OnRobot VGP20 Compatibility issues

The Pally URCap supports a wide range of hardware components, however, unexpected compatibility issues can occur with specific setups.

We have received feedback from customers using grippers with additional URCap that the robot program becomes unstable and stops randomly with the error message “Runtime too much behind” on E-series and “Communication with controller lost” on CB-series robots. Our detailed analysis revealed that these error messages are related to insufficient CPU resources or high peaks in CPU usage. While both Pally and the third party gripper URCap can work as standalone, they can’t be used together without further measures.

There are several options to control CPU usage of the Pally URCap. By default, the program utilizes as much CPU as possible, and provides fast calculations and low response times. In combination with another URCap with high CPU demand however, this can cause the program to stop. In this case we recommend the following actions:

Avoid using OnRobot URcap to turn on/off vacuum

How to use OnRobot VGP20 with Pally

  1. Connect gripper to UR-controll box. (the Compute Box is probably not necessary)

  2. Select Gripper Type Custom Vacuum Gripper, enter dimension and weight, and I/O for vacuum and blow.

Custom vacuum gripper
Dimension and weight


Inputs and outputs



If this does not work for you, please let us know: Hardware Problems

change the Pally parameter

rf_cpuidle_ticks under the initial MoveJ node under the Pally program node

Changing this parameter can significantly eliminate high peaks in CPU usage caused by the Pally program without losing any functionality. Calculations will take longer time, but in most cases this will remain almost invisible for the user, as the major part of the calculations are performed in the background while the robot is moving back from the pallet position to the next pick position.

On E-series, try one of the following values (larger values correspond to faster calculations):




On CB-series, try the following values:





turn off all unused functions in the third party gripper URCap

This may reduce the CPU usage without losing the required functionality

manually optimize Pally to reduce the amount of calculations:

i.e. simplify the patterns and the Pally program as described in the User Manual under CB3.0 compatibility notes:

  • reduce the Pally log level to Error or Warning

  • use inverse approach for all layers where possible

  • use lock direction for all boxes

  • disable 2-ways and 4-ways gripper optimization, and use enforced gripper rotations only at positions where reach is critical

  • disable dynamic positioning of the lifting column, and control the lifting column through zones.json file(s)