A linear motor according to Claim 1, comprising:
In preferred embodiments a cold member is affixed to an exposed edge of the armature member externally of the channel defined by the frame to dissipate heat generated by the at least one coil, an air duct positioned in the fi-ame in or adjacent the cross member and extending along the length of the frame; and a plurality of air injection orifices are spaced along the channel to direct cooling air fed to the said air duct into the channel and across the surfaces of the coil support member towards the cooling member affixed to the exposed edge of the armature member thereby to transfer heat from the surface of the support member to the cooling member.
Preferably the cooling member has a duct formed therein for the flow therethrough of a cooling liquid to dissipate and remove the heat generated in the coil support 4 member and transferred to the cooling member.
In a preferred embodiment the said cross member of the frame comprise two air ducts extending along the length of the channel on opposite sides thereof, each having its own set of air injection orifices for the injection of cooling air into the channel and over a respective surface. of the coil support member towards the said cooling member.
The said coil support member may have a ceramic heat sink plate affixed to one or 10 both faces, the ceramic plate(s) making direct thermal contact with the cold member for the additional transfer of heat from the coil support member to the cold member.
The coil support member may be a ceramic plate having a recessed surface to which the said at least one coil is affixed, the ceramic plate making direct thermal contact with the cold member for the direct transfer of heat from the ceramic plate to the cold member.
Preferably the recessed surface of the ceramic coil support plate is formed with one or more upstanding lands around which the said at least one coil is fitted, the said land(s) projecting into the central opening(s) of the said coil to a level substantially flush with the surface of the coil.
The surface of the ceramic coil support plate may be provided with one or more individual annular recesses to accommodate the said at least one coil, the support plate thus having individual land(s) which extend through the opening(s) in said at least one coil to a level substantially flush with the surface of the coil and other land(s) extending to the same level externally around and/or between the coil, if more than one.
Preferably, the linear motor comprises a second ceramic plate superimposed as a cover over the said at least one coil mounted on the said recessed ceramic support plate.
In preferred embodiments the linear motor further comprises: a base member affixed to an exposed edge of the armature member externally of the channel defined by the frame; an air duct positioned in the U-frame in or adjacent the cross member and extending along the length of the frame parallel to the length of the open channel; a plurality of air througliflow orifices spaced along the length of the channel to feed cooling air from the said air duct into the channel and across the surfaces of the coil support member in the space between those surfaces and the sidewalls of the frame, or alternatively, depending upon the direction of air flow across those surfaces, to extract air from the said channel after passage over the said surfaces of the support member into the said air duct; and an air duct formed in said base member, with orifices extending therefrom to the surfaces of the coil support member adjacent to the said base plate for the purpose of either feeding cooling air over those surfaces in the direction of the air througliflow orifices in the channel, or for venting cooling air after it has been fed into the channel 6 through those orifices and over the opposite surfaces of the coil support member in the direction of the base member.
The base member affixed to the coil support member may have two air ducts located therein and parallel one to the other, one on either side of the coil support member, and wherein the orifices extending from those ducts to the surfaces of the support member extend diagonally across the member thereby to connect the duct on one side of the coil support member to the surface of the coil support member on the other side.
The orifices in the base members may be formed by drilling holes diagonally through a base member having said two air ducts preformed therein, the drilled holes intersecting those air ducts and extending through a top edge of the coil support member to the opposite face of the coil support member adjacent the junction between the coil support member, and then plugging the open ends of the drilled holes in the base member.
Various embodiments of the invention will now be more particularly described, by way of example, with reference to the accompanying drawings, in which:
Figure I is a simplified side view of an armature having single cold plate cooling of the prior art.
Figure 2a is a perspective view of a serpentine cooling tube structure of an embodiment of an armature of the prior art.
Figure 2b is a cross section view, after potting, of the armature shown in 7 Figure 2a taken along line IIb-Ilb.
Figure 3 a is a partial cross section end view of a linear motor of the present invention incorporating dual cold plate cooling.
Figure 3b is an end view of the embodiment of the present invention shown 5 in Figure 3a showing cross-over connecting tubes.
Figure 4 presents simplified end views of three armatures, two of the prior art and one of the present invention, showing locations of temperature measurements taken on the armatures.
Figure 5 is a partial cross section end view of another embodiment of an armature of the present invention.
Figure 6a is a side plan view of yet another embodiment of the present invention having a first ceramic substrate configuration.
Figure 6b is an end view of the ceramic substrate of Figure 6a.
Figure 6c is a cross section bottom view of the embodiment shown in Figure is 6a.
Figure 7a is a side plan view of still another embodiment of the present invention showing a second ceramic substrate configuration.
Figure 7b is a cross section bottom view of the embodiment shown in Figure 7a.
Figure 8 is a partial cross section end view of a farther embodiment of the present invention having ducted air and cold plate cooling.
Figure 9 is a partial cross section end view of a still further embodiment of the present invention having air cooling and cold plate cooling.
Figures 10 and 11 are partial section views of another embodiment of the 8 invention.
Referring to Figure 1, there is shown a side view of an armature assembly of the prior art having a single sided liquid cooling system. An armature 10 is mounted in contact with a cold plate 12. Heat is drawn from the armature 10 into the cold plate 12, however, since the top portion of the armature 10 is furthest from the cold plate 12 it has a path of greater thermal resistance to the cold plate 12 than does a bottom portion of the armature 10 which is close to the cold plate 12. Therefore, heat is transferred inefficiently from the top of the armature 10. Inefficient heat transfer corresponds to higher equilibrium temperatures for a given power dissipation rate. Because the materials and construction have limited ability to cope with high temperatures, the total power dissipation capacity of the armature assembly is limited by the inefficient heat transfer.
Referring to Figure 2a, an alternative cooling method, used in a nonmagnetic armature of the prior art, incorporates an armature frame 14 composed of a serpentine cooling tube 16. Overlapping coils are laid upon the armature frame 14 as indicated by a dashed coil outline 18. Once each coil has been positioned upon the armature frame 14, the entire assembly is potted in resin. In Figure 2b a cross section of a potted armature assembly of Figure 2a is shown. Coils 20 have the serpentine cooling tube 14 positioned between each adjacent coil and a casing 24 of resin provides structural integrity and then-nally conductive medium for transferring heat from the coils 20 to the serpentine cooling tube 14. While this construction is effective in eliminating heat from the armature, assembly is complex and the use of overlapping coils adds bulk to the structure.
9 Referring to Figure 3a, an embodiment of the present invention includes a nonmagnetic armature 30 having a base cold plate 32 and a top cold plate 34. The nonmagnetic armature 30 travels within a U-frame 31 of a linear motor and is carried and retained by a user-supplied slide means (not shown) adapted to a particular user application. The U-frame 31 supports a first and a second array of magnets of which two magnets, 3 1 a and 3 1 b are shown. Flat coils, of which a coil 3 5 is shown, are potted in an armature block 38 formed of a settable resin. The base cold plate 32 and the top cold plate 34 are affixed to a top and a bottom of the armature block 38 by means of the settable resin used to forrn the armature block 3 8. The base and top cold plates 32 and 34, have coolant tubes 40a, 40b, 40c and 40d, affixed therein. The settable resin is selected so as to provide high thermal conductivity. One such settable resin is an epoxy resin sold by Emerson and Cumming, Inc of Canton, Mass under the trademark "SYTCAST 285OMT" which has a thermal conductivity of 20 is BTU/in/hr/ft/Deg.F.
The flat coils of the armature block 38 are cooled by means of a liquid coolant passing through the coolant tubes 40a, 40b, 40c and 40d, in the base and top cold plates, 32 and 34. This configuration allows heat to be removed from a middle portion of the armature block by means of thermal paths to both cold plates, 32 and 34. Thus, the thermal resistance between the portion of the armature block farthest from a cold plate is half that of the single cold plate armature of the prior art. Thus, to a first approximation, the heat sinking capacity is double that of the prior art.
Furthermore, the flat coils are wound using wire of a rectangular of a square crosssection to eliminate the air gaps found in motor coils of the prior art wound from round wire. The elimination of air gaps decreases the thermal resistance from inner windings to outer windings of the flat coils. Therefore, the cooling characteristics of the armature 30 are further enhanced over those of the prior art single cold plate armature.
Referring to Figures 3b and 3c, end and bottom views of the armature assembly 30 show cross-over connecting tubes 40e and 40f. The cross-over connecting tubes 40e and 40f, connect coolant tube 30b to coolant tube 40c and coolant tube 40a to coolant tube 40d, respectively, at a first end of armature assembly 30. On a second end of the armature assembly a single connecting tube (not shown), similar to either of connecting tubes 40e and 40f, connects coolant tubes 40b and 40a. Flexible tubing supplies coolant to tube 40c which feeds coolant to tube 40b via connecting tube 40f which conveys coolant to tube 40d. Coolant runs down tube 40d and out through another attached flexible tube. Thus, all tubes are fed serially while the motor is in operation.
Referring to Figure 4, end views of the armature assembly 30 and two prior art an-nature assemblies, 40 and 41, depict the cooling configuration of each assembly.
Each armature assembly is mounted upon a mount plate 42. Armature assembly 40 has no liquid cooling, armature assembly 41 has liquid cooling via a base cold plate, and the armature assembly 30 has both base and top cold plate cooling as discussed above. Temperature monitoring locations A, B, C and D, are indicated on each armature assembly. The maximum rated temperature for the coils of the armature assemblies, 3 0, 40, and 4 1, is 120C.
To evaluate the effectiveness of the cooling configuration of armature assembly 30, power applied to each armature assembly was increased until the rated temperature was reached at some point on the given armature. Table 1 below shows the results of this test. The single cold plate armature 41 was capable of carrying 3 amps and the no-liquid-cooling armature 40 accepted 2.6 amps before each reaching the rated temperature at position D on the assemblies, which is furthest from the mount plate 42. In comparison, the dual cold plate armature assembly 30 handled 4 Amps before the rated temperature was reached at location B at the base cold plate.
A more uniform operating temperature in a given armature assembly is indicative off efficient heat removal and provides for achieving maximum utility from the armature.
is If a localised area of an armature limits operation due to heating, then maximum utility is not derived from the remainder of the armature which is well within the safe operating temperature region. Thus, the advantage of dual cold plate cooling is demonstrated.
12 TABLE I LOCATION A B C D Max Power Thermal Current Capacity Resistance ARMATURE TEMP TEMP TEMP TEMP (AMPS) (WATTS) (Co/W) (C) (C) (C) (C) (DOUBLE 39 122 114 102 4 254 0.4 SIDED COOLING) (SINGLE 38 73 120 3 138 0.9 SIDED COOLING) 41 (NO 65 79 120 2.6 94 1.3 COOLING) The translation of current capacity into power dissipation capacity provides a further measure of the improvement provided by the cooling configuration of the dual plate armature assembly 30. The power capacity of the dual cold plate armature 30 exceeds that of the single cold plate armature 41 by 84%. This represents a significant improvement in the power capacity of a linear motor, allowing for greater forces and acceleration.
Referring to Figure 5 a cross-section through another embodiment of the present invention is shown. An armature assembly 50 is similar to the above embodiment 13 except as stated herein. A base cold plate 52 and top cold plate 54 are produced from extrusions with integral passages replacing the coolant tubes 40a, 40b, 40c and 40d, in the aforementioned embodiment. The base cold plate 52 includes coolant passages 52a and 52b. The top cold plate 54 includes coolant passages 54a and 54b. The coolant passages 52a, 52b, 54a, and 54b, are readily formed in the extrusions by methods familiar to those skilled in the art of extrusion design. Crossover connections at ends of the coolant passages can be implemented by means realisable by those skilled in the art of manufacture and are not detail herein. Coil lead wires 58a and 58b connect to a trailing cable (not shown) via wiring or a printed circuit board in the base cold plate 52 or cast into the settable resin.
The use of extrusions in the construction of the cold plates, 52 and 54, saves time used and expenses incurred during manufacture by elimination of the need to bond the coolant tubes 40a, 40b, 40c and 40d, into the cold plates, 32 and 34, of the aforementioned embodiment. Furthermore, thermal resistance between the cooling liquid and the armature block 38 is reduced because a thermal resistance of a bonded interface between the coolant tubes 40a, 40b, 40c and 40d, and the cold plates 32 and 34 is eliminated. The lowered thermal resistance produces still ftirther improvements in cooling efficiency.
The extrusions comprising the cold plates, 52 and 54, are formed from aluminium.
Alurninium's low thermal resistance and its lightweight make it particularly suitable to this application. However, aluminium is also electrically conductive which permits the production of eddy currents in the cold plates, 52 and 54, which travel through 14 magnetic fields created by the magnets, 3 1 a and 3 1 b, of the U-shaped frame 3 L Eddy currents produce drag upon the armature and dissipate energy as beat. Therefore, in applications requiring high speed, electrically non-conductive materials which have high thermal conductivities are preferred. Ceramic materials such as silicon carbide and aluminium nitride satisfy these requirements and are used in embodiments requiring these characteristics. Other such materials may be identified by those skilled in the art and are within the scope and spirit of the present invention.
Settable resin 56 is used to bond the armature assembly 50 together. This settable resin 56, as discussed above, is chosen for its high thermal conductivity. Although the thermal conductivity of the settable resin 56 is high for a resin, it is not as high as thermal conductivities of aluminium or ceramics. For example, resin core motors exhibit a typical thermal conductivity of 1 W/C-m while motors employing steel laminations have a typical then-nal conductivity of 30 W/C-m. In order to improve the thermal conductivity of the armature assembly 50, heat sink plates, 60a and 60b, serve to further decrease the thermal resistance between a middle portion for the armature assembly 50 and the base and top cold plates, 52 and 54, because the heat sink plates, 60a and 60b, have a thermal conductivity superior to that of the settable epoxy resin.
The heat sink plates, 60a and 60b, are fort-ned of electrically nonconductive and nonmagnetic but thermally conductive materials such as the aforementioned ceramics.
The components are assembled together into the armature assembly 50 using the epoxy resin described in the embodiment shown in Figure 2. The use of ceramic type materials results in the armature assembly 50 being non-magnetic, and non conductive with the exception of the coils 36, thereby effectively eliminating eddy currents which cause drag and heating of the armature assemblies while improving the thermal conductivity of the armature assembly 50. While the heat sinks plates, 60a and 60b, are shown functioning in conjunction with the base and top cold plates, 52 and 54, other embodiments of the present invention may employ such heat sink plates functioning with a single cold plate or a heat sink member employing fins or other means to dissipate heat aside from liquid cooling.
Referring to Figures 6a, 6b and 6c, a further embodiment of the present invention is shown wherein a ceramic substrate 70 has the coils 36 (not shown in Figure 6b) mounted upon it. The ceramic substrate 70 has a recessed surface 71 from which raised islands 72 extend into openings of the coils 36. A base portion 74 has contours 76 in which lower portions of the coils 36 extend. The ceramic substrate 70 is potted with settable resin and a cold plate (not shown) of one of the above embodiments is affixed to the base portion 74. The islands 72 and contours 76 are dimensioned so as to provide a close fit with the coils 36, minimising the amount of settable resin between the coil 36 and the ceramic substrate 70 and thus, also minimising the thermal junction resistance. The islands 72 draw heat away from the centre of the coils 36 by providing a low thermal resistance path to the base portion 74 and a cold plate (not shown) attached thereto. The thicker base portion 74 increases the surface area through which heat flows from the ceramic substrate 70 into the cold plate, reducing the thermal re'sistance of the junction between the cold plate and the ceramic substrate. Once again, the superior thermal conductivity of the ceramic substrate 70 16 provides for a significant cooling improvement over an armature assembly constructed using only resin encapsulation. Additionally, a ceramic cover plate (not shown) may be affixed over the ceramic substrate 70 thereby further increasing the thermal conductivity to the cold plate. Another embodiment has a second cold plate 5 affixed to the top of the ceramic substrate 70 to further enhance cooling.
Referring to Figures 7a and 7b, another embodiment of the present invention is shown wherein a ceramic substrate 80 has annular recesses 84 forming islands 82. The annular recesses 84 are dimensioned to provide for a close fit with coils (not shown) inserted into the annular recesses 84. A trough 86 is provided to accept coil leads connected to a control cable (not shown). Coils are inserted in to the annular recesses and potted therein using high thermal conductivity settable resin. A ceramic cover plate 88, shown in Figure 7b, is optionally affixed over the ceramic substrate, further improving thermal conductivity of the ceramic substrate assembly. Cold plates (not shown) are affixed to top and base portions of the ceramic substrate assembly in a similar manner as that shown in the above embodiments. The high volumetric content of ceramic material in such an armature assembly serves to provide superior thermal characteristics without the use of electrically conductive or magnetic materials which produce eddy current drag and losses.
Referring to Figure 8 another embodiment of the present invention is shown including air cooling. An armature assembly 90 is similar to the armature assembly 50 of Figure 5 except as provided herein. The armature assembly 90 is provided with a single cold plate, the base cold plate 52. The use of the base cold plate 52 alone 17 allows the armature assembly 90 to be extracted in a downward vertical direction anywhere along U-frame 3 1. Although base cold plate 52 is shown composed of an extrusion, it is realised that a cold plate of proper size using other construction techniques may be employed.
The U-frame 31 includes air passages, 92a and 92b, which provide a flow of cooling air via orifices, 94a and 94b, to a space surrounding a top of armature assembly 90. The flow of cooling air removes heat from the top portion of the armature assembly 90 which is furthest from the base cold plate 52. This provides for more uniform cooling than is achieved if only the base cold plate 52 was employed. Therefore, the armature assembly may operate at higher power levels than similar non-magnetic armatures of the prior art.
The base cold plate 52 further includes a printed circuit board 96 into which leads from the coils 36 connect. A trailing cable (not shown) is then connected to the printed circuit board. Other means of wiring, including harnesses and flexible printed cirucits connected to the trailing cable and coil leads, may be incorporated into the base cold plate 52 or cast in the resin encapsulation. Such methods are included within the scope and spirit of the present invention.
Referring to Figure 9, still another embodiment of the present invention employing air cooling is shown. The annature assembly 90 travels in the Uframe 3 1. The Uframe 31 includes seals, 98a and 98b, mounted along lower edges of the U-frame 3 1.
The seals, 98a and 98b, are formed of a flexible plastic or rubber material and extend 18 along the entire length of the U-frame 3 1. Along portions of the U-frame where the armature assembly 90 is not present, the seals, 98a and 98b, engage each other preventing the escape of air from the U-frame. A flow of cooling air is introduced into a first end of the U-frame 31 and exits by a second end of the U-frame 31.
Adaptors (not shown) on the first and second ends of the U-frame 31 interface with means of supplying cooled air and are readily realisable by those skilled in the art. The cooling air passes over the armature assembly 90 thereby cooling it. The seals, 98a and 98b, are pushed apart by longitudinal movement of the an-nature assembly 90 in the U-frame 3 1. Due to a larger area for passage, a greater flux of flowing air exists around the top portion of the armature assembly 31 which is otherwise subject to heat build-up since it is furthest from the cold plate 52. Thus, uniform cooling of the armature assembly 90 is effected by the combination of the base cold plate 52 and the cooling air flow at the top portion of the armature assembly 3 1.
The embodiment of Figure 9 allows the armature assembly to be removed from the U-frame 31 at any location along its length since there is no cold plate on the top portion of the armature assembly 90 to prevent its removal. Furthermore, the seals, 98a and 98b, serve to prevent debris from entering the U-frame and interfering with operation of the linear motor. Similarly, seals may be incorporated into the embodiment presented in Figure 8. Additionally, vertical cooling fins may be added to the top portion of the armature assembly 90 to further enhance the cooling effect of the flowing air.
Referring to Figures 10 and 11, a base element 132 is provided with an air passage 19 129. Minor channels 130 are drilled through base element 132 to connect major channel 129 to a space 135 between armature bloc 134 and U-frame 3 1. The design of the embodiment of Figures 10 and 11 allows easy manufacture by drilling out minor channels 130. Entry and exit of a drill tool can be accommodated easily as can be seen by noting the positions of entry hole 128 and exit hole 13 1. Entry hole 128 is plugged to seal the air passages so that all the air is injected into space 135. The course followed by cooling air is as follows: Air is distributed through air passage 129 to all of the minor channels 130. Minor channels 130 inject air into space 135. Air flows through the space and is drawn out through apertures 138 into exit channel 136.
Apertures 13 8 are distributed along the length of U-frame 3 1. Ideally apertures are located between exit holes 131 so air must flow diagonally across the armature. In addition, a large number of small apertures can be used to improve distribution of flow across the surface of armature plate 134. Note that air could be distributed and taken up in the opposite direction as well. That is air could be conveyed into the space between U-frame 31 and armature plate 134 and then out through exit holes 131 and duct 129.
Although according to the above embodiments, the upper and lower cooling tubes are connected in series, it is apparent from the present disclosure that each pair of tubes could be fed in parallel. In that case, since heat transfer fluid would be carried in parallel in twice as many tubes for a given section of armature block, the volume of fluid is increased over that of the prior art without increasing the tubing diameter.
This would result in lower temperature rise of the heat transfer fluid and further increasing the rate of heat transfer and the attendant power dissipation capacity.
Having described preferred embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in- the appended claims.
21 CLAIMS 1. A linear motor comprising:
S an elongate frame defining an elongate open channel having a U-shape cross- section formed by side walls and a cross member; a plurality of magnets mounted on the inwardly facing walls of the channel and forming an array of magnets of opposite polarity spaced along the length of the channel; an armature member containing substantially no magnetic material mounted for longitudinal travel in the U-frame, said armature member having an elongate coil support member positioned between the side walls of the frame and to which is mounted at least one coil to which an electric current can be supplied to cause the armature member to travel along the length of the channel, said support member and the said at least one coil being encapsulated in an encapsulating resin; and an air duct located in the cross member of the frame and extending longitudinally therein and a plurality of orifices spaced along the channel, said orifices communicating between the air duct and the channel for either venting cooling air flowing over said inwardly facing walls of the channel in a direction towards the cross member and into the said air duct, wherein the said duct serves as an extraction duct, or alternatively for introducing cooling air fed to said duct into the channel so as to flow over said inwardly facing walls in a direction away from said cross member.