Method for performing operations on elongated curved workpieces and universal operation center operable to practice the method

Abstract

According to one or more embodiments, methods and systems for performing operations on a workpiece are provided. An exemplary method may include holding the workpiece in a feed clamp such that the workpiece is movable in one degree of freedom. The method may further include feeding the workpiece along its length to an operation center and measuring the position of the workpiece in the length direction. A time series of machining vectors on the workpiece defined in a workpiece coordinate system can be transformed into a time series of machining vectors calculated in a machine coordinate system. Using a machine control system, a machining end actuator can be moved using the time series of machining vectors calculated in the machine coordinate system, and one or more operations can be performed on the workpiece.

Description

Background Technology

[0001] Current CNC and general-purpose machining machines require six degrees of freedom (DOF) to hold the workpiece in a fixed configuration relative to the machine. These are typically fixed using a 3-2-1 method, where three supports position the workpiece on a first plane, against which a clamp acts to fix three DOFs—translations perpendicular to the surface and two rotations about a vector located on that plane. Two additional supports, along with the clamp that pushes the workpiece against them, act on a second plane not parallel to the first plane and fix two more DOFs—translations orthogonal to the first direction in a “normal plane” containing the normals to the first and second planes, and rotations about the normal to that plane. A final locator, along with the clamp acting against it in a direction not within the first and second planes, removes the translation along the clamping direction (the sixth and final DOF). In tooling and clamping techniques, six DOFs are sometimes considered a group of twelve DOFs, six in each positive and negative direction.

[0002] The 3-2-1 method actually requires six supports / locators to position the part by constraining it in one direction of each of the six DOFs, and at least three opposing clamps to constrain translation and rotation away from the locators. However, if the frictional forces acting on the supports are sufficient to constrain the movement of the workpiece along its surface, the required number of locators and supports can be reduced. On the other hand, for curved flexible bodies, additional locators and clamps are needed to hold them within the defined / required geometry of the flexible body to achieve accurate operational positioning and to prevent the operating forces from altering the part geometry during operations that apply significant local forces to the workpiece (such as machining). These fixtures require a curved surface of the workpiece into which an accurately machined surface can be nested, and have clamps distributed on the workpiece to locally resist machining forces, requiring significant engineering and manufacturing effort to produce, and driving up the cost and schedule for machining curved parts. Programmable fixtures are used in complex and expensive machines to hold curved parts for machining, but they require significant effort to program each part and do not fully support the part.

[0003] Long, straight parts can be manipulated by a variety of machines that feed the parts and move them through an operating area containing operating points. For a given position of the workpiece relative to the machine, the operating area can include all points or a subset of points accessible to the tool. These machines typically have long tables on which the parts are clamped, or rollers clamped to the parts and feeding them relative to the tool. The position along the length coordinate is determined based on the incremental length of the workpiece fed through the machine relative to a defined origin. Examples include CNC extrusion milling machines, tube lasers, stamping presses, and roll forming machines. The operations performed vary depending on the position of the machining point along the length of the straight workpiece fed through the machine. Roller-feed machines typically use roller clamps to support the straight parts around the operating area while clamping the parts to a rigid member of the machine to move them through the operating area. This has the advantage that there are no locators and fixtures in the machining area and allows machining to occur across the entire perimeter of the part's cross-section. This method can be used when the deflection of the part under the applied force is negligible, either due to the small processing force (e.g., tube laser) or because the workpiece is stiff relative to its unsupported length. This type of processing cannot be applied to bent parts because the movement of the part is controlled by an arm rigidly attached to a straight track, etc. Furthermore, the method of tracking the workpiece position via a roller encoder is limited to parts that are straight and do not move or vibrate significantly due to the processing force.

[0004] Relatively few machines exist that track the position of bent parts moving through the operating area; however, these machines cannot track the length coordinates with the accuracy required for machining bent extrusions used in frame structures, where typical positional tolerances for all features are ±0.030" even for parts up to 20 feet long, and cannot perform other operations on the workpiece's cross-section, such as drilling, trimming, or thinning. Currently, machines that use rollers to move bent parts and track their position for machining do not claim high positioning accuracy along the length coordinate and only support quasi-static operations (e.g., bending) that do not experience the dynamic forces or vibrations experienced in processes such as CNC milling.

[0005] Other machines perform operations at different locations along the curved cross-section of slender workpieces (such as aircraft and pipes). This involves moving the workpiece or tool relative to each other, and the movement is either continuous or indexing motion, allowing the machine to operate at different locations along the length. Either all coordinates are derived from the machine coordinate system, or entirely from the workpiece. Any precise movement required for milling operations, such as precise back-and-forth relative motion with controlled position and velocity as a function of time, is achieved by clamping rigid elements (whose movement is machine-controlled) onto these workpieces. Summary of the Invention

[0006] According to one or more embodiments, methods and systems for performing operations on a workpiece can be provided. An exemplary method may include: holding a workpiece in a feed clamp such that the workpiece is movable along its length in one degree of freedom and constrained in all other degrees of freedom. The method may further include: feeding the workpiece along its length to an operation center, and using one or more sensors to measure the position of the workpiece relative to the feed clamp in the length direction, wherein the measurement may be the cumulative distance of the workpiece over known points, and a zero position may be defined as the position of the workpiece when a known feature is at a known position. The orientation of the workpiece relative to the feed clamp can be calculated as a function of the workpiece position. A time series of machining vectors defined on the workpiece in the workpiece coordinate system is transformed into a time series of calculated machining vectors in the machine coordinate system. Using a machine control system, a machining end actuator can be moved using the time series of calculated machining vectors in the machine coordinate system, and one or more operations can be performed on the workpiece.

[0007] According to another embodiment, a system for performing operations on a workpiece can be provided. The system may include an operation center and a feed clamp that holds the workpiece such that it is movable along its length in one degree of freedom but constrained in all other degrees of freedom, and feeds the workpiece along its length into the operation center. The system may also include one or more sensors that measure the position of the workpiece along its length, the measurement being the cumulative distance the workpiece has traveled over known points, and a zero position being defined as the position of the workpiece when a known feature is in a known position. The system may further include a machine control system that moves a machining end actuator by means of a time series of machining vectors calculated in a machine coordinate system. The operation center may calculate the orientation of the workpiece relative to the feed clamp as a function of the workpiece position, and transforms the time series of machining vectors defined on the workpiece in the workpiece coordinate system into a time series of machining vectors calculated in the machine coordinate system, and may perform one or more operations on the workpiece. Attached Figure Description

[0008] The advantages of embodiments of the present invention will become apparent from the following detailed description of exemplary embodiments. This detailed description should be considered in conjunction with the accompanying drawings, in which: Figure 1A An exemplary apparatus for performing one or more operations on a workpiece is shown.

[0009] Figure 1B An exemplary precision clamping system is shown, illustrating the tool / spindle in a specific position and orientation relative to the clamping system.

[0010] Figure 2 An exemplary precision feeding system is shown.

[0011] Figure 3A An exemplary system is shown for positioning and orienting a tool / spindle at an operation point to perform an operation.

[0012] Figure 3B Another configuration of an exemplary system for positioning and orienting a tool / spindle at an operation point to perform an operation is shown.

[0013] Figure 4A An exemplary precision clamping system is shown.

[0014] Figure 4B Another view of an exemplary precision clamping system is shown.

[0015] Figure 4C Another configuration of the exemplary precision clamping system is shown.

[0016] Figure 4D Another view of an exemplary precision clamping system is shown.

[0017] Figure 5 An exemplary workpiece feeding system with an independent tracking system is shown.

[0018] Figure 6 An exemplary embodiment of a device is shown that provides improved accuracy in tracking operation points on a workpiece.

[0019] Figure 7 Another exemplary embodiment of the device is shown.

[0020] Figure 8A Another view is shown of an exemplary precision clamping system having an encoder within the feed roller, according to an exemplary embodiment.

[0021] Figure 8B Another view of an exemplary precision clamping system according to an exemplary embodiment is shown.

[0022] Figure 8C Another view of an exemplary precision clamping system according to an exemplary embodiment is shown.

[0023] Figure 9A An encoder and roller configuration on the rolling curve of a straight workpiece, according to an exemplary embodiment, is shown.

[0024] Figure 9B An encoder and roller configuration on a rolling curve of a workpiece with variable curvature, according to an exemplary embodiment, is shown. Detailed Implementation

[0025] Various aspects of the invention are disclosed in the following description and accompanying drawings with reference to specific embodiments thereof. Alternative embodiments may be designed without departing from the spirit or scope of the invention. Furthermore, well-known elements of exemplary embodiments of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention. In addition, several terms used herein are discussed below for ease of understanding of the description.

[0026] As used herein, the term "exemplary" means "as an example, instance, or illustration." The embodiments described herein are not limiting but merely exemplary. It should be understood that the described embodiments are not necessarily to be construed as preferred or advantageous over other embodiments. Furthermore, the terms "embodiments of the invention," "embodiments," or "invention" do not require that all embodiments of the invention include the features, advantages, or modes of operation discussed.

[0027] A computer numerical control (CNC) feed-clamping method and feed clamping (FF) device can be provided for positioning and moving an operating point where a tool engages a bent, elongated workpiece to perform an operation. The bent workpiece can be an extrusion, a roll-formed section, a brake-formed section, a sheet, etc., whose cross-section can be bent (sweeped or lofted) along a swept curve to create a longitudinal dimension (length dimension). One or more thickness dimensions defined along the cross-section can be much smaller than the longitudinal and transverse dimensions, while the sweeping / lofting of the transverse segment along the longitudinal direction can create a surface along which an operation can be performed. Segmented or continuous curves (space curves) can be defined on the surface. Time-related traversal of the tool or sensor over the curve can be used to define an operation path or a tracking path, respectively. The term path should be understood as representing a curve with an additional time coordinate that defines the time-related movement of a point along the curve. Each path can be defined as a parametric space curve, which calculates a unique point (position vector) on the curve for each value of the parametric time. It may also have additional orientation vectors corresponding to each point, with up to three additional time functions that define, for example, the orientation vector of the tool at that point.

[0028] According to one or more embodiments, methods and systems for performing operations on a workpiece can be provided. An exemplary method may include: holding the workpiece within a FF such that it can move relative to the FF in only one degree of freedom along the workpiece's longitudinal direction and is constrained in all other degrees of freedom. The method may further include: feeding the workpiece along its longitudinal degree of freedom (a curvilinear coordinate named length) into an operation center, and precisely controlling the length as a function of time using one or more sensors, each of which can sense the movement of the workpiece past a sensing point on the FF, wherein the length coordinate can be the cumulative distance measured by the sensors from a known origin, defined as the length coordinate when the position of a known feature of the workpiece coincides with a known point on the FF. The orientation of the workpiece relative to the FF can be calculated as a function of the workpiece position, and as a function of time when the length is controlled by the FF as a function of time. Machining points defined in the workpiece coordinate system may need to be positioned along a specific operation plane of the operation center. The length coordinate required to achieve this can be uniquely calculated through simulation of the kinematics of the workpiece's movement through the FF. The length coordinate, along with two other coordinates of the machining point in the machine coordinate system (along the operating plane), together constitute the coordinates of the machining point in the machine coordinate system.

[0029] The machining operation to be performed at a point on the workpiece also needs to be performed by a machining tool in a defined orientation relative to the workpiece, which is defined in the workpiece coordinate system. The workpiece machining vector (a 6 DOF entity defined in the workpiece coordinate system) – which may include machining points (3 DOF) and tool orientations for machining (3 DOF) – completely constrains the spatial relationship between the workpiece and the tool required to successfully complete the machining operation at that point. A time series of the machining vector can define the workpiece operation path. This can be transformed into a calculated machine operation path in the machine coordinate system using the known position and orientation of the workpiece relative to the FF and the known position and orientation of the FF relative to the operation center at each time point in the time series. Using a machine control system synchronized with the time series of the workpiece movement via the machining vector through the FF, the machining end actuator of the tool can be interpolated through the machine operation path in the machine coordinate system and can perform one or more operations on the workpiece.

[0030] refer to Figure 1A The diagram illustrates and describes an apparatus 100 operable for practicing the method. The apparatus 100 may include, for example, a feeding device, a clamping device for a workpiece, a precision positioning device for a spindle / tool, a chip removal device, and a length measuring device that may be located at a known measuring point relative to the clamping device.

[0031] refer to Figure 1B An embodiment of a universal feed clamp (UFF) 101 including a feed mechanism, a clamping mechanism for the workpiece, and a precision positioning mechanism for workpiece 202 is shown. The coordinate system shown is a machine coordinate system along the operating plane, which, for the illustrated configuration, is positioned along the plane of symmetry of the UFF. This figure shows a tool and spindle 406 in a specific position and orientation relative to the UFF. The spindle's degrees of freedom may include translation along the X, Y, and Z axes, as well as rotation along an A-axis parallel to the X-axis and rotation about a B-axis perpendicular to the tool axis within the operating plane. The UFF feeds the part along a curve length coordinate generally parallel to the X-axis and may additionally have a rotational degree of freedom along the X-axis (A' axis), which allows it to accommodate a cross-section of the vertical leg (flange) 208 that is not perpendicular to the web (206). Simultaneous, sequential, or tandem positioning and orientation of the tool using the universal feed clamp 101, as well as positioning and orientation of the workpiece 202, allows for relative movement of the tool relative to the workpiece in five degrees of freedom to perform operations, or to perform a series of operations along an operation path with connected movements between different segments of the operation path to produce the desired parts.

[0032] refer to Figure 2A precision feed system 200 can be shown and described. The feed system 200 may have a first degree of freedom (e.g., a curve length coordinate, the tangent of which is along the X-axis at the operating plane 701), the length coordinate of the bent workpiece 202 may be along the intersection of its ridge—the horizontal leg 206 (web) and vertical leg 208 (flange) of the extrusion, and the feed system 200 is capable of smoothly and continuously feeding the bent workpiece 202. The bent workpiece 202 may be, for example, a bent aluminum extrusion having arbitrary shape and curvature. The precision feed system may include one or more sets of parallel friction rollers 204, each set consisting of at least one pair of opposing rollers that clamp the legs of the workpiece on both sides and rotate in opposite directions to move the workpiece along its longitudinal direction. It should be noted that the terms feed roller, friction roller, traction roller, drive roller, etc., are used interchangeably.

[0033] refer to Figures 3A-3B A system 300 for positioning and orienting a tool / spindle at an operation point for performing an operation is shown and described. The system 300 may have a tool and / or spindle 302. The tool and / or spindle 302 can be positioned and oriented in machine coordinates using a CNC machine controller, while the workpiece is simultaneously positioned along a curve length axis. The tool and / or spindle 302 may be, for example, a horizontal tool. The tool and / or spindle 302 can perform one or more operations on the workpiece 202 along a segment 308 of an operation path defined along the surface of the workpiece.

[0034] System 300 may also include a debris removal system 304, which ensures that generated debris can be removed from the precision clamping device. Figure 3A In the example depicted, the debris removal system 304 may be a vacuum hose. In other embodiments, the debris removal system 304 may instead be, for example, a wire brush or an air brush.

[0035] In some embodiments, the tool and / or spindle may instead be a vertically oriented spindle 306. In one embodiment, the vertically oriented spindle 306 may be positioned and oriented in its machine coordinates and perform operations on the workpiece 202 along another segment 310 of the operation path.

[0036] Understandable Figures 3A-3B The configuration shown allows for independent operation on two different axes (e.g., parallel to the machine's Y and Z axes). The operator stations / tools 302 and 306 can be CNC controlled in their local coordinate systems, which can be oriented according to the direction of operation for each spindle. These tools 302 and 306 can be engaged one at a time, sequentially, or simultaneously.

[0037] refer to Figures 4A to 4DA precision clamping system 400 can be shown and described. The precision clamping system 400 may include one or more flange positioning rollers 402 located on the positioning side of the workpiece. The precision clamping system 400 may also include one or more rubber-coated flange holding rollers 404 mating with the flange positioning rollers, which clamp the flange of the workpiece to the positioning rollers. The rubber-coated rollers 404 ensure full contact with the relatively hard rollers 402 and provide sufficient clamping force between rollers 402 and 404 and between the single-sided feed roller 204 and the workpiece, which is required for the feed rollers to drive the part by friction. The axes of all these rollers 204, 402, and 404 may be parallel to the machine's Z-axis, or, when the flange is not at a 90-degree angle to the web, may be rotated about axis A' to clamp perpendicular to the flange. In either case, the two pairs of flange rollers constrain the translation of the workpiece along the Y-axis and its rotation about the X and Z axes.

[0038] The precision clamping system 400 includes additional web positioning rollers 410, which can be located below the web (horizontal leg) of the workpiece. These rollers are free to rotate about their axes, and can circumduct freely in the XY plane, but are otherwise fixed. The axes of the rollers can be oriented in the XY plane to follow workpieces with different curvatures, or can be self-aligned to roll in directions that match the movement of the part in those positions, resulting in minimal friction. These web positioning rollers 410 on the positioning side of the workpiece can also be paired with rubber-coated web clamping rollers 412 on the clamping side of the workpiece. The two pairs of web rollers constrain translation along the Z-axis and rotation about the X and Y axes. Even though some of the roller pairs 402, 404 and one or more of 410, 412 may not be geometrically required for positioning the workpiece, the illustrated configuration can increase the rigidity of workpiece positioning through UFF. In practice, since machining operations may result in the trimming of portions of the web and flange (e.g., along segments 308 and 310 of the operation path), additional redundant positioning and clamping roller pairs help to rigidly hold the part in cases where some roller pairs in the smallest set of rollers may coincide with such trimmed areas and become ineffective in positioning the part.

[0039] For the precision clamping system 400, the operating plane can sometimes be defined as the plane of symmetry of the UFF—when the UFF has such a plane of symmetry. All operations can be performed within this plane, which can be defined as the YZ plane of the machine.

[0040] Now explain Figures 4A-4D In operation, the precision clamping system 400 can feed the workpiece 202 to a predetermined position via the feed roller 204, lock the workpiece 202 in place, position and orient the tool / spindle at the operating point, and use the operator station tool at the predetermined position and operating point. Figure 4A The horizontally oriented spindle 406 and Figure 4B The vertically oriented spindles 414 (which may also be referred to as operator stations 406 and 414) perform operations on the workpiece, such as drilling.

[0041] The precision clamping system 400 can also perform operations (e.g., milling) using operator stations 406 and 414, during which a segment of the workpiece is actively positioned in front of operator stations 406 and 414, which can be synchronously positioned and oriented to perform operations along the operation path. The precision clamping device can act as an active operation, moving the workpiece forward and backward along a curve length coordinate. These operations can be used, for example, for machining pockets and for thinning workpieces. The unique configuration of this device enables this precise execution of the operation process for relatively flexible, thin, slender, and curved workpieces (such as extrusions and other structural elements).

[0042] When operating on a workpiece with a constant radius, the workpiece's cross-section can be perfectly aligned with the operating plane according to the described configuration. Alternatively, for workpieces with variable curvature near the operating point, the operating plane can be slightly adjusted to achieve the accuracy required for the operation (e.g., machining features). This can be achieved by adjusting the position and orientation of the operating (e.g., machining) plane relative to the positioning roller 402. This orientation change, and the offset required to achieve higher operation accuracy (e.g., machining features), is very small and can be achieved by adjusting the relative positioning of the roller group and the precision positioning system.

[0043] refer to Figure 5A system 500 for feeding a workpiece is shown and described. The feeding system 500 may include a rotary encoder wheel or equivalent sensor 502 that measures the workpiece position along a length axis by the rotation of the wheel (the rotation of which is sensed by a rotary encoder), and the feeding system 500 may use this measurement as feedback for closed-loop feedback control of the rotation of the feed roller 204 required to move the workpiece point to the operating point. In some embodiments, at least two such encoder wheels or sensors 502 may be provided. They may be the same as, co-located with, or mounted on one or more of the positioning or clamping rollers 402, 404, 410, and / or 412, or may be mounted elsewhere, and may be used to determine the position of the workpiece 202 relative to the operating plane. The distance between the encoder 502 and the position where the operation is performed may be relatively small, both compared to the workpiece length and the length of the workpiece supported by the precision feeding system 500. A two-level encoder or equivalent sensor can be used to ensure accurate positioning of workpiece 202 and detect any measurement errors caused by encoder wheel slippage, encoder wheel rolling over debris, etc.

[0044] In some embodiments, one or more feeders for the precision feeding system 500 may be mounted externally to the positioning roller system. In some embodiments, the workpiece feeding system 500 may also be provided with one or more support-end actuators. The support-end actuators may be CNC controlled in their local coordinate system. The support-end actuators may provide additional support to the workpiece on a surface opposite the operation position and operation point.

[0045] The operations performed by the system can include, but are not limited to: inspection, cutting, marking, drilling, finishing, milling, thinning, as well as end milling and peripheral milling. Depending on the desired operation, a support end actuator can be configured to provide optimal support in the direction requiring the highest precision. For example, for peripheral milling, support in the machining direction is more important. In such a configuration, the horizontally operating spindle tool 406 can feed material in the Z-direction, while the end actuator can support the workpiece on opposite faces in the Z-direction.

[0046] The position of workpiece 202 can be reset using one or more positioning features (e.g., defined reference features), which may be, for example, holes along the workpiece at known locations. The workpiece's position can also be reset to a reference if significant slippage is detected during operation on the workpiece (e.g., based on differences between actual and expected readings from multiple encoders). Positioning features and / or reference holes can also be defined externally to the workpiece to create reference features for cutting the workpiece to size after the operation is performed.

[0047] Some embodiments of device 100 may be equipped with additional supports opposite the operating point. Furthermore, embodiments of device 100 may also include rollers that can be used to force the workpiece into its ideal configuration for more precise and accurate operation, or device 100 may be additionally provided with rollers used to adjust the position of the workpiece to perform the operation in response to calculated deflection and changes induced in the workpiece and device 100.

[0048] refer to Figure 6 An exemplary embodiment of the device 600, which provides increased precision and accuracy, can be shown and described. The device 600 can modify the local curvature of the workpiece 202 using CNC control of the position of the roller 602 along the operating plane 701. Rollers 402, 404, and 602 can work collaboratively to force part or all of the workpiece into a predetermined curvature and can perform the operation. Roller 602 also provides additional support relative to the operating point 814.

[0049] refer to Figure 7 Another exemplary embodiment of the apparatus 700 can be shown and described. The apparatus can use its CNC capabilities to calculate deflection and the resulting changes in the apparatus and workpiece 202. The apparatus can additionally use its CNC capabilities, along with sensor 702, to measure and compensate for these deflections and the resulting changes. One or more rollers 402 can then adjust the position of the workpiece while the machine simultaneously adjusts the position and orientation of the tool and / or spindle. After the workpiece and tool / spindle are positioned and oriented, one or more operations can be performed on the workpiece.

[0050] Additionally, one or more support-end actuators can be provided. The device 700 can also utilize a stiffness calibration procedure, enabling it to perform precise operations, such as machining. Since both the operating head and the support-end actuators can be mounted on control axes, it is understood that they are not fixed in space. Operating forces can cause system deflection, which can be significant during operation, particularly for operations such as milling. To overcome this source of error, a stiffness calibration procedure can be performed on a given set of tools and support-end actuators—before performing the operation through that given set of tools and support-end actuators. This procedure can measure the stiffness of the system in the local operating (e.g., machining) direction. Stiffness may change non-linearly because the entire system affects stiffness in that direction. Calibration can increase the motor torque that moves the operating axis, causing it to press against the support-end actuator. The calibration can then use the resulting displacement of the operating axis and the opposing support axis to determine the displacement of the operating position. The non-linear stiffness curve can be actively used to compensate for the machine's stiffness during operation.

[0051] refer to Figures 8A-8C An embodiment of a precision clamping system 400 is shown and described. The accompanying drawings show a feed roller 204 with a very thin urethane coating or a coating of another material having a high coefficient of friction with the workpiece 202, serving simultaneously as a flange positioning roller and a feed roller. An encoder roller 414 contacts the measured curve of the part through a slit in the hollow tubular support structure of the feed roller and provides position feedback to the feed roller 204 to control the feed roller to feed the part to the desired longitudinal position, i.e., the curve length coordinate. A clamping roller 404 in the Y direction holds the part against the feed roller 204, allowing it to be driven, positioned, and oriented. A positioning roller 410 defines the part position and establishes a reference in the Z direction so that the clamping roller 412 clamps the part against it.

[0052] refer to Figure 8C It can be noted that the four encoder wheels 414 contact the workpiece 202 along two measurement curves 802 and 804 at measurement points 822, 824, 826, and 828. Each encoder measures the rotational position of its encoder wheel and uses the precisely known circumference of its encoder wheel to infer the position of the corresponding measurement point. Using a kinematic simulation of the encoder wheel rolling along the measurement curves over time, the tracking path of each encoder wheel measurement point on the workpiece can be determined. At any given time, the measured value of the position at the measurement point can be used to estimate the current position 810, i.e., the length coordinate of the part located by the UFF along the longitudinal degree of freedom. Elsewhere, it can be noted that this position 810 can be referred to as in the curvilinear coordinate system used for the workpiece. O ( s p ) = ( s p , 0, 0 ), or in the coordinate system used for the workpiece, it is called r ( s p ) = ( x , y , z ). s p This is the value of the length coordinate along the main tracking path, which needs to be located along the operating plane 701 so that the point... P 814 is positioned along the same operating plane 701. The machine coordinate direction 808 along the UFF is known. X ( s p )), 810 ( Y ( s p )) and 812 ( Z ( sp In addition to the geometry of the workpiece and tools, points can also be determined along the machine coordinate system. P The coordinate values ​​along the operating plane, i.e. ( P y , P z ,), and one or more offset points Q = ( Q x , Q y , Q z The coordinates of 816 are used to establish a new geometry at the offset point through the operation at point 814.

[0053] refer to Figures 9A-9B Different configurations of the measuring and driving components for straight and variable curvature workpieces are shown and described. Note that the operating plane 701 is shown as a plane of symmetry along the two feed rollers 204. The encoder wheel 414 can move back and forth along the encoder movement axis 702. It should be noted that the drive rollers 204 and the encoder wheel 414 can contact the workpiece at different points. This is an important aspect that needs to be correctly represented in the kinematic simulations used to calculate the precise position and orientation of the workpiece as it travels on parts with varying curvature.

[0054] Some embodiments may be particularly useful when the workpiece is flexible (i.e., its deflection due to operating forces, gravity, etc., would exceed the tolerance of the position where the operation will be performed, without FF stabilization). In some embodiments, it may be desirable for the FF to be able to handle a wide variety of cross sections, which may be referred to as a universal feed clamp (UFF). Some embodiments may specify that the UFF positions the workpiece surface at three or more pairs of opposing points and clamps the workpiece across the thickness dimension to constrain translation perpendicular to the surface and rotation about any axis along the surface. Using at least two pairs of rollers or omnidirectional wheels as clamping elements (at least one of which is a drive wheel) allows the workpiece and / or tool to be moved and positioned in one or two degrees of freedom such that at any given time, the operating plane coincides with the cross section of the workpiece where the operation will be performed, and the operating point can traverse the desired operating path.

[0055] Some embodiments may include sensing devices for tracking the relative motion between the UFF and the workpiece along one or more tracking paths along the workpiece. For each sensor, the time series of the corresponding measurement points on the workpiece (i.e., the tracking path) may fall on a sweep curve called a measurement curve, which may extend along the longitudinal direction of the workpiece. The length of each measurement curve that moves past the sensing point within a given time interval may depend in a known, deterministic manner on the curvature of the workpiece and the position of the measurement curve along the cross-section of the workpiece. Then, by selecting one of these tracking paths as the primary tracking path and using a simulation of the workpiece motion through the FF to map the lengths measured along the other tracking paths to the corresponding lengths along the primary tracking path (which the sensors measuring along the primary tracking path can simultaneously read at specific points relative to the UFF), workpiece movement along the length curve coordinates can be measured conflictlessly.

[0056] In some embodiments, all sensors and sensing points, supports and holding points, and the clamps and gripping points of the FF can be close to but offset from the machining point so as to be unaffected by the machining operation (however, it is understood that in some machining operations, having a support opposite to the tool at the machining point can be advantageous, for example, a support with a geometry complementary to the machining tool). Therefore, the position of the workpiece along the master measurement curve may not have a measuring sensor tracking it, but rather can more precisely represent the point where the master measurement curve intersects the machining plane (also referred to as the operating plane, work plane, etc.) defined in the machine coordinate system by the center of operation. The offset between the instantaneous length coordinates along the master tracking path and the position of the machining point along the length coordinates (also referred to as the machine's curve axis) can then be determined by kinematic simulation and can be used in transforming the workpiece machining vector into a machine machining vector. The machining plane can be a plane transverse to the master measurement curve. In some embodiments, the positioning and gripping features of the FF can be arranged symmetrically about this machining plane, for example, when a part with uniform curvature is symmetrically positioned and gripped about the machining plane, which can be perpendicular to all planes tangent to the workpiece. Furthermore, in some embodiments, it may be desirable that the axis of the tool is constrained to extend along a plane coinciding with the machining plane, in which case the transformation from the workpiece machining vector to the machine machining vector may be approximate when the curvature of the workpiece is not constant along its length.

[0057] For the accurate machining of flexible parts with imperfect geometries, where the actual geometry (e.g., curvature) of one or more tracking paths deviates from the defined / desired / assumed geometry, and the length coordinates estimated along the main tracking path have corresponding changes, one or more compensation methods may be included—for example, measuring the actual geometry and compensating for it in a simulation, or using a workpiece support or guide outside the UFF that forces the local geometry (tangents, curvature, and torsion) of a region of the part within the UFF, or at least the region around the machining plane, to be equal to the assumed geometry. In some embodiments, the calculation step may use relative motion sensed along the tracking path to calculate the position and velocity of the operating point along the operating path, and may further use inverse calculation to calculate the movement along the tracking path required to achieve the desired movement along the operating path.

[0058] The UFF and tool can be part of a machine that uses sensed relative motion between the workpiece and the UFF, and the known position of the tool in machine coordinates, to perform feedback control of the tool's relative motion with respect to the workpiece along its length degree of freedom, while all other degrees of freedom are constrained. This minimizes the deviation of the operating point from the desired operating path. Control of the relative motion can include control of all three positions and all three orientations, as well as the speed at which the operating point moves on the workpiece. The relative motion of the workpiece relative to the UFF (measured by the length curve coordinates positioned along the machining plane) can constitute at least one controlled "axis" of the machine motion. The machine structure and control system can be designed to force motion along the operating path (operating point) with the stiffness required to resist operating loads (forces and torques), and to keep deviations from the operating path within specified tolerances for position and vibration. In the context of the operating point, it should be understood that in reality, this point is actually a region that can be approximated as a point or line compared to the other dimensions of the workpiece.

[0059] Exemplary workpieces and coordinate systems for CNC are now described according to one or more embodiments.

[0060] The workpiece can be an elongated object (such as an extrusion) that can be bent along its length. The longitudinal curve can be referred to as, for example, a swept curve, which can be defined on a ridge that can be identified and inspected, and has a transverse cross-section that is constant along its length or varies in a known manner. The cross-section swept or lofted along a straight line can be the primary geometry of the workpiece, wherein the workpiece is produced by a primary processing operation such as extrusion, and the spatial curve along which the swept or lofted cross-section applies a secondary geometry to the workpiece, which can be obtained by a secondary processing operation such as stretching, while a tertiary geometry may require a series of tertiary processing operations, which is the object of the invention in an accurate and economical manner. The workpiece can have a ridge, which can be understood as a part of the object's resistance to changes in length and is generally located at the intersection of different legs of the cross-section. The swept curve can also be a ridge, i.e., the curve presented by the ridge of a bent part. The sweeping of a geometric segment along a longitudinal curve that describes the profile / boundary of the cross-section can produce a surface that defines the geometry of the workpiece's boundary. One or more parts can be produced from the workpiece by performing one or more operations along a processing path defined on the surface of the workpiece. For this reason, the terms "workpiece" and "part" are sometimes used interchangeably.

[0061] Typically, a ridge can be a spatial curve defined in workpiece coordinates (x, y, z), which can be part of an assembly made up of parts produced from the workpiece.

[0062] A space curve can be defined by defining the position vector of each point along the curve, such as... r ( t ) = ( x ( t ) , y ( t ) , z ( t )),in t These are free parameters, and the function x , y and z To uniquely and continuously t The way points are mapped along the curve is defined. Each point can be represented as... r (t), or simply point t .

[0063] In some embodiments, the space curve can be defined by parametric equations, where the parameters... t Equal to the arc length measured from the origin of the curve s , making r ( s ) = ( x (s ) , y ( s ) , z ( s Each point can be called... r (s), or simply point s . s --point r ( s The position along the length of the ridge line—in some cases can be a function of the time parameter—and can further constitute the value of the first coordinate in the local coordinate system of the moving curve, known as the Frenet-Serret frame, which can be used to uniquely identify any point on the workpiece in a manner independent of the rigid body transformation of the workpiece in the workpiece coordinate system.

[0064] The first derivative of the position vector with respect to the arc length parameter, dr / ds = r' ( s ) = ( dx ( s ) / ds , dy ( s ) / ds,dz ( s ) / ds ) = ( x' ( s ) , y' ( s ) , z' ( s )) can be at point r ( s The unit vector at point () that is tangent to the curve. The tangent vector is the coordinate of the curve. s The local change direction, and can be denoted as the local X direction of the workpiece coordinate system, where, X ( s ) = r' ( s ) is the representation of this vector in the workpiece coordinate system. If the tangent vector is not uniquely defined at a point, then it can be said that the sweep curve is kinked at that point. Bending slender workpieces by forming processes typically does not exhibit such kinking because the strain required to kink a straight workpiece with a finite cross-sectional size at a point is infinite and would lead to workpiece breakage. Kinking that can be defined in the geometric model will be approximated as a smooth curve by the bending operation.

[0065] The position vector of the ridge line at point r ( s The second derivative with respect to the arc length parameter at point () is dr' / ds = r'' ( s ) = ( dx' ( s ) / ds , dy' ( s ) / ds , dz' ( s ) / ds ) = ( x'' ( s ) , y'' ( s ) , z'' ( s ), it is at point s Curvature vector at κ ( s ). κ ( s ) = r'' ( s ) = κ ( s ) n ( s () is the curvature vector represented in the workpiece coordinate system. This vector can be understood as the vector originating from the point... r ( s The center of curvature pointing towards the ridge curve. c ( s The position vector of the curvature center can be located in the normal direction. n ( s ) on and point r ( s Distance R ( s (at point) s (radius of curvature at that point). Therefore, the curvature vector κ ( s The size of ) can be the curvature κ ( s ), which is the reciprocal of the radius of curvature, such that (| κ ( s )| = κ ( s ) = 1 / R( s )).

[0066] Includes tangent vector = r' ( s ) and curvature vector κ ( s The plane can be at point s The local (osculating) plane of the curve at a given point. A plane-swept curve can be understood as a curve for which the local plane remains the same for all points along the curve.

[0067] The sweep curve of an actual part formed by metal forming can be smooth because the first derivative (slope) of the curve is continuous at all points (there are no kinks in the curve), which can be interpreted as meaning that the second derivative (curvature) is at least piecewise continuous (continuous except for finite jumps at a finite number of points).

[0068] Located in the workpiece coordinate system at ( x p , y p , z p any point at ) P The cross-section at that point can be understood as the region (closed shape) obtained when a transverse plane passing through that point cuts (or cleaves) the workpiece, where this region is also perpendicular to the ridge line (i.e., perpendicular to the intersection point). s p Tangent vector at point X ( s p ) = r' ( s p Therefore, the term "cross section" as used in this article refers to the "vertical cross section".

[0069] Conversely, the geometry of a workpiece, i.e., the volume it occupies, can be obtained by sweeping or lofting cross sections along a sweep curve, regardless of whether the cross sections (e.g., draft angle or taper) change. The geometry can also be obtained by lofting two or more cross sections along one or more guide curves. Additional CAD modeling operations can then be performed to add or remove volume from the essentially defined shape.

[0070] In one embodiment of the flexible clamp feeding a workpiece along one degree of freedom, the geometry can be restricted to one of two cases: (i) the ridge is a planar curve, and the workpiece has sufficient torsional stiffness about its length axis to cause the ridge to deviate negligibly from the plane when the intended operation is performed with the tool; or (ii) the geometry of the cross-section has features that remain constant along the length of the part (e.g., straight edges, convex angles, involute profiles, etc.) so that a segment of the part near point P can be deterministically positioned or clamped (i.e., positioned and oriented) relative to these features. If the former, any segment of the part can be clamped by forcing the workpiece to conform to a plane and feeding the workpiece such that point P lies within the operating plane. If the latter, a typical cross-section can contain features that can be used to deterministically position the cross-section. For example, it may have at least one nearly straight edge (i.e., its deviation from a straight line is negligible compared to its length). A straight line approximating an edge can be used as the Y-axis, and the unit vector along this direction can be labeled as... Y ( s p A line perpendicular to the Y-axis drawn through any other identifiable feature of the cross-section (not necessarily along the Y-axis) can form the Z-axis, and a unit vector along the Z-axis can be represented as... Z ( s p The intersection of the Y-axis and Z-axis forms a ridge, and is therefore the local origin of the workpiece coordinate system at that cross-section. O ( s p ) = ( s p (0, 0). The origin can be connected to the ridge line and the point passing through it. P The intersection of the cross-sectional planes (i.e., r ( s p The position along the plane of the cross-section may or may not coincide with this intersection point. If the convex corner feature of the cross-section is to be used for clamping the workpiece, any method of choice can be used to uniquely determine the position relative to that feature. Y ( s p ), Z( s p )and O ( s p For example, by making Z ( s p Oriented along the axis of symmetry of the convex angle, and O ( s p Position it so that it coincides with the vertex of the convex corner.

[0071] Point on the cross section P The Y and Z coordinates of (x, y, z) can be obtained by taking the distance Y(x, y, z) from the origin to the perpendicular projection of that point onto the Y-axis and Z-axis, respectively. P ) and Z( P To measure. Coordinates ( s p , Y( P ), Z( P Points that can constitute a workpiece P (x, y, z) is an alternative definition in the Frenet-Serret workpiece coordinate system. For planar parts, the Y coordinate (Y( P ()) and Z coordinate (Z( P )) May be related to point P The Y and Z machine coordinates have an offset (which depends on the curvature), and for other parts, obtaining the machine coordinates may require appropriate transformations.

[0072] Understandably, there may be some sections lacking an edge defining the Y-coordinate direction. For such sections, this direction can then be defined by filling with any material removed from the swept volume, or by interpolation or extrapolation along the Y-coordinate direction. r ( s p The Y-coordinate direction of the adjacent cross-sections containing this edge ( Y ( s p+ ) and / or Y ( sp- This direction is defined by the feature that defines the position of the Z-axis (and therefore the local origin) in any given cross section. Similarly, if the feature that defines the position of the Z-axis (and therefore the local origin) in any given cross section is missing, the position of the Z-coordinate direction (and therefore the origin) can be interpolated or extrapolated from adjacent cross sections.

[0073] Considering the need to position the tool at a point P ( s p , Y ( P ), Z ( P This can be achieved by positioning the curve length coordinates at a point expected based on the geometric definition of the workpiece relative to the machine coordinate system. r ( s p ), and then position the tool along the operating plane at (Y( P ), Z( P Add any offset. Additionally, to place the point... PThe measurement points located on the operating plane, along the main tracking path, may need to be located at... r ( s t However, due to real-world issues such as deviations between the actual and defined geometry of the workpiece, and the workpiece's flexibility, existing technologies may require clamping tools manufactured more accurately than the workpiece itself. These clamping tools may also be significantly more rigid than the workpiece, possessing locating surfaces that match a large area of ​​the workpiece's outer surface, and / or featuring carefully crafted clamping arrangements to force the workpiece to conform to the clamping tool on these large locating surfaces, placing the workpiece in a configuration sufficiently close to the defined arrangement so that the tool is positioned at the point with sufficient accuracy. P Place.

[0074] Therefore, in some embodiments, from the perspectives of cost, positioning accuracy, and ease of implementation, if for locating any point... P The corresponding point O ( s p It is correctly positioned relative to the machine coordinate system, and the corresponding direction is... X ( s p ), Y ( s p )and Z ( s p If the clamping element is oriented in the desired manner, it can be advantageous. This can be achieved using positioning elements and locating elements in the FF method. Assuming the clamping element is in... i cross-sectional plane r ( s i () acts on the surface of the workpiece to control X ( s i ), Y ( s i ), Z ( s i )and O ( s i If one or more of the following are true, then for i Appropriate selection of position and clamping elements can constrain the workpiece segment to be rigidly positioned and oriented, making the point... PLocated within the operating plane and at the desired coordinate position along the operating plane. Since the configuration of the clamping elements is known (i.e., their relative positions and / or orientations, and the directions of the constraints they apply, are known relative to the machine coordinates and the operating plane), it is known that the workpiece is located along any tracking path (e.g., s ti The length coordinates of the workpiece segment within the UFF can be known in machine coordinates.

[0075] The use of rotary rollers as supports will now be explained. In some embodiments, one or more rotary rollers may be used as supports. In an exemplary work center, one or more self-aligning bearings may be utilized, wherein the axis of rotation of the shaft supported by the bearing may not be parallel to the axis of the housing supporting the bearing. In some embodiments, the self-aligning bearing may be a wheel that helps the carriage move on a surface to allow the carriage's motion vector to have a non-zero component along the axis of the wheel, in addition to movement primarily along a direction perpendicular to the normal projection of the axis onto that surface. It is understood that, in one embodiment, the support must be as close as possible to the operating point to reduce deflection of the workpiece in response to the component of the operating force reacted by the support. It is understood that, in this embodiment, the workpiece may act as a beam and deflect between the supports, wherein the deflection increases with the cube of the distance between the supports.

[0076] In one embodiment, to minimize the unsupported length while allowing free access to the workpiece (for the tool) along the operating plane, it may be desirable to use very small bearings as support wheels / rollers. In other embodiments, swivel tip setscrews can be used as axles, where the center of rotation of the swivel tip is located at the mid-plane of the inner raceway of a conventional bearing (which is also available in smaller sizes than self-aligning bearings), so that even very small bearings can be used as supports without applying axial force when the workpiece's direction of movement has a component along the axis of the support.

[0077] In some embodiments, feeding is now described via a drive roller located close to the operating point and the support.

[0078] In some embodiments, one or more drive rollers, drive wheels, or friction wheels may be required to apply a feed force to overcome friction, operating forces, inertial forces, etc., at the support, thereby feeding the workpiece along the operating path. It is understood that in some embodiments, the support may react to a force perpendicular to the longitudinal direction, and the feed force may react to a force in the longitudinal direction. In one embodiment where the applied feed force is far from the force to be reacted, the workpiece may act as a curved beam bearing axial forces, and it is understood that deflection increases with the cube of the distance. Therefore, in some embodiments, this distance can be minimized by using one or more of the nearest support wheels on either side of the operating plane as drive rollers or wheels.

[0079] In one embodiment, to allow access to the workpiece along the operating plane, it is understood that the feed force and minimum distance can be limited by the radius of the drive rollers. Large feed forces can be supported using small feed rollers coated with a high-friction material (e.g., urethane, electroplated diamond, etc.), and the drive torque can be provided by a drive shaft with a universal coupling, friction drive, belt drive, etc. In some embodiments, the use of a friction drive or belt allows the drive roller or wheel to be hollow, and a small read head or encoder wheel can be positioned inside the hollow drive roller or wheel. This read head can measure the position along a linear scale attached to the surface of the workpiece driven by the drive rollers, located in the axial gap between the outer sleeves of the two drive rollers. In this case, the linear scale becomes the measurement curve. The encoder wheel can contact the corresponding measurement curve on the workpiece through a slit in the inner shaft of the drive roller or wheel. The outer sleeve of the drive roller can be driven by a secondary drive pulley that supports the outer sleeve along the contact line and drives it through friction. This contact line can be diametrically opposite to the line of contact between the drive roller and the workpiece. In some embodiments, the friction actuator can also be backlash-free, and lost motion can be minimized by using a rigid wheel or roller with a high friction surface. In some embodiments, a double U-shaped joint spline actuator can also be used to accommodate changes in length and angle without fluctuations in output speed.

[0080] The present description describes, in some embodiments, the measurement of relative motion along a curved axis using multiple thin encoder wheels via slits in the drive rollers.

[0081] When a bent workpiece moves relative to the machine, the typical movement can be understood as a combination of rotation and translation. Rotation can cause different fibers along the workpiece (each fiber being a curve formed by a point on a cross-section swept by a sweeping curve) to travel at different speeds. If a thick disc is used as the encoder wheel to track the movement of the bent workpiece, the tracking path may occasionally change randomly from one curve to another on the workpiece surface. As a result, it may be unclear which curve is actually being tracked. This can lead to uncertainty in the length coordinates of the positioning along the machine's operating plane.

[0082] In one embodiment, a thin disk can be used as the encoder wheel, such that the tracking path on the workpiece is known within the thickness of the disk, which can be selected such that the position is accurately known within a specified tolerance. According to an exemplary embodiment, an ideal encoder wheel can be shaped like a thin disk cut from a sphere of matching radius, wherein the equator is the plane of axial symmetry of the disk. The minimum thickness of the wheel allows for negligible deflection of the wheel due to contact forces applied for tracking, as well as markings on the workpiece surface. An ideal material for the encoder wheel can be, for example, a composite material having a low modulus of elasticity and high friction against the workpiece surface.

[0083] Because the uncertainty of workpiece curvature and workpiece deflection can lead to an increase in the uncertainty of the workpiece's longitudinal position as the distance between the measurement point and the operating plane increases, it may be desirable in some embodiments to measure the position along the tracking path as close as possible to the operating plane, including at one or more of the same length coordinates in the drive rollers. Therefore, this position can be tracked by simulating the change in the tangent of the thin encoder disk as a function of the geometry of the curve segment corresponding to the tangent between each drive roller in the drive rollers.

[0084] A thin-disc narrow encoder wheel can contact the workpiece through a slit in the drive roller, while the encoder itself can be physically located above or below the drive roller. In some embodiments, the entire encoder can even be located within the drive roller, allowing multiple encoders and their wheels to be located inside the hollow inner shaft of the drive roller. The encoder can track the movement of the workpiece at one or more discrete contact positions along one or more tracking paths on the workpiece. The known geometry of the curved workpiece can be used to calculate an estimated equivalent length coordinate along its curve axis (i.e., the position of the workpiece in the longitudinal direction defined by the main tracking path) based on measurements taken by each individual encoder along its corresponding tracking path. This calculation step converts the measured motion along the tracking path into a measured longitudinal position of the workpiece, while also taking into account the different velocities of the curved workpiece along different tracking paths.

[0085] Measurements from multiple sensors can be combined, for example, via Kalman filtering algorithms to fuse the results with a process-physics-based expected position, thereby achieving optimal estimation of the workpiece position, or via clustering algorithms to identify and eliminate outliers that produce inaccurate readings. Clustering algorithms can compare incremental, equivalent-length readings from multiple sensors to identify the encoder wheel with the most accurate reading at any given time. Therefore, the algorithm can detect when the encoder wheel might temporarily slip due to loss of contact with the workpiece or rolling on debris. This can be particularly important when excessive vibration is applied to the workpiece through operation. These sensor fusion techniques also allow the use of different sensors, including non-contact sensors that measure the motion of a surface along one or more dimensions, such as those using digital image correlation, laser speckle interferometry, and laser Doppler velocimetry.

[0086] The following describes, in some embodiments, the compensation for deviations between the actual curvature of the workpiece and the defined geometry.

[0087] The actual geometry of a bent workpiece may deviate from the defined geometry to varying degrees, depending on the workpiece's level of perfection. This can occur, for example, due to deviations in its free state and due to forces applied to the workpiece, especially since it is understood that slender bent workpieces may be particularly flexible. This geometric deviation may cause both the tracking path and the operation path to differ from those assumed based on the definition of the ideal geometry. In some embodiments, this deviation can be accounted for by measuring the actual curvature of the part within the operation area using a distance measuring sensor (within the unsupported length between supports) near the operation plane, and calculating a new operation path on which the operation must be performed so that the part approximates the ideal geometry when its curvature is forced to conform to the actual definition in subsequent steps. The calculation steps can be performed using, for example, but not limited to, simple analytical models or more detailed models (such as finite element models).

[0088] In other embodiments, part supports can be used outside the UFF to bend the workpiece so that its curvature matches the defined geometry (tangent, curvature, and deflection) within the UFF. This ensures that the previously calculated relationship between the tracking path and the machine's curve axis, as well as the relationship between the position along the curve axis and the operating path, holds true.

[0089] The following describes, in some embodiments, the calculation of a tracking path (movement along the curve length axis) in order to force the desired movement of the tool along the operating path.

[0090] It is understood that the following description focuses on an exemplary embodiment in which the workpiece is constrained by roller supports and clamping forces, such that the drive roller can position the part along a single degree of freedom perpendicular to the contact line at the roller. It is understood that other embodiments (e.g., where the workpiece is a curved sheet and an omnidirectional wheel is used to position it in two degrees of freedom) may be extensions of this case.

[0091] It is understood that when referring to a point on a workpiece, that point refers to a specific material point on the workpiece, identified by its position in a workpiece coordinate system that defines the geometry of the workpiece. In one embodiment, any given point on the workpiece may occupy different spatial positions in a Cartesian coordinate system attached to the machine as the workpiece and / or the machine move relative to each other.

[0092] In order to determine the workpiece's operating point P Positioned at the machine's operating plane to perform operations, the Flexible Fixture (FF) method clamps workpieces of known geometry such that their geometry near the operating plane (within the operating area) is determined relative to the machine. This is achieved by constraining features of the part within a region of the FF using supports of known geometry, positioned and oriented in machine coordinates. The location of the operating point can be achieved by tracking the point... P' (Near P, for example, along the main tracing path) r t1 ( s t1 In the machine coordinate system, corresponding to the length coordinate s t The required time is located at the calculated point. In some embodiments, it is preferable to select a measurement curve near the stiffest part of the workpiece (i.e., near the neutral axis of the workpiece and with minimal deflection in response to force). When such a curve lies at the intersection of two surfaces so that it can be visually identifiable, the curve may also be referred to as a ridge. In one embodiment, in order to move this segment while... P' The only available degree of freedom at that point can be along the tracking path (i.e., along the tracking curve at...). P' The tangent at the point (which may have a known direction) represents the curve length coordinates. Two translations in the plane perpendicular to the tracing curve and through the point... P' All three orientations (roll, pitch, and yaw) of the vertical cross-section can be constrained by the support. Considering the known geometry of the part and the known position, orientation, and geometry of the support, the changes in the three orientations of the workpiece can be calculated and taken into account to calculate the changes when along the vertical cross-section. P' Tracking curve feed point of part P The movement. Using this process, the part can be fed along the operating plane to a positioning point. PThe required appropriate distance. The position of point P along the operating plane and the orientation of the workpiece at this point can also be known. Then, the workpiece can be held deterministically within the operating area of ​​FF so that the expected operation can be performed at point P.

[0093] The advantages of the UFF process can be understood as including, for example: avoiding part-specific clamps; being able to machine the entire surface of a part without repositioning clamping elements; being able to deterministically and rigidly hold curved or straight flexible parts; reducing the number of supports (positioners) and fixtures required to clamp parts; clamping parts near the operating point rather than exactly at or opposite the operating point, so that even for high-force operations (such as thinning), the part is stiff enough to be held rigidly; enabling the machine to perform operations on parts much longer than the machine's range; machining parts with complex geometries using simpler machines compared to much more complex machines; using the workpiece's own positioning features as a reference, so that deviations from the curvature of the ridge line have a negligible effect on the positioning accuracy of the operating point near the cross-section containing the positioning features; being able to force the workpiece into a predetermined curvature and configuration within FF; and devices for determining and compensating for deviations from the desired / ideal workpiece geometry, etc.

[0094] The description now includes, according to one embodiment, points in one embodiment. P The steps of the UFF method for locating at a known position along the operating plane.

[0095] Considering the point P —It needs to be positioned within the operating plane, which can be determined by the UFF method using the steps described above. s p 、r ( s p ), X ( s p ), Y ( s p ), Z ( s p ), O ( s p ), Y( P ) and Z( P Let's begin. Then, using the known configuration of the clamping elements of the known segments of the part that are located and oriented near point P, we can calculate... s t1 and points r t1 ( s t1), so that the points along the ridge (whose length coordinates are s p Position it in the desired location. r ( s p ).

[0096] Measurements can be performed using, for example, length measuring devices such as encoder wheels that contact the workpiece's ridge or any other longitudinal curve generally parallel to the sweep curve. Rotary encoder wheels can also be used as one of the positioning features, provided that other positioning and clamping features effectively secure all five DOFs.

[0097] In one embodiment where the workpiece is gently curved, the radius of curvature of the sweep curve is large compared to the cross-sectional area, and the local (curve) X-coordinate of any point on the workpiece within the workpiece's range can be understood as unique. If the radius of curvature is small relative to the cross-sectional area, a given point on the workpiece can be contained at multiple X-coordinates. In this case, the arc length coordinates of the operation point to be positioned according to the operation path requirements can be found by simulating the kinematics of the workpiece being positioned by the UFF.

[0098] Considering the gentle curvature of the workpiece, each segment of the sweep curve (at any X-coordinate) (whose length is several times the length of the workpiece's cross-section) can be considered to lie approximately within a plane containing the tangent vector and the curvature vector. This plane could be, for example, the ridge line and the Y-axis. Y ( s p The local plane of ).

[0099] Furthermore, the workpiece can be conceived as having a “thin cross-section,” which allows the ridge of the segment to be elastically positioned in a plane by a “planarizing force” when constrained by the UFF, and to spring back to its pre-existing geometry after the conforming force is removed.

[0100] For a cross section containing multiple straight edges that can be used to define the Y direction, if one edge is close to a local plane of the ridge over most of the part, that edge can be selected to define the Y coordinate direction, and the XY plane can be close to a local plane of the ridge.

[0101] To obtain the workpiece in the workpiece coordinate system P ( x p , y p , z p Machine coordinates of any point () s p, Y p , Z p This allows drawing an operation plane passing through that point, and using its intersection with the ridge line to locate the length coordinates along the ridge line (i.e., s p (Coordinate values). Then, the Y and Z coordinate directions can be identified as a pair of orthogonal directions (base) for this plane, and the perpendicular projection of the point onto these directions can be used to obtain the coordinate values ​​respectively. Y p coordinates and Z p Coordinates. This is more accurate than using a cross-sectional plane to obtain an approximate estimate, as suggested elsewhere.

[0102] The stiffness calibration process can utilize a stabilization algorithm to ensure smooth compensation for changes in stiffness. This stabilization algorithm can take into account the effects of operational loads. This can vary, for example, in machining operations, because changes in the combined loads that pull the tool in for a specific tool and machining rate lead to changes in the depth of cut during machining.

[0103] The foregoing description and accompanying drawings illustrate the principles, preferred embodiments, and modes of operation of the invention. However, the invention should not be construed as limited to the specific embodiments described above. Those skilled in the art will understand additional variations to the embodiments discussed above.

[0104] Therefore, the embodiments described above should be considered illustrative rather than restrictive. It should be understood that variations can be made to these embodiments by those skilled in the art without departing from the scope of the invention as defined by the following claims.

Claims

1. A method for performing operations on a workpiece, comprising: The workpiece is held in the feed clamp so that the workpiece can move along the length of the workpiece in one degree of freedom and is constrained in all other degrees of freedom; The workpiece is fed into the operation center along its length. One or more sensors are used to measure the position of the workpiece relative to the feed clamp in the length direction. The measurement is the cumulative distance the workpiece moves through a known point on the feed clamp. The zero position is defined as the position of the workpiece when a known feature is in a known position relative to the clamp or the operation center. The orientation of the workpiece relative to the feed clamp is calculated as a function of the workpiece position; The time series of machining vectors defined on the workpiece in the workpiece coordinate system is transformed into the time series of machining vectors calculated in the machine coordinate system; Using a machine control system, the machining end actuator is moved by a time series of machining vectors calculated in the machine coordinate system; and Perform one or more machining operations on the workpiece; During one or more processing operations, the workpiece moves back and forth relative to one or more rigid elements, the position and velocity of the rigid elements are controlled, and the position and velocity of the workpiece are controlled as a function of time.

2. The method according to claim 1, wherein, The workpiece is a curved, slender workpiece, and The elements of the feed clamp are positioned to match the curvature of the workpiece in order to accommodate changes in part configuration transverse to the length.

3. The method according to claim 2, wherein, The operation is performed on the workpiece by keeping one or more machining vectors close to multiple contact points of the feed clamp, such that the deflection of the workpiece due to machining forces and torques is less than the deflection tolerance.

4. The method according to claim 3, wherein, The use of gapless machine components and preloaded bearings increases the rigidity of the device that holds the workpiece and feeds it through the feed clamp.

5. The method according to claim 3, wherein, The workpiece has a sweep curve; and The method further includes using one or more positioning end actuators to force the workpiece such that, when one or more operations are performed, the sweep curve of the workpiece is deformed into a predetermined geometry under the machining vector.

6. The method according to claim 1, wherein, The feed clamp includes one or more traction rollers, each of which further includes a surface with a high coefficient of friction against the workpiece surface.

7. The method according to claim 2, wherein, The sensor includes one or more encoder wheels that roll along the length of the workpiece to measure the position of the workpiece along the length. The wheels are located inside the one or more traction rollers and contact the workpiece through a slit along the periphery of the traction rollers.

8. The method of claim 7, further comprising calculating the workpiece position by utilizing a sensor fusion algorithm to account for imperfect measurement results; and The calculated workpiece position is used as the position of the machine axis controlled by the machine controller.

9. The method according to claim 3, wherein, The feed clamp supports the workpiece on the side of the workpiece opposite to the tool by resisting the force of the machining operation.

10. The method according to claim 9, wherein, The workpiece has a sweep curve; The method further includes using one or more positioning end actuators to force the workpiece such that, when one or more operations are performed, the sweep curve of the workpiece is deformed into a predetermined geometry under the machining vector. as well as The support member that resists the forces caused by the machining operation is dynamically positioned such that the sweep curve of the workpiece is deformed into a predetermined geometry.

11. The method according to claim 10, wherein, The curved, slender workpiece is flexible; In this method, the deflection of the workpiece due to machining force is reduced by maintaining the machining point of the workpiece between multiple contact points of the feed clamp.

12. A system for performing operations on a workpiece, comprising: Operations Center; A feed clamp is configured to hold the workpiece such that the workpiece can move along the length of the workpiece in one degree of freedom and is constrained in all other degrees of freedom. One or more sensors measure the position of the workpiece along a measurement curve on the workpiece in the length direction, the workpiece position being the cumulative distance the workpiece moves along the main measurement curve through known points, and the zero position being defined as the position of the workpiece when a known feature is in a known position; A motion control system that feeds the workpiece to achieve a desired workpiece position in a time sequence and causes the machining tool to move synchronously through a time sequence of calculated machining vectors in the machine coordinate system. The workpiece feeding includes back-and-forth movement relative to one or more rigid elements, the position and speed of which are controlled by the operation center. The operation center calculates the orientation of the workpiece relative to the feed clamp as a function of the workpiece position, and transforms the required time series of the machining vectors defined on the workpiece in the workpiece coordinate system into a time series of the calculated machining vectors in the machine coordinate system; and The operation center performs one or more operations on the workpiece under the machining vector.

13. The system according to claim 12, wherein, The workpiece is a curved and slender workpiece.

14. The system according to claim 12, wherein, The feed clamp includes at least a backlash-free driver and a preloaded bearing to rigidly hold the workpiece in the constrained direction and rigidly feed the workpiece in the length direction.

15. The system according to claim 14, wherein, The operation is performed on the workpiece by keeping one or more machining points close to the multiple contact points of the feed clamp, such that the deflection of the workpiece due to machining force and torque is less than the deflection tolerance.

16. The system according to claim 15, wherein, The workpiece has a sweep curve; and The operation center applies a force to the workpiece outside the feed clamp, causing the sweep curve of the workpiece to deform into a predetermined geometry around the area where the one or more operations are performed.

17. The system according to claim 12, wherein, The feed clamp includes one or more traction rollers, each of which further includes a urethane layer.

18. The system according to claim 12, wherein, The feed clamp is a universal feed clamp that includes one or more encoder wheels located in the slits of each of one or more traction rollers.

19. The system according to claim 18, wherein, The machine controller uses a sliding detection algorithm to obtain a virtual axis for the workpiece.

20. The system of claim 12, further comprising a machine-end actuator that performs the one or more operations on the workpiece; and A connector that connects the machine-end actuator to the feed clamp; in, The machine-end actuator engages with the feed clamp, such that the force and torque applied to the workpiece by the tool flow directly from the workpiece to the feed clamp, to the connector, and back to the machine-end actuator.

21. The system according to claim 12, wherein, The operation center is the operating volume of the robot; The one or more operations performed by the operation center are simple workpiece handling tasks; The feed clamp becomes the end actuator of the workpiece; and The method further includes the robot inserting the workpiece until the robot keeps the workpiece close to its center of gravity; and The robot places the workpieces in different locations with the same or different orientations.

22. The system according to claim 20, wherein, The feed clamp has a mirror-symmetric plane, and the axis of the tool extends along the mirror-symmetric plane; and The distance between the two mirror-symmetrical halves of the feed clamp is adjustable so as to manipulate the flexible portion of the workpiece with minimal deflection.

23. A method for performing operations on an elongated, bent workpiece, comprising: The geometry of the workpiece, defined in the workpiece coordinate system, is decomposed into: The primary geometry includes the cross-section of the part, which is swept along the ridge line of the part. Secondary geometries, comprising deformations of cross-sectional geometries superimposed on the primary geometry as a function of the length along the ridge line, and A three-level geometry, comprising a machining vector, under which one or more defined machining operations will be performed; Create a length coordinate, which is equal to the arc length of the curve along the ridge of the workpiece; The workpiece is supported and clamped by a feed clamp at a defined position along the length of the workpiece, such that the workpiece is fully constrained in six degrees of freedom in a position and orientation known relative to the operation center. The workpiece is moved along the length coordinate by the feed clamp, while the other five degrees of freedom of the workpiece are constrained. The distance along the length coordinate is measured by measuring the movement of the workpiece's ridgeline through a measuring point on the feed clamp; The origin of the length coordinate is set when a specific feature of the workpiece coincides with a specific positioning point of the feed clamp. The workpiece is fed along the length coordinate until the predetermined length of the workpiece is located at the measurement point; The three-level geometry of the segment held within the feed clamp is determined based on the length coordinates and the overall geometry of the workpiece. The time series of transformations of the workpiece's tertiary geometry into a calculated machining vector in machine coordinates is based on the known position and orientation of the segment maintained by the structure of the feed clamp relative to the operation center. The tip of a tool held in the end actuator at the operation center is positioned and oriented along a time sequence of a calculated machining vector in the machine coordinate system, and one or more operations are performed on the workpiece through the operation center.

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