LINE TRACKING APPARATUS

STATEMENT OF CORRESPONDING APPLICATIONS

This application is based on the Provisional specification filed in relation to New Zealand Patent Application Number 617411 , the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a line tracking apparatus. More particularly, the present invention relates to a line tracking apparatus for tracking marked lines on a road surface.

BACKGROUND ART

Line markings are painted on roads in order to guide vehicles safety on the road surface. Such markings include center lines and side-lines.

Currently, road line marking requires skilled operation to ensure accurate manual tracking and re-marking of lines on the road surface. Consequently the cost of training and paying skilled operators of known line marking apparatus can be high.

In addition, the margin of error in remarking road lines is small, which can result in increased costs in the form of wasted paint and increased man-hours to correct mistakes in order to produce road markings to a particular compliance standard. It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country. Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

SUMMARY

According to an exemplary embodiment there is provided a line tracking apparatus comprising: an optical head assembly configured to output optical information relating to a ground surface over which the line tracking apparatus is moved; at least one photoelectric sensor configured to receive the optical information from the optical head assembly and output a signal indicative of the presence of a pre-existing line marking on the ground surface; at least one actuator assembly attached to the optical head assembly and configured to be attached to a prime mover, and controllable to adjust the transverse position of the optical head assembly relative to the direction of movement of the line tracking apparatus; at least one controller configured to: receive the signal from the photoelectric sensor; determine a position of the optical head assembly relative to an edge of the preexisting line marking by comparison of the signal indicative of the presence of a preexisting line marking with a calibration value; and control operation of the actuator based on the determined position of the optical head assembly to adjust the transverse position of the optical head assembly in order to maintain its position relative to the edge of the pre-existing line; and a mounting for securing a ground marking device relative to the optical head assembly such that adjustment of the position of the optical head assembly using the actuator to maintain its position relative to the edge of the pre-existing line also maintains the position of the ground marking device relative to a centre of the pre-existing line. According to an exemplary embodiment there is provided a method of operating a line tracking apparatus comprising: receiving optical information from an optical head assembly, the optical information relating to a ground surface over which the line tracking apparatus is moved; outputting a signal indicative of the presence of a pre-existing line marking on the ground surface; receiving the signal and determining a position of the optical head assembly relative to an edge of the pre-existing line marking by comparison of the signal indicative of the presence of a pre-existing line marking with a calibration value; and controlling operation of at least one actuator assembly attached to the optical head assembly and a prime mover, to adjust the transverse position of the optical head assembly relative to the direction of movement of the line tracking apparatus, wherein adjusting the transverse position also moves a mounting for securing a ground marking device relative to the optical head assembly such that the position of the mounting relative to a centre of the pre- existing line is maintained.

It is envisaged that the line tracking apparatus may have particular application to the painting of road lines, and description of operation of the apparatus may herein make reference to the surface being a road. However, it should be appreciated that the line tracking apparatus may be used in other applications - for example the marking of sports fields, or the floors of a facility (for example within a factory or warehouse). In an exemplary embodiment, the line tracking apparatus may comprise a guide wheel connected to the optical head assembly, configured to maintain the optical head assembly at a predetermined distance from the ground surface.

In an exemplary embodiment, the optical head assembly may comprise at least one fibre optic head. Reference to a fibre optic head should be appreciated to mean a device via which an end face of at least one optical fibre is exposed for the emission and/or receiving of light.

In such an embodiment, the at least one photoelectric sensor may be a fibre optic sensor. For example, in an exemplary embodiment the photoelectric sensor may be an FX-50X series digital fibre sensor manufactured by Panasonic Industrial Devices SUNX Co., Ltd. The at least one photoelectric sensor may be connected by a light guide to the fibre optic head, for example a fibre optic cable, as known in the art.

It is envisaged that the use of fibre optic heads at the optical head assembly may reduce the likelihood of malfunction of the photoelectric sensor by reducing its exposure to the harsh environments associated with line tracking - particularly where the line is on a road. Fibre optic 2014/000249 heads are relatively inexpensive in comparison with photoelectric sensors, and it may be generally preferable to replace a fibre optic head than repair or replace the sensor itself.

However, it should be appreciated that this is not intended to be limiting, and in exemplary embodiments the at least one photoelectric sensor may be incorporated into the optical head assembly. Further description herein with regard to positioning of the at least one fibre optic head within the optical head assembly may also be applied to embodiments in which the at least one photoelectric sensor is located at the optical head assembly.

In an exemplary embodiment the optical head assembly comprises an air flow generator, for example a fan or a pressurised air outlet, configured to generate air flow across the one or more fibre optic heads. Such air flow may assist in reducing the build-up of dust and debris which may otherwise potentially interfere with optical imaging and therefore impair accurate operation of the apparatus.

In an exemplary embodiment, the photoelectric sensor may comprise a modulated light emitter and a light detector. Accordingly, each fibre optic head may comprise both a light emitting portion and a light receiving portion.

Optical information in the form of reflected light from the ground surface may be received at the light detector, and the photoelectric sensor may output a signal - the magnitude or value of which is dependent on characteristics of the light received, particularly intensity.

The amount of light received is dependent on characteristics of the surface from which it is reflected. Typically, the marking which is to be tracked contrasts with the surface to which it is applied - and the resulting differential in light reflection between the marking and the ground surface means that the signal output from the sensor may be indicative of the presence of a pre-existing line marking on the ground surface. It should be appreciated that the signal generated in response to the optical information received may be filtered and amplified using any suitable means known in the art.

It should be appreciated that reference to a photoelectric sensor producing a signal indicative of the presence of a pre-existing line marking on the ground surface is not intended to encompass image sensors which each comprise an array of sensors (i.e. pixels) exposed to the optical information simultaneously, and output a composition of signals to be reconstructed as an image.

It is envisaged that in exemplary embodiments the prime mover to which the line tracking apparatus is attached may travel up to, and in excess of, 30 kph. In order to make transverse adjustments before an immediately trailing ground marking device, fast processing of the line position must occur. The use of photoelectric sensors as opposed to image sensors may assist Z2014/000249 with achieving such responsiveness. In an exemplary embodiment, the optical head assembly may comprise at least three fibre optic heads configured to convey optical information from a predetermined left hand detection area, a centre detection area, and a right hand detection area of the ground surface respectively. In an exemplary embodiment the fibre optic heads may be spaced along a transverse axis of the optical head perpendicular to the direction of movement of the line tracking apparatus.

In an exemplary embodiment, detection areas of the respective fibre optic heads may be defined using vision control plates positioned between the fibre optic heads along the transverse axis. In an exemplary embodiment, vision control plates of adjacent fibre optic heads may be spaced apart.

In an exemplary embodiment the position of the vision control plates along the transverse axis may be adjustable. For example, the apparatus may be used with line markings of different widths, and it may be desirable to adjust the respective detection areas of the fibre optic heads accordingly. In an exemplary embodiment each fibre optic head may be coupled to a dedicated photoelectric sensor. It should be appreciated that this is not intended to be limiting, and that a single photoelectric sensor may be coupled to two or more fibre optic heads. For example, the photoelectric sensor may be configured to switch between receiving optical information from different detection areas, with the controller differentiating between the detection areas in the output signal based on the control scheme of the switching.

In an exemplary embodiment, at least one calibration value may be established by manually positioning the optical head in a position aligned with the pre-existing line marking, and capturing the signal output of the at least one photoelectric sensor at that position. Similarly, a value for the ground surface without the presence of the pre-existing line marking within the one or more detection areas may be captured.

As a rudimentary example, if the differential between the current right hand detection area value and the right hand calibration value is negative (i.e. the current right hand detection area value is less than the right hand calibration value), this may indicate that the optical head assembly has moved to the right of the right hand edge of the line marking. The actuator may be controlled to move the optical head assembly to the left to compensate.

It should be appreciated that where more than one detection area of the optical head assembly is monitored, various correlations may be made between the detection areas to assist in determining the position of the optical head assembly relative to the line marking. 9

In an exemplary embodiment, the optical information from the centre detection area may be referenced to repeatedly recalibrate the one or more calibration values of the other detection areas during movement along the line marking.

The quality of the line may change along its length, in turn having an effect on the optical information. Without recalibration, the comparison between the current and calibration values may be inaccurate. For example, where the line has faded (but is still present) the differential may be disproportionate due to a reduced current value, producing a false indication of the position of the optical head relative to the line. However, it may be inefficient to manually recalibrate the apparatus as described previously - if the human operator were to identify this requirement existing at all.

The central detection area allows for a sample of the current condition of the pre-existing line marking to be taken without interference from the left hand or right hand edges. In an exemplary embodiment this may be compared with the previous calibration value of the central detection area, and if determined that a line is present, the differential may be used to adjust the calibration value of the other detection areas.

In an exemplary embodiment, the line tracking apparatus may comprise a user interface in communication with the controller.

In an exemplary embodiment, the user interface may transmit a signal to the controller indicating an operator's selection of a left or right hand edge of the pre-existing line for determination of the position of the optical head assembly relative to the pre-existing line.

For example, an operator may observe an upcoming portion of the pre-existing line in which one edge of the line is degraded in comparison with the other. Enabling manual selection of the less degraded edge may enable more accurate tracking of the line during that portion.

In an exemplary embodiment, the user interface may transmit a signal to the controller indicating an operator's selection of a speed for actuation of the actuator. This allows for the operator to utilise their skill and experience - for example, an experienced operator may be capable of making rapid responses manually, and not require the apparatus to make rapid adjustments. Further, the nature of the line may require varying speed of response - for example, a curved section may require more rapid correction than a straight line. In an exemplary embodiment the actuator assembly comprises a linear actuator. It should be appreciated that numerous types of linear actuator may be used. For example, the linear actuator may be a hydraulic or pneumatic cylinder, or an electrically powered linear actuator. 0249

For example, the linear actuator may be driven by a 24 volt DC motor - 24 volts being common in electrical power sources of road going vehicles.

In an exemplary embodiment, the actuator assembly may be attached to the chassis of a prime mover - for example a road going vehicle. It should be appreciated that this is not intended to be limiting, and the actuator assembly may be attached in any suitable manner to the prime mover such that it may extend and retract along a transverse axis substantially perpendicular to a longitudinal axis of the prime mover.

Reference to a prime mover should be understood to include human powered vehicles such as trolleys, in addition to powered vehicles. In an exemplary embodiment, the actuator assembly may extend from at least one side of the prime mover. In the case of road markings on the side of a road, this may enable the prime mover to be driven away from the edge of the road, which may be more uneven than closer towards the centre of the road.

In another embodiment, the actuator assembly may extend across the width of the prime mover. Where the prime mover may be driven overlapping the line marking, it is envisaged this may assist the operator of the prime mover with maintaining the position of the prime mover relative to the target line, which extends in front rather than the side of the prime mover. The mounting may be any suitable means for supporting a ground marking device in a fixed relationship with the optical head assembly with respect to at least the transverse axis. In an exemplary embodiment, the apparatus comprises a ground marking device secured to the mounting relative to the optical head assembly such that adjustment of the position of the optical head assembly using the actuator to maintain its position relative to the edge of the preexisting line also maintains the position of the ground marking device relative to a centre of the pre-existing line. The ground marking device may be any suitable means known in the art for the application of marking material to a surface. For example, the ground marking device may be a paint spray gun, a thermoplastic applicator, or a marking tape applicator.

In an exemplary embodiment the ground marking device is positioned downstream from the optical head relative to the direction of movement of the line tracking apparatus. The controller may have at least one processor. The processor may comprise one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices or controllers (PLDs, PLCs), field programmable gate arrays (FPGAs), computers, lap tops, controllers, micro-controllers, microprocessors, electronic devices, other electronic units (whether analogue of digital) designed to perform the functions described herein, or a combination thereof.

In an exemplary embodiment, the controller may be a logic controller - for example a Crouzet "Millenium" XD26 Logic Controller manufactured by Custom Sensors and Technologies (CST). For a firmware and/or software (also known as a computer program) implementation, the techniques of the present invention may be implemented as instructions (for example, procedures, functions, and so on) that perform the functions described. It should be appreciated that the present invention is not described with reference to any particular programming languages, and that a variety of programming languages could be used to implement the present invention. The firmware and/or software codes may be stored in a memory, or embodied in any other processor readable medium - for example Random Access Memory (RAM), flash memory, Read Only Memory (ROM), hard disks, a removable disk such as a CD ROM, or any other suitable storage medium known to a person skilled in the art - and executed by a processor or processors. The memory may be integrated within the processor or external to the processor.

The steps of a method, process, or algorithm described in connection with the present invention may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. The various steps or acts in a method or process may be performed in the order shown, or may be performed in another order. Additionally, one or more process or method steps may be omitted or one or more process or method steps may be added to the methods and processes. An additional step, block, or action may be added in the beginning, end, or intervening existing elements of the methods and processes.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which:

FIG. 1 is a system diagram of components of an exemplary line tracking apparatus;

FIG. 2A is an isometric view of an exemplary optical head assembly for the exemplary line tracking apparatus;

FIG. 2B is a bottom view of the exemplary optical head assembly; FIG. 2C illustrates a first positioning of exemplary detection areas of the exemplary optical head assembly relative to an exemplary line marking;

FIG. 2D illustrates a second positioning of exemplary detection areas of the exemplary optical head assembly relative to an exemplary line marking; FIG. 3 is a top view of an exemplary actuator assembly for the exemplary line tracking apparatus;

FIG. 4 illustrates an exemplary user interface for the exemplary line tracking apparatus;

FIG. 5 is a rear view of a prime mover to which an exemplary line tracking apparatus is mounted; FIG. 6 is a flow diagram for an exemplary method of calibrating the exemplary line tracking apparatus, and

FIG. 7 is a flow diagram for an exemplary method of operating the exemplary line tracking apparatus.

DETAILED DESCRIPTION

FIG. 1 illustrates a system 10 of elements of a line tracking apparatus. The system 10 comprises a optical head assembly 200 comprising three fibre optic heads: left head 202a, centre head 202b and right head 202c. The fibre optic heads 202a, 202b and 202c are connected to dedicated photoelectric sensors 12a, 12b, and 12c respectively using fibre optic cables 14a, 14b, and 14c. Each of the photoelectric sensors 12a, 12b, and 12c may be, for example, FX-50X series digital fibre sensors manufactured by Panasonic Industrial Devices SUNX Co., Ltd.

The photoelectric sensors 12a, 12b, and 12c receive optical communications in the form of light from the fibre optic heads 202a, 202b and 202c, and output a signal - the voltage of which is indicative of light intensity received - to a controller 16. The controller comprises a processor in the form of a programmable logic controller (PLC) 18, coupled with memory 20.

The controller 16 is connected to a motor 314 of an actuator assembly (described below with reference to FIG. 3), a user interface 400 (described below with reference to FIG. 4), and a paint gun 22. 00249

Referring to FIG. 2A, the fibre optic heads 202a, 202b, 202c of the optical head assembly 200 are coupled to a housing 204.

Referring to FIG. 2B, the base of the housing 204 is open to expose the fibre optic heads 202a, 202b, 202c. The fibre optic heads 202a, 202b, 202c comprise emitters 206a, 206b, and 206c for the emission of modulated light received from the sensors 12a, 12b, and 12c, and receivers 208a, 208b, and 208c returning reflected light to the sensors 12a, 12b, and 12c.

A plurality of vision control plates 210 are disposed between the fibre optic heads 202a, 202b, 202c. The vision control plates 210 are secured in place using threaded rods 12 and nuts positioned thereon. The vision control plates 210 define detection areas for each of the fibre optic heads 202a, 202b, 202c across the optical head assembly 200 (illustrated below with reference to FIG. 2C and FIG. 2D).

FIG. 2C shows a pre-existing line marking 250, having a left hand edge 252 and a right hand edge 254. The line marking 250 is applied to road surface 256.

When the optical head assembly (not illustrated in FIG. 2C) is correctly aligned with the line marking 250 - i.e. in a position where an associated paint gun (such as paint gun 22 of FIG. 1) will paint a line centralized on the pre-existing line marking 250 - a left hand detection area 258a of left head 202a may be substantially centred on the left edge 252, a centre detection area 258b of the centre head 202b may be substantially centred on the line 250, and a right hand detection area 258c of the right head 202c may be substantially centred on the right edge 254.

In an exemplary embodiment, the respective widths of the left hand detection area 258a and right hand detection area 258c are substantially 14mm, while the width of the centre detection area 258b is substantially 18mm.

FIG. 2D illustrates a scenario in which the optical head assembly has moved towards the right relative to the line 250. The left hand detection area 258a is now positioned over the line 250, without capturing the left edge 252. The right hand detection area 258c is now positioned over the road surface 256, without capturing the right edge 254.

Variation in the light reflecting properties between the line 250 and road surface 256 means that where the composition of the detection areas 258a, 258b, and 258b changes (for example as between FIG. 2C and FIG. 2D), so too will the amount of modulated light output from the respective sensors 12a, 12b, and 12c and subsequent reflected and detected.

Control of the line tracking apparatus in response to this scenario will be described further below. T/NZ2014/000249

FIG. 3 illustrates an actuator assembly 300, comprising mounting brackets 302 for securing the assembly 300 to a prime mover (not illustrated). The assembly 300 further comprises telescoping support arms comprising shaft guides 304 and telescoping shafts 306 received therein. A mounting plate 308 is attached to one end of the telescoping shafts 306. The mounting plate 308 may be used to secure the optical head assembly 200 and paint gun 22 to the actuator assembly 300. A stabilizer bar 310 may be connected across the other ends of the telescoping shafts 306.

The actuator apparatus 300 comprises a linear actuator 312 attached to the mounting plate 308, driven by the electric motor 314 (for example, a 24 volt DC motor) to extend and retract in order to move the mounting plate 308 (and therefor optical head apparatus 200 and spray gun 22) along the movement path of the linear actuator 312.

FIG. 4 illustrates the user interface 400 of the line tracking apparatus. The interface 400 comprises an actuator speed potentiometer 402, for use by the operator to set the speed of the motor 314 of FIG. 3 during actuation of the linear actuator 312. It is envisaged that the actuator speed may be up to 140 mm/s. A display 404 indicates the current speed setting.

A PLC indicator light 406 indicates whether the controller 16 is in operation, with PLC on/off buttons 408a and 408b respectively used to enable and disable operation thereof.

Calibration button 410 initiates a calibration routine, described below with reference to FIG. 6. Two calibration status lights 412a and 412b are provided.

A sensor selector toggle 414 permits selection of either left hand edge tracking or right hand edge tracking (described further below), with left hand and right hand indicator lights 416a and 416b respectively indicating the current selection.

The user interface 400 further comprises a manual actuator toggle switch 418 for controlling extension and retraction of the actuator assembly 300. A pause toggle switch 420 enables the operator to suspend operation of the line tracking apparatus while the operator assumes manual control.

FIG. 5 illustrates the line tracking apparatus 500 with the actuator apparatus 300 mounted to the rear of a prime mover 502. The optical head assembly 200 is mounted to a pivoting bracket 504, in turn connected to the mounting bracket 308 of the actuator assembly 300. The pivoting bracket 504 comprises a wheel 506 which maintains the height of the optical head assembly 200 from the ground surface on which the wheel 506 bears - for example substantially 75mm. Z2014/000249

An enclosure 508 contains the photoelectric sensors 12a, 12b, and 12c.

FIG. 6 illustrates a method 600 of calibrating the line tracking apparatus. In step 602, the operator positions the optical head assembly 200 such that its detection areas 258a, 258b, and 258c are positioned relative to the line marking 250 substantially as illustrated in FIG. 2C. The calibration button 410 pushed, and the output of the photoelectric sensors 12a, 12b, and 12c read to establish an initial target calibration value for each of the detection areas 258a, 258b, and 258c. Calibration status light 412a activates.

In step 604, the operator positions the optical head assembly 200 such that its detection areas 258a, 258b, and 258c are positioned entirely over the road surface 256. The calibration button 410 is pushed again, and the output of the photoelectric sensors 12a, 12b, and 12c read to establish a negative calibration value for each of the detection areas 258a, 258b, and 258c. The second calibration status light 4 2a activates to indicate that calibration is complete.

FIG. 7 illustrates a method 700 of operating the line tracking apparatus. In step 702 the output of the photoelectric sensors 12a, 12b, and 12c is read to obtain current values for light levels received from each of the detection areas 258a, 258b, and 258c.

In step 704 the position of the optical head assembly 200 relative to an edge of the pre-existing line marking 250 by comparison of the current values with the calibration values established by method 600, and correlating the resulting differential of each of the detection areas 258a, 258b, and 258c. For example, in the scenario illustrated in FIG 2D, the current value of the left designation area 258a will be greater than its calibration value, while the current value of the right designation area 258c will be lower than its calibration value. This indicates that the optical head assembly has moved to the right of the line 250.

Where the sensor selector toggle 414 has selected either left hand edge tracking or right hand edge tracking, one of the designation areas 258a or 258c will be disregarded for position determination.

If the position of the optical head assembly 200 requires correction, in step 706 the controller 16 initiates control of operation of the motor 314 in accordance with the current setting of the actuator speed potentiometer 402. Further, if it is determined that that the misalignment of the optical head assembly 200 and therefore paint gun 22 with the line 250 is greater than a threshold value (for example 20 mm), the paint gun 22 may be turned off until realignment has been achieved. 49

On initiation of motor control, or if position correction is not required, the output of the centre photoelectric sensor 12b is read and compared with its calibration value in step 708. If the differential indicates degradation of the line 250 to the point of introducing intolerable inaccuracies into the calibration values, these values are corrected based on the current value of the centre designation area 258b in step 710. It is envisaged that such recalibration may be performed in the order of 8 to 20 times per second.

If degradation has occurred to a point where automated recalibration cannot be performed reliably, an alert may issue to notify the operator to take corrective action - for example assessing whether manual recalibration may be performed. Simultaneously, operation of the paint gun 22 may be discontinued.

The process 700 then repeats until manually stopped, or the current values of the designated areas 258a, 258b, and 258c indicate that the optical head assembly 200 has deviated beyond a threshold value.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.