Method for overload protection of SMA device

Patent metadata

Field	Value
Publication number	US-8972032-B2
Application number	US-79791110-A
Country	US
Kind code	B2
Filing date	Jun 10, 2010
Priority date	Jun 25, 2009
Publication date	Mar 3, 2015
Grant date	Mar 3, 2015

Abstract

A method for detecting a mechanical overload condition of an energized linear actuator to prevent commanding an activation signal to the linear actuator that may mechanically overload the linear actuator includes monitoring feedback variation of a movable element associated with the linear actuator including monitoring a present feedback signal of the movable element, monitoring a previous feedback signal of the movable element, comparing the present feedback signal and the previous feedback signal and determining the feedback variation based on the comparing. The feedback variation is compared to a feedback variation threshold. An input signal associated with the activation signal for controlling the linear actuator is monitored and the input signal compared to an input signal threshold. The electrical overload condition is detected when the feedback variation is less than the feedback variation threshold and the input signal is greater than the input signal threshold.

First claim

The invention claimed is:

1. Method for detecting a mechanical overload condition of an energized linear actuator and providing a mechanical overload protection scheme to prevent commanding an activation signal to the linear actuator that may mechanically overload the linear actuator when the mechanical overload condition is detected, comprising:
monitoring feedback variation of a movable element associated with the linear actuator comprising monitoring a present feedback signal indicating a present position of the movable element during a present activation cycle of the linear actuator, monitoring a previous feedback signal indicating a previous position of the movable element immediately before the present activation cycle is initiated whilst the linear actuator is deactivated, comparing the present feedback signal and the previous feedback signal and determining the feedback variation based on a difference between the present position and the previous position of the movable element;
comparing the feedback variation to a feedback variation threshold; and one of
if the feedback variation is greater than the feedback variation threshold, determining the mechanical overload condition does not exist and the mechanical overload protection scheme will not be provided;
only if the feedback variation is less than the feedback variation threshold:
monitoring an input signal associated with the activation signal for controlling the linear actuator,
comparing the input signal to an input signal threshold, and
detecting the mechanical overload condition and providing the mechanical overload protection scheme when the feedback variation is less than the feedback variation threshold and the input signal is greater than the input signal threshold.

2. The method of claim 1 wherein the present position corresponds to at least one of a rotary position, a rotary angle, a linear movement through the movable element and an electric resistance of the linear actuator.

3. The method of claim 1 wherein monitoring an input signal associated with the activation signal for controlling the linear actuator comprises:
monitoring a command signal indicating a preferred position of the movable element;
monitoring the present feedback signal indicating the present position of the movable element;
comparing the command signal and the present feedback signal; and
determining an error signal based on the comparing.

4. The method of claim 3 wherein comparing the input signal to an input signal threshold comprises:
comparing the error signal to an error threshold;
monitoring an overload time counter;
comparing the overload time counter to an overload time counter threshold; and
detecting the mechanical overload condition when the feedback variation is less than the feedback variation threshold, the error signal is greater than the error threshold, and the overload time counter exceeds the overload time counter threshold.

5. The method of claim 1 , wherein monitoring the input signal associated with the activation signal for controlling the linear actuator comprises:
monitoring a command signal indicating a preferred position of the movable element;
monitoring the present feedback signal indicating the present position of the movable element;
comparing the command signal to the present feedback signal;
determining an amplified signal based on applying PI control to the comparison of the command signal to the present feedback signal;
monitoring ambient temperature substantially at the linear actuator and voltage potential of an electrical energy storage device utilized for providing energizing current across the linear actuator during periods of activation responsive to the activation signal; and
determining a control signal based on the amplified signal, the ambient temperature and the voltage potential, the control signal including maximum and minimum values associated with the voltage potential and the ambient temperature.

6. The method of claim 5 wherein comparing the input signal to an input threshold comprises:
comparing the control signal to a control signal threshold;
monitoring an overload time counter;
comparing the overload time counter to an overload time counter threshold; and
detecting the mechanical overload condition when the feedback variation is less than the feedback variation threshold, the control signal is greater than the control signal threshold and the overload time counter exceeds the overload time counter threshold.

7. The method of claim 6 wherein the control signal indicates one of pulse width-modulation, current regulation and voltage regulation controlling energizing current across the linear actuator during periods of activation responsive to the activation signal.

8. The method of claim 1 wherein detecting the mechanical overload condition and providing the mechanical overload protection scheme when the feedback variation is less than the feedback variation threshold and the input signal is greater than the input signal threshold comprises immediately de-energizing the linear actuator thereby cooling the linear actuator.

9. The method of claim 8 further comprising reenergizing the linear actuator subsequent to de-energizing the linear actuator after a predetermined duration.

10. The method of claim 1 further comprising monitoring an initial delay period prior to monitoring feedback variation of a movable element associated with the linear actuator, the initial delay period sufficient to allow residual heat across the energized linear actuator to decrease thereby reducing false overload condition detection due to low feedback variation.

11. Method of claim 10 wherein the initial delay period is variably selected comprising selecting a longer initial delay period when substantially no residual heat is retained across the linear actuator prior to energizing, and selecting a shorter initial delay period when residual heat is retained across the linear actuator prior to energizing.

12. Method for detecting of a mechanical overload condition of an energized linear actuator and providing a mechanical overload protection scheme to prevent commanding an activation signal for controlling a movable element associated with the linear actuator that may mechanically overload the linear actuator when the mechanical overload condition is detected, comprising:
monitoring an overload time counter;
monitoring feedback variation of the movable element comprising:
monitoring a present position of the movable element during a present activation cycle of the linear actuator;
monitoring a previous position of the movable element immediately before the present activation cycle is initiated whilst the linear actuator is deactivated;
comparing the present position and the previous position; and
determining the feedback variation based on a difference between the present position and the previous position of the movable element;

comparing the feedback variation to a feedback variation threshold; and one of
if the feedback variation is greater than the feedback variation threshold, determining the mechanical overload condition does not exist and the mechanical overload protection scheme will not be provided;
only if the feedback variation is less than the feedback variation threshold:
monitoring an input signal based upon a preferred position of the movable element and the present position of the movable element,
comparing the input signal to a selected input signal threshold,
comparing the overload time counter to an overload time counter threshold,
detecting the mechanical overload condition when the input signal is greater than the selected input signa

Assignees

• Hao Lei
• Gao Xiujie
• Naik Sanjeev M
• Gm Global Tech Operations Inc

Inventors

• Hao Lei
• Gao Xiujie
• Naik Sanjeev M

Classifications

• H02N2/10

  producing rotary motion, e.g. rotary motors · CPC title

• H02N2/142 Primary

  Small signal circuits; Means for controlling position or derived quantities, e.g. speed, torque, starting, stopping, reversing · CPC title