EP2666899A1

EP2666899A1 - Method for detecting the cycle termination of a household tumble machine

Info

Publication number: EP2666899A1
Application number: EP12168936.8A
Authority: EP
Inventors: Dusan Heldak; Pavol Vasko; Pavol Petracek; Gerd Maentele
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 2012-05-22
Filing date: 2012-05-22
Publication date: 2013-11-27

Abstract

In a method for detecting the cycle termination of a household tumble machine having sensors (28) for measuring at least two different parameters related to drying process, signals from sensors are fed to an electronic circuit in which they are combined according to a predetermined algorithm in order to improve the accuracy of said detection.

Description

The present invention relates to a washing machine having a drum rotating about a substantially horizontal axis, comprising supporting means for rotatably supporting the drum in a tub and detecting means for assessing unbalanced condition of washing and/or spinning.
With the term "washing machine having a drum rotating about a substantially horizontal axis" we mean all washing machines in which the rotational axis of the drum is horizontal or inclined.
Washing machines having sensors for assessing unbalanced conditions are well known in the art, for instance from EP 1154064 and EP 1167609 . In these documents sensors for detecting acceleration and/or movement of the drum are disclosed.
Washing unit, usually defined by the tub, the motor used for rotating the drum inside the tub and the transmission between the motor and the drum, is flexible suspended to cabinet, and this system (mass of washing unit, springs and dampers) has its own natural frequencies.
During water extraction phase of washing machine operation, the rotatable drum is subject to unbalance mass as result of uneven distribution of clothes load within the drum. The unbalance mass creates a spinning axis distinct from the horizontal geometric axis of drum causing vibration during rotation.
Currently, the vibration of washing machine and washing unit is attenuated with measurement of created unbalance mass at low speed. If the unbalance is lower than specified limit, machine goes to spinning phase of cycle. If it is higher, machine tries to redistribute the clothes inside the drum and measure created unbalance mass again. Created unbalance mass is proportional to speed fluctuation of drum (measured by tachometric generator of motor), if the drive system tries to keep constant speed of drum, as described in EP 0071308B1 .
This known system has various disadvantages:

it is not possible to monitor change of unbalance of laundry at high speeds;
current system has quite low accuracy due to high measurement noise. Calculated unbalance is influenced by total inertia of drum and laundry (that is not known with enough precision), actual state of friction between rotatable and non-rotatable components.
Due to these problems, it is needed:
to keep quite big gaps between washing unit and cabinet, to have enough space for washing unit movement during crossing of natural frequencies of washing unit system (usually in range of 200-400 rpm). It must be avoided contact between washing unit and cabinet leading to high noise and jumping of machine;
to create washing unit structure with enough stiffness to resist loads coming from unbalance

Another option is to measure the vibration of washing unit with accelerometers or proximity sensors. If the amplitudes of acceleration are too big, the timer in washing machine interrupts spinning phase, stops the drum and tries to redistribute the laundry to find better laundry distribution with lower unbalance.
This system has following disadvantages:

the signal from accelerometers is useable only at higher speeds - above natural frequencies of suspension system;
this means, that we need to have still unbalance detection system with speed fluctuation at low speeds with low precision;
it is still possible that measured unbalance is lower that real, and machine is crossing natural frequency area with high unbalance and consequently it is possible to have contacts between washing unit and cabinet as mentioned above;
accelerometers can bring additional precision at higher speed, so machine structure can be protected but anyway it is needed to redistribute laundry.

An object of the present invention is to provide a washing machine and a method for detecting unbalance therein which are not affected by the above technical problems, and which can provide a very reliable assessment of unbalanced conditions independently on the speed of rotation of the drum.
According to the invention, the above object is reached thanks to the features listed in the appended claims.
The applicant has surprisingly discovered that a very reliable measurement of unbalanced load and position of unbalanced load, independently on actual rotating speed of the drum of a domestic washing machine, can be carried out by measuring forces or strains acting between rotating and non-rotating parts of washing unit, particularly forces and strains acting on ball bearings supporting the axle of the drum. In the following we will use the terms strains and forces as having the same meaning, since strains are originated by mechanical forces. For front loader horizontal axis washing unit the force or strain sensors are applied in tub or hub area (ball bearing holder) on one side of drum. For top loader horizontal axis washing unit the force or strain sensors can be applied on both sides of washing unit in bearings or on one side only (as in front loaders).
Force sensors (strain gauge sensors, and others) can be attached to outer bearing ring or to bearing holder surface that is usually made from polymeric material, aluminum, cast iron or zinc alloy material. Measured forces from bearings are used to calculate centrifugal force that is created by unbalanced load and position of unbalanced load inside of the drum. Having this information, axial, angular position of unbalance and magnitude of unbalance (either static or dynamic) is known.
The measurement is based on capturing of transmitted forces between two components. Capturing can be done in several physical ways, like using strain gauge sensor, piezoelectric sensor, deformation sensor or others.
Roller bearings with sensors for measuring forces are known in automotive or aircraft industry, for instance from DE 10250340 . In the field of domestic washing machines it is known from EP 1695056 the use of a capacitance sensor for measuring the load on a roller bearing, but there is no suggestion to use this sensor for detecting unbalance. No document of prior art suggests an use of sensors associated to roller bearings for load unbalance detection purposes, particularly in washing domestic appliances.
Moreover the applicant has discovered that by using such sensors applied to components supported by the bearings, i.e. in the proximity of such bearings, the result in terms of unbalance assessment is improved.
Further advantages and features according to the present invention will become clear from the following detailed description, with reference to the attached drawings in which:

figure 1 is a schematic sectioned view of a front loader washing machine showing the general position of the bearing force/strain sensor according to the invention;
figure 2 is a view similar to figure 1 but referred to a top loader washing machine according to the invention;
figure 3 is an enlarged perspective view of the ball bearing zone of figure 1 showing the detailed area for sensor placement;
figure 4 is a perspective view of the hub of figure 3 in which the ball bearings are mounted and where the same area of figure 3 is shown;
figure 5 is a diagram showing a typical speed vs. time pattern of a washing machine drum during washing phase and spinning phase, in which different areas of intervention of traditional vibration sensors and strain/force sensors according to the inventions are pointed out;
figure 6 is a perspective view of a prior art washing unit where accelerometers are placed outside the tub;
figure 7 is a diagram showing a comparison between signals from accelerometers of figure 6 and strain/force sensors according to the invention, for a front loading washers with an unbalance of 0,5 kg placed in a front zone of the drum;
figure 8 is a comparison similar to figure 7, for the same unbalance and at a speed of 100 rpm;
figure 9 is a diagram similar to figure 8 for a speed of 200 rpm;
figure 10 is a diagram similar to figures 8 and 9 for a speed of 300 rpm;
figure 11 is a diagram for a speed of 500 rpm;
figure 12 is a diagram for a speed of 700 rpm; and
figure 13 is a diagram for a speed of 1000 rpm.

With reference to figures 1 and 2, a drum type washing machine 10 is shown, with horizontal axes of drum and which has top (figure 2) or front (figure 1) access to a drum 12 rotatably mounted in a tub 14.
The drum type washing machine 10 includes a cabinet 16 forming an exterior of the washing machine, a washing unit consisting of the tub 14, the drum 12 and a drive system 18 including a motor 18a, a belt 18b and a pulley 18c for driving an axle 20 of the drum 12.
There is a loading door 22 on front side of drum 12 (for front loader machine) or a door 24 on outer diameter of tub and drum (for top loader machine of figure 2). Opening for laundry loading is on drum front or on wrapper. Drum 12 is rotatable provided within the tub 14 with a hub 26 (bearing holder) on one side of drum (for front loader) or on both sides of tub (for top loader).
With reference to figures 3 and 4, a strain gauge sensor 28 is placed on an outside annular surface 26a of the hub 26, i.e. on the surface which is opposite the inner surface 26b on which two ball bearings B are mounted for supporting the axle 20 of the drum 12. In figure 4 is it shown a flange 30 of the hub 26 for fixing the hub to the tub 14.
In the diagram of figure 5, the first part of the speed pattern is related to a washing phase in which the drum turn clockwise and counterclockwise for a predetermined period (tumbling phase A). The phase C, at around 100 rpm, shows an unbalance measurement by means of motor speed fluctuations. With the area D it is indicated a suspension system natural frequency area, while with area E an area where it is possible to get clear signal from known accelerometers. With area F it is indicated an area where clear signals can be derived from sensors according to the invention, i.e. placed in the proximity of the ball bearings for sensing forces/strains. By considering figure 5 it is clear the advantage of the present invention, according to which it is possible to avoid crossing of natural frequency area C with high unbalances and possible contacts of the washing unit with cabinet.
The above advantage is further documented in figures 7 to 13 which are comparisons between a traditional washer with four accelerometers K mounted on the tub 14 (figure 6) and an identical washer modified according to the invention, i.e. in which four strain sensors are installed in the hub as shown in figure 4 .
Figure 7 is a comprehensive comparison for different speeds of the drum and for a fixed (artificial) unbalance of 0,5 kg put in front of the drum. In figure 7, as in the following figures 8-13, on X axis time is reported, while on Y axis, upper part, it is reported the signal from the four accelerometers of figure 6 in m/seC² (front-up, rear-up, front-side and rear-side), the signal from the four sensors 28 of figure 4, and the signal from tachometric generator.
In figure 8 (100 rpm) it is immediately evident how the signals from the four accelerometers cannot be used, while signals from four strain sensors are clear and can be used.
At a speed of 200 rpm (figure 9) signal from accelerometers are still affected by noises and they are hardly usable, while signals from strain sensors are perfectly clear.
From 300 to 1000 rpm (and beyond), according to figures 10 to 13, both signals from accelerometers and from strain sensors are good and can be used.
With reference to the above description, it is clear that by measuring bearing forces it is possible to calculate the unbalance with higher precision than with conventional system using speed fluctuations and accelerometers. By measuring bearing forces it is possible to apply this sensing speed lower than natural frequencies range of the washing unit main suspension system. By measuring unbalanced load and position thereof allows compensating of unbalance and its position by known active balancing systems. Advantage is that unbalanced load can be compensated to minimum which has benefits in a lower wash unit movement and lower structural load acting on wash unit, and in_reducing transmission forces from wash unit to cabinet and by this to reduce vibration and improve noise performance.
Another advantage is that rotating drum is crossing natural frequencies of washing unit with low unbalanced mass, and consequently vibration and movement of washing unit is reduced. Therefore drum volume can be enlarged by increasing diameters of drum and tub and reducing clearances with cabinet. All necessary gaps can be optimized and reduced.
By measuring bearing forces during laundry distribution phase allows to adapt spin profile of laundry distribution to minimize unbalance creation process. By measuring bearing forces during spinning at different spin speeds, it is possible to detect change in unbalance due to water extraction from laundry and compensate it also during spinning. Compensation and reduction of unbalance can be used for decreasing total energy consumption of washing machine due to reduction of deflection of drum and reduction of air friction. By measuring bearing forces before loading the drum and after drum is loaded by comparing forces, weight of laundry inside the drum can be detected and the user, on the basis of this load detection, can use the appropriate amount of detergent. Same principle can be used also for detecting of wet laundry inside drum.
Even if in the above description, provided as a non limitative example, reference is made to a drum rotated by a traditional driving system (motor, belt and pulley), the present invention can be used for washing machine using a so called direct drive system as well.

Claims

Washing machine (10) having a drum (12) rotating about a substantially horizontal axis, comprising supporting means (26, 26a, 30, B) for rotatably supporting the drum (12, 20) in a tub (14) and detecting means (28) for assessing an unbalanced condition of washing and/or spinning, characterized in that said detecting means comprises at least a sensor (28) for detecting strain on or in the proximity of said supporting means (26, 26a, 30, B).
Washing machine according to claim 1, wherein said sensor (28) is selected in the group consisting of strain gauge sensors, piezoelectric sensors, deformation sensors or combination thereof.
Washing machine according to claim 1 or 2, wherein said supporting means comprises at least a ball bearing (B) rotatably supporting an axle (20) of the drum (12) and placed in a seat of the tub (14) or hub (26), said sensor (28) being attached to a ring of said ball bearing (B).
Washing machine according to claim 1 or 2, wherein said supporting means comprises at least a ball bearing (B) rotatably supporting an axle (20) of the drum (12) and placed in a seat of the tub (14) or hub (26), said sensor (28) being attached to a surface (26a) of said seat.
Method for detecting unbalance in a washing machine having a drum (12) rotating about a substantially horizontal axis, comprising supporting means (26, 26a, 30, B) for rotatably supporting the drum (12, 20) in a tub (14) and detecting means (28) for assessing an unbalanced condition of washing and/or spinning, characterized in that it comprises the step of detecting forces transmitted by the drum through the supporting means (26, 26a, 30, B) to the tub (14) by means of at least a sensor (28) located in proximity of said supporting means.
Method according to claim 5, wherein said sensor (28) is selected in the group consisting of strain gauge sensors, piezoelectric sensors, deformation sensors or combination thereof.
Method according to claim 5, wherein said step is carried out after clothes are loaded into the drum (12) in order to assess the mass of such load.