Planetary gearbox, assembly method thereof, associated robot joint and robot

An assembly method of a planetary gearbox, comprising:

• providing a housing extending along a first axis;
• arranging a first coupling member on an inner circumference of the housing;
• providing an input component operable to rotate about the first axis;
• arranging at least one intermediate component between the input component and the first coupling member, each intermediate component comprising a second coupling member and adapted to be driven by the input component to rotate about a second axis offset from the first axis with the second coupling member engaging with the first coupling member;
• and
• providing an output component coupled to the at least one intermediate component and operable to rotate about the first axis with rotation of the at least one intermediate component,
• wherein at least one of the first coupling member and the second coupling member comprises a synchronous belt, and
• wherein the each intermediate component further comprises a wheel for the synchronous belt to be arranged on its outer circumference, and the first coupling member comprises teeth engaging with teeth of the synchronous belt, wherein the wheel comprises teeth arranged on its outer circumference, and the synchronous belt comprises a double-side synchronous belt arranged along the outer circumference of the wheel by arranging teeth of one side of the double-side synchronous belt between the teeth of the wheel.