Measurement
Strain Gauge vs. Piezoelectric Force Sensors in Robotics
If you're sourcing a 6-axis force-torque sensor for a robot, you'll hit this fork early: strain gauges or piezoelectric crystals. Both turn mechanical load into an electrical signal, but the physics underneath could not be more different, and picking the wrong one will cost you months of integration headaches.
How They Actually Work
A strain gauge sensor is conceptually simple. You bond thin resistive foils to a metal flexure inside the sensor body. When force deforms that flexure—even by microns—the gauges stretch, their resistance shifts, and a Wheatstone bridge turns that shift into a proportional voltage. The output is continuous and stable. Apply 50 N, read 50 N. Come back an hour later, still 50 N.
Piezoelectric sensors work differently. Quartz or ceramic crystals produce an electric charge when compressed. The catch: that charge leaks. A piezo sensor measures changes in force, not absolute force. You need a charge amplifier to integrate the signal, and even a good charge amp drifts over time.
Static Loads: The Deal-Breaker
This is where most selection decisions get made. Can the sensor hold a reading under constant load?
With piezo, no. If your robot picks up a 10 kg part and holds it, the sensor output will slowly drift back toward zero. The charge leaks. You can re-zero the amplifier, but that interrupts your process. For anything involving holding, pressing, or slow assembly, this is a non-starter.
Strain gauges give you true DC response. They hold a constant reading for hours with minimal drift—limited only by temperature effects on the gauge material. If your application needs gravity compensation, sustained contact force, or slow-speed insertion, strain gauges are the only option that works. The AXIOM Series is built around this principle.
Bandwidth
Piezo wins here, and it's not close for extreme applications. Because the crystal is so stiff, piezo sensors have natural frequencies in the tens of kilohertz. If you're doing impact testing or ballistics research, that bandwidth matters.
But for robotics? Most industrial arms top out at around 50 Hz of mechanical bandwidth. An AXIOM sensor delivers 1000 Hz over EtherCAT. That's 20× the bandwidth of the arm itself. In practice, the strain gauge sensor is never the bottleneck in a robotic control loop, and its noise performance at lower frequencies is significantly better than piezo.
System Complexity
Here's where piezo gets expensive in ways that don't show up on the BOM. Piezo systems need external charge amplifiers—bulky boxes that are temperature-sensitive and require their own power. The cable between crystal and amplifier carries a high-impedance analog signal. Run that cable anywhere near a motor drive or inverter, and you're picking up noise.
With a strain gauge design, you can digitize inside the sensor body. The AXIOM-HS packs the instrumentation amplifier, ADC, and EtherCAT controller into the housing. One digital cable comes out. No external box, no analog noise pickup, no special cable routing.
For robotic assembly, force-controlled manipulation, and closed-loop contact tasks, strain gauge sensors are the practical choice. They measure static loads, integrate cleanly, and cost less to deploy when you factor in the full system.