Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-08-03
2001-04-24
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S165000, C324S166000, C324S177000, C310S06800R, C318S466000
Reexamination Certificate
active
06222362
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for detecting the position and the direction of motion of a movably mounted part that can be used in particular for the externally powered adjustment of closing parts in motor vehicles, e.g. on an electrically driven window lifter with an anti-jamming function.
Known devices for the detection of position and direction of rotation make use of two-channel sensor systems whose signals are phase-shifted and evaluated in an electronic unit. The sensors used can operate in accordance with very different physical principles (e.g. electrical, magnetic, inductive, optical).
For example, the electric motor drive specified in EP 0 359 853 A1 makes use of two Hall sensors displaced at an angle to each other and allocated to a ring magnet attached to the armature shaft. When the armature shaft rotates, the Hall sensor generates two correspondingly phase-shifted signals that are digitized and then evaluated in an electronic unit and thereafter represent the only foundation for identifying the direction of rotation. Since the corresponding signal pattern is characteristic (different) for each direction of rotation, the count pulses can equally be uniquely assigned to a direction of rotation.
Because the known technical solution requires no fewer than two sensor channels, however, it needs a correspondingly high number of components and conductors for its implementation. Also, the construction space is to be kept free for it can have a negative effect, especially when using small drive units with integrated electronics.
From JP 63-30 43 07 A, a velocity control for a motor drive is known where the phase difference between a velocity control pulse and the incremental pulse of a laser length measuring device is continuously acquired. The control loop used also has a pulse converter and a mechanism for transforming the rotary motion of the motor into a linear motion. An up or a down signal is generated in a transformer from the measurement of the linear motion in accordance with the direction of the positioning command.
The solution described does indeed permit very accurate control of the adjustment velocity of an object but it is not suitable for establishing at the same time its position. Further measures must be provided for this purpose.
Furthermore, from DE 43 15 637 C2, a method for detecting the position and direction of rotation is known, where not only the signal edges of the digitized sensor signal but also the status of the drive is allowed for in that in the event of reversal of the direction of rotation the signal edges are assigned in accordance with an overshoot time that is limited by fixed time thresholds which can be determined empirically or calculated mathematically. Adaptation to the widely varying system conditions is not possible because the variation of the motor current over a period of time while the direction of rotation reverses varies by several orders of magnitude. In particular, a control with fixed thresholds is always limited only to a specific load case which is essentially determined by the mass moment of inertia to be overcome. A rise due, for instance, to a window pane freezing or jamming does lead to deviations. In motor vehicles, the operating supply voltage can certainly drop considerably if the battery is low and other load elements are also being operated. If the motor is used very frequently, as for example in the case of 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 measured, then a particularly smooth running actuator arrangement would perform several revolutions in the opposite direction before being detected by the threshold.
EP 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, where a change in 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 rapid change of direction or if the motion of the part is non-uniform and does not take place in step form in a single step.
It is also known that the behavior of d.c. motors can be described by means of an electromechanical motor state model based on the motor equations. The motor equation U
q
(t)=c
2
·&PHgr;·n(t), also known as generator equation, and the motor equation M
m
(t)=c
1
·&PHgr;·I
M
(t) as well as the electrical relationship
U
q
(
t
)
=
U
M
(
t
)
-
I
M
(
t
)
·
R
a
-
L
·
∂
I
M
(
t
)
∂
t
is also to be found in literature, for instance Lindner and others: Reference material Elektrotechnik—Elektronik, Leipzig, 2. printing 1983, p. 199 ff. The reference symbols signify the following: U
q
induced voltage; c
1
, c
2
motor constants; &PHgr; magnetic flux; n rotational speed; M
L
load moment; M
m
motor moment; M
B
the acceleration moment resulting from the motor moment; I
M
motor current; U
M
motor terminal voltage; R
a
armature resistance; R
k
external terminal resistance; L inductance of the motor winding; J mass moment of inertia of the entire rotating arrangement including the parts to be moved, such as the windows, for example.
SUMMARY OF THE INVENTION
The invention demonstrates a method for detecting the position and the direction of motion of a movably mounted part on an electric motor and which automatically adapts to the present state of the motor.
The motor current is measured, by means of a measuring arrangement (FIG.
1
), starting at least upon driving the switching devices to switch the motor voltage from one direction of motion to the opposite direction. The time T+&Dgr;t
s
at which the maximum of the motor current is reached corresponds approximately to the time T+&Dgr;t
R
at which the direction reverses and the signal edges related by addition or subtraction to the actual position accordingly by the evaluation logic. The essential point here is not that an amplitude value is preset but that preferably a maximum is determined.
Preferably therefore, the motor current maximum is obtained by comparing two adjacent sampling values. Furthermore, a current threshold value is specified beneath which current peaks, that might arise for example as a result of interference, are ignored and only that motor current maximum which exceeds the current threshold value is signaled to the evaluation unit
By means of a reference current value I
a0
immediately before the motor current drops as it begins a polarity change, the current threshold value can also be determined as an actual value and be adapted to the respective load state of the motor. In order to establish the time T+&Dgr;t
s
at which the current maximum drops after the change of sign, the difference between two adjacent sampling values of the motor current is always compared with a specified difference value when the current threshold value is exceeded.
The measured reference current value I
a0
, the actual rotational speed and motor voltage, as well as the model parameters of the motor can be employed in order to ascertain the current threshold value precisely.
Preferably, the calculating unit simulates a motor state model such as that which the expert obtains by conversion from the motor equations. In order to determine the current threshold value on reversal of the direction of motion, it is assumed that the load moment varies only by an insubstantial amount over the time while passing through zero.
Preferably, the physical quantities of the motor state model that no longer vary after the actuating motor has been installed are preset, for instance by programming at the time of installation. By measuring motor current and voltage at the starting time point, before the static friction has been overcome, the ohmic resistance can also be determined to a very good degree of approximation because no v
Driendl Dieter
Kessler Erwin
Kimpfler Stephan
Kleiner Kurt
Schulter Wolfgang
Kunitz Norman N.
Spencer George H.
Strecker Gerard R.
Temic Telefunken Microelectronics GmbH
Venable
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