Robot joint structure

Abstract

A joint structure for a robot, the joint structure comprising a hollow first member (130), a second member (140), and an actuator (2) for relatively rotating the first member (130) and the second member (140) about a first axis (C), wherein: the actuator (2) includes a motor (3) housed within the first member (130) and rotating a shaft (8) about a second axis (D) intersecting the first axis (C), a reduction gear (4) for decelerating the rotation of the shaft (8) and transmitting the rotation to the second member (140), and a power transmission mechanism (5) for transmitting the power of the motor (3) to the reduction gear (4); and the power transmission mechanism (5) is provided with a first gear (15) fixed to the shaft (8), a second gear (16) coaxially mounted on the reduction gear (4) and meshing with the first gear (15), and a holder (6) for mounting the first gear (15) so as to be positionally adjustable in a direction along the second axis (D) and mounting the second gear (16) so as to be positionally adjustable in a direction along the first axis (C).

Description

Technical Field

[0001] The present disclosure relates to a joint structure of a robot.

Background Art

[0002] Conventionally, a joint structure of a robot is known in which a motor is housed inside an arm and the axis of the motor is arranged in a direction orthogonal to the rotation axis of the arm by using bevel gears (see, for example, Patent Document 1). It is difficult to adjust the meshing of the bevel gears while attaching the motor inside the arm. For this reason, a spur gear pair that does not require meshing adjustment is provided in the power transmission member between the motor and the speed reducer, and the bevel gear meshing can be adjusted outside the arm by configuring it to be separable at the position of the spur gear pair.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When configured to be separable in the spur gear pair, an additional part such as a spur gear pair is required, and a space for rotatably supporting a gear shaft having spur gears and bevel gears at both ends around an axis parallel to the axis of the speed reducer is required. That is, the cost increases and the mechanism parts to be housed inside the arm or the like become larger.

[0005] <​​​​​

[0006] One aspect of the present disclosure is a robot joint structure comprising a hollow first member, a second member, and an actuator that rotates the first member and the second member relative to each other about a first axis, wherein the actuator comprises a motor housed in the first member that rotates a shaft about a second axis intersecting the first axis, a reduction gear that reduces the rotation of the shaft and transmits it to the second member, and a power transmission mechanism that transmits the power of the motor to the reduction gear, wherein the power transmission mechanism comprises a first gear fixed to the shaft, a second gear coaxially mounted to the reduction gear and meshing with the first gear, and a holder that mounts the first gear so as to be position-adjustable in the direction along the second axis and the second gear so as to be position-adjustable in the direction along the first axis. [Brief explanation of the drawing]

[0007] [Figure 1] This is a schematic diagram showing an example of a robot equipped with an articulated structure according to one embodiment of the present disclosure. [Figure 2] Figure 1 is an enlarged longitudinal cross-sectional view showing the joint structure. [Figure 3] Figure 1 is an exploded longitudinal cross-sectional view showing the actuator provided in the joint structure. [Figure 4] Figure 3 is a perspective view showing an example of a first shim provided in the actuator. [Figure 5] Figure 3 is a perspective view showing an example of a second shim provided in the actuator. [Figure 6] Figure 3 is a longitudinal cross-sectional view showing the assembly diagram of the actuator. [Figure 7] Figure 4 is an exploded longitudinal cross-sectional view illustrating the process of installing the actuator inside the first arm. [Figure 8] This is an enlarged longitudinal cross-sectional view showing a modified example of the joint structure in Figure 1. [Figure 9] Figure 8 is a longitudinal cross-sectional view showing the assembly diagram of the actuator to be installed. [Modes for carrying out the invention]

[0008] A joint structure 1 of a robot 100 according to one embodiment of this disclosure will be described below with reference to the drawings. The robot 100 equipped with the joint structure 1 according to this embodiment is, for example, a vertical 6-axis articulated robot as shown in Figure 1, and comprises a base 110 installed on the floor surface F and a swivel body 120 that is rotatably supported relative to the base 110 about a vertical axis A.

[0009] Furthermore, the robot 100 includes a first arm (first member) 130 that is rotatably supported relative to the swivel body 120 around a horizontal axis B, and a second arm (second member) 140 that is rotatably supported relative to the first arm 130 around a horizontal first axis C. In addition, the robot 100 is equipped with a three-axis wrist unit 150 at the tip of the second arm 140.

[0010] The joint structure 1 of the robot 100 according to this embodiment is, as shown in Figure 2, a rotary joint structure configured, for example, between a first arm 130 and a second arm 140. This joint structure 1 comprises a first arm 130, a second arm 140, and an actuator 2 that rotates the second arm 140 around a first axis C relative to the first arm 130.

[0011] The first arm 130 and the second arm 140 are each configured as hollow cylindrical shapes with an internal space. The first arm 130 and the second arm 140 are equipped with openings 131 and 141 that connect the inside and outside, and lid members 132 and 142 that detachably open and close the openings 131 and 141.

[0012] The actuator 2 comprises a motor 3, a reduction gear 4, and a gearbox (power transmission mechanism) 5 that transmits the driving force of the motor 3 to the reduction gear 4. The motor 3 comprises a motor housing 7 having a motor flange 7a that is detachably fixed to a holder 6 of the gearbox 5 by bolts (not shown), and a shaft 8 that is rotatable around a second axis D extending from the center of the motor flange 7a in a direction perpendicular to the motor flange 7a. A spigot portion 9 having a cylindrical surface that protrudes one step from the motor flange 7a is provided radially inward of the motor flange 7a. The motor flange 7a is provided with a plurality of through holes (not shown) extending radially outward from the spigot portion 9 in the direction of the second axis D of the shaft 8.

[0013] The reduction gear 4 comprises a cylindrical case 10 that is detachably fixed to the holder 6 of the gearbox 5 by bolts (not shown), and an input shaft member 11 having an annular end face that is provided at one axial end of the case 10 and into which the driving force of the motor 3 is input. The reduction gear 4 also comprises an output shaft member 12 provided at the other end of the case 10 and which outputs the reduced driving force.

[0014] The end face of the case 10 on the side facing the input shaft member 11 is provided with a spigot portion 13 that extends axially with respect to the axis of the reduction gear 4. The case 10 of the reduction gear 4 is provided with a plurality of through holes (not shown) that extend radially outward from the spigot portion 13 in the axial direction of the reduction gear 4 and are spaced apart in the circumferential direction.

[0015] Furthermore, the output shaft member 12 of the reduction gear 4 is provided with a spigot portion 14 that fits into a recess 143 provided on the mounting surface 140a of the second arm 140, and a plurality of screw holes (not shown) for fastening bolts (not shown) that pass through through holes (not shown) provided on the mounting surface 140a of the second arm 140. A central hole 144 is provided in the center of the mounting surface 140a of the second arm 140, which opens the internal space of the second arm 140 to the outside. Furthermore, the reduction gear 4 has a hollow hole 4a that penetrates along the axis in the region containing its central axis.

[0016] The gear box 5 includes a first gear 15 fixed to the shaft 8 of the motor 3, a second gear 16 fixed to the input shaft member 11 of the speed reducer 4, and a holder 6 that defines a housing space for accommodating the first gear 15 and the second gear 16. The first gear 15 and the second gear 16 are constituted by bevel gears that mesh with each other.

[0017] The first gear 15 has a central hole (not shown) that penetrates the shaft 8 of the motor 3. As shown in FIG. 3, the first gear 15 is fixed to the shaft 8 of the motor 3 by fastening a nut 17 to the male thread 8b at the tip of the shaft 8 that penetrates the central hole. A key 8a is attached to the shaft 8 of the motor 3, and a key groove (not shown) for inserting the key 8a is provided in the central hole of the first gear 15. By inserting the key 8a into the key groove and fastening the nut 17 to the male thread 8b at the tip of the shaft 8 that penetrates the central hole, the first gear 15 is fixed to the shaft 8 of the motor 3.

[0018] The second gear 16 is a ring gear having a central hole 16a and has a pitch circle radius that is sufficiently larger than the pitch circle radius of the first gear 15. The second gear 16 includes a plurality of through holes (not shown) formed at intervals in the circumferential direction around the central hole 16a for passing bolts (not shown), and an inlay portion 19 that fits into a recess 18 provided at the tip of the input shaft member 11 of the speed reducer 4. By fitting the inlay portion 19 into the recess 18 and fastening the bolt that passes through the through hole to a screw hole (not shown) formed in the input shaft member 11, the second gear 16 is fixed to the end face of the input shaft member 11 in a positioned state.

[0019] The holder 6 is a hollow box-shaped member that defines a housing space inside, and includes a first mounting surface 20 for fixing the motor flange 7a with bolts (not shown), and a second mounting surface 21 that is orthogonal to the first mounting surface 20 and fixes the case 10 of the speed reducer 4 with bolts (not shown). Further, the holder 6 includes a third mounting surface 22 for fixing the holder 6 to a seating surface provided on the inner surface of the first arm 130 as shown in FIG. 2.

[0020] The first mounting surface 20 is provided with a first fitting hole 23 extending in a direction perpendicular to the first mounting surface 20 and connecting the inside and outside of the holder 6, and a plurality of screw holes (not shown) arranged radially outward from the first fitting hole 23 at circumferential intervals. The first fitting hole 23 is formed in a circular shape with an inner diameter larger than the outer diameter of the first gear 15 attached to the shaft 8, and the shaft 8 of the motor 3 is positioned radially by fitting the spigot portion 9 provided on the motor flange 7a into the first fitting hole 23.

[0021] The position of the screw hole relative to the center of the first fitting hole 23 coincides with the position of the through hole in the motor flange 7a relative to the second axis D of the shaft 8. By fastening a bolt (not shown) that passes through the through hole into the screw hole, the motor 3 can be fixed to the holder 6.

[0022] The second mounting surface 21 is provided with a second fitting hole 24 that extends in a direction perpendicular to the second mounting surface 21 and connects the inside and outside of the holder 6, and a plurality of screw holes (not shown) arranged radially outward from the second fitting hole 24 at circumferential intervals. The second fitting hole 24 is formed in a circular shape with an inner diameter larger than the outer diameter of the second gear 16 attached to the input shaft member 11, and the reduction gear 4 is positioned radially by fitting the spigot portion 13 provided on the end face of the case 10 of the reduction gear 4 on the input shaft member 11 side into the second fitting hole 24.

[0023] The position of the screw hole relative to the center of the second fitting hole 24 coincides with the position of the through hole provided in the case 10 relative to the axis, and the reducer 4 can be fixed to the holder 6 by fastening a bolt (not shown) that passes through the through hole into the screw hole.

[0024] The third mounting surface 22 is formed in an annular shape and is located radially outward from the second mounting surface 21. The seating surface inside the first arm 130 is provided with a third fitting hole 133 that penetrates in a direction perpendicular to the seating surface, and a plurality of through holes (not shown) arranged radially outward from the third fitting hole 133 at circumferential intervals. The third mounting surface 22 is provided with a spigot portion 22a that can be fitted into the third fitting hole 133, projecting in a direction perpendicular to the third mounting surface 22.

[0025] The third mounting surface 22 is provided with a plurality of screw holes (not shown) spaced circumferentially around the central axis of the second fitting hole 24. The holder 6 can be fixed to the first arm 130 in a positioned state by fitting the spigot portion 22a of the third mounting surface 22 into the third fitting hole 133 of the first arm 130 and fastening a bolt (not shown) that passes through the through hole around the third fitting hole 133 into the screw holes of the third mounting surface 22.

[0026] Furthermore, the holder 6 is provided with an opening 25 on the wall surface facing the second fitting hole 24, which opens the housing space to the outside along the extension of the first axis C. When the reduction gear 4 with the second gear 16 attached is mounted to the holder 6, the hollow hole 4a of the reduction gear 4, the central hole 16a of the second gear 16, and the opening 25 of the holder 6 are arranged in a line on the first axis C.

[0027] As shown in Figure 2, a cylindrical body 26 is positioned to penetrate the hollow hole 4a, the central hole 16a, and the opening 25. One end of the cylindrical body 26 is fixed to the second arm 140, and the other end of the cylindrical body 26 is rotatably sealed to the holder 6 by an annular sealing member 27 positioned in the opening 25. As a result, the space around the first axis C from the reduction gear 4 to the opening 25 is partitioned from the housing space in a sealed state. The internal space of the cylindrical body 26 then connects the internal space of the first arm 130 and the internal space of the second arm 140.

[0028] Furthermore, as shown in Figures 2 and 3, the joint structure 1 according to this embodiment includes a first shim 28 sandwiched between the motor flange 7a and the first mounting surface 20, and a second shim 29 sandwiched between the end face of the input shaft member 11 of the reduction gear 4 and the second gear 16. As shown in Figure 4, the first shim 28 has an outer shape equivalent to that of the motor flange 7a, a central hole 28a having an inner diameter equivalent to that of the first fitting hole 23, and a through hole 28b positioned to coincide with the through hole of the motor flange 7a.

[0029] The first shim 28 may be available in various thicknesses, or its thickness may be adjusted by changing the number of shims stacked, as shown in Figure 4. As the thickness of the first shim 28 is increased, the position of the motor flange 7a moves away from the first mounting surface 20 along the second axis D which is perpendicular to the first axis C. This allows the motor 3 and the first gear 15 fixed to the shaft 8 to be mounted on the holder 6 in a position adjustable along the second axis D.

[0030] As shown in Figure 5, the second shim 29 has an outer shape equivalent to the end face of the input shaft member 11 of the reduction gear 4, a central hole 29a with an inner diameter equal to or greater than the outer diameter of the spigot portion 19 of the second gear 16, and a through hole 29b positioned to coincide with the through hole of the second gear 16. The second shim 29 may also be available in various thicknesses, or its thickness may be adjusted by changing the number of layers stacked, as shown in Figure 5.

[0031] As the thickness of the second shim 29 is increased, the position of the second gear 16 relative to the end face of the input shaft member 11 of the reduction gear 4 moves away from the end face of the input shaft member 11 along the first axis C, so that the second gear 16 can be mounted on the holder 6 in a position that can be adjusted along the first axis C.

[0032] The operation of the joint structure 1 of the robot 100 according to this embodiment, which is configured in this manner, will be described below. To assemble the joint structure 1 of the robot 100 according to this embodiment, as shown in Figure 3, the motor assembly is manufactured by fitting the shaft 8 of the motor 3 into the central hole of the first gear 15 and fastening the nut 17 to the male screw 8b, thereby fixing the first gear 15 to the shaft 8.

[0033] Furthermore, a reducer assembly is manufactured by fixing the input shaft member 11 and the second gear 16 of the reducer 4 with a second shim 29 in between. The reducer assembly is manufactured by fitting the spigot portion 19 of the second gear 16 into the recess 18 of the input shaft member 11 and fastening bolts into the screw holes. At this time, the thickness of the second shim 29 is set to an appropriate thickness dimension, for example, the design value.

[0034] Next, the reducer assembly is attached to the holder 6 of the gearbox 5. The spigot portion 13 provided on the input shaft member 11 side of the case 10 of the reducer 4 is fitted into the second fitting hole 24 of the holder 6, and the bolt is fastened into the screw hole, thereby fixing the reducer assembly in a positioned state on the second mounting surface 21 of the holder 6.

[0035] Then, a first shim 28 of an appropriate thickness, for example, the design value, is placed between the motor flange 7a and the first mounting surface 20 of the holder 6, and the first gear 15 of the motor assembly is inserted into the internal space of the holder 6 through the first fitting hole 23 and engages with the second gear 16. After that, the motor 3 is fixed to the holder 6 by fastening bolts.

[0036] In this state, the meshing between the first gear 15 and the second gear 16 is checked, and the motor assembly is attached and detached to adjust the thickness of the first shim 28 until proper meshing is achieved. If proper meshing cannot be achieved by adjusting the thickness of the first shim 28 alone, the reduction gear assembly is removed, the second gear 16 is removed from the reduction gear 4, and the thickness of the second shim 29 is adjusted. In this way, as shown in Figure 6, an actuator 2 is constructed that includes a motor 3, a reduction gear 4, and a gearbox 5, with the meshing between the first gear 15 and the second gear 16 properly adjusted.

[0037] As shown in Figure 7, the actuator 2 configured in this way is inserted into the internal space through the opening 131 of the first arm 130 with the cover member 132 removed, and the spigot portion 22a provided on the third mounting surface 22 is fitted into the third fitting hole 133 provided on the first arm 130. The third mounting surface 22 is then brought into close contact with the seating surface inside the first arm 130, and the actuator 2 is fixed in a position on the first arm 130 by fastening bolts.

[0038] Furthermore, the spigot portion 14 of the output shaft member 12 of the reduction gear 4 is fitted into the recess 143 of the mounting surface 140a of the second arm 140, bringing the end face of the output shaft member 12 and the mounting surface 140a of the second arm 140 into close contact, and the two are fixed together by fastening bolts. Then, the cylindrical body 26 is inserted through the opening 141 with the cover member 142 removed, passing through the central hole 144 of the second arm 140, the hollow hole 4a of the reduction gear 4, and the opening 25 of the holder 6, fixing one end of the cylindrical body 26 to the second arm 140, and fitting the other end to the seal member 27 attached to the opening 25.

[0039] This constitutes the joint structure 1 of the robot 100 according to this embodiment. The cylindrical space containing the first axis C is sealed off from the internal space of the holder 6 and the internal space of the reducer 4 by the cylindrical body 26. By filling the internal space of the holder 6 and the internal space of the reducer 4 with a lubricant such as grease, the reducer 4, the first gear 15 and the second gear 16 are lubricated, while leakage of the lubricant into the inside of the cylindrical body 26 is prevented.

[0040] Thus, according to the joint structure 1 of the robot 100 in this embodiment, the actuator 2, which includes a motor 3, a reduction gear 4, and a gearbox 5, can be assembled outside the first arm 130 and then inserted into the first arm 130. This allows the meshing adjustment work between the first gear 15 and the second gear 16, which are bevel gears rotatable around mutually intersecting axes C and D, to be performed in a large space outside the first arm 130, which has the advantage of good workability.

[0041] The installation of the relatively large motor 3 into the internal space of the first arm 130 and the meshing adjustment work using the first shim 28 and the second shim 29 do not need to be performed in the narrow internal space of the first arm 130, thus greatly improving work efficiency. Furthermore, according to this embodiment, the first gear 15 fixed to the shaft 8 of the motor 3 and the second gear 16 coaxially mounted to the reduction gear 4 are directly meshed together without the interposition of spur gears or the like between the first gear 15 and the second gear 16. This has the advantages of reducing the number of parts, lowering costs, improving transmission efficiency, and miniaturizing the gearbox 5.

[0042] Furthermore, since the second gear 16 is made of a ring gear with a larger pitch circle radius than the first gear 15, the rotation of the motor 3 shaft 8 can be reduced between the first gear 15 and the second gear 16. Therefore, the reduction ratio in the reducer 4 can be reduced, making the reducer 4 smaller and less expensive.

[0043] Furthermore, a cylindrical body 26 is positioned to surround the region including the first axis C, passing through the hollow hole 4a of the hollow reduction gear 4, the central hole 16a of the second gear 16 which consists of a ring gear, and the opening 25 of the holder 6. This allows the internal space of the first arm 130 and the internal space of the second arm 140 to communicate through the internal space of the cylindrical body 26.

[0044] In other words, the wiring of the cable or other wire 160 from the first arm 130 to the second arm 140 can be carried out through the internal space of the cylindrical body 26, as shown by the dashed line in Figure 2. As a result, even if the second arm 140 rotates around the first axis C relative to the first arm 130, it is possible to avoid large bending or twisting of the wire 160, and the wire 160 can be maintained in a durable and sound condition.

[0045] In this embodiment, in addition to the first shim 28 between the motor flange 7a and the holder 6, the meshing is adjusted by a second shim 29 between the input shaft member 11 of the reduction gear 4 and the second gear 16. Alternatively, if the end face on the input shaft member 11 side of the reduction gear 4 can be precisely positioned relative to the holder 6, the second shim 29 may be omitted. The adjustment work using the first shim 28 does not involve removing the first gear 15 from the shaft 8, so it can be performed in a shorter time than the adjustment work using the second shim 29.

[0046] Furthermore, in this embodiment, the actuator 2 is mounted inside the first arm 130, but it may be mounted inside the second arm 140 instead. Furthermore, in this embodiment, the second gear 16 is fixed to the input shaft member 11 of the reduction gear 4. This structure is preferable when the input shaft member 11 of the reduction gear 4 has an end face to which the second gear 16 can be fixed.

[0047] Alternatively, if the input shaft member 11 is provided by a gear (not shown) that meshes with the input gear 31, such as a spur gear or spline gear, which is inserted in the center of the reduction gear 4, it is desirable to configure it as shown in Figure 8. That is, a structure can be adopted in which a gear member 33, having a second gear 30 made of a bevel gear at one end and the input gear 31 at the other end, is rotatably supported by a holder 6 with a bearing 32. In the figure, reference numeral 34 denotes a retaining plate that presses the bearing 32 to one end, and is fixed to the second gear 30 by a bolt (not shown).

[0048] In this case, the gears in the reduction gear 4 and the input gear 31 form a shaft coupling that allows relative movement in the direction along the first axis C and restricts relative rotation around the first axis C. Therefore, when adjusting the position of the second gear 30 in the direction along the first axis C, it is not necessary to move the reduction gear 4. The reduction gear 4 can be fixed to the first arm 130 by fitting the spigot portion 13 provided on the case 10 into the third fitting hole 133 provided on the first arm 130 from the outside. In this case, a second mounting surface 21 is provided on the outside of the first arm 130, and the reduction gear 4 is positioned radially by fitting the spigot portion 13 provided on the end face of the case 10 of the reduction gear 4 on the input shaft member 11 side into the third fitting hole 133.

[0049] In other words, the actuator 2 can be constructed by meshing and adjusting a motor assembly and a holder 6 in which a gear member 33 is supported by a bearing 32, on the outside of the first arm 130, as shown in Figure 9. After fixing the meshed actuator 2 inside the first arm 130, the reduction gear 4 can be fixed from the outside of the first arm 130.

[0050] This configuration requires a bearing 32 and a retaining plate 34 to rotatably support the gear member 33 in the holder 6, but it has the same effect as the above embodiment in that the meshing adjustment can be performed outside the first arm 130.

[0051] Furthermore, in this embodiment, bevel gears were used as examples for the first gear 15 and the second gear 16, whose axes C and D are perpendicular to each other. However, gears that intersect at angles other than 90° may be used, or other gears besides bevel gears that require meshing adjustment may be used. Furthermore, the shape, material, and thickness of the first shim 28 and the second shim 29 may be arbitrary. [Explanation of Symbols]

[0052] 1. Joint structure 2 Actuators 3 motors 4 Reducer 4a Hollow hole 5. Gearbox (power transmission mechanism) 6 holders 8 shafts 15 First gear 16.30 Second gear 16a center hole 25 Opening 26 Cylindrical body (cylindrical body) 100 robots 130 First arm (first member) 140 Second arm (second member) C 1st axis D 2nd axis

Claims

1. It comprises a hollow first member, a second member, and an actuator that rotates the first member and the second member relative to each other around a first axis, The actuator comprises a motor housed within the first member that rotates a shaft around a second axis intersecting the first axis, a reduction gear that reduces the rotation of the shaft and transmits it to the second member, and a power transmission mechanism that transmits the power of the motor to the reduction gear. The power transmission mechanism is removable from the first member and comprises a first gear fixed to the shaft, a second gear coaxially mounted to the reduction gear and meshing with the first gear, and a holder for mounting the first gear so as to be position-adjustable in the direction along the second axis and the second gear so as to be position-adjustable in the direction along the first axis.

2. The motor is mounted on the holder so as to be adjustable in a direction along the second axis. The robot joint structure according to claim 1, wherein the motor and the power transmission mechanism can be removed from the first member while assembled.

3. The reduction gear is detachably attached to the holder. The robot joint structure according to claim 1 or claim 2, wherein the second gear is fixed to the reduction gear so as to be positionable in a direction along the first axis.

4. The reduction gear is attached to the first member, The robot joint structure according to claim 1 or claim 2, wherein the second gear and the reduction gear are connected by a shaft coupling that allows relative movement in a direction along the first axis and restricts relative rotation about the first axis.

5. The holder comprises a housing space for housing the first gear and the second gear, and an opening that opens the housing space to the outside on the extension of the first axis. The second gear is a ring gear having a central hole, The reduction gear is provided with a hollow hole that penetrates along the first axis, A robot joint structure according to any one of claims 1 to 4, comprising a cylindrical body inserted through the hollow hole and the central hole up to the opening, which seals the space around the first axis from the reduction gear to the opening away from the housing space.

6. The robot joint structure according to any one of claims 1 to 5, wherein the pitch circle radius of the second gear is larger than the pitch circle radius of the first gear.

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