Krobohand – Final Product and Business Case Submission – 2017 Beall Competition

Ethan Kirkley 2016-2017, 2016-2017 Krobohand

Let us premise this by saying this is an extensive blog post that arguably should be split up into multiple parts, but as this is the submission we made to the 2017 Beall Competition, we thought it’d be best to keep the entirety of it together in one blog post.

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Krobohand Final Product and Business Case:

Final Product Description –

An opportunity exists in developing a prosthetic hand that can outperform the current prosthetic hands on the market, at a competitive price point, all while creating a brand that resonates with the user. An ideal situation would be to come as close as possible to the degrees of freedom of a human hand. Krobotech’s goal is fill a gap that exists in the upper limb prosthesis industry between cost and functionality with Krobohand.
Krobohand is a 3D printed, low cost, high articulation robotic prosthetic hand. With the use of dual-material 3D printing, the cost of assembly materials required in most prosthesis today can be cut significantly. Krobohand has been designed to be “ready for articulation” immediately after being 3D printed. Effectively, the time needed for assembly can be reduced significantly, if the only assembly required is for articulation. That is, the flexor tendon cables, servo motors, microcontroller, battery, and wiring.
The first and foremost goal of Krobohand is to enable the user to complete essential, everyday tasks. These tasks range from picking up items, typing on a computer keyboard, tying shoelaces, and practically anything a non-amputee can do. Many prosthesis on the market currently can do very few of these functions. Even those that can perform any given function such as picking up an item, do so inefficiently. This inefficiency stems from a lack of lateral movement in the fingers, and lack of imitation of human hand movement.
This biomimicry is a major distinguishing factor between Krobohand, and the vast majority of prosthesis on the market today. Without lateral movement in a finger, and other human-like movement, many tasks that non-amputees overlook as simple motor functions, falls to the wayside. As with any prosthesis, different functions are extremely important. However, the practicality of functions are severely hindered when an amputee can’t move their fingers laterally. This essentially opens up a whole cache of new, more effective functions yet to be seen in the consumer upper-limb prosthetic industry.
The main body of Krobohand is printed from a medical grade, styrene-free 3D polymer called Inova-1800. This material is not only durable, but also complies with certain FDA food contact regulations. Designed within the structure of the hand are flexible tendons, printed from a specially formulated thermoplastic polyurethane, or TPU, called Ninjaflex. These tendons, acting similarly to the extensor tendons in a human hand, have three major purposes – to stabilize the hand and fingers at any given time, smooth the movements of the hand, as well as return the hand to a resting position. Ninjaflex can achieve 660% elongation, so repeated movement and stretching won’t cause wear or cracking, as the material will never leave the elastic region in terms of fatigue. This integration of an extensor tendon is something that has yet to be seen within the industry.
Ninjaflex, having a much higher coefficient of friction compared to any other 3D printed material, is significantly grippy when printed. Due to this, it is printed on sections of the hand that will be needed for grasping, specifically the inner side of all fingers and thumb surfaces, as well as the palm. The tendon and grip will be connected by a core of this filament running through the rigid body of the fingers. A common practice in the industry thus far has been to have separate micro gel fingertips for gripping, but with the grip required printed directly onto the prosthetic, this extra step is avoided.
A single servo motor for each finger, including the thumb, will be responsible for lateral movement. Lateral movement will be achieved by a small pull-pull assembly, much like that of an airplane tailfin, inside the palm through the servo motor, with cables attached to opposite sides of the lateral joint at the base of each finger. When inputs are read from muscle sensors attached to the amputees existing muscle groups, lateral output signals from the Arduino Uno will determine if lateral movement is required. If so, the servo motors will engage, moving the fingers laterally as needed. Lateral movement has yet to be done on such an affordable scale, which we view as vital.
Movement is still required to open and close each finger. To do so, one more servo per finger will be utilized. Kevlar line, an inexpensive but strong cable, will act as the flexor tendon, running throughout each finger, and fastened to the tip. When inputs are read from muscle sensors attached to the amputees existing muscle groups, linear output signals from the Arduino Uno will determine if linear movement is required. If so, the servo motors will engage, pulling the finger as needed for any given function. With the servo motors on each finger working in unison, the fingers will essentially be able to mimic that of a human finger. The next major factor in the functionality of the prosthetic is the thumb design.
Most current prosthesis have thumb articulation that isn’t the most beneficial or even useful. Most will limit the thumb’s movement by having the thumb be articulated by a single actuator. Being able to move the thumb inwards towards the palm, separately from closing the thumb itself, is essential in providing the best functionality. To do so, the Krobohand utilizes two servo motors. One servo motor is dedicated to the simple motion of moving the base of the thumb into the palm, while the other is dedicated to closing the thumb, much like the servos for each finger. Like the fingers, the thumb also has a thermoplastic polyurethane tendon running through it, which acts as a stabilization and extensor tendon for the thumb.
Further, Krobohand is built in a modular way, meaning that if at any moment, one of the fingers were to break, the amputee could easily replace a single digit, instead of buying an entirely new prosthetic device.
The final product will have the amputee using their own muscles to control the Krobohand. There will be product tuning and fitting on a case-by-case basis, since every patient’s interaction with the prosthetic will be different, but this process can be streamlined by having different adaptations of the prosthetic depending on different types of amputees. For example, an amputee at the wrist will have a slightly different interface than an amputee halfway up the forearm. Each amputee will be able to control the Krobohand using their existing muscle groups, but what muscle groups are still existing will vary from amputee to amputee. Other than that, the user interface will be straightforward. They will be directly connected to the prosthetic by a Myo Armband, with which they will have prior knowledge of how to get their Krobohand to function, by flexing and relaxing their muscles.

Market Demand –

The Krobohand is unique in several ways, and patentable in one main way. Three distinct factors make our prosthesis sustainable in the upper limb prosthetic market: innovative design and construction using dual-material 3d printing, streamlined connectivity between amputee and prosthesis, and brand recognition. The design and construction methods that make Krobohand is a patentable process, as it hasn’t been done in any prior art, especially in this industry. Many prosthetic devices lack severely with which they connect to the amputee, which can be incredibly frustrating when using for the first time. We’re in the process of creating Krobohand to be as close to “plug and play” as possible by standardizing functions and grips via electromyography. Brand recognition is also something that is rarely concerned with in the prosthetic market, and even more so in the upper limb prosthetic market. Our goal with this factor is to create a device that amputees are proud to wear, and want to show off. By making Krobohand have a sleek form factor, and clean design, we think this level of brand recognition is possible.
Within the upper limb prosthetic market, there exists a limited number of products, many of which lack severely in movement and integration between the user and the prosthetic. The movement and integration quality of any given prosthetic, as it currently stands, correlates directly with price, with a few exceptions on the higher cost prosthesis. There is a wide spectrum of different prosthetic products, ranging from the inexpensive but low functionality E-Nable open source group and their range of prosthesis, to the costly myoelectric prosthetic hands that can cost up to one hundred thousand dollars for an advanced prosthesis (1). Most E-Nable prosthesis are limited to one, or a few more functions, while the myoelectric hands can have a variety of functions, but still with many limitations. Though each end of this spectrum of prosthesis serve their purpose, there is a gap that needs to be filled with a prosthesis that is both cost effective, and functional.
Annually, there are about two thousand new upper limb amputations occurring at the wrist or above it, which would be our main user. It could also be possible, however, to adjust the design to allow those with partial finger amputations the ability to use the prosthetic. This would represent another fourteen thousand amputees annually. This would be readily achievable, due to Krobohand’s modular design.
There are an estimated two million hand amputees globally (2). This represents a significant market for Krobohand, especially when it outperforms current prosthesis on the market, at an incredibly competitive price point. For an example in terms of price, a split-hook prosthesis with one function can cost an amputee upwards of $10,000. The Krobohand cost of manufacture will be roughly $500. Even at a price margin of $2,000, that still puts Krobohand at $2,500, or one quarter the cost of a less functional split-hook upper limb prosthesis, while still contending with the more immediate competition.
Since Krobohand’s design is standardized and modular, as business grows, costs would go down, and revenues would increase significantly. The machines we use are capable of printing fifteen fingers, or four palms, at once, and each machine being only $3,000, selling two Krobohands at $2,500 and a profit of $4,000 from them, would be enough to buy another production unit with $1,000 left over for materials and electronics.
Krobohand’s two most immediate competitors consist of Unlimited Tomorrow Inc., and Open Bionics. Unlimited Tomorrow’s design is straightforward, but has been released as open source, which severely hinders brand recognition, as any hobbyist can create the device, and could do so incorrectly. Further, their robotic hand has limited functionality, as the entire hand only operates off five servo motors, which is half of Krobohand. Their device has no lateral finger movement. Unlimited Tomorrow doesn’t have a set price on their device, however their 3D printed parts alone sell for $500.
A similar case exists with Open Bionics. Like Unlimited Tomorrow, their design is open source, although they have retained their brand recognition more effectively since their design includes a logo on the backside of the palm. However, just like Unlimited Tomorrow, their functionality is hindered by their design. Their robotic hand uses five linear actuators, once again lacking in lateral finger movement. Further, they use Olimex EMG sensors, which lack a streamlined process of connectivity between amputee and prosthetic. Their device is fairly expensive depending on the model, but their middle-range model runs about $1500.
We think Krobohand will outperform both of these immediate competitors through our increased functionality, ease of use, and drastically decreased cost of labor due to the concurrent joint printing. It is possible to compete in total price as well, but our profit margin would be minimal if we sold direct to consumer instead of through medical outlets such as the United States Department of Veterans Affairs. We’ve tried on multiple occasions to obtain a monetary value from Veterans Affairs with which they allow a veteran amputee to obtain an upper limb prosthesis, but have yet to receive an answer. Once we obtain this value, we think that would be an ideal price point, and that selling direct to consumer isn’t the most viable option for profit, but will keep that avenue open.
Further, no standardized robotic partial finger prosthetic exists on the market that would be a direct competitor, and the Krobohand’s modular design enables it to be easily modified as a functional partial finger prosthesis, with a minimal cost to produce at roughly $100. With no readily available competitor, and a large market for such a device, this would expand our revenues greatly.

User Interface –

We are creating Krobohand to be an incredibly easy prosthetic device for amputees to use. By putting on the Myo armband, and then attaching their Krobohand, with a simple power button, the amputee will be able to use their existing muscle groups to function the device. The battery life will be close to a full day worth of use, and the amputee will be able to plug in their Krobohand to charge, as they would a phone or laptop.
Prior to use, it is required to set a profile on the Myo armband, which will be unique to every amputee. This calibration of the Myo armband is done through an intuitive, free program called Myo Connect. This is something that we think could be done on-site at a company office location for example, which would make it even easier for the amputee. However, if coming to an on-site location isn’t a possibility, it wouldn’t be difficult to create a step-by-step guide on how to complete this step, as most of it is already outlined through the Myo Connect program.
Each Arduino Uno onboard the Krobohand will come pre-programmed with several built-in functions. The Arduino, which wirelessly receives electromyography signal from the Myo Armband, will interpret those signals, and tell the servo motors to perform those functions.
This is the only interface in which the amputee must operate through, as all the coding necessary will come pre-programmed on each Krobohand. Every other aspect of the Krobohand can be treated like any piece of technology, which will allow the amputee an ease of use that is unmatched in the upper limb prosthesis industry.

Product Architecture –

The hardware of the Krobohand is straightforward. Apart from electronics, the entire prosthetic will be 3D printed from two different plastics. Most the Krobohand will be printed from Inova-1800, a medical grade, styrene-free 3D polymer. The sections where the hand will touch objects, as well as the extensor tendons, will be printed from TPU, or thermoplastic polyurethane, which is a flexible but strong material, able to stretch to 660% its original length. The design of the Krobohand’s main body and flexible parts are crucial for the functionality of the prosthetic. This design is another major factor that distinguishes the Krobohand from other prosthesis on the market today. It is designed in a way where it can be printed in one piece, using a dual extrusion printer, allowing for the time for assembly to be cut significantly, as well as streamlining production. The joints of the finger are printed in one piece, and work properly directly off the print bed.
As for the electronics, the Krobohand will consist of ten servo motors, two per digit. Each digit will have a dedicated servo motor for lateral movement, or in the case of the thumb, inward movement. The other servo motor will allow each digit to close linearly. These servos will receive their input from an Arduino Uno micro-controller. To power the Krobohand, we will be using a rechargeable lithium-ion battery pack made from Panasonic NCR18650B Li-ion Battery Cells. It will be designed with a rectifier within it, so that the prosthetic can be charged simply by plugging it in to the wall, giving amputees more ease of use. The Arduino will receive signal inputs from the Myo armband wirelessly via Bluetooth, that will be on the amputee’s existing muscles groups when using the prosthetic, with which it will translate inputs from muscle movements into functions that the Krobohand will process and perform.
The software of the Krobohand is currently under development as well. Most of this is being developed within Arduino IDE. The code being made for the prosthetic is from scratch, and so each function is being made in order. Once this code is in place, it can be applied to specific input signals from the Myo armband, into movement for the servo motors.
The block diagram shown above details this entire process.

Prototype Development –

The Krobohand is being developed from scratch on both the hardware and software point of view. Through the Arduino IDE, the code is designed to receive EMG signal wirelessly from the Myo armband on the amputee’s existing muscle groups, and translate this signal into output signal to engage the servo motors. Though we are not designing and building our own electronics, we will be using these electronics in a new and innovative way that hasn’t been used yet in the prosthesis industry, to create new functionality for amputees. In the long term, however, it may be ideal to optimize the electronics for the Krobohand by developing our own micro-controller PCB board for example, but this can be considered in the future. From the hardware standpoint, the design of the body of the Krobohand is entirely proprietary. The design of the rigid Inova-1800 body, and the flexible thermoplastic polyurethane stabilization and integrated extensor tendons, and grip pads, are crucial for the functionality of the prosthetic. We’re taking a well-known technology, 3D printing, and using it in an innovative, dual-material utilizing way, to create a new type of prosthetic device.
There are some key products that the Krobohand utilizes. For printing the main body, tendons, grips, and joints, we are using Lulzbot Taz 6 printers with the Flexydually tool head. They have the capability to create dual extrusion, different material prints at once. So, the prosthetic will be able to be printed with the Inova-1800 body, and thermoplastic polyurethane parts, all in one piece. The Myo Armband from Thalmic Labs, Inc. will be used with every Krobohand in order to connect the amputee to the device, allowing them to use their existing muscle groups to perform functions. Further, all electronics will be obtained from other manufacturers, such as the Arduino Uno, Panasonic battery cells, and servo motors. We will design our own battery pack from separate cells, however, as it will enable us the ability to optimize power and voltage outputs. This wouldn’t be too difficult either, as it would be composed of separate lithium-ion batteries, which we would need to purchase and wire up. Apart from the Lulzbot Taz 6 printer, Myo armband, and the electronics, everything else will be designed and printed.
In terms of the process of development, fine tuning the structural design of the Krobohand, and the quality at which all parts are printed come first. We have already done rigorous testing on an Instron machine. We tested both the tensile, as well as three-point flexural capabilities of our structure design for the hand. Articulation of the Krobohand will be tested using a Myo armband to demonstrate different functions and grips. Ensuring that the prosthetic works as designed is of the utmost importance, before testing with actual amputees. Also, this will enable us to code as needed for each function or grip more readily. This will prepare us for testing the prosthetic with amputees.
Our prototype demonstrates the capabilities of dual-material 3D printing, and the ability to create a more human-like robotic hand with inexpensive processes and materials. It is important to ensure the prosthesis is working on a non-amputee handily, before taking it to an amputee for testing, as this will avoid any setbacks, ensuring ease of use for the amputee. Further, the prototype of Krobohand outlines how possible it is to create a low-cost, high articulation prosthetic device, and still beat out competitors by a significant margin.

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Thank you,

Krobohand Group