1. Field of the Invention
This invention relates to recirculating bearings, and more particularly to a recirculating bearing that allows two-axis translational motion of a supported member along a bearing surface.
2. Description of the Related Art
Recirculating bearings are used to provide linear motion, and reversible linear motion, in applications that require a large range of motion, much greater than the extent of the bearing itself. For example, recirculating bearings are commonly used to support linear motion of machine parts and tables for heavy duty machine tools.
A typical recirculating bearing has a straight track section under load, a parallel straight return track section and two semi-cylindrical end sections that connect the track sections to form a closed track. Cylindrical rollers or spherical ball bearings recirculate around the closed track in response to linear motion of a supported member such as a machine part or table. Unless restricted by the application, the recirculating bearing has a unlimited range of motion in the linear direction parallel to the track.
The following is a summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not intended to identify key or critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description and the defining claims that are presented later.
The present invention provides a recirculating bearing that allows two-axis translational motion of a supported member along a bearing surface.
In an embodiment, a recirculating bearing that allows two-axis translational motion of a supported member comprises a surface member having a bearing surface upon which a plurality of ball bearings are free to roll in any direction along the bearing surface. The supported member is supported on one or more of the ball bearings allowing two-axis translational motion of the member along the bearing surface. A bearing housing having a recirculating volume connects opposing ends of the bearing surface to form a closed track for recirculating the ball bearings in response to translational motion of the supported member. Unless limited by the application, the recirculating bearing provides for unlimited range of motion of the supported member in both axes.
In an embodiment of a pedestal two-axis recirculating bearing, a disk is supported on a pedestal within the recirculating volume. The disk's top surface provides the bearing surface that allows the ball bearings to roll in any direction. The recirculating volume encompasses the perimeter of the disk such that motion of the supported member in any direction causes ball bearings to roll off the top of the disk into the recirculating volume and to recirculate in a nominal direction to follow the direction of motion of the supported member. Retaining elements may be used to retain three ball bearings in a triad configuration that rolls freely in any direction to reduce friction between the ball bearings.
In an embodiment of a dual-roller two-axis recirculating bearing, the surface member comprises first and second parallel rollers that form a channel along one axis to provide the bearing surface. The recirculating volume connects opposing ends of the channel to form the closed track. The ball bearings roll freely along the channel and recirculate around the closed track in response to translational motion of the supported member along the channel. The ball bearings roll in place causing counter rotation of the rollers in response to translational motion of the supported member along the other axis across the rollers. The freedom of the ball bearings to roll in any direction along the bearing surface is preserved by decomposing arbitrary motion into motion along both axes. The rollers may comprise a single unitary roller or a plurality of independently rolling segments.
In an embodiment of a cylindrical two-axis recirculating bearing, the supported member is a supported cylinder of diameter D1. The surface member and bearing housing comprise an inner cylinder in which the supported cylinder is placed, an outer cylinder and a pair of annular end caps. The inner cylinder's interior cylindrical surface provides the bearing surface. Ball bearings are free to roll axially along the bearing surface in response to translational motion of the supported cylinder axially along the bearing surface and to roll around the bearing surface in response to translational motion of the supported cylinder radially along the bearing surface. The inner cylinder is mounted axially within the outer cylinder to define the recirculating volume as an annular volume around the bearing surface. The annular end caps connect the bearing surface to the annular recirculating volume to form the closed track so that ball bearings rolling axially in response to axial translational motion of the supported cylinder recirculate in the closed track.
These and other features and advantages of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, taken together with the accompanying drawings, in which:
a and 2b are perspective views of an embodiment of a pedestal two-axis recirculating bearing with and without the ball bearings;
a-3c are side and top views of a retaining element for retaining a triad of ball bearings to reduce friction;
a and 4b are perspective and sectional views of an embodiment of a dual-roller two-axis recirculating bearing;
a through 6c are perspective, end and section views of an embodiment of a cylindrical two-axis recirculating bearing.
The present invention describes a recirculating bearing that allows two-axis translational motion of a supported member along a bearing surface. The recirculating bearing combines a bearing surface upon which a plurality of ball bearings are free to roll in any direction along the bearing surface with a recirculating volume that recirculates ball bearings to and from the bearing surface.
Referring now to
A bearing housing 26 has a recirculating volume 28 that connects opposing ends of the bearing surface 16 to form a closed track for recirculating the ball bearings 20 in response to translational motion of the supported member 18. Unlike the bearing surface that is loaded by the supported member resting on the ball bearings, the recirculating volume provides unloaded surfaces that facilitate recirculation of the ball bearings. The volume extends away from the supported member at edges of the bearing surface, through which ball bearings rolling off one edge of the bearing surface move out of contact with the supported members, through which ball bearings on the nominally opposite side move onto the bearing surface and into contact with the supported member, and through which ball bearings are free to move between these two edges. The unloaded ball bearings will tend to move nominally in the direction of translational motion in order to recirculate, and are packed densely enough that bearings leaving the bearing surface will push other bearings through the recirculating volume onto the opposite side of the surface so that there are always bearings on the bearing surface. However, the bearings are free to move around and will do so. In “dual-roller” or “cylindrical” recirculating bearings, the ball bearings are only recirculating through the volume in response to translational motion in one axis. Motion in the other axis either causes the ball bearings to roll in place (dual-roller) or to roll around the inside of cylinder (cylindrical). In a “pedestal” embodiment, the ball bearings recirculating through volume in response to translation motion in either or both axes.
Referring now to
The disk's lower surface 58, pedestal 50, base 44 and walls 46 of the cup form a recirculating volume 60. The recirculating volume encompasses the perimeter of the disk 52 such that motion of the supported member in any direction causes ball bearings 56 to roll off the top of the disk (i.e. the bearing surface) into the recirculating volume 60 and to recirculate in a nominal direction to follow the direction of motion of the supported member. The diameter of pedestal 50 is sufficiently narrow relative to the disk diameter so that the recirculating volume allows at least two ball bearings to move side-by-side in nominally the same direction for any direction of translational motion.
Referring now to
Referring now to
Ball bearings 94 roll freely along the channel 86 in response to translational motion of a supported member 96 along the channel (e.g. along the x-axis). The ball bearings 94 roll in place causing counter rotation of the rollers 82, 84 in response to translational motion of the supported member along the y-axis across the rollers. The freedom of the ball bearings 94 to roll in any direction along the bearing surface is preserved by decomposing arbitrary motion into motion along both the x and y-axes. Pins 97 may be placed between end plates 90 (below the level of the highest point of the ball bearings) to hold the bearings in place when the bearing is not in contact with the supported member.
A recirculating volume 98 connects opposing ends of the channel 86 to form the closed track. The ball bearings 94 roll freely along the channel and recirculate around the closed track in response to translational motion of the supported member along the channel. Recirculating volume 98 includes a lower track section that is defined between parallel rollers 82, 84 and base 92. The ball bearings are confined below by the base 92 and above and to both sides by rollers 82, 84 while given room roll parallel to the channel. The rollers may be tapered at both ends to create openings 99 at both ends of the channel that allow ball bearings 94 to pass back-and-forth. Two semi-cylindrical end sections 100 connect the openings at both ends of the channel 86 to the lower track section to form the closed track.
Referring now to
Referring now to
While several illustrative embodiments of the invention have been shown and described, numerous variations and alternate embodiments will occur to those skilled in the art. Such variations and alternate embodiments are contemplated, and can be made without departing from the spirit and scope of the invention as defined in the appended claims.