Active climbing cam

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Revision as of 01:44, 14 February 2007

Executive Summary

The following analysis consists on the thorough examination of the rock-climbing camming device, following the specifications and requests of Initech Corporation. Information about the product in general was first gathered, such as its function, target customers, etc. After collecting this data, the functions of the product and the customer needs were evaluated. The device itself was then studied, analyzing every component of its mechanism through a complete dissection. The manufacturing process of each component and the assembly of the mechanism were also assessed. Finally, DFMA, FMEA and DFE analyses were performed.

Product Overview

The climbing cam is a rock climbing protection equipment. The main purpose of the camming device is to shorten the distance a climber could fall, and to anchor climbers to the rock.

Product Requirements

The primary product requirement is that it functions reliably during frequent and varied use. Failure during use of a climbing apparatus can result in death or serious injury. In order for the product to be useful in the mountains it must withstand the abuse of the harsh, exposed environment along with the impacts of frequent use. The climbing cam must function properly each time it is placed to protect against a fall. Furthermore, the cam must function to some extent even when placements are not completely ideal. The size, orientation, or shape of a fissure in the rock may not hold the cam in the ideal position, yet the product must still perform outside the bounds of its ideal use. The most salient concern for this product is that the device functions properly to mitigate the inherent dangers in climbing. A more inclusive inventory of product requirements is listed below:

• Reliable functioning in a fall
• Able to withstand the impacts of climbing
• Functions in diverse placements
• Durable and long lasting
• Easy to identify wear or deterioration

Customer Needs

Beyond the performance requirements of the product, the customer also has specialized needs in order for the product to be useful. The customer’s main concern is that the product enhances the climbing experience through safety, allowing people to travel beyond pervious limits. Climbing is typically pursued for sport or leisure, thus the primary goal may be personal enjoyment. The customer needs a product that's benefits outweigh its detractions. In order for the product to enhance the climbing experience it must be easy and efficient to use, and low in weight as not to impede progress. The customer must be able to quickly and easily place and remove the product from the rock. Often times a more experienced climber will place the gear into the rock while a less experienced climber must be able to remove it. In order for the product to enhance the experience it must be of minimal weight. An overly heavy device may impede and slow a climber to the point of it actually putting the climber in danger. The customer needs of this product rely on an increase in safety without seriously slowing a climber’s movement. A more inclusive inventory of customer needs is listed below:

• Low weight
• Quick and easy placement and removal
• Accommodates removal by less skilled climbers
• Easy to handle between harness and rock
• Fast differentiation between sizes
• Compatible with sizes of older models and other types of climbing protection
• Affordable to average climber
• Low maintenance that can be performed in-field
• Accommodates a variety of hand sizes

Functionality

Camming device during triggering process.

On its initial position, the camming device starts with the three lobes aligned horizontally. The trigger is pulled towards the sling using the index and middle finger. This movement slides the trigger down pulling the trigger wires, which are attached to the trigger on one end, and to the lobes on the other end. The tension on the cables causes the lobes to rotate around the axle; the trigger must be pulled until the lobes are completely aligned vertically. During the triggering process, the springs come into action, creating an opposite force that causes the lobes to resist to rotation (and at the same time trying to bring the lobes back to their initial position); the fingers in the trigger must therefore apply resistance to keep the lobes aligned vertically. At this time is when the cam is inserted in the crack. Once the cam is in place, the trigger must be released, causing the lobes to return to their normal position. Now, the springs are in charge of pushing the lobes against the rock walls inside the crack.

Watch a demonstration video on using a climbing cam that we did in the lab.

Analysis of components

Manufacture of parts

The climbing cam is a mechanical device composed of 12 different parts.

Part No.	Name	Weight (g)	Qty.	Function	Manufacture method
1	spring	0.5	2	Creates force that pushes the lobes against the crack walls to maintain position until loaded in a fall or removed by climber	purchased metal wire
2	cam lobes	7	3	Main source of friction and subsequent force holding the cam in place; provides the reaction force to the load.	extruded shape cut into slices by saw and drilled, hole that holds trigger wire has specific shape
	(body)	45	1
3	main cable		1	Holds the trigger and responsible for transmitting the strain of the weight.	purchased cable
4	thin plastic tubes		2	Help the trigger to slide easily through main cable.	purchased plastic tubing
5	sling; plastic tube (orange)		1	Sling (part of the main cable) is the main place where the hanging weight is loaded. The plastic tube protects the main cable from metal carabiners and protects nylon slings from the cable. The color of plastic indicates the size of the cam.	purchased colored tubing
6	trigger		1	Pulls the trigger wires that action the device.	extruded bar sliced and then textured for grip
7	axle		1	Holds the lobes in place, and holds the equilibrium between the load and the resistant force coming from the lobes.	extruded form, hardened metal, sliced to desired length
8	axle ends		2	Keep the axle and the main cable together.	welded metal
9	finger support		1	allows user to apply counter force to retract the trigger	extruded metal rod stamped with "Metolius" and size number
10	spring pin		3	Keeps the spring attached to the lobes.	rolled sheet metal
11	trigger wire		3	Transmits the triggering force from the trigger to the lobes.	purchased narrow cable and wire. wire has nail head and is bent to fit around cam lobes
12	copper connector		3	holds the two pieces of the trigger wire together.	bent around the two sections and welded together
	TOTAL	52.5	24

Assembly Procedure

Active climbing cam after dissection, with parts labeled.

The climbing cam seems to have been assembled roughly using the following process. Most of the parts used in this assembly do not have any external fasteners/screws; this reduces the assembly time considerably. Some parts however require welding to be secured which will increase assembly time. Finally there are many very small parts which would produce handling difficulties during orientation and insertion.

A. Initial Base Assembly

1. Taking the thick cable (3) and inserting it into the thick plastic orange tube (5).
2. Bending the thick cable to form a ‘U’ shape.
3. The bent thick cable seems to have been inserted into the finger support (9) and then fused in place.
4. Two thin plastic tubes (4) were then inserted over the open side of the assembly.

B. Trigger Assembly

1. The three trigger wires (11) were connected and fused into the trigger (6).
2. Then the wires attaching the cam lobes (2) to the trigger assembly are joined and fused using the three copper connectors (12).
3. Spring pins (10) are then inserted into the three cam lobes.

C. Final Assembly

1. The initial base assembly is then inserted through the trigger base assembly.
2. Then the cam lobes along with the two springs (1) are aligned on the axle.
3. Axle ends (8) are then fused onto the initial base assembly.
4. Finally the axle is put through the axle ends and welded shut.

* Note: numbers in parentheses correspond to part number

DFMA, FMEA and DFE

DFMA and DFE Analyses

The design for manufacture-assembly (DFMA) and the environment (DFE) analyses were performed for each individual component of the mechanism. The outcomes are arranged as follows:

Part number	Parts	DFMA	DFE
1	spring	attaching the spring onto the axle is no problem as there is only one way it can go on, attaching the springs to the pins are complicated due to their very small size	spring may be made leaner, metal can be recycled
2	cam lobes	Due to the partial symmetry of the cam lobes, orientation time during assembly is reduced	casting instead of machining to reduce waste metal, recycle metal
3	main cable	Fully symmetrical and large enough to manipulate it easily with bare hands	increase durability to maximize first life, recycle material
4	thin plastic tubes	Designed for easy alignment as they both have axial symmetry	make plastic tube shorter, recycle plastic
5	sling; plastic tube (orange)	Similar to the thin plastic tubes this tube has axial symmetry and thus orientation time during assembly is minimized	less thick plastic, recycle plastic
6	trigger	The trigger can be inserted both directions i.e. it only has one axis which it must be rotated upon insertion	use less material, recycle material
7	axle	The axle is made of extremely durable metal and is a simple cylinder construction which is easy to handle. Additionally the parts which have to be inserted on the axle can be done so easily as there is very little resistance to insertion	use material efficiently, casting instead of machining, recycle metal
8	axle ends	The ends have to be oriented over two axes upon insertion which increased the time of assembly this can be eliminated by making it symmetrical over one face	use less material to weld, use a lower emission production like join/bend
9	finger support	Simple part which only requires two forms of alignment on insertion, also it is large enough to handle with the hands easily	reduce mass, casting instead of machining the holes, recycle material
10	spring pin	the spring pins are symmetrical over one axis but they are extremely small and insertion into the cam lobes would require extra time	use less metal, recycle material
11	trigger wire	The wire is simple and large enough to install without the aid of other tools	increase durability to maximize first life, recycle material
12	copper connector	The copper connectors again are extremely small but they are symmetrical over two axes thus orientation is not a problem with them, insertion and securing though will take additional time as it needs to be welded	use lighter material, recycle less material

DFE

The design for the environment is to analyze this climbing cam's environmental impact, increase its life cycle and reduce its impact. In order to reduce its environmental impact, the material can be made leaner. However, because this product is very hazardous if it fails, safety comes first as to not let the product fail. This product involves the life of the users. Instead of reducing the material for the product, the manufacturing of the components can be chosen so that there will be less waste generated during manufacturing. For example the cam lobes can be manufactured by casting instead of machining. The end of the axle appeared to be weld. The welding may be substituted to a joint or a bend but a test should be done to ensure the product will not fail. After its life cycle, the product should be recycled as most of the components are made of metal and plastic. This design is not very difficult to disassemble so its components can easily be recycled.

FMEA

Two major areas of potential failure were identified in the product. Although several individual parts failures could result in a hazardous failure of the product, the failures are easy to detect and unlikely to occur. The product was designed as a safety device for use in demanding environments, thus the parts are typically reinforced where catastrophic failures could occur. The two parts with high failure RPN values were the main cable, and the trigger wires, both parts made of braided wire cable. In both cases, the cable could incur internal damage that would be difficult for the user to detect that could weaken the product and lead to complete failures. Complete failure of the main cable is very severe and would yield the product inoperable and hazardous. Complete failure of one of the trigger cables would seriously disrupt usage of the product, and failure of all three would yield the product nearly inoperable, yet still safe for climbing if placement is made. A complete failure of the main cable could occur during a climber fall, as the weight of the fall is transferred through the cable to the axle. Complete failure of the trigger cables would be unlikely during a climber fall as they are not impacted in the fall. Both of these weaknesses should be corrected through material selection, and possibly reinforcements surrounding the cables. The trigger cables could be designed to accommodate at home replacement, encouraging and easing maintenance. Below is a more complete FMEA of each part.

Part #	Parts	Failure Mode	Effects of Failure	S	Causes of Failure	O	Design Controls	D	RPN
1	spring	A spring detaches from the spring pin, or is somehow severed	Failure of all 3 springs would result in complete failure of the cam in normal usage. The cam could still be partially functional with one or two failed springs but should not be used for climbing. cam could still function as passive protection without springs.	9	Overuse of spring, spring somehow slipping free from the pin	2	If spring is not properly attached the cam will not function	2	36
2	cam lobes	A cam lobe is crushed or misshapen through use	Failure of one cam lobe by serious deformation would reduce the friction provided by the cam it would also interfere with how the other lobes engaged within the rock.	7	Deformation from dropping or crushing in rock fall	3	Lobes are protected in design and able to withstand high impacts. Easy handling design reduces occurrence of dropping.	1	21
3	main cable	Cable seriously deformed or bent.	A severed cable would result in the cam no longer supporting the weight of a falling climber. Excessively worn or severely bent cables should be used with extreme caution.	9	Cable could become bent after impact on poorly placed cam. This type of impact could also fray or sever the cable.	5	Cable is thick and flexible. Internal damage could be difficult to detect.	6	270
4	thin plastic tubes	Tubes dislodged or worn through	failure of tubing would accelerate the deterioration of the main cable, thus reducing the lifespan of the product. Failure would also increase force needed to retract trigger.	5	After excessive use tubing can deteriorate	6	Primary wear to tubing is in visible regions. Regions with highest wear have minimal affect on performance	1	30
5	sling; plastic tube (orange)	Tubing worn through	Failure of tubing would result in faster wearing of main cable and also wearing on nylon slings often looped onto cam and clipped to rope.	5	Repeated clipping of metal on plastic causes deterioration	5	Thick, durable tubing used. Easy to identify	1	25
6	trigger	Fracture of trigger or housing of trigger cables	Failure of trigger would release trigger cables and make placement and retrieval of cam very difficult yet still possible	7	Fracture or serious deformation from impact	2	Metal trigger used, as opposed to plastic	1	14
7	axle	Fracture of axle	Failure of axle by complete fracture would result in a complete failure of the cam yielding it unsafe for use in climbing	9	Serious impact, probably from rock fall onto cam	1	Axle made from hardened metal, protected from impact by cam lobes	1	9
8	axle ends	Axle end ripped from axle	If both ends were to fail the cam would not support the weight of a falling climber. Failure of one end would result in an unbalanced force on the cam and the lobes would probably be spun free form the rock	9	Very strong impact in a direction difficult to apply during normal or even modified usage.	1	Force would be dissipated by trigger and finger support. Axle ends protected by lobes.	1	9
9	finger support	Fracture or serious deformation	Complete fracture of finger support would make retrieval and placement of cam difficult but still safe for climbing	7	Serious impact from rock fall or dropping	1	Finger support made from metal.	1	7
10	spring pin	Crushing, bending, or fracture of pin	failure of a spring pin would have the same effects as failure of the spring	9	Impact in an unusual direction over a small area	1	Spring pin shielded from impact by cam lobes. Difficult to view.	2	18
11	trigger wire	Fraying or complete failure of wires	Failure of all trigger wires would make placement and retrieval of cam extremely difficult, if not impossible in normal climbing situations. Partial failure of wires would make placement and retrieval difficult.	7	Impact, use in horizontal placements, or normal wearing on thin cables.	6	Wires replaceable in factory. Internal damage may not be dateable.	6	252
12	copper connector	Connectors release trigger wire pieces	Failure of the connectors would be very similar to failure of the trigger wires, making it difficult to place and remove the product	7	Direct impact onto connectors, wear on connectors.	2	Connections are welded. Failure obvious.	1	14

@@ Line 269: / Line 269: @@
 ! 12
 | copper connector || Connectors release trigger wire pieces || Failure of the connectors would be very similar to failure of the trigger wires, making it difficult to place and remove the product || 7 || Direct impact onto connectors, wear on connectors. || 2 || Connections are welded. Failure obvious. || 1 || 14
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