QUESTION:
How to optimize slack rope controller and current equalization controller for a grab crane?

ANSWER:

1. SRC: Adjustment of Slack-Rope-Controller if p-controller is used (not curve):

• rCompareValueSetpointSRC: should be between 5-25 %. Higher values are not usefully, as otherwise the grab will be hoisted.

• If the grab needs to bury itself into the material this value should be between 5-10 %.
• If the ship is empty and the grab needs to be kept in straight position to „sweep“ the bottom of the ship this value should be between 10-20%.
• These two values should be selectable from the operator.

• rpGain: adjust this value so that the speed setpoint is increasing quickly. Practical values are about 0.3 - 0.8. Attention: If this value is too high, the current will oscillate (maybe audibly).
• rVelocitySmoothTime: This input can smooth the velocity output. Practical value is round about 200 ms.

With these three points above the Slack-rope-controller will work well. Further optimization can be done with the following points.

• ruplimit_controller and rlowlimit_controller: If the Slack-rope-controller is too slow or if the slack-rope can not be rolled up during grab closing, the output speed can be increased. But this value should not be too high; otherwise the drive has to stop immediately after slack-rope is rolled up. +/- 30% should be ok.
• rCurrentsmoothtime: if necessary the current setpoint can be smoothed, but strong oscillation of the current is an indication of wrong setting of speed controller in Sinamics. Speed controller in Sinamics should be optimized firstly.

2. CEC: Adjustment of the Current Equalization Controller (if only the p-controller is used:

• rpgaincurrentequalctrl:adjust this value so that the current is increasing quickly. Practical values are about 0.3 - 0.7. Attention: If this value is too high the current will oscillate (maybe audibly).
• rvelocitysmoothtime: This input can smooth the velocity output. Practical value is round about 200 ms.
• revaluationcurrentsetphg and revaluationcurrentsetpcg: Hereby the current setpoint evaluation of Holding-gear and Closing-gear can be adjusted. This is necessary, for example, if the rope of Closing-gear needs to be tauter than the rope for Holding-gear. then the Closing-gear needs more current, the input revalutioncurrentsetpcg should be reduced or the revalutioncurrentsetphg should be increased.

Example: Closing-gear needs more current to make the rope tauter

revaluationcurrentsetphg:100% and revaluationcurrentsetpcg:90%
or
revaluationcurrentsetphg:110% and revaluationcurrentsetpcg:100%
or
revaluationcurrentsetphg:105% and revaluationcurrentsetpcg: 95%

With these three points above the Current Equalization Controller will work well. Further optimization can be done with the following points.

• ruplimitoutvelocity and rlowlimitoutvelocity: Normally the grab is (or should be) closed before hoisting is started, and it is not necessary to set high speed limits, since these can not be reached anyway. Maximum values of +/- 20% should be ok.
• rcurrentsmoothhg and rcurrentsmoothcg: if necessary the current setpoint can be smoothed, but strong oscillation of the current is an indication of wrong setting of speed controller in Sinamics. The Speed controller in Sinamics should be optimized firstly.