Recent Changes for "Updating the APRL Hook" - Open Prosthetics Project Wiki

Updating the APRL Hook

HosmerDude — 2009-03-03 01:36:54

Added response to Darryl's questions

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	+ + ""3-2-09"" + + Howdy. Here are my responses: + + * "1. Are the cad drawings available for aftermarket use? If so we could take it to a high end machinist to have them make the case out of other milled materials( at owners expense) but still be able to send it back to Hosmer for maintenence?" + + Maybe yes maybe no, but why would you want to do this? + The newly improved aprl device is approximately 6 times stronger than the old version. Perhaps this may be good enough? + If you switch to steel, it will get significantly heavier and more expensive. If you switch to titanium, you will have to mortgage your home to buy it. Just to give you an idea I would guess that the aluminum part probably costs $1800 - $2800 for qty 1 and $200-$300 in qty 10. I would guess that steel would be about 25%-40% more and titanium would be about 250%-300% more. + + * "2. Can the wear surfaces on the cam and semi-circular device be redesigned to have a longer wear life?" + + The cam has a carbide insert so it does not wear at all. I suppose it is possible to make the quadrant a little harder, but I am not sure if the small benefit would be worth the cost. I have never heard you mention problems with the quadrant before. Is this an issue? I think you might be able to buy replacement quadrants from hosmer and I don't think they are expensive. I don't know how difficult it is to replace a quadrant, I've never done it before. + + *** "3. Lubed for life? Even though I have been told to lubricate it, and have tried, there is always some sort of leakage from the openings. This will make a mess of clothes." + + I have a few questions about lube: What happens if you don't lube it? Is there a noticable difference in performance? Does it wear out faster? IIRC there is an oiling sponge inside. Does this dry up over time? What happens if you plug the oiling hole to prevent debri from getting in? + + I would love to hear your thoughts. + + -Daniel

Updating the APRL Hook

JonKuniholm — 2009-02-26 22:04:46

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- Darryl has made a very informative [http://www.youtube.com/watch?v=b3HNq1tCd4E "video"] explaining the virtues and limitations of the hook, as well as some ideas for its improvement.	+ Darryl has made a very informative [http://www.youtube.com/watch?v=b3HNq1tCd4E video] explaining the virtues and limitations of the hook, as well as some ideas for its improvement.

Updating the APRL Hook

JonKuniholm — 2009-02-26 22:04:20

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	+ + Darryl has made a very informative [http://www.youtube.com/watch?v=b3HNq1tCd4E "video"] explaining the virtues and limitations of the hook, as well as some ideas for its improvement.

Updating the APRL Hook

Darryl — 2009-01-16 20:09:04

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- In the initial statement about this device, it is mentioned that the APRL is a light duty hook and was designed for a certain type of amputee. For me, I wanted to control the amount of pressure applied to an item(voluntary closing) and have it lock in place, not relying on rubberbands to do the trick. I tried several VO hooks, but everytime I held onto something and reached out, the cable would tighten and release the object I was holding on to. It is now impossible for me to use a VO type hook. It is second nature for me to extend my are and roll my back to get the hook to close. I no longer think about it.	+ In the initial statement about this device, it is mentioned that the APRL is a light duty hook and was designed for a certain type of amputee. For me, I wanted to control the amount of pressure applied to an item(voluntary closing) and have it lock in place, not relying on rubberbands to do the trick. I tried several VO hooks, but everytime I held onto something and reached out, the cable would tighten and release the object I was holding on to. It is now impossible for me to use a VO type hook. It is second nature for me to extend my arm and roll my back to get the hook to close. I no longer think about it.

Updating the APRL Hook

Darryl — 2009-01-16 20:07:12

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- 1/15/09	+ '''1/15/09'''
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- 2. Can the wear surfaces on the cam and semi-circular device be redisigned to have a longer wear life?	+ 2. Can the wear surfaces on the cam and semi-circular device be redesigned to have a longer wear life?
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	+ + + '''Jan 16, 2009''' + + '''Answers to questions posed by Zach:''' + + In using this device now for 18 years, it and I have an intimate relationship. + + A. I have and currently carry 100 lbs or more,from time to time, from the fingers straight down. I have never had any failure in the fingers or the castings where the threads are during a tension type situation. + + B. Twisting force or sudden impact is where failures have occurred. For me, pushing up from a laying position, unexpected contact, or getting caught on something. + + C. Some of these hooks are many years old. Due to the high initial cost, I continually have them refurbished. After 3 or 4 years they all catastrophically fail in some way or another. + + + '''Additional suggested upgrades:''' + + + 1. Cad drawings, as mentioned before, for aftermarket milling options. And, + + + 2. Integrate the wrist threads, for prosthetic attachment, into the milling operation. I understand it may not be feasible with an aluminum milling, but if it were titanium it would seem advantageous to include it as one unit. + + + + + In the initial statement about this device, it is mentioned that the APRL is a light duty hook and was designed for a certain type of amputee. For me, I wanted to control the amount of pressure applied to an item(voluntary closing) and have it lock in place, not relying on rubberbands to do the trick. I tried several VO hooks, but everytime I held onto something and reached out, the cable would tighten and release the object I was holding on to. It is now impossible for me to use a VO type hook. It is second nature for me to extend my are and roll my back to get the hook to close. I no longer think about it. + + I believe that if the APRL is redesigned to heavy duty specifications, there would be a larger group of individuals who find that its abilities exceed those of the VO variety. Graded prehension in a hook is no different than a human hand. We need to try to exploit this technology to our best efforts and make this product suitable for all people at any level of fitness so that it can be used for all applications. + + Zach, keep us updated.

Updating the APRL Hook

Darryl — 2009-01-15 17:55:26

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	+ + 1/15/09 + + I am excited about the improvements that Daniel has helped to complete and the ones Zach is working on. + + I know you noticed grease inside of the hook, that was there from the factory. Never added by me. Dust is all mine!! Also making it water or dust resistant is a great idea. + + My big questions to the Hosmer guys: + + 1. Are the cad drawings available for aftermarket use? If so we could take it to a high end machinist to have them make the case out of other milled materials( at owners expense) but still be able to send it back to Hosmer for maintenence? + + 2. Can the wear surfaces on the cam and semi-circular device be redisigned to have a longer wear life? + + 3. Lubed for life? Even though I have been told to lubricate it, and have tried, there is always some sort of leakage from the openings. This will make a mess of clothes. + + + As a user of this device, all changes are welcomed. I cannot wait for the improvements! + Keep us updated, + Darryl

Updating the APRL Hook

Zack — 2008-12-31 15:24:02

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	+ + Some of the changes I've been considering are: + + 1. Sealed case to reduce water / particle ingress + 2. Dry-lube sleeve bearings (bushings) or sealed bearings - not very expensive, reduced maintenance. + 3. Teflon or coated replaceable substrate between moving components that have rubbing and aren't bearing surfaces to reduce friction / wear, or redesign interfaces to eliminate bearingless surfaces. + 4. Remove oiling hole. + 5. Etch 'Do Not Lubricate' on inside of cover. + + These changes should improve the life of the device, and keep the sliding surfaces lubricated and locking mechanism clean for a long time. None of these should change how the device operates, but could slightly impact cost due to more features being required in the machined components. It's entirely possible that these modifications could be made as 'after-market' changes to evaluate their effectiveness. I know a few machinists who are excellent at this kind of work; they may be willing to do it for free (or almost free) for their own satisfaction. + + Very excited.

Updating the APRL Hook

Zack — 2008-12-31 14:59:49

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- "'More updates, 12/30:"'	+ '''More updates, 12/30:'''
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- "Zack:	+ ''Zack:
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- If you are still interested, I think that there is further potential for improvement. If you have any ideas on improving the device we would love to hear about them."	+ If you are still interested, I think that there is further potential for improvement. If you have any ideas on improving the device we would love to hear about them.''

Updating the APRL Hook

Zack — 2008-12-31 14:58:43

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- More updates, 12/30:	+ "'More updates, 12/30:"'
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	+ + "'12/31:"' + + happy New Years Eve; got a response from an engineer at Hosmer Dorrance - + + "Zack: + + I too share your enthusiasm for making improvements to products that will help people have a better quality of life. In fact we have already made improvements the aprl hook. The new version has a case that is machined instead of cast and will be available sometime in the middle of January. Because the machined aluminum is about 6 times stronger than cast aluminum this should eliminate failures at the hook finger threads, just below the threads, and also at the base where the threads attach. Also the wall thickness at where the stud attaches is thicker to prevent the rivets from loosening. I actually worked on this in March of 2008, and it has taken this long for the new design to trickle though the production process. + + If you are still interested, I think that there is further potential for improvement. If you have any ideas on improving the device we would love to hear about them." + + Looks like the case is the source of most failures that you've experienced; I do have some more suggestions for him that I'll pass on, I really don't care if he takes my ideas and presents them as his own as long as the end product is a better device.

Updating the APRL Hook

Zack — 2008-12-30 17:18:39

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	+ + More updates, 12/30: + + Trying to get in contact with Hosmer Dorrance, MFR. of the hook for some assistance; according to their web page, "This hook is made using aluminum forgings and is generally a light duty terminal device". never seen a forging with casting injection ports... + + anyone have a contact up there I could pursue?

Updating the APRL Hook

Zack — 2008-12-16 00:19:01

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	+ + + =Project Updates= + + Got the APRL hook on 12/10/08 - ripping it down today (12/15). + + First thought: this will not cost $150 to replace. + + Immediately apparent is the fact that the housing is full of sawdust and grease; I'd have to guess that could be why the locking mechanism doesn't work so well. It looks like there is an insert of carbide or other durable material in the clamp of the locking mechanism. + + The housing is cracked at the rivet as shown in picture #2, this is probably the same housing as in the image. + + Both hook mounting lugs are broken off as well; they came off almost as mirror images of eachother. + + It looks like the internals of the hook was designed for long-term use. However, it was not designed to be water (or sawdust)! tight. The cast aluminum components will need to be either redesigned or made with another material for a longer life span. The internal wear surfaces are mainly brass; it looks like they will probably outlast the housing so I don't think I would focus on the materials too much. + One thing that could reduce internal friction would be to add shims of teflon or some other low- + + What is the heaviest item that you would ever pick up with the hook? Does anyone use the hook as just that - a hook, carrying heavy items by hanging them from the prosthetic? Does anyone have pictures of the hook in use, grabbing and holding different objects? I've never seen one used, and I'd like to get an idea of what's causing these hooks to break. Last question, any reason to ever hit or tap something with the hook? + + Anyone live in the NH area? + + Closing thought: this will not cost $150/each to improve. there is a possibility that some of the parts could be re-used from a broken hook, like the springs, lock switch, etc... I'll throw more up here soon.

Updating the APRL Hook

Reto — 2008-05-27 12:55:33

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- 2. Change the wear surfaces on the inside to long wearing materials of which will need to be determined by somone with a materials science background.	+ 2. Change the wear surfaces on the inside to long wearing materials of which will need to be determined by somone with a materials science background, or find a way to make these surfaces disposable and inexpensive.

Updating the APRL Hook

Darryl — 2008-01-05 15:43:35

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- 3. The most common failure is where the stanless steel threaded end is riveted to the case (picture # 2 above). The casting is brittle and cracks and eventually the rivets get loose. Notice how close to the edge the rivets are in relation to the where the two case parts marry together.	+ 3. The most common failure is where the stanless steel threaded end is riveted to the case (picture # 2 above). The casting is brittle and cracks (Picture #7) and eventually the rivets get loose. Notice how close to the edge the rivets are in relation to the where the two case parts marry together. Most of the cases that I have used have cracks in this location. + 4. In picture 10 the break is where the brass colored rectangular piece(this is the lever that allows the fingers to open wide, narrow or just free wheel) and the pin through it meet the casting. You should not be able to see the pin top of casting there is broken away.
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	+ + #7 + [[Image(Rivet break.gif)]] + + #8 + [[Image(casting failure 3.gif)]] + + #9 + [[Image(casting failure 4.gif)]] + + #10 + [[Image(casting failure 5.gif)]] + +

Updating the APRL Hook

Darryl — 2008-01-05 15:33:31

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Updating the APRL Hook

Darryl — 2008-01-05 15:32:45

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Updating the APRL Hook

Darryl — 2008-01-05 15:31:58

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Updating the APRL Hook

Darryl — 2008-01-05 15:30:11

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Updating the APRL Hook

Darryl — 2008-01-05 07:31:12

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	+ 1. The parts that have never failed under any circumstance are the fingers. They are made from milled aluminum and have never broken. + + '''# 1''' + [[Image(shell.gif)]] + + '''# 2''' + [[image(end.gif)]] + + '''# 3''' + [[image(internal 2.gif)]] + + '''# 4''' + [[image(side.gif)]]
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	+ 1. You may be able to see in photo # 5 the voids that exist in the casting where the break is. There is no repair for this type of break, only replacement of the case. + 2. Photo # 6 is a casting failure of the socket for the cable attachment. + 3. The most common failure is where the stanless steel threaded end is riveted to the case (picture # 2 above). The casting is brittle and cracks and eventually the rivets get loose. Notice how close to the edge the rivets are in relation to the where the two case parts marry together. + + '''# 5''' + [[image(casting failure 1.gif)]] + + '''# 6''' + [[image(casting failure 2.gif)]]
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- 1. Upgrade the case from cast aluminum to milled aluminum or to cast or milled titanium. I know the mission statement is directed toward a $150 manufacturing budget, so titanium may be out. If this device could	+ 1. Upgrade the case from cast aluminum to milled aluminum or to cast or milled titanium. I know the mission statement is directed toward a $150 manufacturing budget, so titanium may be out. If this device could
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- 2. Change the wear surfaces on the inside to long wearing materials of which will need to be determined by somone with a materials science background.	+ 2. Change the wear surfaces on the inside to long wearing materials of which will need to be determined by somone with a materials science background.

Updating the APRL Hook

Darryl — 2008-01-05 07:00:32

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Updating the APRL Hook

Darryl — 2008-01-05 06:59:59

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Updating the APRL Hook

Darryl — 2008-01-05 06:59:16

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Updating the APRL Hook

Darryl — 2008-01-05 06:59:01

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Updating the APRL Hook

Darryl — 2008-01-05 06:58:31

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Darryl — 2008-01-05 06:58:13

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Darryl — 2008-01-05 06:57:52

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Darryl — 2008-01-05 06:47:09

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Updating the APRL Hook

Darryl — 2008-01-05 06:43:09

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Updating the APRL Hook

Darryl — 2008-01-05 06:43:09

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Updating the APRL Hook

Darryl — 2008-01-05 06:40:03

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Darryl — 2008-01-05 06:39:30

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Updating the APRL Hook

Darryl — 2008-01-05 06:35:34

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Updating the APRL Hook

Darryl — 2008-01-05 06:26:37

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Updating the APRL Hook

Darryl — 2008-01-04 23:18:52

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- * List proposed design changes	+ * List proposed design changes: + 1. Upgrade the case from cast aluminum to milled aluminum or to cast or milled titanium. I know the mission statement is directed toward a $150 manufacturing budget, so titanium may be out. If this device could + last 5 or 7 years then there may be some room to increase the cost based solely on longevity. Titanium may last forever and the cost may need to reflect that. Once this is reverse engineered a list of usable materials can be compiled and tried + 2. Change the wear surfaces on the inside to long wearing materials of which will need to be determined by somone with a materials science background.

Updating the APRL Hook

JonKuniholm — 2008-01-04 22:15:12

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Updating the APRL Hook

JonKuniholm — 2008-01-04 22:15:01

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- The Army Prosthetic Research Lab (APRL) Hook was developed by the US Army following WWII. A concise summary of the history and function of the hook appeared in the article, "Upper-Limb Prosthetics: Body-Powered Components," by Charles M. Fryer, and John W. Michael, and is reproduced here in part: [[Image(APRL.jpg, right)]]	+ The Army Prosthetic Research Lab (APRL) Hook was developed by the US Army following WWII. A concise summary of the history and function of the hook appeared in the article, [http://www.oandplibrary.org/alp/chap06-01.asp "Upper-Limb Prosthetics: Body-Powered Components,"] by Charles M. Fryer, and John W. Michael, and is reproduced here in part: [[Image(APRL.jpg, right)]]

Updating the APRL Hook

JonKuniholm — 2008-01-04 21:53:56

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- * Document current design - * Detailed failure analysis and more user feedback - * List proposed design changes	+ * Document current design + * Detailed failure analysis and more user feedback + * List proposed design changes

Updating the APRL Hook

JonKuniholm — 2008-01-04 21:48:29

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	+ The Army Prosthetic Research Lab (APRL) Hook was developed by the US Army following WWII. A concise summary of the history and function of the hook appeared in the article, "Upper-Limb Prosthetics: Body-Powered Components," by Charles M. Fryer, and John W. Michael, and is reproduced here in part: [[Image(APRL.jpg, right)]] + + ''The APRL hook was developed by the Army Prosthetics Research Laboratory after World War II. It differs from all hooks previously discussed in several major respects: + + 1. The APRL hook is a voluntary-closing device. + 2. The fingers automatically lock in any position once grasp is accomplished. + 3. A selector switch permits the amputee to choose either + 1. A large finger opening (7.5 cm, 3 in.). + 2. A small finger opening (3.4 cm, l 3/8 in.). + 3. "Freewheeling"-a small opening with the locking function eliminated. + 4. The operating lever or thumb is located on the ulnar side of the device. + + This device was originally developed to use biceps cineplasty as a source for body power. The voluntary-closing mode provides graded prehension: the pinch force is as gentle or strong as the force generated by the amputee. Particularly with a cineplasty, this can improve proprioception. + + Unfortunately, the mechanical complexity of this device makes it both expensive and prone to breakdown. The hollow aluminum lyre-shaped fingers it shares with the "two-load" hook make it somewhat fragile. Combined with the waning popularity of cineplasties, these factors limit its prescription primarily to previous wearers. The graded prehension may also be of value to selected bilateral upper-limb amputees.'' + + This project was proposed by OPP volunteer Darryl DuBre, a longtime APRL VC hook user frustrated with the durability and cost of the hook, but a big fan of its other features. His experience seems to be in line with that described above. + + =Problem Statement= + Redesign the APRL VC hook to correct design and manufacturing defects that lead to early failure. Problems include wear leading to failure to lock in the closed position, and substandard castings with voids leading to mechanical failure in the casting. Any pictures documenting these deficiencies would be helpful. + + =Design Requirements= + We would like the device to be + * Manufacturable for about $150 + * More durable and appropriate for heavy duty use + * Doesn't fail to lock closed with wear + * Improved durability of castings or other structure + * Consider alternate materials (nylon, glass fill, other metals) + + =Tasks= + * Document current design + * Detailed failure analysis and more user feedback + * List proposed design changes

Updating the APRL Hook

JonKuniholm — 2008-01-04 19:57:39

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