SLIDE UNIT FOR RECTILINEAR MOTION

Abstract: A slide unit for rectilinear motion which can be used under heavy load and with high accuracy, or in the case of light load, an overstroke value can be increased. The slide unit (50) comprises: an inner rail (60) being long and having high rigidity; a pair of outer rails (70) reciprocatingly movably secured to the inner rail in the axial direction thereof; and endless track type linear motion guides (30) slidably mounted to the inner rail and fixed to the outer rails. Main bodies of bearings of the linear motion guides have high rigidity, and accordingly, heavy preload is applied to balls (80) loaded in endless tracks.

Description: Technical Field This invention relates to a slide unit for a linear motion to be used for a slide portion such as a drawer, and more particularly, to a linear motion slide unit with high performance for a heavy load. Background Technology In office tables, peripheral devices for computers, copying machines, measuring instruments, telecommunication equipments, medical instruments, various office equipments, and the like, slide portions are utilized by over-stroking them over entire lengths of rails. A slide unit for linear motion is utilized as a mechanical element for smoothly and precisely performing such sliding operation of the slide portion. Fig. 4 represents a typical one example of a slide unit 50 for the linear motion of a conventional structure. The linear motion slide unit 50 is generally composed of a pair of inner rails 60, 60 secured back to back to each other, a pair of outer rails 70, 70 attached to the inner rails 60, 60 respectively to be axially reciprocal, a number of halls 80 interposed between corresponding inner and outer rails 60 and 70 in rolling contact to the rails, and a retainer 90 for holding the balls 80 in a predetermined positional relationship. The inner and outer rails 60 and 70 are formed of steel plates subjected to a precise roll-forming process, and these rails 60 and 70 are formed with ball rolling grooves 61, 61 and 71, 71 on upper and lower surfaces thereof so as to oppose to each other. The retainer 90 is formed with a number of holes 91 corresponding in numbers to the balls 80 and, hence, since the balls 80 are arranged with equal spaces with each other always, respectively, the balls 80 are free from the mutual friction, thus obtaining a smooth sliding mechanism. Then, a case where such linear motion slide unit 50 is applied to a slide portion of a drawer of, for example, an office table will be described hereunder. One of the paired outer rails 70 is fastened to a body 110 of the office table by means of bolt or the like and the other one of the rails 70 is fastened to a side surface of the drawer 100 of the office table by means of bolt or the like. A possible extending length of the drawer 100 is determined to be equal to an over-stroke amount of the other one of the outer rails 70 with respect to one of the outer rails 70. As shown in Fig. 5(a), it is assumed that the linear motion slide unit 50 be composed of a portion X, in which a number of halls 80 are disposed and both side slidable portions X 2 . As shown in Fig. 5(b), when the drawer is fully drawn out, the front end of the other one of the outer rails 70 can be drawn out from the front end of one of the outer rails 70 by an amount four times of the length of the portion X 2 . Accordingly, the over-stroke amount of the linear motion slide unit 50 is made long as the length of the portion X 2 is possibly extended, and in other words, as the length of the portion X 1 is possibly made short. In the slide unit 50 for the linear motion, since the balls 80 are held always with equal space between adjacent ones by the retainer 90 formed by a precise pressing operation, the balls are free from the mutual friction and can be rolled smoothly. Furthermore there is known from US-A-4 348 063 a telescopic linear motion slide unit comprising an elongated inner rail; a pair of outer rails; and linear bearing bodies secured to the outer rails, supported slidable with respect to the inner rail and having endless tracks in which rolling elements are circulated. However, in recent years, there has been required to utilize such kind of linear motion slide unit for a sliding portion on which a heavy load is applied. The described linear motion slide unit 50 is not suitable for the heavy load, and therefore, development of a linear motion slide unit capable of withstanding the heavy load has been required. In the case of requiring an increased over-stroke amount, as described above, the length of the portion X 1 will be shorten. However, in the conventional linear motion slide unit, less number of balls 80 are utilized or less amount of a preload is applied in the present technology in this art, so that there is a limit for making short the length of the portion X 1 . Disclosure of The Invention This invention aims to solve the problems of the prior art described above and to provide a slide unit for linear motion capable of withstanding a heavy load with high precision. According to the invention there is provided a linear motion slide unit as defined in claim 1. It is preferred that the bearing body is a block member having a U-shaped cross section having a central recessed portion into which the inner rail is inserted, and rolling member rolling grooves are formed to the bilateral inner side surfaces of the central recessed portion so as to oppose to those formed to the opposing surfaces of the inner rail. In addition, it is preferred that the inner rail and the bearing body are formed of a material having high rigidity. Furthermore, it is preferred that each of the liniear motion guides is provided with a preload adjustment mechanism for adjusting the preload to be applied to the rolling members. Still furthermore, each of the preload adjusting mechanisms provided for the linear motion guide is characterized by comprising a recessed portion for adjustment formed to the central portion of a surface to which the outer rail of the bearing body is fixed and an adjustment bolt screwed in a screw hole bored to the bottom surface of the preload adjustment recessed portion through a through hole formed to the outer rail. and in that the adjustment recessed portion is pulled towards the outer rails by fastening the adjustment bolt, a moment is caused to the bearing body by this pulling force in a direction narrowing a gap between bilateral inner side surfaces of the central recessed portion to thereby apply the preload to the rolling members, and an amount of the preload of the rolling members is made adjustable in accordance with the fastening force of the adjustment bolt. Since the endless track is formed, it is possible to increase in number the rolling members withstanding the load, thus withstanding the heavy load. Furthermore, the rigidity of the linear motion guide can be improved by applying the preload to the rolling members mounted in the endless track, and accordingly, the rigidity of the slide unit for the linear motion can be improved. Since the linear motion guide having such endless track is utilized, the load withstanding ability to the heavy load can be increased, and in the case of the over-stroke under the heavy load, the slide unit can be utilized without causing a gap between the respective members, and that is, in the case of the heavy load, precise and smooth sliding motion can be achieved. Furthermore, in the case of the light load, the effective length of the linear motion guide can be shortened, and accordingly, the amount of the over-stroke can be made large. Particularly, by applying the preload to the rolling members, the load withstanding ability against the heavy load can be improved, so that a more large preload can be applied by constituting the inner rail and the bearing body by a member having high rigidity. Brief Description of The Drawings: Figs. 1 and 2 represent a linear motion slide unit according to one embodiment of this invention, in which righthand half of the linear motion slide unit of Fig. 1 is a view taken along the line A-A of Fig. 2 and a lefthand half thereof is a view taken along the line B-B in Fig. 2, and Fig. 2 is a front view, partially eliminated, of the linear motion slide unit. Fig. 3 is an illustration for the explanatory of the preload adjustment. Fig. 4 is a perspective view of a conventional linear motion slide unit, partially omitted. Fig. 5 is a view for the explanatory of an over-stroke amount of the linear motion slide unit. Best Mode for Emboding The Invention The details of the linear motion slide unit according to this invention will be described hereunder with reference to the accompanying drawings. With reference to Figs. 1 and 2, one embodiment of the linear motion slide unit of this invention is shown. As shown in these figures, a linear motion slide unit 1 of this invention generally comprises an elongaged inner rail 10 having high rigidity, a pair of outer rails 20 attached to be reciprocally movable in an axial direction of the inner rail 10, and linear motion guides 30 secured fixedly to the outer rails 20 and slidably to the inner rail 10. The inner rail 10 is manufactured by cold-drawing a steel material. The inner rail 10 is formed with two rows of ball rolling grooves 11 on its upper and lower surfaces. The ball rolling grooves 11 are subjected to hardening treatment to apply sufficient hardness. Each of the outer rails 20 has substantially a U-shaped cross section and has a longitudinal length slightly larger than that of the inner rail 10. Each of the outer rails 20 is formed with a plurality of holes 21 for attachment and the outer rail 20 is secured to an office table body or a side surface of a drawer, for example, by means of bolts. The central portion of the outer rail 20 is formed with a through hole 22 provided with a back facing through which an adjustment bolt 40 passes for adjusting the preload amount to the balls, as described hereinlater. Linear motion guides 30 disposed between the inner rail 10 and the respective outer rails 20 are of endless track type structure having high rigidity. In the illustrated embodiment, two linear motion guides 30 are mounted with respect to one outer rail 20 as shown in Fig. 2. The linear motion guide 30 is itself known in this art field (e.g. US-A-4 527 842) and comprises a bearing body 31 made of iron steel, a pair of side covers 32, 32 mounted in abutment to both end surfaces of the bearing body 31 and a number of balls 33 as rolling members. The bearing body 31 is manufactured by cold-drawing a steel material. A recessed portion 31a for receiving the inner rail 10 is formed to a central inside portion of the bearing body 31. Ball rolling grooves 31c opposing to the ball rolling grooves 11 of the inner rail 10 are formed to an inclining surface 31b adjacent to the recessed portion 31a. These ball rolling grooves 31c are also subjected to the hardening treatment to thereby apply sufficient hardness thereto. Furthermore, return holes 31d for the non-loaded balls are formed to the bearing body 31 so as to penetrate it in its axial direction. In the illustrated preferred embodiment, a central outside portion of the bearing body 31 is formed as a shallow recessed portion 31e for adjustment and a female screw hole 31f, which is screw engaged with a male screw of the adjustment bolt 40, is bored at the central portion of the recessed portion 31e. Each of the preload adjustment mechanisms is composed of this recessed portion 31e for adjustment and the adjustment bolt 40. The side covers 32 may be cheaply formed of a dicast alloy or synthetic resin because large load is not applied to these side covers 32. The side covers 32 connect the corresponding ball rolling grooves 31c and the non-loaded ball return holes 31d, thus being provided with ball returning grooves 32a as endless tracks, respectively. A number of balls 33 mounted in the respective endless tracks can apply a large preload for the reason that the inner rail 10 and the bearing body 31 transferring the load are made themselves of a material having high rigidity and the ball rolling grooves 11 and 31c holding the loaded balls are hardened. Accordingly, in the over-stroke use under the heavy load, any gap is not substantially caused between the respective members. In the light load use, the effective length of the linear motion guide 30, corresponding to the portion X 1 in Fig. 5, can be shortened, thus making large the over - stroke amount, corresponding to the four portions X 2 in Fig. 5. The adjustment bolts 40 are screw engaged with the female screw holes 31f of the bearing body 31 through the through holes 22 of the outer rails 20. As described before, since the shallow recessed portions 31e are formed between the outer rails 20 and the bearing body 31 to provide spaces therebetween, the inclining surfaces 31b, i.e. the ball rolling grooves 31c, are minutely moved by fastening the adjustment bolts 40 so as to approach the inner rail 10, thus adjusting the preload amount to the balls 33. Fig. 3 is an illustration showing this preload adjusting condition. That is, when the recessed portions 31e of the bearing body 31 for adjustment are pulled by the fastening of the adjustment bolts 40 towards the outer rails 20 with fastening forces P, the pulling forces P and resisting forces N acting on the fixed surfaces constitute couple of forces, which causes, to the bearing body 31, moments M for narrowing the bilateral inner side surfaces of the central recessed portions 31a. According to the moments M, the preload is applied to the balls 33 and the amount of the preload to be applied to the balls can be adjusted in accordance with the fastening amount of the adjsutment bolts 40. A method of using the linear motion slide unit of this invention is identical to that of the conventional technology, so that the details thereof are omitted herein. Posibility of Industrial Usage As described hereinabove, in the linear motion slide unit according to this invention, it is usable for the sliding portions of office tables, computer peripheral devices, copying machines, measuring instruments, telecommunication equipments, medical instruments, various kinds of office equipments, and the like, and particularly, it is preferable for the use in which a heavy load can be supported by drawing out the sliding portion so as to extend over the entire length of the rail, that is, in the over-stroke condition.

Claims: A linear motion slide unit (1) comprising an elongate inner rail (10), said inner rail (10) having a pair of first rolling grooves (11) extending along the length of the inner rail (10) on a first half of the cross-section of the inner rail (10) and having a pair of second rolling grooves (11) extending along the length of the inner rail (10) on a second half of the cross-section of the inner rail (10); a pair of first and second bearing bodies (31) which are arranged on opposite sides of the inner rail (10) to be reciprocally movable along the inner rail (10), said first bearing body (31) having a pair of rolling grooves (31c) opposing to the first rolling grooves (11) of the inner rail (10) and being reciprocally movable in an axial direction of the inner rail (10) along the first half thereof, said second bearing body (31) having a pair of rolling grooves (31c) opposing to the second side of the inner rail (10) and being reciprocally movable in an axial direction of the inner rail (10) along the second half thereof, said first bearing body (31) having a pair of endless tracks (31c,31d,32a) in which first side rolling members (33) are endlessly circulated and the second bearing body (31) having a pair of endless tracks (31c,31d,32a) in which second side rolling members (33) are endlessly circulated; and a pair of first and second outer rails (20), said first outer rail (20) being fixedly secured to the first bearing body (31) opposing to the inner rail (10) and applying a preload to the first side rolling members (33) of the first bearing body (31) and the second outer rail (20) being fixedly secured to the second bearing body (31) opposing to the inner rail (10) and applying a preload to the second rolling members (33) of the second bearing body (31); the bearing bodies (31) to which the outer rails (20) are secured being movable relative to each other. A linear motion slide unit according to claim 1, further comprising a pair of first and second preload adjustment mechanisms (40,31e), said first preload adjustment mechanism being arranged in said first bearing body (31) and the first outer rail (20) for adjusting an amount of preload to be applied to the first side rolling members (33) and said second preload adjustment mechanism being arranged in said second bearing body (31) and the second outer rail (20) for adjusting an amount of preload to be applied to the second side rolling members (33). A linear motion slide unit according to claim 2, wherein said bearing bodies (31) are composed of block members having substantially a U-shaped cross section having a central recessed portion (31a) into which the inner rail (10) is inserted and rolling member rolling grooves (31c) are formed to the bilateral inner side surfaces (31b) of the central recessed portions (31a) so as to oppose to those formed to the opposing surfaces of the inner rail (10). A linear motion slide unit according to claim 3, wherein said inner rail (10) and said bearing bodies (31) are formed of a material having a high rigidity. A linear motion slide unit according to claim 2, wherein each of said preload adjustment mechanisms provided for said linear motion guides is characterized by comprising a recessed portion (31e) for adjustment formed to the central portion of a surface of the bearing body to which the outer rail is fixed and an adjustment bolt (40) screwed in a screw hole (31f) bored to a bottom surface of the preload adjustment recessed portion (31e) through a through hole (22) formed to the outer rail (20), and in that the adjustment recessed portion is pulled towards the outer rail (20) by fastening the adjustment bolt (40), a moment is caused to the bearing body (31) by this pulling force in a direction narrowing a gap between bilateral inner side surfaces (31b) of the central recessed portion (31a) to thereby apply the preload to the rolling members (33), and an amount of the preload to the rolling members (33) is made adjustable in accordance with the fastening force of the adjustment bolt (40).

Inventors: ASADA MINORU, ASADA, MINORU
Applicants: THK CO LTD, THK CO. LTD.
Application year: 1992
Main classification: F16C29
IPC codes: F16C29, B23Q1, A47B88