Device for extracorporeal blood treatment

1. A linear actuator comprising:

a rotary electric motor,

a piston, and

an interposed device between the electric motor and the piston for transforming a rotation movement of the rotary electric motor into a linear displacement of the piston, the interposed device including,

a peripheral ramp arranged inside the piston,

a bearing configured to cooperate with the peripheral ramp,

a guide allowing the piston to guide the linear displacement,

wherein the peripheral ramp includes,

(i) a threshold located at a summit of the peripheral ramp, and

(ii) a passage configured to release the bearing from the peripheral ramp,

wherein the peripheral ramp is configured such that the piston transits from a first position in which the bearing is in the passage, to a second position in which the bearing is located on the threshold, and back to the first position, by a unidirectional rotation of the rotary electric motor, and

wherein the peripheral ramp forms a structure that is arranged on an inner surface of the piston, a circular side wall of the piston not having any openings that engage with the bearing.

2. The actuator as claimed in claim 1 , wherein the interposed device allows the piston to maintain in an equilibrium position when the bearing rests against the threshold without a need to power the rotary electric motor.

3. The actuator as claimed in claim 1 , further comprising:

compression device that exert a force against the piston in the main axis of a rotor of the rotary electric motor.

4. The actuator as claimed in claim 1 , wherein the peripheral ramp is configured to allow the piston to maintain the first position and the second position without a need to power the rotary electric motor.

5. The actuator as claimed in claim 1 , further comprising:

compression device that exert a force against the piston in the main axis of a rotor of the rotary electric motor,

wherein, in the first position, the compression device forces the piston to a position farther away from the rotary electric motor than the second position.

6. The actuator as claimed in claim 5 , wherein, in the second position, the interposed device forces the piston to a position nearer the rotary electric motor than to the first position.

7. The actuator as claimed in claim 1 , wherein the passage extends from the summit of the peripheral ramp and/or in which the passage is juxtaposed to the threshold.

8. The actuator as claimed in claim 1 , wherein the passage extends below a lower part of the ramp.

9. The actuator as claimed in claim 1 , wherein the bearing includes a shaft fixed perpendicularly to the a rotor of the rotary electric motor.

10. The actuator as claimed in claim 1 , further comprising:

a position sensor for the piston.

11. The actuator as claimed in claim 1 , wherein the passage is arranged in a same axis as an axis of the linear displacement of the piston.

12. An actuation system comprising:

a linear actuator as described in claim 1 ,

a controller having a processor for controlling the linear actuator, and

a power supply for supplying power to the linear actuator,

wherein the controller is configured to displace a piston from a second position to a first position.

13. The actuation system as claimed in claim 12 , wherein the power supply includes at least one of an external power supply and an energy storage, the energy storage configured to be used when the external power supply is no longer operative or is inadequate.

14. A valve system actuable by an actuator according to claim 1 .

15. A linear actuator comprising:

a rotary electric motor;

a piston having a ramp and a passage;

a shaft rotatably connected to the rotary electric motor, the shaft having a transverse shaft configured to engage with the ramp of the piston; and

a spring urging against the piston and the rotary electric motor,

wherein the ramp and the passage are configured such that the piston moves linearly along an rotation axis of the rotary electric motor from a first position in which the transverse shaft is in the passage, to a second position in which the transverse shaft is on the ramp, and back to the first position in which the transverse shaft is in the passage, by a unidirectional rotation of the rotary electric motor, and

wherein the ramp further includes a threshold, wherein the threshold includes a planar portion and a depression, the depression is configured to hold the transverse shaft at its location at the planar portion when the rotary electric motor is not rotating.

16. A linear actuator comprising:

a rotary electric motor;

a piston having a circular side wall, a curved ramp arranged on the side wall to extend along a portion of a circumference of the side wall, a discontinued portion of the curved ramp forming a passage;

a shaft rotatably connected to the rotary electric motor, the shaft having a transverse shaft configured to engage with the curved ramp of the piston and configured to pass through the passage; and

a spring urging against the piston and the rotary electric motor,

wherein, along a circular direction, the passage is arranged adjacent to a summit of the curved ramp and adjacent to a bottom of the curved ramp,

wherein the curved ramp and the passage form a continuous structure that is configured to guide and urge against the transverse shaft during a continuous unidirectional rotation provided by the rotary electric motor for reciprocating the shaft, and

wherein the curved ramp forms a structure that is arranged on an inner surface of the piston, a circular side wall of the piston not having any openings that engage with the transverse shaft.

17. The linear actuator according to claim 16 , wherein the curved ramp includes a plurality of ramps, and the passage includes a plurality of passages, and

wherein, along the circular direction, each passage is arranged adjacent to a summit of a curved ramp and adjacent to a bottom of another curved ramp.

18. The linear actuator according to claim 16 , wherein the ramp further includes a threshold at the summit,

wherein the threshold is configured to hold the transverse shaft at its location when the rotary electric motor is not rotating.