Amanda Steinberg, Alex Steinberg, and Michelle Deem
Maintaining physical activity post-amputation is imperative as it is both mentally and physically beneficial. The Adaptive Sports Center requested that participants with upper extremity amputations be able to ice climb. Ice tools are essential to vertical climbing and require wrist mechanics not replicable for individuals who have received wrist disarticulation and above amputations. We are designing an adaptation to the Grivel Lil’ Monster ice tool for individuals with upper extremity amputations to use when technical ice climbing. We are interfacing with the Colorado School of Mines, the Adaptive Sports Center, and 3D Material Technologies.
Amputation is both physically and mentally taxing on an individual. It causes pain and produces a negative emotional response, which can lead to an additional degradation of health. Physical activity, such as participating in sports, yields a wide variety of benefits. Mentally, it helps improve the individual’s self-esteem and accept their amputation by re-establishing body awareness. Physically, being active helps slow muscle fatigue from daily activities, thus improving the quality of life.
Our client is Adaptive Sports Center (ASC). ASC has requested an enhanced, light-weight device that will not only secure the residual, upper limb to the ice tool but will simulate the wrist action required for ice climbing, be adaptable for varying levels of upper extremity amputation, and be quick to remove in emergency situations.
Our invention is a device that clamps an ice tool to an individual’s prosthetic attachment site and emulates the wrist motion required of ice climbers. The design intent for this ice tool adaptation is to create an opportunity for the intended users. Just as technical ice climbing is not a casual sport for the uninhibited individual, it should not be a casual sport for an individual who has undergone upper extremity amputation. We expect our adaptation to make technical ice climbing feasible for the average individual with upper extremity amputation who is committed to athleticism.
Develop Features and Constraints
Interviews, research, and surveys were conducted with stakeholders, to devise the following feature constraints:
- Safe to use
- Causing no bodily harm
- Maintaining durability for a minimum of 5 years
- Secure an upper extremity residual limb to an ice tool
- Secure connection withstands 86kg – the weight of an average man
- Standardized attachment – USA Standard 1/2 inch diameter x 20 TPI threaded mounting stud
- Simulate single DOF wrist action
- 1 rotational DOF orthogonal to plane of the ice tool, where rotational motion is positive in the counter-clockwise (CCW) direction
We sought to establish basic kinematics and kinetics required for technical ice climbing. Motion capture markers were placed on subjects’ dominant hand index finger knuckle, medial and lateral condyles of the wrist, elbow, and shoulder. Markers were also placed on the Grivel Lil’ Monster (GLM) ice tool’s head, neck, and handle. The subjects were instructed to stand upon a Bertec® force place and mimic a typical ice strike 10 times. Data was collected for 5 seconds at 100 Hz utilizing Qualisys® motion capture software.
The analysis of the motion capture and force data was simplified to the two dimensional coordinate system of the vertical z-axis and the forward y-axis. The wrist angle is defined as the angle between the line of action of the knuckle and medial wrist condyle and the line of action of the medial and lateral wrist condyles. The two states of interest were determined as Pre-Flick state (S1) and Strike state (S2). S1 is defined as occurring at the time of the local minimum wrist angle just before the overall maximum wrist angle. S2 is defined as occurring at the peak displacement of the ice tool in the z-axis. The velocities of the ice tool were calculated for these states and used to determine a range of acceptable spring constants for our device. Governing equations are as follows:
We found a spring constant of approximately 100 lbs/in. From this, we drew two conclusions. Either we did not properly isolate the wrist action for our purposes or, given our design constraints, we are unable to mechanically replicate an intrinsic wrist action. Through some simplifying assumptions, considerations for sources of error, we determined a range of spring constants. We ordered 8 springs ranging from 14 lbs/in to 99 lbs/in. We will evaluate each spring in future work.
Additional calculations were performed to derive the specifications for the case, spacers, lever, and pins. The user was assumed to weigh 200 lbs and the tool to weigh 5 lbs. All parts were assumed to be functioning in a cold environment with corrosion resistant materials.
During ice climbing, our device switches between two states, “Loaded” and “Unloaded”. The ice tool is free to rotate about the Case Pin from an axis in line with the climber’s arm and an axis 40 degrees rotated from the first axis. When the climber hangs on the ice tool, the device is switched to the “Loaded” position. This is when the tool is in the axis 40 degrees from being in line with the arm. When the climber swings an arm, the momentum of the ice tool transitions the device from the Loaded to Unloaded state. This is when the ice tool is in line with the arm.
Wrist Action encompasses the requirement of the tool to emulate the sudden sharp movement of the tool head tip in order for the tool to penetrate the ice at the angle ideal for technical ice climbing. The ball and track system is comprised of two main pieces. The first is a flat-sided ball and shaft assembly, which is manufactured as one piece with a clamping mechanism. The shaft is extensible and tensioned via a spring. The clamp is secured to the handle of the GLM. The second main piece is a track and enclosure. The design is based on a double-jointed ball and socket action, where the ball slides along the curved track and the extensible, tensioned shaft allows for the ball to move, but also snap into two separate states.
Actuation Trigger encompasses the requirement of the tool to be powered with minimal human energy. In order to reduce complexity of design, we have limited our proposed solution to a purely mechanical system. This yielded an actuation trigger of an angular momentum threshold. When the ice tool is swung, the weighted head is one side of a force couple, which we take advantage of by allowing the opposite end to move inside our assembly. As stated above, the assembly is then locked into position until sufficient force is applied in an opposite direction. This is a switch between the open and closed states.
Quick Release Mechanism
Quick Release Mechanism encompasses the requirement of releasing the user from the ice tool. This allows the user to avoid hanging from a fall-induced injury. The proposed solution is currently reliant on the quick release capacity of the case pin. A more robust mechanism is planned in future work.
Socket Attachment encompasses the requirement of securing the tool to the user. We propose to leverage the engineering work completed in the Walter Reed Clamp (WRC), as seen in the WRC assembly and exploded view attachments. In assembly, we propose to secure its attachment sub-system to our case. It will be non-permanently attached so that it can be swapped with ease.
Failure Modes and Effects Analysis
A finite element analysis (FEA) was performed on the key features of our design, the clamp, the case, and the fork. A 250 lbf load was applied to simulate the weight of a person throughout the loading cycle. A range of 40 degrees from loaded to unloaded was determined from the kinematic analysis. Based on a finite element analysis for all significant parts, the lowest factor of safety for any part was 3.11, occurring at the neck of the clamp. The highest stress of the neck of the clamp equals 38,590 psi. While this is an acceptable factor of safety, given our constraint of being greater than a factor of safety of 2, we are going to seek to increase the factor of safety by addressing this stress riser in future work.
At this point in time, we have a light-weight device that will not only secure the residual, upper limb to the ice tool but will simulate the wrist action required for ice climbing while being quick to remove in emergency situations. These are all improvements upon the ASC’s present solution, the WRC.
Our primary legal concerns have been to ensure the safety of the device’s end user and reduce the possibility of an environmental impact; our team has not yet involved patent and trademark laws.
Schedule and Next Steps
Our product has the possibilities for line extensions and customization. The tool may be scalable and adjustable for different ages and levels of upper extremity amputation. Also, an adaptation may be created to allow any individual to climb more optimally.
Presently, we are refining our alpha prototype. We expect to have a final, workable device, comprised of titanium. Upon certainty of a successful product, through testing and analysis, our team will then deliver the device, as well as a few duplicates, to the ASC.
- De Luigi, Arthur J. and Rory A. Cooper. “Adaptive Sports Technology and Biomechanics: Prosthetics.” Paralympic Sports Medicine and Science 6.8S (2014): S40-S57. Print.
- “Determination – Amputee Climbers” 23 August 2013. SummitPost.org. <http://www.summitpost.org/determination-amputee-climbers/821584> 10 October 2014.
- Johnson, Jerry et al. “Air Hose Quick Coupler” Patent 3,873,062. 25 March 1975.
- Ronca, Debra. “How Ice Climbing Works” 13 October 2008. HowStuffWorks.com. <http://adventure.howstuffworks.com/outdoor-activities/climbing/ice-climbing.htm> 30 September 2014.
- Tennent, David J. et al. “Characterisation and outcomes of upper extremity amputations.” Injury 45 (2014): 965-969. Print.
- Tischler, Steve. “Ice Axes: How to Choose” 9 September 2014. REI.com < http://www.rei.com/learn/expert-advice/ice-axe.html> 30 September 2014.
- Truong, Alice. “Amputee Veteran Designs Ice Axe Prosthetic to Help Climb Everest” 16 April 2012. News.Discovery.com <http://news.discovery.com/adventure/extreme-sports/amputee-veteran-designs-ice-axe-prosthetic-to-help-climb-everest.htm> 10 October 2014.
We as a team would like to thank the following individuals for their time, instruction, and overall assistance in the development of this product:
- Dr. Joel Bach, Associate Professor for the Mechanical Engineering Department of Colorado School of Mines (http://inside.mines.edu/~jmbach/)
- Dr. Cameron Turner, Assistant Professor of Colorado School of Mines
- Dr. Briana Lucero, Teaching Assistant for Dr. Cameron Turner of Colorado School of Mines
- Mr. Chris Read, Program Director of Adaptive Sports Center (http://www.adaptivesports.org/)
- 3D Material Technologies (http://www.3dmaterialtech.com/)
- Ms. Rachel Abler, Colorado School of Mines Outdoor Recreation Center Coordinator (http://recsports.mines.edu/REC-Outdoor-Recreation)
- Mr. Zachary Moeller, Ice Climbing Guide and Enthusiast
- Mr. Bob Radocy, the founder and CEO of TRS Inc. (http://www.trsprosthetics.com/)