Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates to a copying device provided with a glass
plate and a cooperating cover Eor keeping documents against the glass plate,
a latching mechanism comprising at least one permanent magnet which keeps
; the cover in the closed position against the glass plate, a mechanism for
unlatching the cover at the end of a copying run and a lifting device for
lifting the cover after the unlatching.
Such a device is known from United States patent specification
3,888,581 or 3,888,582.
In this known device the cover in unlatched at the end of a copying
run by slightly lifting the cover by means of a cam, as a result of which an
air gap is made between the permanent magnet and the cooperating soft iron
mass. Consequently the magnetic attraction between these two elements de-
creases considerably, so that the force of the lifting device is sufficient
for further opening the cover.
The disadvantage of this known device is, that the unlatching
takes place with the aid of moving parts which must transfer a relatively
high force. Therefore these parts are liable to wear, which after frequent
use of the cover may cause the unlatching mechanism not to work reliably.
According to the present invention, there is provided in a device
for covering originals during copying thereof by exposure on a transparent
plate mounted in a frame of a photoco W ing apparatus, including a cover for
pressing an original against said plate, means supporting said cover for
swinging movement to and away from a closed position over said plate, means
constantly exerting a force biasing said cover away from said plate, and
disengageable means on said cover and said plate for ]atching said cover in
closed position against the force of said biasing means, the improvement
consisting in: said latching means comprising on one of said cover and said
frame a permanently magnetic body, on the other of them a magnetically
attractable body that confronts said magnetic body when said cover is in
closed position and on either said cover or said frame an electromagnet the
core of which is constituted by one of said bodies, said permanently magnetic
body in the closed position of said cover attracting said attractable body
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with a force exceeding the force of said biasing means, and means for generat-
ing in said electromagnet an electromagnetic field counteracting the magnetic
field of said magnetic body with a force sufficiently strong that the com-
bined forces of said fields on said attractable body are exceeded by the
force of said biasing means so that said biasing means will itself lift said
cover away from said plate.
Thus, the magnetic force of attraction of the permanent magnet is
reduced without the use of moving parts in such a way, that the cover can
be lifted by the lifting device.
In a preferred embodiment a magnetic field is generated in the
electromagnet during the copying run, which magnetic field has a polarity
being equal to the polarity of the magnetic field of the permanent magnet.
Thereby the magnetic attraction can be increased so much, that it
is very difficult to open the cover by hand, in which way the cover is pre-
vented from being opened during the copying. In this way, when thicker
objects, such as books, must be pressed against the glass plate, the magnetic
force of attrac~ion is sufficient to guarantee an effective contact. This
cannot happen by increasing the magnetic field strength of the permanent
magnet, as it must still be possible to open the cover by hand before the
beginning of the copying run.
Other characteristics and advantages of the invention will become
clear from the following description whereby reference is made to the
enclosed drawings, in which:
Figure 1 is a schematic section of a cover in which the locking
mechanism according to the invention is applied.
Figure 2 is an electric scheme wherein the operation of the locking
mechanism according to the invention can be controlled, and
Figure 3 is a schematic time diagram of the signals which play a
part in the scheme of Figure 2.
In Figure 1 a cover 2, cooperating with a glass plate 1, is schem-
atically represented in section, as described in more details in the U.S.
patent No. 4,035,077 of applicant. The cover 2 can hinge round a shaft, in
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order that it can be moved towards and away from the glass plate 1, whereby
the shaft 43 is installed near a longitudinal edge 30 of the cover 2. As
; described in above-mentioned U.S. patent No. 4,035,077 a spring is installed
on the shaft 43, which spring tries to turn the cover 2 away from the gLass
plate.
Near the opposite longitudinal edge 25 of the cover 2 a block 150
of magnetizable material, for instance a soft iron core, is fixed against
and in the lower side of this edge. In the frame 151 of the copying device
on which the cover 2 is installed, an electromagnet 152 is fixed at a place
which in the closed position of the cover, lies opposite to the block 150.
This electromagnet 152 consists of an electromagnetic coil 153 and a core 154
which in the embodiment represented consists of a permanent magnet.
The operation of the latching mechanism is as follows. In the
closed position of the cover 2, the magnetic attraction between the permanent
magnet 154 and the soft iron block 150 is sufficient to keep the cover in the
closed position against the force of the spring acting on the shaft 43. In
case sheetlike or thin originals lie on the glass plate, this magnetic force
of attraction is also sufficient to keep these in good contact with the glass
plate. As soon as the copying run is finished, a magnetic field is generated
via the electromagnet 152, which magnetic field acts against the magnetic
field of the permanent magnet. This counter-acting magnetic field has in any
case been designed to be so strong that magnetic force of attraction between
the block 150 and the permanent magnet 154 becomes weaker than the upward
force which is exercised via the spring on the shaft 43, so that the cover
turns upwards. As soon as the air gap between the block 150 and the permanent
magnet has become great enough, the excitation of the electromagnet 152 can
be stopped, as the magnetic attraction between block 150 and magnet 154 has
become negligibly low. The original can now be exchanged and the cover can
be closed by hand, after which the following copying run can be started.
In the case of thicker originals the electromagnet 152 can also be
used for generating an additional magnetic attraction of the cover 2, by
generating a magnetic field via the electromagnet 152, which magnetic field
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reinforces the magnetic field of the permanent magnet 154. This extra
magnetic field can for instance be generated when pressing the print knob
for starting the copying run.
In Figure 2 a circuit is representecl with which the above-described
operation can be realized. Hereby it is accepted, that when starting the
copying run a signal pulse PRINT is generated, whereby these signal pulses
can be derived from the control system of the copying device, as described
in more detail in U.S. patent No. 3,912,390. Thereby the signal END will
be generated immediately after the exposure device is excited for the last
time.
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The electromagnet 152 is connected on the one part with the positive
clamp of a diroct current source of for instance ~12 V, and on the other part
via a transistor 160 with a reference tension or earth and via a transistor
151 with the positive clamp of a direct voltage sou~ce of for instance ~24 V.
The base of the transistor 161 is connected via an amplifier 162 with ~he set-
output 163 of an RS-flip-flop 164, of which the set-input is connected with
the signal-emitter END and the reset-input is connected with the signal-
emitter PRINT.
The base of the transistor 160 is connected via an amplifier 165
with the output 167 of a monostable multivibrator 166, of which the input is
connected with the signal-emitter END. The monostable multivibrator 166
lengthens the signalpulse END to a pulse of about 1 sec.
The operation of this electrical scheme is now as follows ~compare
Figure 3). When the copying run is started (at the height of tl), the signal
pulse PRINT is generated, as a resul~ of which the flip-flop 164 is reset.
The signal in the set-output 163 becomes zero, as a result of which the tran-
sistor 161 becomes conductive, Through the electromagnet 152 passes a current
Il, which gensrates a magnetic field which reinforces the magnetic field of
the pormanent magnet 154. The output 167 of the monostable multivibrator
remains zero, so that the transistor 160 keeps blocking. This situation is
maintained9 until the signalpulse END is gsnerated (at the height of t2 in
Figure 3) as a result of which a signal is produced in the set-output 163 of
the flip-flop 164, by which the transistor 161 is bl ked. At the same time '
a signal is produced in the output of the monostable multivibrator 166, by
which the transistor 160 is opened and a current I2 passes through the electro-
magnet 152, which current generates a ma~netic field which acts against the
magnetic field of the permanent ~agnet 154, so that the cover is opened. The
output of the monostable multivibrator becomes zero after about 1 sec, as a
resulS of which the sign~l in the output 167 of the monostabl~ multivibrator
becomes zero and the transistor 160 is blocked. A new copying run can now be
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started.
In the abovetescribed embodiment it is accepted that tho eloctro-
maBnet and the permanont magnet are combined and are installed in tho frame.
This is a preferred embodiment, because in this way it is preventod, that
electrical wires must be brought into the cover via the shaft 43. However,
it is clear, that the invention is not limited to this embodiment, but that
other combinations are possible. It is particularly possible in the embodi-
ment represented to reverse the design, namely the electromagnet and the per-
manent magnet in the cover, and the soft iron block in the frame 151. Other
possible embodiments are a pormanent ~agnet in the cover, co~bined with an
electromagnet provided with a soft iron core in the frame, and reversed, a
permanent magnet in the cover, combined with an electromagnet provided with
a magnetized core in the frame, and reversed, whereby the two permanent mag-
nets attract each other, an electrom2gnet providcd with a soft iron core in
the cover combined with an electromagnet provided with a magnetized core in
the frame and reversed, and an electromagnet provided with a magnotized core
in the cover, combined with an electromagnet provided with a magnetized core
in the frame, whereby the two magnetized cores attract each other magnetically.
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