Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-08-28
2003-03-25
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240
Reexamination Certificate
active
06538428
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a measuring method for a mechatronics apparatus. More specifically, the present invention relates to a measuring method for an electromagnetic device and its associated sensor and electronic circuitry.
This type of mechatronics apparatus is disclosed in German patent document DE-A 100 22 124 (filed in the U.S. Patent Office under Ser. No. 09/841,549), which is incorporated herein by reference. The mechatronics apparatus includes an electronic control circuit and an electromechanical component, e.g., a solenoid valve, which are contained in a common housing made of a material such as aluminum. The electronic control circuit is made up of electronic components installed on a printed circuit board, which is located in a compartment of the mechatronics housing. The electronic components (resistances, capacitors, transistors, micro-controllers, etc.) are soldered to the printed circuit board in a conventional manner. In addition, one or more sensors are also typically included among the electronic components attached to the printed circuit board. These sensors are capable of measuring, e.g., distances, pressures, or temperatures.
An inductive distance sensor, consisting of a coil with a distance-dependent displaceable core, is disclosed in German patent document DE-A 33 43 885 (equivalent to U.S. Pat. No. 4,649,341, Mar. 10, 1997, by Ulbrich et al), which is incorporated herein by reference. The actual distance setting of the core is ascertained at discrete points in time by exciting the coil with a voltage impulse, and the resultant charging current is monitored. The inductivity at a particular point in time is then a measure of the core displacement distance. In this prior art arrangement, the coil is triggered by a microcontroller, and the charging time of the coil is converted by the same. microcontroller into the distance to be measured.
When making mechatronics measurements, however, which involve a magnetically actuated component, such as a solenoid valve, a relay or an operating magnet, there is a significant risk that an inductive sensor within the electronic control circuit may be affected by electromagnetic interference from the above-mentioned magnetically actuated component. As a result, electromagnetically induced interference voltages in the inductive sensor can degrade its measurement accuracy. In addition, interference or influence by electrical fields can cause similar problems.
Although it is known that inductive sensors can be shielded from electromagnetic interference, according to German patent document DE-A 196 24 801 (equivalent to U.S. Pat. No. 5,994,895, Nov. 30, 1999, by Bolte et al), which is incorporated herein by reference, such measures involve the added costs associated with shielding.
Accordingly, it is an object of the present invention to minimize the aforementioned type of electromagnetic interferences in mechatronics sensors, without incurring the added costs of shielding.
SUMMARY OF THE INVENTION
In accordance with an illustrative embodiment of the present invention, a measurement method for a mechatronics apparatus, having an electromagnetically actuated component, an electronic control circuit, and a sensor with a displaceable core, comprises the steps of:
a. at a measurement start time, applying a voltage impulse of a predetermined peak magnitude to the sensor,
b. determining a measurement end time, when the voltage impulse magnitude has decreased to a predetermined level,
c. calculating an inductivity of the sensor, based on the difference between the measurement start and end times, and
d. calculating a position of the displaceable core, based on the calculated inductivity of the sensor,
wherein the measurement start time and the measurement end time define the boundaries of a measurement time window, this time window being restricted to those times when the electromagnetically actuated component does not have a current flow, or when a current flow change in the electromagnetically actuated component is below a predetermined limit value.
Typically, the electromagnetically actuated component is a solenoid valve, and the sensor is an inductive distance sensor, or possibly an angle sensor. The solenoid valve is normally actuated through the application of a switching voltage, which is sufficient to hold it in an energized state. The switching voltage alternates between a maximum level for a switched-on time, and a minimum level for a switched-off time. The measurement time window is positioned such that the measurement start time occurs after a switching time of the switching voltage, and the measurement end time occurs before the next switching time of the switching voltage. In this manner, the measurement is not subjected to the electromagnetic interference that is generated by the high rate of current change in the solenoid valve, at the time of voltage switching.
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Lefkowitz Edward
Proskauer Rose LLP
WABCO GmbH & Co. OHG
Zaveri S
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