Method for detecting the position of an actuator element
Disclosed is detecting the position of an actuator element of an actuator arrangement, having at least one actuator element movable in two opposing directions by two adjustment elements. The adjustment elements electrically connected via only one two-wire connection to a control unit comprise electrically controllable shape memory alloy wires. A resistance measurement circuit formed in the control unit periodically records the resistance values of the two adjustment elements. At an energization time of a currently actuated adjustment element, the resistance value of the adjustment element and, in a subsequent pause in energization, the resistance value of another adjustment element is determined and stored. The differential value of the two resistance values is compared with pairs of values which are stored in a table and describe a correlation between the resistance differential value and a position of the adjustment element, to determine the position of the actuator element.
1. A method for detecting a position of an actuator element of an actuator arrangement, comprising
at least one actuator element movable in two opposing directions by two adjustment elements, wherein the adjustment elements are formed with electrically controllable shape memory alloy wires, and
a control unit electrically connected to the adjustment elements,
wherein the control unit has a controllable control circuit which is configured to connect one or the other adjustment element as required to a voltage source in a pulse width-modulated manner, and
wherein only one two-wire connection is formed between the control unit and the adjustment elements, the method comprising:
periodically recording by a resistance measurement circuit formed in the control unit the resistance values of the two adjustment elements,
at an energization time of a currently actuated adjustment element, determining and storing the resistance value of the adjustment element and, in a subsequent pause in energization, the resistance value of a respective other adjustment element,
forming and comparing a differential value of the two determined resistance values with pairs of values which are stored in a table and describe a correlation between the resistance differential value and a position of an adjustment element, and determining the position of the actuator element therefrom.
2. The method as claimed in claim 1 , wherein the measurement of the resistance of the adjustment element actuated at measurement time is carried out with the same resistance measurement circuit as the measurement of the resistance of the respective other adjustment element.
3. The method as claimed in claim 1 , wherein each of the adjustment elements is connected to the control circuit via a diode, wherein diodes are installed with different polarizations and thermally coupled, so that their resistance values virtually cancel each other out during the formation of the differential value.
4. The method as claimed in one of claim 1 , wherein a current measurement circuit of the resistance measurement circuit is formed with at least one switchable current measurement resistance path, so that different current measurement resistances can be set, to determine resistance characteristics of feed lines from the resistance values thus determined.
5. The method as claimed in claim 1 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
6. The method as claimed in claim 2 , wherein each of the adjustment elements is connected to the control circuit via a diode, wherein diodes are installed with different polarizations and thermally coupled, so that their resistance values virtually cancel each other out during the formation of the differential value.
7. The method as claimed in one of claim 6 , wherein a current measurement circuit of the resistance measurement circuit is formed with at least one switchable current measurement resistance path, so that different current measurement resistances can be set, to determine resistance characteristics of feed lines and the diodes from the resistance values thus determined.
8. The method as claimed in claim 7 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
9. The method as claimed in claim 6 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
10. The method as claimed in one of claim 2 , wherein a current measurement circuit of the resistance measurement circuit is formed with at least one switchable current measurement resistance path, so that different current measurement resistances can be set, to determine resistance characteristics of feed lines from the resistance values thus determined.
11. The method as claimed in claim 10 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
12. The method as claimed in claim 2 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
13. The method as claimed in one of claim 3 , wherein a current measurement circuit of the resistance measurement circuit is formed with at least one switchable current measurement resistance path, so that different current measurement resistances can be set, to determine resistance characteristics of feed lines and the diodes from the resistance values thus determined.
14. The method as claimed in claim 13 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
15. The method as claimed in claim 3 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.
16. The method as claimed in claim 4 , wherein an end position of the adjustment elements is detected and a resistance ratio measured immediately before reaching the end position is assigned to an end position and stored appropriately in the table.