1. Field of the Invention
This invention relates to a compound rolling guide unit incorporated in a semiconductor manufacturing apparatus, a transfer apparatus, an industrial robot and an assembly robot, and having a slider saddled on and slidable relatively to a track rail.
2. Description of the Prior Art
In recent years, the mechatronics techniques have been developed remarkably, and the improvement of the accuracy and operational speed and a decrease in the dimensions of a rolling guide unit have been demanded. The use of a rolling guide unit is being widened at present in accordance with the development of the techniques. For example, the expansion of the use of a rolling guide unit-incorporated assembly robot has been demanded, and assembly robots ranging in size from a large-scale to a small-scale have been manufactured. The rolling guide units incorporated in these assembly robots have been demanded to have an adaptability to the improvement of the accuracy and operational speed and a decrease in the dimensions of the assembly robots.
There is a known linear motion rolling guide unit shown in FIGS. 16 and 17. In this linear motion rolling guide unit, a slider 1 is set in a saddled state on a track rail 2 and moved slidingly via rolling elements 7 rolling circulatingly along raceway grooves 4 in the track rail 2. The track rail 2 is provided with the raceway grooves 4 in both of longitudinally extending side surfaces 3 thereof. The track rail 2 is also provided with a plurality of mutually spaced fixing holes 13 opened in its longitudinally extending upper surface 14. The track rail 2 is fixed on a mount base 20, such as a bed, a machine base and a machining base. Bolts are inserted into the fixing holes 13 made in the track rail 2, and then screwed into threaded holes made in the mount base 20, whereby the track rail 2 is fixed on the mount base 20. The slider 1 has a casing 5 capable of being moved relatively to the track rail 2, and end caps 6 attached to both ends of the casing 5. The casing 5 is provided in its upper portion with fixing holes 19 for use in fixing thereto another machine, a machine part, a chuck and a clamp. The casing 5 and end caps 6 are provided in their lower surfaces with recesses 10 so that the casing 5 and end caps 6 are moved astride the track rail 2, and the portions of the recesses 10 which are opposed to the raceway grooves 4 in the track rail 2 are provided with raceway grooves 9. The rolling elements 7 comprising balls or rollers are inserted in raceways formed by the opposed raceway grooves 4, 9 so that the rolling elements 7 are rolled therein. In order to prevent the rolling elements 7 from falling from the casing 5, retainer bands 18 are fixed to the casing 5 so as to enclose the rolling elements 7. In order to attain the sealing of clearances between the track rail 2 and slider 1, lower seals 8 are provided on a lower surface of the slider 1.
The end caps 6 are provided at both side portions thereof with claws 22, by which the rolling elements 7 are scooped from the raceway grooves 4 constituting loaded raceways with respect to the track rail 2, and direction changing passages 11 used to change the rolling direction of the rolling elements 7 for circulating the same. Side seals 17 for attaining the sealing of the clearances between the track rail 2 and both of longitudinal end portions of the slider 1 are fixed to the end caps 6. The end caps 6 are fixed to both end surfaces of the casing 5 by screws 25 driven through a plurality of fixing holes 24. The rolling elements 7 in a load region which roll in the raceway grooves 4 in the track rail 2 are introduced into the direction changing passages 11 formed in the end caps 6, and they are then moved to return passages 12 formed in upper portions of the casing 5 so as to extend in parallel with the raceway grooves 9, the rolling elements 7 being thus rolled in endless circulating passages. Owing to the rolling of the loaded rolling elements 7 rolling in the raceways formed between the raceway grooves 9, 4 provided in the slider 1 and track rail 2 respectively, the track rail 2 and slider 1 can be moved smoothly with respect to each other.
There is a conventional rolling unit provided with raceway grooves in the upper and lower portions of side surfaces of a track rail, and disclosed in, for example, Japanese Patent Laid-Open No. 172138/1993. The linear slide shaft unit disclosed in this publication provides a linear slide shaft capable of being moved forward and backward accurately with respect to a fixed portion such as a housing, and capable of being thus guided without causing deformation to occur therein even when the slide shaft is formed tubularly. The slide shaft is formed to a square cross sectional shape and provided with ball rolling grooves in the upper and lower portions of a pair of opposite side surfaces thereof. The upper slider and lower slider saddle in the upper and lower surfaces of the slide shaft and move back and forth.
Japanese Utility Model Laid-Open No. 43520/1990 or Japanese Utility Model Laid-Open No. 40124/1990 discloses a double linear guide unit. In the double linear guide unit disclosed in this Japanese Utility Model Laid-Open No. 43520/1990, a guide rail is provided with axially extending rolling grooves doubly in both side surfaces thereof so that a plurality of sliders can be fitted loosely in the guide rail and move past the other slider.
It has been demanded so as to keep pace with the development of the techniques in recent years that a linear motion guide unit be provided with multiple functions and has a compact structure. In order to form a conventional linear motion rolling guide unit to a four-directional structure, it is necessary to set linear motion rolling guide units on four sides of a core member, and carry out such guide unit assembling operations with a high accuracy in each of the four guide unit setting directions, so that the resultant assembly lacks compactness. A linear motion rolling guide unit formed by fitting sliders in the upper and lower portions of a track rail as mentioned previously is also compact as compared with a linear motion rolling guide unit having a single slider. However, in the guide unit having two sliders, the sliders are provided on, for example, the upper and lower sides alone of a track rail by forming raceway grooves in only two surfaces out of four surfaces of the track rail. Moreover, the sliders are provided on only the upper and lower sides of a track rail, and the directivity of the guide unit is limited. Therefore, the range of application of this guide unit to an industrial robot and an assembly robot is limited, so that this guide unit is difficult to be used.