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S profile for Servo motor

DavidKhan
1-Newbie

S profile for Servo motor

Hi all

Could any one help me to make a velocity profile for servo motor which is S profile.the only information i have is that of thetha (position).The total angle rotated by the servo motor is 1800 degree and this angle is covered in 6 seconds.The starting time for this motor is 6th second of simulation and ending time is 12th second.it doesnot start from zero.

thanks.


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1 ACCEPTED SOLUTION

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Let's start here. This is a user defined profile. It has 5 entries. The 6 second delay... the ramp... the hold... the decel ramp... and the final delay.

Note how "t" is used in the expressions because the current value of "t" must be considered to use them in calculations (same with angle for position profiles).

Unfortunately, I cannot find a way to show more datapoints on the graph. It is a bit misleading. If you look at the formulas, and the time domains, you will see where the ramp actually starts and where it ends. You can tweak the position of the "=" sign to fine tune when these milestones are actually hit. It does make a difference in relation to your frame settings during the analysis.

Plot these and see if you get the analysis to run. Remember to use kinematic on the analysis type. Set the time for 19 seconds and I recommend a frame rate of 25 <<== this is so the time will match a video capture at a frame rate of 25. Options are 25, 30 or 50 in the play dialog.

MotionProfile_velocity.PNG

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12 REPLIES 12

Use the user defined profiles.

I am not sure I understand "S" profile, however... from T6 to T12, that do you want the motor to do?

An S profile or sinus profile is the advanced form of traphezoidal profile.which lkooks line the profiles shown in the pictures attached.Picture 1A is the S curve and 1B is the taphezoidal curve.the second picture is the profile mentioned here http://communities.ptc.com/docs/DOC-3546#comment-11213 by Antonius Dirriwachter

while the first picture has taken from http://www.pmdcorp.com/news/articles/html/Mathematics_of_Motion_Control_Profiles.cfm

s+curveee.gif

cos_power_motor_curve.JPG

The one challenge with velocity and acceleration profiles is controlling the total revolutions. In these cases, the revolutions is simply a result so no one really knows where it will stop without some other calculations. How critical is the 1800 total revolutions? For this we might have to consider the "position" profile in order to fit the other 2 curves appropriately.

I have applied a traphezoidal profile for velocity which is shown here and have made this velocity profile by dividing the the total travel into 3 segments.ie the first acceleration portion covers 1/3 of the total angle the second 1/3 of the angle with constatnt accel and the 3rd with deaccel and 1/3 of total anlge.I have attaeched an excel file for velocity data vs time.that might help in converting the attached profile to the requested profile.Elbow+joint+velocity+profile.JPG

Oh yes, that helps a lot!

Let's start here. This is a user defined profile. It has 5 entries. The 6 second delay... the ramp... the hold... the decel ramp... and the final delay.

Note how "t" is used in the expressions because the current value of "t" must be considered to use them in calculations (same with angle for position profiles).

Unfortunately, I cannot find a way to show more datapoints on the graph. It is a bit misleading. If you look at the formulas, and the time domains, you will see where the ramp actually starts and where it ends. You can tweak the position of the "=" sign to fine tune when these milestones are actually hit. It does make a difference in relation to your frame settings during the analysis.

Plot these and see if you get the analysis to run. Remember to use kinematic on the analysis type. Set the time for 19 seconds and I recommend a frame rate of 25 <<== this is so the time will match a video capture at a frame rate of 25. Options are 25, 30 or 50 in the play dialog.

MotionProfile_velocity.PNG

Also, when I evaluate the chart, I get 1770 degrees of rotation... just shy of the 1800 you expected.

thanks a lot Antonius Dirriwachter

Now i got the curve for simulation.yes 1770 is the correct one.I was mistaken to mention it 1800 degrees.

I will add this little video here to expand on graphing of motion profiles. It turns out there are 50 nodes, so if your profile is divisible using this figure, it will make for a cleaner graph. For instance, I used the above example and extended the end time to 25 seconds. This creates a node every 0.5 seconds. Now you can accurately see the transitions of the profile.

I also noted the fact that you -can- read the nodes on the graph itself. Problem is, it is intermittent. If you click one, it will read on the bottom of the graph, and sometimes, you will get a dynamic reading on the face of the graph. I suspect this is a graphics driver issue, but it is an interesting bug. I will submit a CS case on this if others see this same problem. Please post here if you also have intermittent issues with the on-graph readback.

Video Link : 4367

edit: furthermore... you can keep the servo profile at 25 seconds while still making the analysis only 19 seconds(End Time). Just a thought

Nice tip.with these changes you mectioned it looks good now

Hi David. I saw your comment on my document but we can cover that here.

I will see about making an appropriate profile and post it here.

What is the total length of the analysis?

ok thanks for quick response.Total analysis is 19 seconds.Kindly explain it simply so that i could modify it for other servo motors easily.

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