Electric jack ground contact detection method and device

1. An electric jack ground contact detection device for detecting ground contact of an electric motor-driven jack as the jack is being extended to adjust the attitude of a mobile platform, the device comprising:

a controller configured to:

monitor the electrical power draw of an electric motor-driven jack while the jack is being extended for use in adjusting the attitude of a mobile platform;

recognize jack ground contact when the monitored power draw value exceeds a ground contact power draw value consistent with jack ground contact; and

calculate the ground contact power draw value as equaling the sum of a dynamically-adjusted threshold power draw value associated with jack extension before ground contact and a power draw increase value equaling an amount of additional power that the jack is known to draw as a result of jack ground contact; and

a jack motor power draw sensor connected to the controller and configured to sense electrical power drawn by a jack motor and to transmit a corresponding jack motor power draw feedback signal to the controller.

2. An electric jack ground contact detection device as defined in claim 1 in which the controller is further configured to calculate the ground contact power draw value as equaling the sum of the dynamically-adjusted threshold power draw value and a power draw increase value representing the smallest amount of additional power that the jack is known to draw as a result of jack ground contact.

3. An electric jack ground contact detection device as defined in claim 2 in which the controller is further configured to dynamically adjust the threshold power draw value to compensate for changes in jack motor power draw that occur over time.

4. An electric jack ground contact detection device as defined in claim 2 in which the controller is programmed to dynamically adjust the threshold power draw value from a previously-measured no-load power draw value.

5. An electric jack ground contact detection device for detecting ground contact of an electric motor-driven jack as the jack is being extended to adjust the attitude of a mobile platform, the device comprising:

a controller configured to monitor the electrical power draw of an electric motor-driven jack while the jack is being extended for use in adjusting the attitude of a mobile platform;

the controller being further configured to recognize jack ground contact only after the monitored power draw value has exceeded a ground contact power draw value consistent with jack ground contact for a predetermined period of time.

6. An electric jack ground contact detection device as defined in claim 5 in which the predetermined period of time is set long enough to encompass an in-rush period of a jack motor whose power draw the controller is monitoring.

7. A method for detecting ground contact of an electric motor-driven jack as the jack is being extended to adjust the attitude of a mobile platform, the method including the steps of:

providing an electric motor-driven jack on a mobile platform;

predetermining and storing a ground contact power draw value known to be generally equal to the power draw of the jack once the jack has contacted the ground while extending to adjust the attitude of the platform;

monitoring a present electrical power draw value of the jack while the jack is extending to adjust the attitude of the mobile platform;

comparing the present jack power draw value to the stored ground contact power draw value while the jack is extending;

recognizing ground contact of the jack as occurring when the present jack power draw value equals or exceeds the stored ground contact power draw value; and

calculating the stored ground contact power draw value by predetermining a threshold power draw value of the electric jack motor known to result from extension of the jack without encountering an obstruction, predetermining a power draw increase value of the jack known to result from ground contact of the jack, and adding the power draw increase value to the threshold power draw value.

8. The method of claim 7 in which the step of monitoring a present electrical power draw value of the jack includes:

measuring the DC voltage driving the jack;

measuring the current draw of the jack; and

calculating the power draw of the motor as the product of the DC voltage driving the jack and the current draw of the jack.

9. The method of claim 7 in which the step of monitoring a present electrical power draw value of the jack includes:

filtering the DC voltage measurement into a stable RMS value; and

filtering the current draw measurement into a stable RMS value.

10. The method of claim 7 in which the step of monitoring a present electrical power draw value of the jack includes filtering the power draw into a stable RMS value.

11. The method of claim 7 in which the step of monitoring a present electrical power draw value of the jack includes:

determining and storing a motor current in-rush period; and

ignoring the measured power value during the motor in-rush period.

12. The method of claim 7 in which the step of recognizing ground contact of the jack includes:

resetting a debounce confirmation timer value to zero if the present jack power draw value is less than the sum of the threshold power draw value and the power draw increase; and

incrementing the debounce confirmation timer value by an appropriate time unit if the present jack power draw value is greater than the sum of the threshold power draw value and the power draw increase.

13. The method of claim 7 in which the step of recognizing ground contact of the jack includes:

determining a motor load confirmation debounce period; and

determining that jack ground contact has occurred in response to:

a present jack power draw value that exceeds the sum of the threshold power draw value and the power draw increase value, and

a debounce confirmation timer value that exceeds the motor load confirmation debounce period.

14. The method of claim 7 in which the step of calculating the stored ground contact power draw value includes:

dynamically updating the threshold power draw value by:

re-measuring the power draw of the jack as it is extending to adjust the attitude of the mobile platform before ground contact, and

resetting the threshold power draw value to equal the present jack power draw value; and

adding the dynamically updated threshold power draw value to the stored power draw increase value.

15. The method of claim 7 in which the step of calculating the stored ground contact power draw value includes predetermining a minimum power draw increase of the jack known to result from ground contact of the jack.