A strain gauge is a tiny sensor whose resistance changes when it's stretched — the basic element that lets robots feel force and weight, from a gripper's grip strength to a load cell's reading.
A strain gauge is a small foil pattern glued to a part. When the part flexes even slightly, the foil stretches and its electrical resistance changes — and that tiny change reveals how much force is being applied.
How does a robot feel — sense how hard it's gripping, or how heavy an object is? At the bottom of almost every force sensor sits a humble, brilliant device: the strain gauge.
How it works
A strain gauge is a fine metal-foil pattern bonded to a surface. When that surface deforms even microscopically under load, the foil stretches or compresses with it — and stretching a conductor changes its electrical resistance. Measure that tiny resistance change and you know the strain, which (through the material's known stiffness) tells you the force.
Deformation becomes an electrical signal
The gauge turns imperceptible mechanical strain into a measurable resistance change — the raw ingredient of force sensing.
The resistance change is minuscule, so gauges are wired into a Wheatstone bridge — a clever circuit that turns a fractional resistance change into a clean voltage and cancels out temperature drift.
Where it becomes a robot sense
A bare strain gauge is just the element; it becomes useful when bonded to a purpose-built structure:
Load cells — a metal body with gauges that measures weight or a single force axis (robot scales, payload sensing).
Force-torque sensors — arrangements of gauges on a machined element that read force and torque in all six axes, mounted at a robot's wrist for assembly and admittance control.
Tactile sensors and grippers — sensing contact and grip strength.
Strengths and quirks
Strain gauges are cheap, small, accurate, and fast. Their main enemies are temperature (handled by the bridge and compensation gauges) and fatigue — bonded foil under endless flexing eventually cracks, so mounting and material choice matter.
Why it matters
The strain gauge is the foundational transducer of force in robotics. Every time a robot weighs a payload, regulates grip, or detects contact, a strain gauge is almost certainly doing the sensing underneath.
