T-535-MECH Mechatronics II DC Conveyor motor control using Arduino Uno programmed in C Final report. Gunnar Óli Sölvason

Transcription

1 T-535-MECH Mechatronics II DC Conveyor motor control using Arduino Uno programmed in C Final report Gunnar Óli Sölvason February 26, 2014

2 Contents Abstract 2 1 Introduction Background Arduino Uno DC Motors Light sensor Transistors Pulse width modulation Design and progress Requirements Component selection Motor Transistor Light sensor Conveyor and parts Software Hardware Limitations Testing 11 4 Usage Installation Instructions Results and Discussion 12 6 Conclusion Future work Appendix Timeplan Design documents Cad drawings Code

3 Abstract Work in progress. - Abstract chapter will be placed here. 2

4 1 Introduction Conveyors have a wide use in industrial applications. Moving goods around is a common task in the real world, and a conveyor is one way to go about doing so. A wide variety of motors can be used to drive a conveyor, with geared DC motors being a common solution. The project discussed in this report is to use a Ardunio Uno board programmed in the C programming language to control the speed of a small conveyor running on a DC motor with a built in encoder. The speed of the conveyor should keep constant, even though load is applied to it, meaning that power needs to be adjusted dynamically as the load varies with time. At the end of the conveyor a end stop sensor senses if a piece is going to fall of the motor end of the conveyor. The idea for this assignment came from a list of possible topics proposed by the course instructor. At the time the project was chosen I had problems blinking a diode using C, so a project of a fairly low complexity seemed like a good idea. To add a little bit to the idea from the instructor and not just use it raw, a endstop sensor was added to the conveyor. Also, having worked with conveyors before would mean that the focus could be on working with the Arduino microcontroller and the programming part of the assignment. Rather than spending a whole lot of time on physical design, which is maybe not the focus of the course, a bigger portion of the time could go into building the software and learning the ins and outs of the Atmel processor being used, something I have lesser experience with. 1.1 Background The basic idea for the project is this : A Geared DC motor is connected to a power supply and a transistor. The transistor is connected to the Arduino board, and modulated pulses from the Arduino control how much power the motor gets. The determination of power is directly proportional to the percentage time the port controlling the transistor is on, in other words, the duty cycle of the pulse width modulation. If the duty cycle of the pulse width modulation is, for example, 70%, the motor will be running at 70% of maximum power. 1.2 Arduino Uno "The Arduino Uno is a microcontroller board based on the ATmega328. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything needed to support the microcontroller; simply connect it to a computer with a USB cable or power it with a AC-to-DC adapter or battery to get started. The Uno diers from all preceding boards in that it does not use the FTDI USB-to-serial driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed 3

5 Figure 1: Arduino Uno board.[1]. as a USB-to-serial converter. [ ] "Uno" means one in Italian and is named to mark the upcoming release of Arduino 1.0. The Uno and version 1.0 will be the reference versions of Arduino, moving forward. The Uno is the latest in a series of USB Arduino boards, and the reference model for the Arduino platform; for a comparison with previous versions, see the index of Arduino boards [2]." As mentioned in the summary above, from the web page of the producers of the Arduino board, it runs on the ATmega328 microcontroller. The operating voltage of the board is 5V, and runs at a clock speed of 16MHz. Available memory is 32KB (Flash, of which 0.5 is allocated for the bootloader), 2KB SRAM and 1KB EEPROM. The communication to a computer goes on through a USB port on the board, or as phrased on the website : "The Arduino Uno has a number of facilities for communicating with a computer, another Arduino, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega16U2 on the board channels this serial communication over USB and appears as a virtual com port to software on the computer. The '16U2 rmware uses the standard USB COM drivers, and no external driver is needed [2]." 1.3 DC Motors Write background on DC motors. 1.4 Light sensor Write background on sensor (proximity, light...) 1.5 Transistors A transistor is essentially a switch (much like normal mechanical switches), except it has no moving parts. 4

6 Figure 2: A section view of a brushed DC motor. [3]. There are two types of transistors, P-Type and N-Type. This means that the transistors semiconductor is either infused (doped) with a material that has 1 more electrons than silicon (5e ), like phosphorus (N-Type), or you dope the silicon with a material that has 1 less electrons than silicone (3e ), like Bohron (P-Type). What this does is, that conductivity is increased by more electrons being able to move freely inside the semiconducting material. Note that both of the P and N type semiconductors are neutrally charged. What the P and N describes is whether the electron itself moves inside the semiconducting material, or the "hole" left by the missing electron in the material with only (3e ) in it. Figure 3 shows my illustration of a NPN transistor and its basic functionality. Figure 3: A graphical reprisentation of a NPN transistor. When no voltage is applied to the gate, no current ows through the transistor, it is an open switch, much like a mechanical switch when it is not pressed down. When voltage is applied to the gate, the electrons in the semiconductor overcome the barrier of the depletion layer, making a channel for electrons to ow under the oxide layer. Now the transistor is open and current can ow through it. This can be done very fast, and at very high rates. 5

7 1.6 Pulse width modulation In the simplest explenation, pulse with modulation is varying the time between something being on and being o. In this case the pulse with modulation goes on through a 5V pin on an Arduino Uno board. If the pin would be o 100% o the time, it would give out the average voltage of 0V. If the pin was on 100% o the time, it would give an average output of 5V. Equally, if the pin was altered to be on 50% o the time and on 50% o the time, it would give the average power of 2.5V. For someting that would normally run at 5V, lets just say a light, this would mean that the light would be on, but on 50% of its maximum brightness. Pulse width modulation has a wide variety of practical uses, and here it is used to vary the speed of a DC motor using the principle described here above. Figure 4: Graphical representation of Pulse Width Modulation. [4]. Figure 4 shows graphically how the principle behind PWM is executed. 6

8 2 Design and progress The system design started with the scope of the problem being decided. This was done by setting some functional requirements and design parameters. These parameters can be seen Table 1. The diagram is called a FRDPARRC diagram. FR stands for functional requirements, DP for Design Parameters, A for Analysis, R for References, the other R for Risks and C for Countermeasures. The FRDPARRC Diagram helps identify most crucial functional requirements and design parameters, as well as possible risk factors and their countermeasures. Conveyor runs at set speed. Table 1: FRDPARRC Diagram for DC Conveyor. Based on [5]. FR DP A R R C Previous Speed will Dierence experience variate from set speed Realistic goal. working with outside of set is < ±5% conveyors range Only minority of pieces fall of the edge. Conveyor is aesthetically pleasing. Pieces are not to big for conveyor Pieces are not to small for sensor <1% of pieces fall of the edge of the conveyor. Gunnar likes the aesthetics. Max size : 100x400x400 (WxLxH) Min size : 50x50x50 (WxLxH) 100% success rate not realistic. Designers should strive for good looks. Too big pieces could damage conveyor Too small pieces would not trigger sensor. Former experience with conveyors. Good looking things sell better. Physical constraints of conveyor. Sensor datasheet More than 1% fall o edge. Looks bad. Conveyor breaks. Breaks design parameter 2 Design good feed-back loop Position sensor correctly. Quick stopping of conveyor. Use golden ratios in design. Clearly dene maximum size Clearly dene minimum size 7

9 After conguring the design parameters and functional requirements of the project the group made a crude rst sketch of the machine. The sketch can be seen in Figure 5 Figure 5: The gure shows the rst crude sketch of the idea. The sketch shows... This can be described in a step by step manner like so : Requirements All the main requirements for the project have been analysed in the FRDPRRC diagram in section 2. (ADD TEXT HERE) 2.2 Component selection This chapter deals with the reasons behind the selection of components for the project, and goes through a little analysis on each and every one of the parts chosen Motor When selecting a motor for a conveyor, the main selection criteria are most often speed and torque requirements. The maximum load of the conveyor is known in most situations, both the static load due to weight of the belt itself, and the dynamic load added by goods moving on the conveyor. Along with that the maximum time for delivery to the end of conveyor is most often known, so the speed can be calculated. 8

10 Justify selection of motor with the hand calculations already made. Include the formulas. To calculate the speed of the conveyor we need to know two parameters: The rotational speed of the motor, and the diameter of the sprocket. The nominal pitch diameter of the sprocket is ø41. (the sprocket is the smallest one available for Intralox 1100 series at top belt, as can be seen in [insert citation to intralox manual]. The rotation of the motor is 160RPM. u = d π = 120mm = 0, 12 m rev 160 rev min 60 sec min = 2, 667 rev sec v = 0, 12 m 2, 667rev rev sec 0, 35m/s This gives the speed of 0,35 m/s for the conveyor when no frictional factors are considered. From previous experience with conveyors I am happy with that operating speed, since it is strikes a good balance between being fast enough, and not producing a lot of noise Transistor Justify selection of transistor and calculate size Light sensor Justify selection o sensor (numerical values, price, performance, availability). Analyse what is needed from the sensor, and what sensor meets that criteria the best Conveyor and parts Justify selection for parts in conveyor. 2.3 Software The software used to control the motor is written in C using Eclipse equipped with AVRDude to compile the code and send it to the Arduino board. The entire code is written specically for this project, without relying on built in libraries of the ANSI standard C code. An exception for this is the io.h header le and the interrupt.h header le, which were allowed for use by the 9

11 instructor of the course. The software is split into...(add more text here on the software when ready) 2.4 Hardware The hardware used for this project was as follows : - A computer (laptop/desktop pc) for programming. - Arduino Uno board. - USB Cable (to connect the AU board to the computer) - DC Gearmotor with Encoder (Hennkwell HG37D670WE12-052FH was used for this project, others could be considered) - Light sensor (velja sensor...) - Conveyor (Frame, Conveyor belt and supports) - Control circuit (breadboard, transistor, 2x7segment display) The motor was sourced from the Electronics lab of the Reykjavík University and the Arduino Uno board was bought for use in Mechatronics I preliminary class last semester. The most complicated hardware of the project is the conveyor construction. The conveyor was supplied pro bono from a company the remains anonymous by request. This means that all the parts for the project were sourced for free, so there is no cost gure next to the parts in the BOM. 2.5 Limitations Limitations for this project are the same as for most design projects, time and money. The project does have a limited budget, and the timeframe is only 8 weeks. This limits the features the project can have. For the conveyor to work properly, it needs to be on a solid base and placed horizontal. All calculations made assumed that the conveyor would not be inclined, since that adds load on the relatively small motor. Since the control circuit is open, and not in any way protected, the conveyor is obviously not equipped to be used in factory environment since its not waterproof. The conveyor can only handle loads inside of the specications of the motor (INCLUDE MO- TOR CALCULATIONS HERE!!). Since the actual belt itself can carry upwards of a 1000kg without breaking, the motor torque will be a limiting factor long before that load is reached, along with the conveyor frame breaking. Since the constructional integrity of the conveyor was far out of the scope of this project, no calculations were carried out to proof how much it could 10

12 withstand, but it is safe to assume that it will be a matter of no concern here. The maximum torque of the motor is 0,65 Nm, so the motor will stall long before any physical damage is done to the conveyor. Since the width of the conveyor is roughly 100mm, and the length is about 500mm it can obviously not handle pieces or items exceeding that size. For the sensor to be able to sense items on the conveyor, the items must be of adequate size. Maximum and minimum sizes are dened in the FRDPARRC diagram, table 1. Due to the rotational speed of the motor, the conveyor wont be able to run over 0.35 meters per second without seriously lowering the torque the motor can handle. It could probably be run faster, but it won't be guaranteed. The maximum rated speed is 0.35m/s. 3 Testing Work in progress. 11

13 4 Usage To use the conveyor one has to follow a simple procedure. The conveyor is simply connected to power, the speed is set, and the conveyor should run. It should by then run at the set speed, and maintain that speed even though load is added. The physical button allowing or not allowing pieces to fall of the motor-end of the conveyor can be set, allowing either of those two options. 4.1 Installation For the conveyor to be able to run, the correct software needs to be installed onto the Arduino board rst. The software needed can be found in the appendix. Step by step installation guide for for the Conveyor: 1. Turn on a computer. 2. Start operating system of own choice. 3. Start Eclipse software developement enviroment Connect the Arduino via USB cable to one of your computer's USB ports. 5. Upload the conveyor software to the Arduino board. With the software installed on the Arduino board, the conveyor only needs external power to run. This is done by plugging in the power cord supplied with the conveyor. 4.2 Instructions Work in progress. 5 Results and Discussion Work in progress. 6 Conclusion Work in progress. 1 This needs to be installed. If you have not installed Eclipse, it can be downloaded from 12

14 6.1 Future work Work in progress. 13

15 7 Appendix 7.1 Timeplan This is the original timeplan of the project turned in when the project was selected in week 5. Week 6 : Scope project, source parts. Week 7 : Design hardware. Week 8 : Design software. Week 9 : Build circuit. Week 10 : Build hardware. Week 11 : Start on report, nish hardware. Week 12 : Simultaneously work on writing and programming. Week 13 : Writing, programming. Week 14 : Finish writing report, make presentation, ne tune conveyor This is the timeplan as it was executed. Notice the dierence in week numbers. Green tasks have already been nalized. Orange parts are underway. Others have not been started. Week 8 : Scope project, source parts. Week 8 : Design hardware. Week 8 : Design software. Week 9 : Build circuit. Week 10 : Build hardware. Week 11 : Start on report, nish hardware. Week 12 : Simultaneously work on writing and programming. Week 13 : Writing, programming. Week 14 : Finish writing report, make presentation, ne tune conveyor 14

16 7.2 Design documents Cad drawings Work in progress. 15

17 7.3 Code This is the source code that was used for the conveyor??. The code would need to be tweaked for the nal design. belowcaptionskip Work in progress. 16

18 References [1] Web Page. [Online]. Available: 1/1/0/2/1/ a.jpg [2] Arduino, Arduino uno, Webpage, [Online]. Available: arduinoboarduno#.uwyxk_l_s5q [3] 2by, Dc motor anatomy, Web page. [Online]. Available: DC-Motor-Anatomy-sm.png [4] Web page. [Online]. Available: atmega168a_pwm_02_lrg.jpg [5] A. H. Slocum, Precision Machine Design. Society of Manufacturing Engineers,