Patent Description:
Over travel stops are used in rotary transmission systems in situations wherein external envelope constraints require a mechanical stop to limit the amount of turns the transmission can take in either direction. In linear actuators that utilise a lead screw to generate axial movement, an over travel stop is provided by an acme screw thread that drives a nut in an axial direction between two hard stops that each limit travel of the nut. Disadvantages with such systems is that they can take up a lot of space, since the length of the thread must be long enough to allow for the number of rotations required for the full amount of turns. Furthermore, the end stops have a limited load capacity due to limited contact areas at the earthing surface. Over travel stops that rely on axial displacement along a thread do also not scale well with load or stroke requirements.

<CIT> relates to a system for controlling the rotation of two gears by using control members on each of the first and second gears. Cooperation of the first and second control members results in a longitudinal displacement of one of the gears that causes the gear to stop rotating.

<CIT> relates to a stopping mechanism for a rotating member by providing a follower member attached to the rotating member. Rotation of the rotating member causes the follower member to be axially moved into engagement with the fixed stop member in order to stop rotation of the rotating member.

<CIT> relates to a rotary stop mechanism for stopping the rotation of a shaft. A movable stop member is mounted to one of the gears on the shaft. Axial displacement of the moveable stop member from a first position to second position results in the moveable stop member engaging a fixed stop and stopping the rotation of the shaft.

<CIT> discloses in its <FIG> a system for stopping rotation of a first gear and a second gear on a shaft, comprising: the first gear and second gear being concentric to said shaft; wherein the first gear and the second gear are driven by the same input system; wherein the system is configured such that the first gear and the second gear rotate at different speeds relative to each other; wherein the first gear comprises a first end stop and the second gear comprises a second end stop; wherein the first end stop and the second end stop are configured to engage each other when the first gear and the second gear have each rotated a predetermined number of turns relative to each other; and wherein engagement of the first end stop with the second end stop is configured to prevent rotation of the first gear and the second gear and cause a stall in the system.

Claim <NUM> defines a system for stopping rotation of a first gear and a second gear on a shaft. Its dependent claims concern particular embodiments of the invention as defined in claim <NUM>.

Claim <NUM> defines a method for providing an over stop travel system on a gear system. Its dependent claims define particular embodiments of the invention as defined in claim <NUM>.

Described herein is a system and method for an over travel stop mechanism that prevents a gear system from travelling past its design limits.

A schematic of an over travel stop mechanism for a first gear <NUM> and a second gear <NUM> is shown in <FIG>. The first gear <NUM> and the second gear <NUM> are concentric spur gears of differing sizes which are rotatable on shaft <NUM>.

Each of the first gear <NUM> and the second gear <NUM> is run from an input gear <NUM> which is a single two-output spur gear. The first output <NUM> of the input gear <NUM> meshes with the first gear <NUM> and the second output <NUM> of the input gear <NUM> meshes with the second gear <NUM>. The first output <NUM> and the second output <NUM> of the input gear <NUM> are each fixed on shaft <NUM> and therefore they rotate at the same speed. The first gear <NUM> rotates at a different speed than the second gear <NUM>.

According to an embodiment not falling within the feature of claim <NUM> "the first gear (<NUM>) and second gear (<NUM>) being rotatable about said shaft (<NUM>)", one of either the first gear <NUM> or the.

second gear <NUM> can be configured to drive shaft <NUM> as a system output. When the single two-output spur gear <NUM> is turned, the first gear <NUM> and the second gear <NUM> will turn at a different speed because the first gear <NUM> and the second gear <NUM> have differing sizes. The first gear <NUM> will turn in a first direction and the second gear <NUM> will also turn in the same, first direction.

A first end stop <NUM> is provided on the first gear <NUM> and a second end stop <NUM> is provided on the second gear <NUM>. When the input gear <NUM> is turned, the first end stop <NUM> will move either towards or away from the second end stop <NUM>, depending on the direction of input rotation. The first end stop <NUM> and the second end stop <NUM> are configured such that engagement between the first end stop <NUM> and the second end stop <NUM> will prevent further motion of the first gear <NUM> and the second gear <NUM> in the first direction. This prevents travel of the first gear <NUM> and the second gear <NUM> past their design limits. The system stalls upon engagement of the first end stop <NUM> with the second end stop <NUM> because the first gear <NUM> and the second gear <NUM> are driven by the same input gear <NUM>.

The example shown in <FIG> is in accordance with the example shown in <FIG>. <FIG> shows that the first gear <NUM> has a larger circumference than the second gear <NUM>. The first end stop <NUM> of the first gear <NUM> extends radially inwards from the circumferential edge of the first gear <NUM>. The second end stop <NUM> extends radially outwards form the circumferential edge of the second gear <NUM>. The first end stop <NUM> and the second end stop <NUM> are therefore shaped and sized so as to be configured to interlock when they engage each other.

According to embodiments not falling within the features of claim <NUM> "wherein said first end stop (<NUM>) of the first gear (<NUM>) extends radially inwards from a circumferential edge of the first gear (<NUM>), and wherein said second end stop (<NUM>) extends radially outwards form a circumferential edge of the second gear (<NUM>)", other configurations of end stops are also envisaged. For example, any arrangement of end stops that are fixed to the gears and can engage each other directly through rotary engagement is envisaged.

Other systems are also envisaged wherein alongside the end stops, an additional member is provided. This additional member could be fixed to the gearing or translated via a frictional device (i.e. a clutch). Frictional devices are useful for high speed and high inertia systems because the dissipation of speed that results from engagement of the end stops can be controlled through an additional frictional device integrated into the end stops.

In addition to, or as an alternative the above, a pin or roller <NUM> can be provided that is configured to sit between end stops, as shown in <FIG> shows the system in accordance with the embodiment of <FIG> with the addition of two rollers <NUM> positioned on either side of the first end stop <NUM>. When the first end stop <NUM> approaches the second end stop <NUM>, the first end stop <NUM> and the second end stop will impact one of the rollers <NUM>. The result of this is that the load distribution between the end stops will be altered and susceptibility to geometric tolerances will be removed.

The system described in accordance with <FIG> and <FIG> can be adapted for different gear systems and is scalable for many load and stroke applications. In one example in accordance with <FIG> and <FIG>, the distance between the central rotational shaft <NUM> and the centre of the input gear <NUM> is <NUM>. The first gear <NUM> has a diameter of <NUM> and the second gear <NUM> has a diameter of <NUM>. The first end stop <NUM> and the second end stop <NUM> will move either together or apart by <NUM>° per turn of the input gear <NUM>, depending on the direction of the input turn. If the first end stop <NUM> and the second end stop <NUM> are initially set to be <NUM>° apart, the total travel permitted would be <NUM> input turns before the first end stop <NUM> and the second end stop <NUM> engage each other.

In this same example, if the first end stop <NUM> and the second end stop <NUM> are set to be initially <NUM>° apart, the total travel permitted would be <NUM> input turns.

In another example, the distance between the central rotational shaft <NUM> and the centre of the single two-output spur gear <NUM> is again <NUM>. The first gear <NUM> has a diameter of <NUM> and second gear <NUM> has a diameter of <NUM>. The first end stop <NUM> and the second end stop <NUM> will move either together or apart by <NUM>° per input turn, depending on the direction of the input turn. If the first end stop <NUM> and the second end stop <NUM> are initially set to be <NUM>° apart, the total travel permitted would be <NUM> turns.

Systems having other dimensions may also be envisaged.

In addition to, or as an alternative the above, other configurations are envisaged wherein more than one pair of stops are used for redundancy. In these configurations, the gears will comprise a plurality of end stops which are equally spaced around the gears.

<FIG> shows how the over travel stop mechanism can be provided for gears that are stacked in various configurations in order to create a higher load carrying capability. <FIG> shows a first gear <NUM> meshed with an input spur gear <NUM>, a second gear <NUM> meshed with an input spur gear <NUM> and a third gear <NUM> meshed with an input spur gear <NUM>. The first gear <NUM> comprises a first end stop <NUM> and a second end stop <NUM>. The second gear <NUM> comprises a third end stop <NUM>. The third gear <NUM> comprises a fourth end stop <NUM>.

The input spur gears <NUM>, <NUM> and <NUM> are fixed to the same shaft <NUM> so that they rotate at the same speed. The first gear <NUM>, the second gear <NUM> and the third gear <NUM> rotate at different speeds.

According to an embodiment not falling within the feature of claim <NUM> "the first gear (<NUM>) and second gear (<NUM>) being rotatable about said shaft (<NUM>)", any one of the first gear, the second gear <NUM>, or the third gear <NUM> can drive shaft <NUM> as a system output.

According to a further embodiment not falling within the feature of claim <NUM> "the first gear (<NUM>) and second gear (<NUM>) being rotatable about said shaft (<NUM>)", the second gear <NUM> and the third gear <NUM> can be fixed to the shaft <NUM> and the first gear <NUM> can rotate independently of the second gear <NUM> and the third gear <NUM>.

The gear system in <FIG> is configured such that the first gear <NUM> rotates at a different speed than both of the second gear <NUM> and the third gear <NUM>. The second gear <NUM> and the third gear <NUM> rotate at the same speed. The gear system is further configured such that, when the first gear <NUM> has rotated in a first direction up to its design limit, the first end stop <NUM> engages the third end stop <NUM>, and the second end stop <NUM> engages the fourth end stop <NUM> in order to stop further rotation of the first gear <NUM>. The system stalls upon engagement of the end stops because the first gear <NUM>, the second gear <NUM> and the third gear <NUM> are respectively driven by input gears <NUM>, <NUM> and <NUM> that are all fixed to shaft <NUM>.

The load carrying capability of the over travel stop mechanism can be further increased by reducing the gear tooth load. The load carrying capability can also be increased by reducing the load induced in the end stops.

The over stop travel system can be incorporated into existing gear boxes as shown in <FIG>. The left panel of <FIG> shows a first gear <NUM> which is meshed with an input gear <NUM> and an output gear <NUM>. The first gear <NUM> is rotatable on shaft <NUM>, the input <NUM> gear is fixed to shaft <NUM> and the output gear <NUM> is rotatable on shaft <NUM>. The input gear <NUM> rotates at a different speed than the output gear <NUM>.

The right panel of <FIG> shows the system of the left panel of <FIG> with the incorporation of an over travel stop system. All of the elements in the right panel of the <FIG> are identical to the left panel of <FIG> with the additional features of a first end stop <NUM> provided on the first gear <NUM>, a second gear <NUM> provided on shaft <NUM> and second input gear <NUM> fixed to shaft <NUM>. The second gear <NUM> is rotatable on shaft <NUM> and is provided with a second end stop <NUM>. The first gear <NUM> rotates at a different speed than the second gear <NUM>. The second input gear <NUM> meshes with the second gear <NUM>.

The system in the right panel of <FIG> can be configured such that, when the first gear <NUM> has rotated up to its design limit, the first end stop <NUM> engages the second end stop <NUM> in order to stop the motion of the first gear <NUM>. The system stalls upon engagement of the end stops because the first gear <NUM> and the second gear <NUM> are respectively driven by the first input gear <NUM> and the second input gear <NUM> that are both fixed to shaft <NUM>.

In all of the examples described herein, the stopping mechanism does not rely on an axially moving element. The stopping elements described herein are configured so that rotational movement of the stopping elements results in engagement of the end stops to prevent over travel of the gears. The design is therefore not affected by axial vibration characteristics which would be an issue for designs that rely of axially moving stopping elements.

The benefits of the above described over travel stop systems are that they are scalable for many load and stroke applications. In comparison to other over travel stop systems, the examples described herein are of low complexity which enables the cost and weight of the system to be reduced. Furthermore, a minimal space envelope is required because of the compact design. The over travel stop system can be incorporated into many gear mechanisms such as down drive gear boxes by installing a second pair of gears onto one set of existing gears. The over travel stop system is a low drag alternative to using other conventional mechanisms to create differential movement due to the low number of sliding surfaces.

Claim 1:
A system for stopping rotation of a first gear (<NUM>) and a second gear (<NUM>) on a shaft (<NUM>), comprising:
the first gear (<NUM>) and second gear (<NUM>) being concentric to and rotatable about said shaft (<NUM>);
wherein the first gear (<NUM>) and the second gear (<NUM>) are driven by the same input system (<NUM>);
wherein the system is configured such that the first gear (<NUM>) and the second gear (<NUM>) rotate at different speeds;
wherein the first gear (<NUM>) comprises a first end stop (<NUM>) and the second gear (<NUM>) comprises a second end stop (<NUM>);
wherein the first end stop (<NUM>) and the second end stop (<NUM>) are configured to engage each other when the first gear (<NUM>) and the second gear (<NUM>) have each rotated a predetermined number of turns; and
wherein engagement of the first end stop (<NUM>) with the second end stop (<NUM>) is configured to prevent rotation of the first gear (<NUM>) and the second gear (<NUM>) and cause a stall in the system, and wherein said first end stop (<NUM>) of the first gear (<NUM>) extends radially inwards from a circumferential edge of the first gear (<NUM>), and wherein said second end stop (<NUM>) extends radially outwards form a circumferential edge of the second gear (<NUM>)..