ENGI 4933: Electro-Mechanical Systems Term Project Final ...chandima/Project/Final Report.pdf ·...

ENGI 4933: Electro-Mechanical Systems

Term Project Final Report

Crane Safety Systems

Chandima Perera – 200458685

Brianne Luff – 200336451

Jeremy Brown – 200540086

Xiangyu Sun – 200355584

Summary

As required by ENGI 4933 Electro-Mechanical Systems a term project of a mechantronic

nature was completed. Each group was to choose a completely arbitrary area for which the

mechantronic system could be applied. Our group, Crane Safety Systems, chose to create an

electronic safety system to be applied to today’s cranes whose booms are supported at one end

which will ensure the safe loading and operation of the cranes.

The following report gives an overview of the entire project development from the initial

project proposal to future improvements of the prototype system. As well, technical data

including system drawings and program coding will be included for review.

Based on the completion of the project objectives that were outlined within the initial

project proposal the project and system prototype are ultimately a success.

Table of Contents

Introduction .................................................................................................................................................. 1

Project Justification ....................................................................................................................................... 2

Identified Problem .................................................................................................................................... 2

Proposed Solution ..................................................................................................................................... 2

Benefits of This System ............................................................................................................................ 3

Specifications and Design ............................................................................................................................. 4

Objectives of System Design .................................................................................................................... 4

Objectives of Model Design ..................................................................................................................... 5

Prototype Design .......................................................................................................................................... 7

Overview of Prototype .............................................................................................................................. 7

Crane Load Failsafe System - Electronics ................................................................................................ 7

Crane Load Failsafe System - Programming ............................................................................................ 9

Prototype Model Crane Design ................................................................................................................. 9

Difficulties Encountered.............................................................................................................................. 11

Electrical Difficulties .............................................................................................................................. 11

Programming Difficulties ....................................................................................................................... 12

Model Construction ................................................................................................................................ 13

Future Improvements ................................................................................................................................. 14

Conclusion ................................................................................................................................................... 15

Appendix ..................................................................................................................................................... 16

ENGI 4933 Electro-Mechanical Systems Crane Safety Systems

ENGI 4933 Electro-Mechanical Systems Page 1 of 33

Introduction

The following report is an overview of the Crane Load Failsafe System. The success of

this system involved the synergistic integration of geared DC motors, a potentiometer, a load

cell, and microcontroller technology. The cooperative interaction between these components

makes our project “mechatronic” in nature. This mechatronic quality of our Crane Load Failsafe

System is the most important aspect for the required Electromechanical Systems 4933 term

project.

The Crane Load Failsafe System is a preventive of boom failure due to unsafe crane

loadings. This system reduces human error in maximum load crane operations. A load cell

measures the weight of the loading; our system then calculates the maximum boom angle of the

crane that corresponds to that load. The system will then cause the boom to stop or limit

operation if the crane operator tries to go beyond its maximum safety position angle. This safety

position angle is a position at which the moment created by the load is not too large for the crane.

Therefore, accidents due to crane loading failure will be diminished and the safety of the crane,

its vicinity and crane operators will be at a higher level. The complete system overview is

explained in greater detail in the following report.

This report also entails specifications and design objectives of the system’s

instrumentation, programming and the physical crane prototype. The difficulties encountered

associated with all of these constituents, are discussed in great detail; this allows a basis for

discussion of future system improvements. A system justification is also outlined. This

justification summarizes the problems that the Crane Load Failsafe System solves and proves

why it will have an essential impact on crane safety.



Project Justification

Identified Problem

Improper lifting techniques can lead to boom failure due to overloading if the wrong

boom angle is used. Therefore, lifting properties of certain types of modern cranes pose a safety

hazard if guidelines are not adhered to. Each individual crane has a corresponding load chart.

Each load chart describes the maximum crane loading for the various boom angle positions, and

vice versa. To find the maximum boom angle, with respect to the corresponding crane loading,

one has to consider the moment that is created by the weight of the load with respect to the

distance from the boom, or the moment arm. The maximum load decreases as the boom angle

decreases, in other words, as the crane is lowered or extended the weight of the load that the

crane is able to carry decreases. The moment created by the weight cannot be too large for the

crane or failure will occur. If the load chart guidelines are not followed or ignored the safety of

the crane is at risk and the result can be fatal.

According to the official website for reporting crane related accidents, 314 crane

accidents were reported in 2006 alone. 108 of these accidents were fatal. During the years of

1984 to 1994, studies reported 22 deaths in the US alone due to crane overloading. Therefore,

crane overloading causes a big threat to crane safety. A safe working environment should be

prioritized and that is the reason our team, Crane Safety Systems decided to create the Crane

Load Failsafe System.

Proposed Solution

To reduce the risk of safety issues posed by the overloading of today’s modern cranes we

have proposed to create a safety system that ensures the safe operation of these modern cranes.

This System, the Crane Load Failsafe System, would guarantee that the crane load chart is

followed and the guidelines provided by this chart are adhered to. This means that the moment

created by the crane load with respect to the boom angle never exceeds its maximum value and

the crane will only operate in positions where there is no threat of a safety hazard. The Crane

Load Failsafe System will restrict the boom movement or stop the crane completely when lifting

maximum loads.



This restriction will guarantee that no unnecessary crane accidents arise due to excessive

loads. These crane overloading accidents could easily be prevented with a precautionary

warning, such as a limit on the boom angle with respect to the load being handled. We found that

even professional crane operators could misjudge or overestimate the weight that a crane could

lift. Therefore, extra precautions need to be implemented which is what the Crane Load Failsafe

System strives to do.

Benefits of This System

The Crane Load Failsafe System has many beneficial aspects that would have potential in

the crane safety industry. The system reduces the risk of safety hazards that an overloaded crane

generates. It also prevents crane accidents that occur due to overloading. The prevention of these

accidents would ensure the safety of the crane operators and the people in the crane operating

vicinity. Therefore, our system could possibly save lives.

This system would also reduce the risk of collateral damage. It would protect the crane

itself, therefore, benefiting the owner of the crane or the crane operating companies by saving

them money. This system would also protect assets surrounding the crane’s operational area and

avoid property damages caused by crane operating accidents.



Specifications and Design

Objectives of System Design

As stated in the problem identification, the main reason for utilizing such a safety

systems is due to the added complexity of loading a crane with boom is supported at a single

point and that can vary in angle. This type of crane has varying maximum loads corresponding to

different boom angles. The reason for this characteristic is due to the increasing moment at the

pivot point as the boom is lowered. This increasing moment creates higher tension forces in the

boom line and greater moment forces that the boom and crane base will have to resist. Typically

in this type of crane the maximum load for corresponding boom angles will decrease as the boom

is lowered. To know the maximum load for corresponding boom angles crane operators will

follow a load chart specific to each type of crane such as the load chart below. The graph

represents load vs. boom angle and displays two distinct load lines, red for the main line and blue

for the auxiliary line.

To implement a system that would ensure the safe loading of the crane according to a

load chart it was decided that our system should either inhibit certain operations of the crane that

would in effect overload the crane or at least give some sort of warning. Certain scenarios could

occur in which the overloading of the crane would be possible. First would be the attempt to lift

a load from the surface that exceeded the maximum load at that boom angle. The second

scenario would occur if a crane had already lifted a load that was under the maximum load for

that boom angle and then attempted to lower the boom to the angle where the load that is already



on the line exceeded the maximum load for the new boom angle. It was decided that to ensure

the safest operation of the crane halting the operation of the crane during the overload scenarios

would be best. This was the chosen option due to the fact that there should be no scenario in

which the overloading of a crane would be acceptable. To inhibiting the operation of the crane

would require controlling both the function of the main line, which lifts and lowers the load, and

as well the boom line which controls the raising and lowering of the crane’s boom. In order for

the system to know when to halt operation of the crane it would need to calculate and determine

maximum loads for particular boom angles. For these calculations to be performed boom angle

and load values would have to be gathered and implemented into the system. In the end, the final

system design should be created in such a way that if the crane on which it was implemented was

operating within proper ranges the system should have no effect on its operation.

Objectives of Model Design

The primary objective of the model design was to replicate the function of modern day

lifting cranes. Although it was essential to replicate specific aspects of the cranes, there were

characteristics that we felt were not necessary for demonstration purposes of the safety system.

For example: It was not necessary for the model to lift the weights of real cranes; to effectively

demonstrate the safety system functionality we were able to create the model with a low lifting

weight capability by scaling down the maximum load limits in our input programming.

The following details the main design goals of the physical model:

REQUREMENT JUSTIFICATION

Boom angle measurement device Accurately measure boom angle in real

time

Load weighing device Accurately measure load weight in real

time

0⁰-90⁰ boom angle range To reveal the functionality of the safety

system at any angle

High torque, low speed cable motors High torque requirements at low boom

angles

Relatively low speed of lifting action



Sound, stable structure (ie. minimal

vibrations throughout, static base frame,

and smooth load lifting/lowering)

To reduce the effects of “vibrational

noise” which may cause error in load

weight measurements

To allow for reliable data inputs for

safety system programming

Use of pulleys and lubricated pivot point To reduce the effects of friction

Less fatigue on main hoist and load

cables

Accommodate mounting of electrical

components

Aesthetically pleasing and more compact

to have all components on one platform.



Prototype Design

Overview of Prototype

To demonstrate a working prototype our team decided to integrate the Crane Load

Failsafe System with a constructed model crane allowing for complete functionality of the

system to be demonstrated. During the fabrication of the prototype the project was split between

construction of the electronic system, including computer programming, and construction of the

model crane. The electronic portion effectively represents what we have called the Crane Load

Failsafe System. When both systems were finally complete they were integrated together. The

integration in effect demonstrated the safety system being installed on a crane which is more of a

real life installation scenario than if the electronic system had been built right into the model

crane.

Crane Load Failsafe System - Electronics

To satisfy the system specifications set out in the beginning various types of electronics

were required to create the system. The primary control of the system was accomplished using a

PIC 16F877 board. A schematic of the electronic system can be viewed below.



As represented in the drawing the two geared DC motors are the outputs of the system.

One motor drives the winch attached to the boom and the other motor is attached to the main line

winch. Geared DC motors, opposed to stepper motors, were used due to the requirement of high

torque for the raising of the models boom and main line and precision in movement was not a

concern. As well, the system only requires motors that will quickly turn on or off.

The two inputs to the system that were required in out system specifications are a

miniature load cell and a rotational style potentiometer. The load cell provided a representation

of the load on the line and the rotational potentiometer was used to measure boom angle. The

load cell used in the prototype is a Sensotec 31, 0-10lb load cell. A load cell of this range

allowed us to more accurately measure loads that would be applied to the model for testing

opposed to using a load cell of a high load capacity. Due to the load cell design being based off

of a Wheatstone bridge design the output was in the mille volt range. Connecting that output of

the load cell to an instrumentation amplifier provided an increased signal between 0-5V which

could then be read by the PIC board. The rotational style potentiometer was able to give a

reading of the boom angle by having the potentiometer attached to the pivot pin of the boom in

such a way that when the boom rotated so did the shaft of the potentiometer. The signal from the

potentiometer was then directly sent back to the PIC board.

To control the operation of the motors two double pole double throw (DPDT) switches

were used each with three positions, though two single pole double throw switches could have

been used. Center position was the off position for both motors while the other two positions of

each switch were for the forward and reverse motion of the main line and boom motors. Since

the switches are connected directly to the PIC as inputs this meant that the motors would only

operate if the programming of the PIC board allowed for them to operate. This arrangement gave

the level of control that was required by the system. If the PIC determined that from the load cell

and potentiometer inputs that the crane was at maximum load then the PIC would halt the raising

of the main line and the lowering of the boom, but lowering of the line and reversal of the boom

could be accomplished. The programming of the PIC will be discussed in the following section

to give a more comprehensive description of the operation of the system.



Crane Load Failsafe System - Programming

The main purpose of programming for our smart crane is to stop the operation when it’s

overloaded at diverse boom angles. There are two inputs which are a load cell and a

potentiometer to convert analog force and boom angles to digital numbers. These inputs data

flow into PIC and are stored into different parameters. Two two-way switches control lifting the

load and changing the boom angle of crane respectively. Both of them are connected with PIC as

well. An arbitrary equation is programmed in PIC based on the relationship between loads and

boom angles. The boom angles are the key variables in the equation. Several if sentences are

used to determine when the operation of the crane is going to be halted if the result of the

calculation based on a linear load equation is located in the overloaded area. The linear load

equation for the model was created based on the loads the crane could lift at the highest and

lowest boom angles. The chart can be viewed in Appendix X. As soon as it’s overloaded, the PIC

sends a command to cease two motors which lifts the load and adjusts the boom angles

respectively. The whole program is an endless loop so it is able to refresh the data from two

inputs in very little time.

Prototype Model Crane Design

Overall, the model crane end product met all design specifications. Even in the

preliminary testing stages, the model proved to be of sound structure and maintained a high level

of stability in all combinations of load weights and boom angles.

Throughout the model fabrication process, a drawing was used as a reference to ensure

all clearances and appropriate component dimensions were met. This drawing continuously

evolved with the physical model as it was being built, and was updated frequently. The general

process was to convert all individual components from a 2D to 3D format as they went from

concept to fabrication. Then all components were assembled in the final 3D drawing for

clearance checks. Once all dimensions were checked, the physical assembly took place with

minimal errors. The following shows the first and final model drawings. Please note that all final

dimensional drawings can be found in Appendix VI – VII.



Figure 1: Initial Drawing

Figure 2: Final Drawing



Difficulties Encountered

Electrical Difficulties

While completing the electrical component of the project many difficulties were

encountered, but all were eventually overcome therefore resulting in a system which operates in

a very similar manner to the original concept. The main difficulties encountered with the

electrical components were the acquisition of the instrumentation specifically the load cell and

the instrumentation amplifier as well as the stability of the instrumentation signals generated

some difficulties. The instrumentation was eventually acquired through different contacts in the

Technical Services Department and the signal stability issue was resolved through averaging

input values in the programming code. In addition the original purpose of the double pole double

switches were to have the reverse motion of the motors hardwired to the power source, but due

to the motor output design on the PIC board this was not feasible. As a result all switch signals

were sent as inputs to the PIC and the forward and reverse motion of the motors is controlled by

the PIC. The final rather significant problem encountered during the prototype arose from the

geared DC motors. Due to the very high torque produced by the motors they have high

acceleration/deceleration and tended to be very jerky while they were turned off or on. During

the lifting of a load the high upward acceleration caused the load cell to initially read a load

value that was higher then the weight of the actual load. To reduce the acceleration of the motors

the duty cycle in the programming was adjusted to give a proper balance of torque and velocity

while not over compensating.



Programming Difficulties

There were a few problems that arose during the programming. The first problem was

how to control the motors by using PIC. The basic structure of program is based on lab 2, but our

project had one more motor as an input. After an additional code was programmed for the second

motor, the second motor wasn’t running as fast as it should be because we didn’t write any

control program for the second output port. The second problem was to find the point that should

stop the crane when it’s in danger. After the data of load cell output to the hyper terminal, the

numbers were so unstable that it always had about 10% of inaccuracy. One method was to

convert the original numbers to the exact weight of load and boom angles that are actually used

in the calculation. The weight of the load was from 0 to 1 kg, and it was from 0 to 90 degrees for

the boom angle. The boom angle inaccuracy was fixed after the conversion; however, the load

cell input numbers were still swaying around 5%. The second method was take an average of the

input values over seven iterations which added additional stability of the input values. Because

the inputs from the load cell were integer numbers, the computer ignored any figures after the

decimal point. The uncertainty was reduced to a semi reasonable point. There were many small

problems also following along the program design. One PIC was burnt because of an unclear

reason, and the wires took off several times from the ports or broke into half, which caused many

troubles during the test.



Model Construction

A number of difficulties were encountered in creating the crane model. The most

prominent being the Plexiglas machining. Because of the sensitive nature of the Plexiglas

material, it tended to melt and deform when machined at high speeds. In order to compensate for

this it was machined at lower cutting speeds and with the use of cooling fluid.

Although the 3D model proved useful when assembling the final model, one clearance

was overseen and required adjustment upon final assembly. As shown in Figure 3, the lower

most edge of the boom interfered with the mounting bracket at approximately a 30⁰ boom angle.

This was easily corrected by manually filing down the profile of the edge and reassembling the

boom.

During the initial design stages, there were two main concerns. One was on the proper

location of the lower load lifting pulley, and the other was on which method to measure the

boom angle. The decision to was to mount the pulley within the boom (as to ensure a permanent

contact with the load lifting cable), and upon the advice of Mr. Tom Pike we installed a

potentiometer as the angle measurement device.

Figure 3: Clearence Issue



Future Improvements

If given further time and resources, the following additions would be made:

Stable Signal Input:

A more stable load cell and instrumentation amplifier would give a more consistent and

stable input of data to better analyze the real-time boom angle and weight.

Manual Override:

If implemented correctly, a manual override of the CLFS would allow for temporary

“special case” lifting applications (ie. Lifting with various crane attachments).

Audio and Visual Warning System:

This would allow the crane operator to be aware when he/she is approaching near

maximum load weights so they may adjust the boom angle accordingly.

Real-Time Display:

The implementation of a real-time display of the boom angle and load weight would

make the operator aware of the current position and load. This would be tied into the afore

mentioned warning system and installed in an area where the states could be easily seen by the

operator.



Conclusion

To conclude, the project was an overall success. The crane safety system was designed

and programmed to limit the movement of a crane while lifting maximum load weights (relative

to the crane boom angle), and a physical model crane was built which successfully demonstrated

the use and functionality of the safety system.

We learned a great deal about system development in many fields; from the basic concept

design stages to the implementation of final testing. We gained a valuable learning experience in

computer programming, standard electo-mechanical instrumentation hardware (PIC controllers

and associated board components), model drafting/ prototyping procedures, and manufacturing

processes. In addition, we further developed our technical and professional skills through the

creation of formal reports and presentations.

We believe that with additional research and access to more precise equipment, this

system has potential for use as an effective failsafe system in the lifting-crane industry.



Appendix

I. Picture of System Prototype

II. Electrical Drawing - (Rev 01)

III. Electrical Drawing - (Rev 00)

IV. Model Drawing 3D

V. Model Drawing 2D

VI. Model Drawing 2D - Front

VII. Model Drawing 2D - Right

VIII. Model Drawing 2D - Top

IX. System Flowchart

X. Model Crane Load Chart

XI. Programming Code

XII. Spec Sheet – Load Cell

XIII. Picture of PIC 16F877 Board



I Picture of System Prototype



II Electrical Drawing - (Rev 01)



III Electrical Drawing - (Rev 00)



IV Model Drawing 3D



V Model Drawing 2D



VI Model Drawing 2D – Front



VII Model Drawing 2D – Right



VII Model Drawing 2D – Top



Load Cell Boom Angle

PIC16F877

No

The forward motion

is halted

Both motors run

without limitations

Main Line

Hoist Switch

Switcher

Boom Hoist

Switch

Input values are

used to evaluate

the maximum

load equation

Boom

Motor

Main Line

Motor

Main Line

Motor

Boom

Motor

Yes

IX System Flowchart



X Model Crane Load Chart



XI Programming Code

#include<16F877.H> //Using 16f877 PIC

#device adc=10; //Set ADC to 10 bit

#fuses HS,NOWDT,NOPROTECT,NOBROWNOUT,NOPUT //Configuration Fuses

#use delay (clock=20000000) //Set clock delay

#org 0x1F00,0x1FFF{} //Reserve Memory for Bootloader

#use rs232(baud=9600,xmit=PIN_c6,rcv=PIN_C7,PARITY=N,BITS=8) //Use RS-232

#USE FIXED_IO(D_outputs=PIN_D1, PIN_D2) //Set pin D1 for motor 1 output, Set

pin D2 for motor 2 output

#byte PORTB = 6 //Port B is "File Address 06H" in "Bank 0"

#define ALL_OUT 0x00 //Constant to set data direction register to output

#define ALL_IN 0xff //Constant to set data direction register to input

#include<STDLIB.H> //Using STDLIB library

int16 duty1 =0; //Set 16 bit interger parameter 'duty1' as 0

int16 duty2 =0; //Set 16 bit interger parameter 'duty2' as 0

int16 count =0; //Set 16 bit interger parameter 'count' as 0

int16 holdload =0; //Set 16 bit interger parameter 'holdload' as 0

int16 holdloadavg =0; //Set 16 bit interger parameter 'holdloadavg' as 0

int16 holdboom=0; //Set 16 bit interger parameter 'holdboom' as 0

int16 holdboomavg=0; //Set 16 bit interger parameter 'holdboomavg' as 0

int16 boom; //Set 16 bit interger parameter 'boom'

int16 load; //Set 16 bit interger parameter 'load' as 0

void main() {

set_tris_b(0x01); //Set bit 0 of Port B to input, bits 1-7 to output

set_tris_b(0x02); //Set bit 1 of Port B to input, bits 1-7 to output

PORTB = 0; //Clear all bits of Port B

setup_ccp1(CCP_PWM); //Set up PWM on CCP1.

setup_ccp2(CCP_PWM); //Set up PWM on CCP2.

setup_timer_2(T2_DIV_BY_4,254,10); //Set up Timer2 for 4901Hz PWM

Period.

setup_adc_ports(all_analog); //Set all pins on ports A and E to

analog.

setup_adc(ADC_CLOCK_DIV_8); //Set ADC conversion speed for 4 Mhz

Clock.

set_adc_channel(0); //Set ADC channel to 0 (pin 2).

while(true){ //Do the while loop when it's true

count = count + 1; //Set a counter

holdloadavg = holdloadavg + load; //Iterating 'holdloadavg' with 'load'

holdboomavg = holdboomavg + boom; //Iterating 'holdboomavg' with 'boom'

if (count > 6){ //If count>6 do

holdload = (holdloadavg/7); //Counting the average of

'holdloadavg'



holdboom = (holdboomavg/7); //Counting the average of

'holdboomavg'

count = 0; //Set count to be 0

holdloadavg = 0; //Set 'holdloadavg' to be 0

holdboomavg=0; //Set 'holdboomavg' to be 0

}


delay_ms(5); //Delay 5ms

boom = read_adc(); //Input the value from a pot to 'boom'

boom = (0.237*(boom-580)); //Outputing boom angle from 0 to 90 in

the hyperterminal.


delay_ms(1); //Delay 1ms

load = read_adc(); //Input the value from load cell to 'load'

load = (load*2.286); //Convert adc value to kilogram and input to

'load'

printf("Load = %4Lu Boom = %4Lu\r",holdload, holdboom);

//Send adc result to serial port

if (input(PIN_B0)){ //if B0 is 1

if (boom<77){ //and boom less than 77

set_pwm1_duty(1000); //PWM duty cycle for motor 1.

Output_high(PIN_D1); //Setting direction for motor 1.

}

else if (boom>=77){ //If boom more than 77 then duty

cycle is 0 and motor 1 is off


}

}

if (input(PIN_B1)){ //If B1 is 1

if (holdload > ((10*holdboom)+300)){ //and the holdload is

more than (10*holdboom)+300

set_pwm1_duty(0); //stop motor 1

}

else if (holdload < ((10*holdboom)+300)){ //the holdload is

less than (10*holdboom)+300


Output_low(PIN_D1); //Setting direction for motor 1.

}

}

else if ((!input(PIN_B0)) && (!input(PIN_B1))){ // If B0 and B1 are low

then duty cycle is 0 and motor1 is off.


}

if (input(PIN_B2)){ //If B2 is 1

if (holdload > ((10*holdboom)+300)){ //and holdload is more

than (10*holdboom)+300

set_pwm2_duty(0); //motor2 is off

}

else if (holdload < ((10*holdboom)+300)){ //If holdload is less

than (10*holdboom)+300




Output_high(PIN_D2); //Setting direction for motor 2.

}

}

if (input(PIN_B3)){


Output_low(PIN_D2); //Setting direction for motor 2.

}

else if ((!input(PIN_B2))&&(!input(PIN_B3))){ // If B2 and B3 are low

then duty cycle is 0 and motor2 is off.


}

}

}



XII Spec Sheet – Load Cell



XIII Picture of PIC 16F877 Board

ENGI 4933: Electro-Mechanical Systems Term Project Final ...chandima/Project/Final Report.pdf ·...

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