This invention relates to ground printers.

Ground marking is done in a number of ways. Playgrounds are marked with hopscotch and other designs by applying pre-cut pieces of plastic sheet and bonding them to a concrete or tarmacadam substrate using gas torches. Advertising and promotional logos and like ground markings for sporting arenas are made by directional brushing or painting through stencils.

WO2004/100044 discloses creating a visual representation on a plane surface using a free roaming marking device with exchangeable tools that can deposit paint, or bend or cut grass. WO02/18148 discloses ink jet printing on to contoured rigid panels such as office partitions and automobile interior panels, with a multi-jet print head carriage where the print heads are maintained at a fixed distance above the contoured surface. The print head carriage traverses over the print surface on a frame that moves over the surface to print different areas of it.

US2013/0122186 discloses a surface coating arrangement in which a spray head is traversed over successive strips of a surface to coat it. US8696089 describes a large surface are printer comprising a frame on which a print head traverses that is attached to the surface using suction cups.

The present invention provides a compact printer that can print large areas.

The invention comprises a ground printer comprising a chassis on a ground wheel arrangement with a print head on a traverse guide, the traverse guide permitting movement of the print head beyond the width of the ground wheel arrangement.

The traverse guide may be fixed in relation to the ground wheel arrangement, so that it prints one line of an image and then the ground wheel arrangement notches forward for it to print another line. Or the traverse guide may be movable relative to the ground wheel arrangement in the direction of travel, so that an area may be printed while the ground wheel arrangement is stationary, and then the ground wheel arrangement moves forward by the length of the area printed so as to print an adjacent area of image.

The chassis may therefore print a strip of image wider than the width of the ground wheel arrangement and when an entire strip of image has been printed turn around to print an adjacent strip.

In this way, the ground wheel arrangement does not run over any part of the freshly painted ground.

A ground printer according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a plan view;

Figure 2 side elevation; and

Figure 3 is a plan view of a ground printing operation in progress.

The drawings illustrate a ground printer 11 comprising a chassis 12 on a ground wheel arrangement 13 with a print head 14 on a traverse guide 15, the traverse guide 15 permitting movement of the print head 14 beyond the width W of the ground wheel arrangement 13.

The ground wheel arrangement comprises two drive wheels 13a and a steerabie nose wheel 13b that is connected to a control arrangement, not shown, to steer the printer along a path to effect the printing, and this may be under the control of a print file that can be loaded into an on-board control system.

The traverse guide 15 is fixed in relation to the ground wheel arrangement 13, so that it prints one line of an image and then the ground wheel arrangement 13 notches forward for it to print another line. In another arrangement not illustrated the traverse guide 15 can be movable relative to the ground wheel arrangement in the direction of travel, so that an area may be printed while the ground wheel arrangement 13 is stationary, and then the ground wheel arrangement 13 moves forward by the length of the area printed so as to print an adjacent area of image.

The print head 14 can, for example, print a line of 10mm width, then the arrangement 13 notch forward by 10mm. Or an area, say of A4 or A3 paper size can be printed and only then does the printer move forward.

The printer 11 can therefore print a strip 16, Figure 3, of image wider than the width W of the ground wheel arrangement 13 and when an entire strip 16 of image has been printed turn around to print an adjacent strip.

in this way, the ground wheel arrangement 13 does not run over any part of the freshly painted ground, the outer tracks 17 of the ground wheel arrangement being seen in Figure 3 to be well within the width of the strips 16.

The control system can align the printer 11 with a previously printed strip either by dead reckoning or by imaging the edge of the previously printed strip and using an image stitching algorithm ro correctly position the printing with the printing already carried out.

The print head 14 can be height adjustable, whereby to print finer or coarser images or to adapt to ground irregularities.

The print head 14 can use any of a variety of printing techniques, including standard ink jet, spray, and 3D printing techniques involving melting plastic and dropping or shooting it at the ground surface.