1.  Field of the Present Patent Application
The present application is generally directed to dose setting mechanisms for drug delivery devices.  More particularly, the present application is generally directed to a dose setting mechanism comprising a stationary inner housing having a driver positioned inside the inner housing and having a slidable locking or blocking member that locks a flexible tab to an internal groove in the inner housing such that the driver follows the path of the groove during drug dispensing (injection). 
2.  Background
Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs.  This may be increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease. 
There are basically two types of pen type delivery devices: resettable devices (i.e., reusable) and non-resettable (i.e., disposable).  These types of pen delivery devices (so named because they often resemble an enlarged fountain pen) are generally comprised of three primary elements: (i) a cartridge section that includes a cartridge often contained within a housing or holder; (ii) a needle assembly connected to one end of the cartridge section; and (iii) a dosing section connected to the other end of the cartridge section.  A cartridge (often referred to as an ampoule) typically includes a reservoir that is filled with a medication (e.g., insulin), a movable rubber type bung or stopper located at one end of the cartridge reservoir, and a top having a pierceable rubber seal located at the other, often necked-down, end.  A crimped annular metal band is typically used to hold the rubber seal in place.  While the cartridge housing may be typically made of plastic, cartridge reservoirs have historically been made of glass. 
The needle assembly is typically a replaceable double-ended needle assembly.  Before an injection, a replaceable double-ended needle assembly is attached to one end of the cartridge assembly, a dose is set, and then a dose is administered.  Such removable needle assemblies may be threaded onto, or pushed (i.e., snapped) onto the pierceable seal end of the cartridge assembly. 
The dosing section or dose setting mechanism is typically the portion of the pen device that is used to set a dose.  During an injection, a spindle contained within the dose setting mechanism presses against the bung or stopper of the cartridge.  This force causes the medication contained within the cartridge to be injected through an attached needle assembly.  After an injection, as generally recommended by most drug delivery device and/or needle assembly manufacturers and suppliers, the needle assembly is removed and discarded. 
Different types of pen delivery devices, including disposable (i.e., non-resettable) and reusable (i.e., resettable) varieties, have evolved over the years.  For example, disposable pen delivery devices are supplied as self-contained devices.  Such self-contained devices do not have removable pre-filled cartridges.  Rather, the pre-filled cartridges may not be removed and replaced from these devices without destroying the device itself.  Consequently, such disposable devices need not have a resettable dose setting mechanism. 
In contrast to typical disposable pen type devices, typical reusable pen delivery devices feature essentially two main reusable components: a cartridge holder and a dose setting mechanism.  After a cartridge is inserted into the cartridge holder, this cartridge holder is attached to the dose setting mechanism.  The user uses the dose setting mechanism to select a dose.  Before the user injects the set dose, a replaceable double-ended needle assembly is attached to the cartridge housing. 
This needle assembly may be threaded onto or pushed onto (i.e., snapped onto) a distal end of the cartridge housing.  In this manner, a double ended needle mounted on the needle assembly penetrates through a pierceable seal at a distal end of the cartridge.  After an injection, the needle assembly is removed and discarded.  After the insulin in the cartridge has been exhausted, the user detaches the cartridge housing from the dose setting mechanism.  The user can then remove the empty cartridge from the cartridge retainer and replace the empty cartridge with a new (filled) cartridge. 
Aside from replacing the empty cartridge with a new cartridge, the user must somehow prepare the dose setting mechanism for a new cartridge: the dose setting mechanism must be reset to a starting or initial position.  For example, in certain typical resettable devices, in order to reset the dose setting mechanism, the spindle that advances in a distal direction during dose injection must somehow be retracted back into the dose setting mechanism.  Certain known methods of retracting this spindle back into the dose setting mechanism to a restart or an initial position are known in the art.  As just one example, known reset mechanisms require a user to turn back or push back (retract) the spindle or some other portion of the dose setting mechanism. 
Resetting of known dose setting mechanisms have certain perceived disadvantages.  One perceived disadvantage is that the pen device user has to disassemble the device to either remove an empty cartridge or somehow reset the device.  As such, another perceived disadvantage is that such devices have a high number of parts and therefore such devices are typically complicated from a manufacturing and from an assembly standpoint.  For example, certain typical resettable pen type devices are not intuitive as to how a user must replace an empty cartridge and reset the device.  In addition, because such resettable devices use a large number of components parts, such resettable devices tend to be large and bulky, and therefore not easy to carry around or easy to conceal. 
There is, therefore, a general need to take these disadvantages associated with resetting issues into consideration in the design and development of resettable drug delivery devices.  Such desired drug delivery devices would tend to reduce the number of component parts and also tend to reduce manufacturing costs while also making the device less complex to assemble and manufacture.  Such desired devices would also tend to simplify the steps required for a user to reset a dose setting mechanism while also making the device less complex and more compact in size.