Controlling a plurality of devices
Four actuators are instructed to move to a condition indicated by a demand line 81 . Their actual conditions are indicated by four arrows. The method determines if the range 84 of actual conditions exceeds a threshold value, representing an unacceptable mismatch of actuator positions. This comparison is used to establish further demand instructions. For example, if the range is too great, and the average 82 is below the demand line 81 , the devices are instructed to move to the upper extreme position at 88 . If the average position 82 is above the demand line 81 , the devices are instructed to move to the lower end of the range, at 90. This results in the actuator positions moving together, as they also move toward the demand line 81 , reducing risks associated with actuator mismatches.
1. A method of controlling a plurality of devices to respond to a demand, in which:
(a) an initial demand instruction is established for each device, representing the device conditions required to achieve the demanded response;
(b) the actual condition achieved by each device is detected;
(c) a value representing the range of actual conditions is derived from the detected actual conditions, for comparison with a threshold value, wherein the range value is derived as the difference between the maximum and minimum values representing the actual conditions;
(i) wherein when the range value is above the threshold value, a value representing the average of the actual conditions is derived, and further demand instructions are set in dependence on the average value;
(A) wherein when the average value exceeds the average value derived from the conditions required to achieve the demanded response, the further demand instructions are set to achieve a reduced average value of the actual conditions; wherein the further demand instructions are set for at least some of the devices to achieve the minimum actual conditions of those devices; or
(B) wherein when the average value is less than the average value derived from the conditions required to achieve the demanded response, the further demand instructions are set to achieve an increased value of the actual conditions; wherein the further demand instructions are set, for at least some of the devices, to achieve the maximum actual condition of those devices;
(d) the result of the comparison is used to establish further demand instructions for independently controlling the devices; and
steps (b), (c) and (d) are repeated until the demand is fulfilled, whereby the response of the devices to the demand is coordinated until the demand is fulfilled.
2. A method according to claim 1 , wherein the devices are actuators.
3. A method according to claim 1 , wherein the devices are substantially identical.
4. A method according to claim 1 , wherein at least some of the devices are operable together to move a common component.
5. A method according to claim 1 , wherein when the range value is below the threshold value, further demand instructions are set as the initial demand instructions.
6. Apparatus for controlling a plurality of devices to respond to a demand, comprising:
(a) means operable to receive a demand and to establish an initial demand instruction for each device, representing the device conditions required to achieve the demanded response, and to pass the initial demand instruction to the respective device;
(b) detector means operable to detect the actual conditions achieved by each device;
(c) control means operable to derive a range value representing the range of actual conditions from the detected actual conditions; and to compare the range value with a threshold value; and to establish further demand instructions in dependence on the result of the comparison, and wherein the detector means and the control means are operable to repeatedly detect actual conditions and establish further instructions for independently controlling the devices, as aforesaid, whereby the response of the devices to the demand is coordinated until the demand is fulfilled, wherein the range value is derived as the difference between the maximum and minimum values of the actual conditions;
(i) wherein when the range value is above the threshold value, a value representing the average of the actual conditions is derived, and further demand instructions are set in dependence on the average value;
(A) wherein when the average value exceeds the average value derived from the conditions required to achieve the demanded response, the further demand instructions are set to achieve a reduced average value of the actual conditions; wherein the further demand instructions are set, for at least some of the devices, to achieve the maximum actual condition of those devices; or
(B) wherein when the average value is less than the average value derived from the conditions required to achieve the demanded response, the further demand instructions are set to achieve an increased average value of the actual conditions; wherein the further demand instructions are set, for at least some of the devices, to achieve the maximum actual condition of those devices.
7. Apparatus according to claim 6 , wherein the devices are actuators.
8. Apparatus according to claim 6 , wherein the devices are substantially identical.
9. Apparatus according to claim 6 , wherein at least some of the devices are operable together to move a common component.
10. Apparatus according to claim 6 , wherein when the range value is below the threshold value, further demand instructions are set as the initial demand instructions.
11. A gas turbine engine having a plurality of devices which provide, between them, a control function for the engine, the engine further comprising apparatus as defined in claim 6 , for controlling the plurality of devices.
12. An aircraft having a plurality of devices which provide, between them, a control function for the aircraft, the aircraft further comprising apparatus as defined in claim 6 , for controlling the plurality of devices.