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Filter Simulation

The Bode Tool can simulate the response of a system when a post filter is applied without having to retest the system with the newly applied filter. To perform this type of simulation, follow the procedure below.

Note: Filter simulation is not supported with MechaWare.

Step 1 - Get the frequency response of the system

Here is a system with a load that resonates at 6.7 Hz with no post filter. The closed loop response is in red, with the open loop response in blue. The same system will be used for each step in this procedure.

We will use the open loop data to apply the filters and verify at the end that the closed loop response is what we desire. Notice that the resonance appears to be at ~12 Hz in the closed loop response, while it is at 6.7 Hz in the open loop response.

The post filters are applied to the open loop system, so we will use the open loop resonance frequency. This is normal.

Step 2 - Simulate the open loop response

Turn off the axis to be tested and apply the desired filter to the axis being tested. We will use a resonantor at 6.7 Hz in this example.

Once the filter is applied, click on View -> Refresh to get the current filter data from the controller and display the filtered and unfiltered open loop, and filter traces from the Traces menu item.

You can see that the resonance is largely eliminated. You can update the post filter as many times as you want, clicking on View -> Refresh to simulate the updated post filter. When the results are satisfactory, enable the drive and make some moves to make sure that the stage is still stable. If it is stable, proceed to the next step.

Step 3 - Simulate the closed loop response

Change the traces to the filtered and unfiltered closed loop, as well as the filter traces in the traces menu to verify the closed loop response. Repeat the filter and go back to step 2 if needed.

Step 4 - Verify the open loop response

After simulating the filter, retest the system to verify that the simulated system accurately represents the actual system. When simulating a filter, only use the unfiltered output, as the simulated filter trace takes the tested data and simulates the filter, effectively applying the filter twice (once while testing, once while simulating). The plot shown is the open loop response after the resonator has been applied. Comparing the response to the original data shows a good correlation between simulated filter response and actual filter response.

Step 5 - Verify the closed loop response

After getting the closed loop response where you want it, check the closed loop response and compare it to the simulated closed loop system. If the result is too different from the simulated result, make a change to the filter and interate until the results are acceptably close to the intended results.

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