Variable-Speed Power Tool Underspeed Threshold Control

The patent implements dynamic threshold adjustment where the underspeed threshold is no longer fixed but varies based on operating conditions. The controller dynamically determines the threshold based on the relationship between motor speed and torque, allowing the threshold to adapt to different operational states. This resolves the contradiction by making the protection mechanism flexible enough to distinguish between genuine fault conditions and normal operational variations, thereby maintaining reliability while reducing nuisance shutdowns.

The patent changes the parameter of the underspeed threshold from a static value to a dynamic value that changes based on operating conditions. Specifically, the threshold is adjusted according to the motor's torque output and speed characteristics. When the motor operates at high torque, the threshold is raised to accommodate normal speed variations, while maintaining strict protection at low torque conditions. This parameter transformation enables the system to maintain reliable protection without causing unnecessary shutdowns during normal high-torque operation.

The patent implements closed-loop speed control by continuously monitoring the motor's actual speed and comparing it to the target speed. The controller uses this feedback information to adjust the power delivery to the motor, ensuring the actual speed matches the target speed even under varying load conditions. This feedback mechanism provides the speed stability needed for high-torque operations without requiring complex additional hardware, as it utilizes the existing motor control infrastructure.

The patent makes the motor control system multi-functional by having the same controller handle both the closed-loop speed control and the dynamic threshold adjustment for protection. The controller universally manages speed regulation, torque monitoring, threshold determination, and fault detection functions. This consolidation avoids increasing device complexity by using a single control unit to perform multiple functions rather than adding separate dedicated systems for each function.

The patent applies preliminary anti-action by dynamically adjusting the underspeed threshold before power interruption occurs. The controller proactively raises the threshold when high torque conditions are detected, preventing false underspeed detections from triggering power interruption. This preliminary adjustment of the protection criterion ensures that legitimate high-torque operations are not mistakenly interrupted, thereby maintaining productivity while still providing motor protection against genuine fault conditions.

The patent implements preliminary action by continuously monitoring motor speed and torque conditions and preemptively adjusting the protection threshold before an actual fault occurs. The controller anticipates legitimate high-torque operations and prepares the protection system to accommodate these conditions, preventing unnecessary power interruptions. This proactive approach ensures productivity is maintained by avoiding premature shutdowns while still providing timely protection when actual motor faults occur.