FAQ: What is the reason for the long deceleration when using a Direct Drive Motor system with a Sigma 2 Servopack (SGDH) and MP940? What are the steps to properly tune such a system?
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The attached .JPG file is a screen shot of a profile of a Direct Drive servomotor controlled with an MP940. A quick 20mS move was set for acceleration and deceleration.
The SGDH speed loop gains and MP940 position loop gain are too low for the Direct Drive Servomotor system. Once the MP940 memory is cleared, and both the Servopack and controller are re-powered, the MP940 turns off 'adaptive auto tuning'. The MP940 does this by setting Pn110.0 = 2.
Speed loop Gains:
Pn103 (Inertia ratio) in the SGDH is still set to Factory default of 0. In this condition, the speed loop gains in the SGDH (Pn100, Pn101) are very small relative to the high encoder resolution and large inertias of both motor and load. Calculate the inertia of the load and enter the Load to Motor ratio in units of 0.01% into Servopack Parameter Pn103. The factory defaults on the other two gains (Pn100 and Pn101) are a fine starting point for a Direct Drive Servomotor and load.
Since the load is direct drive, speed loop gain tuning should be started from a rigidity setting of 8. If there is too much vibration during an initial move, then it should be decreased, and a test move made again. Please refer to section 6.3.2 in the Sigma 2 manual for adjusting the gain levels for specific rigidity.
Position Loop Gains:
The Position Loop gain and the Position Loop Feed Forward are of equal importance. Both are located in the MP940 controller.
The Motion Works+ software package includes the Position Loop Gain as System Variable 'pGain_PositionLoop'. In MPE720/MotionWorks it is register OWC010, or Set Up Parameter 17 in the SVA module configuration.
Values for Position Loop Gain can vary, but a good starting point for a Direct Drive Servomotor is 50. Increase the gain for improved deceleration performance. When the system starts to oscillate or overshoot slightly, reduce the value about 25~35%.
Once the Position Loop Gain is set, raise the Position Loop Feed Forward. Starting at zero, increase the value until oscillation, and then reduce slightly. Feed Forward is labeled "pGain_FeedForward" in the MotionWorks+ Software package. In MPE720/MotionWorks it is register OWC011, or Set Up Parameter 18 in the SVA module configuration.
If the system performs well without Feed Forward, then leave the feed forward at zero
Using Adaptive Auto Tuning to calculate inertia:
In order to use Adaptive Auto Tuning and have the Servopack calculate the inertia, the feature must be re-enabled. See section 6 of the Servopack manual for details.
Step 1:
With the load is attached, Set Pn110.0=0. This will enable the adaptive auto-tuning algorithm after power is cycled.
Step 2:
The Servopack will calculate the inertia durning the first few moves.
Step 3:
Use function (Fn-007) to copy the inertia ratio to the EE-prom.
Step 4:
Disable auto tuning by setting Pn110.0=2, then cycle power again.
Step 5:
(Optional) Perform manual tuning by commanding open loop speed to the Servopack. This can be done via 'Speed mode' when programming an MP940 in MP720/MotionWorks. A JOG operation in MotionWorks+ is an open loop speed command.
Step 6:
Increase the Position Loop Gain OWC010 (pGain_PositionLoop) until it oscillates or overshoots slightly, then reduce by about 25~35% of the gain value. It may be necessary to raise the Feed Forward gain OWC011 until it overshoots then back it off a bit.
Regardless of the method used. Be sure to record and save the parameter setting in both the software and machine documentation.
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Please read and understand the product instruction manual before installing, servicing or operating Yaskawa products. FAQ content and illustrations are provided as technical advice to augment the information in manual, not supersede it. It is not possible to give detailed instructions for all types of installation or support activities. The information described in the FAQs are subject to change without notice to improve the product or FAQ. Yaskawa assumes no responsibility for errors or omissions or damages resulting from the use of the information contained in any FAQ. All warnings, cautions and product instruction for product use must be followed. Installation, operation and maintenance should be carried out by qualified personnel. Failure to observe these and other precautions highlighted in the product manuals will expose the user to high voltages resulting in, serious injury or death. Qualified personnel are defined as individuals who are familiar with the installation, starting, operation and maintenance of Yaskawa products of the type described and have proper qualifications to perform the work.
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