Sliding Mode Analysis of a Counterbalance Valve Induced Instability in an Electrohydraulic Drive

This paper analyzes dynamic effects of an electro-hydraulic drive which uses a counter-balance valve for rod volume compensation. It shows that local stability analysis is not sufficient in this particular case to get general statements of the system's chattering properties. A reduced-order switched system is proposed to gain deeper insights in system dynamics with saturation effects such as the end-stop of a valve poppet and solutions are compared numerically to the full-system dynamics which incorporates pressure built-up, piston and valve dynamics as well as motor dynamics. It is shown that in cases of e.g. fast valves with small cracking pressures undesirable chattering of the full system exists which can be easily understood in terms of the reduced-order system in form of sliding mode solutions. The paper also describes under which conditions such sliding modes exist, how they behave and how they can be interpreted in terms of the full system.

STUDY OF THE DYNAMICS OF THE EXOSKELETON ACTUATING UNIT

A person has more than 300 degrees of mobility, but it is practically impossible to recreate such a kinematic scheme. In this article, a kinematic scheme of the exoskeleton is proposed that is most necessary for human movement. A 3D model of the exoskeleton actuating unit with an electrohydraulic drive has been developed in the CAD system and the values of masses, coordinates of mass centers, inertia tensors of the links of the exoskeleton actuating unit have been calculated. A launch file has been developed in the MATLAB environment for modeling the dynamics of the exoskeleton actuating unit. The control laws in the degrees of mobility of the actuating unit of the exoskeleton are selected. As a result of the theoretical study, the ranges of changes in the generalized coordinates for the joints under study are determined. The dependences of the power and the moment in the joints 9, 10 on time are obtained. The conducted studies have shown that lifting the leg will require more energy and this makes it necessary to develop power plants, explore various types of drives and ways to control them energy-efficiently. The obtained data can serve in the development of a medical exoskeleton.

Mathematical model of the dynamics of a hydrofoil vessel as a complex technical system

Определена структура единой среды моделирования, состоящая из трёх блоков: блок, где задаются или формируются значения исследуемых параметров, влияющие на выходные показатели судна, как объекта моделирования, блок представляющий собой ядро единой среды моделирования и блок, где формируется совокупность тех или иных показателей, подлежащих анализу. Определена математическая модель динамики возмущенного движения СПК, при этом использованы следующие системы координат: земная прямоугольная горизонтальная правая, связанная с судном прямоугольная правая и вспомогательная нецентральная прямоугольная правая. Определены основные допущения математической модели. Представлены уравнения динамики судна на подводных крыльях в общем виде и определены силы и моменты, действующие на судно на подводных крыльях в крыльевом режиме движения. Гидродинамические силы и моменты, возникающие на каждом из крыльевых устройств, определены расчетным путем. Работа движителей моделируется заданием среднего упора, направленного по оси вала движителя и параллельного диаметральной плоскости судна. В модели динамики предусмотрена возможность задания аэродинамических сил и моментов, действующие на СПК в крыльевом режиме. Разработана математическая модель электрогидравлического привода, состоящая из суммирующего устройства, электрогидроусилителя и силового интегрирующего привода, охваченных общей обратной связью по положению и скорости перемещения, а также модель системы управления движением, которая является одной из важнейших подсистем СПК, формирующей алгоритмы управления, поступающие на входы ЭГП соответствующих ИО, расположенных на несущих поверхностях КУ. При решении некоторых задач, связанных с проектированием СПК и его технических систем, особенно для получения оценочных значений фазовых координат судна на начальных этапах проектирования или решения специальных задач, разработана линеаризованная система дифференциальных уравнений объекта. The structure of a unified modeling environment has been determined, which consists of three blocks: a block where the values of the studied parameters are set or formed, which affect the output indicators of the vessel as an object of modeling, a block that is the core of a unified modeling environment and a block where a set of certain indicators is formed. analysis. A mathematical model of the dynamics of the disturbed motion of the SPK was determined, with the following coordinate systems used: earth rectangular horizontal right, rectangular right connected to the ship and auxiliary off-center rectangular right. The basic assumptions of the mathematical model are determined. The equations of the dynamics of a hydrofoil ship in general form are presented and the forces and moments acting on a hydrofoil ship in the wing mode of motion are determined. The hydrodynamic forces and moments arising on each of the wing devices are determined by calculation. The operation of the propellers is modeled by setting the middle stop directed along the axis of the propeller shaft and parallel to the diametral plane of the vessel. The dynamics model provides for the possibility of setting aerodynamic forces and moments acting on the HFV in the wing mode. A mathematical model of an electrohydraulic drive has been developed, consisting of a summing device, an electrohydraulic amplifier and a power integrating drive, covered by a general feedback on the JJposition and speed of movement, as well as a model of a motion control system, which is one of the most important subsystems of the SPC that forms control algorithms entering the EGP inputs of the corresponding EUT located on the bearing surfaces of the KU. When solving some problems related to the design of the HFV and its technical systems, especially for obtaining the estimated values of the phase coordinates of the vessel at the initial stages of design or solving special problems, a linearized system of differential equations of the object was developed.

Application of the MEMS Accelerometer as the Position Sensor in Linear Electrohydraulic Drive

Various distance sensors are used as measuring elements for positioning linear electrohydraulic drives. The most common are magnetostrictive transducers or linear variable differential transformer (LVDT) sensors mounted inside the cylinder. The displacement of the actuator’s piston rod is proportional to the change in the value of the current or voltage at the output from the sensor. They are characterized by relatively low measurement noise. The disadvantage of presented sensors is the need to mount them inside the cylinders and the high price. The article presents preliminary research on the replacement of following sensors and the use of a microelectromechanical system (MEMS) accelerometer as a measuring element in the electrohydraulic drive control system. The control consisted of two phases: at first, the signal from the acceleration sensor was analyzed during the actuator movement, based on the value determined from the simplified model implemented on the controller. In the range of motion in which the dynamics were the lowest, the signal was integrated and the obtained value was used in the second phase of motion. In the correction phase, a new set point was determined. Conducting the research required building a dedicated research stand. The author conducted the simulation and experimental research.

Determining the Drive Power of the System Controlling the Vibration Amplitude of the Rectifiers for the Continuously Variable Mechanical Transmission with Internal Force Functions

The article discusses the choice of the power and type of the drive motor for the system controlling the vibration amplitude of the rectifier rocker arms of the continuously variable mechanical transmission, intended for use on a motor vehicle. Formulas for calculating the required torque and rotational speed of the drive motor with a planetary differential control gear are given. It is shown that the use of an electrohydraulic drive provides the required speed and power operation of the control system. The results of the system testing are presented.