Drug delivery device

1. A drug delivery device comprising: a housing;

a cylindrical member configured to be rotatably supported inside the housing, wherein an outer surface of the cylindrical member is provided with a single track comprising a sequence of encoded images that are each unique images from adjacent encoded images of the sequence, wherein each encoded image comprises a plurality of adjacent identical code sections, and wherein each encoded image of the sequence of encoded images corresponds to a discrete rotational position of the cylindrical member with respect to the housing; and

a sensor directed at the track of the cylindrical member, wherein the sensor is configured to detect portions of two or more of the adjacent identical code sections.

2. A drug delivery device as claimed in claim 1 , wherein the track is a helical track and wherein the housing and the cylindrical member are configured such that the cylindrical member moves in a first axial direction relative to the housing when rotated in a first rotational direction relative to the housing.

3. A drug delivery device as claimed in claim 1 , wherein the cylindrical member is configured to be rotated from an initial position into a number of discrete rotational positions and wherein each successive rotational position is represented by the next in the sequence of encoded images.

4. A drug delivery device as claimed in claim 1 , wherein the encoded images are optically encoded images and the sensor is an optical sensor configured to detect light intensity values at multiple locations on each encoded image.

5. A drug delivery device as claimed in claim 1 , wherein the housing also supports a light source configured to illuminate the track.

6. A drug delivery device as claimed in claim 1 , wherein the device further comprises a processor configured to receive electrical signals from the sensor and to identify an encoded image from the received signals.

7. A drug delivery device as claimed in claim 1 , wherein the device further comprises a processor configured to receive electrical signals from the sensor, to interpret the signals and to compare the interpreted signals to a stored record of encoded images.

8. A drug delivery device as claimed in claim 1 , wherein the plurality of adjacent identical code sections comprises four identical code sections arranged in a square grid.

9. A drug delivery device as claimed in claim 1 , the device further comprising:

a user actuatable plunger configured to cause expulsion of a drug from the drug delivery device; and

a switch, wherein depression of the plunger is configured to cause the switch to switch from a first position to a second position.

10. A drug delivery device as claimed in claim 6 , wherein the device further comprises a display and a processor configured to control the operation of the display.

11. A drug delivery device as claimed in claim 10 , wherein the processor is configured:

to determine a discrete rotational position of the cylindrical member using a reconstructed encoded image;

to determine a selected drug dose using the discrete rotational position of the cylindrical member; and

to cause the selected drug dose to be displayed on the display.

12. A drug delivery device as claimed in claim 1 , wherein the outer surface of the cylindrical member is further provided with a detectable surface texture.

13. A drug delivery device as claimed in claim 12 , wherein the sensor is an optical sensor and is further configured, when the cylindrical member rotates, to detect changes in light intensity values at a location of the surface texture.

14. A drug delivery device as claimed in claim 1 , further comprising a lens disposed in a line of sight of the sensor.

15. A drug delivery device as claimed in claim 1 , wherein each encoded image of the plurality of encoded images comprises a matrix of points within a grid or a bar code.