CONTROL OF 3 SERVOMOTORS KINETIX TO FILL AREA

[drbitboy]

I wonder if you could use 3D printer code to generate a path in XY, and then that SCARA independent stuff built-in to Logix could convert XY to angles ...

 

[drbitboy]

Hi,

yes i saw his calculations and are similar to one specialized guy that i find and i will in contact with him on monday. This is pure maths, we need maths to get XY position and maths to get the position of servos in º:



doing maths and writing Structured text I guess to be able to manage all that system of 2 o 3 servos depending of machine. It is not pre-defined movement from Rockwell. Hopefully some good motion guy come to this post to add his experience and get more knowledge.

I've appreciate your help mates

It's simpler than that for this application. From what OP has written, I think they want

• α: angle of first servo arm r1 rotated clockwise from "up" in the image, = clockwise from X in the image below, and
• ß: angle of second servo arm r2 rotated clockwise from extending straight out from r1

 

[drbitboy]

I was wrong in some of my earlier posts; I realized the Roomba algorithm will not work here: it's purpose is to ensure every "spot" on the entire floor is vacuumed at least once (maybe twice?); to get that done, statistically some "spots" are vacuumed many more times than that.

 

[KarajoSoft]

It's simpler than that for this application. From what OP has written, I think they want

• α: angle of first servo arm r1 rotated clockwise from "up" in the image, = clockwise from X in the image below, and
• ß: angle of second servo arm r2 rotated clockwise from extending straight out from r1

View attachment 68978

Hi Drtbitboy,

thank you for your time and help. Rockwell, a compactlogix CPU with motion supports this kind of "personalized" kinematics motion to move axis coordinated ?


I mean, i dont have on my head how to start to code this program and how to control the servos coordinately to reach each single point defined trough and HMI. Doing like that is it possible to send comands from one position to other doing straight or circular movement, considering the kinematics and not just move indepently each servo?

I mean, some fast routine to get in 1-4ms servo position XY and then normal motion instructions to move independtly each axis o its possible to make like new motion function to move them coordinated? whats your suggestion?

Many many thanks!

 

[drbitboy]

Hi Drtbitboy,

thank you for your time and help. Rockwell supports this kind of "personalized" motion to move axis coordinated prior calculate from cinematics calculations? I mean, i dont have on my head how to start to code this program and how to control the servos coordinately to reach each single point defined trough and HMI. Doing like that is it possible to send comands from one position to other doing straight or circular movement?

I mean, some fast routine to get in 1-4ms servo position XY and then normal motion instructions to move independtly each axis o its possible to make like new motion function to move them coordinated? whats your suggestion?

Many many thanks!

I think that "SCARA Independent" configuration allows you to not think about, or have to write a program with, the details of radii or angles or arc cosine or any of that at all.

Once you configure the system with the SCARA menu, you program the X,Y movement i.e. in a Cartesian frame, which is much simpler, and the motion control converts the commanded X,Y values to coordinated movement of the two servos. The SCARA menu is analogous to the scaling instruction, e.g. to convert the 0-16383 counts from a 0-10V signal to engineering units (e.g. PSI).

 

[KarajoSoft]

I think that "SCARA Independent" configuration allows you to not think about, or have to write a program with, the details of radii or angles or arc cosine or any of that at all.

Once you configure the system with the SCARA menu, you program the X,Y movement i.e. in a Cartesian frame, which is much simpler, and the motion control converts the commanded X,Y values to coordinated movement of the two servos. The SCARA menu is analogous to the scaling instruction, e.g. to convert the 0-16383 counts from a 0-10V signal to engineering units (e.g. PSI).

Ok, this cara independent is only for 2 axis. If i dont have Z movement, just giving coordinated 0 will be enough right?

what about when i have similar machine with 3 links? I will need to do thi match kinematics calculation but i dont even how start to struct my program to get something like "scara independent with 3 axis". any suggestion?

many thanks!

 

[drbitboy]

Ok, this cara independent is only for 2 axis. If i dont have Z movement, just giving coordinated 0 will be enough right?

what about when i have similar machine with 3 links? I will need to do thi match kinematics calculation but i dont even how start to struct my program to get something like "scara independent with 3 axis". any suggestion?

many thanks!

ignore the third axis in the scara, set the third servo angle to 0 (so it is an extension of the second arm), and use the sum of the two arms' lengths as the second link's length in the SCARA menu?

 

[KarajoSoft]

ignore the third axis in the scara, set the third servo angle to 0 (so it is an extension of the second arm), and use the sum of the two arms' lengths as the second link's length in the SCARA menu?

ok, i will check it.

what about having 3 links? wil lbe another machine having a third link (3 joints in total). Will be forced to do kinematics calculations to be able to control the system? some ideas how to move all 3 of them coordinated like making some personalized planning motion?

many many thanks!

 

[Peter Nachtwey]

Adding a third link greatly complicates things. You have what symbolic mathematicians called the "perfect:" solution for position with two links. If you add a third there is not "perfect" solution. You must calculate Jacobians and do the calculations iteratively. I have an example of making a simple motion with just two links. I then used the Jacobian methods to see if I get the same answer and I did within round of error. Using Jacobians is messy and CPU intensive. Then there is a matter of generating the motion profile. If the motion is fixed, then you could teach points and go from point to point by moving and stopping at each point but it is better to move smoothy between the points. Again, the math gets very messy.

Jacobians are a matrix that have the rate of change of the two angles with respect to changes in x and y. With only two links this is only a 2x2 matrix.

 

[KarajoSoft]

Adding a third link greatly complicates things. You have what symbolic mathematicians called the "perfect:" solution for position with two links. If you add a third there is not "perfect" solution. You must calculate Jacobians and do the calculations iteratively. I have an example of making a simple motion with just two links. I then used the Jacobian methods to see if I get the same answer and I did within round of error. Using Jacobians is messy and CPU intensive. Then there is a matter of generating the motion profile. If the motion is fixed, then you could teach points and go from point to point by moving and stopping at each point but it is better to move smoothy between the points. Again, the math gets very messy.

Jacobians are a matrix that have the rate of change of the two angles with respect to changes in x and y. With only two links this is only a 2x2 matrix.

dear Peter,

thank you for your comments and help. Honestly this level of knowledge is out of my range currently. First time i hear "jacobians" hehe.

about solution of 2 links, can i use "SCARA INDEPENDENT" motion planner directly? Can you advise please?

about third link i see that is super complicated and maybe here the solution is putting a robot instead machine controled by servos. According your experiencie what do you recommend?

EDIT: is it possible to share your example with 2 links?

many many thanks!

 

[padees]

I did not read this thread until today. I looked at pics, watched the video, read all the comments.

It appears you are an independent contractor working for an OEM that has a contract with Magna to provide this solution to replace the manual fill depicted by the person in PPE wearing a hardhat with an automated solution.

I had a lot of comments typed up, but deleted them.

I know who Magna is, and you might want to rethink your involvement in this project.

 

[KarajoSoft]

dear Peter,

thank you for your comments and help. Honestly this level of knowledge is out of my range currently. First time i hear "jacobians" hehe.

about solution of 2 links, can i use "SCARA INDEPENDENT" motion planner directly? Can you advise please?

about third link i see that is super complicated and maybe here the solution is putting a robot instead machine controled by servos. According your experiencie what do you recommend?

EDIT: is it possible to share your example with 2 links?

many many thanks!

I did not read this thread until today. I looked at pics, watched the video, read all the comments.

It appears you are an independent contractor working for an OEM that has a contract with Magna to provide this solution to replace the manual fill depicted by the person in PPE wearing a hardhat with an automated solution.

I had a lot of comments typed up, but deleted them.

I know who Magna is, and you might want to rethink your involvement in this project.

I dont know what you mean with your comment. I'm legimit integrator of this client and i'm looking for information to see the technical feasiblity of the project and if some colleague has been involved in similar motion project. Something wrong?

 

[padees]

It's good to do research, as we all do, but best of luck!

The mechanical engineering could be better suited for the controls task at hand, but it's a retrofit of a manual operation, so you have to deal with that.

You should probably Engineer a new system that covers everything.

You may need to think about this for a bit.

My comment is that Magna is ruthless towards OEM's if they can't deliver. And you, being a contractor for the OEM... If **** hits the fan, you are SOL.

That's really the gist of my comments.

 

[KarajoSoft]

If you can, I would walk away.

I don't need to walk anywhere.I'm very good here and everywhere

Tomorrow we have a metting with specialist guy in motion, no worries we have a lot of work to do. Focus in your bussiness

 

[padees]

Oh, it doesn't matter. Good luck!