Modeling and control of a pneumatically actuated inverted pendulum

This paper presents the results of modeling of an inverted pendulum system driven by a linear pneumatic motor and equipped with relatively low-cost potentiometer-based position measurement system. Based on the nonlinear model of the overall pendulum system, which also includes notable friction effects, a linearized model is derived. The linearized model is used as a basis for the design of state feedback controller based on LQ and LQG optimization procedures. The linear state feedback controllers are augmented by a compensator of nonlinear friction effects whose design is based on the results of experimental identification of an appropriate static friction model. The proposed pendulum controller structures have been verified by means of computer simulations and experimentally on the experimental setup of a pneumatically actuated inverted pendulum.     

Control of a 2-DOF omnidirectional mobile inverted pendulum

In this paper, stabilization of a 2-degrees-of-freedom (2-DOF) omnidirectional mobile inverted pendulum (OM-IP) is studied. The OM-IP consists of the rod that rotates around a rotary point of a universal joint which is connected at the center of the omnidirectional mobile platform (OMP). For ease of analysis, the OM-IP is decoupled into two subsystems: a 2-DOF inverted pendulum (IP) and an OMP. The IP is a rod that rotates around a universal joint with 2-DOF. The OMP is a body consisting of disk and three omnidirectional wheels that moves on plane and keeps the rod in balance. Dynamic modeling of the 2-DOF OM-IP is presented. From the dynamic equation, an adaptive backstepping control method is proposed to keep the rod in balance. Update law is presented as differential equation of an unknown parameter when the distance from the center of gravity of the rod to the rotary point on the OMP is unknown. Stability of the adaptive controller is proven by using Lyapunov function. Simulation and experimental results show the effectiveness of the proposed controller.     

Reducing the stabilizing control order for a double inverted pendulum

The problem of stabilization of an unstable plant by a reduced-order single-channel controller is considered. The possibility of compensating small deviations of a double inverted pendulum on a cart by acting on the cart is studied. An algebraic method for finding the extreme locations of the poles through the construction of root simplexes is proposed. Using this, the Hurwitz stability boundaries for various reduced-order controllers are calculated. It is shown that robust stabilization of the pendulum system in the class of reduced-order controllers is impossible.     

Design and analysis of controllers for a double inverted pendulum

A physical control problem is studied with the Hinfinity, and the micro methodology. The issues of modeling, uncertainty modeling, performance specification, controller design, and laboratory implementation are discussed. The laboratory experiment is a double inverted pendulum placed on a cart. The limitations in the system with respect to performance are the limitation in the control signal and the limitation of the movement of the cart. It is shown how these performance limitations will effect the design of Hinfinity and micro controllers for the system.     

单级倒立摆的模糊控制应用

随着被控对象的日趋复杂,对控制性能的要求不断提高,传统控制理论对解决复杂系统无能为力。该文将人工智能中的模糊控制引入倒立摆控制系统,以提高控制要求,改善控制精度。通过仿真实验表明这种控制思路是可行的,效果良好。     

单级倒立摆的两种控制方法的仿真研究

针对多变量、非线性、强耦合性的倒立摆系统,运用牛顿-欧拉方法建立了倒立摆的数学模型。然后对该模型分别进行LQR控制和模糊控制,并在MATLAB环境下进行仿真,其对比结果对该方向的研究具有理论指导意义。     

A new virtual-real gravity compensated inverted pendulum model and ADAMS simulation for biped robot with heterogeneous legs

Our research team combined humanoid robots with intelligent lower limb prostheses to study the dynamic characteristics of intelligent lower extremity prostheses for disabled people in the walking process, and proposed a biped robot with heterogeneous legs (BRHL). This paper proposes a new virtual-real inverted pendulum system model to unify the models for both single support phase and double support phase in walking process and builds a special simulation platform which can acquire the real-time center of mass (COM) trajectory. Initially, a gravity-compensated inverted pendulum model was built and improved the stability of gait, a natural ZMP trajectory improved the anthropomorphism of the gait. Furthermore, in double support phase, a virtual inverted pendulum model was established and a virtual-real inverted pendulum model was proposed and used to plan the gait of both single support phase and double support phase in the walking process. Additionally, the joint angles were obtained by inverse kinematics; the stability of the system was analyzed to be feasible and effective by phase trajectories. A special ADAMS simulation platform was built to simulate the walking process and acquire real-time COM trajectory. The feasibility of the gait planning was also verified. Finally, the trajectory of COM was optimized based on the minimum energy criterion according to the geodesic equation.

     

Balance control of a 12-DOF mobile manipulator based on two-wheel inverted pendulum robot

Humanoid mobile manipulator which is based on two-wheel inverted pendulum robot has been studied.Balance control is a key problem for this kind of centroid-variable robot.Due to the principle of two wheel inverted pendulum,a timely angle compensation is necessary to make the system keep balance when the centroid changes.In this paper,a method based on coordinate transformation is introduced to get the compensatory angle and a 12-DOF mobile manipulator is also used to check the method.Simulation and experimental results show the effectiveness of the method.     

Implementation of a ball inverted pendulum with omnidirectional moving ability using a robust fuzzy control strategy

A robust fuzzy controller (RFC) is proposed for a ball inverted pendulum (BIP) system control problem. A Mamdani-type fuzzy controller and a compensated control technique are combined in the proposed control system. This controller is used for real-world control of a BIP with unknown system uncertainties. Using this method, the approximation error caused by the trial-and-error fuzzy control design procedure is minimized. Moreover, the decoupled technique provides a simple method for achieving asymptotic stability control for angle and position of a BIP control system. The concept of this approach is to decouple the entire system into two subsystems. Next, the primary subsystem combines the information provided by the secondary subsystem. And then a control force is generated to drive both subsystems toward their targets, respectively. Thus, the platform can move to any position without constraints. The stability of RFC, which is based on the Lyapunov stability theorem, is guaranteed. Furthermore, to verify the effectiveness of the control algorithm, several numerical simulations and dynamic simulation in the automatic dynamic analysis of mechanical systems (ADAMS) environment with MATLAB are implemented. Finally, the efficiency of the RFC is verified with real-time implementation of the BIP.     

Control of the carriage-inverted pendulum system based on a signal-adaptive inverse model

In this paper, we consider typical problems of automatic control for systems consisting of a carriage and a one-link inverted pendulum: stabilization of the pendulum in the absence of constraints on the coordinates of the carriage, control of the speed and position of the carriage with the stabilization of the pendulum, and control of the position with the subordinate system of speed control. Control algorithms were synthesized using a signal-adaptive inverse model based on the requirement of the desired distribution of the poles of the linearized zero system with deliberate implementation of three-rate processes. The results of numerical simulation of the synthesized control systems are presented.     

Coupling of dynamics and contact mechanics of artificial hip joints in a pendulum model

To date, fully coupled dynamics and contact mechanics analysis is still limited by expensive computational cost and long computing time and has not been addressed comprehensively, particularly in the hip joint. To understand the influence of different parameters on the biomechanics of the total hip replacement (THR) and improve its design, two numerical approaches were developed and implemented in finite element models to investigate the coupling between the dynamics response and the contact mechanics for three different THR configurations, metal-on-polyethylene (MOP), metal-on-metal (MOM), and ceramic-on-ceramic (COC). The dynamic force and the contact pressure distribution at the bearing surfaces from the two methods were predicted and compared. The influences of various parameters (motion angle, load applied in the pendulum, friction coefficient, geometry, and material properties) were subsequently investigated. From the comparisons, the decoupled method, based on the rigid-body dynamics and the quasi-static elastic contact mechanics, was adequate to predict the performance of the THRs efficiently. The load had the greatest influence on the dynamics/contact mechanics among other factors.     

Using the modified PSO method to identify a Scott-Russell mechanism actuated by a piezoelectric element

This paper mainly proposes an efficient modified particle swarm optimization (MPSO) method, to identify a Scott-Russell (SR) magnification mechanism driven by a piezoelectric actuator (PA), in which Bouc-Wen model is employed to describe the hysteresis phenomenon. In system identification, we adopt the MPSO to find parameters of the SR mechanism and the PA. This new algorithm is added with “distance” term in the traditional PSO's fitness function to avoid converging to a local optimum. It is found that the MPSO method can obtain optimal high-quality solution, high calculation efficiency, and its feasibility and effectiveness are demonstrated for the modified IEEE 30-bus system. Finally, the comparisons of numerical simulations and experimental results prove that the MPSO identification method for the SR magnification mechanism is feasible.     

Reducing pitch error of a linear motion system actuated by a permanent magnet open face linear motor

When using iron-core open face linear motors, the magnetic attraction between the forcer and the magnet track is about 5–7 times higher than the maximum motor force. The magnetic attraction can be used in a motor-preloaded-bearing concept, e.g. to preload aerostatic or hydrostatic bearings. Based on this concept a high-precision grinding tool machine that moves on aerostatic bearings has been successfully introduced. However, the attraction force also creates an inherent pitch moment and resulting position dependent, periodic pitch error motion due to finite bearing stiffness. A method to model and reduce the resulting pitch error is presented. In experiments the overall pitch was reduced by a factor of 3.     

Cutaneous sensory nerve formations as studied with impregnation techniques: Notes about a simple and reliable method

In spite of the modern immunocytochemical methods employed in the study of peripheral sensory nerve formations, silver impregnations are still frequently used. This paper describes and discusses in detail a simple “Cajal-type” silver impregnation method suitable for the peripheral and central nervous systems, which offers excellent results when used in the study of sensory nerve formations. Essential features are (a) the use of a pretreatment solution containing sodium tartrate and picric acid; (b) the short time needed for the whole impregnation process; (c) its simplicity, and (d) the ability to show the axonal elements of sensory nerve formations and other very thin nerve fibres too difficult to be demonstrated with immunohistochemical methods. Taken together, these properties allow this method to be included among the so-called “routine methods.” © 1996 Wiley-Liss, Inc.     

Reduction of deadweight pendulum motion and its conformation by using a build-up system

Deadweight force machines cause oscillating components strongly related to the pendulum motion of the deadweight in the measured force signals. An estimating method of the pendulum motion using a build-up system has been proposed in previous papers. In this paper, the estimation algorithm was confirmed by comparison with the directly measured trajectory through the analysis of a 500 kN deadweight force standard machine in Korea Research Institute of Standards and Science. After the dynamic analysis of the force machine, it was modified to decrease the pendulum motion effects by accurately controlling its loading speed. As a result of the modification, the oscillating level due to the dynamic behavior of the force machine has been reduced considerably.     

Studies of the dynamics of free microoscillations of a pendulum supported by two balls

Approaches to the measurement of rolling friction by the method of free oscillations of a pendulum are considered. The models of energy dissipation for the oscillation amplitudes within the contact area are analyzed. The friction characteristics are assessed for two surfaces of silicon that differ by the quality of the processing. Criteria for selecting an adequate model based on the nonlinear regression analysis of the experimental results are proposed.     

Experimental study and model validation of selective spinal cord and brain hypothermia induced by a simple torso-cooling pad

In vivo experiments have been performed to test the effectiveness of a torso-cooling pad to reduce the temperature in the spinal cord and brain in rats. Coolant was circulated through the cooling pad to provide either mild or moderate cooling. Temperatures in the brain tissue, on the head surface, and on the spine and back surfaces were measured. During mild cooling, the temperature on the back surface was 22.82 +/- 2.43 degrees C compared to 29.34 +/- 1.94 degrees C on the spine surface. The temperature on the back surface during moderate cooling was 13.66 +/- 1.28 degrees C compared to 24.12 +/- 5.7 degrees C on the spine surface. Although the temperature in the brain tissue did not drastically deviate from its baseline value during cooling, there was a difference between the rectal and brain temperatures during cooling, which suggests mild hypothermia in the brain tissue. Using experimental data, theoretical models of the rat head and torso were developed to predict the regional temperatures and to validate the rat models. There was good agreement between the theoretical and experimental temperatures in the torso region. Differences between the predicted and measured temperatures in the brain are likely to be the result of imperfect mixing between the cold spinal fluid and the warm cerebrospinal fluid that surrounds the brain.     

Description of a propulsion unit used in guiding a walking machine by recognizing a three-point bordered path

A reconfigurable propulsion unit based on the Peaucellier-Lipkin mechanism has the ability to describe exact straight or curved paths depending on the selected ratio between the lengths of two of its links. The Peaucellier-Lipkin mechanism with one degree of freedom is transformed into a more sophisticated parallel kinematic chain by including four more degrees of freedom. The resulting propulsion unit is able to adapt its kinematic structure and reach instant centers of rotation, in accordance with the presence of three points that border a geometric path. A laser sensor mounted on the body of the machine detects each point. Once the machine has detected the exact location of the border of the road, it walks along a curve parallel to that border. Although the proposed research describes only one propulsion unit or leg, the methodology can be applied to all the legs of the walking machine. The novel 5-DOF leg is able to reach different centers of rotation, providing either the concave or convex arcs that satisfy the basic principle of displacement of walking machines.     

A simple model for stability of a long axial surface crack in a thin walled cylinder

Growth in the thickness direction of a long axial surface crack at the inner surface of a thin walled cylinder has been analyzed for loads generated by internal pressure and a thermal gradient through the wall thickness. Plane-strain deformations have been considered. It has been assumed that the cracked cross-section is fully plastic, but that the plastic zone width in the circumferential direction is very small. The cracked cross-section transmits a normal force and a bending moment, which have been considered as external forces on an equivalent cut ring element, to compute the deformation of the cracked cross-aection. An analytical expression has been derived for the crack-opening-displacement, as a function of the loads and the crack depth. Stable and unstable crack growth have been investigated on the basis of a critical crack-opening-displacement and a smoothly rising crack-opening R-curve. The condition for unstable crack growth depends primarily on the magnitude of the internal pressure. A thermal gradient by itself is less likely to cause unstable crack propagation.     

Accuracy analysis of optimal trajectory planning methods based,on function approximation for a four-DOF biped walking model

Based on an introduced optimal trajectory planning method, this paper mainly deals with the accuracy analysis during the function approximation process of the optimal trajectory planning method The basis functions are composed of Hermit polynomials and Founer series to improve the approximation accuracy Since the approximation accuracy is affected by the given orders of each basis function, the accuracy of the optimal solution is examined by changing the combinations of the orders of Hermit polynomials and Fourier series as the approximation basis functions As a result, it is found that the proper approximation basis functions are the 5^th order Hermit polynomials and the 7^th-10^th order of Fourier series