Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Reexamination Certificate
1999-09-23
2001-06-26
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
C324S243000, C056S01020J, C340S684000
Reexamination Certificate
active
06252397
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to agricultural machinery having crop conveyors, and more particularly to a metal detecting device for a crop conveyor. In a preferred embodiment, several closely spaced permanent magnets are fixed within a hollow feed-roller in parallel with the shaft thereof.
A metal detecting device of this type is known from DE 43 01 611 A1. A plurality of permanent magnets are arranged in a row, transversely of the crop feed path, within a hollow feed-roller. One magnetic pole of each magnet is directed toward the feed-roller and is located close to the inner surface thereof. The permanent magnets are surrounded by respective sensing coils and the other poles of the magnets are accommodated in a U-shaped yoke whose two ends terminate close to the inner face of the feed-roller. By this arrangement, the basic sensor field extends through the feed-roller into the adjacent feed-slot to a depth corresponding approximately to half the width of the yoke. The signals from the sensors are added to form the wanted signals and, to compensate for interference signals which arise, in particular, from the movement of the feed ribs of the feed-roller in each sensing field, they are subtracted from one another and then used as reference values. A disadvantage of this arrangement is the relatively small range covered by the sensing fields since there are limits to the amount by which the yoke can be enlarged. This is because the rotating members, which interfere heavily with the sensors, are located at the entry point of the feed-slot. Another disadvantage is that the detection process at the output of the feed-slot occurs too late to allow the conveyor to be stopped before a detected piece of metal reaches the subsequent chopper.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a metal detecting device for a crop conveyor which overcomes one or more of the deficiencies discussed above.
Another object is to improve the metal detecting device in such a way that the effective sensing field will extend deeper into the feed-slot and that the signal-to-noise ratio of the sensor signals will be increased.
In accordance with the invention there is provided a metal detecting device for use with a crop conveyor having a hollow feed roller mounted on a shaft, and an opposite roller spaced from the feed roller to provide a crop feed slot therebetween; the device including a plurality of magnets fixed within the hollow feed roller in parallel with the roller shaft, each magnet having a pole directed radially outwardly to an outer end within the roller, each magnet including a pole shoe arranged on the outer end and extending outwardly toward the roller such that a magnetic field of the magnet penetrates through the roller and the crop feed slot from inside to out, a sensor winding on the pole shoe and within the roller whereby said magnetic field also passes axially through the sensor winding.
A respective pole shoe is arranged on each of the radially outwardly directed poles of the permanent magnets so as to extend up close to the hollow feed-roller, and in that each said pole shoe penetrates the appertaining sensor winding and has a free pole face which is narrower than that of the corresponding permanent magnet so as to produce an enhanced field per unit area through the material of the pole shoe at the free pole face.
The fields of the permanent magnets are preferably oriented in parallel. The signal levels occurring under similar conditions when a standardized metallic body passes through the various regions of the slot covered by the individual sensors are higher at the center than in the lateral side regions so that it is advantageous to normalize the signal levels and to logically combine these normalized signals in order to compensate for interference.
These, and other objects and advantages of the present invention, will become apparent as the same becomes better understood from the following detailed description when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3972156 (1976-08-01), Bennett, Jr. et al.
patent: 4322937 (1982-04-01), Hollmann
patent: 4344074 (1982-08-01), Strosser et al.
patent: 4433528 (1984-02-01), Bohman
patent: 5343676 (1994-09-01), Weiss
patent: 5414353 (1995-05-01), Weischedel
patent: 5426844 (1995-06-01), Suda et al.
patent: 5504428 (1996-04-01), Johnson
patent: 5901534 (1999-05-01), Weiss et al.
patent: 43 01 611 A1 (1994-07-01), None
Behnke Willi
Frosch Andreas
Claas Selbstfahrende Erntemaschinen GmbH
Husch & Eppenberger LLC
Kercher Kevin M.
Muir Robert E.
Strecker Gerard R.
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