How to find out which sates were used for linmod of a SimMechanics model?

Hallo!

Ive set up a multibody model in SimMechanics 2nd Gen. It contains 4 spherical joints as well as 3 rigid bodies. I want to obtain a StateSpace model using the linmod function. Performing a linerization I do get a SS with 27 states. But how can I find out which state refers to which parameter of my SimMechanics model. Is there a way to obtain information on the states like: state 1 refers to the angular displacement in Joint 1.

Sadly, the state names do not contain this information.

G =

             a: [27x27 double]
             b: [27x2 double]
             c: [0 0 0 0 0 0 0 0 0 0 2.0000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0]
             d: [0 0]
     StateName: {27x1 cell}
    OutputName: {'model/Out1'}
     InputName: {2x1 cell}
     OperPoint: [1x1 struct]
            Ts: 0

>> G.StateName

ans =

    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Wrist_Joint_1'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Shoulder_ Joint_2'
    'model/Arm-Object-Arm_System1/Simulink-PS Converter/EVAL_KEY/EXEC_INPUT_1'
    'model/Arm-Object-Arm_System1/Simulink-PS Converter1/EVAL_KEY/EXEC_INPUT_1'
    'model/Arm-Object-Arm_System1/Simulink-PS Converter2/EVAL_KEY/EXEC_INPUT_1'
    'model/Arm-Object-Arm_System1/Simulink-PS Converter3/EVAL_KEY/EXEC_INPUT_1'
    'model/Arm-Object-Arm_System1/Simulink-PS Converter4/EVAL_KEY/EXEC_INPUT_1'
    'model/Arm-Object-Arm_System1/Simulink-PS Converter5/EVAL_KEY/EXEC_INPUT_1'

Thereafter, using minreal function i want to reduce the order of the system. And here is my second question: How to find out which states were eleminated by minreal().

Regards, Florian

Answer 1

[Arkadiy Turevskiy]

Hi,

As you mention, linmod does not support his functionality. linmod is a legacy Simulink function that is no longer actively developed. The actively developed function for linearization is linearize. This function is part of Simulink Control Design which provides a lot of functionality for trimming and linearizing Simulink models.

If you use linearize , you will get the information that you want. For example, linearizing this example with linmod I get these states:

• 'sm_cart_double_pendulum/Cart and Double Pendulum/Guide-CartPrismatic'
• 'sm_cart_double_pendulum/Cart and Double Pendulum/Guide-CartPrismatic'
• 'sm_cart_double_pendulum/Cart and Double Pendulum/Lower Revolute'
• 'sm_cart_double_pendulum/Cart and Double Pendulum/Lower Revolute'
• 'sm_cart_double_pendulum/Cart and Double Pendulum/UpperRevolute'
• 'sm_cart_double_pendulum/Cart and Double Pendulum/UpperRevolute'

Linearizing using linearize I get these states:

• 'Cart_and_Double_Pendulum.Guide_Cart_Prismatic.Pz.p'
• 'Cart_and_Double_Pendulum.Guide_Cart_Prismatic.Pz.v'
• 'Cart_and_Double_Pendulum.Lower_Revolute.Rz.q'
• 'Cart_and_Double_Pendulum.Lower_Revolute.Rz.w'
• 'Cart_and_Double_Pendulum.Upper_Revolute.Rz.q'
• 'Cart_and_Double_Pendulum.Upper_Revolute.Rz.w'

As for the second part of your question, you should be able to see which states were eliminated by doing:

linsys1=minreal(linsys);
linsys1.StateName

and comparing the result with:

linsys.StateName

Hope this helps.

Arkadiy