Abstract:
There is provided a linear guide apparatus which, owing to the use of a gap-free braking device in a rolling guide, has a sufficiently high damping capacity.  
     The linear guide apparatus for guiding a linear motion of a movable body along a guide rail on a fixed structure in a machine tool, includes: a rolling guide section including a rolling element for rolling on a rolling element-rolling surface of the guide rail; and a brake section for enhancing the damping capacity of the rolling guide section, the brake section including a pair of brake shoes, having a flexible structure, for sliding on the rolling element-rolling surface of the guide rail.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to a linear guide apparatus for guiding a movable body, such as a table, in a machine tool.  
           [0003]    2. Description of the Related Art  
           [0004]    In machine tools, sliding guides and rolling guides are primarily employed in guide mechanisms for movable bodies, such as columns, spindle heads, tables, etc.  
           [0005]    Sliding guides, in which a sliding member makes a sliding contact with a guide surface, have a high static rigidity and, as compared to rolling guides, are excellent in damping of vibrations that could cause fluttering.  
           [0006]    On the other hand, rolling guides, which utilize a rolling contact between a rolling member and a guide surface, have a low vibration damping capacity. Because of low frictional force, however, rolling guides are superior in high speed and motion accuracy to sliding guides. Thus, sliding guides and rolling guides have advantages in terms of each other&#39;s disadvantages, and have disadvantages in terms of each other&#39;s advantages.  
           [0007]    Linear guide apparatuses have recently been developed which, with a view to compensating for the drawback of rolling guide, employ a braking mechanism, etc. in a rolling guide to generate a frictional force, thereby enhancing the damping capacity of the rolling guide. Such conventional linear guide apparatuses include an apparatus in which an elastic bag is expanded by air pressure so as to press a damping plate against a brake rail (see Japanese Patent Laid-Open Publication No. 1997-217743), an apparatus in which a brake plate is deformed by the action of a pressurized fluid so as to press the plate against a track rail (see Japanese Patent Laid-Open Publication No. 1997-329141), and an apparatus in which brake shoe is pressed against a guide rail by means of a hydraulic biasing device (see Japanese Patent Laid-Open Publication No. 2000-9655).  
           [0008]    The conventional linear guide apparatuses thus utilize either a hydraulic pressure or air pressure to apply a load to a rail so as to generate a frictional force, which necessarily makes the braking mechanism for enhancing vibration damping complicated. Further, with such a breaking mechanism, a gap may be formed between a braking or damping member and a guide rail. The presence of even a very small gap causes an uncontrollable minute displacement of the braking or damping member in the gap direction, whereby the desired damping capacity cannot be obtained.  
         SUMMARY OF THE INVENTION  
         [0009]    It is therefore an object of the present invention to solve the above-described problems in the prior art and provide a linear guide apparatus which, owing to the use of a gap-free braking device in a rolling guide, has a sufficiently high damping capacity.  
           [0010]    In order to achieve the above object, the present invention provides a linear guide apparatus for guiding a linear motion of a movable body along a guide rail on a fixed structure in a machine tool, comprising: a rolling guide means including a rolling element for rolling on a surface of the guide rail; and a brake means for enhancing the damping capacity of the rolling guide section, wherein said brake section includes a pair of brake shoes, having a flexible structure, for sliding on the rolling element-rolling surface of the guide rail.  
           [0011]    The brake section of the linear guide apparatus according to the present invention, unlike the conventional braking devices, has a flexible structure and does not have such a complicated mechanism or a hard structure that would form a gap between a brake shoe and a guide rail. The brake section can securely provide the linear guide apparatus with a sufficient damping capacity.  
           [0012]    In a preferred embodiment of the present invention, an elastic member, biasing each brake shoe so that the brake shoe presses on the rolling element-rolling surface of the guide rail, is provided in the rear of the brake shoe. In this embodiment, the brake shoe preferably has a thin portion that allows a bend of the brake shoe by the force applied from the elastic member.  
           [0013]    It is preferred that the sliding surface of each brake shoe be comprised of a sliding member, such as a resin sliding member or an oil-free metal sliding member. Further, it is preferred that each brake shoe be fastened to the brake section by means of a plurality of adjustment bolts which adjust the pressing force of the brake shoe so that it acts evenly on the rolling element-rolling surface of the guide rail. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a side view showing a machine tool to which a linear guide apparatus according to the present invention is applied;  
         [0015]    [0015]FIG. 2 is a front view showing, together with a table, a linear guide apparatus according to a first embodiment of the present invention;  
         [0016]    [0016]FIG. 3 is a side view of the linear guide apparatus;  
         [0017]    [0017]FIG. 4 is a cross-sectional view of the rolling guide section of the linear guide apparatus;  
         [0018]    [0018]FIG. 5 is a cross-sectional view of the brake section of the linear guide apparatus;  
         [0019]    [0019]FIG. 6 is a cross-sectional view, partly omitted, of the brake section of a linear guide apparatus according to a second embodiment of the present invention;  
         [0020]    [0020]FIG. 7 is a cross-sectional view, partly omitted, of the brake section of a linear guide apparatus according to a third embodiment of the present invention; and  
         [0021]    [0021]FIG. 8 is a cross-sectional view, partly omitted, of the brake section of a linear guide apparatus according to a fourth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    Preferred embodiments of the present invention will now be described with reference to the drawings.  
         [0023]    [0023]FIG. 1 is a side view showing a machine tool to which a linear guide apparatus according to the present invention is applied. In FIG. 1, the reference numeral  10  designates a bed and  2  designates a column. A spindle head  4  is vertically movably mounted to the column  2 . The reference numeral  5  designates a spindle. A table  12  is provided on the bed  10 , and moves back and forth on the bed  2 .  
         [0024]    In the below-described embodiments, a linear guide apparatus according to the present invention is applied as a guide for the table  12 .  
         [0025]    &lt;First Embodiment&gt; 
         [0026]    [0026]FIG. 2 shows, together with a table, a linear guide apparatus according to a first embodiment of the present invention as viewed from the front in the moving direction of the table. This embodiment relates to application to a roller-type rolling guide for guiding a table in a machine tool.  
         [0027]    In FIG. 2, the reference numeral  10  designates a bed and  12  designates the table. A ball screw  13 , constituting a feed mechanism for the table  12 , is provided on the upper surface of the bed  10 . A pair of guide rails  14 , disposed on either side of the ball screw  13 , is laid in parallel with the axial direction of the ball screw  13 . Guide units  15 , each constituting the linear guide apparatus of this embodiment, are mounted to the lower surface of the table  12  each in engagement with the guide rail  14 .  
         [0028]    [0028]FIG. 3 is a side view of the linear guide apparatus of this embodiment.  
         [0029]    As shown in FIG. 3, each guide unit  15  comprises a rolling guide section  16  and a brake section  17 , disposed on the guide rail  14 . A total of 4 guide units  15  are mounted to the front and back portions on either side of the table  12  shown in FIG. 2. According to this embodiment, the rolling guide section  16  and the brake section  17  are designed as separate components. It is, however, possible to provide the two sections as an integral structure. Further, though in this embodiments the brake sections  17  are of the same number as the rolling guide sections  16 , the number of the brake sections  17  may not necessarily be the same as the rolling guide sections  16 , i.e., more or fewer brake sections than rolling guide sections may be employed depending upon the machine to which the apparatus of the present invention is applied.  
         [0030]    As shown in FIG. 4, the rolling guide section  16  is a known rolling unit having a plurality of rollers  18  within it. On either side of the guide rail  14 , generally V-shaped guide grooves  19  extend in the longitudinal direction. The upper and lower surfaces of the guide grooves  19  have roller-rolling surfaces  19   a ,  19   b  on which the rollers  18  roll. The roller-rolling surfaces  19   a ,  19   b  are symmetrical horizontally and vertically, forming an angle of 90° with each other. The guide unit  15  is so designed that the full weight load of the table  12  is received by the rolling guide section  16 , whereas no weight load is applied from the table  12  to the brake section  17 .  
         [0031]    [0031]FIG. 5 shows a cross-sectional view of the brake section  17 . In FIG. 5, the reference numeral  20  designates amounting block that constitutes the body of the brake section  17 , and  22  designates brake shoes.  
         [0032]    The mounting block  20  of the brake section  17  is a steel block having a U-shaped cross-section. Each brake shoe  22  is a steel shoe which has a generally trapezoidal cross-section, corresponding to the shape of the guide groove  19 , so that the shoe as a whole can closely fit the guide groove  19 . The inclined surfaces of the brake shoe  22  are sliding surfaces which slide on the roller-rolling surfaces  19   a ,  19   b  of the guide rail  14 . According to this embodiment, plate-shaped sliding members  21   a ,  21   b , mounted to the brake shoe  22 , slide on the roller-rolling surfaces  19   a ,  19   b . The sliding members  21   a ,  21   b  may preferably be made of a fluororesin, in particular a polytetrafluoroethylene Turcite (trade name, available from Busak+Shamban K.K.). A metal shoe may also be used. In that case, a solid lubricant may be embedded in the surfaces of the sliding members  21   a ,  21   b . Alternatively, it is possible to use an oil-free sliding member, for example Oiles (trade name, available from Oiles Corporation), which is impregnated with a lubricating agent.  
         [0033]    Compression springs  26  are disposed in the space between the back surface of the brake shoe  22  and the inner side surface of the mounting block  20 , so that the brake shoe  22  is pressed against the roller-rolling surfaces  19   a ,  19   b  at an appropriate pressure by the elastic force of each compression spring  26 . The brake shoe  22  itself has thin portions  27  which are designed to be bent by the force applied from the compression spring  26 .  
         [0034]    The brake shoe  22  has in the peripheral portion flange portions  22   a , and a plurality of adjustment bolts  24  are screwed into the flange portions  22   a  symmetrically with respect to the center. The brake shoe  22  is fastened, against the elastic force of the compression springs  26 , to the inner side surface of the mounting block  20  by means of the bolts  24 . The adjustment bolts  24  are inserted from bolt holes  25  that penetrate the side portion of the mounting block  20 .  
         [0035]    As shown in FIG. 3, end plates  30 ,  31  are mounted to the ends of the brake section  17 . The end plates  30 ,  31  function to remove dust adhering to the roller-rolling surfaces  19   a ,  19   b  of the guide rail  14 . The same end plates  30 ,  31  are provided also in the guide section  16 .  
         [0036]    A detailed description will now be given of the pressing force that presses the brake shoes  22  against the guide rail  14  in the brake section  17 .  
         [0037]    As a result of experiments carried out by using the linear guide apparatus of this embodiment, it has been found that when table  12  of an about one-meter square is supported by the rolling guide sections  16  consisting of four units, two and two on either side of the table, each unit specifically being #55 Linear Roller Way manufactured by Nippon Thomson Co., Ltd., the degree of damping increases about threefold by application of about 1000 N pressing force by each unit of the brake section  17 , as compared to the case of applying no pressing force, achieving an adequate enhancement of damping capacity.  
         [0038]    In this connection, referring to FIG. 5, F RU , F RD , F LU  and F LD  designate the pressing forces that press the sliding members  21   a ,  21   b  of the brake shoes  22  against the roller-rolling surfaces  19   a ,  19   b  of the guide rail  14 . The total pressing force F is as follows:  
           F=F   RU   +F   RD   +F   LU   +F   LD =1000 (N)  
         [0039]    Because of the horizontal and vertical symmetry, the pressing force applied to each of the roller-rolling surfaces  19   a ,  19   b  of the guide rail  14  is as follows:  
           F   RU   =F   RD   =F   LU   =F   LD =1000/4=250 (N)  
         [0040]    Assuming that the sliding members  21   a ,  21   b  each have a width of 8 mm and a length of 120 mm, the specific pressure applied to each of the sliding members  21   a ,  21   b  will be determined as follows:  
         250/0.8×1.2=26 (N/cm 2 )  
         [0041]    The pressure value thus determined falls within a proper pressure range in a practical point of view in the case of utilizing the roller-rolling surfaces  19   a ,  19   b  as sliding surfaces for the brake shoes  22 .  
         [0042]    With respect to the compression springs  26  of the brake section  17 , on the other hand, the forces F R , F L  nipping the guide rail  14  from either side can be calculated as follows:  
           F   R   =F   L   =F   RU /{square root}{square root over ( )}2 +F   RD /{square root}{square root over ( )}2=354 (N)  
         [0043]    Thus, the compression springs  26 ,  26  on either side of the guide rail  14  must have such a spring force as to nip the guide rail  14  at 354 N.  
         [0044]    While the table  12  is moving, it is guided by the rolling guide sections  16 . Taking the advantage of rolling guides, the table  12  can be transferred at a high speed.  
         [0045]    Further, when the table  12  is moving, the brake shoes  22  are pressed against the roller-rolling surfaces  19   a ,  19   b  by the above-described pressing force F, whereby an appropriate frictional force is generated. Accordingly, as described above, the degree of damping increases about threefold as compared to the case of not generating a frictional force, enabling effective damping of cutting vibrations during machining. Further according to the present brake section, each brake shoe  22  is made to closely fit the guide groove  19 , defining the roller-rolling surfaces  19   a ,  19   b , by utilizing the simple shape of the brake shoe, while the brake shoe  22  is spring-biased by the compression spring  26 . In addition, the thin portions  27  are provided in the brake shoe  22 , so that the brake shoe  22  has such a flexible structure that it can bend by the elastic force of the compression spring  26 . Thus, the brake section  17  of this embodiment, unlike the conventional braking mechanisms, does not have a complicated mechanism or a hard structure which could form a gap between a brake shoe and a guide rail. The brake section  17  does not form even a slight gap between the brake shoe  22  and the guide rail  14 , and can securely provide a sufficient damping capacity to the linear guide apparatus.  
         [0046]    The sliding members  21   a ,  21   b  mounted to the brake shoe  22  wear gradually during a long period of operation of the apparatus. However, since a constant force from the compressing springs  26  keeps acting on the brake shoe  22 , a change in the frictional force due to the wear of the brake shoe can be made extremely small. Further, the use of Turcite, which has excellent sliding properties, for the sliding members  21   a ,  21   b  or the use of Oiles sliding members makes it possible to maintain the damping capacity over a long period of time without maintenance and without causing damage to the roller-rolling surfaces  19   a ,  19   b  of the guide rail  14 .  
         [0047]    &lt;Second Embodiment&gt; 
         [0048]    The second embodiment relates to application of the present invention to a ball-type rolling guide. Instead of the known rolling guide using the rollers  18  employed in the first embodiment, a known rolling guide using balls is employed in this embodiment.  
         [0049]    [0049]FIG. 6 shows a cross-sectional view of the brake section  32  of this embodiment. Guide grooves  33 , each having a semicircular cross-section, are formed in the both side surfaces of the guide rail  14 . The curved surface of each guide groove  33  serves as a ball-rolling surface.  
         [0050]    A sliding member  34 , which slides on the ball-rolling surface of the guide groove  33 , is provided integrally in each of the brake shoes  22 . The sliding member  34  has a curved surface, whose curvature is made the same as that of the curved surface of the guide groove  33  so that the sliding member  34  closely fits the guide groove  33 , and extends in the long direction of the guide rail  14 . As with the first embodiment, a resin sliding member or an oil-free metal sliding member, such as the above-described Turcite or Oiles, may be used as the sliding member  34 .  
         [0051]    The components according to the second embodiment, other than the brake shoes  22 , are the same as the first embodiment. The same components are given the same reference numerals, and a description thereof is herein omitted.  
         [0052]    As described hereinabove, the present invention is applicable not only to a roller-type rolling guide but also to a ball-type rolling guide. The brake section according to the present invention, unlike the conventional braking devices, has a soft structure and does not have a complicated mechanism or a hard structure which could form a gap between a brake shoe and a guide rail, and can therefore securely provide a sufficient damping capacity to the linear guide apparatus.  
         [0053]    &lt;Third Embodiment&gt; 
         [0054]    [0054]FIG. 7 shows the brake section of the linear guide apparatus according to a third embodiment of the present invention. The third embodiment adds to the brake section  17  of the first embodiment, shown in FIG. 5, pressing force adjustment bolts  42  for fine adjustment of the pressing force of the brake shoes  22 . The other components are the same as those of the brake section  17  of FIG. 5.  
         [0055]    Screw holes  41 , penetrating the side portions of the mounting block  20 , are provided at locations corresponding to the compression springs  26  disposed in the long direction, and the pressing force adjustment bolts  42  are screwed into the screw holes  41 . The front end of each pressing force adjustment bolt  42  is in contact with the compression spring  26 , while the rear end protrudes from the mounting block  20 . The pressing force adjustment bolt  42  has a male screw portion formed over the full length of the bolt. The portion of bolt  42  protruding from the mounting block  20  is in screw engagement with a lock nut  43 , and the pressing force adjustment bolt  42  is secured by the lock nut  43  to the mounting block  20 .  
         [0056]    According to the third embodiment having the above construction, the pressing force can be adjusted in the following manner: As the pressing force adjustment bolt  42  is screwed and advanced in the screw hole  42 , the compression spring  26  is increasingly compressed, whereby the pressing force of the compression spring  26 , acting on the brake shoe  22  to press it against the roller-rolling surfaces  19   a ,  19   b  of the guide rail  14 , increases accordingly, whereas the pressing force decreases as the pressing force adjustment bolt  42  is moved back in the opposite direction. Accordingly, by adjusting the screwing degree of each pressing force adjustment bolt  42  and fastening the lock nut  43  to fix the screwing degree, the pressing force of the brake shoe  22  as a whole can be distributed evenly over the roller-rolling surfaces  19   a ,  19   b.    
         [0057]    &lt;Forth Embodiment&gt; 
         [0058]    The fourth embodiment, shown in FIG. 8, relates to application of the preceding embodiment, i.e. the embodiment using the pressing force adjustment bolts  42  for evenly distributing the pressing force of the brake shoe  22 , to a ball-type rolling guide. The fourth embodiment is the same as the second embodiment shown in FIG. 6 except for the provision of the pressing force adjustment bolts  42  shown in FIG. 8. The same components as the second embodiment are given the same reference numerals, and a description thereof is herein omitted.  
         [0059]    According to the fourth embodiment, the pressing force of the brake shoe  22  can be distributed evenly over the ball-rolling surface of the guide groove  33 .  
         [0060]    While the linear guide apparatus of the present invention has been described with reference to the preferred embodiments which relate to application as a guide for a table of a machine tool, the present invention can also be applied to various other movable bodies of a machine tool, such as a spindle head, a saddle, a cross rail, etc.  
         [0061]    As described hereinabove, the brake section of the linear guide apparatus according to the present invention, unlike the conventional braking devices, utilizes an elastic member as a biasing means, has a flexible structure, and does not have a complicated mechanism or a hard structure that could form a gap between a brake shoe and a guide rail. The addition of such a gap-free braking device to a conventional rolling guide can provide a sufficient damping capacity to the linear guide apparatus.