Pneumatic Artificial Muscle Driven Trailing Edge Flaps For Active Rotors

This research focuses on the development of an active rotor system capable of primary control and vibration reduction for rotorcraft. The objective is to investigate the feasibility of a novel Trailing Edge Flap (TEF) actuation system driven by Pneumatic Artificial Muscles (PAMs). A significant design effort led to a series of experimental apparatuses which tested various aspects of the performance of the actuators themselves and of TEF systems driven by them. Analytical models were developed in parallel to predict the quasistatic and dynamic behavior of these systems. Initial testing of a prototype blade section with an integrated PAM driven TEF proved the viability of the concept through successful benchtop testing under simulated M = 0.3 loading and open jet wind tunnel tests under airspeeds up to M = 0.13. This prototype showed the ability of PAM actuators to generate significant flap deflections over the bandwidth of interest for primary control and vibration reduction on a rotorcraft. It also identified the importance of high pneumatic system mass flow rate for maintaining performance at higher operating frequencies. Research into the development and improvement of PAM actuators centered around a new manufacturing technique which was invented to directly address the weaknesses of previous designs. Detailed finite element model (FEM) analysis of the design allowed for the mitigation of stress concentrations, leading to increased strength. Tensile testing of the swaged actuators showed a factor of safety over 5, and burst pressure testing showed a factor of safety of 3. Over 120,000,000 load cycles were applied to the actuators without failure. Characterization testing before, during, and after the fatigue tests showed no reduction in PAM performance. Wind tunnel testing of a full scale Bell 407 blade retrofitted with a PAM TEF system showed excellent control authority. At the maximum wind tunnel test speed of M = 0.3 and a derated PAM operating pressure of 28 psi, 18.8° half-peak-to-peak flap deflections were achieved at 1/rev (7 Hz), and 17.1° of half-peak-to-peak flap deflection was still available at 5/rev (35 Hz). A quasistatic system model was developed which combined PAM forces, kinematics and flap aerodynamics to predict flap deflection amplitudes. This model agreed well with experimental data. Whirl testing of a sub-span whirl rig under full scale loading conditions showed the ability of PAM TEF systems to operate under full scale levels of centrifugal (CF), aerodynamic, and inertia loading. A commercial pneumatic rotary union was used to provide air in the rotating frame. Extrapolation of the results to 100% of CF acceleration predicts 15.4° of half-peak-to-peak flap deflection at 1/rev (7 Hz), and 7.7° of half-peak-to-peak flap deflection at 5/rev (35 Hz). A dynamic model was developed which successfully predicted the time domain behavior of the PAM actuators and PAM TEF system. This model includes control valve dynamics, frictional tubing losses, pressure dynamics, PAM forces, mechanism kinematics, aerodynamic hinge moments, system stiffness, damping, and inertia to solve for the rotational dynamics of the flap. Control system development led to a closed loop control system for PAM TEF systems capable of tracking complex, multi-sinusoid flap deflections representative of a combined primary control and vibration reduction flap actuation scheme. This research shows the promise that PAM actuators have as drivers for trailing edge flaps on active helicopter rotors. The robustness, ease of integration, control authority and tracking accuracy of these actuators have been established, thereby motivating further research

A Biomimetically Derived Method for Control of Span-Wise Morphing Wings

© 2022 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. This is the accepted manuscript version of a conference paper which has been published in final form at https://doi.org/10.2514/6.2022-1986The development of novel morphing wings follows common milestones. This work presents the modelling and control of the recently proposed avian wing span-wise morphing concept. The concept primarily consists of three structural members heavily mimicking the skeletal structure birds employ for flight. This structure is actuated, through the range of motion achievable by avian, with the integration of pneumatic artificial muscles (PAMs). Arranged in antagonistic pairs, the PAMs actuate an effective shoulder joint between the aircraft and wing through 90⁰. As well as two joints along the wing through 110⁰, allowing a span-wise reduction of 75% the fully extended span. This adaptive structure is capable of supporting several different aerofoil geometries for application specific aircraft. Initially proposed with a biomimetic derived wing profile more traditional and predictable NACA aerofoils have been applied. In this paper the avian wing span-wise morphing concept is modelled and with the application of inverse kinematics a control system is derived to allow simplified span-length positioning. Similarly, desired wing area is also presented as an input for the system. The model is based on PAM force models to individually model the pneumatic system driving each joint. The mechanical system of each joint is subsequently used to produce a direct kinematic model for wing tip position, and the inverse determined for control. The validity of both the model and system are experimentally tested on a fixed semi-span prototype rig of the morphing concept. Feedback is then introduced. Potentiometers are embedded into each joint to provide joint angle feedback. The tuning of the system is then presented for different dynamic responses. Alongside this development experiments have been conducted into the kinematics avian employ in flight and the flight dynamics they enable. These results are presented and directly applied as parameters for the proposed system. Span morphing retraction and extension rates determined from in vivo flight data of avian, including the Common buzzard (Buteo buteo) and Harris Hawk (Parabuteo unicinctus), are achieved using the avian wing span-wise morphing concept and the proposed control system. These dynamics are used to infer the parameters of an aircraft with the concept wing used as control surfaces

Development of a SMA-fishing-line-McKibben bending actuator

High power-to-weight ratio soft artificial muscles are of overarching importance to enable inherently safer solutions to human-robot interactions. Traditional air driven soft McKibben artificial muscles are linear actuators. It is impossible for them to realize bending motions through a single McKibben muscle. Over two McKibben muscles should normally be used to achieve bending or rotational motions, leading to heavier and larger systems. In addition, air driven McKibben muscles are highly nonlinear in nature, making them difficult to be controlled precisely. A SMA(shape memory alloy)–fishing–line–McKibben (SFLM) bending actuator has been developed. This novel artificial actuator, made of a SMA-fishing-line muscle and a McKibben muscle, was able to produce the maximum output force of 3.0 N and the maximum bending angle (the rotation of the end face) of 61°. This may promote the application of individual McKibben muscles or SMA-fishing-line muscles alone. An output force control method for SFLM is proposed, and based on MATLAB/Simulink software the experiment platform is set up, the effectiveness of control system is verified through output force experiments. A three-fingered SFLM gripper driven by three SFLMs has been designed for a case study, which the maximum carrying capacity is 650.4 ± 0.2 g

Experimental investigation of characteristics of pneumatic artificial muscles

The characteristics of pneumatic artificial muscles (PAMs) make them very interesting for the development of robotic and prosthesis applications. The McKibben muscle is the most popular and is made commercially available by different companies. The aim of this research is to acquire as much information about the pneumatic artificial muscles as we can with our test-bed that was developed by us and to be able to adopt these muscles as a part of prosthesis. This paper presents the set-up constructed, and then describes some mechanical testing results for the pneumatic artificial muscles

Design and Control of the McKibben Artificial Muscles Actuated Humanoid Manipulator

The McKibben Pneumatic Artificial Muscles (PAMs) are expected to endow the advanced robots with the ability of coexisting and cooperating with humans. However, the application of PAMs is still severely hindered by some critical issues. Focusing on the bionic design issue, this chapter in detail presents the design of a 7-degree-of-freedom (DOF) human-arm-like manipulator. It takes the antagonized PAMs and Bowden cables to mimic the muscle-tendon-ligament structure of human arm by elaborately configuring the DOFs and flexibly deploying the routing of Bowden cables; as a result, the DOFs of the analog shoulder, elbow, and wrist of the robotic arm intersect at a point respectively and the motion of these DOFs is independent from each other for convenience of human-like motion. The model imprecision caused by the strong nonlinearity is universally acknowledged as a main drawback of the PAM systems. Focusing on this issue, this chapter views the model imprecision as an internal disturbance, and presents an approach that observe these disturbances with extended-state-observer (ESO) and compensate them with full-order-sliding-mode-controller (fSMC), via experiments validated the human-like motion performance with expected robustness and tracking accuracy. Finally, some variants of PAMs for remedying the drawbacks of the PAM systems are discussed