Load Spectrum Research of Roadheader Cutting Header based on Rain Flow Method

2016 International Congress on Computation Algorithms in Engineering (ICCAE 2016) ISBN: 978-1-60595-386-1

1 INTRODUCTION

When road header cuts coal-rock or hard mining face, the force of cutting mechanism is complicated, and the load fluctuation range is relatively large. With cutting teeth which is gradually being worn and the number that may decrease due to power, each tooth bears larger force, which leads to further vibration. The load of vibration breaks the strength of machine parts, changes normal cutting line spacing, cutting depth and other parameters and affects the life and reliability of machine. While the main cause about the severe vi-bration of road header and the fatigue damage or fragmentation of parts is exactly the complex and mutational load. According to the survey, the stopping probability in work process and instability caused by spatial position is 26%, affecting reliability and re-ducing the productivity and economic benefits of ma-chine [1-3].

If we want to improve the stability and reliability of the machine, it is necessary to rationally design and select the special mechanical structure and part at first. And the load measurement and analysis is very im-portant because the original design of machine and the dynamic modification and optimization of structure

are conducted based on load spectrum [4].

2 RESEARCH BACKGROUND OF LOAD

SIG-NALS

For the mining machinery, the roadheader load re-search has been carried out and gradually in-depth at home. Although the experiences are not that much, there are also some achievements, and the simple in-troduction is shown as follows:

(1) Professor Wu Miao and other people at China University of Mining & Technology (Beijing) have measured and analyzed the load spectrum of AM50 roadheader during cutting cross-section: They discuss the load spectrum drawing method of cross-cutting roadheader. The working load spectrum can be ob-tained after the time-domain statistics, the power spectrum analysis and the amplitude domain statistics. These measured data not only improve the dynamic performance and reliability of roadheader, but also are reference values to explore other new high-power models.

(2) Zhang Hongshun at Taiyuan Institute of China Coal Research Institute has measured and analyzed EBZ2260TY roadheader when it cuts false wall. It can accurately acquire laws of change in load on rocker

Load Spectrum Research of Roadheader Cutting

Header based on Rain Flow Method

Lansheng Zhang1,2, Yuanyu Zhao1, XiushanTang1, Qiang Liu1, Miao Cao1* & Miao Wu1 1

School of Mechanical Electronic and Information Engineering, China University of Mining & Technology (Bei-jing), Beijing, China

2

Shijiazhuang Coal Mining Machinery Co., Ltd. Shijiazhuang, Hebei, China

ABSTRACT: Because underground load spectra measured work is seldom researched, a large capacity data recorder, also called as “black box”, that can be used underground for a long time and storage machine working condition data has been invented and used. Combined the actual measured data with cutting motor current and voltage and other roadheader parameters, the value of torque that cutting head suffered can be calculated and, the one-dimensional load spectrum in time domain can be drawn. By analyzing, it is found that there may be a static component. Moreover, two-dimension load spectrum based on rain flow count method can be drawn and then it is used to conclude the value of the static load and the range of dynamic load.

Keywords: roadheader; load spectrum; “black box”; cutting header

arm by identifying the right side and upside load stress of cutting arm and using the one-dimensional load spectrum theory. Moreover, these can be used in the improvement and optimization of structure.

(3) Zhang Licai at Taiyuan Institute of China Coal Research Institute has simulated continuous miner in underground coal mining conditions and operated the finite element analysis for it. Using underground test data and finite element analysis, he identified the un-derground load of continuous miner. These reveal inner statistical laws of continuous miner at working. Furthermore, he compiled the load spectrum by using the theory of one-dimensional spectrum.

Figure 1. Installation site of partial vibration acceleration sensors and strain rosette.

Here, we take the research of Professor Wu Miao et al. as an example. They approximatively consider roadheader load as three feeding direction forces and the required torque to drive the rotary cutting head, and the coordinates of three feeding forces are fixed in the cutting arm and move with it. In this method, there are three full bridges that are composed of three sets of 12 pieces of strain gauge to test the three-way force,

which are arrangeed in the outer surface of the cutting head main reducer [5]_{. The obvious advantage of this} approach is that the technology of measuring stress by using strain meter is relatively mature, and it can di-rectly measure the cutting arm stress.

Li Zhen at Tiandi (Changzhou) Automation Co. Ltd. obtained the working load of EBZ260 roadheader through using similar method. He arranged strain ro-sette and vibration acceleration sensors in the right side of cutting arm. As shown in Figure 1, vibration acceleration sensors are in the circle and the strain rosette is in the box [6].

3 OBTAINMENT OF LOAD SIGNALS

The first step of load study is mounting position of partial vibration acceleration sensors, strain rosette and load sample acquisition, and this is also the most crucial step. The above mentioned method is relatively mature; however, the subsurface environment is hash and complex, so this approach is impractical. There-fore, a new load sampling method is proposed and put to practice in this paper. That is to say, “Mul-ti-information acquisition program of road header is based on high-capacity data logger boring machine”. High-capacity data logger is also known as “black box”, it can real-timely acquire and record various state parameters and control the information of equipment for excavation at work. The basic principle of “black box” is shown in Figure 2.

The control signal includes pump start and stop, start and stop cutting the voltage select 1140/660, emergency stop, etc. Status signals include lighting

Figure 2. Basic schematic of “black box”.

Intrinsically Safe Vibration Acceleration Sensor

Signal Conditioning Board

Data Acquisition Card Analog

Signals of Roadheader

Status Signals

of Roadheader

Position Signals of Roadheader

Analog Control Signals of Roadheader

Main Control Unit PLC of Roadheader

Motherboard

Vibration Signal

COM Port USB Port

SATA Port

leakage, alarm, overload indicator, two kinds of transport failure, high-speed over-temperature, oil pup failure, etc. Analog includes cutting the current of each motor, pump the phase current of each motor and cutting the motor temperature and the pump tempera-ture.

Moreover, there are the oil pressure monitored by pressure transmitter which is installed in the oil circuit; the information of position and orientation is mainly the horizontal rotary angle of cutting arm monitored by dual speed measuring device which is installed on the rotary table and the vertical angle which is moni-tored by tilt angle sensor. Multi-signals communicate with the motherboard via RS232 communication in-terface of “black box” through the electrical control box, and they are recorded in the solid state drives through using an embedded database SQLite as stor-age containers.

“Black box” with the function of RS232 serial communication, TCP/IP network port communication and multi-channel acquiring vibration acceleration signals uses Inter3954A embedded motherboard, the solid state drives of 512G storage medium and the maximum total sampling frequency which is 250K (adjustable).

By closely working with Shijiazhuang Coal Mining Machinery Co., Ltd., the “black box” is installed on their product—the second generation EBZ160 road header, the machine service is located in 1100 South-ern centralized distribution lane of Xingdong Mine of Jizhong Energy Group Co., Ltd, which is the whole coal lane with a trapezoidal cross-section. After two months down-hole data acquisition, we get a lot of valid data.

The vibration signal input and the power and com-munication interfaces of “black box” are shown in Figure 3 and Figure 4:

Vibration signal input

Figure 3. Vibration signal input.

communications interface

24v power supply

12v power supply

Figure 4. Power and communication interfaces.

4 TRANSFORMATION OF LOAD SIGNALS

“Black box” can record a lot of information, including cutting motor current, voltage, pressure on lifting and rotary cylinders, etc. However, after passed to “black box” by PLC, the information is stored in a SQLite database by hexadecimal number and can only be used for analysis after transformation. Next, we take cutting head torque as example.

PLC takes “41” character as data to transmit open-ing instruction and sends the data of 60 bytes one-time which is stored in SQLite with long strings. The spe-cific example is as follows:

41A600AA00A0005500570057000000000000004 C067B01A301AA005100FE002E0006000000000000 000200000000003004900194011306FC02E4FF

Three to six represents A-phase current of cutting motor, and it converts to decimal number as follows:

1 0 3 2

10 16  6 16  0 16  0 16 166

Where: 10 is A in decimal.

The corresponding input-output relations of current transducer in electrical cabinet of roadheader are shown as follows:

0–1500A corresponds to 0–5V

The corresponding relations of data in FX4N-AD module of PLC are:

0–10V corresponds to 0–4000A

Therefore, the actual current value of 196 is:

166 2000 1500 124.5( )   A

Cutting part of road header with flameproof three-phase induction motors takes cutting action on the coal and rock. The cutting head is subjected to mechanical loads that are in the form of anti-torque pass to the output shaft of the motor.

When motor is at work, rotor current and stator current that pass by the magnetic coupling all increase with the increasing load and the reduced speed. At the same time, current signal changes can reflect load changes. Therefore, the relation in cutting motor cur-rent and cutting head torque is shown in formula (1) and formula (2):

 

If M ₍₁₎

1

( )

M f I (2)

Where: I = motor current of cutting unit asynchro-nous; M = anti-torque of cutting head.

information to reflect the load by monitoring the cur-rent and voltage changes; at the same time, the moni-toring and data transformation of voltage U is similar to the current. Therefore, formula (3) is modified as follows:

1

( , )

Mf U I (3)

Generally speaking, torque transmission sequence is transmitting from cutting head to reducer that comes after cutting motor, and the transformation process must lost energy.

m i

MT i  (4)

In this formula: Tm = motor output torque; i = re-duction ratio; ηi = transfer efficiency. The structure for the reducer is the two planetary gear, so i=31.03 and ηi=0.85.

Motor output torque:

9.55 out m

P T

n

 (5)

Where: Pout = output torque of the motor shaft; n = motor output speed.

Furthermore:

out m in

P 



Pout is the input power of the stator circuit, and it is known that the cutting motor model is YBUD-160/ 100-4/8 and the output speed has two choices, so we can choose the high speed 1470r/min which is rec-orded in “black box” that ηm can be 90%.

What’s more, the electrical power which is deliv-ered from power supply to stator circuit is:

3 cos

in L L

P  U I  (7)

Where: cosφ = power factor.

When motor is in operation, the power factor is changed, and its change is connected with changing loads. The power factor is very low in no-load condi-tion, and it is about 0.2. When the motor is running with loads, it will output mechanical power, the active current component in the stator winding increases, and the power factor also increases to 0.7–0.9. Consider-ing the approximate calculation, we take the rated load power factor of model motor as 0.85.

Thus, we can get the following conversion formula:

i m

9.55 3iη η cosφ

n UI

M  (8)

Other parameters can be got by consulting road-header design books and correlation calculation. Sub-stituting the values into this formula, then we have:

4

2.27 10 ( )

M UI  kN m (9)

U and I in this formula only represent the value af-ter conversion, for convenience, torque’s unit is changed from Nm to kNm.

5 LOAD ANALYSIS OF CUTTING HEAD

Loading on the cutting head is mainly resistance torque when cutting coal wall, using the method de-scribed in the last section firstly to convert cutting motor B-phase current. As shown in Figure 5, “black box” stores B-phase current of road header cutting motor when working at Xingdong Mine roadheader cutting surface in October 13, 2014.

Figure 5. B-phase current of motor in a cutting process.

The red box shows the start segment, and the rest is working section, it will produce big stator current when starting the motor. And the current can usually reach 5–7 times of nominal, however, the rotor pow-er factor is vpow-ery low at this time, thus starting torque is not big. So in order to reduce error, the only method is to conduct analyses on work segment when analyzing torque.

It concludes that the resistance torque loaded on roadheader cutting head according to the calculation formula (6) since the voltage value (which is not given again here) is basically stable at about 1220V. The trends in the time domain of resistance torque are shown in Figure 6:

Figure 6. Resistance torque of cutting head.

Figure 7. Load time-domain of roadheader.

The statistical characteristic value of load spectrum is an important indicator to describe the machine loading intensity of roadheader. For load spectrum, the maximum and minimum determines the maximum dynamic load, the standard deviation reflects how difficult when cutting coal wall, namely the average degree of hardness distribution of coal wall, the root-mean-square value represents the index of the statistical strength, and the average indicates if there is static load component [7].

As shown in the Table 1, there are the torque do-main parameters of cutting head.

Table 1. Cutting head torque domain parameters.

Time Domain Parameters Numerical (kNm)

Maximum 45.58

Minimum 6.344

Standard Deviation 9.709

RMS 18.73

Average 16.02

It can be obtained from Table 1 that in the process of cutting start and stop of roadheader cutting head, the maximum torque is 45.58 kNm, the minimum is 6.344 kNm, the standard deviation is 9.709 kNm and the root-mean-square is 18.73 kNm. However, the average is 16.02 kNm, which deviates more com-pared with the average of maximum and minimum, and it is more likely to prove the existence of static load components. Observing the load time-domain as shown in Figure 7, there is a relatively smooth time period with several segment values under 10 kNm, and this conclusion will be confirmed in the future.

Through the analysis of the stress of cutting head, we can find that there is the acting of cutting coal wall as well as overcoming the weight of rotation. From this, an approximate equation is obtained:

Loads of cutting head = static load + dynamic load = overcome self-weight + cut coal wall

We choose the rain flow counting method in Nsoft, select figure Range-Mean and plot Figure 8.

Figure 8. Load cycle of rainflow histogram.

X-axis represents the magnitude of load cycle, Y-axis represents the mean of rain flow cycle, and Z-axis represents the frequency of rain flow cycle, and this figure can be drawn as Min-Max figure. Here, for the convenience of analyzing, we generate figure Range-Mean.

It can be obtained from Figure 9 and Figure10 that the average of the largest load cycles is 7.86, and the range is 1. Due to the torque of overcoming the weight of cutting head throughout the start-stop process, we estimate the static load components as 7.86 with 0.5 fluctuations. If analyzing dynamic load when the cut-ting head cuts coal wall, this part and gross errors are just removed in the original data.

Figure 9. Mean of load cycles.

Figure 10. Range of load cycles.

6 CONCLUSION

for a long time because they are limited by the harsh and complex downhole environment. The mass of data that recorded in large-capacity data logger in the un-derground for more than two months is discussed in this paper, which means the industry problem is solved.

Moreover, there is no relevant data, and the load research on roadheader cutting head is usually calcu-lated based on experience or simulation.

This article describes calculation formula of road-header cutting head torque based on the analysis of transmission structure and the data recorded in “black box”, thus figuring out load value according to the formula; what’s more, this paper also draws the one-dimensional load spectrum based on time and two-dimensional load spectrum based on rain-flow counting method, which provides the foundation for further load analysis of the roadheader.

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