The Oldham Coupling

The 'Oldham Coupling' transmits power between shafts that are parallel and offset from each other.

A 'floating' disc, in the middle of the coupling, has a raised rib on each face. Each rib is perpendicular[⊥] to each other. The raised ribs engage with slots in flanges on the input and output shafts.

The Oldham Coupling is a kinematically-defined chain that is built with a:

1.Motion-Part, and

Oldham Coupling Video - Click to play

The video shows an 'Oldham Coupling'.

'Input': The Input Crank – the Motion-Part

'Output': The Output Crank – rotates at the same constant speed.

'Middle Disk': This transmits power from the Input to the Output Crank.

MD-EditPart2

Each kinematic-chain has a Motion-Part.

STEP 1: Add the 'Input' Part – a Crank

See Scotch-Yoke, Whitworth Quick Return kinematic-chain or Tutorial 1 to see how to 'Add a Crank'. In summary:

•Add a horizontal Line to the Base-Part. The length of the Line in the Base-Part will give the distance between the input and output shafts.
•Make the Crank approximately 100mm long, and drive it constant velocity.
•Make the length of the Line in the Base-Part approximately 80mm long, so that the centres of the Shafts are 80mm apart.

MD-Oldham-Coupling-Prep1

We now want to add a Dyad. Dyads ALWAYS have two Parts and three Joints. Never forget this!

STEP 2: Add the Dyad

Dyad: Part 2 and Joint 3

The 'Output' Part' of the Oldham Coupling Rotates.

1.Add a Part
2.Join it with a Pin-Joint to the Point at the end of the Line in the Base-Part.

MD-Oldham-Coupling-Prep2

Dyad: Part 1 and Joint 1

1.Add a Part
2.Add a Slide-Joint between the CAD-Line in the Input Crank and the CAD-Line along the centre-line of the new Part.

 

MD-Oldham-Coupling-Prep-3

Dyad: Joint 3 ...Preparation

Specify the position and orientation of Joint 3.

1.Edit the Part that is joined with a Slide-Joint to the Crank
2.Add a Line that is perpendicular[⊥] to the CAD-Line*
3.Close the Part-Editor

MD-Oldham-Coupling-Prep4

Dyad: Joint 3

The Oldham Coupling is almost complete.

Add a Slide-Joint between the two new Parts:

1.Click the CAD-Line in Part 2
2.Click the Line we added to Part 1

Oldham Kinematics - R PPR

The Oldham Coupling is Complete.

You can add Extrusions to the Parts to show the coupling as a Solid model.

 

* Note: The Part may be at 180º to the direction it is in this image. The direction of the +X-axis of the Part is the same direction as the +X-axis of the Line you add to make the Slide-Joint.

The +X-axis of a Line is the same as the direction you drag your mouse-pointer to add the Line.

Kinematics of Oldham Coupling - Crank + RPP Dyad

The Kinematics-Tree shows the Rocker (input Crank) and the new RRP Dyad.

Note: this is the same Dyad as the Scotch Yoke!

In this Oldham Coupling, you connect the R Joint to the Base-Part and the PP Joints are 'internal' to the kinematic-chain.

In the Scotch-Yoke, you connect the P Joint to the Base-Part, and the RP Joints are internal to the mechanism.

Tutorial and Reference Help Files for MechDesigner and MotionDesigner 13.2 + © Machine, Mechanism, Motion and Cam Design Software by PSMotion Ltd