Movement with time parameters; How it works?

Loïc 2021-04-20

Hello,

I've just noticed that we have three choice to set the parameter of a waypoint:

-The parameters by default which takes the speed and acceleration of the move command

-Specfic speed and acceleration if we need to modify the parameters for a waypoint

-Time parameter for the movement

How does the time parameter works?

If I set 2 seconds, I assume that the movement will be done in 2 seconds but what is the limit?

What happens if I set a time of 0.1 seconds for a movement of 2 meters?

Is there a limit in speed and acceleration? Will it keep the security parameters?

Any informations about this type of movement will be appreciated.

Regards,

Loïc

matthewd92 2021-04-20

I have never tried setting a time that low for a long move but we have used it when we know we want a move sequence to take a certain amount of time, such as blowing coolant out of chucks, we just programmed the moves and told them we want them to take 1 second for instance, 3 or 4 moves so that we had a total blow off time of X seconds to, we were then able to just adjust the times until we achieved the blowoff we wanted and know it will always take that time.

I would assume that UR would still use all controls to prevent the robot from exceeding the safety speeds that are set but would use the maximum allowed speed and acceleration to make the move. It might also throw an error, I know when using script commands if you command a speed greater than it is allowed it just will not go that fast, it will only go as fast as allowed and you can actually see this with the speed slider where it will drop the value from 100% to a lower value on those moves.

bcastets 2021-04-20

I would recommend that you read the UR software manual which will give you more details.

Here is a curve extracted from the manual.

Loïc 2021-04-20

Thanks for your answers.

@bcastets I've already checked the UR software manual and there is no clear indications about my questions.

@matthewd92, I assume exactly the same as you said, maximum speed that safety gives and maximum acceleration if the time for the movement is too short.

The fact is, my client don't want their robot to exceed a certain acceleration in order to prevent the robot's wear.

Maybe someone from UR might help?

matthewd92 2021-04-20

Maybe, I have found very few uses for the timed moves, outside of very specific cases where I need something to take a specific amount of time and generally it's solved in another way as I need that time to be variable. If you get some more information from UR please post back here so that we can learn from you.

Loïc 2021-05-03

I have no contact from UR but I have an answer from a french distributor. He confirmed what we assumed. The robot will try to do the trajectory with maximum speed of installation->safety tab and maximum acceleration of the robot.

I'm curious to know if acceleration is always on maximum of the robot or if it can be slower for long movement.

It would be great if someone from UR could tell us more about it, the possible errors/limits of this trajectory's type.

bcastets 2021-05-03

@"Loïc"
Your distributor should have some contact with UR to ask for precision if necessary. You should be able to ask for more details.

matthewd92 2021-05-03

@"Loïc" I can confirm that we did some testing with this last week and the times that we got were generally within 0.1s of the command time but there is no way that it was using the max acceleration of the robot, it was quite low actually, we were doing a joint move and the acceleration appears to have been the default acceleration for a joint move, 80 deg/s/s. In our application because the speeds are very low this did not work, we need very high acceleration to have a constant speed across the entirety of the move and so wound up just doing some math on our end to convert very short joint paths to linear tcp speed. We were quite disappointed. I am talking about linear speeds in the 6-25mm/s range