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Scissor Lift Design 4

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uncia

uncia

Mechanical
Jun 3, 2017
6
Hello All,
I am looking for some kind of supporting solution/ idea for already designed and manufactured scissor lift. We have manufactured scissor lift for our workshop use only. It can lift the load well up to certain limit. When we try yo lift some heavy load, it lifts but not without deflections of the arms. This way it has also hard time to move up unsupported end side as shown in image.
In future we will re engineering it again but for now we are looking for some kind of linkage mechanism or other idea to support the unsupported end go ahead.

Thank you
 
 http://files.engineering.com/getfile.aspx?folder=2cf34f81-39d2-41b9-803f-2d6f87f4826b&file=WP_20170617_12_12_46_Pro.jpg
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Bending = deflecting or permanently deforming ?

Is this a commercially available lift? By how much are you exceeding its load raring?
Using it beyond it's rated load is looking for trouble, maybe even fatalities.

Is this a one time situation, or will you be handling these heavy loads routinely?

Increasing the "I" moment of Inertial of the "arms" will reduce the deflection, and prevent deformation.
But the strength of all the pivoting joints, and even the limits of the lifting cylinder may be exceeded too.
 
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Thanks for replying. No this is not commercially available lift. We built it for our workshop use only. I though to reinforce the arm and that makes sense but load has to go somewhere. It am afraid that it will not good for pivot joints.
When I look the other way around if I can support the unsupported end, it will be more efficient as there will be more transfer of load to all the joints. We might lift heavy load twice or thrice a week.
What happened here is that we have to lift wide load from low ground level. We are not scissor lift manufacturing experts but we decided to do all by ourselves. It ended up selecting long arms(thus reducing mechanical advantage).
Just want to find solution before permanent deformation of beam or damaged pivot pins.

 
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Why are you trying to build this instead of buying one that someone else already designed and has already dealt with the issues AND certified the device as capable of supporting its stated load capacity?
 
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That is interesting question but honest answer is we just wanted to make ourselves as we have facility and also all required resources like power pack, DCV, hoses, fittings, bearings, pins.
 
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Except, apparently, the design experience!

People get killed when stuff like this collapses or falls over. Buy one that's certified for the load you are trying to lift, and follow the information for use that is supplied with it.
 
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I'm confused again. The objective is to transfer the load as efficiently as possible to the base. Assuming that your joints are sufficient robust, beefing up the legs should take care of the problem.

Why do you think that won't work?

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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Your scissor lift has simply been designed with inadequate strength (or stiffness). The only purpose of the scissor mechanism is to keep the platform level under load while using only one hydraulic cylinder for lift.

The safety of your lift is highly questionable if you can see the tilt in the platform.
 
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Add another cylinder the same size as the current one and positioned symetrically to it and under the bending arms. Operate both cylinders hydraulically in parallel. That would shorten the unsupported length of the bending arms. Or, as suggested, increase the arms crossections in the direction of the bending to reduce the bending.

Ted
 
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Brian Petersen : I agree with your point of Except, apparently design experience. Currently, we are not lifting heavy loads but we want would like to lift it. It works well up to certain loading condition. Safety is our priority, too, without any second thought. Moreover, we wanted to develop it at our end as we have some push and pull horizon function in bed of scissor lift, which is not a concern here. It has cross tube mount cylinder in bed for push and pull function.

IR Stuff : My point is that currently I have two points to transfer the load to base as one is free and other end is supported. If I can support free end, it would be more efficient way to transfer the load.

Compositepro : Yes, I agree with you that it has stiffness problem, but I believe that it just need some support to transfer the load as I see all the time how it goes when we lift the load.

Hydtools : You are right. I was thinking the same way that just mirror one cylinder on the opposite which is not supported. It will good to go. It will synchronize with the movement of exiting two cylinders in parallel circuit. To be honest I was trying to visualize some kind of linkage mechanism which can synchronize with cylinders while they move upward (lift) and downward (gravity down).
 
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I took the problem here cause I strongly feel that it has simple solution but need to be brain stormed.
 
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"My point is that currently I have two points to transfer the load to base as one is free and other end is supported. If I can support free end, it would be more efficient way to transfer the load. "

Huh? If your load was within limits, the scissor would work correctly, and works still, since nothing has fallen or broken or permanently deformed. Therefore, the correct answer is to make the original design stronger, not come up with make-shift patches that might make things worse.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! faq731-376 forum1529 Entire Forum list
 
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uncia

you could just position the platform so that the mass center of the heavy load is near to the cylinder side.
 
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IR Stuff : Thank you very much for your suggestion.
CostaV : The platform has function of pushing the load, so even if I set the mass center of heavy of near the base of the cylinder, it has to move forward. towards unsupported ends.

 
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In my opinion, you need to STOP RIGHT NOW and begin a real engineering effort.
Worker safety is clearly at risk.
This is unacceptable
Take a big step back and make sure the "way it has always been done" is acceptable
At the very least, dig up the old design work and interview the people responsible for the existing machine.

Research and find the codes that apply, including OSHA
Define the current static and dynamic loads for all operating conditions
Include fatigue if appropriate
Establish safety factors
Review the current machine and establish safe static and dynamic loads
Stencil those on the machine
Look at "what-ifs" like hydraulic power loss, external forces or impacts, etc to make sure it is still safe
Investigate control systems to cut power or otherwise disable or lock the unit if the design load is exceeded, power fails, the load is off-center, etc
Put it all in writing

Then
Define the new static and dynamic loads for all operating conditions
Design a new or modified system for the new loads
Review all high stress areas, often at the joints
Examine one you can buy to see where you went wrong
Iterate

Your first priority is worker safety
You've been lucky so far but now an engineer is involved and luck ain't good enough any more
It sounds like your company's home-made system is exceeding its (unknown) capacity and putting people at risk
This is your chance to draw a line in the sand and as an engineer take a principled stand against ignorance and possibly stupidity plus protecting your company from a preventable accident

My opinion only, from a cranky old engineer...

 
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Purchasing a commercial unit has several critical advantages to you:
(1) You know it has been tested and retested by both the manufacturer and numerous other customers.
(2) It comes with a tested, verified, certified, and labeled load limit.
(2) It comes with a warranty.
(3) The vendor legally assumes some or all of the liability in case of failure.
(4) If there is a failure, your business is not the only one at risk.

Realistically you are not saving any money building (and rebuilding) this thing yourself. Just because you have some tools and materials is no reason put your employees, and your business, at risk.

Please, please give it up and do this thing right.
 
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it sounds like you've designed and built a scissor lift that works adequately for the loads you're using it to. I suspect it was designed by eye (and not analysis). If so then I think you need to complete the analysis to understand the weak points of the design and the safe limit. The fact that it doesn't deflect under typical loads does not mean that typical loads meet the level of safety required (a SF of about 5 ? or whatever your local Health and Safety people want).

If you have completed an analysis then you know the safe load limit of the lift (and it should be clearly marked on the lift so the people operating it know) and the weak points (and so can answer your concern about reinforcing the arms, sending the load to the joints). Then it becomes a "simple" matter to redesign the lift for a higher load, and possibly dual actuators.

another day in paradise, or is paradise one day closer ?
 
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