Liquid medicine injection device

1. A liquid medicine injection device comprising:

a liquid medicine storage unit including:

a cylinder including a space configured to store liquid medicine therein,

a discharge hole connected to the space, and

a piston arranged inside the cylinder and configured to move toward the discharge hole depending on discharge of the liquid medicine when present;

a first electrode on an outer surface of the cylinder;

a second electrode on the outer surface of the cylinder, the second electrode facing the first electrode with the piston therebetween;

a circuit unit including a substrate electrically connected to the first electrode and the second electrode;

a case configured to receive the liquid medicine storage unit and the circuit unit an inner frame inside the case; and

a conductive member curved along an outer surface of the liquid medicine storage unit

wherein a sum of widths of the first and second electrodes is equal to or greater than 0.85 times an outer circumference of the cylinder,

wherein the first electrode serves as a ground,

wherein the second electrode is configured to receive a pulse signal applied by the circuit unit,

wherein the circuit unit is configured to calculate displacement information of the piston based on a capacitance change between the first electrode and the second electrode due to a difference between pulse response signals, and to thereby calculate an actual injected amount of the liquid medicine based on the displacement information of the piston,

wherein the conductive member is pressurized by the inner frame to stably maintain a contact with the second electrode, and

wherein an elastic member is arranged between the inner frame and the case.

2. The liquid medicine injection device of claim 1 , wherein the first electrode and the second electrode extend in a direction that intersects with a liquid surface of the liquid medicine that contacts the piston.

3. The liquid medicine injection device of claim 1 , wherein one end of the first electrode is adjacent to the discharge hole, and another end of the first electrode extends away from the discharge hole, and

one end of the second electrode is adjacent to the discharge hole, and another end of the second electrode extends away from the discharge hole.

4. The liquid medicine injection device of claim 1 , further comprising a pump connected to the discharge hole.

5. The liquid medicine injection device of claim 1 , wherein the case includes first ribs arranged in a lengthwise direction of the liquid medicine storage unit, and the inner frame includes second ribs facing the first ribs of the case with the liquid medicine storage unit between the first ribs and the second ribs.

6. The liquid medicine injection device of claim 1 ,

wherein the conductive member connects one of the first electrode and the second electrode to the circuit unit.

7. The liquid medicine injection device of claim 6 , wherein the inner frame is configured to regulate a location of the conductive member.