Abstract:
A linear motor system includes a coil assembly, a movable magnet assembly, and a bearing assembly coupled to facilitate movement of one of the magnet assembly and the coil assembly with respect to the other. The bearing assembly includes a single bearing rail, wherein the single bearing rail is a separate component from the coil assembly and the magnet assembly and is mounted to the magnet assembly on a major face thereof opposite the major face thereof adjacent to which the coil assembly is disposed. The single bearing rail is narrower than the coil assembly and the magnet assembly. The single bearing rail includes a profiled rail configured to hold the magnet assembly on the coil assembly while allowing the magnet assembly to move along the coil assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/789,320, entitled “Sealed Linear Motor System”, filed May 27, 2010, which is herein incorporated by reference. 
    
    
     BACKGROUND 
     The invention relates generally to linear motors, and particularly to a linear motor system with a single bearing rail for ease of assembly and improved performance. 
     Linear motors are known in the art and are used in a variety of applications such as machining, robotic positioning and food processing and packaging applications. One type of a linear motor system includes stationary armatures having coils and movable stages containing magnets. Typically, the armature windings may be mounted to a base plate and a stage with a series of magnets is free to move on the base plate. The stage is guided in a desired direction by applying AC or DC excitation to the coils. Another type of linear motor system includes stationary magnets and moving coils. 
     In certain applications, the linear motor systems may be subjected to loads that may cause stresses on alignment structures of the motor systems. For example, side loading may occur that can cause bearings to exert forces on guide rails and other structures in ways that may lead to early wear and limit the life of the motors. Moreover, many linear motor systems comprise a pair of rails or guides that bear such side loading. These must generally be aligned with one another to avoid unwanted excessive side loading that can similarly lead to accelerated wear and limit life. Careful alignment of parallel rails of this type can be demanding during manufacturing and assembly. 
     Accordingly, it would be desirable to develop a linear motor system that can be employed in applications where side and other loading is anticipated. 
     BRIEF DESCRIPTION 
     Briefly, according to one embodiment of the present invention, a sealed linear motor system is provided. The sealed linear motor system includes a sealed coil assembly having a plurality of coil windings within a base plate and comprising covers disposed about the base plate and coil windings to prevent moisture and/or chemical ingress into the base plate and the coil windings. The sealed linear motor system also includes a sealed magnet assembly disposed adjacent to the coil assembly and comprising a plurality of magnets mounted on a magnet mounting plate and a magnet housing disposed on a surface of the magnet mounting plate to cover and seal the plurality of magnets within the housing. 
     In accordance with another aspect, a sealed linear motor system is provided. The sealed linear motor system includes a sealed coil assembly having a plurality of coil windings within a base plate and comprising covers disposed about the base plate and coil windings to prevent moisture and/or chemical ingress into the base plate and the coil windings. The sealed linear motor system also includes a sealed magnet assembly disposed adjacent to the coil assembly and comprising a plurality of magnets mounted on a magnet mounting plate and a magnet housing disposed on a surface of the magnet mounting plate to cover and seal the plurality of magnets within the housing. The sealed linear motor system further includes a motor stage structure secured to the coil assembly or to the magnet assembly and configured to receive a movable machine component and a bearing assembly coupled between the coil assembly or the magnet assembly and the motor stage structure and configured to facilitate linear motion of the magnet assembly relative to the coil assembly. 
     In accordance with another aspect, a sealed linear motor system is provided. The sealed linear motor system includes a sealed coil assembly having a plurality of coil windings within a base plate and comprising covers disposed about the base plate and coil windings to prevent moisture and/or chemical ingress into the base plate and the coil windings. The sealed linear motor system also includes a sealed magnet assembly disposed adjacent to the coil assembly and comprising a plurality of magnets mounted on a magnet mounting plate and a magnet housing disposed on a top surface of the magnet mounting plate to cover and seal the plurality of magnets within the housing. Further, the sealed linear motor system includes at least one encoder sensor sealed within the coil assembly and configured to sense position and/or motion information of the magnet assembly. 
     In accordance with another aspect, a sealed linear motor system is provided. The sealed linear motor system includes a sealed coil assembly having a plurality of coil windings within a base plate and including covers disposed about the base plate and coil windings to prevent moisture and/or chemical ingress into the base plate and the coil windings. The sealed linear motor system includes a sealed magnet assembly disposed adjacent to the coil assembly and comprising a plurality of magnets mounted on a magnet mounting plate and a magnet housing disposed on a top surface of the magnet mounting plate to cover and seal the plurality of magnets within the housing. The sealed linear motor system also includes a sealed sensor assembly disposed adjacent to the magnet assembly and having at least one encoder sensor configured to sense position and/or motion information of the magnet assembly. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  illustrates a sealed linear motor system in accordance with aspects of the present technique. 
         FIG. 2  is an exploded view of the stator assembly of  FIG. 1  in accordance with aspects of the present technique. 
         FIG. 3  is an exploded view of the magnet assembly of  FIG. 1  in accordance with aspects of the present technique. 
         FIG. 4  is a perspective view of the sealed linear motor system of  FIG. 1  in accordance with aspects of the present technique. 
         FIG. 5  illustrates an exemplary configuration of an encapsulated sensor assembly employed in the sealed linear motor system of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     As discussed in detail below, embodiments of the present technique function provide a sealed linear motor system for use in applications such as food processing applications, wet installations and chemical laden environments. In particular, the sealed linear motor system includes individually sealed coil and magnet assemblies to prevent moisture and/or chemical ingress within the system. 
     References in the specification to “one embodiment”, “an embodiment”, “an exemplary embodiment”, indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     Turning now to drawings and referring first to  FIG. 1 , a sealed linear motor system  10  is illustrated. The system  10  includes a coil assembly  12  and a magnet assembly  14  disposed adjacent to the coil assembly  12 . The system  10  further includes a bearing assembly  16  coupled to the magnet assembly  14  and configured to facilitate linear motion of the magnet assembly  14  relative to the coil assembly  12 . The coil assembly  12  includes a plurality of sealed coil windings laminated on an iron core. Further, the magnet assembly  14  includes a plurality of magnets covered by shrouds. 
     In operation, the coil assembly  12  is configured to receive power from a power source (not shown in  FIG. 1 ) such as a three-phase power supply. The bearing assembly  16  includes a rail  18  that facilitates movement of the magnet assembly  14  along the coil assembly  12 . This bearing assembly  16  may include two or more bearing elements (not shown) that engage elongated recesses in the rail  18  to hold the magnet assembly  14  on the coil assembly  12 , while allowing it to move along the coil assembly  12 . A controlled magnetic field produced by the coil assembly  12  acts on the magnet assembly  14  to produce a linear force for driving the magnet assembly  14  and any external load secured to it. 
     In the illustrated embodiment, the system  10  includes a top plate  20  to secured to the magnet assembly  14 . Further, the system  10  also includes side supports such as represented by reference numerals  22  and  24  to link the top plate  20  to any other support structures, such as a lower support plate. 
     In the illustrated embodiment, each of the coil assembly  12 , the magnet assembly  14  and the bearing assembly  16  have an environmentally protected design as will be described in detail below. Moreover, the materials for each of these components are selected for use in environments such as wet installations, chemical laden environments, among others. In a presently contemplated embodiment, the external shells of the assemblies are made of stainless steel. 
     It should also be noted that the arrangement shown in  FIG. 1  may be referred to as a motor stage. The plates and supports associated with the linear motor may take various forms in such a motor stage, but are typically designed to support a moving component. That is, in an embodiment in which the coil assembly  12  is stationary, it will be secured to a machine and powered by an external power source (such as three-phase power supplied via any desired switchgear, circuit breakers, and so forth. The power may be controlled to regulate movement of the magnet assembly  14  along the coil assembly  12  via the bearing rail. The moving machine component, secured to the stage, such as via fasteners interfacing with the supports around the magnet assembly may thus be made to move to desired locations. The stage may be used for a wide variety of operations, such as pick-and-placement, material handling, containing forming, just to mention a few. 
     Furthermore, it should be noted that in the illustrated embodiment, the coil assembly  12  is designed to be stationary, while the magnet assembly  14  moves along it. The arrangement may be reversed, such that a sealed coil assembly  12  moves along a sealed magnet assembly  14 . In such cases, the two assemblies  12  and  14  may be sealed with techniques such as those described below. 
     Still further, the particular stage arrangement may employ various bearing configurations. In the illustrated embodiment, a single bearing rail is provided on the upper side of the coil assembly  12 . In other embodiments, the bearing assembly  16  may be provided on the lower side, and other bearing techniques may be used. Similarly, the entire arrangement may be inverted or otherwise positioned, such that either the coil assembly  12  or the magnet assembly  14  may be located on top of the combined structure, or the structure may be positioned at various angles other than horizontal. 
     In certain exemplary embodiments, the system  10  may include position sensors, such as Hall-effect sensors coupled to the coil assembly  12  for sensing position information of the magnets of the magnet assembly  14 . In certain other embodiments, the system  10  may include such sensors in an encapsulated assembly external to the coil assembly  12 . The encapsulation of the sensors prevents any moisture ingress into the sensors. 
       FIG. 2  is an exploded view  30  of the coil assembly  12  of  FIG. 1  in accordance with aspects of the present technique. As illustrated, the coil assembly  30  includes a plurality of coil windings  32  with an iron core laminated over a base plate  34 . In this exemplary embodiment, the base plate  34  is made of stainless steel. In the illustrated embodiment, the coil windings  32  are disposed in coil retainers such as represented by reference numeral  36 . 
     The coil assembly  30  further includes a top cover  38  and side covers represented by reference numerals  40  and  42  disposed about the coil windings  32  and the base plate  34 . In the illustrated embodiment, the top cover  38  and the side covers  40  and  42  may be bolted to the lamination stack. The top cover  38  and the side covers  40  and  42  are configured to prevent moisture and/or chemical ingress into the base plate  34  and the coil windings  32 . In one exemplary embodiment, the top cover  38  and the side covers  40  and  42  are made of stainless steel. However other suitable materials may be employed for the top cover  38  and the side covers  40  and  42 . 
     In this exemplary embodiment, a sealing material is employed to bond and seal the plurality of coil windings  32  to the base plate  34 . In one exemplary embodiment, the sealing material includes a resin. In this exemplary embodiment, the sealing material includes thermal conducting epoxy such as manufactured and marketed by Emerson &amp; Cummings Stycast that is commercially available in the market. The base plate  34  includes a plurality of grooves and encapsulation plugs such as represented by reference numeral  44  for sealing the coil windings  32  with the sealing material. Furthermore, sealing washers  46  are disposed on the base plate to prevent leakage of moisture and/or chemicals into the coil windings  32  and the base plate  34 . In this exemplary embodiment, the sealing washers  46  include nylon. 
     The coil assembly  34  further includes end caps  48  and  50  disposed on both ends of the coil windings  32 . In this exemplary embodiment, the end cap  48  includes components for facilitating electrical connections of the coil assembly  30  with a power supply and/or a controller. Where an internal encoder sensor is provided, as in the illustrated embodiment, two such electrical connections may be provided, one dedicated to supplying power, and the other for conducting sensed position signals. Both connections are sealed. 
     The coil assembly  34  further includes a printed circuit board  52  having at least one encoder sensor for sensing position and/or motion information of the magnet assembly  14  (see  FIG. 1 ). As will be appreciated by those skilled in the art, the sensed signals may be processed (at least partially) within the coil assembly  12 , or fully by external circuitry. In either case, position signals may be used to derive velocity signals and acceleration signals, where desired, and any such signals may be used as feedback to accurately position and move the stage as needed in the particular application. 
     The printed circuit board  52  may be coupled to the base plate  34  using any suitable connecting arrangement. In this exemplary embodiment, a bracket  54  is employed to connect the printed circuit board  52  to the base plate  34 . In this example embodiment, the at least one encoder sensor includes an analog Hall-effect sensor mounted on the surface mounted printed circuit board  52 . 
     As will be appreciated by those skilled in the art, the coil assembly  34  may include other suitable components such as sealed cable connectors  56  and  58  for facilitating connection with a power supply and a controller respectively. 
     As can be seen, the components of the coil assembly  32 , such as the coils  32 , the base plate  34  and the printed circuit board  52  with the encoder sensors are sealed using corrosion resistant materials in a stainless steel housing. Further, the coil assembly  32  is fully encapsulated and sealed with epoxy matrix to prevent ingress of moisture and/or chemicals into the coil assembly  32 . 
       FIG. 3  is an exploded view  70  of the magnet assembly  14  of  FIG. 1  in accordance with aspects of the present technique. As illustrated, the magnet assembly  70  includes a plurality of magnets such as represented generally by reference numeral  72 , mounted on a magnet mounting plate  74 . The magnets  72  may be mounted on the magnet mounting plate  74  using a suitable adhesive. A magnet housing  76  is disposed on a top surface  78  of the magnet mounting plate  74  to cover the plurality of magnets  72 . In this exemplary embodiment, each of the magnet mounting plate  74  and the magnet housing  76  is made of stainless steel. 
     The magnet assembly  70  further includes a sealing material configured to place and seal the magnet mounting plate  74  and the magnet housing  76 . In one exemplary embodiment, the sealing material is an elastomer. In the illustrated embodiment, O-ring seal is disposed between the magnet mounting plate  74  and the magnet housing  76 . 
     The magnet mounting plate  74  may include grooves for laying a O-ring seal  80  between the magnet mounting plate  74  and the magnet housing  76 . In certain embodiments, the O-ring seal comprises elastomers such as ethylene propylene, fluorocarbon, neoprene, nitrile and silicone. 
     In certain embodiments, the sealed magnet assembly  70  may be mounted to an external mounting plate  82  via fasteners such as represented by reference numeral  84 . In the illustrated embodiment, the magnet assembly  70  also includes a linear guide  86 , corresponding to rail  18  shown in  FIG. 1 , configured to facilitate the movement of the magnet assembly  70 . 
     In this exemplary embodiment, the magnet assembly  70  further includes a magnetic encoder scale (not shown) mounted to the magnet assembly  70 . The magnetic encoder scale is configured to produce an output corresponding to the position and/or motion information of the magnet assembly  70 . In the illustrated embodiment, the magnet assembly  70  includes other suitable components such as block stops  88  and  90  for controlling the movement of the magnet assembly  70 . As can be seen, the magnet assembly  70  with the plurality of magnets  72  and the magnetic encoder scale are sealed in stainless steel housing, thereby protecting the magnets  72  from moisture and/or chemicals during wash down operations such as required in food processing and other applications. 
       FIG. 4  is a perspective view  100  of the sealed linear motor system  10  of  FIG. 1 . As illustrated, the system  100  includes the coil assembly  12 , the magnet assembly  14  and the bearing assembly  16  disposed within a stage support steel housing  102 . As described before, each of these components employ corrosion proof materials such as stainless steel. 
     In the illustrated embodiment, the stage support housing  102  includes a motor stage structure configured to receive a movable machine component. The motor stage structure includes the top plate  20  and the side supports  22  and  24  configured to support the top plate  20 . The top plate  20  is coupled to the bearing assembly  16  and the side supports  22  and  24  through fasteners  104  such as through a screw and washer arrangement. As illustrated, the top plate  20  and the side supports  22  and  24  provide structural integrity of the system  100  while providing supports for the coils  32  (in the coil assembly  12 ) and magnets  72  in the magnet assembly  14 . The top plate  20  further includes encapsulation plugs such as represented by reference numeral  106  for sealing the system  100  using a sealing material. 
     In the illustrated embodiment, the bearing assembly  16  includes the linear guide  86  and other components such as bearings to guide the movement of the magnet assembly  14 . Further, the bearing assembly  16  also includes the block stop such as represented by reference numeral  88  for controlling the movement of the magnet assembly  14 . The system  100  also includes other suitable components like the cable connectors  56  and  58  for connection of electrical cables while providing strain relief at the connection points. 
     In certain embodiments, the components of the coil assembly  12 , the magnet assembly  14  and the bearing assembly  16  are passivated and electropolished thereby resulting in a smooth surface to facilitate wash down of the components. In the illustrated embodiment, the components of the system  100  are assembled with suitable clearances and air gaps between the parts to facilitate minimum build-up of material in the system  100  for easy wash down of such components. 
     Furthermore, compliant sealing materials such as elastomers are utilized to seal such components. The bearing assembly  16  may include stainless steel bearings and food grade grease. Moreover, the components are assembled to avoid any possible water traps in the assembly of the sealed linear motor system  100 . In the illustrated embodiment, the interior spaces of the coil assembly  12  and the magnet assembly  14  are filled with a potting material after the components are assembled. In this exemplary embodiment, the assembly is sealed using thermal conducting epoxy. 
     As can be seen, the individually sealed components such as the coil assembly  12  and the magnet assembly  14  along with other components of the sealed linear motor system  100  are protected from moisture and/or chemical ingress within the housing  102  with the top plate  20 , side supports  22  and  24  and the sealing material. 
     In certain embodiments, the sealed linear motor system  100  may include encoder sensors in an encapsulated assembly external to the coil assembly  12 . The encapsulation of the sensors prevents any moisture ingress into the sensors.  FIG. 5  illustrates an exemplary configuration  120  of an encapsulated sensor assembly. The sensor assembly  120  includes a stationary enclosure  122 . Further, the sensor assembly  120  includes a movable enclosure  124  disposed about the stationary enclosure  122  with the magnet assembly. 
     In the illustrated embodiment, each of the stationary and movable enclosures  122  and  124  is made of stainless steel. The stationary enclosure  122  includes a printed circuit board  126  having encoder sensor arrays such as represented by reference numerals  128  for sensing position and/or motion information. In addition, the printed circuit board  126  includes Hall effect magnetic commutators represented by reference numeral  130 . 
     The sensor assembly  120  further includes encoder magnets  132  and commutation magnets  134 . In addition, the sensor assembly  120  includes a magnet mounting bar  136  that moves along with the movable enclosure  124 . The sensor assembly  120  further includes other suitable components such as a linear guide bushing  138 , an end cap  140  and a linear seal  142  for sealing the end of the assembly  120 . It should be noted that the components described above may be made of suitable corrosion resistant materials. 
     As will be appreciated by those skilled in the art, the sensed signals from the sensor assembly  120  may be processed (at least partially) via a processing circuitry within the assembly  120 , or fully by external circuitry. The sensor assembly  120  may be coupled to the linear motor system  100  using any suitable coupling mechanism. In one exemplary embodiment, the sensor assembly  120  is bolted to the linear motor system  100 . In certain embodiments, the sensor assembly  120  includes integral wipers and self aligning guide bearings. In the illustrated embodiment, interior spaces of the sensor assembly  120  are filled with a potting material. 
     The various aspects of the structures described hereinabove may be used for sealing linear motor systems for use in high pressure wash down or in wet environments. As described above, the technique utilizes sealing features and materials for preventing moisture ingress from high pressure wash down thereby allowing use of such systems in wet applications and in applications with hostile environments such as explosive environments. As will be appreciated by those skilled in the art, the use of such sealing mechanisms substantially enhances the survivability and reliability of such linear motor systems in wet installations, chemical laden environments and explosive environments. 
     While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.