DE19649240A1 - Automatic machine for watering and applying pesticide to plants - Google Patents

Abstract

The machine has a combination of a drive (12) driven by an IC engine for power supply as well as a storage container (4) for supplying the liquid in self-sufficient fashion and guided linearly by a steering device of a spray vehicle driving into and out of the rows of plant culture with a transport platform travelling automatically on a fixed central path for the transverse transport of this spray vehicle to the desired row. There are devices (16) for filling the storage container automatically. The transport platform is equipped with a battery drive which works on rubber wheels on one side and on flanged guide wheels on the opposite side.

Description

For automatic watering of plants and for Application of pesticides are different technical aids used. Hand-guided are known Sprayers that come from portable containers or over Hose lines are supplied. Simple designs only have atomizing nozzles for the sprayed Medium (broth also use more complex constructions an airflow for better penetration of the Plant population and for a more even distribution of Broth. Especially for outdoor crops such as agriculture, the Fruit growing and viticulture are using complex equipment various blowers, air routing devices and Drive systems used. Comparatively few devices were developed for use in greenhouses. Here are Spray bars guided on the floor or on ceiling rails State of the art.

The procedural superior air support is currently only when using portable backpack sprayers possible.

The reason for this low level of technology in greenhouses is based on the one hand that the simple transfer the field-proven technical means in a cramped Greenhouse with the size of the machines and the high Power requirement of the blower fails, on the other hand, because economical solutions with reasonably flexible Operability has not previously been proposed. Furthermore adheres to traditional working techniques important role.

The relatively low usage and thus utilization of the facility and a correspondingly low level economically justifiable investment volume. After the first scientific experiments with through Reduction of outdoor technology adapted to the greenhouse Potential for improvement made clear by air support have now been increasingly asked for technical solutions with  which the procedural requirements have it implemented economically. This use of optimal Technology that through even and targeted wetting Spray agent expenditure to a sufficiently effective minimum reduced, is therefore particularly important in the greenhouse, because pesticides are used particularly intensively here and automation is particularly important here Health care is provided for the executing staff.

The task can be done according to the special conditions describe the greenhouse cultures as follows.

The limited space requires a precisely guided sprayer. The management system accounts for a large proportion of the total costs represents, so it must be carried out particularly inexpensively. Because of the relatively small areas, there is a large one Throughput less important than a small size and one low energy consumption. The position of the device and the The direction of the spray jet must be different plants and the big changes in conditions by fast Growth can be easily adjusted. A reliable one automatic operation must be possible without great control effort be.

According to the invention, the task of a machine Application of pesticides with air support for to create the use in greenhouses by using on wheels self-driving vehicle solved, preferably with a Internal combustion engine is equipped with the mechanical Drive power for the operation of a fan and a High pressure pump is generated and an electric generator drives with which the travel drive, a dosing pump for the Plant protection products and possibly an agitator operated and Directional control devices and valves supplied will.

The orientations given below refer to the direction of travel when manually transporting the spray vehicle, which is similar to a wheelbarrow.

The vehicle carries a stock tank for the broth and behind the drive motor with the blower. In the middle of Spray vehicle are slots on both sides for the exit of the  Air arranged as well as a round opening at the top, which in one removable textile air hose opens. Within the Air nozzles are spray nozzles for the at regular intervals Application of the broth arranged.

As additional equipment, inside the brewing tank, and accessible through its large filling opening, a container attached for the plant protection product (active ingredient concentrate) be the one via a bottom valve and a line with a Dosing pump is connected.

The metering pump is preferably an electrically driven one Peristaltic pump executed and opens above one Shut-off valve in a mixing chamber directly in the line to the Spray nozzles.

For processing suspensions is another Additional equipment provided an agitator, the electric Drive is attached above the liquid level and its propeller with a shaft mounted deep in the tank dipped in the broth tank.

The chassis of the spray vehicle is for straight driving inside designed in a row and with a controller for the automatic course keeping. The easiest way to do this Case be the mechanical guide along a rail. Adapted variants are provided according to the environment. In existing buildings with the same cultures Laying rails on the floor, which are advantageous arranged in pairs and connected with crossbars Angle profiles exist and through between the pairs of rails Layed tiles expanded to a safe walkway can be. In the case of new greenhouses, the combination is the Track with floor heating advantageous. The The rail system then consists of one on one side U-shaped shaped connected to crossbars by welding Pipe, the ends of which are connected to each other or with a hose Distribution lines are connected.

Between the tubes, which serve as a rail, can also a sidewalk will be laid. The rail system must be for one quick assembly from prefabricated sections suitable Fasteners for a tight pipe included. Therefore are preferred in the ends of the for cost reasons welded steel pipe made of line bushings  corrosion-resistant material with a sealant pressed in. These sockets are used during assembly Double nipple inserted with O-ring seals. The connection of rail and heating cable is done by screwing the final crossbars (flanges). When producing A rail system without welding connections can handle large quantities are made by sawing into the ends of the length Pipes are tightly pressed in flanges and the pipes through a Large number of crossbars or flat cross connectors through one elastic clamp connection to be connected to each other represent the walkway at the same time.

In a variant for operation on large areas and without complex infrastructure is the spray vehicle with facilities for the correction of deviations from a straight course equipped. For this purpose, the chassis is preferably four-wheeled two rigid axles, at least the wheels of one Axis are driven independently. Preferably the guide provided along an iron wire, to whose Tracking inductive sensors are provided.

Another advantageous way of controlling the vehicle results from the use of a gyro system. The circle is always in the exact parking position of the Spray vehicle initialized on the transport platform.

Suitable gyro systems are for the control of Model helicopters have been developed and are cheaply available.

The journey in a row is manual or by the Control of the transport platform started. At the end of Row reverses the vehicle automatically. The reversal of direction occurs either after a programmed one has been replaced Distance or it is triggered by a collision sensor, the one that is more flexible and acts on a switch Bumpers is provided.

The transport of the vehicle to the place of use, and at a simple execution also transport from row to row, is done by hand like a wheelbarrow. These are in the back fold-out handles provided. When lifting the rear wheels must have about half the weight of the lifting force Drive elements are applied while the weight of the Brewing tanks in balance on the front axle. By lifting the rear wheels becomes the resistance of the drive system  switched off and on the individually mounted front wheels the vehicle can be rotated at will.

The manual positioning of the vehicle in front of a row can with the help of optical markings or through the use be made easier by concrete blocks or sheet metal parts, which give the wheels a corresponding guidance and at the same time serve to fasten a guide wire.

Corresponding molded parts can also be advantageous for smoothing the transition from a central aisle to one in a row installed rail system can be used.

A coding for identification of the Row can be arranged.

For more extensive automation is in the middle aisle a self-propelled transport platform for the transport of the Vehicle from row to row.

The vehicle automatically drives one on this platform Parking position.

Because the broth supply of the vehicle is not for large greenhouses is sufficient, in this parking position the broth or The vehicle's water supply is automatically supplemented if necessary.

In this case, the vehicle is supplied with Tap water and the preparation of the application broth from the Agent tank of the vehicle provided. The transport platform is in this case only by a towed or wound hose connected to the water pipe. The transport platform preferably has a (battery) electric drive and is installed on a fixed Rail guided.

As the platform is preferably on a concrete track moves, the chassis is on one side with flanged wheels Guide and on the other hand with rubberized drive wheels executed. To recognize the longitudinal position is the Transport platform equipped with a sensor. A expedient design is an inductive sensor that is based on metal cam that responds in a C-shaped Guide rail attached and clamped as needed. When using a roof-shaped angle profile the coding through corresponding holes in the rail respectively. Position detection based on the position is also useful  a preferably non-contact length measurement and their Comparison with a saved target position. Alternatively or in addition, the position can also optically z. B. with barcode Markings along the route are identified.

For the exchange of information between spray vehicle and Transport platform, mutual actuation is easier Limit switch sufficient, which is the starting position of the Spray vehicle, the fill level of the reservoir, the Reaching a longitudinal position and monitoring Record the operational readiness of the spray vehicle. For the Transmission of further data is a serial remote transmission by infrared light or inductive proximity switches. The use of the spray vehicle is from the transport platform managed.

The spray vehicle drives autonomously within a row.

Further design details according to the invention are:

• - The collision sensor in the form of a towards the vehicle movable and by connecting rods with each other connected bumpers serves aside from the automatic Direction control also the personal protection of the automatically moving device.
• - The design of the blower with the arrangement of 2 impellers one above the other, with the lower impeller on the shaft of the Internal combustion engine sits and the upper one on a bearing block the cylinder head of the engine is screwed and over a V-belt variator is driven with adjustable speed. The performance of the blower is therefore tailored to the needs of the Adapt culture.
• - The use of the aggregate of a commercially available Pressure washer as a pump and electrical generator by a pulley on the unit instead of the fan is attached, which the unit via a toothed belt with the Internal combustion engine connects. The electric motor of the unit is with minor modifications as an electrical generator too use.
• - The arrangement of the drug tank within the brewing tank as separate and removable container reduces the risk of Combination of user and environment, during filling and at  the cleaning.
• - The design of the dosing pump as a peristaltic pump multiple wrapping and a roller-mounted eccentric as Displacer or the design as an eccentric screw pump enables both sufficiently high pressure at low Wear for direct feeding, as well as for cleaning Return of the active ingredient by reversing the direction of rotation.
• - The infinitely variable regulation of the dosing pump enables exact Setting the application rate of the plant protection product according to the optimal driving speed.
• - The direct feed avoids residual quantities and reduces that Risk of poisoning from contaminated plant components.
• - The electric travel drive enables reliable Control of the straight line and the reversal of direction, as well as over the infinitely and independently adjustable driving speed an optimal adaptation of the application to the culture.
• - The use of a textile air hose for vertical Air duct enables flexible adaptation to the crop height e.g. B. of cucumbers and tomatoes.

The use of a fixed air baffle with adjustable Air control fins in the lower area enable the targeted Guiding the air flow in direction and strength at dense ones low bush-like cultures such. B. Chrysanthemums and Conifers for optimal penetration of the crop.

• - The wheel axles of the spray vehicle are telescoped into one another to push or replace. The track width is so variably adjustable. The improved stability can Operation on uneven surfaces can be used and it results sufficient stability for the use of horizontal spray or in connection with an air hose also the use of spray bars on the spray vehicle.
• - The transport platform is with a programmable memory equipped for the driving orders. Except for the application the transport platform also as an automatic one Transport system z. B. for planting or harvesting be used.

This enables a better use of the investment. The platform is therefore for loading with others Transport containers and driving with wheelbarrows and Pallet truck designed to be accessible from 4 sides.  

The filling device for the spray vehicle can get out of the way be pivoted. The transport platform is through the all-round accessibility for other means of transport simply too run over and is only a minor obstacle. The platform can be used in conjunction with roller tables additionally also with appropriate receptacles for transport the tables are equipped.

1 shows the automatic application device with various control devices in one perspective.

The spray vehicle ( 1 ) moves back and forth autonomously within rows of the culture.

The spray vehicle carries on a four-wheel undercarriage the drive motor ( 12 ), which drives the blower and broth pump as well as an electric generator, which are arranged inside the housing, as well as a control panel ( 9 ), in front there is a broth tank with an integrated agent container ( 4 ). At the top, the spray vehicle is equipped with a textile air guide hose ( 5 ) with an integrated vertical nozzle assembly ( 28 ). The vehicle is mechanically guided inductively on a rail ( 3 ) in the floor or on a guide wire ( 6 ) which is laid between a molded concrete part ( 7 ) as a guide and a concrete block ( 8 ) as a reversing frame.

The transport platform ( 2 ) runs on a fixed central aisle ( 13 ). It is guided on one side on a steel profile rail ( 14 ) which is profiled to accommodate variable position marks in a C-shape.

When laying on the road, the C-profile can be embedded in a rubber profile ( 15 ) with side ramps to reduce the risk of stumbling.

Rubberized drive wheels are on the opposite side. The energy supply is optionally via a trailing cable or from a battery.

For the application of large areas, a dispenser ( 16 ) is provided for refueling the broth container ( 4 ).

The supply of water takes place via a dragged hose line ( 17 ) directly from the water line.

The target positions can be selected as a menu on a terminal ( 18 ) or saved as a program.

The transport platform is designed on all sides with ramps ( 19 ) for driving on and driving over with any vehicle. The platform is protected against collisions in the direction of travel and to protect people by light barriers ( 20 ).

Fig. 2 shows the spray vehicle in a longitudinal section. Vertical slots ( 22 ) for the air outlet are arranged in the middle between the four wheels, on the left behind the slots there is an internal combustion engine ( 12 ) for driving a double blower and a pump ( 27 ) and an electric generator ( 26 ) between the driven front wheels arranged.

In front of the louvers ( 22 ) is between the individually mounted front wheels of the brewing tank ( 4 ), the inner wall ( 29 ) of which serves as an air guide surface. An active ingredient container ( 31 ) is arranged inside the brewing tank and can be removed through a large filling opening ( 30 ), which dips into a coupling with a tappet-operated bottom valve ( 32 ), which connects it to the metering pump ( 36 ) via a line. A stirring propeller ( 37 ) is arranged in the brewing tank, the shaft of which is mounted at the bottom at the bottom of the tank and is driven by an electric motor ( 38 ) mounted above the tank. The broth pump ( 27 ) is located within the air duct and draws the broth from the bottom of the tank and supplies it to the spray nozzles ( 39 ) connected by the nozzle assembly ( 28 ). The supply can be switched on by a solenoid valve ( 46 ) as required. An adjustable pressure relief valve ( 41 ) is provided to secure the pressure line and to set the system pressure. The dosing pump feeds the active substance into a mixing chamber ( 42 ), which is designed above the shut-off valve as a cyclone mixer ( 67 ) with a subsequent homogenization section ( 68 ) made of sintered metal with a very small volume.

The fan consists of an impeller ( 24 ) on the motor shaft and a second impeller ( 25 ), which is mounted above it in a bearing block ( 43 ), which is screwed onto the cylinder head of the internal combustion engine and which carries a rubber-metal fastening element for suspending the motor . The shaft of the upper impeller is designed as a hollow shaft through which an adjustment device for a V-belt variator ( 44 ) for operation ( 45 ) is guided to the outside.

A corresponding counterpart is arranged on the internal combustion engine as a spring-loaded variator disc ( 46 ). The pump unit ( 27 ) is coupled to the internal combustion engine via a toothed belt drive ( 49 ). The internal combustion engine and pump unit are attached to a common tubular profile frame ( 47 ). This assembly frame is then attached to the vehicle housing ( 48 ) with rubber metal elements. The vehicle housing, which is made of glass fiber reinforced plastic, is reinforced with an inner tubular space frame that connects the vehicle axle, the attachment points of the subframe, the axis of the foldable transport handles and the attachment points for the attachment of horizontal spray bars.

On the operator side, the pull starter of the internal combustion engine is accessible, as well as the other actuating elements for the engine and the petrol tank. The wheelbarrow transport handle ( 53 ) is mounted above it and locks against a stop ( 54 ) when it is lifted. A control terminal ( 9 ) is attached to the air duct, on which operating conditions such as injection pressure and generator voltage can be monitored, the parameters for metering and driving speed can be set, and if necessary a route can be programmed, and various functions can be switched: stirring, spraying, Dosing, cleaning dosing, drive, automatic start / stop.

There are bumpers ( 55 ) at the front and rear of the spray vehicle, which are connected to each other electrically or by push rods running lengthways under the casing and act on a switch for the direction of travel.

The drive is carried out by two independently controlled electric geared motors ( 56 ), each of which acts on the wheels ( 21 ) on the unit side via a chain drive ( 57 ). The drives are fixed to the individual semi-axes ( 58 ) with flange plates. The semiaxes are telescopic against one another, which allows a variation in the track width, as shown in FIG. 3 as a front view. Steering takes place by means of different rotational speeds of the drive motors, which are regulated in accordance with the deviation of the vehicle position from the desired position, the actual position being determined by inductive sensors ( 59 ) mounted at the bottom of the vehicle in relation to a guide wire ( 6 ) in the roadway.

Fig. 4 shows the construction of the metering pump as a peristaltic pump with the eccentrically mounted rolling element ( 60 ), which rolls on the delivery hose ( 62 ) laid in the cylindrical housing ( 61 ) with multiple loops and on the output shaft ( 64 ) of the gear ( 65 ) is mounted with a roller bearing ( 63 ). The peristaltic pump is driven by an electric motor ( 66 ). The peristaltic pump feeds into a cyclone mixer ( 67 ) in which the sintered element ( 68 ) is attached to the outlet for homogenizing the mixture.

Fig. 5 shows an embodiment of the guide rail with angle profiles ( 70 ), which are connected with hat-shaped cross bars ( 71 ) or at the ends with L-shaped cross bars ( 72 ) and between which perforated mats ( 73 ) are laid as a safe walkway can. The rail segments are connected by screws ( 74 ). The wheels ( 21 ) of the spray vehicle are to be provided with wheel flanges ( 75 ).

Fig. 6 shows an embodiment of the guide rail with heating pipes ( 80 ) which are hydraulically tightly connected with pressed-in flanges ( 81 ) and removable double nipples ( 82 ) and are combined by clipped crosspieces ( 83 ) to the track and walkway according to the track width. The heating pipes are connected to a circuit on the one hand by flanging a U-shaped connecting element ( 84 ), on the other hand by hose connections ( 11 ) to the distributor lines ( 10 ) of the heater ( Fig. 1). Rail segments and connections are flanged together using screws ( 85 ). Wheel flanges ( 86 ) with corresponding profiling are provided on the wheels S of the spray vehicle.

Claims (15)

1. Automatic machine for the application of crop protection agents, characterized by the combination of an internal combustion engine drive ( 12 ) for energy supply, and with a storage container ( 4 ) for broth supply, self-sufficient and guided by a steering device straight into the rows of plant culture in and out spraying vehicle ( 1 ) with a transport platform ( 2 ) which moves automatically on a fixed central aisle for the transverse transport of this spray vehicle to the desired row and with devices ( 16 ) for automatically filling the storage container ( 4 ). 2.Automatic for the application of crop protection agents characterized by the design of the transport platform ( 2 ) with a battrieelectric drive which acts on rubberized drive wheels on one side and wheel flange guide wheels arranged on the opposite side, which guide the transport platform along a preferably C-shaped rail with position markings clamped therein ( 14 ), a control terminal ( 18 ) arranged on a corner for the selection and programming of target positions and driving commands, sensors for recognizing the position, devices for exchanging control information with the spray vehicle and, if applicable, devices for initializing a gyro system for controlling the direction of the spray vehicle characterized by the design of the transport platform on all sides with ramps ( 19 ), with light barriers ( 20 ) detecting obstacles in the direction of travel, the equipment with a removable or swiveling B Filling device ( 16 ) for automatically filling the spray tank ( 4 ) of the spray vehicle with tap water. 3. Automatic machine for the application of crop protection agents according to claim 1, characterized in that the housing ( 48 ) of the spray vehicle has vertical air outlet slots ( 22 ) centrally between four wheels ( 21 ) with units for drive ( 12 ) and power generation arranged behind it and inside the housing ( 26 ) as well as the blower ( 24 , 25 ) and pump ( 27 ) and the storage tank ( 4 ) arranged in front of it, as well as the design of the housing as an air duct for an air flow emerging vertically upwards through a round opening ( 53 ) and the formation of this round Opening with a beaded collar for attaching a textile air guide hose ( 5 ), further characterized by attachment points ( 51 ) for horizontal spray and spray bars in the area of the upper air outlet opening. 4. Automatic for the application of crop protection agents according to claim 1 and 3, characterized in that in the spray vehicle a piston pump unit ( 27 ) from a commercially available high-pressure cleaner as a pump for applying the broth through spray nozzles ( 39 ) is installed and the motor of the pump unit for use as an electric Generator ( 26 ) is modified, further characterized by the assembly of the pump unit and the drive motor on a common frame ( 47 ) and the coupling of the pump unit to the drive motor by means of a belt transmission ( 49 ) with a fixed or variably adjustable ratio, the pump side on the second Shaft end is mounted instead of a fan. 5. Automatic machine for the application of crop protection agents according to claim 1 and 3, characterized by a blower unit for supporting the application with an air flow, consisting of two impellers arranged one above the other, the lower propeller ( 24 ) being attached directly to the shaft of the drive motor ( 12 ) and the upper propeller ( 25 ) is mounted with a hollow shaft in a bearing block ( 43 ) which is screwed onto the cylinder head of the internal combustion engine and is driven by a V-belt drive with a variable ratio, the adjusting device of which is guided to the outside by the hollow shaft for actuation ( 45 ) is further characterized by the arrangement of a rubber-metal element for fastening the drive unit to the bearing block and the fastening of the drive unit to a space framework frame which reinforces the housing and which connects the fastening points with the bearing ( 50 ) of the transport handles ( 53 ), the wheel axle and the fastening point kten ( 51 ) for the spray bar. 6. Automatic machine for the application of crop protection agents according to claim 1, characterized in that a stirring propeller ( 37 ) is arranged in the reservoir of the spray vehicle, the shaft of which is mounted in the bottom of the container and the electric drive motor ( 38 ) is arranged above the reservoir. 7. Automatic for the application of plant protection products, characterized in that a storage container ( 31 ) for plant protection product concentrate is arranged inside the brewing tank of the spray vehicle and can be removed through its filling opening, which has a bottom valve ( 33 ) with actuating plunger at the bottom, which is opened during installation and the Connects the container to a metering pump ( 36 ) via a line. 8.Automatic for the application of crop protection agents, characterized by the use of a metering pump ( 36 ), which is preferably electrically driven with a variably adjustable speed, for the direct feeding of the crop protection agent into the spray line and its design as an eccentric screw pump or as a peristaltic pump with a wrapping of the pump tube of more than one Revolution and the use of a displacement rotor ( 60 ) which is eccentrically mounted on the pump hose on the output shaft ( 64 ) of an electric geared motor, further characterized by feeding into a cyclone-like mixing chamber ( 67 ) in which a sintered metal element ( 68 ) is arranged at the outlet for homogenization is. 9. Automatic machine for the application of crop protection agents according to claim 1, characterized in that longitudinally displaceable bumpers ( 55 ) are arranged in the directions of travel in front of the housing, which are connected to one another underneath the housing of the spraying vehicle and guided therein by rods or which are stored independently and are electrically coupled to one another and act on shifting switches for switching the direction of travel and act on the spring elements, preferably designed as a gas pressure spring, for a uniform reversal acceleration. 10. Automatic for the application of crop protection agents according to claim 1, characterized in that the spray vehicle contains a control device for automatic steering along a guide element ( 6 ) along the route by two sensors ( 59 ) are arranged on the underside of the vehicle, which the deviation of the vehicle from the guide element, wherein the guide element is preferably an iron wire and the sensors are sensitive to the distance-dependent change in the inductance. 11. Automatic machine for the application of pesticides Claim 1, characterized in that in the spray vehicle as Control device for straight-ahead driving within rows a gyro system is arranged, and the direction of travel the comparison with this gyro system is regulated and that Gyro system each in the parking position of the spray vehicle on the transport platform or with manual cross transport is balanced by bearing. 12.Automatic for the application of crop protection agents, characterized by the design of the wheel axles as telescopic semi-axles ( 58 ), in that the semi-axles are arranged next to one another and in a guide tube ( 34 ) and devices are provided for fixing the semi-axles in the different track widths, as well as when present of drives, these are independent of one another and are each firmly connected to the axle in the area of the wheel bearing, or devices for exchanging axles with different track width are provided. 13.Automatic for the application of plant protection products, characterized by concrete blocks ( 7 ) or sheet metal parts with guide grooves for the alignment of the spraying vehicle and the fixation of a guide wire, as well as a concrete block ( 8 ) or delimitation post as path limitation and battering ram for the collision sensor of the spray vehicle and for the mutual fixation of the guide wire or by using corresponding molded parts for the production of a smooth transition from a fixed central aisle to guide rails laid in the row. 14.Automatic for the application of crop protection agents, characterized by a travel rail which is formed from a ladder-like arrangement of preferably galvanized and spot welded steel profiles by angular guide rails ( 70 ) with hat-shaped connecting webs ( 71 ) or at the ends of the rail segments with angular ones Flange webs ( 72 ) are connected and the rail segments are connected by screws ( 74 ) in the flange webs, further characterized in that perforated plates ( 72 ) can be inserted between the guide rails as a way of fastening. 15.Automatic for the application of crop protection agents, characterized by a travel rail which consists of pipes arranged in pairs and connected by a large number of connecting webs ( 83 ) or by a plurality of flat connecting elements according to the track gauge ( 80 ), which are pressed in at the pipe ends and to the pipe have hydraulically sealed connecting flanges ( 81 ), with cylindrical sealing surfaces arranged therein for repeated assembly of double nipples ( 82 ) sealed with O-rings, and characterized by the rust-like design of the connecting webs as a walkway and the design of the connection of pipes and webs as an elastic snap connection .