Printing – Stenciling – Rotary machines
Reexamination Certificate
1999-05-06
2001-05-08
Hilten, John S. (Department: 2854)
Printing
Stenciling
Rotary machines
C101S123000, C101S124000, C101S126000, C101S116000
Reexamination Certificate
active
06227108
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a magnet bar for exerting an attracting force on a doctor, which is arranged above the magnet bar, of a screen-printing or coating device, comprising an elongate top plate and an elongate magnet carrier which extends below and substantially parallel to the top plate and on which permanent magnets are arranged next to one another in the longitudinal direction, it being possible to adjust the distance between the magnet carrier and the top plate by means of a displaceable adjustment member which is arranged below the magnet carrier, in order to adjust the magnitude of the attracting force.
BRIEF DESCRIPTION OF RELATED TECHNOLOGY
A magnet bar of this type is known from EP-A-0,769,374.
In a specific embodiment of the known magnet bar, the magnet carrier is connected, via a connecting link guide, to the adjustment member, which can be displaced parallel to the magnet carrier. The magnet carrier is provided on the underside with rolls with an axis of rotation which is transverse to the longitudinal direction of the magnet carrier, which rolls run in inclined slots in the adjustment member. As a result, it is possible, by displacing the adjustment member, to adjust the distance between the magnet carrier and the top plate. The connecting link guide is active both when reducing this distance and increasing it, in order to exert an upward or downward force, respectively, on the rolls.
A drawback of this structure is encountered when removing the magnet carrier and is caused by the fact that the slots in the adjustment member block the rolls in the upward direction. This prevents the magnet carrier from being lifted out of the magnet bar, making it difficult to remove the magnet carrier.
A further drawback is that there will always be a certain degree of play between the outer circumference of the rolls of the magnet carrier and the slot walls, so that the accuracy with which the distance between the magnet carrier and the top plate of the magnet bar can be adjusted leaves something to be desired, especially in the case where the rolls of the magnet carrier are alternately supported against one or the other slot wall.
A further drawback of the known magnet bar is encountered if the power supply for energizing the adjustment member fails, for example as a result of a power cut, while the distance between magnet carrier and top plate is short in order to attract a doctor situated above the top plate (magnetic force turned on) for a screen-printing or coating device which is in operation. If a general power cut or an emergency stop causes the printing or coating device to come to a standstill, the doctor is then held fixedly in the printing or coating paste by the magnetic force. As a result, the doctor can no longer be removed from the paste, so that it will dry into the remaining paste, resulting in damage to the printing device. Therefore, in order to remove the doctor in the event of disruption to the power supply, the magnetic force must be turned off as quickly as possible by pulling the magnet carrier away from the top plate, without any power supply being available, thus increasing the distance between magnet carrier and top plate. To this end, the known device is provided with an additional tension spring structure for displacing the connecting link guide such that the magnet carrier is pulled downwards, counter to the magnetic force.
SUMMARY OF THE INVENTION
The object of the invention is to eliminate the abovementioned drawbacks and to provide a magnetic bar in which the magnet carrier can be easily installed and removed, and for it to be possible to adjust the distance between the magnet carrier and the top plate of the magnet bar in a very accurate, stable and self-aligning manner, while also ensuring that the magnet bar is of simple design.
This object is achieved by means of a magnet bar of the type mentioned at the beginning which is characterized in that the magnet carrier is supported freely on the adjustment member and that the magnet carrier is subject to a downwardly directed force which is greater than the maximum attracting force which can be exerted by the magnets on a doctor which is arranged above the magnet bar.
Since the downwardly directed force on the magnet carrier ensures that the latter is always able to move downwards out of its highest working position, the magnet carrier is always supported directly on the adjustment member. Since the magnet carrier is always supported directly on the adjustment member, there is an unambiguous relationship between the displacement of the adjustment member and the distance between the magnet carrier and the top plate of the magnet bar, and therefore between the displacement of the adjustment member and the attracting force exerted by the magnet bar on a doctor which is situated above the top plate of the magnet bar. Using the structure according to the invention, the magnet carrier, after the top plate has been removed, can simply be lifted out of the magnet bar without further actions being required. The magnet bar has a simple structure which is inherently failsafe.
In order to increase the accuracy of the adjustment of the attracting force on a doctor further, particularly in the area in which this attracting force is strong, and where the working point of the magnet carrier normally lies and the change in the magnetic force in the event of a certain displacement of the adjustment member is relatively strong, it is preferable, in the case of a magnet bar in which the magnet carrier, by means of an end support element at at least one of its ends, is supported against a first end plate, which is substantially perpendicular to the top plate, of the magnet bar, for the first end plate to be provided, on the side of the magnet carrier, in the supporting area of the magnet carrier, with profiling in the direction of displacement of the magnet carrier. This makes it possible to achieve the effect that, in the event of a certain displacement of the adjustment member, the magnet carrier moves not only in a direction perpendicular to the top plate but also in a direction parallel to the top plate, so that a certain displacement of the adjustment member results in a less substantial change in the distance between the magnet carrier and the top plate.
REFERENCES:
patent: 3596595 (1971-08-01), Zimmer
patent: 4557194 (1985-12-01), Zimmer
patent: 5148743 (1992-09-01), Zimmer
patent: 5405487 (1995-04-01), Galchefski et al.
patent: 225 3527A (1974-05-01), None
patent: 0 36 9540B1 (1994-03-01), None
patent: 0 633 135A1 (1995-01-01), None
patent: 0 732 199A1 (1996-09-01), None
patent: 0 769 374A1 (1997-04-01), None
Kempen Henricus G. M.
Lagarde Patrick G. L .H.
Chau Minh
Hilten John S.
Hoffmann & Baron , LLP
Stork Brabank B.V.
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