JP2006177504A - Direct drive motor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a direct drive motor capable of securing the necessary moment rigidity of a bearing even in a structure wherein a motor portion is mounted between a rolling bearing and a rotary head, thus the deflection in the rotating direction on the bearing can be inhibited even if the motor portion repeats its step operation for the sudden acceleration and the sudden stop of the motor portion. <P>SOLUTION: In this direct drive motor 10 wherein the motor portion 18 is mounted between the rolling bearing 20 and the rotary head 17, and a rotating shaft 11 of the rotary head 17 has a cantilever structure, a four-point contact ball bearing, wherein a rolling element 24 is kept into contact with a raceway groove of an inner ring 22 at two points, and kept into contact with a raceway groove of an outer ring 21 at two points, and a pre-load is applied to form a negative clearance, is used as the rolling bearing 20. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a direct drive motor that includes a rolling bearing in a rotation support portion and directly drives a load without using a transmission. For example, the present invention relates to a direct drive motor used in a chip mounter of an electronic board manufacturing apparatus.

A direct drive motor used for a chip mounter of an electronic substrate manufacturing apparatus rotates a rotating head to arrange a plurality of chip mounting nozzles arranged in the circumferential direction of the rotating head at a chip mounting position and a receiving position ( Patent Document 1 to Patent Document 3).
In this case, since it is necessary to position the nozzles of the rotary head in a short time in order to shorten the manufacturing time, the rotary head repeats rapid acceleration / rapid stop. Accordingly, the stepping motion that suddenly accelerates / stops suddenly is repeated for the motor unit that applies the driving force to the rotating shaft of the rotating head.

  In general, the rotary head and the motor unit are installed on a positioning device. However, the positioning device is also required to be positioned at a high speed. A structure in which a motor is placed between the rolling bearing and the rotating head for cantilever support with two bearings, and for improved response, bearing maintenance (replenishment of lubricant, etc.) and assembly. Has begun to be adopted.

In such a conventional direct drive motor, since the rotating head rotates at high speed by repeating the step motion in which the motor unit suddenly accelerates / stops suddenly, the moment rigidity of the rolling bearing supporting the rotating shaft of the rotating head is insufficient. There is a risk of resonance in the direction of rotation about the bearing.
JP-A-5-329420 JP 2003-179083 A JP 2000-139068 A

  The present invention has been made to eliminate such inconveniences, and it is possible to ensure the required moment rigidity of a bearing even in a structure in which a motor portion is disposed between a rolling bearing and a rotating head. Thus, it is an object of the present invention to provide a direct drive motor that can suppress runout in the rotational direction around the bearing even when the motor unit repeats stepping that suddenly accelerates / stops suddenly.

In order to achieve the above object, the invention according to claim 1 provides a rotary head provided at the tip of the rotary shaft, a rolling bearing that rotatably supports the rotary shaft, and a driving force applied to the rotary shaft. A direct drive motor comprising a motor unit, wherein the motor unit is disposed between the rolling bearing and the rotary head, and the rotary shaft has a cantilever support structure,
As the rolling bearing, a rolling element comes into contact with the raceway groove of the inner ring at two points and contacts with the raceway groove of the outer ring at two points, and a preload is applied and a negative clearance is provided. A double-row ball bearing or a cross roller bearing in which the cross-sectional dimension ratio (B2 / H2) between B2 and the radial cross-sectional height H2 is (B2 / H2) <1.2 is used.

According to a second aspect of the present invention, in the first aspect, the outer ring of the rolling bearing is fitted in the housing, the inner ring of the rolling bearing is fitted in the shaft portion, and the rotating shaft is the housing or the shaft. It is characterized by being part.
The invention according to claim 3 is characterized in that, in claim 2, the shaft portion is hollow.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the moment stiffness K (Nm / rad) of the rolling bearing and the inertia J of the rotating shaft and the rotating head centered on the rolling bearing. The relationship with (Nm ⁻² ) is 200 ≦ 1 / 2π · (K / J) ^1/2 ≦ 1000.
According to a fifth aspect of the present invention, in any one of the first to third aspects, the moment stiffness K (Nm / rad) of the rolling bearing, the rotary shaft centered on the rolling bearing, and the inertia J of the rotary head The relationship with (Nm ⁻² ) is 500 ≦ 1 / 2π · (K / J) ^1/2 ≦ 800.

Here, an example of a double row ball bearing in which the sectional dimension ratio (B2 / H2) between the axial sectional width B2 and the radial sectional height H2 is (B2 / H2) <1.2 will be described.
Referring to FIG. 5, in this double row ball bearing 200, a large number of balls 203 are rotatably arranged between double row raceway grooves 201a, 201b of outer ring 201 and double row raceway grooves 202a, 202b of inner ring 202. The sectional dimension ratio (B2 / H2) between the axial sectional width B2 and the radial sectional height H2 (= (outer ring outer diameter D2−inner ring inner diameter d2) / 2) is (B2 / H2) <1. 2 and the inner ring 202 is divided into two divided inner rings 202d at a substantially central portion in the axial direction.

  In the standard single row ball bearings whose dimension series defined by the International Organization for Standardization (ISO) are 18 (for example, 6800), 19 (for example, 6901), 10 (for example, 6003), 02 (for example, 7205A), 03 (for example, 7307A) When the inner diameter of the bearing is φ5 mm to φ100 mm, the cross-sectional dimension ratio (B / H) is set to 0.82 to 1.17. Further, when the bearing inner diameter is φ5 mm to φ500 mm, the above-mentioned cross-sectional dimension ratio (B / H) is set to 0.63 to 1.17.

  Therefore, the cross-sectional dimension ratio (B2 / H2) of the double row ball bearing used in the direct drive motor of the present invention is substantially the same as the maximum value 1.17 of the cross-sectional dimension ratio (B / H) of these single-row ball bearings, By setting it to less than 1.2, it is possible to replace a conventional standard single row ball bearing with two rows. For example, if the cross-sectional dimension ratio (B / H) of the target standard single-row ball bearing is 1.0, the cross-sectional dimension ratio (B2 / H2) of the double-row ball bearing used in the direct drive motor of the present invention = 1. It may be 0.

Here, FIG. 9 and FIG. 10 are each a standard thin ball bearing (bearing inner diameter: φ38.1 mm, bearing outer diameter: φ47.625 mm, bearing width: 4.762 mm, cross-sectional dimension ratio (B / H) = 1) The outer diameter of the double row ball bearing used in the direct drive motor of the present invention and the bearing on the basis of a cross-section (assumed to be replaced with a double row ball bearing) as shown in FIG. Deformation characteristics in the radial direction of the inner and outer ring rings when the inner diameter of the bearing is changed without changing the width (that is, when the value of (B2 / H2) is changed) and the radius direction of the second moment I: shows the result of comparison (see FIG. 15 calculated as I = bh ^3/12).

  11 and 12 are also used as standard thin ball bearings (bearing inner diameter: φ63.5 mm, bearing outer diameter: φ76.2 mm, bearing width: 6.35 mm, cross-sectional dimension ratio (B / H) = 1), the outer diameter of the double row ball bearing used in the direct drive motor of the present invention and the bearing on the basis of the cross section (assumed to be replaced with a double row ball bearing) in which two are combined as shown in FIG. Comparison of radial deformation characteristics and radial cross-section secondary moment I when inner diameter of bearing is changed without changing width (ie, when (B2 / H2) value is changed) Shows the results.

In any of the bearings, (B2 / H2) is less than 1.2, and the change in the rigidity increase rate gradient is noticeable. That is, the increase in the secondary moment I of the cross section becomes significant, and the decrease in the deformation amount of the inner and outer ring in the radial direction becomes saturated. This effect is the same for an inner ring or an outer ring divided at a substantially central portion in the axial direction.
Therefore, in the present invention, it is possible to prevent deformation of the bearing due to lathe processing during inner and outer ring production and processing force during polishing processing, which is a problem with conventional ultra-thin wall bearings used for the purpose of space saving. Bearing accuracy such as degree and uneven thickness can be improved.

Deformation of inner and outer rings when bearings are fixed with inner ring retainers and outer ring retainers (especially when they are assembled with a clearance fit with the shaft or housing). In addition, it is possible to prevent torque defects and rotational accuracy defects caused by deformation, or problems such as increased heat generation, wear and seizure.
In single row ball bearings, it is difficult to apply preload or moment load in a single row, but by using double row ball bearings, radial load, axial load and moment load can be applied. It becomes possible.

In addition, since each ball always contacts the inner and outer raceway grooves at two points with a stable contact angle, a change in spin slip, that is, a change in torque caused by a large automatic change in the direction of the ball can be suppressed.
Furthermore, since the width dimension per one row of the ball array is equivalent to about half of the conventional standard single row ball bearing, the ball diameter is also about half that of the conventional ball bearing. Increasing, the bearing stiffness is increased over conventional ball bearings.

  FIG. 16 is a comparison of calculated moment stiffness of various bearings. For the same size (calculation example is equivalent to bearing name No. 7906A (contact angle 30 °) and the inner and outer diameter dimensions are the same: inner ring inner diameter φ30 mm, outer ring outer diameter φ47 mm), the double row used for the direct drive motor according to claim 1 Angular contact ball bearings (contact angle 30 °: calculation example of total ball bearing (the width is the same as the two-row combination of 7906A)), and the present invention examples A to E in which the radius of curvature of the raceway grooves of the inner and outer rings are changed, Both have higher moment stiffness than standard double-row combination angular contact ball bearings. For example, Example B of the present invention can maintain 1.9 times the moment stiffness of conventional standard 2-row combination angular contact ball bearings. It is.

Each design preload clearance is calculated as a practical standard value of -0.010 mm for the inventive examples A to E and the standard two-row combination angular contact ball bearing.
In addition, the appropriate ball diameter of the narrow double row ball bearing used in the direct drive motor according to the present invention varies depending on whether a seal or the like is mounted, but in order to increase rigidity, if the ball diameter is extremely reduced, Since the surface pressure between the contact portions of the inner and outer rings with the raceway grooves increases and the pressure scar resistance may be lowered, it is generally preferable to be 15 to 45% of the bearing width (B2).

Further, when the double-row ball bearing used in the direct drive motor of the present invention is a double-row angular ball bearing, the contact angle of the bearing is selected depending on the required rigidity (for example, moment rigidity) and the required torque. A range of ° is desirable.
Furthermore, according to the direction and magnitude of the load, the contact angle for each row may be changed as necessary.
Furthermore, the radius of curvature of the raceway grooves of the inner and outer rings is 51 to 60% Da (Da: ball diameter), preferably 52 to 56% Da, more preferably 52 to 54, depending on required rigidity and torque characteristics. About% Da. Further, the radius of curvature of the raceway grooves of the inner and outer rings may not be the same or may be different for each row.

  In the double row ball bearing 200 of FIG. 5, the inner ring 202 is divided into two divided inner rings 202d at a substantially central portion in the axial direction, and an appropriate clearance Δ is set in advance for the two divided inner rings 202d. If the bearing is inserted into the shaft and the inner ring 202 is fixed in the axial direction using a bearing nut or the like (that is, the gap Δ is eliminated and the two divided inner rings 202d are brought into close contact with each other), a preload can be applied. Note that the amount of preload can be easily adjusted with the preset clearance Δ. Although it is possible to add a preload without contact until the clearance Δ becomes zero, the preload is likely to fluctuate. Therefore, it is preferable that the contact is maintained until the clearance Δ becomes zero.

  When the double-row ball bearing 200 is applied to an outer ring rotating application, the outer ring 201 on the rotating shaft side has an integral structure, so the outer ring 201 is temporarily fitted into a housing or the like by clearance fitting (the inner ring 202 is Even if clearance fitting or tightening allowance fitting is possible on the shaft, the rotation of the rotating shaft can be reduced, and the rotational accuracy of the rotating shaft is high while maintaining ease of assembly. Accuracy can be achieved.

That is, referring to FIG. 17, the outer ring center axis C ₂ is inclined relative to the inner ring center axis C ₁ , but the outer ring 201 is an integral structure. When applied, the center of the two outer ring raceway grooves 201a and 201b will not be displaced when assembled even if the bearing is clearance-fitted into the housing to facilitate the assembly. Rotation accuracy is improved. In this case, since the contact angle is a square shape, there is an advantage that the distance between the action points is increased and the moment rigidity is increased. In the case of inner ring rotation, the inner ring center axis C ₁ is relatively inclined with respect to the outer ring center axis C ₂ , and a whirling (sliding motion) occurs due to the rotation.

  According to the present invention, as a rolling bearing that rotatably supports the rotating shaft of the rotary head, the rolling element contacts the raceway groove of the inner ring at two points and contacts the raceway groove of the outer ring at two points, so that a preload is applied. Four-point contact ball bearings having negative clearance, or double row balls in which the cross-sectional dimension ratio (B2 / H2) between the axial cross-sectional width B2 and the radial cross-sectional height H2 is (B2 / H2) <1.2 By using a bearing or a cross roller bearing, the required moment rigidity of the bearing can be ensured even in a structure in which the motor unit is arranged between the rolling bearing and the rotary head. However, even if it repeats the step motion that suddenly accelerates / stops suddenly, it is possible to suppress the vibration in the rotational direction around the bearing.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a part of a direct drive motor according to a first embodiment of the present invention, and FIG. 2 is a schematic diagram of a four-point contact ball bearing having a negative clearance incorporated in the direct drive motor of FIG. FIG. 3 is a schematic sectional view of a direct drive motor according to a second embodiment of the present invention, and FIG. 4 is a graph showing the relationship between moment rigidity / inertia (K / J) and natural frequency. FIGS. 5 to 7 are cross-sectional views of the main parts showing modifications of the rolling bearing, and FIG. 8 is a graph showing the relationship between the moment load and the inclination angle in the present invention example and the conventional example.

  The direct drive motor 10 according to the first embodiment of the present invention is of an outer rotor type, and is attached to the end of a cylindrical housing (rotating shaft) 11 via a screw 16 or the like as shown in FIG. The housing 11 can be rotated by being incorporated between the rotary head 17 and the inner surface of the housing 11 and the outer surface of the hollow fixed shaft (shaft portion) 19 concentrically inserted in the housing 11. A rolling bearing 20 to be supported and a motor part 18 for applying a driving force to the housing 11 are provided. The motor part 18 is disposed between the rolling bearing 20 and the rotary head 17 so that the housing 11 is cantilevered. It is said that.

  The motor unit 18 includes a rotor 11 a attached to the inner diameter portion of the housing 11, and a stator 13 attached to the outer diameter portion of the fixed shaft 19 so as to face the rotor 11 a in the radial direction. A pulsar ring 14 is attached to an axial end portion on the side away from the rotary head 17 so as to be integrally rotatable with the housing 11, and an unevenness of the pulsar ring 14 is detected at an axial end portion on the same side of the fixed shaft 19. The position detector 15 is fixed.

  When the coil 12 of the stator 13 is energized, the housing 11 rotates integrally with the rotary head 17 and the pulsar ring 14, and the unevenness of the pulsar ring 14 is detected by the position detector 15 during the rotation. Based on the signal, the control device controls a motor drive circuit (both not shown), whereby rotational speed control and positioning control are performed.

  Here, in this embodiment, the rolling bearing 20 incorporated between the inner diameter surface of the housing 11 of the direct drive motor 10 and the outer diameter surface of the fixed shaft 19 is fitted into the housing 11 as shown in FIG. The outer ring 21, the inner ring 22 fitted on the fixed shaft 19, and a ball 24 as a rolling element arranged between the outer ring 21 and the inner ring 22 via a cage 23 so as to be able to roll in the circumferential direction. And a seal member 25 mounted on both ends of the outer ring 21 in the axial direction, the ball 24 contacts the raceway groove 22a of the inner ring 22 at two points and contacts the raceway groove 21a of the outer ring 21 at two points. A four-point contact ball bearing with a preload and a negative clearance is used.

Further, the relationship between the moment rigidity K (Nm / rad) of the four-point contact ball bearing 20 and the inertia J (Nm ⁻² ) of the housing 11 and the rotary head 17 centering on the four-point contact ball bearing 20 is expressed as 200. ≦ 1 / 2π · (K / J) ^1/2 ≦ 1000, preferably 500 ≦ 1 / 2π · (K / J) ^1/2 ≦ 800.
That is, in this embodiment, by setting K / J = 150,000 to 40000000 (preferably 1000000 to 25000000) and moment stiffness K to 30000 to 800000 Nm / rad (preferably 200000 to 500000 Nm / rad), the natural frequency is set. 200 to 1000 Hz (preferably 500 to 800 Hz).

  Then, by applying the bearing preload so that the moment rigidity such that the natural frequency becomes 200 Hz can be obtained, resonance in the rotational direction around the bearing can be suppressed. Further, by setting the natural frequency to 1000 Hz or less so that the bearing preload does not become excessive, problems such as heat generation, a decrease in life, and a decrease in manufacturing efficiency due to an increase in dynamic torque can be prevented. it can.

  As described above, in this embodiment, as a rolling bearing used for the rotation support portion of the direct drive motor 10, the ball 24 contacts the raceway groove 22a of the inner ring 22 at two points and the raceway groove 21a of the outer ring 21 at two points. Since the four-point contact ball bearing 20 that is in contact and is preloaded and has a negative clearance is used, the rigidity is greater than when a four-point contact ball bearing having a positive clearance is used.

As a result, even if the motor unit 18 is arranged between the four-point contact ball bearing 20 and the rotary head 17, the required moment rigidity of the bearing can be ensured, so that the motor unit 18 is accelerated rapidly. / Even if the stepping motion to stop suddenly is repeated, it is possible to suppress the vibration in the rotational direction around the bearing, and the moment stiffness K (Nm / rad) of the four-point contact ball bearing 20 and the four-point contact ball The relationship between the housing 11 centering on the bearing 20 and the inertia J (Nm ⁻² ) of the rotary head 17 is 200 ≦ 1 / 2π · (K / J) ^1/2 ≦ 1000, preferably 500 ≦ 1 / 2π ·. By setting (K / J) ^1/2 ≦ 800, resonance in the rotational direction around the bearing can be suppressed, and heat generation, life reduction, and dynamic torque can be reduced without excessive bearing preload. Get bigger It is possible to ensure problem such as reduction in manufacturing efficiency by.

  A direct drive motor 30 according to the second embodiment of the present invention shown in FIG. 3 is of an inner rotor type, and a hollow shaft portion (rotating shaft) 31 is connected to an end portion thereof via a screw (not shown). The shaft 31 can be rotated by being incorporated between the rotating head 37 attached to the shaft and the outer diameter surface of the shaft portion 31 and the inner diameter surface of the cylindrical fixed housing 39 concentrically inserted on the shaft portion 31. And a motor part 38 for applying a driving force to the shaft part 31. The motor part 38 is disposed between the rolling bearing 40 and the rotary head 37 so that the shaft part 31 is a single piece. It has a supporting structure. The reason why the shaft portion 31 is hollow is to incorporate a device for controlling a nozzle (not shown) attached to the rotary head 37.

  The motor portion 38 includes a rotor (not shown) attached to the outer diameter portion of the shaft portion 31 and a stator (not shown) attached to the inner diameter portion of the fixed housing 39 so as to face the rotor in the radial direction. A pulsar ring (not shown) is attached to the axial end of the shaft portion 31 on the side away from the rotary head 37 so as to be rotatable integrally with the shaft portion 31, and on the same side of the fixed housing 39. A position detector (not shown) for detecting unevenness of the pulsar ring is fixed to the end in the axial direction.

Then, by energizing the coil of the stator, the shaft portion 31 rotates integrally with the rotary head 37 and the pulsar ring, and the unevenness of the pulsar ring is detected by the position detector at the time of the rotation. The control device controls a motor drive circuit (both not shown), thereby performing rotation speed control and positioning control.
Here, in this embodiment, as the rolling bearing 40 incorporated between the outer diameter surface of the shaft portion 31 of the direct drive motor 30 and the inner diameter surface of the fixed housing 39, as in the first embodiment, A four-point contact ball bearing with a preload and a negative clearance is used (see FIG. 2).
Further, the relationship between the moment stiffness K (Nm / rad) of the four-point contact ball bearing 40 and the inertia J (Nm ⁻² ) of the shaft portion 31 and the rotary head 37 around the four-point contact ball bearing 40 is expressed as follows: 200 ≦ 1 / 2π · (K / J) ^1/2 ≦ 1000, preferably 500 ≦ 1 / 2π · (K / J) ^1/2 ≦ 800.

FIG. 4 shows the relationship between the natural frequency in the moment direction of the rolling bearing and the moment stiffness in the direct drive motor having the structure shown in FIG. In FIG. 4, the broken line is f = 1 / 2π · (K / J) ^1/2 , and the solid line is the calculation result by the finite element method. Here, the outer diameter of the rotary head 37 is 130 mm, the thickness of the shaft portion 31 is 35 mm, the mass of the rotary head 37 is 4.5 kg, and the inertia J of the shaft portion 31 and the rotary head 37 at the bearing center is 0.02 Nm ^{−. In} order to achieve the required moment rigidity with a single bearing and to achieve low torque, in the four-point contact ball bearing 40, K / J = 15000000 to 40000000 (preferably 10000000 to 25000000), By setting the moment stiffness K to 30000-800000 Nm / rad (preferably 200000-500000 Nm / rad), the natural frequency is set to 200-1000 Hz (preferably 500-800 Hz).

  And resonance can be suppressed by giving bearing preload so that moment rigidity that natural frequency may be set to 200 Hz is obtained. Further, by setting the natural frequency to 1000 Hz or less so that the bearing preload does not become excessive, problems such as heat generation, a decrease in life, and a decrease in manufacturing efficiency due to an increase in dynamic torque can be prevented. it can. Other functions and effects are the same as those of the first embodiment.

The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist of the present invention.
For example, in each of the embodiments described above, a four-point contact ball bearing having a negative clearance and a preload is given as an example of a rolling bearing that supports the rotating shaft of a direct drive motor. Similar effects can be obtained by using the double row ball bearing shown in FIG. 6 or the cross roller bearing shown in FIG. In this case, in any bearing, the relationship between the moment stiffness K (Nm / rad) of the rolling bearing and the inertia J (Nm ⁻² ) of the rotating shaft and the rotating head around the rolling bearing is 200 ≦ 1 / 2π · (K / J) ^1/2 ≦ 1000, preferably 500 ≦ 1 / 2π · (K / J) ^1/2 ≦ 800.

  First, the double row ball bearing will be described. As shown in FIG. 5, there are many double row ball bearings between the double row raceway grooves 201a and 201b of the outer ring 201 and the double row raceway grooves 202a and 202b of the inner ring 202. The ball 203 is a double row angular contact ball bearing 200 in which the ball 203 is rotatably arranged, and the axial sectional width B2 and the radial sectional height H2 (= (outer ring outer diameter D2-inner ring inner diameter d2) / 2). (B2 / H2) <1.2, and the inner ring 202 is divided into two divided inner rings 202d at a substantially central portion in the axial direction.

  As described above, an appropriate clearance Δ is set in advance for the two divided inner rings 202d. Therefore, if the bearing is inserted into the shaft and the inner ring 202 is fixed in the axial direction using a bearing nut or the like (that is, the gap Δ is eliminated and the two divided inner rings 202d are brought into close contact with each other), a preload can be applied. . Note that the preload amount can be easily adjusted by setting the size of the clearance Δ set in advance. Although it is possible to add a preload without contact until the clearance Δ becomes zero, the preload is likely to fluctuate. Therefore, it is preferable that the contact is maintained until the clearance Δ becomes zero.

Further, since the inner ring 202 is divided into two divided inner rings 202d at a substantially central portion in the axial direction, as shown in FIG. 17, when applied to a rotating structure with outer ring rotation, with respect to the inner ring central axis C ₁ Although the outer ring central axis C ₂ is relatively inclined, since the outer ring 201 has a one-piece structure, even if the bearing is loosely fitted to the housing for easy assembly, two rows of outer ring raceway grooves 201a, Since the center of 201b does not shift at the time of assembling, in the case of outer ring rotation, it is difficult for the rotating shaft to swing around and the rotation accuracy is improved. Incidentally, the contact angle of the double-row angular contact ball bearing 200 is, for example, 30 °.

In this embodiment, the pitch circle diameter of the balls 203 is as shown in the following formula (1). However, when it is desired to further increase the moment rigidity by increasing the number of balls per row of the bearing, the following formula (2) is used. 6 and the pitch circle diameter of the balls 203 may be shifted to the outer ring side to form the structure shown in FIG. 6, or the following equation (3) may be adopted as necessary to change the pitch circle diameter of the balls 203 to the inner ring. You may shift to 202 side (not shown).
Ball pitch circle diameter = (inner ring inner diameter + outer ring outer diameter) / 2 (1)
Ball pitch circle diameter> (inner ring inner diameter + outer ring outer diameter) / 2 (2)
Ball pitch circle diameter <(inner ring inner diameter + outer ring outer diameter) / 2 (3)
Further, if necessary, the ball pitch circle diameters of the left and right rows may not be the same value, and the diameters of the balls 203 of the left and right rows may not be the same value.

FIG. 7 shows an example of a cross roller bearing, and this cross roller bearing 50 is a cylinder between an outer ring 3 in which a split outer ring 1 is fastened by a fastening member 2 such as a rivet or a bolt and an integral inner ring 4. A large number of rollers 5 are rotatably arranged, and seal members 6 are attached to both ends of the outer ring 3 in the axial direction.
8 uses a four-point contact ball bearing having a preload type negative clearance having the same structure as in FIG. 2 as Example 1 of the present invention, and a cross roller bearing having the same structure as in FIG. 7 as Example 2 of the present invention. As an example, a four-point contact ball bearing having the same structure as that in FIG. 2 and having a positive clearance is used, and the result of investigating the relationship between the moment load and the inclination angle of each bearing (comparison of rigidity) is shown. The invention examples 1 and 2 and the conventional example have the same bearing size (outer diameter φ180 mm, inner diameter φ120 mm, width 25 mm).

As is clear from FIG. 8, it can be seen that the present invention examples 1 and 2 can obtain higher rigidity than the conventional four-point contact ball bearing having the same normal clearance if the bearing sizes are the same.
As for the structure and dimensions of the direct drive motor, those of various known structures and dimensions other than the rolling bearing can be used, and the materials for the inner and outer rings, balls, cages, seal members, etc. can also be used for the rolling bearing. The shape is not particularly limited.

It is the schematic which cut | disconnected a part of direct drive motor which is the 1st Embodiment of this invention. It is principal part sectional drawing of the 4-point contact ball bearing which has the negative clearance integrated in the direct drive motor of FIG. It is a schematic sectional drawing of the direct drive motor which is the 2nd Embodiment of this invention. It is a graph which shows the relationship between moment rigidity / inertia (K / J) and a natural frequency. It is principal part sectional drawing which shows the double row ball bearing which is a modification of a rolling bearing. It is principal part sectional drawing which shows the double row ball bearing which is a modification of a rolling bearing. It is principal part sectional drawing which shows the cross roller bearing which is a modification of a rolling bearing. It is a graph which shows the relationship between the moment load and inclination angle in the example of the present invention and a conventional example. It is a graph which shows the relationship between a cross-sectional dimension ratio (B2 / H2) and the deformation amount of the inner and outer rings in the radial direction. It is a graph which shows the relationship between a cross-sectional dimension ratio (B2 / H2) and a cross-sectional secondary moment I. It is a graph which shows the relationship between a cross-sectional dimension ratio (B2 / H2) and the deformation amount of the inner and outer rings in the radial direction. It is a graph which shows the relationship between a cross-sectional dimension ratio (B2 / H2) and a cross-sectional secondary moment I. It is principal part sectional drawing for demonstrating the case where the double row | line standard ultra-thin-wall single row ball bearing is replaced with the double row ball bearing used for the direct drive motor of this invention. It is explanatory drawing for demonstrating the deformation amount of the radial direction of an inner ring | wheel. It is explanatory drawing for demonstrating the calculation method of the cross-sectional secondary moment of an inner ring | wheel. It is a graph which shows the comparison of the calculated moment rigidity in various bearings. It is explanatory drawing for demonstrating the effect in the case of inner ring | wheel division | segmentation.

Explanation of symbols

10 Direct drive motor 11 Housing (rotating shaft)
17 Rotating head 18 Motor unit 20 Four-point contact ball bearing (rolling bearing)
21 Outer ring 21a Outer ring raceway groove 22 Inner ring 22a Inner ring raceway groove 24 Ball (rolling element)
30 Direct drive motor 31 Shaft (Rotating shaft)
37 Rotating head 38 Motor unit 40 Four-point contact ball bearing (rolling bearing)
50 Crossed roller bearings (rolling bearings)
200 Double-row ball bearings (rolling bearings)

Claims (5)

A rotary head provided at the tip of the rotary shaft, a rolling bearing that rotatably supports the rotary shaft, and a motor unit that applies a driving force to the rotary shaft, and between the rolling bearing and the rotary head A direct drive motor in which the motor unit is disposed and the rotating shaft has a cantilever support structure,
As the rolling bearing, a rolling element comes into contact with the raceway groove of the inner ring at two points and contacts with the raceway groove of the outer ring at two points, and a preload is applied and a negative clearance is provided. A direct drive characterized by using a double-row ball bearing or a cross roller bearing in which the sectional dimension ratio (B2 / H2) between B2 and the radial sectional height H2 is (B2 / H2) <1.2. motor.   2. The outer ring of the rolling bearing is fitted in a housing, the inner ring of the rolling bearing is fitted in a shaft portion, and the rotating shaft is the housing or the shaft portion. Direct drive motor described.   The direct drive motor according to claim 2, wherein the shaft portion is hollow. The relationship between the moment stiffness K (Nm / rad) of the rolling bearing and the inertia J (Nm ⁻² ) of the rotating shaft and the rotating head around the rolling bearing is 200 ≦ 1 / 2π · (K / J The direct drive motor according to claim 1, wherein ^1/2 ≦ 1000. The relationship between the moment stiffness K (Nm / rad) of the rolling bearing and the inertia J (Nm ⁻² ) of the rotary shaft and the rotary head around the rolling bearing is 500 ≦ 1 / 2π · (K / J The direct drive motor according to claim 1, wherein ^1/2 ≦ 800.

Images