Electricity: motive power systems – Motor-reversing
Reexamination Certificate
2001-07-23
2003-04-08
Hsieh, Shih-Yung (Department: 2837)
Electricity: motive power systems
Motor-reversing
C318S281000, C318S283000, C318S254100, C318S290000, C318S432000, C318S434000, C318S445000, C318S466000, C318S266000
Reexamination Certificate
active
06545439
ABSTRACT:
PRIORITY CLAIM
This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Applications No. 198 55 996.8, filed on Dec. 4, 1998, and No. 198 49 430.0, filed on Oct. 27, 1998, the entire disclosures of which are incorporated herein by reference through the parent case U.S. Ser. No. 09/433,191 the priority of which is also claimed under 35 USC 120.
FIELD OF THE INVENTION
The invention relates to monitoring a part driven by an electric motor. The part may, for example, be a motor driven vehicle window or a tool. In many instances it is desirable to provide information whether a part driven by an electric motor is moving, if so in which direction the part is moving, and which position has been reached. In the case of a vehicle window, especially a rear window, the respective information is used for controlling an electrically driven window lifter to provide an anti-jamming function. The invention also relates to a circuit arrangement for carrying out such monitoring.
BACKGROUND INFORMATION
A group of known devices for detecting the position and the direction of rotation of a power driven part makes use of 2-channel sensor systems which provide signals that are phase-shifted and evaluated in an electronic unit. The sensors used can operate in accordance with different physical principles, e.g. electrical, magnetic, inductive, and optical.
For example, the electric motor drive disclosed in EP 0,359,853 Al makes use of two Hall sensors displaced at an angle to each other and allocated to a ring magnet attached to an armature shaft. When the armature shaft rotates, the two Hall sensors generate two correspondingly phase-shifted signals that are digitized and then evaluated in an electronic unit. After processing, the respective signals represent the only basis for identifying the direction of rotation. Since the corresponding signal pattern is characteristically different for each direction of rotation, the counted pulses can be allocated unequivocally to a definite direction of rotation.
However, the known technical solution mentioned above requires no fewer than two sensor channels, whereby it needs a correspondingly high number of components and conductors for its implementation. Also, the construction space to be provided for the installation can have a negative effect, especially when using small drive units with integrated electronics.
When only one such sensor is used, only one signal exists which is proportional to the number of the revolutions made by the motor and which is then allocated to one direction of motion of the driven part in accordance with the polarity of the motor drive voltage. The signal must be added to or subtracted from the previous position, whichever applies. Signal flanks that occur after the motor drive voltage has been switched off cannot be assigned.
Japanese Patent Publication JP 63-304307 A discloses a velocity control for a motor drive wherein the phase difference between a velocity control pulse and an incremental pulse of a length measuring laser device is continuously acquired. The control circuit used in said Japanese disclosure further includes a pulse converter and a mechanism for transforming the rotary motion of the motor into a linear motion. An up or a down count signal is generated in a transformer from the measurement of the linear motion in accordance with the direction of the positioning command.
The teaching described above does permit a very accurate control of the adjustment velocity of a driven part but it is not suitable. for establishing at the same time its position. Further measures must be provided for this purpose.
Furthermore, German Patent Publication DE 43 15 637 C2 discloses a method for detecting the position and direction of rotation of a drive. Not only the signal flanks of the digitized sensor signal but also the status of the drive is taken into account in that in the event of a direction reversal of the rotation the signal flanks are allocated in accordance with an overshoot time that is limited by fixed time thresholds. On principle, these time thresholds can be determined empirically or calculated mathematically. Adaptation to widely varying system conditions is not possible because the variation of the motor current over a period of time when the direction of rotation reverses, varies by several orders of magnitude. In particular, a control with fixed thresholds is always limited solely to a specific load situation, which is essentially determined by the external moment to be overcome. A current rise due, for instance, to a window pane freezing or jamming does lead to deviations. In motor vehicles, the operating supply voltage can drop quite considerably if the battery is about dead and other electrical power using elements are also being operated. If the electric motor is used very frequently, as is the case, for example, in actuating drives on industrial machine tools, the electrical parameters of the motor also change because of the warming effect. If the time thresholds were to be placed so far apart that all these cases could still be detected, then a particularly smooth running actuator arrangement would perform several revolutions in the opposite direction before being detected by the threshold. 0,603,506 A2 describes a method for determining with a position encoder the position of a part driven in two directions by an electric motor in motor vehicles, wherein a change in the movement direction is to be identified according to the duration of a break period between two pulses from the position encoder.
Errors can occur in such a method due to a rapid change of direction or if the motion of the part is non-uniform and does not take place in a single step.
The applicant's DE 197 33 581 C1, which is not a prior publication, describes a method for measuring the motor current at the latest at the time of driving switching devices for the purpose of switching over the motor voltage from one direction of motion to the opposite direction. On changing the polarity of the externally supplied motor drive voltage, the motor current displays a characteristic curve due to the overshoot as a result of the mass inertia of the motor and the part moved by it, for instance the window pane and its mechanical drive transmission. A voltage that opposes this reversal of direction of motion is induced and superimposed on the external motor drive voltage and causes the characteristic curve of the motor current from which the actual moment in time for the reversal of direction of motion is derived as a function of time, which is considerably later than the time at which the motor drive voltage changes over. The signal flanks of the sensor signal are added to or subtracted from the actual position by the signal evaluation according to the actual direction of motion. This electromechanical behavior of d.c. motors is described by means of so-called motor equations.
In a series of tests it has been found, however, that because of other effects, deviations continue to occur in the position determination. These deviations are not negligible and cumulate over the life of a vehicle.
A substantial cause for the above mentioned deviations that continue to occur in the position determination are signal flanks that arise even after switching off the motor drive voltage. Particularly, after stopping the motor, an overshoot or run-out of the motor occurs because of inertia, which has been neglected heretofore. Such motor run-out can, however, continue for a duration corresponding to several motor revolutions causing respective signal flanks which are not evaluated or which are incorrectly evaluated. Further, this fault is not always compensated by a corresponding run-out in the opposite direction of motion.
The disclosure of Japanese Patent Publication JP 07-222477 A, published on Aug. 18, 1995 has recognized that each of these changes in the motor rotation direction results in a voltage induction in accordance with the generator principle. These deviations, however, occur when the motor is already switched
Kaeufl Georg
Kessler Erwin
Liepold Erich
Pollersbeck Werner
Roedel Reinhold
Daimler-Chrysler AG
Fasse W. F.
Fasse W. G.
Smith Tyrone
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