1.  Field of the Disclosure
The present disclosure relates generally to image forming devices and more particularly to a replaceable, unit for an image forming device having a drive coupler that includes a locking member. 
2.  Description of the Related Art
Image forming devices such as electrophotographic printers, copiers and multifunction devices commonly include one or more replaceable units that have a shorter lifespan than the image forming device does.  As a result, the replaceable unit must be replaced by the user from time to time in order to continue operating the image forming device.  For example, an electrophotographic image forming device's toner supply is typically stored in one or more replaceable units.  In some devices, imaging components having a longer life are separated from those having a shorter life in separate replaceable units.  In this configuration, relatively longer life components such as a developer roll, a toner adder roll, a doctor blade and a photoconductive drum may be positioned in one or more replaceable units referred to as imaging units.  The image forming device's toner supply, which is consumed relatively quickly in comparison with the components housed in the imaging unit(s), may be provided in a reservoir in a separate replaceable unit in the form of a toner cartridge or bottle that supplies toner to one or more of the imaging units).  Other components of the electrophotographic image forming device such as a fuser may also be replaceable.  These replaceable units require periodic replacement by the user such as when the toner cartridge runs out of usable toner, when a replaceable unit's components reach the end of their life due to wear, when a waste toner reservoir fills with waste toner, etc. 
Image forming devices are used in a variety of settings such as businesses and schools.  In settings where physical access to the image forming device is generally unrestricted, the replaceable units of the image forming device may be a target for theft for purposes such as resale or home use.  For example, some schools where theft from image forming devices is common require school staff to remove and securely store the replaceable units at the end of each school day.  In addition to the inconvenience and burden imposed on the staff, daily removal and reinsertion of the replaceable units out of and into the image forming device may, over time, result in electrical system failure due to excessive wear on the electrical contacts of the replaceable units and the corresponding electrical contacts in the image forming device as well as toner leakage due to excessive wear on toner seals. 
One solution is to lock the replaceable unit to the image forming device or to lock an access door on the image forming device that permits access to the replaceable unit using a physical lock and key.  However, this solution requires safekeeping of the key to the image forming device creating an additional burden on the end user.  Another solution known in the art is for the printer to contain a lock mechanism (such as a solenoid lock) on the access door to the image forming device that is controlled by the image forming device and that restricts access to the replaceable unit(s).  However, this approach requires additional parts and installation of those parts in the image forming device thereby adding significant manufacturing cost to the device.  Accordingly, a secure, user-friendly, low cost system for locking a replaceable unit in an image forming device is desired.