Helping Hands Prosthetics
Providing Low Cost Solutions to the World's Prosthetic Needs What is Prosthetics?
A prosthetic is an artificial extension that replaces a missing body part. These have been created using the science of fusing mechanical devices with human muscle, skeleton, and nervous systems to assist or enhance motor control lost by trauma, disease, or defect. Prostheses are typically used to replace parts lost by injury (traumatic) or missing from birth (congenital) or to supplement defective body parts.
Why is Helping Hands Prosthetics different?
Because there is such a great need for cheap, easily manufactured, prosthetic limbs, Helping Hands Prosthetics of the Mechanical, Materials, and Aerospace Engineering Department at the Illinois Institute of Technology chose to undertake the design of a prosthetic hand. Our objective was to design a hand that was relatively cheap and easy to manufacture that met a list of particular technical specifications. Helping Hands Prosthetics undertook the task of developing a low cost, easily manufactured prosthetic hand to be made available for use in underdeveloped communities. This project was in conjunction with the work done in Jaipur, India by Bhagwan Mahaveer Viklang Sahayata Samiti.
By following specific design processes, Helping Hands Prosthetics developed a unique design for a prosthetic hand with a stationary thumb and two moving fingers driven by a worm gear mechanism. The hand has some key features to meet the specific needs of this project to include a built in mechanical locking system and a simple manufacturing process. This simple design has a great deal of promise and has been produced as an alpha prototype.
Background Information & Market
According to a survey done by the National Sample Survey Organization of India in 2003, a little over one percent of the Indian population suffers from loco-motor disability. Their disabilities range from amputations to disease inflicted handicaps. In 1968, the Jaipur foot was developed. This prosthetic device revolutionized the world of prosthetic limbs because it was made of less cumbersome materials,easy to manufactured, and relatively cheap. In 1975, Bhagwan Mahaveer Viklang Sahayata Samiti(BMVSS), Jaipur became a formally recognized society in India. BMVSS states their purpose on their website as follows:
The main objective of the BMVSS is the physical, economic and social rehabilitation of physically challenged, particularly the resource-less, enabling them to regain their mobility, self respect and human dignity so that they can become self-reliant, normal and productive members of the community. BMVSS works today to fit 17,000-20,000 artificial limbs at no cost to the amputees and is the largest organization for the handicapped in the world.
Design & Analysis
By following a classic design process of collaboration, model production, product analysis, and testing, Helping Hands Prosthetics was able to develop a fairly simple prosthetic hand prototype. The design needed to produce 15 lbs of pinching force, cost less than $90, and be easy to manufacture. For a full list of the functional requirements, see Appendix I.
The basic driving mechanism of the design is a worm gear. A 300 rpm motor turns a worm which drives a set of gears that translate the torque into the two moving fingers. As one can see in Figure 2, the gear train beyond the worm gear is a pretty simple connection between two spur gears. The larger of the two spur gears is directly attached to the fingers, so as it turns, they turn.
Another key to this design is the stationary thumb; having fewer moving parts creates less complexity and ultimately leads to reduced cost and manufacturing time. There are two casing pieces, one with the thumb built in, and two fingers. Each of these pieces is designed to have the same basic central shape. These shapes can easily be punched out of sheet metal and then bent to meet the specified manufacturing configurations. Figure 4 shows another view of the alpha prototype.
Ease of Manufacture & Marketability
When starting any design you want to think about how the product will be manufactured. Using good engineering skills in this area will allow the finished product to have a low cost and be quickly and easily assembled allowing for a quick turn-around time. One will always want to pay attention to detail when designing for manufacture (DFM) because many small details can make a big difference in the actual manufacturing process such as rounding corners, making modular pieces, or just using standard components.
With the limited tools and craftsmanship available for the mass production of this design, simplicity is important. To manufacturing the casing, basic shapes can be pressed out of commercially available sheet metal, and then bent to meet shape specifications. Using uniform parts for screws, fasteners, and similar pieces keeps the complexity and cost down. All the nuts and bolts of this design are the same. The assembly of the hand requires only three basic tools, a flat head screwdriver, a 5/8 inch wrench, and an Allen wrench. This provides for mass production by workers with little to no technical training.
One existing prosthetic hand design uses bevel gears to translate torque from the motor to the fingers. In this design additional parts had be incorporated in order to prevent the fingers from opening when the motor is disengaged. One advantage of the design by Helping Hands Prosthetics is that the worm drive system provides a built in mechanical stop. The worm itself provides resistance to movement without additional parts or additional power. This built in feature provides for a simpler design and increases ease of manufacture, a main selling point for this design.
Beta Prototype
Ideally all the design considerations, calculations, and model production that went into this design would lead to a product set for manufacture, but Helping Hands Prosthetics humbly admits there is more work to be done in the design of an affordable, easy to manufacture, prosthetic hand. After a limited amount of testing of the alpha prototype, we began developing a list of suggestions for a future model, the Beta Prototype.
Size and Shape Changes
Overall, the alpha prototype was significantly larger and more bulky that the designers intended. We adapted the design on the spot to reduce finger length, but future installments should begin with smaller fingers in mind. The gear casing could also be minimized by decreasing the axel length, changing to an angular shaped case, and removing unnecessary material all around. These reductions would promote a smaller lighter hand that could fit inside provided covering.
Mechanism Changes
Although our calculations and testing support out design, we believe there may be a more efficient manner to achieve the same goal, and reduce malfunction. For one, the use of shaft keyways or gear pinning would prevent the gears from slipping on the shafts. Set screws worked for us in the short run, but after an extended period of use they were unable to withstand the torque and significantly lowered the power output of the hand. Along the same lines, there is room for improvement by removing gears. Late in the design process we determined that we could get the same or better torque output with a one worm gear setup. A bigger motor would also increase the force output of the hand, but the available current and voltage must be considered.
Hardware and Material Changes
Initially overlooked, the hardware selection could aid in a faster manufacturing process. Because the several gears in use came from different producers, the set screws required different sizes of Allen wrenches. Although we currently advice against the use of set screws, should a future design use set screws, getting the same set screws would be helpful. In the current design there is a potential for friction between the gear shafts and the casing wall. Plastic standoffs between the gears and the casing would prevent this wearing. Finally, to increase friction between the fingers and an item to be gripped, grip tape, or rubber coverings should be added. This function could be filled by the synthetic hand covering that is made to mimic a human hand.
Helping Hands Prosthetics Group
Members: Rebecca Martin, Jesus Cervantes, Lydia Benger, Michal Kaska, Erick Leong, Monmayuri Ray, Alex Kolbasov
Providing Low Cost Solutions to the World's Prosthetic Needs What is Prosthetics?
A prosthetic is an artificial extension that replaces a missing body part. These have been created using the science of fusing mechanical devices with human muscle, skeleton, and nervous systems to assist or enhance motor control lost by trauma, disease, or defect. Prostheses are typically used to replace parts lost by injury (traumatic) or missing from birth (congenital) or to supplement defective body parts.
Why is Helping Hands Prosthetics different?
Because there is such a great need for cheap, easily manufactured, prosthetic limbs, Helping Hands Prosthetics of the Mechanical, Materials, and Aerospace Engineering Department at the Illinois Institute of Technology chose to undertake the design of a prosthetic hand. Our objective was to design a hand that was relatively cheap and easy to manufacture that met a list of particular technical specifications. Helping Hands Prosthetics undertook the task of developing a low cost, easily manufactured prosthetic hand to be made available for use in underdeveloped communities. This project was in conjunction with the work done in Jaipur, India by Bhagwan Mahaveer Viklang Sahayata Samiti.
By following specific design processes, Helping Hands Prosthetics developed a unique design for a prosthetic hand with a stationary thumb and two moving fingers driven by a worm gear mechanism. The hand has some key features to meet the specific needs of this project to include a built in mechanical locking system and a simple manufacturing process. This simple design has a great deal of promise and has been produced as an alpha prototype.
Background Information & Market
According to a survey done by the National Sample Survey Organization of India in 2003, a little over one percent of the Indian population suffers from loco-motor disability. Their disabilities range from amputations to disease inflicted handicaps. In 1968, the Jaipur foot was developed. This prosthetic device revolutionized the world of prosthetic limbs because it was made of less cumbersome materials,easy to manufactured, and relatively cheap. In 1975, Bhagwan Mahaveer Viklang Sahayata Samiti(BMVSS), Jaipur became a formally recognized society in India. BMVSS states their purpose on their website as follows:
The main objective of the BMVSS is the physical, economic and social rehabilitation of physically challenged, particularly the resource-less, enabling them to regain their mobility, self respect and human dignity so that they can become self-reliant, normal and productive members of the community. BMVSS works today to fit 17,000-20,000 artificial limbs at no cost to the amputees and is the largest organization for the handicapped in the world.
Design & Analysis
By following a classic design process of collaboration, model production, product analysis, and testing, Helping Hands Prosthetics was able to develop a fairly simple prosthetic hand prototype. The design needed to produce 15 lbs of pinching force, cost less than $90, and be easy to manufacture. For a full list of the functional requirements, see Appendix I.
The basic driving mechanism of the design is a worm gear. A 300 rpm motor turns a worm which drives a set of gears that translate the torque into the two moving fingers. As one can see in Figure 2, the gear train beyond the worm gear is a pretty simple connection between two spur gears. The larger of the two spur gears is directly attached to the fingers, so as it turns, they turn.
Another key to this design is the stationary thumb; having fewer moving parts creates less complexity and ultimately leads to reduced cost and manufacturing time. There are two casing pieces, one with the thumb built in, and two fingers. Each of these pieces is designed to have the same basic central shape. These shapes can easily be punched out of sheet metal and then bent to meet the specified manufacturing configurations. Figure 4 shows another view of the alpha prototype.
Ease of Manufacture & Marketability
When starting any design you want to think about how the product will be manufactured. Using good engineering skills in this area will allow the finished product to have a low cost and be quickly and easily assembled allowing for a quick turn-around time. One will always want to pay attention to detail when designing for manufacture (DFM) because many small details can make a big difference in the actual manufacturing process such as rounding corners, making modular pieces, or just using standard components.
With the limited tools and craftsmanship available for the mass production of this design, simplicity is important. To manufacturing the casing, basic shapes can be pressed out of commercially available sheet metal, and then bent to meet shape specifications. Using uniform parts for screws, fasteners, and similar pieces keeps the complexity and cost down. All the nuts and bolts of this design are the same. The assembly of the hand requires only three basic tools, a flat head screwdriver, a 5/8 inch wrench, and an Allen wrench. This provides for mass production by workers with little to no technical training.
One existing prosthetic hand design uses bevel gears to translate torque from the motor to the fingers. In this design additional parts had be incorporated in order to prevent the fingers from opening when the motor is disengaged. One advantage of the design by Helping Hands Prosthetics is that the worm drive system provides a built in mechanical stop. The worm itself provides resistance to movement without additional parts or additional power. This built in feature provides for a simpler design and increases ease of manufacture, a main selling point for this design.
Beta Prototype
Ideally all the design considerations, calculations, and model production that went into this design would lead to a product set for manufacture, but Helping Hands Prosthetics humbly admits there is more work to be done in the design of an affordable, easy to manufacture, prosthetic hand. After a limited amount of testing of the alpha prototype, we began developing a list of suggestions for a future model, the Beta Prototype.
Size and Shape Changes
Overall, the alpha prototype was significantly larger and more bulky that the designers intended. We adapted the design on the spot to reduce finger length, but future installments should begin with smaller fingers in mind. The gear casing could also be minimized by decreasing the axel length, changing to an angular shaped case, and removing unnecessary material all around. These reductions would promote a smaller lighter hand that could fit inside provided covering.
Mechanism Changes
Although our calculations and testing support out design, we believe there may be a more efficient manner to achieve the same goal, and reduce malfunction. For one, the use of shaft keyways or gear pinning would prevent the gears from slipping on the shafts. Set screws worked for us in the short run, but after an extended period of use they were unable to withstand the torque and significantly lowered the power output of the hand. Along the same lines, there is room for improvement by removing gears. Late in the design process we determined that we could get the same or better torque output with a one worm gear setup. A bigger motor would also increase the force output of the hand, but the available current and voltage must be considered.
Hardware and Material Changes
Initially overlooked, the hardware selection could aid in a faster manufacturing process. Because the several gears in use came from different producers, the set screws required different sizes of Allen wrenches. Although we currently advice against the use of set screws, should a future design use set screws, getting the same set screws would be helpful. In the current design there is a potential for friction between the gear shafts and the casing wall. Plastic standoffs between the gears and the casing would prevent this wearing. Finally, to increase friction between the fingers and an item to be gripped, grip tape, or rubber coverings should be added. This function could be filled by the synthetic hand covering that is made to mimic a human hand.
Helping Hands Prosthetics Group
Members: Rebecca Martin, Jesus Cervantes, Lydia Benger, Michal Kaska, Erick Leong, Monmayuri Ray, Alex Kolbasov