What is a Coupling?

Engineering Tips: Choosing the Most Suitable Coupling

3 Minute Engineering Tips: The Hidden Key to Speeding Up Servo Systems

Why Do We Need Couplings?

The primary functions of a coupling include:

1. Connecting drive shafts (e.g., motor shafts) to driven shafts (e.g., ball screws)to transmit power.
2. Accommodating misalignment between the axes of drive and driven shafts.
3. Absorbing Impact and Vibration of Equipment.
4. Improving equipment performance.

1. Connecting Drive and Driven Shafts to Transmit Power

The primary role of a coupling is to connect drive shafts (motor) to driven shafts (ball screw) for power transmission, as shown in the figure below.

There are various types of shaft fastening, including set screw types(direct‑screw‑pressure clamping), clamping types (frictional force clamping), and bushing types(wedge‑effect locking).

>>List of Coupling Fastening Methods

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

The offset of the axes between the drive shaft and the driven shaft is called misalignment.There are three different types of misalignment: parallel（eccentricity）, angular, and axial (end-play).To prevent equipment problems such as vibration, noise, and uneven bearing wear, these misalignments must be minimized.

>>Alignment Adjustment

However, perfect alignment during equipment assembly is extremely difficult to achieve.

Couplings accommodate residual misalignment after assembly.

3. Absorbing Impact and Vibration of Equipment

Jaw couplings use an elastomeric element as an intermediate component to absorb impacts and vibration.
>>Jaw Type Couplings

4. Improving equipment performance

Depending on the type of coupling, it can enhance the performance of the equipment in addition to the roles described so far.
For example, NBK's High-Gain Rubber Type XG Series use integrally molded high‑gain rubber to suppress servomotor hunting and increase limit gain, resulting in reduced settling time and improved productivity.
>>For Details on High-Gain Rubber Type

Types and features of NBK's Couplings

NBK's extensive product line reflects accumulated experience and expertise as a coupling manufacturer.
Our product line includes: XG Series high-gain couplings for fast servomotor response; XH Series disc couplings for maximum rigidity; MS Series integral slit couplings for stepper motors; XUT cross joint couplings for reduced bearing loads; MOR oldham couplings for cost-effectiveness; and XRP rigid couplings for exceptional precision.
NBK will propose the optimal coupling to meet 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	★	★	◎	◎	◎	★	★	◎	Best suited for Servomotors ＞＞Click here for details.
Disk Type	★	◎	◎	〇	★		◎		High Torsional Stiffness Made of all stainless steel is available. ＞＞Click here for details.
Jaw Type	〇	★	◎	◎	〇	◎	◎	★	High Torque ＞＞Click here for details.
Beam Type	★	〇	〇	〇	◎		〇		Single-Piece Construction Made of all stainless steel is available. Made of all plastic is available. ＞＞Click here for details.
Oldham Type		★	★	★				★	Low Cost High Allowable Misalignment ＞＞Click here for details.
Cross Joint Type	◎		◎		◎		◎		Small eccentric reaction force  ＞＞Click here for details.
Rigid Type	★	★		★	★		◎		Low Cost High Torsional Stiffness Made of all stainless steel is available. ＞＞Click here for details.
Bellows Type	★	〇	◎	◎	◎				Ideal choice for encoder Made of all stainless steel is available. ＞＞Click here for details.
Serration Type		〇	◎	★				★	Low Cost ＞＞Click here for details.

High Gain Rubber Type

The integrally molded vibration-damping rubber suppresses servomotor hunting.
It reduces the settling time of the equipment and improves productivity.

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 high-torque XH series is 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

A resin sleeve in the coupling's structure provides cushioning, vibration damping, and shock absorption.

Click here to see all products of this series.

Beam Type

Slitting metal cylinders provides the flexibility to accommodate varying degrees of shaft misalignment.

Click here to see all products of this series.

Oldham Type

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

Click here to see all products of this series.

Cross Joint Type

The sliding motion of pins and bushes accommodates shaft misalignments.
Reduced reaction forces due to shaft eccentricity minimizes loads on bearings and other mechanical components.

Click here to see all products of this series.

Rigid Type

Simply designed coupling without flexibility provides high torsional rigidity.

Click here to see all products of this series.

Bellows Type

Metal bellows accommodate misalignments.
Reliability of constant rotational velocity makes this series the best choice for encoder application.

Click here to see all products of this series.

Serration Type

Cost savings and easy assembly are achieved through separable components.

Click here to see all products of this series.

Examples of Coupling Use

As detailed in the "Types and Characteristics of NBK Couplings" , each coupling has distinct features. Therefore, couplings are selected depending on the equipment application and the specific challenges to be addressed.

Examples of ideal coupling selections are provided below. Further examples are available for your reference.
>>MoreExamples of Coupling Use

Surface mount machine

Equipment Challenges

Production Improvement (high throughput)

Selection Factors

Reduced stabilization time through high-gain servomotor support

Recommended product

High-Gain Rubber Type / XGT2

Food Processing equipment

Equipment Challenges

Corrosion Resistance

Selection Factor

All-stainless steel coupling

Recommended product

Slit-type / MSTS