Simulink Control Design 3.0

Linearization of a Conveyor Model (Requires SimMechanics)

Contents

This demonstration introduces the use of the operating point search and snapshot features along with the linearization of a SimMechanics™ model. (Requires SimMechanics)

Operating Condition Search

Open the model

open_system('scdmechconveyor');

SimMechanics visualization is forced to new visualization because of mech_fo
rce_visoption in MATLAB path.

The steady state operating point can now be found using the operating specification object initialized using the simulated operating point. For the steady state operating point search, the Analysis Type for the SimMechanics machine must be set to be in Trimming mode. See the SimMechanics documentation for details on this feature.

set_param('scdmechconveyor/Mechanical Environment','AnalysisType','Trimming'
)
opspec = operspec('scdmechconveyor');

For SimMechanics models, the operating condition search in some cases can converge to a steady state condition more quickly using a nonlinear least squares algorithm. This algorithm is available if the Optimization Toolbox™ is licensed. An iterative report of the search can also be displayed by using the LINOPTIONS command.

opt = linoptions('OptimizerType','lsqnonlin','DisplayReport','none');
opt.OptimizationOptions.MaxFunEvals = 2000;

To ensure that the algebraic constraints in the SimMechanics model are met, the trim output port must be specified to be zero.

opspec.Outputs.y = zeros(8,1);
opspec.Outputs.Known = ones(8,1);

The steady state operating point can now be found using the FINDOP command.

[op,opreport] = findop('scdmechconveyor',opspec,opt);

Display the final report

opreport

 Operating Report for the Model scdmechconveyor.
 (Time-Varying Components Evaluated at time t=0)

Operating point specifications were successfully met.

States:
----------
(1.) scdmechconveyor/Position Controller/H_inf Controller
      x:         -1.08      dx:             0 (0)
      x:    -7.67e-012      dx:     1.37e-012 (0)
      x:         0.199      dx:     6.63e-014 (0)
      x:         0.199      dx:     8.76e-015 (0)
      x:        0.0743      dx:     1.44e-013 (0)
(2.) scdmechconveyor/Position Controller/Loopshaping Weight
      x:     2.59e-007      dx:     5.47e-014 (0)
      x:     2.59e-007      dx:     5.77e-015 (0)
      x:     9.66e-008      dx:    -3.83e-014 (0)
(3.) scdmechconveyor/Position Controller/Prefilter
      x:        0.0103      dx:     2.44e-013 (0)
(4.) scdmechconveyor/Position Controller/inv(W)
      x:    -2.59e-007      dx:    -5.47e-014 (0)
      x:    -2.59e-007      dx:    -5.77e-015 (0)
      x:    -9.66e-008      dx:     1.07e-013 (0)
(5.) Prismatic.P1.Position
      x:         0.103      dx:    -7.99e-021 (0)
(6.) Prismatic.P1.Velocity
      x:    -7.99e-021      dx:    -5.03e-013 (0)
(7.) Revolute.R1.Position
      x:        -0.881      dx:     1.59e-021 (0)
(8.) Revolute.R1.Velocity
      x:     1.59e-021      dx:     4.61e-012 (0)
(9.) Revolute1.R1.Position
      x:          0.83      dx:    -8.91e-021 (0)
(10.) Revolute1.R1.Velocity
      x:    -8.91e-021      dx:    -4.26e-012 (0)
(11.) Revolute3.R1.Position
      x:        -0.172      dx:     2.73e-020 (0)
(12.) Revolute3.R1.Velocity
      x:     2.73e-020      dx:     8.04e-013 (0)
(13.) Revolute5.R1.Position
      x:       0.00175      dx:    -1.53e-021 (0)
(14.) Revolute5.R1.Velocity
      x:    -1.53e-021      dx:     1.04e-013 (0)

Inputs: None
----------

Outputs:
----------
(1.) scdmechconveyor/MSB Trimming Out
      y:    -2.31e-013    (0)
      y:     1.41e-013    (0)
      y:    -9.13e-013    (0)
      y:     1.61e-013    (0)
      y:    -7.99e-021    (0)
      y:     1.83e-021    (0)
      y:     4.74e-021    (0)
      y:     4.57e-021    (0)

Before linearization of the model can be completed, the Analysis Type for the SimMechanics model needs to be restored.

set_param('scdmechconveyor/Mechanical Environment','AnalysisType','Forward d
ynamics')

Linearize the Model

In this model the open loop plant model between the conveyor position and the torque command can be found using the following input and outputs:

io(1) = linio('scdmechconveyor/Joint Sensor',1,'out','on');
io(2) = linio('scdmechconveyor/Position Controller',1,'in');

Linearize the model.

sys = linearize('scdmechconveyor',op,io);

View the linearized model and corresponding Bode plot.

sysm = zpk(sys)
bodemag(sysm)

Zero/pole/gain from input "Torque" to output "Joint Sensor":
      -2.0818
-------------------
(s-3.481) (s+3.481)

Close the model.

bdclose('scdmechconveyor')