Power transmission mechanism

Abstract

To provide a power transmission mechanism that can cancel unintended rotation around the second axis caused by rotation around the first axis. [Solution] The power transmission mechanism 100 comprises a planetary gear mechanism 30, an internal worm gear 60, a rotating frame 70, and a worm wheel 80, and transmits power to the saddle gear 90. The internal worm gear 60 is connected to the ring gear 33 and rotates around the first axis. The rotating frame 70 supports the saddle gear 90 so as to be rotatable around the second axis and is connected to the planetary carrier 37 and rotates around the first axis. The worm wheel 80 is rotatably supported by the rotating frame 70 and rotates the saddle gear 90 around the second axis by the relative rotation between the internal worm gear 60 and the rotating frame 70. With the sun gear 31 fixed, the power transmission operation of the planetary gear mechanism 30, which inputs rotation to the planetary carrier 37, causes the internal worm gear 60 and the rotating frame 70 to rotate in the same direction and at the same rotational speed.

Description

Technical Field

[0001] The disclosure according to this specification relates to a power transmission mechanism that transmits power to an output rotating body.

Background Art

[0002] Patent Document 1 discloses a differential mechanism capable of rotating a saddle gear as an output rotating body around a roll axis and a pitch axis. This differential mechanism includes a rotating frame provided with the saddle gear rotatably around the pitch axis, an internal worm gear coaxially arranged with the rotating frame, and a worm wheel provided rotatably on the rotating frame and meshing with the internal worm gear and the saddle gear. In this differential mechanism, when the internal worm gear is relatively rotated with respect to the rotating frame, the worm wheel rotates the saddle gear around the pitch axis.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the differential mechanism of Patent Document 1, when the saddle gear is rotated together with the rotating frame around a first axis such as a roll axis, relative rotation occurs between the rotating frame and the internal worm gear. As a result, the worm wheel rotates the saddle gear around a second axis such as a pitch axis. That is, an unintended rotation around the second axis may occur in the saddle gear due to the rotation around the first axis.

[0005] The present disclosure aims to provide a power transmission mechanism capable of canceling an unintended rotation around a second axis caused by the rotation around a first axis.

Means for Solving the Problems

[0006] To achieve the above objective, one disclosed embodiment is a power transmission mechanism for transmitting power to an output rotating body (90) having two degrees of rotational freedom, comprising: a planetary gear mechanism (30) having a sun gear (31), a ring gear (33) arranged coaxially with the sun gear, and a planetary carrier (37) that rotatably supports a plurality of pinion gears (36) that mesh with the sun gear and the ring gear; an internal worm gear (60) connected to the ring gear and rotating around a first axis, which is one of the two axes; and a second axis, which is arranged coaxially with the internal worm gear and rotating around the other axis, which is the other of the two axes. The system includes a rotating frame (70) that rotatably supports the output rotating body and is connected to a planetary carrier to rotate around a first axis, and a worm wheel (80) that is rotatably supported by the rotating frame, meshes with an internal worm gear and the output rotating body, and rotates the output rotating body around a second axis by relative rotation between the rotating frame and the internal worm gear. The internal worm gear and the rotating frame are a power transmission mechanism that rotates in the same direction and at the same rotational speed by the power transmission operation of the planetary gear mechanism, in which rotation is input to the planetary carrier with the sun gear fixed.

[0007] In this embodiment, when the output rotor is rotated around the first axis together with the rotating frame connected to the planetary carrier, the internal worm gear connected to the ring gear rotates in the same direction and at the same rotational speed as the rotating frame, while the sun gear is fixed. Therefore, the relative rotation between the rotating frame and the internal worm gear, and consequently the rotation of the output rotor around the second axis driven by the worm wheel, is suppressed. As a result, unintended rotation around the second axis caused by rotation around the first axis can be canceled out.

[0008] Furthermore, the reference numbers in parentheses above and in the claims are merely examples of correspondences with specific configurations in the embodiments described later, and do not in any way limit the technical scope. In addition, combinations of claims not explicitly stated in the claims are also possible, provided that they do not cause any particular problems with the combination. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows the configuration of a power transmission mechanism according to one embodiment of the present disclosure, and is a cross-sectional view taken along line II in Figure 2. [Figure 2] This is a diagram illustrating the configuration of a planetary gear mechanism. [Figure 3] This is a diagram illustrating the configuration of the differential mechanism. [Modes for carrying out the invention]

[0010] The power transmission mechanism 100 according to one embodiment of the present disclosure, shown in Figures 1 to 3, is provided between the roll shaft motor 110 and the pitch shaft motor 120 and the driven rotating body 140. The power transmission mechanism 100 transmits the power of the roll shaft motor 110 and the pitch shaft motor 120 to the driven rotating body 140. The power transmission mechanism 100 can combine the rotations of the roll shaft motor 110 and the pitch shaft motor 120 and transmit them to a single driven rotating body 140.

[0011] The power transmission mechanism 100 has a saddle gear 90. The saddle gear 90 is an output rotating body with two degrees of rotational freedom. In the following description, the center of the saddle gear 90 is used as the reference point, and mutually orthogonal roll axis RA, pitch axis PA, and yaw axis YA are set. The saddle gear 90 is rotatable around the roll axis RA and the pitch axis PA. The roll axis RA is the first axis, one of the two axes from which the saddle gear 90 has a degree of rotational freedom. The pitch axis PA is the second axis, the other of the two axes from which the saddle gear 90 has a degree of rotational freedom. On the other hand, the saddle gear 90 does not rotate around the yaw axis YA. The saddle gear 90 is configured to mesh with the driven rotating body 140 and transmits the rotation around the roll axis RA and the rotation around the pitch axis PA to the driven rotating body 140.

[0012] The driven rotating body 140 is a spherical gear formed in a spherical shape. The driven rotating body 140 has three degrees of rotational freedom. The driven rotating body 140 can rotate indefinitely around three axes with the spherical center as the reference point. The driven rotating body 140 is in contact with the saddle gear 90. The driven rotating body 140 rotates due to the power transmitted by the saddle gear 90. Teeth capable of meshing with the saddle gear 90 are formed on the entire outer surface of the driven rotating body 140. The position where the driven rotating body 140 and the saddle gear 90 are in contact may be changed as appropriate. For example, the driven rotating body 140 may be meshing with the saddle gear 90 on the roll axis RA, or it may be meshing with the saddle gear 90 on the pitch axis PA. Furthermore, multiple saddle gears 90 may be in contact with the driven rotating body 140 in a power-transmitting manner.

[0013] The roll axis motor 110 and the pitch axis motor 120 are servo motors, etc., capable of high-precision control of rotational position, rotational speed, and torque using feedback control. The roll axis motor 110 controls the rotation of the saddle gear 90 around the roll axis RA. The roll axis motor 110 has a first output shaft 111. The first output shaft 111 transmits the output of the roll axis motor 110 to the power transmission mechanism 100. The first motor rotation axis MA1, which is the rotational center axis of the first output shaft 111, is positioned along the roll axis RA and is defined to be substantially parallel to the roll axis RA. The pitch axis motor 120 controls the rotation of the saddle gear 90 around the pitch axis PA. The pitch axis motor 120 has a second output shaft 121. The second output shaft 121 transmits the output of the pitch axis motor 120 to the power transmission mechanism 100. The second motor rotation axis MA2, which is the rotational center axis of the second output shaft 121, is substantially coaxial with the roll axis RA. The second motor rotation axis MA2 is positioned along the first motor rotation axis MA1 and is defined to be substantially parallel to the first motor rotation axis MA1.

[0014] <Configuration of the power transmission mechanism> The power transmission mechanism 100 transmits power input from the roll shaft motor 110 and the pitch shaft motor 120 to the saddle gear 90. The power transmission mechanism 100 is composed of a first reduction unit 10, a second reduction mechanism 20, a planetary gear mechanism 30, a reduction gear unit 40, and a differential mechanism 50, etc. In the power transmission mechanism 100, each element such as gears used for power transmission is formed from steel materials such as alloy steel and stainless steel, which have high strength and excellent wear resistance. Each element may also be formed from high-performance resin materials such as nylon and ceramics.

[0015] The first reduction unit 10 reduces the rotation of the first output shaft 111 by the roll shaft motor 110 and transmits it to the planetary gear mechanism 30 (planetary carrier 37, described later). The first reduction unit 10 is composed of a first reduction mechanism 11 and a reduction gear 13, etc. The first reduction mechanism 11 and the reduction gear 13 are arranged coaxially with the first output shaft 111. That is, the rotation centers of the first reduction mechanism 11 and the reduction gear 13 are located on the axis of the first motor rotation shaft MA1.

[0016] The first reduction mechanism 11 is made up of multiple gears. The first reduction mechanism 11 is connected to the first output shaft 111 of the roll shaft motor 110. The first reduction mechanism 11 reduces the rotation of the first output shaft 111 and transmits it to the reduction gear 13. The value obtained by dividing the rotational speed of the first output shaft 111 by the rotational speed of the output shaft of the first reduction mechanism 11 is the gear ratio of the first reduction mechanism 11 (hereinafter referred to as reduction ratio a).

[0017] The reduction gear 13 is connected to the output shaft of the first reduction mechanism 11 and rotates together with the output shaft. The reduction gear 13 is a gear that meshes with the planetary carrier 37. The reduction gear 13 reduces the rotation of the output shaft of the first reduction mechanism 11 and transmits it to the planetary carrier 37. The value obtained by dividing the number of teeth formed on the reduction gear 13 by the number of teeth formed on the planetary carrier 37 (the input side plate 37a described later) is the gear ratio of the reduction gear 13 (hereinafter referred to as reduction ratio b).

[0018] The second reduction mechanism 20 reduces the rotation of the second output shaft 121 by the pitch axis motor 120 and transmits it to the planetary gear mechanism 30 (sun gear 31 described later). The second reduction mechanism 20 is coaxially arranged with the second output shaft 121. That is, the rotation center of the second reduction mechanism 20 is located on the axis of the second motor rotation shaft MA2. The value obtained by dividing the rotation speed of the second output shaft 121 by the rotation speed of the sun gear 31 (center shaft 32 described later) is the gear ratio of the second reduction mechanism 20 (hereinafter, reduction ratio d).

[0019] The planetary gear mechanism 30 includes a sun gear 31, a ring gear 33, and a planetary carrier 37. The sun gear 31, the ring gear 33, and the planetary carrier 37 are coaxially arranged with each other (see FIG. 2). A rotation center axis of the planetary gear mechanism 30 (hereinafter, planetary center axis CA1) is defined so as to pass through the rotation centers of the sun gear 31, the ring gear 33, and the planetary carrier 37. The planetary center axis CA1 is substantially coaxial with the roll axis RA and the second motor rotation shaft MA2.

[0020] The sun gear 31 is located at the center of the planetary gear mechanism 30. A number of teeth are formed on the outer peripheral surface of the sun gear 31. The sun gear 31 is connected to the second reduction mechanism 20 via the center shaft 32. The center shaft 32 transmits the rotation of the pitch axis motor 120 decelerated by the second reduction mechanism 20 to the sun gear 31.

[0021] The ring gear 33 is coaxially arranged with the sun gear 31. The ring gear 33 is located at the outermost periphery of the planetary gear mechanism 30. An inner gear portion 34 and an outer gear portion 35 are formed on the ring gear 33. The inner gear portion 34 is formed on the inner peripheral surface of the ring gear 33. A number of teeth are arranged on the inner gear portion 34. The outer gear portion 35 is formed on the outer peripheral surface of the ring gear 33. A number of teeth are arranged on the outer gear portion 35.

[0022] The planetary carrier 37 is composed of a plurality of pinion gears 36, an input side plate 37a, an output side plate 37b, a plurality of pinion shafts 37c, etc. The planetary carrier 37 rotatably supports a plurality of pinion gears 36 by the configuration of the input side plate 37a, the output side plate 37b, and the plurality of pinion shafts 37c, etc.

[0023] The pinion gear 36 is accommodated in the space between the sun gear 31 and the ring gear 33. A large number of teeth are formed on the outer peripheral surface of the pinion gear 36. The pinion gear 36 meshes with both the sun gear 31 and the ring gear 33 (inner gear portion 34) simultaneously. The plurality of pinion gears 36 are arranged at equal intervals in the circumferential direction around the planetary center axis CA1. The rotation axis of each pinion gear 36 becomes the pinion center axis CA2. The pinion center axis CA2 is the rotation axis of the pinion gear 36. The pinion gear 36 is a planetary gear and rotates around the pinion center axis CA2 while revolving around the planetary center axis CA1.

[0024] The input side plate 37a is formed in a disc shape. An opening for passing the center shaft 32 is formed at the center of the input side plate 37a. The input side plate 37a is located on the pitch axis motor 120 side with respect to the pinion gear 36. The input side plate 37a is coaxially arranged with the sun gear 31. A large number of teeth meshing with the reduction gear 13 are formed on the outer peripheral surface of the input side plate 37a. The input side plate 37a is driven by the reduction gear 13 and rotates around the planetary center axis CA1.

[0025] The output side plate 37b is formed in a disc shape. The output side plate 37b is located on the opposite side of the input side plate 37a with the pinion gear 36 interposed therebetween. The output side plate 37b is coaxially arranged with the sun gear 31. The output side plate 37b is connected to the differential mechanism 50 (rotation frame 70 described later) and transmits the rotation of the planetary carrier 37 to the differential mechanism 50.

[0026] The pinion shaft 37c is formed in a cylindrical shape. The pinion shaft 37c is held at both axial ends by the input plate 37a and the output plate 37b. The pinion shaft 37c connects the input plate 37a and the output plate 37b to each other. The pinion shaft 37c rotatably supports the pinion gear 36.

[0027] The planetary gear mechanism 30 described above has a configuration in which multiple pinion gears 36, supported by planetary carriers 37, revolve around a sun gear 31 located at the center, and a ring gear 33 is arranged to surround the pinion gears 36. The planetary gear mechanism 30 enables power transmission operations in various ways by fixing one of the sun gear 31, planetary carriers 37, and ring gear 33, and using the remaining two for input and output.

[0028] For example, if the planetary carrier 37 is fixed, the sun gear 31 is used as input, and the ring gear 33 is used as output, the planetary gear mechanism 30 reduces the rotation input to the sun gear 31 while reversing its direction of rotation, and outputs it from the ring gear 33. In this reverse reduction operation, the value obtained by dividing the rotational speed of the sun gear 31 by the rotational speed of the ring gear 33 becomes the gear ratio (hereinafter referred to as the reduction ratio e) of the planetary gear mechanism 30. The reduction ratio e is -Zs / Zr, where Zr is the number of teeth of the ring gear 33 and Zs is the number of teeth of the sun gear 31. The minus sign indicates that the direction of rotation of the output side ring gear 33 is opposite to the direction of rotation of the input side sun gear 31.

[0029] As another example, if the sun gear 31 is fixed, the planetary carrier 37 is used as input, and the ring gear 33 is used as output, the planetary gear mechanism 30 increases the speed of the rotation input to the planetary carrier 37 and outputs it from the ring gear 33. In this speed-increasing operation, the value obtained by dividing the rotational speed of the planetary carrier 37 by the rotational speed of the ring gear 33 becomes the speed ratio of the planetary gear mechanism 30 (hereinafter referred to as the speed increase ratio c). The speed increase ratio c is the value of 1 + Zs / Zr. In this disclosure, a speed ratio greater than 1 is referred to as the "reduction ratio," and a speed ratio less than 1 is referred to as the "speed increase ratio."

[0030] The reduction gear unit 40 reduces the rotation of the ring gear 33 and transmits it to the differential mechanism 50 (worm gear 60, described later). The reduction gear unit 40 is composed of a small-diameter gear 41, a connecting shaft 42, and a large-diameter gear 43, etc. The small-diameter gear 41, the connecting shaft 42, and the large-diameter gear 43 are arranged coaxially on the reduction shaft GA. The reduction shaft GA is located coaxially with the first motor rotation shaft MA1.

[0031] The small-diameter gear 41 is a gear that meshes with the outer gear portion 35 of the ring gear 33. The small-diameter gear 41 is driven by the ring gear 33 and rotates around the reduction shaft GA. The connecting shaft 42 is formed in a cylindrical shape and connects the small-diameter gear 41 and the large-diameter gear 43 to each other. The connecting shaft 42 rotates the large-diameter gear 43 integrally with the small-diameter gear 41.

[0032] The large-diameter gear 43 is a gear with a larger pitch circle than the small-diameter gear 41. The large-diameter gear 43 is connected to the differential mechanism 50 (internal worm gear 60, which will be described later). The large-diameter gear 43 is a gear that meshes with the driven gear portion 62 of the internal worm gear 60. The large-diameter gear 43 transmits the rotation of the connecting shaft 42 to the internal worm gear 60. The value obtained by dividing the rotational speed of the ring gear 33 by the rotational speed of the internal worm gear 60 is the gear ratio of the reduction gear unit 40 (hereinafter referred to as the reduction ratio f).

[0033] The differential mechanism 50 is positioned axially alongside the planetary gear mechanism 30 such that the roll axis RA is coaxial with the planetary center axis CA1. The differential mechanism 50 comprises an internal worm gear 60, a rotating frame 70, a worm wheel 80, and a saddle gear 90 (see Figure 3). The differential mechanism 50 combines the power input from the planetary gear mechanism 30 to the internal worm gear 60 and the rotating frame 70, respectively, and transmits it to the saddle gear 90. The internal worm gear 60 and the rotating frame 70 are coaxially arranged on the roll axis RA.

[0034] The internal worm gear 60 is positioned on the outer circumference of the rotating frame 70 and is rotatable relative to the rotating frame 70. The internal worm gear 60 is connected to the ring gear 33 via the reduction gear unit 40. The internal worm gear 60 rotates around the roll axis RA, which is one of the two axes from which the saddle gear 90 has rotational degrees of freedom, by power input from the reduction gear unit 40. The internal worm gear 60 is composed of a driven ring 61 and a main cylinder 65, etc. The driven ring 61 and the main cylinder 65 are coaxially arranged on the roll axis RA.

[0035] The driven ring 61 is formed in an annular shape that covers the outer circumference of the rotating frame 70 (carrier connecting portion 71 described later). A driven gear portion 62 is formed on the outer circumferential surface of the driven ring 61. The driven gear portion 62 has a number of teeth that mesh with the large-diameter gear 43. The driven gear portion 62 may be a spur gear with straight teeth formed along the axial direction on its outer circumferential surface, or it may be a helical gear with teeth formed at an angle (see Figure 3). The driven ring 61 is driven by the large-diameter gear 43 that meshes with the driven gear portion 62 and rotates around the roll axis RA.

[0036] The main cylinder 65 is connected to the driven ring 61. The main cylinder 65 rotates integrally with the driven ring 61. The main cylinder 65 is formed in a cylindrical shape that covers a part of the rotating frame 70 (the wheel support part 73 described later) and the outer circumference of the worm wheel 80. A worm gear part 66 is formed on the inner circumferential surface of the main cylinder 65. The worm gear part 66 has helical teeth that mesh with the worm wheel 80. The main cylinder 65 transmits the rotation of the internal worm gear 60 to the worm wheel 80.

[0037] The rotating frame 70 is formed in a cylindrical shape overall. The rotating frame 70 is coaxially arranged with the internal worm gear 60. The rotating frame 70 is connected to the planetary carrier 37 and rotates around the roll axis RA. As described above, the roll axis RA is defined in orientation along the planetary central axis CA1 of the planetary gear mechanism 30. The rotating frame 70 has a carrier connecting portion 71, a wheel support portion 73, and a spherical body support portion 75.

[0038] The carrier coupling portion 71 is provided at the end of the rotating frame 70 on the planetary gear mechanism 30 side. The carrier coupling portion 71 is connected to the output side plate 37b. The carrier coupling portion 71 rotates the rotating frame 70 integrally with the planetary carrier 37.

[0039] The wheel support portion 73 is provided between the carrier connecting portion 71 and the spherical support portion 75, with a smaller diameter than the worm gear portion 66. The wheel support portion 73 holds both ends of the cylindrical wheel shaft 74. The wheel shaft 74 rotatably supports the worm wheel 80. The wheel shaft 74 defines the wheel rotation axis WA, which is the center of rotation of the worm wheel 80. The wheel rotation axis WA is defined in a position along (substantially parallel to) the pitch axis PA and intersects the roll axis RA perpendicularly.

[0040] The spherical support portion 75 is provided at the end of the rotating frame 70 on the driven rotating body 140 side. The spherical support portion 75 supports the saddle gear 90 so that it can rotate freely around the pitch axis PA, which is the other of the two axes from which the saddle gear 90 has rotational degrees of freedom. As described above, the pitch axis PA is defined to be perpendicular to the roll axis RA.

[0041] The worm wheel 80 is formed in the shape of a spur gear. The worm wheel 80 has multiple teeth arranged radially. Each tooth surface of the worm wheel 80 is a crowned tooth surface formed in a curved shape. The worm wheel 80 is supported by the rotating frame 70 so as to be able to rotate freely around the wheel rotation axis WA. The worm wheel 80 meshes simultaneously with both the worm gear section 66 and the saddle gear 90. The worm wheel 80 rotates together with the rotating frame 70 and the saddle gear 90 around the roll axis RA. The worm wheel 80 rotates around the wheel rotation axis WA as the teeth are fed to the helical worm gear section 66 by the relative rotation between the rotating frame 70 and the internal worm gear 60. The worm wheel 80 rotates according to the difference between the rotation of the rotating frame 70 (hereinafter referred to as roll rotation RK) and the rotation of the internal worm gear 60 (hereinafter referred to as worm rotation WK).

[0042] The saddle gear 90 is spherical overall. The saddle gear 90 is not limited to a spherical shape and may be formed into various shapes that connect to the driven rotating body 140. Teeth capable of meshing with the driven rotating body 140 and the worm wheel 80 are formed on the entire outer surface of the saddle gear 90. Specifically, the teeth of the saddle gear 90 include conical, frustoconical, or annular drive pole teeth and curved teeth. The tooth surface of the curved teeth is curved along the circumferential direction of the saddle gear 90 and becomes concave towards the drive pole teeth. The curvature of the curved shapes of the multiple curved teeth is smallest at a position rotated 180° from the drive pole teeth (the pole opposite to the drive pole teeth) and increases as it approaches the drive pole teeth.

[0043] The saddle gear 90 is supported by the spherical support 75 and is rotatable around the pitch axis PA. The saddle gear 90 rotates integrally with the rotating frame 70 around the roll axis RA. In addition, the saddle gear 90 is driven by the worm wheel 80 to rotate around the pitch axis PA (hereinafter referred to as pitch rotation PK). By meshing with the driven rotating body 140, the saddle gear 90 controls the rotational motion of the driven rotating body 140 while limiting the degrees of freedom around two of the three axes that the driven rotating body 140 has.

[0044] <Details of the mechanism for canceling the induced rotation> In the differential mechanism 50 described so far, when rotation is input to the rotating frame 70, the saddle gear 90 rotates around the roll axis RA. However, when the rotating frame 70 is rotated with the internal worm gear 60 fixed, relative rotation occurs between the rotating frame 70 and the internal worm gear 60. As a result, the worm wheel 80 is driven by the internal worm gear 60, causing the saddle gear 90 to rotate around the pitch axis PA. In other words, the saddle gear 90 undergoes unintended rotation around the pitch axis PA (hereinafter referred to as "induced rotation"), which is caused by the rotation around the roll axis RA.

[0045] To prevent this kind of symmetrical rotation, it is necessary to input a worm rotation WK synchronized with the roll rotation RK of the rotating frame 70 to the internal worm gear 60. In other words, the internal worm gear 60 needs to rotate in the same direction and at the same rotational speed as the rotating frame 70. In the power transmission mechanism 100, the first reduction unit 10, the second reduction mechanism 20, the planetary gear mechanism 30, and the reduction gear unit 40 function as cancellation mechanisms that passively eliminate the "symmetrical rotation" of the saddle gear 90.

[0046] The cancellation mechanism is configured such that the internal worm gear 60 and the rotating frame 70 rotate in the same direction and at the same rotational speed due to the speed-increasing operation of the planetary gear mechanism 30. As described above, the speed-increasing operation is a power transmission operation of the planetary gear mechanism 30 in which rotation is input to the planetary carrier 37 while the sun gear 31 is fixed. In the speed-increasing operation, the pitch shaft motor 120 stops the rotation of the second output shaft 121 and the sun gear 31. On the other hand, the roll shaft motor 110 inputs rotation to the planetary carrier 37 via the first reduction unit 10.

[0047] With the cancellation mechanism described above, when only the roll axis motor 110 rotates and the planetary gear mechanism 30 performs a speed-increasing operation, the saddle gear 90 rotates only around the roll axis RA. Also, when only the pitch axis motor 120 rotates and the planetary gear mechanism 30 performs a reverse deceleration operation, the saddle gear 90 rotates only around the pitch axis PA.

[0048] To elaborate further, the gear ratios of the first reduction unit 10, the second reduction mechanism 20, and the reduction gear unit 40 are set in relation to the gear ratio of the planetary gear mechanism 30 so that the internal worm gear 60 and the rotating frame 70 rotate in the same direction and at the same rotational speed. As described above, the reduction ratio of the first reduction unit 10 is "a × b", the reduction ratio of the second reduction mechanism 20 is "d", and the reduction ratio of the reduction gear unit 40 is "f". In addition, the speed increase ratio of the planetary gear mechanism 30 during speed increase operation is "c", and the reduction ratio of the planetary gear mechanism 30 during reverse reduction operation is "e".

[0049] For example, when only the roll axis motor 110 is operated, the internal worm gear 60 rotates in sync with the rotating frame 70 due to the cancellation effect of the cancellation mechanism described above. The reduction ratio obtained by dividing the input rotational speed of the roll axis RA by the output rotational speed of the internal worm gear 60 at this time is set to be equal to the reduction ratio obtained by dividing the input rotational speed of the pitch axis PA by the output rotational speed of the internal worm gear 60 when only the pitch axis motor 120 is driven. The relationship between these reduction mechanisms in terms of each reduction ratio is shown in the following equation 1. a × b = a × b × c × f = -1 × d × e × f ... (Equation 1)

[0050] From equation 1 above, the relationships shown in equations 2 and 3 below can be derived. c = 1 / f ···(Equation 2) a × b × c = -1 × d × e ... (Equation 3)

[0051] According to equation 2 above, the reduction ratio f of the reduction gear unit 40 is set to the reciprocal of the speed-increasing ratio c of the planetary gear mechanism 30 during the speed-increasing operation of the planetary gear mechanism 30. In addition, according to equation 3 above, the respective gear ratios of the first reduction mechanism 11, the reduction gear 13, and the second reduction mechanism 20 are set based on the gear ratios during each power transmission operation of the planetary gear mechanism 30. As a result, the roll rotation RK and pitch rotation PK of the saddle gear 90 can be controlled independently of each other by the roll shaft motor 110 and the pitch shaft motor 120. Specifically, the roll rotation RK of the saddle gear 90 is controlled according to the motor rotation of the roll shaft motor 110 input to the planetary carrier 37, without being affected by the motor rotation of the pitch shaft motor 120 input to the sun gear 31. Similarly, the pitch rotation PK of the saddle gear 90 is controlled according to the motor rotation of the pitch shaft motor 120 input to the sun gear 31, without being affected by the motor rotation of the roll shaft motor 110 input to the planetary carrier 37.

[0052] (Summary of implementations) In this embodiment described above, the rotating frame 70 is connected to the planetary carrier 37, and the internal worm gear 60 is connected to the ring gear 33. When the saddle gear 90 is rotated around the roll axis RA together with the rotating frame 70, the internal worm gear 60 rotates in the same direction and at the same rotational speed as the rotating frame 70, while the sun gear 31 is fixed. Therefore, the relative rotation between the rotating frame 70 and the internal worm gear 60, and consequently the rotation of the saddle gear 90 around the pitch axis PA driven by the worm wheel 80, is suppressed. As a result, unintended rotation around the pitch axis PA caused by rotation around the roll axis RA can be canceled out.

[0053] In addition, the cancellation mechanism according to this embodiment does not rely on corrective control in the roll axis motor 110 and the pitch axis motor 120, and passively and mechanically suppresses the "sequential rotation" of the saddle gear 90. Therefore, in a configuration in which a robot arm or the like is driven together with the driven rotating body 140, not only the start and end points of the robot arm's movement are suppressed, but also the deviation of the arm's trajectory from the start point to the end point is suppressed. As a result, it becomes possible to accurately operate the controlled object connected to the driven rotating body 140 while eliminating the need for energy consumption for corrective control.

[0054] In this embodiment, the reduction gear unit 40 reduces the rotation of the ring gear 33 and transmits it to the internal worm gear 60. The reduction ratio f of the reduction gear unit 40 is set to the reciprocal of the speed increase ratio c of the planetary gear mechanism 30 in power transmission operation (speed increase operation) with the sun gear 31 fixed and the planetary carrier 37 as the input side and the ring gear 33 as the output side. With these settings for each gear ratio, the roll rotation RK of the rotating frame 70 and the worm rotation WK of the worm wheel 80 can be reliably synchronized in the power transmission state of the planetary gear mechanism 30 performing the speed increase operation.

[0055] Furthermore, in this embodiment, the first reduction unit 10 reduces the rotation by the roll shaft motor 110 and transmits it to the planetary carrier 37. The second reduction mechanism 20 reduces the rotation by the pitch shaft motor 120 and transmits it to the sun gear 31. The gear ratios of the first reduction unit 10, the second reduction mechanism 20, and the planetary gear mechanism 30 are set so that the internal worm gear 60 and the rotating frame 70 rotate in the same direction and at the same rotational speed. As described above, even with a configuration in which multiple reduction mechanisms are combined with the planetary gear mechanism 30 and the differential mechanism 50, the worm rotation WK and roll rotation RK can be synchronized by appropriately setting the gear ratio of each reduction mechanism.

[0056] In addition, in this embodiment, the roll axis RA, defined in a position along the planetary central axis CA1, is one of the first axes from which the saddle gear 90 has rotational freedom. The pitch axis PA, defined in a position perpendicular to the roll axis RA, is the other second axis from which the saddle gear 90 has rotational freedom. With this configuration, rotation around the roll axis RA and rotation around the pitch axis PA can be controlled independently. Furthermore, the power transmission mechanism 100, including the mechanism for canceling sway rotation, can be easily miniaturized.

[0057] Furthermore, in this embodiment, with the planetary carrier 37 fixed, the power transmission operation (reverse deceleration operation) of the planetary gear mechanism 30, in which rotation is input to the sun gear 31, causes the rotating frame 70 and worm wheel 80 to rotate the saddle gear 90 only around the pitch axis PA. As a result, even in a configuration in which the planetary gear mechanism 30 is combined with the differential mechanism 50, unintended rotation around the roll axis RA caused by rotation around the pitch axis PA can be canceled.

[0058] Furthermore, in this embodiment, the rotation of the roll axis motor 110 is input to the planetary carrier 37, and the rotation of the pitch axis motor 120 is input to the sun gear 31, enabling power transmission operation of the planetary gear mechanism 30. In this power transmission state, the rotating frame 70 rotates the saddle gear 90 around the roll axis RA, while the worm wheel 80 rotates the output rotating body around the pitch axis PA. As a result, while suppressing cascading rotation, the rotation around the roll axis RA and the rotation around the pitch axis PA can be controlled individually.

[0059] In the above embodiment, the first reduction unit 10 corresponds to the "first reduction mechanism," the second reduction mechanism 20 corresponds to the "second reduction mechanism," the planetary gear mechanism 30 corresponds to the "planetary gear mechanism," and the reduction gear unit 40 corresponds to the "output reduction mechanism." Furthermore, the saddle gear 90 corresponds to the "output rotating body," the roll shaft motor 110 corresponds to the "first drive unit," the pitch shaft motor 120 corresponds to the "second drive unit," and the planetary center axis CA1 corresponds to the "rotation center axis."

[0060] (Other embodiments) Although one embodiment of the present disclosure has been described above, the present disclosure is not to be construed as being limited to the above embodiment, and can be applied to various embodiments and combinations without departing from the gist of the present disclosure.

[0061] The specific configurations of the first reduction unit 10, the second reduction mechanism 20, and the reduction gear unit 40 in the above embodiment may be modified as appropriate. For example, in the first reduction unit 10, the reduction gear 13 may be omitted, and the rotation output from the first reduction mechanism 11 may be directly input to the planetary carrier 37. Alternatively, the rotation output from the second reduction mechanism 20 may be reduced by a reduction gear and input to the center shaft 32. Furthermore, the reduction gear unit 40 may be a reduction mechanism that combines multiple gears in addition to the small-diameter gear 41 and the large-diameter gear 43.

[0062] In addition, the arrangement of the first reduction unit 10, the second reduction mechanism 20, and the reduction gear unit 40 may be changed as appropriate. For example, the first reduction unit 10 and the second reduction mechanism 20 may be arranged perpendicular to the planetary gear mechanism 30 so that the first motor rotation shaft MA1 and the second motor rotation shaft MA2 are in a twisted position with respect to the planetary center axis CA1. Also, the second motor rotation shaft MA2 does not have to be located coaxially with the planetary center axis CA1. Furthermore, the first motor rotation shaft MA1 of the first reduction unit 10 and the reduction shaft GA of the reduction gear unit 40 may be offset from each other in the circumferential and radial directions of the planetary gear mechanism 30.

[0063] In the above embodiment, the planetary gear mechanism 30 and the differential mechanism 50 were arranged axially side by side such that the planetary central axis CA1 and the roll axis RA were coaxially positioned. However, the positional relationship between the planetary gear mechanism 30 and the differential mechanism 50 may be changed as appropriate. For example, the planetary gear mechanism 30 may be positioned radially offset from the differential mechanism 50. In such a configuration, the reduction gear unit 40 may be omitted, and the rotation of the ring gear 33 may be directly input to the driven ring 61. Alternatively, the rotation of the planetary carrier 37 may be input to the carrier coupling portion 71 via the reduction mechanism.

[0064] As described above, if the configuration of the reduction mechanism provided in the power transmission mechanism 100 differs from that of the above embodiment, the gear ratio set for each reduction mechanism may also be appropriately changed to match the gear ratio in each power transmission operation of the planetary gear mechanism 30.

[0065] The configuration of the drive unit that inputs rotation to the planetary gear mechanism 30 may be modified as appropriate. For example, the servo motors used as the roll axis motor 110 and the pitch axis motor 120 may be any of DC servo motors, synchronous AC servo motors, or induction AC servo motors. Furthermore, a stepping motor, hydraulic or pneumatic cylinder, piezo actuator, linear actuator, etc., may be used as a drive unit instead of the roll axis motor 110 and the pitch axis motor 120.

[0066] The power transmission mechanism 100 according to this disclosure can operate, for example, a robot arm connected to a driven rotating body 140. The configuration combined with such a driven rotating body 140 is not limited to a robot arm and may be modified as appropriate. Furthermore, in the above embodiment, the two axes on which the saddle gear 90 can rotate were the roll axis RA and the pitch axis PA. However, the first and second axes on which the saddle gear 90 has rotational degrees of freedom are not limited to the roll axis RA and the pitch axis PA. The first and second axes may be modified as appropriate depending on the application of the power transmission mechanism 100.

[0067] The power transmission mechanism 100 in the above embodiment did not include a roll shaft motor 110 and a pitch shaft motor 120. However, the power transmission mechanism 100 may further include at least one of the roll shaft motor 110 and the pitch shaft motor 120. Also, the power transmission mechanism 100 may not include at least one of the first reduction unit 10, the second reduction mechanism 20, and the saddle gear 90.

[0068] In this disclosure, the terms “connected” and “linked” may refer to direct connections and links with other elements, or indirect connections and links through intermediary elements. Similarly, the terms “linked” may refer to direct linking with other elements, or indirect linking through intermediary elements.

[0069] In this disclosure, the phrase "coaxially arranged" is not limited to an arrangement where the two axes are perfectly aligned, but is an expression that allows for tolerances that inevitably occur during manufacturing and assembly. That is, the phrase "coaxially arranged" includes arrangements where the two axes are offset, within the tolerances permissible for the application in which the power transmission mechanism 100 is applied. Similarly, the phrase "rotating at the same rotational speed" is not limited to a state in which the two rotating bodies rotate at perfectly synchronized speeds, but is an expression that includes a state in which the two rotating bodies rotate with a difference in rotational speed within the tolerances permissible for the application in which the power transmission mechanism 100 is applied.

[0070] (Disclosure of technical ideas) This specification discloses several technical concepts, as listed in the following paragraphs. Some paragraphs are written in a multiple dependent form, where subsequent paragraphs optionally refer to preceding paragraphs. Furthermore, some paragraphs are written in a multiple dependent form, referring to other multiple dependent forms. These paragraphs written in multiple dependent forms define several technical concepts.

[0071] (Technical thought 1) A power transmission mechanism for transmitting power to an output rotating body (90) having two degrees of rotational freedom, A planetary gear mechanism (30) having a sun gear (31), a ring gear (33) arranged coaxially with the sun gear, and a planetary carrier (37) that rotatably supports a plurality of pinion gears (36) that mesh with the sun gear and the ring gear, An internal worm gear (60) is connected to the ring gear and rotates around the first shaft, which is one of the two shafts, A rotating frame (70) is coaxially arranged with the internal worm gear, supports the output rotating body so as to be rotatable around the second axis which is the other of the two axes, and is connected to the planetary carrier and rotates around the first axis, The system includes a worm wheel (80) that is rotatably supported on the rotating frame, meshes with the internal worm gear and the output rotating body, and rotates the output rotating body around the second axis by relative rotation between the rotating frame and the internal worm gear, The internal worm gear and the rotating frame are a power transmission mechanism that rotates in the same direction and at the same rotational speed due to the power transmission operation of the planetary gear mechanism, in which rotation is input to the planetary carrier with the sun gear fixed. (Technical thought 2) The system further comprises an output reduction mechanism (40) that reduces the rotation of the ring gear and transmits it to the internal worm gear, The power transmission mechanism according to technical concept 1, wherein the gear ratio of the output reduction mechanism is set to the reciprocal of the gear ratio of the planetary gear mechanism in the power transmission operation with the sun gear fixed, the planetary carrier as the input side and the ring gear as the output side. (Technical Thought 3) A first reduction mechanism (10) reduces the rotation by the first drive unit (110) and transmits it to the planetary carrier, A second reduction mechanism (20) reduces the rotation by the second drive unit (120) and transmits it to the sun gear, The system further comprises an output reduction mechanism (40) that reduces the rotation of the ring gear and transmits it to the internal worm gear, The gear ratios of the first reduction mechanism, the second reduction mechanism, and the output reduction mechanism are set so that the internal worm gear and the rotating frame rotate in the same direction and at the same rotational speed. This is a power transmission mechanism according to technical concept 1 or 2. (Technical Thought 4) The first axis is a roll axis (RA) defined in orientation along the rotational center axis (CA1) of the planetary gear mechanism, The power transmission mechanism according to any one of the technical concepts 1 to 3, wherein the second axis is a pitch axis (PA) defined to be perpendicular to the roll axis. (Technical Thought 5) The power transmission mechanism according to any one of technical concepts 1 to 4, wherein the rotating frame and the worm wheel rotate the output rotating body only around the second axis of the first and second axes by the power transmission operation of the planetary gear mechanism, in which rotation is input to the sun gear with the planetary carrier fixed. (Technical Thought 6) A power transmission mechanism according to any one of technical concepts 1 to 5, wherein the rotation by the first drive unit (110) is input to the planetary carrier, and the rotation by the second drive unit (120) is input to the sun gear, thereby causing the rotating frame to rotate the output rotating body around the first axis, while the worm wheel rotates the output rotating body around the second axis. [Explanation of Symbols]

[0072] 10 First reduction unit (first reduction mechanism), 20 Second reduction mechanism (second reduction mechanism), 30 Planetary gear mechanism (planetary gear mechanism), 31 Sun gear, 33 Ring gear, 36 Pinion gear, 37 Planetary carrier, 40 Reduction gear unit (output reduction mechanism), 60 Internal worm gear, 70 Rotating frame, 80 Worm wheel, 90 Saddle gear (output rotating body), 100 Power transmission mechanism, 110 Roll axis motor (first drive unit), 120 Pitch axis motor (second drive unit), CA1 Planetary central axis (rotation central axis), PA Pitch axis, RA Roll axis

Claims

1. A power transmission mechanism for transmitting power to an output rotating body (90) having two degrees of rotational freedom, A planetary gear mechanism (30) having a sun gear (31), a ring gear (33) arranged coaxially with the sun gear, and a planetary carrier (37) that rotatably supports a plurality of pinion gears (36) that mesh with the sun gear and the ring gear, An internal worm gear (60) is connected to the ring gear and rotates around the first shaft, which is one of the two shafts, A rotating frame (70) is coaxially arranged with the internal worm gear, supports the output rotating body so as to be rotatable around the second axis, which is the other of the two axes, and is connected to the planetary carrier and rotates around the first axis, The system includes a worm wheel (80) that is rotatably supported on the rotating frame, meshes with the internal worm gear and the output rotating body, and rotates the output rotating body around the second axis by relative rotation between the rotating frame and the internal worm gear, The internal worm gear and the rotating frame are a power transmission mechanism that rotates in the same direction and at the same rotational speed due to the power transmission operation of the planetary gear mechanism, in which rotation is input to the planetary carrier with the sun gear fixed.

2. The system further includes an output reduction mechanism (40) that reduces the rotation of the ring gear and transmits it to the internal worm gear, The power transmission mechanism according to claim 1, wherein the gear ratio of the output reduction mechanism is set to the reciprocal of the gear ratio of the planetary gear mechanism in the power transmission operation in which the planetary carrier is the input side and the ring gear is the output side, with the sun gear fixed.

3. A first reduction mechanism (10) reduces the rotation by the first drive unit (110) and transmits it to the planetary carrier, A second reduction mechanism (20) reduces the rotation by the second drive unit (120) and transmits it to the sun gear, The system further comprises an output reduction mechanism (40) that reduces the rotation of the ring gear and transmits it to the internal worm gear, The power transmission mechanism according to claim 1, wherein the gear ratios of the first reduction mechanism, the second reduction mechanism, and the output reduction mechanism are set so that the internal worm gear and the rotating frame rotate in the same direction and at the same rotational speed.

4. The first axis is a roll axis (RA) defined in orientation along the rotational center axis (CA1) of the planetary gear mechanism, The power transmission mechanism according to claim 1, wherein the second axis is a pitch axis (PA) defined to be perpendicular to the roll axis.

5. The power transmission mechanism according to claim 1, wherein the rotating frame and the worm wheel rotate the output rotating body only around the second axis of the first and second axes by the power transmission operation of the planetary gear mechanism, in which rotation is input to the sun gear with the planetary carrier fixed.

6. The power transmission mechanism according to claim 1, wherein the rotation by the first drive unit (110) is input to the planetary carrier, and the rotation by the second drive unit (120) is input to the sun gear, thereby causing the rotating frame to rotate the output rotating body around the first axis, while the worm wheel rotates the output rotating body around the second axis.

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