Example with an external axis?

[robin-gdwl]

Hello, was wondering if there is an examle that uses an external axis or positioner. I have not yet understood how the mechanical coupling works and would love to find out.

I am trying to build my own positioner with a stepper Motor (or rather a closed-loop servo) controlled by an Arduino or something similar, but I want to understand the way this plugin handles external axes first. Additionally, Do you have any ideas on how to synchronise a Stepper motor and a robot, with the possibilites of your plugin? Any help would be greatly appreciated.

[visose]

trackExample.zip
Attached is a minimal example of moving a robot in a track based on the path.
It uses the Bartlett robot library with the KR60 on a track. If you download this library the track might be commented out on the .xml, you'll have to remove the <-- and --> lines.

It moves the robot to keep it aligned with the targets in the direction of the track. You usually would not want to do this as moving the whole robot on every target less desirable that getting close and then moving the rest of the joints to reach a target (since it uses more energy, slower speed/ramping, less precision).

[robin-gdwl]

Thanks a lot, will try it out.

[visose]

The previous reply was written before you added the body of your comment. Regarding a positioner, you will use it in a similar way (the external input will be radians rather than millimeters). You can enable kinematic coupling using the 'create frame' component. The frame (and targets attached to it) will move/rotate together with the positioner. If you have a single robot with the positioner as the only external axis, both inputs G and M should be 0.

[visose]

I understand you want to connect a motor as an external axis to the robot controller so that the controller's computer synchronizes it with the rest of the joints taking its dynamics into account and so on.
I've only done this with motors that are sold by the robot manufacturer as external axis compatible. This makes the integration a lot easier, but they are expensive. There are ways to synchronize a separate servo that comes with its own controller, but i would avoid this if you can as i think it's adding unnecessary complexity (unless you're doing something like moving a gigantic track that the robot controller wouldn't be able to handle). In any case this will only be possible with servos, not with stepper motors (saying closed loop servo is probably redundant).

[robin-gdwl]

I understand you want to connect a motor as an external axis to the robot controller so that the controller's computer synchronizes it with the rest of the joints taking its dynamics into account and so on.

THis is correct

My use case is fairly simple:
I need infinite rotation on the last joint of the robot. To do this I was thinking of adding a DiY version of a rotary table similar to this one to the flange of the robot (a Universal Robots UR5):

As you have already stated this will add a lot of complexity, especially when it comes to trajectory planning and my knowledge of programming is limited. I may have to solve this completely differently....

[robin-gdwl]

I am getting errors when trying to use your example: Track external axis not configured on this target where/how do I have to configure it ?
Happens here :

Robots/Robots/External.cs

Line 44 in 0890ade

if (target.External.Length - 1 < externalNum)

[visose]

Ah, sorry, you have to also comment out or delete the positioner, which is the next mechanism after the track.
If you want to make it work with both enabled, you have to input two numbers to the E input (as a string of two numbers separated by a comma), rather than one as it is right now.

[robin-gdwl]

Do you see a track when you enable the preview of the 'load robot system' component?

Yes, it is there, however the robot is shifted relative to the track and not directly on it

Im guessing that my Bartlett.XML-library is different from yours. The robot cell is also just Bartlett-KR60 as Bartlett-KR60 on Track is not in my XML.

[visose]

The whole robotcell should look like this:

<RobotCell name="Bartlett-KR60 on track" manufacturer="KUKA">
<Mechanisms group="0">
  <RobotArm model="KR60-HA" manufacturer="KUKA" payload="60">
    <Base x="0.000" y="0.000" z="0.000" q1="-0.707107" q2="0.000" q3="0.000" q4="0.707107"/>
    <Joints>
      <Revolute number="1" a ="350" d ="815" minrange = "-185" maxrange ="185" maxspeed ="128"/>
      <Revolute number="2" a ="850" d ="0" minrange = "-135" maxrange ="35" maxspeed ="120"/>
      <Revolute number="3" a ="145" d ="0" minrange = "-120" maxrange ="158" maxspeed ="128"/>
      <Revolute number="4" a ="0" d ="820" minrange = "-350" maxrange ="350" maxspeed ="260"/>
      <Revolute number="5" a ="0" d ="0" minrange = "-119" maxrange ="119" maxspeed ="245"/>
      <Revolute number="6" a ="0" d ="170" minrange = "-350" maxrange ="350" maxspeed ="322"/>
    </Joints>
  </RobotArm>

  <Track model="KL1000-2" manufacturer="KUKA" payload="1000" movesRobot="true">
    <Base x="0.000" y="0.000" z="0.000" q1="1.000" q2="0.000" q3="0.000" q4="0.000"/>
    <Joints>
      <Prismatic number="7" a ="881.6" d ="480" minrange = "0" maxrange ="10000" maxspeed ="1890"/>
    </Joints>
  </Track>

</Mechanisms>
<IO>
  <DO names="1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16"/>
  <DI names="1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16"/>
  <AO names="1,2,3,4"/>
  <AI names="1,2,3,4"/>
</IO></RobotCell>

[robin-gdwl]

Now it works, thanks a lot. I will have to rethink my whole setup to figure out if an external axis is the right way to go or if I have to use other means to get the robot to move like I need it to. Thank you for your quick and helpful response.

[Kuka90lu]

Hi @visose,
Thanks for the example.
I'm having some issues having the robot in real actually follow the targets shown in the simulation.. do you mind sharing what the settings look like for the robot & linear track on the KUKA controller / workvisual? Is there something specific I need to check to make sure that the robot and linear track are working with the same world coordinates or are properly synchronized? Also, I've noticed that the x, y coordinates do not change (when I'm checking the actual position view on the teach pendant) when I manually move the carriage of the linear track.. is that normal?
Thanks in advance 🙏🏻

[visose]

I don't have access to a KUKA or workvisual with an image of track, maybe someone else can share it.
You should use a frame component with the "Coupuled Mechanical Group" input set to 0 (if there's only one robot) and "Coupled Mechanism" input set to the external axis that you want to couple (where 0 = Robot, 1 = first external axis, 2 = second external axis, etc.)
The coordinates not changing is likely due to the robot not being "kinematically coupled" with the track. It's showing the coordinates relative to the base of the robot.

[Kuka90lu]

Thanks, I will try and let you know if that works. Also, is there a way to have the TCP move at a constant speed even when the robot is gliding along the linear track?

[visose]

Yes, the tcp will move at the programmed speed in world space if the track is coupled.