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 Lookahead is not working forever Junior Member  Posts: 4 Threads: 1 Joined: Feb 2020 02-25-2020, 07:42 PM We use Turbo clipper for the first time, we made a test using an example in PMAC training course for the lookahead, as anticipate the velocity will decelerate in the corner if lookahead working, but actually the velocity is remain unchanged. I have no idea about the question, can sb. give me some help pls? the code is as below Undefine All &1 #1->1000X #2->1000Y I5049 = 10 I5000 = 1 I5113 = 5 I5192 = 0 I116 = 50 I117 = .5 I216 = 50 I217 = .5 I5120 = 4/3/2*I116/I117/I5113 End Gat Del Gat Del Rot Del Comp Del Look Close Define Lookahead 13, 50 Open Prog 1 Clear Linear Abs CMD"End Gat" CMD"Del Gat" CMD"Def Gat" Dwell 0 CMD"Gat" Dwell 0 F 50 X 10 Y 10 X 0 Y 20 Dwell 0 Cmd "End Gat" Dwell 0 Close curtwilson Delta Tau Insider        Posts: 683 Threads: 0 Joined: Jun 2008 02-27-2020, 01:23 PM What are your values for TA and TS (I5187 and I5188)? If these do not cause rates of acceleration greater than your motor limits, lookahead will not change the profile. forever Junior Member  Posts: 4 Threads: 1 Joined: Feb 2020 02-27-2020, 06:44 PM (02-27-2020, 01:23 PM)curtwilson Wrote: What are your values for TA and TS (I5187 and I5188)? If these do not cause rates of acceleration greater than your motor limits, lookahead will not change the profile. Tank you for your reply, Wilson. I have not changed I5187 && I5188, they were the default values, respectively 0 and 50. Which limits should be concerned, Ixx17 or Isx78? And we donnot know the radius of the corner, so how to calculate the rates of acceleration here? curtwilson Delta Tau Insider        Posts: 683 Threads: 0 Joined: Jun 2008 02-28-2020, 05:22 PM In lookahead, PMAC compares the rate of acceleration from the programmed trajectory to the Ix17 motor acceleration limit. It also compares the velocity to Ix16. As far as velocity is concerned, if I5190 is at the default value of 1000, so your feedrate is in axis units per second, your peak motor speed is 50 cts/msec, which is equal to I116, so lookahead will not reduce this. (If I5190 is 60000 so feedrate is axis units per minute, your peak motor speed is 0.833 cts/msec, less than your limit.) For the "pure" S-curve acceleration you are using, the peak acceleration is V/TS. With I5190=1000, this is 50/50 = 1 ct/msec^2. So lookahead might stretch out the acceleration profile some to keep each segment under the I117=0.5 limit. But this will not reduce the top speed. forever Junior Member  Posts: 4 Threads: 1 Joined: Feb 2020 02-28-2020, 08:43 PM (This post was last modified: 02-28-2020, 08:47 PM by forever.) (02-28-2020, 05:22 PM)curtwilson Wrote: In lookahead, PMAC compares the rate of acceleration from the programmed trajectory to the Ix17 motor acceleration limit. It also compares the velocity to Ix16. As far as velocity is concerned, if I5190 is at the default value of 1000, so your feedrate is in axis units per second, your peak motor speed is 50 cts/msec, which is equal to I116, so lookahead will not reduce this. (If I5190 is 60000 so feedrate is axis units per minute, your peak motor speed is 0.833 cts/msec, less than your limit.) For the "pure" S-curve acceleration you are using, the peak acceleration is V/TS. With I5190=1000, this is 50/50 = 1 ct/msec^2. So lookahead might stretch out the acceleration profile some to keep each segment under the I117=0.5 limit. But this will not reduce the top speed. Tanks, wilson. I have made some test. First, if I set Isx13 equals to 0(Non-segmented LINEAR mode moves) and feedrate(F) greater than Ixx16, the actual feedrate would be limited to Ixx16, and then, if I set Isx13 equals to 5, Isx20 equals to 13 (lookahead buffer defined and Isx20 greater than 0), the actual feedrate will be greater than IXX16 and equals to the setting feedrate(F). As mentioned in the "Turbo SRM.pdf", "Ixx16 is not used for segmented LINEAR and CIRCLE mode moves when the special lookahead buffer is not active.", so I think someting is wrong with my setting about lookahead, enclose my setting about the motors and all of my motion programs and plc, Looking forward to you reply MOTOR SETTING //PWM Frequency=4.5173Khz //phase frequency=9.0346Khz //servo Frequency=2.2586Khz I7000=6527 I7001=0 I7002=3 I10=3713991 //Motor Type Select //stepper, rotary I101=0 I100=1 I201=0 I200=1 I301=0 I300=1 I401=0 I400=1 //PFM Turbo-PMAC2 Channel1 //PFM frequency setting=2.4576Mhz I7016=3 I102=\$78004 I169=32767 I7003=2258 I130=20000 I131=0 I132=650 I7026=3 I202=\$7800C I269=32767 I230=20000 I231=0 I232=650 I7036=3 I302=\$78014 I369=32767 I330=20000 I331=0 I332=650 I7046=3 I402=\$7801C I469=32767 I430=20000 I431=0 I432=650 //Amp Fault Signal, Ignore Amp Fault //Position Limits Disabled I125=\$78000 I124=\$120001 I225=\$78008 I224=\$120001 I325=\$78010 I324=\$120001 I425=\$78018 I424=\$120001 //Postion Loop Feedback Sensor Setup //Incremental Encoder X4 I103=\$3501 I108=96 I7010=8 I203=\$3502 I208=96 I7020=8 I303=\$3517 I308=96 I7030=8 I403=\$3518 I408=96 I7040=8 //Velocity Loop Feedback Sensor Setup //Incremental Encoder X4 I109=96 I209=96 I309=96 I409=96 //Dead band I164=-16 I264=-16 PROGRAM Undefine All /***********************Setup and Defination*****************************/ &1 ;Enter coordinate system 1 #1->1000X ;Assign motor 1 to X axis #2->1000Y ;Assign motor 2 to Y axis I5049 = 10 ;gather every 10 servo cycle I5000 = 1 ;Strore gather in Ram and do not permit wrap-around I5113 = 5 ;Enable segmentation; compute every 5 ms I5192 = 0 ;Enable blending I116 = 50 ;Set motor 1 max vel. to 50 cts/ms I117 = 0.5 ;Set motor 1 max Accel. to 0.5 cts/ms^2 I216 = 50 ;Set motor 2 max vel. to 50 cts/ms I217 = 0.5 ;Set motor 2 max Accel. to 0.5 cts/ms^2 I5120 = 13 ;Compute number of lookahead segments needed End Gat Del Gat Del Rot Del Comp Del Look Close Define Lookahead 13,50 ;Define lookahead buffer based on the number in I5120 /**************************************Motion Program************************/ Open Prog 1 Clear Linear Abs Cmd "End Gat" ;End gathering Cmd "Del Gat" ;Delete contents of gather buffer Cmd "Def Gat" ;Define gater buffer Dwell 0 Cmd "Gat" ;Begin gathering Dwell 0 F 100 ;Feedrate 50 user units/sec X 10 Y 10 X 0 Y 20 ;Move to X 0 and Y 20 user units Dwell 0 ;Do not blend to next command Cmd "End Gat" ;End gathering Dwell 0 ;Do not blend to next command Close M100=0; OPEN PLC 1 CLEAR IF(M100=0) COMMAND"&1A" COMMAND"&1B1R" M100=1; ENDIF CLOSE curtwilson Delta Tau Insider        Posts: 683 Threads: 0 Joined: Jun 2008 03-10-2020, 11:32 AM Your behavior indicates that lookahead is not active for some reason. In segmentation mode, the move-by-move limits are not active, but the segment-by-segment limits require lookahead to be active. In the Executive program, select the View tab, then select "Specialized Buffers". Does it show a lookahead buffer? Even though you don't seem to need much lookahead, try defining a larger buffer and a longer lookahead distance. forever Junior Member  Posts: 4 Threads: 1 Joined: Feb 2020 03-13-2020, 07:09 AM (03-10-2020, 11:32 AM)curtwilson Wrote: Your behavior indicates that lookahead is not active for some reason. In segmentation mode, the move-by-move limits are not active, but the segment-by-segment limits require lookahead to be active. In the Executive program, select the View tab, then select "Specialized Buffers". Does it show a lookahead buffer? Even though you don't seem to need much lookahead, try defining a larger buffer and a longer lookahead distance. Thank you curt， I had found the reason for this error， the look-ahead buffer was deleted when I used “\$\$\$” to reset the system. « Next Oldest | Next Newest »

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