Mechanical Engineer HW

Wheel chair lifter mechanism design

The concept:

To design such a mechanism for lifting a wheel chair and the person who sit on the chair, we have to first decide a certain mechanism, and for this project, I chose a concept based on a manual hydraulic cylinder with links.

This concept is to have Manual hand to be press equal quantity of oil into two cylinders, and these two cylinders move a link which the wheel chair base connected to , and so raise the whole base into the direction the 1st floor from the bottom level, " the Garage level ",

The following graph is a simple sketch for the idea of the system

Explain of the concept and how it moves:

The cylinder 1 which shown at the graph when extending under the showing link, it takes the wheel chair base towards the 1st floor level, with the rest of the hinged links, " shown at the solid works assembly and simulation " as the links and the cylinders, and the whole system parts should be optimized to adjust the lowering and raising of the system

Also, the wheel chair has two covers to be closed when lowering and raising, but at the start it will be opened, and at the end "when arriving to the 1st floor"

The cylinder # 2 does the same as the cylinder # 1 does, and both cylinders extend at the same level, to keep wheel chair base at one level," a horizontal level ".

The system can be operated manually or automatic, and here for simple I chose the manual hydraulic system, to have a manual hydraulic pump, to be operated by a hand, to press the oil in the two cylinders, and so raising the wheel chair base, by raising the links supported at its base, and rotating the hinged link which is supported at the two sides of the system support " where are the cylinders are supported, at the 1st floor level"

So the linkage system to raise and take the wheel chair towards the 1st floor level, until the edge of it, and at that time the wheel chair cover towards the exit opens and after the wheel chair moves into the 1st floor level,

And the same happens when lowering, to push the linkage system by the two hydraulic cylinders towards the front and then the link which supported at the 1st floor rotate towards the down level, and finally the wheel chair cover opens to let the person move into the garage.

At the sketch, the motion of the system is shown, at the raising case, to be raising vertical first then as a curve towards the 1st floor level and for lowering the same motion occurs but in the direction of the garage level.

The wheel chair base dimensions and load:

Here we will take an example of real wheel chair, and we design the wheel chair base based on this chair dimensions, and for the weight also we take assumptions for this

For the wheel chair dimensions, it's as the following picture:

What concern here for our design, is the layout dimensions of the wheel chair, which are the length of 1200mm, and the width of 700 mm to design the stand based on these dimensions

So the wheel chair base dimension to be with a length of 1500mm, and width of 1000mm, to be more than the wheel chair length and width, and more free distance for the person on the wheel chair

And for the load on the wheel chair base "the wheel chair capacity", they are ranged from 250 – 400 Ibs, so we take it 500 Ibs to be safe loading on the wheel chair base.

So here we design the wheel chair base to handle a total weight of 500 Ibs.

The mechanism parts:

1. The wheel chair base with two covers

2. Two shoulders supported at the base

3. Two links for each shoulder

4. One link hinged and supported at the system fixture

5. Two cylinders fixed at the 1st floor level

6. Hydraulic unit with manual hydraulic pump to press the oil into the cylinders to extend and retract

7. Manual hand for the pump

8. The system support, fixed at the 1st floor, which contain the hydraulic unit and the cylinders and a link connected to the base links

The mechanism parts assembly

The following graph shows the whole mechanism while it's assembled, with different views, from top, and from inside, produced by solid works after assembly, and creating 3D drawing form the assembly

The Dimensions are in Millimeters, so the 3 feet height is converted to 914 Mm, to be the distance the mechanism moves and raise and lower the wheel chair with the person

How the mechanism is assembled

· The two covers are concentric with the base from both sides, and it rotate to open or close , and they rotate around a solid round cylinder concentric also with the base round port

· The two shoulders are fixed at the base

· The two links are hinged at the top of the shoulders and concentric

With the shoulders round ports

· The two cylinders are fixed under the two links and extend at the links, to raise the whole mechanism towards the 1st floor

· The two links are hinged at the two supports, to rotate while the cylinder extend towards the 1st floor, and also rotate while the cylinder retract but towards the garage level

How it moves

Extension stroke:

When the cylinders extends it push the piston inside the two links and so move the links to the front, and while the piston is hinged at the same place of links hinge, so it make the links rotate while the piston extension, and create the motion of rotation to the front, and then to the bottom, taking with it the base with the covers and the shoulders, and when it reaches to the garage level, the exit cover opens to let the person exit and move into the garage level

The next graph shows the mechanism at the garage level position at the end of the extension stroke of the hydraulic cylinder.

Retraction stroke:

When the cylinder retract, it takes the base from the bottom with a motion of rotation and moving towards the 1st floor level

The next graph shows the mechanism at the 1st floor level:

Dimensions of some parts:

1- The support for the mechanism

2- The wheel chair base

3- The shoulder dimensions

4- The base door

Note:

Attached the solidworks file for the whole project assembled, and matlab file for loads estimation while raising and lowering