Sorting of Boxes According to Height Using PLC Based System

Sorting of Boxes According to Height Using PLC Based System 

Abstract – In todays world of technology there is tremendous development and growth in the production rate of industries as well as in the field of automation. Due to these, industries have to face problems related to shortage of labours. Generally, industries manufacture same type of products with variation in weight which is followed by packaging of the products in boxes. Therefore, it becomes necessary to develop an automation system which lower the cost and maintenance that could sort the boxes according to height without any human interference.

Thus, this paper illustrates a system that helps in automatic sorting of boxes according to the heights using sensors and conveyors governed by Programmable Logic Controller (PLC).

Keywords: Automation, Sorting, PLC, 

 I.  INTRODUCTION

Now a days most of the manufacturing industries are implementing automation in sorting system. Automation in sorting system is very reliable as it increases accuracy and saves labor cost and time. Generally, in manufacturing industries raw material get processed and transformed into products with variation in height, shape, etc. Further these products are packed in different boxes. And here sorting plays an important role. In earlier days manual practice were used such as man power for sorting which was very time consuming. But in recent scenario there is a high increase in production rate in manufacturing companies and therefore to minimize labour cost for such unskilled works and reduce the human errors in such work, industries are implementing PLC automation system. 

Figure 1: Basic Block Diagram of PLC [1]

 A. Block Diagram Description

CPU module

Central Processing Unit or CPU module is basically a microprocessor. The main function of CPU is to perform all the necessary process by monitoring the input and control program fed to it. The output of the program is then showed on output devices which can be motor, heater, conveyor belts as well as on the HMI interface and SCADA.

Power Supply

Their system normally works on the power supply of 24V which is used to power CPU module and input-output devices.

Input Module

Inputs are of several types like analog or digital, low or high frequency. They can also be represented by varying voltage, current. Other than this toggle switches, push buttons and relays can also be used to give open / closure type signals.

Memory

All the program information and control logic is stored in the memory module from where the CPU fetching the program instructions.

Interfacing HMI / SCADA

HMI stands for Human-Machine Interfacing and

SCADA stands for Supervisory Control and Data Acquisition. These are called as user interface which connect a machine with a person.

The main aim of the automation system is to develop a system having low maintenance, efficient, reliable and make system user friendly. Other than this our project will deal with increasing accuracy and speed of sorting system and making it cost effective.

The project main purpose is to sort boxes according to different height using sensors and conveyor belts interfaced with PLC. The project consists of one main logic used for sorting manually and automatically both. System also consists of one production logic to count the number of boxes sorted and tower light logic to know the system is working or not.

This system needs interacting at both input and output levels. The number of inputs and outputs are first identified, and appropriate sensors are selected. The sequence of operation is then validated and verified.

 II.  LITERATURE REVIEW

PLCs are normally primary piece of automation industry. Being proficient and solid in application including successive control and the synchronizing of procedures and auxiliary elements in the assembling, chemical and process industries.

The radical idea of sorting the boxes in industry was implemented by using programming language with Allen Bradley Rockwell software. In PLC software we make use of relay schematic diagram, with inputs (Limit switched, Push buttons etc.) presented by the relay contacts, and outputs (To Motor starters, device in harsh environment (Electrical noise, Vibration etc.) encountered in industry. To provide the flexibility, quickness and feasibility through software changes. It must be designed in proper ladder diagram by using relevant subroutine and call function for better understanding of the mechanism for maintenance purpose.

III. DESIGN OF SYSTEM A.Components

1)       Sensors

Sensors are easily interfaced to PLC and a variety of sensors can be used. System consists of 4 main sensors namely infeed sensors, product present sensors and two sensors on turn table. The infeed sensors sense the product entry at the entry conveyer belt and start the belt. Product present sensor presents the product reaches to the turn table. The other two sensors at the turntable senses the boxes according to height which in turn helps the turn table to turn in forward or reverse direction.

2)       Conveyor belt

The two main conveyor belts used in this system are feeder conveyor belt and main conveyor belt. Main conveyor belt further carries the object to turn-table.

3)       Object guider

Guider is a mechanical assembly that will prevent the misalignment of boxes. Guider will force to be at the centre of conveyor. The box sensed by start sensor has to pass through the diverter.

Misalignment of the boxes will cause boxes fall out of conveyor or problem can occur while pushing them. The continuous flow of boxes can be easily arranged using guider.

4)       Programmable Logic Controller

Ladder Logic and Operation (logic diagram): The automation of this system is programmed using Allen Bradley PLC systems. Programming is executed using 25 rungs.

We have also used HMI for better functionality and understanding.

 B. Sequence of Operation

This paper demonstrates the sequence of operation and control of sorting of boxes according to height. The block diagram of PLC schematic is shown in Figure: 2.

As show in block diagram, our system consists of feeder conveyor which is operated by start push button as well as HMI. The feeder conveyor carries the boxes of different height to the main conveyor belt. An infeed sensor is present at the start of main conveyor which senses the present of any box any turns on the main conveyor. The main conveyor then further carries the boxes to the height measuring system. Here we have used the turntable as a height measuring system.

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A product present sensor is present at the turntable which enable OSF (one shot falling) bit that cause the turntable to turn in certain direction for just 1 cycle. Other than this there are 2 other sensors present. First sensor checks for low height and enables the low height bit. Here a timer (TON) is present which gives a delay of 4sec to turn. Second sensor checks of high height boxes, but it will enable high bit only when the first sensor is also enabled. Now, if the box with low height appears, it will enable the low height bit and turn table will turn in reverse direction and the box will pass through left conveyor. When box of high height appears, then both low and high bit will be enabled, and the turntable will turn in forward direction and the box will pass through the right conveyor. An up-counter (CTU) present at the end of turntable monitors count for the number of total boxes sorted and passed through both right and left conveyors.

Figure 3: Flow-chart

Figure 4: Virtual Visualization of Project [4]

IV.  PLC Logic Diagram

Figure 5: PLC Logic 1     Figure 7: PLC Logic 3

Figure 6: PLC Logic 2     Figure 8: PLC Logic 4

 A. Description of Logic Diagram

1) Main Logic

Rung 0: Press auto toggle switch button to connect auto-bit relay so that system runs in continuous cycle.

Rung 1: Press manual toggle switch to operate the system manually.

Rung 2: Press Start push button or HMI push start to start the feeder conveyor until HMI stop, Stop or Emergency stop button is pressed.

Rung 3: Infeed sensor senses the presence of boxes at the entry of conveyor and starts the entry conveyor.

Rung 4: Product present sensor activates the oneshot falling bit. This unlatches Rung 3 relay, so it will start the conveyor only when the new parts come.

Rung 5: When 1^st sensor is ON and you do not press STOP or Emergency Stop then turn table moves in forward direction. Turn, delay for turn and Low  height bit is latched with 1^st sensor.

Figure 9: PLC Logic 5 Rung 6: 2^nd sensor present at turntable enable the turn bit.

Rung 7: Low height sensor senses the box for low height and enable the low height bit.

Rung 8: Turn is On and it delays the turn for 4 seconds.

Rung 9: If both the high height and low height bit are on, then the box has high height.

Rung 10: when part is sensed at left conveyor it activates the motion of the conveyor. Falling left exit sensor is used as a switch to break the latching of left conveyor.

Rung 11: As part enters the left conveyor, it will activate left side one shot falling bit. Rung 10 will be disconnected.

Rung 12: Above left side OSF triggers the low height bit and turn bit.

Rung 13: Turn, Delay for Turn and High height bit is ON without pressing emergency stop activicates the reverse direction of turn table.

  Rung 14: As parts enters the right conveyor, it

Figure 10: PLC Logic 6  activates right conveyor.

Rung 15: As part at right enters, it enables the right OSF.

Rung 16: Right sensor OSF activates the turn and high bit.

Rung 17: As part exits right than right exit OSF activates

Rung 18: As part exits left than left exit falling activates.

2)       Production Logic

Rung 19: A counter up (CTU), counts the boxes present at right as well as left exits.

Rung 20: Reset push button resets the counter.

3)       Tower Light Logic

Rung 21: When feeder conveyor is ON it activates green tower light.

Rung 22: When emergency button is pressed the light will activate the Red tower light.

Rung 23: When all the feeder conveyor, green tower light and red tower light is Off, Yellow tower light will be enabled.

4)       Status on HMI

Rung 24: It shows RUN indication on the HMI screen when the feeder conveyor is ON.

Rung 25: When feeder conveyor is Off, it will show STOP indication on the HMI screen.

5. PLC and I/O Table

 Table 1: Input  Table 2: Output

Table 4: Timer and Counter

Table 3: Memory

6. CONCLUSION

Allen Bradley Rockwell – Rslogix500 software along Factory I/O software is used to construct a general model for sorting of the boxes according to height for Industrial Control System where products are manufactured in bulk. This system is used to reduce the physical labour which makes the automation industries run more efficiently. This system can further be improved by observing and recording the company statistical analysis.

Reference

[1]  S. R. S. A. P. a. V. S. Darshil, “Development of a PLC Based Elevator System,” IEEE, pp. 1-7, 2008. 

[2]  A. D. R. K. R. M. Prof. Nilima Bargal, “PLC

Based Object Sorting Automation,” ISO 9001:2008 Certified Journal , vol. 3, no. 07 July 2016, pp. 103-108, 2016. 

[3]  S. F. Nakamura, ‘Structure analysis of logic control, IECON 2004, 2004. 

[4]  B. B.Riera, HOME I/O and FACTORY I/O: a virtual house and a virtual plant for control education, France: IFAC-PapersOnLine, 2017.