Integration
Integrating a 6-Axis Force-Torque Sensor with UR e-Series
The UR e-Series already ships with a built-in force-torque sensor at the wrist. So why would you bolt another one on? Because for anything beyond basic safety stops and simple insertion tasks, the internal sensor hits its limits fast.
What the Internal Sensor Can't Do
UR's built-in sensor works well for collaborative safety and basic force_mode() commands. It detects collisions, enables simple compliant motion, and handles use cases where "roughly the right force" is good enough.
The trouble starts when you need precision. Deburring operations, active compliance during assembly, or any application where you're closing a force-feedback loop at speed—the internal sensor's noise floor becomes the bottleneck. It also can't be easily isolated from thermal drift. Mount a 3D printing extruder or welding torch on the wrist, and after a few hours the readings wander.
Two Ways to Wire It In
Getting external sensor data into UR's control system comes down to two practical approaches.
Option A: RTDE + Edge PC
UR provides a Real-Time Data Exchange interface running at 500 Hz. The setup: your AXIOM sensor talks EtherCAT to a small edge PC (running ROS, a custom C++ node, or even Python for prototyping). That PC reads the sensor, computes compliance corrections, and pushes them to the UR controller over RTDE. It adds a box to the cell, but you get full control over the data pipeline and can run filters, gravity compensation, or custom algorithms on the raw wrench data before it reaches the arm.
Option B: URCap Plugin
If adding a PC isn't practical—maybe the cell is tight, or IT won't approve another networked device—a URCap plugin runs directly on the teach pendant. It maps sensor data (via UDP or RS-485) into URScript variables, so operators can use native force_mode() with the external sensor as the data source. Bandwidth is lower than the RTDE route, but deployment is simpler.
The Real Problem: Cables
Bolting a sensor to the UR ISO 9409-1-50-4-M6 flange is the easy part. The hard part is figuring out where the cables go.
Running a thick sensor cable along the outside of the arm restricts Axis 6 rotation, creates snag points, and wears out fast during continuous operation. UR's internal tool I/O doesn't support high-speed bus protocols like EtherCAT, so you can't just route through the arm's existing conduit.
A hollow-shaft sensor like the AXIOM-HS solves this. Pneumatic lines, camera cables, and the sensor's own power/data line all route through the center of the sensor, along the rotational axis. No external cable dress, full 360° rotation, and the whole assembly stays clean.
The UR e-Series is a solid platform. Pairing it with a dedicated external sensor removes the sensing bottleneck and opens up applications that the built-in hardware was never designed for.