Electricity: motive power systems – Motor-reversing – Armature or primary circuit control
Reexamination Certificate
1999-07-01
2001-07-17
Ip, Paul (Department: 2837)
Electricity: motive power systems
Motor-reversing
Armature or primary circuit control
C318S254100, C318S608000, C388S907200, C388S907500
Reexamination Certificate
active
06262546
ABSTRACT:
TECHNICAL FIELD
This invention relates to circuitry for determining the position of a motor driven actuator by identifying and counting motor commutation pulses.
BACKGROUND OF THE INVENTION
It is frequently desired, either for control or diagnostic purposes, to detect the position of a motor driven actuator, such as a movable door in an automotive air conditioning duct. In applications where the actuator is driven by a brush-type DC motor, the actuator position may be reliably and inexpensively determined by detecting and counting pulses in the motor current caused by the periodic commutation of motor current by the motor brushes. In general, the pulses are extracted by filtering, and compared to a threshold to distinguish commutation pulses from noise pulses. When a commutation pulse is detected, a one shot is triggered to produce a logic level pulse, and the one shot pulses are counted to provide an output corresponding to the actuator position.
Several different pulse detection circuits have been proposed. In one such circuit, described in U.S. Pat. No. 5,132,602, a resistive shunt is connected in a ground path of the motor drive circuit, and the voltage across the shunt is capacitively coupled to the filter circuit. In another circuit, described in U.S. Pat. No. 5,514,977, a resistive shunt is connected in series with the motor, and the voltage at a node between the motor and shunt is capacitively coupled to the filter circuit. In still another circuit, described in co-pending U.S. patent application Ser. No. 09/249,339, filed Feb. 12, 1999, a high impedance circuit connected across the motor controls the current in a sense resistor in proportion to the motor current, and the sense resistor voltage is provided as an input to the filter circuit. Alternatively, the motor voltage itself may be capacitively coupled to the filter circuit, as also described in the co-pending U.S. patent application Ser. No. 09/249,339.
A problem experienced in each of the above-described circuits concerns reliably distinguishing commutation pulses from noise pulses. The problem occurs particularly with those circuits which are designed to detect commutation pulses both during motor running and motor braking or coasting, because the pulse amplitudes are much higher during running than during braking or coasting. For example, the commutation pulse amplitude during motor running may be 50 mV or more, while the amplitude during motor braking or coasting may be as small as 14 mV. To detect all commutation pulses, the comparator circuitry is generally designed with a detection threshold slightly lower than the smallest expected pulse, say 12 mV. However, the susceptibility to noise increases as the detection threshold decreases, resulting in an increased likelihood of erroneous pulse detection. What is needed is a simple detection circuit that is insensitive to noise pulses, but will reliably detect all commutation pulses.
SUMMARY OF THE INVENTION
The present invention is directed to an improved motor commutation pulse detection circuit for comparing a filtered motor current signal to a threshold value, where the circuit is responsive to the actual or expected amplitude of the commutation pulses for adjusting the motor current signal or the threshold value so that the compared threshold value is substantially equal in amplitude to minimum amplitude commutation pulses in the compared motor current signal. In this way, all of the commutation pulses can be reliably detected, and the likelihood of mistaking a noise pulse for a commutation pulse is dramatically reduced.
According to a first embodiment, the threshold is varied in accordance with the average current flowing through the motor at the time of the commutation event. In the illustrated embodiment, this is achieved by filtering out the low frequency component of the commutation signal, summing it with a minimum threshold value, and applying a gain factor to the sum to form the variable threshold with which the high frequency component of the commutation signal is compared.
According to a second embodiment, the threshold is effectively switched between a high value and a low value depending on the mode of operation of the motor. A run time detection threshold is activated during motor running periods, while a brake/coast detection threshold is activated during motor braking and coasting. The run time detection threshold is set to a relatively high value to detect the relatively high amplitude commutation pulses that occur during motor running, while the brake/coast detection threshold is set to a relatively low value to detect the relatively low amplitude commutation pulses that occur during motor braking and coasting. In the illustrated embodiment, this is achieved with a single comparator and an attenuation circuit that attenuates the commutation signal by a predetermined factor during motor running periods.
REFERENCES:
patent: 5045766 (1991-09-01), Vermersch
patent: 5132602 (1992-07-01), Jorgensen et al.
patent: 5514977 (1996-05-01), Agiman
patent: 5574344 (1996-11-01), Matsuoka et al.
patent: 5796231 (1998-08-01), Kyodo
patent: 5798624 (1998-08-01), Wilke et al.
patent: 5986427 (1999-11-01), Tranquilla
patent: 6078154 (2000-06-01), Manlove et al.
Draves Kenneth George
Werking Paul M.
Delphi Technologies Inc.
Funke Jimmy L.
Ip Paul
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