Doctor Seeks Engineering Input About Wheels

You don't make it clear, are the wheels to be powered in the forward direction, or pushed?

This sounds like some sort of powered Zimmer frame.

If the wheels are powered then the gearing can easilly act as a brake. A simple ratchet in the hub will stop them going backwards. It is easy enough to make it go a set distance. Electric golf trolleys (google Powakaddy) have this as a push button feature...each button press is 10m or some such. Any Electronics designer should be able to do this for you.....(getting it to meet all the medical electronics spec's will be a pain )

The very simplest way to stop it going backwards is a 'sprag', e.g. A shor bar which drags along the floor hanging down at about 45degrees, if you try to go back it digs in and prevents movement.

That'll do for now.. my tea is getting cold....hope it helps

Del

Dohhh!!

I forgot, it needs to be actuated by the user, no electronics or batteries, because your right the FDA will spend 50 years chewing on it. It's a new type of theraputic walker for rehabilitation. Ideally it could be cheap enough, that every Hospital could have one instead of just rehab centers.

Adaminchains

I'd say a ratchet to stop it going back and a simple bulb operated latch to stop it going forward. Pump the bulb once (on a sort of brake lever arrangement) and this lifts the latch, the pneumatics slowly bleed down and drop the latch after a time (adjusted by a bleed valve).

That'll be £5 please! or 25 tins of cat food.

Interesting topic...and right up my alley

I'm Bruce Honaker; inventor of Wheel Anti-Reversing Technology. I've made prototype inline skates using this technology. Visit: http://www.google.com/search?hl=en&q=wheel+anti-reversing+technology&btnG=Google+Search

My website is: inlineskatetech.com I've listed walkers as another application for this innovation.

You may reach me at ideaplace@msn.com to make this happen.

Perhaps to limit forward movement your wheels could run on a ribbon with a stop at the end and that was slightly longer than the distance of travel so that when retracted the wheel would still be on it. a weak spring would be attached to retract the ribbon back to start by removing the weigh from it. adjust the forward distance by having several positions along the ribbon to place the stop( maybe a small dowel pin.

They make a one way roller bearing that will prevent backward motion. My suggestion for limited distance would be something like a mechanical clutch with a release handle to get it going again. Would not actually need the clutch part, just the stopping mechanism. This works by a lever with an edge that is spring loaded that is mounted on the outside of a rotating wheel (steel). The wheel has a notch in it and when the wheel make a full rotation the lever catches in the notch. No electronics and fully user powered. The adjustable distance would be a bit more complicated as you would get into gearing the rotation of the "clutch" to the actual wheels, similar to a 10 speed bike.

Regards,

Keywalker

To me it seems that you are trying to copy the walking steps we all take but without lifting the feet or walking frame.

I should be able to find the non-reversing section fairly easily but have to have a think about limiting the step size.

I don't know of anything off-the-shelf but will ask around.

Another method to prevent reverse movement is the clutch arrangement used on many motorcycle starters -- A central shaft with an outer shell having three "pins" held in slots that are tapered slightly and held in place by light springs - in one direction the pins bind at the short end of the taper locking the assembly, in the other direction the pins are move out from "pinch position". This allows either drive in one direction if shaft driven or lock in one direction if the shaft is fixed and the wheel rotates freely. The advantage I can see is not having the sound and/or mechanical feel of ratcheting as it moves in its freewheeling direction and immediate stop on reversal without have to engage a pawl or stop mechanism along with accompanying wear and catastrophic issues involved in failure.

The adjustment to a specific stride can be approached by using a pulse counter and small servo unit that progressively applies solonoid activated brakes after a specific but adjustable number of impulses (tear apart an old mechanical computer mouse that uses the optical shutter wheel driven by the ball to see this mechanism. If electronics such as this are out of the question, you might use a scaled down variable pulley system such as the drive used on snowmobiles, go carts, variable speed devices such as some lathes, and some european autos (DAK comes to mind). With this method a belt drive has two pulleys, one spring loaded under constant pressure and the second spring loaded but under adjustable pressure. In this case an adjusment knob would control the pressure on the variable pulley, changing the relative ratio of drive and applying braking pressure to a mechanical brake. Release of the brake mechanism could be arranged by slight upward pressure on the handles of the walker which would also indicate that the user is ready and in a safe position to move forward.

I could try to get diagrams if you wish but I'll warn you I'm terrible with autocad.

I'll be happy to share in development and prototyping headaches if you're willing to share in patent and production rights.

Lemme know if you need or want any clarification and I'm sure others on this board will offer good counsel to determine if this is a viable approach.

Yes Guest, the non-reversing clutch is also used on the pinion drive on automotive starter motors. I should be able to find more info on that in some old articles.

Doing the length of step is not so easy without some electronics which others have suggested but which will probably upset the FDA approval time, or with something external to the wheels.

Also known as a sprag clutch. (I've not yet encountered a bearing/sprag clutch combined as suggested above). If the patient is going to have two of these, one under each foot, then a link between the two would prevent him/her doing the 'splits' if that is all that's required. I appreciate that you're probably after something a little more sophisticated, but I bet cost is still an issue.

Preventing the reverse movement could be a simple dog and ratchet.

If you could allow a minuscule "backup" then a spring loaded spool with cable could be used to "measure" the fwd stride, after stopping the fwd limit could be released by a small reverse direction, (or a hand operated release) for the next stride.

Second guessing:

Is this like a wheeled walker the patient would push ahead while supporting some of their weight, then remain relatively stationary while they "step" or support themselves while they take a step fwd into a neutral vertical position? Then the cycle repeats? What is their upper body control?

I am not familiar with the exact design concept that you are trying to achieve but I have a couple of suggestions as to a bearing with a one way sprag clutch. We use the design on very small to very large materials handling conveyors to stop the weigth of product on the carry side from (running backwards) when the drive energy has ceased. We call these ARBs (Anti Run Backs). The sizes go from very large to very small which would be suitable for a wheel. To limit forward movement could also be possible using another Ramp Ring, Cam and Roller which sprags the forward rotational movement to X degs & >360degs of rotation & which releases & resets when the forward pressure is eased (released) when the patient moves their body weight forward. Ie, There is sprag rotational locks on both sides of the main bearings set to different circle rotational angles thereof. Being lubricated, there is minimal chance of damage.

These bearings (Complex Designs) (ARBs) are available along with their specfications from any bearing manufacturer. I believe some of the bearing companies would also support your initiative through their R&D and Community spirit still leaving you with the concept with a non-dsclosure confidentiallity clause. Check the NTN Bearings, Cooper Bearings, CBC Bearing Company, FAG Bearings, SKF Bearing Company, BSC Bearing company and many more. All their website are accessible via Google.

I Hope you are successful in your endeavours and I look forward to hearing of your innovation in the future.

Regards

Les (Tecmate)

As an electronic engineer, designing the forward limited motion of wheels would be a Snap however, mechanically speaking ONLY. May I suggest, seeking a Slip Gear allowing one spring actuated PIN to fall in place on each gear tooth. Attach light cable to PIN for lifting from tooth engagement by Finger Trigger action when desired. The motion of wheel would be unrestricted in the forward movement at all times but, the slip gear would stop motion conversly. That is as far as my thinking takes me. I Hope it might help you! Ron.

I can recall seeing roller boots for children which had a switchable ratchet to prevent the foot moving backwards, maybe that could be a starting point. I can't find them doing a quick web search but will keep trying.

The question you pose is a great one. There are so many ways to accomplish this, the question becomes which would work best for your specific purpose. Just off hand I'd think of using a simple pulse counter (Same as a CNC machine) Distances could be easily accurate up to 1/10,000 of an inch. Or wire in a timer linking a motor of known speed to a wheel of known size. Also very accurate and easily adjustable by the end user. Would be a great weekend project.

It's all been said already, but here's my tuppence worth - I'd ensure it's a sealed unit for low maintenance and durability, a failure would result in deep tragedy or high comedy...........

Bearings available that will turn in one direction only. Look to Torrington

When you say "must only go forward", what do you mean? How much force does it have to resist before it will turn (or skid) in the wrong direction?

When going forward, what is the range of motion that is re-settable by the user (as short as X, as long as Y)? Is it measured in mm or km? Is it acceptable to count revolutions (and part revolutions) of the wheel, assuming no skidding of wheel on surface, or is it absolute measurement regardless of amount of skid that occurred this time? Can it be limited to "n" whole revolutions of the wheel, user choosing "n" (eg. 3" diameter wheel allows adjustment in increments of approx. + 9"?

When you reach the end of the desired travel, what force must the wheel system resist (braking lock-up force)? How will you prevent skidding, or is that important? Is it acceptable to require a slight reverse motion to unlock the braking mechanism at end of travel, before proceeding to next cycle forward?

When user chooses travel distance, is this chosen once in lifetime, unable to re-choose once set, or is it re-chosen every cycle? How long can it take to re-choose distance, special tools, disassemble unit, or at push of button from console, etc.?

My questions may have already solved it for you. If not, we are eager to help you design something that will work for you.

Glenn Black B.A.Sc. P.Eng. CQE CQA
President
Process Quality Associates Inc.
pqa.net

I think we are also missing the point a bit! It has to be economically viable so that all hospitals can afford them, including 3rd world! the system has to be durable, simple, and easy to repair if it fails. Maybe complex systems with pulse counting or slipping notched clutches is not the best direction, but simple sprung loaded latches on a mono directional bearing, with different sized wheels for different length of stride ie, bigger wheel=bigger stride with an airport style break to release the latch and allow the next forward motion!

Just an Idea

Hello Adaminchains,

Are you sure that you are going the right way about solving your problem by asking for suggestions? Wouldn't it better to take an engineer/designer into your confidence and pass the problem over to him/her? As an engineer I wouldn't think it very sensible to to try and solve a medical problem that I might have by appealing on a medical blog.

As you can see from the response so far there must be plenty of capable engineers willing to help you. If its confidentiality that concerns you then that is something we deal with all the time. Engineers are quite ethical you know.

To get a team effort to address your problem you will have to find a a better way of presenting your problem. Maybe that the question you should be asking

Any way, all the best.

If you Google " "r e sauzedde" + roller clutch " you will get a great deal of info on the non reversing type of roller clutch.

I knew I had some info somewhere

First I want to say THANK YOU EVERYONE

There has been almost 23 posts so far, and several e-mailed offers for help in this effort. Right now I am trying to process everything that's been posted and sent, and it might take me a while to get back to everyone that has sent information.

Currently my main problem, is that I don't really know how to design the mechanisms involved, and an utter lack of engineering expertise. Though I have a rough Idea of what it will look like when finished. So right now I need to process the information to get a better specifications put together.

Again, I appreciate all of the help from every one of you.

Adaminchains

Adaminchains:

Thank you Doctor, for the problem set allowing each of us to contribute, our 2-Cents!

Highly enjoyable event!

Ron

Why don't you just leave the design of the device to experts in mechanical design and just clearly state what you want the machine for! Because now you have everyone guessing about what you really want. Or is there some commercial reason for not making the objective clear? If there is there is no point in this excercise.

I suspect you may need two of these skate like aids. If so; only one should move at a time. Am I right?

How about we all chip in for free to get this project moving? Brainstorm the idea and come up with a satisfactory product! We all have our fields of expertize and it is for the good of humanity! Maybe call it the WalCR4!

This news clip http://www.youtube.com/watch?v=IBlQrQQTUfs shows the type of roller wheel I was thinking of in my earlier post.

This pdf http://nsf-pad.bme.uconn.edu/1995/chapter_3.pdf from Binghampton University, on page 20 shows a non-reversing wheel that they developed. As their area of interest seems similar to yours, they may be willing to collaborate with you.

Your mention of a set and adjustable distance brings to mind a retractable tape measure.

Interesting topic...and right up my alley

I'm Bruce Honaker; inventor of Wheel Anti-Reversing Technology. I've made prototype inline skates using this technology. Visit: http://www.google.com/search?hl=en&q=wheel+anti-reversing+technology&btnG=Google+Search

My website is: inlineskatetech.com I've listed walkers as another application for this innovation.

You may reach me at ideaplace@msn.com to make this happen.