LabVIEW-Based Wireless Monitoring System of CNC Machine Tools

Zhongqi Shenga, Zezhong Liangb, Chaobiao Zhangc and Liang Dongd

School of Mechanical Engineering and Automation, Northeastern University,

Shenyang, 110004, China

azhqsheng@mail.neu.edu.cn, blzzh57@163.com, czcb666@126.com, ddongliang902@126.com

Keywords: LabVIEW, Data acquisition, Wireless monitoring system, CNC machine tools.

Abstract. As the development of industry wireless networks, sensor network, innovative sensors,

radio frequency identification (RFID), and micro-electro-mechanical system (MEMS) technologies,

the industry sector has made great progress in data acquisition, treatment, transfer and analysis,

greatly expanded people’s ability to access information, and to control and use them. This paper

developed a wireless data acquisition and storage system of CNC machine tools based on LabVIEW

graphical programming language and IEEE 802.11 wireless communication protocol, effectively

expanded the ability to access and use the CNC machine status information; solved the problem of

data collection caused by the environment complexity of manufacture workshop and the hardness of

wiring; eliminated the dead zone of manufacture workshop in the processing of the data acquisition

of state information of bottom processing equipment; made the bottom machining unit no longer be

the information island for manufacturing enterprises.

Introduction

As the key basic equipment of manufacturing industry and the carrier of advanced manufacturing

technology; CNC machine tools is the important means to promote the equipment modernization of

pillar industries such as energy, transportation, information industries; and relates to the national

security and economic development of the country. The current global market competition makes

the manufacturer focus on the system automation of CNC machine tools, and the increase of the

degree of automation and complexity, which also brings some problems such as the big losses of

downtime and the increase of maintenance budget. As a result, the condition monitoring of CNC

machine tools and the process optimization is becoming more and more important in the numerical

control system.

Basic Structure of Wireless Monitoring System of CNC Machine Tools

There are two major ways for the state information acquisition of CNC machine tools. One way is

to directly obtain the output of state information contained in CNC machine tools system itself. The

other way is to obtain real-time monitoring state information through the decorated sensors in the

key position of machine tool. This paper developed a condition monitoring system based on the

second way to access the information about the state of CNC machine tools. Figure 1 shows the

basic structure of wireless monitoring system of CNC machine tools.

Applied Mechanics and Materials Vols. 121-126 (2012) pp 2075-2079Online available since 2011/Oct/24 at www.scientific.net© (2012) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/AMM.121-126.2075

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Fig.1 The basic structure of wireless-monitoring system of CNC machine tools

Data Acquisition System Based on the Model of Producers and Consumers. This paper used a

producer and consumer model to acquire data and developed the storage program using DAQmx

acquisition functions. The framework of the producers and consumers model is a parallel-loop

structure based on data queue. Its outstanding characteristic is the side-by-side multiple tasks

execution and data transmission based on circular queue [1]. It mainly consists of a circulation

structure and a queue. The operations to the queue include creating queue, putting element into the

queue, extracting element out of the queue, and the destruction of queue [2]. The introduction of

queue realized data transfer and cache between loops .The structure of the producers and consumers

model is shown in figure 2. In figure 2, the above circulation structure acts as the producers, which

constantly produce data information and add data information to the queue. The circular structure

acts as the consumers, which constantly extract data from the queue for storage or processing. Until

the termination of the circulation and the destruction of queue, the whole circulation will come to an

end. The operation process for data in the queue is as follows. First, create queue, then judge

whether to put data into queue or not according to the boolean value in the producers loop.

Secondly, in the consumer circulation structure, use data out of the queue function. Constantly

extract data from the queue to deal with. Finally, queue destroyed, the whole cycle ends.

Fig.2 The producers and consumers model

Adopting the producers and consumers model as the programming model of data acquisition and

storage system can greatly improve the efficiency of data storage, prevent data loss. Because the

data collection rate is higher than the rate of data reading and saving, the data will fill the buffer to

the full soon. The buffer space will eventually be filled with the constant filling, which makes the

new collected data continually cover the data that is not taken away yet, and eventually leads to the

loss of large quantities of data. Therefore, in high-speed real-time data acquisition, the producers

and consumers model can effectively prevent the data loss.

2076 Frontiers of Manufacturing and Design Science II

Data Storage Based on TDMS Data Format File. TDMS is the NI file data format for test and

measurement. Compared with other data file format, TDMS has many advantages such as

convenient, quick, suitable for high speed reading and writing, excellent data organization,

cross-platform support, supporting most NI software products, good compatibility and portability[3].

TDMS files have three different levels of object for data organization. The topmost level is

composed by a single object and acts as the root of the file, and includes the characteristic

information of the file itself. Each TDMS files can contain infinite groups, and each group can

contain infinite channels. The structure and the object of different levels of TDMS are shown in

figure 3.

Fig.3 The structure and the object of different levels of TDMS

The development of data storage program uses the TDMS writing function. The main functions

include TDMS open, TDMS write, TDMS set attributes and TDMS close [4]. LabVIEW mainly

uses the above functions to realize TDMS programming. First of all, it is needed to set the path of

file storage and filename, and to transfer the file path and filename to TDMS open function.

Secondly, TDMS open function transfers TDMS documents cited handle to TDMS set attributes

function. TDMS set attributes function sets the attributes of root, group and channel of TDMS data

files. After finished the above steps, the operation of TDMS file format is complete, then TDMS

documents cited handle is transferred to TDMS write functions. TDMS write function has the data

terminal. Only connecting the data terminal to the data information that is to store, the data storage

can be completed. Finally, TDMS close function is used to close the TDMS files after the

completing the data storage [5]. The diagram of the data storage program of this paper is shown as

figure 4. In this data storage program, a TDMS file viewer is added. When completing the TDMS

file data storage, the TDMS file viewer will spring out to check out the data stored and replay the

data in form of numerical value and chart.

Fig.4 The diagram of the data storage program

Data Acquisition and Storage System. With the above producers and consumers model, data

acquisition program and data storage program become an integrate program, the development of

data acquisition and storage system is completed. First, put the data acquisition program as the

Applied Mechanics and Materials Vols. 121-126 2077

producers in the first cycle of the producers and consumers model, set the data collection

procedures as the producers placed in the producers of the first cycle consumer model, and make

detailed settings of the data acquisition parameters according to the selected data acquisition card

WLS-9234. Then, put the data storage program as the consumers in the second cycle of the

producers and consumers model, and complete the terminal and the definition of data file format.

This paper adopts TDMS data file format, so it defines the queue for TDMS data type when

creating the queue for data storage. Finally, make the data connect between the queue terminals of

two circulation structure. The final programming diagram is shown in figure 5.

Fig.5 The final programming diagram of data acquisition and storage system

The front panel of data acquisition and storage system based on DAQmx data acquisition

functions is shown in figure 6. In the above data acquisition and storage system, data collected by

data acquisition card is real-time displayed by the waveform chart control. In the front panel of this

system, there are three functional areas including data acquisition settings, buffering settings and

data save settings. Before the start of data acquisition, it is needed to select physical channel in

acquisition setting area, and then in turn to set sampling mode, sample number of each channel and

sampling rate. The buffering settings area is used to set the readout rate and the number of data that

can be read in the display buffer. When the data overflow indicator becomes red, it is needed to

improve the buffer readout time, to speed up data readout rate in order to prevent data overflow. In

data collection, it is needed to save the filename, group name and channel name in data save

settings area in advance. Since this system uses TDMS data file format, the filename must use

TDMS data format.

Fig.6 The front panel of data acquisition and storage system

2078 Frontiers of Manufacturing and Design Science II

Summary

The development of wireless communication technology will bring great changes and influences to

manufacturing sector. This paper constructed a wireless data acquisition and storage system of CNC

machine tools based on IEEE 802.11 wireless communication protocol; effectively solved the blind

information area problem in the manufacture workshop; and greatly expanded the ability to access

and monitor the condition of the bottom equipment. This LabVIEW-based wireless data acquisition

and storage system has gone through the test in real workshop environment. The experiments

showed that this system can collect and store data stably, and ensure the security of data

transmission.

Acknowledgement

This work is supported by Fundamental Research Funds for the Central Universities (N090403005)

and Research Funds for Science Technology Projects of Liaoning Province (2009402017,

2010220003).

References

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[4] G.M. Bertolotti, G. Beltrami, A. Cristiani, R. Gandolfi and R. Lombardi: A Multi-Purpose

Wireless Sensor Network Based on Zigbee Technology, Lecture Notes in Electrical

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[5] Jizhen Ruan:I and the LabVIEW - a NI engineer decade programming experience(Beijing

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Applied Mechanics and Materials Vols. 121-126 2079

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