جستجوی مقالات مرتبط با کلیدواژه « کنترل موقعیت » در نشریات گروه « مکانیک »

Sports simulation mechanisms practically have a lot of appeal and application to implement virtual reality environments. Cycling simulator has a more special place in sports and urban transportation due to the popularity of cycling activities. In this paper, the design and construction of a new motion generating mechanism for an interactive cycling simulator is presented. First, by using the references, the range of velocity and acceleration that the user should experience while cycling has been extracted, and by analyzing other cycling simulators, the required degrees of freedom and its range have been determined. Then, a new motion generating mechanism with two degrees of freedom is designed. Genetic algorithm has been used for dimensional optimization of the mechanism parameters. Kinematics and dynamic equations of the mechanism have been extracted. According to the dynamic model of the mechanism, a controller has been designed using the feedback linearization method and the performance have been investigated. Finally, the designed motion generating mechanism has been constructed and the position control has been implemented on the platform.

In this paper, control position of a pneumatic actuator with the PWM solenoid on/off valves using two different pneumatic circuits performed. After deriving the governing dynamic equations, to investigate the circuit effect on system performance, mentioned two pneumatic circuits are introduced. Then in order to control the position of the pneumatic actuator, for both circuits, sliding mode and proportional-integral-derivative controllers are designed. In proceeding, optimum controller parameters are determined by genetic algorithm to achieve minimum control energy and position error. Finally, by performing simulations in Matlab Simulink, performance of designed controllers with optimal parameters is evaluated and compared in the presence of disturbance. According to the obtained results, by comparing the performance of two circuits, it is observed that the first pneumatic circuit with two solenoid valves can track the high-frequency sine reference input better and more precisely in the presence of a nonlinear sliding mode controller. The position tracking error in low-frequency sine reference input using a classic proportional-integral-derivative controller, for a single-valve pneumatic circuit is considerably less than that of a pneumatic circuit of two valves. This indicates the input-output quasi linear behavior of the pneumatic actuator in a single-valve circuit.

In this paper dynamic model analysis, position control and locomotion generation of a 2-link robotic fish has been presented. For this purpose, the dynamic model of a 2-link robotic fish based on Lighthill hydrodynamic theory is employed. The effect of system inputs on robot linear velocity, radius curvature of path and hydrodynamic efficiency is investigated with a large amount of simulations. A position controller is designed to generate path by the point to point method. By defining target point and angle and distance errors, control design strategy is proposed to limit the angle error to the neighborhood of zero. It is shown that bounding angle error in a ten degree neighborhood of zero, makes the distance error tend to zero. Despite former methods in which, driving both angle and distance errors to zero simultaneously result in huge control effort, the proposed control strategy in addition to improve performance by spending less control effort, make the controller structure simpler and no need to velocity feedback. Finally by using the results of model analysis, it is shown that using minimum amplitude for the 2-link robot drives the average hydrodynamic efficiency of path close enough to its optimum value.

Under a constant loading condition, use of a controller with constant coefficients can be acceptable for servo pneumatic systems. However in variable loads with widespread changes, more advanced control methods should be considered to achieve desirable performance. In this paper, an adaptive controller is designed and implemented to a variably loaded servo pneumatic system with PWM driven switching valve. In the under examination servo pneumatic system, PWM driven fast switching valve is used instead of expensive servo or proportional valves. Real time identification of system parameters is performed using input-output data and controller parameters are adjusted instantaneously. “Self-tuning regulators” algorithm, in which controller parameters obtain from solving a design problem, is applied to design the proposed adaptive controller. The designed controller is applied to the servo pneumatic system via an interface board and its performance is compared with PD and multi model controller. Unlike the proposed method in multi model control method, a number of constant loads should be considered and corresponding to each load a fixed controller is designed. Experimental results demonstrate the high performance of the adaptive controller under variable loads.

Hydraulic actuators are widely used where high-magnitude forces are exerted; however, they suffer from low energy-efficiency in many cases. To address this issue, there has been a surge in the volume of researches devoted to improving the efficiency of electro-hydraulic servo systems. Digital Hydraulics is the most recent method, proposed by many researchers to improve the efficiency of hydraulic actuators. Low cost and better energy efficiency are two major advantage of these systems that make them popular among researchers. This paper discusses the possibility of using a fast-switching on/off valve in a novel way, instead of servo valves to improve the efficiency of these systems. For this purpose the flow running through the fast-switching valve controlled, employing proper duty cycle. The excess pump flow is discharged to the tank directly instead of going through the relief valve when the valve is off. Thus the wasted energy, caused by the relief valve, is reduced significantly. A nonlinear backstepping controller is designed to control the duty cycle of the PWM signal of the on/off valve. The effectiveness of this method is tested after conducting experiments on a hydraulic test rig and presenting the experimental results.

In this paper, two position controllers have been developed for a double-acting pneumatic cylinder with two 3/2 on/off solenoid valves, using PWM method. The first one is a PID controller, whose gains have been obtained by Zighler-Nicoltz method. The second one - a Sliding Mode Controller (SMC) - has been designed based on a specific mathematical model, where an appropriate PWM method has been applied to overcome non-linearities such as time delay, during opening or closing of valves, and deadband due to stiction. The results of experimental tests on the closed loop system with the PID controller illustrate that the PWM method is suitable for servo control purposes with high accuracy. Furthermore, high accuracy was also achieved in experimental results in response to step inputs. Small values of maximum and Root Mean Square (RMS) positioning errors in response to sinusoidal inputs with various frequencies show better accuracy of SMC controller in comparison with the PID one. Good performance of the developed SMC is even more evident as frequency increases. These results also show considerable improvements in accuracy in comparison with the results of previous works on costly proportional valves.

In this work, a new mathematical modeling of servo-pneumatic system's dynamics is presented. In this new modeling, internal forces, such as friction and external forces acting on the moving rod of actuator, such as loads or disturbances, are mathematically modeled with their appropriate logic. First, pressure distribution on two sides of moving piston is assigned to cancel out the friction force with respect to the piston velocity sense and to balance the external forces according to their acting direction. The regulation of pressure continues to provide the desired acceleration in the piston. The model of pressure valves is assumed linear. Due to the entrance of non-linear terms into the equations describing dynamics of the system, mathematical modeling is based on sliding mode logic. Also, sliding mode control algorithm is used to achieve the positioning aim. Finally, a numerical simulation is done to show the performance of the control activity in the presence of the new mathematical modeling.