TITLE OF THE INVENTION

METHOD FOR PRODUCING A VIBRATION MEMBER FOR A CLEANING TOOL

BACKGROUND OF THE INVENTION

The invention relates to a cleaning tool using ultrasonic energy to remove biological debris from a surface, in particular a submerged surface.

An example of such a cleaning tool can be found in WO2021/251825A1 from the same applicant. The disclosed cleaning tool includes a vibration member with an emitting surface for emitting vibrational waves caused by a piezoelectric transducer.

Challenges associated with the cleaning tool mainly relate to durability of the cleaning tool as the cleaning tool, and the vibration member in particular, is used in a dirty and wet environment requiring special attention to protect the piezoelectric transducer and any electronics used to drive the piezoelectric transducer, a preferably efficient conversion from electrical energy to vibration energy, and high mechanical loads on the cleaning tool due to the vibrations. Measures taken to improve mechanical durability and/or protection against the dirty and wet environment typically decrease the energy efficiency of the tool. On the other hand, measures taken to improve safety and/or energy efficiency have a negative impact on mechanical durability as a specific example below illustrates.

The vibration member of WO2021/251825A1 includes a piezoelectric transducer clamped between a first component and a second component. The first component is generally used to hold the vibration member in a housing, while the second component includes the emitting surface. The piezoelectric transducer can be operated by applying an electric field to the piezoelectric transducer. To increase displacement for the same voltage, which has the advantage that the voltage can be kept relatively low and is thus safer, it is possible to use a stack of at least two piezoelectric elements in the piezoelectric transducer. However, a drawback of the use of a stack of piezoelectric elements is that it requires additional electrical connections between the piezoelectric elements and a driver applying a voltage to the piezoelectric elements. Because the vibration member is configured to vibrate, the electrical connections are also subject to dynamic loads. The more electrical connections, the higher the chance that an electrical connection will fail because of the dynamic load.

SUMMARY OF THE INVENTION

In view of the above it is an object of the invention to provide an improved cleaning tool based on vibration energy that can withstand a wet and dirty environment while at the same time reaches a relatively high efficiency and is able to withstand the dynamic loads associated with the vibrations for a relatively long period of time.

According to a first aspect of the invention, there is provided a cleaning tool comprising: a housing, a vibration member attached to the housing, wherein said vibration member includes an emitting surface at a free end thereof for emitting vibrational waves caused by a piezoelectric transducer, a driver to operate the piezoelectric transducer at a first frequency being a resonance frequency of the vibration member, and a sealing element arranged between the vibration member and the housing to prevent dirt and/or water from entering the housing in order to prevent dirt and/or water from reaching the piezoelectric transducer and/or driver, wherein the sealing element is arranged at or near a node of a standing wave in the vibration member corresponding to the resonance frequency.

The first aspect of the invention is based on the insight that positioning the sealing element at a node of a standing wave provides two advantages at the same time:

1. the sealing function is best when the sealing element is not or minimally subjected to vibrations, and

2. the efficiency of the vibration member is not compromised by the sealing element when the sealing element is at or near a node and minimally interacting with the corresponding standing wave. It is to be noted that at or near a node does not necessarily mean that the sealing element is exactly at the node. The definition of at or near a node of a standing wave may, depending on the circumstances, e.g. amplitude/energy of the standing wave, be within 1/10 ^th of a corresponding wavelength, preferably within 1/15 ^th of a corresponding wavelength, more preferably within 1/20 ^th of a corresponding wavelength, even more preferably within 1/25 ^th of a corresponding wavelength, and most preferably within 1/30 ^th of a corresponding wavelength from the node. Alternatively, the definition of at or near a node may be within 10mm, preferably within 8mm, more preferably within 6mm, even more preferably within 4mm, and most preferably within 2.5mm from the node, e.g. within 1 or 2 mm from the node.

The sealing element being arranged at or near a node is first of all a practical consideration as the node will be at a specific infinitely small location and the sealing element has a finite dimension and thus will also be arranged next to the node even when a center of the sealing element is exactly at the node location. Second, a further consideration is that the location of the node may, depending on the use cases and circumstances, also including age and wear, not be fixed and may drift or temporarily be at a different location. In such cases, the sealing element may not overlap with the node location but may still be sufficiently near the node location to provide the abovementioned advantages.

In an embodiment, the sealing element is a sealing ring. An advantage thereof is that it is a single continuous element with the least risk of leakage.

In an embodiment, the vibration member includes a groove for receiving the sealing element. An advantage thereof is that the groove will limit movement of the sealing element and keep it at a position at or near a node. The groove may be a recess in the vibration member or may be formed between two protruding side walls extending from the vibration member or a combination thereof. The groove may for instance be formed in a local thickening of the vibration member. In an embodiment, the vibration member further comprises a first component configured to attach the vibration member to the housing, said first component being arranged at one side of the piezoelectric transducer, and a second component comprising the emitting surface, said second component being arranged at an opposite side of the piezoelectric transducer, wherein the sealing element is arranged between the second component and the housing.

In an embodiment, the sealing element is arranged at a distance from the piezoelectric transducer, which distance is substantially 2/3 of a length of the second component. In this way it is possible to provide half a wavelength between the piezoelectric transducer and the sealing element and a quarter wavelength between the sealing element and the emitting surface thereby having an anti-node at the emitting surface to emit vibrational waves.

In an embodiment, the sealing element is arranged close to the piezoelectric transducer allowing for instance to use a dimension of the second component in combination with a resonance frequency such that a distance between the sealing element (and piezoelectric transducer) and the emitting surface corresponds to a quarter wavelength of the standing wave in the second component corresponding to the resonance frequency. This means that compared to the previously described embodiment in which three quarter wavelength is present between the piezoelectric transducer and the emitting surface, a smaller second component can be used for the same resonance frequency while at the same time being able to protect the piezoelectric transducer and electronics from water and/or dirt by arranging a sealing element at or near a node. Hence, in an embodiment, a length of the second component is substantially equal to a quarter wavelength of the standing wave in the second component corresponding to the resonance frequency.

It is noted that the term "close to the piezoelectric transducer" may have the same definition as described above for "at or near a node".

In an embodiment, the piezoelectric transducer includes a stack of piezoelectric elements, e.g. an even number of piezoelectric elements, wherein the vibration member is configured such that a standing wave corresponding to the resonance frequency has a node substantially at the center of the piezoelectric transducer.

In an embodiment, the second component at least partially overlaps with the piezoelectric transducer seen in longitudinal direction, and wherein the sealing element is arranged at or near the overlapping portion of the second component. In this manner, the sealing element can be arranged closer to the node thereby improving performance.

In an embodiment, the first component comprises a flange for attaching the vibration member to the housing.

The cleaning tool may be suitable to clean a toilet, urinal or sink. In such a case the cleaning tool may be moveable, e.g. like a hand tool. It is also possible that the cleaning tool is arranged more permanently in or next to a sink, e.g. to clean glassware, such as beer glasses.

The first aspect of the invention also relates to a vibration member for a cleaning tool according to the first aspect of the invention, comprising: a piezoelectric transducer, a first component configured to attach the vibration member to the housing, said first component being arranged at one side of the piezoelectric transducer, and a second component comprising an emitting surface for emitting vibrational waves caused by the piezoelectric transducer, said second component being arranged at an opposite side of the piezoelectric transducer, wherein the second component comprises a recess for receiving a sealing element, and wherein the recess is arranged at a distance from the piezoelectric transducer, which distance is substantially 2/3 of a length of the second component, or the recess is arranged close to the piezoelectric transducer.

Features and/or embodiments described above for the cleaning tool according to the first aspect of the invention but in relation to the vibration member may also apply, where applicable, to the vibration member according to the first aspect of the invention and vice versa.

The first aspect of the invention may readily be combined with features and embodiments of the second, third and/or fourth aspect of the invention as described below in more detail.

According to a second aspect of the invention, there is provided a method for producing a vibration member for a cleaning tool comprising the following steps: a. providing a stack of piezoelectric elements, wherein the number of piezoelectric elements is even, b. arranging one or more electrodes between adjacent piezoelectric elements in the stack of piezoelectric elements, c. providing an electrically conductive first component to hold the vibration member in a housing of the cleaning tool, d. providing an electrically conductive second component including an emitting surface for emitting vibrational waves, e. providing a protective layer on all external surfaces of the second component except for at least a portion of a surface configured to face the stack of piezoelectric elements, f. mechanically connecting the first component to the second component with the stack of piezoelectric elements and the one or more electrodes arranged between adjacent piezoelectric elements in between the first and second component, wherein an outer electrode is provided between the second component and the stack of piezoelectric elements to contact the portion of the surface of the second component with no protective layer, wherein the mechanical connection between the first and second component also provides an electrical connection.

An advantage of the method according to the second aspect of the invention is that the first and second components electrically connect the outer electrodes sandwiching the stack of piezoelectric elements, so that only one electrical connection is required to electrically connect these two electrodes to a driver instead of two thereby reducing the risk of failure and improving durability.

In an embodiment, step e. comprises the following steps: el. treating all external surfaces of the second component to provide a protective layer, and e2. removing the protective layer at the surface of the second component facing the stack of piezoelectric elements.

In an embodiment, the first component is configured to act as outer electrode for the stack of piezoelectric elements.

In an embodiment, an outer electrode is provided between the first component and the stack of piezoelectric elements.

In an embodiment, the vibration member is configured to provide an electrical connection between a driver and the first component, an outer electrode at the first component side of the stack of piezoelectric elements, or a connecting member at the first component side of the stack of piezoelectric elements providing the mechanical and electrical connection between the first and second component. An advantage of the electrical connection between the first and second component is that the electrical connection to the driver can now be at any suitable location.

In an embodiment, the stack of piezoelectric elements comprises two piezoelectric elements and a single electrode is arranged between the two piezoelectric elements.

In an embodiment, the piezoelectric elements are ring-shaped with a center hole allowing to receive a connecting member configured to connect the first component to the second component.

In an embodiment, the connecting member is a bolt, and the second component comprises a threaded bore to receive and couple with the bolt. In an embodiment, the second component comprises aluminum or an alloy thereof.

In an embodiment, treating the second component includes anodizing.

In an embodiment, the first component comprises stainless steel or an alloy thereof.

In an embodiment, the vibration member is a vibration member for a cleaning tool according to the first aspect of the invention.

In an embodiment, the first and second component include electrically conductive material and the protective layer includes electrically non-conductive material.

In an embodiment, the second component includes a first material, and the protective layer includes a second material, wherein the corrosion resistance of the second material is higher than the first material.

The second aspect of the invention also relates to a cleaning tool comprising: a housing, a vibration member attached to the housing, wherein said vibration member includes an emitting surface for emitting vibrational waves caused by a piezoelectric transducer, a driver for driving the piezoelectric transducer of the vibration member, wherein the vibration member further comprises: a first component configured to attach the vibration member to the housing, said first component being arranged at one side of the piezoelectric transducer, a second component comprising the emitting surface, said second component being arranged at an opposite side of the piezoelectric transducer, two outer electrodes sandwiching the piezoelectric transducer, wherein the first component is mechanically connected to the second component thereby clamping the outer electrodes and piezoelectric transducer together, wherein the mechanical connection between the first and second component also provides an electrical connection between the two outer electrodes, wherein the piezoelectric transducer includes a stack of piezoelectric elements, wherein the number of piezoelectric elements is even, and wherein one or more electrodes are arranged between adjacent piezoelectric elements in the stack of piezoelectric elements, and wherein a single electrical connection is provided between the driver and the two outer electrodes.

The cleaning tool may be suitable to clean a toilet, urinal or sink. In such a case the cleaning tool may be moveable. It is also possible that the cleaning tool is arranged more permanently in or next to a sink, e.g. to clean glassware, such as beer glasses.

In an embodiment, the cleaning tool is also a cleaning tool according to the first aspect of the invention.

In an embodiment, the vibration member is a vibration member according to a third aspect of the invention described below in more detail.

According to a third aspect of the invention there is provided a vibration member comprising an emitting surface for emitting vibrational waves at a free end of the vibration member caused by a piezoelectric transducer, and wherein the vibration member at an opposite end of the free end of the vibration member comprises a flange for attaching the vibration member to a housing.

In an embodiment, the flange has a similar sized cross-section as a piezoelectric transducer of the vibration member, and a recess arranged next to the flange.

In an embodiment, the flange has a larger cross-section than the piezoelectric transducer of the vibration member. In an embodiment, the vibration member includes a first flange, a second flange, and a recess arranged in between the first and second flanges. Preferably, the cross-section of the vibration member at the recess is similarly sized as the piezoelectric transducer.

In an embodiment, the vibration member further comprises a first component configured to attach the vibration member to the housing, said first component being arranged at one side of the piezoelectric transducer, and a second component comprising the emitting surface, said second component being arranged at an opposite side of the piezoelectric transducer, and wherein the flange is arranged at the first component.

In an embodiment, the first component comprises stainless steel or an alloy thereof.

In an embodiment, the driver is configured to operate the piezoelectric transducer at a first frequency being a resonance frequency of the vibration member, wherein a length of the first component corresponds to substantially half a wavelength of a standing wave in the vibration member corresponding to the resonance frequency.

According to a fourth aspect of the invention, there is provided a method to operate a vibration member of a cleaning tool, said method comprising the following steps: a. detecting a resonance frequency of the vibration member, b. operating the vibration member at the detected resonance frequency, c. applying one or more pulses to the vibration member to cause the vibration member to vibrate across a specific spectrum of frequencies in order to generate a burst of sound waves, d. pausing the driving of the vibration member, wherein steps a. and b are alternatingly carried out in a first cleaning mode, wherein steps c. and d. are alternatingly carried out in a second cleaning mode, and wherein the second cleaning mode is carried out after the first cleaning mode.

In an embodiment, a duration of the second cleaning mode is shorter than a duration of the first cleaning mode. In an embodiment, step a. is carried out at a smaller vibration power output than steps b. and/or c.

In an embodiment, during the first cleaning mode, a duration of step a. is smaller than a duration of step b.

In an embodiment, during the second cleaning mode, a duration of step d. is smaller than a duration of step c.

It will be appreciated by the skilled person that embodiments and/or features related to one aspect of the invention can be applied, where applicable, to other aspects of the invention.

Throughout the specification, reference is made to a resonance frequency of the vibration member and a first frequency associated with the operating frequency of the piezoelectric transducer. The resonance frequency of the vibration member may for instance be the first, second, third, fourth, fifth, sixth or seventh harmonic in the vibration member, but is preferably as low as possible. The first frequency is used to drive the piezoelectric transducer to sufficiently excite the resonance frequency. This means that the first frequency does not necessarily have to be exactly the same as the resonance frequency. Although not mentioned explicitly, the driver may also be configured to operate the piezoelectric transducer at a first frequency being a resonance frequency, e.g. a first or second harmonic, in one operating mode, and to operate the piezoelectric transducer at a second frequency being a resonance frequency, e.g. a third or fourth harmonic, in another operating mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in a non-limiting way by reference to the accompanying drawings in which like parts are indicated by like reference symbols, and in which:

Fig. 1 schematically depicts a cross-sectional view of a cleaning tool according to an embodiment of the invention, Fig. 2 schematically depicts a side view of a vibration member according to an embodiment of the invention,

Fig. 3 schematically depicts a detail of a vibration member according to another embodiment of the invention,

Fig. 4 schematically depicts a detail of a vibration member according to a further embodiment of the invention,

Fig. 5 schematically depicts a detail of a vibration member according to yet another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 schematically depicts a cross-sectional view of a cleaning tool 1 according to an embodiment of the invention. The cleaning tool 1 includes an elongated handle 2 with a grip 3 at one free end 2a of the handle 2 to hold the handle 2 by hand, and a vibration member 4 at an opposite free end 2b of the handle 2.

The cleaning tool 1 may be suitable to clean a toilet, urinal or sink. In such a case the cleaning tool may be moveable, i.e. to be manipulated by hand like a hand tool. Alternatively, it is also possible that a similar cleaning tool is arranged more permanently in or next to a sink, e.g. to clean glassware, such as beer glasses. Hence, the handle 2 may also be referred to as housing.

The handle 2 has a longitudinal axis 2c, in this embodiment extending over its entire length. However, designs of the handle may be such that it is partially bend or a portion extends in a different direction. In such cases, the longitudinal axis 2c referred to in this description is the local longitudinal axis at the free end 2b, i.e. the vibration member side of the handle 2.

The vibration member 4 includes a first component 4a, which may alternatively be referred to as counter mass 4a, a transducer 4b, and a second component 4c, which may alternatively be referred to as mass 4c, wherein the transducer 4b is arranged in between the counter mass 4a and the mass 4c. A sealing element 5 may be arranged between the counter mass 4a and the handle 2 to prevent dirt and water from entering the interior of the handle 2, e.g. to protect electronic components inside the handle 2 as explained below in more detail.

Although sealing element 5 in Fig. 1 is arranged between the counter mass 4a and the handle 2, the sealing element may alternatively be arranged between the mass 4c and the handle 2. An advantage may be that the sealing element 5 is also able to protect the transducer 4b from water and/or dirt as will be explained below in more detail.

The transducer 4b is configured to convert electrical energy to mechanical energy in the form of vibrations. The transducer 4b may be a stack of piezoelectric elements.

At a free end of the mass 4c of the vibration member 4, the vibration member 4 includes an emitting surface 4d for transferring (and thus emitting) vibrational waves to another medium, e.g. a fluid like air or water. The vibrational waves are preferably emitted in a direction substantially parallel to the longitudinal axis 2c of the handle 2 as indicated by arrows 6.

Substantially parallel may include the emitting of vibrational waves in a cone-shape having an aperture of at most 90 degrees, preferably at most 60 degrees, more preferably at most 45 degrees, and most preferably at most 30 degrees. It is explicitly noted here that cone-shaped may include a double cone-shape in which the vibrational waves converge first and subsequently diverge. However, it is also possible that the cone-shape has an aperture close to zero degrees and thus is or is close to a cylinder.

Although the emitting surface 4d is depicted as being planar, the emitting surface 4d may be convex or concave, i.e. curved in one or two directions, e.g. resembling a portion of an inside or outside of a sphere.

The transducer 4b, and thus the vibration member 4, may be driven by a control unit 7 arranged inside the handle 2, which control unit 7 may alternatively be referred to as driver 7. The handle 2 may further accommodate a power source 8, in this embodiment in the form of a battery 8. The battery 8 may be rechargeable and/or replaceable for continued operation. However, the cleaning tool may also be connectable to a separate power source, e.g. mains, via a cable or power cord. The toilet cleaning tool 1 may further include visual indicators (not shown) connected to the control unit 7, which visual indicators are used by the control unit 7 to indicate a low power level of the battery 8, so that a user is able to timely charge or replace the battery 8.

In an embodiment, the control unit 7 is configured to drive the transducer 4b with signals, e.g. electrical signals, to let the transducer 4b vibrate at a fixed frequency thereby vibrating vibration member 4 at a resonance frequency. Vibration member 4, or a part thereof, e.g. mass 4c, may have a shape, e.g. an hour-glass shape, double cone-like shape or horn shape to focus and direct the vibrations in a desired direction as indicated above.

The vibrational energy transferred to a medium, such as the water in a toilet bowl, allows to clean the toilet bowl, for instance by transferring sufficient energy to the water for cavitation to occur, which improves the cleaning performance significantly.

The cleaning tool 1 may further be provided with a switch 9, in this case close to the grip

3 so that the hand holding the grip 3 is also able to operate the switch 9. The switch 9 is connected to the control unit 7 and allows to turn the vibrating of the vibration member

4 on and off.

The cleaning tool 1 is further provided with one or more, in this case three, spacers 10. The spacers 10 extend from the handle 2 next to the vibration member 4 to be arranged around the vibration member 4. The spacers 10 are distributed around the vibration member to keep the vibration member 4 free of for instance a toilet bowl during cleaning. In other words, the spacers 10 are arranged to prevent the vibration member 4 from getting into contact with other structures, such as a toilet bowl wall, during use in at least one direction, preferably in two directions, and more preferably in three directions.

Figs. 2-5 schematically depict in more detail possible embodiments of a vibration member

4 that is suitable to be used in the cleaning tool 1 of Fig. 1. Fig. 2 depicts a side view of a vibration member 4 including a first component (or counter mass) 4a, a piezoelectric transducer 4b and a second component (or mass) 4c. The piezoelectric transducer 4b is arranged in between the first and second components 4a, 4c and includes a stack of two piezoelectric elements 20, 21 with an electrode 22 arranged in between the two piezoelectric elements 20, 21.

The second component 4c includes a threaded blind bore 4c'. The first component 4a and the piezoelectric transducer 4a include a through-hole 4a' and 4b', respectively, allowing a bolt 14 to be inserted through the through-holes 4a', 4b' to be received in threaded blind bore 4c' to mechanically connect the first component 4a to the second component 4c with the piezoelectric transducer 4b clamped in between the first and second components 4a, 4c.

When assembling the vibration member 4, an outer electrode 23 is arranged in between the first component 4a and the stack of piezoelectric elements 20, 21, and another outer electrode 24 is arranged in between the second component 4c and the stack of piezoelectric elements 20, 21.

The second component 4c includes a groove 4c" to receive a sealing element 5. Although not necessary, the vibration member 4 has a substantial circular cross-section, so that sealing element 5 may be a ring, e.g. a rubber ring, to engage with both the groove 4c" and a wall of a housing (see for example Fig. 1) to prevent dirt and/or water from reaching the first component side of the vibration member 4 relative to the sealing element 5 thus protecting the piezoelectric transducer 4b and/or any other driving component from getting into contact with water or dirt.

As the emitting surface side of the second component 4c relative to the sealing element 5 may be exposed to water, dirt, or any other kind of substance, the external surfaces of the second component 4c are treated to provide a protective layer. When the second component 4c comprises aluminum, the treatment may be anodizing of the second component thereby covering all external surfaces with an oxide layer. However, also other deposition methods and other protective layers are envisaged. The second component 4c has a surface 4e configured to face the stack of piezoelectric elements 20, 21, in this case opposite the emitting surface 4d. The protective layer at this surface 4e is removed prior to assembly, thereby improving an electrical connection between the surface 4e, and thus the second component 4c, and the outer electrode 24.

Alternatively, the second component is treated such that the surface 4e or at least a portion thereof is not covered with the protective layer. This has the benefit that no material needs to be removed at a later stage.

When the first component 4a, second component 4c, and bolt 14 providing the mechanical connection are mainly made of electrically conductive material, an electrical connection can be made between outer electrodes 23 and 24.

This allows to arrange the piezoelectric elements 20, 21 with opposite polarities and simply apply a voltage difference to electrodes 22 and 23. As a result of the electrical connection between electrodes 23 and 24, opposite electric fields are applied to the piezoelectric elements 20, 21, which due to their opposite polarities, will behave similarly.

Hence, because only the electrodes 22 and 23 need to be connected to a control unit, alternatively referred to as driver, these electrodes 22, 23 are shown with a connecting portion extending from the stack of piezoelectric elements 20, 21, although such an extension portion is not necessary per se. The reduced number of electrical connections between piezoelectric transducer 4b and driver results in less assembly steps and also less chance of failure of the electrical connection.

In an embodiment, the electrical connections made to electrodes 22 and 23 are sliding contacts allowing relative movement of the electrodes 22 and 23 (and thus allowing vibrational movement) while maintaining the electrical connection.

The first component 4a is preferably used to hold the vibration member 4 in a housing of a cleaning tool, e.g. the cleaning tool 1 of Fig. 1. To this end, the first component 4a may include a main body 34, a flange 35, and a recess 36 in between the main body 34 and the flange 35. Engagement by a structural component of the housing, e.g. a handle 2 as shown in Fig. 1, with the recess 36 may result in limiting movement of the first component 4a in a direction parallel to a longitudinal axis of the vibration member 4.

In an embodiment, the recess 36 or the flange 35 is used to provide an electrical connection between a driver, e.g. the control unit 7, and the electrodes 23 and 24.

Driving the piezoelectric transducer at a frequency corresponding to a resonance frequency of the vibration member will result in the formation of a standing wave corresponding to the resonance frequency. Fig. 2 also depicts an example of a waveform below the vibration member indicating a possible standing wave shape.

In this example, the standing wave has three nodes Nl, N2, N3 and three anti-nodes AN1, AN2, AN3 resulting in a 1 1/4 wavelength standing wave in the vibration member. A first node Nl is located at or near the flange 35 and/or recess 36 where the vibration member is connected to a housing. A second node N2 is located in a center of the piezoelectric transducer. A third node N3 is located in the second component 4c at a distance from the piezoelectric transducer that is substantially 2/3 of a length of the second component 4c. The recess or groove 4c" is arranged at or near the third node N3.

The anti-nodes AN1, AN2 are arranged respectively in between the first Nl and second node N2, and in between the second node N2 and the third node N3. The anti-node AN3 is located at the emitting surface 4d.

It is noted that the wavelength of the standing wave portion in the first component may be different from the wavelength of the standing wave portion in the second component due to different material properties. The first component may for instance comprise stainless steel or an alloy thereof, and the second component may for instance comprise aluminum or an alloy thereof. Fig. 3 depicts a detail of a vibration member 4 according to another embodiment of the invention that is suitable to be used in the cleaning tool of Fig. 1. The vibration member 4 comprises a first component 4a, a piezoelectric transducer 4b and a second component 4c. The piezoelectric transducer 4b is arranged in between the first and second components 4a, 4c and include a stack of two piezoelectric elements 20, 21 with an electrode 22 arranged in between the two piezoelectric elements 20, 21.

Arranged between the first component 4a and the stack of piezoelectric elements 20, 21 is an outer electrode 23, and arranged between the second component 4c and the stack of piezoelectric elements 20, 21 is an outer electrode 24. The outer electrodes 23, 24 are electrically connected using the mechanical connection between the first and second components 4a, 4c, similar to the embodiment of Fig. 2. As a result, access to the outer electrode 24 for applying a separate electrical connection is not required thereby providing the possibility to allow the second component 4c to at least partially surround the piezoelectric element 21, in other words to have an overlap with the piezoelectric transducer, or in other words that the piezoelectric transducer is received in a recess of the second component, and to provide a groove 4c" for a sealing element 5 close to the piezoelectric transducer 4b without interfering with the electrical connections.

To provide sufficient electrical contact between second component 4c and the outer electrode 24, it is preferred that the surface 4e, which is the bottom surface of the recess shown in Fig. 3, is free of protective layers. It is alternatively, or additionally, possible that the side walls 4f of the recess in the second component 4c that also face the stack of piezoelectric elements are free of protective layers to engage with the electrode 24 which may also be arranged between the side walls 4f and the piezoelectric elements 21.

As a result, the sealing element 5 can be arranged close to the piezoelectric transducer, and thus close to a node. When the vibration member 4 of Fig. 3 is similar to the vibration member 4 of Fig. 2, the sealing element 5 can be arranged close to node N2. The second component 4c may then have a length such that the emitting surface is arranged at the anti-node AN2 resulting in a much shorter second member while having a similar construction and function of the vibration member 4. In the embodiment of Fig. 2, the recess 36 between the flange 35 and the main body 34 of the first component 4a may be used to hold the vibration member. In an alternative embodiment, the recess 36 is omitted and the flange 35 extends directly from the main body 34. The vibration member 4 may then be held by engagement with the flange 35, e.g. a clamping arrangement.

In an alternative embodiment of the vibration member 4, shown in Fig. 4, the first component 4a includes a main body 34 arranged between a first flange 35.1 and a second flange 35.2 thereby forming a recess 36 in between the first and second flanges 35.1, 35.2. However, compared to the embodiment of Fig. 2, the main body 34 at the recess has a similarly sized cross-section as the piezoelectric element 20 of piezoelectric transducer 4b.

In yet another embodiment of the vibration member 4, shown in Fig. 5, the first component 4a includes a main body 34 and a flange 35 extending from the main body 34 and having a larger cross-section than piezoelectric element 20 of piezoelectric transducer 4b.

In an embodiment, which may apply to all previous embodiments shown in Figs. 2-5, the electrical connection with the outer electrodes sandwiching the piezoelectric transducers is made by providing an electric connection between a driver and the first component 4a, preferably via the mechanical construction holding the vibration member via the first component 4a.

Referring again to Fig. 1, the driver or control unit 7 is used to operate the piezoelectric transducer. This can be done in various ways. The simplest one being the application of a fixed frequency which is at or near a resonance frequency, which does not necessarily correspond to a first eigenmode of the vibration member 4. However, the resonance frequency may shift due to a change in environmental conditions such as the submersion in a liquid, temperature, but also age and wear of the vibration member 4.

Hence, instead of applying a fixed frequency to the transducer 4b, the toilet cleaning tool 1 may be configured to continuously or regularly adjust the frequency applied to the piezoelectric transducer, when in use of course.

To this end, the cleaning tool 1 may include a sensor 11 as part of the control unit 7, that is configured to measure a parameter associated with the vibration member 4. This parameter should be chosen such that a resonance frequency of the vibration member 4 can be determined. The control unit 7 is then subsequently configured to determine the resonance frequency of the vibration member 4 based on an output of the sensor 11 and to drive the vibration member 4 at the determined resonance frequency.

An example of such a parameter is an electrical current supplied by the control unit 7 to the piezoelectric transducer 4b. When the control unit 7 outputs a predetermined sinusoidal voltage signal to the piezoelectric transducer 4b, the current supplied by the control unit 7 to the piezoelectric transducer 4b may be a function of frequency of the sinusoidal signal having a (local) maximum at a resonance frequency.

Hence, a method to operate a vibration member 4 of a cleaning tool 1 may include the following steps: a. detecting a resonance frequency of the vibration member, b. operating the vibration member at the detected resonance frequency, wherein these steps are alternatingly carried out in a first cleaning mode.

The above steps a. and b. may also be carried out in a start-up mode, wherein a difference may be that in the start-up mode a wider frequency window is used to search the resonance frequency and that in the first cleaning mode the frequency window is smaller and centered around the previously detected resonance frequency. Once the resonance frequency is known, the expected shift or deviation is small compared to the absolute value of the resonance frequency. It is then not necessary to search in a wide frequency window, which wider frequency window is advantageous during start-up when the resonance frequency is not known yet.

Due to the wider frequency window, the time period to carry out step a. of the start-up mode may be larger, e.g. 1 second. Subsequently, step b. may be carried out for a time period of e.g. 0.5 seconds. In the first cleaning mode, the duration of step a. may be reduced to about 0.1 seconds.

The start-up mode may include a single step a. followed by a single step b. The first cleaning mode may repeat steps a. and b. 2-7 time, e.g. 4 times.

In an embodiment, step a. is carried out at a smaller vibration power output than step b.

In an embodiment, the vibration power output is gradually or stepwise increased during carrying out step b. This increase in vibration power output is preferably carried out during the first half of step b. so that the remainder of step b. is carried out at full or maximum vibration power output.

Further, a method to operate a vibration member 4 of a cleaning tool 1 may include the following steps: c. applying one or more pulses to the vibration member to cause the vibration member to vibrate across a specific spectrum of frequencies in order to generate a burst of sound waves, d. pausing the driving of the vibration member, wherein these steps are alternatingly carried out in a second cleaning mode.

The duration of step d. is preferably smaller than a duration of step c., for instance half as long. Step c. may for instance be carried out for 10ms while subsequently step d. is carried out for 5ms. The second cleaning mode may for instance be carried out for a time period of e.g. 0.5 seconds. In an embodiment, the first cleaning mode and the second cleaning mode are alternatingly carried out starting with the first cleaning mode, and possibly a start-up mode before the first cleaning mode.