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cmackincmackin Posts: 4 Apprentice
The script manual says to use servoj(q, a, v, t=0.002, lookahead_time=0.1, gain=300) where a and v are not used at this time. When I use movel and movej, I can set the a,v for motion control. How do I control the robot acceleration and velocity for servoj?


  • matthewd92matthewd92 Founding Pro, Tactile Sensor Beta Testers Posts: 1,082 Handy
    With the servoj command you are responsible for planning the path, you tell it how far you want to move in the next cycle of the clock, 0.008 s for CB3 or 0.002 s for e-series. 

    You have to provide the acceleration and deceleration at the start and end of the motion by dictating how far it’s moving in the next clock cycle. 
  • cmackincmackin Posts: 4 Apprentice
    Thank you so much for the quick reply.

    Ok, so I have to tell it how far to move in the next clock cycle. Let's say that I have two waypoints 100 mm apart. How do I tell the servoj that I want to accelerate at 5 mm /s^2 to a velocity of 50 mm/s? Can I get the robot to calculate the changing distance at a given acceleration and then take the distance/0.002 s as the constant velocity? Then if I assume that I can calculate these values, how do I chop up the 100 mm span between my desired waypoints into distance/0.002 s segments?

    What I am actually trying to do is draw a circle with .1 m radius. I am using x=rcos(theta), y=rsin(theta) to convert polar to cartesian. Then I calculate 360/theta to determine how many waypoints I need to complete a full circle. servoj works nicely to get a smooth rotation around the circle but as per my question, I have no control over the acceleration and velocity. 

    By your logic it seems that I need to calculate the distance the robot moves in 0.002 s while traveling at 50 mm/s which is 0.0001 m but the resolution of the robot is larger than 0.0001 m. How will the robot behave? Theta = ATAN (.0001 m /.1 m) = .06 degrees.

    If I place .06 degrees back into x=rcos(theta), y=rsin(theta) to convert to cartesian coordinates to send the servoj to, the robot moves way slower than 50 mm/s. I have to put 5 degrees into theta to get reasonable speed at .1 m radius. The good news is that I can control speed but it feels like a black box because placing 5 degrees in for theta doesn't makes any sense. Moreover, I am stumped as to how to write an equation to calculate the changing distance/0.002 s while we accelerate to constant velocity.

    I have attached the UR-10e URP file to show what I am doing if that helps.
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