Method for operating a valve having a stepper motor as actuator

1. A method comprising:

operating a valve, wherein the valve has at least one valve seat, a valve plunger and a stepper motor for moving the valve plunger with respect to the or each valve seat, namely for moving the valve plunger from a first position into a second position in which the valve plunger is pressed against a valve seat and for compressing a flexible element assigned to the valve plunger in said second position, whereby the stepper motor is driven in such a way that the stepper motor provides a defined number of steps (N TOTAL ) in order to move the valve plunger from the first position into the second position and in order to compress the flexible element thereby providing tightness between the valve plunger and the valve seat, wherein operating the valve comprises driving the stepper motor in such a way that:

for a first number of steps (N 1 ) of said defined number of steps (N TOTAL ), the stepper motor is operated at a first current level (I 1 );

for a subsequent second number (N 2 ) of steps of said defined number of steps (N TOTAL ), the stepper motor is operated at a second current level (I 2 ) being lower than the first current level (I 1 ); and

for a subsequent third number of steps (N 3 ) of said defined number of steps (N TOTAL ), the stepper motor is operated at a third current (I 3 ) level being higher than the second current level (I 2 ).

2. The method of claim 1 , wherein said third electrical current (I 3 ) level is higher than said first current level (I 1 ).

3. The method of claim 1 , wherein said third current (I 3 ) level is lower than said first current level (I 1 ).

4. The method of claim 1 , wherein said third current (I 3 ) level corresponds to said first current level (I 1 ).

5. The method of claim 1 , wherein said defined number of steps (N TOTAL ) comprises:

a) steps needed to travel the valve plunger along a nominal distance between the first position and the second position;

b) steps needed to compensate mechanical tolerances of said nominal distance;

c) steps needed to compress the flexible element assigned to the valve plunger in the second position of the same thereby providing tightness between the valve plunger and the valve seat; and

d) steps needed to decompress a flexible element assigned to the valve plunger in case said valve plunger is pressed against a valve seat in the first position.

6. The method of claim 5 , wherein said first number of steps (N 1 ) is in a range between a minimum first number of steps and a maximum first number of steps, wherein

a) said maximum first number of steps comprises:

a1) steps needed to travel the valve plunger along the nominal distance between the first and the second position;

a2) steps needed to compensate the mechanical tolerances of said nominal distance;

a3) steps needed to decompress the respective flexible element assigned to the valve plunger in case said valve plunger is pressed against a valve seat at the first position;

b) said minimum first number of steps comprises:

b1) steps needed to travel the valve plunger from the first position into a transition position in which forces acting on the valve plunger against the valve plunger movement are lower than the stepper motor force at the second current level; and

b2) steps needed to decompress the respective flexible element assigned to the valve plunger in case said valve plunger is pressed against a valve seat at the first position.

7. The method of claim 5 , wherein said third number of steps (N 3 ) is determined from the steps needed to compress the respective flexible element assigned to the valve plunger in the second position of the same thereby providing tightness between the valve plunger and the valve seat and from the characteristics of the stepper motor.

8. The method of claim 7 , wherein said second number of steps (N 2 ) is determined from the defined number of steps (N TOTAL ), the first number of steps (N 1 ) and the third number of steps (N 3 ) using the formula:

N 2 =N TOTAL −N 1 −N 3 .

9. The method of claim 8 , wherein said second number of steps (N 2 ) is determined in such a way that the same is optimized.

10. The method of claim 1 , wherein the first current level (I 1 ) is determined in such a way that the stepper motor force at the first current is higher than forces acting against the valve plunger movement in the first position.

11. The method of claim 1 , wherein the second current level (I 2 ) is determined in such a way that the stepper motor force at the second current is higher than forces acting against the valve plunger movement in an transition position of the valve plunger between said first position and said second position.

12. The method of claim 1 , wherein the third current level (I 3 ) is determined in such a way that the stepper motor force at the third current is higher than forces acting against the valve plunger movement in the second position.

13. A method comprising:

operating a valve, wherein the valve has at least one valve seat, a valve plunger and a stepper motor for moving the valve plunger with respect to the or each valve seat, namely for moving the valve plunger from a first position into a second position in which the valve plunger is pressed against a valve seat and for compressing a flexible element assigned to the valve plunger in said second position, wherein the valve plunger has a range of motion from the first position to the second position, wherein operating the valve comprises driving the stepper motor in such a way that:

for a first portion of the range of the range of motion of the valve plunger toward the second position, the stepper motor is operated at a first current level (I 1 );

for a subsequent portion of the range of motion of the valve plunger toward the second position, the stepper motor is operated at a second current level (I 2 ) that is lower than the first current level (I 1 ); and

for a subsequent portion of the range of motion of the valve plunger toward the second position, the stepper motor is operated at a third current (I 3 ) level that is higher than the second current level (I 2 ).

14. The method of claim 13 , wherein said third current (I 3 ) level is higher than said first current level (I 1 ).

15. The method of claim 13 , wherein said third current (I 3 ) level is lower than said first current level (I 1 ).

16. The method of claim 13 , wherein said third current (I 3 ) level corresponds to said first current level (I 1 ).

17. A driver comprising:

the driver driving a stepper motor of a valve, the valve having a valve seat and a valve plunger, wherein the stepper motor can move the valve plunger from a first position to a second position in which the valve plunger addresses the valve seat and compresses a flexible element assigned to the valve plunger in said second position, the valve plunger having a range of motion from the first position to the second position, the driver is programmed to:

drive the stepper motor at a first current level (I 1 ) to move the valve plunger along a first portion of the range of motion of the valve plunger toward the second position; and then

drive the stepper motor at a second current level (I 2 ) to move the valve plunger along a second portion of the range of motion of the valve plunger further toward the second position, wherein the second current level (I 2 ) is less than the first current level (I 1 ); and then

drive the stepper motor at a third current level (I 3 ) to move the valve plunger along a third portion of the range of motion of the valve plunger even further toward the second position wherein the second current level (I 2 ) is less than the third current level (I 3 ).

18. The driver of claim 17 , wherein the third current level (I 3 ) is higher than the first current level (I 1 ).

19. The driver of claim 17 , wherein the third current level (I 3 ) corresponds to the first current level (I 1 ).