Minimum Actuation Research Articles

Simultaneous Force and Stiffness Control of a Pneumatic Actuator

This paper proposes a new approach to the design of a robot actuator with physically variable stiffness. The proposed approach leverages the dynamic characteristics inherent in a pneumatic actuator, which behaves in essence as a series elastic actuator. By replacing the four-way servovalve used to control a typical pneumatic actuator with a pair of three-way valves, the stiffness of the series elastic component can be modulated independently of the actuator output force. Based on this notion, the authors propose a control approach for the simultaneous control of actuator output force and stiffness. Since the achievable output force and stiffness are coupled and configuration-dependent, the authors also present a control law that provides either maximum or minimum actuator output stiffness for a given displacement and desired force output. The general control and maximum/minimum stiffness approaches are experimentally demonstrated and shown to provide high fidelity control of force and stiffness, and additionally shown to provide a factor of 6 dynamic range in stiffness.

CONCEPT FOR THE DESIGN OF FLIGHT CONTROL ACTUATION AND LAWS FOR FUTURE ALL-ELECTRIC AIRCRAFT

This paper consolidates advanced techniques for flight control law design with the sizing issues of new technology electrical flight control actuators. An automatic optimisation tool is adapted to modify the control laws for minimum actuator deflection rates, which can be turned into weight savings for the overall aircraft. Thus, the paper outlines a new and up-to-date trade-off study, which is motivated by the recent trend towards the more-electric aircraft concept.

Actuation potentials and capillary forces in electrowetting based microsystems

The minimum and maximum actuation voltages in electrowetting actuated microsystems are investigated in this paper. The minimum actuation voltage corresponds to the electric potential required to obtain motion of a droplet between two electrodes. Below this threshold, a droplet cannot be displaced due to contact angle hysteresis. The maximum actuation voltage corresponds to the electric potential above which there is no more gain in capillary forces because of the saturation effect. Based on the calculation of the electrocapillary forces on a drop in an EWOD system, and taking into account the contact angle hysteresis, an analytical relation is derived for the minimum actuation potential. On the other hand, the Peykov–Quinn–Ralston–Sedev model produces an approximate value of the maximum actuation voltage. Thus, a range of actuation potentials can be predicted depending on the liquid of the droplet, the surrounding gas or fluid and the nature of the solid substrate. The results of the two models are favorably compared with experimental results obtained using different liquids and substrates.

Covariance-based hardware selection-Part I: globally optimal actuator selection

A new covariance based formulation of the actuator selection problem is presented. The proposed optimization problem is aimed at finding the set of minimum cost actuator arrays such that there exists a linear feedback for which all closed-loop signals will satisfy pre-specified variance bounds. Through a linear matrix inequality (LMI) based transformation we exactly convert the original problem into a computationally attractive mixed integer convex program (MICP). The resulting MICP leads to the first computational scheme capable of calculating globally optimal solutions to the covariance based actuator selection problem. It is further shown that the formulation is general enough to incorporate extensions to the actuator noise and actuator dynamics cases. Finally, a set of examples are presented to illustrate the scheme as well as the scalability of required computational effort.

Swashplateless Helicopter Rotor System with Trailing-Edge Flaps for Flight and Vibration Controls

The objective of this study is to demonstrate the concept of active trailing-edge flaps as primary flight control and vibration reduction devices for a typical full-scale helicopter. A comprehensive rotorcraft analysis based on UMARC was developed to analyze the swashplateless rotor. A parametric study of various key design variables involved in the trailing-edge flap design was carried out. An optimal design of a trailing-edge flap system that provides effective control authority within the complete range of advance ratios as well as minimum actuation requirements was achieved. Trailing-edge flaps demonstrated the capability of performing both primary flight control and active vibration control functions. At a high forward speed (advance ratio of 0.32), the 4/rev vertical force and roll and pitch moments at hub are successfully eliminated (by 90%), and the 4/rev in-plane hub forces are reduced by more than 40%. The half peak-to-peak value of the trailing-edge flap deflection for primary flight control is 7.1 deg, and an additional 4.7 deg is required for active vibration control.

Design of a Redundantly Actuated Hip Mechanism

In humanoid robotic system, many human-body motions such as walking, running, and jumping require large power. As one effort to achieve such high power-to-weight ratio, this paper proposes a new hip design using parallel kinematic chain involving redundant actuators. The kinematics for the hip mechanism is derived and a kinematic index to measure force transmission ratio is introduced. It is demonstrated through simulation that incorporation of redundant actuator into the hip mechanism enhances the power of the mechanism approximately 4 times of the minimum actuation. And the validity of the simulation result was verified through experimental works.

2P1-B20 受動歩行規範ロボットにおける足形状の設計

We propose a new foot shape applying to a biped robot to realize the stability of the passive dynamic walk. The shape is aiming at requiring minimum actuator power which drives inclination of foot. It is analyzed and experimented by the experimental mechanism. We report the result of the foot design with passive dynamic walk, and show the possibility of introducing learning onto this configuration.

Development of High-rate, Adaptive Trailing Edge Control Surface for the Smart Wing Phase 2 Wind Tunnel Model

The DARPA/AFRL/NASA Smart Wing program, led by Northrop Grumman Corporation (NGC) under the DARPA Smart Materials and Structures initiative, addressed the development of smart technologies and demonstration of relevant concepts to improve the aerodynamic performance of military aircraft. In Phase 2, Test 2 of the program, the main objective was to demonstrate high-rate actuation of hingeless, spanwise, and chordwise deformable control surfaces using smart materials-based actuators on a 30% scale, full span wind tunnel model of a proposed NGC uninhabited combat air vehicle (UCAV). A minimum actuation rate of 25° flap deflection in 0.33 s, producing a slew rate of 75°/s, was desired. This slew rate is representative of many operational military aircrafts with hinged control surfaces. Numerous trade studies were performed on a variety of smart materials and flexible structure configurations before arriving at the final trailing edge structure design that consisted of a flexcore center and elastomeric outer skin actuated by high-power ultrasonic motors using an eccentric motion. The trailing edge control surface fitted onto the wind tunnel model comprised 10 eccentric-driven segments connected together by a continuous outer skin and a flexible hinge pin at the trailing edge tip. This pinned configuration allowed the segments partial freedom to rotate about each other, but constrained any lateral motion thus giving a smooth trailing edge shape for nonuniform spanwise deflections. To control the 10 segments of the trailing edge, a VME-based control system with high speed, simultaneously sampled A/D and D/A boards and a dedicated DSP board was developed. This paper describes the analysis and design of the flex structure, ultrasonic motor selection and performance, element and coupon tests to verify analysis, control system development, model integration, and results from the wind tunnel test.

Aeroelastic Optimization of Adaptive Bumps for Yaw Control

This paper captures the aeroelastic behavior of adaptable bumps on morphing wings using trained neural networks. Parameters of the bump such as the height, size, location, and shape play a major aerodynamic and structural role. Though other issues such as wave drag minimization, boundary layer control are discussed, the primary problem addressed here is the generation of the lateral directional moment. The shape of the bump is optimized so that it produces maximum yaw moment with a minimum actuation energy spent in creating the adaptive bump. The analysis of fluid separation on the airfoil surface due to various types of bumps and its effects on the aerodynamic forces is performed using the computational fluid dynamics (CFD) software FLUENT TM . This analysis is performed at a low speed of Mach 0.3 and at a transonic speed of Mach 0.7. Structural analysis is performed using the finite element software ANSYS TM using a nonlinear beam model of the bump. In order to perform an aeroelastic analysis, the softwares FLUENT and ANSYS have to be interconnected so that the changing aerodynamic pressure with bump deformation is reflected in the structural analysis. Direct coupling of two such numerical codes, one based on CFD and the other based on finite element modeling (FEM), is computationally expensive. Hence, artificial neural networks are trained from these aerodynamic and structural analysis. Two neural networks are trained, one for the aerodynamic pressure and the other for the structural loads and strain energy. These two neural networks serve as an efficient decoupler, that facilitates an aeroelastic optimization procedure to evaluate the best bump shape for maximum drag for providing micro-yaw control while using the minimum actuation energy and minimizing the loss in the lift.

Nanofluidic bubble pump using surface tension directed gas injection.

A new concept for liquid manipulation has been developed and implemented in surface-micromachined fluid channels. It is based on the surface tension directed injection of a gas into the liquid flow through micrometer-sized holes in the microchannel wall. The injected gas is directed to an exhaust by a cross-sectional asymmetry of the microchannel and thereby moves minute liquid volumes. Successful pumping experiments were performed with single stroke volumes of tens of picoliters at frequencies around 1 Hz. The minimum actuation pressure is 0.6 bar for a 2-microm channel height, in accordance with theoretical predictions.

A Stable Neural Network Controller for Linear Saturated Systems Containing Hysteresis

Abstract This paper introduces a design procedure for detemunation of weight matrices of an MLP-based controller to locally stabilize a class of multi-input nonlineaz systems consisting of a lineaz system together with a nonlineaz saturated actuator with or without hysteresis. No assumption is made on the stability of the open-loop system. Two different design problems aze considered: 1) designing a neural network which maximizes the guazanteed domain of stability of the overall system when the actuator bounds aze given, and 2) designing a neural network which guazantees the stability of the overall system in apre-specified region in state-space with a minimum actuator bound. The proposed controller has excellent advantage over the classical ones, regazding its guaranteed domain of stability. The design procedure replaces eazlier recursive neural network learning algorithms with a simple optimization problem.

Magnetostrictively actuated control flaps for vibration reduction in helicopter rotors—design considerations for implementation

Vibration reduction using blade root pitch control introduces a significant power penalty and may adversely affect the airworthiness of the flight control system. Comparable levels of vibration reduction can be achieved using considerably less power through an actively controlled trailing edge flap mounted on the blade. Such a device would have no effect on helicopter airworthiness since it is controlled by a loop separate from the primary flight control system which utilizes the swashplate. Control flap actuation using the magnetostrictive material Terfenol-D is studied in this paper by designing a minimum weight actuator, subject to a set of actuation and stress constraints. An important ingredient in this design process is the precise characterization of the constitutive relations for the magnetostrictive material which provides valuable guidelines on the practical implementation of magnetostrictive actuators. It is shown that the magnetostrictively actuated flap is capable of producing vibration reduction in high speed forward flight in excess of 90%.

Optimal design and development of a five-bar finger with redundant actuation

In order to develop a human hand mechanism, a five-bar finger with redundant actuation is designed and implemented. Each joint of the finger is driven by a compact actuator mechanism having an ultrasonic motor and a gear set with a potentiometer, and controlled by a VME bus-based control system. Optimal sets of actuator locations and link lengths for cases of a minimum actuator, one-, two-, and three-redundant actuators are obtained by employing a composite design index which simultaneously considers several performance indices, such as workspace, isotropic index, and force transmission ratio. According to the optimization result, several finger-configurations optimized for a special performance index are illustrated, and it is concluded that the case of one redundant actuator is the most effective in comparison to the cases of more redundant actuators, and that the case of two redundant actuators is the most effective in multi-fingered operation in which the force characteristic is relatively important, as compared to the kinematic isotropy and the workspace of the system.

Fault Tolerance with Respect to Actuator Failures in LTI Systems

This paper is concerned with the analysis of fault tolerance properties with respect to actuator failures. Controllability, individual controllability and pseudo-controllability indexes are used to build minimal and pseudo-minimal actuator sets, considering both global and partial state controllability. Pseudo-minimal and minimal actuator sets are organized into an oriented graph which contains all the actuator sets such that the system is controllable. The analysis of this graph allows to compute redundancy degrees, which evaluate the system fault tolerance with respect to actuator failures.

Nonlinear model based control of a piezoelectric actuated hydraulic valve

In the last years piezoelectric actuators have proven to be more and more attractive for many applications with demands for very high speed, very high forces and minimal actuator size. Significant improvements in manufacturing technology of piezoelectric actuators and the electronic components necessary for their operation, are only some of the reasons for this trend.In this paper a nonlinear model based control of a piezoelectric actuated hydraulic valve is presented. The controller structure is developed on the basis of a very realistic nonlinear mathematical model of the actuator's and valve's physical behavior.

A five-bar finger mechanism involving redundant actuators: analysis and its applications

A five-bar finger mechanism driven by redundant actuators is given as an illustrative example. It is shown that judicial choice of the location of one redundant actuator greatly enhances the load handling capacity of the system, when compared to those of minimum actuation and more than two redundant actuators. Also, methodologies for stiffness and motion frequency modulations via redundant actuation are investigated. Internal load distribution associated with the stiffness and motion frequency modulations is further discussed. Specifically, the motion frequency of the system is modulated by employing inertial and spring-like impedance properties created by internal loading. The motion frequency as well as the amplitude of oscillation can be actively adjusted during the motion, and the equilibrium position about which the vibration occurs can also be arbitrarily changed during the motion. Furthermore, using the stiffness modulation capability, a point-to-point motion can be accomplished by a progressive movement of equilibrium posture, which is called a virtual trajectory. To show the effectiveness of the proposed algorithms, several simulation results are illustrated.

Minimum-Force Redundancy Control of Hydraulic Cranes

Abstract This paper deals with the kinematic redundancy of a common type of RRP hydraulic crane moving in a quasistatic manner in the vertical plane. Redundancy is solved by minimizing the norm of actuator forces required to support the load at a given location without exceeding the actuator stroke limits. Approximate analytical solutions are derived showing that minimum actuator forces are obtained either for maximum arm of actuator force 1, for maximum length of actuator 2, for minimum length of actuator 3, or for boom 1 in a horizontal position. The overlapping of these solutions covers most of the crane workspace and is shown to be in excellent agreement with the numerical optimization solution. The proposed redundancy solution is suitable for real-time implementation in a computer-controlled crane, while minimizing the actuator forces will lead also to a cost-effective design.

Minimum-force redundancy control of hydraulic cranes

The kinematic redundancy of a common type of RRP hydraulic crane moving in a quasistatic manner in the vertical plane is considered. Redundancy is solved by minimizing the norm of actuator forces required to support the load at a given location without exceeding the actuator stroke limits. Approximate analytical solutions are derived showing that minimum actuator forces are obtained for maximum arm of actuator force 1, for maximum length of actuator 2, for minimum length of actuator 3, or for boom 1 in a horizontal position. The overlapping of these solutions covers most of the crane workspace and is shown to be in excellent agreement with the numerical optimization solution. The proposed redundancy solution is suitable for real-time implementation in a computer-controlled crane, while the actuator force minimization leads also to a cost-effective design.

Flow Control with Electric Actuators

High levels of measurement noise, nonlinear behavior, and conflicting performance requirements pose challenging problems for flow controllers in heating, ventilating, and air-conditioning (HVAC) systems. In this paper, a strategy is developed which is based on an analysis of the maximum system gain and an estimate of the variance of the noise. The conflicting requirements of good setpoint tracking and minimal actuator motion are managed automatically by control logic that determines when the control actions should be aggressive or conservative. Experimental results from tests on a working VAV air-handling unit demonstrated the benefits of the algorithm.

Restraint analysis of assembly work carriers

Work carrier design is critical to the performance and economic feasibility of automatic assembly systems. Unless parts are securely held throughout transport, insertion, and fastening operations, precision assembly is impossible to achieve. This paper presents analytical techniques for determining whether carrier locators provide sufficient kinematic restraint. It presents techniques for determining whether carrier clamps and locators have the potential to resist arbitrary external forces. Finally, it presents a model for determining the minimum clamp actuator intensities necessary to restrain parts throughout transport and assembly.