POWER TOOL WITH AN OVERSPEED DETECTION MODULE

摘要

A protective redundancy circuit is provided for a power tool having an electric motor (14). The protective redundant subsystem is comprised of: a motor switch (16) coupled in series with the motor (14); a motor control module (18) that controls the switching operation of the motor switch (16); and a protective control module (22) that monitors switching operation of the motor switch (16) and disables the power tool when the switching operation of the motor switch (16) fails. In the context of an AC powered tool, the switching operation of the motor switch (16) is correlated to and synchronized to the waveform of the AC input signal. During each cycle or half cycle, the motor control module (18) introduces a delay period before closing the motor switch (16) and the protective control module (22) determines the operational status of the motor switch (16) by measuring the voltage across the motor switch (16) during the delay period.