[piotrek]

Hi RoboDK team,
I need your advice. 

I'm working with the Dobot CR7 robot. A few days ago I found that there was an issue with the robot model and its flange, here is the thread:
https://robodk.com/forum/Thread-Dobot-CR7-flange-issue

After I got a new, fixed model I started to program the robot and I found that there was a difference between the simulated position and the real robot position.

I programmed a few points on a real robot according to the declared base and tool. After that, I took joint values for that point and put them in RoboDK.
In RoboDK, I have the same values of base and tool, but when I define points by joint values from real robots, I see a difference between the Cartesian values of that point (take a look at the screens in the attachments).

Can you explain to me what can cause that mismatch? Is it about simulation and controller kinematics? How can I improve it to get the same values in simulation?

Best regards,
Piotr

[Albert]

To compare the joints and the Cartesian positions between RoboDK and the real robot you to set the same tool and the coordinate system on both (the TCP and the reference frame should match on the real controller and your active TCP and reference frame in RoboDK).

I recommend you to double click the robot to open the robot panel and set the tool and reference frames the same way you have them setup in the controller. Let us know if there is any mismatch.

[piotrek]

I checked twice if the tool and base in the controller are the same as in RoboDK, and it is.
In the attachment some more screenshots, where you can see this difference between positions. 

I also checked it with other positions and it doesn't seem that the mismatch is constant. I compared the values from the controller and simulation and every time I get different offset values.

[Albert]

It looks like all the mismatch points are within 1-3 mm. It could be that your robot has been calibrated and the DH parameter differ a bit.

Do you have a way to check the table of DH parameters in the robot controller?

[piotrek]

Hi,
I got some information from Dobot support (attachments). They sent me some DH parameters for a particular robot but unfortunately not for CR7 (the one I program). 

Can you look at these parameters and tell me, if this is something which we looking for?

I also got information that the robot was calibrated with a laser tracer in the factory.

[Albert]

This detail is very important:
the robot was calibrated with a laser tracer in the factory.

It explains why you see difference in the position of your robot in the order of 1-3 mm. This basically corrects robot errors and helps improve accuracy. RoboDK kinematics includes the default kinematics.

If you program your robot using Cartesian targets (default targets in RoboDK) you should be able to generate accurate programs that rely on the calibrated robot kinematics.

[piotrek]

Thank you for your reply.

I received DH parameters for my particular robot (attachments). Is it possible to enhance RoboDK simulation with these parameters?

[Albert]

You need the calibrated parameters, not the nominal values. And you should enter these values in the Robot parameters section, in the DH parameter table.

[piotrek]

Thank you for your explanation. I will look for these parameters. Best regards.

[piotrek]

Hi guys,
I found DH parameters for my robot. Please, can you guide me on where exactly I should put those values in Robot parameters?
When I press "more options" in robot parameters I get two tables to fill. There is also an option "Export Table" which makes me confused.