Hydraulic Powered Scissor Lift

It will be raided 1.5m in say 10-20 seconds.

Huh??...as to both the subject, verb, and object of the quoted statement.

To raise a load 1.5m in 20s would need a fair- sized pump. Adding an accumulator would mean that a smaller pump could be used, taking several minutes to build up the volume of pressurised fluid ready for a quick lift. This way, the pump could be run from a battery with no likelihood of overstraining the battery.

To preserve battery power, fit a switch to shut off the motor once the accumulator is fully charged.

Many thanks for your comment. I'll look into it.

I'm also looking into linear actuators as a cheaper and perhaps simpler alternative. The most difficult point will be when the scissor lift is closed.

Is there any way I can begin to work out a reasonable specification for this proposed system?

http://www.google.ca/search?hl=en&safe=off&q=%22scissor+lift%22+%2Btutorial&btnG=Search

Never close to 0degrees, so horizontal linear force will push the lift platform upwards.

Work out horizontal force required to lift load from minimum height (closed), add safety factor, and specify ram from there. Work out volume/pressure required to reach max height - depends on design of frame how long travel will be, so that should be no.1, but check out available rams so the frame can operate - most rams increase in length by ~75%, but there are some double piston types.....

To dimension the pump and the average consumption, choose a proper hydraulic actuator, check its area and operation pressure, and determine its size. Then, choose a pump rated to your pressure, and calculate the flow required to teh actuator by calculating the rate it must be filled while moving up. That's simple, and there you have all the elements you need to dimension the actuator and the pump.

Also, 10-20s is a fair approximation. CHoose 10 or 20, because one is 2 times the other one. To have an approximation of the order of magnitude of your problem, we're talking about a work of 200Kgx9.81m/s2= 1962N x 1.5m = 2943 J / 10s = 294.3 W = 0.4 hp, only to lift the mass, not considering the system inneficiencies.

Lets state that the motor has an efficiency of 80%, as the pump, and you'll have to act against a force of two times the mass lifted due to structure weight and atrict, and you have an initial estimative of 1.25 hp for your pump. It's just an initial average, and you'll find in your way that you'll have to dimension your actuator to a higher force, or to a longer actuation period, or to act slower in the extremes, etc.

Use this value to select some off-the-shelf equipment, check availably cylinders and pumps, as well as control valves. Don't forget to preview pressure losses in the circuit and in the valves, and put some safety margin. I think you're going to have fun.

About energy recover, it's possible by the use of a parallel return circuit with a small generator to charge a capacitor or battery or something like this, but you must calculate, even approximately, the efficiencies and see if it will pay for itself.

Thanks a lot for this - it has given me a good direction of where to go next. I'll look into the motors around this spec and see if they will fit the scale & budget.

As a further suggestion, I have been advised to look at linear actuators with all bearings inside - as the give low resistance and little/no backlash.

I guess I need to look at the input work in the form of a torque from motor/gearbox. Again, if you are still interested - any advice at this stage would probably speed things along!

Kind regards to all who have helped - This was certainly a good first impression of a Forum, for me!

Well, the "linear actuator with all bearings inside" is called ball screw. The mating element is called ball nut. They are a set of screw and nut, but the nut has internal races with spheres, and the screw has the other half of the race. Yes, they have almost no drag, are very efficient. However, a kind of expensive and are more sensitive to dirty, seal leakage, this kind of things.

As far as I remember, saginaw is a key manufacturer of them. You already know the power required to lift the load itself. The rest depends on the screw parameters.

Make your homework, and keep us informed.

What is your purpose, if really serious you purchase it directly from companies like doosan daewoo, or other forklift maker.

If you need calculation that i can guide u.

bakulesh. ( komalbakul@gmail.com )

hi bakulesh

i am interested in also seeing the approach in the design

thanks

raghu