Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
2001-05-01
2004-03-30
Snow, Walter E. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207240, C324S207250
Reexamination Certificate
active
06714004
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a position measuring system (path measuring system—position sensoring system) comprising a transmitter, a sensor which comprises an inductive element to which the transmitter is coupled electromagnetically and an evaluating unit for a sensor signal, wherein the sensor and the transmitter are adapted to be positioned relative to one another.
Position measuring systems of this type are utilised, for example, for measuring the position of pneumatic cylinders, for measuring the position of valves (especially in control loops) or in gripper devices. It is very advantageous in such applications if a relative position between the transmitter and the sensor is measurable absolutely.
In a position sensor known from the state of the art, a secondary coil is wound over a longitudinally extending soft magnetic sensor core. Primary coils are wound around the respective ends of the sensor core. A magnet which is movable along the sensor core is used as a transmitter. A voltage is induced in the secondary coil when current passes through the primary coils. The magnet exerts an influence on this induced voltage thereby causing the magnetic sensor core located in its immediate vicinity to become saturated. The flow of current through the secondary coil is then affected by the relative position between the magnet and the soft magnetic sensor core so that the current through the secondary coil is dependent on the position of the magnet.
In a magneto-inductive sensor-line for magnetically determining the position and/or path of one of the magnets adjacent to the sensor line which is known from DE 43 11 973 A1, a plurality of flat coils that are arranged next to one another and/or above one another is provided on an extensive magnetically conductive layer which can be brought into a state of magnetic saturation, whereby the neighbouring coils form a transmitter-receiver system, and the position of the magnet affects the transmitting/receiving characteristics of the coils thereby allowing its position to be detected.
Inductive position indicators are known from DE 25 11 683 C3 and DE 39 13 861 A1, wherein a ferromagnetic core together with a primary coil traversed by an alternating current form a probe element which itself creates a magnetic flux. This magnetic flux is threaded through a secondary winding and the voltage induced in this winding is dependent on the position of the core.
A displacement sensor is known from FR 2 682 760 A1, wherein a primary circuit and a secondary circuit are arranged on a support. An alternating current is applied to the primary circuit which is coupled to the secondary circuit whereby an alternating voltage is induced therein. This induced voltage is affected by a transmitter consisting of a ferromagnetic material in dependence on the position of the transmitter relative to the secondary circuit.
Based upon the foregoing, the object of the invention is to provide a position measuring system which is of simple construction and can thus be manufactured economically, and which is employable universally.
BRIEF SUMMARY OF THE INVENTION
In accordance with the invention, this object is achieved in the case of a position measuring system as described hereinabove in that the inductive element is coupled to an oscillator which is affected by the Q factor and/or the effective inductance of the inductive element, in that the Q factor and/or the effective inductance of the inductive element is determined by the size of an effective sensor region to which the transmitter is coupled, and/or by the size of an effective transmitter region which is coupled to an effective sensor region, and in that the sensor and/or the transmitter are formed in such a manner that the size of the effective sensor region to which the transmitter is coupled, and/or the size of the effective transmitter region which is coupled to the effective sensor region is dependent on the relative position between the transmitter and the sensor in a direction transverse to a direction of separation therebetween.
Due to the fact that the inductive element is coupled to an oscillator and can affect the parameters of the oscillator such as the amplitude, the phase angle and the frequency thereof by means of its Q factor and/or effective inductance, a location-dependent coupling of the transmitter to the inductive element can be evaluated in a simple manner in that the corresponding parameters of the oscillator are evaluated. The inductive element, which is coupled to the oscillator, is thereby coupled to the oscillator in such a manner that the oscillator itself can be influenced. A special case of coupling between the inductive element and the oscillator arises when the inductive element itself forms the inductance in the oscillator. Thus, in accordance with the invention, it is not a voltage which has been induced in a secondary coil via a primary coil that is measured, but rather, it is the Q factor and/or the effective inductance of the inductive element in the sensor that is evaluated by means of the oscillator. Consequently, energy does not have to be supplied to a primary coil so that the position measuring system in accordance with the invention is constructed in a simpler manner. Moreover, by virtue of the device in accordance with the invention, the transmitter is in the form of a passive element so that, in particular, current does not have to be applied thereto over energy supply lines.
In accordance with the invention, provision is made for the Q factor and/or the effective inductance of the conductive element, which represents a measure for the relative position between the transmitter and the sensor, to be determined from the size of the effective sensor region and/or the size of the effective transmitter region. The sensor signal is thus determined by the geometrical structure of the sensor or the transmitter. The information in regard to the relative position between the transmitter and the sensor and thus the position information or path information regarding the relative position between the transmitter and the sensor is contained in the geometrical form of the effective sensor region or the effective transmitter region which are mutually coupled. In turn, the effective sensor region or the effective transmitter region is determined by the shape of the sensor, and thus especially by that of the inductive element, or by the shape of the transmitter. Consequently, the position measuring system in accordance with the invention is of simple construction and can be produced economically.
The position measuring system in accordance with the invention is employable universally, and may be employed, in particular, in a shaft encoder by virtue of an appropriate shaping of the sensor or the transmitter. Apart from the inductive element, no other secondary coil or the like needs to be provided. Basically, it is sufficient to provide a single inductive element which is constructed in such a manner that an effective sensor region and/or an effective transmitter region, which is coupled to the inductive element, is dependent on the relative position between the transmitter and the sensor. In addition however, it is also possible to provide further inductive elements. For example, difference measurements or sum measurements can be effected in this manner so as to obtain very accurate measurements having a high resolution factor. In accordance with the invention for example, provision may be made for the provision of a plurality of measurement tracks, for example, a measurement track for coarse measurements and a measurement track for fine measurements. Since the location information is in fact contained in the shape of the effective sensor or the effective transmitter region, a plurality of different applications can be implemented by appropriate shaping.
The resolution of the measurement is thereby adapted to be set directly by the shape of the effective sensor region or the effective transmitter region. Resolutions in the order of at least one thousandth of
BALLUFF GmbH
Lipsitz Barry R.
McAllister Douglas M.
Snow Walter E.
LandOfFree
Inductive position measuring system does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Inductive position measuring system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Inductive position measuring system will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3217983