Method of and apparatus for sorting bodies of ferromagnetic materials in magnetic field

FIELD

BACKGROUND OF THE INVENTION

The present invention relates to a method of sorting ferromagnetic articles according to their permeability. The permeability and hardness of ferromagnetic material are inversely proportional to one another and, based on such recognition, the present invention provides a convenient nondestructive way of classifying articles such as ball or roller bearings, travellers on a ring spinning machine, and the like.

In a conventional method of sorting articles made from ferromagnetic material, which is based on discrimination in a magnetic field, the articles to be examined are inserted in the primary coil of an air core transformer. The thus introduced articles change the magnetic field and induce an electromotive force in the circuit of the secondary coil of the transformer.

A drawback of such conventional method is that it furnishes an either/or response and does not discriminate between permeabilities which are higher or lower than those corresponding to a predetermined standard. It only rejects or accepts articles of certain permeability, but does not grade them within a range of values.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a simple method of sorting ferromagnetic articles in a magnetic field.

Another object of the invention is to classify such articles according to different permeability values.

A further object is to provide an inexpensive and reliable method of sorting such articles without adversely affecting the condition or appearance of tested articles.

An additional object of the invention is to provide an apparatus which tests articles in accordance with the above outlined method.

These objects are accomplished by conveying articles made of ferromagnetic material along a predetermined path crossing a series of zones of predetermined and differing magnetic field intensity provided in a non-homogenous magnetic field. For each zone the induced electromotive force is compared with a standard value, to indicate whether an article has the standard permeability predetermined for the particular zone. If it has the required permeability, a preferably mechanical sorting device is actuated to remove the article from the respective zone and to collect it in a corresponding receptacle. If does not have the permeability corresponding to a predetermined value, the article is advanced into the next adjacent zone of different magnetic intensity, where another comparison between the obtained electromotive force, the field intensity and the permeability takes place, and so on, until coincidence of the measured and predetermined permeability values triggers the sorting mechanism for removing the article and introducing it into one of several receptacles provided for articles of higher or lower permeability.

The magnitude of the induced electromotive force is the same when an article of relatively weak permeability passes through a zone of greater field intensity, as when an article of relatively strong permeability passes through a zone of lesser field intensity. If the sequence of zones is such that the articles pass first through a zone of least intensity, articles with strong permeability will induce therein an electromotive force which an article of lesser permeability will not induce until it has been conveyed into a zone of greater field intensity.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

DESCRIPTION OF THE DRAWING

FIG. 1 is a somewhat schematic fragmentary front elevational view of the apparatus which is employed for the practice of the above described method;

FIG. 2 is a sectional view as seen from the line II-II of FIG. l;and

FIG. 3 is a wiring diagram of the circuit used in the apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a measuring coil 1 connected to a source of current, on the U-shaped core 2 on which two pole pieces 3 face each other across an air gap 4. As shown in FIG. 2, the air gap 4 has a trapezoidal cross section defined by the slant of the pole pieces 3 which are furthest apart from one another at the outer face of the core 2, and taper off toward each other in the interior region of the core 2. The maximum width of the air gap 4 corresponds to a zone of least magnetic field intensity, and conversely, the minimum width corresponds to a zone of greatest magnetic field intensity.

The air gap 4 forms a passageway for articles whose permeability is to be examined and which, in the illustrated example, are travellers 5 of a ring spinning machine. The travellers S are placed in radial grooves 6 of a conveyor wheel 7 and are advanced, by the rotation of the wheel, along an arcuate path which intersects the air gap 4 where a retaining device or trap plate 8 on one arm of a two-armed lever 9, prevents their falling off. The other arm of the lever is attached to an armature 10 which is connected to spring means 12 for removal from an electromagnet 11 when the latter is deenergized.

The measuring coil 1 is connected to a Wheatstone bridge 13, as shown in FIG. 3, which has a diagonal 17. This diagonal is also connected to the electromagnet 11.

The operation of the apparatus is as follows:

When a traveller 5 is conveyed across the air gap 4 in the direction of the arrow 18 shown in FIG. 2, a rectification and change in the magnetic flux of the circuit is produced, which is registered as a change of the inductivity of the measuring coil 1, and which is proportional to the permeability of the material of which the article is made, as well as to its relative position in the magnetic field. Calculation of the inductivity Of the coil, respectively, of the induced electromotive force, takes onto account the fact that on entering the air gap 4 an article exerts less of an influence on the magnetic flux than on leaving, since in the latter event the article occupies almost the entire downstream part of the air gap.

The Wheatstone bridge 13 to which the measuring coil 1 is connected is adjustable through the impedances 14, 15 and 16, to be in equilibrium when, for example, a traveller 5 of predetermined hardness that is, permeability, is at the halfway point of its passage through the air gap 4. The equilibrium state of the bridge 13 is coordinated with a zero voltage on the diagonal 17. The zero voltage, in turn is a signal of deenergization of the electromagnet 11 connected to the diagonal 17, whereby the armature 10 is released from the electromagnet, and withdrawn therefrom by the spring means 12. The movement of the armature 10 causes the lever 9 to tilt the trap plate 8 so that a suitably positioned container (not shown) can receive the traveller as it falls out of the groove 6.

If a traveller 5 entering the air gap 4 has a permeability which is greater than the standard value, that is, if the material of which the article is made has less hardness than is specified, the traveller will not reach the half-way mark but will have been removed before getting to that point; greater permeability, that is lesser hardness causes the predetermined zero voltage to be registered when the traveller is in a zone close to the widest diameter of the air gap. At that stage the trap plate 8 is actuated by the zero voltage, and causes articles of greater than standard permeability to enter another container. Conversely, articles of less than standard permeability will be conveyed beyond the half-way mark and close to the narrow end of the trapezoidal air gap before the zero voltage corresponding to the magnitude of the induced electromotive force will

3,539,005 cause the trap plate to swing away and cause articles of less than standard permeability to enter a further container.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods of and apparatus for sorting articles made of ferromagnetic material in a magnetic field differing from the types described above.

While the invention has been illustrated and described as embodied in a method of and apparatus for sorting articles made of ferromagnetic material in a magnetic field, it is not intended to be limited to the details shown, since various modification and structural changes may be made without departing in any way from the spirit of the present invention·

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and. therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence ot the following claims.