INDUSTRIAL PRODUCTION LINE AUTOMATION USING PLC SYSTEMs

Transcription

1 INDUSTRIAL PRODUCTION LINE AUTOMATION USING PLC SYSTEMs Report submitted in partial fulfillment of the requirement for the degree of B.S.c (Honor) In Electrical and Electronic engineering Under the supervision of Uz. Louay farouq & Uz. Samah Mohammed Hashim By Ahmed Omer Taha Ali To Department of Electrical and Electronics Engineering University of Khartoum July 2009

2 Dedication To my family for the lifelong encouragement, support and love & To my friend for all the good times we had together I dedicate this work I

3 Acknowledgment I would like to gratitude to the great god for all physical support he give to me during the project processes. Also I would like to thank Mr. louay Farouq and Mrs. Samah Mohammed Hashim for their patience, support and helpful advices. Thanks to my partner Mihdaaj Ushaari mahmoud for his faith and encouragement. Thanks to my family for all what they do for me among my previous life, and I wish to reward them as soon as I can. II

4 Abstract In the late sixties of the last century the American company general electric developed the programmable logic controllers (PLC) as an alternative to the complex relay control system in order to use it in its car production lines. These controllers showed very high efficiency in control systems and higher reliability in protecting the components being controlled. In addition to this, the latter improved characteristics made PLCs the most control system used in production Processes. The aim of this project is to illustrate the usage of PLC in automation of production lines and the utilization of its high capabilities to process input signals from several sensors. This is done by implementing a small model of the filling stage of a soft drinks production line as an application. Here several processes work in a sequential fashion, in this stage PLCs are used to maintain this sequence. III

5 س : ا مل س ت س ل تل ف أواخش انسز بد ي انقش ان بض اسزحذثذ ششكخ ج شال األيش ك خ ان زحك بد ان طق خ انقبثهخ نهجشيجخ كجذ م ن ظبو رحكى ان شح الد ان ؼقذ و رنك نإلسزفبدح ي هب ف انزحكى ثخطىط إ زبج يصب غ انس بساد انخبصخ ثبنششكخ. أثشصد هز ان زحك بد كفبءح ػبن خ جذ ا ف ظى انزحكى و يىثىق خ ػبن خ ف ح ب خ األ ظ خ ان زحكى ثهب ثبإلضبفخ نه ضاد األخشي انز رى اسزحذاثهب ثؼذ رنك انش ء انز جؼم ي هب أكثش أ ظ خ انزحكى اسزخذاي ب ف ػ ه بد اإل زبج. هذف هزا ان ششوع إن رىض ح اسزخذاو ان زحك بد ان طق خ انقبثهخ نهجشيجخ ف أر زخ خطىط اإل زبج و اإلسزفبدح ي يقذسرهب انؼبن خ ف يؼبنجخ اإلشبساد انذاخهخ ػجش انحسبسبد ان خزهفخ يزؼذدح اإلسزخذايبد و رنك ثأخز ىرج يصغش ن شحهخ انزؼجئخ نخط إ زبج ان ششوثبد انغبص خ كزطج ق نهزا اإلسزخذاو ح ث زى ػ م ػذح ػ ه بد ثشكم رسهسه إل زبج ان ششوة انغبص ف هز ان شحهخ رزى اإلسزفبدح ي ان زحك بد ان طق خ انقبثهخ نهجشيجخ ف حفظ هزا انزسهسم نهز انؼ ه بد حست رضاي يؼ. IV

6 Table of contents Dedication... I Acknowledgment... II Abstract... III المستخلص IV Table of contents. V Chapter 1: Introduction Objective Introduction to industrial automation Categories of automation Advantages and disadvantages of automation Automation tools Automated manufacturing Thesis layout. 4 Chapter 2: Theoretical Background the PLC automation technology methedology how a PLC operates The Siemens S7-200 PLC 7 2.4,1 Ladder logic PLC scan Basic requirements for PLC use Programming device Software Connector cables STEP 7--Micro/WIN Programming Package Using STEP 7--Micro/WIN to Create Your Programs Establishing a connection Downloading the Program Placing the S7-200 in RUN Mode or STOP mode Brushed DC electric motor Speed control Using the PWM (Pulse Width Modulation) Output Configuring the PWM Output Stepper motors Stepper motor features Stepper motor types Stepper motor operation Sensors Proximity detectors Inductive detection Capacitive detection Sensitivity of proximity sensors Photoelectric detectors Different detection systems. 29 Chapter 3: Design And The Implementation Of The model Sensor selection and placement Bottle status, conveyor V

7 3.1.2 Valve Sensor Bottle status, conveyor The filling machine arm The Valve Abnormal situations in the conveyor Conveyor Conveyor Starting and Stopping the system Timing and sequencing of the filling machine PLC protection The whole system Simulation Hardware implementation. 46 Chapter four : Results and Discussions Results Sequencing DC motors speeds Stepper motor timing and delay Valve timing Possible improvements The stepper controller and the PTO (pulse train output) Weight sensors. 49 Chapter five: project evaluation Conclusion Future work 50 References 51 Appendices Main program code Stepper motor subroutine Wiring diagram of design Appendix A Appendix B Appendix C VI

8 Chapter one Introduction Chapter one Introduction 1.1 Objective The project s aim is to illustrate the concept of industrial automation through a simple design of part of a soft drink production line automated by a PLC system. The requirements of the automated system are: 1. Start manually by external switch 2. Manipulate actions on the process according to the sensor readings as desired 3. Be able to automatically deal with abnormal situations that may occur in the process 4. Different processes in the system should be synchronized together 5. System should shutdown either manually by the external switch or automatically due to predetermined cause The design should include all the necessary steps taken by a control systems engineer to implement the automated system, the steps are listed below: 1. Studying the process to be automated 2. Developing an algorithm for the system to operate with 3. Proper selection of control equipment such as sensors and controllers 4. Connecting and placing these selected items properly in the system to meet optimum system performance 5. Developing a program code based on the suggested algorithm 6. Simulation of the automated system 7. Implementation of the system 1.2 Introduction to industrial automation Industrial automation is the use of robotic devices to complete manufacturing tasks. In this day and age of computers, industrial automation is becoming increasingly important in the manufacturing process because computerized or robotic machines are capable of handling repetitive tasks quickly 1

9 Chapter one Introduction and efficiently. Machines used in industrial automation are also capable of completing mundane tasks that are not desirable to workers. In addition, the company can save money because it does not need to pay for expensive benefits for this specialized machinery. There are both advantages and disadvantages for a company when it comes to industrial automation. Automation technology, if used wisely and effectively, can yield substantial opportunities for the future. There is an opportunity to relieve humans from repetitive, hazardous, and unpleasant labor in all forms. And there is an opportunity for future automation technologies to provide a growing social and economic environment in which humans can enjoy a higher standard of living and a better way of life. 1.3 Categories of automation Automated machines can be subdivided into two large categories, open-loop and closed-loop machines, which can then be subdivided into even smaller categories. Open-loop machines are devices that, once started, go through a cycle and then stop. Closed loop machines complete to the cycle described earlier then repeats it until it s stopped. 1.4 Advantages and disadvantages of automation Advantages commonly attributed to automation include higher production rates and increased productivity, more efficient use of materials, better product quality, improved safety, shorter workweeks for labor, and reduced factory lead times. Higher output and increased productivity have been two of the biggest reasons in justifying the use of automation. Despite the claims of high quality from good workmanship by humans, automated systems typically perform the manufacturing process with less variability than human workers, resulting in greater control and consistency of product quality. Also, increased process control makes more efficient use of materials, resulting in less scrap. Another benefit of automation is the reduction in the number of hours worked on average per week by factory workers. 2

10 Chapter one Introduction A main disadvantage often associated with automation is worker displacement. In addition to displacement from work, the worker may be displaced geographically. In order to find other work, an individual may have to relocate, which is another source of stress. Other disadvantages of automated equipment include the high capital to invest in automation, a higher level of maintenance needed than with a manually operated machine, and a generally lower degree of flexibility in terms of the possible products as compared with a manual system. 1.5 Automation tools Different types of automation tools exist: - ANN - Artificial neural network - DCS - Distributed Control System - HMI - Human Machine Interface - SCADA - Supervisory Control and Data Acquisition - PLC - Programmable Logic Controller - PAC - Programmable Automation Controller - Instrumentation - Motion Control - Robotics 1.6 Automated manufacturing Automated manufacturing refers to the application of automation to produce things in the factory way. Most of the advantages of the automation technology have its influence in the manufacture processes. The main advantage of the automated manufacturing are: more quality, reduce the lead times, simplification of production, reduce handling, improve work flow and increase the moral of workers when a good implementation of the automation is made. 3

11 Chapter one Introduction 1.7 Thesis layout Throughout the next chapters the details of the project are shown. The second chapter describes the components used in the project and how they were used. The design and implementation are detailed in the third chapter. Then the results of the automated system are shown and discussed in the fourth chapter. The conclusion reached and possible future works are discussed throughout the fifth chapter. 4

12 Chapter two Theoretical Background Chapter 2 Theoretical Background 2.1 The PLC in automation technology Control engineering has evolved over time. In the past humans were the main method for controlling a system. More recently electricity has been used for control and early electrical control was based on relays. These relays allow power to be switched on and off without a mechanical switch. It is common to use relays to make simple logical control decisions. The development of low cost computer has brought the most recent revolution, the Programmable Logic Controller (PLC) (see figure 2.1). The advent of the PLC began in the 1970s, and has become the most common choice for manufacturing controls. PLCs have been gaining popularity on the factory floor and will probably remain predominant for some time to come. Most of this is because of the advantages they offer. Cost effective for controlling complex systems. Flexible and can be reapplied to control other systems quickly and easily. Computational abilities allow more sophisticated control. Trouble shooting aids make programming easier and reduce downtime. Reliable components make these likely to operate for years before failure. Figure 2.1 5

13 Chapter two Theoretical Background 2.2 methodology PLCs are advantageous over normal computer as they were built for harsh industrial environment and have the facility for extensive input/output (I/O) arrangements. These connect the PLC to sensors and actuators. PLCs read limit switches, analog process variables (such as temperature and pressure), and the positions of complex positioning systems. Some use machine vision. On the actuator side, PLCs operate electric motors, pneumatic or hydraulic cylinders, magnetic relays, solenoids, or analog outputs. The input/output arrangements may be built into a simple PLC, or the PLC may have external I/O modules attached to a computer network that plugs into the PLC. 2.3 How a PLC operates PLCs consist of input modules or points, a Central Processing Unit (CPU), and output modules or points. An input accepts a variety of digital or analog signals from various field devices (sensors) and converts them into a logic signal that can be used by the CPU. The CPU makes decisions and executes control instructions based on program instructions in memory. Output modules convert control instructions from the CPU into a digital or analog signal that can be used to control various field devices (actuators). A programming device is used to input the desired instructions. These instructions determine what the PLC will do for a specific input. An operator interface device allows processing formation to be displayed and new control parameters to be entered.(see figure 2.2) Figure 2.3 6

14 Chapter two Theoretical Background 2.4 The Siemens S7-200 PLC The S7-200 is referred to as a micro PLC because of its small size. The S7-200 has a brick design which means that the power supply and I/O are on-board. The S7-200 can be used on smaller, standalone applications such as elevators, car washes, or mixing machines. It can also be used on more complex industrial applications such as bottling and packaging machines. Figure Ladder logic Ladder logic (LAD) is one programming language used with PLCs. Ladder logic uses components that resemble elements used in a line diagram format to describe hard-wired control. Figure 2.5 7

15 Chapter two Theoretical Background The left vertical line of a ladder logic diagram (figure 2.5) represents the power or energized conductor. The output element or instruction represents the neutral or return path of the circuit. The right vertical line, which represents the return path on a hard-wired Control line diagram, is omitted. Ladder logic diagrams are read from left-to-right, top-to-bottom. Rungs are sometimes referred to as networks. A network may have several control elements, but only one output coil. In the example program shown example I0.0, I0.1 and Q0.0 represent the first instruction combination. If inputs I0.0 and I0.1 are energized, output relay Q0.0 energizes. The inputs could be switches, pushbuttons, or contact closures. I0.4, I0.5, and Q1.1 represent the second instruction combination. If either input I0.4 or I0.5 is energized, output relay Q0.1 energizes PLC scan The S7-200 executes a series of tasks repetitively. This cyclical execution of asks is called the scan cycle. As shown in Figure 2.6, the S7-200 performs most or all of the following tasks during a scan cycle: - Reading the inputs: The S7-200 copies the state of the physical inputs to the process-image input register. - Executing the control logic in the program: The S7-200 executes the instructions of the program and stores the values in the various memory areas. - Processing any communications requests: The S7-200 performs any tasks required for communications. - Executing the CPU self-test diagnostics: The S7-200 ensures that the firmware, the program memory, and any expansion modules are working properly. - Writing to the outputs: The values are stored in the process-image output register are written to the physical outputs. 8

16 Chapter two Theoretical Background Figure Basic requirements for PLC use In order to create or change a program, the following items are needed: PLC Programming Device Programming Software Connector Cable See figure 2.7 Figure 2.7 9

17 Chapter two Theoretical Background Programming device A personal computer (PC), with STEP 7 Micro/WIN installed, can be used as a programming device with the S Software A software program is required in order to tell the PLC what instructions it must follow. Programming software is typically PLC specific. A software package for one PLC, or one family of PLCs, such as the S7 family, would not be useful on other PLCs. The S7-200 uses a Windows based software program called STEP 7-Micro/WIN32. The PG 720 and PG 740 have STEP 7 software pre-installed. Micro/WIN32 is installed on a personal computer in a similar manner to any other computer software Connector cables A special cable, referred to as a PC/PPI cable, is needed when a personal computer is used as a programming device. This cable allows the serial interface of the PLC to communicate with the USB interface of a personal computer. DIP switches on the PC/PPI cable are used to select an appropriate speed (baud rate) at which information is passed between the PLC and the computer. The DIP switches of the RS-232/PPI multi master cable are set as shown on figure 2.8. Figure STEP 7--Micro/WIN Programming Package The STEP 7--Micro/WIN programming package provides a user-friendly environment to develop, edit, and monitor the logic needed to control your application. STEP 7--Micro/WIN provides three 10

18 Chapter two Theoretical Background program editors for convenience and efficiency in developing the control program for your application. Computer Requirements STEP 7--Micro/WIN runs on either a personal computer or a Siemens programming device, such as a PG 760. The computer or should meet the following minimum requirements: - Operating system: Windows 2000, Windows XP (Professional or Home) - At least 100M bytes of free hard disk space - Mouse (recommended) Using STEP 7--Micro/WIN to Create Your Programs To open STEP 7--Micro/WIN, double-click on the STEP 7--Micro/WIN icon, or select the Start > SIMATIC > STEP 7 MicroWIN 32 V4.0 menu command. As shown in Figure 2.9, the STEP 7-- Micro/WIN project window provides a convenient working space for creating your control program. The toolbars provide buttons for shortcuts to frequently used menu commands. You can view or hide any of the toolbars. The navigation bar presents groups of icons for accessing different programming features of STEP 7--Micro/WIN. The instruction tree displays all of the project objects and the instructions for creating your control program. You can drag and drop individual instructions from the tree into your program, or you can double-click an instruction to insert it at the current location of the cursor in the program editor. The program editor contains the program logic and a local variable table where you can assign symbolic names for temporary local variables. Subroutines and interrupt routines appear as tabs at the bottom of the program editor window. Click on the tabs to move between the subroutines, interrupts, and the main program. 11

19 Chapter two Theoretical Background Figure Establishing a connection Click on the STEP 7--Micro/WIN icon to open a new project. Notice the navigation bar one can use the icons on the navigation bar to open elements of the STEP 7--Micro/WIN project. Click on the Communications icon (see figure 2.10) in the navigation bar to display the Communications dialog box. You use this dialog box to set up the communications for STEP 7--Micro/WIN. 12

20 Chapter two Theoretical Background Figure 2.10 This project uses the default settings for STEP 7--Micro/WIN and the RS-232/PPI Multi-Master cable. To verify these settings: 1. Verify that the address of the PC/PPI cable in the Communications dialog box is set to Verify that the interface for the network parameter is set for PC/PPI cable(com1). 3. Verify that the transmission rate is set to 9.6 kbps. 13

21 Chapter two Theoretical Background Figure 2.11 Double-click the refresh icon in the Communications dialog box. STEP 7--Micro/WIN searches for the S7-200 station and displays a CPU icon for the connected S7-200 station. Then select the S7-200 and click OK Downloading the Program Click the Download icon on the toolbar or select the File > Download menu command to download the program. (See Figure 2.12) then click OK to download the elements of the program to the S Figure

22 Chapter two Theoretical Background Placing the S7-200 in RUN Mode or STOP mode For STEP 7--Micro/WIN to place the S7-200 CPU in RUN mode, the mode switch of the S7-200 must be set to RUN. When you place the S7-200 in RUN mode, the S7-200 executes the program: 1. Click the RUN/STOP icon on the toolbar. 2. Click OK to change the operating mode of the S The S7-200 can also be put in RUN or STOP mode directly from the PLC itself. Figure Brushed DC electric motor Brushed DC motors are widely used in applications ranging from toys to push-button adjustable car seats. Brushed DC (BDC) motors are inexpensive, easy to drive, and are readily available in all sizes and shapes. -PRINCIPLES OF OPERATION The construction of a simple BDC motor is shown in Figure All BDC motors are made of the same basic components: a stator, rotor, brushes and a commutator. The following paragraphs will 15

23 Chapter two Theoretical Background explain each component in greater detail. Figure 2.14 Stator The stator generates a stationary magnetic field that surrounds the rotor. This field is generated by either permanent magnets or electromagnetic windings. The different types of BDC motors are distinguished by the construction of the stator or the way the electromagnetic windings are connected to the power source. Rotor The rotor, also called the armature, is made up of one or more windings. When these windings are energized they produce a magnetic field. The magnetic poles of this rotor field will be attracted to the opposite poles generated by the stator, causing the rotor to turn. As the motor turns, the windings are constantly being energized in a different sequence so that the magnetic poles generated by the rotor do not overrun the poles generated in the stator. This switching of the field in the rotor windings is called commutation Speed control Generally, the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. The direction of a wound field DC motor 16

24 Chapter two Theoretical Background can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors). The effective voltage can be varied by inserting a series resistor or by an electronically controlled switching device made of thyristors, transistors, or, formerly, mercury arc rectifiers. In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the "on" to "off" ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage "on" time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% "on" time, the average voltage at the motor will be 25 V. During the "off" time, the armature's inductance causes the current to continue through a diode called a "flyback diode", in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage "on" time is 100%. At 100% "on" time, the supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise. The S7-200 provides three methods of open loop motion control: - Pulse Width Modulation (PWM) -- built into the S7-200 for speed, position or duty cycle control - Pulse Train Output (PTO) -- built into the S7-200 for speed and position control - EM 253 Position Module -- an add on module for speed and position control The S7-200 provides two digital outputs (Q0.0 and Q0.1) that can be configured using the Position Control Wizard for use as either PWM or a PTO outputs. The Position Control Wizard can also be used to configure the EM 253 Position Module. When an output is configured for PWM operation, the cycle time of the output is fixed and the pulse width or duty cycle of the pulse is controlled by your program. The variations in pulse width can be used to control the speed or position in your application. When an output is configured for PTO operation, a 50% duty cycle pulse train is generated for open loop control of the speed and position for either stepper motors or servo motors. The built in PTO 17

25 Chapter two Theoretical Background function only provides the pulse train output. Direction and limit controls must be supplied by your application program using I/O built into the PLC or provided by expansion modules. The EM 253 Position Module provides a single pulse train output with integrated direction control, disable and clear outputs. It also includes dedicated inputs which allow the module to be configured for several modes of operation including automatic reference point seek. The module provides a unified solution for open loop control of the speed and position for either stepper motors or servo motors. To simplify the use of position control in your application, STEP 7--Micro/WIN provides a Position Control wizard that allows you to completely configure the PWM, PTO or Position module in minutes. The wizard generates position instructions that you can use to provide dynamic control of speed and position in your application. For the Position module STEP 7--Micro/WIN also provides a control panel that allows you to control, monitor and test your motion operations Using the PWM (Pulse Width Modulation) Output PWM provides a fixed cycle time output with a variable duty cycle. The PWM output runs continuously after being started at the specified frequency (cycle time). The pulse width is varied as required to affect the desired control. Duty cycle can be expressed as a percentage of the cycle time or as a time value corresponding to pulse width. The pulse width can vary from 0% (no pulse, always off) to 100% (no pulse, always on). See Figure 9-1. Since the PWM output can be varied from 0% to 100%, it provides a digital output that in many ways is analogous to an analog output. For example the PWM output can be used to control the speed of a motor from stop to full speed or it can be used to control position of a valve from closed to full open. Figure Configuring the PWM Output To configure one of the built-in outputs for PWM control, use the STEP 7--Micro/WIN Position Control wizard. To start the Position Control wizard, either click the Tools icon in the navigation bar 18

26 Chapter two Theoretical Background and then double-click the Position Control Wizard icon, or select the Tools> Position Control Wizard menu command. (See Figure 2.16) Figure a window then pops up with two options to choose from, the first option is chosen for PWM or PTO operation. (figure 2.17) Figure Then another window opens which asks to which output is the motor going to be connected. The S7-200 PLC gives two outputs for such operation (Q0.0 and Q0.1) (see figure 2.18) 19

27 Chapter two Theoretical Background Figure after specifying the output a new window opens which decides whether the chosen output operates on PWM or PTO. (See figure 2.19) Figure

28 Chapter two Theoretical Background -the PWM subroutine block then appears in the instruction menu and was dragged into the program block as shown on figure Figure 2.20 The PWM subroutine must be excited in order to start operation, this is done by the external start switch which is connected to I0.0 as show on figure The Cycle input is a word value that defines the cycle time for the PWM output. The allowed range is from 2 to units of the time base (microseconds or milliseconds) that was specified within the wizard. The Duty Cycle input is a word value that defines the pulse width for the PWM output. The allowed range of values is from 0.0 to units of the time base (microseconds or milliseconds) that was specified within the wizard. The Error is a byte value returned by the PWMx_RUN instruction that indicates the result of execution. 21

29 Chapter two Theoretical Background 2.6 Stepper motors Stepper motors are type of DC motors that are commonly used. Stepper motors provide considerable advantage over typical DC motors as they may be used for precise positioning in a wide range of applications including robotics, automation, printers, copy machines rollers and disk drivers. Stepper motors provide open-loop, relative position control. Open loop means that, when you command the motor to take 42 steps, it provides no direct means of determining that it actually did so. The control is relative, meaning that there is no way to determine the shaft position directly. You can only command the motor to rotate a certain amount clockwise or counter-clockwise from its current position. These "commands" consist of energizing the various motor coils in a particular sequence of patterns. Each pattern causes the motor to move one step. Smooth motion may be obtained from presenting the patterns in the proper order Stepper motor features: Stepper motors provides a number of valuable features such as: Excellent rotational accuracy. Large torque. Small size. Work well over a wide range of speeds. Can be used for motion or position control. 22

30 Chapter two Theoretical Background Stepper motor types: Stepper motors are available in two types: 1) Bipolar motors, with two coils. These have four wires on them. They are tricky to control because they require changing the direction of the current flow through the coils in the proper sequence. 2) Unipolar motors (used in project). These have six or eight (or sometimes five) wires, and can be controlled from a microprocessor. A Unipolar stepper motor has four fixed coils arranged around a magnetized rotor, as shown on figure. Typically, the coils are arranged in two centre tapped pairs, on opposing sides of the motor. Driving current through any coil will cause the rotor magnet to be attracted to it, and by sequencing the drive current though each coil in turn, the motor can be made to rotate continuously. Higher torque can be achieved if two coils are energized at a time, and by alternating between one and two coil drive states, half stepping mode can be realized. Stepper motors vary in the amount of rotation delivered per step. They can turn as little as 0.72 degree to as much as 90 degrees per step. The most common motors are in the 7.5 degrees- to 18 degrees-per-step range. Many have integral reduction gear trains so that they have even higher angular resolution. Because the motors are openloop, if you do manage to mechanically overwhelm the motor and turn the shaft to a new position, the motor will not try to restore itself to the old position. 23

31 Chapter two Theoretical Background Figure 2.21 unipolar stepper motor coils configuration Stepper motor operation To illustrate this, let s consider the unipolar motor( shown in figure 2.22 below). Say that it is required to rotate the permanent magnet rotor four steps in a clockwise direction. Figure 2.22 unipolar motor operation At first look, it seems that the simplest way to do this is by energizing coil a so that the permanent magnet rotor is attracted to it. Then energizing coil b and cutting the current from coil a. the energizing coil c and cutting the current from coil b and so on. By this sequence the rotor will rotate in a clockwise direction, to reverse the rotation just apply voltage to coils in a reverse sequence. The method mentioned above is simple but doesn t afford the maximum possible torque. Maximum torque is achieved by energizing two coils at a time so that the rotor is always between the two coils. Energizing sequences are given in table.1 and table.2 below. 24

32 Chapter two Theoretical Background Step Coil a Coil b Coil b Coil c Table.1 Full stepping half torque sequence Step Coil a Coil b Coil b Coil c Table.2 Full stepping double torque sequence Both methods are called full-stepping approach because the rotor steps from coil to coil or the midpoint of two coils to the other midpoint. This is in contrast to half-stepping where it possible to move the rotor from one coil to the midpoint next to that coil. This operation mode is demonstrated in table.3. The major drawback of this mode is that the torque is not constant; when the rotor steps to the midpoint between two coils it experienced double the torque when it is attracted by a single coil. In the first case the current running through two coils provides the necessary power for the rotor holding torque. 25

33 Chapter two Theoretical Background Step Coil a Coil b Coil b Coil c Table.3 half stepping sequence 2.7 Sensors Proximity detector Proximity detectors operate by remote control without physical contact with the object detected. They are thus a common feature of automated systems in all sectors of industry (mechanical, foodstuff and chemistry). There are two main types of proximity sensors, inductive and capacitive. Figure 2.23 show a proximity sensor 26

34 Chapter two Theoretical Background Figure Inductive detection The main component of an inductive detector is an oscillator whose windings form the sensitive surface. An ac magnetic field is created at the front of this surface. When a metal screen is placed in this field, induced currents form an additional load which causes oscillations to stop. Figure Capacitive detection The main component of a capacitive detector is an oscillator whose capacitors form the sensitive surface. When a conductive or insulating material with a permittivity > 1 is placed in this field, it modifies the coupling capacitances and causes oscillations. 27

35 Chapter two Theoretical Background Figure 2.25 Advantages of this type of device - No wear, possibility of detecting fragile, freshly painted objects, etc... -Ideal for electronic automation systems -Consideration of short duration information. -Excellent withstand to industrial environments -Lifetime not affected by the number of operating cycles Sensitivity of proximity detectors The sensitivity of both sensors may be adjusted in order to read objects within a specified range. - This adjustment is done by changing the potentiometers value as shown in figure Figure

36 Chapter two Theoretical Background Photoelectric detectors These are the best known detectors: their possibilities (large range, detection without contact and of all kinds, diversity of mounting and accessibility thanks to fiber optics, etc...) make them the most popular sensors at present in a wide variety of areas. Composition - These detectors are made up of a light emitter, often of a light emitting diode (LED) which is able to emit radiation invisible to the human eye. Moreover its modulated emission guarantees a high degree of immunity to stray light as well as a virtually unlimited lifetime. Figure These detectors are made up of a light emitter, often of a light emitting diode (LED) which is able to emit radiation invisible to the human eye. Moreover its modulated emission guarantees a high degree of immunity to stray light as well as a virtually unlimited lifetime. They are also fitted with a light receiver, in many cases a phototransistor which is a transistor switching due to the presence of light. The light emitter and receiver can be housed in the same box or in two separate boxes according to which detection technique is used. -Shaping and amplification of the informational image is the task of electronic components either built into or separate from the sensor (Schmitt trigger and operational amplifiers). The object is detected when it causes the intensity of the light beam to vary on the receiver or when it interrupts this beam Different detection systems Photoelectric sensors detect objects in two manners 1. Detection by sending back the light emitted 2. Detection by blocking the light emitted 29

37 Chapter two Theoretical Background In this type three systems are available - Barrier (used in project) - Reflex - Polarized reflex The barrier system consists of a transmitter device and a receiver device mounted facing each other. When an object passes between the two devices it blocks the light from reaching the receiver which in turn gives a signal. Figure

38 Chapter three Design And The Implementation Of The model Chapter three Design And The Implementation Of The model Several industrial plants were visited which included Coca Cola, Vita and Sigmatau. They helped in understanding the nature of the automated processes and its implementation issues. These issues start from the proper selection of required automation equipment such as sensors and controllers to the required sequencing and timing of the inter-process operations and how to combine all of these aspects into one coherent system. The coca-cola and vita visits helped in studying the soft drink production line. At first it was intended to design a PLC automation system for such a production or part of it. But due to the limited financial resources as well as the inability of verifying the design, it was decided to build a small simple model of part of the production line then apply an automation system to it. This model represents the filling stage of the production line. In this stage the following operations occur:- 1. the empty bottles enters the filling machine from a conveyor which is moving at a constant speed, 2. after entering the filling machine the bottle rests in one of four arms (at right angles to each other) mounted on a stepper motor which moves the empty bottle precisely to where the valve is and stops, 3. the valve then opens for a predetermined time quantum and closes, 4. then the arm moves the bottle to the other end of the filling machine where it exits via the second conveyor, 5. sometimes an abnormal situation occurs were a bottle may fall while on the conveyor so it is to be removed using a solenoid arm, The intended design is as follows. First conveyor 1 starts moving as it is influenced by dc motor which it s speed is controlled moving the empty bottles towards the filling machine at constant rate and equally spaced at a predetermined distance to avoid jamming at the filling machine as well as 31

39 Chapter three Design And The Implementation Of The model maintaining process synchronization, this will be described later. Then as an empty bottle approaches the filling machine it s position should be sensed as whether it s standing up or lying down, if it s standing up it should be let into the filling machine otherwise it s removed by the solenoid arm. If the bottle was let in then the stepper controlled arm should move this bottle towards the valve location at some predetermined speed to meet process synchronization. The bottle position is then sensed to verify it had reached the valve then the valve opens for a predetermined amount of time and closes. Meanwhile when the first bottle is under the valve a second bottle enters the filling machine and rests at the next arm. Then this arm moves the second bottle toward the valve and since these arms move together the first bottle moves towards its exit point (conveyor 2). At the end of conveyor 2 the exiting bottles are counted to keep record of the number of filled bottles. Sometimes some bottles may leave the filling machine empty or partially filled, this occurs due to a valve fault. This issue is to be overcome by sensing the status of the bottles and either they are removed or let through. The process is to be started manually by the operator using a switch and then terminated either automatically or manually. Manual termination maybe due to some fault in one or more of the machines of the production line. Automatic termination is when the number of filled bottles reaches some predetermined value according to the supply and demand conditions. 3.1 Sensor selection and placement Proper selection and installment of condition sensing equipment are a critical task to enhance optimum system performance. This section gives an insight to the how the used sensors were designed to indicate all necessary information required by the PLC in each stage Bottle status, Conveyor 1 In this stage the empty bottles are to be sensed to whether they are standing up or lying down. The latter situation occurs very rarely in the conveyor due to the slow conveyor speed and relative large weight of the bottles, in the vita factory the filling machine was placed slightly higher than the conveyor so that lying bottles would just slide under it to some collection basket. Two capacitive proximity sensors were chosen for this case after testing and yielding good results in the laboratory. The tests showed that this sensor could detect glass presence within a specific distance range. 32

40 Chapter three Design And The Implementation Of The model The two sensors were placed on top of each other as shown schematically on figure 3.1. The bottom sensor detects the bottle presence and the top one indicates that if this bottle is standing up or not. Throughout the rest of this text the bottom and top sensors will be referred to as S1 and S2 respectively for convenience. S1 and S2 are connected to the PLC inputs I0.1 and I0.2 and will provide a high logic state to these inputs when an object is sensed. In the program code they resembled as normally open switches. (See appendix A for program code) Figure Valve sensor Here the empty bottle should be sensed that it has reached the valve in order to open the valve. For this case two techniques have been introduced and tested but one of them was used. The first technique suggested placing light reflectors on all four arms and one photoelectric reflex sensor on the side opposite to the valve. When one arm reaches the valve location the adjacent arm will face the sensor, as all four arms rotate together, thus resulting in a sensor reading. This technique was easy in implementation and yielded good results in indicating the arm position but it had one drawback, it only showed that one arm was at the valve location but not showing whether that arm had a bottle or was the bottle already filled or not. 33

41 Chapter three Design And The Implementation Of The model The second technique helped overcome the first issue by using a capacitive proximity sensor instead placed below the valve as shown on figure 3.2. The sensor showed the existence of a bottle underneath the valve. Throughout the rest of the text this sensor will be referred to as S3. This sensor is connected to I0.3 of the PLC and resembled in program code as normally open switch. Figure Bottle status, conveyor 2 In the third stage the objective is to sense the number of exiting full bottles. In the vita factory this was a real problem and was done literately manually, a worker sat next to the second conveyor holding a specimen bottle. If any off the bottles in the conveyor mismatched the specimen s level the worker removes the bottle. For this stage a polarized photoelectric transmitter/receiver sensor was placed as shown on figure 3.3. Assuming that the filled bottle contained an opaque liquid, as in most of the cases, the light will be blocked from reaching the receiver thus indicating a filled bottle. Laboratory tests were done to verify the theorem and yielded good results. For the rest of the text this sensor will be referred to as S3, it s connected to I0.4 of the PLC and resembled as a normally open switch in the program code. 34

42 Chapter three Design And The Implementation Of The model Figure 3.3 The removal techniques is discussed in section The filling machine arm As was described earlier the four arms in the filling machine are tied as one mechanism that routes the bottles through the filling machine. Every time a bottle enters the filling machine the arm mechanism rotates by 90 degrees moving an empty bottle to the valve and a full one to conveyor 2. This rotation action occurs at a predetermined constant speed as to hold for the whole process synchronization. The operation of the stepper motor was fully described in chapter 2, next is shown how the desired mode of operation is designed. The stepper motor used makes a full revolution of 360 degrees in 48 steps that is 7.5 degrees per step. Therefore 90 degrees is done by moving 12 steps. Each of these steps was excited by a pulse to one of the stepper inputs as was described in chapter 2, the stepper inputs are to be connected to the PLC outputs Q0.4 to Q0.7 indirectly via protection relays. The protection relays are discussed later. The length of each pulse determined the speed and was calculated as follows. 35

43 Chapter three Design And The Implementation Of The model Desired speed for 90 degrees revolution (12 steps) = 4 seconds Time for 1 step = 4/12 =0.25 seconds length of one pulse = 0.25 seconds = 250 millisecond frequency of the pulse switching between outputs = 1/0.25 = 4 Hz In order to implement the above requirements using Microwin software a separate program was written to control the stepper motor and is called from the main program as a subroutine. This subroutine is excited or called when S1 and S2 indicate a bottle has entered the machine. The logic of this subroutine is shown in the algorithm in figure

44 Chapter three Design And The Implementation Of The model 2 capacitive proximity sensors NO Bottle entered? YES Call stepper subroutine Clear counter Put pulse on line 1 for 0.25 seconds Put pulse on line 2 for 0.25 seconds Put pulse on line 3 for 0.25 seconds Put pulse on line 4 for 0.25 seconds Increase counter by 1 NO Counter = 3 YES Exit subroutine Figure

45 Chapter three Design And The Implementation Of The model The software implementation for such logic is as follows. 1. First a subroutine block must be inserted into the main program, this block is dragged from the instruction menu under call subroutines. See figure 3.5. Figure 3.5 From the figure it s shown that this subroutine is initiated by I0.1 and I0.2 which are the two capacitive proximity sensors S1 and S2 respectively. 2. Next an icon at the bottom of the page labeled SBR_0 navigates to a new window to write the subroutines code. See figure 3.6. Figure 3.6 Note the icon on the right PWM0_RUN, this is the subroutine for the PWM operation discussed earlier but is locked and the user may not modify it unlike a normal subroutine. To construct the loop the simple FOR instruction was used to repeat the loop three times. The FOR instruction was dragged from the instruction menu from under Program control. See figure

46 Chapter three Design And The Implementation Of The model Figure 3.7 The INIT field shows the starting count number and FINAL shows the final count number. The INDX field species a memory address to store current count value in. Next timers were used to control the output pulse length. Each timer introduced a delay of 0.25 seconds before switching the pulses between the 4 lines. For program code see appendix A and appendix B. 3.3 The valve The valve was programmed to open for 2 seconds when the S3 reads a bottle and then closes. The 2 seconds seems as a small amount of time to fill a bottle but because the liquid is pumped at very high pressure 2 seconds is fairly enough. This is not just a clueless assumption but a fact observed during the field visits. The control of the valve was very simple compared to the control of the dc motor and dc stepper motor. The input from the sensor enables a timer which in turn activates the output to the valve for 2 seconds. For program code see appendix A 39

47 Chapter three Design And The Implementation Of The model 3.4 Abnormal situations in the conveyor. As was described earlier two abnormal situations may occur in the conveyors. Next is described how these behaviors are dealt with Conveyor 1 In this conveyor the problem faced was a bottle lying down. It was shown earlier how this situation is sensed by the two sensors. When these two sensors indicate a falling glass a solenoid arm, which moves across the conveyor, removes the bottle. The solenoid arm is connected to the output Q0.3 of the PLC which is activated only when I0.1 reads ON (bottom sensor) and I0.2 reads OFF (top sensor). The placement of the arm is shown below in figure 3.8. Figure Conveyor 2 The situation of a lying down bottle would not occur in the second conveyor as it was designed to operate at lower speed compared to conveyor 1 for reasons described later. The problem faced here is an empty bottle or partially filled bottle, this may occur due a valve fault which occurs very rarely. This situation is solved by introducing an electromagnet controlled gate placed on the conveyor as shown on figure 3.9. The gate is connected to Q0.3 output from the PLC. When the sensor reads a full bottle it activates the output Q0.3 in order to open the gate for that bottle to pass, otherwise the bottle is discarded from the conveyor. 40

48 Chapter three Design And The Implementation Of The model Figure Starting and stopping the system To start the system a switch was designed to be manually closed (put on ON state). This switch is connected to I0.0 of the PLC and promotes the activation of the outputs Q0.0 and Q0.1 which are connected to the DC motors moving the conveyors as was shown earlier. To stop the system manually the same switch is opened and the whole system then terminates, this action is done by using the STOP instruction which is activated by opening the manual switch. The STOP instruction causes a transition in the PLC from RUN mode to STOP mode thereby terminating the whole process. For the system to stop automatically a counter is assigned to count the number of full bottles exiting through conveyor 2, when this counter reaches a predetermined value it activates the STOP output. The counter was set to activate STOP when 100 bottles were counted, the counter itself was incremented with each reading of the photoelectric sensor. In the program the counter is first reset by I0.0 (manual switch) and incremented by I0.4 (photoelectric sensor) 3.6 Timing and sequencing of the filling machine It was earlier calculated that the 90 degree revolution of the arm mechanism took 4 seconds, and the arm then stayed still for 2 other seconds under the valve. That is a total of 6 seconds, this means that the next bottle should about 4-6 seconds apart from the first one. That is the second bottle should 41

49 Chapter three Design And The Implementation Of The model enter the filling machine and rest in the available arm while the first bottle is being filled. A difference of 5 seconds was designed to be the time interval at which successive bottles entered the filling machine. How this time interval was attained was the tricky part and is described below. First a distance between two successive bottles should be defined, this distance should be just big enough so that a falling bottle may not interrupt other bottles. An adequate distance of 0.25 meters was decided. Therefore to obtain a time interval of 5 seconds the speed of conveyor 1 should be 0.25 meters per 5 seconds, that is 0.05 meters per second. Another aspect in the timing design was that of the initialization of the stepper motor. As it was shown the rotation action is excited by the reading of the two sensors, S1 and S2. This causes the rotation to start before the bottle rests in an arm because the sensors are placed before the filling machine at a distance of m. This spacing was designed to give adequate space for the arm to move freely and not disturb the sensor readings. This problem was solved by introducing a time delay before starting the rotation. Since the conveyor is moving at 0.05 meters per second the bottle will rest at the arm after 2.5 seconds from passing the sensors (time = distance / speed). Therefore the time delay was chosen to be 3.5 seconds (2.5 seconds + 1 second for the valve to close) and was programmed using a timer that is excited by the 2 sensors which in turn calls the stepper subroutine after 3.5 seconds. 3.7 PLC protection Although PLCs are designed to stand the harsh conditions of the industrial plants they must still be protected from electrical damage especially from inductive loads such as motors. Inductive loads may damage the PLC because of their feedback current, thus they are supplied by an external source (see figure 3.10). This external source is connected to the motors with relays and these relays are energized by the PLC outputs. Next the PLC outputs current was also provided by an external source. This was done although the PLC had an internal current source (see figure 3.10) so as not to draw much current from the PLC thereby causing over heating of the PLC. 42

50 Chapter three Design And The Implementation Of The model Figure The whole system Throughout the previous sections in this chapter every part of the process was explained. Although some hints may have been shown earlier to how some parts are related to others, in this section it is shown how all these parts are grouped together to form the whole process. The algorithm on figure 3.11 shows the whole process. 43

51 Chapter three Design And The Implementation Of The model start External switch state OFF No Operation / Terminate whole process ON OFF Start conveyor 1 Start conveyor 2 Clear bottle counter Sensor 4 staus OFF YES Sensor 1 status Open gate ON NO Activate arm to remove bottle OFF Sensor 2 status Increment bottle counter ON ON Wait for 3.5 s then rotate arm for 90 degrees Counter = 100 YES No Operation OFF Sensor 3 status Terminate whole process ON Open valve and start timer End Close valve YES Timer = 2 s NO No Operation Figure

52 Chapter three Design And The Implementation Of The model Remarks on the algorithm -the details of each independent procedure were shown earlier like for the stepper motor, therefore the reader should look back into the previous sections for the detailed logic. As was mentioned above this algorithm shows the interconnection of the system. -note that the algorithm states that the check for S3 occurs only after the 90 degrees revolution, this was intended to remove the ambiguity of whether the bottle under the valve was the filled bottle or a new one. In the program code this issue was solved by merging the valve operation within the stepper motor s subroutine. -also the status of sensor 2 is checked only if S1 reads an object unlike sensor 1 and sensor 4 which are checked continuously. For whole program code see appendix A For the connections of the system see appendix C 3.9 Simulation Unexpectedly the simulation of the design turned out to be one of the most tedious stages of the project due to the following reason. The Siemens Company never supplied a software simulator with its product, so a free license simulator that was found in the laboratory was used. This simulator did not have many essential instructions built in it such as the subroutine and loop instructions which were used extensively in the program as was shown earlier throughout this chapter. In this section it is shown how the project was simulated although of the previously mentioned facts. The available simulator was used as follows, 1. The outputs to the two DC motors were changed from PWM operation to normal operation as simple contactors. Also the four outputs to the stepper motor were substituted for one output which was Q0.5 to operate as a normal contactor, and the input from sensor 3 was removed. These two actions were done to verify that the logic sequence will call any of the subroutines as desired by the design. 2. Then the configuration of the simulator was matched to design, this was done by changing CPU TYPE to S XP and CPU no. to 1 3. Then the program code was loaded into the simulator 45

53 Chapter three Design And The Implementation Of The model 4. The simulator was then put on run mode 5. Finally by manipulating input values the outputs were observed for all possible input patterns by observing the sequencing of operations as well as their timing Hardware implementation The hardware implementation was the disappointing stage during the lifetime of the project as it was not funded. First, the PLC, its connecting cable, and all four sensors were available in the laboratory. Then individual efforts helped in acquiring the 2 DC motors and the stepper motor. Then due to the limited resources, the parts of the process (conveyor, valve, solenoid arm etc) were not acquired. The valve, solenoid arm and electromagnetic gate were modeled as LEDs connected to the PLC outputs shown earlier. The conveyor was not built thus the required output speed of the DC motor to attain a conveyor speed of 0.05 meters per second could not be calculated as discussed earlier. Therefore only a flag was connected to the motors shafts to observe there speed. All necessary relays and power sources were available in the laboratory and were connected as it was suggested in the design. A 24 volts DC source was used to drive the PLC outputs as well as the stepper motor which operated under 24 volts, and a 9 volts DC source was used to drive the two DC motors. Finally the physical model was built by substituting the unavailable parts as was shown and put into action. For connections see appendix C 46

54 Chapter four Results and Discussions Chapter four Results and Discussions 4.1 Results After the connection of the physical system that was shown in the previous chapter, the system was put into action and yielded relatively good results but still had some flaws. These results and flaws are discussed throughout this chapter Sequencing First the sequencing of the operations was perfect. The outputs from the PLC were excited as desired according to different input patterns, these input patterns were all taken into consideration in chapter 3. - The two DC motors started and stopped when the start switch was ON and OFF respectively. - The stepper motor took its 90 degrees revolution when S1 and S2 where on. - The LED connected to Q0.2 (arm) lighted when only S1 was ON - The LED connected to Q0.3 (valve) lighted when S3 was ON - The LED connected to Q1.0 (was) lighted when S4 was ON - The system shutdown automatically after 100 readings for S4. This part was tedious in testing as S4 was put on ON state then OFF state exactly 100 times to test the system. These results verified that the logic of the program code drives the application in the desired sequence of events DC motors speeds Second the speeds of the two motors were observed. This test was done by putting identical flags in both motors and counting how many revolutions each flag took in 10 seconds. The result showed that DC motor 1 was faster than DC motor 2 as desired, but these speeds were not measured Stepper motor timing and delay Then the speed of the stepper motor was tested. The results showed that the time for a 90 degree revolution was slightly larger than that desired. The error was not constant throughout the tests and was in the range of 1-4 seconds approximately, the term approximately was introduced because the timing measurement was done by a stop watch thus not accurate but it was obvious that there was an error which was not constant. 47

55 Chapter four Results and Discussions This timing error was not due to program fault but due to the mechanical nature of the physical PLC outputs. After deeper investigation in the PLC structure it was found that the outputs of the PLC were relays which are energized by internal small signals from the microprocessor of the PLC. These relays could not adapt to the high switching frequency of the pulses suggested by the design which was 0.25 seconds. A test was made to verify this point, the pulse times were slightly increased (decreasing motor speed) by changing the program code and it was observed that the error has been reduced but not eliminated. The pulse time could only be slightly increased as to keep the stepper motor from heating up thus being damaged. This fact was retrieved from the stepper motor s manual itself which suggested that the motor should be operated within a specific range of speeds, slower speeds may damage the motor as more current is applied to it. Unfortunately before a solution could be figured for this issue the stepper motor was damaged due to short circuit that resulted from improper wiring. How this issue may be solved is discussed in the next section. Note that this would have not been an issue in the outputs Q0.0 and Q0.1 as they were specially designed with high-speed switching capabilities. Also a delay of 2.5 second occurred before the stepper started operation as desired, Valve timing The LED on Q0.3 (valve) showed good results in its timing, it started after S3 was ON and closed after exactly 2 seconds. 4.2 Possible improvements In this section it s shown what improvements could be added to the design and how these improvements upgrade the performance of the system The stepper controller and the PTO (pulse train output) A stepper controller is a device that receives a specific number of pulses from an external source through one line, then this controller moves the stepper motor by a number of steps equal to the number of the pulses. It does this by distributing the pulses among the four motor lines in increasing order. To clarify this point suppose that the input was 6 pulses, the controller then puts a pulse in each of the lines in the following sequence, Also the width of the input pulses is equal to the width of each output pulse. A pulse train is simply a sequence of pulses of 50% duty cycle as shown in figure 4.1. Figure

56 Chapter four Results and Discussions The S7-200 as was shown earlier supports pulse train output (PTO) through Q0.0 and Q0.1. Then this output could be used as an input to the stepper controller. This method totally eliminates the timing error described in section as the stepper controller was specially designed for accurate positional and speed control. Another advantage of this method is that it reduces the number of outputs from the PLC needed to drive the stepper. The stepper controller was not used in the design because of the inability to acquire it Weight sensors An analogue weight sensor could be used instead of the photoelectric sensor to sense the status of the exiting bottles. This weight sensor is advantageous over the photoelectric sensor because the latter one measures only the presence of a full bottle but cannot differentiate between a partially full bottle or no bottle, but the weight sensor provides the ability to differentiate between a full bottle, an empty or partially filled bottle, and no bottle. Thus if a weight sensor was used the logic of operation may be improved as follows. Instead of opening the gate for each full bottle the photoelectric sensor reads, the gate will be normally open and closes when a partially filled bottle is read by the weight sensor. The reader should note that an analogue weight sensor provides an analogue signal relative to the measured weight, such an input must be connected to the PLC indirectly through an analogue input module. Both the analogue weight sensor and input module could not be acquired for use in the project. 49

57 Chapter five Project Evaluation Chapter 5 Project Evaluation 5.1 Conclusion After the project was fulfilled in all stages (design-simulation-implementation) several facts were concluded. Next is shown why these conclusions were reached. 1. In order to achieve optimum automation performance operation oriented devices must be used. This is because of the timing errors observed in the stepper motor operation, these errors could be eliminated by using a stepper motor controller (as was discussed in chapter four). Also a DC motor speed controller is available. 2. Different equipment may give similar results for a specific task but some of them may provide larger system flexibility than others. This was concluded because it was learned that a weight sensor provides a more readings than the photoelectric polarized sensor. Recall the discussion in section In addition to the components used in the project, the previous two conclusions, a third conclusion is reached. That is although industrial automation is cost-effective in the longterm its initial costs are very high since in order to achieve optimum performance high quality components are required. 5.2 Future work The project considered only part of the production line, thus it is extendable. Much more future work can be done to complete the whole production line. When introducing new stages of the production line for example the washing machine (which comes prior to the filling stage), as well controlling the washing machine it must be synchronized with the filling machine. In the same manner all processes of the production line must be synchronized as well as inter-process synchronization which was considered in this project. After finishing the whole production line design a further step could be taken that is to develop cost estimation for the system. The cost estimation is an important stage that the control system engineer is entitled to after finishing the design. 50

58 Chapter five Project Evaluation Also a human machine interface (HMI) may be developed in order to monitor process variables and system performance and apply changes remotely. Although an HMI system will be very useful it is not recommended to apply to such an application. That s because soft drink production lines are considered to be a simple kind of production lines compared to other industrial applications such as the car industry and petrochemical industry. Therefore the high cost of HMI installment makes the HMI system undesired as the system can operate just fine without it. 51

59 References References [1] [2] [3] Siemens SIMATIC S7 200 programmable controller manual, SIEMENS company. [4] Ladder logic language reference, unknown author [5] DC Motor Control Systems, Rick Bickle [6] Computer Control #2 PM stepping motors, unknown author [7] [8] Detection workshop technical manual, SHNIEDER company [9] Detection workshop exercise book, SHNIEDER company [10] Automating manufacturing systems with PLCs, version 5.0, Hugh Jack [11] Towards automatic verification of ladder logic programs, Bohum Zoubek, Jean-Marc Roussel, Marta Kwiatkowska [12] Speed control and Positioning using standard drives, Micro Automation SET 1, SIEMENS company 51

60 Appendix A main program code Appendix A program code A-1

61 Appendix A main program code A-2

62 Appendix A main program code A-3

63 Appendix B stepper motor subroutine Appendix B stepper motor subroutine B-1

64 Appendix B stepper motor subroutine B-2

65 Appendix B stepper motor subroutine B-3

66 Appendix C Wiring diagram of the design Appendix C Wiring diagram of design gate valve Output from PLC Input from PLC Cable DC motor 1 External switch S2 (top sensor) S3 (valve sensor) S4 (photosensor) Conveyor 1 Conveyor 2 S1 (bottom sensor) arm DC motor 2 Nuetral lines and relay connections are not shown on diagram. Stepper motor C-1