Experimental results have shown that by using this intelligent algorithm, the performance index of system was improved greatly.

Simulation and Experimental Study of Dynamic Characteristics of a Pneumatic Actuator in Air Splicer

Splicing process parameters determined by dynamic characteristic of pneumatic actuator in air splicer have a significant influence on the performance of spliced yarn. Both gas thermodynamic and pneumatic actuator dynamic models, which were solved by the Runge-Kutta algorithm, were established to analyze the relationship among structural parameters of a pneumatic actuator and splicing process parameters such as splicing duration and gas consumption. Additionally,a visualization test bench to observe the dynamics of the pneumatic actuator and a mass flow measurement system to track splicing duration and gas consumption were designed. Comparisons between experimental data and simulation results show that the mathematical model accurately accounts for the dynamic characteristics of the pneumatic actuator,and consequently predicts splicing process parameters, which provides a theoretical foundation for the design optimization of air splicer.

Pneumatic Rotary Actuator Angle Control System

Based on the adaptive control method, a kind of parameter adjustor was used to control pneumatic rotary actuator to track the expected output. The system uses electropneumatic proportional valve as control device, which adjusts the gas flow of actuator 's two cavities, then changes the pressure of cavity and pushes the piston of actuator to move, so the rotary actuator 's axis can be made to revolve to the required angle at last. According to the characteristic of pneumatic system, the control system was described with a fourth-order mathematic model. The control rule is deduced by model reference adaptive control method. By the result of experiment, it was proved that by using the adaptive control method, the output of rotary actuator could track the expected value timely and accurately.

Biomimetic soft robotic wrist with 3-DOF motion and stiffness tunability based on ring-reinforced pneumatic actuators and a particle jamming joint

The human wrist, a complex articulation of skeletal muscles and two-carpal rows, substantially contributes to improvements in maneuverability by agilely performing three-degree-of-freedom(3-DOF) orienting tasks and regulating stiffness according to variations in interaction forces. However, few soft robotic wrists simultaneously demonstrate dexterous 3-DOF motion and variable stiffness;in addition, they do not fully consider a soft-rigid hybrid structure of integrated muscles and two carpal rows.In this study, we developed a soft-rigid hybrid structure to design a biomimetic soft robotic wrist(BSRW) that is capable of rotating in the x and y directions, twisting around the z-axis, and possessing stiffness-tunable capacity. To actuate the BSRW, a lightweight soft-ring-reinforced bellows-type pneumatic actuator(SRBPA) with large axial, linear deformation(η_(lcmax)=70.6%,η_(lemax)=54.3%) and small radial expansion(η_(demax)=3.7%) is designed to mimic the motion of skeletal muscles. To represent the function of two-carpal rows, a compact particle-jamming joint(PJJ) that combines particles with a membrane-covered ballsocket mechanism is developed to achieve various 3-DOF motions and high axial load-carrying capacity(>60 N). By varying the jamming pressure, the stiffness of the PJJ can be adjusted. Finally, a centrally positioned PJJ and six independently actuated SRBPAs, which are in an inclined and antagonistic arrangement, are sandwiched between two rigid plates to form a flexible,stable, and compact BSRW. Such a structure enables the BSRW to have a dexterous 3-DOF motion, high load-carrying ability,and stiffness tunability. Experimental analysis verify 3-DOF motion of BSRW, producing force of 29.6 N and 36 N and torque of2.2 Nm in corresponding rotations. Moreover, the range of rotational angle and stiffness-tuning properties of BSRW are studied by applying jamming pressure to the PJJ. Finally, a system combining a BSRW and a soft enclosing gripper is proposed to demonstrate outstanding manipulation capability in potential applications.

Investigation of mechanical and electrical characteristics of selfsensing pneumatic torsional actuators

Soft pneumatic actuators are one of the most promising actuation for soft robots,and great achievements have been obtained.But it remains challenging to endow sensing capabilities to pneumatic actuators,especially for the sensing ability originating directly from the actuator architecture.Herein,a self-sensing pneumatic torsional actuator(SPTA)is designed based on the electromagnetic induction effect and magnetically responsive materials.The SPTA can generate feedback voltage and current with the deformation,in which the sensing function comes from its inherent structure.To investigate the mechanical and electrical characteristics,an experimental platform and a finite element model are established,respectively.We find that the torsion angle and output torque increase in nonlinear with the actuating pressure.The maximum torsion angle is 66.35°,which is 84.34%of that for the actuator fabricated by pure rubber.The maximum output torque(24.9 N mm)improves by 23.19%compared with the actuator made by pure rubber.As regards the electrical characteristics,the maximum feedback voltage and current are 2.90μV and 29.50 nA when the SPTA is actuated by a pressure of−40 kPa.We also demonstrate that the relationship between the torsion angle and the magnetic flux change is approximately linear.Finally,the number of turns of wires,magnetic powders contents,and magnetic direction on the feedback voltage and current are studied.Results show that the feedback voltage and current can be enhanced by increasing the number of turns and magnetic powders contents.We envision that the SPTA would be promising for soft robots to realize their accuracy control and intelligentization.

Pneumatic and tendon actuation coupled muti-mode actuators for soft robots with broad force and speed range

Broad output force and speed ranges are highly desired for actuators to endow soft robots with high performance,thereby increasing the range of tasks they can accomplish.However,limited by their low structural stiffness and single actuation method,most of the existed soft actuators are still difficult to achieve a broad force and speed range with a relatively compact body structure.Here,we propose a pneumatic and tendon actuation coupled soft actuator(PTCSA)with multiple actuation modes,mainly composing of a multi-joint thermoplastic polyurethanes(TPU)-made skeleton sealed in a film sleeve.The TPU skeleton with certain structural stiffness combined with soft joints allows PTCSA to output small force and respond rapidly under pneumatic actuation,as well as output high force and flexibly regulate response speed under tendon actuation,therefore achieving a broad force and speed range with a compact structure.The multiple modes constructed from the two actuation methods with different force and speed properties can cover diverse application scenarios.To demonstrate its performance,PTCSA is further used to construct a soft robotic arm(with a maximum lifting speed of 198°/s and can easily lift a load of 200 g),an inchworm-inspired wheel-footed soft robot(moves at a high speed of 2.13 cm/s when unload or pulls a load of 300 g forward),and a soft gripper(can grasp diverse objects,from 0.1 g potato chips to an 850 g roll of Sn-0.7 Cu wire,from a high-speed moving tennis ball to an upright pen).This work indicates the potential of combining multiple complementary actuation methods to improve the force and speed range of soft actuators,and may provide inspiration for related research.

Three-dimensional Construction and Omni-directional Rolling Analysis of a Novel Frame-like Lattice Modular Robot

Lattice modular robots possess diversity actuation methods, such as electric telescopic rod, gear rack, magnet, robot arm, etc. The researches on lattice modular robots mainly focus on their hardware descriptions and reconfiguration algorithms. Meanwhile, their design architectures and actuation methods perform slow telescopic and moving speeds, relative low actuation force verse weight ratio, and without internal space to carry objects. To improve the mechanical performance and reveal the locomotion and reconfiguration binary essences of the lattice modular robots, a novel cube-shaped, frame-like, pneumatic-based reconfigurable robot module called pneumatic expandable cube（PE-Cube） is proposed. The three-dimensional（3D） expanding construction and omni-directional rolling analysis of the constructed robots are the main focuses. The PE-Cube with three degrees of freedom（Do Fs） is assembled by replacing the twelve edges of a cube with pneumatic cylinders. The proposed symmetric construction condition makes the constructed robots possess the same properties in each supporting state, and a binary control strategy cooperated with binary actuator（pneumatic cylinder） is directly adopted to control the PE-Cube. Taking an eight PE-Cube modules＇ construction as example, its dynamic rolling simulation, static rolling condition, and turning gait are illustrated and discussed. To testify telescopic synchronization, respond speed, locomotion feasibility, and repeatability and reliability of hardware system, an experimental pneumatic-based robotic system is built and the rolling and turning experiments of the eight PE-Cube modules＇ construction are carried out. As an extension, the locomotion feasibility of a thirty-two PE-Cube modules＇ construction is analyzed and proved, including dynamic rolling simulation, static rolling condition, and dynamic analysis in free tipping process. The proposed PE-Cube module, construction method, and locomotion analysis enrich the family of the lattice modular robot and provide the instruction to design the lattice modular robot.

Modeling and Experimental Evaluation of a Bionic Soft Pneumatic Gripper with Joint Actuator

The pneumatic gripper in industrial applications has the advantages of structure simplicity and great adaptability,but its gripping power is usually limited due to the low modulus of soft materials.To address this problem,a novel bionic pneumatic gripper inspired by spider legs is proposed.The design has two pairs of symmetrical fingers,each finger consists of two pneumatic actuated joints,two rigid links and one pneumatic soft pad.The rigid link connects the pneumatic chamber which is enclosed in a retractable shell to increase the actuation pressure and the gripping force.The compressibility and elasticity of the soft joint and pad enable the gripper to grasp fragile objects without damage.The modeling of the bionic gripper is developed,and the parameters of the joint actuators are optimized accordingly.The prototype is manufactured and tested with the developed experimental platform,where the gripping force,flexibility and adaptability are evaluated.The results indicate that the designed gripper can grasp irregular and fragile items in sizes from 40 to 140 mm without damage,and the lifting weight is up to 15 N.

Joint Motion Control of a Powered Lower Limb Orthosis for Rehabilitation

Many patients with spinal injures are confined to wheelchairs, leading to a sedentary lifestyle with secondary pathologies and increased dependence on a carer. Increasing evidence has shown that locomotor training reduces the incidence of these secondary pathologies, but the physical effort involved in this training is such that there is poor compliance. This paper reports on the design and control of a new ＂human friendly＂ orthosis （exoskeleton）, powered by high power pneumatic Muscle Actuators （pMAs）. The combination of a highly compliant actuation system, with an intelligent embedded control mechanism which senses hip, knee, and ankle positions, velocity, acceleration and force, produces powerful yet inherently safe operation for paraplegic patients. This paper analyzes the motion of ankle, knee, and hip joints under zero loading, and loads which simulate human limb mass, showing that the use of ＂soft＂ actuators can provide a smooth user friendly motion. The application of this technology will greatly improve the rehabilitative protocols for paraplegic patients.

Effective enhanced model for a large deformable soft pneumatic actuator

Soft pneumatic actuators have been widely used for implementing sophisticated and dexterous movements,due to numerous fascinating features compared with their rigid counterparts.Relatively speaking,modeling and analysis of an entire soft pneumatic actuator considering contact interaction between two adjacent air chambers is extremely rare,which is exactly what we are particularly interested in.Therefore,in order to establish an accurate mechanical model and analyze the overall configuration and stress distribution for the soft pneumatic actuator with large deflection,we consider the contact interaction of soft materials rather than hard materials,to produce an effective enhanced model for soft contact of a large deformable pneumatic actuator.In this article,a multiple-point contact approach is developed to circumvent the mutual penetration problem between adjacent air chambers of the soft actuator that occurs with the single-point contact approach employed in linear elastic rigid materials.In contrast to the previous simplified rod-based model that did not focus on contact interaction which was adopted to clarify the entire deformation of the actuator,the present model not only elaborates nonlinear large deformation and overall configuration variations,but also accurately delineates stress distribution law inside the chamber structure and the stress concentration phenomenon.By means of a corresponding static experiment,a comparison of the simulation results with experimental data validates the effectiveness and accuracy of this model employing a multiple-point contact approach.Excellent simulation of the actual bending deformation of the soft actuator is obtained,while mutual penetration is successfully circumvented,whereas the model with single-point contact cannot achieve those goals.Finally,as compared with the rod-based model,the results obtained using the proposed model are more consistent with experimental data,and simulation precision is improved.

Pneumatic bio-soft robot module:Structure,elongation and experiment

Soft robotics,often taking inspirations from biomimetics,is an exciting novel research field and has great capability to work with creatures.A new type of bio-soft robot inspired by elephant trunk and octopus was proposed,which has a promising application in robotic agricultural harvesting.The two modularized structures,basal segment and caudal segment,were elaborated in detail.They both have three side chambers and one central chamber,which are reinforced by springs for better stretch performance in axial direction without radial expansion.All the chambers can act as drivers when inflated with compressed air.More importantly,the central chamber was designed for regulating the stiffness of the robot module as needed in application.The primary static model for axial elongation was established for the fundamental analysis of the bio-soft robot module’s features,such as iso-force,isobaric and isometric characteristics.Simulation and experimental results showed that the motion of the proposed bio-soft module has approximate linearity in iso-force and isobaric conditions,and strict linearity in isometric condition.

Extended state observer-based pressure control for pneumatic actuator servo systems

A pneumatic actuator is a fast and economical tool that converts compressed air into mechanical motion.In this paper,an extended state observer(ESO)-based sliding mode controller(SMC)is developed to adjust the air pressure of the actua-tor for accurate position control,Specifically,an impedance control module is established to produce desired air pressure based on the relationship between forces and desired positions.Then,the ESO-based SMC is implemented to adjust the air pressure to the required level despite the presence of system uncertainties and disturbances.As a result,the position of the actuator is controlled to a setpoint through the regulation of pressure.The performance of ESO-based SMC is compared with that of a classic active disturbance rciection controller(ADRC)and a SMC.Simulation results demonstrate that the:ESO-based SMC shows comparable performance to ADRC in terms of precise pressure control.In addition,it requires the least control effort ncessary to excite valves among the three controllers.The stability of ESO based SMC is theoretically justifed through Lyapunov approach.