Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Work or object holding type
Reexamination Certificate
1998-06-11
2001-09-11
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Work or object holding type
C335S289000
Reexamination Certificate
active
06288623
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a holding apparatus for the transport of conveyed items, in particular the lifting, transporting, imbricating and stacking of ferromagnetic conveyed parts, having at least one permanent magnet for generating a permanent magnetic field, also at least one electrical magnet coil for generating a temporary magnetic field and compensation of the permanent magnetic field, and having a magnetically conductive housing for the permanent magnet and the magnet coil, the permanent magnet usually being magnetized in the direction of its smallest dimension, the permanent magnet also being arranged in the direction of magnetization at the rear with one pole against the housing, forming a magnetic yoke, and at the front with the other pole in the direction of a working clearance opposite the conveyed parts, and the housing having in cross section two or more webs rising up from a baseplate. For the purposes of the invention, a working clearance is generally to be understood as a clearance of which the width is dimensioned such that a displacement or compensation of the permanent magnetic field by the temporary magnetic field takes place principally at this location. That is to say, all the magnetic field changes to be set for the secure holding and letting go of the conveyed parts are ideally restricted to the region of the working clearance. The webs are of a regular finger-like design in cross section.
A holding apparatus of the type described at the beginning is disclosed by German Patent 34 23 482.
In this case there is provided a single permanent magnet, which is arranged centrally in a magnetically conductive iron yoke. Arranged between this permanent magnet and the working clearance are a magnetically conductive compensation plate with a magnetically conductive web and a magnetically conductive central pole, in this sequence. This is disadvantageous with regard to possible stray fields. This is so since the permanent magnet is not arranged directly in the region of the working clearance but is set back from it. As a consequence, losses in magnetic field strength are unavoidable.
Added to this is that only one electrical coil is provided between the compensation plate and the central pole for the compensation or displacement of the magnetic field out of the region of the working clearance. That is to say, this one coil must be designed such that the permanent magnetic field is reliably compensated. Adaptation to differently designed conveyed parts is not accomplished by this means. It must also be taken into consideration that, due to the necessary design of the electrical coil to suit the maximally occurring adhesive forces between the conveyed part and the holding apparatus, the achievable switching frequency is often adversely influenced. This can be attributed to the fact that coils of adequate magnetic field strength for generating an opposing field have at the same time a great inductance (measured in henries).
According to Lenz's law, however, large inductances (formerly self-inductance coefficients) effect a lessening or slowing of the rise of a switching current, with the result that the switching frequency is reduced. This is to be regarded as disadvantageous in particular in the transport of conveyed items with the required high cycle times.
Austrian Patent 282 878 discloses a load lifting magnet for handling ferromagnetic loads, having a plurality of magnetic poles and excitation windings assigned to the poles, the load lifting magnet having a primary magnetic circuit which has an internal group of first poles and at least one first excitation winding which can be switched on independently. There is also provided an additional magnetic pole, which is magnetically isolated from the primary circuit and to which there is assigned at least one second excitation winding, which can be switched on independently. This is intended overall to provide a load lifting magnet with which it is possible to be certain to lift only the uppermost plate in each case off a stack of single ferromagnetic plates. At the same time, it is intended to be ensured that, during further transport of the lifted-off plate, an adequately great adhesive force can be exerted on the single plate. If need be, it is also to be possible to transport safely relatively large customary ferromagnetic loads. —Problems associated with the achievable switching frequencies are not mentioned. —This is where the invention overall wishes to provide a remedy.
The invention is based on the object of developing a holding apparatus of the embodiment described at the beginning in such a way as to make it possible to adapt to different conveyed parts while retaining at the same time a high switching frequency and simple construction.
SUMMARY OF THE INVENTION
To achieve this object, the invention proposes in the case of a holding apparatus of the generic type that at least one permanent magnet is provided in each web and at least two mutually independently energizable magnet coils are provided in at least one inter-web space. The webs rising up from the baseplate are usually arranged hanging down in the installed state of the holding apparatus, with the result that the permanent magnet or magnets hold or attract the conveyed parts taken past underneath against the action of gravity. A compensation of the permanent magnetic field then causes dropping off of the conveyed parts on account of gravity. At the same time, the direction of magnetization of the permanent magnets is defined such that it is from the north pole (N) in the direction of the south pole (S). Generally, the permanent magnets are arranged in the webs in each case at the bottom, at the top or in a position in between. According to a preferred embodiment, there may be provided 3, 5, 7, 9, . . . webs, i.e. (2n+1) webs, or 2, 3, 4 . . . , i.e. (n+1) webs, where n=1, 2, 3, . . . , with permanent magnets in each case, the webs being arranged in cross section lying respectively opposite one another in pairs in comparison with a central middle web. Moreover, the permanent magnets fastened in the longitudinal extent of the webs generally have—starting from the middle web—respectively alternating directions of magnetization, with the result that the webs lying opposite one another in pairs in comparison with the middle web in each case have permanent magnets with the same direction of magnetization. The webs generally rise up perpendicularly from the baseplate, the permanent magnets being fastened in perpendicular prolongation of the webs such that their respective direction of magnetization coincides with the direction of the extent of the web. Consequently, the direction of magnetization and the baseplate are arranged perpendicularly with respect to each other.
A particularly simple design from a production engineering viewpoint is obtained in the case where the webs are arranged equidistantly in comparison with the middle web and enclose between them equally sized inter-web spaces. The topology of the holding apparatus is chosen principally such that the baseplate is of a circular design and the webs are arranged concentrically with respect to the cylindrical middle web, forming a rotationally symmetrical holding pot with inter-web spaces in the form of annular channels. As an alternative to this, there is also the possibility of making the baseplate of a rectangular design and arranging the webs mirror-symmetrically in the longitudinal direction with respect to the I-shaped middle web, forming a cuboidal holding bar with interweb spaces in the manner of longitudinal channels. This holding bar can be adapted without any problem to, for example, metal plates to be transported.
The measures of the invention described above not only make possible a simple construction but also allow different conveyed parts to be lifted, transported and stacked with at the same time a high switching frequency. This is attributable on the one hand to the fact that the adhesive force required for securely holding the co
Donovan Lincoln
Neuhauser, GmbH Co.
Rosenman & Colin LLP
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