GB2623481A

GB2623481A - A system and method for the thermoplastic marking of hard surfaces

Info

Publication number: GB2623481A
Application number: GB2211787.3A
Authority: GB
Inventors: David George Rhoades Anthony; Cassidy Lewis; Paul Cornish-Evans Samuel
Original assignee: Micropply Ltd
Current assignee: Micropply Ltd
Priority date: 2022-08-12
Filing date: 2022-08-12
Publication date: 2024-04-24
Also published as: GB202211787D0

Abstract

Methods and system for applying durable ground markings to a target position on a ground surface are provided. The device comprises a print head comprising at least one dispenser for dispensing molten plastics material at the target position, wherein the molten plastics material is deposited in discrete droplets at the target position where the discrete droplets harden into a durable ground marking. The patterned ground marking may be formed by layering the discrete droplets at the target position wherein the droplets may be layered to a threshold thickness. The droplets may be overlapped to form bevelled, chamfered and/or rounded edges after hardening. The method may further comprise receiving an image and dividing it into printable segments, wherein each segment comprises instructions for applying a plurality of discrete droplets at a target location on the ground surface and applying the discrete droplets according to the printable segments to form the image, wherein the patterned ground marking represents the image.

Description

A SYSTEM AND METHOD FOR THE THERMOPLASTIC MARKING OF HARD SURFACES

[0001] This invention relates to ground markings, such as, for example, road markings, playground markings and step markings, and generally to the application of surfacing to ground traversed by pedestrians and vehicles, particularly for the purpose of imparting or improving slip or skid resistance, awareness of road defects, or road marking awareness.

SUMMARY

[0002] Road and playground markings are applied by a variety of methods, which typically include painting. For example, white or yellow lines on roads, car park markings, and yellow paint step edges. For improved durability, thermoplastic strips or sheets are fused to tarmac or concrete surfaces by heat from gas torches to permanently mark, for example, car parks, roads, cycleways, airports, playgrounds, and the like. For playground markings, the plastics can be formed into shapes and be multi-coloured so that it is aesthetically pleasing. For slip or skid resistance, the strips or sheets can contain, glass, flint, or alumina particles, which are applied while the plastic is molten. Glass microbeads may also be applied to provide retro-reflectivity, these being applied after the other particles and when the surface temperature is lower. Thermoplastics are for hard-wearing, quick and easily applied surface marking solutions. However, the process for creating road markings demands a considerable degree of skill, is weather dependent, and location-specific, as it cannot be cried out at all in most indoor situations, such as platform edges on underground railway stations, where naked flames are prohibited.

[0003] The appropriate choice of surface course material plays a key role in providing road markings that are safe, meet the needs of the user, and offer good value for money. High friction surface (RFS) tnaterials give road and highway engineers one of the most cost-effective road safety solutions. HFS materials are designed to reduce braking distances at critical locations, especially in wet conditions. In dry conditions, all clean, surfaced roads have high skidding resistance. However, in wet conditions, the skidding resistance is reduced. Using aggregates and/or additives to thermoplastic materials with appropriate resistance to polishing for a particular site and traffic loading should result in a surfacing giving wet skidding resistance above the appropriate investigatory level required by local regulations. Indeed, some jurisdictions regulate the use of surface markings such that the markings are required to have a minimum friction value to prevent slipping, for vehicles and/or pedestrians. For example, in the UK, CD236 Surface course materials for construction, part of the Design Manual for Roads and Bridges, and AASHTO-American Association of State Highway Transportation Officials, designation: M 249-98; which give the requirements for the use of surfacing materials, including high friction surfacing, installer requirements, and the like.

[0004] Pavement markings convey information to drivers and pedestrians by providing exposed visible, reflective and/or tactile surfaces that serve as indicia upon a traffic surface.

In the past, such a function was typically accomplished by painting a traffic surface. Modern pavement marking materials offer significant advantages over paint such as dramatically increased visibility and/or retro reflectance, improved durability, and temporary removable marking options. Examples of modern pavement marking materials are thermoplastic, preformed pavement marking sheet materials, tapes and raised pavement markers. Signage in many cases is shipped to a job site as articles of the whole, depicting specific information or a visual theme and requiring assembly of the articles into the desired pattern. Assembly steps, without sequential assembly indicators, consutne time and etTort and pose a risk that the completed signage may be incorrect after adhesion to the ground surface.

[0005] A problem with pre-loaded anti-slip/anti-skid particles in such strip or sheet is that on gas torch application the particles sink into the plastic, and more must be spread on top while the material is molten. These are supported, at least to some extent, by the sunken particles. With thinner layers, such as those that are possible with the present disclosure, as will be described in more detail below, much less particulate matter can be held in the plastic, and it is closer to the surface so that it supports surface particulate matter even when the upper surface is molten.

[0006] Document JP2006070466 describes a method for printing a pattern on a surface of the pavement, the method comprises laying down, on an asphalt surface, a primer laver, followed by an ink-jet printed image layer, then a surface protective layer, for decorating the surface of pavement such as a footpath, carriageway or cycle track. 3P2006070466 lacks durability and requires an additional surface protective layer. Furthermore, JP2006070466 does not involve hardening plastic material. Document TP2002070465 discloses the same, however, a silk screen process is also used in the method, the method also comprises laying dow-n, on an asphalt surface, a primer layer, followed by an ink-jet printed image layer, then a surface protective layer, for decorating the surface of pavement such as a footpath, carriageway or cycle track, JP2006070465 and JP2006070466 may be categorised as typical 2D printing techniques. which is to say that they comprise printing of inks on an image, and therefore lack durability, requiring an additional surface protective layer. Furthermore, these documents do not involve hardening plastics material, such as thermoplastics.

[0007] The present invention provides methods and systems for applying durable surface markings that have multiple advantages over the conventional methods described above. A first aspect of the invention provides a method for applying a durable ground marking to a target position on a ground surface. The method comprises depositing a first molten plastics material in discrete droplets at the target position on the ground surface, wherein the discrete droplets harden into a durable ground marking.

[0008] In some examples, the method further comprises controlling a print head to form the discrete droplets into a patterned ground marking. In some examples, the patterned ground marking is obtained by layering the discrete droplets at the target position. In sonic examples, the discrete droplets are layered to a threshold thickness. In some examples, the threshold thickness is 2mm. In some examples, the layers of the discrete droplets overlap to create beveled, chamfered and/or rounded edges after hardening.

[0009] In some examples, the step of depositing the first molten plastics material further comprises projecting the discrete droplets at a first velocity. In some examples, the method further comprises the step of arranging the discrete droplets in a machine-readable pattern.

[0010] In some examples, the method further comprises receiving an image; dividing the image into printable segments, wherein each printable segment comprises instructions for applying a plurality of discrete droplets at a target location on the ground surface; and applying discrete droplets according to the printable segments to form the image, wherein the patterned ground marking represents the image.

[0011] In some examples, the method further comprises depositing a second molten plastics material in discrete droplets on the ground surface, the second molten plastics material having at least one characteristic which is different to at least one characteristic of the first molten plastic material. In some examples, the characteristic is at least one of hardness, brittleness, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, oil resistance, or colour. In some examples, after the first and second molten plastics material have hardened, the first molten plastics material has a higher coefficient of friction than the second molten plastics material.

[0012] In some examples, after hardening, the ground marking comprises at least two colours. A marking may be applied in a design using more than one colour by printing individual colours in separate areas of the marking. However, as with inkjet colour printing, a wide range of colours may be printed by melding primary colours. Whereas, using die conventional technique, multi-coloured surface markings for roads, playgrounds and the like are made in a restricted range of colours, sharply delineated, using methods according to the invention, a much wider range of colours may be had, which may blend smoothly into one another.

[0013] A second aspect of the invention provides a printing device for applying durable ground markings to a target position on a ground surface. The printing device comprises at least a print head comprising at least one dispenser; and a control unit operable to control the dispenser to deposit molten plastics material at the target position, wherein the molten plastics material hardens into a durable ground marking. In some examples, the dispenser is controllable to deposit the molten plastics material in discrete droplets at the target position.

[0014] In some examples, the control unit is operable to control the print head to form the discrete droplets into a patterned ground marking. In some examples, the patterned ground marking is obtained by layering the discrete droplets at the target position. In some examples, the discrete droplets are layered to a threshold thickness. In some examples, the threshold thickness is 2mm. In some examples, the layers of the discrete droplets overlap to create beveled, chamfered and/or rounded edges after hardening. Accordingly, the print head may comprise a device to determine the thickness of a layer of deposited thermoplastics material.

[0015] In some examples, the print head is controllable to project the discrete droplets at a first velocity. The print head is further controllable to arrange the discrete droplets in a machine-readable pattern.

[0016] In some examples, the controller is configured to receive an image; divide the image into printable segments, wherein each printable segment comprises instructions for applying a plurality of discrete droplets at a target location on the ground surface. In addition, the controller is operable to control the print head to apply discrete droplets according to the printable segments to form the image, wherein the patterned ground marking represents the image.

[0017] In some examples, the print head comprises a first and second dispenser, wherein a first molten plastics material is deposited front the first dispenser fluidly connected to a first plastics material hopper; and a second molten plastics material is deposited from the second dispense fluidly connected to a second plastics material hopper. In some examples, the first and second plastics materials comprise different physical properties after hardening, the different physical properties being one of: hardness, brittleness, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, oil resistance, or colour. In some examples, each plastics material hopper comprises a hydrocarbon-based thermoplastic or an alkyd-based thermoplastic. In some examples, the plastics material hoppers are configured to melt the plastics material into a liquid phase prior to deposition at the target site.

[0018] In some examples, the method further comprises an anti-slip material dispenser, wherein the anti-slip material is deposited from the anti-slip material dispenser across a surface of the molten plastics material prior to hardening. in some examples, the anti-slip material is at least one of: glass, flint, sand, calcium carbonate, alumina particles, or mixtures thereof [0019] In some examples, the print head further comprises a retroreflective particle dispenser, wherein the retroreflective particles are deposited from the retroreflective particle dispenser across the surface of the molten plastics material prior to hardening. In some examples, the retroreflective particles are glass beads. In some examples, the retroreflective particles arc partially submerged in the plastics material. In some examples, the retroreflective particles are partially submerged by 30-70% of their volume. In some examples, the retrorefiective particles arc deposited in a coded visible or machine-readable marking.

[0020] Additionally, coded visible or machine-readable markings may be introduced in special materials, which may include retro-reflective materials or metallic particles, such as magnetic particles, that can be used for guidance for pedestrian or vehicular traffic.

Retro-reflective beads may simulate cats' eyes in road markings, for example, or appear as coded symbols warning of hazards or defining a route which an autopilot system may follow. Rather than having multiple identical such markings, as is necessary with conventional cat's eyes, which arc mass produced, it will be easy to print 'custom' markings that can indicate distance from road junctions, for example.

[0021] An advantage of the application technique of the present disclosures over the conventional gas torch application is that the range of ground surfaces to which the marking may be applied is extended. Gas torch application is only applicable for outdoor concrete or tarmac, while the present printing techniques work on a wider variety of surfaces including wood and composite surfaces (e.g., by incorporating rubber crumb as a filler), as well as indoor surfaces.

[0022] A third aspect of the invention provides an autonomous printing device for applying durable ground markings to a target position on a ground surface. The autonomous printing device comprises at least traction means for supporting the printing device on the ground surface; drive means for driving the traction means; and a control system configured to control the drive means to guide the autonomous printing device across the target position on the ground surface.

[0023] The autonomous printing device further comprises the print device of the first example, as described above. In particular, the print head comprises at least one dispenser, and a print control unit operable to control the dispenser to deposit molten plastics material at the target position, wherein the molten plastics material hardens into a durable ground marking. Aspects of the first example, as described above, are herein compatible with the second example. In some examples, the ground marking may be applied using a line of dispensers, which are traversed in a direction perpendicular to the line, or a two-dimensional array of dispensers, whereby to print in blocks of colour or pattern.

[0024] For the avoidance of doubt, the system and methods for applying durable ground markings, according to any of the examples described herein, may be used to impart or improve slip or skid resistance on markings, such, for example, road markings, playground markings and step markings, and generally to the application of ground traversed by pedestrians and vehicles. Furthermore, surface preparation prior to ground marking, novel structures and shapes of the ground markings, deposition of I-IFS and components therein are disclosed. In addition, novel control mechanisms utilizing various sensors and the like are also disclosed. Whilst the benefits of the systems and methods may be described by reference to asphalt concrete, it is understood that the benefits of the present disclosure are not limited to this specific type of "blacktop" and other such types of composite materials commonly used to surface roads, parking lots, airports, and the surfaces of playgrounds would also benefit from an improvement in friction, grip, and anti-slip.

[0025] These examples and other aspects of the disclosure will be apparent and elucidated with reference to the example(s) described hereinafter. It should also he appreciated that particular combinations of the various examples and features described above and below are often illustrative and any other possible combination of such examples and features is also intended, notwithstanding those combinations that are clearly intended as mutually exclusive.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The above and other objects and advantages of the disclosures herein will be apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: [0027] FIG. I illustrates a cross-section through a three-layer ground marking on a surface, in accordance with at least one of the examples described herein; [0028] FIG. 2 illustrates a cross-section of a chamfered edge of a ground marking as shown in FIG. 1, in accordance with at least one of the examples described herein; [0029] FIG. 3A is a view of a first relief surface, in accordance with at least one of the examples described herein; [0030] FIG. 3B is a view of a second relief surface, in accordance with at least one of the examples described herein; [0031] FIG. 4 shows an area of print in close-up, in accordance with at least one of the examples described herein; [0032] FIG. 5 shows a line printer arrangement, in accordance with at least one of the examples described herein; [0033] FIG. 6 is a diagrammatic plan view of one embodiment of ground marking apparatus, in accordance with at least one of the examples described herein; [0034] FIG. 7 is a front elevation of the apparatus of Figure 3, in accordance with at least one of the examples described herein; [0035] FIG. 8 is a diagrammatic view of another embodiment of ground marking apparatus, in accordance with at least one of the examples described herein; [0036] FIGS. 9A-9D illustrate components on a print head of a device suitable for ground marking, in accordance with at least one of the examples described herein; [0037] FIG. 10 is a schematic diagram of an exemplary apparatus for applying ground markings, in accordance with at least one of the examples described herein; [0038] FIG. II is a schematic diagram of an exemplary autonomous system for applying ground markings, in accordance with at least one of the examples described herein; and [0039] FIG. 12 illustrates a block diagram of a computing module, in accordance with at least one of the examples described herein.

DETAILED DESCRIPTION

[0040] As mentioned above, the appropriate choice of surface course material plays a key role in providing road markings that are safe, meet the needs of the user, and offer good value for money. A mixture of glass beads, pigments, binder, and filler materials, and commonly a thermoplastic are ubiquitous materials in the field of ground markings.

Thermoplastics, as their name suggests, become liquid when heat is applied and are a popular choice due to being an environmentally and user-safe compound. Generally, glass beads provide the retro-reflectivity necessary for visualising ground markings during darkness; pigments provide desired colours and opacity; binders are a mixture of plasticizer and resins that provide toughness, flexibility, and bond strength while holding all the components together; and fillers, such as calcium carbonate, sand and/or other inert substances, provide bulk.

[0041] There arc two basic types of thermoplastic available. The two, hydrocarbon and alkyd, take their names from their binder types. Hydrocarbon thermoplastic is made from petroleum-derived resins. Hydrocarbon tends to be more heat stable, with more predictable application properties, than alkyd. Because it tends to break down under oil drippings and other automobile contaminants, hydrocarbon is recommended for long-line, skip lines and edge-line applications and not for high-traffic areas where cars arc stationary (e.g., stop bars, crosswalks, turn arrows, and the like).

[0042] Alkyd thermoplastic is made from wood-derived resins that are resistant to petroleum products. Alkyd thermoplastic exhibits some advantages over hydrocarbon materials such as higher retroreflective values; being oil impervious; and higher durability.

Alkyd is recommended for inner-city markings and other high-traffic areas where petroleum drippings are common.

[0043] Both hydrocarbon and alkyd thermoplastics are available in granular or block form. Hot applied thermoplastic is prepared for road application in a melting kettle where the granular or block material is introduced and heated until it liquefies at temperatures exceeding 4000F. An agitator blends the ingredients until thermoplastic is transferred into a screed, ribbon or spray device where it is then shaped into its specified width and thickness as a line, legend or symbol; in the art, this is where a large amount of variation and waste is generated as the skill of the user at application is paramount. Retroreflective particles and anti-slip material are immediately applied and sink into the molten thermoplastic material. When applied on asphaltic surfaces, thermoplastic material develops a thermal bond via heat-fusion. When applied on Portland Concrete Cement and on oxidized or aged asphaltic surfaces, and a recommended sealer is properly applied, a tenacious mechanical bond is achieved.

[0044] Providing that all necessary conditions are met concerning the temperature of material and substrate, absence of moisture, road preparation and minimum thickness, excellent performance can be achieved using thermoplastic pavement marking compounds. Typical performance life ranges from 4 to g years depending on roadway conditions. However, currently, there is a great deal of subjective assessment from the installers of previous ground markings. Quantifying values (such as thickness and surface friction values) and preparing surfaces accordingly, leads to more controller application of ground markings.

[0045] FIG. 1 illustrates a cross-section through a three-layer ground marking on a surface, in accordance with at least one of the examples described herein. As mentioned above, conventionally, ground markings are created by fusing plastic strip or sheet material to a ground surface using a gas torch. The markings are pre-cut to size and shape and laid in position prior to fusing to the ground. Once fused, the plastic surface hardens, and the material is then very difficult to remove. So exact placement is essential. During the fusing operation, anti-slip or anti-skid particles are cast onto the molten plastic surface and become embedded. If retro-reflectivity is required, glass microbeads are scattered after the particles when the plastic has cooled by some amount. Judging how much material to scatter and when calls for expertise and experience and can lead to the markings needing remelting or waste if not done correctly.

[0046] The method of the present invention can use the same plastic material as is currently applied conventionally. However, it is not necessary to supply the material in strip or sheet form. One example method comprises depositing a molten plastics material 110 at a target position on a ground surface 120, wherein the molten plastics material hardens into a durable ground marking. In some examples, the molten plastic material 110 is deposited in discrete droplets 105. In some examples; the method further comprises controlling a print head (e.g., print head 800 of FIG. 8) to form the discrete droplets into a patterned ground marking. hi some examples, the patterned ground marking is obtained by layering the discrete droplets at the target position into a plurality of layers 1 0A-C.

[0047] In some examples, the discrete droplets are layered to a threshold thickness. In some further examples, the threshold thickness is 2rnm. In some examples, the step of depositing the first molten plastics material further comprises projecting the discrete droplets at a first velocity. In some examples, the method further comprises depositing a second molten plastics material in discrete droplets on the ground surface, the second molten plastics material having at least one characteristic which is different to at feast one characteristic of the first molten plastic material. The second molten plastics material may be layered on top of the first molten plastics material. For example, the bottommost layer, in contact with the ground surface, may be a hydrocarbon-based thermoplastic, which is more heat stable and therefore easier to apply to the ground surface and ensure good bonding. However, because hydrocarbon thermoplastics tend to break down under oil drippings and other automobile contaminants, the second (and indeed subsequent layers) 110A-B may be an alkyd-based thermoplastic, is applied after the first layer has cooled. Using both thermoplastic types is avoided in the current art, as the risk of cross-contamination of the hydrocarbon and alkyd is high and the different types ofthermoplastics must be kept separate (i.e., separate kettles, applicators, etc.).

[0048] The layers of the molten thermoplastics material 110 may each have different characteristics, such as, blitheness, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, oil resistance, or colour.

[0049] Temperature is the most important factor in the proper mixing, melting and bonding of thermoplastic. Heated to a temperature between 400 and 440 F and agitated properly, the thermoplastic compound becomes a homogenized liquid. Applied at this temperature, the thermoplastic melts into the upper surface of the asphalt, forming a thermal bond. When installed on porous surfaces, such as open-graded asphalt or tined concrete, the hot liquid thermoplastic fills all voids, creating a good mechanical lock on concrete. The thickness of the applied thermoplastic should be as specified. A minimum thickness of around 2mm (90 mils) is important to the material's ability to hold the heat necessary for good bonding. The thermal bonding that occurs when the application is at the proper thickness ensures the thermoplastic's durability and long-term retro-reflectivity. A minimum thickness of around 0 75turn (30 mils) is required to hold the heat necessary for proper bonding when recapping a line because of poor reflectivity or inadequate thickness. The discrete droplet 105 minimum thickness may be in the order of 0.75mm.

[0050] FIG. 2 illustrates a cross-section of a chamfered edge 210 of a ground marking 200 after the discrete droplets 105, as shown in FIG. 1, harden, in accordance with at least one of the examples described herein. FIG. 2 illustrates a chamfered edge 210, however, rounded edges, bevelled edges, or the like are also possible. A chamfered edge provides a number of advantages, in particular around trip hazards. In the art, if the thickness of the ground marking approaches 4-6mtn, pedestrians arc likely to trip. Chamfered edges help to mitigate that risk. In addition, chamfered edges reduce the impact from fool or vehicular traffic, and aid in the durability of the ground marking. At 2min thick, a marking edge would not represent a trip hazard, but a chamfered or rounded edge may bc less liable to damage from foot or vehicular traffic. A thickness of 2mm is adequate for most purposes, depending on the properties of the plastic. However, compared to the methods of applying plastic conventionally with gas torches, 2mm is a very adequate thickness, and this represents a material saving over the conventional gas torch application, which requires the plastic to be thicker, often in the order of 4mm to 4.5mm, in order not to bubble during application (overheating).

[0051] 111 some examples, the layers 110A-C of the discrete droplets overlap to create beveled, chamfered and/or rounded edges after hardening. For example, the edge discrete droplets 105 are layered within the boundary of the discrete droplet 105 of a layer below.

In some examples, the molten plastics material is deposited in discrete droplets 105, that overlap with each other in the same layer I 10A-C. Overlapping in this way creates a surface texture when the molten plastics material hardens into the durable ground marking, aiding in anti-slip properties or adding in "rumble" effects when driven over by a car.

[0052] Typically, the marking will be created in monotone (e.g., white lane marking in roads or yellow parking control lines), however, multiple colours are possible using the present invention and allow for patterning or for the creation of artistic or utility markings, as in the application of promotional or warning signs, lettering or symbols to steps and other ground markings. This can be done by laying a foundation layer 110C having one colour topped with a layer or layers 110A-B of a different colour or colours in a design.

The foundation layer 110C may show through the topping layer or layers 110A-B in the fashion of a stencil, or the topping layer may cover the whole of the foundation layer, or each colour may be built up in a block from the ground up, all to be level at the surface, without any single colour foundation layer. FIG. 1 shows discrete droplets 105 building up layer on layer, with the surface layer 1 I OA differently coloured to the lower layers 110B-C.

[0053] FIG. 3A is a view of a first relief surface, in accordance with at least one of the examples described herein. As shown in FIG. 3A, the ground markings may be raised frustoconical 310. For example, the discrete droplets 105 may be formed in layers 110 to create frustoconical shapes 310, commonly found on wheelchair access ramps and road crossings. In between the frustoconical-shaped ground markings 310 there is the ground surface 120 with no ground markings, or alternatively, a thin layer of deposited plastics material.

[0054] FIG. 3B is a view of a second relief surface, in accordance with at least one of the examples described herein. As shown in FIG. 3B, the ground marking may be raised parallel strips 320. For example, the discrete droplets 105 may be formed in layers 110 to create parallel-shaped ground markings 320, commonly used for rumble strips at road junctions or ahead of speed restrictions. In some alternative examples, the plastics material is deposited as a softened filament or prior to undergoing glass transition; after, undergoing a heat treatment to liquify and melt into the road or previous layer.

[0055] Desirably, the plastics material as laid will be durable and heat resistant -as it may need to survive atmospheric temperatures substantially in excess of 40°C and direct sunlight in tropical and subtropical areas, for example in Australia, wherein the ground surface temperature regularly exceeds 60°C. The plastics material currently used for ground surface markings develops such resistance as a result of the gas torch heating by which they are fused to the ground surface. As 3D printed materials are not necessarily subject to such high temperatures during the application, it may be necessary to subject the ground markings to a post-application hardening treatment, which may be by microwave or infra-red heating, for example. Anti-slip/anti-skid treatment may also be applied during this post-application treatment, as may the addition of microbeads.

[0056] FIG. 4 show-s an area of print in close-up, in accordance with at least one of the examples described herein. In some examples, the methods further comprise receiving an image; dividing the image into printable segments 410, wherein each printable segment comprises instructions for applying a plurality of discrete droplets 105 at a target location on the ground surface. In some examples, the instructions comprise a type of molten plastics material, colour, number of layers, or another physical characteristic. The instructions may be referred to as a 3D printing map of the ground marking. The methods further comprise applying discrete droplets 105 according to the printable segments to form the image, wherein the patterned ground marking represents the image.

[0057] In some examples, after hardening, the ground marking comprises at least two 30 colours. A marking may be applied in a design using more than one colour by printing individual colours in separate areas of the marking. How-ever, as with inkjet colour printing, a wide range of colours may be printed by melding primary colours. Whereas, using the conventional technique, multi-coloured surface markings for roads, playgrounds and the like are made in a restricted range of colours, sharply delineated, using methods according to the invention, a much wider range of colours may be had, which may blend smoothly into one another.

[0058] FIG. 4 shows a small area of discrete droplets of different primary colours Red (R) 422, Blue (B) 426, Green (G) 424, Black (B1) 434 and white (W) 432. These markings can be applied using a single print head comprising a plurality of dispensers, dispensing plastic in the form or droplets or as a filament, as will be described in more detail below. Such a single print head may comprise a plurality of dispensers for different colours, for example, five such dispensers, one for white, one for black and three for primary colours. A further dispenser may be provided for clear plastic, acting perhaps as a varnish or other surface texture finish. The head may be scanned to produce a layer at a time. A surface layer or layers only may be coloured or patterned.

[0059] In some examples, the print instructions further comprise the step of arranging the discrete droplets in a machine-readable pattern. For example, some discrete droplets 105 may be deposited in a fashion that computer vision can read as an instruction. Such discrete droplets may comprise paints or inks that are invisible to the human eye, such as ultraviolet or infrared markings.

[0060] In some examples, it may be desired that after the first and second molten plastics material have hardened, the first molten plastics material has a higher coefficient of friction than the second molten plastics material. This can be achieved by incorporating into the printing instructions the step of applying anti-slip material to improve the coefficient of friction of the molten plastics material. In some examples, the anti-slip material is applied at a first temperature. In some examples, the first temperature is in the range of 170C - 230C. In some examples, the anti-slip particles comprise at least one of glass, flint, sand, calcium carbonate, alumina particles, or mixtures thereof Moreover, certain visibility of the ground marking 110 may be desired. Therefore, the printing instructions may comprise the step of applying retro-reflective particles. In some examples, the retroreflective particles are applied while the molten plastics material is at a second temperature, wherein the second temperature is lower than the first temperature. In some examples, the retro-reflective particles arc glass beads. Accordingly, the plastics material may be deposited in a liquid phase such that the application of anti-slip material or retrorefleetive particles is keyed into the thermoplastics material adequately.

[006 l] High friction surface (HFS) materials give road and highway engineers one of the most cost-effective road safety solutions. HFS materials are designed to reduce braking distances at critical locations, especially in wet conditions. In dry conditions, all clean, surfaced roads have high skidding resistance. However, in wet conditions, the skidding resistance is reduced. Using aggregates and/or additives to thermoplastic materials with appropriate resistance to polishing for a particular site and traffic loading should result in a surfacing giving wet skidding resistance above the appropriate investigatory level required by local regulations. Aggregate selection Polished stone value (PSV) and aggregate abrasion value (AAV) are terms known in the art tbr the required friction values for road surfaces. For example, in the UK, coarse aggregates or chippings undergo PSV testing in accordance with BS EN 1097-8 [Ref 4.N] to determine the resistance to polishing under the action of traffic. The appropriate PSV for the coarse aggregate shall be selected from Table 3.3a or Table 3.3b based on the relevant site categories and traffic levels. Approaches to and across minor and major junctions, approaches to roundabouts and traffic signals anything over 500 commercial vehicles/lane/day require HFS. Same for Approaches to pedestrian crossings and other high-risk situations. Similar for Gradients 5- 10% longer than 50m; Gradient >10% longer than 50m, and Bends with a radius <500m.

[0062] FIG. 5 shows a line printer arrangement, in accordance with at least one of the examples described herein. The line printer arrangement comprises a print head 620 and a plurality of dispensers 625. The dispensers 625 are adapted to dispense different colours of plastics material, ant-slip material and retroreflective material. Accordingly, the dispensers 625 are fluidly connected to hoppers comprising, as described above, white, black and three primary colours of plastics materials. A further dispenser 625 can be adapted to dispense clear molten plastics material (or at least a molten plastics material that goes clear after hardening), where, for example, a lower layer is required to show through.

[0063] The print head 620 may comprise a line, as shown in FIG. 5, or a two-dimensional 30 array (not shown) of dispensers 625, that are moved in the direction of Arrow A. The dispensers can be adapted to dispense different colours according to instructions for applying a plurality of discrete droplets 105 at a target location (e.g., target location 710 of FIG. 7) on the ground surface 120 so that the desired marking is built up.

[0064] The marking can be applied, however, using a line of dispensers 625, similar to a line printer in paper printing, which is traversed in the direction of Arrow A perpendicular to the line, or a two-dimensional array of dispensers, whereby to print in blocks of colour or pattern.

[0065] In addition to 3D printing plastics material, anti-slip/anti-skid finish is applied at time of printing, in the form, for example, of particles of glass or flint, which materials do not adversely affect the colour of the plastic, or aluminium oxide. In order to be retained in the surface and not sink in so flu-that they are completely absorbed, whereby they contribute nothing to anti-slip or anti-skid protection, such particles are applied at a given temperature of the plastic surface, which will depend on the physical properties of the material but can, for any particular material, be deteimined empirically. Likewise, rnicrobeads, imparting retro-reflectivity, can also be applied, and this may be at a temperature different to that at which anti-slip/anti-skid particles are applied, and they may be applied after anti-slip/anti-skid particles. The anti-slip/anti-skid and retro-reflective treatment can be applied to the whole or to selected parts of the marking.

[0066] Desirably, the plastics material as laid will be durable and heat resistant -it may need to survive atmospheric temperatures substantially in excess of 40°C and direct sunlight in tropical and subtropical areas, for example in Australia. The plastics materials currently used for ground surface markings develop such resistance as a result of the gas torch heating by which they are fused to the ground surface. As 3D printed materials are not necessarily subject to such high temperatures during application, it may be necessary to subject them to a post-application hardening treatment, which may be by microwave or infra-red heating, for example, or a chemical treatment such as a cross-linking or curing treatment. Anti-slip/anti-skid treatment can also be applied during this post-application treatment, as may the addition of microbeads.

[0067] It has been noted above that the modalities of applying ground marking discussed herein can result in markings of reduced thickness as compared to conventionally applied plastic strips or sheet. A problem with pre-loaded anti-slip/anti-skid particles in such strip or sheet, available from at least one supplier thereof, is that on gas torch application the particles sink into the plastic, and more must he spread on top while the material is molten. These are supported, at least to some extent, by the sunken particles. With thinner layers such as are possible with 3D printing applications, much less particulate matter can be held in the plastic, and it is closer to the surface so that it supports surface particulate matter even when the upper surface is molten, perhaps as a result of hardening heat treatment.

However, the layer-by-layer application of the molten plastic material means in any event that only the surface layer needs to be heated while the particulate material is being applied. If just a surface layer is required to be heated, an infra-red heater may be used instead of the microwave treatment, which may tend to penetrate further.

[0068] An advantage of the application technique of the present disclosures over the conventional gas torch application is that the range of ground surfaces to Which the marking may be applied is extended. Gas torch application is only applicable for outdoor concrete or tarmac, while the present printing techniques work on a wider variety of surfaces including wood and composite surfaces (e.g., by incorporating rubber crumb as a filler), as well as indoor surfaces.

[0069] FIG. 6 is a diagrammatic plan view of one embodiment of ground marking apparatus, in accordance with at least one of the examples described herein. The ground marking apparatus, or printing device 610, applies durable ground markings to a target position on a ground surface. The printing device 610 comprises at least one print head 620 comprising a plurality of dispensers 625; and a control unit (not shown) operable to control the dispensers 625 to deposit plastics material 645 at the target position, wherein the molten plastics material hardens into a durable ground marking. The plastics material 645 may be stored/housed in a hopper 640. In some examples, the dispenser 620 is controllable to deposit the molten plastic material in discrete droplets 105 at the target position. In some examples, the hoppers 640 may be adapted to gravity or pressure feed the dispensers they are fluidly connected to. In some examples, the dispensers may comprise nozzles through which the molten plastics material emerges in drops (or as a filament) under the control of valve means.

[0070] In some examples, the print head further comprises a print rack, the print rack comprises at least a horizontal rail, arranged orthogonal to a direction of movement of the printing device; a vertical rail, arranged orthogonal to the horizontal rail; and wherein the print head is affixed to the vertical rail.

[0071] FIG. 7 is a front elevation of the apparatus of FIG. 6, in accordance with at least one of the examples described herein. A second aspect of the invention provides an autonomous printing device 700 for applying durable ground markings to a target position on a ground surface 710. The autonomous printing device 700 comprises at least traction means 720 for supporting the printing device on the ground surface 120; drive means (not shown) for driving the traction means 720, and a control system (such as control system 1050 of FIG. 10) configured to control the drive means to guide the autonomous printing device across the target position on thc ground surface, The autonomous printing device further comprises the print device 610 of the example in FIG. 6, as described above. In particular, the print head 620 comprises at least one dispenser 625, and a print control unit (not shown) operable to control the dispenser 625 to deposit molten plastics material at the target position 720, wherein the molten plastics material hardens into a durable ground marking. Aspects of the ground marking apparatus, as described with reference to FIG. 6, are herein compatible with the autonomous printing device.

[0072] FIG. 8 is a diagrammatic view of another embodiment of ground marking apparatus, in accordance with at least one of the examples described herein. FIG. g shows a vacuum nozzle 810, a heat source 820, a plastics dispenser 830, an aftertreatment device 840, a baffle 850, a grit dispenser 860 and a retroreflective bead dispenser 870. The entirety of the apparatus moves in the direction of An-ow B. [0073] Glass beads (e.g., retroreflective particles) from the retroreflective bead dispenser 870 are to be evenly dropped onto the hot thermoplastic stripe immediately after its application, embedding and anchoring at a depth of 30% to 70%, preferably 50 to 60%, by volume. The purpose of the glass beads is to provide initial night-time retro-reflectivity of the pavement marking which, without them, would be barely visible to the motorist. The bead dispenser 870 shall be inspected frequently to ensure proper operation and to ensure uniform rates of each application over the entire marking surface. In some examples, the glass beads are deposited in a coded visible or machine-readable marking. Additionally, coded visible or machine-readable markings may be introduced in special materials, which may include retro-reflective materials or metallic particles, such as magnetic particles, that can be used for guidance for pedestrian or vehicular traffic. Retro-reflective beads may simulate cats' eyes in road markings, for example, or appear as coded symbols warning of hazards or defining a route which an autopilot system may follow. Rather than having multiple identical such markings, as is necessary with conventional cat's eyes, which are mass-produced, it is efficient and simple to print 'custom' markings that can indicate distance from road junctions, for example. A baffle 850 separates the bead dispenser from vacuum nozzle 810, heat source 820, plastics dispenser 830, an aftertreatment device 840. [0074] In some examples, the print head further comprises a thermometer (not shown) for detecting the temperature of the ground surface at the target position, an ambient temperature, and/or a temperature of a surface of the plastics material after deposition to the target position. Based on the sensed temperature, heat source 820 provides a thermal energy adequate to pre-treatment the ground surface or provide an aftertreatment to the plastics material. In addition to applying molten plastics material, an anti-slip/anti-skid finish may be applied at the time of printing, in the form of materials that do not adversely affect the colour of the ground marking once hardened from grit dispenser 860. To be retained on the surface and not sink in so far that they are completely absorbed, whereby they contribute nothing to anti-slip or anti-skid protection, such particles should be applied at a given temperature of the plastic surface -specific to the composition of the molten plastics material. Likewise, glass beads, imparting retro-reflectivity, may also be applied, and this may be at a temperature different to that at which anti-slip/anti-skid particles are applied from bead dispenser 870, and they may be applied after anti-slip/anti-skid particles.

The anti-slip/anti-skid and retro-reflective treatment may be applied to the whole or to selected parts of the marking.

[0075] FIGS. 9A-9D illustrate components on a print head of a device suitable for ground marking, in accordance with at least one of the examples described herein. There are various devices used to screed/extrude thermoplastic material onto the pavement. The device should be positioned to protect it from the wind, sometimes the use of a baffle 850 or housed within a housing is suitable. In sonic examples, the print head further comprises a print rack, the print rack comprises at least a horizontal rail 912, arranged orthogonal to a direction of movement of the printing device; a vertical rail 914. arranged orthogonal to the horizontal rail 912; and wherein the print head is affixed to the vertical rail 914 moveable by a motor 910.

[0076] FIG. 9A comprises priming equipment for use on the ground surface 120 at the target position 710 before the application of the thermoplastic material. The priming equipment comprises a heater 924, such as heater 1072 of FIG. 10, and a primer material dispenser 922. The primer material shall be sprayed on the surface at the specified rates recommended by the manufacturer of the primer/sealer material. All of the priming equipment should be inspected and checked to ensure that it is completely operational and capable of disbursing the primer/sealer at the rate prescribed by the manufacturer. Because bond failures are most likely application related, they can be minimized by proper application controls, This can be accomplished through correct inspection at the target site and adapting the pre-treatment of the ground surface based on the condition of the target site; therefore, computer vision is employed to provide this inspection (not shown). If specified prior to the thermoplastic application, the primer must be applied to all pavement surfaces at the manufacturer's recommended application rates. It must set for the specified cure or evaporation time prior to thermoplastic being applied. Primed pavement surfaces must be striped within the specified set time or within the same working day. If the primed surfaces are not striped within these time limits, they must be reprimed prior to the thermoplastic application at the prescribed rate denoted by the manufacturer. If an approved epoxy primer is used, proportional mixing must be checked, and thermoplastic application must occur before epoxy has cured. Improper primer/sealer application will cause bond failure between the thermoplastic and substrate. Improper application may also result in physical degradation of the thermoplastic material by excessive pin holing and blistering of the line. This degradation may occur through extraction of the binder by the solvent system contained in the primer/sealer promoted by improper drying time and application rates.

[0077] FIG. 9B comprises a print head with a plurality of dispensers 932. In addition to coloured molten thermoplastics material, as described above (e.g., with reference to FIG. 4). One of dispensers 932 may be a ribbon dispenser (e.g., soft filament dispensers), which typically requires heaters to complete the anchoring/melting of the thermoplastic once applied to the ground surface. Ribbon dispensers are and are suspended above the road surface, applying a forced-extrusion, well-defined thermoplastic line. Another type of dispenser 932 is spray dispensing devices, which create thennoplastit, spray patterns that result in a uniformly thick, well-defined and securely bonded stripe as specified. Another type of dispenser utilizes a screed extrusion technique, that dispenses shoe rides (e.g., nimble strips) directly on the road surface and a continuous line is formed by a three-sided die with a control gate set to a pre-determined thickness -typically over 8mm. Although alkyd and hydrocarbon materials will fuse to one another on the road, they are incompatible in a melting kettle, hence separate dispensers are required for separate materials. Failure to completely clean out kettles during material changeovers can cause severe equipment problems, this is mitigated in the present system.

[0078] FIG. 9C comprises a heater 932 and temperature sensor 934 cleaner to clean the ground surface prior to the priming equipment treating the surface. The ground surface 120 should be more than visibly dry. Moisture is the most detrimental factor in bonding. Subsurface moisture can be present in amounts sufficient to affect proper bonding. Early morning dew and fog conditions will usually cause dampness. If excess pavement moisture exists, it will usually result in blistering the hot-applied marking. Blisters will form as surface bubbles which may or may not have burst open. They are easily spotted, and if the condition occurs, marking operations should be stopped until the pavement dries. The only way to be certain whether moisture is present is to conduct a test. There are numerous ways to test for moisture. When heating the target position 720 of the ground surface 120, nearby thermoplastic material can be monitored by the temperature sensor 934, if thermoplastic material is overheated, the colour pigments tend to break down and change in colour: white thermoplastic turns beige or creamy; yellow develops a brown or greenish tint.

[0079] FIG. 9D comprises a vacuum cleaner 944 to clean the ground surface prior to the priming equipment treating the surface. Ground surfaces must be clean, dust free, and dry. Heavy deposits of existing painted pavement markings, polymer traffic tapes, built-up roadside accumulations of dirt, etc., will all require removal. In some cases, an air blast or manual or mechanical brooming will be sufficient to clean the surface. In others, more effort or different methods such as abrasive-blasting, water blasting, or mechanical removal will be needed. New thermoplastic applications should successfully bond to worn existing thertnoplastic lines or preform thermoplastic markings, therefore, a sensor or camera (not shown) to detect the previously applied thermoplastics may be present next to the vacuum to determine if priming is needed or if a full 2mm of deposition is required. For example.

it may be that due to a worn down prior thermoplastic marking, with a thickness of 1mm, no priming but application of an additional limn of thermoplastic is all that is required. [0080] FIG. 10 is a schematic diagram of an exemplary apparatus for applying ground markings, in accordance with at least one of the examples described herein. A compressor (e.g., an air compressor) 1010 is fluidly connected to a solenoid 1020 and solenoid valve 1022 to provide an air supply 1015. The air supply to dispense the molten plastics material from dispenser 1024. A controller 1050 and battery 1055 are electrically connected through wires 1052 to the solenoid valve 1022 and compressor 1010, as well as the other components as described below. The controller 1050 provides control to devices and the battery 1055 provides power, however, the battery may be replaced or used in conjunction with a "shoreline" power system, mains power, or the like. A hopper 1032, such as a metal kettle or the like, comprising the plastics material (typically in a molten state), is fluidly connected to a pump/extruder 1034, controllable by controller 1050 through wires 1052 (from point A to point A) to pump the molten plastics material through a hose 1036 to the solenoid 1020 and solenoid valve 1022. In some examples, the compressed air provided by the compressor 1010 atomises the molten plastics material into a spray as a deposition modality. In some examples, hose 1036 comprises insulation, heating elements, or a combination thereof In some examples, a hopper 1032 may comprise anti-slip material or retroreflective particles to be fluidly connected to a dispenser such as a solenoid 1020.

[0081] Compressor 1010, air supply 1015, solenoid 1020, solenoid valve 1022, dispenser 1024, hopper 1032, pump/extruder 1034, and hose 1036 are collectively referred to as the deposition system. A baffle 1040 is utilized to separate the deposition system from the treatment system. The treatment system may be used for pre-treatment or after-treatment of the ground surface 120 (or more particularly, the target position 720 on the ground surface 120). The treatment system comprises a ground temperature sensor 1060, for example, an IR temperature sensor; a heater 1072, which may be a ground fan heater, a microwave heater, or an open flame gas torch; a vacuum ground cleaner 1074; and rotary encoder 1080 which may be a mechanical, optical, on-axis magnetic, or off-axis magnet rotary encoder; absolute or incremental.

[0082] The rotary encoder 1080 is used for converting the angular position or motion of a shaft or axle to analogue or digital output signals; useful for knowing the position of the print head, and position of the autonomous (or semi-autonomous) device. For example, an optical encoder uses a light shining onto a photodiode through slits in a metal or glass disc. Reflective versions also exist. This is one of the most common technologies. However, optical encoders are sensitive to dust, but this is typically not a problem with molten plastics material deposition. Power from battery 1055 and control from controller 1050 is delivered to the treatment system by wires 1052. That is to say that the components of the aftertreatment system are electrically connected to the controller 1050 and the battery 1055. [0083] Mixing and agitating equipment, may be incorporated in the hoppers 1032. Such equipment, such as kettles, must be equipped with material agitators to prevent hardening in the liquid phase, and must be capable of thoroughly mixing the material at a rate which will ensure even disbursement and uniform temperatures throughout the material mass. [0084] FIG. 11 is a schematic diagram of an exemplary autonomous system for applying ground markings, in accordance with at least one of the examples described herein. The autonomous printing system 1100, comprises driving means 1110, which may be independently controllable motors affixed to wheels. The driving means 1110 move the autonomous system across the ground surface. The autonomous system may be semiautonomous. In the present disclosure semi-autonomous refers to devices and systems that require minimum human intervention and utilise advanced driver assist technologies, such as adaptive cruise control, lane keep assist, and intelligent park assist, to reduce the effort required to manoeuvre the autonomous system and create the desired ground markings. Autonomous refers to devices and systems that are capable of manoeuvring without a human operator. The Society of Automotive Engineers (SAE) International and the US National Highway Traffic Safety Administration (NEITSA) have defined five different levels of semi-autonomous and autonomous vehicles based on the amount of human intervention required. The autonomous system comprises the exemplary apparatus for applying ground markings as described with reference to FIG. 10.

[0085] FIG. 12 illustrates a block diagram 1200 of computing module 1202, in accordance with some embodiments of the disclosure. In some examples, computing module 1202 may be communicatively connected to a user interface. In some examples, computing module 1202, may be the controller of the apparatus 1000 as described with reference to FIG. 12. In some examples, computing module 1202 may include processing circuitry, control circuitry, and storage (e.g., RAM, ROM, hard disk, a removable disk, ctc.). Computing module 1202 may include an input/output, I/O, path 1206. I/0 path 1220 may provide device information, or other data, over a local area network (LAN) or wide area network (WAN), and/or other content and data to control circuitry 1210, which includes processing circuitry 1214 and storage 1212. Control circuitry 1210 may be used to send and receive commands, requests, signals (digital and analog), and other suitable data using I/0 path 1220. I/0 path 1220 is connected to control circuitry 1210 (and specifically processing circuitry 1214) to one or more communications paths. In some examples, computing module 1202 may be an on-hoard computer of the apparatus for paint markings, such as apparatus 1000. In some examples, the control circuitry 1210 is operable to receive an image to be printed. In some examples, the controller is configured to demarcate the image into a plurality of segments to be printed. In some examples, the control unit is operable to control the dispenser to deposit molten plastics material forming the image. [0086] Control circuitry 1210 may be based on any suitable processing circuitry such as processing circuitry 1214. As referred to herein, processing circuitry should be understood to mean circuitry based on one or more microprocessors, microcontrollers, digital signal processors, programmable logic devices, field-programmable gate arrays (FPGAs), application-specific integrated circuits (AS1C5), etc., and may include a multi-core processor (e.g., dual-core, quad-core, hexa-core, or any suitable number of cores) or supercomputer. In some examples, processing circuitry may be distributed across multiple separate processors or processing units, for example, multiple of the same type of processing units (e.g. two Tntel Core i7 processors) or multiple different processors (e.g., an Intel Core i5 processor and an Intel Core i7 processor). In some examples, processing circuitry 1214 executes instructions for computing module 1002 stored in memory (e.g., storage 1212).

[0087] The memory may be an electronic storage device provided as storage 1212, which is part of control circuitry 1210. As referred to herein, the phrase "electronic storage device" or "storage device" should be understood to mean any device for storing electronic data, computer software, or firmware, such as random-access memory, read-only memory, hard drives, solid-state devices, quantum storage devices, or any other suitable fixed or removable storage devices, and/or any combination of the same. Non-volatile memory may also be used (e.g., to launch a boot-up routine and other instructions). Storage 1212 may be sub-divided into different spaces such as kernel space and user space. Kernel space is a portion of memory or storage that is, e.g., reserved for running a privileged operating system kernel, kernel extensions, and most device drivers. User space may be considered an area of memory or storage where application software generally executes and is kept separate from kernel space so as to not interfere with system-vital processes. Kernel mode may be considered as a mode when control circuitry 1010 has permission to operate on data in kernel space, while applications running in user mode must request control circuitry 1210 to perform tasks in kernel mode on its behalf.

[0088] Computing module 1202 may be coupled to a communications network. The communication network may be one or more networks including the Internet, a mobile phone network, mobile voice or data network (e.g., a 30, 40, 50 or LTE network), mesh network, peer-to-peer network, cable network, cable reception (e.g., coaxial), microwave link, DSL reception, cable interne reception, fibre reception, over-the-air infrastructure or other types of communications network or combinations of communications networks.

Computing module 1202 may be coupled to a secondary communication network (e.g., Bluetooth, Near Field Communication, service provider proprietary networks, or wired connection). Paths may separately or together include one or more communications paths, such as a satellite path, a fibre-optic path, a cable path, a path that supports Internet communications, free-space connections (e.g., for broadcast or other wireless signals), or any other suitable wired or wireless communications path or combination of such paths. [0089] In some examples, the control circuitry 1210 is configured to carry out any of the methods as described herein. For example, storage 1212 may be a non-transitory computer-readable medium having instructions encoded thereon to be carried out by processing circuitry 1214, which cause control circuitry 1010 to catty out a method for applying ground markings.

[0090] Various embodiments have been described above. The following examples are non-limiting, and do not define or Limit the scope of the invention in any way. Rather the following examples are within the scope of the appended claims.

[0091] A first aspect of the invention provides a printing device for applying durable ground markings to a target position on a ground surface. The printing device comprises at least a print head comprising at least one dispenser; and a control unit operable to control the dispenser to deposit molten plastics material at the target position, wherein the molten plastics material hardens into a durable ground marking.

[0092] In some examples. the dispenser is controllable to deposit the molten plastics material in discrete droplets at the target position. In some examples, the print head further comprises a vacuum or air compressor for cleaning the ground surface at the target position prior to deposition of the molten plastics material.

[0093] In some examples, the print head further comprises a heat source for preparing the ground surface at the target position prior to deposition of the molten plastics material. In some examples, the heal source can also be used for post-application treatment. In some examples, the heat source is an infrared or microwave beat source. In alternative examples, the heat source is an open flame gas torch.

[0094] In some examples, the print head further comprises a thermometer for detecting a temperature of the ground surface at the target position, an ambient temperature, and/or a temperature of a surface of the plastics material after deposition to the target position.

[0095] In some examples, the print head further comprises at least one baffle deflector. In some examples, the print head further comprises a print rack, the print rack comprises at least a horizontal rail, arranged orthogonal to a direction of movement of the printing device; a vertical rail, arranged orthogonal to the horizontal rail; and wherein the print head is affixed to the vertical rail.

[0096] In some examples, the print head comprises a first and second dispenser, wherein a first molten plastics material is deposited from the first dispenser fluidly connected to a first plastics material hopper; and a second molten plastics material is deposited from the second dispense fluidly connected to a second plastics material hopper. In some examples, the first and second plastics materials comprise different physical properties after hardening, the different physical properties being one of: hardness, brittleness, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, oil resistance, or colour. In some examples, each plastics material hopper comprises a hydrocarbon-based thermoplastic or an alkyd-based thermoplastic. In some examples, the plastics material hoppers are configured to melt the plastics material into a liquid phase prior to deposition at the target site.

[0097] In sonic examples, further comprises an anti-slip material dispenser, wherein the anti-slip material is deposited from the anti-slip material dispenser across a surface of the molten plastics material prior to hardening. In some examples, the anti-slip material is at least one of: glass, flint, sand, calcium carbonate, alumina particles, or mixtures thereof.

In some examples, the print head further comprises a retroreflective particle dispenser, wherein the retroreflective particles are deposited from the retroreflective particle dispenser across the surface of the molten plastics material prior to hardening. In some examples, the retroreflective particles are glass beads, In some examples, the retroreflective particles are partially submerged in the plastics material. In sonic examples, the retroreflective particles are partially submerged by 30-70% of their volume. In some examples, the retroreflective particles are deposited in a coded visible or machine-readable marking. Additionally, coded visible or machine-readable markings may be introduced in special materials, which may include retro-reflective materials or metallic particles, such as magnetic particles, that can be used for guidance for pedestrian or vehicular traffic. Retro-reflective beads may simulate cats' eyes in road markings, for example, or appear as coded symbols warning of hazards or defining a route which an autopilot system may follow. Rather than having multiple identical such markings, as is necessary with conventional cat's eyes, which are mass produced, it will be easy to print 'custom' markings that can indicate distance from road junctions, for example.

[0098] In addition to applying molten plastics material, an anti-slip/anti-skid finish may be applied at the time of printing, in the form of materials that do not adversely affect the colour of the ground marking once hardened. In order to be retained on the surface and not sink in so far that they are completely absorbed, whereby they contribute nothing to anti-slip or anti-skid protection, such particles should be applied at a given temperature of the plastic surface -specific to the composition of the molten plastics material. Likewise, microbeads, imparting retro-reflectivity, may also be applied, and this may be at a temperature different to that at which anti-slip/anti-skid particles are applied, and they may be applied after anti-slip/anti-skid particles. The anti-slip/anti-skid and retro-reflective treatment may be applied to the whole or to selected parts of the marking.

[0099] In some examples, the print head further comprises a primer dispenser, fluidly connected to a primer hopper containing a primer material, wherein the primer material is deposited to the ground surface at the target position prior to the molten plastics material. In some examples, a single print head may comprise a plurality of dispensers for different colours, and may comprise five such dispensers, one for white plastic, one for black and three for primary colours; the control unit operable to control the dispensers to applying discrete droplets that combine to make any colour presented by a hex code. Further dispensers may bc provided for clear plastic, acting as a varnish or other surface texture finish.

[0100] In some examples, the controller is operable to receive an image to be printed. In some examples, the controller is configured to demarcate the image into a plurality of segments to be printed. In some examples, the control unit is operable to control the dispenser to deposit molten plastics material forming the image.

[0101] In some examples, the molten plastics material is applied in layers to achieve a mimimum threshold thickness. In some examples, the minimum threshold thickness is 2mm. Tn some examples, the molten plastics material is applied in layers up to a maximum threshold thickness. In some examples, the layers are overlapping. For example, the ground marking may be formed, layer by layer, to the desired thickness by the multiple applications of discrete droplets. A thickness of 2mm is adequate for most purposes, depending on the properties of the plastic. However, using plastic that is conventionally applied by gas torches, requires the plastic to be thicker, in the order of 4nun to 5nim so as not to bubble during application. The present disclosure, requiring only 2mm for the adequate robustness and durability required for ground markings is a very adequate comparable thickness and represents a significant material saving over the conventional gas torch application. The layer-by-layer application of the 3D printed plastic material means in any event that only the surface layer needs to be heated which the particulate material is being applied.

[0102] An advantage of the application technique of the present disclosures over the conventional gas torch application is that the range of ground surfaces to which the marking may be applied is extended. Gas torch application is only applicable for outdoor concrete or tarmac, while the present printing techniques work on a wider variety of surfaces including wood and composite surfaces (e.g., by incorporating rubber crumb as a filler), as well as indoor surfaces.

[0103] In some examples, the hoppers may be adapted to gravity or pressure feed the dispensers they are fluidly connected to. In some examples, the dispensers may comprise nozzles through which the molten plastics material emerges in drops (or as a filament) under the control of valve means.

[0104] A second aspect of the invention provides an autonomous printing device for applying durable ground markings to a target position on a ground surface. The autonomous printing device comprises at least traction means for supporting the printing device on the ground surface; drive means for driving the traction means; and a control system configured to control the drive means to guide the autonomous printing device across the targel position on the ground surface. The autonomous printing device further comprises the print device of the first example, as described above. In particular, the print head comprises at least one dispenser, and a print control unit operable to control the dispenser to deposit molten plastics material at the target position, wherein the molten plastics material hardens into a durable ground marking. Aspects of the first example, as described above, are herein compatible with the second example.

[0105] in some examples, the ground marking may be applied using a line of dispensers, which are traversed in a direction perpendicular to the line, or a two-dimensional array of dispensers, whereby to print in blocks of colour or pattern.

[0106] A third aspect of the invention provides a method for applying durable ground markings to a target position on a ground surface. The method comprises depositing a molten plastics material at the target position, wherein the molten plastics material hardens into a durable ground marking. In some examples, the molten plastics material is deposited in discrete droplets. Aspects of the third example are herein intended to be compatible with aspects of the first and second example.

[0107] In some examples, the method further comprises the step of applying anti-slip material to improve the coefficient of friction of the molten plastics material. In some examples, the anti-slip material is applied at a first temperature. In some examples, the first temperature is in the range of 170C -230C. In some examples, the anti-slip particles comprise at least one of glass, flint, sand, calcium carbonate, alumina particles, or mixtures thereof.

[0108] Desirably, the plastics material as laid will be durable and heat resistant -as it may need to survive atmospheric temperatures substantially in excess of 40°C and direct sunlight in tropical and subtropical areas, for example in Australia, wherein the ground surface temperature regularly exceeds 60°C. The plastics materials currently used for ground surface markings develop such resistance as a result of the gas torch heating by which they arc fused to the ground surface. As 3D printed materials arc not necessarily subject to such high temperatures during the application, it may be necessary to subject the ground markings to a post-application hardening treatment, which may be by microwave or infra-red heating, for example. Anti-slip/anti-skid treatment may also be applied during this post-application treatment, as may the addition of microbeads.

[0109] In some examples, the method further comprises the step of applying retroreflective particles. In some examples, the retroreflective particles are applied while the molten plastics material is at a second temperature, wherein the second temperature is lower than the first temperature. In some examples, the retro-reflective particles are glass beads.

[0110] In some examples, the plastics material is deposited in a liquid phase. Tu some alternative examples, the plastics material is deposited as a softened filament or prior to the glass transition.

[0111] In some examples, the molten plastics material is deposited in overlapping layers to create a surface texture when the molten plastics material hardens into the durable ground marking. In some examples. the method further comprises measuring a coefficient of friction of at the target position on the ground surface. In some examples, the molten plastics material comprises a first and second molten plastics material. In some examples, the first molten plastics materials is a hydrocarbon-based thermoplastic, and the second molten plastics material is an alkyd-based thermoplastic. In some examples, the different plastics materials comprise different physical properties. In sonic examples, the physical characteristics are at least one of: hardness, brittle, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, or colour. In some examples, the method further comprises selecting the first or second molten plastics material based on a measured surface coefficient of friction at the target position of the ground surface.

[0112] A fourth aspect of the invention provides a method for applying durable ground markings to a target position on a ground surface. The method comprises preparing the ground surface at the target position to receive molten plastics material; sensing a temperature of the target position; depositing, based on the preparation and temperature of the target position surface, a molten plastics material at the target position, wherein the molten plastics material hardens into a durable ground marking. Aspects of die fourth example arc herein intended to be compatible with aspects of the first, second, and third examples.

[0113] In sonic examples, preparing the ground surface further comprises at least one of: cleaning the ground surface at the target position to remove debris and dust; applying a primer to the ground surface to aid bonding of the molten plastics material to the ground surface; or preheating the ground surface with a heat source based on the sense temperature of the ground surface.

[0114] In some examples, the molten plastics material is deposited in discrete droplets at the target position. In some examples, depositing the molten plastics material at the target position, further comprises: depositing a first molten plastics material from a first dispenser fluidly connected to a first plastics material hopper at the target position at a first temperature; and depositing a second molten plastics material from a second dispenser fluidly connected to a second plastics material hopper at the target position at a second temperature. In some examples, the method further comprises melting the plastics material into a liquid phase, in the plastics material hoppers. In some examples, each plastics material hopper comprises a hydrocarbon-based thermoplastic or an alkyd-based thermoplastic.

[0115] In some examples, the method of further comprises: sensing a temperature of a surface of the molten plastics material, after deposition to the ground surface at the target position; and applying an anti-slip material to the surface of the molten plastics material before the surface of the molten plastics material reaches a first threshold temperature. In some examples, the method further comprises determining that the surface temperature of the molten plastics material has fallen below the first target temperature, during application of the anti-slip material, and: increasing a velocity deposition of the anti-slip material; and/or activating a heat source to increase the surface temperature of the molten plastics material above the first threshold temperature. In some examples, the anti-slip material comprises: glass, glass bcad aggregate, flint, sand, calcium carbonate, alumina particles, or mixtures thereof [0116] In some examples, the method further comprises: sensing a temperature of a surface of the molten plastics material, after deposition to the ground surface at the target position; and applying retroreflective particles to the surface of the molten plastics material before the surface of the molten plastics material reaches a second threshold temperature. In some examples, the retroreflective particles are glass beads. In some examples, the method further comprises determining that the surface temperature of the molten plastics material has fallen below the second threshold temperature, during application of the retroreflective particles, and: increasing a velocity deposition of the retroflected particles; and/or activating a heat source to increase the surface temperature of the molten plastics material above the second target temperature. In some examples, the second target temperature is lower than the first target temperature.

[0117] In some examples, applying the molten plastics material further comprises projecting the molten plastics material at a first velocity based on the sensed temperature of the ground surface at the target position.

[0118] In some examples, the method further comprises arranging the molten plastics material into a coded visible or machine-readable pattern.

[0119] A fifth aspect of the invention provides a method for applying a durable ground marking to a target position on a ground surface. The method comprises depositing a first molten plastics material in discrete droplets at the target position on the ground surface, wherein the discrete droplets harden into a durable ground marking.

In some examples, the method further comprises controlling a print head to form the discrete droplets into a patterned ground marking. In some examples, the patterned ground marking is obtained by layering the discrete droplets at the target position.

[0120] In some examples, the discrete droplets are layered to a threshold thickness. In some examples, the threshold thickness is 2mm. In some examples, the layers of the discrete droplets overlap to create beveled, chamfered and/or rounded edges after hardening. In some examples, the step of depositing the first molten plastics material further comprises projecting the discrete droplets at a first velocity.

[0121] In some examples, the method further comprises the step of arranging the discrete droplets in a machine-readable pattern. In some examples, the method further comprises receiving an image; dividing the image into printable segments, wherein each printable segment comprises instructions for applying a plurality of discrete droplets at a target location on the ground surface; and applying discrete droplets according to the printable segments to form the image, wherein the patterned ground marking represents the image. In some examples, the method further comprises depositing a second molten plastics material in discrete droplets on the ground surface, the second molten plastics material having at least one characteristic which is different to at least one characteristic of the first molten plastic material. In some examples, the characteristic is at least one of hardness, brittleness, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, oil resistance, or colour. In some examples, after the first and second molten plastics material have hardened, the first molten plastics material has a higher coefficient of friction than the second molten plastics material.

[0122] In some examples, after hardening, the ground marking comprises at least two colours. A marking may be applied in a design using more than one colour by printing individual colours in separate areas of the marking. However, as with inkjet colour printing, a wide range of colours may be printed by melding primary colours. Whereas, using the conventional technique, multi-coloured surface markings for roads, playgrounds and the like are made in a restricted range of colours, sharply delineated, using methods according to the invention, a much wider range of colours may be had, which may blend smoothly into one another.

[0123] It should be understood that the examples described above are not mutually exclusive with any of the other examples described with reference to FIGS. 1 -12. The order of the description of any examples is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. [0124] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed disclosure, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures arc recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

[0125] This disclosure is made to illustrate the general principles of the systems and processes discussed above and is intended to be illustrative rather than limiting. More generally, the above disclosure is meant to be exemplary and not limiting and the scope of the disclosure is best determined by reference to the appended claims. In other words, only the claims that follow are meant to set bounds as to what the present disclosure includes. [0126] While the present disclosure is described with reference to particular example applications, it shall be appreciated that the disclosure is not limited thereto. II will be apparent to those skilled in the art that various modifications and improvements may be made without departing from the scope and spirit of the present disclosure. Those skilled in the art would appreciate that the actions of the processes discussed herein may be omitted, modified, combined, and/or rearranged, and any additional actions may be performed without departing from the scope of the disclosure.

[0127] Any system feature as described herein may also be provided as a method feature and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure. It shall be further appreciated that the systems and/or methods described above may be applied to, or used in accordance with, other systems and/or methods.

[0128] Any feature in one aspect may be applied to other aspects, in any appropriate combination. In particular, method aspects may he applied to system aspects, and vice versa. Furthermore, any, sonic, and/or all features in one aspect can be applied to any, some, and/or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspect can be implemented and/or supplied and/or used independently.

Claims

CLAIMS1. A method for applying a durable ground marking to a target position on a ground surface, the method comprising: depositing a first molten plastics material in discrete droplets at the target position on the ground surface, wherein the discrete droplets harden into a durable ground marking.
2. The method of claim 1, further comprising controlling a print head to form the discrete droplets into a patterned ground marking.
3. The method of claim 2, wherein the patterned ground marking is obtained by layering the discrete droplets at the target position.
4. The method of any of claims 1 to 3, wherein the discrete droplets are layered to a threshold thickness.
5. The method of claim 4, wherein the threshold thickness is 2mm.
6. The method of any of claims 3 to 5, wherein the layers of the discrete droplets overlap to create beveled, chamfered and/or rounded edges after hardening.
7. The method of any of claims 1 to 6, wherein the step of depositing the first molten plastics material further comprises projecting the discrete droplets at a first velocity.
8. The method of any of claims 1 to 7, further comprising the step of arranging the discrete droplets in a machine-readable pattern.
9. The method of any of claims 1 to 8, further comprising: receiving an image; dividing the image into printable segments, wherein each printable segment comprises instructions for applying a plurality of discrete droplets at a target location on the ground surface; and applying discrete droplets according to the printable segments to form the image, wherein the patterned ground marking represents the image.
10. The method of any of claims 1 to 9, further comprising depositing a second molten plastics material in discrete droplets on the ground surface, the second molten plastics material having at least one characteristic which is different to at least one characteristic of the first molten plastic material.
11. The method of claim 10, wherein the characteristic is at least one of hardness, brittleness, opacity, electrical resistance, heat resistance, stress and strain characteristics, acidic resistance, oil resistance, or colour.
12. The method of claims 10 or 11, wherein after the first and second molten plastics material have hardened, the first molten plastics material has a higher coefficient of friction than the second molten plastics material.