What is a coupling?

A coupling is a mechanical element part that connects two shafts together to accurately transmit the power from the drive side to the driven side while absorbing the mounting error (misalignment), etc. of the two shafts. Coupling in the machine industry is interpreted as “a part that connects two shafts together”, and is generally called “coupling”, “shaft coupling” or “joint”.
Serpentine spring coupling
Serpentine spring coupling
Power can be transmitted by using a coupling, even between axes of different diameters as shown in the following figures.
Power can be transmitted by using a coupling, even between axes of different diameters as shown in the following figures.
  The role of a coupling (shaft fitting)

The role of a coupling is mainly as follows.

1.Power is transmitted from the driving side (turning side) to the driven side     (turned side). 2.Absorbs mounting errors between the axes of the driving side (turning side)    and the driven side (turning side). 3.Absorbs vibration from the driving side (turning side) and protects surrounding products. 4.Does not transfer heat from the motor on the drive side (turning side), etc.    to the driven side (turned side).
The role of a coupling (shaft fitting)

1.Transmit power

The primary reason for using a coupling is to connect the drive shaft to the driven shaft. It is difficult to manufacture a machine connected with one-piece shaft instead of using a coupling. It creates problems in terms of cost and accuracy, but also transportation and assembly are very difficult, so it takes extra man-hour. Also, in the case of one-piece shaft, it must be replaced in its entirety, if either the drive side or the driven side is broken.
Transmit power

2.Absorb misalignment

It takes a considerable amount of time to align the drive shaft to the driven shaft with high precision. If the axes of two shafts are misaligned, an extra force is repeatedly applied to the surrounding parts as it rotates, which causes vibration and noise. In addition, even though the same parts are used to manufacture units, there are errors such as machining accuracy, so it is very difficult to assemble every unit with accuracy, because the dimensions are different one by one. Therefore, a coupling should be used to absorb such mounting errors. Coupling has the role of transmitting power dynamically and accurately even if there is a misalignment (eccentricity / declination angle, axial displacement, etc.) between the two shafts.
Absorb misalignment
What is mounting error?
What is mounting error?

3.Absorb vibrations to protect surrounding products

Vibration and shock may be transferred to surrounding parts when using the machine. For example, if the vibration of a motor, etc. in the driving side is transmitted to the ball screw, etc., it deviates the machine from the prescribed position and it is impossible to make the good use of the machine’s performance. Also, if a machine with no coupling receives an impact from the outside, the impact may be transmitted directly to the motor and may cause damage to the motor. A coupling is the solution to this problem. It absorbs vibration in order to move the driven side with high accuracy, and/or shock to prevent expensive motors, etc. from damaging.
Absorb vibrations to protect surrounding products

4.Do not transfer the heat of the motor, etc. to the driven side.

A motor generates a lot of heat when it is used. When it is transmitted to the driven side, the ball screw, etc. expand by heat and the length will be changed. As a result, the positioning accuracy is affected, and the expected machine precision will be not realized. However, by using a coupling, it is possible to prevent the heat transfer of the motor, etc. so that the parts will not be deformed or shifted from its correct position.
Do not transfer the heat of the motor, etc. to the driven side.
As explained so far, the necessity to use couplings varies depending on the application and situation. Couplings can provide multiple performances such as absorption of mounting errors (flexibility), high positioning accuracy (high rigidity), contribution to higher accuracy and longer service life by absorbing vibration and blocking of heat transfer. There are many kinds of couplings. It is necessary to understand what kind of features are available and what kind of application they will be suitable, and then select an appropriate coupling suitable for the intended use.

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