Patent ID: 7005824

Claim:
A shutter mechanism, comprising: a drum including an object wound thereon; a stepping motor electrically connected to the drum for rotating the drum to selectively wind and unwind the object; a chopper-type current source driver electrically connected to the stepping motor for supplying a drive current to the stepping motor and for generating chopper signals to chop out square waves output by the driver; a controller for controlling the driver to enable the driver to supply the drive current to the stepping motor, the controller including a memory for storing motor control data for use by the controller; and a load magnitude detection circuit in electrical communication with the stepping motor for detecting a magnitude of a load at the stepping motor, and for outputting a load signal indicative of the magnitude of the load at the stepping motor to the controller, wherein the controller is for starting and stopping an output of command pulses to the driver based on the load signal and on the motor control data stored in the memory.