Linearmotor

Abstract

Linear motor utilizing a magnetic field generated by a field magnet (23) and a current flowing through several coils (24) to generate thrust for linear movement of the coils (24) relative to the field magnet (23), the linear motor comprising: the field magnet (23) having magnets arranged such that north and south poles are magnetized alternately in the direction of linear movement;and an armature that surrounds the coils (24) surrounding the field magnet (23), a coil holder (25) for holding the coils (24), and a shaped body (22) that covers the coils (24) and the coil holder (25), a rod (21) having the field magnets (23) passing through the coils (24), wherein the coil holder (25) has a holder main body (25a) extending in the direction of linear motion over the length of the coils (24), and several spacers (25b), each of which is provided between adjacent two of the coils (24), wherein the shaped body (22) is an insulator and has a thermal conductivity of 2 W / (m·K) or more, and wherein the coil holder (25) is an insulator and has a thermal conductivity of 2 W / (m·K) or more.

Description

TECHNICAL FIELDThe present invention relates to a linear motor capable of generating thrust for linear motion by utilizing current flowing through coils and a magnetic field generated in field magnets.PRIOR ARTThe linear motor includes a flat type linear motor having an elongated plate-shaped field magnet and an armature disposed so as to provide a space therebetween, and a rod type linear motor (also called a "wave type") having a rod-shaped (wave-shaped) field magnet and a cylindrical armature disposed around the field magnet.In the case of the flat linear motor, the armature moves linearly with respect to the elongate, plate-shaped field magnet. The field magnet has a plurality of plate-shaped magnets arranged such that north and south poles are alternately formed on the surface of the field magnet. The armature has U, V and W coils located opposite the field magnet, with a space being provided between the coils and the field magnet. When a three-phase alternating current flows through the coils, the magnetic field generated in the magnet and the current flowing through the coils cause a thrust for linear motion (see, for example, Patent Document 1).In order to obtain a strong thrust, a flat linear motor having a core inserted into the coils is known.On the other hand, in the linear rod motor, the rod (the shaft having the north and south poles alternately magnetized is surrounded by the cylindrical armature which moves linearly with respect to the rod. The armature has U, V and W coils wound around the field magnet with a magnetic space being provided therebetween. The U, V and W coils are arranged in the axial direction of the rod. When three-phase alternating current having phases U, V, and W flows through the coils, the magnetic field generated in the magnet and the current flowing through the coils cause a thrust for linear motion (see, for example, Patent Document 2).The linear motor must generate a larger thrust, but it should be compact. Here, the thrust of the linear motor is proportional to the product of the square of the current I flowing through the coils and the magnetic flux density B generated in the magnet. In order to increase the magnetic flux density of the magnet, ferrite magnets were occasionally replaced with rare earth magnets in the development history of the linear motors. However, there is a limit for increasing the magnetic flux density B of the magnet, and it is difficult to increase it beyond that.The thrust can be increased by increasing the current flowing through the coils. However, there is a need to prevent heat generation by the coils when increasing the current flowing through the coils. The reason is that the coil conductor wire has a resistance and, when a large amount of current flows through the coils, Joule heat proportional to the square of the current is generated. When the temperature of the coils further rises due to Joule heat, an insulating layer of the lead wire melts, thus losing insulation of lead wires. If the insulation of the conductor wires is lost, such a state is equivalent to a reduced number of turns of the coils, resulting in a decrease in the thrust of the linear motor, which is proportional to the number of turns of the coils. Therefore, the current flowing through the coils is limited to the temperature at which the insulating coating of the lead wires does not melt. The prevention of heat generation of the coils is closely related to the increase in the thrust generated by the engine.In order to prevent heat generation of the coils, gold, silver or a superconducting material having no electric resistance may be used instead of copper. When the electric resistance is low, heat generation by the coils can be avoided, a large amount of current can be conducted through the coils, and thus the thrust of the linear motor can be increased.In addition, in order to prevent heat generation of the coils, cooling fins are sometimes formed in a case covering the coils, or a core is inserted into the coils, thereby releasing heat from the cooling fins to the air. When the heat generated in the coils is dissipated, an increase in the temperature of the coils can be avoided even if a large amount of heat is generated by the coils.[Patent Document 1] Japanese Patent Application Laid-Open JP 2006-74 975 A[Patent Document 2] Japanese Patent Application Laid-Open No. 2002-354,780 AJP H09-154 272 A discloses a cooling structure of a linear motor. JP 2005-253 259 A discloses a linear electromagnetic actuator. DE 295 01 109 U1 discloses a stator for an electric linear motor. DE 100 57 111 C1 discloses potting compound.DISCLOSURE OF THE INVENTIONPROBLEMS TO BE SOLVED BY THE INVENTIONHowever, the technique of using superconducting material or gold instead of copper is difficult to realize from the viewpoint of cost reduction. Moreover, as for the technique of forming cooling fins in the core or casing of the coils to thereby conduct heat, almost all the structural ideas have been put in, reaching the level beyond which the cooling efficiency cannot be improved.Thus, the present invention has an object to provide a novel linear motor which is compact in size and capable of generating more thrust.MEANS FOR SOLVING THE PROBLEMSA linear motor that uses a magnetic field generated by a field magnet and a current flowing through a plurality of coils to generate thrust for linear motion of the coils with respect to the field magnet, the linear motor comprising: the field magnet having magnets arranged such that north and south poles are alternately magnetized in the direction of the linear motion, and an armature having the coils facing the field magnet with a gap provided therebetween, a core having a plurality of comb teeth inserted into the respective coils, and a bobbin disposed between each of the coils and a corresponding one of the comb teeth and having a thermal conductivity of 2 W / (m·K) or more.A linear motor using a magnetic field generated by a field magnet and a current flowing through a plurality of coils to generate thrust for linear motion of the coils with respect to the field magnet, the linear motor comprising: the field magnet having magnets arranged such that north and south poles are alternately magnetized in the direction of the linear motion, and an armature having the coils facing the field magnet with a space provided therebetween, a core having a plurality of comb teeth inserted into the respective coils, and a molded body for covering the coils and connecting the coils to the core, wherein the molded body is an insulator and has a thermal conductivity of 2 W / (m·K) or more.The invention is a linear motor according to claim 1.The invention according to claim 2 is characterized in that in the linear motor according to claim 1, the bobbin, the bobbin or the molded body is made of resin mixed with insulating metal oxide particles having different average diameters.The invention according to claim 3 is characterized in that in the linear motor according to claim 2, the bobbin, the bobbin or the molded body is produced by injection molding thermoplastic resin mixed with the insulating metal oxide particles.The invention according to claim 4 is characterized in that in the linear motor according to claim 3, the molded body is made by casting in which thermosetting resin mixed with the insulating metal oxide particles is poured into a mold.The invention according to claim 5 is characterized in that in the linear motor according to any one of claims 1 to 4, the coil body, the coil holder or the molded body has a linear expansion coefficient which is in the range of 10×10 -6 to 30×10 -6 inclusive.EFFECTS OF THE INVENTIONIn the flat linear motor, as an example of the system for dissipating heat generated by the coils, heat is dissipated from the coils to the core via the bobbin. The bobbin is an insulator interposed between the coils and the comb teeth, and has a function of insulating the coils from the comb teeth of the core. By using the insulating material having a thermal conductivity of 2 W / (m·K) or more in the bobbin, the thermal conductivity is improved to ten times or more that of the bobbin made of insulating paper, and the heat generated from the coils can be efficiently dissipated to the core. Accordingly, the current flowing through the coils can be increased and the thrust of the linear motor can be increased.In the flat linear motor, as an example of the system for dissipating heat generated by the coils, heat is discharged from the coils to the air via the molded body. The molded body serves as a cover of the coils and as a connector of the coils with the core. By using the insulating material having a thermal conductivity of 2 W / (m·K) or more in the molded body, the thermal conductivity is improved to ten times or more that of the molded body made of resin, and the heat generated from the coils can be efficiently released to the air. Accordingly, the current flowing through the coils can be increased and the thrust of the linear motor can be increased.In the linear rod motor, as an example of the system for dissipating heat generated by the coils, heat is discharged from the coils to the air via the molded body. The molded body serves as a cover for the coils and as a housing. According to the invention of claim 1, by using the insulating material having a thermal conductivity of 2 W / (m·K) or more in the molded body, the thermal conductivity can be improved to ten times or more that of the molded body made of resin, and the heat generated from the coils can be efficiently released to the air. Accordingly, the current flowing through the coils can be increased and the thrust of the linear motor can be increased.In the rod linear motor, as an example of the system for dissipating heat generated by the coils, heat is dissipated from the coils into the coil holder. The coil holder has a function of holding the coils and insulating the adjacent coils from each other. By using the insulating material having a thermal conductivity of 2 W / (m·K) or more in the bobbin, the thermal conductivity is improved to ten times or more that of the resin bobbin, and the heat generated from the coils can be efficiently released to the air. Accordingly, the current flowing through the coils can be increased and the thrust of the linear motor can be increased.According to the invention of claim 2, by mixing multiple insulating metal oxide particles having different average diameters into the resin, any space between large-diameter metal oxide particles can be filled with small-diameter metal oxide particles. Since the heat can be transferred via the metal oxide particles filled with a higher filling factor, the thermal conductivity can be improved.According to the invention of claim 3, the coil body, the coil holder or the molded body can be manufactured in series with higher dimensional accuracy.According to the invention of claim 4, it is possible to reduce the cost of molding and to manufacture the molded article at a low cost.According to the invention of claim 5, the linear expansion coefficient of the molded body, the bobbin, or the bobbin is an order of magnitude smaller than that of the resin (120×10 -6) and is close to those of metals such as steel (11 to 13×10 -6), copper (19 to 20×10 -6) and aluminum (22 to 23×10 -6). Since, with an increase in temperature, the expansion of the molded body, coil holder or bobbin is almost equal to the expansion of the coils and the core, it is possible to keep them in contact with each other. Therefore, it is possible to avoid formation of a vacuum space or an air layer between them due to a temperature rise which would lead to difficult heat transfer.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1 is a perspective view of a flat linear motor according to a first exemplary embodiment of the present invention. FIG. 2 is a front view of the linear motor of FIG. 1. FIG. 3 is a plan view of an armature. FIG. 4 is a perspective view of an armature. FIG. 5 is a cross-sectional view taken along a moving direction of an armature. FIG. 6 is a perspective view of the upside down anchor. FIG. 7 is a perspective view of the coil corper. FIG. 8 is a frame [flame] used for casting. FIG. 9 is a graph showing the relationship between the mass percent and the particle diameter of a metal oxide. FIG. 10 is a schematic enlarged cross-sectional view of the bobbin. FIG. 11 is a perspective view of a rod linear motor according to a second exemplary embodiment of the present invention. FIG. 12 is a view showing the positional relationship between coils and magnets of the linear motor. FIG. 13 is a perspective view showing a coil unit held by a coil holder.FIGS. 14A and 14B are detailed views of the bobbin holder (FIG. 14A is a front view thereof and FIG. 14B is a cross-sectional view thereof).FIGS. 15A to 15C are diagrams showing the relationship between the temperature of the coils and the current flowing through the coils (FIG. 15A is a diagram for the current value I×1, FIG. 15B is a diagram for the current value I×1.15, FIG. 15C is a diagram for the current value I×1.63.REFERENCE NUMERALS2... Field magnet, 3... Coil, 9... Anchor, 11... Core, 11a to 11c... Comb teeth, 14... Coil former, 16... Shaped bodies, 21... Stab, 22... Molded body (housing), 23... Field magnet, 24... Coil, 25... Bobbin holdersMODE FOR CARRYING OUT THE INVENTIONHereinafter, with reference to the accompanying drawings, an exemplary embodiment of the present invention will be described in detail. FIGS. 1 and 2 show a flat type linear motor according to a first exemplary embodiment which does not form part of the invention. FIG. 1 is a perspective view, while FIG. 2 is a front view. The linear motor according to this embodiment is a uniaxial actuator, and is used to move a movable body such as a table in the uniaxial direction.On an elongated base 1, a plate-shaped field magnet 2 is provided as a stator of the linear motor. The field magnet 2 faces coils 3 of an armature 9. Current flowing through the coils 3 of the armature 9 and the magnetic field of the field magnet 2 thereby generate thrust to move the armature 9 linearly with respect to the field magnet 2.As shown in the front view of FIG. 2, a magnetic gap g is provided between the armature 9 and the field magnet 2. This gap g is firmly maintained as the armature 9 moves with respect to the field magnet 2.As shown in FIG. 1, the base 1 extends in the direction of linear movement of the armature 9. the base 1 has a rectangular bottom plate 1a and a pair of side walls 1b provided at respective ends in the width direction of the bottom plate 1a. On an upper surface of each of the side walls 1b, a rail 5 of the linear guide is attached. The rail 5 extends over almost the entire length of the side wall 1b. On an outer circumferential surface of the rail 5, a rolling element raceway is formed along the rail 5, where rolling elements such as balls or rollers of the linear guide roll.On an upper surface of the bottom plate 1a of the base 1, there is provided the field magnet 2 in which north and south poles are alternately magnetized in the direction of linear movement of the armature 9. As shown in FIG. 3, the field magnet 2 has a plurality of plate-shaped magnets 10 shaped as parallelograms arranged in a row. Each of the plate-shaped magnets 19 is magnetized with north and south poles in a direction orthogonal to the length direction of the field magnet 2 (direction orthogonal to the plane of the figure). In order that the north and south poles are magnetized alternately in the long direction of the field magnet 2, the magnetic pole faces the surface of the plate-shaped magnet 19, the magnetic pole faces the surface of each plate magnet, that of its adjacent plate magnet 19.As shown in FIG. 1, the left and right rails 5 are slidably mounted with linear guide blocks 6, respectively. On the left and right blocks 6, a gate-shaped upper board 7 is mounted. In addition, the anchor depends from the bottom surface of the connecting upper board.The connecting upper board 7 has a ceiling part 7 aextending in the width direction and a pair of leg parts 7 bprovided at the respective widthwise ends of the ceiling part 7 aand extending downward. At the lower end of each leg part 7b, the linear guide blocks 6 are fixed. The anchor 9 is attached to the lower surface of the ceiling part 7 a. The movable body is attached to the upper surface of the ceiling portion 7a.Each block 6 is formed like a saddle covering the rail. In this embodiment, two blocks 6 are mounted on a rail 5. In each block 6, a loaded rolling element raceway is formed opposite to the rail 5, and a circular rolling element circulation passage is provided for circulating the rolling elements. In the rolling element circulation passage of the block 6, the plural rolling elements are arranged and accommodated. When the block 6 slides with respect to the rail 5, the rolling element rolls between the rolling element raceway of the rail 5 and the loaded rolling element raceway of the block 6. The rolling motion of the rolling elements serves to reduce the frictional resistance of the block 6 as it slides with respect to the rail 5.FIGS. 4 and 5 show detailed views of the armature 9. the armature 9 has three-phase coils 3 (3a, 3b, 3c) opposed to the field magnet 2, a core 11 for amplifying the generated magnetic field to the coils 3, and a heat sink 12 for releasing the heat generated by the coils 3 to the air.Each of the coils 3 is a conductor wire wound around a corresponding one of the comb teeth 11 a, 11 b, and 11 cof the core 11 (more specifically, the bobbin 14 covering the comb teeth), and is formed like a ring extending in the width direction of the armature 9. The three-phase coils 3 a, 3 b, and 3 care arranged adjacently to each other in the direction of the linear movement of the armature 9. When a three-phase alternating current having waveforms phase-shifted by 120° from each other is applied to the three-phase coils 3 a, 3 band 3 cof the U, V and W phases, the movable magnetic field is generated in the direction of the linear movement of the armature 9.The current flowing through the coils 3 is controlled by a regulator (not shown). A linear scale for detecting the position of the armature 9 is mounted on the base 1. The controller feeds back speed information and position information of the armature 9 detected by the linear scale, calculates a difference between detected values and target values, and causes current to flow through the three-phase coils 3 a, 3 b, and 3 cso as to bring the position and the speed of the armature 9 close to the target values.The core 11 has a board-shaped base plate 11 dextending in the arrangement direction of the plurality of coils 3, and a plurality of comb teeth 11 a, 11 b, and 11 cthat project from the base plate 11 dinto the inside of the three-phase coils 3 a, 3 b, and 3 c, respectively. The base plate 11d has an upper surface which is in contact with the lower surface of the cooling body 12. The plural comb teeth 11a, 11b and 11c project in the direction orthogonal to the base plate 11d. The core 11 is made of a magnetic material such as silicon steel.The heat sink 12 is shaped like a vortex, and a plurality of grooves 12a extending in the moving direction of the armature 9 are formed in the upper surface thereof. Since the plurality of grooves 12 are formed, in the upper surface of the cow body 12 are formed cow ribs which increase the area. The cooling body 12 is made of aluminum or aluminum alloy with a high thermal conductivity.FIG. 6 is a perspective view of the upside-down armature 9 (for the sake of convenience in showing the bobbins 14, the coils 3 are cut off along the moving direction of the armature 9). Each coil 3 is a conductor wire which is a copper wire covered with an insulating layer, the conductor wire being wound like a ring. The conductor wires are insulated from each other by the insulating layers drawn over the wires. However, when the coils 3 are inserted into the comb teeth 11 ato 11 c, they may not be insulated by the insulating layers of the wires because, when the coils 3 are directly wound on the comb teeth 11 ato 11 c, the insulating layers of the conductor wires may be damaged and the comb teeth 11 ato 11 cand the conductor wires may be short-circuited. Therefore, the coils are not directly wound on the comb teeth 11 ato 11 c, and bobbins 14 are disposed between the comb teeth 11 ato 11 cand the coils 3 for insulation.FIG. 7 is a perspective view of a coil body 14. the coil body 14 has a frame-shaped coil body 14 athat surrounds the comb teeth and a flange part 14 bthat is provided at the end of the bobbin main body 14 in the axial direction. The flange part 14 bis disposed between the base plate 11 dof the core 11 and the end surface of the coil 3 in the axial direction for insulation therebetween. Conventionally, insulation paper called "Nomex" (registered trademark) is used for insulation. This paper, even if thin, has excellent insulation performance, and for example, paper of several tens of μm in thickness can insulate several thousands of volts electricity. When this insulating paper is used, it is wound around each of the comb teeth 11a to 11c, and the coil 3 is wound around the insulating paper. However, this operation must be performed manually. Since the operation of winding the insulating paper is cumbersome, instead of completely covering each of the comb teeth 11a to 11c, the coil body 14 of a molded body is used. After the coil 3 is wound around the coil body 14, the bobbin 14 is set around the comb tooth. Since the bobbin 14 is an insulator, it is possible to insulate the coils 3 from the comb teeth 11 ato 11 c.The coil body 14 is a molded body and is at least 0.2 mm, 0.3 mm, 0.5 mm in thickness. If the bobbin 14 is formed by injection molding of heat resistant liquid crystal polymer (having a thermal conductivity of about 0.2 W / (m·k) or more), it has low thermal conductivity and a large thickness, and the thermal strength is increased. When the heat resistance of the coil bobbin 14 is increased, it becomes difficult to dissipate heat of the coils 3 to the core 11. Therefore, the bobbin 14 is made of a material having a thermal conductivity of 2 W / (m·k) or more, or preferably 6 W / (m·k) or more.The coil 3 is in contact with the bobbin 14. The bobbin 14 is in contact with the core 11, and the core 11 is in contact with the heat sink 12. Therefore, heat generated from the coils 3 is transmitted to the coil bobbin 14, the core 11, and the heat sink 12 and discharged to the air from the cooling fins of the heat sink 12. When the thermal conductivity of the bobbin 14 is 2 W / (m·k) or more, the generated thrust may be larger than that when insulation paper of about one tenth of the thickness of the bobbin 14. It is particularly advantageous in a high-accuracy application in which a heat problem such as thermal expansion occurs and temperature rise can be prevented.The bobbin 14 is made of a molding material which is thermoplastic resin mixed with insulating metal oxide particles as a filler. The bobbin 14 is made by injection molding thermoplastic resin mixed with metal oxide particles.As shown in FIG. 9, the metal oxide particles are a mixture of small-diameter metal oxide particles B having an average particle diameter of 0.5 to 2 μm and large-diameter metal oxide particles A having an average particle diameter of 5 to 20 μm. The particle diameter of the metal oxide particles B is about one tenth of that of the metal oxide particles A. The metal oxide particles B may be mixed with metal oxide particles C having a particle diameter which is about one tenth of the diameter of the metal oxide particles B. The mass percent of a part d where the distributions of the metal oxide particles A and B overlap each other is 40 mass % or less, and preferably 1 mass % or less. When the mass percent is 1 mass % or less, the distribution of the metal oxide particles A and the distribution of the metal oxide particles B hardly overlap each other, and the overall distribution curve is discontinuous.When the average particle diameter of the metal oxide particles A and B is set in this manner, the space of resin between large-diameter metal oxide particles A is occupied by small-diameter metal oxide particles B. This makes it possible to increase the filling factor of the metal oxide particles A and B. By transferring the heat through the metal oxide particles A and B filled in at a high filling factor, the thermal conductivity increases. Here, when the metal oxide particle diameter is smaller than 0.5 μm, the particles agglomerate remarkably (like lumps) and the dispersion efficiency deteriorates, resulting in that the thermal conductivity deteriorates unpreferably. In addition, when the particle diameter is larger than 20 μm, thin molding becomes difficult and the product becomes thicker. Specifically, a product having a thickness of 1 mm or less is hard to form, and the heat resistance is disadvantageously raised. A thermally conductive element must be thinner. Even if it has excellent thermal conductivity, the heat resistance eventually increases and the heat dissipation deteriorates.The insulating metal oxide particles include, among others, alumina (Al 2 O 3), silica (SiO 2), zirconia (ZrO 2), titania (TiO 2), magnesia (MgO), mullite (3Al 2 O 3-2 SiO 2), zircon (particularly, ZrO 2- SiO 2), cordierite (2MgO-2Al2O3-5SiO2), Manganese oxide (MnO 2), iron oxide (Fe 2 O 3) and cobalt oxide (CoO). To improve the heat dissipation performance of the linear motor, other insulating metal particles having a thermal conductivity of 1 W / (m·K) may also be used, for example, silicon nitride (Si 3 N 4), silicon carbide (SiC), boron nitride (BN), or aluminum nitride (AlN).The volume percent of the metal oxide particles in the total volume of the molding composition is at least 50% by volume and is preferably in the range of 55 to 60% by volume. When the volume percent is less than 50% by volume, the thermal conductivity drastically decreases. When 50 volume % is exceeded, thermal conductivity starts to increase. The range of 55 to 60% by volume is a preferable range for compatibility of thermal conductivity and fluidity in injection molding. If exceeding 65% by volume, the fluidity in molding is extremely lowered, and disadvantageously leads to difficulties in that a thin molding becomes difficult and a complicated three-dimensional shape cannot be formed.The thermoplastic resin is melt-moldable synthetic resin and includes, as concrete examples, non-liquid crystalline polyester such as semi-aromatic non-liquid crystalline polyester and fully aromatic non-liquid crystalline polyester, liquid crystalline polymer (liquid crystalline polyester, liquid crystalline polyester amide, etc.), polycarbonate, polyamide such as aliphatic polyamide, aliphatic aromatic polyamide and fully aromatic polyamide, polyoxymethylene, polyimide, polybenzimidazole, polyketone, polyetheretherketone, polyetherketone, polyethersulfone, polyetherimide, modified polyphenylene ether, polysulfone, polyarylene sulfide, polypropylene, polyethylene and other olefin polymers, ethylene-propylene copolymer and other olefin copolymers, ABS, AS, polystyrene and other styrene copolymers, methacrylic resin, polyester-ether elastomer, polyester elastomer, Polyamide elastomer and other elastomers and a mixture of at least two thereof. Generally, the resin, nylon 6, PPS, LCP or PET is preferably used.Regarding the electrical insulation of the thermoplastic resin, the resistivity is preferably 1012 Ω·cm or more, while the dielectric strength is 10 kV / mm or more. In addition, the thermal conductivity is in the range from a minimum of 1 W / (m·K) to a maximum of 20 W / (m·K).The above-mentioned metal oxide particles are mixed to form thermoplastic resin by injection molding. Then, it is possible to produce a bobbin 14 having a thermal conductivity of 2 W / (m·K) or more, for example, 6 W / (m·K), 8 W / (m·K), 10 W / (m·K),..., 20 W / (m·K) at maximum.As shown in FIG. 5, the coil corpers 14 around which the coils 3 ato 3 care wound are fixed to the comb teeth 11 ato 11 cof the core 11 by an adhesive. However, the attachment is unstable only by the adhesive, and it is not certain that the bobbins 14 are completely attached to the core 11. When the adhesion of the coils 3 to the core 11 is insufficient, there arises a problem that the coils 3 move with respect to the core 11 when current flows therethrough. Therefore, after the bobbins 14 are bonded to the core 11, the core 11, the bobbins 14, and the coils 3 are integrally formed by the molded body 16. The coils 3 are covered by the molded body 16 so as not to be unprotected. In order to stably fix the coils 3 to the core, the molded body 16 requires sufficient mechanical strength. In addition, this molded body 16 must be an insulator. The reason is that current can be transmitted from the coils 3 to the conductive field magnet 2 or to the tip ends of the comb teeth 11 ato 11 cduring their diversion around the bobbins. When the molded body 16 is an insulator, it results in a decrease in the heat dissipation capability of the molded body 16. If the heat dissipation capability of the molded body 16 is low, heat generated inside the molded body 16 by the coils 3 develops, resulting in an increase in the temperature of the coils 3. Therefore, it is necessary to improve the heat dissipation capability of the molded body 16 in order to release the heat of the coils 3 to the air.The molded body 16, like the bobbins 14, is made of a molding material that is thermoplastic resin mixed with insulating metal oxide particles as a filler. The molded body 16 is manufactured by injection molding thermoplastic resin mixed with insulating metal oxide particles or by casting or injection molding thermosetting resin mixed with the insulating metal oxide particles into a mold 17 (see FIG. 8 ).The composition and kind of metal oxide particles and the kind and thermal conductivity of the thermoplastic resin for injection molding the molded body 16 are the same as those for injection molding the bobbins 14. The composition and kind of metal oxide particles for molding the molded body are the same as those for injection molding the bobbins 14. It may be selected from epoxy resin, polyurethane, phenolic resin, urea resin and melamine resin or a mixture of at least two thereof.The above-mentioned metal oxide particles are mixed to form thermoplastic resin by injection molding, or metal oxide particles are mixed with thermosetting resin and then subjected to molding. Then, it is possible to produce a bobbin 14 having a thermal conductivity of 2 W / (m·K) or more, for example, 6 W / (m·K), 8 W / (m·K), 10 W / (m·K),..., 20 W / (m·K) at maximum.In the coil corpers 14 and the molded body 16, since the molding material having a thermal conductivity of 6 W / (m·K) or more is used, the current flowing through the coils 3 can be increased by 1.4 times (although when the current is 1.4 times larger, the temperature does not change), and the thrust of the flat linear motor can be increased by about 1.4 times. The thrust increase by 40% is innovative. Using this technique, it is possible to produce a flat linear motor which is compact but capable of generating the strongest thrust worldwide.In addition, the linear expansion coefficient of the molded body 16 and the bobbin 14 (flow ratio / perpendicular thereto) is set to be in the range of 10×10 -6 to 30×10 -6 inclusive. The linear expansion coefficient of the bobbins 14 and the molded body is smaller by an order of magnitude than that of the resin (120×10 -6) and is close to those of metals such as steel (11 to 13×10 -6), copper (19 to 20×10 -6) and aluminum (22 to 23×10 -6). Since, as the temperature rises, the expansion of the bobbins 14 and the molded body 16 can be almost equal to that of the core 11, they can be held in contact. This makes it possible to avoid the formation of an air layer or a vacuum space therebetween due to a temperature rise which would become an obstacle to the heat transfer.FIG. 11 is a perspective view of a linear rod motor according to a second embodiment of the present invention. The linear motor of this embodiment is a uniaxial actuator having a rod 21 (a shaft) that moves in an axial direction with respect to a molded body (housing) 22. This linear motor is used to move a movable body such as an electronic component in a uniaxial direction. Specifically, it is used in a head shaft of a chip mounting apparatus to mount a chip-shaped electronic component at a predetermined location. This linear motor is used not only singly but also in combination with further linear motors arranged in parallel as a multiaxial actuator in order to increase the operating performance.The linear motor receives the force for linear movement of the rod by the current flowing through coils 24 and the magnetic field of a field magnet 23, and a plurality of coils 24 stacked in the axial direction are placed around the rod 21. In other words, the rod 21 passes through the stacked coils 24.FIG. 12 shows the positional relationship between the coils 24 and the field magnet 23 of the linear motor. In a cavity inside the rod 21, a plurality of disk-shaped magnets 31 (segment magnets) are stacked as the field magnet 23 in such a manner that the same poles are opposed to each other, that is, the north pole is opposed to the north pole and the south pole is opposed to the south pole. A plurality of coils 24 surrounding it are stacked around the rod 21. The plurality of coils 24 are three-phase coils of the U, V, and W phases. When three-phase current having waveforms phase-shifted by 120° to each other is applied to the coils 24, a movable magnetic field is generated that moves in the axial direction of the coils 24. Then, the field magnet 23 inside the rod 21 receives thrust by the moving magnetic field so as to move linearly with respect to the coils and in synchronism with the velocity of the moving magnetic field.As shown in FIG. 11, the rod 21 of the linear motor is supported by a molded body 22 so as to be movable in its axial direction. The coil unit is held by a coil holder 25, wherein this coil unit and the coil holder 25 are covered by the molded body 22.The rod 21 is made of a non-magnetic material such as stainless steel and has a hollow like a tube. In the hollow of the rod 21, as described above, a plurality of columnar magnets 31 (segment magnets) are stacked such that same poles are opposed to each other. Between adjacent two of the magnets 31, for example, a pole shoe 27 (magnetic pole block) made of a magnetic material such as iron is disposed. Since the pole piece 27 is disposed between the magnets 31, the magnetic field formed by the field magnet 23 more closely resembles a sine wave.Since the coils 24 are made of a helically wound conductor wire and held by the coil holder 25. The coils 24 and the coil holder 25 are covered by the molded body 22. A plurality of cooling fins 22 are formed on the molded body 22 to enhance the heat dissipation performance. A screw 22b is formed in the mold body 22 for attachment to another separate component. Since the molded body 22 is attached to the separate component, it must have higher mechanical strength. Since it must also be insulated from the coils 24, the molded body 22 must have a high insulating capacity.The molding material 22 is formed of molding material which is thermoplastic resin blended with metal oxide insulating particles as a filler as in the molding material of the first embodiment described above. The molded body 22 is produced by injection molding thermoplastic resin mixed with the insulating metal oxide particles. The coils 24 and the coil holder 25 are placed in a mold for injection molding, and a molding compound is introduced. Then, the molded body 22 is formed as a unit with the coils 24 and the coil holder 25.The composition and kind of metal oxide particles and the kind and heat conductivity of the thermoplastic resin for injection molding of the molded body 22 are the same as those for injection molding of the coil body 14. Since the thermoplastic resin blended with metal oxide particles is used in injection molding, it is possible to produce the molded body 22 having a thermal conductivity of 2 W / (m·K) or more, for example, 6 W / (m·K), 8 W / (m·K), 10 W / (m·K),..., 20 W / (m·K) at maximum.The rod 21 floats within the coil 24 during operation of the linear motor. To assist in the linear movement of the rod 21, a metal bushing 28 is provided. The bushing 28 is fixed to an end member 29 provided at both ends of the mold body 22.Fig. 13 shows the coil unit held by the coil holder 25. The coil unit has a plurality of, for example, a plurality of ten, coils 24, each of which is made of a helically wound conductor wire. Lead wires 24 aof the respective coils 24 must be connected to each other. In order to simplify the wiring of the lead wires 24 aof the coils 24, an insulation board 26 is used. In the insulation board 26, a wiring pattern for wiring the plurality of coils 24 is formed. The conductive pattern is formed such that the U-phase coils are connected to each other, the V-phase coils are connected to each other, and the W-phase coils are connected to each other.Figs. 14A and 14B are detailed views of the coil holder 25 for holding the coils 24. The spacer 25b is formed like a ring like the front shape of each coil 24. The spacer piece 25 bis formed integrally with the plate-shaped holder main body 25 aextending in the arrangement direction of the coils 24.The length of the holder main body 25a in the arrangement direction of the coils 24 is almost equal to the total length of the coil unit, while the width is almost equal to the diameter of the coils 24. The insulation board 26 is attached to the upper surface of the holder main body 25 a. In addition, on each side surface of the holder main body 25 a, protrusions 25 c(see FIG. 13 ) for fixing the bobbin holder 25 to the mold in injection molding are provided. This serves to prevent the bobbin holder 25 from being displaced due to pressure in injection molding. On the lower surface of the holder main body 25a, a curved recess 25d is formed which conforms to the outer shape of the coils 24a. As shown in FIG. 13, each coil 24 has a lead wire 24a. In order to lead the lead wire 24 ato a through hole of the insulating board 26, a plurality of wiring holes are formed in the holder main body 25 aat the same locations of the through holes of the insulating board 26.As shown in Figs. 14A and 14B, the spacer 25b is in the form of a ring like the front shape of each coil, and projects downward from the plate-shaped main body 25a. Spacer 25b is disposed between all adjacent two of coils 24 and also at each end of the coil unit. Accordingly, the number of spacers 25b is larger than the number of coils 24 by one.The bobbin 25, like the bobbins 14 of the above-described first embodiment, is made of a molding material that is thermoplastic resin mixed with metal oxide insulating particles as a filler. The coil is made by injection molding thermoplastic resin mixed with the insulating metal oxide particles.The composition and kind of the metal oxide particles and the kind and thermal conductivity of the thermoplastic resin for injection molding the bobbin holder 25 are the same as those for injection molding the bobbin corpers 14, Since the thermoplastic resin blended with metal oxide particles is used in injection molding, it is possible to produce the bobbin holder 25 with a thermal conductivity of 2 W / (m·K) or more, for example, 6 W / (m·K), 8 W / (m·K), 10 W / (m·K),..., 20 W / (m·K) at maximum.In the coil holder 25 and the molded body 22, since the molding material having a thermal conductivity of 6 W / (m·K) or more is used, the current flowing through the coils 3 can be increased by 1.4 times (although when the current is 1.4 times larger, the temperature does not change), and the thrust of the rod linear motor can be increased by about 1.4 times. The thrust increase by 40% is innovative. Using this technique, it is possible to produce a linear rod motor which is compact but capable of producing the strongest thrust worldwide.In addition, the linear expansion coefficient of the molded body 22 and the coil holder 25 (fluidity / perpendicular thereto) is set to be in the range of 10×10 -6 to 30×10 -6 inclusive. The linear expansion coefficient of the bobbin 25 and the molded body 22 is smaller by an order of magnitude than that of the resin (120×10 -6) and is close to those of metals such as steel (11 to 13×10 -6), copper (19 to 20×10 -6) and aluminum (22 to 23×10 -6). Since, as the temperature rises, the expansion of the coil bodies 14 and the molded body 16 can be almost equal to that of the cores 24, they can be held in contact. This makes it possible to avoid the formation of an air layer or a vacuum space therebetween due to a temperature rise which would become an obstacle to the heat transfer. Furthermore, the mold body 22 serves as a housing of the anchor, wherein a screw (FIG. 11 ) for attachment to another separate component is formed in the mold body. When the molded body 22 is attached to the separate component made of metal such as aluminum, the dimension of a mounting pitch of the screw 22 bof the molded body 22 can be made more equal to that of a mounting pitch of the separate component, thereby preventing an excessive force from being applied to the molded body 22.The present invention is not limited to the above-mentioned embodiments, but may be concreted in various forms unless it deviates from the scope of the invention. In the above-described embodiment of the flat linear motor, the armature moves linearly with respect to the field magnet, but the field magnet may move linearly. In the above-described embodiment of the rod linear motor, the rod moves linearly with respect to the armature, but the armature may also move linearly.EXAMPLESIn the flat linear motor, a molding material having a thermal conductivity of 6 W / (m·K) is used for the coil body and the mold body. Then, when the current value I is multiplied by 1, 1.5, and 1.63, the temperature of the coils 24 is measured.FIGS. 15A to 15C are graphs of measurement results. FIG. 15A shows the temperature when multiplying the current I by 1, FIG. 15B shows the temperature when multiplying the current I by 1.15, and FIG. 15C shows the temperature when multiplying the current I by 1.63.As is apparent from the examples of the present invention, by using a material having high thermal conductivity in the molded body and the bobbin, the temperature of the coils can be prevented from rising. In addition, as shown in FIGS. 15B and 15C, the temperature of the coils in the comparative example when multiplying the current value I by 1.15 (91.5 degrees) and the temperature of the coils in the example of the present invention when multiplying the current value I by 1.63 (91.2 degrees) are almost equal to each other. In the example of the present invention, the applied current is 1.63 / 1.15 (almost equal to 1.4) times larger than that of the comparative example.The present application is based on Japanese Patent Application No. 2008-032518, filed on Feb. 14, 2008, the contents of which are incorporated herein by reference.

Claims

A linear motor using a magnetic field generated by a field magnet (23) and a current flowing through a plurality of coils (24) to generate thrust for linear motion of the coils (24) with respect to the field magnet (23), the linear motor comprising: the field magnet (23) having magnets arranged such that north and south poles are alternately magnetized in the direction of the linear motion; and an armature having the coils (24) surrounding the field magnet (23), a coil holder (25) for holding the coils (24), and a molded body (22) covering the coils (24) and the coil holder (25), a rod (21) having the field magnets (23) passes through the coils (24), wherein the coil holder (25) includes a holder main body (25a), which extends along the length of the coils (24) in the direction of linear movement and has a plurality of spacers (25b), each of which is provided between adjacent two of the coils (24), wherein the molded body (22) is an insulator and has a thermal conductivity of 2 W / (m·K) or more, and wherein the coil holder (25) is an insulator and has a thermal conductivity of 2 W / (m·K) or more.The linear motor according to claim 1, wherein the bobbin (25) or the molded body (22) is made of resin mixed with insulating metal oxide particles having different average diameters.The linear motor according to claim 2, wherein the bobbin (25) or the molded body (22) is manufactured by injection molding thermoplastic resin mixed with the insulating metal oxide particles.The linear motor according to claim 2, wherein the molded body (22) is manufactured by molding in which thermosetting resin mixed with the insulating metal oxide particles is molded into a mold.The linear motor according to any one of claims 1 to 4, wherein the bobbin (25) or the molded body (22) has a linear expansion coefficient ranging from 10 × 10 -6 to 30 × 10 -6 inclusive.

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