1. Field of the Invention
The present invention relates to a cross roller guide such as a linear-motion guiding apparatus, a swivel cross bearing, etc., using cross rollers arranged at right angles with respect to each other, and particularly to a cross roller connector or assembly having cross rollers serially connected with each other.
2. Description of the Related Art
A conventional cross roller guiding apparatus of this type is constructed such that it has a train of first rollers and a train of second rollers disposed in a pair of roller traveling grooves or track grooves of a V-shaped cross section respectively formed on mutually opposing surfaces of two relatively moving members with the axes of rotation of the first and second rollers being alternatively arranged at an angle of 90 degrees different from each other so as to guide relative movements of the two members through the first and second rollers. Such a roller arrangement is known as a so-called cross roller structure, which can receive, with the single row of rollers, loads acting thereon in every direction, e.g., in downward, upward, rightward and leftward directions, so that it is applicable to a variety of apparatuses which are subject to varying loads from all directions including fore and aft directions, right and left directions, etc.
In the case of a cross roller bearing, however, the axes of rotation of the first and second rollers are alternatively arranged or inclined at an angle of 90 degrees relative to each other, so it is difficult to always maintain the axes of rotation in their correct or desired postures with respect to the direction in which the rollers travel. When there takes place a skew in a roller, a half portion of the skewed roller is subject to a so-called edge load (i.e., an edge of the skewed roller is locally loaded), thereby damaging the roller and its associated roller rolling surfaces of a roller travelling path and hence degrading the durability thereof.
Moreover, the occurrence of such damage results in generation of vibrations and/or changes in the rolling resistance during rolling or travelling movement of the rollers on the roller rolling surfaces, and hence precludes smooth travel of the rollers from this point of view.
In order to prevent such a roller skew, there has conventionally been used a roller connector or assembly having a retainer for holding the first and second rollers in their predetermined postures, but such a conventional roller assembly is not at all satisfactory.
The present invention is intended to solve the problems of the prior art described above, and has for its object to provide a cross roller assembly which is suitable for use with rollers of a cross roller arrangement and which is capable of preventing rollers from being skewed as much as possible so as to guide the rollers in a stable manner.
In order to achieve the above object, according to one aspect of the present invention, there is provided a roller assembly comprising: a train of first rollers and a train of second rollers; and a retainer for holding the first and second rollers with their axes of rotation alternatively arranged at right angles with respect to each other, the retainer comprising a plurality of pairs of end holders for supporting opposite ends of the first and second rollers, each of the end holders having an outer surface formed of a flat guide surface. Thus, the first and second rollers are regulated or restricted in their postures so that they can roll and travel in a smooth manner.
The first and second rollers roll or slide while being regulated in their postures, whereas the retainer moves while being guided by the rollers. Thus, the first and second rollers and the retainer function to regulate or restrict their postures with each other to thereby facilitate mutual smooth movements. As a result, swaying or shaking of the rollers and the retainer, which are conventionally deemed as causes for roller skewing, can be effectively regulated or restricted with each other so as to permit smooth operation of the roller assembly.
Preferably, each of the retainers further comprises: a side holder for connecting roller-aligning direction opposite ends of each end holder with each other to thereby hold a side surface of each roller; and a connector member for connecting roller- non-holding side surfaces of each side holder with each other.
Preferably, engaging means may be provided between the opposite faces of each of the first and second rollers and the end holders for supporting each roller through the end holders while permitting rotation of the rollers relative to the end holders.
Preferably, a recess is formed in an inner surface of each end holder for loosely receiving or engaging an end of an associated roller so as to permit rotation of each roller relative to the associated end holder.
The above arrangements serve to increase the effect of preventing skewing of the rollers. In particular, when the rollers are passing semicircular turning passages of a circulation path, the roller can keep the same postures and positions thereof relative to the retainer as when they are passing the other portions of the circulation path, so that roller skewing can be positively precluded to suppress an increase in the contact bearing pressure against part of the roller retainer, thus making it possible for the cross roller assembly to circulate smoothly.
Moreover, the engaging means or loose fitting engagement between the rollers and the end holders also has a function of preventing the rollers from falling off from the retainer. Accordingly, maintenance operation for the cross roller assembly becomes easy and facilitated.
In addition, in the case of the cross roller assembly of the invention, a lubricant circulates while being retained in portions (so-called grease pockets) formed between the side holders of the retainer and the rollers adjoining each other via the side holders. This serves not only to prevent mutual friction between the rollers but also to enhance a retention capacity for the lubricant, thereby making it possible to greatly increase the durability of the cross roller assembly as a whole.
Still further, for a material forming the retainer, synthetic resin such as polytetrafluoroethylene (PTFE), etc., can be used as a concrete example.
With the use of such synthetic resin, the cross roller assembly can be fabricated by insert molding, i.e., injecting a resin material into cavities in a molding frame for the retainer with the rollers being pre-inserted in the molding frame.
Here, it is to be noted that a lubricant such as grease can be presented between respective portions of the first and second rollers and the respective portions of the retainer which are in mutual contact with each other. Due to the presence of such a lubricant as well as the use of a flexible and slippery material for the retainer, it is possible to prevent an increase in the mutual frictional resistance between the first and second rollers and the retainer, thus ensuring smooth movement of the cross roller assembly as a whole.
According to another aspect of the present invention, there is provided a cross roller guiding apparatus comprising: an elongated track shaft having an upper surface and opposite side surfaces; and a moving object mounted on the track shaft for movement therealong, the moving object having a horizontal portion disposed in opposition to the upper surface of the track shaft, a pair of hanging portions provided on the opposite sides of the horizontal portion in opposition to the opposite side surfaces of the track shaft, each of the hanging portions having a circulation path formed therein. Each of the circulation paths comprises a rolling track of V-shaped cross section with an included angle of 90 degrees formed on each of the opposite sides of the track shaft and on an inner surface of each of the hanging portions opposing to the track shaft one side, a return passage of a substantially rectangular cross section provided in each of the hanging portions in parallel with the rolling track, and a pair of turning passages connecting between the opposite ends of the rolling track and the return passage. A cross roller assembly is incorporated in the circulation path of each hanging portion. The cross roller assembly includes a train of first rollers and a train of second rollers, and a retainer for holding the first and second rollers in respective alignment with their axes of rotation alternatively arranged at right angles with respect to each other, the retainer comprising a pair of end holders for supporting the opposite ends of each roller, each of the end holders having an outer surface which is a flat guide surface.
In particular, with the cross roller guiding apparatus as defined above, there is a tendency that when the cross roller assembly passes the turning passages of each circulation path, the rollers are drawn to the inner peripheral sides of the turning passages. Despite such a tendency, the interval or distance between the opposed end holders in each pair is constantly held at a predetermined value and hence not varied during the movement of the roller assembly through the turning passages, whereby the postures of the rollers are maintained constant by virtue of the end holders. As a consequence, the axes of rotation of the rollers will not be caused to sway or deflect from the direction in which the rollers are travelling, thus preventing the rollers from being skewed.
The cross roller assembly as described above is applicable to a roller guide bearing having a pair of linear track shafts disposed in parallel with each other, or to a swivel or pivot bearing having a pair of track rings disposed in opposition to each other.
The roller guide bearing may be constructed such that the cross roller assembly as described above is serially incorporated in a pair of V-shaped track grooves respectively formed on the opposed surfaces of the respective track shafts at right angles with respect to each other so as to support the respective track shafts for movement relative to each other.
The swivel bearing is constructed such that the cross roller assembly as described above is incorporated in a pair of V-shaped track grooves respectively formed on the opposed surfaces of the respective track rings for supporting the respective track rings for rotation thereof relative to each other.
The above and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description of presently preferred embodiments of the invention taken in conjunction with the accompanying drawings.