Actuator Mechanisms Research Articles

Investigation of a Planetary Rover Locomotion System with Wheel-walking Propulsion by Applying the Method of Object-oriented Modeling

Objectives: The study aims to identify the capabilities of the locomotion systems based on the wheel-walking propulsion as the means of improving the mobility and maneuverability of the planetary rovers. Method: Principal method of this study is represented by object-oriented modeling that helps undertake complex investigation of the object. Findings: Current importance of the study is predetermined by the intensive investigations of celestial bodies assisted by mobile robotic systems and planetary rovers that are delivered to the surface of the planet. The study considers the opportunities provided by computerized modeling for the purposes of estimating the behavior of a planetary rover in the process of overcoming such obstructions as escarp, sloping surface of hard and loose soils and sinusoidal profile of surface that imitates coarse irregularities of the relief. The locomotion system under investigation is represented by a four-wheeled platform equipped with the two-lever wheel-walking mechanisms. The algorithms have been suggested for controlling the actuator mechanisms of the locomotion systems in the course of overcoming the obstacles under consideration. Improvements: The results make it possible to evaluate qualitative and quantitative kinematic and force requirements to the drives of the locomotion systems of planetary rovers and are of practical engineering significance.

Spring or string: does tendon elastic action influence wing muscle mechanics in bat flight?

Tendon springs influence locomotor movements in many terrestrial animals, but their roles in locomotion through fluids as well as in small-bodied mammals are less clear. We measured muscle, tendon and joint mechanics in an elbow extensor of a small fruit bat during ascending flight. At the end of downstroke, the tendon was stretched by elbow flexion as the wing was folded. At the end of upstroke, elastic energy was recovered via tendon recoil and extended the elbow, contributing to unfurling the wing for downstroke. Compared with a hypothetical 'string-like' system lacking series elastic compliance, the tendon spring conferred a 22.5% decrease in muscle fascicle strain magnitude. Our findings demonstrate tendon elastic action in a small flying mammal and expand our understanding of the occurrence and action of series elastic actuator mechanisms in fluid-based locomotion.

Computational algorithm of forming program motion in a scheduled turn of small spacecraft

A mathematical model and software implementation of a computational algorithm of forming program motion in a scheduled turn of small spacecraft are described in the article. The algorithm is intended to calculate the key parameters of the path of a scheduled turn of small spacecraft, to specify the time moments when spacecraft motion has to be changed, and motion parameters at these points to determine the intervals characterized by the constancy of object motion laws and the positions of the object rotation axes during these intervals. Information on the equipment used (sensors, mechanisms, flywheels), the basic modes of operation, the principles of organizing the motion control system and flight control software is presented in the article. The AIST-2D Experimental Small Spacecraft has a mass of less than 500 kilograms and can operate on a near-circular orbit of 600 kilometers. The Spacecraft Orientation System comprises sensors and actuator mechanisms as well as its own computer. The Flight Control Software is organized as software incorporated in the technical system and implements full support of spacecraft motion control logic both in normal and abnormal situations. The software is subjected to a multiphase debugging process that ensures the achievement of the required indicators of quality and robustness.

Design and Research on Actuator of Robot Joint Based on GMM

The actuator of robot joint is designed based on Power source of the GMM. The working principle and characteristics of the GMM are discussed in detail and the work performance is validated by experiment. The differential decline amplifier configuration, the rotor and housing part are designed and the assembly drawings are gotten. After designing, the intensity of each portion is analyzed. Not only the mechanism of design of actuator of the robot joint is changed, and also the large-mass problem of the actuator mechanism of biomimetic micro-mechanical is solved. The reference is provided for other actuator mechanisms.

Limitations for the control of wind-loaded slender bridges with movable flaps

This article presents theoretical investigations on techniques for the improvement of the dynamic characteristics of slender bridges under wind action. Aerodynamically effective control shields are applied as controlled actuators. The first part of the article describes the modelling of the uncontrolled aeroelastic system. Acting aerodynamic forces are consistently characterised using linear time-invariant transfer elements in terms of rational functions. On this basis, two configuration levels of the uncontrolled system are represented with linear time-invariant state-space models and investigated. The second part of the article addresses controller design and the behaviour of the controlled aeroelastic system. Both fundamental limits for stabilisation and the efficiency for attenuating the influence of gusts are described for different actuator mechanisms. The results are derived and discussed with methods of control theory.

Nickel-plated thermal switch with electrostatic latch

An innovative parallel gap bistable switch is demonstrated, based on a nickel-plating process with a polymer mold. It combines two different actuator mechanisms to yield extremely low steady state power consumption: thermal actuation is used for the stroke movement, whereas electrostatic actuation is used to latch the on state. This makes it useful for low-power applications where continuous thermal drive is not possible. Strokes of 20 μm can be achieved, with thermal actuation power of 1 W during the switching movement. In a second stage, the position can be electrostatically held with a voltage of 15 V, requiring no further power. The actuator's size is approximately 1.5 mm 2.

Design of an Artificial Left Ventricular Muscle: An Innovative Way to Actuate Blood Pumps?

Blood pumps assist or take over the pump function of a failing heart. They are essentially activated by a pusher plate, a pneumatic compression of collapsible sacs, or they are driven by centrifugal pumps. Blood pumps relying upon one of these actuator mechanisms do not account for realistic wall deformation. In this study, we propose an innovative design of a blood pump actuator device which should be able to mimic fairly well global left ventricular (LV) wall deformation patterns in terms of circumferential and longitudinal contraction, as well as torsion. In order to reproduce these basic wall deformation patterns in our actuator device, we designed a novel kind of artificial LV "muscle" composed of multiple actively contracting cells. Its contraction is based on a mechanism by which pressurized air, inside such a cell, causes contraction in one direction and expansion perpendicular to this direction. The organization and geometry of the contractile cells within one artificial LV muscle, the applied pressure in the cells, and the governing LV loading conditions (preload and afterload) together determine the global deformation of the LV wall. Starting from a simple plastic bag, an experimental model based on the above mentioned principle was built and connected to a lumped hydraulic model of the vascular system (including compliance and resistance). The wall deformation pattern of this device was validated visually and its pump performance was studied in terms of LV volume and pressure and heart rate. Our experimental results revealed (i) a global LV motion resembling a real LV, and (ii) a close correlation between our model and a real LV in terms of end-systolic volume and pressure, end-diastolic volume and pressure, stroke volume, ejection fraction and pressure-volume relationship. Our proposed model appears promising and it can be considered as a step forward when compared to currently applied actuator mechanisms, as it will likely result in more physiological intracavity blood flow patterns.

Special Issue on Precise Positioning

Precise positioning is a basic, essential technology in a wide variety of automation considerations. It has recently been extended to micron and nanometer positioning including basic components such as mechanical elements, mechanisms, actuators, and controllers. Improving positioning accuracy requires advances in individual components, behind which there has been conducted much research and development. This special issue focuses on actuator, control technology, and mechanical elements and mechanisms. Constructing precise positioning involves conventional electrical, hydraulic, and pneumatic actuators. A piezoelectric actuator is useful for micron and nanometer positioning. An appropriate mechanism is required to transmit power from the actuator to the object being positioned. An effective control scheme must also be introduced into system with available sensors. In this regard, this issue includes advanced papers representative of individual fields that should prove interesting, stimulating, and of great practical use to both general readers and specialists. We thank the authors for their many interesting papers contributed to this issue.

Characteristics of In-pipe Mobile Robot with Wheel Drive Mechanism using Planetary Gears

This paper describes the running static analysis of an in-pipe mobile robot using a wheel drive mechanism for straight piping. The wheel mechanism, which is driven by planetary gears and worm gears, can both drive the wheels and press them the wheels against the pipe wall using only an actuator and simple mechanisms. The relation among the size of the load, wheel revolution angle, and the pressing load against the pipe wall is theoretically analyzed and is experimentally examined. The traction force of the robot is calculable with motor driving torque, and the maximum traction force is estimated with no-load driving torque of robot and torque constant of the motor. From the running experiments by the prototype robot, which is 45mm in diameter and 130mm in length, the maximum traction force was at least 20 times the weight of the robot.

On the modelling of actuator dynamics and the computation of prescribed trajectories

The dynamics of actuator mechanisms is presented using a multibody modelling approach to concisely express the structure of the system equations. The Lagrange equations are used to obtain the Newton–Euler equations to which constraint equations are augmented to form a system of differential algebraic equations. The differential algebraic equations are cast as ordinary differential equations and computed using the numerical integrator LSODAR of Petzold and Hindmarsh. Constraint compliance is investigated to ensure the accuracy of the results. Animation of an excavator and wheel loader system is presented and graphs of constraint forces show the nature of the actuator dynamics involved in maintaining specified bucket trajectories. The model is general in nature and caters for arbitrary mechanism connectivity and physical properties.

Multi-objective control synthesis: an application to 4WS passenger vehicles

The vehicle dynamics and control play an important role in an automated highway system for passenger cars. This study addresses the problem of designing active controllers for four-wheel-steering (4WS) vehicles. We first obtain a set of linear maneuvering equations representing the four-wheel steering motions and independent wheel torques for lateral/directional plus roll dynamics. We then formulate simultaneous H 2 and H ∞ (sub)-optimal controls with a desired pole assignment via linear matrix inequalities (LMIs). The steering angles are actively controlled by steering wheel commands through the actuator mechanisms for the lateral/directional and roll motions. Further the wheel power and braking are directly controlled by independent torques. Numerical simulations are performed on a complex vehicle model in order to evaluate the vehicle performance (noise and disturbance attenuation), stability, and robustness under a given class of uncertainty. Finally, the presented autopilot controller provides greater maneuverability and improved directional stability for passenger vehicles.

Direct control and coordination using neural networks

The performance of an industrial process control system equipped with a conventional controller may be degraded severely by a long system-time delay, dead zone and/or saturation of actuator mechanisms, model and/or parameter uncertainties, and process noises. The coordinated control of multiple robots is another challenging problem. In a multiple-robot system, each robot is a stand-alone device equipped with commercially designed servo controllers. When such robots hold a solid object, failure of their effective coordination may damage the object and/or the robots. To overcome these problems, we propose to design a direct adaptive controller and a coordinator using neural networks. One of the key problems in designing such a controller/coordinator is to develop an efficient training algorithm. A neural network is usually trained using the output errors of the network, not controlled plant. However, when a neural network is used to directly control a plant, the output errors of the network are unknown, because the desired control actions are unknown. A simple training algorithm is proposed. that enables the neural network to be trained with the output errors of the controlled plant. The only a priori knowledge of the controlled plant is the direction of its output response. A detailed analysis of the algorithm is presented and the associated theorems are proved. Due to its simple structure, algorithm and good performance, the proposed scheme has high potential for handling the difficult problems arising from industrial process control and multiple-system coordination. >

Application of neural networks to temperature control in thermal power plants

In a thermal power plant with once-through boilers, it is important to control the temperature at the middle point where water becomes steam. However, there are many problems in the design of such a control system, due to a long system response delay, dead-zone and saturation of the actuator mechanisms, uncertainties in the system model and/or parameters, and process noise. To overcome these problems, an adaptive controller has been designed using neural networks, and tested extensively via simulations. One of the key problems in designing such a controller is to develop an efficient training algorithm. Neural networks are usually trained using the output errors of the network, instead of using the output errors of the controlled plant. However, when a neural network is used to control a plant directly, the output errors of the network are unknown, since the desired control actions are unknown. This paper proposes a simple training algorithm for a class of nonlinear systems, which enables the neural network to be trained with the output errors of the controlled plant. The only a priori knowledge of the controlled plant is the direction of its output response. Due to its simple structure and algorithm, and good performance, the proposed controller has high potential for handling difficult problems in process-control systems.

A moving-actuator type electromechanical total artificial heart. I. Linear type and mock circulation experiments

A new type of motor-driven total artificial heart system with a moving-actuator mechanism has been developed. The prototype system consists of a brushless dc motor inside of a rolling-cylinder, two arc-shaped pusher-plates and two polyurethane sacs. The moving-actuator type electromechanical pump has structural advantages of small size and light weight, as compared to other reported motor-driven pumps with fixed-actuator mechanisms. The results of the mock circulation tests are reported in this paper with a cardiac output of 9 L/min at an aortic pressure of 120 mmHg and a heart rate of 120 bpm. The fulfillment of the basic control requirements of the artificial heart was also confirmed, i.e., preload sensitive and afterload insensitive cardiac output response and balanced right and left ventricular outputs.

Mathematical models for time-domain design of electrohydraulic servomechanisms

IN THE ANALYTICAL DESIGN of high-speed electrohydraulic servomechanisms, an accurate mathematical model of the valve-actuator mechanism is generally helpful in determining the controller and system configuration required to achieve the desired over-all performance. During past years, various forms of electrohydraulic valves and actuator mechanisms have been realized. Detailed descriptions of these devices can be found in a book by Blackburn et al.1 Most previous works on the analysis of these systems have resorted to linearization techniques.2,3 Recently, Butler and Turnbull presented detailed analysis of simplified nonlinear models.4,5 Also, Zaborszky and Harrington derived describing functions for both single and two-stage electrohydraulic valves, which permit analytical design in the frequency-domain.6?9 The limitations of linearized models are discussed by Rausch.10