The invention relates to a
cliff detecting method and device and a floor sweeping
robot. The method comprises the following steps that: an ultrasonic
signal is sent to a front lower side of a floor sweeping
robot; whether an
echo signal returned by the ultrasonic
signal after meeting a reflection object is received within a predetermined time is determined; if so, a distance between the bottom ofthe floor sweeping
robot and an emitting object is obtained according to the
echo signal; the distance is compared with a preset
distance threshold to determine whether a
cliff exists at the lower front side of the moving direction of the floor sweeping robot. Therefore, a problem that the
infrared signal cliff detecting mode is susceptible to the influences of the color of the reflector and the interference of the strong light is solved. With multiple gears for ultrasonic signal emission, the distance range of the ultrasonic
ranging is greatly increased; in a short-distance state, the refection objet is detected at a low gear, so that
power consumption of the
machine is reduced, the endurance of the floor sweeping robot is enhanced, and the noises are reduced. The method is implemented simply; the environmental adaptability is high; the detection reliability is high; and the performance of the floor sweeping robot is improved substantially.