Question: how to derivate?

Hi everyone. Does anyone know how to derivate such function: piecewise(t and avoid in result: Float(undefined) in points where function is not continuous. You can see what I'm writing about in file trajectory I appended. The problem is that I have a big simulation of constrained robot and I need to derivate my equations which are not continuous and I cannot change it. Thanks for any help. Piotr P.S. I forgot to write I use MAPLE version 8
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