UR Path problems on small radii

Tyler_Berryman 2016-09-08

Hello all,

I have a question from @dfiedler :

We have a RTV dispensing process and found that the UR goes off path around the radii because they are too small for the speed we need to run. How do you keep a constant amount of material dispensed along the path if the robot changes speed and in some cases stops in the middle?

Any ideas? @matthewd92 @Kaleb_Rodes @Ryan_Weaver

Sebastien 2016-08-26

@dfiedler Have you tried using MoveP (see this post)
Another way would be to get the tcp speed using UR script (get actual tcp speed()) and adjust dispensing flow according to the speed value. This however requires some sort of adjustable valve to control the flow and would require a bit of programming.

dfiedler 2016-09-03

Yes, we used MoveP. When you watch the Robotiq FT300 force torque sensors video, their plug and play software allows for path generation. However, the robot is changing speeds around the arcs. I want to dispense a uniform, continuous bead but so far we've learned the UR can't handle our dispense speed because of the small arc radii in our path. The UR goes off path. You can't slow down just around the arcs with the MoveP. Changing to an arc move causes the robot to stop before the arc and after the arc. I wanted to know if Robotiq's path generating software allows the robot to slow down around the arcs and if so, can we tie the speed of the robot to the gear pump (via an encoder) to achieve a uniform, continuous bead.

Etienne_Samson 2016-09-06

@dfiedler the Path recording speed controls all of the Path speed and try to make it a uniform speed. You should definitely try that option, doing a single path, using constant speed option and choosing that speed. If it's not enough, then you should try cutting down your path to a couple of recordings to play with the constant speed & speed option around each of your arc.

matthewd92 2016-09-06

@dfiedler how small is the radius that you are trying to go around? I have not had any issues where the robot goes off path during a moveP. Yes its possible to tie the motion of the robot back to the gear pump if you put the pump on a variable speed motor, you could drive the pump at the speed that matches the actual speed of the robot at any given point in time using the get_actual_tcp_speed() as @Sebastien recommended. I have done that in my past long ago, not for a robot but an actual dispensing application with a gear motor. For that project we used a stepper motor but any variable speed motor would work so long as you could control it with the robot via an analog signal out