Non-recirculating rolling element bearing in overrunning cage configuration, cage and adapter therefor

Abstract

A non-recirculating rolling element bearing (100) in an overrunning cage configuration includes a guide (103), a motion stage (101) and a cage (102). The guide defines a direction of motion and includes a first guide surface (108) that is essentially V-shaped. The first guide surface includes first and second rolling surfaces. The motion stage is configured to move along the direction of motion between a first end (112) and a second end (113) of the guide. The motion stage includes a second guide surface (109) that includes third and fourth rolling surfaces that are disposed opposite the first and second rolling surfaces, respectively. The cage is disposed to be partially interposed between the guide and the motion stage. The cage includes a first (105), second and third (106, 107) sets of rolling elements. The first set is disposed to roll on the first and third rolling surfaces. The second set is arranged to roll on the second and fourth rolling surfaces. The third set is arranged to roll on the first rolling surface. The guide and the rolling elements of the third set are arranged to magnetically attract each other to deflect the cage towards the guide. In a first state in which the motion stage is moving towards the first end of the guide, the first rolling element of the third set is arranged between the second end of the guide and a first end (115) of the motion stage arranged closest to the second end of the guide. In a second state in which the motion stage is moving towards the second end of the guide, the second rolling element of the third set is arranged between the first end of the guide and a second end (114) of the motion stage arranged closest to the first end of the guide.

Description

[Technical field]

[0001] The present invention relates generally to non-recirculating rolling element bearings, and more particularly to a cage for such rolling element bearings or an adapter for a cage. [Background technology]

[0002] Linear rolling element bearings typically offer a good trade-off between attributes for guiding linear displacement with high precision. Such linear rolling element bearings can be divided into linear recirculating rolling element bearings and linear non-recirculating rolling element bearings.

[0003] Linear recirculating rolling element bearings have theoretically no limit on stroke length, however such bearings are more complex and are limited in accuracy, precision and maximum speed.

[0004] Linear non-recirculating rolling element bearings provide the highest accuracy, precision and speed, but usually have a short stroke. Non-recirculating rolling element bearings in an overrunning cage configuration can provide a longer finite stroke compared to conventional non-overrunning cage configurations. However, a drawback is that the overhangs formed by the unsupported protruding cage ends tend to bend away from their respective rolling surfaces due to lack of cage stiffness and vibrate under gravity and acceleration forces, which has a negative effect on accuracy, speed and precision. Furthermore, in embodiments where the cage overhang can be very long, this bending can result in damage to, for example, the rails, the cage and the surroundings. It can even result in the cage bursting. For this reason, the maximum cage overhang is usually limited to keep the cage deformation due to gravity and acceleration forces at an acceptable level to prevent damage and failure.

[0005] DE2916229 B discloses a linear non-recirculating rolling element bearing in which the cage includes protrusions that project into recesses running along the guide. By such mechanical means the cage is prevented from bending away from the guide. However, such linear bearings including protrusions and recesses are more complicated to manufacture, less rigid, more fragile, heavier and create additional friction.

[0006] DE102006024765 A1 discloses a linear non-recirculating rolling element bearing in an overrunning cage configuration, in which at least one magnet is disposed on or in the cage or on or in the guide rail, the magnet being configured to exert a magnetic force between the cage and the guide rail. Thus, the cage is deflected towards the guide rail, which results in the cage being pressed against the rolling elements and / or the guide rail. As a result, friction is generated, resulting in reduced accuracy and lifespan. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] DE2916229 B [Patent Document 2] DE102006024765 A1 Summary of the Invention [Problem to be solved by the invention]

[0008] It is an object of the present invention to overcome the disadvantages associated with known non-recirculating rolling element bearings (e.g., linear or curved) generally in an overrunning cage configuration. Such non-recirculating rolling element bearings provide a finite stroke, also known as a limited stroke. Specifically, it is an object of the present invention to reduce or eliminate limitations on the maximum length of cage overhang, allowing a longer (finite) stroke to be achieved. [Means for solving the problem]

[0009] Non-recirculating rolling element bearings typically provide translation along a linear path, but can also provide motion (e.g., translation) along a curved path. Non-recirculating bearings are in contrast to recirculating, or infinite stroke, bearings. Thus, non-recirculating rolling element bearings do not include bearings that are configured to provide more than 360 degrees of rotational motion (i.e., infinite stroke), such as rotating or swivel bearings.

[0010] According to a first aspect of the present invention, there is provided a rolling element bearing in an overrunning cage configuration as set out in the accompanying claims. Such a rolling element bearing solves the problems associated with rolling element bearings in an overrunning cage configuration known in the art by providing a guide and a cage including rolling elements which magnetically interact with each other to bias the cage towards the guide, thereby limiting or preventing the cage overhang from bending away from the guide, resulting in a reduction of vibration and / or bending forces exerted on the cage. Furthermore, the magnetic interaction between the rolling elements and the guide itself prevents unwanted friction between the cage, the rolling elements and their respective rolling surfaces.

[0011] A non-recirculating rolling element bearing in an overrunning cage configuration preferably includes a guide defining a direction of motion between a first end and a second end thereof, a motion stage configured to move along the direction of motion between the first and second ends of the guide, and a cage arranged to be partially interposed between the guide and the motion stage. The cage may include a plurality of rolling elements arranged along the direction of motion, which may for example form an array. A first set of the rolling elements may be arranged to roll on a rolling surface of the guide and a rolling surface of the motion stage, for example to support movement of the motion stage along the guide. A third set of the rolling elements may be arranged to roll on a rolling surface of the guide. The third set and the guide may be arranged to magnetically attract each other to bias the cage towards the guide, thereby preventing the cage overhang from bending away from the guide.

[0012] In an exemplary embodiment of the invention, the rolling element bearing includes a guide, a motion stage, and a cage. The guide defines a motion direction and includes a first guide surface that can include first and second rolling surfaces defining a V-shape, such that the first guide surface can be arranged to be essentially V-shaped. The motion stage can be configured to move along the motion direction between a first end and a second end of the guide. The motion stage includes a second guide surface that can include third and fourth rolling surfaces arranged opposite the first and second rolling surfaces, respectively. Such second guide surface can also be arranged to be essentially V-shaped. The cage is partially interposed between the guide and the motion stage. The cage includes first, second, and third sets of rolling elements. The first set can be arranged to roll on the first and third rolling surfaces. The second set can be arranged to roll on the second and fourth rolling surfaces. The third set can be arranged to roll on the first rolling surface and optionally the third rolling surface. The guide and each of the rolling elements of the third set are arranged to magnetically attract each other to bias the cage towards the guide. The third set of rolling elements is arranged such that in a first state of the rolling element bearing in which the motion stage is moving towards the first end of the guide, a first rolling element of the third set is arranged between a second end of the guide and a first end of the motion stage that is arranged closest to the second end of the guide. Further, the third set of rolling elements is arranged such that in a second state in which the motion stage is moving towards the second end of the guide, a second rolling element of the third set is arranged between the first end of the guide and a second end of the motion stage that is arranged closest to the first end of the guide.

[0013] In a preferred embodiment of the rolling element bearing according to the invention, each rolling element of the third set is configured to magnetically attract the first rolling surface stronger than the second rolling surface. This has the advantage that the cage is deflected mainly towards the first rolling surface which provides the surface on which the rolling elements of the third set are arranged to roll and which is relevant for limiting or preventing the cage overhang from bending away from the guide, and to a lesser extent towards the second rolling surface which does not provide the surface on which the rolling elements of the third set are arranged to roll. This improves the overall performance of the rolling element bearing, for example by reducing friction forces which may arise due to the magnetic attraction between the rolling elements of the third set and the second rolling surface. This can be achieved in various ways, as will become clear from the rest of the disclosure.

[0014] Preferably, each rolling element of the third set is further configured to magnetically attract the first rolling surface stronger than at least one of the third and fourth rolling surfaces, since the third and fourth rolling surfaces act only on a portion of the cage that is enclosed between the first and second guide surfaces, which portion is consequently prevented from bending away from the guide. Thus, the magnetic attraction between the rolling elements of the third set and the third and / or fourth rolling surfaces is usually not helpful in achieving the goal of the invention. Furthermore, there may be a correlation between the forces associated with such magnetic attraction and a decrease in the overall performance of the rolling element bearing, for example due to increased friction. Thus, the strength of the magnetic attraction between the rolling elements of the third set and the third and / or fourth rolling surfaces is preferably kept as low as possible. This can be achieved in various ways, as will become clear from the remainder of the disclosure.

[0015] Each rolling element of the third set may comprise at least a part essentially made of a material suitable for providing a magnetic attractive interaction with the guide. Each rolling element of the first set has a first volume. At least a part of each rolling element of the third set has a second volume. Advantageously, the first volume is greater than the second volume. Preferably, the part of each rolling element of the third set is arranged to roll on the first rolling surface. This material may comprise, for example, a permanently magnetized material such as a hard magnetic material (for example AlNiCo or ferrite) or is essentially made of such a material. This material may comprise, for example, a composite including a magnetic substance such as a powder (for example NdFeB, SmCo, ferrite) embedded in a plastic matrix (for example polyamide or epoxy resin) or is essentially made of such a composite, which has the advantage of providing a complex shape and optimizing the magnetic properties. The guide (for example the guide surface) may comprise a non-magnetized ferromagnetic material including a soft ferromagnetic material, for example iron or an iron alloy such as (stainless) steel. Such an arrangement is fairly simple and inexpensive, and moreover, guides comprising soft ferromagnetic material have good mechanical properties for the guide surfaces. Although the previous embodiment is preferred, it is also possible to optionally switch the choice of material for the third set and the guides.

[0016] The non-recirculating rolling element bearing of the present invention can include a first state in which the motion stage is moving toward the first end of the guide, and a second state in which the motion stage is moving toward the second end. In the first state, the first rolling elements of the third set can be positioned outside the first overlap between the first and second guide surfaces. For example, the first rolling elements of the third set can be positioned between the second end of the guide and a first end of the motion stage positioned closest to the second end of the guide. Magnetic interaction between the first rolling elements of the third set and the guide deflects a first portion of the cage extending from the first end of the motion stage toward the second end of the guide toward the guide. In the second state, the second rolling elements of the third set can be positioned outside the second overlap between the first and second guide surfaces. For example, the second rolling elements can be positioned between the first end of the guide and a second end of the motion stage positioned closest to the first end of the guide. A magnetic interaction between the second rolling elements of the third set and the guide deflects a second portion of the cage, which extends from the second end of the movement stage towards the first end of the guide, towards the guide. Preferably, the first and second rolling elements of the third set are each flanked by at least a portion of the first set at either end. Advantageously, the distance between the first and second rolling elements of the third set is greater than the length of the movement stage along the direction of movement. Preferably, the first and second rolling elements are provided near both ends of the cage along the direction of movement, for example the first and second rolling elements form the outermost rolling elements of the combination of the first and third sets. This can prevent the cage from bending away from the guide when a relatively large cage overhang is used.

[0017] The cage of a non-recirculating rolling element bearing in an overrunning cage configuration is usually only partially interposed between the guide and the motion stage. The first guide surface extends along the direction of motion over a first length between the ends of the first guide surface. The cage can extend along the direction of motion over a second length between the ends of the cage. The second guide surface can extend along the direction of motion over a third length between the ends of the second guide surface. The second length is preferably smaller than the first length and larger than the third length. Beneficially, the second length can essentially correspond to the average of the first and third lengths, since this provides a maximum stroke for a given length of the guide. The bearing can be arranged such that the movement of the second guide surface essentially corresponds to twice the difference in length between the second and third lengths. These measures provide an optimal range of movement given a specific construction length of the bearing along the direction of motion.

[0018] Preferably, the guide includes a first guide surface that is essentially V-shaped, and the first guide surface can include first and second rolling surfaces. The second guide surface of the motion stage can be essentially V-shaped and complementary to the first guide surface. The second guide surface can include third and fourth rolling surfaces. The third and fourth rolling surfaces can be arranged opposite the first and second rolling surfaces, respectively. Preferably, the first and second rolling surfaces are arranged to be essentially parallel to the third and fourth rolling surfaces, respectively.

[0019] In an embodiment including a V-shaped guide surface, the cage may include a first, second and third set of rolling elements arranged along the direction of motion. Optionally, a fourth set of rolling elements is provided. The first set may be arranged to roll along the first and third surfaces. The second set may be arranged to roll along the second and fourth rolling surfaces. The third set may be arranged to roll along the first rolling surface and optionally the third rolling surface. The optional fourth set may be arranged to roll along the second rolling surface and optionally the fourth rolling surface. An advantage of such first and second guide surfaces, each configured to have a V-shaped cross section perpendicular to the direction of motion, is that this restricts the movement of the cage and the motion stage to a direction perpendicular to the direction of motion. Preferably, the V-shaped guide surface includes a groove provided at the intersection of the first and second rolling surfaces to simplify the manufacture of such rolling surfaces. In an alternative embodiment, the guide surface is configured such that a cross section of the guide surface perpendicular to the direction of motion has any suitable shape, such as a circular arc shape, a gothic arc shape, or a combination of the aforementioned shapes.

[0020] Advantageously, the cage for the embodiment comprising the V-shaped guide surface comprises a cage body comprising a first and a second surface, the second surface being adjacent to the first surface. When projecting the cage onto a plane perpendicular to the direction of movement or when intersecting the cage according to this plane, the first and second surfaces define first and second normals, respectively, which may intersect each other. The first and second surfaces may be arranged to face the first and second rolling surfaces. Preferably, the first and second surfaces are arranged to be essentially parallel to the first and second rolling surfaces, respectively. A portion of each rolling element of the first and third set may have a first and second gap, respectively, relative to the second surface. Preferably, the first gap is smaller than the second gap. This allows to reduce the force of attraction between each rolling element of the third set and the guide, resulting in less frictional forces.

[0021] There are essentially two configurations of rolling element bearings according to the invention including V-shaped guideways. The first configuration, often called cross roller bearings, usually offers better precision, and the second configuration, often called needle bearings, usually offers better load capacity and stiffness. In the cross roller bearing configuration, the V-shape of the first guideway is configured to face away from the V-shape of the second guideway, preferably facing away from the V-shape of the second guideway. In a linear bearing having such a cross roller bearing configuration, the rolling elements of the first set and the rolling elements of the second set at least partially overlap when the cage is projected onto a plane perpendicular to the direction of motion. In a V-shaped roller bearing configuration, such as a needle bearing configuration, the V-shape of the first guideway is configured to face in the same direction as the V-shape of the second guideway. In a linear bearing having such a configuration, the rolling elements of the first set and the rolling elements of the second set do not overlap when the cage is projected onto a plane perpendicular to the direction of motion. In a needle bearing configuration, the rotation axes of the first and second sets preferably intersect each other.

[0022] In non-recirculating rolling element bearings, the cage is typically arranged so that the rolling elements of each set have an essentially fixed relative position with respect to the cage. Such a non-recirculating element configuration has the advantage of improved accuracy and precision compared to recirculating element bearings. Additionally, it may improve the robustness of the rolling element bearing.

[0023] The cage may be configured to hold the rolling elements of each set, as this simplifies assembly and improves the robustness of the rolling element bearings. Preferably, the cage includes a cage body configured to hold the rolling elements of each set. This may be achieved, for example, by a cage including first and second elongated cage body portions configured to form an enclosure partially surrounding the rolling elements of the plurality of rolling elements. Additionally or alternatively, the cage body may be configured to include or accommodate a set of shafts configured to mount the rolling elements of the set of rolling elements (e.g. the third and optionally fourth set) and provide an axis of rotation for each rolling element. In embodiments where the cage body is configured to accommodate a set of shafts, each rolling element of each set preferably includes a shaft, which is advantageously rigidly attached to such rolling element. Each set of rolling elements may form an array of rolling elements arranged along the direction of motion. The cage body may include cage body sections along the length of the cage body.

[0024] The rolling elements in the present disclosure are preferably rollers, since they provide higher stiffness and load capacity (e.g. static, dynamic) while at the same time having a minimal amount of friction, resulting in less wear and improved life of the rolling element bearings. Rollers in this disclosure should be interpreted in a broad sense and also include needle rollers. Advantageously, the rolling elements in the present disclosure have a uniform shape defined by a diameter and a height, the height being defined as the distance between the opposing ends along a direction essentially parallel to the axis of rotation of the corresponding rolling element. Each rolling element of the first set can have a first height, and a portion of each rolling element of the third set can have a second height. The first and second heights can be different to allow for a simple and independent optimization of the load capacity and the magnetic interaction with the guide. Advantageously, the second height is smaller than the first height. This allows for a reduction in the magnetic attraction between the portion and the surroundings other than the rolling surface on which the portion is arranged to roll, thereby limiting or preventing the generation of frictional forces. Additionally or alternatively, each rolling element of the first set may have a first diameter and a portion of each rolling element of the third set may have a second diameter, the second diameter being smaller than the first diameter. The smaller second diameter has the advantage that a portion of each rolling element of the third set may be configured to roll only along a first guiding surface of the guide (e.g. a first rolling surface), which represents an associated surface for reducing or preventing bending of the cage away from the guide.

[0025] For example, in embodiments including a third and / or fourth set of rolling elements of different dimensions (e.g. smaller diameter and / or height) or including a material (e.g. AlNiCo) having substantially different material properties (e.g. lower modulus of elasticity and / or hardness) than the corresponding first or second set of rolling elements, to achieve uniform load-bearing capacity and precision along the entire stroke of the motion stage, it may be beneficial to configure the bearing such that the outer rolling elements of the third and / or fourth rolling elements remain outside the overlap of the guide and the motion stage in either state. For example, a non-recirculating rolling element bearing may be configured such that the second rolling element is disposed between the first end of the guide and the second end of the motion stage in the first state, and the first rolling element is disposed between the second end of the guide and the first end of the motion stage in the second state. In such embodiments, the first and second lengths are preferably compensated for by the offset created by such outer rolling elements.

[0026] Preferably, each part of the rolling elements of the third set is magnetized with a magnetization direction that is essentially axial, i.e. in other words essentially parallel to the axis of rotation of the part of the rolling elements. These are the easiest and often the cheapest to manufacture. Alternatively, the parts can be magnetized in other directions, such as radial to the axis of rotation. In the embodiment in which the parts form an annular ring, the magnetization direction is preferably axial or radial.

[0027] An optional fourth set of rolling elements may be provided, the fourth set being arranged to roll along the second rolling surface. Each rolling element of the fourth set may include at least a portion essentially made of a permanently magnetized material. Such a fourth set may further reduce or prevent the cage from bending away from the guide. Each rolling element of the second set and each part of the rolling elements of the fourth set may have a third and fourth gap, respectively, relative to the first surface. Preferably, the third gap is smaller than the fourth gap. The preferred features of the rolling elements of the third set apply mutatis mutandis to the rolling elements of the fourth set. In an advantageous embodiment, the rolling elements of the fourth set are essentially similar to the rolling elements of the third set.

[0028] An exemplary embodiment of a rolling element bearing according to the present invention is configured to provide linear motion of a motion stage. For example, the first guide surface defines a first longitudinal axis of motion and the second guide surface defines a second longitudinal axis of motion. Preferably, the first longitudinal axis and the second longitudinal axis are configured to be essentially parallel.

[0029] The cage may include a plurality of first recesses arranged to retain the rolling elements of the first set. The cage may, for example, not be configured to directly retain the rolling elements of the third set. In such a case, the rolling element bearing may include a set of adapters received in a subset of the plurality of first recesses, the adapters configured to rotatably retain the rolling elements of the third set.

[0030] Each adapter may include an adapter body configured to be received in one of the plurality of first recesses, e.g., in one of a subset of the plurality of first recesses. Preferably, the adapter body includes or is made essentially of a non-ferromagnetic material, such as a ceramic or plastic material. The adapter body may be configured to partially occupy one of the plurality of first recesses. The adapter body may be configured to vacate an unoccupied portion, which may be configured to rotatably hold the third set of rolling elements. Preferably, the adapter body includes a second recess configured to rotatably hold the third set of rolling elements. The unoccupied portion may at least partially include the second recess.

[0031] Preferably, the adapter body is fixed (e.g. clamped or glued) to the first recess such that movement of the adapter body within the first recess relative to the cage is prevented while the cage moves along the first guide surface (e.g. the first rolling surface).

[0032] In an alternative embodiment, the rolling element bearing comprises a set of adapters including an adapter body fixedly connected to an end (one or both ends along the direction of motion) of the cage, for example forming an extension of the cage. The adapter body may for example comprise a second recess arranged to rotatably hold a third set of rolling elements. Preferably, the adapter body is fixedly connected at either end of the extension of the cage along the direction of motion. Each adapter body may be fixedly connected to the cage in a removable manner.

[0033] In addition to or instead of rotatably retaining the third set of rolling elements, either type of adapter body may include or be configured to accommodate a shaft configured to mount the third set of rolling elements, providing an axis of rotation for the rolling elements mounted (fixedly or rotatably) on the shaft. In embodiments in which the adapter body is configured to accommodate a set of shafts, each rolling element of the third set preferably includes a shaft, which is advantageously rigidly attached to such rolling element.

[0034] Such an adapter as described in the previous paragraph can equally be provided to hold the fourth set of rolling elements. In such a case, the cage can include a plurality of third recesses arranged to hold the second set of rolling elements. The cage may not be configured to hold the fourth set of rolling elements directly, for example. The rolling element bearing may include a second set of adapters received in a subset of the plurality of third recesses, the adapters configured to rotatably hold the fourth set of rolling elements. In this alternative embodiment, the adapter body is fixedly connected to the end of the cage, the adapter body may include a fourth recess configured to rotatably hold the fourth set of rolling elements, or an additional adapter body may be provided that is configured to rotatably hold the fourth set of rolling elements, and the additional adapter body may be connected to at least one of the cage and the adapter configured to hold the fourth set of rolling elements.

[0035] According to a second aspect of the invention there is provided an assembly including a mover and two rolling element bearings in an overrunning cage configuration according to the first aspect of the invention. The rolling element bearings may be arranged substantially parallel. A motion stage may be fixedly connected to opposite sides of the mover.

[0036] According to a third aspect of the invention there is provided a cage for a rolling element bearing in an overrunning cage configuration. The cage may be any cage as described in relation to the rolling element bearing according to the first aspect of the invention.

[0037] Preferably, the cage is arranged to be partially interposed between the guide defining the direction of motion and the motion stage. The cage may include a cage body including a first surface and a second surface. The cage may further include a first, second and third set of rolling elements. The first and third sets may be provided along the first surface and the second set may be provided along the second surface. Each rolling element of the third set may include at least a portion made of a permanently magnetized material. Optionally, a portion of each rolling element of the first set and the third set has a first and second gap, respectively, with respect to the second surface, the first gap being smaller than the second gap. Optionally, at least a portion of each rolling element of the third set is arranged to roll along the first rolling surface. Optionally, each rolling element of the first set has a first height and a portion of each rolling element of the third set has a second height, the second height being smaller than the first height. Optionally, each rolling element of the first set has a first diameter and a portion of each rolling element of the third set has a second diameter, the second diameter being smaller than the first diameter. Optionally, each rolling element of the third set is magnetized with a magnetization direction that is essentially axial. Optionally, the third set includes first and second rolling elements arranged to flank at least a portion of the first set at one or both ends thereof. Optionally, the cage includes a fourth set of rolling elements disposed along the second surface, preferably essentially similar to the third set, including any combination of the features described for the third set.

[0038] According to a fourth aspect of the invention there is provided an adaptor for a cage of a rolling element bearing in an overrunning cage arrangement according to the first aspect of the invention, an adaptor for a cage of an assembly according to the second aspect of the invention or an adaptor for a cage according to the third aspect of the invention, the adaptor comprising an adaptor body, the adaptor body preferably comprising or made essentially of a non-ferromagnetic material such as a ceramic or plastic material.

[0039] The adapter body is arranged to be received in a first recess of a plurality of first recesses of the cage arranged to hold the first or second set of rolling elements, the adapter body further arranged to match a dimension of the first recess by occupying a portion of the first recess and leaving another portion free for the rolling elements of the third or fourth set to be rotatably held in the first recess. The adapter body may for example include a second recess arranged to rotatably hold the rolling elements of the third or fourth set. Preferably, the adapter body is configured to be fixed (e.g. clamped or glued) to the first recess such that movement of the adapter body within the first recess relative to the cage is prevented while the cage moves along the first guide surface (e.g. the first rolling surface).

[0040] Alternatively, the adapter body can be arranged to be fixedly connected to an end (either or both ends along the direction of motion) of the cage, for example forming an extension of the cage. The adapter body can for example include a second recess arranged to rotatably hold the third or fourth set of rolling elements. Preferably, the adapter body is fixedly connected at either end of the extension of the cage along the direction of motion.

[0041] In addition to or instead of rotatably retaining the third or fourth set of rolling elements, either type of adapter body may include or be configured to accommodate a shaft configured to mount the third or fourth set of rolling elements, providing an axis of rotation for the rolling elements mounted on the shaft. In embodiments where the adapter body is configured to accommodate a set of shafts, each rolling element of the respective set preferably includes a shaft, which is advantageously rigidly attached to such rolling element.

[0042] According to a fifth aspect of the present invention there is provided a use of a cage according to the third aspect.

[0043] Aspects of the present invention will now be described in more detail with reference to the accompanying drawings, in which like reference numerals denote like features. [Brief description of the drawings]

[0044] [Figure 1A] 1A-1D are cross-sectional views along the direction of movement of an embodiment of a rolling element bearing according to the invention in various states; [Figure 1B] 1A-1D are cross-sectional views along the direction of movement of an embodiment of a rolling element bearing according to the invention in various states; [Diagram 2] FIG. 1 is a perspective view of one embodiment of a rolling element bearing according to the present invention for a V-shaped guideway in a cross roller bearing configuration. [Diagram 3] FIG. 1 is a perspective view of one embodiment of a rolling element bearing according to the present invention for a V-shaped guideway in a needle bearing configuration. [Figure 4A] 13A-13D represent a cross section perpendicular to the direction of motion of an embodiment of a third set of rolling elements according to the invention. [Figure 4B] 13A-13D represent a cross section perpendicular to the direction of motion of an embodiment of a third set of rolling elements according to the invention. [Figure 4C] 13A-13D represent a cross section perpendicular to the direction of motion of an embodiment of a third set of rolling elements according to the invention. [Figure 4D] 13A-13D represent a cross section perpendicular to the direction of motion of an embodiment of a third set of rolling elements according to the invention. [Figure 4E] 13A-13D represent a cross section perpendicular to the direction of motion of an embodiment of a third set of rolling elements according to the invention. [Figure 4F] 13A-13D represent a cross section perpendicular to the direction of motion of an embodiment of a third set of rolling elements according to the invention. [Figure 5A] 1 is a cross-sectional view of one embodiment of a rolling element bearing according to the present invention; [Figure 5B] FIG. 5B is a cross-sectional view of the embodiment of FIG. 5A taken perpendicular to the direction of motion along BB. [Figure 5C] FIG. 5B is a cross-sectional view of the embodiment of FIG. 5A taken perpendicular to the direction of motion along CC. [Figure 5D] FIG. 5B is a cross-sectional view of the embodiment of FIG. 5A taken orthogonal to the direction of motion along DD. [Figure 5E] FIG. 5B is a cross-sectional view of the embodiment of FIG. 5A taken perpendicular to the direction of motion along EE. [Figure 6A] 1A-1D are cross-sectional views of various embodiments of a cage for a rolling element bearing according to the present invention. [Figure 6B] 1A-1D are cross-sectional views of various embodiments of a cage for a rolling element bearing according to the present invention. [Figure 6C] 1A-1D are cross-sectional views of various embodiments of a cage for a rolling element bearing according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] 1A and 1B, a rolling element bearing 100 according to the present invention includes a motion stage 101 disposed on a first side of a cage 102 and a guide 103 disposed on a second side of the cage 102 opposite the first side. The cage 102 includes a cage body 104, a first set of rolling elements 105, and a third set of rolling elements including a first rolling element 106 and a second rolling element 107 flanking (at least a portion of) the first set. The cage body 104 can be configured to act as a cage by holding a plurality of rolling elements 105, 106, 107. The rolling elements 105, 106, 107 are configured to roll on a first guide surface 108 of the guide 103 and optionally a second guide surface 109 of the motion stage 101.

[0046] The motion stage 101 is configured to move relative to the cage 102 along a first direction of movement 110, for example towards a first end 112 of the guide 103. The rolling elements 105, 106, 107 of the cage 102 can be configured to roll on a second guide surface 109 of the motion stage 101. As a result, the rolling elements interacting with the second guide surface 109 rotate in a first rotational direction 111 corresponding to the first direction of movement 110. As the rolling elements interacting with the second guide surface 109 roll on the first guide surface 108 of the guide 103, these rolling rolling elements then move the cage 102 along the guide 103 in the first direction of movement 110. Obviously, as a result of the motion stage 101 moving in a second direction of movement opposite to the first direction of movement 110, the rolling elements also rotate in a second rotational direction opposite to the first direction of movement 111. As a result, the cage 102 moves in the second direction of motion.

[0047] Each rolling element 106, 107 of the third set is configured to be magnetically attracted towards the guide 103, for example to deflect the cage 102 towards the guide 103. This limits or prevents the cage 102 from bending away from the guide 103 (see dashed outline in FIG. 1B). The rolling elements 106, 107 of the third set can therefore be configured to roll on the first guide surface rather than the second guide surface. In a first state (see FIG. 1B) in which the motion stage 101 is moving towards the first end 112 of the guide 103, the first rolling element 106 of the third set is disposed between the first end 115 of the motion stage 101 and the second end 113 of the guide 103. This prevents or limits the overhang of the cage 102 disposed between the first end 115 of the motion stage 101 and the second end 113 of the guide 103 from bending away from the guide 103. In a second state (not shown) in which the motion stage 101 is moving towards the second end 113, the second rolling elements 107 of the third set are arranged between the second end 114 of the motion stage 101 and the first end 112 of the guide 103. This prevents the overhang of the cage 102 arranged between the second end 114 of the motion stage 101 and the first end 112 of the guide 103 from bending away from the guide 103. Possibly, the third set comprises more than one rolling element 106 and / or 107. These can also be provided between adjacent rolling elements 105 of the first set. According to a preferred embodiment, at least the outer rolling elements 106, 107 are rolling elements belonging to the third set. These rolling elements 106, 107 comprise or are essentially made of a magnetized hard magnetic material, and the first guide surface 108 comprises or is essentially made of a soft ferromagnetic material.

[0048] 2 and 3, a cross roller bearing 200 or needle roller bearing 300 according to the present invention can be configured such that the first guide surface 208, 308 of the guide 203, 303 includes a first rolling surface 216, 316 and a second rolling surface 217, 317, and the second guide surface 209, 309 of the motion stage 201, 301 includes a third rolling surface 218, 318 and a fourth rolling surface 219, 319. In such an embodiment, the cage 202, 302 includes a plurality of rolling elements including a first set 205, 305 of rolling elements configured to roll on the first rolling surface 216, 316 and the third rolling surface 218, 318, and a second set 220, 320 of rolling elements configured to roll on the second rolling surface 217, 317 and the fourth rolling surface 219, 319.

[0049] According to a preferred embodiment, the first rolling elements 206, 306 and second rolling elements (not shown) of the third set flank the first set 205, 305 of rolling elements at either end along the direction of motion. In the illustrated state, the first rolling elements 206, 306 of the third set are disposed between the second end 213, 313 of the guide 203, 303 and the first end 215, 315 of the motion stage 201, 301. The rolling elements optionally include a fourth set of first rolling elements 221, 321 and second rolling elements (not shown) configured to flank the second set 220, 320 of rolling elements at either end along the direction of motion. Each rolling element of the third set and optionally the fourth set includes at least a portion essentially made of a permanently magnetized material, such as a magnetized hard magnetic material. Furthermore, the first rolling surface 216, 316 and the second rolling surface 217, 317, and optionally the third rolling surface 218, 318 and the fourth rolling surface 219, 319, include or are made essentially of a soft ferromagnetic material.

[0050] 4A to 4F, the cage 402 of the cross roller type bearing 400 may include a cage body 404 configured to form a cage for holding rolling elements 423, 424, 425, 426, 427, 428, with the cage 402 or cage body 404 configured to partially surround such rolling elements. The guide 403 may include a first rolling surface 416 and a second rolling surface 417, which may form a first guide surface 408. The cage body includes a first surface 429 disposed opposite the first rolling surface 416 and a second surface 430 disposed opposite the second rolling surface 417. The cage 402 is suitable for use in the cross roller type bearing 200 shown in FIG. 2.

[0051] Various embodiments of the rolling elements 423, 424, 425, 426, 427, 428 are suitable for use as the rolling elements of the third and optionally fourth set. Parts of such rolling elements 423, 424, 425, 426, 427, 428 are essentially made of permanently magnetized material (hatched and filled). The permanently magnetized material is magnetized according to a magnetization direction to form a first pole (hatched portion) with a first sign and a second pole (filled portion) with a second sign opposite to the first sign. Preferably, the rolling elements 423, 424, 425, 426, 427, 428 are axially magnetized, the magnetization direction being advantageously essentially parallel to the rotation axis 431 of the rolling elements 423, 424, 425, 426, 427, 428. Beneficially, the magnetic material is arranged rotationally symmetrically about the axis of rotation 431 and configured to magnetically interact more strongly with one rolling surface of the guide, such as the first rolling surface 416 associated with the rolling elements 423, 424, 425, 426, 427, 428, than with another rolling surface of the guide, such as the second rolling surface 417 not associated with the rolling elements 423, 424, 425, 426, 427, 428. To this end, the gap between the magnetic material of the third set of rolling elements and the first surface 429 is smaller than the gap between the magnetic material of the third set of rolling elements and the second surface 430.

[0052] For example, the rolling elements 423, 424, 425 can have the same height as the rolling elements of the first set and optionally the second set. In one such embodiment, the rolling element 423 includes or is essentially made of a permanently magnetized material. The rolling element optionally includes a central region free of magnetic material, so as to form an annular ring made essentially of magnetic material, preferably axially or radially magnetized. Other such embodiments include rolling elements 424, 425 that include or are essentially made of a permanently magnetized material only in portions 432, 433. In a first example, the portion 432 of the rolling element 424 is configured to roll along a rolling surface, such as the first rolling surface 416. The portion 432 optionally includes a central region free of magnetic material, so as to form an annular ring made essentially of magnetic material. In a second example, the portion 433 of the rolling element 425 is not exposed to a rolling surface, such as the first rolling surface 416. Optionally, portions 432, 433 are axially flanked at either end by another material, which other material is preferably a non-hard magnetic material such as a ferromagnetic, ceramic or plastic material. If only portions 432, 433 are magnetized, the rolling elements are preferably configured such that the portions magnetically interact stronger with rolling surfaces of the guide, such as first rolling surface 416 associated with rolling elements 424, 425, than with rolling surfaces of the guide, such as second rolling surface 417 not associated with rolling elements 424, 425.

[0053] Alternatively, the rolling elements 426, 427, 428 can have a smaller height than the rolling elements of the first set and optionally the second set. Two such embodiments include rolling elements 426, 428 made essentially of permanently magnetized material. In a first example, the rolling elements 426 have essentially the same diameter as the rolling elements of the first set. The rolling elements 426 optionally include a central area free of magnetic material so as to form an annular ring essentially made of magnetic material, preferably axially or radially magnetized. In a second example, the rolling elements 428 have a smaller diameter than the rolling elements of the first set. Another embodiment includes a rolling element 427 having essentially the same diameter as the rolling elements of the first set, with only the central portion 434 of the rolling element including or essentially made of permanently magnetized material. Preferably, the dimensions of the configured cage recess are adapted using an adapter 437 configured such that the rolling elements 426, 427, 428 are rotatably held by the cage.

[0054] 5A-5E, the bearing 500 includes a guide 503, a cage 502, and a motion stage 501. The guide 503 includes a first guide surface 508 that is essentially V-shaped and includes a first rolling surface 516 and a second rolling surface 517. The motion stage 501 includes a second guide surface 509 that is essentially V-shaped and includes a third rolling surface 518 and a fourth rolling surface 519. The cage includes a first set 505, a second set 520, a third set 506, 507, and a fourth set 521 (only one shown) of rolling elements. The rolling elements of the first set 505 are configured to roll along the first rolling surface 516 and along the third rolling surface 518 when the motion stage 501 is positioned in correspondence with the rolling elements of the first set 505. The third set of rolling elements 506, 507 are configured to roll only along the first rolling surface 516. The second set of rolling elements 520 are configured to roll along the second rolling surface 517 and, if the motion stage 501 is positioned correspondingly with the rolling elements of the second set 520, along a fourth rolling surface 519. The fourth set of rolling elements 521 (only one shown) are configured to roll only along the second rolling surface 517.

[0055] In a first state (as shown), the motion stage 501 has been moved to a first final position closest to the second end 513 of the guide. In this state, a first portion 540 of the cage 502 extends from the first end 515 of the motion stage 501. This first portion 540 includes adapters 537 for the outer rolling elements of the third and fourth sets 506, 521, and therefore includes rolling elements that do not support rolling along the rolling surfaces 518 and 519, respectively. Similarly, in a second state (not shown), the motion stage 501 has been moved to a second final position closest to the first end 512 of the guide. In this state, a second portion 541 of the cage 502 extends from the second end 514 of the motion stage 501. The first and second portions form an offset that allows the first and second lengths to be compensated for.

[0056] 6A, the cage 602 can be configured to have different sized recesses configured to hold the rolling elements. A first recess 635 for holding the rolling elements of the first set 605 and the second set 620 can have a first size. A second recess 636 configured to hold the rolling elements of the third set 606 and optionally a fourth set can have a second size smaller than the first size.

[0057] 6B, the cage 602 can be configured to have a first recess 635 of similar size configured to hold the rolling elements. The rolling elements of the first set 605 and the second set 620 are directly received in such first recess 635. An adapter 637 can be placed in the first recess 635 of the cage 602 intended to hold the rolling elements of the third set 606 and optionally the fourth set. The adapter 637 includes a second recess 636 that is smaller than the first recess 635, which is suitable for directly receiving the rolling elements of the third set 606 and optionally the fourth set.

[0058] 6C, the cage 602 can be configured to have a first recess 635 of similar size configured to hold the rolling elements. The rolling elements of the first set 605 and the second set 620 are directly received in such first recess 635. Such a cage 602 can further include connectors 639 at both ends along the direction of movement of the cage 602, which are configured to connect a cage extender 638 as an adapter suitable for directly receiving the rolling elements of the third set 606 and optionally the fourth set. The cage extender 638 includes a second recess 636, smaller than the first recess 635, which is suitable for directly receiving the rolling elements of the third set 606 and optionally the fourth set. [Explanation of symbols]

[0059] 100 Bearings 101 Exercise Stage 102 Cage 103 Guide 104 Cage body 105 First set of rolling elements 106 first rolling element 107 Second rolling element 108 First guide surface 109 Second guide surface 110 First direction of movement 111 First rotation direction 112 First end of guide 113 Second end of guide 114 second end of motion stage 115 First end of the motion stage 200 Cross roller bearing 201 Exercise Stage 202 Cage 203 Guide 205 First set of rolling elements 206 First rolling element 208 First guide surface 209 Second guide surface 213 Second end of guide 215 First end of the motion stage 216 First rolling surface 217 Second Rolling Surface 218 Third rolling surface 219 Fourth Rolling Surface 220 Second set of rolling elements 221 first rolling element of the fourth set 300 needle roller bearing 301 Exercise Stage 302 Cage 303 Guide 305 First set of rolling elements 306 First rolling element 308 First guide surface 309 Second guide surface 313 Second end of guide 315 First end of the motion stage 316 First rolling surface 317 Second Rolling Surface 318 Third rolling surface 319 Fourth Rolling Surface 320 Second set of rolling elements 321 the first rolling element of the fourth set 400 Cross roller bearing 402 Cage 404 Cage body 408 First guide surface 416 First rolling surface 417 Second Rolling Surface 423, 424, 425, 426, 427, 428 Rolling elements 429 First Surface 430 Second Surface 431 Rotating Axis 432, 433 part 434 Central part 437 Adapter 500 bearings 501 Exercise Stage 502 Cage 503 Guide 505 First set of rolling elements 506, 507 Third set of rolling elements 508 First guide surface 509 Second guide surface 512 First end of guide 513 Second end of guide 514 Second End of Motion Stage 515 First End of Motion Stage 516 First rolling surface 517 Second Rolling Surface 518 Third rolling surface 519 Fourth Rolling Surface 520 Second set of rolling elements 521 Fourth set of rolling elements 537 Adapter 540 First part of the cage 541 Second part of the cage 602 Cage 605 First set of rolling elements 606 Third set of rolling elements 620 Second set of rolling elements 635 First recess 636 Second recess 637 Adapter 638 Cage Extender 639 Connector

Claims

1. a guide (103, 203, 303, 403, 503) including a first guide surface (108, 208, 308, 408, 508) that defines a direction of movement and is essentially V-shaped, said first guide surface including a first rolling surface (216, 316, 416, 516) and a second rolling surface (217, 317, 417, 517); a motion stage (101, 201, 301, 501) configured to move along the motion direction between a first end (112, 512) and a second end (113, 213, 313, 513) of the guide, the motion stage (101, 201, 301, 501) including a second guide surface (109, 209, 309, 509) including a third rolling surface (218, 318, 518) and a fourth rolling surface (219, 319, 519) arranged opposite the first and second rolling surfaces, respectively; a cage (102, 202, 302, 402, 502, 602) arranged to be partially interposed between the guide and the motion stage, the cage including first (105, 205, 305, 505, 605), second (220, 320, 520, 620), and third sets of rolling elements (106, 107, 206, 306, 423, 424, 425, 426, 427, 428, 506, 507, 606), the first set being arranged to roll on the first and third rolling surfaces, the second set being arranged to roll on the second and fourth rolling surfaces, and the third set being arranged to roll on the first rolling surface; Including, the guide and each rolling element of the third set are arranged to magnetically attract each other to bias the cage towards the guide; In a first state in which the motion stage is moving toward the first end of the guide, a first rolling element (106, 206, 306, 506, 606) of the third set is disposed between the second end of the guide and a first end (115, 215, 315, 515) of the motion stage disposed closest to the second end of the guide, and in a second state in which the motion stage is moving toward the second end of the guide, a second rolling element (114, 514) of the third set is disposed between the first end of the guide and a second end (114, 514) of the motion stage disposed closest to the first end of the guide. Non-recirculating rolling element bearings (100, 200, 300, 400, 500) in an overrunning cage configuration.

2. 2. The rolling element bearing of claim 1, wherein each rolling element of the third set is configured to magnetically attract the first rolling surface stronger than the second rolling surface, and preferably each rolling element of the third set is further configured to magnetically attract the first rolling surface stronger than at least one of the third and fourth rolling surfaces.

3. 3. A rolling element bearing as claimed in claim 1 or 2, wherein each rolling element of the third set comprises at least a portion made of a permanently magnetised material.

4. 4. The rolling element bearing of claim 3, wherein each rolling element of the first set has a first volume and the at least a portion of each rolling element of the third set has a second volume, the first volume being greater than the second volume.

5. 5. A rolling element bearing as claimed in any one of claims 2 to 4, wherein the cage comprises a cage body (104, 404) including first (429) and second (430) surfaces arranged to face the first and second rolling surfaces, and wherein the portion of each rolling element of the first set and the third set have first and second gaps, respectively, with respect to the second surface, the first gap being smaller than the second gap.

6. 6. A rolling element bearing according to claim 2, wherein the portion of each rolling element of the third set is arranged to roll on the first rolling surface.

7. 7. A rolling element bearing as claimed in any one of claims 2 to 6, wherein each rolling element of the first set has a first height and the portion of each rolling element of the third set has a second height, the second height being less than the first height.

8. 8. A rolling element bearing as claimed in any one of claims 2 to 7, wherein each rolling element of the first set has a first diameter and the portion of each rolling element of the third set has a second diameter, the second diameter being smaller than the first diameter.

9. 9. A rolling element bearing according to claim 2, wherein the portion of each rolling element of the third set is magnetized with a magnetization direction that is essentially axial.

10. 10. A rolling element bearing as claimed in any one of claims 1 to 9, comprising a fourth set of rolling elements (221, 321, 521) arranged to roll on the second rolling surface, each rolling element of the fourth set comprising at least a portion made of a permanently magnetised material, each rolling element of the second set and each rolling element of the fourth set having a third and fourth gap, respectively, with respect to the first surface, the third gap being smaller than the fourth gap.

11. 11. A rolling element bearing as claimed in claim 10, wherein the fourth set of rolling elements are essentially similar to the third set of rolling elements.

12. A rolling element bearing according to claim 1 , wherein the guide, the cage and the motion stage are each configured to provide linear motion of the motion stage.

13. 13. A rolling element bearing as claimed in any one of the preceding claims, wherein the first and second rolling elements of the third set are each configured to flank at least a portion of the first set.

14. 14. A rolling element bearing as claimed in any one of claims 1 to 13, wherein a first distance between axes of the first and second rolling elements of the third set is greater than a second distance between the first and second ends of the motion stage.

15. 15. A rolling element bearing according to any one of claims 1 to 14, wherein along the direction of movement the first guide surface extends over a first length between corresponding said first and second ends, the cage extends over a second length and the second guide surface extends over a third length between corresponding said first and second ends, the second length being smaller than the first length and larger than the third length, preferably the second length being essentially the average of the first and third lengths, preferably the movement of the second guide surface is twice the difference in length between the second and third lengths.

16. 16. A rolling element bearing according to any one of claims 1 to 15, comprising an adapter (437, 537, 637) including an adapter body arranged to be received in a first recess of a plurality of first recesses (635) of the cage arranged to hold the first set of rolling elements, the adapter body configured to partially occupy the first recess and leave an unoccupied portion arranged to rotatably hold the third set of rolling elements, preferably the adapter body including a second recess (636) configured to rotatably hold the third set of rolling elements.

17. 17. An assembly comprising a moving body and two rolling element bearings according to any one of claims 1 to 16, wherein the rolling element bearings are arranged substantially in parallel and the motion stage is fixedly connected to both ends of the moving body.

18. 18. A cage for a rolling element bearing in an overrunning cage configuration according to any one of claims 1 to 17.

19. 17. An adapter for a rolling element bearing in an overrunning cage configuration as claimed in claim 16.

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