issn: 0976-1353 volume 23 issue 6 –october …...positioning stepper motor and servo motor are...

International Journal of Emerging Technology in Computer Science & Electronics (IJETCSE) ISSN: 0976-1353 Volume 23 Issue 6 –OCTOBER 2016 (SPECIAL ISSUE)

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Automation of Belt Conveyor System

Sanjeev Kumar Patti S Nagendra Prasad Final Year M.Tech (CAID) Student Associate Professor

Department of Electrical & Electronics Engineering Department of Electrical & Electronics Engineering The NIE, Mysuru-08

(Autonomous Institute under VTU, Belagavi) The NIE, Mysuru-08

(Autonomous Institute under VTU, Belagavi)

Abstract - In this paper, a multi load on a multiple belt conveyor system (BCS) is considered for implementation of automated control system using PLC to ensure proper belt conveyor for steady and safe operation. The closed loop control system uses motor current as the feedback signal. The current changes with the load and changes the control signals for steady operation in real time. A control strategy is implemented to control the speed of a motor-driven belt conveyor by maintaining v/f a constant. The use of variable frequency drive improves performance and productivity. Index Terms - Programmable Logic Control (PLC), Variable Frequency Drive (VFD), Belt Conveyor System (BCS), Ladder Diagram (LD), Human Machine Interface (HMI)

I. INTRODUCTION

Since technology for motion control of electric drives is available, the use of programmable logic controllers (PLCs) with power electronics in electric machine applications is used in the manufacturing and automation [1], [5]-[7]. This offers advantages such as lower voltage drop when turned on with near to unity power factor. PLC’s in automation are used to reduce production cost and to increase quality and reliability. To develop industrial electric drive systems, it is necessary to use PLCs interfaced with power converters, personal computers, and other electric equipment

Many applications of induction motors require besides the motor control functionality, the handling of several specific analog and digital I/O signals, to name a few: trip signals, on/off/reverse commands etc. To make electric drive system versatile PLC must be added to the system structure. This paper presents a PLC-based monitoring and control system for three-phase induction motors used in BCS. It describes the design and implementation of the configured hardware and software.

The test results obtained on induction motor performance using PLC, show improved efficiency and increased accuracy in variable-load constant-speed-controlled operation [2]. Thus, the PLC correlates and controls the operational parameters such as the speed set point requested by the user and monitors the induction motor for its operation.

A PLC is a microprocessor-based device, designed for automating processes in industrial environments [1, 6-7]. It uses a programmable memory for the internal storage of user-orientated instructions for implementing specific functions such as arithmetic, counting, logic, sequencing, and timing. A PLC can be programmed to sense, activate and control industrial equipment and therefore, incorporates a number of I/O pins, which allow electrical signals to be interfaced. Input devices and output devices of the process are connected to the PLC and the control program is entered into the PLC memory by PLC software. A. Literature Survey:

• Maria G. Ioannides [1] has discussed the

implementation of a monitoring and control system for the induction motor based on programmable logic controller (PLC) technology is described. Also, the implementation of the hardware and software for speed control and protection with the results obtained from tests on induction motor performance is provided. The PLC correlates the operational parameters to the speed requested by the user and monitors the system during normal operation and under trip conditions. Tests of the induction motor system driven by inverter and controlled by PLC prove a higher accuracy in speed regulation as compared to a conventional V/f control system. The efficiency of PLC control is increased at high speeds up to 95% of the synchronous speed. Thus, PLC proves themselves as a very versatile and effective tool in industrial control of electric drives.

• D. Sowmiya [2] has discussed the implementation of monitoring and control of a variable frequency drive (VFD) fed three phase induction motor (IM) using programmable logic controller (PLC) technology for a powder compacting hydraulic press (HP) machine is described. The PLC co-ordinate the operational parameters such as ram down, ram dawdling, ram clasp and ram up in HP machine, during the operation. Typical techniques for three phases IM are commonly provided by mechanical and electrical equipment’s, but it has many limitations of stator insulation failures and reduces the life and efficiency of the system. In this proposed method,


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new control method based on the PLC has been introduced The HP machine Solenoid valves are controlled using PLC as per the operation cycle. The efficiency of a PLC control is increased at variable speeds and thus increases the power consumption. Thus, the PLC proves as a resourceful and effective tool for controlling industrial electric drives.

II. HARDWARE DESCRIPTION

A. Variable Frequency Drive: Induction motors operate at fixed designed speeds and are ideally suited to applications where a constant output speed is required. However motor applications have some kind of varying speed demand and this includes processes such as moving air and liquids (fans and pumps), winding reels and

precision tools. Historically in applications requiring precise speed control such as paper winding reels expensive direct current (DC) motors or hydraulic couplings are used to regulate the machine speed, whereas in other applications the processes have been controlled by opening and closing dampers and valves, or changing output speeds with gears, pulleys, and similar devices whilst the motor works at constant speed.

In the 1980's and 1990's, variable frequency drives started appearing on the electric market offering an alternative method of control. A variable frequency drive, also called as adjustable speed drive. The basic working principle is to vary the frequency and voltage to change the motor's speed and torque output.

Fig. 2 VFD block diagram

Variable frequency drives applied to AC motors are by far the most common [4]. Their basic design consists of four elements (Fig. 2):

• Converter: The working principle of rectifier is changing the incoming alternating current (AC) supply to direct current (DC). Different designs are available and these are selected according to the performance required of the variable frequency drive. The rectifier design will influence the extent to which electrical harmonics are induced on the incoming supply. It can also control the direction of power flow.

• Intermediate circuit: The rectified DC supply is then conditioned in the intermediate circuit, normally by a combination of inductors and capacitors. The

majority of VFDs currently in the marketplace use a fixed-voltage DC link.

• Inverter: The inverter converts the rectified and conditioned DC back into an AC supply of variable frequency and voltage. This is normally achieved by generating a high frequency pulse width modulated signal of variable frequency and effective voltage. Semiconductor switches are used to create the output; different types are available, the most common being the Insulated Gate Bipolar Transistor (IGBT).

• Control Logic: The control unit controls the whole operation of the variable frequency drive; it monitors and controls the rectifier using PWM technique, the intermediate circuit and the inverter to deliver the correct output in response to an external control signal.


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B. Belt Conveyor System (BCS): The belt is supported along its length by rotating idler rolls and suspended between pulleys at either end (Fig. 3). A drive pulley is powered to rotate the belt and move the materials on the belt forward.

Selection of motor For BCS Control:

• For fixed speed or constant speed conveyors and conveyor systems: AC induction motors are ideal for conveyor systems that operate continuously in one direction while AC reversible motors are ideal for conveyors that must reverse or change directions repeatedly.

Fig. 3 Cross section of belt conveyor

• For conveyors where the speed needs to controlled or vary during operation: AC Speed Control Motors as well as Brushless DC Motors (BLDC Motors) that offer a wide speed control range and constant torque regardless of load.

• For conveyors that require higher accuracy, positioning Stepper Motor and Servo Motor are used. Stepper motors, with their ability to product high torque at a low speed while minimizing vibration, are

ideal for applications requiring quick positioning over a short distance.

C. Proposed Block Diagram: As shown in Fig. 4 PLC acts as interface between HMI and VFD. SMPS is used to convert 3-ϕ AC to 24V DC, which is given as input to PLC. VFD is used for smooth speed control of conveyor belt system. System consists of Conveyor Belt Forward. / Reverse motion and Bowl up / down motion, which is controlled by VFD. Inputs can be given manually using push buttons or directly through HMI.


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Fig. 4 Proposed Block Diagram

D. List of Components:

TABLE 1: LIST OF COMPONENTS

SL.NO.

COMPONENT NAME

PURPOSE RATING

1 MCB Protection 6A, 10A, 16A 3ф

2 Choke To limit fluctuations in the main supply

6A, 12.5A 3ф

3 Contactor Protection 12A, 3ф

4 OLR Over load protection

10A, 3ф

5 VFD For smooth speed control of motor

0.75 KW, 3.7KW 3ф

6 Transformer To step down

supply voltage to 24V DC

300VA, 415/220V

7 SMPS To convert AC to

DC for control circuit and PLC

6.5A 1ф

8 PLC For monitoring and control of speed of

motor 40 I/O’s

9 Motor 1 For conveyor belt

control 3.7 KW, 3ф

10 Motor 2 For Bowl speed

control 0.75 KW,

3ф

11 Motor 3 For Furnace outlet

control 3.7 KW, 3ф

12 Motor 3 For Furnace outlet

control 3.7 KW, 3ф

III. SOFTWARE DESCRIPTION

A. PLC Programming: The function of the CPU is to control the operation of memory and I/O devices and to process data according to the program. Each input and output connection point on a PLC has an address used to identify the I/O bit. The method for the direct representation of data associated with the inputs, outputs, and memory is based on the fact that the PLC memory is organized into three regions: input image memory (I), output image memory (Q), and internal memory (M). Any memory location is referenced directly using %I, %Q, and %M.

The programming used is the ladder diagram method. The PLC system provides a design environment in the form of software tools running on a host computer terminal which allows ladder diagrams to be developed, verified, tested, and diagonised. First, the high-level program is written in ladder diagrams. Then, the ladder diagram is converted into binary instruction codes so that they can be stored in random-access memory (RAM) or erasable programmable read-only memory (EPROM). Each successive instruction is decoded and executed by the CPU.


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Fig. 5: Flowchart for main program

The PLC program uses a cyclic scan in the main program loop such that periodic checks are made to the input variables (Fig. 5). The program loop starts by scanning the inputs to the system and storing their states in fixed memory locations (input image memory I). The ladder program is then executed rung-by-rung.

The software regulates the speed (Fig. 6) and monitors the constant speed control regardless of torque variation. The inverter being the power supply for the motor executes this while, at the same time, it is controlled by PLC’s software. The inverter alone cannot keep the speed constant without the control loop with feedback and PLC. From the control panel, the operator selects the speed set point (nsp) and the forward/backward direction of rotation.

Fig. 6: Flowchart for speed control program

Software used to write Ladder Program is CX-One Ver. 9.2, Cx Programmer of OMRON make. Ladder Program (LD )is written for two cases as shown in Fig. 7 & 8

CASE 1: WHEN CONVEYOR BELT IS STOPPED. CASE 2: WHEN CONVEYOR BELT IS MOVING.

B. HMI Screen Development: Human Machine Interface (HMI) screen developed using

Cx-Designer of OMRON make is shown in below Fig. 9 to Fig. 12. Once the HMI screen is developed user can press to enter the exact screen through which parameters can be changed.


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Fig. 7: Ladder Diagram for Case 1

Fig. 8: Ladder Diagram for Case 2

• Screen 1 displays Main Screen (Fig. 9), which indicates Time, Alarm , Voltage, Current, Actual Speed, Starting settings, Conveyor control screen, Bowl control screen, emergency stop in case system to be shut down during critical cases.

• Screen 2 displays conveyor control screen (Fig. 10), which indicates Time, Alarm, Reference and Actual Speed of BCS, Forward / Reverse motion of BCS. If Conveyor button is clicked it shows the BCS of process. Also it contains options to go to Main Screen, Bowl Screen, settings screen and an Emergency Stop switch.


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Fig. 9: HMI Screen 1


• Screen 3 displays Bowl control screen (Fig. 11), which indicates Time, Alarm, Reference and Actual Speed of BCS, Upward / Downward motion of BCS. If Bowl button is clicked it shows the BCS of process. Also it contains options to go to Main Screen, Bowl Screen, settings screen and an Emergency Stop switch.


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Fig.11: HMI Screen 3

• Screen 4 displays Start up Settings screen (Fig. 12), which can be used to enter Reference Speed value, Acceleration time, Deceleration time. To start the main program and go to other screens directly.



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IV. RESULTS ANALYSIS AND DISCUSSIONS

The main objective of the project is to develop and implement an automated control for a conventionally (using gears & pulley) operating conveyor belt system using VFD and PLC in order to increase the productivity and accuracy. Fig. 13 & Fig. 14 show Hardware circuit. Output of two cases is provided with Ladder diagram as shown in Fig. 15 & Fig. 16.

Fig. 13: Inside View of Control Panel

Fig. 14: Front & Side View of Panel


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Fig. 15: Output for Case 1

Fig. 16: Output for Case 2

CONCLUSION

Successful experimental results were obtained from the previously described scheme indicating that the PLC can be used in automated conveyor belt systems.

The monitoring control system of the induction motor driven by inverter and controlled by PLC proves its high accuracy in speed regulation at constant-speed-variable-load operation.

Each rung of the program is executed and it will energise the respective valves when the desired input is true. Initially when the supply is on, the VFD will start and the belt motor will be driven through the VFD.

The efficiency obtained by using PLC control is increased as compared to the open-loop configuration of the induction motor fed by an inverter.

HIGHLIGHTS OF IMPLEMENTATION:

• The system is running successfully through newly automated system.

• The high accuracy and high productivity rate is achieved.

• Frequent maintenance is not required.

• System is monitored continuously; the fault occurrence if any can be cleared immediately without any delay.

• Since there is no human interference it leads to improved accuracy and productivity.

• Overall System efficiency is improved after automation.

Thus, the PLC has proved to be a versatile and efficient control and monitoring tool in industrial electric drives applications.

REFERENCES

[1] Maria G. Ioannides “Design and Implementation of PLC-Based Monitoring Control System for Induction Motor” in Proc. IEEE Transactions on Energy Conversion, VOL. 19, NO. 3, Sep 2004.

[2] D. Sowmiya “Monitoring and Control of a PLC Based VFD Fed Three Phase Induction Motor for Powder Compacting Press Machine” in Proceedings of 7th International Conference on Intelligent Systems and Control (ISCO 2013)

[3] Yusong Pang, Handbook on “Intelligent Belt Conveyor Monitoring and Control”.

[4] B.Jayant Baliga, “Power Semiconductor Devices for Variable Frequency Drives”, Invited Paper in IEEE, Vol. 82 No. 8, Aug 1994.


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[5] Victor L. Kitts, William K. Stees, P.E, “The Application of Medium Voltage VFD on Underground Mine Belt Conveyor System”, IEEE,2000

[6] G. Kaplan, “Technology 1992. Industrial electronics,” IEEE Spectr., vol. 29, pp. 47–48, Jan. 1992.

[7] A. Hossain and S. M. Suyut, “Monitoring and controlling of a real timeindustrial process using dynamic model control technology,” in Proc.IEEE Ind. Applicat. Soc. Workshop on Dynamic Modeling Control Applications for Industry, 1997, pp. 20–25.G. Kaplan, “Technology 1992. Industrial electronics,” IEEE Spectr., vol.29, pp. 47–48, Jan. 1992.

issn: 0976-1353 volume 23 issue 6 –october …...positioning stepper motor and servo motor are...

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