Oldham Coupling: 19 Important Factors Related To It

Oldham Coupling:

Invention: John Oldham (1821)-solve paddle steamer design.
Flexible coupling has 3 types. Oldham coupling is one of the type of the flexible coupling.

Oldham coupling definition:

Oldham coupling transmits torque between shaft through mating slots on the center discs mounted on the hub.
Oldham coupling is useful for parallel alignment applications. It can acquire axial and angular misalignments.

Basic applications of couplings:
To transmit power and torque.
To accommodate misalignments (angular, axial, parallel)
To absorb shock loads and vibrations.

Oldham coupling parts:

Oldham Coupling has three discs. All discs are attached to each other using the grooves.
The discs are mounted at the mid-sections of the shafts. The disc is mounted on the input shaft. Another the disc mounted on the output shaft. The three discs are connected to each other.

Central disc: It is the coupling part consisting of two hubs. It contains two shafts on the sides of the discs perpendicular to the hub axis and plugged into the hub axis. The center is used to reduce the backlash. And hence it is press-fitted at the center. It is designed to behave as a mechanical fuse. Mainly Oldham coupling working is based on the parallel misalignment, so the discs sliding motion acquire a large amount of parallel misalignment.

The hubs: Oldham coupling consists of two hubs that are connected at the end of the shafts. It is a round circular type of disc. Hubs are grooved into the center of the discs.

Oldham coupling: Working principle

Oldham coupling has three main parts(three discs).

One input shaft is connected to the disc and the disc is connected to the output shaft.
each one is coupled to input and output shafts, and one is joined to the first two discs with the grooves.
The disc at the center rotates at same speed and same axis as both the shafts.
Its center rotates about the center axis orbit twice per rotation at the midpoint of input and output shafts. Springs are used in the mechanism to reduce the backlash.
The discs are used to connect the driving and the driver shaft in mechanical power transmission assemblies.

Oldham coupling advantages | advantages and disadvantages of Oldham coupling

  • It has a low moment of inertia.
  • Material used for the center disc is plastic. Hence the electrical isolation between the discs is not possible. All three are aligned to each other.
  • If the first disc breaks, the torque limit is exceeded in the center disc so as to prevent the torque transmission.
  • It is economical compared to other couplings.
  • It has a high torque capacity.
  • Easy to dismantle and disassemble.
  • Due to the backlash, there is a need for replacement. Hence the replacement is inexpensive compared with other couplings as it is compact in size.
  • Accommodate large parallel and radial misalignments.
  • It gives protection to the driven components and support bearings.
  • It is compact in size, so it is easy installation.
  • It has high torsional stiffness.
  • Longer service life
  • Tighter machining tolerances with one shaft connected to another maintain a consistent performance rate.
  • Good surface finish.
  • Very low restorative force compared with other coupling designs:
  • Low maximum speed=3000 rpm.

Oldham coupling disadvantages | Advantages and Disadvantages of Oldham coupling

  • It can accommodate even small angular misalignments.
  • It can accommodate very limited angular displacement.
  • At the high torque, the axial load which is reactive, can be applied on the support bearings.

Oldham coupling applications:

It can accomodate slightest misalignments.
The driving shafts and the driven shafts generate at a similar speed.
It behaves as an electrical insulator.
It can transmit power and torque.
The material used in the three discs leads to the use of Oldham of coupling in many device applications.

Oldham shaft coupling:

Oldham coupling applications are mainly used to join the two parallel coaxial rotating shafts. It can transmit the torque at the same speed and same rotation mechanism.
An Oldham type coupling is part of the flexible type coupling. It is a better design for the coupling shafts, which has misalignments, and it can transmit torque between the shafts at the same speeds and same direction. The coupling can acquire any slightest amount of misalignment. Oldham coupling has three discs and two hubs, and one center connected by the use of grooves that fit the fins on the midsection, each side, and perpendicular to each other.

Shaft coupling linkages system requirements:

It should be easy to disassemble
It should allow the misalignment between the rotating shafts rotating along any axis.
It should not be any projecting parts.
It should reduce the further misalignments that can occur in the running operations that can increase the power transmission and machine runtime.
It should reach the manufacturer’s target machine train to define non-zero alignment.

Oldham coupling used in:

Robotics and servo applications
Printer and copy machines.

Uses of Oldham coupling:

The purpose of the couplings is to connect two rotating shaft types of equipment, allowing some misalignment.
Careful selection and installation, and maintenance of the couplings at reduced costs.
The coupling provides the connection between the shafts that are even manufactured separately. It also provides disconnections between the repairs and replacements.

Couplings allow misalignments along with lateral, axial, and angular directions.
It provides protection to the support bearings and shaft hubs from overloading.
It can change the vibration characteristics of the rotating shafts.

Oldham coupling design:

It is an old design mechanism with identical slotted elements put together to slide between them. The Oldham designing is used for the machine shafts, which have a parallel misalignment.

Bore diameter= Diameter of coupling bore mounted on the connecting shafts.
Overall length is the length of the coupling end to the end face.
Hub width is the end face to internal face width.
Slider block material
Coupling diameter
Maximum rated torque
Lateral offset – Lateral offset is the parallel misalignment.
Angular offset – Angular misalignment
Axial offset – maximum axial deviation along with the shaft Shaft coupling fastening method

Design calculation of Oldham coupling| Oldham coupling dimensions:

The length L, L=1.75d,
The diameter, D2=2d,
The thickness of the flange, t=0.75d,
Diameter of the disc, D=3L,
Centerline distance, a=D-3d,
The breadth of groove W=D/6,
The groove thickness, h1=W/2,
The disc thickness, h=W/2,
The total pressure on each coupling=F=1/4(p*D*h)
The torque on each side of coupling=T

Oldham coupling drawing:

disassembled oldham coupling
Image credit:anonymous, Klauenkupplung 3CC BY-SA 3.0
assembled oldham coupling
Image credit:anonymous, Klauenkupplung 1CC BY-SA 3.0

Oldham coupling material:

For the Oldham coupling, the material used is different for the parts of the mechanism, Mentioned as follows:
Slider block is manufactured by the polymer material (nylon, acetal, or combination) to reduce the backlash.
The slotted mating halves are manufactured from aluminum to reduce inertia. It can also be manufactured from brass material of smaller sizes.
Materials can be used for mid disc:
Materials can be used for side disc(hubs):
stainless steel.
Aluminum alloy.

Oldham coupling mechanism:

An Oldham coupling is the mechanism that is a combination of the rigid connections bodies(kinematic linkages) with definite relative motion. Mechanisms generally have linkages that can move relative to each other—for example, gear and gear train, belt and chain drive, cam and follower.

This also includes the friction devices such as brake and clutches, and structural components, fasteners, bearings, springs, lubricants, etc. And the different types of the machine element parts like spline, pins, and keys.
To perform the mechanical work machine elements mechanism transmits power to the resistance to overcome.
A coupling is a device that is a connection between the two shafts for transmission of the power.

A coupling can allow the misalignment but it does not allow disconnection of shafts during the procedure.
The torque limiting couplings can disconnect or slip due to the torque limit is exceeded.
Oldham coupling is the inversion of the double slider crank mechanism. It is obtained by the connecting links.
It can join the elements having lateral misalignments.

Oldham coupling consists of three discs and two flanges with the slots with two tongues attached to the central floating part perpendicularly to each other. Pins are provided, which pass through the flanges and the floating disc. When the tounge1 are fitted in the slot, it allows relative motion between shafts.

The tounge2 is fitted in the other slot allowing the relative vertical motion between the shafts. The resultant motion of the two components allows motion to accommodate the misalignment of the rotating shafts. The Oldham coupling mechanism is based on the three discs with hubs. The sliding friction develops wear of slider block that creates a backlash in the misaligned systems.

Oldham coupling mechanism applications:

Oldham coupling mechanism is mostly used for the stepper motor-driven positioning stages.
The elements of the coupling absorb the shock loads and the vibrations from the frequent starts and stop of the load reversals.
The Oldham coupling is designed for the motion systems, which are idle half of the time.
The latter is available for mounting the driving and the driven shafts without any disturbance within the shaft alignments.

Misalignments in the Oldham coupling:

  • Misalignment is the displaced alignment between the shafts.
  • Misalignment can be parallel, angular or axial, or combinations.
  • In the Oldham coupling, parallel misalignment is generally observed.
  • An angular misalignment in the machine train is that in which the shafts intersect at angles less than 180.
  • Tighter alignments have higher energy efficiency.
  • The tighter alignments have less wear on the machine parts.

Generalized Oldham Coupling:

Oldham coupling is the inversion of the double slider crank mechanism[citation]
an Oldham coupling is the device used to transmit motion and power between parallel rotating coaxial shafts.
Oldham coupling is the flexible coupling part. It gets its flexibility from the disc materials,

The following shows Oldham coupling types based on the shape:
with circular slots,
with curvilinear slots

The figure shows the generalized Oldham coupling with circular slots (link1),
an input disc mounted at the midsection of the input shafts (link2)
an output disc mounted at the midsection of the output shaft(link4),floating disc(link3).

Image credit:https://www.researchgate.net/publication/282390310_On_the_Kinematic_of_Generalized_Oldham_Couplings

The radii r1 and r2 are the radii of the centerlines of the slots.
The radii may or may not be equal .It is not necessary that the radii has to be equal.
The radii intersect at the centerline axis of the floating disc.

The primary Oldham coupling type transmits torque at the same speed of both the shafts.
The generalized Oldham coupling has two types of slots. One is circular slots and the another is curvilinear slots.
Using either of the slots. the Oldham coupling can transmit non uniform motion and also It can produce quick return motion.
and It can used in many applications where devices require non-uniform transmission.

FAQ/Short Notes:

How to reduce backslash in Oldham coupling, and what is it?

Backlash is the angular movement in the mating parts of the mechanical parts. It is often possible that backlash occurs in the coupling movement. The excessive backlash can wear out the coupling parts.
Backlash is the angular movement in between the mating parts. Coupling inserts inspection needs for the proper precision of the shaft alignment. A backlash has to be less than a 2-degree angular movement.

Control and reduce of the backlash methods:
Replacement of the couplings inserts and defective components.
Reduce the backlash by rotating shafts, and maintain torque at a consistent level.

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