Mechanical joint, mechanical arm, and self-moving cleaning apparatus

A mechanical arm, comprising a mechanical joint, wherein the mechanical joint is applicable to a mechanical arm, the mechanical arm comprises a rotatable base and a support arm hinged to the rotatable base, and the mechanical joint comprises:

• a first guiding nut, a first screw rod and a first driving part, wherein the first guiding nut is in threaded connection with the first screw rod and hinged to the rotatable base, the first driving part is arranged on the support arm, a first end of the first screw rod is connected to the first driving part, and a second end of the first screw rod passes through the first guiding nut and faces the rotatable base;
• and
• the first driving part is configured to drive the first screw rod to rotate, such that the first screw rod and the first guiding nut move relative to each other to drive the support arm to raise or lower relative to the rotatable base.