TABLE OF CONTENTS
1 Introduction
1.1 Introduction ................................................................................. 1
1.2 Objective…………….................................................................. 1
2 Project Design
2.1 Project Description...................................................................... 2
2.2 Design Specifications.................................................................. 2
2.3 Design Iterations ......................................................................... 3
3 Final Product
3.1 Hardware Components ............................................................... 4
3.2 Programming............................................................................... 5
4 Difficulties Encountered
4.1 Problems/Difficulties.................................................................. 5
4.2 Trade-offs.................................................................................... 6
5 Improvements and Recommendations
5.1 Improvements ............................................................................. 7
5.2 Recommendations ....................................................................... 8
6 Conclusions .............................................................................................. 9
Appendix A – Product Sketch (July 7)........................................................ 10
Appendix B – C Code .................................................................................. 11
PRETTY BOY PROJECTS
Creators of the Vendor 38-0
1
Introduction
1.1
Introduction
In partial fulfillment of the course requirements for Electromechanical Systems
4933, the group of Nathan Cooke, Nicholas Croke, Mark Lynch and Mark Sutton
successfully constructed a small-scale vending machine. The group advertised their
functional prototype as the “Pretty Boy Vendor 38-0” and the incorporation of a number
of “mechatronic” components in the machine’s design made the Pretty Boy Vendor a
suitable term project. The mechanical arrangement of the Pretty Boy 38-0 and the use of
actuators, microcontrollers, and additional electrical components will be discussed in the
following report. The Pretty Boy Projects Team would also like to draw attention to the
evolution of the Vendor 38-0’s design and possible improvements should the team decide
to continue the project in the future.
1.2
Objective
The purpose of the Pretty Boy Vendor 38-0 project is to demonstrate the
mechatronic equipment and techniques included in the every-day vending machine. The
modern vending machine incorporates a variety of different functions and the internal
mechanics of a conventional machine are more complicated than most people realize.
The group visited several vending machine suppliers including Kool-Rite Ltd. and
Avalon Vending Services before deciding upon the Vendor 38-0’s final design. The most
significant difference between the Pretty Boy Vendor and the convention machine is the
power of the dispensing motors. The stepper motors used in the Vendor 38-0 were much
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Creators of the Vendor 38-0
smaller than those used in larger machines. For this reason, the capacity of the Pretty Boy
Vendor was reduced to ensure that the smaller motor still has sufficient power to rotate a
can out from the bottom of the stack. A more detailed description of the design is
available in the next section.
2
Project Design
2.1
Project Description
The team at Pretty Boy Projects created the Pretty Boy Vendor 38-0. This is your
typical drink vending machine scaled down. Basically this vending machine contains all
the essentials to dispense a can plus a few novelties (ex. LCD display), however, it does
not contain a money slot or a refrigeration system as they are not necessary for this
course. On one side of the Pretty Boy Vendor 38-0 are the electrical components, where
the machine takes the input from the buttons and outputs signals to the motors and the
LCD display. On the other side of the vending machine are the mechanical components.
This is where the cans are placed and the motors operate in order to dispense a can.
Since Pretty Boy Projects created this machine for demonstrational purposes, the front
was made from lexan in order to allow viewers to see in real time how the insides of the
Pretty Boy Vendor 38-0 functions.
2.2
Design Specifications
Each cam is powered by one stepper motor connected to a 12V battery source.
The cans are placed in columns which can hold four cans, however, the size of the
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Creators of the Vendor 38-0
stepper motor limits our capacity to three cans for each column. The vending machine is
16” long by 16” wide by 19” high. The cams are 6.5” long. From the time a button is
pressed, it takes three seconds to dispense a can.
2.3
Design Iterations
The objectives for Pretty Boy Projects were to build a vending machine and there
were many ways to execute this task. With little knowledge about vending machines the
team decided to seek answers from the experts. After visiting Avalon Vending and KoolRite Ltd., Pretty Boy Projects had a few options for their vending machine. The early
day machines did not use any electronics and over time they became more complex.
Today the machines take a lot of engineering and design and can become extremely
complicated. One specific problem the team had to deal with was how to get the motors
to stop at right time in order to dispense one can at a time. The first idea was to put
notches in the cams so that after the motor passes each notch it would stop, this however
did not meet the course requirements and was too simple. The next two ideas were to
either have the cams spin 360 degrees each time or to have a sensor in the vending
machine that would stop the motor when the dispensed can would fall on it. After much
contemplation the team went with spinning the motors 360 degrees each time in order to
provide a constant and predictable vending machine. There was one other idea to solve
this problem; it was a laser sensor that would stop the motor as the can passed through
the laser. This was outside the scope of the Pretty Boy Vendor 38-0 and was not given
much thought. This vending machine is based on today’s conventional vending machine.
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Creators of the Vendor 38-0
It has a good mixture of electrical and mechanical components and meets the
requirements of the course Electromechanical Systems 4933.
3
Final Product
3.1
Hardware Components
Mechanical
The vending machine consists of a 19” x 16” x 16” (height/width/depth) wooden
box acting as the supporting frame. The drink columns (2) are made up of three pieces of
sheet metal mounted to the back of the box. These extend three quarters of the way out to
the front, and are supported at the free end by two pieces of sheet metal running from the
sides to improve stability. At the base of the frame is a sheet metal catch pan, angled
towards the front of the box. Two ‘U’ shaped cams made from rolled sheet metal lie
underneath the columns and above the catch pan, acting as the dispensing mechanism.
These were mated to two stepper motors attached to the back wall, using machined
aluminum cylinders.
Three normally open buttons were used in the operation of the vending machine.
The two responsible for controlling the stepper motors were mounted into lexan glass at
the front, while the other was mounted in front of the catch pan. The latter was used for
the detection of a can, and was protected by a spring and lever mechanism.
Electrical
A single PIC16F877 microcontroller was used to relay the input information to
the motors and LCD screen, and was placed in a blocked off compartment. An additional
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Creators of the Vendor 38-0
H-Bridge was incorporated off of Port C to run the second stepper motor. The board and
motors were powered by a 12 volt battery. The 2 x 16 LCD display required only an AC
adapter to display greetings and vend status.
3.2
Programming
The main function of our code was to continuously sweep through a loop looking
for inputs from the two stepper motor buttons while displaying a scrolling greeting on an
LCD display. Once either button was pressed, the respective stepper motor would make
one full rotation, and the status would be updated on the display. Before stepping back
into the original loop, the controller would look for the third button to be pressed, to
determine whether to display a sold out or thank you message. See Appendix B for the
complete C code.
4
Difficulties Encountered
4.1
Problems/Difficulties
The majority of problems encountered by the Pretty Boy Team related to the
sensitivity of the electrical components used. Transportation of the machine frequently
resulted in loose connections and damage to fragile hardware such as the LCD display.
Loose connections were often difficult to find due to the PIC controller’s orientation
within the box and diagnosing such problems often resulted in substantial disassembly
and troubleshooting. Although the group had the electrical components working as
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Creators of the Vendor 38-0
planned a week prior to the presentation, damage to components required the replacement
of the LCD and the PIC board before the final presentation could be made.
Additional difficulties were also discovered when implementing the “sold-out”
switch. The force from a can rolling down the catch pan proved to be too large for the
switch to resist and occasionally the epoxy securing the switch in place would let go. To
correct the problem a spring was added to the trip switch assembly which effectively
dampens the force from the can while still allowing the switch to be pressed. The spring
also aids in the rebound of the switch (back to the open position) when the weight of the
can is removed.
Some of our less significant design problems included the effective orientation of
components within the vending cabinet (box) since we had limited lexan to use for the
front face and had to maximize the usage of interior space. Furthermore, getting the
“please make a selection” command to scroll across the LCD required trial and error and
some ingenuity from the group members.
4.2
Trade-offs
The original Pretty Boy Vendor proposal specified a vending machine with three
different selections. This original plan had to be scaled back to only two columns (i.e.
two selections) due to confined space within the cabinet and accessibility to electrical
components. Powering a third stepper motor would have required an additional H-bridge
and the Technical Services Department did not have any extra H-bridges available at the
time of construction. Nonetheless, the use of two stepper motors effectively demonstrated
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Creators of the Vendor 38-0
that the group was capable of implementing multiple independent operating stepper
motors.
The common trade-off between stepper motor torque and stepper motor speed
was also analyzed by the Pretty Boy Team. Speed of vending is an obvious design
consideration but increasing speed decreases torque to a point where the motor can no
longer successfully rotate the weight of a can. After experimentation the group decided
upon a delay of ten milliseconds for each motor which resulted in a total vending time of
approximately three seconds.
5
Improvements and Recommendations
5.1
Improvements
Although the finished prototype of the Pretty Boy Vendor 38-0 was a successful
product that served its purpose for this project, there is still room for improvement. In
terms of performance, the vending machine functioned very well. But, when considering
producing the machine as a commercial item, the team realizes that improvements can be
made in cost efficiency and in the overall sustainability of the machine.
The cams, the component that dispensed the beverage from the column down to
the catch pan for retrieval, could have been made sturdier. The vending machine was
designed to hold four cans of beer in each of the two columns. While performing tests,
the cams occasionally struggled to complete their required revolution and dispense a beer
while there were four cans stacked in the column. Reinforced cams could be a possible
solution for this problem. Also, larger stepper motors would help to enable the cams to
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PRETTY BOY PROJECTS
Creators of the Vendor 38-0
rotate while under greater amounts of force. In the typical modern day vending machine,
larger steeper motors are used that require greater power input than that of the prototype
vendor.
Another area for improvement would be to minimize all open space. The Pretty
Boy Vendor 38-0 was designed to be a smaller representation of a conventional vending
machine. Even though the machine is fairly portable and light weight, it can be made
more cost efficient by making the cabinet more compact. Empty space between the
column and the cabinet wall could be reduced which in turn would reduce significant
amount of sheet metal, wood and lexan needed to build the vending machine.
5.2
Recommendations
If the Pretty Boy Projects team were to turn the Pretty Boy Vendor 38-0 into a
viable commercial product, several recommendations would have to be considered. The
purpose of the vending machine is to give the consumer access to the beverage that they
choose. For a typical beer consumer, he or she prefers that the product is cold and
refreshing. To provide this quality to the cans, the Pretty Boy would recommend the
insertion of a refrigeration unit which would keep the beers refreshingly cold. The
refrigeration unit could be attached to the side of the cabinet facing the two columns.
To turn this into a commercial product, the obvious suggestion would be to
develop a coin operating mechanism for the machine. This mechanism would be a
complicated addition but would still be a realistic option. For the purpose of the term
project, the Pretty Boy Vendor 38-0 already demonstrated the fundamentals of electro
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Creators of the Vendor 38-0
mechanics. The coin mechanism would require extra resources that were not available to
the Pretty Boy team and would also be prove to be very expensive.
6
Conclusions
Our final product was much like we intended it to be from the beginning. Minor
changes in design and implementation were made throughout the process as obstacles
were met; however this had little impact on the overall functionality of our product. From
researching and examining existing vending machines we found that they all function in a
similar way, and while complexity varied throughout the different models, the overall
layout was the same. We felt that a smaller scale vending machine would be suitable to
emulate and demonstrate all of the important components and processes found in any full
size machine. The main restrictions were the torque needed from the motors and the
limited number of motors that our PIC board could handle. The code required to operate
the machine was fairly simple, and could easily be altered to suit a much bigger machine.
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Creators of the Vendor 38-0
Appendix A
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Creators of the Vendor 38-0
Appendix B
//* This program runs a stepper motor connected to bits B1-B4.
*//
#include<16F877.H>
//Using the PIC 16F873
#device adc=10;
//Set ADC to 10 bit
#fuses HS,NOWDT,NOPROTECT,NOBROWNOUT,NOPUT
//Configuration Fuses
#use delay(clock=20000000)
//20Mhz Clock
//#use i2c(Master,sda=PIN_C4,scl=PIN_C3)
#use rs232(baud=9600,xmit=PIN_c6,rcv=PIN_C7,PARITY=N,BITS=8)//Use RS-232
#org 0x1F00,0x1FFF{}
//Reserve Memory for Bootloader
//#USE FIXED_IO(B_outputs=PIN_B4,PIN_B3,PIN_B2,PIN_B1)//Set pin B4,B3,B2,B1 for output
//#USE FIXED_IO(C_outputs=PIN_C4,PIN_C3,PIN_C2,PIN_C1)//Set pin C4,C3,C2,C1 for output
#include <lcd.c>
//include LCD Driver
// PORT B bits 1 to 4 will be connected to The L298 H-Bridge inputs
// The following 8 bit words will be output to PORT B in forward or reverse
// order to control the movement of the stepper motor.
BYTE const step_number[4] = {0b00010100,
0b00010010,
0b00001010,
0b00001100};
int8 step = 0;
//Holds current step for step_number table.
int8 step2 = 0;
int16 i,p=0;
int16 conversion;
void lcd_scroll_left(void){
lcd_send_byte(0, 0x18);
}
void main(){
PORT_B_PULLUPS(True);
//enable_interrupts(INT_AD);
enable_interrupts(global);
enable_interrupts(INT_TIMER2);
//Enable internal Pullup resistors on Port B
setup_timer_2(T2_DIV_BY_4,254,10);
//setup ADC for 20 mhz on Channel 0
setup_adc_ports(ALL_ANALOG);
setup_adc(ADC_CLOCK_DIV_32);
set_adc_channel(0);
//initialize LCD
lcd_init();
printf(lcd_putc,"\f Please make a selection.
for(;;){
delay_ms(300);
lcd_scroll_left();
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Pretty Boy Vendor 38-0");
PRETTY BOY PROJECTS
Creators of the Vendor 38-0
OUTPUT_B(0b00000000);
OUTPUT_C(0b00000000);
//Motor off
//Motor off
//PORT B - MOLSON CANADIAN
while(!input(pin_b7)){
printf(lcd_putc,"\fMolson Canadian");
delay_ms(1500);
printf(lcd_putc,"\f");
for
(i=0;i<200;++i){
step = ++step;
//increment position in step sequence.
lcd_gotoxy(1,1);
printf(lcd_putc,"Vending...");
if (step > 3) step = 0;
//After step four, start at step 1 again.
OUTPUT_B(step_number[step]);
//send step to port B.
delay_ms(10);
//delay 10ms to set speed at 100 steps
per second.
}
delay_ms(1000);
if(!input(pin_b5)){
printf(lcd_putc,"\f Thank You!");
delay_ms(3000);}
else{
printf(lcd_putc,"\f Sold Out");
delay_ms(3000);}
printf(lcd_putc,"\f Please make a selection.
Pretty Boy Vendor 38-0");
}
// PORT C - COORS LIGHT
while(!input(pin_b6)){
printf(lcd_putc,"\fCoors Light");
delay_ms(1500);
printf(lcd_putc,"\f");
for
(i=0;i<200;++i){
step2 = ++step2;
//increment position in step sequence.
lcd_gotoxy(1,1);
printf(lcd_putc,"Vending...");
if (step2 > 3) step2 = 0;
//After step four, start at step 1 again.
OUTPUT_C(step_number[step2]);
//send step to port B.
delay_ms(10);
//delay 10ms to set speed at 100 steps
per second.
}
delay_ms(1000);
if(!input(pin_b5)){
printf(lcd_putc,"\f Thank You!");
delay_ms(3000);}
else{
printf(lcd_putc,"\f Sold Out");
delay_ms(3000);}
printf(lcd_putc,"\f Please make a selection.
Pretty Boy Vendor 38-0");
}
}
}
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