Ski boot walking attachment initial

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Revision as of 18:20, 21 September 2008

Executive summary goes here. (Waiting for other content.)

Brandon

Needs & Stakeholders

Overview

Alpine downhill skiing

Alpine skiing is a popular sport worldwide. The premise is nothing more than affixing stiff runners to one’s feet and proceeding down the side of a mountain to the equipment installed to transport the skier uphill for another round of downhill skiing. However, such a simple sport has ballooned into a multi-billion dollar industry. Every year, some 6.3 million Americans visit the 481 alpine skiing resorts operating in the United States<ref>National Ski Areas Association. "Industry Stats." <http://www.nsaa.org/nsaa/press>.</ref>. They spend, on average, 9 days on the slopes. Their ages span from pediatric to geriatric, averaging to 33. The ski mountains frequented by day are often surrounded by a resort village sized to accommodate the large amount of often wealthy tourists. As many once-booming coal towns became ghost towns once the coal supply was exhausted, these ski towns would face certain downsizing and restructuring were the ski industry to collapse<ref>"Mild Winter Affects the Economy." Vermont Business Magazine. May 2007. <http://findarticles.com/p/articles/mi_qa3675/is_200705/ai_n19430501/pg_5></ref>. These owners, proprietors, and employees are dependent on an industry of enjoyment.

Alpine downhill skis

High-quality downhill ski boots

Downhill skiing would not be possible without its namesake equipment, the ski. In turn, a ski is useless without a way to attach it to the human body. The ski boot fulfills this surprisingly complicated role. Skis generate forces and moments in all directions upon the foot, and the rider exerts forces upon the skis to turn, jump, and stop. Boots must strike a balance between weight, stiffness, comfort, and price. Quality ski boots sell for between $200 and $600 and must be fitted properly to give the skier control over the skis<ref>C.f. Alpine Ski Shop, a ski equipment retailer. <http://www.alpineskishop.com/skiboot.html>.</ref>. Ski boots are shaped largely like a normal boot, though have three major additional features. First, ski boots must largely immobilize the ankle. Pressure from the shin against the tall tongue of the boot is necessary for ski control, so a rigid boot is necessary to transmit that force. Second, these rigid boots use metal buckles to tighten their exoskeleton around the foot. Buckles provide a convenient method of tightening and loosening the boots as necessary, for wear and for removal. Third, ski boots must attach to the skis. In the early days of skiing, boots were clamped securely to skis with no means of emergency detachment<ref>SkiingHistory.org: "The First Release Bindings."<http://www.skiinghistory.org/releasebindings.html></ref>. After the problem of broken legs and ankles arose, emergency-detach ‘bindings’ were developed to allow a ski to break free of a (crashing) skier. Modern bindings (and thus, modern boots as well) follow a standardized interface design. A hard heel and toe of the boot are mandatory, as are slight protrusions from the heel and toe.

The heel and toe hardness, along with the ankle stiffness, make walking in ski boots a harrowing task (more on this below). Walking is a necessity: upon arriving at the ski slope, the typical skier will put on his ski boots, place his shoes in a locker - lest he carry them - and proceed – skis in hand – across an icy surface to the ski slope. Crowds and stairs are frequent obstacles. Ski boots commonly include treaded pads on the sole to improve traction on slippery surfaces. And, in an attempt to regain ankle mobility, a universal solution is to unbuckle the boots. As a tradeoff for ankle flexibility, the foot is exposed to cold air and snow; small children and novice skiers may be unable to re-buckle their own boots. And in the end, walking is still awkward.

[diagrams]

This walking problem is a nuisance 60 million skier-days per year. Manufacturers are tied to an industry-standard design which prevents modification of the boots themselves, and ski resorts are partially exempted from liability for personal injury<ref>"Survey of Ski Law in the United States" <http://www.skilaw.com/skilawsurvey.html></ref>. As such, the consumer (wearer) is the party most directly affected by the difficulty of walking. With 40% of the skiing population having a household income of over $100,000, these consumers have the economic means to purchase or rent additional beneficial equipment, such as inexpensive, convenient attachments to make walking easier.

Detail: Kinesiology of Walking

Ankle during step

During the walking step, the ankle flexes positively and negatively.

As the heel strikes, the ankle provides a negative power - resistance to flex. Then, as the step continues towards toe-off, the ankle provides forward propulsion and height control.

During the normal human walking gait, periods of two-foot ground contact are separated by longer periods of one-foot contact. These long periods are when the front foot takes the weight load from the rear foot and the rear foot swings forward to take the next step. During this process of taking a step, the ankle flexes to control body height and shin-to-foot angle, and to provide forward propulsion.<ref>Soutas-Little, Robert. "Motion Analysis and Biomechanics." <http://www.laboratorium.dist.unige.it/~piero/Teaching/Gait/SOUTAS-LITTLE%20Motion%20Analysis%20and%20Biomechanics.htm></ref> (see above).

However, while immobilized in a ski boot, the ankle is unable to flex. This alters the walking gait and changes the procession of the body's center of gravity relative to the point of load on the sole.

In light of the aforementioned difficulty, risks, and necessity of walking with locked ankles, there is a need for a solution to this awkward gait modification.

Product Use & Function

Device installed on a ski boot. Compare to bare ski boot above.

Not surprisingly, an inexpensive attachment to facilitate walking does exist. The attachment replaces the flat walking surface of the ski boot with a curved surface which smoothes the stride. And, unlike the boot sole, it can be cushioned and can use materials selected to provide increased traction.

Major Functions

• Smooth the stride
• Traction
• Cushioning

[diagrams]

Device folds for storage and carry.

The device attaches to the standard binding tongues on the ski boot using a simple clip mechanism found on other ski products. It can be installed and removed quickly with the flip of a lever: the toe tongue of the boot is placed in the front orifice, the heel tongue is set in place, and a lever is tightened to secure the boot to the device. For the sake of convenience, it folds in half for easy stowage when not in use. It feels and appears rugged enough to support the repetitive stresses of the user’s weight, yet the design is reasonably lightweight, as carrying heavy gear while on the slopes is unpopular.

Major Characteristics

• Lightweight
• Simple
• Easy to install & remove
• Rugged

Bill of Materials

Jarrett

Assembly Number	Part Number	Image	Name	Qty	Weight	Function	Material	Manuf. Process
1	N/A		Assembly, Main Body	1		To provide an area in which the boot rests and to create a shape that aids in walking and makes it a more natural motion	See individual Components	See individual Components
	1		Frame, Front	1		To provide the main support for the front of the ski boot	Rubber/Plastic	Dunno
	2		Frame, Back	1		To provide the main support for the back of the ski boot	Rubber/Plastic	Dunno
	3		Side Plate, Front	2		To improve the appearance of the walking attachment and to prevent anything from getting into the frame	Plastic	Stamping
	4		Side Plate, Back	2		To improve the appearance of the walking attachment and to prevent anything from getting into the frame	Plastic	Stamping
	5		Pin	2		Creates an axis about which the Links can rotate so that the entire walking attachment can be folded in half	Steel	Drawing
	6		Links	5		Attaches to the Pins on both the front and back Frame pieces so that the entire walking attachment can be folded in half	Steel	Stamping
2	N/A		Assembly, Locking Mechanism	1		Clips down against the ski boot to lock the walking attachment in place, is a combination of assemblies 2a and 2b	See individual Components	See individual Components
2a	N/A		Assembly, Plastic Clip	1		Actually makes contact with the ski boot to hold walking attachment in place	See individual Components	See individual Components
	7		Clip, Large	1		Attaches to the Small Clip with the Clip Screw to create the Plastic Clip	Plastic	Injection Molding
	8		Clip, Small	1		Attaches to the Large Clip with the Clip Screw to create the Plastic Clip	Plastic	Injection Molding
	9		Clip Screw	1		Holds the Large and Small Clip pieces together to create Plastic Clip	Steel	Dunno
2b	N/A		Assembly, Metal Frame	1		Attaches the plastic clip portion to the walking attachment main body and provides rigid support to keep the boot attached	See individual Components	See individual Components
	10		Spring	2		Allows the user to lengthen the entire Metal Frame in order to properly position the Plastic Clip to secure the ski boot	Steel	Winding
	11		Spring Retention Nut	2		Keeps spring within the Spring Containment Tube and allows it to be compressed, attaches to the Metal Frame End Piece	Steel	fadsff
	12		Spring Containment Tube	2		Attaches to the Metal Frame Attachment and contains the Spring	Steel	Worked Tube Stock
	13		Metal Frame Attachment	2		Attaches to the Spring Containment tube and to the Pin to join the Main Body to the Locking Mechanism	Steel	Stamping

Design for X

“Design for X” (DFX) analyses of a product evaluates the efficiency of the product design from various perspectives. In this report, three major analyses are conducted on several individual components and sub-assemblies of the ski boot and the walking attachment – “Design for Manufacture” (DFM), “Design for Assembly” (DFA), and “Design for Environment” (DFE). By conducting three types of DFX analyses, the overall efficiency of the product design during the manufacturing stage (DFM), assembly process (DFA), and post end-use impact to the environment (DFE) will be determined.

Design for Manufacture (DFM)

The design for manufacture analysis discusses how individual components of the ski boot and the walking attachment were designed in order to minimize the time and cost of manufacturing process. The product design can be optimized for manufacturing process through (1) reducing the number of components, (2) homogenizing the components, or (3) redesigning of the component. Reducing number of components or homogenizing the components cuts the capital cost of production as fewer numbers of machineries are required to manufacture the product. On the other hand, redesigning of the product aims to reduce the material cost per unit product by subtracting the unnecessary portions (deadweights) of the components from the original design. The following analyses on the main components of the ski boot and the walking attachment discuss the three features (listed above) of the components that optimize the product design.

Ski Boot: The components of ski boot could be divided into five major categories – the plastic frame, the inner plastic sole, the inner boot, series of (four sets per each boot) locking mechanisms, and front and rear bottom covers. In the following analyses, the design features that optimize the efficiency of manufacturing process, found in the plastic frame, locking mechanisms, and bottom covers are summarized.

Plastic frame of the boot –

Locking mechanisms – Each boot has four sets of locking mechanisms (sub-assemblies) that consist of a geared belt and a spring loaded hook that hold the two sides of the boot tight to provide better fit for users. For more user friendly design, one of the buckling mechanisms (the bottom buckling mechanism of high ankle component) needs to have a rotating hook. However, manufacturing rotating hook requires production of two parts (the outer frame that will secure the hook to the boot and an inner hook that locks on the channel). In order to reduce the cost of manufacturing, the ski boot uses two rotating hooks and two rigid hooks as opposed to using four rotating hooks. Rigid hook (which is a single component as opposed to a sub-assembly) allows lower cost of manufacturing; therefore, by replacing rotating hooks with rigid ones where the hooks do not need to rotate, the manufacturing cost goes down. What is even more interesting about the buckling mechanisms used in this particular ski boot is that as opposed to using three rigid hooks and one rotating hook (the boot only needs one hook that needs to rotate), it uses two of each. This decision was made in order to reduce the time of production. While manufacturing rigid hooks would cost less, having to manufacture three rigid hooks for every rotating hook manufactured would cause idle time for the machinery that manufactures rotating hooks. By using equal numbers of the two hooks, manufactures not only reduce the cost, but also achieve the minimum time of production achievable. For a product like a ski boot (whose market demand fluctuates from season to season), minimal time of production could be essential as that would allow the manufactures to meet volatile market demand without having to spend significant amount of inventory cost. Thus, the locking mechanism of ski boot is an excellent example of product design features that optimize both the time and the cost of manufacturing process.

Front and Rear rubber covers of the ski boot – Although ski boot itself requires separate castings for manufacturing right boot and left boot, the rubber covers for both feet are identical (just like the walking attachments). Also, the pattern on the bottom of the covers (made to provide the user with more traction) suggest that the front and the rear halves of the covers were manufactured in one casting, then cut into two separate pieces. Thus, identical designs used for both feet; and use of one casting for manufacturing front and rear halves allow significant reduction in capital cost.

Walking Attachment The walking attachment of the ski boot consists of three main sub-assemblies – front and rear soles, joint sub-assemblies (five joint pieces and a pair of pins), and spring loaded locking sub-assemblies. Following DFM analyses discuss the design features of each sub-assembly.

Front and Rear Soles – The soles of the attachment provide the user with better traction and more comfort during walking process than a normal ski boots do. These components are made of rubber to allow reasonable amount of elastic deformation under operations to serve as cushions that absorb impact of landing while providing the user’s feet with sufficient support. Unlike the ski boot itself (or any other foot ware), the attachment soles’ design are identical for both feet. This leads to a significant reduction in manufacturing cost as the manufacturing process requires only one set of casting for rubber molding as opposed to two.

Spring loaded adjustable locking mechanism –

Design for Assembly (DFA)

A design for assembly analysis discusses how each component of the product was designed to minimize the time and cost of assembly. Efficient product design for assembly involves (1) simple configurations of the assembly and (2) ease of aligning the components. Simple configuration prevents confusion and misplacement during the assembly process, while ease of aligning the components speeds up the assembly. The DFA on the main components (and sub-assemblies) of the ski boot and the walking attachment are provided below.

Ski Boot:

Plastic frame of the boot – The bottom of the ski-boot (where the rubber covers are put on) has series of channels so that the covers can be secured even without using screws. This allows manufactures to easily place the covers on the right place without having to line up the parts.

Walking Attachment

Front and Rear Soles – Spring loaded adjustable locking mechanism –

More text to come

Design for Environment (DFE)

Taka

FMEA

The table below shows several ways in which the ski boot walking attachment may fail. The item and function states the major components and their purpose, possible failure mode includes the possible ways the components may not perform as they are intended to do, effects of failure describes the consequences of the failed components, causes of failure explains the possible sources of failures, and design controls are methods in which the chance of failure mode can be reduced. S stands for severity, which is a measure of the significance of the effects of failure, O stands for occurrence, which is a measure of the likelihood that a component would fail, D stands for detection, which is a measure of the ability to detect the flaw whether during the manufacturing process or by implementing the proposed methods mentioned in design controls, and finally, RPN stands for risk priority number, which is a measure of design risk. RPN is the product of S, O, and D. The last few columns represent: recommended actions, which are the proposed methods that can be done to reduce the risk priority number, responsibility, which is a group or an individual who would be responsible for the recommended action, actions taken, which are actions that have been executed, and the updated risk priority number due to the corrective action.

Any failures that jeopardize the functionality of the walking attachment and endanger the user would receive a severity score of an eight. For example, failures in connectors and pins would result in the walking attachment to be divided in half, which is inoperable at this point. If the failures occur while someone is walking, then he/she could very well be hurt. The smoothening of the rubber grips receive a seven because the system would still be operable, but it would no longer be safe to walk on especially on slippery surfaces like ice.

Occurrence and detection are typically rated very low (between two and three) because most of the components serve a simple purpose, contain almost no complexity in their geometry, and are visible without taking anything apart. Furthermore, the only components that would have a slightly more difficult time to notice when failing are the compression springs. Each spring is located inside a hollow cylindrical chamber that is part of the metal frame, but even if one spring fails fail, it would be noticeable because the metal the piece containing the spring would not be adjustable. The occurrence values are estimated by examining the material of each component, the purpose each component serves, and the complexity of its geometry.

Analysis

Taka, Jarrett, Randy, Brandon

References

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