JP2009207295A - Electric motor and motorized rotary joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric motor which can effectively radiate a switching element and can be reduced in size totally, including a power substrate, and to provide a motorized rotary joint. <P>SOLUTION: The electric motor 4 has a front bracket 7, pivotably supporting a rotary shaft 5 and a rear bracket 8, wherein the power substrate 50 for switching conduction to each phase coil is arranged on the front bracket 7 side via a heat-dissipating sheet 46, while an encoder 40 for detecting the rotation angle of the rotary shaft 5 is arranged on the rear bracket 8 side; and the power substrate 50 is electrically connected to the encoder 40. The power substrate 50 includes the switching element 48, constituting a bridge circuit, wherein the heat dissipating sheet 46, is interposed between the switching element 48 and the front bracket 7, allowing the heat generated in the switching element 48 to be transferred to the front bracket 7 via the heat-dissipating sheet 46. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric motor and an electric rotary joint using the same.

Generally, when an electric motor is driven using a DC power source such as a battery, an inverter circuit that converts DC power from the DC power source into AC power is used so that AC power is supplied to the coils of each phase of the electric motor. It has become. The inverter circuit includes a switching element and a smoothing capacitor for switching energization of DC power to the coils of each phase.
In recent years, with the demand for further miniaturization of the electric motor, the inverter circuit is also housed in the motor case of the electric motor, and in addition to the electric motor, the devices necessary for driving the electric motor are totally included. Various techniques for miniaturization have been proposed (see, for example, Patent Document 1).
JP 2007-215299 A

By the way, in the above-mentioned prior art, the switching element which is a heat generation source of the inverter circuit is provided in the motor casing of the electric motor, so that the heat generated from the switching element is radiated through the motor casing.
However, since the switching element is directly disposed on the motor case, depending on the difference in the outer shape of the switching element and the manufacturing accuracy of the motor case, the degree of contact between the two becomes insufficient, and the heat generated from the switching element is reduced by the motor. There is a problem that it cannot be reliably transmitted to the casing and it is difficult to obtain a sufficient heat dissipation effect.
In addition, there is no disclosure regarding the location of the control circuit board (power board) that performs on / off switching control of the switching elements, and it is difficult to reduce the size of the electric motor and the device necessary for driving the motor. There is a problem.

  Therefore, the present invention has been made in view of the above-described circumstances, and can effectively dissipate heat from the switching element and can be miniaturized in total including the power board and the like. And an electric rotary joint.

In order to solve the above-described problems, the invention described in claim 1 includes a front bracket and a rear bracket that pivotally support a rotating shaft, and switching the energization to the coils of each phase on the front bracket side. An electric power board is disposed through a heat dissipation sheet, and an encoder for detecting a rotation angle of the rotary shaft is disposed on the rear bracket side, and the power board and the encoder are electrically connected. The power board includes a switching element constituting a bridge circuit, the heat dissipation sheet is interposed between the switching element and the front bracket, and heat generated from the switching element is transferred to the heat dissipation sheet. Through the front bracket.
By configuring in this way, even if there is a solid difference in terms of heat dissipation in the switching element, if the switching element and the heat dissipation sheet are brought into close contact with each other, the heat generated from the switching element is reliably transmitted to the heat dissipation sheet. be able to. Even when the manufacturing accuracy of the front bracket is rough, if the front bracket and the heat dissipation sheet are brought into close contact with each other, the heat of the heat dissipation sheet can be reliably transmitted to the front bracket.
In addition, while the power board having the switching element is disposed on the front bracket side, the relatively heat-sensitive encoder can be disposed on the rear bracket side away from the power board that is a heat source.

The invention described in claim 2 is an electric rotary joint in which one frame and the other frame are rotatably connected via the electric motor and the speed reducer according to claim 1, and the front bracket and The electric rotary joint is formed integrally with the one frame.
As described above, in the electric rotary joint in which one frame and the other frame are rotatably connected via the electric motor and the speed reducer, the front bracket on which the power board is disposed is connected to the one frame. By integrally molding, the heat dissipation area of the power board can be set large.

According to a third aspect of the present invention, the power board is divided into a motor drive circuit board on which the switching element is arranged and a power supply circuit board that supplies a current to the motor drive circuit board and has a smoothing capacitor. The motor drive circuit board is arranged inside the front bracket via the heat dissipation sheet, and the power circuit board is arranged inside the one frame. As described above, by disposing the motor drive circuit board and the power supply circuit board constituting the power board at different locations, the empty space can be used effectively.

According to the first aspect of the present invention, even if the switching element has a solid difference in terms of heat dissipation, if the switching element and the heat dissipation sheet are brought into close contact with each other, the heat generated from the switching element is surely secured to the heat dissipation sheet. Can be transmitted. Even when the manufacturing accuracy of the front bracket is rough, if the front bracket and the heat dissipation sheet are brought into close contact with each other, the heat of the heat dissipation sheet can be reliably transmitted to the front bracket. For this reason, the heat generated from the switching element can be reliably transmitted to the front bracket via the heat dissipation sheet, and the switching element can be effectively dissipated.
In addition, while the power board having the switching element is disposed on the front bracket side, the relatively heat-sensitive encoder can be disposed on the rear bracket side away from the power board that is a heat source. For this reason, it is possible to reduce the total size of the electric motor including the power board and the encoder while preventing damage to the encoder due to heat.

  According to the invention described in claim 2, in the electric rotary joint in which one frame and the other frame are rotatably connected via the electric motor and the speed reducer, the power board is disposed. By integrally molding the front bracket with one frame, the heat radiation area of the power board can be set large. For this reason, the switching element can be radiated more effectively, and the coil that is the heat source of the electric motor can be effectively cooled.

  According to the invention described in claim 3, the empty space can be effectively utilized by arranging the motor drive circuit board and the power supply circuit board constituting the power board at different locations. For this reason, in the electric rotary joint, the occupied space of the electric motor can be set small.

Next, embodiments of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the electric rotary joint 1 is used, for example, in a joint portion of an industrial robot such as an articulated robot, and electrically drives the first frame 2 and the second frame 3. The motor 4 and the speed reducer 6 are connected so as to be rotatable. The first frame 2 and the second frame 3 are formed in a rectangular tube shape, and both ends are closed. The first frame 2 and the second frame 3 are arranged on the same straight line, and are rotated around an axis J intersecting the straight line. In FIGS. 1 and 2, the left side of the paper is the front side and the right side is the rear side.

The electric motor 4 is disposed such that the axis of the rotating shaft 5 coincides with the axis J, and a speed reducer 6 is attached to the rotating shaft 5.
The electric motor 4 is provided rotatably on the front bracket 7, the rear bracket 8, the stator 10 fixed to the inside of the front bracket 7 and the rear bracket 8, and the radially inner side of the stator 10. And the rotor 11. A power board 50 for driving the electric motor 4 is arranged inside the front bracket 7, and an encoder 40 for detecting the rotation angle of the rotary shaft 5 is arranged inside the rear bracket 8.

The front bracket 7 is formed in a bottomed cylindrical shape and is integrally formed with the first frame 2. That is, a part of the first frame 2 serves as the front bracket 7. The outer peripheral portion of the stator 10 is press-fitted and fixed to the peripheral wall 12 of the front bracket 7. A bearing 14 that rotatably supports the front side of the rotary shaft 5 is provided at the center in the radial direction of the front bracket 7.
As described above, the first frame 2 and the front bracket 7 are integrally formed, whereby the stator 10 and the rotating shaft 5 are held on the first frame 2 by a configuration in which a part of the first frame 2 is the front bracket 7. A function can be provided.

On the other hand, the rear bracket 8 is made of resin and formed in a bottomed cylindrical shape, and is provided so as to close the opening of the front bracket 7. A bearing 17 that rotatably supports the rear side of the rotary shaft 5 is provided at the center in the radial direction of the rear bracket 8.
The outer peripheral portion of the stator 10 is press-fitted and fixed to the peripheral wall 18 of the rear bracket 8 on the opening side. That is, the stator 10 is in a state of being fitted and fixed to the front bracket 7 and the rear bracket 8 respectively. The axial lengths of the peripheral walls 12 and 18 of the front bracket 7 and the rear bracket 8 are set such that a gap cannot be formed in a state where the stator 10 is housed in the brackets 7 and 8. Yes. Thereby, it is possible to prevent dust from entering from the mating surface of the front bracket 7 and the rear bracket 8.

The stator 10 is formed by laminating magnetic metal plates in the axial direction or pressurizing soft magnetic powder, and has a substantially cylindrical stator core 21. . The outer peripheral portion of the stator core 21 is press-fitted into the front bracket 7 and the rear bracket 8.
On the inner peripheral side of the stator core 21, a plurality of teeth portions 22 projecting radially inward are provided at equal intervals in the circumferential direction. The teeth part 22 is formed in a substantially T shape in the axial direction plan view. In addition, an insulator (not shown) is attached to each tooth portion 17, and a coil 23 is wound through the insulator.

  Each terminal portion of the coil 23 is connected to the power substrate 50 via the terminal 24. The power board 50 is configured by dividing a motor drive circuit board 51 formed in a substantially annular shape and a power supply circuit board 52 formed in a substantially rectangular shape in plan view. Is electrically connected.

  The power board 50 is in a state in which the motor drive circuit board 51 of the two circuit boards 51 and 52 is arranged inside the front bracket 7 and the power supply circuit board 52 is arranged in the first frame 2. . Therefore, the motor drive circuit board 51 is set such that the diameter of the hole formed in the center is set to a size allowing the rotation shaft 5 to be inserted, and the outer diameter is set smaller than the inner diameter of the peripheral wall 12 of the front bracket 7. ing. On the other hand, the outer shape of the power circuit board 52 is set to a size that can be accommodated in an empty space in the first frame 2.

The motor drive circuit board 51 switches the energization to each coil 23, and a plurality of switching elements 48 are mounted on the surface opposite to the stator 10, and the switching elements 48 are turned on / off. A pre-drive circuit (not shown) for controlling the above is mounted.
The switching element 48 connects a transistor such as a field effect transistor (FET) and a diode that prevents reverse flow between the drain and source of the FET (transistor) in parallel to a motor drive power supply (not shown). It has the structure. A bare chip is used as the FET, and the space occupied by the FET is reduced by resin molding the bare chip. The switching element 48 forms an H-bridge circuit for each phase, and the current supplied to each coil 23 is switched for each phase by switching each on / off.

The power circuit board 52 is for supplying a current to the motor drive circuit board 51, and is fixed to a mounting base 47 provided inside the first frame 2 via a stud bolt 49.
The power supply circuit portion 45 is mounted with an aluminum electrolytic capacitor 58 for smoothing the power supply, a connector portion 54 for connecting the lead wires 53, and the like. The aluminum electrolytic capacitor 58 is connected to a motor drive power supply (not shown), and is a circuit for smoothing the pulsating current contained in the rectified current to a state closer to direct current. As a result, a smoothed current can be supplied to the H bridge circuit of the motor drive circuit board 51.

  Here, a heat dissipation sheet 46 is provided on the switching element 48 mounted on the motor drive circuit board 51. The heat dissipation sheet 46 is formed in a substantially annular shape so as to correspond to the location where the switching element 48 is disposed. The motor drive circuit board 51 is fixed to the front bracket 7 via the heat dissipation sheet 46. Therefore, the heat dissipation sheet 46 is in a state where one surface is in contact with the switching element 48 and the other surface is in contact with the front bracket 7.

  In addition, by providing the heat radiating sheet 46 on the switching element 48, the switching element 48 and the heat radiating sheet 46 can be surely adhered to each other even if there is an individual difference in the outer shape of each switching element 48. It has become. Further, by bringing the heat radiating sheet 46 and the front bracket 7 into contact with each other, both the 46 and 7 can be reliably brought into contact with each other even if the processing accuracy of the surface of the front bracket 7 on the heat radiating sheet 46 side is rough. .

The rotor 11 includes a rotating shaft 5 and a cylindrical ring magnet 26 that is externally fixed to the rotating shaft 5. The rotating shaft 5 is formed in a hollow shape, and wiring (not shown) or the like can be routed in the hollow portion 5a.
The ring magnet 26 is magnetized so that the magnetic poles change in order in the circumferential direction. Under such a configuration, when a current flows through the coil 23 wound around the teeth portion 22 of the stator 10, a magnetic field is formed, and a magnetic attractive force generated between the magnetic field and the ring magnet 26 is reduced. The rotating shaft 5 rotates by the repulsive force.

  The rear side end of the rotating shaft 5 is in a state of protruding from the rear bracket 8, and a sensor magnet 28 is provided here via an attachment member 29. The sensor magnet 28 constitutes one of the encoders 40 for detecting the rotation angle of the rotary shaft 5 and is magnetized in two poles. The mounting member 29 is formed by integrally molding a cylindrical portion 29a that is externally fitted and fixed to the rotary shaft 5 and an outer flange portion 29b that is provided at the outer end of the cylindrical portion 29a. The outer flange portion 29b is for positioning the sensor magnet 28 in the axial direction. The sensor magnet 28 is fixed such that one end surface thereof is in contact with the outer flange portion 29b.

On the outer side in the axial direction of the rear bracket 8, a substantially annular encoder substrate 30 is disposed on the inner side in the axial direction from the sensor magnet 28. The encoder board 30 is fastened and fixed to the rear bracket 8 by a bolt 32 via a collar 31.
The encoder board 30 constitutes the other side of the encoder 40. On the encoder board 30, four Hall elements 41 are mounted, and a rotation angle detection circuit (not shown) is mounted. .

  The hall elements 41 are arranged at equal intervals in the circumferential direction at positions facing the sensor magnet 28 on the encoder substrate 30. The Hall element 41 detects a change in the magnetic field generated from the sensor magnet 28 as position information of the rotation shaft 5 and outputs a signal having a predetermined waveform to the rotation angle detection circuit. The rotation angle detection circuit detects the rotation angle of the rotation shaft 5 based on the output signal from the hall element 41.

  The encoder board 30 is electrically connected to the motor drive circuit board 51 of the power board 50 provided on the front bracket 7 side via a lead wire or a flexible board (not shown). That is, the Hall element 41 and the rotation angle detection circuit can be driven by supplying the power of the power board 50 to the encoder board 30, and the rotation angle position information of the rotary shaft 5 in the encoder board 30 is output to the power board 50. You can also

The front side end of the rotary shaft 5 is in a state of protruding outward in the axial direction through the motor drive circuit board 51 of the power board 50, the heat dissipation sheet 46, and the front bracket 7. A reduction gear 6 is attached to the protruding front side end of the rotating shaft 5.
As shown in FIGS. 1 and 3, the speed reducer 6 is obtained by integrating a cross roller bearing 61 and a harmonic drive (registered trademark) that can receive loads in both the thrust direction and the radial direction. That is, the speed reducer 6 includes a wave generator 62 that is externally fitted and fixed to the rotary shaft 5, and a flex spline 63 that is disposed on the outer periphery of the wave generator 62. Is arranged. The inner ring (inner race) 61a of the cross roller bearing 61 also serves as a circular spline 64 of Harmonic Drive (registered trademark).

  The wave generator 62 includes a cam 65 having an elliptical shape in plan view and a ball bearing 66 provided on the outer periphery thereof. A shaft hole 67 for connecting the rotary shaft 5 and the cam 65 is formed at the center in the radial direction of the cam 65, whereby the rotary shaft 5 and the cam 65 rotate together.

A flex spline 63 provided on the outer peripheral surface of the ball bearing 66 of the wave generator 62 is an elastic gear, and has a cylindrical gear main body 68 and an outer flange portion 69 integrally formed at the outer end of the gear main body 68. It consists of and.
The gear body 68 is deformed into an ellipse by the wave generator 62, and the inner peripheral surface is formed to be slidable with the wave generator 62. A tooth portion 70 is formed on the outer peripheral surface of the gear body 68.

  In the outer flange portion 69 of the flex spline 63, a thick portion 71 is formed on the entire outer periphery. The radial width of the thick portion 71 is set to substantially match the radial width of the outer ring (outer race) 61 b of the cross roller bearing 61. A plurality of bolt holes (not shown) are formed in the thick portion 71. The bolt 72 is screwed into the bolt hole, so that the outer flange portion 69 and the second frame 3 are fastened together with the outer ring (outer race) 61 b of the cross roller bearing 61. Here, a plate-like mounting stay 73 is integrally provided at a portion corresponding to the flex spline 63 of the second frame 3. As a result, the outer flange portion 69 and the second frame 3 can be fastened together with the outer ring 61 b of the cross roller bearing 61.

  The inner ring 61 a of the cross roller bearing 61 is formed with a tooth portion 74 that meshes with the tooth portion 70 of the flexspline 63 on the inner peripheral surface side. Since the gear main body 68 of the flexspline 63 is deformed into an ellipse by the wave generator 62, the toothed portion 70 of the gear main body 68 and the toothed portion 74 of the inner ring 61a, that is, the circular spline, are formed at the elliptical long axis portion of the flexspline 63. 64 is engaged. On the other hand, in the minor axis portion of the ellipse of the flexspline 63, the tooth portions 70 and 74 are completely separated from each other.

Further, the number of teeth of the tooth portion 74 of the inner ring 61 a (circular spline 64) of the cross roller bearing 61 is set to be larger than the number of teeth of the tooth portion 70 formed on the flexspline 63.
Further, a plurality of bolt holes 75 are formed in the inner ring 61 a of the cross roller bearing 61, and the bolts 76 are screwed into the inner ring 61 a so that the inner ring 61 a of the cross roller bearing 61 is fastened to the first frame 2. Fixed.

Next, the operation of the electric rotary joint 1 will be described based on FIG.
First, when the rotating shaft 5 rotates, for example, clockwise (in the direction of arrow B in FIG. 3), the wave generator 62 of the speed reducer 6 rotates together with the rotating shaft 5.
Then, the gear main body 68 of the flexspline 63 is elastically deformed so as to follow the rotation of the wave generator 62, and the meshing positions of the teeth 70 of the flexspline 63 and the teeth 74 of the circular spline 64 (inner ring 61a) are sequentially changed. Moving.

At this time, the circular spline 64 (the inner ring 61 a of the cross roller bearing 61) is fastened and fixed to the first frame 2 by the bolt 76, and the number of teeth of the tooth portion 70 of the flexspline 63 is the tooth portion 74 of the circular spline 64. Therefore, the flex spline 63 rotates counterclockwise (in the direction of arrow C in FIG. 3) by the smaller number of teeth.
Then, the second frame 3 that is fastened together with the bolts 72 to the outer flange portion 69 of the flexspline 63 and the outer ring 61b of the cross roller bearing 61 rotate integrally with the flexspline 63 in the counterclockwise direction. Accordingly, the second frame 3 rotates about the axis J (see FIG. 1) with respect to the first frame 2.

Next, based on FIG. 4, a transmission path of heat generated from the stator 10 of the electric motor 4 and heat generated from the motor drive circuit board 51 of the power board 50 will be described.
Here, in the electric rotary joint 1, main heat sources are the coil 23 of the electric motor 4 to which current is supplied via the power board 50, and the switching element 48 that is repeatedly turned on / off while being supplied with current. It is.

  As shown by the arrow A in FIG. 4, the heat generated in the coil 23 is first transmitted to the stator core 21. Since the stator core 21 is fitted and fixed to the front bracket 7, the heat of the coil 23 is transmitted to the front bracket 7. Since the front bracket 7 is integrally formed with the first frame 2, the heat of the coil 23 is transmitted to the first frame 2.

On the other hand, as shown by the arrow B in FIG. 4, the heat generated by the switching element 48 is transmitted to the heat dissipation sheet 46. At this time, even if there is an individual difference in the outer shape of the switching element 48, the switching element 48 and the heat dissipation sheet 46 are in close contact with each other, so that the heat of the switching element 48 is reliably transmitted to the heat dissipation sheet 46. .
Since the heat dissipation sheet 46 is in close contact with the switching element 48 and also in close contact with the front bracket 7, the heat of the switching element 48 is transmitted to the front bracket 7 through the heat dissipation sheet 46. The speed reducer 6 is attached to the surface of the front bracket 7 opposite to the surface corresponding to the heat dissipation sheet 46. For this reason, the heat of the switching element 48 transmitted to the front bracket 7 is transmitted to the speed reducer 6.

Therefore, according to the above-described embodiment, the heat generated from the switching element 48 can be reliably transmitted to the front bracket 7 and the speed reducer 6 through the heat dissipation sheet. For this reason, it becomes possible to dissipate the switching element 48 effectively.
In addition, the front bracket 7 is formed integrally with the first frame 2. For this reason, since a heat radiation area can be set large, it becomes possible to radiate the switching element 48 more effectively.
On the other hand, since the heat generated from the coil 23 of the electric motor 4 is also transmitted to the front bracket 7 and the first frame 2, the coil 23 can be effectively dissipated.

In addition, the power board 50 having the motor drive circuit board 51 which is a heat generation source is disposed on the front bracket 7 side, while the encoder 40 which is relatively heat-sensitive is disposed on the rear bracket 8 side. Can be separated from the motor drive circuit board 51, which is a heat source. For this reason, it becomes possible to prevent the encoder 40 from being damaged by heat.
Further, the power board 50 is divided into a motor drive circuit board 51 and a power circuit board 52, and the power board 50 is arranged inside the front bracket 7, while the power circuit board 52 is arranged inside the first frame 2. Has been established. For this reason, the space occupied by the electric motor 4 in the electric rotary joint 1 can be reduced by effectively utilizing the empty space of the first frame 2. Therefore, the electric rotary joint 1 (electric motor 4) including the power board 50 and the encoder 40 can be downsized in total.

The present invention is not limited to the above-described embodiment, and includes various modifications made to the above-described embodiment without departing from the spirit of the present invention.
In the above-described embodiment, the so-called magnetic type constituted by the sensor magnet 28 and the Hall element 41 that detects a change in the magnetic field generated from the sensor magnet 28 as the encoder 40 that detects the rotation angle of the rotating shaft 5. The case where the rotary encoder is used has been described. However, the present invention is not limited to this, and an optical rotary encoder or resolver may be used instead of the magnetic rotary encoder.
Furthermore, although the case where the rotating shaft 5 is formed in a hollow shape has been described in the above embodiment, the present invention is not limited to this, and a solid rotating shaft may be used instead of the rotating shaft 5.

It is a section perspective view of the electric rotary joint in an embodiment of the present invention. It is a disassembled perspective view of the electric motor in the embodiment of the present invention. It is a cross-sectional view of the reduction gear in the embodiment of the present invention. It is explanatory drawing which shows the heat transfer path | route in embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric rotary joint 2 1st frame 3 2nd frame 4 Electric motor 5 Rotating shaft 6 Reduction gear 7 Front bracket 8 Rear bracket 10 Stator 11 Rotor 23 Coil 30 Encoder board 40 Encoder 46 Heat radiation sheet 48 Switching element 50 Power board 51 Motor drive circuit board 52 Power supply circuit board

Claims (3)

It has a front bracket that supports the rotating shaft, and a rear bracket,
On the front bracket side, a power board for switching energization to each phase coil is disposed via a heat dissipation sheet,
An encoder for detecting a rotation angle of the rotary shaft is disposed on the rear bracket side, and an electric motor in which the power board and the encoder are electrically connected,
The power board includes a switching element constituting a bridge circuit,
An electric motor characterized in that the heat dissipation sheet is interposed between the switching element and the front bracket so that heat generated from the switching element can be transmitted to the front bracket via the heat dissipation sheet. An electric rotary joint in which one frame and the other frame are rotatably connected via the electric motor and the speed reducer according to claim 1,
An electric rotary joint, wherein the front bracket and the one frame are integrally formed. The power board is configured by dividing a motor drive circuit board on which the switching elements are arranged, and a power supply circuit board that supplies current to the motor drive circuit board and has a smoothing capacitor,
The motor drive circuit board is disposed inside the front bracket via the heat dissipation sheet,
The electric rotary joint according to claim 2, wherein the power circuit board is disposed inside the one frame.

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