2. 2
Table of Contents
MECA 340 Prosthetic Hand ......................................................................................................................3
Problem Statement..................................................................................................................................3
Engineering specifications & Performance ..........................................................................................4
Concepts and Sketches ...........................................................................................................................5
Engineering Design.................................................................................................................................6
Gauntlet.................................................................................................................................................6
Servo Base ............................................................................................................................................6
Servo Pulley..........................................................................................................................................7
Assembled Servo System......................................................................................................................7
Hand Design..........................................................................................................................................8
3D Printing Settings for Hand...............................................................................................................9
Circuit Design........................................................................................................................................10
Components ........................................................................................................................................10
Battery Design ....................................................................................................................................10
Circuit .................................................................................................................................................10
Analysis..................................................................................................................................................11
Conclusion .............................................................................................................................................14
MECH 440 Senior Design Project...........................................................................................................16
Project Statement..................................................................................................................................16
Engineering Design...............................................................................................................................17
Analysis..................................................................................................................................................19
3. 3
MECA 340 Prosthetic Hand
Problem Statement
The purpose of the project is to design a custom fitted prosthetic hand for our burn victim, Tito.
Tito lost the ability to use both his hands in a fire as a young boy in Mexico City, Mexico in which he
suffered 3rd degree burns over eighty-five percent of his body. As a result of the fire, surgeons at the UC
Davis medical center had to amputate all of his fingers, both thumbs and all of his knuckles. Tito only has
the use of his misshapen palms to do everyday tasks with.
Figure 1 - Tito's Right Hand and Wrist
This prosthetic is intended to increase Tito’s daily function capabilities. The hand should reduce
the time it takes to perform certain tasks as outline below. The prosthesis will also make Tito appear more
normal, which is important because he attracts attention whether it is warranted, or not.
Providing a hand to Tito would improve his quality of life and make performing everyday tasks able
bodied people take for granted easier such as:
Holding a glass of water for drinking
Opening doors
Holding a fork or other utensils to eat with
Holding a pen or pencil
Grasping objects
If our design is successful, it can be made into open source design and allow others in the same
situation to benefit from the design.
4. 4
Engineering specifications & Performance
Total weight should be between 5-6 lbs when fully assembled including electronics, hardware. A
portable battery supply may be include if one can be found that delivers sufficient power. This supply
would be connected via cable.
The cavity of the palm must be within a +5 mm around the perimeter of hand as shown in Appendix C,
which is custom fitted. This tolerance will allow for the inclusion of medical foam which is placed
between the palm and gauntlet pieces and the skin. The large range is due to the uncontrollable and
varying amount of shrinkage we will experience when printing parts on the 3D printer. From the wrist to
the elbow, there are 8 inches in length to create the necessary platform to mount the motors for
controlling the fingers.
As specified per the instructor, the hand needed to be able to complete the following task:
Pick an egg up off the table without crushing it,
Hold a cylindrical glass of water or water bottle,
Pick up medium to large size objects, and hold a pen or pencil.
Initially the hand was to be powered using Muscle Wire which is a nickel-titanium alloy that
contracts when current is applied. After extensive research, testing, and talking with the vendors, it was
determined to be incapable of meeting the manufactures specifications due to a necessary forming process
that the wire needed to undergo. After presenting our findings, approval was given to move forward with
servo motors. The following specifications were chosen:
Must be able to lift more than 2 pounds
Must be small enough to fit on forearm of teenager
Must close hand in less than 5 seconds
Must open hand in less than 5 seconds
5. 5
Concepts and Sketches
Figure 2 - Hand Draw Sketches by William Cortez
As a team, it was agreed upon that the finger with three sections would articulate better than the
two piece system that is pictured below. The muscle wire was replaced by several servos for several
safety related and functionality issues. It was decided that we would have to construct a separate motor
and control piece that is mounted off the gauntlet piece itself due to space constraints.
It took us over six iterations of our final concept and an addition four iterations of our original
design before we arrived at the concept we put into production.
Figure 3 - Solidworks Model of Final Design
6. 6
Engineering Design
Gauntlet
The purpose of this part is to direct the wires that run from the servo motors to the individual fingers.
Also, it is the main connection between the prosthetic and the person’s arm.
Servo Base
The purpose of this part was to allow the servos to be securely mounted and also be attached to the pip
and gauntlet part. The sixing of this part was determined by the size of the servos chosen.
Design Specs:
Must have easy cable routing for servo wires
Must be light weight and durable
Must have holes for securing the servos to part
Figure 5 - Isometric View of Servo Base
Figure 4 - Gauntlet
7. 7
Servo Pulley
The purpose of this part was to linearize the movement of the fingers. The sizing of the pulleys was
determined by the travel length of the fishing line required to close the fingers.
Design Specs:
Must have a center hole that has a tight tolerance for fitting onto servo gear
Must have a groove that circles the pulley to guide the fishing line around the pulley
Must be strong enough to handle torques from motors
Assembled Servo System
The whole system was 3D printed using ABS plastic because it was cheap, easy to use, and strong enough
to handle the loads.
Figure 7 - Isometric View of the Servo System
Figure 6 - Isometric View of Servo Pulley
8. 8
Hand Design
The fingers were made up of four different parts, three sections with the tip of the finger having two parts
that were glued together after the fishing line elastic cord had been tied off. The palm is made of one
piece, which took multiple attempts at printing to make sure it was not deformed or cracked. There were
also three different types of pins printed to connect the different parts.
Figure 8 - Final Version of the Entire Hand
9. 9
3D Printing Settings for Hand
Support structures were also used in the printing process to make sure the part adhered to the bed and
printed without failure or collapsing in on itself. The picture below shows the graphical user interface
with the two most critical parts of the hand assembly. The overall hand to over twenty-four hours to print
and required multiple print sessions which would require about 500 kg of filament.
For the finishing process, acetone was applied conservatively to all parts of the assembly. Acetone
acts to fuse the ABS on a molecular level, increasing the overall strength of the parts. This leads to a
glazed look.
Figure 9 - 3D Printer Settings in Cura
10. 10
Circuit Design
Components
Arduino Uno Board
Wire Jumpers
Rotatory Potentiometer
Flex Sensor
Towerpro MG946R Servo (x5)
2200 mAh Battery
Battery Design
The battery that we chose was a 2200 mAh lithium polymer battery because I had one available
so we didn’t have to spend money on a new battery.
Battery Life = ((Battery Capacity in Milli amps per hour) / (Load Current in Mill amps)) * 0.70
Battery Life = ((2200 mAh)/(250 mA)) *0.7 = 6.16 hours
*The factor of 0.7 makes allowances for external factors which can affect battery life.
Circuit
Figure 10 - Wiring Diagram
11. 11
Analysis
Figure 12 - Torque vs. Time Graph for the Fingers
Figure 11 - Torque vs. Time Graph for Thumb
12. 12
Figure 13 - Angular Velocity vs. Time Graph for Fingers
Figure 14 - Angular Velocity vs. Time Graph for Thumb
13. 13
Figure 15 - Picture of ADAMs Hand Simulation and Analysis Model (Open)
Figure 16 - Picture of ADAMs Hand Simulation and Analysis Model (Closed)
14. 14
Conclusion
Overall, the project was successful. The team created a hand capable of grasping a war bottle or
glass, holding a pencil, grasping objects, as well as being able to pick objects up such as an egg without
crushing it.
The hand itself was well under the weight limit we were looking to achieve. With the electronics
and display mounting, the hand weighed just over a 1lb. and came out within about ±1.5 mm of its
specified dimension. Ambient conditions and humidity played a role in dictating how well the piece will
print. The palm and gauntlet were the two parts that varied the most. The aforementioned conditions as
well as long print job duration times made the parts larger or smaller in certain areas.
The final cost for the project was $153.58, which was $53.58 over the allotted budget. A majority
of the budget was spent on the servo motors which accounted for about a third of the overall project costs.
Without donations the project would not have been possible. An additional $100.00 was spent on muscle
wire and the necessary equipment needed to test the wire.
Below is a picture of the hand we demonstrated to the class which shows the complete assembly
of the hand on the pipe with the external motor system. We did not use an external battery, but calculated
the number of duty cycles achievable with the batteries already in our possession. The Arduino micro
controller is not pictured and is on a separate board. We were not able to integrate the entire system onto
the hand as we originally intended.
Figure 17 - Final Assembly of Robotic Arm
16. 16
MECH 440 Senior Design Project
Project Statement
My senior project group has been contracted by the San Francisco U.S. Mint to partially automate
their blank transfer process. The coin blanks arrive in 1800 kg bins from the Philadelphia and need to be
broken down into smaller, more manageable weights so workers can easily transport them throughout the
mint. Currently, the way the mint does this is to have a worker hand scoop the blanks out of the large bin
and dump them into smaller bins using what is essentially an ice scoop. This process puts a lot of physical
strain on the workers and increases the risk of on the job injuries.
The goal of our project is to reduce the manual labor required and therefore reduce the liability of
on the job injuries. We will know we have been successful when we can transfer 7 kg of blanks in 15
minutes, accurately measure 10 kg in the smaller bins within +/- 2 kg, and have a reliable uptime of 91%.
To do this, our group has decided on a vacuum-hopper system. A shop vacuum with a high water
lift and CFM was chosen to pick up the blanks. Once the blanks have entered the vacuum they will drop
down into the funnel shaped hopper, which will have a strain gauge on the frame to measure the change in
weight of the system. Once 10 kg is reached, the motor will be stopped then the hopper flap door will be
opened by a linear actuator. Below the hopper will be one of the smaller bins that are used throughout the
mint, which the blanks will fall into. Once the hopper has been fully emptied the worker will need to pull
the full bin and replace it with an empty one. The system will be programmed to leave the hopper door
open long enough to empty all of the blanks out of it, as well as give the motor enough time to cool.
When the timer runs all the way down the system will be ready for the worker to restart the process by
pressing the START button once again.
Our group has finished the initial design stage of this project and have ordered the necessary parts
to build our system. The following figures show the design we have develop along with a few of the
calculations performed to make sure this design will work.
17. 17
Engineering Design
Figure 19 - Final Design for Entire System
Figure 20 - Funnel Hopper w/out Modifications Figure 21 - Funnel Hopper w/ Modifications
18. 18
Figure 22 - Vacuum-Hopper Assembly Main Connections
Figure 23 - Close Up of Vacuum-Hopper Assembly w/ Labels
19. 19
Analysis
Figure 24 – Factor of Safety Values for Funnel Hopper
Figure 25 - FEA of Funnel Hopper
