Patent Description:
The present invention relates to laser welding and more particularly, to a laser welding head according to the preamble of claim <NUM> (see for example <CIT>), with dual movable mirrors providing beam movement and laser welding systems and methods using same.

Lasers such as fiber lasers are often used for materials processing applications such as welding. A conventional laser welding head includes a collimator for collimating laser light and a focus lens for focusing the laser light to a target area to be welded. The beam may be moved in various patterns to facilitate welding two structures along a seam, for example, using a stir welding technique. One way to move the beam for stir welding is to rotate the beam using rotating prism optics to form a rotating or spiral pattern. Another way to move a beam for welding is to pivot or move the entire weld head on an X-Y stage to form a zig zag pattern. These conventional methods of moving the beam to perform weld patterns do not allow quick and precise movements of the beam.

According to a first aspect of the present invention, a laser welding head is defined in claim <NUM>, and includes a collimator configured to be coupled to an output fiber of a fiber laser and at least first and second movable mirrors configured to receive a collimated laser beam from the collimator and to move the beam in first and second axes within only a limited field of view defined by a scan angle of about <NUM>-<NUM>°. The laser welding head also includes a focus lens configured to focus the laser beam relative to a workpiece while the beam is moved.

Consistent with another embodiment, a laser welding head includes a collimator configured to be coupled to an output fiber of a fiber laser, at least first and second movable mirrors configured to receive a collimated laser beam from the collimator and to move the beam in first and second axes, and at least first and second thermal sensors proximate the first and second movable mirrors, respectively, and configured to detect a thermal condition. The laser welding head also includes a focus lens configured to focus the laser beam.

Consistent with a further embodiment, a laser welding head includes a collimator module including a collimator configured to be coupled to an output fiber of a fiber laser and a wobbler module coupled to the collimator module. The wobbler module includes at least first and second movable mirrors configured to receive a collimated laser beam from the collimator and to move the beam in first and second axes. The laser welding head also includes a core block module coupled to the wobbler module. The core block module includes at least a focus lens configured to focus the laser beam.

These and other features and advantages will be better understood by reading the following detailed description, taken together with the drawings wherein:.

A laser welding head with movable mirrors is used to perform welding operations, for example, with wobble patterns and/or seam finding/tracking and following. The movable mirrors provide a wobbling movement of one or more beams within a relatively small field of view defined by a scan angle of <NUM>-<NUM>°. The movable mirrors may be galvanometer mirrors that are controllable by a control system including a galvo controller. The laser welding head may also include a diffractive optical element to shape the beam or beams being moved. The control system may also be used to control the fiber laser, for example, in response to the position of the beams relative to the workpiece and/or a sensed condition in the welding head such as a thermal condition proximate one of the mirrors.

Referring to <FIG>, a laser welding system <NUM> includes a laser welding head <NUM> coupled to an output fiber <NUM> of a fiber laser <NUM> (e.g., with a connector 111a). The laser welding head <NUM> may be used to perform welding on a workpiece <NUM>, by welding a seam <NUM> to form a weld bead <NUM>. The laser welding head <NUM> and/or the workpiece <NUM> may be moved relative to each other along the direction of the seam <NUM>. The laser welding head <NUM> may be located on a motion stage <NUM> for moving the welding head <NUM> relative to the workpiece <NUM> along at least one axis, for example, along the length of the seam <NUM>. Additionally or alternatively, the workpiece <NUM> may be located on a motion stage <NUM> for moving the workpiece <NUM> relative to the laser welding head <NUM>.

The fiber laser <NUM> may include an Ytterbium fiber laser capable of generating a laser in the near infrared spectral range (e.g., <NUM>-<NUM>). The Ytterbium fiber laser may be a single mode or multi-mode continuous wave Ytterbum fiber laser capable of generating a laser beam with power up to <NUM> kW in some embodiments and higher powers up to <NUM> kW in other embodiments. Examples of the fiber laser <NUM> include the YLR SM Series or YLR HP Series lasers available from IPG Photonics Corporation. The fiber laser <NUM> may also include a multi-beam fiber laser, such as the type disclosed in International Application No. PCT/<CIT> filed <NUM> August <NUM> and entitled Multibeam Fiber Laser System, which is capable of selectively delivering one or more laser beams through multiple fibers.

The laser welding head <NUM> generally includes a collimator <NUM> for collimating the laser beam from the output fiber <NUM>, at least first and second movable mirrors <NUM>, <NUM> for reflecting and moving the collimated beam <NUM>, and a focus lens <NUM> for focusing and delivering a focused beam <NUM> to the workpiece <NUM>. In the illustrated embodiment, a fixed mirror <NUM> is also used to direct the collimated laser beam <NUM> from the second movable mirror <NUM> to the focus lens <NUM>. The collimator <NUM>, the movable mirrors <NUM>, <NUM>, and the focus lens <NUM> and fixed mirror <NUM> may be provided in separate modules <NUM>, <NUM>, <NUM> that may be coupled together, as will be described in greater detail below. The laser welding head <NUM> may also be constructed without the fixed mirror <NUM>, for example, if the mirrors <NUM>, <NUM> are arranged such that the light is reflected from the second mirror <NUM> toward the focus lens <NUM>.

The movable mirrors <NUM>, <NUM> are pivotable about different axes <NUM>, <NUM> to cause the collimated beam <NUM> to move and thus to cause the focused beam <NUM> to move relative to the workpiece <NUM> in at least two different perpendicular axes <NUM>, <NUM>. The movable mirrors <NUM>, <NUM> may be galvanometer mirrors that are movable by galvo motors, which are capable of reversing direction quickly. In other embodiments, other mechanisms may be used to move the mirrors such as stepper motors. Using the movable mirrors <NUM>, <NUM> in the laser welding head <NUM> allows the laser beam <NUM> to be moved precisely, controllably and quickly for purposes of seam finding and following and/or beam wobbling without having to move the entire welding head <NUM> and without using rotating prisms.

According to the present invention, movable mirrors <NUM>, <NUM> move the beam <NUM> within only a relatively small field of view (e.g., less than <NUM> x <NUM>) by pivoting the beam <NUM> within a scan angle α of less than <NUM>° and more particularly about <NUM>-<NUM>°, as shown in <FIG>, thereby allowing the beam to wobble. In contrast, conventional laser scan heads generally provide movement of the laser beam within a much larger field of view (e.g., larger than <NUM> x <NUM> and as large as <NUM> x <NUM>) and are designed to accommodate the larger field of view and scan angle. Thus, the use of the movable mirrors <NUM>, <NUM> to provide only a relatively small field of view in the laser welding head <NUM> is counter-intuitive and contrary to the conventional wisdom of providing a wider field of view when using galvo scanners. Limiting the field of view and the scan angle provides advantages when using galvo mirrors in the welding head <NUM>, for example, by enabling faster speeds, allowing use with less expensive components such as lenses, and by allowing use with accessories such as air knife and/or gas assist accessories.

Because of the smaller field of view and scan angle in the example embodiment of the welding head <NUM>, the second mirror <NUM> may be substantially the same size as the first mirror <NUM>. In contrast, conventional galvo scanners generally use a larger second mirror to provide for the larger field of view and scan angle and the larger second mirror may limit the speed of movement in at least one axis. A smaller sized second mirror <NUM> (e.g., about the same size as the first mirror <NUM>) in the welding head <NUM> thus enables the mirror <NUM> to move with faster speeds as compared to larger mirrors in conventional galvo scanners providing large scan angles.

The focus lens <NUM> may include focus lenses known for use in laser welding heads and having a variety of focal lengths ranging, for example, from <NUM> to <NUM>. Conventional laser scan heads use multi-element scanning lenses, such as an F theta lens, a field flattening lens, or a telecentric lens, with much larger diameters (e.g., a <NUM> diameter lens for a <NUM> diameter beam) to focus the beam within the larger field of view. Because the movable mirrors <NUM>, <NUM> are moving the beam within a relatively small field of view, according to the present invention, a larger multi-element scanning lens (e.g., an F theta lens) is not required and not used. In one example embodiment of the welding head <NUM> consistent with the present disclosure, a <NUM> diameter plano convex F300 focus lens may be used to focus a beam having a diameter of about <NUM> for movement within a field of view of about <NUM> x <NUM>. The use of the smaller focus lens <NUM> also allows additional accessories, such as air knife and/or gas assist accessories, to be used at the end of the welding head <NUM>. The larger scanning lenses required for conventional laser scan heads limited the use of such accessories.

Other optical components may also be used in the laser welding head <NUM> such as a beam splitter for splitting the laser beam to provide at least two beam spots for welding (e.g., on either side of the weld). Additional optical components may also include diffractive optics and may be positioned between the collimator <NUM> and the mirrors <NUM>, <NUM>, as will be described in greater detail below.

A protective window <NUM> may be provided in front of the lens <NUM> to protect the lens and other optics from the debris produced by the welding process. The laser welding head <NUM> may also include a welding head accessory <NUM>, such as an air knife for providing high velocity air flow across the protective window <NUM> or focus lens <NUM> to remove the debris and/or a gas assist accessory to deliver shield gas coaxially or off-axis to the weld site to suppress weld plume. Thus, the laser welding head <NUM> with movable mirrors is capable of being used with existing welding head accessories.

The illustrated embodiment of the laser welding system <NUM> also includes a detector <NUM>, such as a camera, for detecting and locating the seam <NUM>, for example, at a location in advance of the beam <NUM>. Although the camera/detector <NUM> is shown schematically at one side of the welding head <NUM>, the camera/detector <NUM> may be directed through the welding head <NUM> to detect and locate the seam <NUM>.

The illustrated embodiment of the laser welding system <NUM> further includes a control system <NUM> for controlling the fiber laser <NUM>, the positioning of the movable mirrors <NUM>, <NUM>, and/or the motion stages <NUM>, <NUM>, for example, in response to sensed conditions in the welding head <NUM>, a detected location of the seam <NUM>, and/or movement and/or a position of the laser beam <NUM>. The laser welding head <NUM> may include sensors such as first and second thermal sensors <NUM>, <NUM> proximate the respective first and second movable mirrors <NUM>, <NUM> to sense thermal conditions. The control system <NUM> is electrically connected to the sensors <NUM>, <NUM> for receiving data to monitor the thermal conditions proximate the movable mirrors <NUM>, <NUM>. The control system <NUM> may also monitor the welding operation by receiving data from the camera/detector <NUM>, for example, representing a detected location of the seam <NUM>.

The control system <NUM> may control the fiber laser <NUM>, for example, by shutting off the laser, changing the laser parameters (e.g., laser power), or adjusting any other adjustable laser parameter. The control system <NUM> may cause the fiber laser <NUM> to shut off in response to a sensed condition in the laser welding head <NUM>. The sensed condition may be a thermal condition sensed by one or both of the sensors <NUM>, <NUM> and indicative of a mirror malfunction resulting in high temperatures or other conditions caused by the high power laser.

The control system <NUM> may cause the fiber laser <NUM> to shut off by triggering a safety interlock. A safety interlock is configured between the output fiber <NUM> and the collimator <NUM> such that the safety interlock condition is triggered and the laser is shut off when the output fiber <NUM> is disconnected from the collimator <NUM>. In the illustrated embodiment, the laser welding head <NUM> includes an interlock path <NUM> that extends the safety interlock feature to the movable mirrors <NUM>, <NUM>. The interlock path <NUM> extends between the output fiber <NUM> and the control system <NUM> to allow the control system <NUM> to trigger the safety interlock condition in response to potentially hazardous conditions detected in the laser welding head <NUM>. In this embodiment, the control system <NUM> may cause the safety interlock condition to be triggered via the interlock path <NUM> in response to a predefined thermal condition detected by one or both sensors <NUM>, <NUM>.

The control system <NUM> may also control the laser parameters (e.g., laser power) in response to movement or a position of the beam <NUM> without turning off the laser <NUM>. If one of the movable mirrors <NUM>, <NUM> moves the beam <NUM> out of range or too slowly, the control system <NUM> may reduce the laser power to control the energy of the beam spot dynamically to avoid damage by the laser. The control system <NUM> may further control selection of laser beams in a multi-beam fiber laser.

The control system <NUM> may also control the positioning of the movable mirrors <NUM>, <NUM> in response to the detected location of the seam <NUM> from the camera/detector <NUM>, for example, to correct the position of the focused beam <NUM> to find, track and/or follow the seam <NUM>. The control system <NUM> may find the seam <NUM> by identifying a location of the seam <NUM> using the data from the camera/detector <NUM> and then moving one or both of the mirrors <NUM>, <NUM> until the beam <NUM> coincides with the seam <NUM>. The control system <NUM> may follow the seam <NUM> by moving one or both of the mirrors <NUM>, <NUM> to adjust or correct the position of the beam <NUM> continuously such that the beam coincides with the seam <NUM> as the beam <NUM> moves along the seam to perform the weld. The control system <NUM> may also control one or both of the movable mirrors <NUM>, <NUM> to provide the wobble movement during welding, as described in greater detail below.

The control system <NUM> thus includes both laser control and mirror control working together to control both the laser and the mirrors together. The control system <NUM> may include, for example, hardware (e.g., a general purpose computer) and software known for use in controlling fiber lasers and galvo mirrors. Existing galvo control software may be used, for example, and modified to allow the galvo mirrors to be controlled as described herein.

<FIG> illustrate examples of wobble patterns that may be used to perform stir welding of a seam <NUM>. As used herein, "wobble" refers to reciprocating movement of a laser beam (e.g., in two axes) and within a relatively small field of view defined by a scan angle of less than <NUM>°. <FIG> show a circular pattern and a <FIG> pattern, respectively, being formed sequentially along the seam <NUM>. <FIG> show a zig-zag pattern and an undulating pattern, respectively, being formed along the seam <NUM>. Although certain wobble patterns are illustrated, other wobble patterns are within the scope of the present disclosure. One advantage of using the movable mirrors in the laser welding head <NUM> is the ability to move the beam according to a variety of different wobble patterns.

<FIG> illustrate a comparison of welds formed by a <FIG> wobble pattern (<FIG>) compared to a conventional non-manipulated beam (<FIG>). In one example (<FIG>), a two pieces of aluminum <NUM>-T6 alloy are welded with a <NUM> diameter beam spot moving with a <FIG> pattern at <NUM>° with a <NUM> wobble, a power of <NUM> kW, a speed of <NUM>/min and with a <NUM> in. In the other example (<FIG>), two pieces of aluminum <NUM>-T6 alloy are welded with a beam spot with no wobble, a power of <NUM> kW, a speed of <NUM>/min and with a <NUM> in. As shown, the weld quality on the surface with the <FIG> wobble is improved as compared to the non-manipulated beam. In particular, uniformity through the weld is improved as shown in <FIG> compared to <FIG>. The cross section in <FIG> also shows less reduction in area at the weld (as compared to <FIG>), which is due to the <FIG> wobble pattern bridging the gap of the seam <NUM> more effectively. The laser welding systems and methods described herein may also be used to improve welding with materials, such as titanium, that are typically difficult to weld.

<FIG> illustrate an embodiment of the laser welding head <NUM> in greater detail. Although one specific embodiment is shown, other embodiments of the laser welding head is included within the scope of protection as defined in the appended claims. As shown in <FIG>, the laser welding head <NUM> includes a collimator module <NUM>, a wobbler module <NUM>, and a core block module <NUM>. The wobbler module <NUM> includes the first and second movable mirrors as discussed above and is coupled between the collimator module <NUM> and the core block module <NUM>.

<FIG> show the collimator module <NUM> in greater detail. As shown in <FIG>, an input end <NUM> of the collimator module <NUM> is configured to be coupled to an output fiber connector and includes a fiber interlock connector <NUM> that connects to the output fiber connector (not shown) to provide a safety interlock for when the output fiber is disconnected. As shown in <FIG>, an output end <NUM> of the collimator module <NUM> is configured to be coupled to the wobbler module <NUM> (see <FIG>) and includes a fiber interlock connector <NUM> to extend the safety interlock path into the wobbler module <NUM>. The collimator module <NUM> may include a collimator (not shown) with a fixed pair of collimator lenses such as the type known for use in laser welding heads. In other embodiments, the collimator may include other lens configurations, such as movable lenses, capable of adjusting the beam spot size and/or focal point.

<FIG> show the wobbler module <NUM> in greater detail. The illustrated embodiment of the wobbler module <NUM> includes an input aperture <NUM> for coupling to the collimator module <NUM> and an output aperture <NUM> for coupling to the core block module <NUM> (see <FIG>). The input aperture <NUM> may include a water cooled limiting aperture.

As shown in <FIG>, the illustrated embodiment of the wobbler module <NUM> also includes first and second galvanometers <NUM>, <NUM> for moving galvo mirrors <NUM>, <NUM> about different perpendicular axes. Galvanometers known for use in laser scanning heads may be used. The galvanometers <NUM>, <NUM> may include connections <NUM> for connecting to a galvo controller (not shown). The galvo controller may include hardware and/or software for controlling the galvanometers to control movement of the mirrors and thus movement and/or positioning of the laser beam. Known galvo control software may be used and may be modified to provide the functionality described herein, for example, the seam finding, the wobbler patterns, and communication with the laser.

As shown in <FIG>, the wobbler module <NUM> includes a fiber interlock connector <NUM> for connecting to the collimator fiber interlock connector <NUM>. The wobbler module <NUM> also includes a galvo fiber interlock connector <NUM> for connecting to the galvo controller. The safety interlock is thus extended to the wobbler module <NUM> and to the galvo controller. The galvo controller may be configured to trigger a safety interlock condition, for example, in response to sensed conditions within the wobbler module <NUM>.

As shown in <FIG>, the wobbler module <NUM> includes thermal probes <NUM>, <NUM> proximate each of the respective mirrors <NUM>, <NUM>. The thermal probes <NUM>, <NUM> sense a thermal condition (e.g., temperature) at the respective locations within the wobbler module <NUM> and may be connected via the galvo connections <NUM> to the galvo controller. The galvo controller may thus monitor the thermal probes <NUM>, <NUM> to determine if a predefined condition occurs, such as a high temperature indicating a potentially hazardous condition within the wobbler module <NUM>. If one of the movable mirrors <NUM>, <NUM> malfunctions, for example, the high power laser directed into the wobbler module <NUM> may not be reflected properly and may cause the hazardous condition. The galvo controller may thus trigger the safety interlock to shut down the laser in response to the hazardous condition. The thermal probes may include known sensors such as bimetal strips inside of ceramic.

<FIG> shows the core block module <NUM> in greater detail. The core block module <NUM> includes a fixed mirror (not shown) that redirects the beam received from the wobbler module <NUM> to a focus lens <NUM> and then to the workpiece. As shown, the core block module <NUM> includes a core block housing <NUM> and a focus and window housing <NUM> coupled to one side of the core block housing <NUM>. A camera module (not shown) may be coupled to an opposite side of the core block housing <NUM> for monitoring the focused beam and/or the workpiece within the field of view provided through the focus and window housing <NUM>.

The focus and window housing <NUM> contains the focus lens <NUM> and a protective window <NUM>. As shown in <FIG>, the protective window <NUM> may be removable and replaceable. The focus and window housing <NUM> also contains a window status monitoring circuit <NUM> with sensors such as a thermistor <NUM> and photodiode <NUM> to monitor a status of the protective window <NUM>. The core block housing <NUM> further includes a status monitoring connector connector <NUM> for connecting to the status monitoring circuit <NUM> in the focus and window housing <NUM> and a welding monitor connector <NUM> for connecting to a welding head monitor (not shown).

<FIG> show the assembled laser welding head <NUM> with each of the modules <NUM>, <NUM>, <NUM> coupled together and emitting a focused beam <NUM>. A laser beam coupled into the collimator module <NUM> is collimated and the collimated beam is directed to the wobbler module <NUM>. The wobbler module <NUM> moves the collimated beam using the mirrors and directs the moving collimated beam to the core block module <NUM>. The core block module <NUM> then focuses the moving beam and the focused beam <NUM> is directed to a workpiece (not shown).

<FIG> shows the path of a collimated beam <NUM> inside of the wobbler module <NUM> and the core block module <NUM> when coupled together. As shown, the collimated beam <NUM> input to the wobbler module is reflected from the first galvo mirror <NUM> to the second galvo mirror <NUM> and then reflected from the fixed mirror <NUM> inside the core block module and output from the core block module. The fixed mirror <NUM> may be an infrared mirror to allow use with a camera for monitoring the beam <NUM>.

Referring to <FIG>, further arrangements of a laser welding head <NUM> with movable mirrors and a laser welding system are described in greater detail. This arrangement of the laser welding head <NUM> further includes at least one beam shaping diffractive optical element <NUM> for shaping the beam. The beam shaping diffractive optical element <NUM> is located between a collimator <NUM> and movable mirrors <NUM>, <NUM> in the welding head <NUM>. The beam shaping diffractive optical element <NUM> shapes the collimated beam and the shaped beam is then moved by the mirrors <NUM>, <NUM>, for example, as described above.

One example of the beam shaping diffractive optical element <NUM> includes a top hat beam shaping element that receives an input beam with a Gaussian profile and circular beam spot, as shown in <FIG>, and produces a shaped beam with a uniform square or "top hat" profile and a rectangular or square beam spot, as shown in <FIG>. Other beam shaping diffractive optical elements may include, without limitation, a diffractive beam splitting element that converts an input beam into a <NUM> or <NUM> dimensional array of beamlets, a ring generator element that shapes an input beam into a ring or a series of rings, and a diffractive vortex lens that shapes an input beam into a donut-shaped ring, as shown in <FIG>.

Different beam shaping diffractive optical elements <NUM> may thus be used providing different shapes and/or sizes of beams. A donut shaped beam spot may also have a more uniform power distribution by eliminating a high power concentration at the center of the beam. As shown in <FIG>, different diffractive optical elements may provide rectangular beams having different sizes, thereby enabling different "brush sizes" and resolutions for welding and other applications. Smaller beam spots or "brush sizes" may be used, for example, for smaller areas or around edges where a higher resolution is desired.

In an embodiment, the beam shaping diffractive optical element <NUM> is located in a beam shaping module <NUM>, which may be removably positioned between a collimator module <NUM> and a wobbler module <NUM>, for example, as described above. Thus, beam shaping modules <NUM> with different diffractive optics may be used interchangeably in the welding head <NUM>. The beam shaping module <NUM> may also provide a safety interlock path <NUM> as described above.

In yet another arrangement, the welding head <NUM> may be coupled to a multi-beam fiber laser <NUM> capable of selectively delivering multiple beams. One example of a multi-beam fiber laser is described in greater detail in International Application No. PCT/<CIT> filed <NUM> August <NUM> and entitled Multibeam Fiber Laser System. The multiple beams may have different characteristics such as different modes, powers, energy densities, profiles and/or sizes. <FIG>, for example, shows multiple beams having different sizes. Multiple beams may be delivered at the same time or individual beams with different characteristics may be delivered separately and selectively at different times to provide different operations (e.g., heating, welding, and post-processing). Multiple beams may also be shaped by the diffractive optics <NUM> to produce multiple shaped beams, for example, as shown in <FIG>. The shape and/or size of multiple beams may thus be changed for different operations or applications using the multi-beam fiber laser <NUM> and/or different diffractive optical elements <NUM>. For some welding applications, for example, one or more beams may be shaped in a ring or donut shape to provide more uniform power distribution.

Accordingly, a laser welding head with movable mirrors, consistent with embodiments described herein, allows improved control over the movement, size, and/or shape of a laser beam used for various welding applications. Embodiments of the laser welding head with movable mirrors may thus be used to form stronger, smoother and more uniform welds.

Claim 1:
A laser welding head (<NUM>) comprising:
a collimator (<NUM>) configured to be coupled to an output fiber of a fiber laser (<NUM>);
at least first and second movable mirrors (<NUM>, <NUM>) configured to receive a collimated laser beam (<NUM>) from the collimator (<NUM>);
a focus lens (<NUM>) configured to focus the laser beam relative to a workpiece while the beam is moved; and
characterized in that the at least first and second movable mirrors (<NUM>, <NUM>) are configured to move the beam (<NUM>) in first and second axes within only a limited field of view defined by a scan angle of about <NUM>-<NUM>°; and
in that the focus lens (<NUM>) is not a scanning lens and is not a multi-element scanning lens, wherein an F theta lens is a multi-element scanning lens.