| The wind tunnel is a crucial experimental equipment for aerodynamic research and aircraft design,which can generate a relative motion between the wind and the model to simulate the airflow through the test model.Varies wind tunnel tests have been conducted such as force and pressure measurement tests.In force tests,the wind tunnel balance,as a precise force sensor,is used for measuring the magnitude,direction and acting point of the aerodynamic load on test models.The test results can be affected directly due to different performances of the repeatability and error of balance.In recent years,with increasing requirements of the high-performance wind tunnel balance in the field of aircraft research and development,how to accurately calibrate the balance is becoming a key research field for various aerodynamic research institutions.As a crucial equipment to provide the standard load for balance,it should be concerned about the performance and application of the force loading system.The existing loading system has the problems such as large volume,low operating efficiency,unable to load continuously and so on.Therefore,it is important to develop a loading system with high precision and apply it to the balance calibration platform to solve the existing problems.This subject firstly analyzes the shortcomings of the existing loading system in the application of the balance calibration platform,and then proposes the design requirements in combination with the actual application conditions.This system should has the functions of automatic loading,automatic adjustment,data storage,as well as high reliability,high security and strong electromagnetic compatibility,which could meet the technical requirements of national military standards for the balance calibration platform.According to the design requirements,an electromechanical force generator loading system is presented based on the double closed loop control theory,which mainly consists of a servo control subsystem and a data acquisition subsystem.Secondly,a servo control subsystem is designed,in which how to make a balance load accurately is the key issue.The relationship between the load and its control system has been studied,and an application method of converting the load to the motor rotational position is proposed.The servo control system contains servo controller,servo motor and encoder,which is developed from several aspects such as controller program,I/O interface and PID parameter adjustment.Lab VIEW language is used for software development.By using the multi-level calling software architecture and the technology of the Ethernet bus based on TCP/IP protocol,the data can be transmitted between the computer and the servo controller to realize the loading function.Thirdly,a data acquisition subsystem is designed.Based on the PXI bus technology,high-performance acquisition module and force sensors are selected for composing a data acquisition system with high-speed,high-precision,high-reliability and stability.Through NI virtual instrument technology,the data acquisition software is designed by using Lab VIEW and DAQmx platform to achieve fast,stable and accurate acquisition of loading.At the same time,the NI shared variable engine based on OPC-UA protocol is used to realize the high-speed data transfer between the two subsystems,so that the servo control subsystem can use the acquired data to accomplish the closed-loop control of the loading action.Finally,performance tests of the loading system are carried out.In order to finalize the balance loading for testing purposes,according to the test principle from simple to complex,from the bottom layer to the top layer,the test of single-load axis without load,the test of single-load axis with load,and the balance load test are performed in turn.The problems existing in the system are solved through the test results.By recording the test process and analyzing the test data,the system performance is evaluated,and a conclusion is given in the end.After testing and verification,the proposed system can realize all the functional requirements including computer control,fully automatic operation and stepless loading within the loading range,and the performance indicators have reached the advanced level of national military standards. |
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