Eliminating head-to-head offsets along common chuck travel direction in multi-head laser machining systems

The embodiments disclosed herein provide systems and methods for correcting a head-to-head offset in a laser machining system with two or more processing heads. A focusing lens is associated with each processing head, and is configured to receive an incident laser beam along an incident beam axis of propagation. The incident beam axis of propagation is offset from the primary axis of the focusing lens. The focusing lens is further configured to rotate about the incident beam axis of propagation in order to steer the incident laser beam's path with respect to a workpiece.

TECHNICAL FIELD

This disclosure relates to multi-head laser machining systems with a common part carrier, and in particular, to systems and methods for correcting a head-to-head offset in such systems.

BACKGROUND INFORMATION

A laser machining system, in which a plurality of processing heads share a common part carrier (“chuck”), may exhibit a head-to-head offset along the direction of chuck travel. A head-to-head offset is a misalignment between the processing heads in the direction of chuck travel. Failing to correct a head-to-head offset may result in degradation of the laser machining system's accuracy and performance.

FIG. 1illustrates a two-head laser processing system100with a head-to-head offset160. The system100includes a chuck142that moves a workpiece143in the direction of the Y-axis (as indicated by arrow138). The chuck is shared by a processing head126and a processing head130, which may concurrently process the workpiece143. The processing heads126,130are connected to an X-axis beam132. The processing heads126,130may move independently along the X-axis beam132, in the direction of the X-axis (as indicated by arrows134,136). The processing heads126,130emit laser beams120,128. Each processing head126,130is optically associated with a focusing lens112,110that focuses a respective incident laser beams128,120on the workpiece143. As illustrated, the head-to-head offset160is a misalignment of the laser beams128,120in the direction of chuck travel. Because the chuck142is shared between the processing heads126,130, the head-to-head offset160may not be corrected by repositioning the chuck142.

There are at least three common ways of addressing a head-to-head offset in a laser processing system: 1) the offsets are measured, and the chuck is commanded to move to an “average” position that minimizes the maximum deviation from the desired location for any one head; 2) the offsets are measured, and then eliminated as much as possible by adjusting the position of one or both processing heads in the direction of chuck travel (e.g., by using shims or set-screws); or 3) in the case of laser processing systems that include a secondary beam positioner (such as a tip-tilt mirror or a pair of galvanometers) for each processing head, the offsets are measured and compensated for by the secondary beam positioner. There are substantial problems with the three standard approaches outlined above for correcting a head-to-head offset. The details of the three standard approaches are illustrated inFIGS. 2,3, and4.

FIG. 2illustrates a prior art approach for minimizing the error introduced by a head-to-head offset. This approach “splits the differences” of a head-to-head offset260between the processing heads226,230by commanding a chuck242to move to an average or “compromise” position. Using this approach, the chuck242is positioned such that two target feature locations270,274are along a line262that is at the midpoint of the head-to-head offset260. As will be appreciated, the two processing heads226,230cannot create the features at the target feature locations270,274because of the head-to-head offset260. Accordingly, the distance between the actual feature locations272,276and the target feature locations270,274, respectively, is half of the total head-to-head offset260. While this approach minimizes the worst-case feature placement error introduced by a head-to-head offset260, this approach does not improve the spread of feature placement error, which remains equal to the total head-to-head offset260.

FIG. 3illustrates another prior art approach for correcting a head-to-head offset360between the processing heads326,330by adjusting the position of a processing head330in the direction of chuck travel. In this approach, the processing head330is moved from a first position to a second position (shown as repositioned processing head330′ in phantom lines). The repositioning of the processing head330is in the direction of chuck travel (the Y-axis direction), and may thus compensate for the head-to-head offset360. In other words, the repositioned processing head330′ may be aligned with the processing head326. The processing head330may be repositioned by using shims or set screws. While this approach corrects the head-to-head offset360, designing a processing head that allows for repositioning along the direction of chuck travel may be difficult, and the procedure for correcting the head-to-head offset360by repositioning the processing head330may also be difficult and time-consuming. A processing head that can be repositioned with respect to the X-axis beam332, may not be as secure as a processing head that is permanently attached to the X-axis beam332. This degraded stage stiffness may introduce vibration into the system when the processing head is moved. Finally, set screws or shims may move over time, which may cause the head-to-head offset to return.

FIG. 4illustrates another prior art approach, where one or more secondary beam positioners480,485are used to compensate for a head-to-head offset460. Two processing heads (not shown) may be optically associated with the secondary beam positioners480,485. Each processing head may emit an incident laser beam420,428. The secondary beam positioners480,485may each include a pair of galvanometers481,482and486,487connected to beam steering mirrors483,484and488,489, respectively. The secondary beam positioners480,485allows the incident laser beams420,428to be quickly steered within respective limited scan fields490,492. The secondary beam positioners480,485enable “fast” laser beam steering because the laser beams420,428may be repositioned without moving the processing head (not shown) or the chuck442. As illustrated, the secondary beam positioner485may be positioned so as to eliminate the head-to-head offset460. This approach, however, requires sacrificing a portion of the limited scan field492associated with the secondary beam positioner485. Only a portion491of the total limited scan field492may be used when the secondary beam positioner485is used to correct a head-to-head offset460. While this approach may be tolerable in cases where the head-to-head offset is small in relation to the total limited scan field492, this approach imposes additional limitations. For example, in laser machining systems that use assist gas flow that is substantially coaxial with the processing laser beam, the limited scan field may already be severely restricted because of a nozzle with a small orifice to direct the assist gas flow. In such systems, there may not be a substantial portion within the limited scan field to sacrifice for head-to-head offset compensation purposes.

SUMMARY OF THE DISCLOSURE

This disclosure relates to multi-head laser machining systems and, in particular, to systems and methods for correcting a head-to-head offset in systems in which multiple processing laser heads share a common part carrier. In one embodiment, a focusing lens is associated with each processing head, and is configured to receive an incident laser beam along an incident beam axis of propagation. The incident beam axis of propagation is offset from the primary axis of the focusing lens. The focusing lens is further configured to rotate about the incident beam axis of propagation in order to steer the incident laser beam's path with respect to a workpiece.

In another embodiment, a method is employed to steer an incident laser beam's path with respect to a workpiece. According to the method, a plurality of laser beams are emitted and are focused at respective target locations on the workpiece using a focusing lens. The laser beams are received along an incident beam axis of propagation, which is offset from a primary axis of the focusing lens. The focusing lens may be rotated about the incident beam axis of propagation to steer the incident laser beam's path with respect to the workpiece. The laser beam's path may be steered to a point where a head-to-head offset is eliminated.

In certain embodiments, the offset between the incident beam axis of propagation and the primary axis of the focusing lens is adjustable. In one embodiment, the offset may be introduced by a mechanical offset adapter.

In another embodiment, a secondary beam positioner may steer the incident laser beam within a limited scan field. The secondary beam positioner may include a pair of galvanometers. Each galvanometer may be connected to a steering mirror. In another embodiment, the secondary beam positioner may include a tip-tilt mirror.

In another embodiment, an assist gas flow may be used in conjunction with the incident laser beam. A nozzle may include an orifice through which an assist gas flows along a flow axis, and through which the incident laser beam propagates. The flow axis may be substantially coaxial with the incident beam axis of propagation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, numerous specific details are provided for a thorough understanding of the embodiments disclosed herein. However, those skilled in the art will recognize that the embodiments can be practiced without one or more of the specific details, or with other methods, components, or materials. Further, in some cases, well-known structures, materials, or operations are not shown or described in detail in order to avoid obscuring aspects of the embodiments. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

As illustrated inFIGS. 5A,5B,5C, and5D, a focusing lens510may be used to focus and deflect an incident laser beam520. The focusing lens510may be embodied as a single-element lens, or it may be embodied as a multi-element lens. In various embodiments, the focusing lens510may be formed of glass, fused silica, or any other suitable material known to one having skill in the art. InFIG. 5A, the focusing lens510is symmetrical about a primary axis of the focusing lens530and is a converging lens. The focusing lens's focal distance578is the distance at which the incident beam520converges to a focal point540. When the incident beam axis of propagation of the incident laser beam520is coaxial with the primary axis of the focusing lens530, the focal point540is collinear with the primary axis of the focusing lens530.

InFIG. 5B, the incident beam axis of propagation522of an incident laser beam520is offset a distance595from the primary axis of the focusing lens530. If the focusing lens510is at its focal length578, the focal point540is collinear with the primary axis of the focusing lens530, and the distance between the focal point540and the incident beam axis of propagation522is equal to the distance of the offset595.

FIG. 5Cshows a perspective view illustrating the result of rotating the focusing lens510by 180 degrees about the incident beam axis of propagation522. The rotated position is shown in phantom lines. When the incident beam520passes through the rotated focusing lens510′, the resulting focal point540′ is opposite from the focal point540with respect to the incident beam axis of propagation522. Accordingly, if the focusing lens510is at its focal length, the focal point540remains collinear with the primary axis of the focusing lens530, and the distance between the focal point540and the incident beam axis of propagation522is equal to the distance of the offset595.

The focusing lens510may be arbitrarily rotated about the incident beam axis of propagation522. As the focusing lens510is rotated about the incident beam axis of propagation522, the focal point540follows a circular trajectory544, with the center of the circular trajectory544being collinear with the incident beam axis of propagation522and with a radius equal to the offset595between the incident beam axis of propagation522and the primary axis of the focusing lens530. The circular trajectory544is in the plane defined by the X-axis and the Y-axis.

FIG. 5Dillustrates that the radius of the circular trajectory544may be increased by increasing the distance595between the primary axis of the focusing lens530and the incident beam axis of propagation522. The radius of the circular trajectory544resulting from rotating the focusing lens510about the incident beam axis of propagation522is correspondingly increased. By rotating the focusing lens510, the focal point540is moved in the direction of the Y-axis.

FIG. 6illustrates a laser processing system600with a head-to-head offset660. The system600comprises a chuck642carrying a workpiece643. The chuck642moves the workpiece643in the direction of the Y-axis (as indicated by arrow638). Focusing lenses610,612are disposed in the optical path of laser beams620,628. Offsets695,696are present between the axes of beam propagation622,624of the incident laser beams620,628and the primary axes of the focusing lenses630,631. The focusing lenses610,612are rotateable about their respective axes of beam propagation622,624.

Rotating the focusing lens610about its incident beam axis of propagation622allows the focal point640to be steered in a circular trajectory644on a workpiece643. The circular trajectory644is in the plane of the surface of the chuck642and the workpiece643(i.e., the plane defined by the X-axis and the Y-axis). Because the direction of chuck travel is in the plane of the chuck642, the focal point640may be manipulated in the direction of chuck travel (i.e., the Y-axis) by rotating the focusing lens610to a desired location. The circular trajectory644has a component of motion in a direction perpendicular to the chuck axis of travel (i.e., the X-axis); however, the processing heads (not shown) may be movable along the X-axis, and thus may be able to compensate for movement in the X-axis caused by rotating the focusing lens610about the incident beam axis of propagation622.

As is illustrated inFIG. 6, the focusing lens610is rotated from a first position to a second position (shown as rotated focusing lens610′ in phantom lines). The rotated focusing lens610′ has been rotated by an angle662. Rotating the focusing lens610between the first position and the second position moves the focal point640of the incident laser beam620along the circular trajectory644to a focal point640′ such that the head-to-head offset660is substantially eliminated. The radius of the circular trajectory644(assuming the lens610is at its focal length) is equal to the offset695between the incident beam axis of propagation622and the primary axis of the focusing lens630.

As illustrated, the laser beam620may have a non-vertical angle of attack with respect to the workpiece643. The non-vertical angle of attack may advantageously prevent back-reflections of the incident laser beam620.

It will be appreciated by those having skill in the art that for a multi-head laser machining system having N number of processing heads, only N−1 of those processing heads need be equipped for offset and rotation of their associated focusing lenses. Such an arrangement might be problematic in practice, however, because it forces all N−1 “adjustable” processing heads to match the nonadjustable processing head, which may not be possible, depending on the amount of offset one is trying to compensate for. If, by chance, the one nonadjustable processing head happens to have an offset itself, there would be a halving of the overall adjustment range (in a worst case scenario) by keeping that processing head fixed and trying to adjust all other processing heads to match it.

FIG. 7shows an embodiment of a laser processing system that includes secondary beam positioners780,785optically associated with two processing heads (not shown). Each secondary beam positioner780,785comprises a pair of galvanometers781,782and786,787. The galvanometers781,782and786,787are connected to respective mirrors783,784and788,789that steer respective laser beams720,728. The laser beams720,728are focused and deflected by focusing lenses710,712. The focusing lens710has been rotated about an incident beam axis of propagation722so as to compensate for a head-to-head offset (not shown). Accordingly, the secondary beam positioners780,785are able to steer the laser beams720,728within the full areas of their respective limited scan fields790,791. In alternative embodiments, a secondary beam positioner may comprise a tip-tilt mirror.

An offset between an axis of propagation of an incident laser beam and the primary axis of a focusing lens may be created by an offset adaptor800.FIGS. 8A,8B, and8C illustrate one embodiment of an offset adaptor800. InFIG. 8A, a first end801of the offset adapter800may be connected to a processing head (not shown) configured to emit a laser beam. A second end802may be connected to a cutting head containing a focusing lens (not shown). As illustrated in the cross-section view shown inFIG. 8B, a first section805of the offset adaptor800may be symmetrical about a first axis803, while a second section808may be symmetrical about a second axis804.FIG. 8Cshows a top view looking through the offset adaptor800and further illustrates the offset between the axes of symmetry803,804(each designated by a “+” symbol) of the first end801and the second end802, respectively. The offset adaptor800may be manufactured from aluminum, stainless steel, or the like. In other embodiments, the offset between the axes of symmetry803,804may be adjustable.

The offset adaptor800may be incorporated into a laser processing system where the first axis803corresponds to an axis of propagation of an incident laser beam and the second axis804corresponds to a primary axis of a focusing lens. In this way, an offset may be created between the axis of propagation of an incident laser beam and the primary axis of a focusing lens. The offset adaptor800may be connected to a processing head configured to generate an incident laser beam aligned with the first axis803. The offset adaptor800may be connected to a processing head in such a way that the offset adapter is rotateable about the first axis803.

FIG. 9illustrates an embodiment of an offset adaptor900connected to a cutting head901. The cutting head901is configured to direct an assist gas along a flow axis. The cutting head901comprises a nozzle902, through which the assist gas flows, and through which an incident laser beam passes. One or more nozzle centering adjustment screws904may adjust the nozzle902position in the X-Y plane. The incident laser beam may be substantially coaxial with the flow axis. The cutting head901may further comprise an adjustable focus ring903for focusing the incident laser beam. The cutting head901further comprises a focusing lens (not shown).

In one embodiment, the offset adaptor900may be secured to the cutting head901by set screws. The other side of the offset adaptor900may be secured to a processing head (not shown) or galvanometer block (not shown) by servo clamps. The focusing lens, which is comprised within the cutting head901, may be rotated about the incident beam axis of propagation by loosening the servo clamps that hold the adapter against the bottom of the processing head or galvanometer block, manually rotating the offset adapter900. Once the desired position has been achieved, the servo clamps may be tightened to secure the adapter in a new rotated position. In another embodiment, an electromechanical mechanism, such as a worm drive driven by a motor, may be used to rotate the offset adaptor900with respect to the processing head or galvanometer block.