Couplings can be divided into two categories: rigid couplings and flexible couplings.

Rigid couplings do not have to cushion and the ability to compensate for the relative displacement of the two axes. The two shafts are required to be strictly aligned, but this type of coupling has a simple structure, low manufacturing cost, and assembly and disassembly. 2. Convenient maintenance can ensure high alignment of the two shafts, massive transmission torque, and full application. Commonly used are flange coupling, sleeve coupling, and clamp coupling.

Flexible couplings can be divided into flexible couplings without elastic elements and flexible couplings with elastic features. The former type only can compensate for the relative displacement of the two axes, but it can not buffer the vibration. Block couplings, toothed couplings, universal couplings, and chain couplings, etc .; the latter category contains elastic elements, in addition to the ability to compensate for the relative displacement of the two axes. It also has the function of buffering and damping; However, due to the limitation of the strength of the elastic element, the transmitted torque is generally not as good as the flexible coupling without the elastic element. The common ones are the elastic sleeve stud coupling, the elastic stud coupling, the plum blossom coupling, and the tire type—couplings, serpentine spring couplings, reed couplings, etc.

According to different working conditions, the coupling must have the following performance:

(1) Removability. The movability of the coupling refers to the ability to compensate for the relative displacement of the two rotating components. Factors such as manufacturing and installation errors between connected members, temperature changes during operation, and deformation under load all put forward requirements for mobility. Removable performance compensates or alleviates additional pressures between shafts, bearings, couplings, and other parts caused by relative displacement between rotating components.

(2) Buffering. For occasions where the load is frequently starting or the effective load changes, the coupling needs to have elastic elements that play a role in buffering and damping to protect the prime mover and working machine from damage or damage.

(3) Safe and reliable, with sufficient strength and service life.

(4) The structure is simple, easy to assemble and disassemble, and maintain.
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