Universal Robots Forum

UR additional axis control

Hi All,

How can I add an additional axis to the UR System? (Like a linear axis in which the robot is mounted), Could it be by means of conveyor tracking? Or how can I add it to be programed from the UR interface?


We have done it two ways, the first was to program the 7th axis to use digital I/O to reference positions then we just simply turned on and off outputs to tell the slide what to do, it was rather easy but the only way to change the performance or characteristics of the slide was to alter the program on the motion controller for that axis. With the newest robot we actually wrote our own XMLRPC library for motion, we then just send the command from the robot to the stepper drive directly and tell it what to do. So when I want it to go home I just send the home command, if I want to feed to a length I send it that command and the length to feed (number of steps to take). This has given us great control over the 7th axis directly from the program interface and is the way that we are moving forward on new projects as well. We are currently using a stepper driver from Automation Direct as we built this 7th axis from scratch, we are looking at some other motion drivers though that have an API interface to allow us to control the system totally from the robot.

There are also systems out like the Parker PAC that you can control over Modbus. You pass commands via the modbus interface, I know there are some videos out there demonstrating it like this one

Festo demonstrated a system in the US at Automate earlier this year that had a URCap but we have since been informed that project is on hold indefinitely due to safety concerns on their part.


Is the 7th axis synced with the robot or not?

I managed to sync the UR with a Siemens drive axis, now I am trying to enhance the performance because at certain speeds the robot vibrates a little bit.

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What I mean by “syncing” is can you move the robot and the additional axis simultaneously as desired?


may I ask which servodrive of Siemens is used for the solution (1FK7, 1FK2,…) and is the UR robot controller in use as Master controlling the servopack via MODBUS or an additional Siemens PLC exchanging the data via ProfiNET with the UR robot controller? Thank you!

Bye Andreas

Yes, simultaneously and in an interpolated way, this means that the robot and the axis starts and ends its movement at the same time (even if having different motion profiles because of the distance required). The robot “follows” the axis, if you slow down the speed on the axis, robot is also slowing down.
It is important to say that this synchronization is only working at velocity < 1m/s (because of the maximum velocity of the robot) .

We are using 1FK2 and we use a PLC S7 1500 as a master, exchanging data via profinet.

Mille gracie for very fast reply! This platform is working very fine…

@sofia.miranda are you doing the motion planning in the PLC and passing points back to the robot or are you planning the total motion on the robot and then passing positions to the drive for the servo? Or something different?