[0001] The present invention relates to devices for operating sliding doors, particularly
automatic sliding doors of the type which are operated, for example, as a result of
the activation of a presence detector situated in the region of the floor in front
of the door.
[0002] The operating devices used up to now for this type of doors comprise a rotary, direct-current,
alternating current, or brushless electric motor which drives an endless belt, usually
a toothed belt, by means of a reduction unit, the belt having two parallel passes
connected rigidly to the two leaves of the sliding door so that the rotation of the
belt in one sense or the other causes the leaves to open or close, respectively.
[0003] The main disadvantage of the solution indicated above lies in the fact that the transmission
which brings about the movement of the leaves is quite complex, being constituted
by a moderate number of parts, and is consequently the source of a series of possible
problems such as, for example, wear of the belts or of the brushes of the motor, the
need to tension the belt periodically, the generation of dust resulting from the wear
of the belt and, finally, noise due to the reduction unit and to the belt.
[0004] The object of the invention is to prevent the problems indicated above by means of
an operating system which is particularly simple and reliable.
[0005] In order to achieve this object, the subject of the invention is a device for operating
a sliding door comprising at least one leaf mounted for sliding on guide means, characterised
in that the device comprises a brushless, direct-current, linear electric motor including:
a main stator constituted by a bar of ferromagnetic material mounted on a fixed structure
parallel to the direction of sliding of the leaf,
at least one electrical winding which is disposed around a portion of the bar and
is intended to be supplied with direct current,
a unit which is movable linearly relative to the bar and is connected rigidly to the
leaf, the movable unit carrying permanent magnets facing two opposite sides of the
bar, and
two auxiliary stator bars parallel to the main bar and spaced from opposite sides
thereof.
[0006] A brushless, direct-current, linear motor of the type indicated above formed the
subject of the technical article "Analysis of a slotless permanent-magnet brushless
DC linear motor" by B. Brunelli, D. Casadei, G. Serra, published in the Proceedings
of "ICEM 90" - International Conference on Electrical Machines, Cambridge, Massachussetts,
USA - 1990.
[0007] Various advantages result from the use of this electric motor in the operating device
according to the invention. First of all, the transmissions of known systems (the
reduction units, belts and pulleys) are eliminated with the consequent elimination
of the corresponding problems. The number of components is thus minimised. The system
does not require mutually sliding parts and is not therefore subject to wear as in
known systems. Noise is reduced to a minimum and is due simply to the rolling of the
carriage of each leaf on the respective guide. There is no need to make adjustments
after mounting, such as the tensioning of the belt which is necessary in the known
devices. Naturally, the elimination of the belt also eliminates the problem of dust
generated by its wear. The elimination of the transmission, of course, maximises the
performance of the device. Friction is reduced to a minimum.
[0008] The use of the linear electric motor indicated above also enables the leaf of the
door to be braked electrically by the reversal of the polarity of the supply, which
would be difficult to achieve with an asynchronous, linear electric motor.
[0009] Naturally, the reversal of the movement of the leaf is also brought about simply
by the reversal of the polarities of the terminals of the stator winding.
[0010] A door with two leaves, of course, may have a single main stator with its two auxiliary
stator bars, and two movable units associated with the two leaves, respectively.
[0011] The linear electric motor indicated above is also free of the problems which would
affect other types of linear electric motors such as a linear stepper motor (which
would have poor starting acceleration, an unsuitable working voltage and extreme sensitivity
to dirt) or an asynchronous linear motor which would require a very complicated piloting
system in order to achieve electrical braking.
[0012] The invention will now be described with reference to the appended drawings, provided
purely by way of non-limiting example, in which:
Figure 1 is a front view of a sliding door with two leaves,
Figure 2 is a view of the detail indicated by the arrow II in Figure 1, on an enlarged
scale, and
Figure 3 is a section taken on the line III-III of Figure 2, on an enlarged scale.
[0013] In Figure 1, the reference numeral 1 generally indicates an automatic sliding door,
that is, a door of the type which is operated automatically as a result of the activation
of presence sensors disposed on each side of the door in the region of the floor 2
which is in front of the door.
[0014] The door 1 comprises two leaves 3 (in the embodiment illustrated, two glass leaves,
the frame 3a of each of which bears a pair of carriages 4). Each carriage 4 comprises
a substantially T-shaped support bracket 5 (see also Figures 2, 3) which is fixed
to the upper part of the respective frame 3a and on which three wheels 6 are mounted
idly. The central wheel 6 of the three and the other two end wheels 6 engage, respectively,
two facing guide tracks 7, 8 (Figure 3) of a guide rail 9 fixed horizontally on a
fixed structure 10, for example, by means of screws 11, so that each leaf 3 is supported
for sliding, preferably along a straight path, in the directions indicated by the
arrows A in Figure 1.
[0015] One of the two carriages 4 of each leaf 3 is associated with the movable unit of
a brushless, direct-current, linear electric motor, generally indicated 12.
[0016] The electric motor 12 comprises a stator constituted by a bar 13 of ferromagnetic
material, for example, of steel, the ends of which are anchored to the fixed structure
10 and which is disposed parallel to the guide rail 9. A substantial portion of the
length of the bar 13 is covered by one or more electrical windings which are intended
to be supplied with direct current. One of the two carriages 4 of each leaf 3 rigidly
supports a movable unit 15 by means of a bracket 14, the unit 15 being mounted for
linear movement on the stator bar 13 without having parts in contact therewith. The
movable unit 15 comprises two permanent magnets 16 facing the two opposite sides 13a
of the stator bar 13 and joined together by two plates 17. Finally, the electric motor
is completed by two auxiliary stator bars 18 (Figure 3) disposed parallel to the main
bar 13 and spaced from its two opposite sides so as not to interfere with the passage
of each movable unit 15. The auxiliary bars are preferably connected at their ends
to facilitate the closure of the lines of the magnetic field generated by the main
bar 13 at the moment when the winding associated therewith is supplied with direct
current.
[0017] The supply of current to the winding causes each movable unit to move in one direction
or the other according to the polarity of the supply to the motor. It therefore suffices
to reverse the polarity in order to reverse the movement of each leaf.
[0018] As can be seen from the foregoing description, the operating device according to
the invention has no transmission between the motor and the leaf and is therefore
free of all the problems of the prior art indicated above.
[0019] Naturally, the details of construction relating to the structural parts of the motor
and to the manner in which the leaves of the door are guided for sliding may also
differ from those illustrated purely by way of example. The two auxiliary bars 18
may also be used as guides for the movement of each unit 15. In this case, for example,
each unit 15 has two appendages constituting two bushes which are mounted for sliding
on the bars 18.
1. A device for operating a sliding door, comprising at least one leaf (3) mounted for
sliding on guide means (9), characterized in that the device comprises a brushless,
direct-current, linear electric motor (12), including:
a main stator (13) constituted by a bar of ferromagnetic material mounted on a fixed
structure parallel to the direction (A) of sliding of the leaf (3),
at least one electrical winding which is disposed around a portion of the bar and
is intended to be supplied with direct current,
at least one auxiliary stator bar (18) parallel to the main bar (13) and spaced therefrom,
and
at least one unit which is movable linearly relative to the main bar (13) and is connected
rigidly to the leaf (3), the movable unit carrying at least one permanent magnet (16)
disposed between the main bar (13) and the at least one auxiliary stator bar (18).
2. An operating device according to Claim 1, characterized in that the linear electric
motor (12) includes at least two auxiliary stator bars (18) parallel to the main bar
(13) and spaced from the two opposite sides thereof, permanent magnets (16) facing
opposite sides of the main bar (13).
3. An operating device according to Claim 1, characterized in that the leaf (3) slides
in the direction (A) along a substantially straight path.
4. An operating device according to Claim 1, for a sliding door with two leaves (3),
characterized in that it comprises a single main stator bar (13) associated with two
movable units (12) connected rigidly to the two leaves (3) of the door, respectively.
5. A device according to Claim 1, characterized in that the two auxiliary bars (18) support
each movable unit (15) slidably.
6. An automatic sliding door, characterised in that it comprises an operating device
according to one or more of the preceding claims.