[0001] The present invention relates to a sensor device for determining the angular position
of a wash drum of a washing machine.
[0002] As is known, certain latest-generation washing machines are fitted with a device
for determining the angular position of the wash drum, to enable an electric control
system to set the wash drum to a predetermined angular position at the end of the
wash cycle.
[0003] More specifically, the wash drum is normally mounted inside a wash tub to rotate
about a longitudinal axis, and is rotated by an electric drive unit via an external
pulley fitted to the shaft rotating the wash drum.
[0004] Patent Application
FR-2784402 describes a device for determining the angular position of a wash drum of a washing
machine, and which comprises a magnetic switch device; a permanent magnet; and a strip
or band of ferromagnetic material fixed to the wash drum rotation pulley, and which
is interposed between the permanent magnet and the magnetic switch device when the
wash drum is in a predetermined angular position.
[0005] More specifically, the magnetic switch device comprises an internal switch with two
normally-open blades of conducting material, which are brought into contact with each
other when subjected to a magnetic field of intensity above a given threshold, and
are parted, thus opening the switch, when subjected to a magnetic field of intensity
below the threshold.
[0006] The switch device is fixed stably to the rear wall of the wash tub, in such a position
as to face the outer peripheral edge of the pulley; the permanent magnet is fixed
stably to the rear wall of the wash tub, inwards of the pulley and facing the inner
peripheral edge of the pulley, on the opposite side with respect to the magnetic switch;
and the band of ferromagnetic material is of predetermined length and fixed to a portion
of the pulley.
[0007] As the pulley and the wash drum rotate, the ferromagnetic band is interposed cyclically
between the permanent magnet and the switch device, so that the switch closes temporarily
whenever the pulley is set to a given angular position. In fact, when interposed between
the switch device and the permanent magnet, the ferromagnetic band conducts the field
lines towards the switch device, so that the intensity of the field on the switch
blades exceeds the predetermined threshold, thus closing the switch.
[0008] The above device has a number of drawbacks, on account of the way in which it is
installed on the washing machine. That is, in the event the permanent magnet and the
switch device are positioned too far apart, the magnetic field towards the switch
device may decrease, thus resulting in failure of the switch device to close when
the band is interposed between the switch device and the permanent magnet, and hence
in failure to determine the angular position of the wash drum.
[0009] Moreover, the device must be assembled before the pulley is fitted to the wash drum
shaft, which obviously complicates both assembly of the washing machine and subsequent
servicing of the device itself. In the latter case, in fact, the device can only be
removed from the wall of the wash drum after first removing the pulley from the wash
drum shaft, which is not only awkward but also a time-consuming job, thus increasing
customer service cost.
[0010] It is therefore an object of the present invention to provide a device for determining
the angular position of the wash drum of a washing machine, which, besides being cheap
to produce and install, is also independent of assembly of the pulley to the washing
machine.
[0011] According to the present invention, there is provided a device for determining the
angular position of a wash drum of a washing machine, as claimed in the accompanying
Claims.
[0012] A non-limiting embodiment of the present invention will be described by way of example
with reference to the accompanying drawings, in which:
Figure 1 shows, schematically, a portion of a washing machine fitted with a device
for determining the angular position of a wash drum in accordance with the teachings
of the present invention, and with the wash drum in a first angular position;
Figure 2 shows, schematically, the Figure 1 washing machine portion, with the wash
drum in a second angular position.
[0013] Number 1 in Figure 1 indicates as a whole a washing machine substantially comprising
an outer casing 2; and a wash assembly 3, in turn comprising a wash tub 4 housed stably
inside outer casing 2, and a laundry wash drum 5 (shown partly in the attached drawings)
housed inside wash tub 4.
[0014] Wash drum 5 is mounted inside wash tub 4 to rotate about an axis of rotation A, and
has a shaft 16 extending, coaxially with axis of rotation A, through a vertical rear
wall 6 of wash tub 4, and projecting partly outwards of wash tub 4.
[0015] The end of shaft 16 projecting from vertical wall 6 of wash tub 4 is fitted with
a pulley 7, which is connected by a drive belt 8 to an output shaft 9 of an electric
motor 10 for rotating wash drum 5.
[0016] Washing machine 1 also comprises a sensor device 11 for determining the angular position
of wash drum 5.
[0017] Sensor device 11 substantially comprises a permanent magnet 12 generating a magnetic
field of predetermined intensity; a sensor 13 for determining the intensity of the
magnetic field; and a strip or band 14 of ferromagnetic material, which is fixed stably
to pulley 7 in a predetermined position related to a given angular position of wash
drum 5.
[0018] Unlike known devices, permanent magnet 12 and sensor 13 of sensor device 11 are both
fixed stably to wall 6 in a position facing and outwards of the outer peripheral edge
15 of pulley 7.
[0019] More specifically, in the example shown schematically in the attached drawings, permanent
magnet 12 and sensor 13 are located on wall 6 at a distance D1, from axis of rotation
A, greater than the outside diameter DE of pulley 7, so as to be located completely
outwards of pulley 7.
[0020] More specifically, permanent magnet 12 and sensor 13 are located a given distance
D2 apart on wall 6, so that both are located completely outwards of the projection
of outer peripheral edge 15 of pulley 7 onto wall 6.
[0021] In the example shown, sensor 13 comprises a Hall-effect sensor, which supplies an
electric output signal of a current/voltage value proportional to the intensity of
the measured magnetic field to which the sensor is subjected; and band 14 has a predetermined
length, so as to extend along a circular portion of pulley 7.
[0022] Sensor device 11 also comprises a core 18 of ferromagnetic material, which is fixed
stably to wall 6 of wash tub 4, between sensor 13 and permanent magnet 12, and outwards
of pulley 7.
[0023] In actual use, when band 14 of ferromagnetic material on pulley 7 is positioned alongside
and adjacent to permanent magnet 12 and sensor 13 (as shown in Figure 1), it defines
a magnetic circuit which closes the flux lines of the magnetic field generated by
permanent magnet 12 on sensor 13, thus increasing the intensity of the field on sensor
13.
[0024] Conversely, when band 14 of ferromagnetic material on pulley 7 is not positioned
adjacent to sensor 13 and permanent magnet 12 (as shown in Figure 2), sensor 13 is
only subjected to a small portion of the flux lines of the magnetic field generated
by magnet 12, which in this case travel through the air surrounding sensor 13.
[0025] By appropriately processing the magnetic field intensity contained in the signal
generated by sensor 13, it is therefore possible to determine whether or not band
14 on pulley 7 is positioned facing a fixed angular reference associated with the
portion of wall 6 in which sensor device 11 is positioned, and so determine the instant
in which pulley 7 and hence wash drum 5 reach a predetermined angular position.
[0026] Sensor device 11 as described above is extremely advantageous : locating sensor 13
and permanent magnet 12 completely outwards of pulley 7 simplifies assembly of sensor
device 11 to wall 6, by making assembly of the device completely independent of assembly
of pulley 7.
[0027] Moreover, using a Hall-effect sensor, the angular position of the wash drum is determined
by processing the variation in the intensity of the magnetic field, a condition which
is independent of the distance between permanent magnet 12 and sensor 13.
[0028] Clearly, changes may be made to the angular position sensor device as described and
illustrated herein without, however, departing from the scope of the present invention
as defined in the accompanying Claims.
1. A sensor device (11) for determining the angular position of a wash drum (5) of a
washing machine (1); said wash drum (5) being mounted inside a wash tub (4) to rotate
about an axis of rotation (A), and having a shaft (16) coaxial with said axis of rotation
(A) and which extends through a wall (6) of said wash tub (4); said shaft (16) being
fitted with a pulley (7) rotated about said axis of rotation (A) by drive means (10);
said sensor device (11) comprising a permanent magnet (12) generating a magnetic field,
sensor means (13) for determining the intensity of the magnetic field, and a band
(14) of ferromagnetic material fixed to said pulley (7) so as to occupy a portion
of the pulley (7); and said sensor device (11) being characterized in that said sensor means (13) and said permanent magnet (12) are fixed stably to said wall
(6) of said wash tub (4) so that both face the same peripheral edge (15) of said pulley
(7).
2. A device as claimed in Claim 1, wherein said sensor means (13) and said permanent
magnet (12) are fixed stably to said wall (6) of said wash tub (4) outwards of said
pulley (7), so that both are positioned facing the outer peripheral edge (15) of the
pulley (7).
3. A device as claimed in Claim 1 or 2, wherein said sensor means (13) and said permanent
magnet (12) are fixed stably to said wall (6) of said wash tub (4), at a distance
(D1), from said axis of rotation (A), greater than the outside diameter (DE) of said
pulley (7), so as to be located completely outwards of the pulley (7).
4. A device as claimed in any one of the foregoing Claims, wherein said sensor means
(13) and said permanent magnet (12) are located a given distance (D2) apart on said
wall (6), so that both are located completely outwards of the projection of the outer
peripheral edge (15) of the pulley (7) onto said wall (6).
5. A device as claimed in any one of the foregoing Claims, wherein said sensor means
(13) comprise a Hall-effect sensor.
6. A device as claimed in any one of the foregoing Claims, and comprising a core (18)
of ferromagnetic material, which is located outwards of said pulley (7), between said
sensor means (13) and said permanent magnet (12).
7. A washing machine (1) comprising an outer casing (2) housing a wash tub (4); and a
wash drum (5) mounted inside the wash tub (4) to rotate about an axis of rotation
(A), and having a shaft (16) coaxial with said axis of rotation (A) and which extends
through a wall (6) of the wash tub (4); the washing machine (1) also comprises a pulley
(7) fitted to said shaft (16), and drive means (10) for rotating said pulley (7) about
said axis of rotation (A); and said washing machine being characterized by comprising a sensor device (11) for determining the angular position of said wash
drum (5), as claimed in any one of the foregoing Claims.