Can any master give me some idea

[sporty]

I am trying to add some linkage bar or gear mechanism to a wheelchair which can use to rise or lift the patient to the half standing position. This is to help the patient to stand up from a wheelchair by himself witount using motor or any circuit. To rise the body weight by using hand force is it possible? Can anyone provide me the draft of that mechanism design?

Thanks a lot...i am just a begineer, hoping people may share their idea to me..thanks

 

[Danger]

Welcome to PF, Sporty.
Your post implies to me that the patient is capable of standing up unassisted as opposed to having to be resituated in a different seat. In that case, it's a lot simpler. I would think that a slightly forward-angled scissors jack would work. A hand crank running something along the line of an old-style automotive window mechanism should provide enough mechanical advantage to achieve elevation.

 

[sporty]

yes, you are right, the person on the wheelchair is able to stand up,because they are only temporaly use the wheelchair like the people suffer from the accident or elder men or women in home, due to their leg is not able or no energy to stand directly from sitting . SO wish to lift the rear seat to make it in tilt position so they can easily stand up and use walker to walk.
I have draw the draft but i think the linkage is not good enaugh to support and lift the whole body weight by a hand push force.
the draft link,
http://www.fileupyours.com/view/295883/dsg.bmp
http://www.fileupyours.com/view/295883/55.bmp

And thanks for your reply , help, and your idea...i wish to make a middle complexity mechanism with small forces to rise himself or herself up

 

[Danger]

Well, Sporty... your first diagram seems to be inadequate. No offense intended, but it doesn't conform to either what you said in your post or what I would require as a handicapped person. It tilts, fair enough, but in a dump-truck manner. From my understanding of the needs involved, I would think that both the front and the rear of the seat should rise, but the latter more so.

 

[sporty]

Thanks to your replied,
because i am thinking that is the handicapped person they don't need much for tilt the seat because they are seldom leave the wheel chair for walking using walker so I only assume to design the seat for aging people. Do you have any idea or any mechcanism using gear or linkage to lift up the both front and rear seat with the rear part rise more? I hope the hydraulic is not needed. because it is heavily with pump is need. Can you share your idea to me? or show me your draft or idea or drawing, so i can instantly modified my grandmother wheel chair to comfortable stage. Thanks a lot. Hopefully by sharing your idea in here may help a lot of people in need. Thanks

 

[Danger]

Well, if you're familiar with a "scissors jack" as is used to change tires on a lot of small cars, that is the kind of mechanism that I'm thinking of. By using longer "legs" on the back side, the whole thing should tilt forward as it rises. Although you could use an electric pack, I think that a hand-powered unit should suffice for most purposes (if the attendant, rather than the patient, is doing the cranking).

 

[sporty]

ic, do you have any reference to share, i am not very familiar in scissors jack mechanism, i only know it is a cross mechanism. but i look the equipment in my father's car which used to change tires is its rise the car by using the screw thread and i think need to turn a number of time to rise it. Thanks for your idea, now i am going to search online about scissors jack mechanism, if facing any problem or doubt, i will post here, hopefully you you reply. Please, If you have anymore idea or link that can share to me, I am here to say thanks.

 

[sporty]

Danger, i am thinking if using scissors jack, the person need to turn numbers of time in order to rise the seat in tilt, and the mechanism for scissors jack is we need a strong base support for the reaction force, is it?
I am also thinking one of the equipment that the reverse turning would not affect anythings, while forward turning only will rise the things up..so we can continuous turn forward and backward in set angle range, to rise the things up, so don't need to adjust the position... i don't know what is the name of that equipment ,do you know it?
Sorry for my bad explanation and poor english.
If i am using above mechanism, it is no way to lower down the seat back.. so what can i do?

I am also thinking of floor jack mechanism that use to rise the car. but i don't know well in it.
Can you provide me some ideas, drawings or references.. Thank you Danger, and anyone interested may also provide your idea here. thanks

 

[Jasongreat]

The problem that I see is that with the weight transfer, up and forward, the rear of the wheelchair would want to raise and possibly tip over. Adding a battery, and an electrical mechanism would add some weight to the rear to make it more stable while making it easier to operate the lifting mechanism, but then would make it harder to move around the rest of the time, but so would the extra weight added by reinforcing the frame.

My thought is that if you could use their body weight to assist them, instead of trying to lift all their weight. Perhaps instead of moving the foot pads to the side when exiting the chair, you could use some cables and pulleys to transmit that force to under their armpits, assisting them instead of lifting them. I would think it possible to maybe give them a third of their body weight in lifting assistance, for a foot or so, since the foot pads are only about 4 inches off the ground, but then when they went to step off the pads, they would want to pop up, some type of locking mechanism could prevent that. Once I find my camera, i'll draw something and post it.

The easiest way to lift them would be with a simple lever, bent at around 90 deg(cantilever?) and rotating on a center pivot point. A threadscrew attached to the lower point, the chair seat attached to the upper. When the threadscrew was turned it would raise the seat and move it forward at the same time, you could either use arm strength to turn the threadscrew(you could even use a ballscrew to reduce friction making it easier, but that would increase cost quite a bit) or a battery powered electric motor. Either way I think you would want some type of outrigger on the front to stop the chair from wanting to tip forward, or to roll backwards.

I am off to find my camera to post some pictures.

 

[sporty]

thanks a lot jasongreat, u bring a new idea to me, but i still have a little bit blur about the foot pad, hope you can found your camera as soon as possible, may god bless you, because i am really exciting in waiting your idea and drawing..anyway thanks again.

 

[Danger]

I agree that Jason pointed out a couple of things that I had glossed over. For some reason, I thought that simply locking the brakes would be enough to prevent the chair from moving in response to the patient relocation. It just escaped me that the chair would also want to "nose-over" due to the shifting centre of mass. I can see the underarm harness thing being a logistical nightmare, but it's certainly a valid proposal. I look forward to seeing his drawings. If I see a point that I think might be improved upon, I'll chirp up.

 

[sporty]

Thanks for your help danger.

 

[Jasongreat]

I agree that Jason pointed out a couple of things that I had glossed over. For some reason, I thought that simply locking the brakes would be enough to prevent the chair from moving in response to the patient relocation. It just escaped me that the chair would also want to "nose-over" due to the shifting centre of mass. I can see the underarm harness thing being a logistical nightmare, but it's certainly a valid proposal. I look forward to seeing his drawings. If I see a point that I think might be improved upon, I'll chirp up.

Danger, you are right about the underarm harness idea, I think that using the existing arm rests would be the better solution, that way the weight of the person would be transferred to the ground, instead of supported wholey by the seat. I have a couple drawings, kind of rubeish though, but I can't find my digital camera anywhere to post them here. The easiest way I figure is to use some linear actuators similar to http://dcactuators.com/Detail.asp?Product_ID=306.120_6118" to replace the supports of the arm rests, and set to move up and forward, a simple on/off switch on the arm rest, so it can be easily reached while seated or while standing after getting aided up so the arm rests will recede. One could possibly use a small transformer instead of a battery system, to save weight and bulk, but then you would need to make a little power station they could wheel over to and easily plug in the chair to operate it.

I will continue my search for my camera. Sporty have you had any other ideas come to mind?

 

[sporty]

I have no idea about the linear actuator.what is its function? sorry for my limited knowledge in linear actuator. How it can support the weight of the body to ground?
In my mind i am thinking using a gear mechanism by turning or supply a torque and rise the scissor jack. but i am worry the chair will tip over or move backward when the mass of the body is rise. and i don't know any other good mechanism beside using gear to transfer to screethread and to rise up the scissor jack , or hydraulic( i am not very sure in hydraulic mechanism ) to rise up a linkage mechanism (like floor jack..?)and the seat. Or the drawing like what i put in my few previous thread.

Can you further explain in details or drawing because i am not very good in comprehend becaouse my english is quite poor.
thanks you jasongreat and danger.

 

[sporty]

If i am trying using a gear to drive another gear that stick on scissor jack, is it possible to drive the gear by hand to lift the scissor jack? Anyone? danger, jasongreat..? Thanks

 

[Danger]

If i am trying using a gear to drive another gear that stick on scissor jack, is it possible to drive the gear by hand to lift the scissor jack

It certainly is. Depending upon the gear ratio, it can take very little effort.
I have to leave for a wee while now, but I'll get back to you soon to continue this.

 

[sporty]

Thanks a lot danger. May i know 1 more things ,the scissor jack is it using screw thread to turn and rise the things up? I think i have to use your idea scissor jack, that is the only way i know, thanks a lot danger.

 

[sporty]

Any one, or danger, I want to ask that if I want to use rack and pinion with ratchet function install at the side of the wheelchair, may i know what mechanism i can use to connect with rack and pinion to lift up the seat with a small applied force? Please help me, Thanks a lot.

 

[Danger]

Any one, or danger, I want to ask that if I want to use rack and pinion with ratchet function install at the side of the wheelchair, may i know what mechanism i can use to connect with rack and pinion to lift up the seat with a small applied force? Please help me, Thanks a lot.

Hmmm... that would be a bit more difficult, and I suspect counter-productive. I can't help thinking that you will still need some sort of scissors linkage to connect the seat to the chair, so using that as the motivator as well would save a lot of hassle. Track-and-roller systems such as are used to mount car windows might work, but they seem to me to be overly complicated.
In answer to your previous question, yes... a scissors jack uses a lead-screw and follower system. The good ones actually have both left-hand and right-hand threads on opposite ends of the driveshaft, with one follower for each. That ensures an even load distribution between the front and rear legs. (That's not really a great explanation, but I'm tired and find myself somewhat at a loss for words today.)
A linear actuator, as Jason suggested to use, is simply a lead-screw inside a tube. You can most frequently find them on the tongues of small trailers such as for boats, used to hold the thing up when it's unhitched.
Jason's mention of the foot pads gave me another idea as well. The weight transfer problem can be alleviated by dropping the pads to the ground to use as "wheelie bars".

 

[sporty]

Danger ,thanks for your reply,i also thinking in its mechanism linkage if using pinion and jack. don't have any idea come my mind, very down. some people told me that if i don't know well in balance of center of mass gravity action, don't do this design. so i try another way by letting the mass act downward too when lift. This is the situation below link.
before,
http://www.fileupyours.com/view/295883/untitled.bmp
after,
http://www.fileupyours.com/view/295883/untitled1.bmp
but inside drawing the lifting mechanism is not on floor, it is an example only.
By this i can prevent the chair move backward when lift ,is it? is it better than tilt lift the whole seat instead remain some part of it horizontal.
But the problem now is i can't calculate out and use scissor linkage,because the seat is move forward when lift, it is not direct lift up vertically.
I am not very understand in Track-and-roller system, how it function in wheelchair..? and i also quite worry i can't make it because as you said it is complicated.
wheelie bars used by drop them to the rear or front ground ?
When the person stand up, will it applied a force in backward or to tilt seat to push the wheelchair to move backward? how we can solce it?
Thanks for you explanation and helpful idea.

 

[Danger]

I'm afraid that my next response will have to wait. It's 4:30 am in my time zone, I haven't slept in over 30 hours, and I'm fatigued. I have to, simply due to curiosity, check out GD and maybe make a minor post or two, but anything technical such as this will just have to go on hold until I've had some rest. Sorry about that, because I've very interested in this project. Catch you tomorrow.

 

[Danger]

Sporty, I just remembered that I once draughted a diagram for another project that I was helping someone with. The main part of the diagram is irrelevant to your purposes, but it includes a scissors jack mechanism which might be of help to you.

"[PLAIN
By null at 2007-07-13"][PLAIN]http://img368.imageshack.us/img368/7404/ballasttankwu6.png
By null at 2007-07-13[/URL]

 

[p1ayaone1]

All rotational actuators here, but still a remarkable design. It's called the M-V Chair:

http://www.mvpowerwheelchairs.com/chair.html

It is now a commercial product, plus it comes with an incredible story:

http://www.opb.org/programs/millertwins/

 

[Danger]

Wow! That is quite an impressive machine.
I'm still wondering about that weight-transfer compensation, though. Maybe they stash all of the heavy bits like batteries and motors close to the rear wheels?

 

[p1ayaone1]

With the reach they can achieve with that thing, I'm sure it's the only way. They're not too forthcoming with technical details though

 

[sporty]

thanks Danger and p1ayaone1, bring me a new idea. i thk what danger analysis for weight-transfer compensation is right for that chair.
danger, if i pin the scissor link to the rack which will drive horizontally backward by a pinion by using ratchet concept instead using the threaded scissor jack?because it is more convenient for an aging to lower down the seat to original position rather than turn number of turn to return down? i Don't know is it work possible for this idea and is it will reduce the applied force too to lift up a human weight?
and about the seat i post, i have tried draw a draft, but it is hard to put a scissor mechanism inside with the seat where it is pivot at a point and only front part of the seat tilted lift and the ramain is horizontal lift. any more suggestion please?thanks
thanks you very much danger and p1ayaone1..

 

[sporty]

[PLAIN]http://www.fileupyours.com/view/295883/example.bmp
This is what i try to make, Danger ,p1ayaone1,or jasongreat? or anyone else know that if i am using mechanism above and pin the moveable point in scissor mechanism to pinion and rack, using ratchet to drive it.. is it possible to lift it up? and the force needed to push will it lower?
or any other mechanism more effective? Please help , don't hestitate to post and share ur idea here... thanks.
And one more is anyone know how to calculate the static equilibrium analysis on this mechanism with distributed load...? thanks

 

[p1ayaone1]

I'm not a mechie myself, but maybe you want to look as linear actuators?

http://www.robotshop.ca/ProductSearch.aspx?qs=linear+actuator

 

[sporty]

thanks for your information.
if have anymore idea, welcome to sharing here.Thanks

 

[sporty]

if using linear actuator, I think we need a cell to supplied electric sources, and the electric source need to recharge, and will increase the overall weight of wheelchair, i hope to use manual type,
is it supportable or affordable if i am using ratchet mechanism to drive pinion and rack ,with the movement of rack to lift the scissor jack linkage, without using screw type scissor jack? I hope base on your experience in the design field can share to me the possibility working for this mechanism.
can you teach me too how to calculated formula for the force analysis and stress analysis on scissor linkage , i wish to make an analysis and learn on it before fabricate it and use.
and the linkage is like the drawing i post on previous thread.
i wish to lift 50 degree and height 14.5cm, i do not know is it the suitable dimension for them to easily get stand? Please share your idea with me, appreciate and thanks a lot.

 

[Danger]

I'm a bit busy to get into it too much right now, but it certainly is possible to use a rack and pinion with a scissors mechanism.
As for calculations, I have no clue about any of that stuff. If you want to skip down to Mechanical Engineering, though, Timma300 has a thread entitled "Scissor Lift Force" that deals with it.

 

[Danger]

Okay, I'm fueled with pizza and ready to roll.
I can see why you would want an easier way to lower the thing when it's not under load. While the rack and pinion would work, it would be horrendously complicated and possibly even heavier than a motor/battery combination. With the possible exception of an epicyclic gear train, a lead-screw gives the best mechanical advantage for it's size and weight.
A possible compromise comes to mind, though. Perhaps you could use a dual-acting lead-screw as I suggested earlier, but build small locking ratchets into the followers to allow them to "skip" down the threads for retraction. They could be locked in for powered lowering under load.
I like your diagram. Just make sure that the two sets of arms don't lie in the same vertical plane, or they'll be scraping on each other.

 

[sporty]

Finally you are back Danger,thanks a lot.. i need a lot of your help.. so u mean it really complicated if using rack and pinion. I also worried that the gear tooth will wear easily if the load support about 70 to 80 kg. I really have no idea in linear actuator, i wish to know the mechanism and operation inside. and i also don't know how to design the structure if using linear actuator, where to put it.
epicyclic gear train, how is the combination with the lead screw in order to lift up? can you show me some picture or draft? I really wish to use the things where it can reduce our applied force needed to lift a things up.
build a small locking ratchets into the followers to allow them to "skip" down the threads for retraction, it sound nice, but how is this mechanism work? as what i know the follower also have the thread, how it can skip it? Please explain to me more. Really need your help. Thanks a lot.
Forgive me for bring a lot of trouble to you.
For timma300 the site he show i went in before, but due to the problem i face is my scissor linkage is not equally length so it is not symmetric, and 2 pinned linkage have different degree of tilt, so ,i feel a bit crazy because i can't get any calculation on any site. What should i do. I am too stress.

 

[Danger]

I'm pretty inebriated right now, having just returned from a pool match, but I'll try to sort things out in a limited fashion before I pass out.
First off, I suggested an epicyclic gear train in lieu of a lead-screw, rather than in conjunction with one. That would give some sort of advantage if using a rack and pinion approach.
The complications involved in using a rack and pinion are incredibly formidable.
As for the "skipping" followers... traditionally, most followers do indeed have threads that match the screw drive rod. I'm going to say this in the simplest way that I can, to try to compensate for our language differences. Think, if you will, of a solid piece of pipe that just barely fits over the screw rod and can slide up and down it. Now, drill and tap a hole in the side of that pipe. Screw in a bolt with a rounded end, until it stops just short of the interior diameter of the pipe. The whole thing can still slide up and down on that screw rod. Now, when you want to engage, you just twist the bolt a couple of times until the rounded end catches in the threads of the screw rod. That whole pipe is then a follower.
A linear actuator is any device that provides a straight-line force in any particular direction. As it is normally considered, as has been done in this thread, it consists usually of a simple lead-screw contained within a cylindrical metal housing.
I really have to bag some ZZZ's now, but I'll try to get back to you within a couple of days.

And by the bye... chill a bit. Stress does no good for anyone, and is counter-productive when you are actually trying to achieve something. Think like a Vulcan.

 

[sporty]

thanks a lot t oyour reply danger, you make me more understand on skipping follower, but is it too troublsome for a person to screw the bolt to follow and unsrew it frequently? or is it have other mechanism to substitude the screw bolt to lock the thread?
Now i am more understand to the linear actuator, actually i need the mechanism for analysis for my project, my project is to design a mechanism for analysis so if i using actuator, it is only one things and no mechanism to analysis in my report.I propose wheelchair seat lift to my lecture because i saw a lot of leg broken patient, aging people like my grandma in my home , i wish to help them too beside can finish my project.
Before this, i bought a ratchet with rack and pinion mechanism, it is a device use to hold tightly the line to tighten the box. so i thinking to modified it by put the rack to a rectagular hollow bar and fixed the bar on side of wheelchair fixed also the pinion ratchet too. and that rectangular bar i open a slot at one of its side to pin the linkage with rack. so they can move together to lift a human. but i am not sure is it can work for my mechanism . with help in reduce the applied force by patient.

and my linkage also got problem, because it is unsymetric scissor linkage. different length for the leg. and one of the linkage is both end moveable. So i don't know wheather it will work ?
[PLAIN]http://www.fileupyours.com/view/295883/example1.bmp. Further Question is in my picture.
you are very kind danger. thanks for your advice. and your helpfulness.