Infusion pumps

1. A method of operating an infusion pump apparatus including a plunger pusher, a removable medicament cartridge having a cartridge front wall with an outer surface, a reservoir with medicament, and a plunger having a dry side and movable by the plunger pusher towards the cartridge front wall, and a housing formed from a material with a first modulus of elasticity and having a cartridge receiving area and an opening through which the removable medicament cartridge can be inserted and removed, the method comprising the step of:

after the removable medicament cartridge has been inserted into the cartridge receiving area by way of the opening in the housing through which the medicament cartridge can be inserted and removed, applying a clamping force, by applying an action force to the plunger and transferring a reaction force originating at the plunger to the outer surface of the cartridge front wall, with a clamp that clamps the reservoir between the dry side of the plunger and the outer surface of the cartridge front wall and applies a clamping displacement that adjusts incrementally as the plunger pusher advances the plunger towards the front wall, wherein the clamp includes

a chassis that applies the reaction force, the chassis being formed from a rigid material with a second modulus of elasticity that is greater than the first modulus of elasticity and having a front wall that engages the cartridge front wall, a rear wall, and first and second spaced side walls extending between the front and rear walls, and

a drive line that applies the action force, the drive line including a lead screw having first and second ends, a thrust bearing on the first end of the lead screw and that engages an inner surface of the chassis rear wall, and the plunger pusher, which is positioned over the second end of the lead screw and is movable along the lead screw.

2. A method as claimed in claim 1 , wherein the clamping displacement adjusts incrementally by 0.001 inch.

3. A method as claimed in claim 1 , wherein

the lead screw has a 0.5 mm pitch; and

the clamping displacement adjusts incrementally by 0.5 mm per revolution of the lead screw.

4. A method as claimed in claim 1 , wherein the chassis and the drive line together define a C-shaped clamp.

5. A method as claimed in claim 1 , wherein

the removable medicament cartridge defines a longitudinal axis and first and second longitudinal ends;

the plunger moves along the longitudinal axis; and

the cartridge front wall is located at the first longitudinal end.

6. A method as claimed in claim 1 , wherein the portion of the chassis that is adjacent to the cartridge front wall is in direct contact with the cartridge front wall.

7. A method as claimed in claim 1 , wherein the second modulus of elasticity is greater than 1 million psi.

8. A method as claimed in claim 1 , wherein the second modulus of elasticity is greater than 3 million psi.

9. A method as claimed in claim 1 , wherein the second modulus of elasticity is between 10 million psi and 30 million psi.