BEVEL GEAR SET AND WRIST MECHANISM OF INDUSTRIAL ROBOT USING SAID BEVEL GEAR SET

Abstract: A bevel gear unit comprising a bevel gear (11), a ball bearing (B1) coaxially mounted on the shaft of the bevel gear (11) and in contact with the back surface (17) thereof, a double spacer including an inner race spacer (12) and an outer race spacer (13) and mounted on the shaft of the bevel gear (11) behind the ball bearing (B1), ball bearings (B2, B3) mounted on the shaft of the bevel gear (11) behind the double spacer, and a bearing nut (15) screwed onto a threaded portion of the shaft of the bevel gear (11) behind the ball bearings (B2, B3). The axial length (l1) of the inner race spacer (12) is made smaller than the axial length (l2) of the outer race spacer (13) by a preloading allowance ( delta ), and the outer race spacer (13) is provided with threaded holes (t1) in the rear surface (f1) thereof. When applied to a mechanism having a plurality of coaxial bevel gears, particularly, to a wrist mechanism for an industrial robot, the bevel gear unit facilitates the preloading of the bearings.

Description: The present invention relates to a bevel gear unit comprising a plurality of coaxial bevel gears and facilitating preloading work and, more particularly, to such a bevel gear unit suitable for use in the wrist mechanism of an industrial robot. Some current industrial robots are provided with a wrist mechanism having two coaxial bevel gears, and Figs. 4A to 4C of the accompanying drawings show an essential portion of a conventional robot wrist mechanism for an industrial robot. As shown in Figs. 4A to 4C, a bevel gear 11' is attached to the extremity of a shaft A₁ for an α-drive, and a bevel gear 21' is attached to the extremity of an outer shaft A₂ for a β-drive. A ball bearing B₁ is pressed against the back surface of the inner bevel gear 11', and a ball bearing B₂ is held in place with a bearing nut 15. A protrusion P₀ formed in the inner circumference of the boss of the outer bevel gear 21' extends between the ball bearings B₁ and B₂. A shim 19 is provided between the front shoulder of the protrusion P₀ and the ball bearing B₁. A ball bearing B₂₁ is pressed against the back surface 27 of the outer bevel gear 21', and a ball bearing B₂₂ is held in place with a bearing nut 25. A protrusion P formed in a housing H extends between the ball bearings B₂₁ and B₂₂ , and the bearing nut 25 engages a threaded portion 26. When assembling the robot wrist mechanism, the ball bearings supporting the bevel gears are properly preloaded by adjusting the bearing nuts, and appropriate shims are used to adjust the tooth contact and backlash. A backlash adjustment is also necessary when the teeth of the bevel gears are abraded. The tooth contact adjustment for the outer bevel gear of the bevel gear unit shown in Figs. 4A to 4C of the conventional robot wrist mechanism requires a relatively easy procedure including the steps of, unfastening bolts S₂, pulling out an outer bevel gear assembly in the direction of the arrow F₁ as shown in Fig. 4B, changing the shim 29 for another shim 29, replacing the outer bevel gear assembly, and refastening the bolts S₂. On the other hand, the tooth contact adjustment for the inner bevel gear requires a relatively difficult procedure, as shown in Fig. 4C, including the steps of, unfastening the bolts S₂, removing the outer bevel gear assembly, removing the bearing nut 15, pulling out the inner bevel gear 11' in the direction of the arrow F₂, putting a new shim 19 on the boss of the inner bevel gear 11' so as to be in contact with the ball bearing B₁, inserting the inner bevel gear 11' in the outer bevel gear 21' so as to press the shim 19 against the ball bearing B₁ by the protrusion P₀, and fastening the bearing nut 15. Once the bearing nut 15 is thus removed, the preloading must be again performed for the ball bearings B₁ and B₂. Thus, the conventional bevel gear unit requires much time and difficult work for preloading the ball bearings and tooth contact adjustment when assembling the bevel gear unit or changing the shim. The present invention provides a compound bevel gear unit having a new construction, to solve the foregoing problems. According to the present invention, a multistage bevel gear unit comprising an inner bevel gear; a ball bearing coaxially mounted on the shaft of the bevel gear and in contact with the back surface thereof; and an outer bevel gear coaxially receiving the inner bevel gear therein; is characterised by a double spacer including an inner race spacer and an outer race spacer and mounted on the shaft of the inner bevel gear behind the ball bearing; ball bearings mounted on the shaft of the inner bevel gear behind the double spacer; a bearing nut screwed onto a threaded portion of the shaft of the inner bevel behind the ball bearings; the axial length of the inner race spacer being smaller than the axial length of the outer race spacer by a preloading allowance, and the outer race spacer being provided with threaded holes in a rear surface thereof; the outer bevel gear having a tubular body internally provided with an annular protrusion provided with bolt holes, and being detachably connected to the rear surface of the outer race spacer with bolts passing through the bolt holes and screwed into the threaded holes with a shim held therebetween; and the inner bevel gear including its ball bearings, the double spacer and the bearing unit being capable of being pulled axially out of the outer bevel gear after removing the bolts. The invention will be better understood by reference to Figs. 1A to 3C of the accompanying drawings, by way of example. As shown, inner race spacer 12 and an outer race spacer 13 are disposed concentrically between a ball bearing B₁ located on the shaft of a bevel gear 11 so as to be contiguous with the back surface of the bevel gear 11, and ball bearings B₂ and B₃ to be held in place with a bearing nut 15. The length ℓ₁ of the inner race spacer 12 is made smaller than the length ℓ₂ of the outer race spacer 13, by a preloading allowance δ, and threaded holes t₁ are formed in the rear surface f₁ of the outer race spacer 13. A double bevel gear unit is assembled by pressing an inner annular ridge P₂ formed in the inner circumference of an outer bevel gear 21 and provided with bolt holes h₁ against the rear surface f₁ of the outer race spacer, with a shim 19 held therebetween, and fastening the outer bevel gear 21 to the outer race spacer 13 with bolts S₁. Therefore, as shown in Fig. 1B, once the bearing nut 15 is fastened, while measuring the fastening force to apply an appropriate force K to the inner races of the ball bearings B₁ , B₂ , and B₃ for preloading, the shim 19 can be changed simply by removing the bolts S₁. Thus the shim 19 can be changed independently of the work for preloading the ball bearings B₁ , B₂ and B₃. The tooth contact of the inner bevel gear can be adjusted by using a shim without affecting the preloaded ball bearings, which reduces the time and labor needed for assembling the bevel gear unit, simplifies the assembling work, and prevents a deterioration of the reliability thereof. The present invention enables the parts maker to complete the bevel gear unit, and rationalizes the manufacturing process. In the accompanying drawings: Figure 1A is a sectional view of a bevel gear unit embodying the present invention; Figure 1B is a sectional view of the bevel gear unit after preloading; Figure 2 is an enlarged sectional view of spacers employed by the present invention; Figure 3A is a fragmentary sectional view of a robot wrist mechanism incorporating the present invention; Figure 3B is an explanatory sectional view showing a double bevel gear unit when removed from the robot wrist mechanism of Fig. 3A; Figure 3C is an explanatory sectional view separately showing an inner bevel gear assembly and an outer bevel gear assembly; Figure 4A is a fragmentary sectional view of a conventional robot wrist mechanism; Figure 4B is an explanatory sectional view showing a double bevel gear unit removed from the robot wrist mechanism of Fig. 4A; and Figure 4C is an explanatory sectional view separately showing the inner and outer bevel gear assemblies of the robot wrist mechanism of Fig. 4A. The present invention is applied to a wrist mechanism for an industrial robot. Figure 3A shows a double bevel gear unit included in the wrist mechanism, Figs. 3B and 3C are illustrations of assistance in explaining the function of the double bevel gear unit, and Figs. 1A, 1B and 2 are illustrations of assistance in explaining an inner bevel gear assembly. Referring to the drawings, an inner bevel gear 11 having an axis X-X engages a bevel gear 10 having an axis Y-Y perpendicular to the axis X-X, and an outer bevel gear 21 engages a bevel gear 20 included in the wrist mechanism. As shown in Figs. 1A and 1B, an inner bevel gear assembly comprises the inner bevel gear 11, a ball bearing B₁ having a radius r₁ located on the inner bevel gear 11 and in contact with the back surface 17 of the inner bevel gear 11, a double spacer including an inner race spacer 12 having a length ℓ₁ and an outer race spacer 13 having a radius r₁ and a length ℓ₂ and located on the inner bevel gear 11 contiguously with the ball bearing B₁ , a ball bearing B₂ and B₃ each having a radius r₃ and located on the bevel gear 11 next to the double spacer, and a bearing nut 15 having a radius r₂ and screwed onto a threaded portion 16 of the inner bevel gear 11. Threaded holes t₁ are formed in the rear surface f₁ of the outer race spacer 13 with the axes thereof in parallel to the axis X-X of the inner bevel gear 11, so that the major diameters of the threaded holes t₁ are at a tangent to a circle of radius r t . The length ℓ₂ of the outer race spacer is made greater than the length ℓ₁ of the inner race spacer by a preloading allowance δ (Fig. 2). The relationship among the radii of those components is: r₁ > r t > r₃ ≧ r₂. As shown in Figs. 3A to 3C, the outer bevel gear 21 is a tubular member provided at the front end thereof with gear teeth 28, and an outer annular ridge P₁ is formed on the outer circumference of the tubular body of the outer bevel gear 21 near the gear teeth 28. A ball bearing B₂₁ is mounted on the tubular body in contact with the rear surface f₂ of the outer annular protrusion P₁ , a double spacer having a preloading allowance and including an inner race spacer 22 and an outer race spacer 23 is mounted on the tubular body and in contact with the ball bearing B₂₁ , a ball bearing B₂₂ is mounted on the tubular body and in contact with the rear end of the double spacer, and a bearing nut 25 is screwed onto a threaded portion 26 of the tubular body, to fasten the inner races of the ball bearings B₂₁ and B₂₂ , and the double spacer, through a collar 24, to the tubular body. An inner annular protrusion P₂ having an inside radius r₁ (r₁ ≧ r₂) provided with bolt holes h₁ is formed on the inner circumference of the tubular body, and a ring R having an inside diameter greater than the outside diameter of the collar 24 and provided with bolt holes h₂ is provided between the ball bearing B₂₂ and the bearing nut 25. Threaded holes t₂ are formed in the inner shoulder f₃ of a wrist case C. The tooth contact of the outer bevel gear 21 of the wrist mechanism is adjusted by a shim 29. The bearing nut 25 is fastened properly for the preloading adjustment of the ball bearings B₂₁ and B₂₂ by pressing the inner race of the ball bearing B₂₂ through the collar 24 and pressing the inner race of the ball bearing B₂₁ through the inner race of the ball bearing B₂₂ and the inner race spacer 22. Bolts S₂ are screwed through the ring R in the threaded holes t₂ of the wrist case C to fasten the ring R to the wrist case C. The outer race spacer 13 mounted on the inner bevel gear 11 is fastened to the front surface of the inner annular protrusion P₂ of the outer bevel gear 21 with a shim 19 held between the front surface of the inner annular protrusion P₂ and the rear surface f₁ of the outer race spacer 13 by screwing bolts S₁ through the bolt holes h₁ in the threaded holes t₁. The bearing nut 15 is fastened as shown in Fig. 1B to shift the respective inner races of the ball bearings B₃ , B₂ and B₁ axially relative to the corresponding outer races for preloading, by applying an axial force K to the inner races of the ball bearings B₃ and B₂ and applying a reaction force K to the inner race of the ball bearing B₁ by the back surface 17 of the inner bevel gear 11. When changing the shim 19 of the inner bevel gear assembly, the bolts S₁ are removed and the inner bevel gear assembly is pulled out in the direction of the arrow F₂ from the outer bevel gear assembly, as shown in Fig. 3C, the shim 19 is changed for another shim, and then the inner and outer bevel gear assemblies are combined again with the bolts S₁. Thus, the bearing nut 15 need not be moved during the changing of the shim 19, and thus the previously adjusted preloading condition of the ball bearings B₁ , B₂ and B₃ is not changed; i.e., the shim 19 can be changed without changing the preloading condition of the inner bevel gear assembly as shown in Fig. 1B. Although the inner bevel gear assembly in this embodiment is provided with the two ball bearings B₂ and B₃ having the same outside diameter, the inner bevel gear assembly may be provided with only a single ball bearing between the double spacer and the bearing nut. Essentially, the preloading of the ball bearing or bearings is possible provided that the inner race spacer 12 is in contact with the inner races of the ball bearings, respectively, on the opposite sides thereof, and the outer race spacer 13 is in contact with the outer races of the ball bearings, respectively, on the opposite sides thereof. Although the present invention has been described as applied to a wrist mechanism for an industrial robot, the present invention is also applicable to mechanisms having a plurality of coaxial bevel gears, namely, a multistage bevel gear unit comprising a plurality of coaxial bevel gears associated with each other by ball bearings.

Claims: A multistage bevel gear unit comprising an inner bevel gear (11); a ball bearing (B₁) coaxially mounted on the shaft of the bevel gear (11) and in contact with the back surface (17) thereof; and an outer bevel gear (21) coaxially receiving the inner bevel gear therein; characterised by a double spacer including an inner race spacer (12) and an outer race spacer (13) and mounted on the shaft of the inner bevel gear (11) behind the ball bearing (B₁); ball bearings (B₂, B₃) mounted on the shaft of the inner bevel gear behind the double spacer; a bearing nut (15) screwed onto a threaded portion of the shaft of the inner bevel gear (11) behind the ball bearings (B₂, B₃); the axial length ( l ₁) of the inner race spacer (12) being smaller than the axial length ( l ₂)of the outer race spacer (13) by a preloading allowance (δ), and the outer race spacer (13) being provided with threaded holes (t₁) in a rear surface (f₁) thereof; the outer bevel gear having a tubular body internally provided with an annular protrusion (P₂) provided with bolt holes (h₁), and being detachably connected to the rear surface (f₁) of the outer race spacer (13) with bolts (S₁) passing through the bolt holes (h₁) and screwed into the threaded holes (t₁) with a shim (19) held therebetween; and the inner bevel gear including its ball bearings (B₁, B₂, B₃), the double spacer and the bearing unit (15) being capable of being pulled axially out of the outer bevel gear (21) after removing the bolts (S₁). A wrist mechanism for an industrial robot provided with the multistage bevel gear unit in accordance with claim 1 in a wrist case.

Inventors: IWASAKI KYOZI FANUC MANSION HA, MIZUNO HITOSHI FANUC MANSION H, TORII NOBUTOSHI FUYO HAITSU, IWASAKI, KYOZI FANUC MANSION HARIMOMI 8-209, MIZUNO, HITOSHI FANUC MANSION HARIMOMI 8-310, TORII, NOBUTOSHI FUYO HAITSU 308
Applicants: FANUC LTD, FANUC LTD.
Application year: 1989
Main classification: F16H1
IPC codes: F16H1, F16C35, B25J9, B25J17