Reusable injection pens

1. A medicine injection pen, comprising:

a body;

a drive member disposed within the body and configured to rotate in a first rotational direction relative to the body from a first position to a second position to dispense liquid medicine, the drive member configured to rotate in a second rotational direction from the second position to the first position to reset the drive member;

a rotary encoder including:

a first part rotationally fixed relative to the body; and

a second part configured to rotate with movement of the drive member to enable determination of an amount of liquid medicine dispensed based on a rotation of the second part relative to the first part; and

a gear set operably coupled to the second part of the rotary encoder, wherein the second part is configured to rotate freely relative to the gear set during movement of the drive member in the first rotational direction and to engage the gear set during movement of the drive member in the second rotational direction.

2. The medicine injection pen according to claim 1 , wherein the gear set is a planetary gear set.

3. The medicine injection pen according to claim 2 , wherein the planetary gear set includes a sun gear and a plurality of planet gears in meshing engagement with the sun gear, the second part configured to rotate about the sun gear with the planet gears in the second rotational direction.

4. The medicine injection pen according to claim 3 , wherein the sun gear is configured to rotate with the drive member in the second rotational direction as the drive member moves from the second position to the first position.

5. The medicine injection pen according to claim 4 , wherein the second part of the rotary encoder is configured to:

rotate with the drive member in the first rotational direction at the same rate as the drive member as the drive member moves from the first position to the second position; and

rotate with the planet gears via the sun gear in the second rotational direction at a lesser rate than the drive member as the drive member moves from the second position to the first position.

6. The medicine injection pen according to claim 5 , wherein the drive member and the second part are configured to be rotated by a motor.

7. The medicine injection pen according to claim 6 , further comprising a processor in communication with the motor, wherein the processor is configured to automatically control the motor to rotate the drive member in the second rotational direction upon the drive member moving to a predetermined position.

8. The medicine injection pen according to claim 1 , wherein the drive member is a drive screw configured to rotate and translate relative to the body to urge a piston to slide to dispense the liquid medicine.

9. The medicine injection pen according to claim 8 , wherein the rotary encoder is configured to sense rotation of the drive screw to enable determination of the amount of the liquid medicine dispensed.

10. The medicine injection pen according to claim 9 , further comprising an electronics unit configured to determine the amount of the liquid medicine dispensed based on the sensed rotation.

11. The medicine injection pen according to claim 1 , further comprising a cartridge housing releasably engageable with the body and configured to retain a medicine cartridge therein, the medicine cartridge configured to retain the liquid medicine therein and including a piston configured to slide within the medicine cartridge, wherein the drive member is configured to move relative to the body upon actuation thereof to urge the piston to slide within the medicine cartridge to thereby dispense at least some of the liquid medicine through a dispensing end of the medicine cartridge.

12. A medicine injection pen, comprising:

a body;

a drive member disposed within the body and configured to rotate in a first rotational direction relative to the body from a first position to a second position to dispense liquid medicine, the drive member configured to rotate in a second rotational direction from the second position to the first position to reset the drive member;

a rotary encoder including:

a first part rotationally fixed relative to the body; and

a second part configured to rotate with movement of the drive member to enable determination of an amount of liquid medicine dispensed based on a rotation of the second part relative to the first part; and

a gear set operably coupled to the second part of the rotary encoder, wherein the second part of the rotary encoder is configured to:

rotate with the drive member in the first rotational direction at the same rate as the drive member as the drive member moves from the first position to the second position; and

rotate with the gear set in the second rotational direction at a lesser rate than the drive member as the drive member moves from the second position to the first position.

13. The medicine injection pen according to claim 12 , wherein the gear set is a planetary gear set.

14. The medicine injection pen according to claim 13 , wherein the planetary gear set includes a sun gear and a plurality of planet gears in meshing engagement with the sun gear, the second part configured to rotate about the sun gear with the planet gears in the second rotational direction.

15. The medicine injection pen according to claim 14 , wherein the sun gear is configured to rotate with the drive member in the second rotational direction as the drive member moves from the second position to the first position.

16. The medicine injection pen according to claim 12 , wherein the drive member and the second part are configured to be rotated by a motor.

17. The medicine injection pen according to claim 16 , further comprising a processor in communication with the motor, wherein the processor is configured to automatically control the motor to rotate the drive member in the second rotational direction upon the drive member moving to the second position.

18. The medicine injection pen according to claim 12 , wherein the drive member is a drive screw configured to rotate and translate relative to the body to urge a piston to slide to dispense the liquid medicine.

19. The medicine injection pen according to claim 18 , wherein the rotary encoder is configured to sense rotation of the drive screw to enable determination of the amount of the liquid medicine dispensed.

20. The medicine injection pen according to claim 19 , further comprising an electronics unit configured to determine the amount of the liquid medicine dispensed based on the sensed rotation.