Toroidal gearbox for slewing mechanisms

Abstract

A high transmission ratio gearbox of ring shape for easy integration inside mechanisms with limited space and robotic rotating joints for moving robotic arms. The toroidal gearbox includes at least one dual function gear, a toroidal spiral face drive to mesh with the at least one dual function gear and a cylindrical gear to mesh with the at least one dual function gear.

Claims

1. A toroidal gearbox comprising: at least one dual function gear; a toroidal spiral face drive to mesh with said at least one dual function gear; an output gear to mesh with said at least one dual function gear: an internal ring; a spiral face drive bearing mounted on said internal ring and supporting said toroidal spiral face drive; an output gear bearing mounted on said internal ring and supporting said output gear; a gear shaft mounted on said internal ring and supporting said at least one dual function gear; and shaft bearings mounted on said internal ring and supporting said gear shaft.

2. The gearbox of claim 1, wherein said at least one dual function gear has teeth which have a combined worm and cylindrical gear teeth shape.

3. The gearbox of claim 1, wherein said at least one dual function gear has an axis perpendicular to a central axis of said toroidal spiral face drive.

4. The gearbox of claim 1, wherein said at least one dual function gear has an axis perpendicular to a central axis of said cylindrical gear.

5. The gearbox of claim 1, wherein said toroidal spiral face drive has at least one spiral start.

6. The gearbox of claim 1, wherein said output gear is one of: a spur gear, and a helical gear.

7. The gearbox of claim 2, wherein said at least one dual function gear has one of: a barrel profile and an hourglass profile.

8. The gearbox of claim 2, wherein at least a portion of said teeth are cut with crowning.

9. The gearbox of claim 1, comprising a toroidal motor to drive said toroidal spiral face drive.

10. The gearbox of claim 1, wherein said toroidal spiral face drive and said output gear have a toroidal shape surrounding a circular opening centered around a gearbox axis.

11. The gearbox of claim 1, wherein said at least one dual function gear is a plurality of said dual function gears arranged in a planetary arrangement.

12. The gearbox of claim 1, wherein said shaft bearings are rolling bearings fabricated from at least one of: steel, plastic, ceramic, and bronze.

13. The gearbox of claim 1, wherein said shaft bearings are at least one of: rolling bearings, sliding bearings, and magnetic bearings.

14. The gearbox of claim 1, wherein said gearbox is configured to transmit rotational reverse motion from said cylindrical gear to said toroidal spiral face drive.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

(2) FIG. 1A is a schematic illustration of an internal cylindrical gear driven internally by a cylindrical drive;

(3) FIG. 1B is a schematic illustration of an external worm gear driven externally by a worm drive;

(4) FIGS. 2A and 2B are an expanded and a schematic illustration of a toroidal gearbox, constructed and operative in accordance with a preferred embodiment of the present invention;

(5) FIGS. 3A, 3B and 3C are bottom, sectional and isometric views, respectively, of a spiral face drive, useful in the gearbox of FIG. 2A;

(6) FIGS. 3D and 3E are schematic illustrations of a revolution of the spiral face drive when meshed with a cylindrical gear;

(7) FIGS. 4A, 4B and 4C are schematic illustrations of spiral rack profiles;

(8) FIGS. 5A, 5B and 5C are isometric views of a spur gear, a worm gear and a dual function gear having combined spur and worm gear profiles, respectively;

(9) FIGS. 6A and 6B are schematic illustrations of a toroidal gearbox with multiple dual function gears, constructed and operative in accordance with a second preferred embodiment of the present invention;

(10) FIGS. 7A, 7B and 7C are top, sectional and exploded views of a complete toroidal gearbox, constructed and operative in accordance with a third preferred embodiment of the present invention; and

(11) FIG. 8 is a schematic illustration of a toroidal gearbox with an externally geared output gear, constructed and operative in accordance with a fourth preferred embodiment of the present invention.

(12) It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

(13) In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

(14) Applicant has realized that slewing systems are assemblies that are customized for each application. The design of these customized solutions requires a high level of engineering expertise and design time to achieve requisite high positioning accuracy.

(15) Applicant has also realized that slewing assemblies may require electricity, fluids, optical signals, electromagnetic waves, cables and other physical objects to pass through the slewing assembly to the mounted equipment. This requires a central passage, usually in a cylindrical form, in order to allow the integration of slip rings for current transmission and rotary joints for waveguide and fluid transmission.

(16) Applicant realized that a slewing assembly solution in a toroidal format may be achieved using worm gearing and worm meshing, and by converting perpendicular meshing to parallel meshing, within a concentric axis gearbox.

(17) Reference is made to FIGS. 2A and 2B, which illustrate a toroidal gearbox 20, constructed and operative in accordance with a preferred embodiment of the present invention. Gearbox 20 comprises a toroidal motor 21, a spiral face drive 22, a dual function gear 23, and an output gear 25, where toroidal motor 21, spiral face drive 22 and output gear 25 may all have a toroidal shape surrounding a circular opening 5 centered around a gearbox axis 6. Dual function gear 23, which may have an axis 7 which may be perpendicular to gearbox axis 6, may be small enough not to operate within circular opening 5.

(18) In accordance with a preferred embodiment of the present invention and as seen in FIG. 2B, it is through circular opening 5 that physical objects, such as cables 8, may pass.

(19) Toroidal motor 21 may drive spiral face drive 22 around its central axis, which may typically be parallel to gearbox axis 6. In accordance with a preferred embodiment of the present invention, spiral face drive 22 may interface with, and in turn, may drive dual function gear 23 to turn around its perpendicular axis 7. Since dual function gear 23 may be geared to interface simultaneously with both spiral face drive 22 and output gear 25, the turning of dual function gear 23 around its perpendicular axis 7 may drive output gear 25 around its central axis, which may be gearbox axis 6 or may be an axis parallel to it.

(20) Applicant has realized that the rack profile of a spiral face drive is analogous to a cylindrical gear rack profile, and hence may mesh with and drive another cylindrical gear. Reference is made to FIGS. 3A, 3B and 3C, which are bottom, sectional (along line B-B in FIG. 3A), and isometric views, respectively, of spiral face drive 22. FIG. 3A illustrates the bottom view of spiral face drive 22 and shows a rack profile 31 along a spiral curve. Rack profile 31, which has a trough 32 (FIG. 3B) between peaks 33 of spiral rack profile 31, is similar to rack profiles described by the teeth and gashes of a cylindrical gear. FIG. 3C shows, in an isometric view, how a cylindrical gear 35 meshes with spiral track 32.

(21) It should be noted that rack profile 31 may be analogous to a cylindrical gear rack profile with straight lines; however, it may also have other profiles which may mesh with other cylindrical gear teeth profiles, such as helical profiles. Furthermore, the profiles of the gear teeth may be any conjugating profile, such as, but not limited to, ‘involute’ and ‘cycloid’ profiles.

(22) Reference is made to FIGS. 3D and 3E which together illustrate what happens after a single revolution of spiral face drive 22 when meshed with cylindrical gear 35. FIGS. 3D and 3E have a point marked on their cylindrical gear 35, where the point is indicated as 36 in FIG. 3D and as 36′ in FIG. 3E. At the beginning of the rotation, shown in FIG. 3D, point 36 is along a horizontal line 38 while, at the end of the rotation, shown in FIG. 3E, a radial line 39 defining point 36′ has moved from the horizontal such that point 36′ is above horizontal line 38 by an angle a. In other words, as spiral face drive 22 advances by a single revolution, it may advance cylindrical gear 35 by a fixed amount, such as one tooth. A spiral track is analogous to a start on a worm drive, as mentioned hereinabove. If there are multiple spirals, cylindrical gear 35 may advance by an equivalent number of teeth.

(23) Reference is now made to FIGS. 4A, 4B and 4C which illustrate different spiral rack profiles. FIG. 4A illustrates a single spiral profile 40 which can be described by parametric equation 1:
r(t,θ(t))  (1)
where r is the radius as function of a parameter t, and θ(t) is the phase angle as function of t.

(24) Equation 1 may be converted to a Cartesian coordinate system where each point on the spiral in FIG. 4A is described by coordinates (x, y) as shown in equations 2 and 3:
x=N.Math.pitch.Math.t.Math.cos(2.Math.π.Math.t+φ(u,N))  (2)
y=N.Math.pitch.Math.t.Math.sin(2.Math.π.Math.t+φ(u,N)),a<t<b  (3)
where N is the number of spirals in the range of {1, 2, 3 . . . n}, pitch is the pitch of a gear, labeled 41 in FIG. 4A, and φ(u, N) is the phase angle, which is equal to

(25) $u\frac{{360}^{\circ }}{N},$
where u is the spiral number. The spiral may be “right handed” (i.e., counter clockwise) or “left handed” (i.e., clockwise). In the latter case, 90° is added to phase angle φ(u, N).

(26) The linear distance during a single rotation of spiral *face drive 22 is a function of the number of spiral starts and the pitch, as described by equation 4:
distance=N.Math.pitch  (4)

(27) FIGS. 4B and 4C illustrate two exemplary rack profiles and respectively show a spiral rack profile 43 with two spirals, or two starts, and a spiral rack profile 45 with three spirals, or three starts. It will be appreciated that other rack profiles, with different numbers of spirals, are also possible.

(28) As mentioned hereinabove, dual function gear 23 meshes with spiral face drive 22 and output gear 25 simultaneously. It will be appreciated that in order to mesh with spiral face drive 22, dual function gear 23 may require a cylindrical gear teeth shape, similar to that of a spur, helical or other cylindrical gear. However, in order to mesh with and drive output gear 25, dual function gear 23 may also require a worm or screw teeth shape. In accordance with a preferred embodiment of the present invention, dual function gear 23 has teeth which have a combined worm and cylindrical gear teeth shape.

(29) Reference is now made to FIGS. 5A and 5B which illustrate two gears from which dual function gear 23 may be designed. FIG. 5A shows an exemplary spur gear having cylindrical gear teeth 51 which can mesh with spiral face drive 22. FIG. 5B shows an exemplary worm gear having worm teeth 52, where each tooth is curved rather than straight, which may mesh with output gear 25.

(30) As mentioned hereinabove, dual function gear 23 has teeth whose shape is formed of a combination of worm teeth 52 and cylindrical gear teeth 51, as shown in FIG. 5C, to which reference is now briefly made. Cylindrical gear teeth 51 may be implemented along the helical curve of worm teeth 52, resulting in a combined tooth profile for dual function gear 23.

(31) It will be appreciated that dual function gear 23, as a whole, may have a short worm profile, or it may have a barrel profile, similar to those used in internal gear applications, or it may have an hourglass profile as used in external gear applications. Alternatively, the teeth of dual function gear 23 may be inclined with respect to output gear 25 which may cause the central axis of output gear 25 to be inclined to gearbox axis 6. the teeth of dual function gear 23 may also be crowned or may have other longitudinal profile modifications similar to crowning.

(32) Attention is once again drawn to FIG. 2A. Spiral face drive 22 may drive dual function gear 23 via the portion of its profile which is similar to cylindrical teeth 51, of which there may be Z.sub.Cyl teeth. As discussed above with respect to FIGS. 3D and 3E, a single revolution of spiral face drive 22 may advance dual function gear 23 by a number of teeth equal to the number N of spirals on spiral face drive 22. Dual function gear 23 may simultaneously mesh with output gear 25 via the portion of its profile which is similar to worm teeth 52, of which there may be Z.sub.Wormgear teeth. Moreover, dual function gear 23 may also have a number N.sub.Worm of starts of its teeth, similar to the starts of a worm gear. When dual function gear 23 may rotate a single turn) (360° around its axis of rotation 7, it may advance output gear 25 by N.sub.Worm teeth. Accordingly, a gearbox transmission ratio i of toroidal gearbox 20 may be characterized by equation 5:

(33) $\begin{array}{cc}i=\frac{N_{\mathrm{input}}}{N_{\mathrm{Output}}}=\frac{Z_{\mathrm{Cyl}}}{N_{\mathrm{starts}}}.Math.\frac{Z_{\mathrm{Wormgear}}}{N_{\mathrm{Worm}}}& \left(5\right)\end{array}$

(34) where N.sub.Input is the number of input revolutions of spiral face drive 22, and N.sub.Output is the number of output revolutions of output gear 25.

(35) Gearbox ratio i may range from a low ratio of 1:30 to a high ratio of 1:1000. A low ratio may be achieved, for example, using Z.sub.Cyl=6, N.sub.Starts=3, Z.sub.Wormgear=45 and N.sub.Worm=3. A high ratio may be achieved, for example, using Z.sub.Cyl=10, N.sub.Starts=1, Z.sub.Wormgear=100 and N.sub.Worm=1. It should be noted that the gearing ratio may be as low as 1:1.

(36) Gearbox ratio i may reduce the motor speed by a factor of i, as described by equation 6:

(37) $\begin{array}{cc}{S}_{\mathrm{output}}=\frac{S_{\mathrm{input}}}{i}& \left(6\right)\end{array}$

(38) where S.sub.Output equals the gearbox output speed, and S.sub.input equals the gearbox input speed.

(39) Correspondingly, gearbox ratio i increases the output torque as described in equation 7:
T.sub.output=T.sub.input.Math.i  (7)

(40) where T.sub.output equals the gearbox output torque and T.sub.input equals the gearbox input torque. It should be noted that toroidal gearbox 20 may also have frictional losses, as known in the art, that have not been shown in this example.

(41) The forces acting between dual function gear 23 and output gear 25 may cause stresses and deflection of teeth. These stresses and the strength of gearing may limit the load size that can be handled by toroidal gearbox 20.

(42) In an alternate embodiment, a plurality of dual function gears 23 may be positioned in a planetary fashion, around gearbox axis 6, to distribute torque between them. In this embodiment, toroidal gearbox 20 may have a plurality N.sub.s of dual function gears 23 each meshing with output gear 25 and situated in planetary form (i.e., equidistant) around gearbox axis 6. Attention is briefly drawn to FIGS. 6A and 6B which respectively illustrate a toroidal gearbox 20′ with two dual function gears 23′ arranged 180 degrees apart, and a toroidal gearbox 20″ with three dual function gears 23″ arranged 120 degrees apart. Such an arrangement may divide transmitted torque across all dual function gears 23 as described by equation 8:
T=T.sub.allowed.Math.N.sub.s  (8)

(43) where T is the total torque capacity, and T.sub.allowed is the allowed torque transmission capacity per dual function gear 23.

(44) It should be noted that when a plurality of dual function gears 23 are used, the forces acting between each gear 23 may vary, due to imperfections of geometry caused by production technology. Since loads cannot be shared equally between each gear 23, transmission ability may be decreased by a factor c, called the load sharing efficiency, where 0<c<1 and for a perfect geometry c.fwdarw.1.

(45) It will be appreciated that, when multiple dual function gears 23 are located as planetary gears, their locations with respect to each should be determined as a function of phase angle limitations, as known in the design of planetary gear trains. In addition, and in accordance with a preferred embodiment of the present invention, the location should also be determined from the number N.sub.starts of starts and number of teeth Z.sub.Wormgear and Z.sub.Spiral of the output gear and the spiral face gear, respectively. Accordingly, the total torque capacity of equation 8 may be better described by equation 9:
T=c.Math.T.sub.allowed.Math.N.sub.s  (9)

(46) Reference is made to FIGS. 7A, 7B and 7C which illustrate multiple views of complete toroidal gearbox 20. FIG. 7A illustrates a top view of toroidal gearbox 20, showing motor 21, the outside of output gear 25, and the inside of an internal ring 26 or cage. FIG. 7B illustrates a sectional view of toroidal gearbox 20, showing a single instance of dual function gear 23, and FIG. 7C illustrates an exploded view of complete toroidal gearbox 20, comprising dual function gear 23, output gear 25, spiral face gear 22, an internal ring 26 upon which the other gears may be mounted, output gear bearings 27, spiral face gear bearings 28, shaft bearings 29, and a gear shaft 24.

(47) Dual function gear 23 may be mounted on internal ring 26 using gear shaft 24 and associated shaft bearings 29. Spiral face gear 22 may be mounted on internal ring 26 using spiral face gear bearings 28 and may then be meshed with dual function gear 23. Output gear 25 may be mounted on internal ring 26 using output gear bearings 27, also known as slewing bearings, and may then be meshed with dual function gear 23. Toroidal gearbox 20 may be contained in a housing (not shown).

(48) Bearings 27 and 28 may be rolling or sliding bearings and may be magnetic bearings or other known bearings capable of carrying axial, radial and moment loads. These may be made from steel, plastic, ceramic, bronze, or other known materials that provide a low frictional rotation. Bearings 29 may be rolling bearings made of steel, bronze, plastic, ceramic or combination of mentioned materials or alternative materials or other known materials which provide an ability to rotate with low friction. Alternatively, bronze bushings, plastic bushings, or other materials with friction reducing coatings, like DLC, dry lubricants, Teflon coatings, or other known solutions, may be used to keep friction low during rotation.

(49) It will be appreciated that toroidal gearbox 20 may be operated in 3 modes: (1) spiral face gear 22 may be fixed to a housing such that rotation of the entire assembly results in rotation of output gear 25; (2) output gear 25 may be fixed to the housing such that rotation of spiral face gear 22 results in rotation of the entire assembly; and (3) spiral face gear 22 and output gear 25 may be free to rotate with respect to the housing. It will be appreciated that toroidal gearbox 20 may also comprise a plurality of dual function gears 23, as described herein above. In an alternative preferred embodiment of the present invention, shown in FIG. 8 to which reference is now briefly made, a toroidal gearbox 20′″ may comprise an externally geared output gear 25′. Toroidal gearbox 20′″ comprises an externally geared, output gear 25′. Toroidal gear box 20′″ may also comprise a plurality of dual function gears 23 as described hereinabove.

(50) It will also be appreciated that each of toroidal gearboxes 20, 20′, 20″ and 20′″ may be fitted with an anti-backlash mechanism.

(51) It will be further appreciated that, for low transmission ratios, toroidal gearboxes 20, 20′, 20″ and 20′″ may be operated so as to transmit rotational reverse motion (i.e., from output gear 25 to spiral face drive 22).

(52) It will be appreciated that the various toroidal gearboxes 20, 20′, 20″ and 20′″ may provide a high drive torque vs. mass and volume, through high ratio gearing and dual gearing techniques. Dual gearing ratios are higher than single gear solutions and are able to generate higher torques required for loads that develop high moments of inertia under high acceleration. The toroidal gearboxes may also increase effective load handling through use of multiple dual function gears 23 as described hereinabove.

(53) It will be further appreciated that toroidal gearboxes 20, 20′, 20″ and 20′″, which comprises dual gearing and a toroidal motor, may provide an effective off-the-shelf, drop-in solution that may remove the need for expert design services and fabrication, lowering costs and design cycles. The design also incorporates opening 5 (FIG. 2A) through which to thread supply lines, waveguides and optical lines. Slip rings may easily be integrated into the design for device electrical supply. Toroidal gearboxes 20, 20′, 20″ and 20′″ may provide a high transmission ratio gearbox device of ring shape for easy integration inside mechanisms with limited space, such as robotic rotating joints for moving robotic arms.

(54) It will be appreciated that the toroidal gearboxes of the present invention may be installed into the same housing as rolling bearings, for use in positioning mechanisms with rotary joints.

(55) While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.