Patent ID: 12253159

DETAILED DESCRIPTION

The present disclosure relates to mechanical gear assemblies, gear systems, other types of power transmission assemblies and systems, and methods in which interfacing gears or other corresponding interfacing structures are not only configured to engage one another physically in at least some operational circumstances, but also configured to engage one another magnetically in at least some operational circumstances. Further, in at least some embodiments encompassed herein, the present disclosure relates to a magnetically-assisted mechanical gear mesh or gear assembly, which includes a plurality of ferromagnetic gears arranged with a magnetomotive force (MMF) source to form a magnetic circuit. The magnetic circuit serves to impose attractive force(s) between the interfacing gears, so as to bias the gears such that contact between the gears occurs along particular sides of the gear teeth of the gears (rather than along the opposite sides of the gear teeth), which in turn can reduce backlash between the interfacing gears, or even eliminate backlash between the interfacing gears and thereby achieve zero backlash operation. Also, in at least some other embodiments encompassed herein, the present disclosure relates to a magnetically-assisted mechanical gear mesh or gear assembly that employs permanent magnet gears to achieve magnetic forces between the interfacing gears. Further, in at least some additional embodiments encompassed herein, the present disclosure relates to other types of magnetically-assisted mechanical power transmission systems that employ electromagnets and/or permanent magnets to achieve power transmission between interfacing gears, screws, nuts, racks, pinions, and other types of interfacing structures.

Referring toFIG.1, a cutaway view is provided of a gear assembly100having two interfacing gears, including a first gear that is a driving gear102and a second gear that is a driven gear104. In the present example, each of the driving gear102and driven gear104is a respective spur gear. Nevertheless, the present disclosure is intended to encompass any of a variety of embodiments that employ any of a variety of different types of gears and gear assemblies, including embodiments that employ, for example, helical gears, bevel gears, worm gears, and planetary gears. Additionally, as will be described further with respect toFIG.2, the gear assembly100can be considered to be part of a magnetically-assisted mechanical gear system in which forces are communicated between the driving gear102and the driven gear104not only mechanically but also magnetically, and which (from a magnetic standpoint) can be represented as a magnetic circuit200as shown inFIG.2.

More particularly as shown inFIG.1, the driving gear102includes driving gear teeth106arranged around the driving gear along a first circular path represented by a first dashed line108and extending about a first central axis (not shown) of the driving gear. Also, the driven gear104includes driven gear teeth110arranged along a second circular path represented by a second dashed line112and extending about a second central axis (not shown) of the driven gear. In this illustration, the first and second dashed lines108and112respectively extend substantially through respective midregions of the driving gear teeth106and driven gear teeth110, respectively, such that, when the driving gear102is interfacing the driven gear104, the first and second dashed lines108and112are tangent with one another at a location114at which the driving gear teeth106and driven gear teeth110are most closely intermeshed.

Further as shown inFIG.1, the driving gear102particularly is rotated relative to the driven gear104so that a counter-clockwise-facing side116of a first one118of the driving gear teeth106is physically in contact with a counter-clockwise-facing side120of a first one122of the driven gear teeth110. Consequently, a gap124exists between a clockwise-facing side126of the first one118of the driving gear teeth106and a clockwise-facing side128of a successive (second) one130of the driven gear teeth110that is located counter-clockwise of the first one122of the driven gear teeth110.

Additionally, in the present embodiment, a magnetic field is applied in relation to the interfacing driving and driven gears102and104that creates an attractive magnetic force between the gears. The strongest attractive magnetic force between the driving and driven gears102and104occurs between the counter-clockwise-facing sides116and120of the first ones118and122of the driving and driven gears, respectively. In particular, the attractive magnetic force is strongest at a location132at which the counter-clockwise-facing side116of the first one118of the driving gear teeth106is in contact with the counter-clockwise-facing side120of the first one122of the driven gear teeth110, within a region134, due to magnetic flux flowing through that location132as indicated by a primary magnetic flux path136shown inFIG.1. By comparison, even though there is an attractive magnetic force also between the clockwise-facing side126of the first one118of the driving gear teeth106and the clockwise-facing side128of the successive one130of the driven gear teeth110, such as within a region138, that attractive magnetic force is substantially weaker than the attractive magnetic force within the region134at the location132due to the gap124.

In the present illustration ofFIG.1, it can be assumed that the driving gear102is rotating in a counter-clockwise direction indicated by a first arrow140, and thereby causing the driven gear104to rotate in a clockwise direction indicated by a second arrow142, due to contact between respective contacting pairs of the driving gear teeth106and driven gear teeth110. The driven gear teeth110respectively are pushed by the driving gear teeth106as the respective counter-clockwise-facing sides of the respective driving gear teeth come in to physical contact with the respective counter-clockwise-facing sides of the respective driven gear teeth. As an example, as shown inFIG.1, the first one118of the driving gear teeth106can be understood to be physically pushing against the first one122of the driven gear teeth110when the driving gear102is rotating in the counter-clockwise direction consistent with the first arrow140.

In a conventional arrangement, the existence of the gap124would be a source of backlash movement during operation if the driving gear102switched from being rotated in the counter-clockwise direction to being rotated in a clockwise direction, opposite the direction indicated by the first arrow140(that is, the driving gear102would start to move in the clockwise direction and not initially cause incremental movement of the driven gear104). However, this is not the case in the present embodiment. Rather, due to the application of the magnetic field, the respective counter-clockwise-facing sides of the respective driving gear teeth106continue to be in contact with the respective counter-clockwise-facing sides of the respective driven gear teeth110even if the direction of rotation of the driving gear102is switched from counter-clockwise rotation to clockwise rotation. In such an operational circumstance, the driven gear teeth110respectively are pulled by the driving gear teeth106.

As an example with reference toFIG.1, if the driving gear102and driven gear104have the positions as illustrated and the driving gear102is switched to rotate in the clockwise direction, contrary to the direction indicated by the first arrow140, then the first one118of the driving gear teeth106will physically pull the first one122of the driven gear teeth110due to the attractive magnetic force occurring between those teeth along the primary magnetic flux path136(as possibly supplemented by some other attractive magnetic forces also pulling in that same direction). This pulling action particularly will tend to rotate the driven gear104in the counter-clockwise direction, opposite the direction indicated by the second arrow142, provided that countervailing forces are not excessive (as discussed further below). As this pulling action begins, the counter-clockwise-facing side116of the first one118of the driving gear teeth106will remain in contact with the counter-clockwise-facing side120of the first one122of the driven gear teeth110. In contrast, the gap124between the clockwise-facing side126of the first one118of the driving gear teeth106and the clockwise-facing side128of the successive one130of the driven gear teeth110will generally remain present (albeit the gap can vary in extent somewhat as the gears rotate).

Generally speaking, after such pulling action has begun and the driving gear102continues to rotate in the clockwise direction opposite that indicated by the first arrow140, the driving gear102will continue to pull the driven gear104in the counter-clockwise direction opposite that indicated by the second arrow142. It will be appreciated that, as such rotation of the driving gear102and the driven gear104occurs, eventually sufficient rotation will occur that the first ones118and122of the driving gear teeth106and driven gear teeth110will rotate apart from one another. As this occurs, respective counter-clockwise-facing sides144and146of respective next ones148and150of the driving gear teeth106and driven gear teeth110, respectively, will come into contact with and be attracted to one another by an attractive magnetic force between those teeth, such that the pulling of the driven gear104by the driving gear102will continue to occur. This manner of operation will occur, with respect to successive pairs of the driving gear teeth106and driven gear teeth110, until the direction of rotation of the driving gear102again is reversed, again provided that countervailing forces are not excessive (as discussed further below).

Referring additionally toFIG.2, as already mentioned above, the gear assembly100ofFIG.1should be understood to form part of a magnetically-assisted mechanical gear system that can be represented by the magnetic circuit (or magnetic circuit diagram)200as shown inFIG.2. As illustrated, the magnetic circuit200is a closed magnetic circuit that includes, arranged in series, a magnetomotive force (MMF) source202, a lumped source reluctance (Rs)204, a first gear reluctance (Rg1)206, and a second gear reluctance (Rg2)208. In the present embodiment, it is envisioned that the MMF source202will be a permanent magnet, although in other embodiments the MMF source can be an electromagnet or a combination of two or more magnets of the same or different types.

Given this arrangement, as illustrated inFIG.2, a magnetic flux (phi, Φ) generated by the MMF source202circulates in the magnetic circuit200, by passing from the MMF source to and through the lumped source reluctance204, then through the first gear reluctance206, next through the second gear reluctance208, and then back to the MMF source. With reference to the example ofFIG.1, the first gear reluctance206can be considered to be the reluctance of the driving gear102and the second gear reluctance208can be considered to be the reluctance of the driven gear104that interfaces/mates/meshes to the driving gear. Also, the lumped source reluctance204can be considered to represent the sum of the reluctances of all other structures, and/or gaps, other than the driving gear102and driven gear104, through which magnetic flux flows as it proceeds from and back to the MMF source202. Figuratively, a link210shown inFIG.2connecting the first gear reluctance206and the second gear reluctance208can be considered to represent the magnetic flux communicated between the driving gear102(and particularly the driving gear teeth106thereof) and the driven gear104(and particularly the driven gear teeth110thereof).

The magnetic flux communicated between the driving gear102and the driven gear104can take multiple paths, and these paths can vary during rotation of those gears. For example, in the operational circumstance illustrated byFIG.1, some of the magnetic flux between the driving gear102and the driven gear104can follow the primary magnetic flux path136(e.g., through the location132within the region134) and also some of that magnetic flux can follow an alternate magnetic flux path across the gap124(e.g., within the region138). Nevertheless, although multiple flux paths (and associated flux lines) exist, the majority of the magnetic flux, and associated attractive magnetic force between the driving gear102and the driven gear104, will be concentrated along the path of least reluctance. InFIG.1, this path of least reluctance occurs within the region134and particularly at or near the location132at which the respective first ones118and122of the driving and driven gear teeth106and110are touching, along the primary magnetic flux path136.

Because the magnetic flux between the driving gear102and the driven gear104is concentrated along the primary magnetic flux path136, the attractive magnetic force associated with that primary magnetic flux path occurring between the counter-clockwise-facing sides116and120of the first ones118and122of the driving gear teeth106and driven gear teeth110constitutes the dominant attractive magnetic force between the driving gear102and the driven gear104. Because of the dominance of this particular attractive magnetic force when the driving gear102and driven gear104are positioned as shown inFIG.1, all of the attractive magnetic forces existing between the driving gear102and driven gear104overall tend to maintain the counter-clockwise-facing sides116and120of the first ones118and122of the driving gear teeth106and driven gear teeth110in contact with one another. Consequently, when the driving gear102and driven gear104are positioned particularly as shown inFIG.1, the gears are in an equilibrium state, magnetically-speaking.

More generally, when a magnetic flux is caused to flow through the driving gear102and driven gear104in accordance with the magnetic circuit200, there will be a greater flux density at the location (or region) of contact of the touching sides of a given pair of the driving gear teeth106and driven gear teeth110(such as at the location132), than across a gap (such as the gap124) between non-touching sides of any pair of the driving gear teeth and driven gear teeth. Further, because magnetic force is proportional to flux density squared, the attractive magnetic force between the touching sides of such a given pair of the driving gear teeth106and driven gear teeth110will be much greater than the attractive magnetic force between non-touching sides of any pair of the driving gear teeth and driven gear teeth that are separated by a gap such as the gap124. Thus, even though multiple magnetic flux paths and associated attractive magnetic forces can exist between different pairs of the driving gear teeth106and driven gear teeth110at any given time, the attractive magnetic force between the touching sides of any given pair of the driving gear teeth106and driven gear teeth110that are in contact at that given time will constitute the dominant attractive magnetic force between the driving gear102and driven gear104. Because of the dominance of this attractive magnetic force, an equilibrium state will exist when such a given pair of the driving gear teeth106and driven gear teeth110are in contact with one another.

The gear assembly100, when operating as a magnetically-assisted mechanical gear system in accordance with the magnetic circuit200, will tend to avoid backlash movement in the operational circumstance illustrated byFIG.1. That is, backlash movement will be avoided when the direction of rotation of the driving gear102switches from being in the direction of the first arrow140to the opposite direction, so long as the attractive magnetic force experienced between the counter-clockwise-facing sides116and120of the first ones118and122of the driving gear teeth106and driven gear teeth110(and any other attractive magnetic forces tending to cause those surfaces to remain in contact) is not exceeded by other countervailing forces. Such countervailing forces can include the mechanical driving force (or torque) applied to the driving gear102causing that driving gear to rotate in the direction opposite that of the first arrow140, as well as any mechanical force applied to the driven gear104by any load that is directly or indirectly borne by the driven gear tending to prevent rotation in the direction opposite that of the second arrow142. Also, such countervailing forces can include other magnetic forces that tend to pull the counter-clockwise-facing sides116and120apart from one another, such as any attractive magnetic force existing between the clockwise-facing sides126and128of the first one118of the driving gear teeth106and the successive one130of the driven gear teeth110across the gap124.

However, it should be recognized that, additionally with respect to the operational circumstance illustrated byFIG.1, backlash movement can occur if the countervailing forces exceed the attractive magnetic force experienced between the counter-clockwise-facing sides116and120of the first ones118and122of the driving gear teeth106and driven gear teeth110(as supplemented by any other attractive magnetic forces tending to cause those surfaces to remain in contact). In such case, the first one118of the driving gear teeth106(of the interfacing gear mesh) will transiently travel through the gap (or backlash region)124until the clockwise-facing side126of the first one118of the driving gear teeth106contacts the clockwise-facing side128of the successive one130of the driven gear teeth110.

When the clockwise-facing sides126and128are in contact, such that the contact and non-contact sides of the gear teeth are swapped between the counter-clockwise-facing sides116and120and the clockwise-facing sides126and128, a new equilibrium situation or state will have been reached. In this equilibrium state, the strongest attractive magnetic force will be occurring between the clockwise-facing sides126and128, due to a new primary magnetic flux path extending from the first one118of the driving gear teeth106to the successive one130of the driven gear teeth110. After this new equilibrium state arises, to the extent that the driving gear102continues to rotate in the clockwise direction opposite the direction indicated by the first arrow140, successive ones of the driving gear teeth106(beginning with the first one118) will mechanically push successive ones of the driven gear teeth110(beginning with the successive one130) so that the driven gear104is driven to rotate in the counter-clockwise direction opposite the direction indicated by the second arrow142.

Notwithstanding the above description regarding how backlash can occur, the present disclosure is intended to encompass embodiments and implementations that are configured, designed, and/or operated to reduce, minimize, or eliminate such backlash movement from occurring. In particular, in accordance with at least some embodiments encompassed herein, backlash movement can be avoided by sizing or configuring the magnetic circuit200so that the amplitude (or magnitude) of the attractive magnetic force occurring along the primary magnetic flux path (e.g., along the primary magnetic flux path136) between any given pair of contacting teeth of the driving gear and driven gear is greater than the maximum mechanical force the gear mesh will realize in operation. This can be achieved, for example, by appropriately sizing the MMF source202of the magnetic circuit200, so that a sufficiently large magnetic field and associated magnetic flux is communicated along the link210, between the driving gear102and the driven gear104. Also or additionally this can be achieved by appropriately configuring the shapes of the driving gear teeth106and/or the driven gear teeth110so that the proportion of magnetic flux that is communicated between a given contacting pair of teeth is much greater than the proportion of magnetic flux that is communicated between non-contacting pairs of teeth (e.g., by way of air gaps, etc.).

Although at least some embodiments encompassed herein are intended to entirely or substantially eliminate the occurrence of backlash movement, at least some other (or alternate) embodiments encompassed herein can be configured to allow backlash movement to occur under certain operational circumstances but to prevent, reduce, or minimize the occurrence of backlash movement under other operational circumstances. For example, in some such embodiments, the magnetic circuit (e.g., corresponding to the magnetic circuit200) can be sized so that the magnetically-assisted mechanical gear system is suited for backlash-free operation in relation to a lower volume and mass (e.g., in terms of the load borne by the driven gear) than that required for the maximum operating force/torque to be delivered to the driven gear. If sized in this manner, the magnetically-assisted mechanical gear system will still eliminate backlash movement under part-load conditions but allow backlash movement if the load borne by the driven gear increases above a reversing backlash force threshold. This sizing method can be desirable for systems that must apply large forces (torques) to quickly settle in on a position and then apply lower forces in alternating directions to move in small increments to reject disturbances and provide precise positioning in a localized region where the holding torque is smaller than the maximum torque.

It should be appreciated that the present disclosure encompasses numerous variations of magnetically-assisted mechanical gear systems that can operate in accordance with, or substantially or largely in accordance with, the description provided above regarding the gear assembly100ofFIG.1and the magnetic circuit200ofFIG.2. For example, referring toFIG.3, a top perspective view is provided of a first additional example embodiment of a magnetically-assisted mechanical gear system300that, as described in further detail, includes two (rather than merely one) MMF sources. As shown, the gear system300includes an input shaft302that extends along an input axis304from an input terminal306, through a first input shaft bearing308and to a second input shaft bearing310. Additionally, the gear system300includes an output shaft312that extends along an output axis314from an output terminal316, through a first output shaft bearing318and to a second output shaft bearing320. The input axis304extends parallel to the output axis314.

Also, the first input shaft bearing308and second output shaft bearing320are positioned along a first end322of a support structure324, and the second input shaft bearing310and first output shaft bearing318are positioned along a second end326of the support structure324, such that the input terminal306and output terminal316are respectively located at (adjacent to) the first end322and the second end326of the support structure, respectively, opposite one another. Although the input terminal306and output terminal316are respectively located at (adjacent to) the first end322and the second end326of the support structure in the embodiment ofFIG.3, in alternate embodiments the input terminal and output terminal both can be located at the same end of the support structure.

Further as shown, the input shaft302supports thereon, as one proceeds from the first input shaft bearing308toward second input shaft bearing310, a driving (input) gear330, a first MMF source332, and a first hollow cylinder334, all of which are coaxial about the input axis304. Also, the output shaft312supports thereon, as one proceeds from the second output shaft bearing320toward first output shaft bearing318, a driven (output) gear340, a second MMF source336, and a second hollow cylinder338, all of which are coaxial about the output axis314. Further, the driving gear330is aligned with the driven gear340, so that driving gear teeth328of the driving gear330intermesh with, and can impart mechanical force/torque to, driven gear teeth342of the driven gear340. Also, the first hollow cylinder334is aligned with the second hollow cylinder338, and the two hollow cylinders respectively have diameters such that the two hollow cylinders are not in contact with one another but rather are separated from one another by an air gap344. Although each of the driving gear330, first hollow cylinder334, driven gear340, and second hollow cylinder338is a ferromagnetic structure that can conduct magnetic flux and experience magnetic attractive (or repulsive) forces, the input shaft302and output shaft312are non-magnetic structures.

Further with respect toFIG.3, each of the first MMF source332and the second MMF source336is a respective ring magnet (or annular magnet), with the first MMF source332being positioned immediately between (and adjacent to each of) the driving gear330and the first hollow cylinder334and the second MMF source336being positioned immediately between the driven gear340and the second hollow cylinder338. In the present embodiment, the first MMF source332has a diameter that is equal or substantially equal to that of the first hollow cylinder334(but less than the outer diameter of the driving gear330determined by the driving gear teeth328. Also, the second MMF source336has a diameter that is equal or substantially equal to that of the second hollow cylinder338but less than the outer diameter of the driven gear340determined by the driven gear teeth342. Consequently, in the present embodiment, the air gap344is also present between the first and second MMF sources332and336.

Further, so as to generate a magnetic circuit, the first MMF source332can be understood to have north and south poles respectively at first and second axial ends of the first MMF source332that are respectively adjacent to the driving gear330and the first hollow cylinder334, and the second MMF source336can be understood to have south and north poles respectively at first and second axial ends of the second MMF source336that are respectively adjacent to the driven gear340and the second hollow cylinder338(or vice-versa, with respect to both of the MMF sources332and336). In this regard, the magnetic circuit200ofFIG.2can be considered to be representative of the magnetically-assisted mechanical gear system300if one not only considers the first and second gear reluctances206and208to correspond to the reluctances of the driving gear330and driven gear340respectively, but also considers the MMF source202to be have two parts that respectively correspond to the first and second MMF sources332and336and the lumped source reluctance204to be representative of the sum total of the reluctances associated with each of the first and second hollow cylinders334and338and the air gap344(among other things).

Given this arrangement, magnetic flux flows through and from the first MMF source332to the first hollow cylinder334, across the air gap344to the second hollow cylinder338, through the second MMF source336, through the driven gear340, through the driving gear330, and back to the first MMF source. As described in regard toFIG.1, the magnetic flux that flows through the gear mesh creates an attractive force at interfacing ones of the driving gear teeth328and driven gear teeth342that are interfacing at the gear mesh, so as to maintain contact between those teeth notwithstanding switching of the rotational direction of the driving gear330, and thus serves to eliminate (or reduce) backlash movement. The first and second hollow cylinders334and338(which are ferromagnetic hollow cylinders) are used to complete the magnetic circuit flux path between the two axes of motion (associated with the input shaft302and output shaft312) without being in contact with one another.

In the present example embodiment ofFIG.3, it is assumed that each of the first and second MMF sources332and336is a respective axially magnetized permanent magnet (or each includes one or more respective axially magnetized permanent magnets). Nevertheless, in alternate embodiments, one or both of the MMF sources332and336can respectively be a respective electromagnet. In such an embodiment, any such electromagnet can be formed by way of an electrical coil (e.g., wire loops) surrounding a ferromagnetic core. The electrical coil can include leads that are coupled to an electric power source, and be operated to carry (conduct through the coil) electric current provided by the electric power source. Also, in at least some alternate embodiments, only one of the first MMF source332and second MMF source336is present or serves to generate magnetic flux (e.g., one of the MMF sources can be omitted and ferromagnetic material used in its place) to complete the magnetic circuit.

To the extent that one or both of the first and second MMF sources332and336is an electromagnet, this can introduce controllability to the magnetically-assisted mechanical gear system300(and the magnetic circuit200), and/or can allow the system to be operated at temperatures beyond those which are attainable if only permanent magnets are utilized as the first and second MMF sources332and336. More particularly, it should be appreciated that, if one or both of the MMF sources332and336is an electromagnet, the magnetically-assisted mechanical gear system300not only can be operated in a manner that eliminates (or reduces) backlash movement if the electromagnet is energized (results in zero backlash), but also can be operated in a manner that does not eliminate (or reduce) backlash movement if the electromagnet is de-energized. In such an embodiment, the gear system300in some operational circumstances can be operated so that a constant level of current is directed to flow through the electromagnet, so that the electromagnet provides a constant MMF amplitude and delivers a constant or substantially constant level of magnetic flux. Also, in at least some other operational circumstances, the electromagnet is de-energized (such that current does not flow through the coil, and the coil is switched off), in which case the gear system300can behave as though it is a conventional gear mesh and experience backlash movement.

In additional embodiments in which one or both of the first and second MMF sources332and336are electromagnets, the MMF source(s) are not limited to being fully-switched-on and fully-switched-off, but rather can be energized to varying degrees. In some such embodiments, a controller (not shown) is provided that governs the current (or currents) flowing through one or both of the first and second MMF sources332and336. Such a controller can for example be a microprocessor-based controller. Based upon the level of the current(s) flowing through the first and second MMF sources332and336, the magnetic flux generated by those MMF sources and passing through the gear system can be varied to suit different operational circumstances or conditions. For example, in some cases, by causing the current(s) flowing through the MMF sources332and336to be non-zero but less than a maximum amount, backlash movement is allowed to occur to some extent but not as frequently as it would occur if no magnetic flux was present in the gear system. That is, the current(s) are controllable in order to adjust the maximum anti-backlash torque level. Also, in at least some embodiments, the excitation current is controlled to set a desired backlash reverse driving torque threshold. Current can be lowered to reduce the torque threshold, which improves efficiency, and current can be increased to increase the torque threshold, which reduces efficiency. Additionally in at least some embodiments, the coil can be energized transiently prior to reversing the direction of angular velocity and de-energized after the reversing transition is complete. This approach allows for higher efficiency operation (more backlash) during continuous forward/reverse rotation, and yet also retains zero (or reduced) backlash operation upon direction reversal.

Further with reference to the gear system300ofFIG.3, it should also be appreciated that, depending upon the embodiment, the air gap344can be adjustable during the manufacturing or assembly of the gear system300. More particularly, the air gap344can be adjusted based upon the selection and/or implementation of the first hollow cylinder334and/or the second hollow cylinder338, for example, by changing the diameter(s) of one or both of those cylinders or the axial location(s) of one or both of those cylinders. By adjusting the air gap344in any of these manner, this can result in adjustments to the maximum torque achievable before backlash movement occurs. That is, such adjustments allow for the maximum anti-backlash torque level to be set during assembly.

Referring now toFIG.4, a side perspective view is provided of a second additional example embodiment of a magnetically-assisted mechanical gear system400that, as described in further detail, includes two pairs of driving and driven gears (rather than merely a single driving gear and a single driven gear). As shown, the gear system400includes an input shaft402that extends along an input axis404from an input terminal406, through a first input shaft bearing408and to a second input shaft bearing410. Additionally, the gear system400includes an output shaft412that extends along an output axis414from an output terminal416, through a first output shaft bearing418and to a second output shaft bearing420. The input axis404extends parallel to the output axis414.

Also, the first input shaft bearing408and second output shaft bearing420are positioned along a first end422of a support structure424, and the second input shaft bearing410and first output shaft bearing418are positioned along a second end426of the support structure424, such that the input terminal406and output terminal416are respectively located at (adjacent to) the first end422and the second end426of the support structure, respectively, opposite one another. Although the input terminal406and output terminal416are respectively located at (adjacent to) the first end422and the second end426of the support structure in the embodiment ofFIG.4, in alternate embodiments the input terminal and output terminal both can be located at the same end of the support structure.

Further as shown, the input shaft402supports thereon, as one proceeds from the first input shaft bearing408toward second input shaft bearing410, a first driving (input) gear430and a second driving (input) gear432, all of which are coaxial about the input shaft402. Also, the output shaft412supports thereon, as one proceeds from the second output shaft bearing420toward first output shaft bearing418, a first driven (output) gear434, a MMF source436, and a second driven (output) gear438, all of which are coaxial about the output shaft412. Further, the first driving gear430is aligned with the first driven gear434, so that first driving gear teeth428of the first driving gear430intermesh with, and can impart mechanical force/torque to, first driven gear teeth440of the first driven gear434. Additionally, the second driving gear432is aligned with the second driven gear438, so that second driving gear teeth442of the second driving gear432intermesh with, and can impart mechanical force/torque to, second driven gear teeth444of the second driven gear438. Although each of the first and second driving gears430and432and the first and second driven gears434and438is a ferromagnetic structure that can conduct magnetic flux and experience magnetic attractive (or repulsive) forces, the input shaft402and output shaft412are non-magnetic structures.

Further with respect toFIG.4, the MMF source436is a respective ring magnet (or annular magnet), and is positioned immediately between (and adjacent to each of) the first driven gear434and the second driven gear438. So as to generate a magnetic circuit, the MMF source436can be understood to have north and south poles respectively at first and second axial ends of the MMF source436that are respectively adjacent to the first driven gear434and the second driven gear438, respectively. In the present embodiment, the MMF source436has a diameter that is less than the outer diameter of the first and second driven gears434and438. Although the MMF source436is positioned between the first and second driven gears434and438, no corresponding MMF source or other structure is positioned between the first and second driving gears430and432. Rather, in the present embodiment the first and second driving gears430and432are positioned immediately adjacent one another along the input shaft402. Although the first and second driving gears430and432are considered distinct gears in the present embodiment, in an alternate embodiment the first and second driving gears can be integrally formed with one another as a single gear that interfaces both of the first and second driven gears434and438.

It should be recognized that the gear system400ofFIG.4differs from the gear system300ofFIG.3in that (among other things) the gear system400includes not just one but rather two distinct gears along each of the input shaft402and the output shaft412(that is, a second gear is added within each axis of motion) to complete the magnetic circuit flux path. Thus, as illustrated by a looping arrow450inFIG.4, in the gear system400, magnetic flux flows through and from the MMF source436through the first driven gear434, then through the first driving gear430, then through the second driving gear432, then through the second driven gear438, and finally back to the MMF source436to complete the magnetic circuit. Further, as described in regard toFIG.1, the magnetic flux that flows through the gear mesh between the first driven and driving gears434and430creates an attractive force at interfacing ones of the first driving gear and driven gear teeth428and440. Likewise, the magnetic flux that flows through the gear mesh between the second driving and driven gears432and438creates an attractive force at interfacing ones of the second driving gear and driven gear teeth442and444. These attractive magnetic forces between the first driving and driven gears430and434and between the second driving and driven gears432and438serve to cause contact between the interfacing teeth of those pairs of gears to maintain contact notwithstanding switching of the rotational direction of the driving gears430and432, and thus serves to eliminate (or reduce) backlash movement.

Because the gear system400ofFIG.4includes not one but two pairs of interfacing gears, it will be appreciated that a modified version of the magnetic circuit200of FIG. is applicable as a representation of the gear system400. In particular, although the MMF source436can be considered to correspond to the MMF source202, the modified version of the magnetic circuit will include not only the first and second gear reluctances206and208, which can correspond to the first driven gear434and first driving gear430, but also third and fourth gear reluctances, which can correspond to the second driving gear432and the second driven gear438, where all four of the gear reluctances can be coupled in series with the MMF source. The lumped source reluctance204need not be present or, alternatively, can be considered to be representative of (among other things) the reluctance associated with any discontinuity between the first and second driving gears430and432. Although the gear system400ofFIG.4does not include an air gap directly corresponding to the air gap344of the gear system300ofFIG.3, in alternate embodiments one or more air gaps can also be provided in regard to the gear system400(e.g., by creating spaces between the MMF source436and the adjacent ones of the gears434and438or between the first and second driving gears430and432).

In the present embodiment ofFIG.4, the MMF source436includes an axially magnetized permanent magnet (or one or more axially magnetized permanent magnets). Nevertheless, in alternate embodiments, the MMF source436can be an electromagnet (or one or more electromagnets). In such an embodiment, the electromagnet can be formed by way of an electrical coil (e.g., wire loops) surrounding a ferromagnetic core. The electrical coil can include leads that are coupled to an electric power source, and be operated to carry (conduct through the coil) electric current provided by the electric power source. Use of an electromagnet as the MMF source436can introduce controllability to the magnetically-assisted mechanical gear system400, and/or can allow the system to be operated at temperatures beyond those which are attainable if only permanent magnet(s) is or are utilized as the MMF source436. More particularly, it should be appreciated that, if the MMF source436is an electromagnet, the magnetically-assisted mechanical gear system400not only can be operated in manner that eliminates (or reduces) backlash movement if the electromagnet is energized (results in zero backlash), but also can be operated in a manner that does not eliminate (or reduce) backlash movement if the electromagnet is de-energized. In such an embodiment, the gear system400in some operational circumstances can be operated so that a constant level of current is directed to flow through the electromagnet, so that the electromagnet provides a constant MMF amplitude and delivers a constant or substantially constant level of magnetic flux. Also, in at least some other operational circumstances, the electromagnet is de-energized (such that current does not flow through the coil, and the coil is switched off), in which case the gear system400can behave as though it is a conventional gear mesh and experience backlash movement.

In additional embodiments in which the MMF source436is formed using an electromagnet, the MMF source is not limited to being fully-switched-on and fully-switched-off, but rather can be energized to varying degrees. In some such embodiments, a controller (not shown) is provided that governs the current flowing through the MMF source436. Based upon the level of the current flowing through the first MMF source436, the magnetic flux generated by the MMF source and passing through the gear system can be varied to suit different operational circumstances or conditions. For example, in some cases, by causing the current flowing through the MMF source436to be non-zero but less than a maximum amount, backlash movement is allowed to occur to some extent but not as frequently as it would occur if no magnetic flux was present in the gear system. That is, the current is controllable in order to adjust the maximum anti-backlash torque level. Also, in at least some embodiments, the excitation current is controlled to set a desired backlash reverse driving torque threshold. Current can be lowered to reduce the torque threshold, which improves efficiency, and current can be increased to increase the torque threshold, which reduces efficiency. Additionally in at least some embodiments, the coil can be energized transiently prior to reversing the direction of angular velocity and de-energized after the reversing transition is complete. This approach allows for higher efficiency operation (more backlash) during continuous forward/reverse rotation, and yet also retains zero (or reduced) backlash operation upon direction reversal.

It should be appreciated, with respect to the embodiments ofFIG.1,FIG.3, andFIG.4, that in these embodiments the various driving gear teeth and driven gear teeth can each have an involute gear profile in terms of the shape of each respective tooth. Yet the present disclosure also is intended to encompass other embodiments in which one or more of the teeth of one or more of the driving gear(s) and/or driven gear(s) have one or more other shapes. For example, in some alternate embodiments, one or more of the driving gear teeth and/or one or more of the driven gear teeth can have a cycloid profile. Also it should be appreciated that, in some alternate embodiments, the teeth of a driving gear of a pair of interfacing gears can have a different shape than the teeth of a driven gear of that pair of interfacing gears.

Further in this regard,FIG.5shows a cutaway view of an additional gear assembly500having two interfacing gears, including a first gear that is a driving gear502and a second gear that is a driven gear504. In this example ofFIG.5, each of the driving gear502and driven gear504again is a respective spur gear as shown inFIG.1, and the additional gear assembly500again can be considered to be part of a magnetically-assisted mechanical gear system in which forces are communicated between the driving gear502and the driven gear504not only mechanically but also magnetically, in accordance with the magnetic circuit200ofFIG.2. Additionally as shown, the driving gear502includes driving gear teeth506arranged around the driving gear along a first circular path represented by a first dashed line508and extending about a first central axis (not shown) of the driving gear. Also, the driven gear504includes driven gear teeth510arranged along a second circular path represented by a second dashed line512and extending about a second central axis (not shown) of the driven gear. In this illustration, the first and second dashed lines508and512respectively extend substantially through respective midregions of the driving gear teeth506and driven gear teeth510, respectively, such that, when the driving gear502is interfacing the driven gear504, the first and second dashed lines508and512are tangent with one another at a location514at which the driving gear teeth506and driven gear teeth510are most closely intermeshed.

Although the additional gear assembly500ofFIG.5in many respects is the same as the gear assembly100ofFIG.1, the two gear assemblies are different from one another in that the driving gear teeth506and driven gear teeth510of the additional gear assembly500have a different shape relative to the driving gear teeth106and driven gear teeth110of the gear assembly100. In particular, although each of the driving gear teeth106and driven gear teeth110of the gear assembly100has an involute gear profile, each of the driving gear teeth506and driven gear teeth510of the additional gear assembly500has a semi-involute gear profile. More particularly, each of the driving gear teeth506and driven gear teeth510has a gear profile in which a respective counter-clockwise-facing side516of the respective tooth is consistent in shape with an involute gear profile, but also in which a respective clockwise-facing side518of the respective tooth has a contour that follows a respective path that is closer to a respective radially-extending midline520of the respective tooth (radially-extending, in terms of extending radially outward from a respective central axis of the respective driving gear or driven gear on which the respective tooth is formed) than would be the case if that respective clockwise-facing side had a shape consistent with an involute gear profile. That is, the respective contour of each respective clockwise-facing side518of each respective tooth of the driving gear teeth506and driven gear teeth510is closer to the respective radially-extending midline520of the respective tooth than is the respective contour of the respective counter-clockwise-facing side516of the respective tooth.

In this respect, as illustrated inFIG.5, each of the driving gear teeth506and driven gear teeth510is missing a respective tooth section522that otherwise would have been present if the driving gear teeth and driven gear teeth had the involute gear profile of the driving gear teeth106and driven gear teeth110ofFIG.1. The respective tooth sections522are particularly illustrated inFIG.5as extending between the respective clockwise-facing sides518of the driving gear teeth506and driven gear teeth510and respective dashed lines524indicative of where the respective clockwise-facing sides of the teeth would be if those respective teeth had the involute gear profile illustrated inFIG.1. Although not necessarily the case in all embodiments, in the present example embodiment the respective counter-clockwise-facing sides516having the involute gear profile can be substantially convex in shape and the respective clockwise-facing sides518can be substantially concave in shape. Further, in the illustration provided byFIG.5, the respective counter-clockwise-facing sides516of the respective driving gear teeth506and respective driven gear teeth510are intended to be the respective contact sides of the respective teeth, and the respective clockwise-facing sides518of the respective driving gear teeth and respective driven gear teeth are intended to be the respective non-contact sides of the respective teeth. For example, the respective counter-clockwise-facing side516of a first one526of the driving gear teeth506is shown to be in contact with the respective counter-clockwise-facing side516of a first one528of the driven gear teeth510, as can be the case when the driving gear is rotating in a counter-clockwise direction consistent with a first arrow530and providing mechanical force/torque causing the driven gear504to rotate in a clockwise direction consistent with a second arrow532.

Given this to be the case, it can be seen that the particular shape of the clockwise-facing sides518of the driving gear teeth506and driven gear teeth510serves to increase the spacing between respective ones of the non-contact sides of neighboring ones of the driving gear teeth506and driven gear teeth510from what that spacing would otherwise be. For example, with respect toFIG.5, it can be seen that the respective clockwise-facing side518of a successive (second) one538of the driven gear teeth510that is located counter-clockwise of the first one528of the driven gear teeth510is positioned (at least by one measure) a first distance536from the respective clockwise-facing side518of the first one526of the driving gear teeth506. Further, it can also be seen that the first distance536is significantly greater than a second distance534between the respective dashed lines524extending from those respective clockwise-facing sides518of the successive one538of the driven gear teeth510and the first one528of the driven gear teeth510. Thus, in the embodiment and operational circumstance illustrated byFIG.5, the respective clockwise-facing sides518of the successive one538of the driven gear teeth510and the first one528of the driven gear teeth, which are the non-contacting sides of those respective teeth, are farther apart from one another than in the embodiment and operational circumstance illustrated byFIG.1.

The shape of the driving gear teeth506and driven gear teeth510can be beneficial to the operation of the additional gear assembly500in terms of further eliminating or reducing backlash movement. More particularly, it will be recognized that, because the non-contacting sides of respective ones of the driving gear teeth506and driven gear teeth510that are in proximity with one another are spaced apart by greater distances than would otherwise be the case (e.g., in the embodiment ofFIG.1), this reduces the attractive magnetic forces between the non-contacting sides of proximate pairs of the driving gear teeth506and driven gear teeth510of the gear mesh. That is, because of the semi-involute profile of the driving gear teeth506and driven gear teeth510(and particularly the absence of material eliminated along the non-contact sides of the respective teeth corresponding to the respective tooth sections522) and consequent increased spacing between interfacing driving and driven gear teeth along the non-contact sides of the teeth, the amplitude of weaker attractive forces referred to in regard toFIG.1(e.g., as occurring in the region138) is further reduced.

With this being the case, if the direction of rotation of the driving gear502is reversed from a direction consistent with the first arrow530to a direction opposite that indicated by the first arrow, there is less magnetic attraction between the non-contact sides of neighboring teeth that might cause (in combination with any mechanical forces or momentum of the driven gear504) the magnetic attraction between the contact sides of contacting ones of the teeth to be overcome. More particularly, in the illustration ofFIG.5, there is less likelihood that any magnetic attraction between the clockwise-facing sides518of the first one526of the driving gear teeth506and the successive one538of the driven gear teeth510would (in combination with any mechanical forces or momentum of the driven gear504) cause the counter-clockwise-facing sides516of the first one526of the driving gear teeth506and first one528of the driven gear teeth510to be separated. Given this to be the case, the embodiment of the gear assembly500with the gear tooth profile shown inFIG.5is less likely to experience backlash movement than the gear assembly100ofFIG.1.

Turning toFIG.6, the present disclosure is not limited to gear assemblies but also encompasses other forms of assemblies, including for example assemblies involving screws, bolts, and nuts. In this regard,FIG.6particularly shows a cross-sectional, cutaway view of a screw-and-nut gear assembly600that includes a lead screw602and a ferromagnetic nut604, as well as a MMF source606and a hollow cylinder608. The particular cross-section that is shown inFIG.6can be understood to be taken along a mid-plane passing through a central axis610of the lead screw602, which coincides with central axes of each of the ferromagnetic nut604, the MMF source606, and the hollow cylinder608.FIG.6particularly shows portions612of the assembly600that are positioned above the central axis610as illustrated inFIG.6. The portions of the assembly600that are cut away and not shown inFIG.6are those which would be positioned below the central axis610as illustrated inFIG.6.

The portions612of the assembly600that are shown inFIG.6particularly include first (e.g., male) threads614formed on the lead screw602, and extending around a central shaft616of the lead screw, as well as complementary (e.g., female) threads618formed on the ferromagnetic nut604, and extending along an inner perimeter of an annular exterior structure620of the ferromagnetic nut. Further as shown, the hollow cylinder608, MMF source606, and ferromagnetic nut604are distributed in series axially along the lead screw602, with the MMF source being positioned axially in between the ferromagnetic nut604and the hollow cylinder608. Also, an air gap609is formed in between the threads614of the lead screw602and an inner circumference (or interior annular surface)611of the hollow cylinder608. It should be appreciated that the cutaway portions of the assembly600that are not shown inFIG.6would be identical to the portions612, except insofar as the cutaway portions would be inverted relative to (e.g., a mirror image of) the portions612about the central axis610, and also except insofar as the first threads614and complementary threads618of the cutaway portions would be shifted along the central axis610relative to the first threads614and complementary threads618of the portions612.

Although the screw-and-nut gear assembly600is not a gear assembly, nevertheless the screw-and-nut gear assembly can operate in accordance with, or substantially in accordance with, the magnetic circuit200ofFIG.2. Indeed, in the screw-and-nut gear assembly600, the MMF source606applies a magnetic field so as to generate magnetic flux that proceeds within and around the assembly600, and between component parts thereof, so as to complete the magnetic circuit200. More particularly as shown inFIG.6, the magnetic flux generated by the MMF source606first proceeds axially, generally parallel or substantially parallel to the central axis610, from the MMF source606into the annular exterior structure620of the ferromagnetic nut604as represented by a first arrow622, and then proceeds radially inward into respective ones of the complementary threads618of the ferromagnetic nut as indicated by respective second arrows624.

Further, the magnetic flux then crosses from the respective ones of the complementary threads618to respective neighboring ones626of the first threads614of the lead screw602, as indicated by respective third arrows628. As shown, the respective neighboring ones626of the first threads614of the lead screw602are those ones of the first threads that are closest to, in terms of axial positioning along the central axis610, the respective complementary threads618. Consequently, the magnetic flux passing between the respective complementary threads618and respective neighboring ones626of the first threads is at respective maximum levels at respective locations630between those respective pairs of threads and, correspondingly, the attractive magnetic forces between the ferromagnetic nut604and the lead screw602are strongest at those locations.

Upon reaching the lead screw602via the neighboring ones626of the first threads614, the magnetic flux further passes axially through the central shaft616of the lead screw as indicated by a fourth arrow632, with the direction of the fourth arrow632being opposite the direction of the first arrow622. The magnetic flux proceeds in this direction axially until it arrives at additional ones634of the first threads614that are aligned with the hollow cylinder608. Upon reaching the respective additional ones634of the first threads614, the magnetic flux then passes radially outward through and out from the respective additional ones of the first threads and into the hollow cylinder608surrounding those first threads by way of the air gap609, as indicated by respective fifth arrows636. After entering the hollow cylinder608, the magnetic flux then proceeds axially in the same direction as the first arrow622, parallel to the central axis610, and returns to the MMF source606as indicated a sixth arrow638.

The magnetic flux imparted by the MMF source606through the magnetic circuit formed by the lead screw602, ferromagnetic nut604, and hollow cylinder608imposes attractive magnetic forces between the lead screw602and ferromagnetic nut604in a manner that biases contact between the first threads614and complementary threads618to one side of the mesh. More particularly, because the attractive magnetic forces are strongest at the locations630, the respective complementary threads618in the present illustration tend to be biased so that respective left sides of those respective complementary threads approach respective right sides of the respective neighboring ones626of the first threads614. Given these attractive magnetic forces, the screw-and-nut gear assembly600can be operated in a manner that avoids backlash movement (achieves zero backlash operation) or at least achieves reduced backlash movement.

More particularly, during operation, the ferromagnetic nut604may initially be applying mechanical force toward the left (as illustrated inFIG.6), so that the respective complementary threads618push against the respective neighboring ones626of the first threads614of the lead screw602that are positioned immediately to the left of those respective complementary threads. Correspondingly, the respective neighboring ones626of the first threads614of the lead screw602can be considered to be applying mechanical force to the right (as illustrated inFIG.6) against the respective complementary threads618that are positioned immediately to the right of those respective first threads. With such interaction, there exist gaps (or backlash regions)640separating the respective complementary threads618from respective other ones of the first threads614that are respectively on the opposite sides (e.g., right sides as illustrated inFIG.6) of those respective complementary threads by comparison with the respective neighboring ones626of the first threads closest to those respective complementary threads.

Given such an arrangement, in a conventional screw-and-nut gear assembly, when the direction of mechanical force applied by either the nut or lead screw is reversed, the driving nut will travel through the backlash regions (e.g., the gaps640) relative to the lead screw without corresponding incremental movement of the lead screw that might tend to maintain the backlash regions. However, in the present embodiment ofFIG.6, and assuming that the ferromagnetic nut604is providing the driving force, when the direction of applied mechanical force is reversed, the ferromagnetic nut will “pull” the lead screw602toward the right via the attractive magnetic force on the contact sides (e.g., the right sides of the neighboring ones626of the first threads614) of the lead screw602. Further, assuming that the applied mechanical force (and any other magnetic forces) is not so strong as to overcome the attractive magnetic force between the complementary threads618and the neighboring ones626of the first threads614, the ferromagnetic (driving) nut604will continue to “pull” the lead screw602until the direction of force is reversed again. Thus, in this operational circumstance, the lead screw602will not be subject to a backlash region of non-movement.

Likewise, in the embodiment ofFIG.6and assuming that it is the lead screw602that is providing driving force, if the lead screw switches from rotating in a first direction tending to cause the respective neighboring ones626of the first threads to mechanically push against the respective complementary threads618to rotating in the opposite direction, the respective complementary threads618will tend to be maintained alongside or near the respective neighboring ones626of the first threads614(which are respectively closest to those respective complementary threads). Thus, with respect to the embodiment ofFIG.6and regardless of whether it is the ferromagnetic nut604or the lead screw602that is providing the driving force, even though there exist the gaps (or backlash regions)640separating the respective complementary threads618from the respective other ones of the first threads614that are respectively on the opposite sides (e.g., right sides as illustrated inFIG.6) of those respective complementary threads by comparison with the respective neighboring ones626of the first threads closest to those respective complementary threads, the respective complementary threads618will not tend to move through or close those respective gaps640(albeit the gaps can vary in extent somewhat as the lead screw602rotates relative to the ferromagnetic nut604).

Further in this regard, although additional magnetic flux lines exist between the respective complementary threads618and the respective other ones of the first threads614that are (as illustrated inFIG.6) to the right of those respective complementary threads, the majority of magnetic flux will be concentrated along the paths of least reluctance where the respective complementary threads618of the ferromagnetic nut604are contacting (or closest to) the respective neighboring ones626of the first threads614of the lead screw602. Correspondingly, there will be a greater flux density between the contacting/touching sides (e.g., the right sides as illustrated inFIG.6) of the neighboring ones626of the first threads614of the lead screw602than between the non-touching sides of the respective first threads614that are respectively positioned to the right of the respective complementary threads618(e.g., the respective left sides of those respective first threads as illustrated inFIG.6) at which the gaps640exist. Because magnetic force is proportional to flux density squared, the overall attractive magnetic force between the touching sides of the neighboring ones626of the first threads614of the lead screw602and the respective complementary threads618adjacent respectively thereto is much greater than the overall attractive magnetic force between the non-touching sides of the respective other ones of the first threads614and the respective complementary threads618that are on opposite sides of the respective gaps640.

Notwithstanding the above discussion, if the driving mechanical force between the ferromagnetic nut604and the lead screw602(plus any additional magnetic forces) is in opposition to and greater than the attractive magnetic forces between the complementary threads618of the ferromagnetic nut604and the neighboring ones626of the first threads614of the lead screw602, backlash movement can still occur. That is, if the driving mechanical force between the ferromagnetic nut604and the lead screw602(plus any additional magnetic forces) exceed the attractive magnetic forces between the respective complementary threads618and the respective neighboring ones626of the first threads614, the ferromagnetic nut (and lead screw) will transiently travel through the gaps (backlash regions)640. If this occurs, then a new equilibrium will be attained when the contact and non-contact sides of the interfacing complementary threads618and first threads614are swapped-when, instead of the left sides of the complementary threads618contacting the right sides of the neighboring ones626of the first threads614, the right sides of the complementary threads contact the left sides of the respective other ones of the first threads614positioned on opposite sides of those complementary threads (assuming the arrangement illustrated inFIG.6).

It should be appreciated that such a situation, in which backlash occurs, can be avoided by sizing the magnetic circuit (and correspondingly sizing the magnetic field applied by the MMF source606) such that the amplitude of the overall magnetic force communicated between the complementary threads618and the neighboring ones626of the first threads614is greater than the maximum mechanical force the lead screw602will realize in operation relative to the ferromagnetic nut604. Additionally, in alternate embodiments, the magnetic circuit can be sized appropriately for a lower volume and mass than that required for the maximum operating force/torque, still eliminating backlash under part-load conditions but allowing backlash above a reversing backlash force threshold. This sizing method can be desirable for systems that are configured to apply large forces for fast response times but also to apply lower forces in alternating directions to move in small increments to reject disturbances and provide precise positioning in a localized region where the holding force is smaller than the maximum force.

Further with reference to the screw-and-nut gear assembly600ofFIG.6, it should also be appreciated that, depending upon the embodiment, the air gap609can be adjustable during the manufacturing or assembly of the screw-and-nut gear assembly600. More particularly, the air gap609can be adjusted based upon the selection and/or implementation of the hollow cylinder608, for example, by changing the inner circumference611of the hollow cylinder608(e.g., the inner diameter surrounding the first threads614of the lead screw602) or the axial location of the hollow cylinder. By adjusting the air gap609in any of these manners, this can result in adjustments to the maximum torque achievable before backlash occurs. That is, such adjustments allow for the maximum anti-backlash torque level to be set during assembly.

Referring next toFIG.7, additional embodiments encompassed herein can relate to other types of gear assemblies or assemblies that involve intermeshed gear teeth. More particularly in this regard,FIG.7particularly shows a side elevation view of a rack and pinion gear assembly700that includes a ferromagnetic pinion702and a ferromagnetic rack704, as well as a MMF source706and a ferromagnetic hollow cylinder708. Further as shown, the pinion702includes pinion gear teeth710and the rack704includes rack gear teeth712that interface with the pinion gear teeth. Additionally,FIG.7shows that both the pinion702and the hollow cylinder708are supported upon a shaft714and positioned coaxially with respect to a central axis716of the shaft, with the hollow cylinder also being shifted axially along the central axis relative to the pinion. Although the rack gear teeth712of the rack704are generally positioned alongside the pinion702and have a length718that is equal or substantially equal to the axial length of the pinion702, in the present embodiment the rack also includes a ferromagnetic (or simply magnetic) iron extension720that generally extends parallel to the central axis716alongside the hollow cylinder708. The MMF source706is positioned in between the hollow cylinder708and the magnetic iron extension720.

Further with respect to the rack704, it should be appreciated that the rack is generally an elongated, flat structure that extends inwardly into (and/or out of) the page as shown inFIG.7and that supports numerous ones of the rack gear teeth712along the length of that structure into (and/or out of) the page. Given this arrangement of the rack gear teeth712, it should be appreciated that there are some differences between the rack and pinion gear assembly700ofFIG.7and the gear assembly100ofFIG.1in terms of the gear teeth of the two assemblies. More particularly, in addition to having the rack gear teeth712arranged along a straight support structure instead of being arranged along the curved periphery of a gear as is the case with both the driving gear teeth106and driven gear teeth110, the respective shapes of one or both of the rack gear teeth712and the pinion gear teeth710may also be modified from the shapes of the driving and driven gear teeth106and110to facilitate intermeshing of those rack and pinion gear teeth. The present embodiment is intended to encompass either of two operational implementations, in which either the rack704can exert mechanical force upon the pinion702to drive rotation of the pinion, or the pinion702can exert mechanical force to drive linear movement of the rack704.

It should be understood that the rack and pinion gear assembly700also can operate in accordance with, or substantially in accordance with, the magnetic circuit200ofFIG.2. Indeed, in the rack and pinion gear assembly700, the MMF source706applies a magnetic field so as to generate magnetic flux that proceeds within and around the assembly700, and between component parts thereof, so as to complete the magnetic circuit200. More particularly as shown inFIG.7, the magnetic flux generated by the MMF source706first proceeds from the MMF source into the magnetic iron extension720of the rack704as represented by a first arrow722, and then proceeds through the magnetic iron extension to the rack gear teeth712as indicated by a second arrow724. Further, the magnetic flux then crosses from the rack gear teeth712to the pinion gear teeth710(the contacting gear mesh) as indicated by a third arrow726. Upon reaching the pinion gear teeth710, the magnetic flux then passes axially from the pinion702to the hollow cylinder708, as indicated by a fourth arrow728. After entering the hollow cylinder708, the magnetic flux then proceeds radially outward toward and to, so as to return to, the MMF source706, as indicated by a fifth arrow730. In the present example embodiment, an air gap732exists between the hollow cylinder708and the MMF source706, such that the magnetic flux proceeding from the hollow cylinder to the MMF source as represented by the fifth arrow730also proceeds through the air gap.

It should be recognized that, due to the magnetic flux imparted by the MMF source706through the magnetic circuit formed by the pinion702, the rack704(including the magnetic iron extension720), and the hollow cylinder708(and including the air gap732), operation of the rack and pinion gear assembly700can achieve zero backlash operation, or at least operation that involves significantly less backlash movement than would otherwise occur in conventional arrangements. Such operation can be achieved in substantially the same manner as described above in regard toFIG.1, if one assumes that the driven gear teeth110of the driven gear104constitute the pinion gear teeth710of the pinion702and also that the driving gear teeth106of the driving gear102are modified so as to be arranged in the manner of the rack gear teeth712of the rack704(such that those gear teeth are spaced along a straight support structure rather around the curved periphery of a gear), or vice-versa. That is, operation involving no backlash movement or reduced levels of backlash movement can be achieved in the rack and pinion gear assembly700including the MMF source706in substantially the same manner as described in regard toFIG.1if one assumes that either the pinion gear teeth710respectively take the place of the driving gear teeth106in terms of imparting mechanical force, and the rack gear teeth712respectively take the place of the driven gear teeth110in terms of receiving the imparted mechanical force, or vice-versa.

Regardless of whether it is the pinion gear teeth710or the rack gear teeth712that correspond to the driving gear teeth106in terms of imparting mechanical force, as described in regard toFIG.1there will be locations (typically one location corresponding to the location132ofFIG.1at any given time) at which certain ones of the pinion gear teeth710and rack gear teeth712come into contact with one another. At these locations at which contact occurs, maximum flux will flow between the contacting ones of the pinion gear teeth710and rack gear teeth712. Even though additional magnetic flux lines will exist at other locations between non-contacting sides of various ones of the pinion gear teeth710and rack gear teeth712, the majority of flux will be concentrated along the path of least reluctance where the rack704and pinion702are touching. Therefore, there will be a greater flux density on the touching side of the rack and pinion mesh than the non-touching side.

Correspondingly, maximum attractive magnetic forces will occur between those respective contacting ones of the pinion gear teeth710and rack gear teeth712, along the respective sides of the contacting ones of the teeth that are in contact with one another (e.g., along respective sides of the contacting ones of the teeth that correspond to the counter-clockwise-facing sides116and120inFIG.1). Indeed, as discussed above, because force is proportional to flux density squared, the attractive magnetic force on the touching sides of the rack and pinion gear teeth712and710is much greater than that existing between the non-touching sides. Thus, even though there will be a gap existing between certain non-contacting ones of the rack and pinion gear teeth712,710corresponding to the gap124shown inFIG.1, backlash movement will not occur due to relative movement of the rack and pinion gear teeth (as could occur in a conventional rack and pinion gear assembly) when the direction of movement by the force-imparting gear teeth (whether of the pinion702or the rack704) switches, provided that the attractive magnetic force between the contacting gear teeth is not exceeded by other forces.

Further with reference to the rack and pinion gear assembly700ofFIG.7, it should also be appreciated that, depending upon the embodiment, the air gap732can be adjustable during the manufacturing or assembly of the rack and pinion gear assembly700. More particularly, the air gap732can be adjusted based upon the selection and/or implementation of the hollow cylinder708, for example, by changing the diameter of the hollow cylinder or the axial location of the hollow cylinder. By adjusting the air gap732in any of these manner, this can result in adjustments to the maximum torque achievable before backlash movement occurs. That is, such adjustments allow for the maximum anti-backlash torque level to be set during assembly.

In a further example embodiment of an assembly involving intermeshed gear teeth,FIG.8shows a side elevation view of a bevel gear assembly800that includes a first ferromagnetic bevel gear802and a second ferromagnetic bevel gear804, as well as a MMF source806and a ferromagnetic hollow cylinder808. Further as shown, the first bevel gear802includes first bevel gear teeth810and the second bevel gear804includes second bevel gear teeth812that interface with the first bevel gear teeth. The first bevel gear802is supported upon and coaxial with a first shaft813that extends along a first central axis815. Each of the second bevel gear804, the MMF source806, and the hollow cylinder808are supported upon a second shaft814and positioned coaxially with respect to a second central axis816of the second shaft. The first and second central axes815and816are perpendicular (or, in other embodiments, substantially or largely perpendicular, or oblique) to one another and within the same plane, and the hollow cylinder808is positioned axially sufficiently far along the second central axis816that the first central axis815passes through the hollow cylinder. The MMF source806is located along the second central axis816at a location in between the second bevel gear804and the hollow cylinder808.

Additionally as shown, given the relative positioning of the first central axis815relative to the second central axis816, the first bevel gear802and second bevel gear804also are positioned relative to one another at right angles (or, in alternate embodiments, substantially or largely at right angles). Further, the first bevel gear802and second bevel gear804are respectively positioned along the first central axis815and the second central axis816so that the first bevel gear teeth810mesh with the second bevel gear teeth812. Additionally in the present embodiment a cylindrical magnetic iron surface (or structure)818is supported upon the first shaft813and positioned coaxially along the first central axis815at a location between the first bevel gear802and the hollow cylinder808. Although the cylindrical magnetic iron surface818is positioned adjacent to, so as to be in contact with, the first bevel gear802, an air gap820exists in between the hollow cylinder808and the cylindrical magnetic iron surface818. It will be appreciated that the components shown inFIG.8are supported relative to one another by one or more support structures (not shown).

The bevel gear assembly800also can operate in accordance with, or substantially in accordance with, the magnetic circuit200ofFIG.2. Indeed, in the bevel gear assembly800, the MMF source806applies a magnetic field so as to generate magnetic flux that proceeds within and around the assembly800, and between component parts thereof, so as to complete the magnetic circuit200. More particularly as shown inFIG.8, the magnetic flux generated by the MMF source806first proceeds from the MMF source into the hollow cylinder808as represented by a first arrow822, and then proceeds from the hollow cylinder through the air gap820and then through the cylindrical magnetic iron surface818and to the first bevel gear802as indicated by a second arrow824, generally in an axial manner along or parallel to the first central axis815. Further, the magnetic flux then proceeds radially outward within the first bevel gear802as represented by a third arrow826and then crosses from the first bevel gear teeth810to the second bevel gear teeth812(the contacting gear mesh) as indicated by a fourth arrow828. Upon reaching the second bevel gear teeth812, the magnetic flux then proceeds radially inward within the second bevel gear804as represented by a fifth arrow830, and then proceeds axially from the second bevel gear804back to the MMF source806, generally in an axial manner along or parallel to the second central axis816as indicated by a sixth arrow832.

It should be recognized that, due to the magnetic flux imparted by the MMF source806through the magnetic circuit formed by the hollow cylinder808, cylindrical magnetic iron surface818, first bevel gear802, and second bevel gear804(and including the air gap820), operation of the bevel gear assembly800can achieve zero backlash operation, or at least operation that involves significantly less backlash movement than would otherwise occur in conventional arrangements. Such operation can be achieved in substantially the same manner as described above in regard toFIG.1, if one assumes that the driving gear teeth106of the driving gear102constitute the first bevel gear teeth810of the first bevel gear802and also that the driven gear teeth110of the driven gear104constitute the second bevel gear teeth812of the second bevel gear804, or vice-versa. That is, operation involving no backlash movement or reduced levels of backlash movement can be achieved in the bevel gear assembly800including the MMF source806in substantially the same manner as described in regard toFIG.1if one assumes that either the first bevel gear teeth810respectively take the place of the driving gear teeth106in terms of imparting mechanical force, and the second bevel gear teeth812respectively take the place of the driven gear teeth110in terms of receiving the imparted mechanical force, or vice-versa.

Regardless of whether it is the first bevel gear teeth810or the second bevel gear teeth812that correspond to the driving gear teeth106in terms of imparting mechanical force, as described in regard toFIG.1there will be locations (typically one location corresponding to the location132ofFIG.1at any given time) at which certain ones of the first bevel gear teeth810and second bevel gear teeth812come into contact with one another. At these locations at which contact occurs, maximum flux will flow between the contacting ones of the first bevel gear teeth810and second bevel gear teeth812. Even though additional magnetic flux lines will exist at other locations between non-contacting sides of various ones of the first bevel gear teeth810and second bevel gear teeth812, the majority of flux will be concentrated along the path of least reluctance where the first and second bevel gears802and804are touching. Therefore, there will be a greater flux density on the touching side of the bevel gear mesh than the non-touching side.

Correspondingly, maximum attractive magnetic forces will occur between those respective contacting ones of the first bevel gear teeth810and second bevel gear teeth812, along the respective sides of the contacting ones of the teeth that are in contact with one another (e.g., along respective sides of the contacting ones of the teeth that correspond to the counter-clockwise-facing sides116and120inFIG.1). Indeed, as discussed above, because force is proportional to flux density squared, the attractive magnetic force on the touching sides of the first bevel gear teeth810and second bevel gear teeth812is much greater than that existing between the non-touching sides of the gears/gear teeth. Thus, even though there will be a gap existing between certain non-contacting ones of the first bevel gear teeth810and second bevel gear teeth812corresponding to the gap124shown inFIG.1, backlash movement will not occur due to relative movement of the first bevel gear teeth810and second bevel gear teeth812(as could occur in a conventional bevel gear assembly) when the direction of movement by the force-imparting bevel gear teeth (whether of the first bevel gear802or the second bevel gear804) switches, provided that the attractive magnetic force between the contacting gear teeth is not exceeded by other forces.

Further with reference to the gear assembly800ofFIG.8, it should also be appreciated that, depending upon the embodiment, the air gap820can be adjustable during the manufacturing or assembly of the gear assembly800. More particularly, the air gap820can be adjusted based upon the selection and/or implementation of the hollow cylinder808, for example, by changing the diameter of the hollow cylinder or the axial location of the hollow cylinder. By adjusting the air gap820in any of these manner, this can result in adjustments to the maximum torque achievable before backlash movement occurs. That is, such adjustments allow for the maximum anti-backlash torque level to be set during assembly.

In a further example embodiment of an assembly involving intermeshed gear teeth,FIG.9shows a side elevation view of a worm gear assembly900that includes a ferromagnetic first gear902, which can be a spur gear, and a ferromagnetic worm gear904, as well as a MMF source906and a ferromagnetic flux-conducting structure908. Further as shown, the first gear902includes gear teeth909and is supported upon a first shaft910that extends along a first central axis911. In addition, the MMF source906is supported upon the first shaft910between the first gear902and the flux-conducting structure908(alternatively, the MMF source906can be rigidly affixed to the flux-conducting structure, and the first shaft910and first gear902can be rotatably mounted to the flux-conducting structure). Both the MMF source906and the first gear902are coaxially arranged about the central axis911.

Additionally, the worm gear904includes threads913that extend around the worm gear, and that particularly are formed by helical ridges that extend outward from inner valleys914(shown in phantom) to an outer periphery915of the worm gear. The worm gear904(including the threads913) is supported upon a second shaft916, and both are configured to rotate about (and are coaxial with) a second central axis917. The first and second central axes911and917are perpendicular to one another and offset from one another, so that the threads913of the worm gear904interface and mesh with the gear teeth909of the first gear902. The flux-conducting structure908in the present embodiment is C-shaped, and the MMF906is positioned adjacent to a middle section918of the flux-conducting structure, between first and second brackets919and920, respectively. Although the MMF906is positioned adjacent to the middle section918of the flux-conducting structure908, the worm gear904is positioned alongside the second bracket920of the flux-conducting structure. In the present embodiment, the position of the second bracket920relative to the worm gear904is at 90 degrees or substantially 90 degrees rotated about the second central axis917relative to the position at which the worm gear904interfaces the first gear902. Further, an air gap921exists in between the worm gear904and the second bracket920of the flux-conducting structure908.

It should be understood that the worm gear assembly900also can operate in accordance with, or substantially in accordance with, the magnetic circuit200ofFIG.2. Indeed, in the worm gear assembly900, the MMF source906applies a magnetic field so as to generate magnetic flux that proceeds within and around the assembly900, and between component parts thereof, so as to complete the magnetic circuit200. More particularly as shown inFIG.9, the magnetic flux generated by the MMF source906first proceeds from the MMF source into the middle section918of the flux-conducting structure908, as indicated by a first arrow922, and then proceeds through the flux-conducting structure from the middle section to the second bracket920, as indicated by a second arrow924. Next, the magnetic flux travels through the second bracket920, across the air gap921, and into the worm gear904, as represented by a third arrow926. Further, the magnetic flux additionally travels from the threads913of the worm gear904to the gear teeth909of the first gear902(through the contact mesh) and radially inward toward the first central axis911, as represented by a fourth arrow928. Finally, the magnetic flux then travels generally along the first central axis911from the first gear902back to the MMF source906, as indicated by a fifth arrow930.

It should be recognized that, due to the magnetic flux imparted by the MMF source906through the magnetic circuit formed by the first gear902, worm gear904, and flux-conducting structure908(and including the air gap921), operation of the worm gear assembly900can achieve zero backlash operation, or at least operation that involves significantly less backlash movement than would otherwise occur in conventional arrangements. Such operation can be achieved a manner that is similar to that described above in regard toFIGS.1and6. More particularly, it will be appreciated that the worm gear assembly900generally operates in a manner in which the threads913of the worm gear904when turning impart mechanical force upon the gear teeth909of the first gear902.

As described in regard toFIG.1andFIG.6(and particularlyFIG.6), there will be locations at which certain respective sides of certain respective ones of the threads913of the worm gear904come into contact with certain respective sides of certain respective ones of the gear teeth909of the first gear902. Further, the magnetic flux imparted by the MMF source906through the magnetic circuit formed by the first gear902, worm gear904, and flux-conducting structure908imposes attractive magnetic forces between the threads913of the worm gear904and the gear teeth909of the first gear902in a manner that biases contact between those threads and gear teeth, to one side of the mesh. In particular, the attractive magnetic forces are strongest at the aforementioned locations at which contact between the certain respective sides of the certain respective ones of the threads913of the worm gear904and the certain respective sides of the certain respective ones of the gear teeth909are in contact (e.g., at locations corresponding to the locations630ofFIG.6). Consequently, those certain respective sides of those certain respective ones of the threads913will tend to be biased to remain in contact with those certain respective sides of those certain respective ones of the respective gear teeth909with which those certain respective ones of the threads are in contact. Given these attractive magnetic forces, the worm gear assembly900can be operated in a manner that avoids backlash movement (achieves zero backlash operation) or at least achieves reduced backlash movement.

More particularly with respect to the illustration provided byFIG.9, during operation the worm gear904initially may be applying mechanical force in a direction into the page (as illustrated inFIG.9), where respective threads913of the worm gear push against respective ones of the gear teeth909that are positioned immediately inwardly of those respective threads (again as illustrated inFIG.9). With such interaction, there will exist gaps (or backlash regions) separating the respective threads913of the worm gear904from respective other ones of the gear teeth909that are respectively positioned on the opposite sides of those respective threads, that is, respectively positioned outwardly of those respective threads (again as illustrated inFIG.9) rather than respectively positioned immediately inwardly of those respective threads as in the case of the respective ones of the gear teeth909with which those respective threads are in contact.

Given such an arrangement, in a conventional worm gear assembly, when the direction of applied mechanical force is reversed, the threads of the worm gear904will travel through the backlash regions (e.g., corresponding to the gaps640ofFIG.6) without incremental movement of the first gear902. However, in the present embodiment ofFIG.9in which the MMF source906together with the first gear902, worm gear904, and flux-conducting structure908(along with the air gap921) form a magnetic circuit, when the direction of applied mechanical force is reversed, the threads of the worm gear904will “pull” the first gear902via the attractive magnetic force on the contact sides of the threads913of the worm gear. That is, if the worm gear904switches from rotating in a first direction tending to cause the respective threads913of the worm gear to mechanically push against the respective ones of the gear teeth909to rotating in the opposite direction, contact between the respective threads and the respective ones of the gear teeth909will tend to be maintained.

Further in this operational circumstance, assuming that the applied mechanical force (and any other magnetic forces) is not so strong as to overcome the attractive magnetic force between the respective threads913of the worm gear904and the respective ones of the gear teeth909with which those threads are in contact, the threads of the worm gear will continue to “pull” the first gear902until the direction of rotation of the worm gear (and associated force imparted by the worm gear) is reversed again. Thus, in this operational circumstance, the first gear902will not be subject to a backlash region of non-movement. Indeed, even though there exist the respective gaps (or backlash regions corresponding to the backlash regions640) separating the respective threads913of the worm gear904from the other ones of the gear teeth909that are respectively on the opposite sides of those respective threads by comparison with the respective ones of the gear teeth closest to those respective threads, the respective threads will not tend to move through or close those respective gaps (albeit the gaps can vary in extent somewhat as the worm gear904rotates relative to the first gear902).

Further in this regard, although additional magnetic flux lines exist between the respective threads913of the worm gear904and the respective other ones of the gear teeth909that are respectively separated from those respective threads by the respective gaps, the majority of magnetic flux will be concentrated along the paths of least reluctance where the respective threads of the worm gear are contacting (or closest to) the respective ones of the gear teeth909. Correspondingly, there will be a greater flux density between the contacting/touching sides of the respective threads913of the worm gear904and respective ones of the gear teeth909with which those respective threads are in contact than between the non-contacting/non-touching sides of the respective threads and the respective other ones of the gear teeth at which the respective gaps exist. Because magnetic force is proportional to flux density squared, the overall attractive magnetic force between the touching sides of the respective threads913of the worm gear904and the respective ones of the gear teeth909adjacent respectively thereto is much greater than the overall attractive magnetic force between the non-touching sides of the respective threads913of the worm gear and the respective other ones of the gear teeth909that are separated from those respective threads by the respective gaps.

Notwithstanding the above discussion, if the driving mechanical force between the worm gear904and the first gear902(plus any additional magnetic forces) is in opposition to and greater than the attractive magnetic forces between the respective threads913of the worm gear and the respective ones of the gear teeth909closest to those respective threads, backlash movement can still occur. That is, if the driving mechanical force between the worm gear904and the first gear902(plus any additional magnetic forces) exceed the attractive magnetic forces between the respective threads913of the worm gear and the respective ones of the gear teeth909closest to those respective threads, the worm gear will transiently travel through the gaps (backlash regions). If this occurs, then a new equilibrium will be attained when the contact and non-contact sides of the respective threads913and gear teeth909are swapped.

It should be appreciated that such a situation, in which backlash occurs, can be avoided by sizing the magnetic circuit (and correspondingly sizing the magnetic field applied by the MMF source906) such that the amplitude of the overall magnetic force communicated between the respective threads913of the worm gear904and the respective ones of the gear teeth909closest to those respective threads is greater than the maximum mechanical force the first gear902will realize in operation relative to the worm gear904. Additionally, in alternate embodiments, the magnetic circuit can be sized appropriately for a lower volume and mass than that required for the maximum operating force/torque, still eliminating backlash under part-load conditions but allowing backlash above a reversing backlash force threshold. This sizing method can be desirable for systems that are configured to apply large forces for fast response times but also to apply lower forces in alternating directions to move in small increments to reject disturbances and provide precise positioning in a localized region where the holding force is smaller than the maximum force.

Referring toFIG.10, it should be appreciated that the present disclosure encompasses other embodiments of worm gear assemblies in addition to the worm gear assembly900ofFIG.9, such as a worm gear assembly1000. As shown, the worm gear assembly1000ofFIG.10is similar to the worm gear assembly900ofFIG.9in that the worm gear assembly1000also includes a ferromagnetic first gear1002, a ferromagnetic worm gear1004, a MMF source1006, and a flux-conducting structure1008, which respectively correspond to the first gear902, the worm gear904, the MMF source906, and the flux-conducting structure908ofFIG.9. The first gear1002includes gear teeth1009, the MMF source1006again is supported adjacent to the first gear1002on a first shaft1010, and all of the MMF source, first gear, and first shaft are positioned coaxially about a first central axis1011. Additionally, the worm gear1004includes threads1013that extend around the worm gear, and that particularly are formed by helical ridges that extend outward from inner valleys1014(shown in phantom) to an outer periphery1015of the worm gear. The worm gear1004(including the threads1013) is supported upon a second shaft1016, and both are configured to rotate about a second central axis1017. The first and second central axes1011and1017are perpendicular to one another and offset from one another, so that the threads1013of the worm gear1004interface and mesh with the gear teeth1009of the first gear1002in the same or substantially the same manner as the threads913of the worm gear904interface and mesh with the gear teeth909of the first gear902ofFIG.9.

However, in contrast to the worm gear assembly900, the flux-conducting structure1008of the worm gear assembly1000is L-shaped rather than C-shaped. More particularly, the flux-conducting structure1008includes a bracket1020that extends around the worm gear1004, along a side of the worm gear opposite the side of the worm gear that interfaces the first gear1002, such that the worm gear is positioned in between the bracket1020and the first gear1002. Consequently, although the air gap921inFIG.9is located at a position that is 90 degrees or substantially 90 degrees relative to the position at which the worm gear904interfaces the first gear902, in the worm gear assembly1000ofFIG.10a first air gap1021exists in between the worm gear1004and the bracket1020at a position that is 180 degrees or substantially 180 degrees relative to the position at which the worm gear1004interfaces the first gear1002.

Also, in contrast to the worm gear assembly900, in the worm gear assembly1000ofFIG.10the MMF source1006is separated from the flux-conducting structure1008by way of an additional (second) air gap1019. That is, even though the first gear1002and MMF source1006are supported upon the first shaft1010and even though the first shaft extends through and is supported relative to the flux-conducting structure1008, there is an additional physical space constituting the second air gap1019that exists between the MMF source1006and the flux-conducting structure1008.

The worm gear assembly1000operates in nearly the same manner as the worm gear assembly900. Again, the threads1013of the worm gear assembly1000can impart mechanical forces in relation to the gear teeth1009of the first gear1002. Also, the worm gear assembly1000also can operate in accordance with, or substantially in accordance with, the magnetic circuit200ofFIG.2. Indeed, in the worm gear assembly1000, the MMF source1006applies a magnetic field so as to generate magnetic flux that proceeds within and around the assembly1000, and between component parts thereof, so as to complete the magnetic circuit200. Further, as described in regard to the worm gear assembly900ofFIG.9, during operation of the worm gear assembly1000there will be locations at which certain respective sides of certain respective ones of the threads1013of the worm gear1004come into contact with certain respective sides of certain respective ones of the gear teeth1009of the first gear1002. It is at these contacting sides at which magnetic flux communicated between, and associated attractive magnetic forces between, the worm gear1004and first gear1002are strongest. Thus, as with respect to the worm gear assembly900, during operation of the worm gear assembly1000, due to the attractive magnetic forces between the respective threads1013and the respective ones of the gear teeth1009with which those respective threads are in contact, contact between those respective threads and those respective ones of the gear teeth tends to be maintained notwithstanding changes in the rotational direction of the worm gear1004. Correspondingly, backlash movement is avoided or reduced.

Notwithstanding the operational similarities between the worm gear assembly900and the worm gear assembly1000, there are also several operational differences due to the differences in the configuration of the worm gear assembly1000relative to the worm gear assembly900as described above. As already described, the MMF source1006is positioned axially in line with the first gear1002, and separated by the second air gap1019from the flux-conducting structure1008(which can be considered a ferromagnetic flux return path structure), where that flux-conducting structure is also separated from the worm gear1004by the first air gap1021. Thus, in the worm gear assembly1000, the magnetic flux path from and back to the MMF source1006passes through not only each of the first gear1002, the worm gear1004, the flux-conducting structure1008, and the first air gap1021between the flux-conducting structure and the worm gear (which corresponds to the air gap921of the worm gear assembly900), but also passes through the second air gap1019to complete the magnetic (flux) circuit.

Further, due to the shape of the flux-conducting structure1008in which the bracket1020extends around the worm gear1004, a larger surface area (e.g., of a portion of the bracket1020facing the worm gear) is provided for magnetic flux transfer than is the case with the second bracket920of the worm gear assembly900. Given this to be the case, it should be appreciated that, depending upon the embodiment, the flux-conducting structure (serving as a ferromagnetic flux return path structure) may be shaped to provide a larger (or smaller) surface area for flux transfer. The worm gear assembly1000can also entail a reduction in rotating mass by comparison with the worm gear assembly900, which can be beneficial in terms of reducing system inertia.

Additionally with reference to the respective worm gear assemblies900and1000ofFIGS.9and10, respectively, it should also be appreciated that, depending upon the embodiment, one or more of the respective air gaps921,1019, and1021can be adjustable during the manufacturing or assembly of the respective gear assemblies900and1000. More particularly, the air gap921can be adjusted based upon the selection and/or implementation (e.g., the shape) of the flux-conducting structure908or by adjusting some other parameter of the worm gear assembly900, for example, by changing the diameter of the worm gear904or the axial alignment of the worm gear relative to the first gear902and/or the flux-conducting structure. Also, the first air gap1021can be adjusted based upon the selection and/or implementation (e.g., the shape) of the flux-conducting structure1008or by adjusting some other parameter of the worm gear assembly1000, for example, by changing the diameter of the worm gear1004or the axial alignment of the worm gear relative to the first gear1002and/or the flux-conducting structure. Further, the second air gap1019also can be adjusted based upon the selection and/or implementation (e.g., the shape) of the flux-conducting structure1008. By adjusting the air gaps921,1019, and/or1021in any of these manners, this can result in adjustments to the maximum torque achievable before backlash movement occurs in the respective worm gear assembly900or worm gear assembly1000, as applicable. That is, such adjustments allow for the maximum anti-backlash torque level(s) for the respective worm gear assemblies900and/or1000to be set during assembly.

Although each of the embodiments shown in and described in relation toFIGS.1through10envisions the generation of magnetic flux by one or more MMF sources that are distinct from the intermeshing gears or other corresponding interfacing structures (e.g., threads, nuts, racks, etc.) by which power transmission is achieved, the present disclosure is not limited to such mechanical gear or other power transmission systems. Rather, the present disclosure also is intended to encompass embodiments in which it is the intermeshing gears or other corresponding interfacing structures themselves that generate the magnetic flux. In at least some such embodiments, the intermeshing gears or other corresponding interfacing structures are manufactured from permanent magnet materials (or otherwise have permanent magnet materials integrated or included therewithin) so that those interfacing gears or corresponding structures exert magnetic forces relative to one another. Also, in at least some other embodiments, one or more electromagnets can be included within the intermeshing gears or other corresponding interfacing structures.

In at least some embodiments, the present disclosure encompasses embodiments having a magnetically-assisted gear mesh, having a plurality of gears, wherein the gears are manufactured from permanent magnet materials. Referring toFIG.11in this regard, in at least some such embodiments, such gear assemblies employ permanent magnets taking the form of ring magnets.FIG.11particularly illustrates an example first permanent magnet gear1100that is formed by the combination of a first inner portion1102and a first outer portion1104. As shown, the first inner portion1102in the present embodiment is annular and the first outer portion1104is substantially annular but also includes first outer gear teeth1106arranged along an outer circumference of the first outer portion. Both of the first inner portion1102and first outer portion1104are coaxially positioned about a first central axis1108, with the first inner portion1102and first outer portion1104respectively being sized so that an outer circumference1110of the first inner portion1102is identical in size and adjacent to an inner circumference1112of the first outer portion1104.

The first inner portion1102can be understood to form a first pole and the first outer portion1104can be understood to form a second pole having a polarity opposite to that of the first inner portion. For example, as illustrated inFIG.11, the first pole associated with the first inner portion1102can be a north pole and the second pole associated with the first outer portion1104can be a south pole, although in other embodiments, there can be an opposite assignment of poles. Given this arrangement of poles among the first inner portion1102and first outer portion1104, the first permanent magnet gear1100overall can be understood to have a polarity that is radially directed along radial axes extending radially outward from the first central axis1108, including (for example) a first radial axis represented by an arrow1114. At the same time, it should be appreciated that the illustration of the permanent magnet gear1100as having the first inner portion1102and the first outer portion1104is not provided to suggest that the permanent magnet gear1100necessarily has two distinct annular portions that are distinct structures. Rather, the first inner portion1102and first output portion1104can be integrally formed as a single structure made from a single permanent magnet material serving as a single permanent magnet gear. Further, the junction between the first inner portion1102and first outer portion1104formed at the outer circumference1110/inner circumference1112need not be a physical junction or physical attribute. Instead, the junction is merely provided to figuratively illustrate the existence of two concentric regions of the permanent magnet gear1100, which are respectively associated with the first inner portion1102and the first outer portion1104, at which are provided the first (e.g., north) and second (e.g., south) poles of the permanent magnet gear.

Further, given this overall polarity, it should be appreciated that magnetic flux lines generated by the first inner portion1102and first outer portion1104generally proceed radially outward through the first inner portion1102and first outer portion1104beyond the first outer gear teeth1106, at all circumferential locations around the gear. The second (e.g., south) pole in the present embodiment can be understood to exist particularly at the outer tips of the first outer gear teeth1106. Then the magnetic flux lines curve outward away from the first permanent magnet gear1100, in a manner generally parallel to the first central axis1108on either side of the first permanent magnet gear1100(into and out of the page when viewingFIG.11) and at all circumferential locations around the gear, and then proceed generally radially inwardly toward the first central axis1108on either side of the gear. Finally, upon reaching locations positioned radially inward of a first further inner circumference1116of the first inner portion1102(that is, closer to the first central axis1108than the further inner circumference), the magnetic flux lines then curve inward back toward the first permanent magnet gear1100, again in a manner generally parallel to the first central axis1108(out of and into the page when viewing theFIG.11). Upon the magnetic flux lines reaching a first interior region1118within the first permanent magnet gear1100, within the first further inner circumference1116of the first inner portion1102, the magnetic flux lines then proceed generally radially outward again into the first inner portion1102at the first further inner circumference1116, at which can be understood to exist the first (e.g., north) pole. Upon passing radially outward through the first further inner circumference1116, the flux then further proceeds radially outward through the first inner portion1102and the first outer portion1104.

The first permanent magnet gear1100ofFIG.11in the present embodiment can be considered a spur gear. As discussed in further detail below with respect toFIG.12andFIG.13, the present disclosure is intended to encompass gear assemblies and systems employing multiple spur gears each taking the form of (and having the same polarity as) the first permanent magnet gear1100, as well as gear assemblies employing multiple spur gears in which the different spur gears have different polarities (e.g., one having the same polarity as the first permanent magnet gear, and one having an opposite polarity). Also, notwithstanding the description provided herein in regard toFIG.11,FIG.12, andFIG.13, the present disclosure is also intended to encompass other types of permanent magnet gear assemblies and systems employing other types of intermeshing gears, as well as other types of power transmission systems employing other corresponding interfacing structures, such as those described above, including gears with any of a variety of gear tooth profiles, bevel gears, rack and pinion assemblies, worm gears, screw and nut assemblies, etc.

Referring additionally toFIG.12in this regard, a first permanent magnet gear assembly1200has two interfacing gears, including a first gear that is a driving gear1202and a second gear that is a driven gear1204. In this example ofFIG.12, the driving gear1202is a first spur gear taking the form of the first permanent magnet gear1100ofFIG.11. In contrast, the driven gear1204is a second spur gear but takes the form of a second permanent magnet gear1150that is identical to the first permanent magnet gear1100ofFIG.11except insofar as has a polarity that is opposite to the polarity of the first permanent magnet gear. Thus, the second permanent magnet gear1150has a second inner portion1152, a second outer portion1154, a second outer gear teeth1156, an outer circumference1160, an inner circumference1162, a second further inner circumference1166, and a second interior region1168, which respectively correspond to and are identical in shape to the first inner portion1102, the first outer portion1104, the first outer gear teeth1106, the outer circumference1110, the inner circumference1112, the first further inner circumference1116, and the first interior region1118, respectively. Also, just as the first inner portion1102and first outer portion1104extend concentrically around a first central axis1108, the second inner portion1152and second outer portion1154extend concentrically around a second central axis1158.

Notwithstanding the similarities between the first permanent magnet gear1100and the second permanent magnet gear1150, as noted the second permanent magnet1150has a polarity that is opposite the polarity of the first permanent magnet gear1100. This is illustrated inFIG.12by a second radial axis represented by an arrow1164, which is labeled in a manner opposite that of the arrow1114. That is, inFIG.12, although the arrow1114associated with the first permanent magnet gear1100is labeled to show the north pole as being positioned within the interior region1118and the south pole as being positioned along the first outer gear teeth1106of that gear, the arrow1164associated with the second permanent magnet gear1150is labeled to show the south pole as being positioned within the second interior region1168and the north pole as being positioned along the second outer gear teeth1156of that gear. In alternate embodiments, the respective polarities of the first and second permanent magnet gears1100and1150can be reversed from that shown inFIG.12.

Because of the opposite polarities associated with the first permanent magnet gear1100and second permanent magnet gear1150, attractive magnetic forces exist between those respective gears, particularly at contacting ones of the first outer gear teeth1106and second outer gear teeth1156, which are collectively shown as intermeshing gear teeth1206inFIG.12. In the present embodiment, the attractive magnetic forces at the intermeshing gear teeth1206can have the same or substantially similar effects as the attractive magnetic forces described above in regard to embodiments such as those shown in and described in regard toFIGS.1through10. That is, the first outer gear teeth1106can contact and mechanically push the second outer gear teeth1156in the same manner that the driving gear teeth106can mechanically push the driven gear teeth110in the embodiment ofFIG.1.

Also, contacting ones of the first outer gear teeth1106and second outer gear teeth1156have stronger attractive magnetic forces therebetween than non-contacting ones of the first outer gear teeth1106and second outer gear teeth1156, in the same manner that contacting ones of the driving gear teeth106and driven gear teeth110have stronger attractive magnetic forces therebetween than do non-contacting ones of the driving gear teeth106and driven gear teeth110. Consequently, if the direction of rotation of the first permanent magnet gear1100is reversed, contact between the contacting ones of the first outer gear teeth1106and second outer gear teeth1156will be maintained, and occurrences of backlash movement will still be avoided or reduced, due to the attractive magnetic forces between those teeth (provided that those attractive magnetic forces are not overwhelmed by other countervailing forces, including mechanical or loading forces and/or other attractive magnetic forces between non-contacting ones of the first outer gear teeth1106and second outer gear teeth1156). Indeed, in the same manner as described in regard to the gear assembly100ofFIG.1, upon a reversal of the direction of the first permanent magnet gear1100, the first outer gear teeth1106of that gear will tend to pull the second outer gear teeth1156of the second permanent magnet gear1150, until such time as the direction of rotation of the first permanent magnet gear1100is reversed again.

In addition to the embodiment ofFIG.12, the present disclosure also is intended to encompass additional permanent magnet gear assemblies that employ intermeshing gears that share in common the same polarity. In this regard,FIG.13shows a second permanent magnet gear assembly1300with two interfacing gears, including a first gear that is a driving gear1302and a second gear that is a driven gear1304. In this embodiment, each of the driving gear1302and driven gear1304is a spur gear taking the form of the first permanent magnet gear1100ofFIG.11. Each of the driving gear1302and driven gear1304can be manufactured for example from the same radially oriented ring magnets, such that all of the gear teeth of both of the gears have the same polarity.

Thus, in contrast to the first permanent magnet gear assembly1200, each of the driving gear1302and driven gear1304of the second permanent magnet gear assembly1300has the same polarity, namely, the polarity illustrated inFIG.11in which the north pole of the first permanent magnet gear1100is along the first interior region1118and the south pole of the gear is along the outer periphery of the first outer gear teeth1106. Although in the present example each of the driving gear1302and driven gear1304has the polarity of the first permanent magnet gear1100, in alternate embodiments each of the driving gear and driven gear can instead have the opposite polarity in which it is the south pole that is along the interior region and the north pole that is along outer gear teeth (as with the second permanent magnet gear1150ofFIG.12).

Because the driving gear1302and driven gear1304in the second permanent magnet gear assembly1300share in common the same polarity, the second permanent magnet gear assembly1300operates in a manner that is different than the first permanent magnet gear assembly1200—indeed, the second permanent magnet gear assembly1300operates in a manner that also is different from the other embodiments discussed above in regard toFIGS.1through10. In particular, because the driving gear1302and driven gear1304of the second permanent magnet gear assembly1300share in common the same polarity, repulsive magnetic forces exist between driving gear teeth1306of the driving gear1302and driven gear teeth1308of the driven gear1304. These repulsive magnetic forces particularly are strongest at those of the driving gear teeth1306and driven gear teeth1308that are meshing with one another, which are shown as intermeshing gear teeth1310inFIG.13. As a result of these repulsive magnetic forces, the driving gear teeth1306and driven gear teeth1308tend not to come into physical contact with one another.

Indeed, due to the repulsive forces between the intermeshing gear teeth1310, as any given one of the driving gear teeth1306approaches a given one of the driven gear teeth1308, that given one of the driven gear teeth1308will tend to be pushed away from the given one of the driving gear teeth1306simply by virtue of the repulsive magnetic forces existing between those teeth, without any physical contact or mechanical forces coming into play. This manner of operation is true regardless of the direction of rotation of the driving gear1302. Thus, in this embodiment, in which the driving gear teeth1306and driven gear teeth1308that are meshed are all associated with the same magnetic pole, opposing forces can be used to transmit forces/torques without or substantially without physical contact, in a manner that prevents or reduces backlash movement. Backlash movement is avoided or at least reduced insofar as each given one of the driving gear teeth1306, as it meshes with the driven gear teeth1308and regardless of the direction of rotation, tends to remain positioned substantially midway between the neighboring ones of the driven gear teeth on opposite sides of that given one of the driving gear teeth, and vice-versa.

At the same time, it should be noted that, depending upon other forces (e.g., the mechanical load borne by the driven gear1304), it is not necessarily the case that any given one of the driving gear teeth1306will be positioned exactly midway in between the neighboring ones of the driven gear teeth1308on opposite sides of that driving gear tooth (or vice-versa) when those teeth are meshing with one another. Indeed, depending upon the forces (or torques) involved or other operational circumstances, any given one of the driving gear teeth1306that is meshing with a pair of the driven gear teeth1308may be closer to one or the other of those driven gear teeth, and likewise any given one of the driven gear teeth1308that is meshing with a pair of the driving gear teeth1306may be closer to one or the other of those driving gear teeth. Additionally, in the embodiment ofFIG.13, it is even possible that in some circumstances given ones of the driving gear teeth1306and driven gear teeth1308will physically come into contact with one another and communicate forces (and/or torques) between one another mechanically due to such contact. In view of this type of behavior, and given that the driving gear1302and driven gear1304retain the physical shape and structure (except for their magnetic properties) of other types of mechanical gears such as those described above in regard toFIG.1, the second permanent magnet gear assembly1300can also be considered a magnetically-assisted mechanical gear assembly or system.

In addition to the embodiments described above in regard to each ofFIGS.1through13, the present disclosure is also intended to encompass numerous other embodiments. Among other things, although some of the embodiments described above employ electromagnetic MMF source(s) to generate magnetic flux and associated magnetic forces electromagnetically and others of the embodiments described above employ permanent magnet(s) as MMF source(s) to generate magnetic flux and associated magnetic forces, the present disclosure also encompasses embodiments in which the MMF source(s) that are employed include both one or more permanent magnet(s) and one or more electromagnetic source(s). In at least some such embodiments employing both permanent magnet(s) and electromagnetic source(s) in which the electromagnetic source(s) include one or more coil structures or elements, the current(s) flowing within the coil structures can be adjusted in sign and amplitude. Depending upon the embodiment or implementation, such current(s) flowing within the electric coil structures can be adjusted to selectively strengthen, reduce or cancel the magnetic flux (e.g., MMF) provided from the permanent magnet(s). This approach allows for a default, unpowered, anti-backlash torque handling ability, allows for conventional backlash operation when the current(s) within the coil structures are controlled to perfectly cancel the magnetic flux (MMF) provided from the permanent magnet(s), and also allows for increased anti-backlash torque handling when the current(s) are controlled to so that the magnetic flux generated electromagnetically is additive relative to the magnetic flux provided by the permanent magnet(s). Additionally, it should be appreciated that one or more additional sources of MMF can be applied to any of the circuits described herein, and that, indeed, any arbitrary number of sources of MMF can be employed depending upon the embodiment.

Also, notwithstanding the above description, the present disclosure is also intended to encompass a variety of other magnetically-assisted mechanical gear systems or assemblies, and other systems or assemblies with other corresponding interfacing structures allowing for power transmission (such as screw-and-nut assemblies with threads, worm gear assemblies, and rack and pinion assemblies, etc., as described above) that are configured to allow for the application of magnetic fields to and through interfacing gears and other structures to achieve power transmission operation. Such different magnetically-assisted mechanical gear systems and assemblies, and other related systems or assemblies, can vary from one another and from those described above in terms of any of a variety of structural features and/or in any of a variety of other manners. For example, any plurality of gears may be placed in series or parallel to produce a variety of arrangements driving flux in a circuit between pairs of gears. Any of a variety of types of gear arrangements and meshes are intended to be encompassed herein, including for example planetary arrangement gear meshes. Although in some embodiments, any given gear assembly can include two or more gears that have the same shape and size, in alternate embodiments, any given gear assembly can include two or more gears that respectively have different shapes and/or sizes, and/or different numbers of gear teeth, respectively, or gear teeth respectively having different shapes or profiles, respectively.

Additionally, although the present disclosure envision interfacing structures such as gears, racks, screws, and nuts, which include formations such as gear teeth and/or threads by which those interfacing structures can interact with and communicate forces/torques among each other, the present disclosure is not intended to be limited to the particular interfacing structures or formations descried above. Rather, the present disclosure is also intended to encompass other types of interfacing structures and/or interfacing structures that have other types of formations that can allow for mechanical and/or magnetic interactions and the communication of forces/torques. Further, the present disclosure is intended to encompass any of a variety of different embodiments having any one or more intermediary structures such as the hollow cylinders or other structures, as well as any number of air gaps or structures affecting reluctances or other aspects of the flow or communication of magnetic flux or achievement of magnetic forces, and is not limited to the particular embodiments described above.

Further, it should be recognized that whether a particular interfacing structure constitutes a driving gear (or other interfacing structure that serves to impart movement, force, or torque to another interfacing structure) or a driven gear (or other interfacing structure that serves to move, or receive applied force or torque from another interfacing structure) can vary with time for a given device or system, or can vary in dependence upon the manner of operation of a given device or system. That is, for a given device or system, it is possible that a gear (or other interfacing structure) that constitutes a driving gear (or other driving interfacing structure) at one moment in time or in one operational circumstance may serve as or become a driven gear (or other driven interfacing structure) at another moment in time or in another operational circumstance, or vice-versa. Such switching of the roles of interfacing gears (or other interfacing structures) between being driving gears (or other driving interfacing structures) and being driven gears (or other driven interfacing structures) can occur in any of a variety of types of implementations, arrangements, applications, or systems.

For example, in one system, a first gear can be driven to rotate by a motor at a first time so as to cause rotation of a second gear that in turn is coupled to a spring load. In such system, at the first time, the first gear constitutes the driving gear and the second gear constitutes the driven gear. However, also with respect to such a system, the first gear and second gear of the system can respectively switch in their respective roles to become the driven gear and driving gear of the system, respectively, if at a second time the motor is switched off. At such a second time, the spring coupled to the second gear will tend to drive the second gear to rotate (in a direction contrary to the direction in which the second gear was previously driven to rotate by the first gear), and the second gear in turn will tend to drive the first gear to rotate (in a direction contrary to the direction in which the first gear was previously caused to rotate by the motor). At that second time, the second gear constitutes the driving gear and the first gear constitutes the driven gear.

Thus, although the description provided herein includes descriptions of one or more embodiments in which a particular gear (or other interfacing structure) is referred to as a driving gear (or other driving interfacing structure) and in which a particular other gear (or other interfacing structure) is referred to as a driven gear (or other driven interfacing structure), such description should not be interpreted as implying that those particular gears (or other interfacing structures) necessarily always serve as driving and driven gears, respectively (or as driving and driven interfacing instructions, respectively). Rather, with respect to at least some embodiments encompassed herein, depending upon the implementation or operational circumstance, any given one of a pair of interfacing gears or structures of such embodiment can serve as the driving interfacing structure or the driven interfacing structure at different times or operational circumstances.

It should be appreciated that one or more embodiments described herein are capable of providing any one or more of a variety of advantages. For example, delays in movement or the transmission of power, which might otherwise arise due to backlash within a given conventional system, can be avoided, eliminated, or reduced in one or more of the embodiments encompassed herein that eliminate, avoid, or reduce backlash. Also for example, errors in output rotation relative to input rotation, which might otherwise arise due to backlash within a given conventional system, can be avoided, eliminated, or reduced in one or more of the embodiments encompassed herein that avoid, eliminate, or reduce backlash. Further, although unsteady rotation (e.g., output rotation) might produce overall system instability in a conventional system having backlash, one or more of the embodiments encompassed herein that avoid, eliminate, or reduce backlash can achieve operation that remains stable notwithstanding such unsteady rotation. In at least some such embodiments, such system stability can be achieved at least in part because, due to the absence of or reduction in backlash, details regarding the angular positions of the gears (or other gear train components or other interfacing components) of the system can be sensed/tracked and taken in another account at any given moment.

It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.