Linear motor curve module with improved geometry

A linear motor system has multiple modular track sections joined end-to-end to form a track along which movers may be displaced by the control of magnetic fields generated by coils disposed in each track section. A curved track section is provided that includes a non-constant radius of curvature that is a non-linear function of the run length along the curved track section. The curved track section may have a number of different radii of curvature, and one or more of them may be based on a non-linear function of the run length. The resulting curvature provides improved dynamic performance of movers driven along the curved track section.

BACKGROUND

The invention relates generally to linear motor systems having curved sections, and more particularly, to motors in which modular track and motor sections have unique geometries designed to provide improved dynamic characteristics.

A range of linear motors are known and in use throughout industry, particularly in manufacturing, filling, and material handling applications. Such motors typically include an elongated track in which motor coils are associated with a stator core, such as a laminated core. The coils may have various orientations, depending upon the motor design. A permanent magnet mover may be placed on the track, and fields resulting from selective energization of the track coils interact with permanent magnets of the mover to cause the mover to move along the track in desired directions, speeds, and accelerations, and to stop and start at desired locations. Highly flexible and precise control of movement of one or many movers may be achieved by control and driver circuitry associated with the coils of the track sections.

Because available track sections may need to be designed for a wide range of applications, orientations, and path layouts, they are typically made modular. Currently available tracks include either straight sections or curved sections, and these are typically joined end-to-end to provide the desired transport path for the movers. At turns or curves, modular curved sections may be joined to form various angles, such as 45 degrees, 90 degrees, and 180 degrees. Following a desired change in direction, then, the ends of the curved sections are joined with modular straight sections to continue the desired layout.

While such modular designs provide highly flexible design alternatives, they are not without drawbacks. For example, the geometry of the tracks in curved sections, and the transition between straight sections and different radii of curvature can significantly affect the dynamics of the system, and may require slowing movers as they progress around the tracks. In particular, control signals applied to displace movers along the tracks typically regulate position and derivatives of position, specifically velocity and acceleration. But even higher order derivatives of position can affect the dynamics of the movers and payloads carried by them. These may be somewhat improved by the use of geometries such as clothoids and splines, as well as the use of multiple different clothoid or spline geometries in each curve, but the dynamics resulting from higher order derivatives of position still limit performance.

There is a need, therefore, for improved linear motor designs that can address at least some of these concerns.

BRIEF DESCRIPTION

The present disclosure relates to linear motor systems designed in view of such needs. In accordance with certain aspects of the disclosure, a linear motor system comprises a permanent magnet mover configured to be displaced by a controlled magnetic field, a modular straight track section, and a modular curved track section positionable adjacent to the modular straight track section to provide a continuous track. Each track section comprises a plurality of coils energizable to create the controlled magnetic field for movement of the mover, and each track section is configured to support and guide the mover in movement along the track sections. Control and driver circuitry is coupled to the coils and configured to control energization of the coils to create the controlled magnetic field. The curved track section has a curvature non-constant radius of curvature that is a non-linear function of a run length along the curved track section.

In accordance with another aspect of the disclosure, a modular curved track section is provided that is positionable adjacent to other modular track sections to provide a continuous track, wherein the curved track section has a curvature non-constant radius of curvature that is a non-linear function of a run length along the curved track section.

In accordance with a further aspect of the disclosure, a linear motor system comprises a permanent magnet mover configured to be displaced by a controlled magnetic field, a modular straight track section, and a modular curved track section positionable adjacent to the modular straight track section to provide a continuous track. Each track section comprises a plurality of coils energizable to create the controlled magnetic field for movement of the mover, and each track section is configured to support and guide the mover in movement along the track sections. Control and driver circuitry is coupled to the coils and configured to control energization of the coils to create the controlled magnetic field. The curved track section has a curvature following a geometry that results in the mover, when moving under the influence of coils energized at a fixed rate along the curved track section, experiencing a non-linear jerk.

DETAILED DESCRIPTION

Turning now to the drawings, and referring first toFIG. 1A, a linear motor system10as illustrated for moving articles or products around a track12. As will be appreciated by those skilled in the art, in many applications, the linear motor system will be configured to inter-operate with other machines, robots, conveyers, control equipment, and so forth (not separately shown) in an overall automation, packaging, material handling or other application. The linear motor system itself generally comprises a “linear motor” as discussed below, in which the moving components are positioned, accelerated, decelerated, and generally moved under the influence of controlled magnetic and electromagnetic fields. In the illustrated embodiment, the track12comprises straight track modules14and curved track modules16. As discussed below, at least one of the curved track modules incorporates an improved curve geometry that offers enhanced dynamic performance. These modules may be generally self-contained and mountable in various physical configurations, such as the oval illustrated inFIG. 1A. It should be noted that other configurations are equally possible as discussed below. The configurations may form closed loops of various shapes, but may also comprise open-ended segments. The system further comprises one or more movers18which are mounted to and movable along the track. Again, the position, velocity, acceleration, and higher order derivative parameters are controllable for these movers by appropriate control of the coils of the system that are energized and de-energized as discussed below. In the illustrated embodiment, the movers18interact with stationary elements in and around an outer periphery20of the track modules, although other configurations are envisaged. A sensor system22is provided to detect positions of the movers around the track, and such center systems may comprise permanent magnets, energized coils, Hall effect sensors, or any other suitable devices. In general, one component of the sensor system will be mounted on the movers, while another component will be mounted at fixed locations around the track.

Each mover further comprises a mounting platform24. In an actual implementation, various tools, holders, support structures, loads, and so forth may be mounted to this mounting platform. The movers themselves may be configured differently from those shown in order accommodate the various loads. While a horizontal configuration is illustrated inFIG. 1A, other orientations may also be provided, such as ones in which the illustrated oval is generally stood on a side or end, or at any angle between.

The system further comprises circuitry for controlling a movement of the movers. In the embodiment illustrated inFIG. 1A, this circuitry includes a drive circuitry26that provides signals to each track module, and specifically individual coils (see below) of the track modules to create electromotive forces that interact with magnets on the modules to drive the modules to specific locations, and at specific velocity, accelerations, and so forth. This drive circuitry may typically include inverter circuitry that makes use of power electronic switches to provide drive power to the individual coils of each module in a controlled manner. In some embodiments, the drive circuitry may be included in each individual module, and signals provided to the drive circuitry by power and control circuitry28. This power and control circuitry (and the drive circuitry) may receive feedback from the movers and/or from the sensor system to detect the location, velocity, acceleration, and so forth of each mover. In certain embodiments the movers may also be configured to be recognized by the power and control circuitry28as individual axes that are independently controlled, but with regulation of their position, velocity and acceleration to avoid conflicts, collisions, and so forth. The particular motion profile implemented by the power and control circuitry28will typically be configured and implemented upon the design and commissioning of the system, here again, depending upon the particular task to be performed. Finally, various remote control and/or monitoring circuitry30may be provided and this circuitry may be linked to the system by one or more networks32. Such remote circuitry may generally allow for coordination of the operation of the transport system with other automation components, machine systems, manufacturing and material handling machines, and so forth.

FIG. 1Billustrates an alternative configuration for a similar linear motor system. However, in this configuration, rather than motor coils being positioned around the periphery of the system, coils are positioned around the top of the system, in a generally planar arrangement. Magnet assemblies of each mover16face these coils and are spaced from the coils by a small air gap. Straight and curved track modules are assembled, as above, to form an oval, although other shapes and layouts may be formed. The curved track modules may be adapted with modified spline geometries, as in the case of the system shown inFIG. 1A, and as described in greater detail below. Moreover, in this embodiment as well, at least one of the curved modules comprises an improved curve geometry that offers enhanced dynamic performance.

FIG. 2is a diagrammatical representation of the linear motor system showing one track module36and one mover18positioned along the track module. The track module illustrated inFIG. 2may be a straight or curved track module, these two differing in their physical configuration, and certain of the actual characteristics owing to the curved nature of the curved modules as discussed below. In general, however, each mover comprises a magnet array38on which a number of magnets40are mounted. These will typically be permanent magnets and are mounted such that a small air gap is provided between the magnets and coils of the track module described below. As shown inFIG. 2, the track module36further comprises a sensor component42, such as a permanent magnet. It should be noted, however, that the particular sensor component included in the track module will depend upon the nature of the sensing strategy, the sensing resolution, the position of the sensor on the mover (and cooperating components on the track module), and so forth. The platform44is provided on the mover while mounting tools and the like as discussed above. Finally, bearings and associated components (e.g., rollers) are mounted to the mechanical structure of the mover and serve to interact with one or more rails, as indicated by reference numerals46and48, respectively. These bearings and rails allow the mover to remain securely attached to the track modules while allowing relatively free movement of the movers along the track modules and supporting mechanical loads and forces encountered during motion.

The track module36will typically include a series of parallel coils50that are associated with a stator or armature52. In currently contemplated embodiments, these coils are mounted into slots in the stator, and the stator itself may be made of magnetic material formed into a stack of laminates and structured to allow for mounting within the track module housing. Particular configurations, magnetic, mounting structures and the like of the coils and stator components are generally beyond the scope of the present disclosure. Drive circuitry54may be included in each module as discussed above to allow for controlled power signals to be applied to the coils in order to drive and position the movers appropriately around the track module. Finally, a sensor array56is provided in each track module to allow for interaction with the sensor components of the movers. This sensor array will typically provide feedback that can indicate the position of the movers, and can be used to derive velocity, acceleration, jerk and other motion parameters. In the illustrated embodiment a plurality of track modules may be mounted end-to-end and interconnected with one another and/or with the power and control circuitry to received signals used to power the coils.

As will be appreciated by those skilled in the art, track modules, along with the magnet arrays of the movers, will generally form what may be considered a linear motor system. That is, electromotor force is generated by the controlled fields of the coils and interaction between these fields and the magnetic fields of the magnet array serve to drive the mover into desired positions, at desired speeds, and so forth. As noted above, these coils and the linear motor itself may be designed in accordance with various configuration strategies, such as ones having the coils arranged around a periphery of the track modules, ones in which the coils are generally planar (in a top or bottom position of the modules), and so forth. Although the “linear” motor system may be used in the present disclosure, it should be appreciated that curved modules in various configurations are intended to be included under this rubric.

In addition to the configurations shown inFIGS. 1A and 1B, various other physical layouts may be employed, such as those shown inFIGS. 3A, 3B and 3C.FIG. 3Aillustrates a linear motor system having an oval configuration58. Here the configuration is made of several straight modules60and end modules62that form 180 degree curves. Any number of straight modules may be provided, and as described more fully below, the curved modules may be provided in a single unit forming 180 degrees to close the oval or in smaller units of 90 degrees, 45 degrees, 30 degrees, and so forth. As shown inFIG. 3B, square configurations64may be similarly formed by insertion of straight modules66between 90 degree modules68. In the rectangular configuration70ofFIG. 3C, straight modules72are inserted between 90 degree modules74, with a different number of straight modules on each side to form a generally rectangular configuration. Other configurations may include various turns, interior and exterior curves, S-shapes, open-ended track sections, and so forth.

It should also be noted that a number of different coil and magnet configurations may be employed with the innovations summarized in the present disclosure. These may include, for example, the peripheral coil and facing magnet arrangements discussed above, and the generally planar coil arrangements with facing magnet arrangements also discussed above. Other arrangements may include opposing coils and/or magnets, with the cooperating magnets/coils in facing relation, T-shaped magnet and/or coil structures, and so forth.

As discussed in greater detail below, the curved track modules of the transport system are configured with a curvature that has a non-constant radius, but that is a non-linear function of the run length along the curved track module. That is, for example, the radius of curvature may be function of a higher or different order of the run length. In some presently contemplated embodiments, for example, the entry of the curved track module may have a gentle curvature, such as with a radius proportional to the inverse of an order of the run length less than one (e.g., the square root). Other radii of curvature may be proportional to the inverse of higher orders of the run length, such as the square, or cube. Still further, more complex geometries may be used that may be defined as a polynomial where the run length is a term. It is also contemplated that more than one radius may be used, such as a gentle radius portion (e.g., proportional to an inverse of a order of the run length less than one) at the entry (and exit), a constant radius section at a point near or adjacent to this portion, and a more aggressive radius thereafter (e.g., proportional to an inverse of an order of the run length greater than one).

In practice, to accommodate smooth transitions, the curved track section may be laid out as a progression of curvatures having progressively greater and/or progressively smaller radii. One or more of the curvatures may have a constant radius, and one or more of the curvatures may comprise a conventional clothoid form. Still further, integral straight sections may be provided on one or both ends of the curved track section.

Combinations of these may be used to provide desired dynamics. Control signals applied to the coils of the curved track section may afford some degree of control of the mover dynamics, but the curvature of the track aids in achieving smooth control and improved dynamics. In particular, the track geometry enables control of position, velocity, and acceleration, but also of higher order derivatives of jerk (rate of change of acceleration) and snap (rate of change of jerk). In some cases the control signals may be simplified by virtue of the dynamics offered by the improved track geometry. That is, assuming constant pitch of the coils in the curved track section, and energization of successive coils at fixed intervals, the geometries may provide for jerk and/or derivatives of jerk that are finite (as opposed to instantaneous and theoretically infinite as in conventional geometries).

FIG. 4is a diagrammatical view of an example curved track section having the new geometry according to the disclosure. This generic view is provide for the following discussion of options for improved curvatures that enhance the dynamic characteristics of the resulting linear motor system. The curved track section76is shown as having a curved portion78, and optional integral straight portions80and82at either end. A direction of travel is indicated by arrow84. It should be noted, however, that while a section of approximately 180 degrees is illustrated, and a direction of travel is indicated, other extents can be defined (as discussed below), and the direction of travel could be reversed. In some embodiments, the curvatures are defined to accommodate a particular direction of travel (e.g., into or out of the curved section), while in others, the curved section is essentially symmetrical, such that the direction of travel can be reversed without materially altering the dynamic performance.

The illustration ofFIG. 4shows several points or portions along the curved section, including what may be termed a per-entrance location86, an entrance location88, a curve90, an exit location94, and a post-exit portion96. As discussed below, by selection of the curvatures of one or more of these portions or locations, different motion profiles may be obtained. Example motion profiles are shown inFIGS. 5 and 6.

In the example ofFIG. 5, a motion profile98is illustrated graphically as centripetal acceleration along axis100, as a function of travel distance along axis102. Assuming a constant linear velocity (e.g., resulting from moving under the influence of coils energized at a fixed rate along the curved track section), the mover would experience a finite jerk and/or a finite snap. In the graphical illustration ofFIG. 5, points along the profile correspond to locations or portions ofFIG. 4as follows: location104corresponds to per-entrance location86, location106corresponds to entrance location88, location108corresponds to curve90, location112corresponds to exit location94, and location114corresponds to post-exit portion96. Location110inFIG. 5is a point between the curve and the exit location.

In this example, the geometry of the curved section has been selected to provide a “gentle” entry, such as by creating a radius of curvature that is proportional to an inverse of the square root of the run (arc) length (that is, the length of travel from the entrance point. As the radius decreases, the selected radius changes to a curvature that is proportional to the inverse of the run length (e.g., a clothoid curvature). The minimum radius is pre-determined, such as based upon the design and performance of bearings and other mechanical components of the track, the mover, or both, or upon such factors as the anticipated loading of the mover. Other factors may include, for example, the anticipated envelope or space available for the curve. The peak centripetal acceleration is higher than it would be for a constant (fixed, circular) radius, however, the transition is linear, resulting in a constant, finite third derivative of position (i.e., derivative of acceleration, or jerk). In this case, the fourth derivative of position (snap) may also be finite during the straight-to-curve transition, but may still have an “infinite” nature between the variable and constant radius portions. There is a tangential acceleration throughout the variable radius portion, which stops once on the constant radius portion, and the jerk in that portion is zero.

FIG. 6illustrates another motion profile available by another selection of the curvatures of the curved section ofFIG. 4. In this case, the motion profile116is again depicted graphically as centripetal acceleration as a function of travel distance. Here, the points along the profile correspond to locations or portions ofFIG. 4as follows: location118corresponds to per-entrance location86, location120corresponds to entrance location88, location122corresponds to curve90, location124corresponds to exit location94, and location128corresponds to post-exit portion96. Location124inFIG. 5is a point between the curve and the exit location.

In this example, as the mover would move from the straight portion to the curved portion, the radius is changes as a function of the inverse of the run (arc) length (e.g., clothoid). Approaching the apex of the curve, a higher order function is applied to the curvature, such as a radius that changes proportionally with the inverse of the square of the inverse of the run length. As a result, the snap is still has an “infinite” nature for a brief moment, but only at the start and end of the curve. At the apex it has smooth transitions.

It should be noted that in practice, various combinations of these features may be incorporated in to the curved track section. For example, the multiple curvatures may be used, including portions that have a changing radius that is a function of an inverse of a power of the run length lower than unity, portions that have a changing radius that is a function of an inverse of a power of the run length greater than unity, as well as integral straight portions, integral clothoid portions, and integral portions having a constant radius (circular). The resulting geometries may be allow for coil control signals that are coordinated to provide much improved dynamic characteristics of movers as they advance from straight sections, into curved sections, through curved sections, and out of curved sections.

FIGS. 7A-7Gare line diagrams of various curved track section configurations incorporating the new geometries offered by the present techniques.FIGS. 7A-7Crepresent example curved track section configurations that cover approximately 90 degrees of travel. The section130shown inFIG. 7Ahas a first portion132followed by a second portion134. The first portion has a radius of curvature136that varies as a function of the run length, indicated by arrow138, while the second portion has a radius of curvature136that varies as a function of the run length142. As noted above, the two portions may differently varying radii (e.g., changing progressively as a different function of the run length, such as proportionally with the inverse of a different power of the run length). Also illustrated as two optional integral straight portions144and146(either or both may be provided, or in some embodiments no integral straight portion is provided). In the embodiment ofFIG. 7B, the curved track section148has three different portions150,152, and154, that each have differently changing curvatures, as indicated by reference numerals156,158, and160. Here again, such curvatures may include radii that vary with an inverse of a different power of the run length, or that may be clothoid in form, constant radius in form, or some other geometry.

The illustration ofFIG. 7Cis intended to demonstrate that, in practice, a curved track section164may comprise a large number of portions166each having a differently changing curvature168. Such shapes may facilitate manufacture, such as by “stepwise” changing the curvature of each portion to provide an overall curvature that offers the dynamic performance desired (e.g., acceleration, jerk, snap), in conjunction with control signals applied to the coils of the track section.

FIGS. 7D-7Fillustrate that different segments may be formed by the present techniques. These might include, for example, a section170of approximately 22.5 degrees, as shown inFIG. 7D, a section172of approximately 45 degrees as shown inFIG. 7E, and a section174of approximately 174, as shown inFIG. 7F. In these illustrations, the different track sections are shown as using a single varying radius, but it should be understood that any and all of the multi-curvature techniques described above may be employed on these as well. The resulting collection of sections may form a modular product line from which system designers may select to configure a wide variety of track shapes and layouts.

Similarly,FIG. 7Gillustrates an embodiment in which a curved track section130of the type described above with reference toFIG. 7Ais formed symmetrically and in a manner that makes it “flippable”, as indicated by reference numeral130′. Such configurations could also be used for track sections that have any of the geometries and extends described above.