Field of the invention

The invention relates to the field of mobile marking apparatuses, such as line- marking machines for marking ground surfaces, which are configured to be propelled across the ground while spraying a marking material.

Background of the invention

Mobile marking machines are used for marking indoor or outdoor playing surfaces, for example, or sports fields, car-parks, exhibition halls, roadways, airfields, building sites etc. The mobile marker is an appropriate solution for applications where a hand-held marking device would be insufficient, but where a permanent installation is undesirable on grounds of cost, complexity or practicability. In the following description, the example of pedestrian line-marking machines for sports fields will be used. However, references to line-marking and line-marking apparatuses should be understood to apply more generally to any mobile marking apparatus which is suitable for spray-marking the ground surface, such as the surface of an indoor or outdoor playing surface, over which it travels. Such machines may be user-propelled or battery-powered and light enough to travel over soft ground, or over prepared surfaces vulnerable to damage by road vehicles or other heavy equipment. They can move independently of any mains power supply, for example, carrying a battery for electrical power, a reservoir of marking material and the components necessary for spraying the marking material.

Prior art

Line-marking machines which apply marking material by spraying it as a liquid under pressure have been known for some time. The marking liquid, or paint, may typically be a water-borne or water-based suspension or emulsion of white particulate solids, for example. The marking liquid is conventionally forced under pressure through a nozzle having a small hole, emerging as a spray of small droplets of the liquid, the spray usually having the form of a fan, a full cone or a hollow cone, depending on the geometry of the nozzle at the outlet aperture from which the paint emerges. Standard nozzles, in which the paint is simply forced through an orifice, have generally performed satisfactorily for many line-marking purposes. Such nozzles are relatively cheap and can be replaced easily. Forcing the paint through a fine nozzle hole imparts energy to the liquid in the form of shear forces which break up the liquid into droplets. The spraying characteristics of a conventional line-marker can be adjusted within traditionally acceptable parameters by exchanging the nozzle for one with a different spray pattern or a different diameter hole, by changing the properties of the marking liquid, or by varying the pressure at which the marking liquid is supplied to the nozzle. A hollow cone nozzle, for example, may be provided on its inlet side with directional baffles or rifling guides which impart an angular momentum to the marking liquid as it enters the nozzle hole. On issuing from the nozzle outlet, angular momentum in the liquid is at least partially conserved, and the sprayed droplets are urged outwards to form the wall of a hollow cone. The droplet size, and the flow rate of marking liquid through such a nozzle are influenced by the pressure of the liquid and the viscosity of the liquid. It is not possible to vary the droplet size without varying the flow rate, or to vary the flow rate without varying the droplet size. Similarly, it is not possible to use the pressure or viscosity to increase both the flow rate and the droplet size, or to decrease both the flow rate and the droplet size. For a given nozzle geometry and a given viscosity, there is a minimum operating pressure, below which the marking liquid does not form a usable spray of droplets. There is thus a minimum flow rate of the marking material when using such nozzles. In practice, this minimum practicable flow rate for a 0.8mm hollow cone nozzle may be in the region of 120 ml/minute, for example.

Environmental and economic considerations mean that manufacturers of line- marking equipment must pay careful attention to the amount of marking liquid used for a particular marking task, and to the time necessary for carrying out the task. Small, lightweight marking machines such as the Ki ^® from Fleet (Line Markers) Limited are now being used which are designed to carry much smaller quantities of marking liquid and thus require a more concentrated marking liquid in order to ensure adequate marking opacity while avoiding continually having to replenish the machine's marking liquid supply. A contractor who marks dozens or hundreds of sports fields may use a larger mobile marking apparatus (eg a pedestrian or ride-on marker, or a groundskeeper's utility vehicle with marking attachment), and it is likewise a significant advantage for such contractors to be able to mark using a small volume of concentrated marking fluid for each sports field, thereby permitting longer periods of uninterrupted marking. In order to reduce the spray rate (volume of liquid passing through the nozzle per unit time) of liquid, the conventional solution is to vary one or more of the parameters mentioned above, namely pressure, viscosity, solid content and nozzle hole size. A lower spray rate may normally be achieved by selecting a more restrictive nozzle geometry (eg with more baffles or rifling, or a smaller hole). However, the viscosity and/or the solid content of the marking liquid would then typically need to be reduced, and the liquid pressure increased, in order to work with the more restrictive nozzle. The lower viscosity allows the liquid to pass more easily through the hole, while the higher pressure imparts more energy, and therefore shear force, to the liquid. By way of illustration, a spray rate of approximately 120 ml/minute may be achieved using a fine (0.8mm diameter) hollow-cone nozzle with a marking liquid viscosity of 150 cP and a solid content of 30% at a pressure of 60 psi (420 kPa). Viscosity values in this text refer to measurements made at 20°C using a Brookfield DV2T viscometer and LV-63 spindle at speed 10, and measured after 45 seconds. Such low-viscosity and low-solid-content marking liquids have the

disadvantages of reduced opacity and poorer suspension characteristics (the solids settle out of suspension more readily).

The marking material may typically be supplied ready-to-use (ie without dilution or mixing), and it is important that such ready-to-use marking liquids have an adequate shelf-life without the solids settling out. A storage shelf-life of at least a year is desirable. Low-viscosity marking materials are typically not storable for such extended periods. Even in situations where the marking material is left in the line-marker for a shorter period, such as between fortnightly pitch-markings, enough settling may happen to cause clogging, or uneven marking or damage to the pump or other components of the line-marking apparatus. Such effects can be exacerbated by cold weather, when settling occurs much more quickly. Although the low-viscosity marking liquid is intended to work with very fine nozzles to reduce spray rate, in practice such fine nozzles may still clog, and a groundsman may prefer to swap the very fine nozzle for a larger nozzle to avoid clogging. The combination of low viscosity marking fluid and a larger nozzle means that the real spray rate will be far higher than the specified spray rate. Thus, whereas a low spray rate may be claimed for some low-viscosity marking materials (for example one litre of paint per football pitch), in reality a real groundsman, marking a real football pitch, may use significantly more than one litre per pitch.

Low viscosity paints also suffer from the disadvantage that they run and puddle on the surface to be marked. When marking on grass, for example, low-viscosity paint tends to run down the blades and seep into the soil. The marking is thus less visible on the grass, and the soil may over time become contaminated with accumulated paint. Low- viscosity paints are also unsuitable for marking hard surfaces such as wood, concrete or asphalt, partly because the paint is easily absorbed into the surface and partly because it runs into small surface unevennesses, thereby rendering the marking edges indistinct. Low-viscosity marking liquid also runs quickly off the line guides used on many line- marking machines, causing an unsightly and uneven puddling of paint along the line edges.

The use of fine or high back-pressure nozzles requires marking machines to operate at higher liquid pressures, such as 80 psi (560 kPa) or more in order to achieve sufficient energy in the liquid to create a fine spray with low flow rate. Indeed, some machines using piston-type liquid pumps may generate much higher pressures, as high as 1200 psi (8400 kPa) or more, in order to achieve an even spray pattern with a viscous marking liquid and using a fine nozzle. Such machines require that components such as pressure vessels, connectors and hoses be capable of withstanding the higher pressures, with the attendant safety considerations and increased probability of component failure. As mentioned above, for a given marking liquid viscosity, the spray rate and the droplet size depend largely on the liquid pressure to the nozzle. However, the relationship is not linear, such that even a small change in the spray parameters (increase in the spray rate or reduction in droplet size, for example) may require a comparatively large change in the marking material pressure in order to achieve it. The use of a fine nozzle at a very high pressure may in theory permit the use of more viscous marking materials, but this would not be a practical solution, because more viscous marking fluids tend to have higher solid content and would quickly clog the fine nozzle. There is also a limited range of climatic conditions in which conventional nozzles and low viscosity marking liquid can operate: in hot (eg above 40 C) or low (eg below 0 C) temperatures, the marking liquid more easily blocks the nozzle, either because of rapid drying of the liquid in the nozzle, or through low-temperature effects such as clumping of the solids or freezing of the marking liquid in the nozzle. Conventional nozzles are also not ideal for windy conditions, because the fine nozzle produces a relatively low-velocity spray which is easily perturbed by wind.

The use of a fine nozzle and low-viscosity, low-solids marking fluid also imposes restrictions on the speed at which the marking apparatus can travel. If the marking is performed too fast, the sprayed mark will be too faint. If the speed varies, then the line quality will also vary.

There is thus a need for a marking apparatus which is capable of marking ground surfaces at a lower spray rate (eg capable of marking a football field with good-quality white lines using less than one litre of marking liquid), and which is capable of using more viscous marking liquid, while avoiding at least some of the disadvantages described above.

Brief description of the invention

The present invention aims to overcome at least some of the above

disadvantages of the prior art apparatuses and methods described above. To this end, the invention foresees a marking apparatus as described in claim 1, and a marking method as described in claim 15. Further variants of the invention are described in the dependent claims. Although the use of a two-fluid atomising nozzle may increase the complexity of the marking apparatus, it allows the marking apparatus to achieve very low spray rates and precise control of the spraying parameters, without the need for high pressures or low-viscosity paint. It enables marking with a high colour density (opacity) and with well- defined, clear line edges, with an even distribution of solids across the sprayed area. Thanks to the large number of parameters which can be controlled independently of each other, and the large range of each parameter, the invention affords a greatly superior controllability of the marking process. When marking at varying speeds, for example, the application rate can be varied in dependence on the forward velocity of the marking apparatus, even over large variations in velocity, from zero to 10 m/s or more. The higher droplet velocity of the spray of an atomising nozzle permits improved definition of the marked line, even under windy conditions. Because the invention allows higher viscosity marking liquids, or those with a higher solids content, to be applied at a lower spray rate, this in turn allows a better coating performance when spraying on uneven surfaces such as grass. In other words, the marking liquid adheres better to the grass foliage. This better coating performance, in turn, permits a significant reduction in the amount of marking fluid which is required to achieve a given marking quality for a given sports field, for example. The invention also permits marking to be carried out under a wider range of climatic conditions, including windy days, at high temperatures (eg above 40 C), and in sub-zero temperatures. The spray nozzle is less likely to clog, because nozzles with wider apertures can be used, and because it can be automatically cleaned (using the cleaning arrangement described in one variant of the invention). Generally, the invention permits a line marking apparatus and method which can combine the advantages of marking fluids which are more viscous, more stable and/or more opaque, with the advantages of a very low spray rate (which may be as low as 50 ml/minute or even less). It can even be used to achieve a reliable and controllable spray rate right down to zero.

Detailed description of the invention

The invention will be described in detail with reference to the attached drawings, in which:

Figure 1 shows an example of a marking apparatus according to the invention. Figure 2 shows a schematic cross-section of a first example spray nozzle for use in the marking apparatus of figure 1.

Figure 3 shows an enlarged schematic cross-section view of the nozzle head of figure 2.

Figure 4 shows a cross-section view through the nozzle head of figure 3 in a plane denoted in figure 3 as A-A.

Figure 5 shows a schematic plan view of the air cap 52 of the nozzle head of figure 3.

Figure 6 shows a schematic cross-section of a second example spray nozzle for use in the marking apparatus of figure 1. Figure 7 shows a schematic cross-section of a third example spray nozzle for use in the marking apparatus of figure 1.

Figure 8 shows a schematic side elevation cutaway view of an example of a component arrangement in the marking apparatus of figure 1.

Figures 9 and 10 show in schematic plan view two example arrangements of nozzle and line-guides for the marking apparatus of figure 1.

Figure 11 shows a schematic circuit diagram corresponding to the component arrangement of figure 8. Figure 12 shows a simplified flow diagram of a marking method according to the invention.

It should be noted that the figures are provided merely as an aid to understanding the principles underlying the invention, and should not be taken as limiting the scope of protection sought. Where the same reference numbers are used in different figures, these are intended to indicate similar or equivalent features. It should not be assumed, however, that the use of different reference numbers is intended to indicate any particular degree of difference between the features to which they refer.

Detailed description of the invention An example of a marking apparatus according to the invention is illustrated in figure 1. In this example, a pedestrian line-marker 1 comprises a wheeled chassis 2 with wheels 5, the chassis 2 supporting a housing 3, a reservoir 4 for marking liquid, and a spray assembly 8 for spraying the marking material supplied from reservoir 4 through marking material conduit 15 to a nozzle 10, so as to mark a line 11 on the ground surface. The line-to-be-marked 11" is indicated with dotted lines. The ground surface may be turf (ie mown grass) or other natural surface, or it may be an artificial playing surface such as carpet, vinyl, wooden boards, asphalt, artificial grass or concrete, for example. The reservoir 4 advantageously comprises a collapsible container, such as a bag, with a connector which can be attached to the marking fluid input connection (not shown) of the marking apparatus such that the reservoir, the internal marking liquid conduit and component system of the marking apparatus, and the marking fluid conduit 15 to the nozzle 10, together form a closed (ie substantially airless) system. This has the advantage that the marking liquid can be left in the machine for extended periods of time (for example between weekly or fortnightly markings), without requiring those internal components of the marking apparatus which come into contact with the marking fluid to be cleaned by flushing through with water, as is currently required with conventional marking apparatuses.

The pedestrian line-marker 1 can be propelled and steered by the operator using a handlebar 6 fitted with controls 7 for operating the spray assembly 8. The housing 3 accommodates components, which will be described in more detail with reference to figures 8 and 11, for delivering marking fluid from reservoir 4 via marking fluid conduit 15 to the nozzle 10 of the spray assembly 8. In the example, the housing 3 also accommodates components for delivering air at a first pressure via air conduit 14, and at a second pressure via air conduit 16, to the nozzle 10. The conduits may comprise PVC, silicone rubber or other suitable tubing. The air conduits may comprise reinforced flexible hoses. The spray assembly 8 is secured to the wheeled chassis 2 by means of an arm 13, which may be a fixed arm, static with respect to the chassis 2, or an actuator arm, movable laterally with respect to the chassis 2 under control of a guidance or navigation system such as laser or GPS guidance (not shown). The spray assembly 8 comprises left- hand and right-hand line guides 17 and 18 which serve to confine the spray 9 emanating from nozzle 10 to the desired width of the line 11. The line-guides 17 and 18 may be moveable laterally, so that a desired marking width can be adjusted, and they may have a vertical freedom of movement in order that they can maintain contact with the ground surface, even if the ground surface is uneven, as the marking apparatus 1 moves across the ground surface. The nozzle 10 is secured, for example using one or more rigid mounting elements, to the fixed support arm or actuator arm 13. Figure 1 illustrates one possible configuration of its various components. Other configurations are possible. For example, the spray assembly 8 may be mounted to the left, or in front, or behind the wheeled chassis 2, and various components for air or marking material supply may be mounted outside the housing 3, or the housing 3 may be dispensed with altogether.

The example line-marker shown in figure 1 is a pedestrian machine. Such machines are typically designed to be light (eg less than 40kg when empty of marking liquid, or less than 50 kg when charged with marking fluid) and manoeuvrable. However, the invention may also be implemented on ride-on markers machines such as the eROK ^® electric ride-on marker from Fleet (Line Markers) Limited or for line-marking attachments for general purpose utility vehicles (UV). A ride-on marking apparatus may typically weigh less than 300 kg, net of marking material, or less than 500 kg when fully laden with paint and operator.

The line-marking liquid may be a water-based dispersion of particulate solid material such as silica and titanium dioxide, having a shear viscosity of up 200cP to 3000cP, for example, and an average spherical particle size (solids content) of between 0.1 pm and 40 pm, for example.

Unless stated otherwise, shear viscosity values given in this text relate to

Brookfield rotational viscosity measurements made at 20°C using a DV2T viscometer with LV63 spindle at speed 10 for 45 seconds.

Figure 2 shows a vertical cross-section through an example two-fluid nozzle 10, also referred to as an atomising nozzle, suitable for use in the marking apparatus 1 of the invention. Figures 3 to 5 show parts of the nozzle 10 of figure 2 in greater detail. Instead of relying on fluid pressure for providing the energy required to generating shear forces in the marking liquid, and thereby break the liquid up into spray droplets, the two fluid nozzle 10 uses a second fluid, such as air, to break up the marking fluid. The atomising nozzle 10 comprises a marking material supply inlet 15, through which the marking material is introduced at a first pressure into a marking material chamber 45 within the nozzle body 40. Atomising fluid, such as air, is introduced at a second pressure into the atomising fluid chamber 44 through atomising air conduit 16. In operation, marking fluid at the first pressure exits from the marking fluid chamber 45 through marking fluid orifice 51 and enters the mixing chamber 49, where it mixes with the atomising fluid exiting from the atomising fluid chamber 44 at the second pressure through atomising fluid orifice 48 (in this example formed as a ring gap between the wall 40 of the atomising fluid chamber and the the tip of the marking fluid chamber wall 50. The turbulent mixture of marking fluid and atomising gas is then forced out of the mixing chamber, at substantially the second pressure, through spray orifice 53 formed in air cap 52.

Note that dual-fluid nozzles are known in other technical fields. For example, dual fluid mixing nozzles are used in applications for vapourising viscous liquids, such as burner nozzles for heavy fuel oil, or in high-throughput industrial processing plant, or in complex applications where it is critical to be able to control the droplet-size precisely. However, because of the relative complexity of the infrastructure required (mains power, air line, control electronics, control mechanics, and storage equipment etc), dual-fluid nozzles are typically only used where such infrastructure is readily available.

An actuation arrangement is provided for blocking the passage of marking fluid through the marking fluid orifice 51. In this example, the actuation arrangement comprises a stop-pin 47 which is shaped to be inserted into the marking fluid orifice 51 so as to block the orifice 51 and dislodge any marking material in the orifice 51. The stop-pin 47 is at the end of an actuator pin 41, which is biassed towards the orifice 51 by an actuator urging means (shown as helical spring 42). When the nozzle 10 is in operation, actuation fluid (eg air) is introduced at a third pressure into actuation fluid chamber 46 so as to move and then hold the actuation pin piston-fashion in a withdrawn position with its stop pin 47 withdrawn from from the marking fluid orifice 51, as illustrated in figures 2 and 3, thereby allowing free passage of marking fluid out of the marking fluid chamber 45 through the marking fluid orifice 51 and into the mixing chamber 49. A vent 43 is provided so that the actuator pin 41 is not impeded by a counteracting pressure of air around the spring 42. Note that the illustrated pneumatic actuation arrangement is just one possible

arrangement - a similar result could be achieved using a solenoid, for example, or a mechanical linkage operated manually. As mentioned above, the marking fluid reservoir and the marking fluid delivery system of the marking apparatus may form a closed system. The marking liquid is thus not exposed to air until it issues from the marking liquid orifice 51. Thanks to the actuator pin 41, which is provided with a seal for sealing off the marking liquid chamber 45 from the external atmosphere, the marking liquid remains isolated from the air when the spray is not operating. Thanks to the stop-pin 47, any accumulation of marking material in the marking liquid orifice 51 is mechanically expelled by the force of the biassing means (eg helical spring 42) when the actuator pin 41 closes.

In the example nozzle shown in figures 2 to 5, the air cap 52 may be removably secured to the body 40 of the nozzle 10, for example by means of a bayonet or screw- thread fitting (not shown). The spray orifice 53 may have a rectangular or elongated oval shape, so as to generate a fan-shaped spray 9. Other shapes of spray 9 may be achieved with other geometries of spray orifice 53. The tip of the marking fluid chamber wall 50, in which the marking fluid orifice 51 is formed, may also be formed as a separate, removably secured, component, in such a manner that one or more of the marking fluid orifice 51, the atomising fluid orifice 48 and/or the spray orifice 53 may be exchanged for one of a different size or geometry. If the marking fluid orifice 51 is changed, then the actuating pin 47 may also be changed to match.

By way of an illustrative example, a line-marking apparatus having the nozzle 10 depicted in figures 2 to 5 may advantageously be operated using parameters or parameter ranges as follows:

Marking fluid orifice 51 hole diameter (or equivalent area if not a circular hole): less than 1 mm, or more preferably less than 0.6mm, or more preferably less than 0.4mm.

Spray orifice 53 area: less than 5mm ² , or preferably less than 3mm ² .

First pressure (marking material): eg less than 50 psi (350 kPa), or preferably between 5 psi and 30 psi (35 kPa to 210 kPa).

Second pressure (atomising fluid): eg less than 50 psi (350 kPa), or preferably between 5 psi and 35 psi (35 kPa to 245 kPa), or more preferably between 10 psi and 25 psi (70 kPa to 175 kPa). The atomising fluid pressure may advantageously be

substantially equal to the first pressure, or it may be greater than the first pressure - for example by a factor of 1.5 or more, or by a factor of 2 or more. Third pressure (nozzle actuation): eg greater than 35 psi (245 kPa) or greater than 50 psi (350 kPa). The third pressure may advantageously be less than 80 psi (560 kPa).

Flow rate of marking material through the marking fluid orifice 51: less than 150 ml/minute, or more preferably less than 100 ml/minute, or more preferably less than 60 ml/minute.

Flow rate of atomising fluid though the atomising fluid orifice 48: more than 20 litres/minute, or preferably more than 30 litres/minute.

Viscosity of marking fluid: at least 150 cP, or preferably at least 600 cP, or more preferably at least 800 cP. The unit of cP (centipoise) refers here to dynamic shear viscosity as measured at 20°C by a Brookfield rotational viscosity measurements using a DV2T viscometer with LV63 spindle at speed 10.

Solids content of marking material: eg at least 40% by weight, or preferably at least 50%. The above parameter possibilities can be selected in any combination to suit particular marking requirements, or to suit particular marking materials.

Figure 6 shows a variant of the nozzle 10 of figures 2 to 5, in which the same fluid (eg air) supply, and thus the same pressure, is used for both atomising and actuating. In this variant, the atomising pressure is selected such that it is also sufficient to actuate the flow of marking material by withdrawing the actuation pin 41, thereby reducing the complexity and number of air lines required to supply the nozzle.

Figure 7 shows a modification of the connection arrangement of the nozzle 10 of figures 2 to 5. The nozzle 10 of figure 6 may also be connected in a similar manner.

According to this connection arrangement, a cleaning fluid conduit 36 (eg a flexible tube for conveying water) is connected into the atomising air conduit 16. The cleaning fluid conduit 36 may advantageously be connected into the atomising air conduit 16 at or near the nozzle 10. Alternatively, the cleaning fluid conduit 36 may be connected directly into the atomising fluid chamber 44 of the nozzle 10, or even directly into the mixing chamber 49 of the nozzle 10. A one-way valve 37 may be provided in the cleaning fluid conduit 36 in order to prevent the second pressure in the atomising fluid conduit 16 from propelling the cleaning fluid back up the cleaning fluid conduit 36.

The one-way valve 37 may advantageously be located at or near the point at which the cleaning fluid conduit 36 joins the atomising fluid conduit 16 or the atomising fluid chamber 44 or the mixing chamber 49. As will be described below, the cleaning fluid conduit 36 can be used to supply a small amount (eg less than 5 ml, or less than 10 ml, or other amount) of water or other cleaning fluid into the atomising air line, preferably once the flow of marking fluid has been stopped by the operation of the actuation arrangement 41, 42, 43, 47, and as soon as the marking fluid has mostly been expelled through the spray orifice 53. The cleaning fluid is then propelled by the flow of atomising fluid (eg air) into the mixing chamber 49, where it mixes with any remaining marking fluid under turbulent flow conditions, swirling around the mixing chamber as it is expelled under the second pressure through the spray orifice 53. In this manner, the parts of the nozzle 10 which are susceptible to clogging (eg the spray orifice 53 and mixing chamber 49) can be cleaned quickly and effectively, using very little cleaning fluid. Because of the relatively large air flow (eg 0.5 litres per second) through a relatively small (eg 5mm internal diameter) atomising conduit, the small (eg less than 5 ml) dose of cleaning fluid is quickly propelled through and out of the mixing chamber 49. From the point of view of the operator, when he or she instructs the marking apparatus to stop spraying (eg by releasing a switch), the operation of the nozzle actuator and the cleaning fluid injection are experienced as substantially instantaneous (eg completed within a few tenths of a second), which are carried out automatically as part of the "off" sequence controlled by control circuitry 21 of the line marking apparatus 1. Thanks to the very small amount of cleaning fluid (eg as little as 3ml or 5 ml) required for flushing the mixing chamber 49 and the spray orifice 53, the flushing operation can be carried out such that the cleaning fluid is sprayed on to the ground surface at the end of spraying, substantially without affecting the quality of the sprayed mark 11. Thanks to the automated flushing, and the closed marking fluid system, the line-marking apparatus can effectively be used and then stored, without being flushed through by the operator, ready for immediate use for the next marking task.

Thanks to the small amount of cleaning fluid required for each automated flush- through when spraying is halted, the flushing can be carried out many times before the cleaning fluid reservoir needs to be replenished. The cleaning fluid reservoir may thus advantageously have a capacity of less than 1 litre, or less than half a litre, or even less than quarter of a litre.

The example atomising nozzles described above are of the internal mixing type, in which the marking material and atomising fluid are mixed in an enclosed space (mixing chamber 49). However, similar advantages could be achieved, with suitable adjustments, using an external-mixing atomising nozzle.

Figures 8 and 11 show different schematic views of a fluid flow and control circuit which may be used in a marking apparatus of the invention. Figure 8 shows the housing 3, marking fluid reservoir (eg bag) 4 and wheeled chassis 2 of the line-marking apparatus of figure 1.

In the illustrated example, the housing is shown containing a power source 22 (eg a 24V rechargeable battery), a control unit 21, a pump 20 for pumping the marking fluid from the reservoir 4 to the nozzle 10 via one-way-valves 30 and 12 and marking fluid conduit 15 at a predetermined first pressure. A compressor 23 is provided for pressurising air in a pressure vessel 24 via one-way valve 32 to a pre-set third pressure; a fluid control valve 26 is provided for controlling a supply of compressed atomising fluid (air) from the pressure vessel 24 via atomising fluid conduits 34 and 16 to the nozzle 10 at the second pressure; a cleaning fluid reservoir 25 is provided for supplying cleaning fluid via cleaning fluid conduits 33 and 36 into the atomising fluid conduit 16; and another flow control valve 29 is provided for switching air at the third pressure on or off to the actuation arrangement of nozzle 10 via air conduits 31 and 14. Flow control, valve 29 may be a 3/2 solenoid valve which allows reverse airflow through vent 39 when in its "off" state. This allows a rapid turning off of the nozzle actuation. A pressure reducing valve 38 is provided to provide a different (lower) second pressure for the atomising air than the (higher) third pressure for the actuation arrangement. An adjustable pressure-actuated bypass valve 28 is provided for controlling the first predetermined pressure of the marking fluid supplied to the nozzle 10. When the output pressure of pump 20 exceeds the preset first pressure (which is set by adjusting the bypass pressure at the bypass valve), marking fluid is diverted around recirculation line 35 to the input line to the pump 20, thereby controlling the downstream pressure to the nozzle 10 and simultaneously providing an initial energy input into the liquid for improving the shear viscosity and flow characteristics of the marking liquid in preparation for spraying. One-way valve 30 prevents the marking fluid from travelling back into the reservoir bag 4. In this way, the combination of the pump 20, and the recirculation components 28, 35 and 30, provide an output pressure control arrangement for the closed marking fluid system. Optional one-way valve 12, downstream of the recirculation/bypass valve 38, ensures that the closed marking fluid remains closed to the outside atmosphere, even when the nozzle 10 is in operation. Note that this arrangement may be used in fields other than marking, for output pressure control in spraying or other fluid systems more generally. The bypass/recirculation valve 28 may be configured to be able to vary the downstream pressure right down to a very low value, or even substantially to zero. The flow rate of the marking fluid can also be influenced by varying the second (atomising) pressure relative to the first (marking liquid) pressure. At a nominal first pressure of 10 psi (70 kPa) set at the bypass valve 28, for example, it is possible to reduce the flow rate of marking liquid by increasing the second pressure to a value which, via the mixing chamber 49, exerts a back-pressure on the marking liquid emerging from the marking liquid orifice 51. The spray rate of marking fluid may thus be controlled by varying the second pressure, for example by controlling regulator 38 under control of the control unit 21. The second pressure may even be increased to a value at which the flow rate of marking fluid is limited substantially to zero. Optional one-way valve 12 may be included to ensure the integrity of the closed marking liquid supply system, even when the second pressure exceeds the first.

As will be described with reference to figure 12, the cleaning fluid from reservoir 25 can be introduced into the atomising fluid conduit 16 or into the nozzle 10 via cleaning fluid conduit 36. A pump (eg peristaltic pump) or other dosing means 27 is provided for moving a predetermined amount (eg 3 ml or 5ml, or 10ml) of the cleaning fluid (eg water) into the atomising fluid conduit 16, or into the nozzle 10, through the one-way valve 37.

While the atomising fluid supply has been described as comprising a pressure vessel 24, this may not be necessary if a compressor or air pump 23 is used which is capable of delivering the atomising air to the nozzle 10 directly at the required volume flow rate and the required pressure. If a compressor is used, then the temperature of the air increases as it is compressed, and the warm air can be used as a means of pre-warming other components of the marking apparatus such as the nozzle 10, the conduits or other components which come into contact with marking liquid or cleaning fluid, thereby protecting the components and the marking liquid or cleaning fluid from frost when marking in sub-zero temperatures.

Controller 21 is provided for controlling the various flow control components, for example the controllable valves 26, and 29, and the pumps 20 and 27. The controller 21 may also be arranged to control the first and second pressures by controlling the pressure settings of the compressor 23, bypass/recirculation valve 28 and/or pressure reducing valve 38.

The controller 21 may be programmed or otherwise configured to control the various controllable components of the marking apparatus so as to automatically vary the operation of the components in response to operating conditions such as vehicle speed, wind speed, spray angle (line width), ambient temperature and so on. Such control sequences may be carried out automatically, and/or in response to input from the operator (for example via controls 7 or via a control interface such as a graphical user interface of a tablet computer), or they may be programmed to work with input from a control system such as the guidance control system of a laser-guided or GPS-guided or other

autonomous or semi-autonomous marking machine. The flow of marking liquid and air can be separately controlled so as to achieve a precise control of the spraying parameters.

In the arrangement illustrated in figures 8 and 11, the pressure vessel 24 is pressurised to the third pressure (required for operating the nozzle actuation

arrangement). Alternatively, the pressure vessel may be pressurised to the second pressure (required for atomisation), in which case the nozzle actuation can be done electrically, or a second compressor may be provided for providing the third pressure (for example by further compressing air at the second pressure in the pressure vessel).

Figures 9 and 10 show how the nozzle 10 may be arranged between the left and right-hand line-guides 17, 18 of the spray assembly 8 of figure 1, such that the smallest required line width D ₂ can be marked without the nozzle 10 interfering with the line-guides. D ₂ may be 40 mm or 50 mm, for example. The nozzle 10 is preferably shaped and dimensioned such that the nozzle body can fit between the line guides at their smallest width setting D ₂ (figure 10), allowing enough clearance for the line guides 17,18 to move, ie to rotate in the case of disks, and/or to move up and down on uneven terrain. The fluid connections 14, 15 and 16 to the nozzle 10 are arranged substantially on a longitudinal axis 54 (with respect to the line to be marked 11, 11' and with respect to the chassis 2 of the marking apparatus 1), so that the fluid connections also do not interfere with the line guides 17, 18. The fluid connections 14, 15 and 16 may be arranged to the front of the nozzle 10, as indicated by reference 14, or to the rear, as indicated by reference sign 14'. Two or more of the nozzle connections may advantageously be combined into a single connector (not illustrated), so that two or more connections may be attached to or removed from the nozzle 10 at once.

The line-marking apparatus has been described with one nozzle. However, multiple nozzles may be used. Two nozzles can be fitted between the line guides 17 and 18, for example, with one angled forward and one angled back, so improve coverage on uneven surfaces such as grass. Or multiple nozzles 10 may be arranged for generating multiple markings. Multiple nozzles can be mounted on a lateral boom, for example, for marking parallel lines for running or cycling tracks.

Figure 12 shows an example sequence of operations 60 to 62 which may be initiated automatically when the operator of the line-marking apparatus instructs it to start marking (eg by pressing a switch). In a first step 60, the atomising air flow is established to the nozzle 10 at the second pressure. The marking fluid pump 20 is subsequently switched on, so that the marking fluid is delivered to the nozzle 10 at the first pressure. After a short delay (for example half a second), the nozzle actuation arrangement is operated, and marking fluid flows into the mixing chamber 49 and is sprayed under atomisation through the spray orifice 53.

When the operator instructs the line-marking apparatus to stop spraying, a second sequence of operations 64 to 69 may be carried out automatically. First, in step 64, the supply of marking fluid into the mixing chamber 49 is interrupted, for example by switching off pump 20 and the nozzle actuation arrangement 41, 42, 47.

After a short delay 66, or at the same time, a predetermined amount of cleaning fluid (eg water) is automatically introduced into the mixing chamber 49 via the atomising fluid chamber 44 (steps 65, 66, 67). The atomising air flow continues for long enough to expel the cleaning fluid from the mixing chamber 49, and is then switched off, for example using control valve 26. Note that the nozzle cleaning method described above may also be used in a wide variety of applications for two-fluid or multi-fluid atomising nozzles, and is not confined to its application in marking apparatuses.

The start and stop sequences described above can be used for extended spraying periods, for example when spraying along the sideline of a football pitch, or they can be used for much shorter spraying periods, such as when spraying intermittently (eg for marking dotted lines).

The marking material has been describe above as a fluid, however, it may be supplied to the nozzle as a solid, or as a two or multi-component material. Where the marking material is supplied as a solid, heat from the pressurised atomising fluid may be used to melt the marking material so that it can be atomised. Where the marking material is supplied as two or more components, the components can be mixed at, near or in the nozzle and atomised together to form a mist of reacting components.