Method of controlling an automotive mirror

• US 5,952,802 A
• Filed: 12/08/1997
• Issued: 09/14/1999
• Est. Priority Date: 12/08/1997
• Status: Expired due to Term

• Current Assignee: Delphi Technologies, Inc. (BorgWarner Incorporated)
• Original Assignee: Delco Electronics Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Pimley, John Thomas
• Primary Examiner(s): MARTIN, DAVID S
• Application Number:
  US08/986,344
• Time in Patent Office: 645 Days
• Field of Search: 318/280-300, 318/466-470, 359/871-883, 248/476-487
• US Class Current: 318/468
• CPC Class Codes: B60L 1/00 Supplying electric power to auxiliary equipment of vehicles circuit arrangements for charging batteries H02J7/00
• CPC Class Codes: G05B 19/351 the positional error is used to control continuously the servomotor according to its magnitude
• CPC Class Codes: G05B 2219/34048 Fourier transformation, analysis, fft
• CPC Class Codes: G05B 2219/37622 Detect collision, blocking, stall by change, lag in position
• CPC Class Codes: G05B 2219/37632 By measuring current, load of motor
• CPC Class Codes: G05B 2219/42289 Avoid overload servo motor, actuator limit servo torque
• CPC Class Codes: G05B 2219/45185 Auto mirror

Abstract

A mirror motor is coupled to the mirror by a ratchet coupling. A feedback signal representing the drive current of the mirror motor is digitally sampled and analyzed by a type of Fourier transform, preferably a discrete cosine transform, to determine the low frequency components of a current pulse which arises when the mirror reaches a stop at its end of travel and the ratchet operation begins to occur. A fundamental component is due to the pulse rise. Motor current is terminated if that component exceeds a threshold for a set time. A harmonic component is due to the ratchet action and pulse fall. Motor current is terminated if the harmonic element reaches another threshold.

Claims

1. In an automotive mirror assembly including a motor for moving a mirror through a range bounded by limits in response to switch actuation and a ratchet coupling to permit the motor to continue operating when the mirror reaches a limit whereby current to the motor increases when a limit is reached and then decreases when a ratchet event occurs to thereby define a current pulse, a method of stopping current to the mirror when such a limit is reached comprising the steps of:

developing a feedback signal corresponding to motor current;

analyzing the feedback signal for a low frequency component wherein the amplitude of the low frequency component increases when the current pulse occurs; and

stopping motor operation when the low frequency component exceeds a threshold value.

2. The method as defined in claim 1 wherein the step of analyzing the feedback signal comprises:

digitally sampling the feedback signal; and

applying a Fourier transform to the digital samples to determine the magnitude of the low frequency component.

3. The method as defined in claim 2 wherein the step of applying a Fourier transform comprises applying a discrete cosine transform.

4. The method as defined in claim 1 wherein:

the ratchet operation causes signal pulsations at a given frequency if motor current were continued when the mirror reaches a limit; and

the step of analyzing the feedback signal for a low frequency component comprises analyzing for a component near the given frequency.

5. The method as defined in claim 1 wherein:

the step of analyzing the feedback signal includes analyzing the feedback signal for a first low frequency component;

analyzing the feedback signal for a second component at a harmonic of the first low frequency; and

the step of stopping motor operation includes stopping motor operation when the first component exceeds a threshold value which is sustained for a minimum period or when the second component exceeds a second threshold value.