Positioning mechanism, rotary joint and mechanical arm

The utility model relates to a locating mechanism, a rotary joint and a mechanical arm, the locating mechanism is used for locating a first component and a second component which are rotationally connected, the locating mechanism comprises a fixing disc, a locating disc and a locking assembly, and the fixing disc is used for being fixed with the first component; the positioning disc is arranged between the fixing disc and the first component, the positioning disc can rotate relative to the fixing disc, the positioning disc is used for being fixed to a second component, a plurality of positioning sliding grooves are formed in the first side face, facing the fixing disc, of the positioning disc, each positioning sliding groove comprises a locking groove section and a guiding sliding groove section which are continuous, and the groove depth of the locking groove section is larger than that of the guiding sliding groove section; the locking assembly is connected to the fixing disc and comprises a limiting part ca