Force Function In UR3e Series

Prasanna

i wanted to insert a piece into the slot and it is glass piece. So how can i use force function in order to prevent damaging or pushing the glass piece into the slot.
i do not have experience in Force Torque sensor and its functions.
also when exceeding particular force, the robot should switch to another subprogram.
Note: there is no Force Torque sensor attached. It is e series UR robot. Hope it comes along with FT sensor in its flange.

Prasanna

@matthewd92

Nicholas_Francoeur

@Prasanna, there should be no compatibility issue when upgrading to 5.3 unless you have specific third party software installed (URCaps). Version 5.3 of the Polyscope software can be downloaded directly from the UR support website. 

In addition to what @matthewd92 said, you can also use the get_tcp_force() function to get only specific forces or moments instead of the norm of the x-y-z forces.

matthewd92

@Prasanna how complex is the motion that you are trying to do? Is the slot always in position and so you are just trying to make sure that you don't push the part in with too much force or are you needing to find the slot first using a force search function then insert the part?

One thing you might want to look at is the Robotiq Force Co-Pilot software for the E-Series robot.  It comes with a lot of skills pre-built.

If you are trying to do a simple motion there are rather straightforward ways to do that in the current software.

For example, if I am trying to put a part into a known position such as loading a piece into a lathe chuck I can do something like this.



On the `if` statement if you check the box for Check Expression Continuously then the IF statement becomes a WHILE statement so the robot will move toward Waypoint 1 only as long as the force remains less than 10N.  The else is executed anytime the force exceeds 10N and in this case a stop command is issued so that the robot knows to stop and a protective stop is not encountered.

Another option on the 5.3 software is the Move until command, it looks like this.  It allows the robot to move in a direction until some condition is met, in this example the force exceeds 10N.

Prasanna

Thanks Mr. Matthew unfortunately am at other customer place and i will work with your answers and get back to you by Tuesday for sure.

Prasanna

Hi @matthewd92
 Am using 5.2.   where can i get 5.3 version....will it be a problem, if i updated to 5.3? because i faced similar situations in Other robot. After upgrading old programs shows some error.

Prasanna

@matthewd92
@Nicholas_Francoeur
Thanks to both of you...... Upgraded to 5.3 and the function is working nicely.....Thank again 

matthewd92

You’re welcome

Prasanna

@matthewd92
Hi,
UR5e, version 5.3
Case-1:
the force function is not working as expected. The tool pushes my part though my force value is small. 
for Example,
Move----->z-----> until force()>4
Feature- Tool
Speed - 25mm/s Acceleration 120mm/s^2
Note: force()>3  will stop the motion before reach destination.

is there any other function to achieve this?

Case-2:
UR3e, version 5.3
Am working on a Pick and place operation, in one case i place the job with rz=0 and in another rz=90deg
force()>10
a)  rz=0
b) rz=90
when rz=0 the robot force is less than 5 and the expression works fine.
when rz=90, the  robot force is more than 15 to 20, so the force value in the expression is not sufficient.

matthewd92

You can bias the sensor so that you zero out the acting forces on the arm so that the applied force is consistent regardless of pose. Use the command zero_ftsensor() before you want to use fine force control. 

Prasanna

Thanks
I will check and let know by tomorrow. 

Prasanna

Hi @matthewd92

Thanks now force value changes due to rZ rotation is resolved. still, the force function is not so good. Here is my Pgm

 command zero_ftsensor() 
moveL
>>direction Z-
  >>until the force()>4
wait(0.25)
Gripper open
moveL
>>direction Z+
  >>until the distance 40mm

The problem is the pushing and retracting is not so smooth. the lens placing was not so fine and robot jerks when it place.
4 is the least value of force.

Prasanna

gentle Reminder..... I want the retraction movement of robot to be smooth.....
cannot judge proper force value, if I use random 10, then it pushes the job like anything.....Kindly suggest to me.....

matthewd92

Have you tried turning the acceleration value way down?  Without seeing exactly what the robot is doing it’s very hard to tell you precisely what to fix. 

If you have a ave a very high acceleration value then the robot is basically going to “jump” to your speed of 25mm/s so it may look jerky on a change of motion. You might even want to slow down. When we are doing really fine force motion we will get close to our final point and then slow way down, sometimes just 2-5 mm/s so that the sensor has the best chance of detecting the force as possible. 

I would recommend first cutting your acceleration down to 100mm/s and see if that helps the issue