Laser processing apparatus and method of operation

Abstract

There is described a method of processing a target with a laser processing apparatus, the method comprising, performing a distance measurement comprising generating measurement data indicative of a distance between the target and a portion of the laser processing apparatus, wherein performing the distance measurement comprises radiation passing along at least a portion of a shared optical path from the target towards the laser processing apparatus, and performing a laser processing operation based on the measurement data, wherein performing the laser processing operation comprises radiation passing along at least a portion of the shared optical path from the laser processing apparatus towards the target.

Description

[0001] LASER PROCESSING APPARATUS AND METHOD OF OPERATION

[0002] The present disclosure relates to a laser processing apparatus and method of operation.

[0003] In laser processing operations, such as marking, it is important to ensure that the target to be processed (e.g. a product) by a processing radiation beam is suitably placed prior to processing. That is, the target must be located within the laser processing apparatus’ processing field. The term processing field refers to a volume in which a surface of a target to be processed must be located in order that it is able to be processed by the laser processing apparatus. If the product is not correctly located, the result may be a misprint, such as a missing or unreadable print. Additionally, or alternatively, the processing radiation beam may escape the confines of the processing field if there is no target to intercept the processing radiation beam in the processing field. There can be serious safety implications associated with processing radiation beams that extend beyond the processing field. Such escaped processing radiation beams may cause harm to a user or damage to external equipment or materials.

[0004] During laser processing operations, targets to be processed are typically transported along a conveyor on a conveyor belt and past the laser processing apparatus. As the targets pass the laser processing apparatus, and enter the laser processing apparatus’ processing field, the laser processing apparatus generates a processing radiation beam and directs the processing radiation beam onto the target in order to process the target. Typically, laser processing apparatus rely on external triggers from external sensors in order to determine when a target is within the processing field, and thus ready to be processed.

[0005] In the case where targets are transported along a conveyor, a product detect sensor, such as a light barrier sensor, is typically mounted on, or associated with, the conveyor and is used to detect an edge of a target travelling along the conveyor. When the product detect sensor detects an edge of a target, the product detect sensor outputs a trigger towards the laser processing apparatus. The detection of the target using the product detect sensor allows the laser processing apparatus to determine where the target is at a time associated with the trigger. The trigger can thus be used by the laser processing apparatus to determine when the target will be within the processing field. However, the physical location of the product detect sensor is typically not aligned with the processing

[0006] 69947591-1field of the laser processing apparatus. That is, once a target is detected by the product detect sensor, the target has to travel a distance along the conveyor before it arrives within the processing field of the laser processing apparatus. In some cases, a second sensor is used to help track where the target is after it has trigger the product detect sensor. Typically, the second sensor is a shaft encoder which monitors a shaft coupled to the conveyor belt. That is, the shaft encoder monitors the movement of the conveyor belt, and hence indirectly monitors movement of the target. An output from the shaft encoder may be sent to the laser processing apparatus. The output may be in the form of pulses, each pulse corresponding to a known rotation amount of the shaft. Given a known relationship between one or more rotations of the shaft and a linear displacement of the conveyor belt, the number of pulses output by the shaft encoder can be used to determine a linear displacement of the target. Using both of the product detect sensor and the shaft encoder allows for the determination of the likely position of the target along the conveyor. As such, it can be determined when the target is likely to be within the processing field and thus the laser processing apparatus can determine when to process the target.

[0007] However, the above method can still lead to errors in the processing of the target. In many installation situations there is a substantial distance between the product detect sensor and the processing field. Often, this is because of convenience or lack of mounting options during installation of the equipment, Also, production machines used on the conveyor, such as a beverage filler, may feature an integrated product detect sensor with no additional option to mount a second one or influence the mounting position. The distance between the product detect sensor and the processing field leaves room for problems during transport of the target to the processing field. Additionally, the conveyor belt often has only loose contact to the targets place on the conveyor belt. In wet environments, such as in the beverage industry, this loose contact may cause slippages between the target and the conveyor belt. This in turn causes the shaft encoder to lose precise control over the target position. A similar risk exists when the shaft encoder is coupled to the conveyor belt via a friction wheel, where the friction wheel may lose traction with the conveyor belt.

[0008] In a first aspect there is described a method of processing a target with a laser processing apparatus. The method comprises performing a distance measurement comprising generating measurement data indicative of a distance between the target and a portion

[0009] 69947591-1of the laser processing apparatus, wherein performing the distance measurement comprises radiation passing along at least a portion of a shared optical path from the target towards the laser processing apparatus. The method further comprises performing a laser processing operation based on the measurement data, wherein performing the laser processing operation comprises radiation passing along at least a portion of the shared optical path from the laser processing apparatus towards the target.

[0010] Performing a laser processing operation based on the measurement data is intended to mean that the outcome of the distance measurement in some way affects the performance of the laser processing operation. That is, the performance of the laser processing operation may be conditional on the distance measurement (i.e. the measurement data), or may be controlled in someway based on the measurement data.

[0011] The distance measurement and the laser processing operation both comprising radiation passing along at least a portion of the shared optical path means that during each of the distance measurement and the laser processing operation, radiation (i.e. electromagnetic radiation) is caused to travel along the same (i.e. the shared) optical path in order for the distance measurement and the laser processing operation to be completed.

[0012] The direction of travel along the shared optical path need not be the same. That is, the processing radiation for the processing operation travels in a first direction along the shared optical path (i.e. from the laser processing apparatus towards the target), whereas the measurement radiation travels in a second direction, opposite to the first direction, along the shared optical path (i.e. from the target towards the laser processing apparatus). In some circumstances, measurement radiation may travel in both the first and the second direction along the shared optical path.

[0013] The target may comprise a target surface. Thus, the distance between the target and a portion of the laser processing apparatus may comprise the distance, along a processing beam path, between a portion of the surface of the target at a particular location and a portion of the laser processing apparatus.

[0014] The particular location may be a location at which it is intended to process (e.g. mark) the target.

[0015] 69947591-1The radiation used when performing distance measurement is referred to herein as measurement radiation, or a measurement radiation beam. The radiation used when performing a laser processing operation is referred to herein as processing radiation, or a processing radiation beam.

[0016] Performing the laser processing operation may comprise directing a processing radiation beam along the shared optical path towards a processing location on the target by a beam steering apparatus.

[0017] The processing location may be a location defined by coordinates (e.g. predetermined x-y coordinates) in a two-dimensional processing field (e.g. a marking field). The beam steering apparatus may be comprised within the laser processing apparatus.

[0018] The beam steering apparatus may comprise a pair of rotatable mirrors. The rotatable mirrors may be driven by galvanometer motors. Rotation axes of the rotatable mirrors may be substantially orthogonal. Rotation axes of the rotatable mirrors may be substantially parallel.

[0019] Performing the distance measurement may comprise receiving, by the beam steering apparatus, measurement radiation from the target along the shared optical path, directing, by the beam steering apparatus, the measurement radiation towards a distance measurement system and generating the measurement data based upon the measurement radiation.

[0020] The shared optical path may extend from the processing location to the beam steering apparatus. That is, the measurement radiation and the marking radiation may both travel along a common optical axis between the article being processed (and measured) and the beam steering apparatus. Such a configuration may be referred to as a co-axial laser processing and distance measurement apparatus. The shared optical path may further extend from the beam steering apparatus to a beam splitter / combiner component.

[0021] Performing the distance measurement may further comprise directing, by the beam steering apparatus, a measurement radiation beam towards a measurement location along at least a portion of the shared optical path from the laser processing apparatus

[0022] 69947591-1towards the target, and wherein the received measurement radiation comprises at least a portion of the radiation contained within the measurement radiation beam that has been reflected by a surface at the measurement location.

[0023] Performing the distance measurement may thus comprise radiation passing along at least a portion of the shared optical path in two directions, i.e. both towards and away from the target.

[0024] The measurement location may comprise an intended processing location. Where a target is present at the measurement location, the surface may comprise a surface of the target.

[0025] Performing the distance measurement may further comprise receiving the measurement radiation from the beam steering apparatus and directing at least a portion of the received measurement radiation towards a distance measurement system.

[0026] The method may further comprise receiving processing radiation reflected from the target from the beam steering apparatus and preventing the received reflected processing radiation from reaching the distance measurement system.

[0027] The selection and rejection of radiation may be performed by a wavelength sensitive component configured to direct radiation having a first wavelength along a first optical path, and direct radiation having a second wavelength along a second optical path. The optical component may comprise a dichroic mirror.

[0028] The measurement radiation may have a first wavelength (e.g. 905nm). The marking radiation may have a second wavelength different from the first wavelength (e.g.

[0029] 1064nm).

[0030] The shared optical path may extend from the beam splitter / combiner to the processing location. A processing radiation optical path may extend from a processing radiation source to the beam splitter / combiner. A measurement radiation optical path may extend from the beam splitter / combiner to the distance measurement system.

[0031] The method may further comprise receiving a processing trigger signal, the processing trigger signal comprising a signal indicating that a target for processing is at an intended

[0032] 69947591-1processing location, a target for processing has entered a processing region containing the intended processing location, a target for processing is expected to be at the intended processing location at a predetermined future time, or a target for processing is expected to be at the intended processing location after travelling a predetermined distance.

[0033] The processing trigger signal may be generated based on an output of a product detection sensor (e.g. an optical sensor). The processing trigger signal may be generated based on an output of a product movement sensor (e.g. a line encoder, or shaft encoder). The processing trigger signal may be based upon a combination of an output of a product detection sensor and an output of a product movement sensor. For example, the processing trigger signal may be generated after a product is expected to have moved a predetermined distance (as indicated by the line encoder) after an output of the product detection sensor has been received.

[0034] The distance measurement described herein may be used to confirm the accuracy of the processing trigger signal received from a secondary detector or sensor before performing marking or other processing.

[0035] Performing the laser processing operation based on the measurement data may comprise, if the measurement data satisfies a processing condition performing the laser processing operation and if the measurement data does not satisfy the processing condition, not performing the laser processing operation.

[0036] The processing condition may comprise a safety condition. If the processing condition is not satisfied, it may be determined that it is not safe to proceed with processing, and processing may be prevented.

[0037] If the measurement data does not satisfy the processing condition, a warning or alert may be generated.

[0038] If the measurement data does not satisfy the processing condition, a fault condition may be generated. The fault condition may be configured to stop a processing line.

[0039] Laser processing operations may be performed on a series of targets as they are conveyed along a conveying apparatus (e.g. a processing or packaging line). Since one or more target may become dislodged from an expected location on the line, a distance

[0040] 69947591-1measurement may be performed to provide confidence that processing can be safely carried out.

[0041] The processing condition may comprise the measurement data being greater than a minimum processing distance.

[0042] The condition may comprise the distance measurement indicating that a distance to the target is greater than a minimum marking distance. In this way, it is possible to prevent making (or other processing) on a foreign object (e.g. an operator’s hand, a piece of misplaced equipment) that is too close to the marking (or processing) head.

[0043] A minimum processing distance may be configurable. For example, the minimum processing distance may be determined during setup of a production line / processing apparatus.

[0044] The processing condition may comprise the measurement data being less than a maximum processing distance.

[0045] The condition may comprise the distance measurement indicating that a distance to the target is less than a maximum marking distance.

[0046] In this way, it is possible to prevent incorrect processing of an object that is behind the intended processing (e.g. marking) location. For example, if it was attempted to mark on a product that had fallen from a production line, marking could be carried out on part of the production line apparatus, or an article in the background behind the production line (e.g. an operator standing adjacent to a production line, another piece of equipment).

[0047] A maximum processing distance may be configurable. For example, the maximum processing distance may be determined during setup of a production line / processing apparatus.

[0048] The maximum and / or minimum processing distances may be based on one or more criteria. For example, the maximum and / or minimum processing distances may be based on the properties of the processing radiation beam, such as the Rayleigh length of the processing radiation beam. For example, a Gaussian Laser beam may still be

[0049] 69947591-1considerably focussed along a length, or potion thereof, of the Rayleigh length. As such, the maximum processing distance may be based on the Rayleigh length. For example, if the target to be processed is to be processed at a nominal distance, the maximum processing distance may be the nominal distance plus half of the Rayleigh length, and the minimum processing distance may be the nominal distance minus half of the Rayleigh length.

[0050] The maximum and / or minimum processing distances may be based on the target, such as its dimensions. The maximum and / or minimum processing distances may be based on conveyance of the target along a conveyor. For example, the target may vibrate as it travels along the conveyor. The displacement from a nominal, or expected, position experienced by the target during vibration may be taken into account when selecting a maximum and / or minimum processing distance.

[0051] Performing the laser processing operation based on the measurement data may comprise controlling a focal length of a laser processing beam based on the measurement data.

[0052] The method may comprise adjusting the focal length such that the focal length of the marking beam coincides with the position of the surface at the intended processing location.

[0053] The method may further comprise performing a plurality of processing operations on the target, each one of the plurality of processing operations comprising directing the processing radiation beam towards a respective processing location by the beam steering apparatus along the shared optical path, and performing a plurality of distance measurements, each one of the plurality of distance measurements comprising generating measurement data indicative of a distance between a respective measurement location of the target and a portion of the laser processing apparatus. Each of the plurality of distance measurements may be performed between consecutive ones of the plurality of processing operations, and each of the laser processing operations following a distance measurement may be performed based on the corresponding measurement data.

[0054] That is, between consecutive processing operations, i.e. at a time when a processing radiation beam is not being directed towards the target, additional distance

[0055] 69947591-1measurements may be made. This allows the distance to the target to be checked frequently, and further processing stopped (e.g. if a target is not present in the required processing zone) or adjusted (e.g. if the focal length is required to change, based on a change in measured distance).

[0056] A plurality of distance measurements may be performed between consecutive ones of the plurality of processing operations.

[0057] That is, rather than performing a single distance measurement between consecutive processing operations, in some circumstances, a plurality of distance measurements may be performed.

[0058] In this way it is possible to monitor the distance between the target and the processing apparatus at frequent intervals, without interrupting the processing (e.g. marking).

[0059] The method may comprise performing the plurality of distance measurements at a predetermined measurement rate. The predetermined measurement rate may be, for example, between 25kHz and 100 kHz.

[0060] During the period of time between consecutive ones of the plurality of processing operations the laser processing apparatus may be configured to adjust the beam steering apparatus (e.g. reconfigure the beam steering mirrors) to direct the laser processing beam at a start location for the next processing operation.

[0061] The laser processing apparatus may thus be configured to perform a non-processing stroke (i.e. causing the beam steering apparatus to move from the end location of a first processing operation to the start location of a next processing operation, while not directing a processing radiation beam at the target), while performing a plurality of distance measurements.

[0062] Performing a plurality of distance measurements between consecutive ones of the plurality of processing operations may comprise performing a first distance measurement prior to performing a first laser processing operation and performing a second distance measurement after performing the first laser processing operation.

[0063] 69947591-1The laser processing operation may be to apply a mark to the target using a processing radiation beam. Prior to doing so, a distance measurement may be made to ensure that the target is located an appropriate distance from the laser processing apparatus. After the mark has been applied, a second distance measurement can be made to check that the target is still located an appropriate distance from the laser processing apparatus. If the second distance measurement indicates that the target is not located an appropriate distance from the laser processing apparatus, action can be taken, such as preventing further processing operations on the target.

[0064] The or each laser processing operation may comprise a laser marking operation, and wherein performing the or each laser processing operation comprises creating a mark on the target.

[0065] The or each mark may have a start location and an end location. The mark may define a marking path extending from the start location to the end location. The mark may comprise a vector polygon. Performing the marking operation may comprise steering the laser processing beam along the marking path with the beam steering apparatus.

[0066] The method may further comprise creating a plurality of marks on the target, each mark having a respective start location and a respective end location, and defining a respective marking path extending from the respective start location to the respective end location.

[0067] The plurality of marks may comprise a respective plurality of marking strokes defining a plurality of characters, arranged in one or more lines.

[0068] The one or more lines may comprise a code. Each of the characters may comprise one or more marking strokes. Each of the characters may comprise an alphanumeric character (e.g. a letter or a digit).

[0069] The method may comprise performing a respective distance measurement before beginning to mark each of the one or more lines, and / or each of the plurality of characters, and / or each of the plurality of marking strokes, and wherein performing the marking of the line and / or character and / or marking stroke following each of the or each distance measurement may be based upon the respective measurement data.

[0070] 69947591-1For one or more of (or each of) the marking operations, the focal length may be adjusted based on measurement data obtained during an immediately preceding distance measurement. The immediately preceding distance measurement may be performed at substantially the same location as the start location of a next marking operation.

[0071] In this way, it is possible to track a complex or moving surface to ensure that the focal length is correctly set, even if the surface is not flat, or if the surface moves relative to the marking apparatus between individual marking strokes.

[0072] Creating the plurality of marks may comprise performing a plurality of marking operations, and the method may further comprising between consecutive ones of the plurality of marking operations, performing a non-marking operation comprising adjusting a configuration of the laser processing apparatus, and performing a plurality of distance measurements during the non-marking operation.

[0073] The non-marking operation may comprise adjusting the beam steering apparatus from addressing an end location of a preceding marking operation to addressing a start location of a subsequent marking operation.

[0074] That is, between marking strokes (i.e. movements of the beam steering mirrors that direct the marking radiation), there are often non-marking strokes, which are performed to allow the marking radiation to be correctly positioned at the start of the next marking stroke. During such non-marking strokes, one or more distance measurements may be performed so as to accurately track the position of the target surface. In this way, an accurate marking configuration can be achieved (e.g. since small focal adjustments can be made as needed between adjacent marking operations).

[0075] In a second aspect there is described a laser processing apparatus comprising, a distance measurement system configured to generate measurement data, an optical element configured to receive a processing radiation beam for use in a laser processing operation, a processor, and a memory storing computer readable instructions which when executed by the processor, cause the processor to carry out the method of the first aspect.

[0076] 69947591-1The laser processing apparatus may comprise a processing beam radiation source. The processing beam radiation source may comprise a laser. The laser processing apparatus may be configured to connect to an optical fiber carrying the processing beam.

[0077] The distance measurement system may comprise a measurement radiation source configured to generate a measurement radiation beam.

[0078] The optical element may comprise a dichroic mirror.

[0079] The optical element may be configured to direct the processing radiation beam towards the target.

[0080] The optical element may be further configured to receive measurement radiation; and, redirect one of the processing radiation beam and the measurement radiation to form a junction between a shared optical path, a processing radiation beam optical path and a measurement radiation optical path.

[0081] The measurement radiation may comprise a portion of a measurement radiation beam. The measurement radiation beam may be generated and directed at the target, and the reflected measurement radiation beam may be measurement radiation. The processing radiation beam and the measurement radiation beam may have different wavelengths. The optical element may direct the measurement radiation towards the distance measurement system.

[0082] The processing radiation beam and the measurement radiation beam may pass along at least a portion of a shared optical path. For example, when performing the distance measurement the measurement radiation beam may pass along at least a portion of the shared optical path from the target towards the laser processing apparatus. When performing the laser processing operation, the processing radiation beam may pass along at least a portion of the shared optical path from the laser processing apparatus towards the target.

[0083] The laser processing apparatus may comprise a focusing lens configured to receive the processing radiation beam.

[0084] 69947591-1The laser processing apparatus may comprise a focusing lens configured to receive a processing radiation beam comprising a first wavelength, wherein the distance measurement system may be configured to receive measurement radiation comprising a second wavelength that is different to the first wavelength.

[0085] The distance measurement system may generate the measurement data based at least partly based on the measurement radiation.

[0086] The laser processing apparatus may further comprise an adjustable focus system configured to adjust a focal length of the optical system in at least partial dependence upon the measurement data.

[0087] The distance measurement system may comprise a measurement radiation source configured to generate a measurement radiation beam.

[0088] The distance measurement system may be configured to detect at least a portion of the measurement radiation beam that reflects from the target. That is, the portion of the measurement radiation beam that reflects from the target may be measurement radiation.

[0089] The adjustable focus system may comprise a shared module located on the shared optical path configured to adjust focal lengths of the processing radiation beam and the measurement radiation beam in at least partial dependence upon the measurement data.

[0090] The shared module may comprise a movable lens. The movable lens may be movable along the shared optical path.

[0091] The shared module may comprise a variable optical path length assembly configured to define an optical path from an input to an output. The variable optical path length assembly may comprise a rotatable path length adjuster.

[0092] The shared module may be configured to set the focal lengths experienced by the processing radiation beam and the measurement radiation beam to be substantially equal to the distance indicated by the measurement data.

[0093] 69947591-1The laser processing apparatus may further comprise a beam steering apparatus configured to direct the processing radiation beam about the target.

[0094] The beam steering apparatus may be located on the shared optical path.

[0095] The beam steering apparatus may further be configured to direct the measurement radiation beam about the target.

[0096] The distance measurement system may comprises a first sensor region configured to generate a first signal that is proportional to an amount of measurement radiation incident on the first sensor region, a second sensor region configured to generate a second signal that is proportional to an amount of measurement radiation incident on the second sensor region, a sensor lens configured to receive measurement radiation from the target and illuminate the first and second sensor regions with the measurement radiation, and an optical arrangement configured to introduce an unequal distribution of measurement radiation between the first and second sensor regions that varies with a distance between the sensor lens and the target in accordance with a mathematical relationship.

[0097] The processor may be configured to determine the measurement data based at least partly based on, the first and second signals; and, the mathematical relationship.

[0098] The laser processing apparatus may comprise an I / O interface. The I / O may be configured to couple to one or more I / O devices, such as keyboards, mice, speaker systems, computer displays, user interfaces, and / or touchscreens.

[0099] Any feature described in the context of one aspect of the present disclosure can be applied to other aspects of the present disclosure.

[0100] Embodiments of the present disclosure will now be described, by way of example, with reference to the accompanying drawings, in which:

[0101] Figure 1 schematically depicts a laser processing apparatus in accordance with the present disclosure;

[0102] 69947591-1Figure 2 schematically depicts a distance measurement system in accordance with the present disclosure;

[0103] Figure 3 schematically depicts a ray diagram showing four target locations and corresponding image formation locations formed by the lens shown in Figure 2;

[0104] Figure 4A schematically depicts a ray diagram corresponding to that of Fig. 3 with a sensor plane present;

[0105] Figure 4B schematically depicts a view of the front of the sensor plane showing four cross-sectional areas of measurement radiation associated with the four target locations of Figure 3;

[0106] Figure 5 schematically depicts a front view of the first and second sensor regions of the distance measurement system of Figure 2 along with the cross-sectional areas of measurement radiation of Figures 4B;

[0107] Figure 6 shows a graph of a normalized difference between cross-sectional areas of measurement radiation incident on the first and second sensor regions with a varying distance between the target and the sensor lens for different values of focal length of the sensor lens;

[0108] Figure 7 is a schematic illustration of a laser processing apparatus carrying out a measurement operation;

[0109] Figure 8 is another schematic illustration of a laser processing apparatus carrying out a measurement operation;

[0110] Figure 9 is another schematic illustration of a laser processing apparatus carrying out a measurement operation;

[0111] Figure 10 is a schematic illustration showing possible beam paths for a measurement radiation beam;

[0112] 69947591-1Figure 11 is a schematic illustration of a collection of individual strokes to be applied by a laser processing apparatus;

[0113] Figure 12 is a further schematic illustration of a collection of individual strokes to be applied by a laser processing apparatus;

[0114] Figure 13 is a flow diagram according to the present disclosure; and

[0115] Figure 14 is a schematic illustration of a processing system.

[0116] Aspects and embodiments disclosed herein are not limited to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. Aspects and embodiments disclosed herein are capable of being practiced or of being carried out in various ways.

[0117] Aspects and embodiments disclosed herein include a marking head for projecting a radiation beam of a laser scanning or marking system and a laser scanning or marking system including such a system. Laser marking systems may be utilized in production lines for marking various types of articles. Laser marking systems may be utilized to imprint bar codes, unique identifying marks, expiration dates, or other information on items passing through a production line.

[0118] Laser processing systems, such as laser marking systems, may include the use of various sources such as CO2 lasers, fiber lasers, diode lasers, diode-pumped solid state lasers, etc. In some aspects and embodiments, laser processing systems may utilize lasers that operate in the ultraviolet, visible, or near infrared wavelengths or any other type of laser or optical illumination source. A laser processing system may also be referred to herein as a laser processing apparatus.

[0119] Figure 1 schematically depicts an optical system 300 comprising a focusing lens 302 configured to receive a processing radiation beam 304. The optical system 300 may comprise a processing radiation source (not shown) configured to generate the processing radiation beam 304. Alternatively, the optical system 300 may be configured to receive the processing radiation beam 304 from an external source via, for example, an optical fiber (not shown). The processing radiation beam 304 comprises a first

[0120] 69947591-1wavelength. The first wavelength may, for example, be about 1064 nm. In the example of Fig. 1 , the optical system 300 forms part of a laser processing apparatus, such a laser marking apparatus configured to mark a target 312. The laser marking apparatus comprises a beam steering mechanism 322, 324 (also referred to herein as a beam steering apparatus) configured to steer the processing radiation beam 304 about a marking field 326 of the laser marking system. In the example of Fig. 1, the beam steering mechanism comprises a pair of galvanometer-driven rotatable mirrors 322, 324. One of the mirrors 322, 324 is configured to steer the processing radiation beam 304 about a first axis and the other of the mirrors is configured to steer the processing radiation beam 304 about a second axis that is perpendicular to the first axis. As such, the beam steering mechanism 322, 324 acts to steer the processing radiation beam 304 to mark different locations about a two dimensional marking field 326. An example marking path 328 is shown in Fig. 1.

[0121] It is important that the processing radiation beam 304 is in focus at the desired processing location for desired processing of the target to occur. For example, marking errors may occur if a laser marking beam is not in focus at the desired location on a target. The total distance between the focusing lens 302 and the target 312 (e.g. a substrate) at least partly depends upon on a location of the processing radiation beam spot within the marking field 326. For example, for a substantially flat target arranged substantially perpendicularly to the laser processing apparatus, when the target is at the centre of the marking field 326, the distance between the focusing lens 302 and the target is at a minimum. When the target is at a peripheral corner of the marking field 326, the distance between the focusing lens 302 and the target 312 is at a maximum. Consequently, the processing radiation beam 304 is precisely in-focus only at the center of the marking field 326 (or on a concentric ring around the center of the marking field 326). At all other areas of the marking field 326, the processing radiation beam spot size on the target increases, which, in the example of laser marking, may cause different line widths when scribing and / or fading of marking content and / or even no substrate reaction at all. Any slight installation flaw in the laser processing apparatus may cause an undesired change in the distance between the focusing lens 302 and the target 312 or an undesired tilt angle between the target and the marking field 326. In addition, when laser processing more complex three-dimensional shapes such as beverage bottles, household cosmetic containers, etc., the distance between the focusing lens 302 and different parts of the target 312 varies.

[0122] 69947591-1The optical system 300 comprises a distance measurement system 306. The distance measurement system 306 is configured to receive measurement radiation 308 comprising a second wavelength that is different to the first wavelength. The second wavelength may be, for example, about 905 nm. The distance measurement system 306 is configured to generate a signal 342 at least partly based on the measurement radiation 308 that is indicative of a distance between a representative portion of the laser processing apparatus, such as the focusing lens 302, and a target 312 to be processed by the processing radiation beam 304. The signal 342 is referred to herein as measurement data. An example of a distance measurement system 306 is shown and described in connection with Figs. 2-4. Other distance measurement systems may be used such as, for example, a confocal pinhole distance measurement system. Alternatively, other distance measurement systems may utilise time of flight (ToF), LIDAR, or interferometry to obtain measurement data.

[0123] The optical system 300 comprises an optical element 314 configured to receive the processing radiation beam 304 and receive the measurement radiation 308. The optical element 314 is configured to redirect one of the processing radiation beam 304 and the measurement radiation 308 to form a junction between a shared optical path 316, a processing radiation beam optical path 318 and a measurement radiation optical path 320. In the example of Fig. 1, the optical element 314 comprises a dichroic mirror. The dichroic mirror has different reflection and transmission properties at two different wavelengths (i.e. the first wavelength of the processing radiation beam 304 and the second wavelength of the measurement radiation 308). The dichroic mirror 314 is configured to transmit substantially all of the processing radiation beam 304 and reflect substantially all of the measurement radiation 308. Other types of optical elements may be used such as, for example, a polarization-based optical element configured to have different reflection and transmission properties at two different polarizations, a coupling prism formed from wavelength-sensitive material that has different reflection and transmission properties at two different wavelengths, a metasurface, etc. The optical element 314 may act as a beam combiner to precisely set the outgoing processing radiation beam 304 and the incoming measurement radiation 308 coaxial to each other. By forming a shared optical path 316, the optical element 314 allows the distance measurement system 306 to measure the distance to the location on the target 213 that the processing radiation beam 304 is due to process. This increases an accuracy of the

[0124] 69947591-1optical system 300 compared to known optical systems. In the example of Fig. 1, the optical element 314 is located such that the junction between the processing radiation beam optical path 318 and the measurement radiation optical path 320 is located proximate the beam steering mechanism 322, 324. Other arrangements may be used. The optical system 300 may comprise one or more wavelength filters (not shown) on the measurement radiation optical path 320 configured to block wavelengths other than the second wavelength to protect components of the distance measurement system 306, e.g. from unwanted back reflections or other unwanted sources of light entering the optical system 300.

[0125] The optical system 300 comprises an adjustable focus system 330 configured to adjust a focal length of the optical system 300 in at least partial dependence upon the signal 342 generated by the distance measurement system 306. In the example of Fig. 1 , the adjustable focus system 330 comprises a movable lens 331 and the focusing lens 302. The movable lens 331 is movable along an optical axis of the focusing lens 302. The movable lens 331 may be movable relative to the focusing lens 302. The movable lens 331 is configured to expand the processing radiation beam 304 before the processing radiation beam 304 is incident upon the focusing lens 302. By moving the movable lens 331 , the processing radiation beam 304 is able to expand either more or less before being incident upon the focusing lens 302, thereby changing a focal length of the optical system 300. The adjustable focus system 330 may take other forms. For example, the adjustable focus system 330 may comprise a variable optical path length assembly configured to define an optical path from an input to an output. The variable optical path length assembly may comprise a rotatable path length adjuster. In the example of Fig.

[0126] 1, the optical system 300 comprises a controller 340 configured to receive the signal 342 generated by distance measurement system 306 and control the adjustable focus system 330 in at least partial dependence upon the signal 342. The adjustable focus system 330 may be configured to set the focal length of the optical system 300 to be substantially equal to the distance indicated by the signal 342. In the example of Fig. 1, the adjustable focus system comprises a processing radiation beam module located on the processing radiation beam optical path 318 configured to adjust a focal length experienced by the processing radiation beam 304 in at least partial dependence upon the signal 342. For example, if the distance measurement system 306 determines that the distance between the focusing lens 302 and the target 312 has increased (e.g. due to steering by the beam steering mechanism 322, 324 and / or due to movement of and / or

[0127] 69947591-1three-dimensional shape variation of the target), the controller 340 may control the adjustable focus system 330 to move the movable lens 331 such that the focal length experienced by the processing radiation beam 304 substantially matches the distance measured by the distance measurement system 306. In this way, the processing radiation beam 304 can be kept in-focus despite distance changes, thereby ensuring that desired laser processing can occur at the target 312.

[0128] A relationship between the distance measured by the distance measurement system 306 and a corresponding required position of the movable lens 331 to bring the processing radiation beam 304 into focus could be derived analytically and / or a calibration measurement may be performed to provide a database (e.g. a lookup table) of adjustable focus system setting values and / or some coefficients for a higher order equation that describes the behaviour of the adjustable focus system. The database of movable lens 331 positions and / or the set of coefficients may be stored in memory to be accessed by the controller 340. The database of movable lens 331 positions and / or the set of coefficients may be unique to a given optical system 300 (e.g. a laser marking head).

[0129] A focal depth of the processing radiation beam 304, once adjusted to the correct focal distance by the adjustable focus system 330, may be limited. For example, a beam diameter of about 250pm at a working distance from the focusing lens 302 of about 150mm would substantially increase for shorter or longer distances (i.e. for a mismatch between the required focal length and a focal length set by the adjustable focus system 330). Accurately setting a desired focal length by, for example, moving a movable lens 311 , changing optical path lengths, or other means, may not pose the greatest problem. A more complex problem involves measuring the distance between the focusing lens 302 and the target 312 with a required accuracy for at least some laser processing applications, such as laser marking. The required accuracy of the distance measurement may be derived from the Rayleigh length of the processing radiation beam 304 (i.e. the distance from the beam waist in the propagation direction where the beam radius is increased by a factor of the square root of two). In practice, the minimum achievable beam diameter at least partly depends on the wavelength of the processing radiation beam 304 and its beam quality.

[0130] For laser processing applications, such as laser marking, it is important to maintain a sufficiently small processing radiation beam 304 diameter at the target 312 to maintain

[0131] 69947591-1sufficient power density for desired processing to take place. As the focal length experienced by the processing radiation beam 304 moves away from an ideal focal length, the beam diameter of the processing radiation beam 304 increases in a substantially linear relationship with the distance from the ideal focal length. Problematically, if the processing radiation beam diameter increases by a factor of x then the power density of the processing radiation beam 304 would vastly decrease in accordance with an inverse square relationship (i.e. ^). In an area close to the ideal focal length however, the beam diameter increases at a significantly slower rate with increasing distance from the ideal focal length. This area extends from a negative value of the Rayleigh length to a positive value of the Rayleigh length on both sides of the optimal focus (both sides of the beam waist). This distance ZR is named Rayleigh length. As such, in order to allow for some margin of error, the distance measurement device preferably provides an accuracy that is equal to or better than the Rayleigh length of the processing radiation beam 304.

[0132] The Rayleigh length increases as the focal length experienced by the processing radiation beam 304 increases. As such, a required accuracy of the distance measurement performed by the distance measurement system 306 decreases as the focal length of the processing radiation beam 304 increases. That is, less accurate distance measurements are required at greater working distances. Providing a minimum absolute accuracy across the entire range of working distances of a laser processing system that would be sufficient for the smallest focal length would provide far more distance measurement accuracy (and hence complexity, cost and size) than what is actually needed at longer focal lengths (i.e. the majority of the working distances). Alternatively, providing a specified relative accuracy, which may be a constant percentage over the entire range of working distances, would also be significantly more accurate than what is actually required across greater focal lengths. The distance measurement system 306 described and depicted in connection with Figs. 2-4 advantageously provides a higher accuracy at smaller focal lengths and a lower (but still acceptable) accuracy at greater focal lengths, thereby satisfying the Rayleigh length requirement whilst avoiding complexity, cost and bulkiness.

[0133] Fig. 2 schematically depicts the distance measurement system 306 of Fig. 1 in greater detail. The distance measurement system 306 comprises first and second sensor regions 201, 202. The first sensor region 201 is configured to generate a first signal that

[0134] 69947591-1is proportional to an illuminated area of the first sensor region 201. The second sensor region 202 is configured to generate a second signal that is proportional to an illuminated area of the second sensor region 202. The distance measurement system 306 comprises a sensor lens 204 configured to receive measurement radiation 206d from the target 312 and illuminate the first and second sensor regions 201, 202 with the measurement radiation 206d. The distance measurement system 306 comprises an optical arrangement configured to introduce an unequal distribution of measurement radiation 206d between the first and second sensor regions 201, 202 that varies with a distance 208 between the sensor lens 204 and the target 312 in accordance with a mathematical relationship. In the example of Fig. 2, the optical arrangement comprises an offset between an optical axis 220 of the sensor lens 204 and a midpoint between the first and second sensor regions 201, 202. The distance measurement system 306 comprises a processor 210 configured to determine a distance between the distance measurement system 306 and the target 312 at least partly based on the first and second signals and the mathematical relationship. It will be appreciated that the distance may be converted or modified to align with another part of the laser processing apparatus, such as the focusing lens 302, or an output surface (e.g. exit window) of the laser processing apparatus. In the example of Fig. 2, the processor 210 is configured to determine the distance 208 between the sensor lens 204 and the target 312 at least partly based on the first and second signals and the mathematical relationship. The processor 210 may be configured to determine the distance between the target 312 and any fixed component of the distance measurement system 306. For example, the processor 210 may be configured to determine the distance between the target 312 and any one of the firstand second sensor regions 201, 202, the polarizing beamsplitter 218, etc. The positions of fixed components of the optical system 300, including the distance measurement system 306, relative to each other may be known. As such, determining the distance between the target 312 and one of the fixed components of the distance measurement system 306 would allow for the distance between the target 312 and all other fixed components of the optical system 300 to be determined (e.g. by adding or subtracting a known distance offset as necessary). For example, the distance between the sensor lens 204 and the target 312 is indicative of the distance between the focusing lens 302 of Fig. 1 and the target 312 given that the relative positions of the sensor lens 204 and the focusing lens 302 are known.

[0135] 69947591-1In the example of Fig. 2, the distance measurement system 306 comprises a measurement radiation source 212 configured to generate outgoing measurement radiation 206a. The measurement radiation source 212 may comprise a laser. The laser may comprise, for example, a laser diode or a diode-pumped solid state laser. The measurement radiation source 212 may be configured to generate pulsed electromagnetic radiation. The measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength that is typically used for LiDAR applications. For example, the measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of between about 1500nm and about 2000nm such as those used for meteorology and / or Doppler scientific LiDAR applications. As another example, the measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of between about 850nm and about 940nm such as those used for terrestrial mapping LiDAR applications. As a further example, the measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of between about 500nm and about 750nm such as those used for bathymetry LiDAR applications. As a yet further example, the measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of about 250nm such as those used for meteorology LiDAR applications. The measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of about 250nm or more. The measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of about 2000 nm or less. The measurement radiation source 212 may be configured to generate electromagnetic radiation having a wavelength of, for example, about 905 nm. In general, measurement radiation source 212 is configured to generated electromagnetic radiation having a wavelength that is different to the wavelength of the processing radiation beam. The wavelength of electromagnetic radiation generated by the measurement radiation source 212 may therefore vary depending on the type of lase processing that is to be performed. The distance measurement system 306 comprises a second lens 214 configured to receive the outgoing measurement radiation 206a generated by the measurement radiation source 212 and focus the outgoing measurement radiation 206a. In the example of Fig. 2, the distance measurement system 306 comprises a mirror 216 configured to receive the outgoing measurement radiation 206a from the second lens 214 and reflect the outgoing measurement radiation 206a towards a polarizing beamsplitter 218. In the example of Fig. 2, the measurement radiation source 212 is

[0136] 69947591-1configured to generate polarized outgoing measurement radiation 206a. The polarizing beamsplitter 218 is oriented relative to a polarization direction of the outgoing measurement radiation 206a such that the polarizing beamsplitter 218 reflects substantially all of the outgoing measurement radiation 206a along an optical axis 220 of the sensor lens 204.

[0137] The outgoing measurement radiation 206a is incident upon the target 312 and undergoes diffuse reflection from the target 312. A portion of the reflected measurement radiation 206b is reflected back towards the distance measurement system 306 along the same path as the outgoing measurement radiation 206a. That is, in the example of Fig. 2, a portion of the reflected measurement radiation 206b travels back towards the distance measurement system 306 along the optical axis 220 of the sensor lens 204. It will be appreciated that whilst a portion of the reflected measurement radiation 206b is coaxial with the outgoing measurement radiation 206a, said portion of reflected measurement radiation 206b may include individual light rays that are not substantially parallel to said axis. That is, the reflected measurement radiation 206b may comprise a divergent beam having its origin at the target 312. However, even if not substantially parallel, said light rays that are incident on the sensor lens 204 will form part of the first and second signals generated by the first and second sensor regions 201, 202. The outgoing measurement radiation 206a and the portion of the reflected measurement radiation 206b are co-axial. The portion of the reflected measurement radiation 206b is incident upon the polarizing beamsplitter 218. Due to undergoing diffuse reflection at the target 312, the portion of the reflected measurement radiation 206b lacks polarization. As such, the polarizing beamsplitter 218 reflects about half of the portion of the reflected measurement radiation 206c towards the mirror 216 (i.e. off the optical axis 220 of the sensor lens 204) and transmits about half of the portion of the reflected measurement radiation 206d towards the sensor lens 204. The sensor lens 204 focuses the transmitted half of the portion of the reflected measurement radiation 206d to the first and second sensor regions 201, 202.

[0138] In the example of Fig. 2, the measurement radiation source 212 and the first and second sensor regions 201, 202 are located within a single module 222. In other embodiments, the measurement radiation source 212 and the first and second sensor regions 201, 202 may be housed in separate modules.

[0139] 69947591-1Fig. 3 schematically depicts a ray diagram showing four target locations and corresponding image formation locations formed by the sensor lens 204 of Fig. 2. The sensor lens 204 has a focal length 228 and a radius 230. The lens equation may be used to determine a distance between a lens and an image formed by the lens as follows:

[0140] 1 _ 1 1

[0141] =D+d

[0142] where f is a focal length of the lens, D is a distance between an object and the lens, and d is a distance between the lens and an image of the object formed by the lens. The lens equation may be rearranged to the following equation:

[0143]

[0144] The above equations are derived using a thin lens approximation. That is, the above equations assume a thin lens (i.e. a lens having a thickness that is negligible relative to a radii of curvature of the lens’ surfaces) having a point light source placed at a distance D from the lens along an optical axis of the lens. In practice, the point source may correspond to an illuminated area of a target to be processed or a plasma formed on the target to be processed. The thin lens approximation allows optical effects due to the thickness of the lens to be excluded, thereby simplifying the ray diagram and associated calculations. It will be appreciated that strict adherence to the thin lens approximation may be not be necessary or possible in practice. Practical considerations such as, for example, a non-negligible thickness of the sensor lens 204 may result in optical behaviour that does not strictly adhere to the equations provided above. Nevertheless, it will be appreciated that such equations may be useful, but not necessarily essential, for understanding and implementing the invention.

[0145] Four different target locations 232, 234, 236, 238 are shown along the optical axis 220 of the sensor lens 204. A first target location 232 is a furthest distance away from the sensor lens 204. A second target location 234 is closer to the sensor lens 204 than the first target location 232. A third target location 236 is closer to the sensor lens 204 than the second target location 234. A fourth target location 238 is closest to the sensor lens 204. A first image 242 formed by the sensor lens 204 of the target located at the first target location 232 is closest to the sensor lens 204. A second image 244 formed by the sensor lens 204 of the target located at the second target location 234 is further away from the sensor lens 204 than the first image 242. A third image 246 formed by the sensor lens 204 of the target located at the third target location 236 is further away from the sensor lens 204 than the second image 244. A fourth image 244 formed by the

[0146] 69947591-1sensor lens 204 of the target located at the fourth target location 234 is furthest away from the sensor lens 204 (and is not visible in Fig. 3). As demonstrated by Fig. 3, the closer a target is to the sensor lens 204, the further away the image of the target is formed along the optical axis 220 of the sensor lens 204. As such, for relatively close targets, detecting the in-focus image directly would require a sensor to be located relatively far away from the sensor lens 204, resulting in a bulky distance measurement system. The distance measurement system of the present disclosure overcomes this problem through use of the optical arrangement and mathematical relationship.

[0147] Fig. 4A schematically depicts a ray diagram corresponding to that of Fig. 3 with a sensor plane 203 present. Fig. 4B schematically depicts a view of the front of the sensor plane 203 showing four cross-sectional areas of measurement radiation associated with the four target locations of Fig. 3. In the example of Fig. 4A, a separation 241 between the sensor lens 204 and the sensor plane 203 is less than the focal length 228 of the sensor lens 204. This arrangement may advantageously contribute to the mathematical relationship comprising a monotonic function (i.e. the mathematical relationship being entirely non-decreasing or entirely non-increasing) between a size of the cross-sectional area of the measurement radiation at the sensor plane 203 and the distance to the target, such that each cross-sectional area is uniquely coupled to a corresponding distance to the target. The separation 241 between the sensor lens 204 and the sensor plane 203 may, for example, be about 20mm or more. The separation 241 between the sensor lens 204 and the sensor plane 203 may, for example, be about 30mm or less. The sensor plane 203 and is arranged substantially perpendicularly to the optical axis 220 of the sensor lens 204. An area of the sensor plane 203 may be greater than or equal to an area of a circle formed by the radius 230 of the sensor lens 204. For example, in the case of a square or rectangular sensor 202, the width and the height of the sensor plane 203 may both be greater than or equal to a diameter of the sensor lens 204. A first cross-sectional area of measurement radiation 252 at the sensor plane 203 corresponds to the first target location 232. A second cross-sectional area of measurement radiation 254 at the sensor plane 203 corresponds to the second target location 234. A third cross-sectional area of measurement radiation 256 at the sensor plane 203 corresponds to the third target location 236. A fourth cross-sectional area of measurement radiation 258 at the sensor plane 203 corresponds to the fourth target location 238. Each distance between the sensor lens 204 and a target corresponds to an illuminated area on the sensor plane 203. As demonstrated by Figs. 4A and 4B, the closer a target is to the

[0148] 69947591-1sensor lens 204, the larger the cross-sectional area of the sensor plane 203 that is occupied by measurement radiation. The geometry of the ray diagram may be expressed by the following equation:

[0149] R r

[0150] d d — S

[0151] where R is the radius 230 of the sensor lens 204, d is the distance between the sensor lens 204 and an image 242-248 formed by the sensor lens 204, r is a radius of the illuminated area 252-258 of the sensor plane 203, and S is the separation 228 between the sensor lens 204 and the sensor plane 203. This equation can be solved for the image distance d as follows:

[0152]

[0153] Combining the above equation with the lens equation provides the following:

[0154] RS > Df

[0155] R — r D — f

[0156] which, when solved for the distance between the sensor lens 204 and the target 312, provides the following equation:

[0157]

[0158] Given that the radius of the lens R, the separation between the lens and the sensor plane S, and the focal length of the lens f are known, a distance between the lens and the target may be calculated by determining the radius of the illuminated area 252-258 of the sensor plane 203. The distance measurement system of the present disclosure achieves this through use of the optical arrangement and mathematical relationship.

[0159] Fig. 5 schematically depicts a front view of the first and second sensor regions 201, 202 of Fig. 2 along with the cross-sectional areas of measurement radiation 252-258 of Fig.

[0160] 4B. In the example of Figs. 2 and 5, the optical arrangement comprises an offset 260 between an optical axis 220 of the sensor lens (not shown in Fig. 5) and a midpoint 262 between the first and second sensor regions 201, 202. The first sensor region 201 is configured to generate a first signal that is proportional to an amount of measurement radiation incident on the first sensor region 201, and the second sensor region 202 is configured to generate a second signal that is proportional to an amount of measurement radiation incident on the second sensor region 202. The first and / or second sensor regions 201, 202 may have an area of about 3X3mm. A dividing line extends between the first and second sensor regions 201, 202 through the midpoint 262. The

[0161] 69947591-1measurement radiation incident on the sensor regions 201, 202 may be produced by diffuse reflection from the target or by emission from a plasma generated at the target, and therefore has a substantially constant energy density throughout its cross-section. As such, the first signal generated by the first sensor region 201 is proportional to the cross-sectional area of measurement radiation that is above the dividing line, and the second signal generated by the second sensor region 202 is proportional to the cross-sectional area of measurement radiation that is below the dividing line. This may be expressed by the following equations:

[0162] a = cA

[0163] b = cB

[0164] where a is the first signal generated by the first sensor region 201, A is the cross-sectional area of measurement radiation that is incident on the first sensor region 201 , b is the second signal generated by the second sensor region 202, B is the cross-sectional area of measurement radiation that is incident on the second sensor region 202, and c is a proportionality constant which may depend on, for example, one or more of a reflectivity of the target, an angle between the target surface and the measurement radiation beam, a distance to the target, etc.

[0165] The offset 260 introduces an unequal distribution of measurement radiation between the first and second sensor regions 201, 202 that varies with a distance between the lens and the target in accordance with a mathematical relationship. For the first cross-sectional area of measurement radiation 252 associated with the first target location 232, a first pair of cross-sectional areas A4, B4 of measurement radiation are incident on the sensor regions 201 , 202. For the second cross-sectional area of measurement radiation 254 associated with the second target location 234, a second pair of cross-sectional areas A3, B3 of measurement radiation are incident on the sensor regions 201, 202. For the third cross-sectional area of measurement radiation 256 associated with the third target location 236, a third pair of cross-sectional areas A2, B2 of measurement radiation are incident on the sensor regions 201, 202. For the fourth cross-sectional area of measurement radiation 258 associated with the fourth target location 238, a fourth pair of cross-sectional areas A1, Bi of measurement radiation are incident on the sensor regions 201 , 202. In the example of Fig. 5, the offset 260 ensures that the cross-sectional area of measurement radiation incident on the first sensor region A4-1 is less than the cross-sectional area of measurement radiation incident on the second sensor region B4-1. As such, the offset 260 ensures that the second signal produced by the second sensor

[0166] 69947591-1region 202 is always greater than the first signal generated by the first sensor region 201 for any given radius of measurement radiation r4-i. The circular segments of measurement radiation incident on each sensor region 201, 202 may be calculated as follows:

[0167]

[0168] where r is the radius of the cross-sectional area of measurement radiation incident on the first and second sensor regions 201 , 202 and h is the offset 260. It will be appreciated that the radius of the cross-sectional area of the measurement radiation incident on the first and second sensor regions 201, 202 must be greater than or equal to the offset 260 for both sensor regions 201, 202 to produce a signal. As such, it may be beneficial in some applications for a suitably small offset 260 to be used for larger target distances (and thus smaller cross-sectional areas of measurement radiation at the sensor regions) to be measured. However, in general, increasing the offset 260 provides greater differentiation between the first and second signals generated by the first and second sensor regions 201, 202, thereby improving measurement resolution and accuracy. As such, a balance may be struck for a given application based on desired working distance range and desired measurement accuracy and resolution. The size of the offset 260 may, in general, depend upon the size of the optical system and / or its components, such as the sensor lens. For example, for a sensor lens having a diameter of about 3mm, the offset 260 may be about 0.2mm or more. For example, for a sensor lens having a diameter of about 3mm, the offset 260 may be about 1 ,5mm or less. Larger offset may be used for larger sensor lenses.

[0169] It will be appreciated that other variables, such as the focal length of the sensor lens, may influence the distance measurement range. The focal length of the sensor lens may, for example, be about 10mm or more. The focal length of the sensor lens may, for example, be about 30mm or less. A normalised difference between the cross-sectional areas of measurement radiation incident on each sensor region 201, 202 may be calculated as follows:

[0170]

[0171] 69947591-1Given that the cross-sectional areas of measurement radiation incident on the sensor regions are proportional to the signals generated by the sensor regions, the normalized difference between the signals may be calculated as follows:

[0172]

[0173] where Si is the first signal generated by the first sensor region 201 and S2is the second signal generated by the second sensor region 202. Using a normalised difference advantageously cancels out various laser and / or target material variables that may vary between distance measurements. Fig. 6 shows a graph of the normalized difference W with a varying distance D between the target and the sensor lens for different values of focal length f of the sensor lens. In the example of Fig. 6, the distance between the target and the sensor lens varies from 0mm to 2000mm, and the focal length of the sensor lens varies from 10mm to 30mm. As shown by Fig. 6, smaller focal lengths result in smaller gradients and distance measurement ranges, whereas greater focal lengths result in greater gradient and greater distance measurement ranges. For example, for a focal length of 10mm, the normalized difference W varies from a minimum at a target distance of 0mm to a maximum at a target distance of about 650mm. For a focal length of 30mm, the normalized difference W varies from a minimum at a target distance of 0mm to a maximum at a target distance of about 2000mm. As such, the focal length of the sensor lens may be selected for a given application based on a desired working distance range and desired measurement accuracy and resolution.

[0174] A shown by the example of Fig. 6, and with reference to Fig. 2, the normalised difference W between the first and second signals (which corresponds to the unequal distribution of measurement radiation 206d between the first and second sensor regions 201 , 202) varies with the distance 208 between the sensor lens 204 and the target 312 in accordance with a mathematical relationship. That is, a mathematical relationship, such as a function and / or equation, may be used to convert the first and second signals generated by the first and second sensor regions 201 , 202 into a measurement of the distance 208 between the sensor lens 204 and the target 312. The mathematical relationship may be stored in memory for access by the processor 210 of the distance measurement system 306. The mathematical relationship may comprise an equation. The equation may be known via knowledge of the optical arrangement (e.g. the offset 260). For example, knowledge of optical principles (such as the lens equation previously described) and a geometry of the optical arrangement (such as the circular segments of measurement radiation described in relation to Fig. 5) may be used to determine an

[0175] 69947591-1equation that converts the first and second signals to the distance 208 between the sensor lens 204 and the target 312. Alternatively or additionally, the mathematical relationship may comprise a database, such as a lookup table. The database may comprise an input set of first and second signal values and a corresponding output set of distances 208 between the sensor lens 204 and the target 312. The database may be determined during manufacture of the distance measurement system 306 and stored in memory for access by the processor 210. Alternatively or additionally, the database may be determined in-situ via calibration measurements performed by a user of the distance measurement system 306. For example, the data shown in Fig. 6 may be used by the processor 210 to convert the first and second signals into distance measurements for a given distance measurement system 306.

[0176] The mathematical relationship may comprise a monotonic function. That is, the mathematical relationship may be entirely non-decreasing or entirely non-increasing. For example, as shown in Fig. 6, the normalised difference W between the first and second signals never decreases with increasing distance 208 between the sensor lens 204 and the target 312. The optical arrangement may be such that the illuminated areas A, B of the first and second sensor regions 201 , 202 do not increase as the distance between the sensor lens 204 and the target 312 increases. For example, as shown in Fig. 5, the cross-sectional areas A4-1, B4-1 of the measurement radiation on the sensor regions 201, 202 never increase as the distance between the target and the sensor lens increases.

[0177] The mathematical relationship may comprise a bijective function. That is, each input pair of first and second sensor signals may be associated with a unique output value of the distance 208 between the sensor lens 204 and the target 312. The mathematical relationship may comprise a substantially continuous bijective function. An inverse of the mathematical function may comprise a continuous function. The mathematical relationship may comprise a homeomorphism or a bicontinuous function. For example, as shown in Fig. 6, each normalised difference W between the first and second signals corresponds to a unique measurement of distance D between the sensor lens 204 and the target 312.

[0178] In general, the mathematical relationship allows different values of first and second signals to be converted to different distances 208 between the sensor lens 204 and the

[0179] 69947591-1target 312. It will be appreciated that strict adherence to the mathematical relationships described above may be not be necessary or possible in practice. Practical considerations such as, for example, a limited resolution of the distance measurement system 306 may result in input and output values that do not strictly adhere to the mathematical relationships described above. Nevertheless, it will be appreciated that such mathematical relationships may be useful, but not necessarily essential, for understanding and implementing the invention.

[0180] Figure 7 schematically illustrates a target 502 travelling along a conveyor 504 and arriving adjacent a laser processing apparatus 500. The laser processing apparatus 500 may comprise the optical system 300 described with respect to Figure 1. The laser processing apparatus comprises a distance measurement system, such as the distance measurement system 306 described with respect to Figure 2. It will however be appreciated that other distance measurement systems may be used. The target may be any suitable object to be processed. For example, the target 502, may be an object such as a box, carton, bottle, etc. The target 502 travels along conveyor belt 504 in direction A such that it is brought within the processing field 506 of the laser processing apparatus 500. When the target 500 is located within the processing field 506, the laser processing apparatus 500 processes the target 502. For example, the laser processing apparatus 500 may be a laser marking apparatus, configured to apply a mark on the target 502 when the target 502 enters the processing field 506.

[0181] As described above, the laser processing apparatus 500 may use one or more external sensor signals provided by, for example, a product detect sensor and a shaft encoder, to infer when the target 502 is in the processing field 506. However, as described above, use of such external sensor signals may not be reliable. In order to assist in reliably determining if the target 500 is actually within the processing field 506, the laser processing apparatus 500 can perform a distance measurement operation. The outcome of the distance measurement operation can be used to determine if the target 500 is in the processing field 506 and / or if the target 500 is incorrectly placed within the processing field 506.

[0182] The laser processing apparatus 500 performs the distance measurement operation by using a distance measurement system, such as that described above with respect to Figure 2 to generate a measurement radiation beam 512. The measurement radiation

[0183] 69947591-1beam 512 is directed towards an intended measurement location 530 on the target 502 using beam steering apparatus (such as the beam steering mechanism 322, 324 described above). The measurement location 530 may comprise an intended processing location. For example, the measurement location 530 may be a start location at which the start of a mark is to be applied. If a surface of the target 502, or any other surface, is present along the measurement radiation beam’s 512 path, a portion of the radiation contained within the measurement radiation beam 512 will be reflected by the surface. This reflected radiation will be diffuse and thus scattered in all directions such that a portion of the reflected radiation will pass back along at least a portion of the shared optical path 316 of the measurement radiation beam 512 and the processing radiation beam. Based on the arrangement described above, this portion of reflected radiation is received by the distance measurement system. The distance measurement system determines measurement data based on the received reflected radiation. The measurement data may be data indicative of a distance D1 between the target 502 (e.g. the surface of the target 502 at the measurement location 530) and a representative portion of the laser processing apparatus.

[0184] Any suitable portion of the laser processing apparatus 500 may be chosen as the representative portion. For example, the distance measurement system may calculate a measured value for a distance that the radiation beam travels, from the target 502 to a lens within the distance measurement system, such as sensor lens 204. Alternatively, the measured value can be modified to align with another part of the laser processing apparatus 500. For example, if the representative portion of the laser processing apparatus 500 is selected to be the focusing lens 302 of the processing radiation beam, then the known differential distance between the sensor lens 204 within the distance measurement system and the focusing lens 302 can be used to modify the value of the distance measured such that the modified value indicates the distance between the projection lens 302 and the target 502. If the representative portion of the laser processing apparatus 500 is selected to be a part of a housing of the laser processing apparatus 500, then the known differential distance between the lens 204 within the distance measurement system and the portion of the housing can be used to modify the value of the distance measured such that the value indicates the distance between the portion of the housing and the target 502.

[0185] 69947591-1Based on the measurement data, a laser processing operation may be performed. For example, if it is determined that the measurement data indicates that the target 502 is present in the processing field 506, the laser processing apparatus may be perform a processing operation by generating and directing a processing radiation beam onto the target 502. The determination that the measurement data indicates that the target 502 is present in the processing field 506 may comprise determining that the measurement data satisfies a processing condition. Determining that the measurement data satisfies the processing condition may, for example, comprise comparing the measurement data to threshold data. Threshold data may indicate one or more thresholds that define distances from the representative portion of the laser processing apparatus 500 at which a processing radiation beam can be applied.

[0186] Figure 7 illustrates two thresholds. A first threshold 508 is shown which indicates a maximum distance T 1 from the representative portion of the laser processing apparatus 500 (e.g. the focusing lens) at which a target 502 can be in order to be processed. The first threshold may be referred to as a maximum processing distance. A second threshold 510 is shown which indicates a minimum distance T2 from the representative portion of the laser processing apparatus 500 (e.g. the focusing lens) at which a target 502 can be in order to be processed. The second threshold may be referred to as a minimum processing distance. The thresholds 508, 510 are shown as straight lines in the Figures, but it will be appreciated that the thresholds 508, 510 may be curved, having radii equal to T1, T2 respectively, and with origin of the curves aligned with the representative portion of the laser processing apparatus 500.

[0187] It will be appreciated that two thresholds may not be required. For example, only a single threshold may be used, such as the first threshold 508. The thresholds 508, 510 may be set based on the dimensions of the target being processed. For example, if it is known where a surface of the target should normally be located to be processed, the thresholds can be set a predefined distance from this known location. The predefined distance may be sufficient to allow for tolerances in the targets and / or in the conveyor 504. One or more thresholds may be set at manufacture of the laser processing apparatus 500 and / or may be configurable to account for a particular target. For example, the laser processing apparatus 500 may be capable of focusing a processing radiation beam between a range, such as 100 mm and 200 mm. However, a target 500 to be processed may be processed ata nominal distance between 100 mm and 200 mm, such as 166 mm. In this

[0188] 69947591-1case, the distance T1 of the first threshold 508 may be set as 167 mm and the distance T2 of the second threshold 510 may be set at 165 mm. This would allow to + / - 1 mm tolerance to any movement of the target during conveyance. It will be appreciated, of course, that the tolerances may vary depending upon various characteristics of the laser processing apparatus.

[0189] With reference to Figure 8, there is shown a schematic illustration of a situation in which the target 502 has fallen over onto its side during conveyance. For example, the target may have been initially upright when placed onto the conveyor belt 504, with the intention that a top surface is to be processed. However, during transport the target 502 has accidentally been displaced onto its side. As such, the target 502 is now not correctly positioned to be processed. That is, the surface that was intended to be processed is not aligned to receive a processing radiation beam. Furthermore, the target 502 is now too far from the laser processing apparatus 500 to be processed without possible adverse effects, such as poor processing quality or increased safety risk.

[0190] Prior to processing the target 502, the laser processing apparatus 500 performs a distance measurement operation described above, by directing measurement radiation beam 514 towards the target 502 and monitoring the reflected radiation. Based on the distance measurement operation, measurement data is generated that indicates a distance D2 between the target 502 and the portion of the laser processing apparatus 500 (e.g. the focusing lens). The laser processing apparatus 500 compares the measurement data with the threshold data. More specifically, the laser processing apparatus 500 compares distance D2 with the distance T1 of the first threshold 508 and determines that D2 is greater than T1. As such, the laser processing apparatus 500 can determine that the target 502 is beyond a maximum distance at which processing can take place, and can thus take appropriate action. For example, the laser processing apparatus 500 may not generate and direct the processing radiation beam onto the target 502. The laser processing apparatus may output an alert. The alert may be any suitable alert. For example, the alert may be an audio alert generated by a speaker system. Alternative, or additionally, the alert may be a visual alert generated by a computer display. In this way, a user can be informed of the issue and can take appropriate action if necessary. Alternatively, or additionally, if the measurement data does not satisfy the processing condition, a fault condition may be generated. The fault condition may be configured to cause the processing line to stop.

[0191] 69947591-1The processing condition may be referred to as a safety condition, since satisfying the processing condition may enable a process to be performed more safely.

[0192] In the situation shown in Figure 8, in the absence of the distance measurement operation as described, the laser processing apparatus 500 would have used the external signals, such as those provided by the product detect sensor and encoder shaft, to infer that the target 502 is present in the processing field 506, and would have proceeded to process the target 502. This may have led to adverse effects, such as poor processing quality or an increased safety risk.

[0193] Figure 9 shows a situation in which the target 502 is too close to the laser processing apparatus 500 to be processed. In this case the measured distance D3 is less than the distance T2 of the second threshold 510. By performing the distance measurement operation, the laser processing apparatus can determine that D3 is less than T2 and can thus take appropriate action, such as not carrying out a processing operation on the target 502. Such a situation may occur if an incorrect target is installed on the conveyor, if the target has been accidentally deformed during conveyance, or a foreign object (e.g. an operator’s hand, a piece of misplaced equipment), is present that is too close to the laser processing apparatus 500.

[0194] Figure 10 shows a schematic illustration similar to Figures 7, 8 and 9, but where first, second, third and fourth possible paths for measurement radiation beams 516, 518, 520, 522 are shown. The possible paths for measurement radiation beams 516, 518, 520, 522 are shown at different angles relative to the vertical axis of the figure to illustrate the fact that the processing radiation beam will sweep across the target surface by sweeping through an angular displacement via the beam steering apparatus, as described above. The first and second possible paths for measurement radiation beams 516, 518, shown in solid lines, terminate at the surface of the target 502 and are within the thresholds 508, 510. As such, the first and second possible paths for measurement radiation beams 516, 518 represent locations at which the processing radiation beam can be applied. The third and fourth possible paths for measurement radiation beams 520, 522, shown in a dotted lines, extend past the target 502 and do no terminate until they reach the conveyor 504. As such, the third and fourth possible paths for measurement radiation beams 520, 522

[0195] 69947591-1extend beyond the first threshold 508, and thus represent locations at which the processing radiation beam cannot be applied.

[0196] Given that processing a target will often comprise performing a single processing operation will that extends over a surface of the target, or a plurality of processing operations that extend over the surface of the target, it can be advantageous to carry out multiple distance measurement operation at different locations over the surface of the target. This can help identify issues, such as if the target 502 is not correctly aligned (e.g. too far forward, or too far behind, a nominal position within the processing field), if the target 502 is deformed, or if the wrong target 502 is located on the conveyor.

[0197] The distance measurement operation may be carried out immediately prior to processing the target 502. For example, when it is determined that the target 502 is likely within the processing field 506 (based on external sensor signals, for example), the laser processing apparatus 500 may first perform the distance measurement operation. The outcome of the distance measurement operation may then be used to determine whether or not to process the target 502. Alternatively, or additionally, the outcome of the distance measurement operation may be used to set one or more characteristics of the processing radiation beam. For example, based on the distance measurement operation, a focal length of the processing radiation beam may be determined and set.

[0198] Multiple (i.e. a plurality of) distance measurement operations may be carried out during the application of the mark, or wider mark. For example, during the application of a complex mark which is applied by multiple processing operations, multiple distance measurement operations may be performed, e.g. between consecutive ones of the processing operations. A distance measurement operation may be carried out over any suitable frequency. For example, a distance measurement operation may be carried out prior to the start of each processing step (or operation). In the case where processing is marking, a distance measurement operation may be carried prior to applying each mark. The mark may be an individual stroke that forms part of a wider mark, such as part of a character, such as an alpha-numeric character, part of code, such as a barcode, or part of an image. When applying an individual stroke, sometimes referred to as vector polygon, the laser processing apparatus 500 will direct the processing radiation beam onto the target and, using the beam steering apparatus described above, will sweep the processing radiation beam across the target from a start location to an end location to

[0199] 69947591-1form the mark. The path followed by the processing radiation beam may be referred to as a marking path. Once the individual stroke is applied the processing radiation beam is turned off, and the beam steering apparatus moves such that the processing radiation beam’s path aligns with the start location of the next stroke. Movement of the beam steering apparatus may be referred to as a non-marking operation.

[0200] A schematic illustration of a collection of individual strokes is shown in Figure 11, where the wider mark to be applied is the word “TEXT”. The word “TEXT” is formed of several individual strokes, shown as solid lines in Figure 11 having arrows showing the direction of application (e.g. the direction of sweep of the processing radiation beam, or the marking path for each stroke). The dotted lines in Figure 11 connect individual strokes and show how the beam path sweeps across the target when the processing radiation beam is powered down between strokes, sometimes referred to as vector jumps, or nonmarking operations. A measurement operation takes place at the start of each stroke in Figure 11, highlighted by the solid circles. The first measurement operation takes place at measurement location 530 (as shown in Figure 7), which in the example is the bottom portion of the vertical stroke that makes up the letter “T”.

[0201] While not shown in Figure 11, a distance measurement operation may also take place at the end of each stroke. That is, after a mark, such as an individual stroke, has been applied, a distance measurement operation can take place in order to check that the target 502 is still located an appropriate distance from the laser processing apparatus 500. If this distance measurement indicates that the target 502 is not located an appropriate distance from the laser processing apparatus 500, action can be taken, such as preventing further processing operations on the target. Thus, a plurality of distance measurements may be performed, each one being performed between consecutive ones of a plurality of processing (e.g. marking) operations. Each of the laser processing operations following a distance measurement may be performed based on the corresponding measurement data. It will be understood, however, that it is not necessary for a distance measurement to be performed after (or before) every processing operation.

[0202] Additionally, or alternatively, a distance measurement operation may take place during vector jumps. For example, Figure 12 shows the schematic illustration of Figure 11, but where a distance measurement operation is also carried out at multiple positions along

[0203] 69947591-1vector jumps (indicated by the solid circles). That is, a plurality of distance measurements may be performed between consecutive ones of a plurality of processing operations. Advantageously, carrying out distance measurement operations during vector jumps does not slow down processing throughput as the process does not need to be interrupted by the distance measurement operation. The measurement frequency during vector jumps could be any suitable frequency, such as 25KHz - 100kHz.

[0204] Alternatively, or alternatively, rather than perform a distance measurement operation at the start of each stroke, and / or during vector jumps, a distance measurement operation may be carried out at the start of each new line. For example, where the processing is to apply multiple lines of text, or marks, to a target, a distance measurement operation may take place at the start, and optionally end, of each new line.

[0205] That is, a plurality of distance measurements may be performed between consecutive ones of a plurality of processing operations. For example, for one or more of the marking operations, a first distance measurement may be performed prior to performing the marking operation, and a second distance measurement may be performed after performing the marking operation.

[0206] Alternatively, or alternatively, distance measurement operations may take place before beginning to mark each of a plurality of characters. For example, where the wider mark to be applied is the word “TEXT”, a measurement operation may take place before each individual letter is applied.

[0207] With reference to Figure 13, there is now described a method 600 of processing a target 502 with a laser processing apparatus 500.

[0208] At step 602, a distance measurement is performed comprising generating measurement data indicative of a distance between the target and a portion of the laser processing apparatus, wherein performing the distance measurement comprises radiation passing along at least a portion of a shared optical path from the target towards the laser processing apparatus. The distance measurement may be that described above.

[0209] At step 604, a laser processing operation is performed based on the measurement data, wherein performing the laser processing operation comprises radiation passing along at

[0210] 69947591-1least a portion of the shared optical path from the laser processing apparatus towards the target. For example, the processing operation may be conditional on the distance measurement (i.e. the measurement data). As described above, if the measurement data indicates that the target is not located in a desirable location, such as being located beyond a threshold, the processing operation may be omitted. Alternatively, or additionally, the processing operation may be controlled based on the measurement data. For example, a focus length of the radiation (e.g. processing radiation beam) may be set based on the measurement data.

[0211] Any suitable processing system may be used to implement the described methods. The processing system may be incorporated into, or otherwise coupled to, the laser processing apparatus described above. Figure 14 schematically illustrates an example processing system 1800. The processing system 1800 comprises the processor 1802 which is configured to read and execute instructions stored in either (or both) a volatile memory 1803a which may take the form of a random access memory and a non-volatile memory 1803b. The memories 1803a, 1803b may store instructions for execution by the processor 1802 and data used by those instructions. For example, the instructions may include the instructions for causing the laser processing apparatus to carry out any method described herein.

[0212] The processing system 1800 may further comprises an I / O interface 1806 to which peripheral devices may be connected. For example, a display 1813 may be configured so as to display output from the processing system 1800. Input devices may also be connected to the I / O interface 1806. Such input devices may include a keyboard 1811 and a mouse 1812 which allow user interaction with the processing system 1800. Of course, it will be appreciated that the input devices and display may be combined in a touch screen arrangement. The processing system 1800 may comprise a network interface 1810, allowing the processing system 1800 to be connected to appropriate computer networks, such as the Internet or an intranet, and so as to be able to send and receive from and to other computing devices. The processor 1802, volatile memory 1803a, the storage device 1803b, I / O interface 1806, and network interface 1810, are connected together by a bus 1814. It will be appreciated that the arrangement of components illustrated in Figure 14 is merely exemplary, and that the processing system 1800 may comprise additional or fewer components than those illustrated in Figure 14.

[0213] 69947591-1M&C PM365878W0

[0214] 41

[0215] Although specific embodiments have been described above, it will be appreciated that various modifications can be made to the described embodiments without departing from the scope of the claims. That is, the described embodiments are to be considered in all respects exemplary. In particular, where a particular form has been described for particular processing, it will be appreciated that such processing may be carried out in any suitable form arranged to provide suitable output data.

[0216] 69947591-1

Claims

42CLAIMS:

1. A method of processing a target with a laser processing apparatus, the method comprising:performing a distance measurement comprising generating measurement data indicative of a distance between the target and a portion of the laser processing apparatus, wherein performing the distance measurement comprises radiation passing along at least a portion of a shared optical path from the target towards the laser processing apparatus;performing a laser processing operation based on the measurement data, wherein performing the laser processing operation comprises radiation passing along at least a portion of the shared optical path from the laser processing apparatus towards the target.

2. The method of claim 1, wherein performing the laser processing operation comprises directing a processing radiation beam along the shared optical path towards a processing location on the target by a beam steering apparatus.

3. The method of claim 2, wherein performing the distance measurement comprises:receiving, by the beam steering apparatus, measurement radiation from the target along the shared optical path;directing, by the beam steering apparatus, the measurement radiation towards a distance measurement system; andgenerating the measurement data based upon the measurement radiation.

4. The method of claim 3, wherein performing the distance measurement further comprises:directing, by the beam steering apparatus, a measurement radiation beam towards a measurement location along at least a portion of the shared optical path from the laser processing apparatus towards the target;wherein the received measurement radiation comprises at least a portion of the radiation contained within the measurement radiation beam that has been reflected by a surface at the measurement location.69947591-1435. The method of any one of claims 2 to 4, wherein performing the distance measurement further comprises receiving the measurement radiation from the beam steering apparatus and directing at least a portion of the received measurement radiation towards a distance measurement system.

6. The method of any preceding claim, further comprising receiving a processing trigger signal, the processing trigger signal comprising a signal indicating that:a target for processing is at an intended processing location;a target for processing has entered a processing region containing the intended processing location;a target for processing is expected to be at the intended processing location at a predetermined future time; ora target for processing is expected to be at the intended processing location after travelling a predetermined distance.

7. The method of any preceding claim, wherein performing the laser processing operation based on the measurement data comprises:if the measurement data satisfies a processing condition performing the laser processing operation; andif the measurement data does not satisfy the processing condition, not performing the laser processing operation.

8. The method of claim 7, wherein the processing condition comprises the measurement data being greater than a minimum processing distance.

9. The method of claim 7 or 8, wherein the processing condition comprises the measurement data being less than a maximum processing distance.

10. The method of any preceding claim, wherein performing the laser processing operation based on the measurement data comprises controlling a focal length of a laser processing beam based on the measurement data.

11. The method of any preceding claim, comprising:performing a plurality of processing operations on the target, each one of the plurality of processing operations comprising directing the processing radiation beam69947591-144towards a respective processing location by the beam steering apparatus along the shared optical path; andperforming a plurality of distance measurements, each one of the plurality of distance measurements comprising generating measurement data indicative of a distance between a respective measurement location of the target and a portion of the laser processing apparatus;wherein:each of the plurality of distance measurements is performed between consecutive ones of the plurality of processing operations; and each of the laser processing operations following a distance measurement is performed based on the corresponding measurement data.

12. The method of claim 11, comprising performing a plurality of distance measurements between consecutive ones of the plurality of processing operations.

13. The method of claim 12, wherein performing a plurality of distance measurements between consecutive ones of the plurality of processing operations comprises performing a first distance measurement prior to performing a first laser processing operation and performing a second distance measurement after performing the first laser processing operation.

14. The method of any preceding claim, wherein the or each laser processing operation comprises a laser marking operation, and wherein performing the or each laser processing operation comprises creating a mark on the target.

15. The method of claim 14, further comprising creating a plurality of marks on the target, each mark having a respective start location and a respective end location, and defining a respective marking path extending from the respective start location to the respective end location.

16. The method of claim 15, wherein the plurality of marks comprises a respective plurality of marking strokes defining a plurality of characters, arranged in one or more lines.69947591-117. The method of claim 16, wherein the method comprises performing a respective distance measurement before beginning to mark:each of the one or more lines; and / oreach of the plurality of characters; and / oreach of the plurality of marking strokes; and wherein:performing the marking of the line and / or character and / or marking stroke following each of the or each distance measurement is based upon the respective measurement data.

18. The method of any one of claims 15 to 17, wherein creating the plurality of marks comprises performing a plurality of marking operations the method further comprising:between consecutive ones of the plurality of marking operations, performing a non-marking operation comprising adjusting a configuration of the laser processing apparatus; andperforming a plurality of distance measurements during the non-marking operation.

19. A laser processing apparatus comprising:a distance measurement system configured to generate measurement data; an optical element configured to receive a processing radiation beam for use in a laser processing operation;a processor;a memory storing computer readable instructions which when executed by the processor, cause the processor to carry out the method of any preceding claim.

20. The laser processing apparatus of claim 19, wherein the optical element is further configured to:receive measurement radiation; and,redirect one of the processing radiation beam and the measurement radiation to form a junction between a shared optical path, a processing radiation beam optical path and a measurement radiation optical path.

21. The laser processing apparatus of claim 19 or 20, wherein the laser processing apparatus comprises a focusing lens configured to receive a processing radiation beam comprising a first wavelength;69947591-1M&C PM365878W046wherein the distance measurement system is configured to:receive measurement radiation comprising a second wavelength that is different to the first wavelength.

22. The laser processing apparatus of any of claims 19 to 21, comprising an adjustable focus system configured to adjust a focal length of the optical system in at least partial dependence upon the measurement data.

23. The laser processing apparatus of any of claims 19 to 22, wherein the distance measurement system comprises a measurement radiation source configured to generate a measurement radiation beam.

24. The laser processing apparatus of any of claims 19 to 23, further comprising a beam steering apparatus configured to direct the processing radiation beam about the target.69947591-1

Images