A six-axis force-torque sensor lets a robot feel contact with the world instead of only following programmed positions. It is usually mounted between the robot wrist and the end-effector, so every push, pull, twist, and bend passes through the sensor. This matters in assembly, polishing, surgery, testing, and any task where the robot must react safely to contact.
The sensor reports three force components and three torque components in real time.
Key Facts
- A six-axis force-torque sensor measures Fx, Fy, Fz, Tx, Ty, and Tz.
- Force is a push or pull measured in newtons, N.
- Torque is rotational effect measured in newton-meters, N·m, with τ = rF sinθ.
- Strain gauges change electrical resistance when sensor beams stretch or compress.
- Strain is often modeled as ε = ΔL / L, where ΔL is change in length and L is original length.
- Compliant control uses force feedback so a robot can adjust motion during contact instead of rigidly following a path.
Vocabulary
- Six-axis sensor
- A device that measures three force components and three torque components along and about the x, y, and z axes.
- Strain gauge
- A small electrical sensor whose resistance changes when the material it is attached to stretches or compresses.
- Force vector
- A quantity that describes the size and direction of a push or pull.
- Torque
- A measure of how strongly a force tends to rotate an object about an axis.
- Compliant control
- A robot control method that changes motion based on measured contact forces to make interaction softer and safer.
Common Mistakes to Avoid
- Confusing force with torque is wrong because force causes linear pushing or pulling while torque causes rotation about an axis.
- Ignoring the sensor coordinate frame is wrong because Fx, Fy, Fz, Tx, Ty, and Tz are reported relative to defined sensor axes, not always the world or tool directions.
- Treating one strain gauge as measuring all six loads is wrong because six-axis sensing requires multiple strain measurements and calibration to separate combined forces and torques.
- Forgetting to subtract the tool weight is wrong because gravity from the end-effector can appear as a constant load and hide the actual contact force.
Practice Questions
- 1 A robot presses straight down on a part with Fz = 35 N. If the controller target is Fz = 50 N, how much additional downward force is needed?
- 2 A force of 12 N acts perpendicular to a wrench point 0.08 m from the sensor center. What torque magnitude does the sensor measure about that axis?
- 3 A robot is inserting a peg into a hole and the force-torque sensor detects a sideways force Fx but little Fz. Explain what the robot should change in its motion and why compliant control helps.