Development of an Automatic Plastic Spur Gear Moulding System

INTRODUCTION

The process of recycling plastics is the recuperating of waste or scrap plastic product and recovering the material to another useful product that may be similar or far different from its original state.  The Development of an Automatic Plastic Spur Gear Moulding System from Scrap Plastic Materials is an automation system designed and developed to fabricate plastic spur gears out of recyclable thermoplastic scrap materials specifically PET (Polyethylene terephthalate) bottles. The system will be employed by the use of Programmable Logic Controllers (PLCs) for flexible automation, effective costing, reduction of complexity, and efficiency of plant space.

BACKGROUND

 The production of plastic materials has increased widely ever since industrialization has begun. This is because plastics are cheap, light in weight, and also a type of material that is durable that can be easily and readily moulded different kinds of products that can be used in a variety of applications. PET or Polyethylene terephthalate is a very popular plastic in comparison with other valuable plastic materials. It is the type of plastic that is deemed              safe. PET bottles usually have embossed “1” denoting that it is a safe option. When this type of plastic is recycled, it can be used in many industrial applications such as in fabrics, strapping, and automobile parts. [1]

 Figure 1 below shows the most common product made of Polyethylene terephthalate and commonly called PET bottles.

Figure 1: PET Bottles

Nevertheless, to achieve an efficient recycling process that is also cost-effective, automation of the recycling process can be unheeded. Automation had made a huge difference in the industry nowadays especially in manufacturing and production. Automation simply means the utilization of the system of controls and technology to reduce human work necessity in producing materials or rendering services. With the introduction and existence of automation in a plant, human error can be eliminated. Total integration of automation places this steadiness into reliable practice and shelters the whole production line, from the receiving of raw materials, down to the production process, to filling and packaging, and up to delivery and shipment of products. [2]

The Programmable Logic Controller or commonly just termed as PLC is a special type of controller that is microprocessor-based that utilises a memory that is programmable and can able to store commands and instructions to perform functions such as timing, counting, logic, sequencing, and arithmetic to be able to control processes and machines. [3]

Figure 2 below shows the network diagram of the operation of a Programmable Logic Controller

Figure 2: PLC Operation

In the automation industry, Programmable Logic Controllers are usually used.  For example, in a heat treatment plant, control systems that are PLC based are used for hardening and tempering furnace. The effects of this automation are in the increase of efficiency in the process of hardening and tempering of bits or raw steel materials. Not only that but also lesser time and increase in production are observed as well as safety for the workers for the handling of machines and materials are reduced. Another advantage of using PLC in the industry is in the automation and monitoring of industrial crane where large drawbacks were reduced like reducing and eliminating mechanical fault, troubleshooting difficulties, wiring, and repair works. [2]

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The central processing unit of the PLC performs two programs: the operating system and the user program. The operating system categorizes all sequence, functions, and operations of the central processing unit that aren’t related to the control task. On the other hand, the user program is the combination of different functions which are needed to process a task for automation. This should be made by the user and must be downloaded to the central processing unit of the PLC.  The Figure below shows a typical example of a PLC.

Figure 3: OS and UAP of PLC

In today’s industrial automation period, there are many manufacturers of PLC that develop typical controllers in different ranges from small scale to high-end. Usually, they develop their own compatible software that will be used to control and program the hardware. With this, the language used in programming also varies from manufacturer to manufacturer. Basically, there are two types of PLC programming language: the text language and the graphical language and it is easy to understand the difference between both as per their names. Text language has two subtypes: Instructions List and Structure Text. On the other hand, Graphical Language has three subtypes: The Ladder Diagram, Functional Block Diagram, and the Sequential Function Chart. [4]

Industrial robots have been introduced over the past decade and with the advancement of technology, manufacturing industries are now adapting to this change. Types of industrial robots are classified according to their configurations. These types are namely: polar robots, cylindrical robots, delta robots, SCARA robots, cartesian robots, and articulated robots. Beside their configurations, robots are also classified according to their motion, control on the power supply, and physical characteristics. The figure below shows the 6 Major types of Industrial Robot according to their configurations. [5]

Figure 4: Types of Industrial Robot

PROBLEM STATEMENT

Industrial automation has gained significance in arrears to the rampant demand for an increase in productivity, maximum use of resources and efficient manpower. Due to the increase of use of plastics specifically PET bottles, there is a need to recycle in order to reduce waste and also maintain the threatened resources used in the production of new materials. Thus, there is a need for the development of an automatic system to produce a new product from scrap or waste plastic materials.

OBJECTIVES

• To create an automatic system that would create plastic spur gears from scrap material.
• To be able to use Machine Simulator 3 in creating the system and use Nirtec Easy PLC in creating the ladder diagram.
• To be able to connect the ladder diagram with the created system.

METHODOLOGY

 The Automatic Spur Gear Moulding System is designed to be a Programmable Logic Controller based system automated with the less human workload. The whole will be composed of three major stages each having several interrelated stages or processes. The first stage will be the collection of raw materials which is the plastic the pet bottles in preparation for melting in the furnace. The second stage is the moulding process to create the desired product which is the plastic spur gear. The third and last stage will be the drilling and packaging of the plastic spur gear. The last stage focuses on the Robotic part of the system. The driller robot and the gear stopper will have a linear robotic joint that performs translational and sliding movement.

The figure below shows the principle of Linear Robotic joint for the driller robot and gear stopper.

Figure 5: Linear Robotic Joint

 Figure 6 below shows the network diagram of the whole Automatic Spur Gear Moulding System that is divided into three stages along with its processes under these stages.

Figure 6: Network Diagram

 The whole system will activate by pushing the Start Push-button. It can be deactivated by pushing the Stop Button under it. Once the Start button is pushed, the conveyor for the box will automatically move heading to the furnace. It will only stop once the photocell sensor will detect it. The photocell sensor to detect the box is placed under the conveyor for bottles to stop the box directly where the bottle will drop for its conveyor. Upon detection of the box, the conveyor for the box will stop while the conveyor for the bottle will on as well as the work part creator for the bottle will also activate – producing three types of PET water bottle. A sensor is placed at the end of the conveyor to count the bottles passing through its laser. Once the 10 bottles have passed, the conveyor for the bottle and the work part creator will stop while the box conveyor will reactivate delivering the box with 20 bottles going to the furnace. A work part transporter is placed inside the furnace to transfer the box back to its original position while a work part destructor is also placed inside the furnace to destroy all bottles imagining it melts. This cycle continuous along. Theoretically, the bottle has been melted and goes through pipe going through the injector machine. A photocell sensor is placed inside the furnace to detect the bix going inside and activates the main conveyor for the mould and the work part creator for the mould. The mould will enter the injector area and imagining the injector to inject molten plastic into the mould. It will exit the injector machine going to the cooling area. The cooling area is provided with a photocell sensor to detect the mould passing through its laser and responsible for activating the spray water as the mould passes. The mould will pass 4 sprays as it exits the cooling area. Then the mould will enter the separator area where theoretically the gear will be taken out of the mould. It has a sensor inside where it will activate the workpart creator creating the gear and activating another conveyor. The mould exits on the adjacent side where the gear exits and it is destroyed. The gear created is transferred by the conveyor going to the drill. A sensor is placed under the drill to detect the gear that will cross and stops the conveyor and activates the gear stopper. Then the drilling operation will undergo for 5 seconds as programmed. Then the workpart modifier will turn the gear into gear with a hole. Once the cycle is done, the conveyor will then turn on again transferring the gears to the box waiting at the end of the line.

The figures below show the flowchart of the PLC operation for the Automatic Spur Gear Moulding System.

Figure 7: Flowchart Start to B

Figure 8: Flowchart Start to D

Figure 9: Flowchart D to End

RESULTS AND DISCUSSION

 The figure below shows the bird’s eye view for the Automatic Spur Gear Moulding System.

Figure 10: Automatic Spur Gear Moulding System

Table 1: Input Systems

 The table above shows all the input variables assigned to each component. All input variables are digital and Boolean.

Table 2: Output Systems

 The table above shows all the output variables assigned to each component. All output variables are also digital and Boolean.

Table 3: Sequence, Counter, and Timers

 The table above shows the sequence, counter, and timers used in the system. The Step is for the sequencing done in the drilling which does not require an address and is an integral type while the counter is long type yet they mean the same just in 32-bit while time is in Boolean. The sequence function was used in the step by step operation of the driller robot while the timer is used for the stop and start of the drill conveyor and the gear stopper. Also, timer is used for delays on the drilling work. On the other hand, counter is used on the counting of the collection of waste PET bottles.

 The figure below shows the first stage of the system from the Push Button, to the collection of the bottles and going to the furnace.

Figure 11: First stage of the System

 The figure below shows the Start and Stop push button switches. The start button will activate the whole system. It is latched in the program that once the start button is released, the system will still continue to work unless the stop button is pushed.

Figure 12: Start and Stop Push Button     

 The figure below shows the collection of waste or scrap plastic bottles. The photocell placed on the box conveyor will detect the presence of the box and stop the conveyor to activate the bottle creator. A sensor is also placed in the bottle conveyor to count the bottles passing through it. Once 10 bottles have passed, the box conveyor will move to transfer the box with bottles to the furnace.           

Figure 13: Bottle Collection Process

 The figure below shows the furnace where the waste plastic bottles will be melted. This furnace is connected through the injection machine through the connecting pipes where melted plastic will pass through.

Figure 14: Furnace

The figure below shows the beginning of the second stage of the system which is the entering of the mould in the injection. In this process, the melted plastic will be injected into the mould to form a plastic spur gear.

Figure 15: Molten Plastic Injector Machine

 The figure below shows the transparent view of the process of injection of the melted plastic in the mould. A photocell sensor is placed to detect the box passing through it that will activate the injection machine.

Figure 16: Molten Plastic Injection Process

 The figure below shows the hot mould entering the cooling are. The mould will be sprayed with a cooling agent as it passes through the sensor placed on the spray area.

Figure 17: Cooling Area

 The figure below shows the end of the second stage which is the separator machine where the gears are separated from the mould. The gears go to the conveyor for drilling while the mould goes to the adjacent side for stacking.

Figure 18: Mould-Gear Separator Area

 The figure below shows the gear from the separator machine arriving and stopping at the drilling robot with the help of the photocell sensor. This is the beginning of the last stage. The robotic process is focused on this area.

Figure 19: Detection of Gear          

 Next figure below shows the gear stopper that has been activated once the sensor detects and stops the gear. Its purpose is to hold the gear in place while drilling operation is going on.

Figure 20: Gear Stopper Activated

 The figure below shows the going down movement and the drilling process of the driller robot. It is programmed to drill for 5 seconds.

Figure 21: Drilling of Gear       

 The figure below shows the gear after the drilling process is done. The gear will have a centre hole on it. It will be the end product of this system.                                           

Figure 22: Gear with Hole

 Figures 23 and 24 below show the returning of the driller robot to its original position after the drilling process is done.  Also once the drilling process is done, the gear stopper will also be deactivated to allow the gear to go leave the drilling area.

                  Figure 23: Drill Released                                                 Figure 24: Gear Stopper Deactivated           

 Figures 25 below shows the plastic gear leaving the drilling area after the drilling process. It will go directly to the box waiting at the end of the conveyor as shown in figure 26.

Figure 25: Gear Leaving the drill

Figure 26: Finished Products

 The figure below shows the ladder diagram for the Automatic Spur Gear Moulding System

Figure 27: Ladder Program

In conclusion, the system utilises Programmable Logic Controller or PLC in monitoring the condition of the processes and also in controlling the switching of components and devices. The system will provide a more efficient and more productive system of instigating a plastic recycling plant with less or without human intervention and minimum power consumption. This system design is flexible thus, more features can still be added, and alterations of processes can easily be made through the easy changing of the ladder program.

BIBLIOGRAPHY