StallGuard™ provides sensorless load measurement for stepper motors. We call it StallGuard™ because the primary use is to safely detect motor stalls and replace mechanical stop switches. There are, however, many different uses of StallGuard2™ including load detection and load dependent motor current control (CoolStep™). StallGuard2™ monitors the load by measuring electrical energy flowing in and out of motors and how much energy returns to the power supply. This is important because the motor will likely stall when no energy remains.
While the energy-based principle is very deterministic, parasitic effects like resistive losses within the motor and motor construction dependence contribute to measurement quality. StallGuard2™ can mitigate these impacts with proper deployment and usage, but only in certain velocity ranges, so it's important to understand the limitations.
As noted, one basic StallGuard2™ limitation is velocity range. At zero velocity, motor efficiency is zero, and no mechanical energy is delivered to the application. This is a problem because many applications require standstill torque to operate. Similarly, efficiency at low velocities is low, because most energy goes to thermal power dissipation in the motor coils. In contrast, motor drivers cannot deliver full current to motors at high velocity, and energy returning to the power supply decreases. Therefore, the applicable range of StallGuard2™ is limited to mid-range velocities. Application Note 002 shows how to determine usable ranges and required settings.