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Low Cost Automation Tutorial

#044 Motion Mechanism Design - 14 : Connecting a Motor Shaft and Ballscrew

Category : Drive mechanism design
June 4, 2010

Components used to transmit motor's torque (force) and rotation (moving distance) to a ballscrew may largely affect the system accuracy, reliability, and ease of assembly. Couplings are explained in this tutorial.

(1) Role of couplings

When connecting both shafts of a motor and a ballscrew, the arrangement may be accurate statically but can include possible variables dynamically, as show below.

1. Ballscrew shaft deflection when rotating.
2. Shaft deformation and stress due to heat expansion.
3. Deformation of ballscrew support unit.
4. Friction resistance variances due to bearing wear, after extended usage.

Therefore, couplings that can solve the variables from issues 1~4, instead of using a rigid body to connect the two shafts.

(2) Coupling types, construction, and characteristics

Slit typeA spiral slit is made in the center section of a metal (alum. alloy, etc.) cylinder body. One piece construction  offers spring function and shaft retaining function.Smooth torque transmission due to one piece construction. Can absorb large alignment error amounts. No backlash. Waterproof, oil resistant, chemical resistant.
Disc typeA disc is provided in the body center. Disc material and shape can be selected to adapt to wide range of transmission capabilities.Good adaptability to high torque and high torsional scenarios. No backlash. Electrically insulating type available.
Oldham typeTwo shaft hubs are connected by a resin spacer. (see [Photo 1])Small size for small torque applications. Good balance in torque transmission, torsional rigidity, and misalignment absorption. Good electrical insulating property.
Bellows typePhosphor bronze or stainless steel made bellows connects two shaft hubs.Good performance in transmitting constant rotational velocity. Suitable for connecting rotary encoders.
Rigid typeOne piece solid construction made of alum. alloys or stainless steel.High torsional rigidity and no backlash, but has no misalignment absorption capability.

[Photo 1]