Six-Axis Force/Torque Sensors Explained

Six-Axis Force/Torque Sensors Explained: How They Measure and How to Read the Datasheet

By Sourcebotics · Robotics procurement & integration

Source review: 2026-10·8 min read

Source: https://sourcebotics.com/guides/six-axis-force-torque-sensors-explained/

Short answer
A six-axis force/torque sensor measures three forces and three moments with strain gauges on a machined body, then converts the readings through a calibration matrix. Choose the range from the forces and moments at your mounting point, then compare accuracy, crosstalk, overload capacity, interface and sampling rate under the manufacturer's stated conditions.

How a six-axis sensor measures load

The sensor body is a machined metal structure, often a hub connected to an outer ring by beams. When load is applied, the beams bend slightly. Strain gauges bonded to the beams change resistance with that bending, and are wired into Wheatstone bridges whose output voltage changes with strain. A typical design has six or more bridge channels.

No single channel corresponds to one axis. A force along X also bends beams that contribute to other channels. The manufacturer applies known loads during calibration and computes a decoupling matrix that converts the channel readings into Fx, Fy, Fz, Mx, My and Mz. Digital sensors apply this matrix internally; analog sensors supply it for your software to apply.

Reading the measuring range

Datasheets list a range for each force and moment axis. The moments matter as much as the forces: a tool that extends from the sensor turns a modest force into a large moment. Calculate the worst-case force and moment at the sensor face, including tool weight, acceleration and contact forces, then choose the smallest range that covers them with margin. A larger range than necessary reduces the resolution of the forces you care about.

Accuracy figures and what they mean

Accuracy, nonlinearity, hysteresis and crosstalk are usually stated as a percentage of full scale. Crosstalk describes how much load on one axis appears as a reading on another. Because these figures scale with the range, a small percentage of a large range may still be larger than the force you need to resolve.

Temperature also matters. Strain gauges and the sensor body respond to temperature changes, so manufacturers state a compensated temperature range. In practice you will zero the sensor after warm-up and periodically during long tasks.

Datasheet item	What it tells you	How to use it
Force and moment range	Loads where stated accuracy applies	Cover worst-case loads at the sensor face with margin
Accuracy / nonlinearity	Deviation from ideal output, % of full scale	Convert to newtons or newton-metres for your range
Crosstalk	Error leaking between axes, % of full scale	Critical when one axis is loaded far more than others
Overload capacity	Load survived without damage	Size for collisions, tool changes and handling
Sampling rate	How often readings are produced	Match to your force-control loop rate
Interface	Analog bridge or digital bus output	Check controller support and cabling
Mass and dimensions	Added load and stack height at the flange	Subtract from robot payload and reach
Ingress protection	Protection against dust and water	Match to cleaning and environment

Overload, collisions and handling

The measuring range is where accuracy applies; overload capacity is what the sensor survives. Applications with impacts, manual guiding or tool changes need a generous overload rating. Many sensors also include mechanical stops that protect the gauges, and some offer overload indication in the digital output.

Analog or digital output

Analog sensors output small bridge voltages and need an amplifier and data acquisition system, plus the decoupling matrix in software. They allow high sampling rates and flexible signal chains. Digital sensors integrate the amplifier and matrix and output through EtherCAT, Ethernet, CAN or RS-485, which simplifies integration and cabling. Confirm that your robot controller supports the bus and that drivers or examples exist for your software.

Mounting and integration

The sensor sits between the robot flange and the tool, so it adds mass and height, which reduces the robot's usable payload and changes the tool centre point. Adapter plates for common robot flanges are often available. Cable routing must avoid strain on the connector during motion. After installation, compensate the tool's weight and centre of mass in software so that only external forces remain.

Checklist for a force/torque sensor inquiry

Robot model and tool flange.
Worst-case forces and moments at the sensor face.
Smallest force you need to resolve.
Overload scenarios: collisions, manual guiding, tool changes.
Interface and sampling rate required by your controller.
Environment: temperature range, dust, water and cleaning.
Documents: datasheet, calibration certificate, drawing and software examples.

Sources

FAQ

Do I need a six-axis sensor, or is a single-axis load cell enough?

If the load always acts along one known direction, a single-axis cell can be enough. Assembly, polishing, guiding and contact-rich tasks involve forces and moments in several directions and need six axes.

Why does my sensor reading drift?

Temperature changes, cable movement and creep in the structure cause drift. Zero the sensor after warm-up and before force-critical steps, and route cables with strain relief.

What does a calibration certificate show?

The applied reference loads, the measured outputs, the resulting matrix and the accuracy achieved. Ask for it with the shipment.