FAQ: What should the inertia ratio parameter, Pn103, be set to in the Sigma II amplifier when the inertia ratio is not known?
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Pn103 only takes effect when the amplifier is in Speed Mode or Position Mode (Pn000.1=0 or 1). If the amplifier is in Torque Mode (Pn000.1=2), then Pn103 has no effect on the servo tuning parameters.
If machine performance is satisfactory with the default setting of Pn103, it can be left at the default setting. However, it is important to note that if Pn103 (inertia ratio setting) is set to the true inertia ratio, then Pn100 value itself will accurately represent the actual speed loop frequency response in Hz.
But when high performance is required, Pn103 should always be set as close as possible to the true inertia ratio before beginning to manually tune the Sigma II and/or controller. There are 3 methods for determining the inertia ratio.
1. Use the inertia ratio from the sizing results in "SigmaSize" based on the dimensions and material properties of all the parts that the servomotor causes to move.
2. Use the amplifier's built-in online auto-tuning algorithm. (Fn007 on the digital operator).
3. Use graphical analysis techniques.
When the components of the machine cannot be accurately measured or modeled with SigmaSize, the preferred method is #3 - graphical analysis techniques.
Yaskawa has developed a spreadsheet to be used for this purpose. This spreadsheet is attached below.
Yaskawa has also developed an "eLearning Module" on this subject.
This interactive training tutorial simulates both SigmaWin100 and the attached spreadsheet. The user is guided through a real-life example, while being given the opportunity to click and enter data at the appropriate times as if the software was actually being used. This eLearning Module takes 15-20 minutes to complete. It is attached below.
The eLearning Module runs as an executable file on any PC.
A sound card and speakers are recommended since there is audio. However, the audio is not absolutely necessary since all information and instructions are also displayed as text.
Screen resolution of 800X600 or greater is recommended.
The Inertia Ratio Parameter, Pn103, is only one part of tuning the SigmaII amplifier. Yaskawa also offers a complete Tuning Class.
For further information, see the eLearning module, doc # eLM.Sigma2.01.InertiaBGA
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