Abstract: A data storage and retrieval system. In a preferred embodiment, the data storage and retrieval system includes a polygonal array of cells that are inwardly disposed with openings configured to receive data storage units. A first robot unit to transport a data storage unit to and from the polygonal array of cells is located within the polygonal array of cells. A second robot unit is also located within the polygonal array of cells to transport a data storage unit to and from the polygonal array of cells. The second robot unit manipulates the data storage units placed in the cylindrical array of cells independently of the first robot unit.

Abstract: Method and apparatus for monitoring bi-directional currents in a multi-phase brushless DC motor. The current in each separate phase is separately monitored to generate a feedback signal that is used to dynamically adjust the instantaneous levels of the winding currents in accordance with a specified torque required of the motor. Both negative and positive currents in the motor windings are monitored at all times to provide precision control of the feedback signals.