Hengkai Technology-Focus on Data Collection and Motion Control for 10 Years

Design of Control System of Electron Microscope Stretching Table Based on LabVIEW

 

This article designs a set of control system for the stretching stage used in electron microscope, including hardware and software. Among them,


The hardware includes: motor drive and preprocessing and acquisition of force and displacement sensor signals. The stretching table used in this system has a ruler


It has the characteristics of small size, short stroke, large load and high precision of motion. Through the force, displacement sensor signal


Certain pre-processing, using LabVIEW software to collect and process through the acquisition card to achieve real-time display of the initial signal


Display and save; at the same time, realize the control of the stretching table through a certain feedback adjustment.


1 Stretching table structure


The technical indicators of the stretching table are shown in Table 1. The stretching table in the system is placed in an electron microscope and is used to support and fix the test.


And the loading of the test piece through the horizontal movement of the stretching table, so that the electron microscope can observe the change of the material;


The stretching table has the characteristics of small size, short stroke, large load and high motion accuracy.



As shown in Figure 1, the stretching table is composed of displacement, force sensor fixture transmission device and motor, etc.; including the transmission device


The main body of the stretching table including the fixture is made of stainless steel.



The gear pair is used in the transmission device to achieve the speed change function. In order to ensure the accuracy during the operation, the precision of the gear processing


Degree is higher.


In order to save space, the clamp is connected to the lead screw through threads to realize the linkage of the clamp. At the same time, the design of the test piece


The fixture is used to fix the test piece and install the sensor, where the sensor is fixed on the four walls of the groove. Through the slot at the front of the fixture and


The screw hole is used to fix the test piece, and the fixture is fixed through the counterbore.


2 Control system hardware introduction


In the process of loading the test piece, it is required to be able to monitor the force of the test piece in real time and the tensile and compression speed


Control, so it is necessary to collect the signals of the force sensor and displacement sensor, and at the same time control the speed of the motor.



2.1 Signal acquisition card


This system uses Hengkai USB6202 data acquisition card, including 32 analog input channels, 4 analog channels


To be output, 16-bit resolution; 48 digital I/O ports; used to collect signals from force and displacement sensors and output the motor at the same time


Drive signal.


2.2 Motor drive module and signal processing module


The motor used in this system is FAULHABER's 2642CR series DC motor, the rated drive voltage is 12V,


The pressure difference between the two ends is controlled by the output signal of the drive module, and the input signal of the drive module is generated by the USB6202 acquisition card.


What is adopted is the dual 675 operational amplifier differential amplifier circuit. The differential circuit is used to effectively shield the common mode signal. Circuit diagram


As shown in Figure 3, after calibration, the output voltage and output voltage show a more accurate linear relationship.


The errors of the fitting results are all less than 0.5%.



Since the range of the displacement signal does not match the input range of the acquisition end of the acquisition card, for the displacement signal, by shifting it,


The enlargement method makes it possible to fully use the input range of the capture card; on the other hand, in order to be able to monitor the entire stretching table travel


The sensor signal of the sensor and the sensor signal of the effective travel of the stretching table are more effectively processed. The two-way shift amplifier is designed but has different magnification.

 

xzhktech.com Hengkai 10:59:08

Way to achieve the above functions. Because the force signal is relatively weak, the force sensor uses a bridge circuit,


At the same time, an adjustable resistor is designed to ensure that the force signal output is zero before loading the test piece. As shown in Figure 4.




Considering the design of the human-computer interaction interface and the hardware requirements of the control system itself, the software design platform of this system is


LabVIEW, from a functional point of view, this control system is mainly divided into the following parts:


3.1 Motor driver


The function of the motor driver is mainly to control the USB6202 capture card to output the input signal of the motor drive circuit, from


And control the movement process of DC motor and stretching table.


Driving process: the actual linear motion speed is controlled when the front panel is operated, and the displacement sensor is used to calibrate the number within the program


Convert it to the voltage across the DC motor, and then input and output the calibration result through the motor drive circuit to convert it into a drive


The input of the circuit finally controls the output of the capture card.


3.2 Signal acquisition and processing


The most important thing about the entire control system is the acquisition and processing of displacement and force signals. Provide professional data acquisition and output module DAQmx in LabVIEW. In this system, multi-channel simultaneous acquisition mode is adopted to collect force and displacement sensors.


The signal of the device is based on the existing noise and other interference signals, and the average method is used to obtain the arithmetic average of the sampled data within a certain period of time.


The mean, as a sample.


During the collection process, you can control the collection process through the program: control whether to collect and adjust the sampling period


And the sampling result shows the adjustment of the image.


Whether to acquire and adjust the display results of the sampling results, LabVIEW can be easily implemented.


Due to the limitations of LabVIEW itself, if the sampling period is directly adjusted, the program may not run smoothly, even


There will be errors, so the indirect adjustment method is used. The adjustment procedure is shown in Figure 6.



The sampling frequency is preset to 1000Hz, and the sampling number is 20, that is, 1000 points per second, and every 20 data


Output once. If the sampling period is set to 500ms externally, the original 50 data per second output becomes 2 data per second


For output, you can use the program control to output 1 group for every 25 groups of data.


After the data collection is completed, the calibration results of the force and displacement sensors can be converted to the original data and used


LabVIEW's own PID and fuzzy logic toolkit implement its speed control and adjustment.


3.3 Data storage and export


After the experiment is completed, if you want to save the experimental data and the displayed image, you can use the "save file" function to divide


Don't save it as a file with txt and bmp as the suffix, the saved file will also contain some basic settings of the experiment, including


Sampling period, sample size, etc. At the same time, if you want to open the previously saved file, you can also complete it through the main program.


The saved data will also be loaded.


If you want to organize the data and images of multiple experiments into a report, you can also use the "Generate report" of the main program.


"Table" function to achieve, by sequentially adding data and image files to complete the report generation.


4 Experimental results


Figures 7 and 8 are the experimental results. The material of the test piece used in the experiment is 42CrMo.



5 Conclusion


For offer

 

xzhktech.com Hengkai 10:59:09

The stretching table and supporting displacement sensors and signal sensors, this paper designed the motor drive and sensor


Signal processing hardware module; at the same time, a signal acquisition program and a control signal output program are designed for the hardware.


The overall program of the control system is constructed on the above. Through experiments, the system completes the functions of control and signal acquisition and achieves the corresponding precision


Degree requirements.


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Attachment: Hengkai USB6202-S acquisition card used in this system This acquisition card provides a wealth of function interface, programming is also very simple.


HK-USB6202-S V1.1 (purchase link)


l AI: 16bit, 200Ksps, 4-channel synchronous acquisition, multi-range optional.


l AO: 12bit, 2 channels, 10V range.


l DIO: 32 channels, 5V level.


l Additional functions: 2-channel PWM measurement, 2-channel PWM output


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