Linear bearing

Abstract: The straight sliding bearing and a straight sliding table according to the present invention are formed so as to m the frictional resistance occurring when a slide block (1) is moved slidingly on a track base (2), by pressing the side surfaces of rollers (4a) by a braking plate (5) which is adapted to be moved in accordance with the pressure of a fluid, and suppressing the rolling of the rollers (4), (4a) by utilising the frictional force generated by this roller pressing operation. Since a predetermined level of rigidity can be obtained in the axial direction as well of the track base by arbitrarily increasing and decreasing the sliding resistance, the sliding bearing and sliding table enable a high precision machined product to be obtained when these sliding devices are used in a mechanical apparatus, such as a machine tool.

Description: The present invention relates to a linear bearing for linearly guiding a moving member in a machine tool such as a NC machine or an industrial robot. When a workpiece is to be machined by a machine tool, for example, loads accompanying the machining in various directions are generally exerted between the machine tool and the workpiece, although they depend upon the kind of machining, such as cutting or polishing, the material of the workpiece or the machining conditions. The loads act as reaction forces upon the machine tool and the workpiece. If the machine tool and the workpiece are completely fixed at the instant of machining against the loads, the machining can be ideally accomplished with a drastically improved precision. In the case of machining of the workpiece using such a machine tool, one of the machine tool or the workpiece is fixed whereas the other is moved by means of a mechanism such as a linear bearing. A linear bearing known to be used for this purpose is constructed to include: a track base having axial races; a bed having endless tracks which are formed of load regions having load races facing the races of the track base and no-load regions providing the communicating connections between the two ends of the load regions; and rollers circulating in the endless tracks for bearing the loads between the races of the track base and the load races of the bed. Thus, the linear bearing can bear the loads in the four directions, i.e., radial, inversely radial and rightward and leftward directions. In the linear bearing of this kind, moreover, the rigidities in the four directions are enhanced by applying a pre-pressure to the rollers to bear the four-directional loads to be generated between the machine tool and the workpiece during the machining, so that the accompanying chatter marks and vibrations may be suppressed as much as possible to improve the machining precision. In connection with the axial direction of the track base, on the other hand, frictions in the movements are suppressed with a view to lightening the loads upon the feeding drive system such as a feeder of screw and nut type or a motor mechanism. The rigidity necessary for the machining in the axial direction of the track base relies exclusively upon that of the feeding drive system. As an example of the prior art one can cite US-A-4715729 which discloses the preamble of claim 1. Incidentally, the rigidity of the feeding drive system is determined, if the system is a feeder of screw and nut type, by the rigidity of the feed screw or nut itself, the rigidity of the support of the feed screw or nut, and the rigidity of the motor for applying a rotating force to the feed screw. In order to increase the rigidity of the feeding drive system, it is necessary to enlarge the size of the feed screw or nut or to raise the output of the motor. Thus, the increase in rigidity of the feeding drive system is intrinsically limited by the problems which are caused by increasing the size of the apparatus or by raising the cost for the feeding drive system. As various products are required to be more precise in the industry of recent years, a machine apparatus such as the machine tool for machining the products is required to have its machining precision improved. Thus, a linear bearing taking a leading role for the machining precision of the various machine apparatus is needed to improve the machining precision. It is, therefore, an object of the present invention to provide a linear bearing which can have not only the rigidities of four directions, i.e., the radial, inversely radial, rightward and leftward directions but also a predetermined rigidity in the axial direction of the track base. Another object of the present invention is to provide a linear bearing which can apply the rigidity in the axial direction of the track base, if necessary, and adjust the level of the rigidity. Still another object of the present invention is to provide a linear guide table which can mount a machine apparatus such as a machine tool for machining of high precision. The present invention provides a linear bearing as defined by claim 1 and a linear guide table as defined by claim 7. According to the invention the pressure means presses the end faces of the load rollers in the axial direction toward side wall portions formed on the bed or beds. As a result, the rollers have their end faces pressed between the pressure means and the bed or beds so that their rolling motions are suppressed by the frictional forces to increase the resistances of the bed or beds rolling on the track base or bases. Preferred embodiments of the subject-matter of claim 1 are defined by the claims 2 to 6. Some embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is a front elevation showing a first embodiment of a linear bearing according to the present invention; Figs. 2 and 3 are a side elevation and a top plan view of the linear bearing of the first embodiment; Fig. 4 is a cut-away perspective view showing the linear bearing according to the first embodiment; Fig. 5 is a section taken along line I-I of Fig. 3; Fig. 6 is a section taken along line II-II of Fig. 3; Fig. 7 is a top plan view showing a braking plate exemplifying the pressure means of the linear bearing according to the first embodiment; Fig. 8 is a section taken along line III-III of Fig. 7; Fig. 9 is a section taken along line IV-IV of Fig. 7; Fig. 10 is an exploded perspective view showing the assembly of the braking plate of the linear bearing according to the first embodiment; Fig. 11 is a section showing a portion in the state, in which no oil pressure is applied to the braking plate while the linear bearing according to the first embodiment is used; Fig. 12 is a section showing a portion in the state, in which an oil pressure is applied to the braking plate while the linear bearing according to the first embodiment is used; Fig. 13 is a sectional front elevation showing a second embodiment of the linear bearing of the present invention; Fig. 14 is a sectional front elevation showing a third embodiment of the linear bearing of the present invention; Fig. 15 is a sectional front elevation showing a fourth embodiment of the linear bearing of the present invention; and Fig. 16 is a sectional front elevation showing an embodiment of the linear guide table according to the present invention. The linear bearing according to a first embodiment is constructed, as shown in Figs. 4 and 5, to include: a bed 1 formed generally into a C-shaped section having a horizontal portion 1a and righthand and lefthand skirts 1b depending from the two ends of the horizontal portion 1a to leave a groove in its lower side; a pair of roller guides 6 mounted on the lower ends of the righthand and lefthand skirts 1b of the bed 1; a track base 2 fixed to a machine apparatus by fixing means such as fixing bolts; a number of rollers 4 circulating in an endless roller race formed in the bed 1 for bearing a load between the bed 1 and the track base 2; and a braking plate 5 positioned between the lower side of the horizontal portion 1a and the upper surface of the track base 2 and made suitably movable up and down in accordance with the pressure of a fluid introduced from the bed 1 for pushing the sides of load rollers 4a rolling on a load race formed on the bed 1. The bed 1 constitutes load regions of an upper endless roller track and a lower endless roller track in the moving direction of the bed, respectively, on the two ends of the lower side of the horizontal portion 1a and the lower ends of the surfaces of the righthand and lefthand skirts 1b on inner sides of the groove. The load regions are formed with load races on which the rollers 4 are caused to roll. Above the righthand and lefthand skirts 1b, moreover, there are formed relief roller tracks 11 which correspond to the load regions of the upper endless roller tracks. On the other hand, the righthand and lefthand skirts 1b are formed at their lower ends with no-load regions which correspond to the load regions of the lower endless roller tracks. At the lower ends of the load races of the righthand and lefthand upper endless roller tracks, moreover, there are formed side walls 12 for regulating the movements in the moving direction of the bed of the load rollers 4a which are caused to roll on those load races. Incidentally, the aforementioned load regions are inclined at such predetermined angles that their four races are parallel with the upper races and the lower races of the track base 2 when the bearing of the present invention is assembled. The bed 1 is formed at its two widthwise end portions with mounting holes 13 into which mounting bolts are inserted from the lower to upper surfaces. On the other hand, the lower side of the horizontal portion 1a of the sliding bed 1 provides a portion for mounting the braking plate 5 acting as pressure means for pushing the sides of the load rollers 4a and is formed at its center with an oil hole 14 which extends vertically therethrough to admit the oil for applying the pressure to the braking plate 5. The lower side of the horizontal portion 1a is further formed with mounting holes which are to be engaged with screws 9 extending through the braking plate 5. To each of the longitudinal end portions of the bed 1 described above, there is fixed by fixing bolts 31 a cover 3 which is made of a synthetic resin. These covers 3 are formed with grooves for establishing the communicating connections between the load regions formed in the sliding bed 1 and the corresponding relief roller tracks 11 or the no-load regions. On the other hand, the aforementioned roller guides 6 are formed to have a generally L-shaped section by pressing a metallic plate or injection-molding a hard synthetic resin, as shown in Fig. 5, and are secured to the lower ends of the righthand and lefthand skirts 1b of the sliding bed 1 by means of screws. Thus, the load and no-load regions formed at the lower ends of the righthand and lefthand skirts 1b form the endless roller tracks to guide the individual rollers, together with the roller turning portions which are formed in the covers 3. On the other hand, the aforementioned track base 2 is formed into a section having an upper portion resulting from a rectangle having its corners bevelled to form shoulders defining downward slopes and upward slopes. Of these slopes, the lower ones provide lower races 21 which correspond to the lower endless roller tracks formed at the lower ends of the skirts 1b of the bed 1, whereas the upper ones provide upper races 22 which correspond to the upper endless roller tracks formed at the two ends of the lower side of the horizontal portion 1a of the bed 1. Moreover, the track base 2 is formed at its central portion with fixing bolt mounting holes 23 for receiving fixing bolts which are fastened to a stationary portion. The bolt mounting holes 23 are vertically extended in the upper surface of the track base 2 and are bored at a suitable spacing in the longitudinal direction of the track base 2. As shown in Fig. 5 or 6, the aforementioned braking plate 5 is a generally plane plate having a rectangular shape, which is positioned, when assembled, in the gap between the lower side of the horizontal portion 1a of the bed 1 and the upper surface of the track base 2. The braking plate 5 is made of a softer material such as brass than that of the rollers and is given functions to push, if necessary, the sides of the load rollers 4a rolling on the upper races of the track base 2 and to align and retain the load rollers 4a. As better seen from Figs. 7, 8 and 9, the upper surface of the braking plate 5 is recessed to form an oil pocket 51 which is to be filled up with the oil flowing into and out of the oil hole 14 formed in the center of the horizontal portion 1a of the bed 1. The braking plate 5 is formed on its two widthwise end portions with pressure surfaces 52 which are sloped to face downward the sides of the load rollers 4a, when the bearing is assembled, thereby to suitably press the sides of the load rollers 4a rolling on the upper races of the track base 2. Those pressure surfaces 52 are longitudinally formed at their lower ends with retaining surfaces 53 for preventing the load rollers 4a rolling on the upper roller tracks of the track base 2 from coming out so that they may be associated with the side walls 12 formed in the sliding bed 1, to prevent the load rollers 4a from coming out. Moreover, the braking plate 5 is formed at its widthwise center with through holes 54 which are vertically extended from the bottom to the top for receiving screws to be fastened to the lower side of the horizontal portion 1a of the bed 1. Here, the lower side and pressure surfaces 52 of the braking plate 5 are so finished that the gap between the lower side of the braking plate 5 and the upper surface of the track base 2 may be larger, when the bearing is assembled, than that between the pressure surfaces 52 and the sides of the load rollers 4a belonging to the upper endless roller tracks. The braking plate 5 thus constructed is mounted in the bed 1, as better seen from Fig. 10, by fitting an O-ring 7 in the inner periphery of the aforementioned oil pocket 51 for preventing the oil leakage, by inserting screws 9 together with dish-spring washers 8 into the lower sides of the aforementioned through holes 54 and by fastening the screws 9 in the mounting holes formed in the lower side of the horizontal portion 1a of the sliding bed 1. At this time, the fastening forces of the screws 9 are decided: such that the dish-spring washers 8 sandwiched between the heads of the screws 9 and the lower side of the braking plate 5 are freely subjected to elastic deformations by the pressures exerted upon the braking plate 5 whereas the aforementioned O-ring 7 is always retained in close contact with the lower side of the horizontal portion 1a; and such that the braking plate 5 is pushed up to the lower side of the horizontal portion 1a of the bed 1 by the elastic forces of the dish-spring washers 8 when no pressure is applied to the braking plate 5. The linear bearing thus constructed according to the present embodiment is used by fixing the track base 2 to the machine apparatus by means of the fixing bolts, by mounting a table carrying a variety of machine tools on the bed 1 sliding along the track base 2 by means of the mounting bolts, by connecting a hydraulic apparatus (although not shown) to be driven in response to an instruction signal outputted from a control unit (although not shown) to the oil hole 14 of the bed 1, and by applying an arbitrary pressure to the oil which fills up the oil pocket 51 of the braking plate 5 in a necessary place over the track base 2. If, at this time, no oil pressure is applied to the oil pocket 51, the braking plate 5 is raised to the lower side of the horizontal portion 1a of the sliding bed 1 by the elastic forces of the dish-spring washers 8 to keep its pressure surfaces 52 away from contact with the sides of the load rollers 4a rolling on the upper races of the track base 2, so that the load rollers 4a can freely roll on the races of the track base 2 to slide the bed 1 on the track base 2 with a slight resistance (as seen from Fig. 11). If, on the contrary, the oil pressure is applied to the oil pocket 51, it pushes the braking plate 5 downward so that the pressure surfaces 52 of the braking plate 5 push the sides of the load rollers 4a in the axial direction to bring the other sides of the load rollers 4a into contact with the side walls 12 formed on the bed 1. As a result, frictional forces are established between the sides of the load rollers 4a and the pressure surfaces 52 and the side walls 12 to increase the rolling resistances of the load rollers 4a so that high resistances are exerted upon the bed 1 moving on the track base 2 (as seen from Fig. 12). Thus, in the linear bearing of the present embodiment, the resistance of the bed 1 can be increased by applying the pressure to the oil pocket 51 of the braking plate 5, thereby to strengthen the axial rigidity of the track base 2 of the linear bearing. In the linear bearing of the present embodiment, moreover, the oil pressure to be applied to the oil pocket 51 can be suitably adjusted to establish the axial rigidity of the track base 2, if necessary, and to adjust it to an arbitrary level. A linear bearing according to a second embodiment is substantially identical to that of the first embodiment except in that two braking plates 5 are disposed at the inner sides of the recess on the righthand and lefthand skirts 1b of the bed 1 to push the sides of two rows of load rollers 4a rolling on the upper and lower races of the track base 2, as shown in Fig. 13. The bed 1 is formed between the load regions of the upper endless roller track and the lower endless roller track with grooves for housing the braking plates 5 and at its righthand and lefthand skirts 1b with bolt mounting through holes in which are fastened pressure bolts 10 for pressing the braking plates 5. Thus, the braking plates are housed in the grooves, and the pressure bolts 10 fitted in their mounting holes are driven forward internally of the skirts. Then, the fastening forces of the pressure bolts 10 are exerted as the pressures upon the braking plates 5 so that the braking plates 5 push the sides of the load rollers 4a rolling in the load regions. As a result, the resistance of the bed 1 is increased as in the first embodiment. Thus, in the linear bearing of the present embodiment, the axial rigidity of the track base 2 can be strengthened by adjusting the turns of the pressure bolts 10. A linear bearing according to a third embodiment is substantially identical to that of the first embodiment except in that adjust bolts 10 are extended through the bed 1 from the top horizontal surface to engage with the braking plates 5 positioned at the inner sides of the recess on the righthand and lefthand skirts of the bed 1 so that they may be fastened to raise the braking plates 5 to push the sides of the load rollers 4a rolling on the upper races of the track base 2, as shown in Fig. 14. The axial rigidity of the track base 2 can also be strengthened according to the present embodiment. A linear bearing according to a fourth embodiment is a modification of the third embodiment and is substantially identical to that of the third embodiment except in respect of the angle of inclination of the load races of the upper endless roller tracks, and in that the braking plate 5 is arranged at the lower side of the horizontal portion 1a of the bed 1, as shown in Fig. 15, so that the sides of the righthand and lefthand upper load rollers 4a may be pushed by the single adjust bolt 10. Fig. 16 shows an embodiment of the linear guide table according to the present invention. A pair of righthand and lefthand track bases 2 are arranged in parallel at a suitable spacing, and a pair of righthand and lefthand beds 1 having braking plates 5 are slid along the external sides of the track bases 2. A table T is mounted to ride over the paired beds 1 so that it may linearly guide a machine apparatus carried thereon. According to the linear guide table of the present embodiment, like the linear bearings of the foregoing embodiments, the resistance can be increased, while the beds 1 are moving on the track bases 2, to strengthen the rigidity of the linear table in the axial direction of the track bases. As has been described hereinbefore, according to the linear bearing of the present invention, the resistance of the bed moving on the track base can be adjusted to apply or adjust the rigidity in the axial direction of the track base, if necessary. By applying a strong pressure to the load rollers by the pressure means to prevent the load rollers from rolling, moreover, the bed can be continuously fixed in one portion on the track base so that the pressure means can function as the locking mechanism of the linear bearing. According to the linear guide table of the present invention, still moreover, like the aforementioned linear bearing, the rigidity in the moving direction of the track bases can be applied to the table or adjusted so that a workpiece can be machined highly precisely in case the machine apparatus such as a machine tool is placed on the table.

Claims: A linear bearing comprising: a track base (2) fixed to a machine apparatus and having linear roller races (22), a bed (1) formed with endless tracks, which have load regions having load races facing said roller races (22) and no-load regions (11) for effecting the communicating connections between the two ends of said load regions, the bed (1) being made movable along said track base (2) by a multiplicity of rollers (4,4a) circulating in said endless tracks for bearing the load between the load races of said bed (1) and the races (22) of said track base (2), said bed (1) including at each of the load races a side wall portion (12) extending along the load race adjacent to one of the end faces of said rollers (4a) rolling on said load races; characterised by pressure means (5,14,10) for regulating the axial movement of the rollers (4a) rolling on said load races by pressing the end faces of the rollers (4a) located opposite the side wall portions (12) in the axial direction of the rollers (4a) thereby pressing the rollers (4a) with their other end faces against the side wall portions (12). A linear bearing as claimed in claim 1, wherein said bed (1) includes a horizontal portion (1a) and a pair of skirts (1b) extending from two sides of said horizontal portion (1a) to form a recess in its lower side, said skirts (1b) being formed with a pair of righthand and lefthand upper load races and lower load races extending in the moving direction of the bed (1) on the inner sides of said recess, and wherein said pressure means (5,14) is arranged at the lower side of said horizontal portion (1a) for pressing the load rollers (4a) rolling on said righthand and lefthand load races. A linear bearing as claimed in claim 1, wherein said bed (1) includes a horizontal portion (1a) and a pair of skirts (1b) extending from two sides of said horizontal portion (1a) to form a recess in its lower side, said skirts (1b) being formed with a pair of righthand and lefthand upper load races and lower load races extending in the moving direction of the bed (1) on the inner sides of said recess, and wherein said pressure means (5,10) is arranged at the inner side of a said skirts (1b) for pressing at least those of the load rollers (4a) which roll on said upper load races and/or said lower load races. A linear bearing as claimed in claim 1, wherein said bed (1) is formed into a generally rectangular shape and is formed longitudinally along one side with a pair of upper and lower load races, and wherein said pressure means (5,10) is arranged between said upper load races and said lower load races for pressing at least those of the load rollers (4a) which roll on said upper load races and/or said lower load races. A linear bearing as claimed in any of claims 1 to 4, wherein said pressure means (5) includes a pressure surface (52) extending in the moving direction along said track base (2) and facing said end faces of the rollers (4a) located opposite said side wall portions (12) and for pressing against these end faces, said pressure surface (52) being formed with a retaining surface (53) at its end directed to the track base side of said roller end faces for preventing said load rollers (4a) from coming out of said load region when under a non-pressure condition. A linear bearing as claimed in claim 2, wherein said pressure means comprises a movable plate (5) having a pressure surface (52) formed on each transverse side, and an oil pocket (51) formed on its upper surface, said pressure surfaces (52) facing the end faces of said rollers (4a) opposite said side wall portions (12), for establishing frictional forces between these end faces and the pressure surfaces (52) and between said ones of the end faces adjacent said side wall portions (12) and said side wall portions (12). A linear guide table comprising a bearing as claimed in any preceding claim and a table (T) placed on the upper surface of the bed (1) of the bearing.

Inventors: TERAMACHI HIROSHI, TERAMACHI, HIROSHI
Applicants: THK CO LTD, THK CO. LTD.
Application year: 1989
Main classification: F16C29
IPC codes: B23Q1, F16C29