# The bungee lift system - Design help.

Discussion in 'Homework Help' started by Mitchy190, May 2, 2013.

1. ### Mitchy190 Thread Starter Member

Apr 23, 2012
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0
Attached is a block diagram of a lift system, which has a bungee for its cord. This is not a linear system, however I have worked out a model of the lift system at a certain linear region of the lifts height, this should allow my design results to be adequate to meet the specification. Or not! haha.

The Closed Loop Specification:

It is required that the maximum transit time from the ground (0m) to the top floor (100m) is 50seconds and from any one floor to the next (up or down 10m) is 20 seconds. Transients are a hazard to passengers, as well as being uncomfortable to experience. These should be constrained to be less than 0.4g.

The parameters I need to establish, such that they satisfy the closed loop specification above, are:
pc, zc, Ki and Ko as labeled in the attachment.

Anyway the dotted line around the the two blocks in the attachment is a model for the lift system. A unit step input is applied! (Reference)

Important information:

The lift of mass m=200kg moves on runners with friction K_f=370 N.s.m-1
The cable has a linear stretch with spring constant K_s=0.0001m.N-1
The motor inertia, J, is 0.5 N.s,rad-1 and the motor friction, K_r, is 4 N.m rad-1.s
The total length of the cable, L, unwound, is 110m
The radius of the cable winding drum, R, is 0.14m
A governor on the motor shaft limits the maximum angular velocity of the drum to 20 rad.s-1 in either direction.
The maximum specified safety weight for the cage plus load is 425 kg

So! I have worked out a suitable model, I just don't know where to go from here! Any guidance would be appreciated? A root locus plot G(s) can be provided, but I do not know what to do with it haha!

Many thanks Mitch.

Last edited: May 2, 2013