Pancake motor helps digitise film heritage

Transferring these many decades of film heritage onto digital media is a big task, which has now been made easier by a pancake motor developed by Printed Motor Works (PMW) for a film scanner.

To guarantee faithful reproduction, the film has to be driven at a precise and absolutely constant speed through the scanner's optomechanical transfer head. This requirement for precise speed control is very similar to that for the tape drives once common in computer storage systems, and for this reason PMW used the same type of pancake motor technology.

Its iron-free printed armature with over 100 commutator paths per revolution enables it to produce no ripple or cogging torque, and it can maintain the extremely smooth speed required across a very wide range of speeds.

The powerful motor can accelerate from stationary to top speed in less than one revolution and can decelerate just as quickly. It can also run as smoothly in either direction of rotation.

As with all PMW's larger diameter motors, the company had to be certain it could carry the load without the risk of shaft deflection causing touchdown of the armature onto the magnets.

The shaft was therefore strengthened and the bearings supporting the radial load were recessed within strengthened aluminium housings on both ends of the motor. Bearings were chosen to a high specification fit and clearance, and axial preload was increased to ensure positional accuracy under load.

The motor's very low inductance also ensures long brush life due to the absence of arcing during commutation.

This type of motor is suitable for a wide range of other applications requiring rapid stop-start, zero cogging, low inductance, precise electronic motor control, low thermal time constant or just an axially flat profile.