Lifting Structure Help

Did you investigate any of the information provided to you one month ago when you asked the same question?

If yes, what conclusions did you draw?

Thanks for your replied..Yup, i have do a lot online research, and due to i am not very good in mass balancing, so i decided to design the seat in front half part is tilt and the back half is horicontal, so the mass of human bdy will act vertically and not push against the chair to move.

This is what i draw using working model and test to run the seat mechanism.
i will make these mechanism at 2 side of the chair and each drive with different pinions and racks which both also have locking mechanism (only allow 1 direction movement/ ratchet) and have release gear too. The 2 ratchet will run together/synchronise by a bar connect them.i have scatche a drawing on a paper but i don't have scanner to put it online. The problem now is i want to know does this mechanism will work to lift up a human weight about 80kg as capacity, and the height to lift only 14.5 cm. Hopefully you can help me. Before this i wish to use hydraulic, due to i can't find any information or mechanism in hydraulic and my capacity load is only 80kg so i change to use rack and pinion combination.Please help me . idon't know will it work because i don't know make the analysis on my drawing..please help ...appreciated..thanks

It can work and even be simplified.

I'm not fully clear on what this mechanism does (exactly what pivots, slides, rolls, stays fixed, etc.) I would be inclined to base any design on a single electrical linear actuator. They are made in 12- or 24-vdc versions that will lift 200 lb or so.

If a spring can be incorporated to counteract about 85% of the user's weight, a lighter actuator or even user cranking might work.

my suggestion is to not use a pinion but a worm gear (or pair of worm gears w chain), and that way the ratchet is not required. also I believe that less power will be required in the motor.

Chris

Thanks a lot for so many replied..
Tornado ,electrical linear actuator will it too heavy to put under a wheelchair, actually i wish to put it on wheelchair to help the person after accident and have leg broken, so can lift them to certain height for them convenient to stand from a chair when they need a walk using walker actually i don't know well the mechanism for actuator Do you have more information on it or mechanism on it? Cause i need to do it detail in my project...and What is user cranking actually? Do you have any existing example for me to reference? thanks

This is basically a mechanism project, and my teacher want me to do the project related to mechanism and this is my first time doing design work. hope getting help from master here.Actually i have think before using electric motor, or hydraulic, but it seen it will reduce the mechanism where it is what my teacher wish to seen (he want see mechanism in my project), so my mind is too stress to achieve it. and that is why i use manual type, or using user hand to lift.

nick name, do you know any calculation on my type of mechanism , because i need to do analysis, i can't get it online. How we can simplified this mechanism, Do you have any reference for me? thanks.

chrisg288 Do you mean the scissor linkage above is work? ya less power used is what i wish to have... but without ratchet the worm gear can lock to prevent it to reverse back? Can you explain more detail how the lift mechnaism to lift a person using worm gear or provide me some reference? Thanks

Sorry everyone, i have bring a lot of trouble to yours, and thanks to providing me a lot of idea. as a beginner i am very appreaciate to have your help in my project. Thanks again.

my worm gear idea would be applied to the sliding leg of the scissor (see post #7 excellent diagram) where you would otherwise place your pinion gear.

or you can use the worm to drive the pinion gear

Chris

By "user cranking" I meant any type of wheel, handle, or crank that could be operated by the wheelchair user or attendant.

A satellite dish positioner is an example of linear actuator, but it might not be strong enough for this. Duff-Norton is one company that makes industrial-type linear actuators. They probably have a Website; McMaster-Carr and Grainger Industrial Supply also sell them.

Thanks everyone for yours replied.nick name do you still know the link of that full thread for compute and discuss the load? The simplified linkage you showed is good, thanks a lot, i want to ask some my doubt ,the height lift is too short..how to lift it to higher, if too short it look like no effect to lift him up to half standing position? and the space for scissor linkage is limited. When the front part of the seat tilted, much of the seat is drop downward compared to seat position before lifting (thigh part), will it influense the ease of a patient to stand up in ergonomic?forgive me for my innocent question, because i have not much knowledge in this.

chrisg288 thanks a lot, so if i am using worm gear (a in your diagram?), fix it in a position and turn it manually( the b in your diagram is it a rack?), so the rack will move togethet with the pinned scissor leg (c?)on it? and the Worm gear drive the pinion gear and how pinion connect to scissor leg? using rack? Thanks a lot, forgive me for my innocent question, because i have not much knowledge in this.

thanks Tornado, if using linear actuator, so we don't need any mechanism linkage to lift up? only substitude with one actuator and lift up directly? and the linear actuator i look in youtube,the platform normally put in on the floor so the force can directly act to the floor, but my installation is on wheelchair, so patient weight action force will act to the bar use to support it on the wheelchair?so i don't know the mechanism and function inside or internal the linear actuator, so i don't know what mechanism to show in my report later.?Thanks a lot, forgive me for my innocent question, because i have not much knowledge in this.

Thanks a lot

sorry this took so long.. this is what I was thinking of. hope it makes sense.

working...lol

here is an animated version.

You've done it again Mate. Good work.

this one has the worm speed at a more reasonable (fast) rotation speed.

chris

Hi Chris,

Good example of "works in modeling" but has real world issues.

Have a closer look at worm thread forms and you will see the 'wheel' is like helical, or more correctly a "spiral" form. This is incompatible with a 'rack', outside Meccano fudging, which is quite inefficient.

What you'd need to do is either make a very tricky rack, like half a worm form, or put a conventional gear along side the worm wheel, to do the rack part.

34.5

_{(I'm on 'you've done it too much') (intentionally this time, for data gathering purposes)}

I think you are right.

nick name do you have any more scissor design or which can lift the seat to more higher? I am too stress now, because tried many time but fail, i hope lifting height around13 to 15cm. DO you still remember what is the thread name for calculate the force analysis..because your idea design in simplified is very good.

Please save me.Do you still remember the name of the thread thatshow the calculation on lifting discussion? Thanks a lot.

nick name or anyone
One more thing i want to ask, in the previous picture i post, one of my scissor linkage, the 2 end of that linkage is moveable only middle is lock with with other scissor linkage... is it possible to work after load?

And i tried out static force analysis, but,In free body diagram, i don't know how to start calculate ? and how to load the distributed load to the linkage? help me..

Nick name, it is a incredible design, i wonder to know how you can think of this critical type of design. You must be very experience in mechanism. thanks a lot .
And i want to ask that is it possible to work if using ratchet mechanism and pin the moveable leg in this mechansim to the rack which drive by ratchet? so scissor leg will move along with the rack to lift a person up?
And in scissor llinkage mechanism is it must be 2 leg is fixed ans 2 leg is moveable? how about 3 leg moveable?
I don't know how to make your design to lift the seat to more higher.

What are the things should i found before i make a sketch?

1- try to dimension the components by defining the loads and 2- do the sketch as you think You will learn more if your ideas are corrected than if you get all explained. It is a normal human behaviour : we learn by error's correction a lot more since we have to compare what we did with what should be done and this is much more in the depth process. You may use as well the private channel if you are affraid of negative comments with respect to your solutions. Do not forget - it is not in my sketch - that the 2 scisor legs are connected in the middle to form 2 triangles.

Thanks for Nickname and chrisg replied. I wish to get correction from yours opinion, I am using a software name "working model" It is a type of software used to make a sketch and run the animation, we also can add the powers sources ,like motor, torque and so on to our sketch, then run the simulation. what i get from this mechanism is it is about using 180N to lpush the scissor leg to lift, but i haven't add the ratchet mechanism yet, due to i am not very familiar in this software, still learning.
Now i am wish to learn more from your who have more experience. In your sketch, it is a new idea for me to combined more than 1 scissor leg in 1 follower. but i don't know how to make it to lift up to 14-15 cm height. and the wheelchair seat what i assume is 42cm depth size. and middle of the seat is have a pivot to allow the front part tilt.Now only i relize that you do not have a connection in the middle of your scissor leg.
Before this i sketch it on the paper with the standard dimension of wheelchair seat depth, and try to draw the linkage to match it when lift up to 15cm.Then i try to draw what i sketch on paper to a working model software, it have a bit different after i draw on this software compare to initially what i assume early in paper sketch when run the simulation. now 2 moveable leg in bottom which i wish to pin to rack is not move in simultaneously, and i don't have idea how to modify it, if both are pin on rack, it can't move if both fixed to move simultaneous..

You need ONLY a screw with self-locking property and no other ratchet or other mechanical components.

What you need is: motor-gear box - screw and of course a nut on the scissor' s sliding ends.

I am sorry that I forgot to mention the shaft in the middle of the scissor, it was obvious for me.

List your questions in short sentences they will be easier to understand.

Nick name, i have sent a message to your mail box, would you give me some advice on my drawing? It is not quite clear, but the mechanism is same as what i post in previous thread. Thanks.

Here is a picture of an example actuator: http://www.duffnorton.com/products/mech3.aspx

In nick name's version of a scissors lift, this actuator would be mounted horizontally with the motor assembly attached to the right (stationary) pivot point in the lower rail. The end of the screw would be attached to the left (sliding) pivot point.

To get the correct amount of lift movement, you can adjust the lengths of the linkage components, using CAD or manual drafting techniques to "map out" where everything can move.

***

In a different approach, you might think like an adjustable-height office chair, with a clampable air spring lifting vertically.