Getting Started with xPC Target ME4803C

1
Getting Started with xPC TargetME4803C
2
System Identification of Structure Dynamics in
Flexible Robotics
RALF (Robotic Arm Large and Flexible)

• RALF
• Hydraulically Actuated
• 20 Reach
• Lightweight and Flexible
• DFT Averaging Analysis
• Structure Dynamics
• Actuator Model
• Computer Interface
• Analog Control with LabVIEW DAQ
• Math Works XPC Target

3
PNNL TEST BED

• Spar 2500 Macro Manipulator
• 3.4 Meter Aluminum Beam
• Schilling Titan II
• 2.14 Hz First Natural Frequency
• 0.006 Damping Ratio

4
Computer Basics

• Login into host computer as
• Username lab
• Password student (or students)
• There is a directory called C\xPC_Tutorial
  that has a number of useful Simulink models and
  tutorial files.
  
• Create a directory on C\ for your lab and make
  sure this is selected as the working directory in
  Matlab when using xPC Target.

5
Intro to xPC target

• Matlabs xPC target takes your Simulink model
  from the host computer, compiles it into C-code
  and runs it using a real-time operator system on
  the target computer.
• The target computer repeatedly executes this code
  at a defined iteration period.
  
• The target computer can interface with physical
  components through Input / Output cards.
  
• More information can be found at the Mathworks
  websites xPC-target page. There is also the file
  xpc_target_gs.pdf in the tutorial directory.

6
Useful xPC Target Functions

• Xpctargetping checks if communication is
  working
  
• Xpctest tests to see if target is fully
  functional
  
• xpcrctool remote control tool useful for
  general operation
  
• tg is structure that is generated in the
  workspace that has relevant data including
  uploaded data.
  
• tg.start, tg.stop, . Can start, stop, the
  program on the target.

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Testing xPC Target Machine Connection

• Make sure the target PC is turned on
• Type xpctest, if everything is ok you should
  see the following report in Matlab.

8
Opening a Program

• Programming an xPC file is similar to programming
  a regular Simulink simulation, but there are
  several settings that need to be changed in the
  Simulation ? Simulation Parameters menu.
• For simplicity start with a Simulink file already
  configured for xPC-target such as
  C\xPC_tutorial \blank_project.mdl. Save the
  file in your directory located on C\

9
Things to Know

• You will be making a discrete controller meaning
  it will update at a specified sampling rate.
  Later labs will discuss selection of sampling
  rate, for now use 1 KHz, or a sampling period of
  0.001 seconds.
• This rate can be set in Simulations menu and all
  discrete simulink blocks must match.
  
• Start, stop time can be set in the main menu or
  using xpcrctool.
  
• inf (infinite) stop time is often useful.

10
Setting Controller Sampling Rate
Click on Simulation and select Simulation
Parameters
Enter Stop Time (pick a large number or enter
inf)
Enter Controller Iteration Period (select 0.001
seconds for now)
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Adding Input / Output interface Blocks

• Open simulink library
• view ? library browser
• Place a D/A interface block. In the library
  browser go to
  
• xPC Target ? D/A ? Computer Boards ? CIO-DAS1602
  12
  
• Place a A/D interface block. In the library
  browser go to
  
• xPC Target ? A/D ? Computer Boards ? CIO-DAS1602
  12
  
• Drag the blocks to your Simulink Model
• Double Click on the Simulink Blocks in your model
  and modify the settings as illustrated on the
  next page.

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Model with Interfaces (settings)
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Adding Additional Components

• Add a Signal Generator to your model and wire
  it to the D/A block
  
• Simulink ? Sources ? Signal Generator
• Add a xPC Target Scope to your model
• xPC Target ? Misc ? Scope (xPC)
• Place a Simulink signal Mux to your model
• Simulink ? Signal Routing ? Mux
• Place an Output Block in the model
• Simulink ? Sinks ? Out1
• Wire the A/D card into the upper Mux input
• Wire the lower Mux input to the signal
  Generator
  
• Wire the Mux output to both the xPC Target
  Scope and Out1 block
  
• Verify your model looks similar to the following
  page and then save it to your directory as
  xPC_Tutorial.mdl

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xPC Tutorial Block Diagram
Build Model Button

• Build your model by selecting
• Tools? Real -Time Workshop ? Build Model
• (Alternatively the Build Model button on the
  Simulink header or the menu options in
  xpcrctool may be used to build the model.)
  
• If you receive an error message try building it
  again. If you continue to receive an error
  message then something is not correctly set in
  your model.

15
Running Your Program

• Option A xpcrctool
• Open the xpcrctool
• Hit the play stop buttons to run stop the
  target
  
• Option B command prompt
• Type tg.start to start target
• Type tg.stop to stop target
• Run your program and look at the monitor of the
  Target machine. Inspect the wiring of the signal
  generator, physical scope, and wiring to the
  Target machine (pins 37 18 are A/D and 9 7
  D/A). Play with the physical signal generators
  frequency setting and see what happens on the
  scope and Target Machines monitor.

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Changing Parameters While Program is Running (A)

• Option A xpcrctool
• Open xpcrctool
• Select Tools ? Tune Parameters
• This will open a window that looks like the
  Simulink model. Double click on the block you
  wish to modify settings. When done entering new
  settings select OK or Apply
• When done, close the Tune Parameters Window.
• This method does not change the saved Simulink
  model file.
  
• Use this method to change the frequency and
  amplitude of the virtual scope being generated by
  the program. Watch the results on the Target
  Machines monitor and physical scope.

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Changing Parameters While Program is Running (B)

• Option B Using external Mode of the Simlink
  File
  
• In the Simulink file select Simulation ?
  External
  
• In the Simulink file select Simulation ? Connect
  to Target
  
• This will automatically download to the target
  all values set in the Simulink file. Any
  Parameter change you make while connected to the
  target will also be downloaded to the target.
• When done, select Simulation ? Disconnect from
  Target
  
• This method is more powerful than using
  xpcrctool, but it changes the Simulink model
  file and care must be taken to reset all
  parameters to initial desired start up values
  before rebuilding.
• Use this method to change the frequency and
  amplitude of the virtual scope being generated by
  the program. Watch the results on the Target
  Machines monitor and physical scope.

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Saving Data (A)

• Option A Using Output Log
• Any data wired into an output block at the
  highest model level (out1 in this example) will
  be recorded to the matlab workspace.
  
• Recorded data can be accessed through the
  variable tg.OutputLog which is automatically
  saved to the workspace when stopping the Target
  Machine.
• The amount of data stored can be specified
  under
  
• Tools ? Real Time Workshop ? Options, Category
  xPC Target Code Generation
  
• The Target machine must be stopped to access the
  logged data.

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Saving Data (B)

• Option B Using Host Scopes in xpcrctool
• Make sure the simlink model is not Connected to
  Target
  
• Using xpcrctool interface create a Host
  Scope
  
• If your model is simple, use the Add signals
  button to open a signal selection window that
  looks like the Simulink Model File.
  
• Right Click the curser over signal lines and
  select Add to scope 2 (Blue lines can be
  selected, red lines can not. Go into subsytems to
  select signals that are red lines)
• When done selecting signals close the model
  browser window.
  
• To Access the Host Scope select
• Tools ? Host Scope Manager
• If you close the Host Scope without saving it
  through the Manager window you will have to
  rebuild the host scope.

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Adding Host Scope Selecting Signals
Select Host Scope
Add Scope
Add Signals
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Setting Host Scope Parameters (1)

• Number of Sample Select an appropriate number of
  samples to give an accurate picture of the data.
  Use the programs sampling rate for determining
  corresponding time length of sampled data.
• Set the fixed Y-axis limits by using
• Plot ? Y-Axis ? Manual
• For now use Y_max 11 and Y_min -11
• Signals can be added through the Add/Remove
  button and selecting appropriate signals in the
  sub menu.
  
• Start and Stop the Scope using the interface
  buttons

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Setting Host Scope Parameters (2)

• Once Stopped, export the data to the Matlab
  workspace using the Export button.
  
• Be careful, the scope will always export to the
  workspace using the same variable names. Make
  sure you rename the data variable, both the scope
  signals (scopename_data) and time variable
  (scopename_time), or else they will be
  overwritten next time you export data from the
  scope to the workspace.
• Data can be saved and plotted in Matlab through
  traditional workspace / variable saving commands
  and plotting commands (for more information type
  help save and help plot)
• Use the Host Scope to record and save signals.
  Change settings on the Virtual Scope being
  generated by the Target Machine and the Physical
  Scope to get several data sets.

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Illustration of Host Scope
Number of Samples Setting
Start Stop Buttons
Export and Add/Remove Signals Buttons
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Modify Block Diagram

• Modify your file by adding summers, constants,
  gains, and other signals as illustrated by

Set both the Signal Generators amplitude and
the Constant Reference to 0
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Using Modified Block Diagram

• Build and run the modified block diagram
• View the Target Machines Monitor and physical
  scope as you change Constant, Virtual Signal
  Generator, Gain, and physical signal
  generator's setting / values.
• Build a Host Scope to record and save to Matlabs
  workspace the resulting signals from different
  settings. Be sure to rename data exported from
  the host scope, preferably with descriptive names
  (both time and signal variables).
• Are you recording and viewing what you expect?