US Patent 11439059 Grass trimmer and control method of grass trimmer

A grass trimmer includes a grass trimmer head, a brushless motor, a drive circuit, and a controller. The grass trimmer head includes a spool and a head housing. The spool is configured to wind a grass trimmer rope. The head housing is configured to accommodate the spool. The grass trimmer has an automatic winding mode. In the automatic winding mode, the brushless motor drives at least one of the spool and the head housing so that the spool and the head housing rotate relatively and the grass trimmer rope is automatically wound onto the spool. The controller is configured to: in the automatic winding mode, output a control signal to the drive circuit according to at least one of the given voltage and the given current so that the rotation speed of the brushless motor is basically constant.