Cleaning device for cleaning the air-ionizing part of an electrode

Abstract

The present invention provides a cleaning device (1) for cleaning the air-ionizing part (4) of an electrode (3), said device comprising a cleaning member (5) arranged to be in physical contact with the said air-ionizing part of said electrode, the air-ionizing part of electrode and the cleaning member being arranged to slide relative to each other. The cleaning device further comprises an actuator (6, 8, 9) arranged to activate the relative motion between said air-ionizing part (4) of the electrode (3) and the cleaning member (5). There is also provided an ionization electrode comprising an air-ionizing part and the cleaning device, as well as a ultrafine particle sensor, an air ionizer or an electrostatic air cleaner comprising such an electrode.

Claims

1. A cleaning device for cleaning an air-ionizing part of an electrode, wherein the air-ionizing part of the electrode comprises a needle-tip or a thin wire, said device comprising: a cleaning member arranged to be in physical contact with a circumference of the needle-tip or the thin-wire, the air-ionizing part of the electrode and the cleaning member being arranged to slide relative to each other; and an actuator arranged to activate a relative motion between the air-ionizing part of the electrode and the cleaning member, wherein the cleaning member comprises a foil containing at least one perforation through which the air-ionizing part of the electrode slides, wherein the at least one perforation is substantially closed by having edges in contact with each other when the needle-tip or the thin wire does not protrude through the at least one perforation, and wherein a shearing force applied by the cleaning member to the needle-tip or the thin-wire is changed by selecting a thickness of the foil in a range of 25-100 m.

2. The cleaning device according to claim 1, wherein the actuator is an electromagnetic assembly comprising a spring, an electrical-wire coil and a magnet.

3. The cleaning device according to claim 2, wherein the cleaning device further comprises a moveable piston assembly that is spring-loaded via the spring in a support assembly, the piston assembly comprising either the magnet or the electrical-wire coil.

4. The cleaning device according to claim 3, wherein the cleaning member is connected to the piston assembly such that the cleaning member moves relative to the air-ionizing part of the electrode between a first position and a second position due to an action of the spring, the first position corresponding with a first degree of compression of the spring, the second position corresponding with a second degree of compression of the spring.

5. The cleaning device according to claim 4, wherein the second position is attained when the actuator is electromagnetically activated by passing an electrical current through the electrical-wire coil, and wherein the first position is attained when the actuator is electromagnetically de-activated by withdrawing the electrical current from the electrical-wire coil.

6. The cleaning device according to claim 4, wherein the cleaning member is slideable along substantially an entire length of the air-ionizing part of the electrode from the first position to the second position or vice-versa.

7. The cleaning device according to claim wherein the at least one perforation is a central hole, a central square cross or a central triangular cross through which the air-ionizing part of the electrode may protrude.

8. The cleaning device according to claim 1, wherein the cleaning member comprises a flexible porous fibrous material.

9. The cleaning device according to claim 1, wherein the cleaning member comprises a supported granular material.

10. The cleaning device of claim 1, wherein the cleaning member is moveable relative to the air-ionizing part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention.

(2) FIG. 1 shows a cross-section of a cleaning device for a needle-tip ionization electrode according to an embodiment of the present invention.

(3) FIG. 2 shows the cleaning device of FIG. 1, in which the spring of the system is in a more compressed state compared to the situation shown in FIG. 1 due to closing of the switch that allows an electric current to flow through the electrical-wire coil.

(4) FIG. 3 shows a cross-section of a cleaning device for a thin-wire ionization electrode according to an embodiment of the present invention.

(5) FIG. 4 shows the cleaning device of FIG. 3, in which the spring of the system is in a more compressed state compared to the situation shown in FIG. 3 due to closing of the switch that allows an electric current to flow through the electrical-wire coil.

(6) FIG. 5 shows three types of perforations on a flexible, perforated foil that may be used as the cleaning member according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENT

(7) The schematic design of a cleaning device 1 for removing deposits from a needle-tip ionization electrode according to an embodiment of the invention is shown in FIGS. 1 and 2. The needle-tip ionization electrode 4 is situated at the top of a high voltage (HV) electrode 3, which itself maintains a fixed position on a support plate 2. The HV electrode 3 is operated by a high-voltage supply V.sub.cor.

(8) The cleaning device 1 comprises a cleaning member 5 arranged to be in physical contact with the outer surface of the needle-tip 4 of the electrode. In this embodiment, the cleaning member 5 is in the form of a clamped perforated flexible foil that is in physical contact with the circumference of the fixed needle-tip electrode.

(9) The cleaning member 5 is attached to a piston assembly 7, which encloses the central high voltage HV electrode 3. There is also a support assembly 11 that surrounds and supports the piston assembly 7 around the electrode 3.

(10) The needle-tip 4 and the cleaning member 5 are arranged to slide relative to each other, as the piston assembly 7 moves relative the central electrode 3. In this embodiment, the needle-tip 4 and the electrode 3 are in a fixed position and the cleaning member 5 slides along the length of the needle as the piston assembly 7 slides along the outer surface of the HV electrode 3, i.e. the cleaning member 5 slides along the surface of the needle-tip 4 during a stroke of the piston 7, the length of which is referred to as S in FIG. 1.

(11) The cleaning device comprises an electromechanical actuator that activates the relative motion of the piston assembly 7 with respect to the electrode 3. The actuator features a spring 6 attached to a permanent magnet, here embodied as a hollow-cylinder magnet 8, and an electrical wire coil 9, which is arranged to exert a magnetic force onto the magnet 8 when an electrical current flows through the electrical wire coil 9. In case no electrical current flows through the coil 9 from V.sub.coil, i.e. when switch 10 is open, no magnetic force is exerted onto the magnet 8 and the piston assembly 7 remains in the fixed position due to the presence of the partly compressed helical spring 6, as shown in FIG. 1. The partly compressed state of the helical spring also ensures that the piston assembly 7 remains fixed in its position with respect to the support assembly 11 without possible disturbances from the influence of gravity or incidental mechanical shocks. In case an electrical current flows through the coil 9, i.e. when switch 10 is closed, a magnetic force is exerted onto the magnet 8. With a properly applied electrical current direction and a sufficiently high current density, the magnet 8 experiences a sufficiently strong upward force which results in an upward motion of the piston assembly 7 along a defined distance S, which is the stroke of the piston, as shown in FIG. 2. The spring 6 is then transferred to a more compressed state compared to when switch 10 is in open position. The piston returns to its original position due to the action of the spring 6 when the current is nullified, i.e. when switch 10 is open again. During a single stroke of the piston, which thus may be enabled by applying a single electrical current pulse through the coil 9, the cleaning member 5, i.e. the flexible perforated foil, slides twice along the entire length of the needle-tip ionization electrode 4, thereby applying a shearing force onto the surface of the needle-tip, which removes deposited material from the needle-tip electrode 4. The shearing force can be altered by changing the stiffness of the foil 5 e.g. by changing its thickness or changing the material from which the foil 5 is made. In the embodiment shown in FIGS. 1 and 2, the entire needle-tip electrode 4 can be drawn through the perforated foil 5 during a single stroke. The piston assembly 7 is thereby shaped such that the ionization electrode 4 is always sufficiently supported to remain in position without any danger of substantial deformation. By controlling the transfer of switch 10 from open to closed e.g. setting or programming the transfer to occur after specific time intervals, the cleaning device 1 as shown in FIGS. 1 and 2 is capable of periodically performing automatic cleaning of the needle-tip ionization electrode 4 from undesirable deposits. The cleaning frequency can be chosen such that a sufficiently clean ionization electrode 4 is guaranteed at all times. The presence of this actuator 1 ensures a much extended maintenance-free operational period of an UFP sensor, air ionizer or air cleaner. A schematic design of a cleaning device 1 for removing deposits from a thin-wire electrode according to another embodiment of the invention is shown in FIGS. 3 and 4. The thin-wire electrode therein replaces the needle-tip electrode in FIGS. 1 and 2. The thin-wire electrode is the air-ionizing part of the high-voltage electrode 3. On one end, the thin-wire electrode is attached to electrode 3. On the opposite end, the thin-wire electrode is capped and supported in its position by the insulating element (13) which will normally be part of the apparatus in which the cleaning device 1 is comprised. The cleaning device 1 shown in FIGS. 3 and 4 functions entirely analogous to the cleaning device 1 shown in FIGS. 1 and 2 and it is referred to the previous discussion pertaining to the cleaning device 1 comprising a needle-tip electrode for a detailed explanation about the cleaning device 1 comprising a thin-wire electrode. As in the device shown in FIGS. 1 and 2, the cleaning member 5 of the device in FIGS. 3 and 4 is contained in the piston assembly 7. The piston assembly 7 and the support assembly 11 in the device shown in FIGS. 3 and 4 are configured such that the length of the piston stroke S is sufficient to shear the cleaning member 5 along substantially the entire length of the thin-wire electrode, thereby enabling the removal of contaminating deposits from the surface of the thin-wire electrode. FIG. 5 shows further examples of the type of perforations that may be advantageous to use when a perforated foil 5 is used as the cleaning member. In FIG. 5a, the foil 5 is perforated with a more or less central perforation. In FIG. 5b, the foil 5 is perforated by a more or less central cross, in which the needle tip may protrude through the centre of the cross. In FIG. 5c, the foil 5 is perforated by a more or less triangular perforation, and the needle-tip may protrude through the centre of the triangle, i.e. where the three lines or slits meet. A soft non-brittle foil material may be used as the foil 5, which may be cut without incurring any substantial loss of foil material from the position where cutting has occurred, which means that the edges of the perforations are still able to touch each other after the perforations have been cut. As a result, when the needle-tip electrode 4 protrudes through the central part of the perforation, the foil 5 exerts a shearing force onto the electrode 4 along its entire circumference.

(12) The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiment described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the actuator may be of another type than an electromechanical actuator.

(13) Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.