Sheet alignment with FH vision

[AMSMARTINS 0]

Hi all.

I have a new project on hand and some help will be appreciated.

The idea is to square or align a plastic sheet using two clamping grippers controlled by servo motors.

The sheet is being gripped from two points left hand gripper and right hand gripper. We got it pretty much working but to achieve that I have to take 3 or 4 pictures and execute the correction after each picture. The way we are doing it is to take a picture and get the Y positions looking for a target that can be a square or a circle etc.. and then move the gripper to the reference position ( origin on the vision ). to match the Y position of the circle or square shape whit the camera reference position.

And with only 1 or 2 pictures the accuracy is not very good. I think the reason why this is happening is because when the servo moves the left-hand gripper to the reference position the other side (right-hand ) goes out of position.

The vision system we are using is the  FH .

Has anyone done something similar before?. If yes how do you do to move the right distance, to get the sheet square?.

Please see the pictures.

Thanks

Edited 7 Dec 2023 by AMSMARTINS

[photovoltaic 121]

If correcting one side disrupts the other side I think you should be looking at a mechanical fix first. If you're simply looking to get real world units out of the camera the math is pretty straightforward and there is also the ability to setup real world units and the vision tools can inherit that scaling factor. I'm a little unsure what you are asking exactly.

[IO_Rack 181]

2 hours ago, AMSMARTINS said:

And with only 1 or 2 pictures the accuracy is not very good. I think the reason why this is happening is because when the servo moves the left-hand gripper to the reference position the other side (right-hand ) goes out of position.

That would be my guess as well.

Are you able to calibrate LH CAM and RH CAM so that zero is square for both cameras? If so, pull until LH CAM and RH CAM are equal, rather than some offset. 

If I understand correctly.

[AMSMARTINS 0]

Thanks for your response.

I'm sorry if I was not very clear with my explanation.

The zero origin for the camera is in the top left corner. The idea or what we are doing at the moment is :

1- Move the sheet to the LH and RH camera FOV.

2- Both cameras take a picture and measure the Y position of an abject (circle or square ...)

3- PLC calculates the distance the servo has to travel to move the sheet to the reference position ( Reference position is a constant value defined from the 0 or origin of the camera, in my application is 20)

For the LH servo:

Ex:  The Servo stops on the FOV of the camera and takes a picture and the Y=15mm, so the servo has to move 18mm(camera ref.) - 15mm = 3mm the same applies to the RH servo.

LH servo:

Ex:  The Servo stops on the FOV of the camera and takes a picture and the Y=16mm, so the servo has to move 18mm(camera ref.) - 16mm = 2mm the same applies to the RH servo.

So the idea is to take a picture and then calculate the distance the servo has to travel to the camera reference to make the sheet square.

The problem is:

If I just take one picture or one correction the accuracy is out and with two as well. Looks ok when we take 4 pictures and 4 corrections. This is probably because when the LH servo moves (servos start the move to reference at the same time ) to the reference position and reaches that position first then the RH and then after the RH finishes the move to reference will make the LH sheet to pivoting on the opposite direction. 4 Pictures  + 4 corrections slow down the machine.

My questions are:

- I was looking into the FH manual and there is a "calc axis move" tool that looks like it can calculate the servo offset automatically. Has anyone used this tool before?

- The calibration was done using the Omron pattern available on Sysmac,  but in this situation should the calibration be done using a "PLC Master Calibration" This processing item is specialized for calibration between the camera coordinate system and the control equipment coordinate system.

- 1 picture should be enough to square the sheet up but is not working. Maybe I should correct the LH servo to the correct distance to make it square but not pivoting on the RH side. But the problem is to know how to know or calculate that distance.?

Thanks

 

 

[pturmel 160]

2 hours ago, AMSMARTINS said:

PLC calculates the distance

Sounds like you aren't using trigonometry to calculate both movements together, as vectors.  You need to have the camera supply position and orientation of the paper, then compute both moves.