The most important factor is the selection of the type of material covering the greenhouse roof. In the market there are different kinds of covering materials of various types which are divided in to two groups: the first one is rigid, for example, Glass and plastic plates like polycarbonate. The second group is flexible (soft) covering materials of plastic sheets such as PVC and polyethylene.

The most popular and most extensively used covering in Israel is the soft plastic sheeting.

The roofs accumulate large quantities of dust, which prevent the transfer of light into the greenhouse and retard the development rates of the produce and delay the ripening process. Reduction of light transfer has a negative effect on the size of the fruit, plants produce est. With certain types of flowers the time between blooming of the flowers found to be longer.

Many researches investigated the, effect of light transfer in greenhouses on plant development. It was found that after regular cleaning of the greenhouse's roof during the growth of the produce, the result was 30% increase of produce, increase of fruit size and quality and flowers with longer stems. It also shortens the time between each blooming and in general a greater number of stems and branches was found per plant.

This data has a great economic influence on agriculture. Where by the use of a given area and amount of water, there is an increase in quantity and quality of the produce by a factor up to 30%. This is a major achievement.

At present, some farmers in Israel confront these problems by manual and expensive washing, which is time consuming and made when the workers are free from other work <BR> <BR> 1 in the greenhouse. For this reason greenhouse roofs are rarely cleaned, just once or twice per growth season, which is definitely not enough.

There is a great advantage to be gained by the regular and periodic cleaning of the greenhouse roof. The preferred solution is to clean it by mechanical and automation means.

On the market there is a wide range of greenhouses of different dimensions: width, height, length est. some are characterized by different roof cross section e. g. symmetrical or asymmetrical.

At the present moment there do not exist roof cleaning devices that answer to these conditions, although VIKA company produce a cleaning machine for glass greenhouses with one uniform shape.

It is an object of the invention to provide a method and apparatus for cleaning soft plastic sheeting roofs automatically.

Summary of the invention The invention provides a method for cleaning plastic covered greenhouse roofs automatically including several rows of the roofs continuously. The cleaning method can be made by various means such as: rotary brushes, moving sponges, strips of cloth or materials of varying textures, which provide soft touch to the plastic cover material. The method provides automatic pressure control between the cleaning device and the plastic roof while adjusting the height of each of the device to the irregular surface. The pressure control is needed to prevent damage to the sensitive plastic cover. Scratches on the plastic sheeting reduce light transfer and accumulate more dust than before.

The pressure control can be of several types: pneumatic system with pistons, Hydraulic system with pistons, springs systems or electric systems, and connected to an over running bridge.

The mechanical method for removing dust and grit from the plastic sheet can be combined with air suctioning system or with water washing system. The dust separators of the air suctioning system can be of the following types: Gravitational and Inertial Collectors, ESP's, Sacks or Filters.

The over running bridge is moving along the greenhouse roof by a controlled motor which drives the wheels running along the gutters at each side of the roof. At the end of the roof the bridge is collected by a moving base, which moves it to the second roof and let it start moving along it and clean it.

The cleaning device is mounted to the bridge via a moving platform, which can move along the bridge. In a preferred embodiment the platform moves along the bridge, while the cleaning device cleans a path of its own width perpendicular to the length of the greenhouse. At the end of the bridge the cleaning device stops and is lifted from the roof.

The bridge moves to its next stop along the gutters and the cleaning device cleans another path. The stops along the gutters are defined by a sensing system.

In another preferred embodiment at least one platform with at least one cleaning device moves with the bridge along the gutters of the roof and cleans a lengthwise path. At the end of the roof the bridge stops and the cleaning device is lifted from the roof. The platform with the cleaning device moves along the bridge to its next position, and the cleaning device is lowered to the roof. Sensors define the positions of the platform with the cleaning device on the bridge. The bridge moves to the other direction along the gutters and cleans another lengthwise path. After reaching the other end the platform with the cleaning device moves along the bridge to its new position, and the cleaning device is lowered to the roof to clean another path and so on, until the whole roof is clean. At the end of the roof the bridge moves to the second roof and starts moving along its gutters and cleans it.

In a preferred embodiment a moving base at the end of the roof collects the bridge. The moving base with the bridge moves to the next arch of the roof and the bridge starts to clean it. In a preferred embodiment the moving base moves on rails on the wall of the greenhouse. In another preferred embodiment the rails are on the ground near the wall of the greenhouse. In another preferred embodiment the rails are on a structure near the wall of the greenhouse. In another preferred embodiment the base with the bridge on it is being taken by any kind of lift vehicle to another greenhouse to clean its roof.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a symmetrical greenhouse covered with three sections' roof (symmetrical arches) with the cleaning device running along the bridge.

Fig. 2 is a perspective view of an asymmetrical greenhouse covered with three sections' roof (asymmetrical arches) with the cleaning device running along the bridge.

Fig. 3 is schematic cross section of roofs of an asymmetrical nature, with the cleaning device running along the bridge.

Fig. 4 is a perspective view of a symmetrical greenhouse covered with three sections' roof (symmetrical arches) with the two cleaning devices stationed along the bridge in order to clean two paths along the roof.

Fig. 5 is a perspective view of a symmetrical greenhouse covered with three sections' roof (symmetrical arches) with several cleaning devices stationed along the bridge in order to clean the whole width while the bridge runs along the roof.

Fig. 6 is a perspective view of a cleaning device with a rotating brush.

Fig. 7 is a perspective view of a cleaning device with a stationary sponge running on the roof.

Fig. 8 is a perspective view of a cleaning device with rotating strips of cloth.

Fig. 9 is a perspective view of a cleaning device mounted to the bridge via a platform with two pressure control devices and a universal joint, for cleaning along the bridge.

Fig. 10 is a perspective view of a cleaning device mounted to the bridge via a platform with two pressure control devices and a universal joint, for cleaning along the roof.

Fig. 11 is a schematic diagram of a pneumatic pressure control system.

Fig. 12 is a schematic diagram of a hydraulic pressure control system.

Fig. 13 is a schematic diagram of an electric powered pressure control system.

Fig. 14 is a perspective view of a cleaning device with the driving motor near the universal joint.

Fig. 15 is a perspective view of a cleaning device with the driving motor connected directly to the rotating shaft of the cleaning element of the cleaning device. Fig. 16 is a side view of the platform for the cleaning device with the powered pulley running along a welded chain along the bridge.

Fig. 17 is a perspective view of a running system of one side of the bridge inside the roofs gutter.

Fig. 18 is a schematic diagram of the moving control system of the platform for the cleaning device along the bridge and of the moving control system of the bridge with the cleaning device along the roof.

Fig. 19 is a perspective view of an air suction system to collect and separate the dust.

DETAILED DESCRIPTION Fig. 1 is a perspective view of a symmetrical greenhouse covered with three sections' roof 1 (symmetrical arches) with the cleaning device 2 running along the bridge 3.

The platform 4 is running along the stationary bridge 3 with the cleaning device 2 connected to it. The bridge 3 is supported and moved by the running system 5 on its two sides. The running systems 5 are supported and directed by the gutters 6.

The running systems 5 stop the bridge at predetermined stops to cover the whole length of the roof. The dust separator 7 is part of the air suction system (not shown here). The end vehicle 8 is collecting the bridge 3 at the end of the gutters 6 and moves it to the next arch 1 while running along the rails 9 on the wall.

Fig. 2 is a perspective view of an asymmetrical greenhouse covered with three sections' roof 10 (asymmetrical arches) with the cleaning device 2, mounted to the platform 4, running along the stationary bridge 3. The height of the running systems 5 is adjusted to the shape of the asymmetrical arch 10. The dust separator 7 is part of the air suction system (not shown here). The rails 11 at the end of the gutters 6 are to support the bridge 3 while moving from one arch 10 to the next one. A section of the rails 11 can be moved with the bridge 3 by any kind of lift vehicle to another greenhouse to clean it.

Fig. 3 is a schematic cross section of roofs 10 of an asymmetrical nature, with the cleaning device 2, mounted to the platform 4 via pressure controlled devices 12.

The cleaning direction is along the bridge 3.

Fig. 4 is a perspective view of a symmetrical greenhouse covered with three sections' roof 1 (symmetrical arches) with the two cleaning devices 3, mounted to the platforms 4 via pressure controlled devices 12. The cleaning direction is along the roof 1 and the cleaning devices 2 are stationed along the bridge 3 in order to clean two paths along the roof 1. At the end of the roof 1, the cleaning devices 2 move to new positions on the bridge 3 to clean two other paths in parallel to the first ones. The two cleaning devices 2 move again to new position at the other end until the entire arch of the roof 1 is clean. At the end of the arch 1 the bridge 3 moves to the next arch.

Fig. 5 is a perspective view of a symmetrical greenhouse covered with three sections' roof 1 (symmetrical arches) with several cleaning devices 2 stationed along the bridge 3 in order to clean the entire width of the arch 1 while the bridge 3 runs continuously along the roof. One or more motors 13 power the cleaning devices 2.

The motors 13 can be electric, pneumatic, or hydraulic ones. The cleaning devices 2 are supported to the bridge via pressure controlled devices 12 in order to adjust their height to the irregular surface of the roof 1. The cleaning devices 2 are connected to each other by flexible couplings 18 to rotate them while moving up and down, and changing angles along the irregular surface of the roof 1.

Fig. 6 is a perspective view of a cleaning device 2 using a rotating brush 14 covered with a hood 15.

Fig. 7 is a perspective view of a cleaning device 2 with a stationary sponge 16 running on the roof cover 1. Fig. 8 is a perspective view of a cleaning device 2 with rotating strips of cloth 17 running on the roof cover 1.

Fig. 9 is a perspective view of a cleaning device 2 mounted to the bridge 3 via a platform 4 with two pressure controlled devices 12 and a universal joint 19, for cleaning the roof cover 1 along the bridge 3. The two pressure-controlled devices 12 control the pressure between the cleaning element (14,16 or 17) of the cleaning device 2 and the roof cover 1 at each side separately. The universal joint 19 is the third mounting point and it enables the cleaning device 2 to move up and down at each side separately, to follow the irregular surface of the roof cover 1.

Fig. 10 is a perspective view of a cleaning device 2 mounted to the bridge 3 via a platform 4 with two pressure controlled devices 12 and a universal joint 19, for cleaning along the roof cover 1 while following its irregularity.

Fig. 11 is a schematic diagram of a pneumatic pressure control system. Air pump 31 supplies air pressure to accumulator 32, air release valve 33 governs constant air- pressure gap to pistons 12.

Fig. 12 is a schematic diagram of a hydraulic pressure control system. Electric motor 34 drives a hydraulic pump 35 which supplies hydraulic pressure to hydraulic pistons 12, the pressure is regulated by a pressure control system 37.

Fig. 13 is a schematic diagram of an electric powered pressure control system. Electric motors 38 drive bolts 39, force gauge 40 measures the force and sends the measurements to the control system 41.

Fig. 14 is a perspective view of a cleaning device 2 with the driving motor 13 near the universal joint 19 to lower the weight on the pressure controlled devices 12. The transmission 20 changes the number of revolutions to be adequate to the revolutions of the cleaning element (14 or 17) of the cleaning device 2. The chain transmission 21 connects the transmission 20 to the shaft 22 of the cleaning element (14 or 17) of the cleaning device 2.

Fig. 15 is a perspective view of a cleaning device 2 with the driving motor 13 connected directly to the rotating shaft 22 of the cleaning element (14 or 17) of the cleaning device 2.

Fig. 16 is a side view of the platform 4 for the cleaning device 2 with the powered pulley 23 running along a welded chain 24 along the bridge 3. The motor 25 powers the pulley 23 via transmission means 26. The motor 25 can be electric, pneumatic, or hydraulic one. The sensors 27 senses the location of the platform 4 with the cleaning device 2 in order to stop it at the end when running along the bridge 3, or at the right location when running along the roof 1 and changing position for the next run. The sensors 27 can be on the bridge, on the pulley or in the driving system of the motor.

Fig. 17 is a perspective view of a running system 5 of one side of the bridge 3 inside the roof's gutter 6. The wheels 28 run in the gutter 6 and powered by the motor 29.

The motor 29 can be electric, pneumatic, or hydraulic one. The guiding wheel 30 controls the angle of the bridge 3 to be perpendicular to the gutter 6. The sensors 31 sense the location of the bridge 3 along the gutter 6 to stop it for each step while cleaning a path perpendicular to the gutter 6, and at the end.

Fig. 18 is a schematic diagram of the movement control system of the platform 4 for the cleaning device 2 along the bridge 3 and of the movement control system of the bridge 3 with the cleaning device 2 along the roof 1. Sensor 31 sends data of the position of the bridge 3 to the control system 41. Sensor 27 sends data of the position of the platform 4 to the control system 41. Emergency button 45 stops the system and alarm device 44 warns by flashing light and siren and communication system (SMS, Telephone, Internet ect...) to notify the user of a malfunction.

8 Fig. 19 is a schematic diagram of an air suction system 49 to collect and separate dust by cyclone 48 or filters (not shown) or ESP's (not shown) and flexible plastic hose 47 from the cleaning device 2.