Patent Publication Number: US-9407117-B2

Title: Shaped electrical conductor

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly-assigned U.S. patent application Ser. No. 13/445,114, filed Apr. 12, 2012, and granted as U.S. Pat. No. 8,623,226, entitled MAKING STACKED PANCAKE MOTORS USING PATTERNED ADHESIVES, by Schindler et al.; the disclosure of which is incorporated herein. 
     FIELD OF THE INVENTION 
     This invention relates to electric motors in general and in particular to electric motors having a flat armature wherein the armature comprises a conductive pattern formed on an insulating substrate. 
     BACKGROUND OF THE INVENTION 
     Electric motors are used in a wide variety of applications. In many of these applications, the weight of the motor is of critical importance. For example, in an electric car the overall weight of the vehicle is an important factor limiting the distance that the vehicle can be operated given a fixed battery capacity. However, given current designs, the electric motor itself can be among the heavier components in the vehicle. Thus while it is desirable to provide an electric motor have a high-power output for vehicle use, it is also desirable to have such a motor remain at a lower weight. 
     It will be appreciated that lighter weight electrical motors are otherwise desirable in many other applications as such motors and the manufactured goods in which such electric motors are incorporated are more easily transported, carried, manipulated, and used. Further, cost reductions and recycling advantages can be obtained where weight reductions are achieved by lighter weight electrical motors that require less material. 
     However, conventional wound motor designs do not readily lend themselves to weight reduction. One reason for this is that conventional wound coil motor designs require an armature or a stator having coiled conductors thereon. The coils are typically formed by winding wire on metallic laminates. The laminates provide shaped features about which the coils, typically made from a metal such as copper, can be wound. 
     These laminates add significant mass to the motor. This mass affects the operation of the system in which the motor is used by lowering the power-to-weight ratio of the system. In some cases, eddy currents can arise in the laminates, further reducing motor efficiency and lowering power-to-weight ratios. 
     In the case of an armature, the laminate mass can cause motor inefficiency in two additional ways. First, this laminate mass increases the inertia that must be overcome to start and stop rotation. Second, the laminate mass is at a distance from the axis of rotation of the armature. In an armature that has a shaft that has any eccentricity, or that has laminates that are not aligned with the shaft, this can create static and dynamic balance problems that consume energy. Additionally, shaft eccentricity and misaligned laminates affect the placement of the windings on the laminates, so the effects of any shaft eccentricity or laminate misalignment are further enhanced by the mass of the windings. 
     One effort to reduce the use of such laminates involves pancake or flat motors. Conventional flat motors are used in a variety of applications. For example, U.S. Pat. No. 8,076,808 describes a flat vibration motor, such as can be used in a cellular telephone. EP 0548362A1 describes construction of a typical prior-art flat motor, also known as a “pancake motor.” The example described is a flat coreless DC motor having flat armature coils mounted on a disk. The coils are wound into sectors of the disk. The disk can be the rotor and can be mounted over a stator including a field magnet. When current is passed through the coils via a commutator, the rotor turns. 
     Various ways of manufacturing pancake motors, and specifically windings and rotors for pancake motors, have been described. WO 2009/038648 describes applying insulating material over a pre-formed electrical conductor and heating the assembly to activate an adhesive that bonds the insulating material to the conductor. However, this requires an insulator that includes the heat-activated adhesive, and requires that the conductors be formed to shape before being insulated. 
     U.S. Patent Publication No. 2002/0105237 describes a stator for a planar linear motor. The stator includes magnetic sheets (i.e., sheets of a material that can complete a magnetic circuit) set vertically and bound together, e.g., using a fluid hardening material or an epoxy resin. 
     However, such pancake motors use laminate structures that extend typically further from an axis of rotation than do conventional motors, creating increased balance problems, and adding weight. Further such motors have limited performance characteristics compared to conventional wound laminate motors. 
     What is needed in the art are motors that provide conventional performance characteristics while offering reduced motor mass. What is also needed in the art are new methods for motor manufacture. 
     SUMMARY OF THE INVENTION 
     Briefly, according to one aspect of the present invention a shaped electrical conductor includes a first sheet of metal with a first thermoplastic adhesive pattern on a first surface and a second thermoplastic adhesive pattern on a second surface. The second pattern is justified with the first pattern. The first sheet is etched to remove metal not covered by the thermoplastic adhesive patterns so that no metal bridges remain between disconnected coated portions of the first sheet. A second sheet of metal has a third thermoplastic adhesive pattern on a first surface and a fourth thermoplastic adhesive pattern on a second surface and the fourth pattern is justified with the third pattern. The second sheet is etched to remove metal not covered by the thermoplastic adhesive patterns so that no metal bridges remain between disconnected coated portions of the second sheet. First and second contact regions in the second and third adhesive patterns are bonded so that the contact regions are in electrical contact. 
     The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an elevational cross-section of an electrophotographic reproduction apparatus; 
         FIG. 2  shows various embodiments of methods of making a shaped electrical conductor; 
         FIG. 3A  is a top view of various examples of patterns; 
         FIG. 3B  is a cross-section along the line  3 B- 3 B in  FIG. 3A ; 
         FIG. 4  is a partial perspective view showing a pancake motor according to the prior art; 
         FIG. 5  is a cross-section of a pancake motor according to various embodiments; and 
         FIG. 6  is a top view of magnets and thermoplastic adhesive patterns according to various embodiments. 
     
    
    
     The attached drawings are for purposes of illustration and are not necessarily to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows various embodiments of methods of making a shaped electrical conductor. Processing begins with step  210  or step  250 . In step  210 , a first sheet of metal having a first thickness is provided. The first sheet of metal, and other sheets of metal described herein, can be any electrically-conductive metal. For example, copper or aluminum can be used. Step  210  is followed by step  215  and step  220 , which can be performed in any order. 
     In step  215 , a first thermoplastic adhesive pattern is applied to a first surface of the first sheet. The term “adhesive,” as used herein, does not require a pressure-sensitive adhesive, or one that is tacky under normal environmental conditions. An adhesive has the capability of adhering during bonding, described below with reference to step  290 , but is not necessarily a glue, tape, cement, or epoxy (although it can be any of those in various embodiments). In various embodiments, step  215  includes steps  217  and  225 . Step  215  is followed by step  225 . 
     In step  217 , an electrophotographic print engine is used to deposit thermoplastic particles in a corresponding deposition pattern. Electrophotography can also be used for steps  220 ,  255 , and  260 . More detail of electrophotographic deposition is given in  FIG. 1 , discussed below. The first plastic pattern can also be applied by flood-coating or spin-coating over a mask that defines the deposition pattern. Step  217  is followed by step  218 . 
     In step  218 , the deposited particles are fixed to the corresponding sheet under heat or pressure. This is also described below with reference to  FIG. 1 , and can also be used in steps  220 ,  255 , and  260 . 
     In step  220 , a second thermoplastic adhesive pattern is applied to a second surface of the first sheet. The second pattern is fully justified with the applied first pattern. “Fully justified” means that, within tolerances, the first and second thermoplastic adhesive patterns overlap completely as viewed along a normal to the first sheet. In various embodiments, the first and second thermoplastic patterns are mirror-images of each other. As a result, within tolerances, at any point on the first sheet, a ray passing through the point along the normal to the sheet at that point either passes through both the first and second thermoplastic patterns, or through neither pattern. Step  220  is followed by step  225 . 
     In step  225 , the first sheet is etched to remove metal not covered by the thermoplastic adhesive patterns so that no metal bridges remain between disconnected coated portions of the first sheet. Since the metal is covered on both sides by the fully justified first and second thermoplastic patterns, the sheet will be etched through where the patterns are absent, and protected where the patterns are present. Some under-cutting due to over-etching can occur at the edges of protected areas. Step  225  is followed by step  290 . 
     In step  250 , a second sheet of metal having a second thickness is provided. This is as described above with reference to step  210 . Step  250  is followed by step  255  and step  260 . 
     In step  255 , a third thermoplastic adhesive pattern is applied to a first surface of the second sheet. This is as described above with reference to step  215 . The third thermoplastic adhesive pattern can be the same as, or different from, either the first or second thermoplastic adhesive patterns. Step  255  is followed by step  265 . 
     In step  260 , a fourth thermoplastic adhesive pattern is applied to a second surface of the second sheet, the fourth pattern being fully justified with the applied third pattern (as above, step  220 ; same or different, as in step  255 ). Step  260  is followed by step  265 . 
     In step  265 , the second sheet is etched to remove metal not covered by the thermoplastic adhesive patterns so that no metal bridges remain between disconnected coated portions of the second sheet. This is as discussed above with reference to step  225 . Step  265  is followed by step  290 . 
     The result of steps up to  290  is a pair of metal sheets carrying patterned conductors. The first and second patterns can be the same as, or different from, the third and fourth patterns. The first and second metal sheets can be at least 0.1 mm thick. At least one of the thermoplastic adhesive patterns can include a plurality of traces (e.g., lines, curves, or segments thereof), each having a trace width less than 2 mm (e.g., 50 mil=1.25 mm). Spaces between traces can have space widths less than 2 mm (e.g., 50 mil=1.25 mm). Traces and spaces can also be 2 mm or wider. 
     In step  280 , a first contact region in the second adhesive pattern is selected. In step  285 , a second contact region in the third adhesive pattern is selected. Steps  280  and  285  can be performed in any order. The first and second contact regions are selected so that current will be able to flow through the conductors. An example is shown in  FIG. 3 . Steps  280  and  285  are followed by step  290 . 
     In step  290 , the second and third adhesive patterns are bonded to each other at more than one point. The sheets are brought together so that the second and third patterns can be bonded. No orientation of the sheets is implied by the designation of certain patterns as the second and third. Step  290  is followed by step  295  and optional step  292 . 
     In step  295 , the first and second sheets are mated so that the first contact region is in electrical contact with the second contact region. Step  295  can be performed as described with reference to optional steps  292  and  294 . Step  295  is followed by optional step  297 . 
     In optional step  292 , the two sheets are heated and pressed together to bond them. This step can be used with toner-based thermoplastic patterns by heating the patterns above their glass transition temperatures T g . The patterns are then pressed together to squeeze toner out from between the metal in the first and second contact regions, so that the metal areas in the two sheets come into electrical contact. The toner is then cooled below T g  to fix the sheets together. This type of bonding is described below with respect to fuser  60  ( FIG. 1 ) in the context of fusing toner to a receiver. In other embodiments, conductive toner can be used, or not all the toner squeezed out from between the sheets in the contact areas. In other embodiments, toner can be removed from the first and second contact regions by softening the toner (temperature &gt;T g ) with a heat source, then removing the toner with a skive, vacuum, blow-off gun, abrasion wheel, or other mechanical device adapted to move or remove viscous toner. The heat source can be part of the device; for example, a heated skive can be used to simultaneously heat and move the toner. Step  292  is followed by step  295 . 
     In optional step  294 , the mating step includes applying a conductive adhesive to the first or second contact region and bringing the two contact regions into mechanical contact with the applied adhesive. For example, dimethyl, methylhydrogen siloxane, e.g., DOW CORNING 7920, can be used. Silver-containing siloxane, e.g., DOW CORNING® DA 6524, can also be used. Adhesives can include &gt;80 wt % silver, or 90 wt % silver. Step  294  is followed by step  295 . 
     In optional step  297 , the mating step includes soldering or welding the first contact region and the second contact region together. 
     In various embodiments, steps corresponding to steps  210 ,  215 ,  220 ,  225  are performed to apply fifth and sixth fully-registered thermoplastic patterns on a third metal sheet having a third thickness. The third sheet is then etched. This is as described above. Contact areas are selected in the fourth and fifth thermoplastic layers, and the second and third sheets are bonded and mated as described above (steps  290 ,  295 ). This forms a three-metal-sheet structure. The thicknesses of the metal sheets can be the same as or different from each other. 
     In various embodiments, a third sheet of metal having a third thickness is provided. A fifth thermoplastic adhesive pattern is applied to a first surface of the third sheet, and a sixth thermoplastic adhesive pattern fully justified with the applied fifth pattern is applied to a second surface of the third sheet. The third sheet is etched to remove metal not covered by the thermoplastic adhesive patterns so that no metal bridges remain between disconnected coated portions of the third sheet. This is as described above for the first and second sheets. 
     A third contact region is then selected in the fourth adhesive pattern, e.g., as described above for the first contact region. A fourth contact region is selected in the fifth adhesive pattern, e.g., as described above for the second contact region. The fourth and fifth adhesive patterns are bonded to each other at more than one point, resulting in a structure with three metal layers: the first and second metal layers bonded to each other, and the second and third metal layers bonded to each other. The second and third sheets are then mated, as described above, so that the third contact region is in electrical contact with the fourth contact region. 
       FIG. 3A  is a top view of various examples of patterns. First pattern  311  (and also the second, hidden in the top view since the patterns are in register) is shown solid; third pattern  333  (and the fourth pattern) is shown dashed. The edges of the patterns are shown; for example, the dashed shape of third pattern  333  encloses the area in the pattern where thermoplastic and metal are intended to be. In the example shown here, the first and second patterns are circular and the third and fourth patterns are elliptical spirals. The long axis of the elliptical spirals (e.g., third pattern  333 ) is twice a length of an axis of the first and second circular patterns (first pattern  311 ). 
     First contact region  315  in second adhesive pattern (hidden under first adhesive pattern  311 ) is a small disk. Second contact region  335  in third pattern  333  is a slightly larger disk. The two contact regions  315 ,  335  overlay, forming electrical contact between the metal protected from etching in regions  315 ,  335 . As a result, current into electrode  360  defined by third pattern  333  travels through the spiral conductor defined by third pattern  333 , the conductor defined by second contact region  335 , the conductor defined by first contact region  315 , electrode  370  defined by first pattern  311 , the circle defined by first pattern  311 , and out electrode  380  defined by first pattern  311 . 
     Corners in the patterns can be chamfered or not. The width of the pattern can vary or not at various points on the pattern; the example shown does not vary the width of the pattern at corners. 
       FIG. 3B  is a cross-section along the line  3 B- 3 B in  FIG. 3A . First conductor  610  is defined by first pattern  311  and second pattern  312 . In this section, two segments of conductor  610  are visible. Second conductor  630  is defined by third pattern  333  and fourth pattern  334 . Conductor  630  is shown below conductor  610 , but can be above it. In this section, twelve segments of conductor  630  are visible. First conductor  610  and second conductor  630  are, respectively, the etched first and second metal sheets  319 ,  339 . First contact region  315  and second contact region  335  are shown electrically connected by conductive adhesive  355  to carry current between them. In the embodiment shown, toner has been removed from first contact region  315  and second contact region  335  prior to applying conductive adhesive  355 , as discussed above. 
     First pattern  311  is formed in first metal sheet  319 . For clarity, metal sheet  319  is labeled on only one of the visible conductor segments. However, as shown in  FIG. 3A , all of the visible conductor segments corresponding to first pattern  311  are part of metal sheet  319 . Likewise, second pattern  312  is formed on second metal sheet  339 . The sides of the segments of first metal sheet  319  and second metal sheet  339  are shown undercut to represent graphically the possibility of over-etching of the metal sheet. No particular cross-sectional shape of the conductor segments is required. 
     First metal sheet  319  has first thermoplastic pattern  311  on its top surface and second thermoplastic pattern  312  on its bottom surface. Second metal sheet  339  has third thermoplastic pattern  333  on its top surface and fourth thermoplastic pattern  334  on its bottom surface. For clarity, only one segment is labeled, even though the thermoplastic patterns are continuous within a layer, as shown in  FIG. 3A . As shown, second thermoplastic pattern  312  and third thermoplastic pattern  333  have been pressed together to bond first metal sheet  319  to second metal sheet  339 . 
     In various embodiments of the use of this structure as a motor winding, fluid is passed through the winding as indicated by the “FLUID FLOW” arrow. The fluid can be ethylene glycol, deionized water, air, nitrogen, or another fluid adapted to remove Joule heat from the conductors in metal sheets  319 ,  339 . Fluid can be pumped or otherwise moved actively, or permitted to flow passively by convection. 
     Referring to  FIGS. 3A and 3B , bonding area  390  (shown hatched with horizontal lines) is an area in which the second and third patterns overlap. Consequently, when first metal sheet  319  and second metal sheet  339  are bonded together, the thermoplastic adhesive of second pattern  312  and of third pattern  333  in bonding area  390  adhere to each other. This adhesion of metal sheets  319 ,  339  to each other provides mechanical strength to the resulting assembly. In various embodiments, a plurality of the regions of overlap between second pattern  312  and third pattern  333 , or all of the overlap regions, are bonding regions.  FIGS. 3A and 3B  show several bonding regions hatched with horizontal lines. Other bonding regions besides those shown hatched can be used. 
     In various embodiments described above in which three sheets of metal are used, the fifth thermoplastic pattern (not shown) is a rotation of first thermoplastic pattern  311 . That is, respective rotation centers of the first and fifth thermoplastic patterns are aligned and the fifth thermoplastic pattern is rotated about its rotation center with respect to first thermoplastic pattern  311 . Other than the rotation, the fifth thermoplastic pattern is identical to first thermoplastic pattern  311  (within manufacturing tolerances). Since the fifth and sixth thermoplastic patterns are fully justified, the sixth thermoplastic pattern is also a rotation of second thermoplastic pattern  312 . 
     As is shown here, the motor so formed does not have a laminate portion and therefore can have reduced mass and density as compared to the prior art. Moreover, in embodiments in which no laminate or other core is used, there are no losses due to in-core eddy currents. 
       FIG. 4  is a partial perspective view showing a pancake motor according to the prior art. The pancake motor is brushless motor having housing with upper housing  410  and lower housing  412 . Printed circuit board (PCB)  420  is installed in upper housing  410 . Stator  430  is disposed over underside  429  of PCB  420 . Stator  430  includes a plurality of coil layers piled up on top of each other, e.g., by photolithography. Rotor  440  is spaced apart from the lower surface of stator  430  and includes permanent magnets  442  disposed at an inner peripheral surface of rotor  440 . The permanent magnets have opposite orientations as they are around the rotor, as shown (alternating N and S poles facing down). Rotating shaft  460  is rotatably connected to upper housing  410  by a bearing in opening  415 , and an electric signal control unit  470  installed at an end portion of the PCB  420  and periodically supplying electric current to stator  430 . 
     PCB  420  includes an annular base  421  and an elongated plate  423  integrally formed at an end portion of annular base  421 . Elongated plate  423  extends out of upper housing  410  through opening  418  formed at a side wall of upper housing  410 . 
     Stator  430  can be formed over underside  429  of PCB  420  by photolithography. In various embodiments, a conductive material such as copper is applied on underside  429  of PCB  420  to form a copper layer. A photo-active solution is deposited over the copper, and a photo mask on which the coil shape is printed is placed on the solution. 
     When the photo mask is irradiated, a coil shape that is similar to the photo mask is patterned on the surface of the solution on the copper layer. After exposure, an etching solution is applied to PCB  420 . The etching solution reacts with the photoactive layer and copper layer so that a first coil layer is formed, i.e., by removing undesired copper. After forming the first coil layer, a first insulation layer is formed on the underside of the first coil layer. Multiple conductive layers can be formed in this way, and vias can be drilled and plated between them to connect them. 
     Rotor  440  is spaced apart from the underside of stator  430  by the predetermined distance. Rotor  440  has a cylindrical shape, and has permanent magnets  442  which are radially disposed on an upper surface of rotor  440  in such a manner that adjacent permanent magnets  442  have different poles from each other to generate a magnetic field which makes electromagnetic-interaction with the electric field of stator  430  to rotate rotor  440 , rotating shaft  460  is integrally formed at a center of rotor  440 , so as to rotate when rotor  440  rotates. 
     Upper housing  410  is formed at an upper portion thereof with a circular opening  415 , and an upper and lower bearings  452  and  454  are mounted at an inner portion of upper housing  410 . Accordingly, rotating shaft  460  is rotatably attached to upper housing  410  by upper and lower bearings  452  and  454 . 
     Upper housing  410  includes bracket  413  formed on the bottom edge thereof, including hole  411 . Lower housing  412  includes bracket  414  formed on the top edge thereof, including hole  481 . A fixing member  416  such as a bolt penetrates holes  411  and  481  so that upper and lower housings  410  and  412  are integrally assembled. Other assembly techniques can also be used. Multiple brackets per housing can also be used, as shown here. 
     Further details of pancake motors are given in U.S. Pat. Nos. 6,005,324; 7,112,910; 7,608,964; and 7,573,173, the disclosures of which are incorporated herein by reference. 
       FIG. 5  is a cross-section of a pancake motor according to various embodiments. This section is taken along the line  5 - 5  in  FIG. 6 . 
     There are two commonly-used types of configurations of pancake motor windings. In a first configuration type, wires are arranged to extend substantially radially on rotor  515 , and to be substantially straight where they pass magnets  442 D,  442 E. The Lorentz force on the charge carriers in the conductors is tangential, in accordance with Fleming&#39;s left-hand rule for motors. In some of these configurations, individual wires extend radially out rotor  515 , past one magnet (e.g., magnet  442 D), then radially back in past a different magnet (e.g., magnet  442 E). In other configurations, squared-off spiral windings in the plane of rotor  515  are used, and the tangential portions of those spirals are arranged beyond magnets  442 D,  442 E so they do not contribute significant radial Lorentz forces. The sections of the spirals that pass the magnets contribute tangential forces. 
     In a second type of configurations, the wires are formed into tight, approximately circular spirals. These coils act as solenoids and produce distinct north and south magnetic poles when current is passed through them. These poles attract and repel the poles of magnets  442 D,  442 E, providing tangential forces. 
     In this example, rotor  515  is mounted on bearings  518 . Shaft  510  is connected to the center of rotor  515  to transmit rotary motion. Magnets  442 D,  442 E, which can be permanent magnets or electromagnets, are attached on one face of rotor  515 . Any number of magnets can be used, arranged in a circle around the face of rotor  515 , as shown by magnets  442  ( FIG. 4 ). Rotor  515  can also include optional bracket supporting optional magnets  521 . Arrows indicate the direction of the magnetic field between magnets  442 D,  442 E, and  521 . Other configurations can be used, such as magnets only over or only under the stator, magnets around the stator, or combinations of these. The shaft can pass through an opening in the stator, and can be attached to the top or bottom of the rotor. 
     Stator  550  is arranged opposite magnets  442 D,  442 E, or between those and magnets  521 . Stator  550  includes first conductor  610  defined by first and second thermoplastic patterns  311 ,  312  ( FIG. 3B ). Stator  550  also includes second conductor  630  defined by third and fourth thermoplastic patterns  333 ,  334  ( FIG. 3B ). In this section, two segments of each conductor  610 ,  630  are visible. The direction of current flow in each segment is shown by vector symbols. As shown, the direction of force on each conductor segment F is to the right according to the left-hand rule (pointer finger for magnetic field direction, middle finger for current direction; thumb for resultant force on the conductor). Since the stator is fixed, the equal and opposite force turns the rotor, as shown in  FIG. 6 . 
       FIG. 6  is a top view of magnets and first and third thermoplastic adhesive patterns according to various embodiments, including embodiments useful in the motor shown in  FIG. 5 . As in  FIG. 3A , the second and fourth thermoplastic patterns are not visible. For clarity, only the centerline of the conductors in each pattern is shown; the patterns are broader than the indicated centerlines. First pattern  311  is shown solid and third pattern  333  is shown dashed. First pattern  311  defines first conductor  610 ; third pattern  333  defines second conductor  630 , which is formed from the second metal sheet. The configuration of conductors  610 ,  630  and AC supply  609  shown here is a stator; rotors can also be formed as described above with reference to  FIG. 2 . Where patterns  311 ,  333  overlap, e.g., at bonding area  390 , conductors  610 ,  630  are bonded together for mechanical support. In various embodiments, a rotor for a brushless motor is formed. Rotors or stators can have two or any higher number of layers. 
     For clarity, conductors  610  and  630  are shown passing only once around the stator. Each conductor can have any number of nested turns with the same pattern, but progressively smaller. Conductors  610 ,  630  are arranged so that the force provides rotational motion, as described below. 
     Current is provided to the stator by AC supply  609 . In  FIG. 6 , current flow is shown at a point in time at which the supply is providing current into second conductor  630 . Conductors  610 ,  630  are electrically connected in respective contact areas  315 ,  335 , as discussed above with reference to  FIGS. 3A and 3B . Current flows from the positive terminal of AC supply  609  through second conductor  630 , contact area  335 , contact area  315 , and conductor  610 , then to the negative terminal of AC supply  609 . 
     This stator can be used with an eight-pole rotor including magnets  442 A,  442 B,  442 C,  442 D,  442 E,  442 F,  442 G, and  442 H. The magnets can be over or under the stator, e.g., as shown in  FIG. 5 . Arrows on conductors  610 ,  630  represent the direction of current I in those conductors, and arrows orthogonal to conductors  610 ,  630  represent the direction of force F. The direction of the magnetic field from each magnet is shown by standard vector symbols (dots and crosses). Magnets  442 A,  442 C,  442 E, and  442 G have the magnetic field (N-S) into the plane of the drawing. Magnets  442 B,  442 D,  442 F, and  442 H have the magnetic field (N-S) out of the plane of the drawing. 
     Where conductor  630  passes magnet  442 A (i.e., crosses over or under, or passes near or adjacent to, magnet  442 A), the direction of current flow is in towards the center of the stator, as shown. The magnetic field is into the page. The resulting force on the stator is clockwise, as shown. Since the stator is fixed, the equal and opposite reaction will drive the rotor counter-clockwise. Conductor  610  is arranged so that the current through conductor  610  where it passes magnet  442 A is also towards the center of the stator, so the force on the stator is also clockwise, as shown. Current is also inward, and force on the stator clockwise, where conductors  610 ,  630  pass magnets  442 C,  442 E, and  442 G. 
     In this example, the forces from conductors  610 ,  630  where they pass magnet  442 A are not entirely tangential. This is because conductors  610 ,  630  are not entirely radial where they pass magnet  442 A. Conductors can be entirely radial or not, as long as the tangential components of the forces from the magnets sum to provide torque in a particular direction. Tangential arcs  619 ,  639  are shown for comparison between the directions of the force vectors and the tangential directions. 
     Where conductors  610 ,  630  pass magnet  442 D (and also magnets  442 B,  442 F, and  442 H), current flow is away from the center of the stator. Magnetic field is directed out of the page. Since the directions of current flow and magnetic field are both reversed from the situation over magnet  442 A, the force on the stator is still clockwise, so the rotor is driven counterclockwise. 
     When the rotor rotates so that magnet  442 B is passing the stator conductors that formerly passed magnet  442 A, AC supply  609  reverses polarity. Current is provided into conductor  610  and out of conductor  630 , so that the direction of force continues to be clockwise and the direction of rotation counterclockwise. 
     In embodiments in which conductors  610 ,  630  form a rotor, the conductors are driven clockwise. In these embodiments, brushes can be used to transmit current between AC supply  609  and conductors  610 ,  630 . In normal operation, the polarity of AC supply  609  reverses once per magnet, so current over magnet  442 A is directed inward in the position shown, and also inward after ⅛ revolution of the rotor together with a polarity change of AC supply  609 . To change the direction of rotation of the motor, the polarity of AC supply  609  over each magnet is reversed. That is, in the position shown in  FIG. 6 , current over magnet  442 A is directed outward rather than inward. 
     As shown, contact regions  315 ,  335  are not centered in the stator. They can be centered (e.g. as shown in  FIG. 3A ) or not. In embodiments in which conductors  610 ,  630  are used as a rotor, an axle can be attached at center of rotation  628 . In various embodiments, particularly rotor embodiments, it is desirable to mechanically balance conductors  610 ,  630  to reduce lateral forces acting at center of rotation  628 . Static or dynamic balance, or both, can be desirable. 
     In various embodiments, first pattern  311 , third pattern  333 , or both, along with corresponding second or fourth patterns, include balancing features that give the rotor uniform centrifugal force as it rotates past a selected observation point. Specifically, the first and second patterns, or the third and fourth patterns, define or include balancing features in the metal not removed from the corresponding metal sheet by the corresponding etching step. The balancing features can be located in areas of the patterns  311 ,  333  that do not pass any magnets (e.g.,  442 A). 
     In this example, balancing feature  615  is an area of conductor  610  of the same mass as contact area  315 , disposed diametrically opposite contact area  315  with respect to center of rotation  628 . Consequently, while conductors  610 ,  630  rotate, contact area  315  and balancing feature  615  exert on the axis of rotation centrifugal forces equal in magnitude but opposite in direction. These forces cancel out to maintain balance. Likewise, balancing features  635 A,  635 B together exert a centrifugal force cancelling out that of contact area  335 . A balancing feature can include one or more areas of additional mass, or one or more areas of reduced mass. Mass can be reduced, e.g., by thinning the conductors. Balancing features can also include extra mass along the length of conductors  610  or  630  except for certain areas. In this way, mass can effectively be reduced to balance, but without reducing the current-carrying capacity of the conductors. 
     In another example, one or more balancing features  616  can be frangible. A frangible balancing feature can be separated from the conductor  610 ,  630  of which it is part. This separation can be performed after manufacture of a complete motor, or after bonding step  290  or mating step  295  ( FIG. 2 ). Separation can provide balance adjustments to improve dynamic or static balance. Frangible balancing feature  616  can be connected to a conductor  610 ,  630  with a perforated pattern or narrow neck that can be fractured, or with metal that is stamped or punched thinner than the rest of the metal sheet  319 ,  339  ( FIG. 3B ). In various embodiments, the metal sheet (e.g., sheet  319  or  339 ) corresponding to frangible balancing feature  616  can be stamped or punched to define break line  617  (e.g., of thinner or perforated metal) along which frangible balancing feature  616  can be separated from the corresponding metal sheet  319 ,  339 . In the example shown here, feature  616  is attached to conductor  610  at a bend thereof, along two perforated break lines  617  (for clarity, only one is shown). 
     Referring to  FIG. 6  and also to  FIGS. 3A-3B , in other embodiments forming a rotor using conductors  610 ,  630 , one or more of the conductors  610 ,  630  is deliberately unbalanced. For example, first pattern  311  and second pattern  312  can define optional unbalanced feature  657 . Feature  657  is an area of metal not etched from first metal sheet  319  that is not balanced by a corresponding feature opposite center of rotation  628  from feature  657 . As a result, when the rotor spins, it will vibrate. This can be used for non-audio indication, e.g., in a cellular telephone. Feature  657  can be positioned and sized to produce a desired vibration. More than one unbalanced feature can be included. Specifically, first and second patterns  311 ,  312 , or third and fourth patterns  333 ,  334 , can define an unbalanced feature  657  in the metal not removed from the corresponding metal sheet  319 ,  339  by the corresponding etching step. 
     The electrophotographic (EP) printing process can be embodied in devices including printers, copiers, scanners, and facsimiles, and analog or digital devices, all of which are referred to herein as “printers.” Electrostatographic printers such as electrophotographic printers that employ toner developed on an electrophotographic receiver can be used, as can ionographic printers and copiers that do not rely upon an electrophotographic receiver. Electrophotography and ionography are types of electrostatography (printing using electrostatic fields), which is a subset of electrography (printing using electric fields). 
     A digital reproduction printing system (“printer”) typically includes a digital front-end processor (DFE), a print engine (also referred to in the art as a “marking engine”) for applying toner to the receiver, and one or more post-printing finishing system(s) (e.g. a UV coating system, a glosser system, or a laminator system). A printer can reproduce pleasing black-and-white or color onto a receiver. A printer can also produce selected patterns of toner on a receiver, which patterns (e.g. surface textures) do not correspond directly to a visible image. The DFE receives input electronic files (such as Postscript command files) composed of images from other input devices (e.g., a scanner, a digital camera). The DFE can include various function processors, e.g. a raster image processor (RIP), image positioning processor, image manipulation processor, color processor, or image storage processor. The DFE rasterizes input electronic files into image bitmaps for the print engine to print. In some embodiments, the DFE permits a human operator to set up parameters such as layout, font, color, media type, or post-finishing options. The print engine takes the rasterized image bitmap from the DFE and renders the bitmap into a form that can control the printing process from the exposure device to transferring the print image onto the receiver. The finishing system applies features such as protection, glossing, or binding to the prints. The finishing system can be implemented as an integral component of a printer, or as a separate machine through which prints are fed after they are printed. 
     The printer can also include a color management system which captures the characteristics of the image printing process implemented in the print engine (e.g. the electrophotographic process) to provide known, consistent color reproduction characteristics. The color management system can also provide known color reproduction for different inputs (e.g. digital camera images or film images). 
     In an embodiment of an electrophotographic modular printing machine, e.g. the NEXPRESS 3000SE printer manufactured by Eastman Kodak Company of Rochester, N.Y., color-toner print images are made in a plurality of color imaging modules arranged in tandem, and the print images are successively electrostatically transferred to a receiver adhered to a transport web moving through the modules. Colored toners include colorants, e.g. dyes or pigments, which absorb specific wavelengths of visible light. Commercial machines of this type typically employ intermediate transfer members in the respective modules for transferring visible images from the photoreceptor and transferring print images to the receiver. In other electrophotographic printers, each visible image is directly transferred to a receiver to form the corresponding print image. 
     Electrophotographic printers having the capability to also deposit clear toner using an additional imaging module are also known. As used herein, clear toner is considered to be a color of toner, as are C, M, Y, K, and Lk, but the term “colored toner” excludes clear toners. The provision of a clear-toner overcoat to a color print is desirable for providing protection of the print from fingerprints and reducing certain visual artifacts. Clear toner uses particles that are similar to the toner particles of the color development stations but without colored material (e.g. dye or pigment) incorporated into the toner particles. However, a clear-toner overcoat can add cost and reduce color gamut of the print; thus, it is desirable to provide for operator/user selection to determine whether or not a clear-toner overcoat will be applied to the entire print. A uniform layer of clear toner can be provided. A layer that varies inversely according to heights of the toner stacks can also be used to establish level toner stack heights. The respective toners are deposited one upon the other at respective locations on the receiver and the height of a respective toner stack is the sum of the toner heights of each respective color. Uniform stack height provides the print with a more even or uniform gloss. 
       FIG. 1  is an elevational cross-section showing portions of a typical electrophotographic printer  100 . Printer  100  is adapted to produce print images, such as single-color (monochrome), CMYK, or hexachrome (six-color) images, on a receiver (multicolor images are also known as “multi-component” images). Images can include text, graphics, photos, and other types of visual content. An embodiment involves printing using an electrophotographic print engine having six sets of single-color image-producing or -printing stations or modules arranged in tandem, but more or fewer than six colors can be combined to form a print image on a given receiver. Other electrophotographic writers or printer apparatus can also be included. Various components of printer  100  are shown as rollers; other configurations are also possible, including belts. 
     Referring to  FIG. 1 , printer  100  is an electrophotographic printing apparatus having a number of tandemly-arranged electrophotographic image-forming printing modules  31 ,  32 ,  33 ,  34 ,  35 ,  36 , also known as electrophotographic imaging subsystems. Each printing module  31 ,  32 ,  33 ,  34 ,  35 ,  36  produces a single-color toner image for transfer using a respective transfer subsystem  50  (for clarity, only one is labeled) to a receiver  42  successively moved through the modules. Receiver  42  is transported from supply unit  40 , which can include active feeding subsystems as known in the art, into printer  100 . In various embodiments, the visible image can be transferred directly from an imaging roller to a receiver  42 , or from an imaging roller to one or more transfer roller(s) or belt(s) in sequence in transfer subsystem  50 , and then to receiver  42 . Receiver  42  is, for example, a selected section of a web of, or a cut sheet of, planar media such as paper or transparency film. 
     Each printing module  31 ,  32 ,  33 ,  34 ,  35 ,  36  includes various components. For clarity, these are only shown in printing module  32 . Around photoreceptor  25  are arranged, ordered by the direction of rotation of photoreceptor  25 , charger  21 , exposure subsystem  22 , and toning station  23 . 
     In the EP process, an electrostatic latent image is formed on photoreceptor  25  by uniformly charging photoreceptor  25  and then discharging selected areas of the uniform charge to yield an electrostatic charge pattern corresponding to the desired image (a “latent image”). Charger  21  produces a uniform electrostatic charge on photoreceptor  25  or its surface. Exposure subsystem  22  selectively image-wise discharges photoreceptor  25  to produce a latent image. Exposure subsystem  22  can include a laser and raster optical scanner (ROS), one or more LEDs, or a linear LED array. 
     After the latent image is formed, charged toner particles are brought into the vicinity of photoreceptor  25  by toning station  23  and are attracted to the latent image to develop the latent image into a visible image. Note that the visible image may not be visible to the naked eye depending on the composition of the toner particles (e.g. clear toner). Toning station  23  can also be referred to as a development station. Toner can be applied to either the charged or discharged parts of the latent image. 
     After the latent image is developed into a visible image on photoreceptor  25 , a suitable receiver  42  is brought into juxtaposition with the visible image. In transfer subsystem  50 , a suitable electric field is applied to transfer the toner particles of the visible image to receiver  42  to form the desired print image  38  on the receiver, as shown on receiver  42 A. The imaging process is typically repeated many times with reusable photoreceptors  25 . 
     Receiver  42 A is then removed from its operative association with photoreceptor  25  and subjected to heat or pressure to permanently fix (“fuse”) print image  38  to receiver  42 A. Plural print images, e.g. of separations of different colors, are overlaid on one receiver before fusing to form a multi-color print image  38  on receiver  42 A. 
     Each receiver  42 , during a single pass through the six printing modules  31 ,  32 ,  33 ,  34 ,  35 ,  36 , can have transferred in registration thereto up to six single-color toner images to form a pentachrome image. As used herein, the term “hexachrome” implies that in a print image, combinations of various of the six colors are combined to form other colors on receiver  42  at various locations on receiver  42 . That is, each of the six colors of toner can be combined with toner of one or more of the other colors at a particular location on receiver  42  to form a color different than the colors of the toners combined at that location. In an embodiment, printing module  31  forms black (K) print images,  32  forms yellow (Y) print images,  33  forms magenta (M) print images,  34  forms cyan (C) print images,  35  forms light-black (Lk) images, and  36  forms clear images. 
     In various embodiments, printing module  36  forms print image  38  using a clear toner or tinted toner. Tinted toners absorb less light than they transmit, but do contain pigments or dyes that move the hue of light passing through them towards the hue of the tint. For example, a blue-tinted toner coated on white paper will cause the white paper to appear light blue when viewed under white light, and will cause yellows printed under the blue-tinted toner to appear slightly greenish under white light. 
     Receiver  42 A is shown after passing through printing module  36 . Print image  38  on receiver  42 A includes unfused toner particles. 
     Subsequent to transfer of the respective print images  38 , overlaid in registration, one from each of the respective printing modules  31 ,  32 ,  33 ,  34 ,  35 ,  36 , receiver  42 A is advanced to a fuser  60 , i.e. a fusing or fixing assembly, to fuse print image  38  to receiver  42 A. Transport web  81  transports the print-image-carrying receivers (e.g.,  42 A) to fuser  60 , which fixes the toner particles to the respective receivers  42 A by the application of heat and pressure. The receivers  42 A are serially de-tacked from transport web  81  to permit them to feed cleanly into fuser  60 . Transport web  81  is then reconditioned for reuse at cleaning station  86  by cleaning and neutralizing the charges on the opposed surfaces of the transport web  81 . A mechanical cleaning station (not shown) for scraping or vacuuming toner off transport web  81  can also be used independently or with cleaning station  86 . The mechanical cleaning station can be disposed along transport web  81  before or after cleaning station  86  in the direction of rotation of transport web  81 . 
     Fuser  60  includes a heated fusing roller  62  and an opposing pressure roller  64  that form a fusing nip  66  therebetween. In an embodiment, fuser  60  also includes a release fluid application substation  68  that applies release fluid, e.g. silicone oil, to fusing roller  62 . Alternatively, wax-containing toner can be used without applying release fluid to fusing roller  62 . Other embodiments of fusers, both contact and non-contact, can be employed. For example, solvent fixing uses solvents to soften the toner particles so they bond with the receiver  42 . Photoflash fusing uses short bursts of high-frequency electromagnetic radiation (e.g. ultraviolet light) to melt the toner. Radiant fixing uses lower-frequency electromagnetic radiation (e.g. infrared light) to more slowly melt the toner. Microwave fixing uses electromagnetic radiation in the microwave range to heat the receivers (primarily), thereby causing the toner particles to melt by heat conduction, so that the toner is fixed to the receiver  42 . 
     The receivers (e.g., receiver  42 B) carrying the fused image (e.g., fused image  39 ) are transported in a series from the fuser  60  along a path either to a remote output tray  69 , or back to printing modules  31 ,  32 ,  33 ,  34 ,  35 ,  36  to create an image on the backside of the receiver (e.g., receiver  42 B), i.e. to form a duplex print. Receivers (e.g., receiver  42 B) can also be transported to any suitable output accessory. For example, an auxiliary fuser or glossing assembly can provide a clear-toner overcoat. Printer  100  can also include multiple fusers  60  to support applications such as overprinting, as known in the art. 
     In various embodiments, between fuser  60  and output tray  69 , receiver  42 B passes through finisher  70 . Finisher  70  performs various media-handling operations, such as folding, stapling, saddle-stitching, collating, and binding. 
     Printer  100  includes main printer apparatus logic and control unit (LCU)  99 , which receives input signals from the various sensors associated with printer  100  and sends control signals to the components of printer  100 . LCU  99  can include a microprocessor incorporating suitable look-up tables and control software executable by the LCU  99 . It can also include a field-programmable gate array (FPGA), programmable logic device (PLD), microcontroller, or other digital control system. LCU  99  can include memory for storing control software and data. Sensors associated with the fusing assembly provide appropriate signals to the LCU  99 . In response to the sensors, the LCU  99  issues command and control signals that adjust the heat or pressure within fusing nip  66  and other operating parameters of fuser  60  for receivers. This permits printer  100  to print on receivers of various thicknesses and surface finishes, such as glossy or matte. 
     Image data for writing by printer  100  can be processed by a raster image processor (RIP; not shown), which can include a color separation screen generator or generators. The output of the RIP can be stored in frame or line buffers for transmission of the color separation print data to each of respective LED writers, e.g. for black (K), yellow (Y), magenta (M), cyan (C), and red (R), respectively. The RIP or color separation screen generator can be a part of printer  100  or remote therefrom. Image data processed by the RIP can be obtained from a color document scanner or a digital camera or produced by a computer or from a memory or network which typically includes image data representing a continuous image that needs to be reprocessed into halftone image data in order to be adequately represented by the printer. The RIP can perform image processing processes, e.g. color correction, in order to obtain the desired color print. Color image data is separated into the respective colors and converted by the RIP to halftone dot image data in the respective color using matrices, which comprise desired screen angles (measured counterclockwise from rightward, the +X direction) and screen rulings. The RIP can be a suitably-programmed computer or logic device and is adapted to employ stored or computed matrices and templates for processing separated color image data into rendered image data in the form of halftone information suitable for printing. These matrices can include a screen pattern memory (SPM). 
     Various parameters of the components of a printing module (e.g., printing module  31 ) can be selected to control the operation of printer  100 . In an embodiment, charger  21  is a corona charger including a grid between the corona wires (not shown) and photoreceptor  25 . Voltage source  21   a  applies a voltage to the grid to control charging of photoreceptor  25 . In an embodiment, a voltage bias is applied to toning station  23  by voltage source  23   a  to control the electric field, and thus the rate of toner transfer, from toning station  23  to photoreceptor  25 . In an embodiment, a voltage is applied to a conductive base layer of photoreceptor  25  by voltage source  25   a  before development, that is, before toner is applied to photoreceptor  25  by toning station  23 . The applied voltage can be zero; the base layer can be grounded. This also provides control over the rate of toner deposition during development. In an embodiment, the exposure applied by exposure subsystem  22  to photoreceptor  25  is controlled by LCU  99  to produce a latent image corresponding to the desired print image. All of these parameters can be changed, as described below. 
     Further details regarding printer  100  are provided in U.S. Pat. No. 6,608,641 and in U.S. Publication No. 2006/0133870, the disclosures of which are incorporated herein by reference. 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
     
         
           21  charger 
           21   a  voltage source 
           22  exposure subsystem 
           23  toning station 
           23   a  voltage source 
           25  photoreceptor 
           25   a  voltage source 
           31  printing module 
           32  printing module 
           33  printing module 
           34  printing module 
           35  printing module 
           36  printing module 
           38  print image 
           39  fused image 
           40  supply unit 
           42  receiver 
           42 A receiver 
           42 B receiver 
           50  transfer subsystem 
           60  fuser 
           62  fusing roller 
           64  pressure roller 
           66  fusing nip 
           68  release fluid application substation 
           69  output tray 
           70  finisher 
           81  transport web 
           86  cleaning station 
           99  logic and control unit (LCU) 
           100  printer 
           210  provide first metal sheet step 
           215  apply first plastic pattern step 
           217  deposit electrophotographically step 
           218  fix deposited particles step 
           220  apply second plastic pattern step 
           225  etch first sheet step 
           250  provide second metal sheet step 
           255  apply third plastic pattern step 
           260  apply fourth plastic pattern step 
           265  etch second sheet step 
           280  select first contact region step 
           285  select second contact region step 
           290  bond patterns step 
           292  heat and press sheets step 
           294  apply adhesive step 
           295  mate sheets step 
           297  solder or weld step 
           311  pattern 
           312  pattern 
           315  contact region 
           319  metal sheet 
           333  pattern 
           334  pattern 
           335  contact region 
           339  metal sheet 
           355  conductive adhesive 
           360  electrode 
           370  electrode 
           380  electrode 
           390  bonding area 
           410  upper housing 
           411  hole 
           412  lower housing 
           413  bracket 
           414  bracket 
           415  opening 
           416  fixing member 
           418  opening 
           420  printed-circuit board (PCB) 
           421  base 
           423  plate 
           429  underside 
           430  stator 
           440  rotor 
           442  magnet 
           442 A magnet 
           442 B magnet 
           442 C magnet 
           442 D magnet 
           442 E magnet 
           442 F magnet 
           442 G magnet 
           442 H magnet 
           452  bearing 
           454  bearing 
           460  rotating shaft 
           470  control unit 
           481  hole 
           510  shaft 
           515  rotor 
           518  bearing 
           521  magnet 
           550  stator 
           609  AC supply 
           610  conductor 
           615  balancing feature 
           616  frangible balancing feature 
           617  break line 
           619  tangential arc 
           628  center of rotation 
           630  conductor 
           635 A balancing feature 
           635 B balancing feature 
           639  tangential arc 
           657  unbalanced feature 
         I current 
         F force