coprimeunc.m - Hydraulic Manipulator

Dear Professor Skogestad,

Thank you for your prompt response regarding my query about the
availability in DOS format of the m-files featured in your book.

I am wondering if you can assist me with some problems I am having in applying
one of the methods described in the book.

I am attempting to design a 2 degrees-of-freedom controller for a
hydraulic robot manipulator following the procedure you described. I
have achieved a pretty good loop shape, but on using coprimeunc.m two
problems occur
  
    a} Warnings for poorly conditioned matrices
    b} At different times either of the Riccatti systems are
          ill-posed. Both my (A,Q,R) systems are minimal, ie
          controllable and observable, so I am somewhat confused

I am hoping that you will be able to provide brief answers to the following

1 How well does the coprime factorisation method work on
     non-minimum phase systems

2 My nominal model is actually a very accurate 8th order model (5
     zeros) obtained by using invfreqs.m to identify transfer function
      measurements taken from a non-linear simulation. Would taking a
    lower order nominal model alleviate my conditioning problems.
    (companion form state-space realisations of MIMO systems do have
     a lot of noughts). Could the ill-conditioning be leading
    directly to the ill-posedness.

Thank you for your attention. I look forward to hearing from you.

Much regards

A. H. Fraser, Development Engineer (Control Systems)
UK Robotics Ltd.
Derwent House,
Clarence Avenue,
Trafford Park,
Manchester,
M17 1QS.

email ainsley.fraser@robotics.uk.co
Tel: +44 (0) 161 876 3200
Fax: +44 (0) 161 876 3201
Received on Wed Sep 11 18:28:05 1996