Technical Field The present invention relates to linear bearings and assemblies that are used for supporting moving loads. In particular, it relates to improved bearing designs for high load carrying capacity with high precision.

Background

Recirculating rolling-element linear bearings and assemblies of such bearings are used to support moving loads in many types of positioning applications. Such bearings typically comprise a base component and a carriage component in which the carriage moves linearly with respect to the base. Linear raceways are typically located in grooves that have been appropriately formed in the base and carriage components. Rolling elements (such as balls or rollers) are located between the raceways to allow for low friction, linear movement of the carriage with respect to the base. Such linear profile raceways for recirculating rolling elements are most commonly created as a surface feature cut directly into a carriage and/or a base made of solid steel, with both being precision ground (often to 10 μπι accuracy) with rolling elements. Some designs exist that use hardened steel raceways attached to an extruded aluminum base and/or carriage. These attached raceways are usually press-fit, rolled in, or held to the base by the force applied by the carriage. It is harder to obtain good tolerances with such designs however.

Four-row linear recirculating bearing assemblies have a complex design and are well known in the art for being able to move and position heavy loads with high precision. Such assemblies have two recirculating rolling-element linear bearings positioned on either side of a carriage and engaged to a base. Each linear bearing comprises two rows of roller elements and thus the assembly has a total of four rows of roller elements. Four-row assemblies have high rigidity and are more compliant to changes in load and/or dimensions. For instance, using balls as the roller elements, as a ball is compressed in a four-row assembly, the ball is allowed to "ovalize" and act like a spring. This allows a four-row bearing assembly to accommodate higher loads. On the other hand, in a bearing in which a ball is contacted on four sides, the ball is prevented from ovalizing and the stresses rapidly increase. This results in the carriage getting noticeably tighter and looser as it moves down the track. Four-row linear recirculating bearing assemblies are typically assembled preloaded and can be made in long sections. EP353396 discloses examples of prior art four-row linear recirculating bearing assemblies. It is suggested that an inexpensive and easily producible rotary guide is achieved by this design. However, the bearing rail or raceways therein are rolled or press fit in the base (thus being fixed to the base so they cannot rotate and also they cannot slide in) which does add cost for rolling or press fit equipment. Because this is required over the length of the base component, this disadvantage becomes more significant with longer stages. Balls can be used as the rolling elements and the raceways are shaped with a radius for the balls.

JPH09-210059 discloses examples of other linear recirculating bearing assemblies in the prior art that do not have a four-row design. The purpose here was to provide a rail guide stably slid and reciprocated and generating no failure and no noises by slidably inserting bearings of a linear guide between two rail rods, and reciprocating the linear guide along the rail guide. The rail rods or raceways can be slid into grooves in the bearing assembly and additionally the rail rods can rotate therein. The design employs two rows of bearings and each ball (rolling element) is contacted on four sides (as opposed to being contacted only on two sides in a four-row design). The rail rods comprise no radius for a ball to roll in. Thus the bearing assembly here cannot handle the same heavy loads as a four-row design. While the rail rods can rotate in this example, they do not serve to accommodate any misalignments because there is none to accommodate with the disclosed round or flat sided rail rods. The disclosed designs were not four-row designs.

Numerous other linear bearing and assembly designs are available commercially and additionally have been suggested in the literature. Despite the many improvements which have been suggested and developed, there remains a continuing desire for less expensive linear bearings and assemblies which are capable of moving and positioning heavy loads with high precision. The present invention addresses this desire and provides further advantages as discussed below.

Summary

The present invention relates to a geometry and arrangement of linear bearing elements that result in improved linear accuracy, improved load capability, and lower cost than the prior art. For instance, high accuracy and load capability can be obtained with base and carriage components made from lower precision extrusions. High precision raceways are separate components which can simply be slid into appropriately shaped grooves in the base and/or carriage. Two linear bearings of the invention can be employed in a four-row assembly which allows for high loads and other advantages associated with such designs. Specifically, a linear bearing of the invention allows for recirculating linear motion in a linear direction and comprises first and second components; first and second rows of rolling elements; and first and second sets of raceways. The first component comprises at least a first groove in the linear direction and the first groove has a shaped surface. The second component is capable of motion relative to the first component in the linear direction. The first and second rows of rolling elements are located between the first and second components. The first set of raceways is in the first component and comprises at least a first raceway in the first groove. A portion of the first raceway surface engages the first groove. The second set of raceways is in the second component. Each of the rolling elements in the first and second rows engages with the first and second sets of raceways at interface surfaces. These interface surfaces consist essentially of first component interface surfaces where each of the rolling elements engages with a portion of a raceway in the first set of raceways, and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements engages with a portion of a raceway in the second set of raceways. The inventive linear bearing is characterized in that the first raceway is slidably insertable into the first groove and is shaped to allow for rotation within the first groove about a linear axis.

In a like manner to the first component, the second component can comprise at least a second groove in the linear direction and having a shaped surface. The second raceway can then be in the second groove with a portion of the second raceway surface engaging the second groove. Alternatively though, the second raceway can instead be integrally formed with the second component (i.e. the second raceway and second component are a single piece).

Depending on the geometry and arrangement selected, the first component can be a base and the second component a carriage, or vice versa.

In the linear bearing of the invention, the first and second rows of the rolling elements can for instance be balls or cylindrical rollers. Further, the surfaces of the portions of the raceways in the first and second set of raceways engaging the interface surfaces of the rolling elements can be shaped to essentially conform to the interface surfaces of the rolling elements. For instance, in embodiments in which the first and second rows of the rolling elements are balls, the portions of the raceways in the first and second set of raceways engaging the interface surfaces of the balls can be shaped with round cross-sections. In this way, because the raceways are shaped with radii for the balls to roll in, the linear bearing can take almost 10 times the load as one without (i.e. an embodiment with flat raceways).

In the linear bearing of the invention, the first groove and the portion of the first raceway engaging the first groove can also be shaped with round cross-sections. As illustrated in the Example below, excellent alignment results were obtained in an embodiment in which the first raceway was allowed to rotate greater than or about 10° in the first groove.

In one embodiment of the invention, the first component can comprise an additional groove in the linear direction in which the additional groove has a shaped surface. The first set of raceways in the first component can consist of just the first raceway and an additional raceway in the additional groove. Further, a portion of the additional raceway surface can engage the additional groove. The second set of raceways in the second component can consist of just the second raceway. Here, the interface surfaces then consist essentially of first component interface surfaces where each of the rolling elements in the first row of rolling elements engages with a portion of the first raceway and each of the rolling elements in the second row of rolling elements engages with a portion of the additional raceway, and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements in the first and second rows of rolling elements engages with a portion of the second raceway. In a like manner to the first raceway, the additional raceway is slidably insertable into the additional groove and is shaped to allow for rotation within the additional groove about a linear axis. However, the second raceway can optionally be shaped so as to be essentially fixed against rotation in the second groove. In such an embodiment, the centres of the first and additional raceways are oriented 90 degrees apart with respect to the centre of the second raceway. If the first and second components are a base and carriage respectively, the preceding describes, for instance, features of the embodiment depicted in Figures la-lc). If the first and second components are a carriage and a base respectively, the preceding describes, for instance, features of the embodiment depicted in Figure 2.

In a variation of the above, the second raceway can also be slidably insertable into the second groove and be shaped to allow for rotation within the second groove about a linear axis. This describes, for example, features of the embodiment depicted in Figure 5.

If adequate tolerances are obtained (e.g. using raceways of cold drawn bearing steel), certain raceways in inventive embodiments can be combined or integrated into "unitary" raceways. As an example of this, the first set of raceways in the first component can consist of the first raceway, the second set of raceways in the second component can consist of the second raceway, the interface surfaces can consist essentially of first component interface surfaces where each of the rolling elements in both the first and second rows of rolling elements engages with a portion of the first raceway and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements in both the first and second rows of rolling elements engages with a portion of the second raceway, and the second raceway can be shaped so as to be essentially fixed against rotation in the second groove. This describes, for instance, representative features of the embodiment depicted in Figure 6.

In a still further variant of the invention, the first set of raceways in the first component can consist of the first raceway, the second component can comprise an additional groove in the linear direction in which the additional groove has a shaped surface, the second set of raceways in the second component can consist of the second raceway and an additional raceway in which a portion of the additional raceway surface engages the additional groove, the interface surfaces can consist essentially of first component interface surfaces where each of the rolling elements in both the first and second rows of rolling elements engages with a portion of the first raceway, and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements in the first row of rolling elements engages with a portion of the second raceway and each of the rolling elements in the second row of rolling elements engages with a portion of the additional raceway, and the second raceway and the additional raceway can be slidably insertable into the second groove and the additional groove respectively and be shaped to allow for linear movement in their respective grooves perpendicular to the linear direction. In such a variant, here the bottoms of the second groove and the additional groove can be shaped with flats. This describes, for instance, representative features of the embodiment depicted in Figure 7. In a yet further variant of the invention, the first component can comprise an additional groove in the linear direction in which the additional groove has a shaped surface, the first set of raceways in the first component can consist of the first raceway and an additional raceway in the additional groove in which a portion of the additional raceway surface engages the additional groove, the second component can comprise a second additional groove in the linear direction in which the second additional groove has a shaped surface, the second set of raceways in the second component can consist of the second raceway and yet another (i.e. a second) additional raceway in the second additional groove in which a portion of the second additional raceway surface engages the second additional groove, the interface surfaces can consist essentially of first component interface surfaces where each of the rolling elements in the first row of rolling elements engages with a portion of the first raceway and each of the rolling elements in the second row of rolling elements engages with a portion of the additional raceway, and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements in the first row of rolling elements engages with a portion of the second raceway and each of the rolling elements in the second row of rolling elements engages with a portion of the second additional raceway, and the additional raceway can be slidably insertable into the additional groove and be shaped to allow for rotation within the additional groove about a linear axis, while the second raceway and the second additional raceway can be shaped so as to be essentially fixed against rotation in the second groove and the second additional groove respectively. This describes, for instance, representative features of the multiple raceway embodiment depicted in Figure 3.

Linear bearings of the invention can be made in which the first and second components are extruded components, such as aluminum extrusions, steel extrusions, and the like. Even plastic extrusions may be contemplated. The first raceway and any other raceways employed can however desirably be made of cold drawn steel in order to obtain the required tolerances in the parts without the need for additional processing such as precision grinding. When made of cold drawn steel, the raceways can be subsequently hardened while maintaining a dimensional consistency within 5 micrometers along the linear direction.

A pair of the aforementioned linear bearings may be used to provide a four-row linear bearing assembly. Such a linear bearing assembly allows for recirculating linear motion in a linear direction and comprises a base and a carriage which is capable of motion relative to the base in the linear direction. Each of the pair of linear bearings is located on opposing sides of the carriage and between the base and the carriage. Further, the base and carriage components are common to each of the pair of linear bearings.

A method of making the aforementioned linear bearing generally comprises the steps of: manufacturing the first component comprising the first groove, manufacturing the second component, obtaining the first and second rows of rolling elements, manufacturing the first raceway, slidably inserting the first raceway into the first groove such that a portion of the first raceway surface engages the first groove, providing the second set of raceways in the second component, and assembling the first component, the second component, and first and second rows of rolling elements such that the first and second rows of rolling elements are located between the first and second components and each of the rolling elements in the first and second rows engages with the first and second sets of raceways at interface surfaces consisting essentially of: first component interface surfaces where each of the rolling elements engages with a portion of a raceway in the first set of raceways, and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements engages with a portion of a raceway in the second set of raceways.

In an exemplary method of making the linear bearing, the steps of manufacturing the first and second components can comprise extruding them. Further, in embodiments in which the first raceway and any other raceway employed are made of cold drawn steel, the steps of manufacturing any or all of these raceways can comprise cold drawing, induction hardening, quenching, and tempering them.

Brief Description of the Drawings Figure la shows a perspective view of a four-row linear bearing assembly of the invention. The assembly here comprises two linear bearings, each having two rotatable, insertable raceways in the base and a single raceway essentially fixed in the carriage.

Figure lb shows a cross-sectional view of the linear bearing assembly of Figure la in a plane perpendicular to the linear direction.

Figure lc shows an enlarged view of a linear bearing in the assembly of Figure la.

Figure 2 shows a schematic cross-sectional view of another linear bearing assembly of the invention. The assembly here is similar in principle to that of Figure la except that the carriage in this embodiment surrounds the base as opposed to the other way around. Figure 3 shows a schematic cross-sectional view of yet another linear bearing assembly of the invention. In this assembly, the base surrounds the carriage and each of two linear bearings has two rotatable, insertable raceways in the carriage and two raceways that are essentially fixed in the base.

Figures 4a to 4f show optional shapes of raceways in cross-section that are suitable for use in essentially fixing the raceway in a groove.

Figures 4g to 4k show optional shapes of raceways in cross-section that are suitable for use as rotatable insertable raceways in accordance with the invention. Figure 5 shows a schematic cross-sectional view of another embodiment of a linear bearing assembly of the invention. The assembly shown here is similar to that shown in Figure 2 except that the rows of rolling elements are cylinders (as opposed to balls) and now the raceway in the base is also a rotatable insertable raceway. Figure 6 shows a schematic cross-sectional view of a linear bearing of the invention that only employs one raceway in each of the two components. The embodiment here employs a suitably shaped, single (or unitary) rotatable insertable raceway in the base and a single raceway essentially fixed in the carriage. Figure 7 shows a schematic cross-sectional view of a further linear bearing assembly of the invention. In the assembly shown here, the carriage surrounds the base. In each bearing in the assembly, the base employs a single rotatable insertable raceway while the carriage employs two raceways that can move linearly within their grooves perpendicular to the linear direction.

Detailed Description

Unless the context requires otherwise, throughout this specification and claims, the words "comprise", "comprising" and the like are to be construed in an open, inclusive sense. The words "a", "an", and the like are to be considered as meaning at least one and are not limited to just one. The terms "slidably insertable" and "shaped to allow for rotation" as used herein are intended to apply to the relevant elements in an unloaded condition and not necessarily to the elements in a preloaded or otherwise loaded condition. For instance as those skilled in the art are well aware, a raceway that is slidably insertable and/or rotatable in an unloaded condition can effectively become fixed both linearly and against rotation when loaded sufficiently. It should be noted that "slidably insertable" is not intended to exclude other means of insertion. For instance, in some embodiments, it may additionally be possible to employ a raceway design that allows for insertion into its intended groove from above by properly orienting the raceway prior to insertion and then reorienting thereafter.

The term "essentially conform" is used herein to refer to the relationship in shape between certain elements such as that between rolling elements and grooves in which they are located. It is intended to mean that the shapes are similar but not generally identical in order that the former conform to the latter in a practical manner. For instance, as those skilled in the art are aware, the radii of grooves shaped to practically conform to inserted balls are often about 2-5% larger than the radii of the inserted balls. (Although exactly matching the radii can work well too, if the ball radius is bigger than the raceway radius then it switches from one point to two small points of contact and that can cause problems. Also, using a slightly larger raceway radius is another way to accommodate for misalignment on a finer scale.)

The term "essentially fixed against rotation" as used herein is intended to indicate that the element being referred to may be capable of some minute, non-zero rotation but not so much as to be capable of accommodating any significant misalignment in other elements in the linear bearing.

In linear bearings and assemblies of the present invention, precise rotatable, insertable raceways are used to compensate for modest misalignments which may originate from the use of other lower precision components in the bearings. In addition, the raceway and rolling element designs and configurations can provide for relatively high load carrying capacities. This allows bearings and assemblies of high precision and high load carrying capability to be made more simply and inexpensively.

In general, the linear bearings comprise two components (typically a base and a carriage) which can move relative to each other in a linear direction. A bearing also comprises two rows of rolling elements between the two components and two sets of raceways (one set in each of the two components) that engage appropriately with the rolling elements. Specifically, appropriate engagement involves a portion of raceway in each of the two components contacting each of the rolling elements on opposing surfaces only (i.e. two opposing contact surfaces only). That is, each of the rolling elements in the first and second rows engages with the first and second sets of raceways at interface surfaces consisting essentially of first component interface surfaces where each of the rolling elements engages with a portion of a raceway in the first set of raceways, and second component interface surfaces directly opposite the first component interface surfaces where each of the rolling elements engages with a portion of a raceway in the second set of raceways. And in a linear bearing and/or assembly of the invention, at least one rotatable, slidably insertable raceway is used in a groove formed in one of the two components in the linear direction. The groove and associated raceway are shaped to allow for rotation within the groove about a linear axis.

Figures la to lc show a representative four-row linear bearing assembly of the invention. Figure la shows a perspective view of a complete four-row linear bearing assembly 1 which comprises two linear bearings 2 that provide for linear movement of carriage 4 relative to base 3 in the linear direction represented by arrow X. Each linear bearing 2 in assembly 1 has two rotatable, insertable raceways 5a, 5b located in corresponding grooves 6a, 6b formed in base 3. Further, each linear bearing 2 has a single raceway 7 that is essentially fixed in groove 9 formed in carriage 4. Two rows of balls 8a, 8b are used for rolling elements in linear bearing assembly 1. However, complete bearing assembly 1 also includes covers 2a that serve to cover single raceways 7 and balls 8a, 8b in bearings 2 and also to act as a "U-turn" for the balls. With covers 2a in place, certain elements are not visible in Figure la. Cover 2a and base 3 on the right side of Figure la have therefore been shown partially cutaway so as to expose balls 8a, 8b and also to expose channels 10 which are formed in each cover 2a to provide a connection for balls 8a, 8b to access recirculating holes 1 1 formed in carriage 4.

The elements making up bearings 2 are more clearly visible in Figure lb which shows a cross- sectional view of linear bearing assembly 1 in a plane perpendicular to linear direction X, and in Figure lc which shows an enlarged view of the linear bearing 2 appearing on the right side of assembly 1 in Figures la and lb. In each linear bearing 2, the set of raceways in base 3 includes two precisely-made rotatable raceways 5a, 5b which are slidably insertable and rotatable within respective grooves 6a, 6b formed in base 3. Grooves 6a, 6b and those portions of raceways 5a, 5b that engage with grooves 6a, 6b are all shaped with round cross-sections with matching radii so as to allow for rotation of the latter within the former about linear axes parallel to direction X. Because raceways 5a, 5b are rotatable, they can "self-align" by rotating modestly to compensate for other lower tolerance components and/or slight misalignments in other components in bearings 2, and thereby obtain a bearing of higher overall precision. The set of raceways in carriage 4 consists of a single raceway 7 which is essentially fixed in groove 9 formed in carriage 4. The set of raceways 5a, 5b rotatably inserted in base 3 engage rows of balls 8a, 8b respectively at base interface surfaces 8ai and 8bi respectively. Single raceway 7 fixed in carriage 4 has two surfaces that are shaped so as to engage rows of balls 8a, 8b respectively at carriage interface surfaces 8aii and 8bii respectively. Carriage interface surfaces 8aii and 8bii are directly opposite base interface surfaces 8ai and 8bi respectively. As discussed above, this arrangement allows balls 8a, 8b to "ovalize" under load thereby allowing for greater loads to be accommodated. Further, all the raceway surfaces which engage with balls 8a, 8b at these various interfaces (i.e. 8ai, 8bi, 8aii, and 8bii) are all shaped with round cross-sections to essentially conform to balls 8a, 8b. As those skilled in the art are aware, typically these raceway surfaces would then be made with radii that are slightly larger than those of balls 8a, 8b. As shown in these linear bearings, the centres of raceways 5a and 5b are oriented 90 degrees apart with respect to the centre of raceway 7.

In the enlarged view of Figure lc, arrows show the directions of rotation possible for raceways 5a and 5b in their respective grooves 6a and 6b. In order to sufficiently compensate for lower tolerances in base and carriage dimensions and/or misalignments following assembly, it can be desirable to provide for at least about 10° of rotation of the raceways in their respective grooves. However those skilled in the art will appreciate that lesser amounts, such as about 3-5°, may also work fine too and that what is required depends on the specific geometry and accuracy of all the parts.

As with other four-row linear bearing assemblies in the art, assembly 1 typically comprises a relatively short carriage 4 but a very long base 3. For instance, a base up to 4 meters in length is possible and is a common product. In the fully assembled, linear bearing assembly 1, carriage 4 is held onto base 3 by a preload force (e.g. typically in the range of about 1 -10% of the bearing load capacity which is applied via springs or some mechanical jig). Thus in principle, the raceways in a relatively short carriage do not need to be fixed in a groove but can instead be maintained in place by the preload force. However, the raceways in a long extended base will typically separate from the base when the carriage is not in close proximity. The present invention provides a method of retaining raceways in a lengthy component (e.g. base) regardless of the length of the linear bearing. For instance, rotatable raceways 5a, 5b can slide freely into base 3 and can rotate to some extent within grooves 6a, 6b but they are held in place in their grooves by features 3a formed in base 3 which loosely mate with features of raceways 5a, 5b. A significant advantage that the present invention offers over prior art embodiments is that it provides a mechanism by which the bearing raceways and rolling elements can self-align to accommodate poor tolerances in the base and carriage components. For instance, to reduce cost, it is desirable to make carriage and base components from inexpensive materials using an inexpensive process, e.g. aluminum extrusions. However, extrusions have relatively poor dimensional tolerances and can be inconsistent from batch to batch. As an example, dimension Y shown in Figure lc may have a tolerance greater than 0.1 mm from batch to batch (or piece to piece). However, within a single batch or piece, extrusions typically have good dimensional consistency along their length. It is common for dimension Y to be consistent to within 5-10 μπι along the length of a single extruded part. Thus, in order to prepare precise, very long linear bearing assemblies, conventional designs required either the carriage or base component to be precision machined or ground so that the rolling elements aligned well and transferred the load properly between the carriage and base. It is challenging and costly to machine material to 5-10 μπι accuracy and parallelism. In the present invention however, the rotatable raceway or raceways are constrained in such a way that they are still free to rotate and self-align with the rolling elements in the bearings. Previous designs cannot achieve centered contact between the rolling elements and raceways while accommodating large tolerances in the base and carriage components. Another prior art method of holding bearing raceways in place is by press -fitting them in place which adds cost and can introduce geometric inconsistency down the length of the bearing, increasing runout as well as pitch, roll and yaw errors. A related advantage that the present invention offers over this approach is that it eliminates the associated cost of press-fitting raceways, and reduces runout and pitch, roll and yaw errors.

As mentioned above, the invention advantageously allows for the use of less expensive, more easily manufactured components for the base and carriage components. However, the rotatable raceways themselves are high precision components made of hard, strong materials (e.g. hardened steel) of precise dimensions. One suitable method for manufacturing such rotatable raceways is to make them of cold drawn steel. Thereafter, the cold drawn steel raceway is hardened (e.g. via induction hardening), then quenched, and finally tempered appropriately to prepare suitable precise rotatable raceways for use in the inventive bearings. An advantage of using these materials and methods of preparation is that the tolerances of cold drawn steel are very good and generally they do not need to be precision ground as a result. A desired dimensional consistency of 5 μιη down the length of the components can be achieved for instance without precision grinding. Once suitable rotatable raceways have been prepared, a bearing and/or assembly of the invention can be manufactured simply by sliding these raceways into appropriate grooves formed in extruded base and carriage components and otherwise completing the manufacture of the rest of the bearing and/or assembly in a conventional manner (e.g. preparing the carriage component from different parts that are fastened together, preloading the bearings, tightening certain fasteners to lock everything in place, and so on).

While Figures la to lc describe a desirable embodiment of the invention, it should be appreciated that numerous variants of bearings and assemblies thereof are possible. For instance, embodiments in which a rotatable raceway is employed in the carriage or even both the base and carriage are contemplated. Further, embodiments include those in which the base surrounds the carriage (e.g. as in Figures la-lc) or alternatively in which the carriage surrounds the base. Further still, suitable embodiments can include more than one rotatable raceway in either or both of a base and carriage component. As is apparent in Figures la-lc, raceways that are not rotatable can be employed in suitable embodiments. One or more such non-rotatable raceways may be employed in either or both of a base and carriage component. Further, such non-rotatable raceways may be firmly fixed in an associated groove or may be essentially fixed in place against rotation (e.g. by preloading force). Further still, in some situations, such non-rotatable raceways may be formed integrally with the component it appears in (e.g. may be employed in a carriage in which both the carriage and the non- rotatable raceways are formed in a single, hardened steel piece and precision ground for accuracy thereafter). Yet further, even though any of the aforementioned raceways may be slidably insertable into an associated groove, this is not intended to exclude the possibility of additionally being able to insert the raceways in other manners if desired. For instance, in certain embodiments, a raceway design may be chosen that can be inserted in its groove by orienting in a first manner, dropping it into its groove, and then orienting in a second manner such that it is retained in place once the entire assembly of the bearing is completed.

While Figures la to lc show an embodiment using balls as roller elements and generally round shapes for the various grooves, raceways, and of course the balls, numerous other options can be contemplated (e.g. cylinder rolling elements, other raceway and groove geometries) . In addition, numerous other materials and production methods may be considered for the various elements making up the bearings (e.g. steel, even certain plastics, etc. may be considered instead of aluminum extrusions for the carriage and base) . The following figures and description represent some of the numerous variants possible. However, those skilled in the art will appreciate that these are only representative and that other options and combinations thereof are possible. Figure 2 shows a schematic cross-sectional view of a variant of a linear bearing assembly of the invention. The assembly here is similar in principle to that of Figures la-lc except that the carriage in this embodiment surrounds the base as opposed to the other way around. Otherwise the shapes, number and configuration of the grooves and raceways employed are quite similar. For instance, this embodiment comprises two linear bearings 22 each comprising base 23, carriage 24, rotatable raceways 25a, 25b, rows of balls 28a, 28b, and raceway 27 fixed in base 23. Yet another variant of a linear bearing assembly is shown in the schematic cross-sectional view of Figure 3. In this assembly, base 33 surrounds carriage 34 and each of two linear bearings 32 have two rotatable, insertable raceways 35a, 35b in carriage 34 and, in this embodiment, two raceways 37a, 37b that are essentially fixed in base 33. This embodiment also comprises rows of balls 38a, 38b as roller elements in each of the two linear bearings 32. An optional different shape for fixed raceways 37a, 37b is depicted in Figure 3. Otherwise though, the shapes and configuration of the grooves and raceways employed are quite similar to those of the preceding figures.

As exemplified in part in Figure 3, suitable bearing raceways and associated component grooves may have any geometry that allows the raceway to be retained loosely by the component while still exposing a surface or multiple surfaces of the raceway to the rolling elements. To illustrate some of the other optional shapes for the various raceways that may be employed, Figures 4a to 4f show optional shapes of raceways in cross-section that are suitable for use in essentially fixing the raceway in a groove. The raceway profile of Figure 4e was employed as the shape for fixed raceways 37a, 37b in Figure 3. In addition, Figures 4g to 4k show optional shapes of raceways in cross-section that are suitable for use as rotatable insertable raceways in accordance with the invention. Those skilled in the art will appreciate that the invention is not however limited to the geometries shown in these figures.

Another variant of a linear bearing assembly is shown in the schematic cross -sectional view of Figure 5. The assembly shown here is similar to that shown in Figure 2 except that the rows of rolling elements are cylinders (as opposed to balls) and now the raceway in the base is also a rotatable insertable raceway. (When the rolling elements are cylinders, all the raceways can be rotatable.) For instance, this embodiment comprises two linear bearings 42 each comprising base 43, carriage 44, rotatable raceways 45a, 45b in carriage 44, rows of cylinders 48a, 48b, and raceway 47 which is now slidably insertable and rotatable in base 43. The shape of raceways 47 and their associated grooves (not called out in Figure 5) are shown as being similar to those of raceways 45a, 45b and their associated grooves (again not called out in Figure 5). Otherwise the shapes, number and configuration of the grooves and raceways employed in this variant are quite similar to that of Figure 2.

Figure 6 shows a schematic cross-sectional view of a variant of a single linear bearing of the invention. Here, only one "unitary" raceway is employed in each of the base and carriage components. As depicted, suitably shaped, single (unitary) rotatable insertable raceway 55 is employed in base 53 and single raceway 57 is essentially fixed in carriage 54. Raceways 55, 57 engage with rows of balls 58a, 58b in much the same manner as shown in the embodiment of Figure 2 and thus, with the exception of the "unitary" raceway design, the bearing shown here is otherwise quite similar to either of bearings 22 in Figure 2. As may be apparent to those skilled in the art, tighter tolerances and more attention thereto may be required to control the distance between the rolling elements (balls) well enough for enablement of this embodiment. However raceways can be made of cold drawn bearing steel, even without post-precision grinding, with excellent tolerances that may be suitable per se.

Yet another variant of a linear bearing assembly of the invention is shown in the schematic cross - sectional view of Figure 7. In the assembly shown here, carriage 64 is configured so as to surround base 63. In each bearing 62 in the assembly, base 63 employs a single rotatable insertable raceway 67 while carriage 64 employs two raceways 65a, 65b that can move linearly within their grooves (not called out in Figure 7) perpendicular to the linear direction X. The grooves for raceways 65a, 65b are shaped more open than those in previous figures, thereby allowing raceways 65a, 65b to be inserted simply by dropping them in. However these raceways are retained in place solely by the load applied between carriage 64 and base 63. In certain embodiments, this can be found sufficient.

As is evident from the preceding, the invention offers many advantages over conventional linear bearings and assemblies thereof. A rotatable raceway or raceways is/are employed that readily slide into a base or carriage component without the need for special equipment (e.g. as required to roll or press-fit raceways in place.) Advantageously, the rotatable raceway rotates so as to accommodate for misalignments and/or poor tolerances elsewhere in the bearing, thereby providing a bearing of higher precision. By using raceway shapes that essentially conform to those of the rolling elements employed, high load carrying capacities and lifetimes can be obtained. Assemblies with desirable four-row bearing designs can be made and very long (unlimited length) and/or modular stages can be assembled in the field from shorter sections. For instance, the joints where the raceways meet can be offset from the base section joints. The inserted rotatable raceways can force the base sections to align well so that the carriage slides smoothly between sections. The sections of the base can be attached together with clamps in T-slots provided therein.

The following Example has been included to illustrate certain aspects of the invention but should not be construed as limiting in any way. Example A four-row recirculating linear bearing assembly was made as depicted in Figures la-lc and as generally described above. Base and carriage components were manufactured of aluminum extrusions. Slidably insertable raceways (both the rotatable and the non-rotatable raceways shown in Figures lc-lc) were made of cold drawn steel that had been subsequently induction hardened, quenched, and tempered. These raceways were inserted into the base as shown in Figures la-lc and were able to rotate up to about 10° in their respective grooves. The dimensional consistency of these raceways was determined to be within 5 micrometers along the linear direction. The manufactured assembly comprised a carriage approximately 100 mm in length and base approximately 500 mm in length. 3 mm diameter balls were used in the carriage. The stage maintained 0.008° pitch accuracy, 0.007° roll accuracy, 0.009° yaw accuracy, 10 μιη horizontal runout, and 5 μιη vertical runout when mounted to a flat surface. A 1.0 m travel version of the stage ran 3000 km under a 500 kg load. Multiple base stages were assembled in series to produce a very long linear bearing assembly about 4 m in length.

All of the above U.S. patents, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification, are incorporated herein by reference in their entirety. While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications may be made by those skilled in the art without departing from the spirit and scope of the present disclosure, particularly in light of the foregoing teachings. Such modifications are to be considered within the purview and scope of the claims appended hereto.