US Patent 11014254 Hair cutting apparatus comprising a current detector

The present invention is directed to a hair cutting apparatus (600), such as a shaver, which is enabled to detect whether hair is currently being cut in a robust way. Such apparatus has a motor (102) for driving a cutting element. The motor current (106) is evaluated by filtering and amplifying it in such a way that a time derivative of the motor current (106) is processed and other parts of the motor current (106), such as noise and DC-5 parts, are eliminated. An evaluator determines whether the time derivative of the motor current is above a predefined threshold value.