Unit for regulating motor RPM and cutting cord follow=up of lawn trimmer - uses electric motor to drive rotating cutting tool which by its rotation tightens cutting cord and allows rotation

摘要

The length of the cutting cord (F) is controlled conditionally by the wearing out of its free end. A detection unit e.g. a measurement resistance (12) is provided for determining a signal corresp. to the actual motor current (Im). A first regulating circuit, which dependent on the determined signal, if this fulfills a first specified condition, the motor rpm (n) is held constant at a desired value (n0,n1). A second regulating circuit (13, 15, 17) which also is dependent on the detected signal, if this does not fulfill the first specified condition, ensures the use of a cord coil (19) for a readjustment of the cutting cord. The first specified condition corresponds to the exceeding of a first current threshold value of the motor current. The first specified condition is fulfilled, if the motor current lies in a first value range. USE/ADVANTAGE - Regulating unit for regulating motor rpm and readjusting cutting cord of lawn trimmer. Facilitates space saving, matching application condition of lawn trimmer.