About Couplings

Coupling is a component used to connect a drive shaft and a driven part, for example, a motor shaft and a ball screw for the purpose of transmitting the torque. Also, Coupling introduces mechanical flexibility providing misalignment for the shafts. As a result, this coupling flexibility can prevent uneven wear, vibration, and other mechanical troubles due to misalignment.

【engineering tips】Choosing the most suitable coupling

【3 min engineering tips】The hidden key to speeding up Servo Systems

Why Do We Need Couplings?

The main roles of a coupling include the following:

  1. Connecting drive shafts of motors, etc. with driven shafts of ball screws etc. to transmit power.
  2. Providing tolerance for errors (misalignment) between the cores of the drive shaft and the driven shaft.
  3. Absorbing equipment impacts and vibration.
  4. Improving equipment performance.
These will be further explained in the following sections.

1. Connecting drive shafts with driven shafts to transmit power

The most important role of a coupling (shaft coupling) is to connect the drive shaft of a motor etc. with the driven shaft of a ball screw etc. to transmit the motor power to the driven shaft, as shown in the figure below.

There are various types of shaft fastening, such as the set screw type which fastens by directly pressing screws against the shaft, the clamping type which fastens with frictional force, and the bushing type which uses the wedge effect.

>>List of Coupling Fastening Methods

2. Providing tolerance for mounting errors (misalignment) between the drive shaft and the driven shaft

The offset between the cores of the driving shaft and the driven shaft is called misalignment. There are three different types of misalignment: lateral, angular, and axial (offset in axial direction). These should be minimized in order to avoid equipment issues such as vibration, noise, uneven wear on the bearing and so on.

>>Alignment Adjustment

However, it is extremely difficult to completely eliminate misalignment when assembling equipment.

Couplings provide tolerance for the misalignment remaining after assembly.

3. Absorbing equipment impacts and vibration

Jaw type couplings have elastic bodies such as elastomer built in as an intermediate component to absorb impacts and vibration.
>>Jaw Type Couplings

4. Improving equipment performance

Depending on the type of coupling, it can also work to improve equipment performance in addition to the roles described so far.
One example is NBK's "High-Gain Rubber Type XG Series" (link in "High-Gain Rubber Type" below), using high-gain integrally molded rubber which suppresses servomotor hunting and improves limit gain, thus reducing settling time and improving productivity.
>>For Details on High-Gain Rubber Type

Types and features of NBK's Couplings

The extensive product line-up NBK offers is the fruit of experiences and expertise accumulated as a coupling manufacturer.
The line-up : XG Series high gain type coupling can meet requirements of the fast response to servomotor's order, Disc-type XH Series achieved the highest rigidity ever, MS Series has integral slits structures and it is best suited for stepper motors, cross joint XUT coupling reduces loads and reaction forces to bearings, Oldham MOR has superior cost effectiveness, and rigid XRP coupling has achieved exceptional high precision. Select one from NBK's broad line-up that meets your specifications.

Features

★:excellent ◎:very good 〇:good

  Zero
Back
lash
High Torque Allow
able
Misalig
nment
Cost Torsio
nal
Stiff
ness
Vibra
tion
absorp
tion
Applicable Motor Characteristics
Servo
motor
Stepping Motor
General
purpose motor
High Gain Rubber Type
高減衰能ゴムタイプ
Best suited for Servomotors
>>Click here for details. 
Disk Type
ディスクタイプ
    High Torsional Stiffness
Made of all stainless steel is available.
>>Click here for details. 
Jaw Type
ジョータイプ
High Torque
>>Click here for details. 
Slit Type
スリットタイプ
    Single-Piece Construction
Made of all stainless steel is available.
Made of all plastic is available.
>>Click here for details. 
Oldham Type
オルダムタイプ
        Low Cost
High Allowable Misalignment
>>Click here for details. 
Cross Joint Type
クロスジョイントタイプ
        Small eccentric reaction force 
>>Click here for details. 
Rigid Type
リジットタイプ
      Low Cost
High Torsional Stiffness
Made of all stainless steel is available.
>>Click here for details. 
Bellows Type
ベローズタイプ
      Ideal choice for encoder
Made of all stainless steel is available.
>>Click here for details. 
Serration Type
セレーションタイプ
        Low Cost
>>Click here for details. 

High Gain Rubber Type

Integrally molded vibration-resistance rubber damps hunting of servomotors. It shortens stabilization time required for machine setting and contributes to productivity improvement.

Click here to see all products of this series. Click here for details of functions. (Video available.)

Disk Type

The flexibility of disc (metal spring) allows misalignments.
The XH series couplings for high torque applications are best suited for servomotors with instantaneous maximum torque of 350%.

Click here to see all products of this series. Click here for details of functions.

Jaw Type

Resin sleeve placed in the middle of the structure provides cushioning that damps vibration and absorbs shock.

Click here to see all products of this series.

Slit Type

Slitting metal cylinders gives the flexibility to accommodate varying degrees of misalignments.
Contact us for couplings with custom made slit patterns that meet specific spring property requirements.

Click here to see all products of this series. Click here for custom made couplings.

Oldham Type

Sliding of the spacer in the midportion accommodates larger misalignments.
Less reaction force contributes to reduction of loads to bearings or other mechanical components.
Separable components enable easy assembling.

Click here to see all products of this series.

Cross Joint Type

Sliding motion of pins and bushes accommodates misalignments.
Less eccentricity reaction force contributes to reduction of loads to bearings or other mechanical components.

Click here to see all products of this series.

Rigid Type

Simply structured coupling without flexibility. High torsional rigidity.

Click here to see all products of this series.

Bellows Type

Metal bellows accommodate misalignments.
Reliability of constant rotation velocity makes this series the best choice for encoders.

Click here to see all products of this series.

Serration Type

Low Cost. Separatable components enable easy assembling.

Click here to see all products of this series.

Examples of Coupling Use

As explained in the section "Types and features of NBK's Couplings", different types of couplings have different features. Therefore, the ideal coupling selection depends on the equipment to which it will be mounted and the issues to be addressed.

Following are examples. Various other examples of ideal coupling selection according to the equipment and the issues are provided for your reference.
>>MoreExamples of Coupling Use

Surface-mount machine

Potential Issue
Production improvement (high throughput)
Selection point
Reduction of the stabilization time by supporting high gain in servomotor

Food Processing equipment

Potential Issue
Corrosion resistance
Selection point
Coupling made of all stainless steel

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