Chapter 1: Getting Started with UR Robot Control

About This Chapter

This chapter explains the fundamentals required to control Universal Robots (UR) from Python.

It is intended for:

  • People using a UR robot for the first time

  • People who want to control a UR robot from Python

  • People using ur_ctrl.py described in this documentation

By the end of this chapter, readers should understand:

  • UR communication interfaces

  • The meaning of Remote Control

  • Python libraries

  • How to verify an initial connection

1.1 What Is Universal Robots?

Universal Robots (UR) is a major manufacturer of collaborative robots.

Representative models include:

Model

Payload

UR3 / UR3e

3 kg

UR5 / UR5e

5 kg

UR10 / UR10e

10 kg

UR16e

16 kg

UR20

20 kg

UR30

30 kg

This documentation primarily addresses the UR3 / UR3e, but many of the Python APIs introduced here are common to other models.

1.2 CB Series and e-Series

UR robots have two major generations.

CB Series

  • UR3

  • UR5

  • UR10

These models use an older controller running PolyScope 3.x.

e-Series

  • UR3e

  • UR5e

  • UR10e

  • UR16e

These models use PolyScope 5.x.

Many capabilities were added, including an integrated force sensor.

1.3 Ways to Control a UR Robot from Python

In Universal Robots systems, URControl in the Control Box is the core of robot control. PolyScope on the teach pendant (TP) provides the operating, teaching, and programming environment. Robot programs created in PolyScope execute on URControl as URScript. URScript can also be sent directly from an external PC.

Several official interfaces are available for communication with an external PC.

Interface

Primary role

RTDE

Bidirectional exchange of controller state, I/O, general-purpose registers, and other data

Primary / Secondary Interface

Retrieval of controller information, transmission of URScript, etc.

Dashboard Server

Operational management, including power, Brake Release, and program execution

ROS / ROS2 Driver

Integration with ROS / ROS2

In addition to these official interfaces, the implementation described here uses SDU Robotics’ ur_rtde.

1.4 What Is the Official RTDE Interface?

RTDE stands for Real-Time Data Exchange. It is an official bidirectional data interface provided by Universal Robots for communication between external applications and the UR controller.

RTDE can read joint and TCP states, robot mode, safety information, I/O, general-purpose registers, and other data. It can also write to exposed I/O, the speed slider, general-purpose input registers, and other writable fields.

However, the official RTDE protocol does not itself define URScript motion commands such as movej or movel. The official RTDE protocol must be distinguished from SDU Robotics’ ur_rtde, described in the next section.

1.5 SDU Robotics’ ur_rtde

The library used in this documentation,

ur_rtde

is a third-party open-source library developed by SDU Robotics, not an official Universal Robots SDK.

ur_rtde uses the official Universal Robots RTDE interface and primarily provides:

  • RTDEControlInterface

  • RTDEReceiveInterface

  • RTDEIOInterface

Among these, RTDEControlInterface combines the official RTDE interface with a dedicated control URScript running on the robot to provide PC-side motion APIs such as moveJ, moveL, and servoJ.

Example installation:

pip install ur_rtde

Details are covered in subsequent chapters.

1.6 Difference from Dashboard Server

Dashboard Server is an official Universal Robots management interface and is separate from SDU Robotics’ ur_rtde.

It handles robot operation management, including loading, playing, and stopping programs; power management; Brake Release; and recovery from Protective Stop.

This implementation uses SDU Robotics’ ur_rtde for motion control, state acquisition, and I/O, together with Dashboard Server when operational management is required.

1.7 Architecture Used in This Documentation

Python
    │
    │
ur_ctrl.py
    │
    ├──────── RTDEControl
    ├──────── RTDEReceive
    ├──────── RTDEIO
    └──────── Dashboard
            │
        Ethernet
            │
         UR Robot

Users generally only need to interact with ur_ctrl.py.

ur_ctrl.py manages the low-level APIs internally.

Next Chapter

The next chapter covers:

  • PC configuration

  • IP addresses

  • Remote Control

  • Communication verification