Internal Actuation Research Articles

Optimization and Design of a Flexible Droop Nose Leading Edge Morphing Wing Based on a Novel Black Widow Optimization (B.W.O.) Algorithm—Part II

This work presents an aerodynamic and structural optimization for a Droop Nose Leading Edge Morphing airfoil as a high lift device for the UAS-S45. The results were obtained using three optimization algorithms: coupled Particle Swarm Optimization-Pattern Search, Genetic Algorithm, and Black Widow Optimization algorithm. The lift-to-drag ratio was used as the fitness function, and the impact of the choice of optimization algorithm selection on the fitness function was evaluated. The optimization was carried out at various Mach numbers of 0.08, 0.1, and 0.15, respectively, and at the cruise and take-off flight conditions. All these optimization algorithms obtained effectively comparable lift-to-drag ratio results with differences of less than 0.03% and similar airfoil geometries and pressure distributions. In addition, an unsteady analysis of a Variable Morphing Leading Edge airfoil with a dynamic meshing scheme was carried out to study its flow behaviour at different angles of attack and the feasibility of leading-edge downward deflection as a stall control mechanism. The numerical results showed that the variable morphing leading edge reduces the flow separation areas over an airfoil and increases the stall angle of attack. Furthermore, a preliminary investigation was conducted into the design and sensitivity analysis of a morphing leading-edge structure of the UAS-S45 wing integrated with an internal actuation mechanism. The correlation and determination matrices were computed for the composite wing geometry for sensitivity analysis to obtain the parameters with the highest correlation coefficients. The parameters include the composite material qualities, thickness, ply angles, and the ply stacking sequence. These findings can be utilized to design the flexible skin optimization framework, obtain the target droop nose deflections for the morphing leading edge, and design an improved model.

Implicit neural representation for physics-driven actuated soft bodies

Active soft bodies can affect their shape through an internal actuation mechanism that induces a deformation. Similar to recent work, this paper utilizes a differentiable, quasi-static, and physics-based simulation layer to optimize for actuation signals parameterized by neural networks. Our key contribution is a general and implicit formulation to control active soft bodies by defining a function that enables a continuous mapping from a spatial point in the material space to the actuation value. This property allows us to capture the signal's dominant frequencies, making the method discretization agnostic and widely applicable. We extend our implicit model to mandible kinematics for the particular case of facial animation and show that we can reliably reproduce facial expressions captured with high-quality capture systems. We apply the method to volumetric soft bodies, human poses, and facial expressions, demonstrating artist-friendly properties, such as simple control over the latent space and resolution invariance at test time.

Development of a multi-sample acquisition technique for efficient planetary subsurface exploration

Improving the efficiency of a subsurface sample acquisition process provides operational benefits such as reduced bit wear and power consumption, and may increase the sample fidelity by minimising alterations caused by the drilling operation to the surrounding substrate. This could be achieved by acquiring multiple samples during a single drilling procedure. Although some recent planetary drills have incorporated a hybrid cored and cuttings sampling technique, there are currently no systems that have been designed to obtain and separately store multiple comparable samples. The Internal Actuation Mechanism, developed as part of the latest generation of the Dual-Reciprocating Drill, will incorporate a rotating shutter mechanism capable of acquiring up to four samples. In the first demonstration of the fully-integrated prototype using layers of differently-coloured sand, the shutter mechanism was shown to be able to take multiple samples in a single drilling operation. These experiments also confirmed the observations of numerical simulations, which showed that the drill’s teethed design results in regolith from the surface layer being dragged down with the descending drill and collected by the sampling system. By optimising the geometrical design to increase sample value and refining the shutter mechanism to improve reliability, a multi-sample acquisition system for planetary subsurface exploration could become a viable technology.

Bidirectional robust and fault-tolerant [formula omitted] non-sensitive compensation filter controller based on amorphous flattened air-to-ground wireless self-assembly system

With the cross-fertilization development of automatic control technology, electronic science and technology, and wireless communication technology, a single filter is no longer able to solve the fault problem of the control system and communication system simultaneously and in a balanced manner. In this paper, we design a bidirectional robust fault-tolerant H∞ non-sensitive compensation filter controller based on the robust adaptive fault-tolerant control algorithm, and further optimize the fault-tolerance correction factor and robust adaptive factor by the LMI (Linear-Matrix-Inequation) method under the regulation of the feedback matrix K, so that the system estimation error can converge to zero asymptotically. It can simultaneously solve the optimization problems of unknown faults (including external disturbances, partial failure of internal actuators, and random interruptions) of the self-assembling node and the acquisition of SNR (Signal-Noise-Ratio) by wireless self-assembling nodes. The simulation results show that the system eventually tends to be asymptotically stable in all performance metrics with feedback adjustment under the designed filter controller, and the estimation error asymptotically tends to zero. The robustness and fault tolerance performance indicators are good against external disturbances and internal actuator failure of the wireless self-assembling network node. The control rate of the network system all increases significantly as the total feedback constraint rate of the system increases, allowing the system to eventually obtain the optimal SNR. The experimental results show that the network nodes of the amorphous flat wireless air-to-ground self-organizing network system can change flexibly and adaptively with the change of scenes, and the wireless communication distance between the network nodes is relatively improved by 86.36%, 110%, and 79.91%, and the loop success rate appears to be stable fluctuation interval, which can greatly improve the survival rate of the self-organizing network nodes. This paper is of great research significance for further realizing the long-spacing transmission of self-organizing nodes and laying the foundation for future low-altitude fly-by-wire research.

Power-Efficient Soft Pneumatic Actuator Using Spring-Frame Collateral Compression Mechanism

With the ongoing research on soft robots, the performance of soft actuators needs to be enhanced for more wide robotic applications. Currently, most soft robots based on pneumatic actuation are capable of assisting small systems, but they are not fully suited for supporting joints requiring large force and range of motion. This is due to the actuation characteristics of the pneumatic artificial muscle (PAM); they are relatively slow, inefficient, and experience a significant force reduction when the PAM contracts. Hence, we propose a novel PAM based on a spring-frame collateral compression mechanism. With only a single compressed air source, the external mesh-covered and inner spring-frame actuators of the proposed PAM operate simultaneously to generate considerable force. Additionally, the design of the internal actuator within the void space of PAM reduces the air consumption and consequently improves the actuator’s operating speed and efficiency. We experimentally confirmed that the proposed PAM exhibited 31.2% greater force, was 25.6% faster, and consumed 21.5% lower air compared to the conventional McKibben muscles. The performance enhancement of the proposed PAM improves the performance of soft robots, allowing the development of more compact robots with greater assistive range.

Optimal control of the multi-module vibration-driven locomotion robot

The vibration-driven robot utilizes the periodic inertia force from the oscillator to realize locomotion. Because its movement does not rely on wheels or legs, the robot's body can be designed very neatly for working in restricted circumstances such as pipeline inspection and post-disaster rescue. Because high mobility is essential in these applications, the issue of actuation design to maximize the robot's average locomotion velocity emerges. Distinct from parameter optimization at given actuation patterns, the present paper represents the actuation design as the problem of optimal control and constructs an evolutionary algorithm to solve it. First, taking advantage of the periodicity, the internal actuation is represented as the Fourier series with the unknown period, harmonic coefficients, and phase shifts. Then, the multi-objective evolutionary algorithm based on decomposition (MOEA/D) is employed to optimize the unknown multi-parameters. Numerical results show that the optimal actuation of the one-module robot with isotropic friction is consistent with existing theoretical solutions, which verifies the correctness and practicability of our general scheme. Further explorations of the multi-module robot reveal that the optimal actuation continuously degenerates from the three-phase pattern to the two-phase when the friction ratio gradually attenuates to zero. Most importantly, although the optimal actuation phase shift between adjacent robot modules has been commonly accepted as half of the actuation period, the proposed scheme finds that the average velocity indeed maintains the maximum within a certain phase margin. As can be expected, this robustness will relax the burden of sophisticated actuation tuning in practice.

Internal Rotor Actuation and Magnetic Bearings for the Active Control of Rotating Machines

Passive rotors are often limited in rotational speed due to bearing constraints, stability and excessive vibration levels. To address the vibration issue, Active Magnetic Bearings (AMBs) levitating the rotor with a magnetic field can be used. They offer a clearance and variable stiffness and damping to the rotor support, which help to mitigate greatly the vibration issue. However, they are also limited at large rotational speed because of the high frequency control force required to levitate the rotor safely. To overcome the frequency limitation, a dual AMBs/internal bending control concept is investigated with associated modelling and control algorithms. This approach is examined in simulation with a 19 kg rotor running up to 10,000 RPM, where three resonance frequencies are present at 2700, 5300, and 9300 RPM, with the first resonant frequency being the most strongly excited. Using internal rotor bending control, a maximum radial displacement of 15 μm for the rotor mid-point is achieved, which gives a reduction in vibration amplitude of 45% compared to the case of no control. Variations of the algorithm are presented and discussed, showing the potential of the proposed approach.

Necessary conditions for oscillatory instabilities in active mechanical networks

Active mechanical networks represent systems spanning many domains and length scales, from actin meshes in cellular systems to limbs in animals and robots. Understanding the stability properties of internally actuated active networks is central to biological and engineering applications. Stability is governed by an interplay between actuation, kinematic constraints, external forces, and the viscoelastic properties of the mechanism. Unlike passive mechanisms, active systems under kinematic constraints are subject to loads that are a function of the internal actuation.

The unsteady force response of an accelerating flat plate with controlled spanwise bending

The unsteady force response of an accelerating flat plate, subjected to controlled spanwise bending, is investigated experimentally. The flat plate was held normal to the flow (at an angle of attack of $90^{\circ }$ ), and it was dynamically bent along the spanwise direction with the help of internal actuation. Two bending directions were tested. In one case, part of the plate (denoted by flexion ratio) was bent into the incoming flow (the bend-down configuration). In another case, the plate was bent away from the flow (the bend-up configuration). We used two different aspect ratio ( $AR$ ) plates, namely $AR = 2$ and 3. Three acceleration numbers, namely $A_c = 0.57$ , 1.6 and 3.2 (corresponding to dimensional acceleration of 0.036, 0.1 and 0.2 m s $^{-2}$ , respectively) were tested with a fixed terminal Reynolds number (Re) of 18 000. For each acceleration number, three bending durations, namely 1.2, 2.4 and 3.6 s were implemented. The results indicate that the highest impulse was imparted by the highest bending rate (duration 1.2 s) during all three accelerations tested. We show that controlled spanwise bending can significantly change the unsteady force response by manipulating the inertial forces during a start-up manoeuvre. The unsteady forces depend on the vector sum of the forward acceleration and the bending acceleration of the plate. The unsteady drag was augmented when the plate was bent towards the incoming flow. The initial force peaks were significantly reduced when the bending direction was reversed. The development of the edge vortices from the flat plate was measured with the help of particle image velocimetry (PIV) at the 70 % and the 90 % span locations. The PIV measurements were also carried out at the midchord plane closer to the tip region to capture the growth of the tip vortex. The vorticity field calculated from these PIV measurements revealed that controlled bending contributed to a variation in the circulation growth of the edge vortices. During the bend-down case, the circulation growth was faster and the tip vortices stayed closer to the plate. This resulted in increased interaction with the edge vortex at the 90 % span. This interaction was more severe for $AR = 2$ . During the bend-up case, the growth of the edge vortex was delayed, but the vortex grew for a longer time compared with the bend-down case. Finally, a mathematical model is presented which correctly captured the trend of the force histories measured experimentally during both the bend-up and bend-down cases.

Lock-in thermography using miniature infra-red cameras and integrated actuators for defect identification in composite materials

A novel approach for thermographic Non-Destructive Evaluation (NDE) of laminated polymer composite structures is presented. The technique is based on Lock-In Thermography (LIT), which traditionally uses an external heat source. Here a new means of internal heating, via a lightweight embedded actuator capable of providing highly repeatable and uniform heating is presented. The equipment cost, complexity and hence size is reduced by removing the need for high power external thermal excitation. Instead, the necessary temperature modulation of the internal actuator is achieved with a compact and low-cost Arduino controlled circuit. The size and cost of the equipment is further reduced by demonstrating that a miniature printed circuit board mounted thermal core type micro-bolometer can be used effectively for LIT. The performance of the thermal core is quantitatively compared with the more expensive and bulky traditional infra-red cameras. It is shown that the thermal core can detect defects with similar overall performance as a cooled photon detector and an uncooled micro-bolometer. The low-cost, compact nature and small mass of the thermal core offers great potential in thermographic inspection opening the possibility of deploying devices permanently on structures in conjunction with the embedded actuators for in-situ monitoring in the service environment.

Three-Fingered Soft Pneumatic Gripper Integrating Joint-Tuning Capability

Compared with traditional rigid grippers, soft grippers are made of lightweight and soft materials and have the characteristics of flexible contact and strong adaptability, which are widely utilized to grasp fragile objects with complex contours and shapes. In this article, we design and fabricate a three-fingered stiffness-tunable soft gripper by integrating the joint-tuning capability. The soft fingers are composed of an internal bending actuator and an external fiber-jamming jacket, under an actuation of pneumatic pressure. Static and kinematic models are established to detect the bending angle and end trajectory of the internal bending actuator. Meanwhile, the bending angle and blocking force of bending actuator are experimentally measured and are comparably analyzed with the theoretical predictions. Jamming pressure is applied in the stiffness-tunable jacket to explore the variable stiffness and load-carrying capability of the soft finger. By incorporating the stiffness-tunable property, the grasping performance of various weights and types of goods, as well as the maximum grasping force of the soft gripper, is investigated. Finally, by patterning the stiffness-tunable jacket on the bending actuator, the variable curvature bending deformation and joint-tuning capability of the soft finger are achieved. This proposed soft gripper holds great potential applications in soft robotics community.

Robust real-time feedback algorithms for plasma kinetic control in advanced tokamak scenarios

Robust real-time control algorithms for tracking plasma kinetic parameters in advanced tokamak scenarios are developed based on linear state-space (LSS) dynamic models. The real-time control algorithms under study comprise the robust control, the linear quadratic integral control and the internal model control. The plasma models used in this work are restricted to LSS models identified from dedicated simulation/experimental data, though the proposed control algorithms can conveniently be extrapolated to broadly incorporate linear models obtained from first-principles plasma theory. The control objective is to track plasma kinetic parameters of interest to desired operating points in advanced tokamak scenarios by actuating additional heating & current drive systems in real-time. Plasma kinetic parameters involve the poloidal pressure parameter β p , the internal inductance , the average toroidal rotation angular speed and the electron temperature on axis while the actuators are the ion cyclotron resonance heating and lower hybrid current drive systems. In order to achieve enhanced control performance, two control layers are designed. The outer layer, i.e. an internal model-based proportional-integral actuator controller, operating on a fast timescale ( the energy confinement time τ E ) aiming at tracking the commands requested by the inner kinetic controllers, while the inner layer, i.e. a kinetic controller chosen from various alternatives, running on a slow timescale () is dedicated to tailoring plasma kinetic parameters. Simulation results for the experimental advanced superconducting tokamak (EAST) tokamak are provided and compared to show the capabilities of each control approach. Dedicated kinetic control experiments conducted in an H-mode scenario on EAST are reported as well. The advantages and limits of these control algorithms are discussed and summarised.

Towards spherical robots for mobile mapping in human made environments

Spherical robots are a format that has not been thoroughly explored for the application of mobile mapping. In contrast to other designs, it provides some unique advantages. Among those is a spherical shell that protects internal sensors and actuators from possible harsh environments, as well as an inherent rotation for locomotion that enables measurements in all directions. Mobile mapping always requires a high-precise pose knowledge to obtain consistent and correct environment maps. This is typically done by a combination of external reference sensors such as Global Navigation Satellite System (GNSS) measurements and inertial measurements or by coarsely estimating the pose using inertial measurement units (IMUs) and post processing the data by registering the different measurements to each other. In indoor environments, the GNSS reference is not an option. Hence many mobile mapping applications turn to the second option. An advantage of indoor environments is that human-made environments usually have a certain structure, such as parallel and perpendicular planes. We propose a registration procedure that exploits this structure by minimizing the distance of measured points to a corresponding plane. Further, we evaluate the procedure on a simulated dataset of an ideal corridor and on an experimentally acquired dataset with different motion profiles. We show that we nearly reproduce the ground truth for the simulated dataset and improve the average point-to-point distance to a reference scan in the experimental dataset. The presented algorithms are required to work completely autonomously.

A remeshed vortex method for mixed rigid/soft body fluid–structure interaction

We outline a 2D algorithm for solving incompressible flow–structure interaction problems for mixed rigid/soft body representations, within a consistent framework based on the remeshed vortex method. We adopt the one-continuum formulation to represent both solid and fluid phases on an Eulerian grid, separated by a diffuse interface. Rigid solids are treated using Brinkman penalization while an inverse map technique is used to obtain elastic stresses in the hyperelastic solid phase. We test our solver against a number of benchmark problems, which demonstrate physical accuracy and first to second order convergence in space and time. Benchmarks are complemented by additional investigations that illustrate the ability of our numerical scheme to capture essential fluid–structure interaction phenomena across a variety of scenarios involving internal muscular actuation, self propulsion, multi-body contact, heat transfer and rectified viscous streaming effects. Through these illustrations, we showcase the ability of our solver to robustly deal with different constitutive models and boundary conditions, solve disparate multi-physics problems and achieve faster time-to-solutions by sidestepping CFL time step restrictions.

Learning active quasistatic physics-based models from data

Humans and animals can control their bodies to generate a wide range of motions via low-dimensional action signals representing high-level goals. As such, human bodies and faces are prime examples of active objects, which can affect their shape via an internal actuation mechanism. This paper explores the following proposition: given a training set of example poses of an active deformable object, can we learn a low-dimensional control space that could reproduce the training set and generalize to new poses? In contrast to popular machine learning methods for dimensionality reduction such as auto-encoders, we model our active objects in a physics-based way. We utilize a differentiable, quasistatic, physics-based simulation layer and combine it with a decoder-type neural network. Our differentiable physics layer naturally fits into deep learning frameworks and allows the decoder network to learn actuations that reach the desired poses after physics-based simulation. In contrast to modeling approaches where users build anatomical models from first principles, medical literature or medical imaging, we do not presume knowledge of the underlying musculature, but learn the structure and control of the actuation mechanism directly from the input data. We present a training paradigm and several scalability-oriented enhancements that allow us to train effectively while accommodating high-resolution volumetric models, with as many as a quarter million simulation elements. The prime demonstration of the efficacy of our example-driven modeling framework targets facial animation, where we train on a collection of input expressions while generalizing to unseen poses, drive detailed facial animation from sparse motion capture input, and facilitate expression sculpting via direct manipulation.

Control Allocation of a GEO Satellite for Station-Keeping and Momentum Management by Using Thrusters and Reaction Wheels

This paper presents a control allocation method for simultaneous station-keeping and momentum management maneuvers. The considered satellite model is equipped with internal and external actuators to control the satellite’s orbit and attitude and, concurrently, unload the angular momentum stored in the reaction wheels. Our method allocates the external and internal actuators to achieve the control objectives. Internal actuators such as reaction wheels generate torque based on the conservation of the momentum. In this study, two different controllers are utilized to control satellite attitude and reaction wheel speeds. To manage the satellite attitude in three axes, at least three reaction wheels are needed. In this study, four reaction wheels are used to ensure control in case of failure of a reaction wheel. In addition, with six chemical thrusters, east-west and north-south orbit correction maneuvers are performed. For the satellite to serve throughout its service life, fuel optimization of the satellite is required. The proposed control allocation method will enforce constraints that maintain orbital accuracy and the satellite in a nadir pointing attitude configuration while minimizing the use of thrusters, significantly reducing fuel consumption. The method combines the two generally separated objectives of orbital and attitude control through constraints determined by the propulsion system. Numerical simulations are performed to validate the proposed method. The simulations show that using the proposed control allocation method can significantly increase the service life of geostationary satellites.

Motion Design with Efficient Actuator Placement for Adaptive Structures that Perform Large Deformations

Adaptive structures have great potential to meet the growing demand for energy efficiency in buildings and engineering structures. While some structures adapt to varying loads by a small change in geometry, others need to perform an extensive change of shape to meet varying demands during service. In the latter case, it is important to predict suitable deformation paths that minimize control effort. This study is based on an existing motion design method to control a structure between two given geometric configurations through a deformation path that is optimal with respect to a measure of control efficiency. The motion design method is extended in this work with optimization procedures to obtain an optimal actuation system placement in order to control the structure using a predefined number of actuators. The actuation system might comprise internal or external actuators. The internal actuators are assumed to replace some of the elements of the structure. The external actuators are modeled as point forces that are applied to the structure nodes. Numerical examples are presented to show the potential for application of the motion design method to non-load-bearing structures.

Analysis and Design of a Leading Edge with Morphing Capabilities for the Wing of a Regional Aircraft—Gapless Chord- and Camber-Increase for High-Lift Performance

In order to contribute to achieving noise and emission reduction goals, Fraunhofer and Airbus deal with the development of a morphing leading edge (MLE) as a high lift device for aircraft. Within the European research program “Clean Sky 2”, a morphing leading edge with gapless chord- and camber-increase for high-lift performance was developed. The MLE is able to morph into two different aerofoils—one for cruise and one for take-off/landing, the latter increasing lift and stall angle over the former. The shape flexibility is realised by a carbon fibre reinforced plastic (CFRP) skin optimised for bending and a sliding contact at the bottom. The material is selected in terms of type, thickness, and lay-up including ply-wise fibre orientation based on numerical simulation and material tests. The MLE is driven by an internal electromechanical actuation system. Load introduction into the skin is realised by span-wise stringers, which require specific stiffness and thermal expansion properties for this task. To avoid the penetration of a bird into the front spar of the wing in case of bird strike, a bird strike protection structure is proposed and analysed. In this paper, the designed MLE including aerodynamic properties, composite skin structure, actuation system, and bird strike behaviour is described and analysed.

Design and modeling of an improved bridge-type compliant mechanism with its application for hydraulic piezo-valves

Bridge-type compliant mechanisms have been frequently utilized as the micro displacement amplifier for a variety of precision manipulation applications. However, the inertial movement of internal actuators (e.g. piezo-stacks) limits the system’s dynamic bandwidth in some traditional design. This paper presents an improved bridge-type compliant mechanism with double output ports that can generate homodromous bi-motions actuated by only one group of piezo-stacks. The inertial motion of piezo-stacks is avoided and the dynamic bandwidth is enhanced. The two-port dynamic stiffness model is established to straightforwardly capture its kinetostatic and dynamic characteristics from the perspective of input and output ports. The displacement amplification ratio, input stiffness, fundamental frequency and dynamic response spectrum of the improved bridge-type compliant mechanism are curved against key geometric parameters, then the optimal performance can be confirmed. Of particular interest for the mechanism application is applying it to develop a new type of piezoelectric two-stage flow control valve with relatively fast dynamic response and large flow rate. The inner leakage and oil contamination is effectively overcome in contrast to traditional nozzle-flapper servovalves. The presented piezoelectric flow control valve is fabricated and experimentally measured with the step response time of 8.5 ms, frequency bandwidth of 120 Hz, and stroke of ±0.8 mm (corresponding to the flow rate of 180 L/min at the supply pressure of 210 bar).

Constrained motion design with distinct actuators and motion stabilization

AbstractThe design of adaptive structures is one method to improve sustainability of buildings. Adaptive structures are able to adapt to different loading and environmental conditions or to changing requirements by either small or large shape changes. In the latter case, also the mechanics and properties of the deformation process play a role for the structure's energy efficiency. The method of variational motion design, previously developed in the group of the authors, allows to identify deformation paths between two given geometrical configurations that are optimal with respect to a defined quality function. In a preliminary, academic setting this method assumes that every single degree of freedom is accessible to arbitrary external actuation forces that realize the optimized motion. These (nodal) forces can be recovered a posteriori. The present contribution deals with an extension of the method of motion design by the constraint that the motion is to be realized by a predefined set of actuation forces. These can be either external forces or prescribed length chances of discrete, internal actuator elements. As an additional constraint, static stability of each intermediate configuration during the motion is taken into account. It can be accomplished by enforcing a positive determinant of the stiffness matrix.