Investigation of Dynamic Characteristics of an Automated Position Long-Stroke Pneumatic Actuator of Fabrication System

Abstract

Introduction.  Long-stroke  movements  in  automated pneumatic  drives  account  for  a  significant  number  of  executive movements  in  coordinate  tables,  automated  warehouses,  cutting  machines,  etc. Long-stroke  movements  degrade  the dynamic quality and positioning of the drive. This is due to the friction of the piston and the nonlinear characteristics of the compressed gas flow in significant volumes of the pressure and drain cavities of the cylinder. Thus, it seems promising to create an automated position pneumatic actuator for long-stroke movements. This will increase the productivity of processes  while  providing  the  declared  accuracy.  The  objective  of  the  work  is  to  obtain  a  mathematical  model  and dependences of the critical parameters of the proposed automated position long-stroke pneumatic drive of fabrication system in the areas of acceleration, steady-speed movement, deceleration, and braking.Materials and Methods. The basis for calculations and modeling was the scheme of two trajectories of movement from point A to point E, taking into account the forces expended on these processes. The optimal displacement was determined using the Portnyagin’s principle (i.e., optimal performance). Proportional drive control was presented as a method of achieving the result. For long-stroke drive movements, schematic solution and design scheme were visualized in detail (presented as drawings). An original jet sensor with an internal pneumatic connection and a pneumo-mechanic discrete-proportional device for the control loop performance were proposed. The mathematical model included the movement and braking of the piston, the balance of mass flow, the pressure at points, and the control loop. The system of equations was solved by the Runge — Kutta method in the SimInTech software product. Based on the results of the study of a generalized mathematical model, the dependences of changes in the kinematic, power and pneumatic properties of the drive were constructed in real time during a typical positioning cycle. The information was summarized and presented as a set of graphs.Results. The mathematical model was formed according to a set of calculations. It took into account the dependences characteristic of the movement of the piston of the pneumatic cylinder. The balance of mass flow was investigated by the equations of gas flow during compression in the chamber, through distributors and throttles, in the discharge and drain cavities and in the control device. Inequalities describing the pressures at the points and the control loop were considered. A complex mathematical model was solved in the SimInTech software environment by the Runge — Kutta method with a variable integration step. A fragment of the program was selected as one of the illustrations. It showed that the software used the following indicators for calculations: target and reduced coordinates; absolute gas constant; coefficients of spring stiffness, resistance, adiabatic and viscous friction in the piston; compressor pressure; mass of the moving parts of the pneumatic actuator; strength of external resistances; diameters of the pipeline, the pneumatic cylinder piston and the braking device; length of the stroke of the cylinder piston; area of piston cavities and throttles; length of the pipeline and its internal volume. Thus, the program manipulated a significant set of data, which made it possible to obtain meaningful and adequate results. The relationship of blocks and diagrams used in solving the model was schematically shown. We are talking about graphs of movements, areas, pressures, velocities and temperatures. Blocks with the program text and intended for integration were used. Thus, a mathematical model of an automated pneumatic drive of the fabrication system and the dependences of the basic parameters of its operation were obtained. The graphs indicated that the operating mechanism of the pneumatic actuator properly followed the proposed trajectory.Discussion and Conclusion. The research results allowed us to consider several stages of long-stroke movement of the drive, to determine the time frame of these processes (from 0 to 0.65s), as well as changes in pressure and speed of movement  of  the  pneumatic cylinder  carriage  recorded  in  these  intervals.  There  were  five  such  stages:  acceleration, steady-speed movement, deceleration, movement with positioning speed, and braking. Further research will focus on optimizing the system to reduce the duration and maintain accurate positioning under external influences.