I posted this in the structural forum & additional infor was requested:<br>
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The application for the safety device is to stop a free fall of a vertical traveling platform. The safety device is a mechanical backup system and is replaced after one use. The safety device is a rotating cam with serrated teeth. In a free fall the cam teeth rotate onto a W-section flange. The hardened teeth "imbed" and lock onto the flange. Thru testing we have established a cam load limit. I'm look for information to understand the dynamics and limits for a redesign of the cam teeth.
I have done something a little like this although it was not a dynamic situation. Design was aided with our in house FEA. If you want to know more please contact me MWest@hatch.com.au
Have you found a solution to your serrated teeth problem??
Would you not be better to attach an opposing profiled rack on the column to lock against the cam to reduce damage-due to the teeth biting into the column??
I too am working on a safety system, for catching a beam if the support ropes let go for some unlikely reason. The beam runs up and down two rails at either end of the beam. The rails are manufactured with the two sides parallel to the beam profiled in a saw tooth design. The beam has a four toothed cam that pushes out via a cylinder and grabs onto the rail stopping it in its tracks.
My problem is trying to model and analyse the impact or shock load on the rail and the cam teeth. I have looked at strain energy theory, but have found it quite involved and haven't had the time as yet to understand it fully.
Our beam should only fall about 300mm if there is an incident, this safety device is also going to be able to be used for maintenance purposes. When the beam or its dynamic parts are in need of service the cams can be actuated and the suspension ropes removed.Our beam weighs a heavy 25 tonnes so it will not move once the cam is actuated, unless it is lifted upwards first..
I am now looking at cosmos motion to give me an idea on stresses and then i will at some stage go back to strain energy theory and try to nut it out.
I have looked at kinematics to solve the problem. i.e F=ma, first i find the speed at which the beam is travelling after it has been dropped.
v^2=2ax,
Then i roughly estimate the stopping time it will take to absorb the impact energy.
and use this to find the decceleration speed
a=v1/t
From this i can find the force due to the serrated teeth deccellerating the beam.
F=ma
This is of course not accurate as i cannot closely estimate the time it would take to absorb the energy...
What have you done to analyse the stresses in your cam teeth, i suppose the impact will be less severe for your teeth as they have to push into the column first before they get the upward force.
I would appreciate your help if yo have found a solution to your problem.
