Design of intelligent controller for fault display of belt conveyor

Belt conveyor is a friction-driven machine that transports materials in a continuous manner. It can form a material conveying process from the initial feeding point to the final unloading point on a certain conveying line. Belt conveyor is now widely used.

Widely used in docks, coal mines and industrial batching, the safe and efficient operation of belt conveyors directly affects the efficiency of production. For a long-distance transportation system composed of multiple belt conveyors, if a failure of one of them cannot be predicted and eliminated in time, it will affect the entire production line.

1 Belt conveyor failure analysis

Since the sponge pad needs to be dried during production, and the newly produced sponge pad has too much water and cannot withstand excessive tension, otherwise it will break, so the belt is selected as the carrier of the transmission process in industrial production. The belt is prone to slippage, overload and belt breakage during operation, and these faults can be judged by detecting the belt speed.

Belt slippage is mainly due to the reduced friction between the belt and the drive roller. On the one hand, the belt may not be tensioned. On the other hand, the belt may be aged, resulting in poor grip. The direct manifestation is that the belt speed is lower than the set speed.

The main reason for overload failure is that the belt is too tight or the transported items exceed the rated load. This failure may cause the belt drive to alarm and stop running, and the direct manifestation is that the speed is less than the set value. The monitoring method can be judged by monitoring the current of the drive.

The cause of belt breakage may be belt aging or mechanical failure of the coupling. When a failure occurs, the belt speed will drop sharply and may stop running instantly.

2 How to detect belt failure

2.1 Belt slippage

When the belt slips, the direct impact is that the main transmission speed is inconsistent with the set speed. Assuming the main rotation speed is Vp and the set speed is Vs, we ignore the impact of the speed deviation within a certain range when slipping. Assuming the limit is 10%, it is necessary to check

Repair, then the fault is judged as

In this process, a passive roller is set on the belt, and a proximity switch is used to detect the number of revolutions of the passive roller per unit time. The running speed of the belt can be calculated by multiplying the circumference of the passive roller. The installation of the proximity switch is shown in Figure 1.

 

Assuming that the number of proximity switch pulses measured within T seconds is n, and the circumference of the passive roller is C, then

, Vs can be obtained according to the voltage set to the driver. Assuming the voltage is E and the voltage and speed coefficient is K, then Vs=K*E. In this way, these parameters can be used to determine whether the belt is slipping.

2.2 Belt deviation

The deviation detection adopts the photoelectric tube, and the installation method is shown in Figure 2.

 

By detecting the opening and closing of the photoelectric tube, it can be determined whether the belt is deviating, and the alarm system will be triggered to sound and light alarm to prevent serious machine failure. The inner side is the first-level deviation detection, and the outer side is the second-level deviation detection.

2.3 Overload detection

In industrial production, in order to better meet production needs, frequency converters are generally used to drive motors for speed regulation. When the load increases, the current of the frequency converter will also increase. We protect the motor by setting the current of the frequency converter so that it works in a safe state. When the motor current exceeds the set current threshold, an alarm is output and an external sound and light alarm is driven.

2.4 Belt breakage and coupling roll-off detection

When the belt or coupling is off the roller, the first thing affected is the belt speed. The speed of the belt drops rapidly and may become 0 within a few seconds. In the detection of these faults, the most attention is paid to the detection of belt speed. Through the influence of some faults on the speed, the reverse method can basically achieve full monitoring of the fault.

3 Intelligent Controller Hardware Circuit Design

This system is based on the single-chip microcomputer STC90C516, and its periphery is mainly composed of proximity switches, photoelectric tubes, frequency converters, LED displays, D/A conversion modules PCF8951T and some auxiliary circuits. Figure 3 below shows the schematic diagram of the hardware.

 

By inputting the external motor start signal into the P1.2 port, the stop signal into the P1.3 port, and the start relay into the P2.2 port, when the P1.2 button is detected to be pressed, the relay is energized and the motor starts; when the P1.3 button is detected to be pressed, the relay is disconnected and the motor stops. The system uses two 8-segment LED displays, one displays the belt number of the faulty belt, and the other displays the fault code.

The preset fault codes are: 0-normal; 1-slip; 2-break or coupling not connected; 3-belt deviation. If a fault occurs, P2.6 will drive the buzzer to alarm, and P2.7 will flash the indicator light to achieve the effect of sound and light alarm. The system uses the PCF8951T A/D conversion chip, directly through the I2C bus of SCL and SDC, the output analog quantity of AOUT is used as the speed signal of the transmission roller, and acceleration and deceleration are realized through P1.5 and P1.6.

Connect the speed probe detection signal of the passive roller to P1.4, and obtain the running speed of the belt by measuring the number of pulses per unit time. By comparing it with the given speed signal, it can be analyzed whether the belt is running normally. One belt uses 4 pairs of photoelectric tubes, which are divided into two groups to detect whether the belt is running off. When there is a first-level deviation, an early warning will be issued, and when there is a second-level deviation, the belt will be stopped to prevent unnecessary property losses.

4 Software Design

This system is programmed in C language and consists of a main program and various subroutines. The program flow chart of the intelligent controller is shown in Figure 4.

 

After the program is initialized, it checks the belt for slippage, deviation, motor overload alarm and other faults in turn, and handles them accordingly according to the fault level. The LED displays the fault code by calling the subroutine. The programming software is designed using Keil, and the corresponding program is modularized.
 

5 Conclusion

The main purpose is to analyze and study the faults that are prone to occur in the mainstream sponge production lines in China today, and design an automatic system that integrates alarm, display, and operation. The system is mainly based on the single-chip microcomputer, which fully utilizes the characteristics of the single-chip microcomputer, such as high integration, strong functions, small size, low power consumption, and high reliability. In the test, the error is small and can basically meet the requirements of use.