Surface cleaning system

Abstract

A surface cleaning system, comprising a cleaning unit for cleaning a substantially flat surface, such as a top surface of a solar panel or a window, the flat surface optionally being inclined, wherein the cleaning unit is movable with respect to the flat surface in a movement plane parallel to the flat surface by linear actuator means, wherein the linear actuator means comprise a rotation member and a translation member which engage with each other to provide a linear translating movement of the cleaning unit in the movement plane upon rotation of the rotation member, wherein the translation member is a beam- or rod- like member.

Description

[0001] Surface cleaning system

[0002] The present invention relates to a surface cleaning system, comprising a cleaning unit for cleaning a substantially flat surface, such as a top surface of a solar panel or a window.

[0003] The invention in particular relates to a surface cleaning system which is designed to be installed to clean large surfaces, which may have different sizes in each instance. The system is in particular aimed at large “solar farms”, which may comprise a large amount of photovoltaic solar panels arranged in a field in PV-arrays of tens or hundreds of meters long. In order to maximize the power generated by the solar panels, it is important that the surface of the panels is regularly cleaned from dirt.

[0004] For cleaning solar panels, semi-automatic cleaning robots are typically used. Specifically, standalone cleaning robots are used which are placed directly on top of a solar panel and therefore rest on the solar panel. A drawback of this solution is that the robot may slip off the solar panel when the solar panel is placed at a tilt angle. Moreover, as the robot rests with its full weight on the solar panel, the solar panel can get damaged by the robot.

[0005] The above drawbacks play less of a role in known surface cleaning systems which comprise a frame which carries a surface cleaning device. This way, the cleaning device is suspended above the surface to be cleaned. Specifically, the frame may consist of two parallel longitudinal frame members arranged on either side of the surface and a transverse frame member arranged across the surface between the longitudinal frame members, the transverse frame carrying the cleaning device. Next to their supporting function, the frame members also function as guide members along which the device is guided in its automated movement across the surface. Despite the significant advantages of these systems over standalone cleaning robots, it has been found that the cleaning performance of these surface cleaning systems decreases over time.

[0006] It is an object of the present invention to provide a surface cleaning system which maintains its high performance over time.

[0007] Hereto, the present invention provides a surface cleaning system comprising a cleaning unit for cleaning a substantially flat surface, such as a top surface of a solar panel or a window, wherein the flat surface is optionally inclined. The cleaning unit is movable with respect to the flat surface in a movement plane parallel to the flat surface by linear actuator means. The linear actuator means comprise a rotation member and a translation member which engage with each other to provide a linear translating movement of the cleaning unit in the movement plane upon rotation of the rotation member. The translation member is a beam- or rod-like member. An advantage of the translation member being a beam- or rod-like member is that the translation member is rigid and, as such, resists bending when loaded, also over time. Since the translation member resists bending, it maintains its shape, as a result of which any skipping of the rotation member (i.e. incidental disengagement between the rotation member and the translation member) under normal operating conditions of the system is avoided. Thereby, any uncontrollable movement of the cleaning unit along the translation member is avoided, so that its intended position on the surface can be guaranteed. As such, the surface cleaning system is considered fully automatic and labour free.

[0008] Skipping may typically occur when using a translation member which is less rigid than a beam or a rod, such as a timing belt. If engagement between the rotation member and the translation member is lost due to skipping, a deviation arises between the cleaning unit’s known position and its true position. Moreover, the cleaning unit might no longer be able to clean the entire flat surface. A particular problem arises when the linear actuator means comprise a second translation member which is parallel to the first translation member and a second rotation member that engages therewith. Skipping of one of the two rotation members will desynchronise the movement between the two sets of members. The alignment of the cleaning unit will in this case be skewed. As a result, parts of the surface to be cleaned will not be cleaned by the cleaning unit or the cleaning unit will get stuck such that it cannot move anymore.

[0009] Preferably, the beam- or rod-like member is made of steel, aluminium, a nickel alloy, a titanium alloy, a composite material, or the like.

[0010] In a preferred embodiment, the rotation member and the translation member are a gear wheel and a linear gear, respectively, such as a rack-and-pinion. A geared transmission ensures a highly reliable coupling enabling transmission of large force.

[0011] In a preferred embodiment, the translation member is arranged parallel to a longitudinal direction of the flat surface. By aligning the translation member accordingly, movement of the cleaning unit is along the same longitudinal direction. An advantage of this alignment is that the linear translating movement is predictable. Furthermore, the cleaning operation is optimised for an efficient route of the cleaning unit on the flat surface.

[0012] Preferably, the gear wheel comprises regularly spaced apart teeth which radially extend from an outer surface of the gear wheel, wherein the linear gear comprises a gear wheel facing surface which is flat with regularly spaced apart holes therein, wherein the holes are arranged in a straight line and the holes are configured to accommodate the teeth of the gear wheel to provide the translating movement.

[0013] In a preferred embodiment, the holes are through holes. The through holes have the advantage that any dirt or dust that accumulates on the gear wheel facing surface of the linear gear will be pushed through the holes away from the linear actuator means or pushed away from the gear wheel facing surface. As such the linear actuator means are self-cleaning. In a preferred embodiment, the gear wheel facing surface of the translation member is arranged to extend in a plane parallel to the flat surface. This allows uniform cleaning of the entire flat surface in an easier manner than when the gear wheel facing surface would be tilted with respect to the flat surface.

[0014] Preferably, the gear wheel facing surface of the translation member is coplanar with the flat surface.

[0015] In a preferred embodiment, the linear actuator means are first linear actuator means, the rotation member is a first rotation member, the translation member is a first translation member, and the linear translating movement is a first linear translating movement, wherein the surface cleaning system further comprises second linear actuator means comprising a second rotation member and a second translation member which engage with each other to provide a second linear translating movement of the cleaning unit in the movement plane upon rotation of the second rotation member, wherein the second translation member is supported by the first translation member and extends in a direction perpendicular to a longitudinal direction of the first translation member, so that the second linear translating movement is in a direction perpendicular to the first translating movement, wherein the second translation member is a beam- or rod-like member. The second linear actuator means enable movement of the cleaning unit in a two-dimensional movement plane. Perpendicular arrangement of the second translation member with respect to the first translation member provides a predictable movement trajectory for the cleaning unit. Consequently, the flat surface can be efficiently cleaned. An advantage of the second translation member also being a beam- or rod-like member is that second the translation member is thereby also rigid and, as such, resists bending when loaded, also overtime. Since the second translation member resists bending, it maintains its shape, as a result of which any skipping of the rotation member (i.e. incidental disengagement between the rotation member and the translation member) under normal operating conditions of the system is avoided. Thereby, any uncontrollable movement of the cleaning unit along the second translation member is also avoided, so that its intended position on the surface can be guaranteed.

[0016] Preferably, the beam- or rod-like member constituting the second translation member is made of steel, aluminium, a nickel alloy, a titanium alloy, a composite material, or the like.

[0017] In a preferred embodiment, the first translation member comprises two first translation members arranged on either side of the flat surface and the second translation member is arranged transversely with respect to the first translation members across the flat surface, wherein the second translation member is supported on either side of the flat surface by the two first translation members. Preferably, the first translation members are identical in shape, size, and / or material.

[0018] In a preferred embodiment, the second rotation member and the second translation member are a second gear wheel and a second linear gear, respectively, wherein the second gear wheel comprises regularly spaced apart teeth which radially extend from an outer surface of the second gear wheel, wherein the second linear gear comprises a gear wheel facing surface with regularly spaced apart holes therein, wherein the holes are arranged in a straight line and the holes are configured to accommodate the teeth of the second gear wheel therein to provide the second linear translating movement, wherein the second linear gear has a length dimension, measured in the direction of the second linear translating movement, and a height dimension, measured perpendicular to both the flat surface and the direction of the second linear translating movement, and a width dimension, measured perpendicular to the directions of both the height and length dimensions, wherein the height dimension is larger than the width dimension. In an arrangement wherein the second linear gear is supported only on either side of the flat surface, bending of the second linear gear is a concern. Dimensioning the second linear gear such that it extends perpendicular to the flat surface is beneficial, because the bending strength of a rectangular beam is dependent on the second moment of area of that beam. The second moment of area with respect to the longitudinal direction of the second translation member is linearly dependent on the width and dependent on the height to the third power. Meaning that the orientation of the second linear gear, wherein the height is larger than the width, gives the linear gear better bending resistance against its own weight. In this manner, damage to the flat surface by the weight of the second linear gear is avoided. It is noted that the deflection degree is also dependent on the material of which the second linear gear is made.

[0019] Preferably, the second linear gear, which is arranged transversely with respect to the first translation members, is supported near its longitudinal ends. The length of the second linear gear depends on the dimension of the flat surface as measured perpendicular to the first translation members.

[0020] Preferably, the second linear gear is designed such that the maximum deflection of the second linear gear is 15 millimetres or less in the height direction. A limited deflection of 15 millimetres of the second linear gear is absorbable in a coupling between the cleaning unit and the second linear gear. The coupling is designed to only allow movement of the cleaning unit in the height direction of the surface cleaning system. If the deflection of the second linear gear is absorbed in the coupling with the cleaning unit, the cleaning unit is not pushed into the flat surface. The flat surface therefore does not have to bear any unnecessary extra load other than the weight of the cleaning unit itself.

[0021] Preferably, the height of the second linear gear is such that the maximum deflection of the second linear gear is 15 millimetres or less in the height direction. The second moment of area of the linear gear is dependent on the height of the second linear gear to the third power. Increasing the height of the second linear gear is thus an efficient and cost-effective option to reduce the deflection in the height direction of the second linear gear. Furthermore, most of the other components of the surface cleaning system can remain the same for second linear gears with different heights. Reusing parts lowers the overall costs of the surface cleaning system. Alternatively, deflection of the second linear gear can be reduced by increasing the width thereof or by making the second linear gear from a material with a higher bending stiffness.

[0022] The choice for one or more of the three above options (i.e. height increase, width increase and / or using a material with higher bending stiffness) to reduce the deflection of the second linear gear depends on the specific circumstances in which the surface cleaning system is used. In general, increasing the height of the second linear is typically preferred over increasing its width, as the second moment of area of the second linear gear is only linearly dependent on its width.

[0023] For the sake of completeness, it is noted that the tendency to bend in the height direction is largely dependent on the inclination of the flat surface. An increase of the inclination of the flat surface is associated with a decrease in deflection in the height direction.

[0024] In a preferred embodiment, the length dimension is approximately 6 metres and the height dimension is at least 80 millimetres, preferably between 80 and 120 millimetres. With a height dimension of at least 80 millimetres at an approximate length of the second linear gear of 6 metres, the deflection of the second linear gear will be less than the maximum deflection of 15 millimetres as mentioned above. By keeping the height dimension of the second linear gear lower than 120 millimetres for a length dimension of approximately 6 metres, the second linear gear is not over-engineered and is not unnecessary heavy. The additional weight of a second linear gear with a height dimension above 120 millimetres may damage the first translation members on which it is supported.

[0025] In a preferred embodiment, the length dimension is approximately 9 metres and the height dimension is at least 110 millimetres, preferably between 110 and 150 millimetres. With a height dimension of at least 110 millimetres at an approximate length of the second linear gear of 9 metres, the deflection of the second linear gear will be less than the maximum deflection of 15 millimetres as mentioned above. By keeping the height dimension of the second linear gear lower than 150 millimetres for a length dimension of approximately 9 metres, the second linear gear is not over-engineered and is not unnecessary heavy. The additional weight of a second linear gear with a height dimension above 150 millimetres may damage the first translation members on which it is supported.

[0026] In a preferred embodiment, the length dimension is approximately 12 metres and the height dimension is at least 140 millimetres, preferably between 140 and 180 millimetres. With a height dimension of at least 140 millimetres at an approximate length of the second linear gear of 12 metres, the deflection of the second linear gear will be less than the maximum deflection of 15 millimetres as mentioned above. By keeping the height dimension of the second linear gear lower than 180 millimetres for a length dimension of approximately 12 metres, the second linear gear is not over-engineered and is not unnecessary heavy. The additional weight of a second linear gear with a height dimension above 180 millimetres may damage the first translation members on which it is supported. In alternative applications, in which a clear span of the second linear gear can be (significantly) shorter, a (significantly) smaller height dimension of the second linear is acceptable, as long as the maximum deflection is limited to 15 millimetres. For alternative applications with a shorter span of the second linear gear, a smaller cleaning unit can be used which has a smaller contact surface with the flat surface to be cleaned.

[0027] In a preferred embodiment, the gear wheel facing surface is arranged perpendicular to the flat surface.

[0028] In a preferred embodiment, the holes in the gear wheel facing surface of the second linear gear are through holes. The through holes have the advantage that any dirt or dust that accumulates on the gear wheel facing surface of the second linear gear will be pushed through the holes away from the linear actuator means or pushed away from the gear wheel facing surface of the second linear gear. As such the second linear actuator means are self-cleaning.

[0029] In a preferred embodiment, the cleaning unit comprises a brush plate and a circular brush rotatably mounted onto the brush plate, such that a brush surface in which ends of bristles of the circular brush are located extends parallel to an extension surface of the brush plate, wherein the brush plate is arranged parallel to the flat surface, such that the brush surface is arranged parallel to the flat surface so that all bristles of the circular brush touch the flat surface. With help of a brush, the flat surface can be adequately cleaned. By arranging the brush parallel to the flat surface, consistent cleaning by the brush is ensured. The pressure of the brush on the flat surface is constant in this manner. Rotating the brush perpendicular to the flat surface makes the cleaning operation more effective. For a circular brush, a rotating movement is easily attainable.

[0030] In a preferred embodiment, the brush plate is substantially square, and a diameter of the circular brush is substantially equal to a length / width dimension of the brush plate. Due to the design described above, the brush is able to clean the entire flat surface.

[0031] Preferably, the cleaning unit further comprises a ring gear attached to the circular brush, wherein the ring gear is configured to rotate the circular brush.

[0032] In a preferred embodiment, the surface cleaning system comprises at least one tension wire for eliminating slack in a power cable, water hose, and / or control cable which is / are fixed between the cleaning unit and an outer end of the first translation member. Slack in the power cable, water hose, and / or control cable could lead to the power cable, the water hose, and / or control cable getting stuck between, for example, the gear wheel and the linear gear. If the power cable, water hose, and / or control cable get stuck, damage could occur as a result.

[0033] Preferably, the surface cleaning system comprises a water hose, a power cable, and / or control cable for supplying water and / or electrical power to the cleaning unit from an external water / power source, and / or a control signal from the cleaning unit to a controller, respectively, wherein the water hose, power cable, and / or control cable is / are fixed between the cleaning unit and an outer end of the first translation member, wherein the at least one tension wire is configured to eliminate slack in the water hose, the power cable, and / or control cable.

[0034] In a preferred embodiment, the surface cleaning system comprises at least one pull-back wire which is attached to the water hose, the power cable, and / or the control cable on multiple fixed locations which are regularly distributed along a length of the water hose / power cable / control cable, wherein the Young’s modulus of the pull-back wire is higher than the Young’s modulus of the water hose, the power cable, and / or the control cable such that strain in the pull-back wire is lower than strain in the water hose, the power cable, and / or the control cable to absorb any tension that is put on the water hose / power cable / control cable by the at least one tension wire and / or the movement of the lateral guide and / or the cleaning unit. Alternatively, the pull-back wire can also be integrated into the wall of the water hose, power cable, and / or control cable. The pull-back wire minimises stretching of the water hose, and / or power cable, and / or control cable. Too much stretching eventually breaks the water hose / power cable / control cable.

[0035] In a preferred embodiment, the surface cleaning system comprises the water hose for supplying water to the cleaning unit from an external water source, the power cable for supplying electrical power to the cleaning unit from an external power source, and the control cable for supplying a control signal to a controller, wherein the water hose, the power cable and the control cable extend substantially parallel to each other. By running the water hose, the power cable, and the control cable together, the surface cleaning system is simplified. Parts that are necessary for the three systems can be shared between them.

[0036] Preferably, the cleaning unit comprises an electrical motor which is configured to at least rotate the ring gear, wherein the electrical motor is powered by the power cable.

[0037] In a preferred embodiment, the cleaning unit further comprises two parallel obstacle surmounting members which are rotatably mounted to the brush plate on both sides of the circular brush. The obstacle surmounting members are useful for navigating any features that are protruding from the flat surface, such as fastening means. In this manner, the cleaning unit is less likely to get stuck than without such obstacle surmounting members.

[0038] In a preferred embodiment, the flat surface comprises a top surface of solar panel or a coplanar arrangement of top surfaces of a series of solar panels. Preferably, the solar panels in the series of solar panels are arranged abutting each other, as this is the most efficient use of the available area. The surface cleaning system is particularly useful for solar panels as any dust or dirt on the top surface of the solar panels is detrimental for the performance of the solar panels. In a preferred embodiment, the top surface or each of the top surfaces is inclined with respect to the horizontal plane. Normally, solar panels are arranged at an inclined angle with respect to the ground, as such an orientation allows the top surfaces of the solar panels to collect the most amount of sun rays during the day.

[0039] In a preferred embodiment, the flat surface comprises the coplanar arrangement of top surfaces of a series of solar panels, wherein the first translation member extends is in a length direction of the series of solar panels. Such an arrangement places the second translation member in the smaller direction. The span that has to be crossed by the second translation member is therefore smaller than when the first translation member is arranged along the other direction. Consequently, the bending of the second translation member is minimised.

[0040] The present invention is further illustrated by the following figures, which show a preferred embodiment of the surface cleaning system according to the invention, and are not intended to limit the scope of the invention in any way, wherein: figure 1 shows a bottom perspective view of a preferred embodiment of a surface cleaning system according to the present invention; figure 2 shows a top perspective view of a preferred embodiment of a surface cleaning system according to the present invention; figure 3 shows a different top perspective view of a preferred embodiment of a surface cleaning system according to the present invention from an angle that is different than in figure 2; figure 4 shows a detailed perspective view of a preferred embodiment of the surface cleaning system according to the present invention; figure 5 shows a cross-sectional side view of a preferred embodiment of the surface cleaning system according to the present invention; figure 6 shows a perspective plan view of a preferred embodiment of the surface cleaning system according to the present invention, wherein the water hose system, power cable system, tension wire system, pull-back wire system, and control cable system are accentuated; figure 7 shows a top plan view of a preferred embodiment of the surface cleaning system according to the present invention, wherein the water hose system is accentuated; figure 8 shows a top plan view of a preferred embodiment of the surface cleaning system according to the present invention, wherein the power cable system is accentuated; figure 9 shows a top plan view of a preferred embodiment of the surface cleaning system according to the present invention, wherein the tension wire and the pull-back wire systems are accentuated; and figure 10 shows a top plan view of a preferred embodiment of the surface cleaning system according to the present invention, wherein the control cable system is accentuated.

[0041] The surface cleaning system 1 according to the present invention is intended for cleaning large surfaces, in particular the top surface 3 of solar panels 2 consisting of photovoltaic cells. A dirty solar panel 2 has a lower power output than a clean solar panel 2 with an equal solar intensity. Therefore, it is of the utmost importance to regularly clean the top surface 3 of the solar panels 2. The surface cleaning system 1 contains a circular brush 41 that is mounted in the brush housing 42 of a brush assembly 4. The circular brush 41, as shown in figure 1, cleans the top surface 3 of solar panels 2. As the diameter of the brush 41 is substantially equal to the length and width of the brush housing 42, the entire top surface 3 of the solar panel 2 can be efficiently cleaned with the single circular brush 41. The brush assembly 4, as shown in figure 2, is mounted in a support frame comprising three guides 5, 6, 7. Two longitudinal guides 6, 7 are placed along the upper edge 31 and the lower edge 32 of the solar panels 2. A lateral guide 5 is mounted perpendicular across the two longitudinal guides 6, 7 above the top surface 3 of the solar panel 2 and is connected to the brush assembly 4. The brush assembly 4 can be moved over the entire top surface 3 of solar panel 2 along the guides 5, 6, 7 in the longitudinal direction X and lateral direction Y. To achieve this movement the surface cleaning system 1 uses three rack-and-pinion systems. These rack-and- pinion-systems consist of chain bars 9, 10, which are incorporated in the guides 5, 6, 7, and gear wheels 8. To transfer and synchronise the movement in the longitudinal direction X between the two gear wheels 8 for the longitudinal direction X, an axle 20, jaw couplers 24, and gear boxes 23 are used. The axle 20 is rotatably mounted to the lateral guide 5. The two gearboxes 23 are connected to the axle 20 through jaw couplers 24. The jaw couplers 24 compensate any small misalignment between the gear boxes 23 and the axle 20 and isolate vibrations that pass through the lateral guide 5. By isolating unwanted vibrations, the performance of the rack-and-pinion systems is optimised. The gear boxes 23 are connected to the gear wheels 8 that run on the longitudinal chain bars 9 on the upper and lower edges 31, 32 of the solar panel 2. For further support of the brush assembly 4 and the lateral guide 5, the gearboxes 23 are provided within sliders 19, 22 that are supported by a set of vertical guides wheels 15. The vertical guide wheels 15 are placed on opposite sides of the sliders 19, 22, seen in the longitudinal direction X of the longitudinal guides 6, 7. The vertical guide wheels 15 are constrained between the longitudinal alignment lip 11 and the slide surface 21 of the longitudinal guides 6, 7. To provide movement in the longitudinal direction X a first electric motor 16 is provided and connected through a first set of bevel gears 18 to the gear wheel 8 and one of the two gearboxes 23. By connecting the two gear wheels 8, simultaneous movement of the sliders 19, 22 of both longitudinal guides 6, 7 is ensured. In this manner, the lateral guide 5 will always remain perpendicular to the longitudinal guides 6, 7. The first set of bevel gears 18 allows the first electric motor 16 to be placed in line with the longitudinal direction X of the longitudinal guide 6, 7 to save space. Two pairs of longitudinal horizontal guide wheels 14 laterally align the gear wheels 8 on the chain bar 9 such that gear wheels 8 can correctly engage with the hole pattern in the longitudinal chain bar 9.

[0042] Similarly, a second electric motor 17 is provided to move the brush assembly 4 in the lateral direction Y along the third lateral chain bar 10 that is mounted on the lateral guide 5. The third gear wheel 8 is connected to the second electric motor 17 with a second set of bevel gears 18. The second electric motor 17 is placed in line with the lateral direction Y to reduce the amount of used space.

[0043] To align the brush assembly 4 with the top surface 3 of the solar panel 2, four in-plane guide wheels 12 are provided on both sides of the lateral guide 5 and on the respective sides of the gear wheel 8, as can be seen in the cross-sectional view of figure 5.

[0044] For vertical alignment, a horizontally extending lateral alignment lip 11 is added to the lateral guide 5. The lateral alignment lip 11 is centred between a pair of vertical guide wheels 13 that are attached to the brush assembly 4. The number of guide wheels (12,13) that is shown is not essential to achieve the desired alignment. The same alignment is also achievable with fewer guide wheels.

[0045] To ease the movement of the brush 41 on the top surface 3 of the solar panel 2, the brush assembly 4 comprises four sets of caterpillar tracks 44, 45. The sets of caterpillar tracks 44, 45 are placed inside the four comers of the brush housing 42. Each set of caterpillar tracks 44, 45 consists of a longitudinal caterpillar track 44 and a lateral caterpillar track 45 for movement of the brush assembly 4 in the respective direction. The goal of the caterpillar tracks 44, 45 is to navigate any gaps or lips between solar panels 2 and ease the movement of the circular brush 41 over the top surface 3. Depending on the moving direction of the brush assembly 4, the longitudinal caterpillar tracks 44 or the lateral caterpillar tracks 45 will engage with the top surface 3 of the solar panel 2. A spray bar, which is not shown in the figures, is mounted inside the brush housing 42 to spray water on the top surface 3 of the solar panel 2. On opposite sides of the brush 41, parallel to the upper and lower edges 31, 32 of the solar panel, the brush assembly 4 further comprises two obstacle surmounting tubes 43 which allow the brush assembly 4 to safely navigate any bigger obstacles that might trigger a movement blocking of the brush assembly 4 otherwise. Such obstacles could be framing elements that are dividing the different solar panels 2.

[0046] Cleaning of the top surface 3 is done with a rotating movement of the circular brush 41. To rotate the brush 41 , a ring gear, not shown, is mounted to the brush 41. The ring gear is rotated by a third electric motor. The ring gear reduces the amount of torque that is needed for rotation of the circular brush 41. Electric power for the third electric motor is provided by the power cable 110. Additionally, the brush 41 is aided by water coming from the spray bar. The spray bar is supplied through a water hose 100. Information about the position of the brush assembly 4 is transported by a control cable 105.

[0047] To avoid slack in the water hose 100, control cable 105, and power cable 110, the surface cleaning system 1 is provided with tension wires 130, 131. The tension wires ensure that during movement of either the sliders 19, 22 or the cleaning unit 4 the water hose 100, control cable 105, and power cable 110 do not have a length that is longer than necessary. If they are longer than required, the risk arises that the water hose 100, control cable 105, or the power cable 110 will get trapped between the gear wheel 8 and one of the chain bars 9, 10. To relief the stretching force that the combination of movement and the tension wires 130, 131 puts on the water hose 100, control cable 105, and the power cable 110, two pull-back wires 140, 150 are added to the surface cleaning system 1. An overview of all hoses, cables and wires is visible in figure 6. It is preferred that all hoses, cables, and wires are covered to protect them from weathering.

[0048] As shown in figure 7, the water hose 100 is fixed between the outer end 61 of the first longitudinal guide 6 and the brush assembly 4. The water hose 100 is routed in the longitudinal direction X over a first longitudinal pulley 101 which is movable along the guide 6 in the longitudinal direction X, and from the first longitudinal pulley 101 towards the connector 191 on the slider 19. From there the water hose 100 is routed from the connector 191 on the slider 19 in the lateral direction Y over a first lateral pulley 102 which is movable in the lateral direction Y, and from the first lateral pulley 102 towards a connector 46 on the brush assembly 4, which is connected to the spray bar.

[0049] As shown in figure 8, the electrical power cable 110 is likewise fixed between the outer end 61 of the first longitudinal guide 6 and the brush assembly 4. The power cable 110 is routed in the longitudinal direction X over a first longitudinal pulley 111 which is movable along the longitudinal guide 6 in the longitudinal direction X, and from the first longitudinal pulley 111 towards the connector 191 on the slider 19. From there the power cable 110 is routed from the connector 191 on the slider 19 in the lateral direction Y over a first lateral pulley 112 which is movable in the lateral direction Y, and from the first lateral pulley 112 towards a connector 47 on the brush assembly 4, which connector 47 is connected to the electric motor in the brush assembly 4. The longitudinal pulleys 101, 111 are mounted on a single pulley clement 120 which is slidable along the longitudinal guide 6, and the lateral pulleys 102, 112 are also mounted on a single pulley element 121.

[0050] A first tension wire 130, shown in figure 9, is fixed between the other outer end 62 of the first longitudinal guide 6 and the first slider 19, and is routed from the outer end 62 over a second longitudinal pulley 302 on the pulley element 120, and from the second longitudinal pulley 302 to a set of third longitudinal pulleys 303 which are fixed to the outer end 62, and from the set of third longitudinal pulleys 303 to a set of fourth longitudinal pulleys 304 which are fixed to the first outer end 61 and from the set of fourth longitudinal pulleys 304 to the first slider 19.

[0051] A second tension wire 131, visible in figure 9 as well, is fixed between the second slider 22, and the brush assembly 4, and is routed from the second longitudinal slider 22 that slides on the second longitudinal guide 7 on the opposite side of the solar panel 2, over a second lateral pulley 305 which is fixed to the pulley element 121, and from the second lateral pulley 305 to a set of third lateral pulleys 306 which are fixed to the second slider 22, and from the set of third lateral pulleys 306 to a set of fourth lateral pulleys 307 which are fixed to the first slider 19, and from the set of fourth lateral pulleys 307 to the brush assembly 4.

[0052] If the pulley element 120 moves away from the outer end 61, an unwanted pulling force would be applied on the water hose 100 and the power cable 110. This pulling force could stretch and eventually break the water hose 100 and / or power cable 110. The two outer ends of a first pull-back wire 140 are therefore fixed to the outer end 61 of the longitudinal guide 6. The first pull-back wire 140 is routed around a fifth longitudinal pulley 141 that is attached to the pulley element 120. A pulling force which acts on the water hose 100 and the power cable 110 between the outer end 61 and the slider 19 is absorbed by the first pull-back wire 140.

[0053] Similarly, the water hose 100 and the power cable 110 could encounter pulling forces when the brush assembly 4 moves away from the slider 19 in the lateral direction Y. Hence, a second pull-back wire 150 is fixed with one of its outer ends to the slider 19 and with the other outer end to the brush assembly 4. The second pull-back wire 150 runs around a fifth lateral pulley 151 that is mounted to the lateral pulley element 121.

[0054] Alternatively, the pull-back wires 140, 150 could also be integrated into the wall of the water hose 100 or the power cable 110.

[0055] In this manner the brush assembly 4 can move in both the longitudinal direction X and the lateral direction Y to any location on the top surface 3 while the water hose 100 and power cable 110 remain tensioned by the tension wires 130, 131 without putting significant tension on both the water hose 100 and power cable 110 themselves. The surface cleaning system 1 comprises an external controller, which is programmed to control the third electrical motor and the caterpillars 44, 45 automatically in accordance with a predetermined schedule to perform a cleaning cycle. The controller receives, through control cable 105, position information about the brush assembly and the caterpillars 44, 45. The control cable 105 is routed from the slider 19 over a sixth lateral pulley 308 on the lateral pulley element 121 towards connector 46. Communication between the external controller and the brush assembly may also be wireless. The brush assembly 4 may also comprise the programmed controller inside or on the brush housing 42, which may be programmed to control the third electrical motor and the caterpillars 44, 45 automatically in accordance with a predetermined schedule to perform a cleaning cycle.

[0056] The chain bars 9, 10 have the advantage over a more conventional surface cleaning system with a timing belt that they will not age, as they are made from metal. Additionally, the metal chain bar has a high degree of stiffness. The gear wheel 8 will not be able to skip a hole in the chain bar 9, 10. The alignment between the two chain bars 9 for movement in the longitudinal direction X will thus remain synchronised. Furthermore, the chain bars 9, 10 are self-cleaning. Any dust that accumulates on the chain bars 9, 10 will be pushed through the holes of the chain bars 9, 10 by the gear wheels 8. Additionally, the sliders 19, 22 can push dust or dirt away from the chain bars 9, 10.

[0057] Due to the present design of the invention most of the weight of the cleaning equipment is carried by the lateral and longitudinal guides 5, 6, 7. The load of the cleaning equipment on the solar panel 2 is therefore decreased. It reduces the risk of damaging the top surface 3 of the solar panel 2. A further advantage of the surface cleaning system 1 emerges when the solar panel 2 is angled with respect to the ground surface. It is common practice to place the solar panel 2 such that it faces the sun as directly as possible. The brush assembly 4 according to the present invention has no risk of falling of an angled solar panel due to mounting of the brush assembly 4 in the frame. The brush assembly 4 is continuously powered by an external power source through the power cable 110. Therefore, no batteries need to be carried by the brush assembly 4.

[0058] The height of the lateral guide 5 can be chosen depending on the span that has to be crossed between the longitudinal guides 6, 7. The span is determined by the dimension and the number of solar panels that are used.

[0059] Typically, solar panels 2 are placed at an angle with respect to the horizontal ground plane to maximize exposure by the sun during the day. Preferably, the longitudinal guide 6, which comprises the connection of respectively the power cable 100 and the water hose 110 to the external power source and the external water source, is arranged at the lower edge of the solar panels 2 to keep the weight low and avoid the need for long cables and hoses. However, if needed, longitudinal guide 6 can also be placed at the upper edge of the solar panels 2.

[0060] The present invention is not limited to the embodiment shown but also extends to other embodiments falling within the scope of the appended claims.

Claims

Claims1. A surface cleaning system, comprising a cleaning unit for cleaning a substantially flat surface, such as a top surface of a solar panel or a window, the flat surface optionally being inclined, wherein the cleaning unit is movable with respect to the flat surface in a movement plane parallel to the flat surface by linear actuator means, wherein the linear actuator means comprise a rotation member and a translation member which engage with each other to provide a linear translating movement of the cleaning unit in the movement plane upon rotation of the rotation member, wherein the translation member is a beam- or rod-like member.

2. The surface cleaning system according claim 1, wherein the rotation member and the translation member are a gear wheel and a linear gear, respectively, such as a rack and pinion.

3. The surface cleaning system according to claim 1 or claim 2, wherein the translation member is arranged parallel to a longitudinal direction of the flat surface.

4. The surface cleaning system according to claim 2 or claim 3, wherein the gear wheel comprises regularly spaced apart teeth which radially extend from an outer surface of the gear wheel, wherein the linear gear comprises a gear wheel facing surface which is flat with regularly spaced apart holes therein, wherein the holes are arranged in a straight line and the holes are configured to accommodate the teeth of the gear wheel to provide the translating movement.

5. The surface cleaning system according claim 4, wherein the holes are through holes.

6. The surface cleaning system according to claim 4 or 5, wherein the gear wheel facing surface of the translation member is arranged to extend in a plane parallel to the flat surface.

7. The surface cleaning system according to claim 6, wherein the gear wheel facing surface of the translation member is coplanar with the flat surface.

8. The surface cleaning system according to any one of the preceding claims, wherein the linear actuator means are first linear actuator means, the rotation member is a first rotation member, the translation member is a first translation member, and the linear translating movement is a first lineartranslating movement, wherein the surface cleaning system further comprises second linear actuator means comprising a second rotation member and a second translation member which engage with each other to provide a second linear translating movement of the cleaning unit in the movement plane upon rotation of the second rotation member, wherein the second translation member is supported by the first translation member and extends in a direction perpendicular to a longitudinal direction of the first translation member, so that the second linear translating movement is in a direction perpendicular to the first translating movement, wherein the second translation member is a beam- or rod-like member.

9. The surface cleaning system according to claim 8, wherein the second rotation member and the second translation member are a second gear wheel and a second linear gear, respectively, wherein the second gear wheel comprises regularly spaced apart teeth which radially extend from an outer surface of the second gear wheel, wherein the second linear gear comprises a gear wheel facing surface with regularly spaced apart holes therein, wherein the holes are arranged in a straight line and the holes are configured to accommodate the teeth of the second gear wheel therein to provide the second linear translating movement, wherein the second linear gear has a length dimension, measured in the direction of the second linear translating movement, and a height dimension, measured perpendicular to both the flat surface and the direction of the second linear translating movement, and a width dimension, measured perpendicular to the directions of both the height and length dimensions, wherein the height dimension is larger than the width dimension.

10. The surface cleaning system according to claim 9, the length dimension is approximately 6 metres and the height dimension is at least 80 millimetres, preferably between 80 and 120 millimetres.

11. The surface cleaning system according to claim 9, the length dimension is approximately 9 metres and the height dimension is at least 110 millimetres, preferably between 110 and 150 millimetres.

12. The surface cleaning system according to claim 9, the length dimension is approximately 12 metres and the height dimension is at least 140 millimetres, preferably between 140 and 180 millimetres.

13. The surface cleaning system according to any one of the claims 9 - 12, wherein the gear wheel facing surface is arranged perpendicular to the flat surface.

14. The surface cleaning system according to any one of the claims 9 - 13, wherein the holes in the gear wheel facing surface of the second linear gear are through holes.

15. The surface cleaning system according to any one of the preceding claims, wherein the cleaning unit comprises a brush plate and a circular brush rotatably mounted onto the brush plate, such that a brush surface in which ends of bristles of the circular brush are located extends parallel to an extension surface of the brush plate, wherein the brush plate is arranged parallel to the flat surface, such that the brush surface is arranged parallel to the flat surface so that all bristles of the circular brush touch the flat surface.

16. The surface cleaning system according to the claim 15, wherein the brush plate is substantially square, and a diameter of the circular brush is substantially equal to a length / width dimension of the brush plate.

17. The surface cleaning system according to claim 15 or claim 16, wherein the cleaning unit further comprises a ring gear attached to the circular brush, wherein the ring gear is configured to rotate the circular brush.

18. The surface cleaning system according to any one of the preceding claims, wherein the surface cleaning system comprises at least one tension wire for eliminating slack in a power cable, water hose, and / or control cable which is / are fixed between the cleaning unit and an outer end of the first translation member.

19. The surface cleaning system according to any one of the preceding claims, wherein the surface cleaning system comprises a water hose, a power cable, and / or a control cable for supplying water and / or electrical power to the cleaning unit from an external water / power source, and / or a control signal from the cleaning unit to a controller, respectively, wherein the water hose power cable, and / or control cable is / are fixed between the cleaning unit and an outer end of the first translation member, wherein the at least one tension wire is configured to eliminate slack in the water hose the power cable, and / or control cable.

20. The surface cleaning system according to claim 19, wherein the surface cleaning system comprises at least one pull-back wire which is attached to the water hose, the power cable, and / or the control cable on multiple fixed locations which are regularly distributed along a length of the waterhose / power cable / control cable, wherein the Young’s modulus of the pull-back wire is higher than the Young’s modulus of the water hose, the power cable, and / or the control cable such that strain in the pullback wire is lower than strain in the water hose, the power cable, and / or control cable to absorb any tension that is put on the water hose / power cable / control cable by the at least one tension wire and / or the movement of the lateral guide and / or the cleaning unit.

21. The surface cleaning system according to claim 19 or claim 20, wherein the surface cleaning system comprises the water hose for supplying water to the cleaning unit from an external water source, the power cable for supplying electrical power to the cleaning unit from an external power source, and the control cable for supplying a control signal to a controller, wherein the water hose, the power cable, and the control cable extend substantially parallel to each other.

22. The surface cleaning system according to any one of the claims 17 - 21, wherein the cleaning unit comprises an electrical motor which is configured to at least rotate the ring gear, wherein the electrical motor is powered by the power cable.

23. The surface cleaning system according to any one of the preceding claims, wherein the cleaning unit further comprises two parallel obstacle surmounting members which are rotatably mounted to the brush plate on both sides of the circular brush.

24. The surface cleaning system according to any one of the preceding claims, wherein the flat surface comprises a top surface of solar panel or a coplanar arrangement of top surfaces of a series of solar panels.

25. The surface cleaning system according to claim 24, wherein the top surface or each of the top surfaces is inclined with respect to the horizontal plane.

26. The surface cleaning system according to claim 24 or 25, wherein the flat surface comprises the coplanar arrangement of top surfaces of a series of solar panels, wherein the first translation member extends is in a length direction of the series of solar panels.

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