# 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,

```text
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:

```bash
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

```text
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