Brushless

Known in the trade by a multitude of names the Printed Armature or Pancake electric motor is still as relevant a technology today as it was at its conception in the late 60’s. Originally designed as a solution to smoothly wind magnetic tape for the budding computer industry, the Pancake technology has found its way into a whole host of new applications with the number of advantages the technology has over conventional electric motor technologies. The Flat Armature design is essentially an ironless disc with coils punched from sheet copper and formed onto non-magnetic disc insulators. The brushes short across two or more points to create a path through the copper thereby creating a magnetic field which interacts with the permanent magnets to create motion. With no magnetic material present in the armature undesirable ‘cogging’ is completely eliminated, providing smooth operation and continuous torque down to zero RPM, with minimal torque ripple. Torque is proportional to current and not limited by saturation, whilst speed is directly proportional to voltage. The ironless design of the printed armature means that there is virtually zero inductance. The result of this feature is that when the magnetic field collapses energy does not discharge by arcing to the brushes. The effect of this is twofold; firstly the printed armature exhibits low EMC properties, essential for most of today’s applications. Secondly this means the wear rate of the brush is minimal, as it is arcing not friction that is the major contributing factor when calculating brush life. In certain applications PML have achieved over 10,000 hours working life expectancy on a high volume product. In conventional permanent magnet DC motors internal losses increase with speed. These losses are associated with the inductance, and therefore arcing, which means that the motor must use some of the torque developed in order to keep itself rotating, thereby reducing the torque available in the application. This also can cause the motor to behave irregularly at high speed. The minimal inductance if the Printed armature motor means that these losses are small and the motor can deliver torque much more effectively at high speeds. Also because the inductance has a negative effect on the initial development of torque the printed armature motor can reach maximum torque in a fraction of the time, compared with conventional motors.