Linearmotor

Abstract

A linear motor comprising a rod (11) provided with magnets (13), coils (4) surrounding the rod (11) and a housing (5) covering the coils (4), wherein the rod (11) is caused to move linearly relative to the coils (4) by magnetic fields from the magnets (13) and by the current flowing through the coils (4), wherein the rod (11) has an outer peripheral surface with a keyway (10a) extending along an axial direction of the rod (11), the housing (5) has a rotation stop (8) which fits into the keyway (10a) and prevents the rod (11) from rotating about its axial line, the rod (11) has a magnet shaft (9) on which no keyway (10a) is formed and the magnets (13) are provided, and wherein a keyway (10) is connected to one end of the magnet shaft (9) and has the keyway (10a) formed thereon, wherein the magnets (13) are inserted into a cavity of the magnet shaft (9), and wherein the wedge shaft (10) is connected to the magnet shaft (9) by inserting one end of the wedge shaft (10) into one end of the cavity of the magnet shaft (9).

Description

TECHNICAL FIELD

[0001] The present invention relates to a linear motor provided with a magnet and a coil for obtaining thrust for linear motion based on a magnetic field from the magnet and a current flowing through the coil. More specifically, the present invention relates to a rod-type linear motor comprising a rod with a magnet inserted into a plurality of laminated coils. STATE OF THE ART

[0002] A linear motor consists of a stator and a rotor, which are similar in principle to those of a rotary motor, but are linearly elongated. In the linear motor, electrical energy is converted into a thrust force for linear motion. Because of this linear thrust force, the linear motor is used as a single-axis drive to enable a moving object to move linearly.

[0003] In terms of shapes, the linear motor can be classified into a rod type and a planar type. The rod-type linear motor is provided with a plurality of cylindrical coils laminated together, with a rod containing magnets inserted into a hole (cavity) formed by the laminated coils. For example, the plurality of coils are formed in the shape of three phases including U, V, and W phases. When three phase currents, each of which differs by 120° from each other, are supplied to the coils, magnetic fields are generated accordingly, moving along the axis line direction of the coils. These moving magnetic fields exert a thrust force on the rod, causing the rod to move linearly relative to the coil in synchronization with the speed of the moving magnetic fields.In contrast, the planar linear motor is equipped with multiple plate-shaped magnets arranged on a track rail and multiple coils arranged facing the track rail. Regarding the linear motion of the coils relative to the magnets, this planar linear motor follows the same principle as the rod-type linear motor.

[0004] For the rod-type linear motor, the present applicant has previously proposed a rod-type linear motor disclosed in Patent Document 1. In this linear motor, a bracket is fixed to a base, and a rod is fixed at both ends to the bracket. Coils are capable of linear movement relative to the rod. In other words, the rod side is fixed, while the coil side undergoes linear movement. The coils are covered by a housing, and the coils and the housing are linearly moved together, using a linear guide interposed between the base and the housing as a guide.

[0005] Patent document 1: JP 2004- 248 490 A.

[0006] Furthermore, JP H07-336 993 A shows a linear motor comprising a rod equipped with magnets, coils surrounding the rod, and a housing covering the coils, wherein the rod is caused to move linearly relative to the coils by magnetic fields from the magnets and by the currents flowing through the coils, wherein the rod has an outer peripheral surface with a keyway formed extending along an axial direction of the rod, wherein the housing has a rotation stopper which fits into the keyway and prevents the rod from rotating about its axis line, wherein the rod has a magnet shaft on which no keyway is formed and the magnets are provided, and wherein a keyway is connected to one end of the magnet shaft and has the keyway formed thereon. DISCLOSURE OF THE INVENTION Problems to be solved by the invention

[0007] If it is possible to move the rod linearly using both the coils and the attached housing, the linear motor has a wide range of applications as a drive. During the development phase of the linear motor, the applicant attempted to fix the housing to the base and arrange the bushing on the housing to guide the rod and move it linearly.

[0008] However, in this configuration, the rod is suspended within the coils, and only the axial thrust from the coils acts on the rod. Thus, when an impulse occurs that exerts a rotational force on the rod, the rod is forced to rotate. In some cases, a moving body is attached to the rod, or a linear scale for control is attached to the rod. Accordingly, when the rod rotates, various problems arise. For example, the moving body is also forced to rotate, or the linear scale cannot detect the speed and travel distance of the rod.

[0009] In the linear motor disclosed in the foregoing Patent Document 1, in which the coil side moves linearly, a linear guide disposed between the housing and the base prevents the coil side from rotating. In cases where the linear motor support technique described in Patent Document 1 is applied to the linear motor with the rod side moving linearly, it is possible to reduce the rotation of the rod. In other words, both the coils and the housing are fixed to the base, and the linear guide is disposed between the base and the rod, and the rod can be prevented from rotating when the rod is caused to move linearly. However, in this arrangement, the linear motor is forcibly enlarged by the linear guide disposed between the base and the rod, thereby limiting the strokes of the rod.

[0010] It is therefore an object of the present invention to provide a linear motor which is compact in size and capable of limiting the rotation of a rod which moves linearly relative to the coils. MEANS TO SOLVE THE PROBLEMS

[0011] To solve the foregoing problem, a linear motor according to claim 1 is provided. A linear motor disclosed herein comprising a rod equipped with magnets, coils surrounding the rod, and a housing covering the coils, wherein the rod is caused to move linearly relative to the coils by magnetic fields from the magnets and by currents flowing through the coils, wherein the rod has an outer peripheral surface with a keyway formed extending along an axial direction of the rod, wherein the housing has a rotation stopper that fits into the keyway and prevents the rod from rotating about its axis line, wherein the rod has a magnet shaft on which no keyway is formed and the magnets are provided, and wherein a keyway is connected to one end of the magnet shaft and has the keyway formed thereon.

[0012] According to the present invention described in claim 1, it is possible to prevent the rod, which moves linearly relative to the coil, from rotating while maintaining low cost and compact size. Since no keyway is formed on the magnet shaft, the thickness of the magnet shaft can be reduced.

[0013] Preferably, the rotation stopper comprises: a spline bushing having an inner peripheral surface with a rolling element rolling groove formed thereon and a rolling element circulation passage, and rolling elements arranged in the rolling element circulation passage of the spline bushing and moving and rolling between the rolling element rolling groove and the spline groove in response to relative movement of the spline bushing to the spline groove.

[0014] This utilizes the rolling contact of the rolling elements so that the sliding resistance of the rod, which moves linearly relative to the coil, can be reduced.

[0015] According to the invention, the magnets are inserted into a cavity of the magnet shaft.

[0016] This makes it possible to insert the magnets into the magnet shaft with the cavity formed therein.

[0017] Furthermore, the wedge shaft is connected to the magnet shaft by inserting one end of the wedge shaft into one end of the cavity of the magnet shaft.

[0018] This makes it possible to mutually connect the magnet shaft and the wedge shaft in a state in which their axis lines coincide.

[0019] Preferably, the housing is provided with the wedge bushing guiding the wedge shaft and a bushing guiding the magnet shaft, wherein the rod is supported at two support locations provided by the wedge bushing and the bushing.

[0020] This means that both the wedge bushing and the bushing are capable of guiding linear movements of the rod in a stable manner. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an external perspective view of a linear motor according to an embodiment of the present invention; Fig. 2 is a perspective view of a disassembled state of a motor body portion, a rod portion, and a detection portion of the linear motor; Fig. 3 is a sectional view showing a magnet and a coil of the linear motor; Fig. 4 is a perspective view of the engine body portion (in this figure, (A) shows the perspective view of the engine body portion, while (B) shows a perspective view of a disassembled state of the components of the engine body portion); Fig. 5 is a perspective view showing a coil unit; Fig. 6 is a perspective view of the rod portion (in this figure, (A) shows the perspective view of the rod portion, while (B) shows a perspective view of a disassembled state of the components of the rod portion); Fig. 7 is a sectional view showing a connection between a magnet shaft and a wedge shaft; Fig. 8 is a perspective view showing the wedge shaft and a wedge bushing; Fig. 9 is a perspective view showing the detecting section (in this figure, (A) shows the perspective view of the detecting section, while (B) shows a perspective view of a disassembled state of the components of the detecting section). DESCRIPTION OF REFERENCE SYMBOLS 4 coil 5 housings 7 socket 8 Wedge bushing (rotation stop) 9 Magnetic shaft 10a keyway 10 wedge shank 11 staff 13 Magnet 28 Ball (rolling element) 31 Return track (rolling element circulation passage) 32 Direction change passage (rolling element circulation passage) BEST MODE FOR CARRYING OUT THE INVENTION

[0021] An embodiment of the present invention will be described below with reference to the accompanying drawings. Fig. 1 shows an external perspective view of a linear motor according to the embodiment of the present invention. The linear motor according to the embodiment is manufactured as a single-shaft actuator used to convey a moving member, such as electronic components, in a single-shaft direction. More specifically, this linear motor is used in a head shaft inserted into a chip holder that places chip-like electronic components in place. The linear motor includes an elongated rectangular solid-state motor body portion 1 in which a rod portion 2 capable of moving back and forth is mounted. The speed and travel distance of the rod portion 2 are detected by a detecting portion 3 attached to the rear end of the motor body portion 1.

[0022] Fig. Figure 2 shows the linear motor disassembled into the motor body section 1, the rod section 2, and the sensing section 3. These components will now be presented first.

[0023] The motor body section 1 is provided with a housing 5 that covers the plurality of coils 4 stacked together (see Fig. 4). A single pair of end members 6 is attached to both ends of the housing 5. A bushing 7 is attached to one of the two end members 6, which guides the rod section 2, while a wedge bushing 8 is attached to the remaining end member 6, which guides the rod section 2. Although Fig. 2 shows the state in which the wedge bushing 8 is fitted externally onto the rod portion 2. The wedge bushing 8 is fitted externally onto the rod portion 2 and arranged on one of the end members 6. The rod portion 2, which is caused to move linearly relative to the motor body portion 1, is supported at two support points provided by the bushing 7 and the wedge bushing 8.

[0024] The rod section 2 includes a rod 11 connecting a magnet shaft 9 equipped with magnets and a key shaft 10 on which a keyway is formed, and a linear scale 12 connected to the rear end of the elongated rod 11. The linear scale 12 cooperates with the detection section 3 to detect the speed and travel distance of the rod section 2.

[0025] The detection section 3 includes a encoder for reading a scale of the linear scale 12. This detection section 3 is attached to the base of a dedicated portion where the motor body section 1 of the linear motor is mounted. That is, both the motor body section 1 and the detection section 3 are attached to the base. As a variation, the detection section 3 may be attached to the rear end of the motor body section 1.

[0026] The operating principle of the preceding linear motor is described below. Fig. Figure 3 shows the magnets and coils incorporated into the linear motor. Similar to a rotary motor, the linear motor is designed to generate power for movement using magnetic fields from the magnets and a current flowing through the coils. Furthermore, since the linear motor is intended to move linearly, the coils 4 are stacked linearly to form a cavity therebetween, with the magnet shaft 9 inserted through the cavity.

[0027] The magnet shaft 9 forms the tubular cavity, which allows the insertion of the plurality of magnets 13. In the cavity, a plurality of magnets (segmented magnets), which are cylindrical, are stacked so that the same polarities face each other, that is, two N poles face each other and two S poles face each other. The plurality of coils 4 are arranged around the magnet shaft 9 to cover the magnet shaft 9. The coils 4 include sets of three-phase coils, each set consisting of three phase coils of phases U, V, and W. Combining the plurality of coil sets 4 forms the coil unit.

[0028] When three phase currents, each of which has a phase difference of 120°, are passed through the plurality of coils 4 divided into three-phase coils U, V, and W, traveling magnetic fields are generated that move in the axial direction of the coils 4. The traveling magnetic fields cause a thrust force, so that the magnet shaft 9 can move relative to the coils 4 synchronously with the speed of the traveling magnetic fields.

[0029] The respective components of the linear motor, i.e. the motor body section 1, the rod section 2 and the detection section 3, are described in more detail below in this order with reference to their configurations.

[0030] Fig. 4 shows the motor body portion 1. This motor body portion 1 is a part in which the plurality of coils 4 are housed. The coils 4 are elements formed by winding copper wires in a helical shape. In the present embodiment, in order to limit the dimensions of the housing 5, the coils 4 are inserted into an injection mold, and injection molding is performed using molten synthetic resin or special ceramics, thereby manufacturing the housing 5. After molding, when the molded elements are removed from the mold, the coils 4 are already surrounded by the housing 5. This injection molding offers the advantage of making the housing 5 thinner. For example, in cases where linear motors are used in a parallel arrangement, the lateral width of each linear motor should be smaller.Alternatively, without using injection molding, the coils 4 can be attached to the housing 5 by accommodating the coils 4 in the housing 5, which is made of aluminum, for example, and filling adhesive into the gaps between the coils.

[0031] The housing 5 can be attached to a section that uses the linear motor as a single-shaft drive. Thus, a material with high mechanical rigidity is used for the housing. Furthermore, the housing should be electrically insulated from the coils, so a material with high insulation properties is used for the housing. Furthermore, to enhance heat dissipation from the coils, several fins are formed on the housing.

[0032] Positioning pins 15 and nuts 16 are embedded in the upper surface of the housing 5 for attaching the linear motor to the base of a dedicated part. End members 17 are attached to both ends of the housing 5. The end members 17 can be manufactured together with the housing 5 by injection molding, or connected to the housing 5 using fasteners such as screws. Of these paired end members 17, one member is attached to the bushing 7 to guide the magnet shaft 9 of the rod 11, while the remaining member is attached to the keyed bushing 8 to guide the keyed shaft 10 of the rod 11. The bushing 7 and the keyed bushing 8 are each attached to the end members 17 using fasteners such as screws 19. Positioning pins 20 are inserted into one of the end members 17 to thereby position the detection section 3.

[0033] As in Fig. As shown in Fig. 4(A), the coil unit (the plurality of coils 4) is arranged within only a region of the housing in which the magnet shaft 9 of the rod 11 is caused to move, and not in a wider region of the housing in which the wedge shaft 10 is caused to move. This arrangement is based on the fact that the wedge shaft 10 cannot generate thrust even if coils 4 are present, since the wedge shaft 10 does not have a magnet.

[0034] Fig. 5 shows the coil unit. This coil unit is a member comprising a plurality of coils 4, for example, seven dozen coils stacked together, each coil formed by winding a copper wire in a helical shape. Each coil 4 has connecting wires 4a, and the connecting wires 4a of the coils 4 are connected by skipping two coils between the U-phase coils, between the V-phase coils, and between the W-phase coils. Each coil 4 should be electrically insulated from the other coils 4, with a resin spacer 14 interposed as an insulator between adjacent coils 4.

[0035] Each spacer 14 is formed in a circular shape corresponding to the front view shape of each coil 4.

[0036] Fig. 6 shows the rod section 2. This rod section 2 includes the rod 11, which includes the magnet shaft 9 and the wedge shaft 10, as well as the linear scale 12 attached to the rear end of the rod 11. The magnet shaft 9 is manufactured as a hollow member made of non-magnetic materials, including stainless steel, and has a tubular member 23 in which the magnets 13 are housed. A plurality of cylindrical magnets 13 (segmented magnets) are stacked in the hollow space of the tubular member 23 such that the magnets face each other with the same polarity, as explained above. A pole piece (magnetic block) 24, made of a magnetic material such as iron, is arranged between the magnets 13 as a yoke. A magnet holder 25 is attached to the distal end of the magnet shaft 9 by means of an adhesive or the like in order to fix the magnets 13 in the tubular element 23.

[0037] A wedge shaft 10 is attached to the rear end of the magnet shaft 9. As shown in Fig. As shown in Figure 7, the wedge shaft 10 has one end inserted into the cavity of the magnet shaft 9, so that the wedge shaft 10 is coupled to the magnet shaft 9, thereby allowing their axis lines to coincide. This end of the wedge shaft 10 also serves to hold the magnets 13 accommodated in the magnet shaft 9. As shown in Fig. 6, the wedge bushing 8 is mounted on the outer peripheral surface of the wedge shaft 10. Both the wedge shaft 10 and the wedge bushing 8 limit rotation of the rod 11 on its axial line.

[0038] Fig. Figure 8 shows a perspective view of the key shaft 10 and the key bushing 8. A plurality of keyways 10a are formed on the outer peripheral surface of the key shaft 10, extending in the axial direction thereof. The key shaft 10 is made of a material such as stainless steel, which is non-magnetic and has high rigidity. Since the keyways 10a are to be subjected to rolling action by the balls serving as rolling elements, quench hardening is applied to the keyways 10a during manufacturing.

[0039] The spline bushing 10 includes an outer cylinder 27 fitted with clearance on the spline shaft 10, a plurality of balls 28 rollingly disposed between the spline shaft 10 and the outer cylinder 27, and a retainer 29 installed in the outer cylinder 27 and shaped to provide a circular ball circulation passage (rolling element circulation passage) along which the plurality of balls 28 are aligned. The outer cylinder 27 has an inner peripheral surface on which a plurality of ball rolling grooves (rolling element rolling grooves) are formed so as to extend in the axial direction thereof so as to oppose the spline grooves 10a of the spline shaft 10. A stopper ring 30 is disposed at each of both ends of the outer cylinder 27 in the axial direction to retain the retainer 29 in the outer cylinder 27.

[0040] As the key shaft 10 moves linearly relative to the key bushing 8, the balls 28 roll and move along a passage between the keyways 10a of the key shaft 10 and the ball rolling grooves of the outer cylinder 27. Each ball that has rolled and reached one end of the ball rolling groove of the outer cylinder 27 is then skimmed off from the keyway 10a by the retainer 29. The skimmed ball is guided through a U-shaped direction-changing passage 32 to reverse the rolling direction and enter the respective return path 31, which runs parallel to the ball rolling groove. After passing through the return path 31, the ball is caused to pass through the direction-changing passage 32 located at the opposite end and is then caused to return to the respective keyway 10a.In this case, the return path 31 is formed so as to be arranged between the holder 29 and the outer cylinder 27, whereby the balls 28 in the return path 31 are prevented from contacting the keyways 10a.

[0041] Since the balls 28 are present between the ball rolling grooves formed on the key bushing 8 and the keyways 10a on the key shaft 10, the key bushing 8 may prevent the key shaft 10 from rotating about its axial line. Thus, both the key bushing 8 and the balls 28 form a rotation stop.

[0042] As in Fig. As shown in Figure 6, a holder 35 is attached to the rear end of the wedge shaft 10 using fasteners such as screws 34. The linear scale 12 is adhesively bonded to this holder 35. This linear scale 12 cooperates with a encoder of the detection section, so that the linear scale and the encoder serve as a linear encoder. Fine scales are placed at intervals on the linear scale 12.

[0043] Fig.9 shows the detection section 3. This detection section 3 includes a holder 36 disposed at the rear end of the housing 5 with the end member 6 interposed therebetween, and a encoder 37 is attached to the holder 36. The holder 36 has a cavity formed therein, and the linear scale 12 is inserted into this cavity. A window is formed in the upper surface plate of the holder 36 through which the interior of the holder 36 can be viewed. A encoder substrate 38 is attached to this window using screws or other fasteners. Nuts 41 are embedded in the upper surface plate of the holder 36 and are screwed together with the screws 39. A encoder 37 is provided on the lower surface of the encoder substrate 38 for reading the scales of the linear scale 12.This encoder 37 includes a light-emitting diode serving as a light source and a photodiode for reading the scales on the linear scale 12. Using pulse signals generated by the encoder 37 based on its readings, the travel distance of the rod 12 is detected. The detected distance is used to perform control and other applications. The end of the holder 36 is closed by a cover 40.

[0044] Incidentally, the present invention is not limited to the structure of the above embodiment, but can be modified to a variety of other structures without departing from the scope of the present invention. Instead of placing the balls rolling and in contact between the spline bushing and the spline grooves, projections may be provided on the spline bushing to fit into and slide into the spline grooves, so that the projections act to stop the rotation of the rod. Furthermore, the linear motor according to the present invention is not limited to use as a single-axis actuator, but can be used as a multi-axis actuator in which multiple linear motors according to the present invention are combined.

Claims

A linear motor comprising a rod (11) equipped with magnets (13), coils (4) surrounding the rod (11), and a housing (5) covering the coils (4). The rod (11) is caused to move linearly relative to the coils (4) by magnetic fields from the magnets (13) and by the current flowing through the coils (4). The rod (11) has an outer peripheral surface with a keyway (10a) extending along an axial direction of the rod (11). The housing (5) has a rotation stopper (8) that fits into the keyway (10a) and prevents the rod (11) from rotating about its axial line. The rod (11) has a magnet shaft (9) on which no keyway (10a) is formed and on which the magnets (13) are provided. A keyway shaft (10) is connected to one end of the magnet shaft (9). and has the keyway (10a) formed thereon, wherein the magnets (13) are inserted into a cavity of the magnet shaft (9),andwherein the wedge shaft (10) is connected to the magnet shaft (9) by inserting one end of the wedge shaft (10) into one end of the cavity of the magnet shaft (9)., A linear motor according to claim 1, wherein the rotation stopper (8) comprises:a spline bushing (8) having an inner peripheral surface on which a rolling element rolling groove is formed and having a rolling element circulation passage (31, 32), androlling elements (28) arranged in the rolling element circulation passage (31, 32) of the spline bushing (8) and moving and rolling between the rolling element rolling groove and the spline groove (10a) in response to relative movement of the spline bushing (8) to the spline groove (10a). Linear motor according to claim 1 or 2, wherein the housing (5) is provided with the wedge bushing (8) guiding the wedge shaft (10) and with a bushing (7) guiding the magnet shaft (9), and the rod (11) is supported at two support points provided by the wedge bushing (8) and the bushing (7).

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