Moving plane feature like in CNC-machining

Puolikas

Hi.

What is the best way to use the feature plane?

My rig is Universal Robots UR10, Robotiq wrist camera and Robotiq 2F140 Gripper.

I have a portable assembly station and I want to move it around, take it to storage and put it back in a different place etc.
Now what I have done is to make a plane feature, points representing the corners of the station. Then in program I choose the feature plane under the MoveL command. Everything going great when the program is very simple.

I get the problems when the program is complicated. I cannot use MoveJ command (cannot choose the plane feature). Then in palletizing when I make rectraction after I have gripped the part the added Waypoints make weird moves. Like they are calculated from the Base feature.

Everything is resolved when I know how to move the base feature origin to the work origin before programming.

This method is widely used in CNC-machining:



So we have the Machine origin and then we tell the Machine where the origin of the part is. Then if we tell the Machine to move to X0,Y0,Z0 it will go to the origin of the part, not the Machine origin. This is like using feature plane, but every move is automatically related to part origin. So if you just make a MoveL command X0,Y0,Z0 without choosing the feature plane, it should go to part origin, not to the base feature origin.

If you can help me with this I would be very thankful! At our company (Oulu University of Applied Sciences) we have 30 students, 10 groups, sharing 4 UR-robots. That means robot cells moves all the time and without easy way to move the origin of the program, students have to always show the moved waypoints all over again. That can be frustrating..

Please feel free to ask more specifics if you need.

/ Lassi Kaivosoja - Project Engineer OUAS 

louis_bergeron

@Puolikas

I think you can't use MoveJ in this case.  MoveJ is a motion in Joint space, not in Cartesian space.  It means, there is no x,y,z coordinate. The coordinates are in degrees for each joint for a MoveJ.  You will also see that acceleration and speed are represented in degrees/second and degrees/sec2.  It means MoveJ is neither in the Base coordinate.  Asking the robot to put joint number 2 at 35 degrees, for example, it means it's always at the same place in space.  That's why it look like in base coordinate because it's a fixed position in space.  It's a fixed angle for each joint.  The base is also in Cartesian space with X,Y and Z.  To use Cartesian coordinates like X,Y,Z, I think you must use MoveL or MoveP.

  

Puolikas

Thank you for your clarification louis_bergeron. 

matthewd92

There is a way to use a movej with a feature but it requires that the movej use variable waypoints.  If you wanted to use taught waypoints you could teach a movel sequence in the before start section of the program and wrap it inside an if statement that never tests true such as if false.  The next step is to use the fixed waypoints as variables, you would need to assign then fixed waypoint to a variable, behind the scenes it is already doing a pose_trans() function to calculate the pose in base coordinates from the feature coordinates.  You can see this in the screenshot below where I am basically assigning waypoint1 to a variable but I put an error in the assignment so that this error screen popped up


  Then your movej would just use those variable waypoints instead of fixed waypoints.  This results in a program that is rather simple still, you have fixed points to go change if needed and a way to control your feature frame as well.  In this example, I made the feature variable and used pose_add() to cause the feature frame to step down in 100 mm increments.  Notice in the pose_add I am not using the feature but rather the features variable, I did this so that it will do more than 1 step down.

Puolikas

Thanks.

I'm familiar with this method but still not what I'm looking for. Some day I will figure this problem out and bring it to you guys.

/Lassi K.

matthewd92

@Puolikas have you ever tried making the Base feature a variable?  You could then change the base feature frame of reference, this might be what you are looking for. Basically in your before start you could ask for some offsets in the X, Y ad Z direction and then use those offsets to offset the base coordinate system.

Is this more along the line of what you are looking for?

Puolikas

Yes. This is exactly what I need.
Didn't know that you can do that.

So In the begining of the program I show the new base feature offset with trans_pose. I just need to make a jig which helps me to show the correct angle of the assembly station.

I'll get back to you when I have tested this out.

Thanks for your help.

abeachy_HG24

@matthewd92 @Puolikas ;Whenever one of you gets a chance, could you post a sample of how you would program this? I had a few free moments this morning and I was attempting to do this but I was unsuccessful. Not urgent or anything, just curious. Thanks.

matthewd92

Fortunately I have to do this for a customer so will be working on it over the next week or so as we are deploying the robot.  I am not sure yet how I would go about reteaching the plane feature easily, have some ideas but have not completely baked them all the way through and am just pulling a robot out of the box this week for the test.  Hard to do what I am planning to do on the simulator.  I'll keep you posted though.

K_Bing

@matthewd92
Any updates? I feel like its a common need to move the cobot around and then reteach the base feature.

matthewd92

@K_Bing I don't have an update currently, we are still working on the best solution for getting accurate points and calculating the new coordinates to pass to the base feature.  As soon as we have something working I will post something up for the group.