Motor Couplings

Motor couplings are flexible devices that provide distance changes along a lateral axis between a motor shaft and a device. Flexible shaft couplings are necessary to connect shafts that are slightly misaligned. The degree of misalignment a coupling can tolerate depends on its material and its application but in general, up to 5° of misalignment can be tolerated.

Although they vary significantly, motor couplings are always composed of an outer casing with an axis and two sides and a carriage shaft, where a carriage moves sideways along an axis of rotation and is surrounded by ball bearings.

Motor couplings exhibit high torsional stiffness which prevents system resonance. There are five main types of flexible shaft couplings that are used for motor applications: beam, Oldham, jaw, disc and bellows. Components of motor couplings are mostly made out of metal like steel, stainless steel and aluminum. Certain parts, like the spider in jaw couplings, are made of polyurethane or other plastic resin-based materials.

Each motor coupling has different degrees of torque, shaft misalignment, stiffness, rotations per minute and space requirements and these factors must be taken into account when choosing a coupling for a motor application. Motor couplings are used in medical systems like scanners, DNA analyzers and x-ray equipment, as well as home appliances like blenders, dishwashers and washing machines.

The five kinds of motor couplings are different in size, shape and characteristics. Beam couplings have zero backlash and are machined with several spiral cuts to absorb impact. Oldham couplings have high parallel misalignment capabilities while jaw couplings are best for shock absorption because of their plastic dampening component called a spider.

Shaft Couplings
Motor Couplings – Ringfeder Power Transmission

It serves to dampen impulse loads and minimize shock to a motor. These couplings are considered fail safe because if the spider malfunctions, the jaws of the two hubs interlock and create direct power transmission so the vehicle can shut down safely. Jaw couplings perform the best for applications that use a stop-and-go type of movement that also require accuracy; they are not optimal for applications in which precise movements are required during movement.

Disc couplings are torsionally rigid and therefore have high misalignment capability. Bellows couplings offer the most rigid torsional stiffness. They offer a near-infinite life span and are virtually maintenance free. Their connection is hidden within the fit-length of the hub, enabling exact transmission of angular motion and torque.

One of the most common methods of construction for motor couplings is electroforming where the part is built by adding layers of metal on a mandrel until the desired thickness is reached. Another method is mechanical forming such as roll-forming or extrusion. Welded couplings are made by welding a series of rings or washers inside and outside.