update colorbar

Dear list,

I am making a 3d plot of a set of functions one after the other.
Actually I do this interactively, but what matter should only be that
I plot, clear the axis, plot again and so on.

I want to display a colorbar for each of those plots. The first thing
I tried was calling
  fig.colorbar(surf, shrink=0.5, aspect=10)
each time. This produced a new colorbar each time I called it. So
thats not working, but thats ok.

My question is now, how do I update the colorbar? I tried several methods:
but none of them updated the colorbar. So the plot clearly used colors
from [0, 0.2] but the colorbar always stays at [0, 0.05] (which are
the values from the first time I drew).

How to correctly update the colorbar?