Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-05-28
2001-05-22
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S229000, C324S232000, C324S239000, C324S243000
Reexamination Certificate
active
06236198
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and a device for non-contacting measurement of measures such as height, width, etc., and positions of objects of electrically conductive material based on electro-magnetic induction.
The invention may be used when manufacturing metal products such as tubes rods or beams, in which it is desired to measure the measures and positions of these products. The invention may also be used for measurement on products made of graphite, electrically conductive ceramic, or the like.
BACKGROUND OF THE INVENTION
One known method for non-contacting measurement of positions and various measures, such as height and width, of tubes, rods, beams or like products is to use optical methods based on shading or reflection of beams, or by processing of images taken by a video camera.
The environment in many manufacturing processes, involving, above all, pollution and often high temperatures, deteriorates the reliability and the accuracy of such equipment.
It is previously known to measure the measures and position of an electrically conductive measuring object by means of inductive methods. In that case, a transmitter coil is used which generates a time-varying magnetic field which induces currents in the conductive measuring object. These currents generate a magnetic field which, in turn, induces a voltage in a receiver coil, this voltage being dependent, among other things on the shape, the conductivity, and the magnetic permeability of the measuring object, as well as on the geometrical conditions. From this voltage, under certain conditions, geometrical dimensions, such as distances and the position of the measuring object, may be calculated. For generating a time-varying magnetic field, sinusoidal currents in the transmitter coil may be used, as described in U.S. Pat. No. 4,475,083, or a constant current which is suddenly interrupted, such as described in U.S. Pat. No. 5,059,902, may be used. The latter method is more robust from the point of view of a measurement technique and facilitates the separation of different properties of the measuring object. One problem with these measurement devices, however, is to determine the measures of the measuring object when its position is changed.
U.S. Pat. No. 5,270,646 discloses a method of arranging coils so as to achieve measurement of the width of a strip. However, the technique can only be used for a strip of relatively limited width. Further, it is assumed for correct function that the edge of the strip is substantially plane. For many applications, the accuracy is not sufficient, primarily when there are large distances between the strip and the measuring coils, which is due to difficulties in correctly compensating for variations in the distance.
Common to prior art devices for inductive measurement of distance, thickness and measures of electrically conductive objects, derived therefrom, is that the transmitter and receiver coils are arranged with the same symmetry axis or are located on different sides of the measuring object. It also occurs that the same coil is used as transmitter and receiver coil. The magnetic field generated by the transmitter coil then becomes substantially perpendicular to the surface of the measuring object at the measuring point, or at least has a large component towards the surface of the measuring object. This results in currents and magnetic fields from different depths into the measuring object contributing to the measurement signal which thus becomes both material-dependent and dependent on the thickness and shape of the measuring object in a relatively large region around the location where measurement is to take place.
SUMMARY OF THE INVENTION
The invention is based, as shown in
FIG. 1
, on placing a measuring object
1
, a transmitter coil
2
, and a receiver coil
3
in relation to each other in such a way that magnetic field
4
generated by the transmitter coil at a measuring region
5
, defined as the region around a conceived measuring point
6
, is substantially parallel to the surface of the measuring object at the measuring region, or, for a measuring object with a curved surface, parallel to a tangential plane
7
at the measuring point
6
. The measurement device then becomes most sensitive to movements in the direction of a line
8
, indicated below as the x direction or the x line, perpendicular to the tangential plane at the measuring point. The receiver coil is to be located such that a conceived field line
4
, which symbolizes the magnetic field, touches the measuring region and in its extension reaches the receiver coil. This is achieved by a substantially symmetrical location of the coils in relation to the measuring region in question and where the transmitter coil, the measuring region, and the receiver coil lie on one and the same circular arc and where the circular arc at the measuring region is curved outwardly. A more detailed definition of the location of the coils will be given in the appended figures and the following description of embodiments. The invention also functions in the case of a minor deviation from a location according to the above. Measurements with an arrangement of the coils according to the invention are sensitive to movement of the measuring object perpendicular to the magnetic field at the measuring region, that is, in the x direction, whereas the measurements are only influenced to a marginal extent by the movements of the measuring object in parallel with the magnetic field, indicated below as the y direction or the y line.
The currents which are induced in the measuring object because of the magnetic field which is parallel to the measuring region are concentrated at the measuring region. This means that the voltage which is induced in the receiver coil is substantially dependent on the magnetic field in the measuring region and the position of the receiver coil. In this connection, the shape of the measuring object and its position outside the measuring region will have a negligible influence on the result of the measurement.
A small change of the position of the measuring region in the x direction results in a linear change of the voltage induced in the receiver coil. On the other hand, the voltage induced in the receiver coil is stationary with respect to small changes of the position of the measuring region in the y direction. This means that the measurement signal is sensitive to small changes in position perpendicular to the surface of the measuring region but is influenced only to a marginal extent by small changes in position parallel to the measuring region. Changes in position perpendicular to the surface of the measuring object can thus be measured selectively.
U.S. Pat. No. 5,059,902 describes an advantageous method of supplying a transmitter coil. It describes supply with a constant current which has a sufficient duration for the magnetic field to be considered quasi-static. The magnetic field which is generated when this current is interrupted has the same shape as the quasi-stationary field, but the opposite direction. In this way, after interruption of the current, the field continues to be parallel to the measuring region. When supplying the primary coil with sinusoidal alternating current, the direction of the field at the measuring region varies during one period of the alternating voltage. For a correct measurement, the direction of the field at the measuring region must, on average, be parallel for one period, which is difficult to obtain.
The voltage induced in the receiver coil as a function of the time, after the constant current in the transmitter coil has been interrupted, comprises a short and a rapidly diminishing voltage pulse which is induced by the rapidly decreasing magnetic field in the air between the coils and the measuring object, and a considerably more slowly diminishing voltage pulse which relates to the magnetic field within the measuring object which decreases slowly because of the skin effect (current diffusion). The fast voltage pulse immediately after closing of t
Asea Brown Boveri AB
Connolly Bove & Lodge & Hutz LLP
Strecker Gerard R.
LandOfFree
Method and device for non-contact measurement of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for non-contact measurement of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for non-contact measurement of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2507340