Injection device with replacement cartridge

1. An injection device for injection of a medicament from a medicament cartridge 40 , the injection device comprising a main housing 4 , a piston 50 and an end stop switch 52 in which access to the main body 4 for replacement of the medicament cartridge 40 may only be obtained when the piston 50 trips the end stop switch.

2. An injection device according to claim 1 , characterised in that tripping of the end stop switch 52 releases a catch or other fastening device to allow access to the main body 4 for replacement of the medicament cartridge 40 .

3. An injection device according to claim 1 , in which the injection device further comprises a drive mechanism 42 to drive the piston 50 , an electronic control unit and a door release catch characterised in that when door release catch is operated the electronic control unit operates the drive mechanism 42 to withdraw the piston 50 until the end stop switch is contacted.

4. An injection device according to claim 3 in which the injection device further comprises a contact switch to detect the presence or absence of a medicament cartridge 40 , characterised in that upon detection of a new cartridge and closing of the door release catch, the electronic control unit operates the drive mechanism 42 to advance the piston 50 into contact with the new medicament cartridge.

5. An injection device according to claim 2 , in which the injection device further comprises a drive mechanism 42 to drive the piston 50 , an electronic control unit and a door release catch characterised in that when door release catch is operated the electronic control unit operates the drive mechanism 42 to withdraw the piston 50 until the end stop switch is contacted.