1/14/2021 8:02 PM  
Joined: 3/10/2020 Last visit: 6/20/2021 Posts: 21 Rating: (0) 
I've setup dual ramp function following the manual and I can't get my head around why the timings are incorrect as per manual formula. To reach my specific ramping up times I had to modify Time Scaling to what looks like random numbers altogether... Dual Ramp function Timings: Max speed = 3000 rpm Ramp up Speed  P1120 = 20 sec Ramp Down Speed  P1121 = 60 sec Ramp Up Level 1  p29571  25Hz (1500RPM) Ramp Down Level 1  p29574  40Hz (2400RPM) Actual values to reach the goal: Ramp Up Level 1 Scaling P29570 = 200% takes 20 sec ramp up time to 25Hz Ramp Up Level 2 Scaling P29572 (max Speed) = 50% takes around 7 sec to reach maximum speed Ramp Down Level 1 Scaling P29573 = 515% gives 60 sec ramp down time to 40Hz Ramp down Level 2 Scaling P29575 (Stop speed) = 50% takes around 25 sec to reach stop speed Based on picture attached I've tried various values and the formula A*B doesn't seem to lead anywhere. E.g. If you change Ramp up scaling to 100% it will take 10 seconds to reach 25Hz, how? If you change Ramp down scaling to 100% it will take around 10 seconds to reach 40Hz. I assumed that 100% of 20 sec should be 20sec? It doesn't seem to be my case so I take that motor selftuning calculations are taking priority over my desired ramp timings. Have anyone had similar issue with this function? 
1/14/2021 8:34 PM  
Joined: 7/7/2010 Last visit: 6/21/2021 Posts: 10884 Rating: (1791) 
Let me first explain how ramp rate works and if you are still confused, please post back. From 0 to 100% speed (p2000) is 100% ramp rate. For 3000 rpm in p2000, p1120 = 20s means from increase rpm every second by 3000÷20 = 150 rpm/sec. Likewise for ramp down, it's 30000 rpm, and 3000/60 = 50 rpm/sec. This is "straightline" ramping. If the lead in/out are adjusted, then it will smooth the transitions and take more time. For 100% scaling factors, from 0 to n rpm, if you want it done in x seconds, you have to do some math to adjust the ramp up rate (p1120) & ramp down rate (p1121). Or, do what Siemens recommended to me: set p1120 and p1121 to the slowest rpm/sec rate required, project that for 0p2000 (max rpm) for how long it would take (say 120 seconds). Then configure the profinet telegram (assuming PN is being used) to include the ramp up / down scaling factors. Then you can adjust the 0100% to achieve a faster or slower rate when updating the speed setpoint. Since 50 Hz = 3000 rpm for your application, if you want a ramp up of 25 Hz (1500 rpm) to take 20 seconds, that's 1500 rpm ÷ 20 sec = 75 rpm/sec. Scale that for 03000 rpm: 3000 rpm ÷ 75 rpm/sec => 40 sec goes to ramp up rate (p1120). Same idea for ramp down rate.

science guy 

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