Patent Description:
The invention relates to a sensor assembly comprising an optical sensor having a sensing surface and a cleaning device as described above.

Such sensor assemblies and cleaning devices are known in the art.

It is a widely known issue that sensors, especially optical sensors, need to be kept clean in order to guarantee their reliable functionality, i.e. assure correct values being captured by the sensor. This is the case for nearly all kind of sensors being used in industrial environments and especially applies to optical sensors being used in paper or cardboard processing machines. In such machines optical sensors are used for detecting the presence and/or a correct position of a sheet of paper or cardboard to be processed.

In this field of application, the problem of cleaning sensors has already been tackled by cleaning devices being designed for discharging gas, especially air, on the sensor and thus being able to blow aside dirt and dust particles. In terms of cleaning effectiveness, these cleaning devices still are inferior to manual cleaning. For this reason, even if such cleaning devices are used, manual cleaning of the sensors is still necessary.

It is an object of the present invention to further improve such cleaning devices and sensor assemblies equipped therewith. More precisely, a cleaning device shall be provided which is both efficient and effective in operation. Consequently, manual cleaning of sensors shall be avoided.

The invention is defined by the sensor assembly of claim <NUM>.

<CIT> discloses a system to clean the headlights of a car with a spraying nozzle. The system is built for spraying liquid but is not suitable for using a gas.

<CIT> discloses an optical system with an integrated air blower to remove dust from the front lens. The blower is adjacent to the lens.

<CIT> uses a flushing channel with air to clean a double window on an optical path. The air outlet is implemented as a hole in a wall of the device.

<CIT> discloses a handheld leaf blower with lateral openings. The lateral openings allow for an increase of the air flow of the blower, thus improving the blower efficiency. The device is handheld and includes no teachings about the optimal blowing spatial configuration.

<CIT> provides a computer dust removal mechanism based with an S-shaped air pipe. The dust removal does not include any blowing efficiency enhancement mechanisms like lateral air intakes or variable pipe size.

The problem is solved by a cleaning device as described above, wherein an outlet of the gas flow channel is facing the target surface and a central axis of the outlet intersects the target surface substantially at a center thereof and is oriented substantially at an angle of <NUM>° to <NUM>° to the target surface. It has been found that an angle of <NUM>° to <NUM>° leads to effective and efficient cleaning of sensors to which the cleaning device is applied. Also, the fact that the central axis intersects the center of the target surface leads to good cleaning results. In doing so, the pressure of the gas being discharged on the target surface is able to separate dirt particles from the target surface even if the particles adhere thereto to a certain degree. Additionally, these dirt particles may be led away from the target surface by the discharged gas. As a consequence thereof, manual cleaning is rendered unnecessary.

According to a preferred embodiment, the central axis of the outlet is oriented substantially at an angle of <NUM>° to <NUM>° to the target surface, more preferably at an angle of <NUM>° +/- <NUM>°. With such a cleaning device the same effects as described above may be achieved to an even higher degree.

The outlet of the gas flow channel may be formed as a nozzle. In this context, a nozzle is a portion of a gas flow channel with a cross-section decreasing along a central axis thereof. As a result thereof, a gas flow inside the gas flow channel is accelerated. Therefore, the gas is discharged from the gas flow channel at relatively high speed. This leads to efficient and effective cleaning of a sensor associated with the cleaning device.

According to an embodiment, the gas flow channel comprises an inlet, wherein a central axis of the gas flow channel is substantially S-shaped between the inlet and the outlet, in particular wherein a center plane of the S-shape comprising the central axis of the gas flow channel is oriented substantially orthogonally with respect to the target surface. In other words, the gas flow channel has the shape of a swan neck. Consequently, the outlet may be positioned as described above and at the same time the inlet may be arranged such that it is easily accessible in order to connect it to a supply pipe or supply tube providing gas to the gas flow channel. Moreover an S-shaped arrangement of the gas flow channel only requires a very limited amount of space. Therefore a cleaning device with an S-shaped gas flow channel is compact.

According to the invention, a cross-section of the gas flow channel decreases in a gas flow direction. This means that the cross-section of the gas flow channel decreases in a direction from the inlet to the outlet. In a preferred alternative the gradient of the decreasing cross-section is bigger in the nozzle than in the rest of the gas flow channel. Thereby, sufficient speed of the gas flow is assured leading to good cleaning results.

According to the invention, at least one air suction void is provided adjacent to the outlet for providing air to be dragged onto the target surface by the gas flow discharged from the outlet. In this context, a void is to be understood as an aperture in the cleaning device or a space adjacent to the cleaning device which is left free from any components thereof or any components of other parts. The gas being discharged onto the target surface may thus drag additional air toward the target surface. The gas being discharged thus works analogously to a waterjet pump. According to a preferred solution, the at least one air suction void is provided on the left and/or on the right and/or on top of the central axis of the outlet, when regarded in the direction of discharge with the target surface being at the bottom. With the additional air being dragged by the discharged gas cleaning efficiency and effectivity is enhanced since most air supplied by the outlet will reach the target. If no void was provided, part of the air flow discharged from the outlet would undergo a turbulence swirl, and thus be ineffective for cleaning the target surface.

Advantageously, the gas flow channel comprises an inlet portion comprising the inlet, an outlet portion comprising the outlet and a middle portion being interposed between the inlet portion and the outlet portion, wherein a support wall is provided supporting the outlet portion on the middle portion and/or on a base component of the cleaning device. The support wall increases the mechanical stability of the cleaning device making it especially suitable for industrial environments. Consequently, the cleaning device is robust and is able to provide a gas flow in a reliable manner. If the cleaning device is equipped with voids for providing air to be dragged onto the target, the supporting wall may separate two voids being provided on opposing sides of the gas flow channel. Thereby, the air to be dragged may be provided by different locations and the wall may avoid some turbulence swirl under certain conditions. Consequently, cleaning efficiency is enhanced. Additionally, by providing the supporting wall, the number of undercuts provided on the cleaning device is reduced. As a result thereof, it is easier to manufacture the cleaning device.

The support wall may extend substantially perpendicular to the target surface. This allows for a reliable support of the gas flow channel and simple manufacturing at the same time.

In an alternative the cleaning device is a single piece and/or produced by additive manufacturing. As a single piece, the cleaning device does not need to be assembled. When being produced by additive manufacturing, all geometrical features of the cleaning device, especially the geometry of the gas flow channel, may be freely chosen. Restrictions imposed on the geometry by the manufacturability of the cleaning device are minimal. Preferably, the cleaning device is manufactured by a 3D printing technology. If a support wall is provided, manufacturing of the cleaning device by an additive manufacturing technology is further simplified since the support wall reduces overhanging geometries.

The problem is also solved by a sensor assembly as described above, wherein the sensing surface and the target surface substantially coincide such that the central axis of the outlet of the gas flow channel intersects the sensing surface substantially at a center thereof and is oriented substantially at an angle of <NUM>° to <NUM>° to the sensing surface. In doing so, the sensing surface of the optical sensor is efficiently and effectively cleaned thereby ensuring highly reliable values being captured by the sensor. Manual cleaning is not necessary.

According to a preferred embodiment, the central axis of the outlet is oriented substantially at an angle of <NUM>° to <NUM>° to the sensing surface, more preferably at an angle of <NUM>° +/- <NUM>°. With such a cleaning device the same effects as described above may be achieved to an even higher degree.

The optical sensor may comprise an optical fiber, wherein the sensing surface is an end surface of the optical fiber. Such optical fibers are used in a wide variety of applications. An example thereof is paper or cardboard processing machines such as printing machines. In these machines optical fibers are used to detect the arrival of a sheet to be processes or to be printed upon. Usually, the end surface of the optical fibers is oriented vertically such that it is exposed to dirt particles and dust. In the sensor assembly, this problem is mitigated by the cleaning device.

According to an embodiment the optical sensor and the cleaning device are attached to a shared support part. Consequently, the sensor assembly is easy to assembly to a machine where it is applied. The optical sensor and/or the cleaning device may be simply bolted or screwed to the shared support part.

The invention will now be described with reference to the enclosed drawings. In the drawings,.

<FIG> shows a sensor assembly <NUM> which comprises an optical sensor <NUM> and a cleaning device <NUM> being associated to the optical sensor <NUM>. Such a sensor assembly may be used in a paper processing machine for detecting the presence of a sheet of paper, e.g. in a printing machine.

Both the optical sensor <NUM> and the cleaning device <NUM> are attached to a shared support part <NUM>.

In the example shown the optical sensor <NUM> comprises an optical fiber <NUM> having an end surface <NUM>. This end surface <NUM> constitutes a sensing surface <NUM> of the optical sensor <NUM>.

In <FIG> and <FIG>, the cleaning device <NUM> is shown in more detail. It comprises a gas flow channel <NUM> which has an inlet portion 24a, a middle portion 24b and an outlet portion 24c (cf.

The inlet portion 24a comprises an inlet <NUM> to which a gas flow may be provided.

The outlet portion 24c comprises an outlet <NUM> for discharging the gas flow onto a target surface <NUM> of the cleaning device <NUM>.

To this end the outlet <NUM> is facing the target surface <NUM> and a central axis <NUM> of the outlet <NUM> intersects the target surface <NUM> substantially at a center <NUM> thereof.

Furthermore, the central axis <NUM> is oriented at an angle of substantially <NUM>° to the target surface <NUM>.

The middle portion 24b is arranged between the inlet portion 24a and the outlet portion 24c.

In the middle portion 24b and the outlet portion 24c a cross-section A of the gas flow channel <NUM> decreases in a gas flow direction 24d, i.e. the cross-section A of the gas flow channel <NUM> decreases in a direction from the inlet <NUM> to the outlet <NUM>.

Moreover, the outlet <NUM> is specifically designed as a nozzle. This means that also within the outlet a cross-section of the gas flow channel <NUM> is decreasing. In the example shown a gradient of the decreasing cross-section is bigger in the nozzle than in the rest of the gas flow channel <NUM>.

Additionally, a central axis <NUM> of the gas flow channel <NUM> is substantially S-shaped. In other words, the gas flow channel <NUM> has an S-shape. This applies to the gas flow channel <NUM> in its entirety, thus between the inlet <NUM> and the outlet <NUM>.

A center plane of the S-shape corresponds to the section plane in <FIG> and is substantially orthogonal with respect to the target surface <NUM>.

Furthermore, a support wall <NUM> is provided supporting the outlet portion 24c on the middle portion 24b and on a base component <NUM> of the cleaning device <NUM>.

The support wall <NUM> extends substantially perpendicular to the target surface <NUM>. As can be seen from <FIG> and <FIG> the support wall <NUM> at least partially closes the S-shape.

The cleaning device <NUM> is also equipped with two voids <NUM>, <NUM> which are provided adjacent to the outlet <NUM> for providing air to be dragged onto the target surface <NUM> by the gas flow discharged from the outlet <NUM>.

According to <FIG>, the voids <NUM>, <NUM> are provided on the left and on the right of the central axis <NUM> of the outlet <NUM> respectively, when regarded in the direction of discharge with the target surface <NUM> being at the bottom.

The cleaning device <NUM> is designed as a single piece which is produced by additive manufacturing, e.g. 3D printing.

Within the sensor assembly <NUM> the cleaning device <NUM> is arranged on the support part <NUM> such that the sensing surface <NUM> of the optical sensor <NUM> and the target surface <NUM> substantially coincide.

Consequently, the central axis <NUM> of the outlet <NUM> of the gas flow channel <NUM> also intersects the sensing surface <NUM> substantially at a center <NUM> thereof and is oriented substantially at an angle of <NUM>° to the sensing surface <NUM>.

During operation of the sensor assembly <NUM> also the cleaning device <NUM> may be operated.

In this situation a gas flow is provided at the inlet <NUM> and therefore the gas flows through the gas flow channel <NUM> and is discharged onto the target surface <NUM>.

Due to the decreasing cross-section A and the nozzle the gas is discharged at relatively high speed, i.e. at a speed higher than in the inlet portion 24a.

In combination with the angle of substantially <NUM>° between the central axis <NUM> and the sensing surface <NUM> and the fact that the discharged gas is directed to the center <NUM> of the sensing surface <NUM>, this arrangement is able to blow aside dust and dirt particles being present on the sensing surface <NUM>. This also applies to dust or dirt particles adhering to the sensing surface <NUM>.

This leads to good cleaning results, i.e. effective cleaning.

Thanks to the voids <NUM>, <NUM> the gas <NUM> being provided by the gas flow channel <NUM> may drag an additional amount of air <NUM>,<NUM>. The air drag happens in any case, but in the absence of voids, the gas must stem from the sides, causing the some turbulence swirl <NUM> on the sides of the gas <NUM> stream. Put in other words, with the voids <NUM>,<NUM> most - if not all - the air <NUM> provided via the gas flow channel <NUM> is used for cleaning the sensing surface <NUM>. In the absence of voids <NUM>,<NUM>, thus in a situation where air would not be allowed to flow next to the gas channel 24b,24c, part of the gas provided by the gas flow channel would be lost in turbulences <NUM>, and thus not reach the sensor surface <NUM>, as depicted on <FIG>. In other words, the gas flow reaching the sensor surface <NUM> would be weaker.

Claim 1:
Sensor assembly (<NUM>) comprising an optical sensor (<NUM>) having a sensing surface (<NUM>) and a cleaning device (<NUM>)for the optical sensor (<NUM>),
the cleaning device (<NUM>) comprising a gas flow channel (<NUM>) oriented towards a target surface (<NUM>) such that a gas (<NUM>) flowing through the gas flow channel (<NUM>) is discharged onto the target surface (<NUM>),
wherein an outlet (<NUM>) of the gas flow channel (<NUM>) is facing the target surface (<NUM>) and a central axis (<NUM>) of the outlet (<NUM>) intersects the target surface (<NUM>) substantially at a center (<NUM>) thereof and is oriented substantially at an angle of <NUM>° to <NUM>° to the target surface (<NUM>) and
wherein a cross-section (A) of the gas flow channel (<NUM>) decreases in a gas flow direction (24d)
characterized in that
two air suction voids (<NUM>,<NUM>) are provided on opposing sides of the gas flow channel adjacent to the outlet (<NUM>) for providing air to be dragged toward the target surface (<NUM>) by the gas flow discharged from the outlet (<NUM>), and
wherein the sensing surface (<NUM>) and the target surface (<NUM>) substantially coincide such that the central axis (<NUM>) of the outlet (<NUM>) of the gas flow channel (<NUM>) intersects the sensing surface (<NUM>) substantially at a center (<NUM>) thereof and is oriented substantially at an angle of <NUM>° to <NUM>° to the sensing surface (<NUM>).