Abstract:
A method and structure improves the dynamic characteristics of a linear roller guideway for precision machine tool, robot or automation equipment by: adding a nonlinear component to the linear roller guideway to provide better dynamic stiffness and damping effects. The nonlinear component has a nonlinear contact characteristic of hardening so that during mounting or in a quick movement of the slide units of the linear roller guideway, the nonlinear component has a relatively lower stiffness to reduce its friction with the rail surface; on the other hand, when bearing a load or during a cutting work, the nonlinear component has a relatively higher stiffness. The nonlinear component also provides a planar contact, overcoming the drawbacks of low damping of point or line contact of the slide units of the nonlinear roller guideway, and enhancing the cutting precision of the machine tool.

Description:
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to linear roller guideway technology, and more particularly to a method and structure for improving the dynamic characteristics of a linear roller guideway for use in a precision machine tool, robotic or industrial automation equipment to provide a linear motion of low frictional resistance and to bear a load. 
     (b) Description of the Prior Art 
     Linear roller guideway is a high precision motion mechanism assembly, as illustrated in  FIG. 1 , generally comprising a rail  10 , at least one slide unit (slider, slide block, or carriage)  20 , and rolling elements  30 . The slide unit  20  is adapted for holding and carrying work platforms and workpieces. The rolling elements  30  can be balls or rollers. By means of the rolling elements  30 , the rail  10  and the slide unit  20  are movable relative to each other to further carry the work platform, achieving a high precision linear motion. Because the contact between the rail  10  and the slide unit  20  is points or a line, the frictional resistance is very low, about 2% of sliding friction, and the coefficient of friction is about 0.004. 
     According to the theory of elasticity, when an external force is applied to the surface of the slide unit  20 , the rolling elements  30  in the linear roller guideway are slightly elastically deformed (see the imaginary line in  FIG. 2 ). This elastic deformation is not a permanent deformation. After the external force disappears, the rolling elements  30  immediately return to their former shape. Thus, if the applied external force varies with time, or the size of the applied external force (e.g. the machine tool cutting force) is changed, a number of negative factors can arise during the elastic deformation process of the rolling elements  30 . Therefore, many different design methods or techniques are developed. Throughout these methods or patents, in addition to the method of enabling a controller to actively make compensation, they can be roughly divided into several categories as follows: 
     (A) Increase the stiffness of the linear roller guideway by: reducing the elastic deformation of rolling elements, for example, changing the geometric size, amount and/or relative allocation of the rolling elements, or pre-stressing the rolling elements. 
     (B) Increase the damping force of the linear roller guideway by: enabling the elastic deformation of the rolling elements to be rapidly stopped, i.e., rapidly attenuating or stopping the vibration when it is produced, for example, putting a large amount of mini sliding components in between the slide unit and the rail, using high damping materials, or using a hydraulic slide unit having an oil film to provide a high level of damping properties. 
     (C) Improve the stiffness and damping of the linear roller guideway by: adding an additional nonlinear element. This method is a more progressive way in line with the industry&#39;s needs. 
     SUMMARY OF THE INVENTION 
     A linear roller guideway needs to provide different functions for matching with the status of a work platform supported on slide units thereof. A work platform for this application generally assesses: (a) translational motion status, and (b) processing status where an external force is applied to the workpiece, 
     (a) Translational Motion Status: 
     When moving the work platform, the linear roller guideway needs to provide a function of low frictional resistance so that the work platform can be rapidly moved and quickly positioned in position. In this status, the contact between the rail and rolling elements of the linear roller guideway and the contact between the rolling elements and slide units of the linear roller guideway are preferably of point or line contact to meet the requirement of low frictional resistance. 
     (b) Processing Status: 
     In this status, the work platform stands still or is moved at a low speed. Under this condition, the feature of low friction resistance is not the main requirement for the linear roller guideway; on the contrary, the linear roller guideway needs to provide a function of high stiffness at this time, preferably a stiff structure for giving a support to minimize the deformation of the linear roller guideway. 
     If the workpiece machining precision requirement is not high, commercial linear roller guideways can meet the engineering requirements. However, if the workpiece machining precision requirement is high, surface contact hard rails such as V-rails or dovetail rails are still widely used in commercial and industrial linear roller guideways for the reason that they can provide high stiffness to lower the effects caused by deformation. In order to compensate for the drawback of insufficient stiffness of a linear roller guideway during a cutting work, the invention provides a nonlinear component for mounting on a rail of a linear roller guideway between two slide units to meet the requirements for the aforesaid two work platform statuses. 
     However, simply adding a surface contact nonlinear component to the linear roller guideway can cause a problem of increased frictional resistance during a quick movement of the work platform. Further, the hard contact between the nonlinear component and the rail of the linear roller guideway imparts a barrier to the installation. In order to solve this problem, the invention designs the contact surface relationship between the nonlinear component and the rail to have a nonlinear contact characteristic of hardening so that the contact between the nonlinear component and the rail becomes a soft contact or contact with less stiffness in the mounting procedure or during a translational motion, and a hard contact during a cutting work. 
     Thus, adding a nonlinear component constructed in accordance with the present invention to a linear roller guideway achieves the effect of improving the stiffness and damping of the linear roller guideway as described in the aforesaid category (C) of improvement measure. Further, it can be seen from the above description that a linear roller guideway having a relatively higher stiffness will produce a relatively smaller amplitude of vibration, and thus, the damping force required for eliminating the vibration can be relatively smaller, or, the vibration can be eliminated more quickly. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic transverse sectional view of a linear roller guideway according to the prior art. 
         FIG. 2  is a schematic drawing illustrating an elastically deformed status of one rolling element in the linear roller guideway according to the prior art. 
         FIG. 3  is a schematic drawing of a nonlinear component mounted in a linear roller guideway in accordance with the present invention. 
         FIG. 4  is a surface contact stiffness curve having a nonlinear contact characteristic of hardening required according to the present invention. 
         FIG. 5  illustrates the surface contact stiffness curve of  FIG. 4  simplified into a curve of bilinear contact. 
         FIG. 6  is a schematic sectional view of a nonlinear component in accordance with a first embodiment of the present invention. 
         FIG. 7  is an oblique top view illustrating the nonlinear component of the first embodiment of the present invention mounted on a rail for a linear roller guideway. 
         FIG. 8  is a schematic drawing illustrating a stiff support status of the nonlinear component of the first embodiment of the present invention. 
         FIG. 9  is an oblique top view of a nonlinear component in accordance with a second embodiment of the present invention. 
         FIG. 10  is a schematic drawing illustrating a nonlinear component of a third embodiment of the present invention mounted on a rail for a linear roller guideway. 
         FIG. 11  is an oblique top view of the nonlinear component of the third embodiment of the present invention. 
         FIG. 12  is a schematic drawing illustrating an allowable clearance defined between the high-stiffness first support surface and the high-stiffness second support surface in the nonlinear component of the third embodiment of the present invention. 
         FIG. 13  is an oblique top view of a nonlinear component of a fourth embodiment of the present invention. 
         FIG. 14  is an exploded view of the nonlinear component of the fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 3 , the invention provides a method and a structure for improving the dynamic characteristics of a linear roller guideway comprising a rail  11 , a plurality of slide units  12 , and rolling elements (not shown) set in between the rail  11  and each slide unit  12 . The method is to slidably mount a nonlinear component  2  on the rail  11  between each two adjacent slide units  12 , allowing the nonlinear component  2  and the slide units  12  to concomitantly carry a vertical load generated by a work platform  3  and/or a workpiece  4 . 
     The invention particularly designs the aforesaid nonlinear component  2  to have a nonlinear contact characteristic of hardening so that when mounting the nonlinear component  2  on the rail  11  or when the nonlinear component  2  carries no load, the contact between the nonlinear component  2  and the rail  11  can be a soft contact or a contact with less stiffness; when an external force is applied to the work platform  3  and/or the workpiece  4 , the nonlinear component  2  is capable of providing an effect of high stiffness. The so-called “nonlinear contact characteristic of hardening” means that the nonlinear component  2  can provide a hardening support surface against the increasing vertical load of the work platform  3 . Thus, when the vertical load of the work platform  3  is gradually reduced, the surface of contact between the nonlinear component  2  and the rail  11  will be gradually softened. On the contrary, when the vertical load of the work platform  3  is increased, the surface of contact between the nonlinear component  2  and the rail  11  will be relatively hardened to increase the stiffness of the nonlinear component  2  for support between the work platform  3  and the rail  11 , enabling the nonlinear component  2  to achieve the expected effect. 
     Referring to  FIG. 4 , the nonlinear contact characteristic of hardening of the nonlinear component is the slope of the OBC curve shown in the drawing, where Point B is the reversal point or cut-off point between the high stiffness region and the low stiffness region. During the installation of the linear roller guideway after the mounting of the nonlinear component  2  or during a platform movement status, no force processing is performed. At this time, the total load is relatively smaller, or should be below F B , and thus, the nonlinear component  2  provides the OB section of low stiffness. Assume that the stiffness in this OB section is k S,OB , the rolling stiffness of one single slide unit  12  is k R , k R &gt;&gt;k S,OB , and the work platform  3  is supported on two linear roller guideways in each direction (four slide units, two nonlinear components), in this case, the total equivalent static stiffness k eq  can be expressed by:
 
 k   eq   (1) =4 k   R +2 k   S,OB ≈4 k   R   (1)
 
     In other words, the increased stiffness after adding the nonlinear component  2  is negligible, and the linear roller guideway still only presents the original stiffness of the slide units  12  (see  FIG. 1 ), maintaining the function of low frictional resistance. 
     On the other hand, if is processing load is (F D −F B ) or the total load is F D  during a cutting operation, then, as expressed by the characteristic curve in  FIG. 4 , the stiffness in the BC section is rapidly increased with the change of the amount of elastic deformation or load. Assume the stiffness in the BC section in the cutting operation is k S,BC  wherein k S,BC &gt;&gt;k S,OB  and k S,BC &gt;k R , thus, the total equivalent static stiffness k eq  can be expressed by:
 
 k   eq   (2) =4 k   R +2 k   S,BC   (2)
 
     In other words, in addition to the original stiffness of the slide units  12 , the linear roller guideway has the stiffness of the nonlinear component  2  in the BC section added thereto. 
     Further, unlike the slide units  12 , the nonlinear component  2  essentially provides a planar contact, and the friction between the nonlinear component  2  and the rail  1  is a sliding friction (kinetic friction), thus, the oil film of the applied lubricant and this sliding friction can increase the damping effect of the nonlinear component  2  in the OB section and the BC section. The above description explains the theoretical correctness and inventive step of the present invention. 
     For better understanding of the present invention, the method for improving the dynamic characteristics of a linear roller guideway is explained hereinafter by way of the following preferred embodiment. According to this preferred embodiment, the method for improving the dynamic characteristics of a linear roller guideway comprises the steps of: 
     Step I: Establish a Surface Contact Having a Nonlinear Contact Characteristic of Hardening. 
     In this step, as described above, establish a curve for a surface contact having the said nonlinear contact characteristic of hardening (see  FIG. 4 ). This curve can be presented in any of a variety of forms that satisfy the nonlinear contact characteristic of hardening as defined according to the present invention. 
     Let the load and amount of deformation of the surface contact between the nonlinear component  2  and the rail  11  satisfy the linearly increasing characteristic; thus, simplify the relationship between the OB section (namely, the low stiffness region) and the BC section (namely, the high stiffness region) to a relationship between two straight lines, thus, as illustrated in  FIG. 5 , the nonlinear component defined between the OB section and the BC section is composed of two straight lines, i.e., nonlinear or the so-called “bi-linear”, as shown in  FIG. 5 , and thus, the stiffness of the OB section and the stiffness of the BC section in the nonlinear component  2  are respectively the slopes of the two straight lines, and therefore, k S,OB  and k S,BC  in the formula (1) and formula (2) are constants, and, the values of these two constants determine the stiffness value of the nonlinear component in the low stiffness region and the high stiffness region. 
     Step II: Establish the Stiffness of the High Stiffness Region and the Stiffness of the Low Stiffness Region. 
     In this step, calculate the stiffness of the nonlinear component in the OB region and the BC region according to the results obtained from Step I and shown in  FIG. 5 , and let the load and the amount of deformation to be F and x respectively, and thus, the stiffness of the nonlinear component in the OB region and the stiffness of the nonlinear component in the BC region shown in  FIG. 5  can be respectively obtained as: 
     
       
         
           
             
               
                 
                   
                     k 
                     
                       S 
                       , 
                       OB 
                     
                   
                   = 
                   
                     
                       F 
                       B 
                     
                     
                       x 
                       B 
                     
                   
                 
               
               
                 
                   ( 
                   3 
                   ) 
                 
               
             
           
         
       
     
     And 
     
       
         
           
             
               
                 
                   
                     k 
                     
                       S 
                       , 
                       BC 
                     
                   
                   = 
                   
                     
                       
                         F 
                         D 
                       
                       - 
                       
                         F 
                         B 
                       
                     
                     
                       
                         x 
                         D 
                       
                       - 
                       
                         x 
                         B 
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Step III: Design a Nonlinear Component. 
     Design the nonlinear component  2  to have a low stiffness region, and a high stiffness region having a stiffness higher than the low stiffness region, wherein the low stiffness region will elastically deform when bearing the vertical load of the aforesaid work platform  3  and/or workpiece  4 ; the high stiffness region approaches the rail surface  111  of the rail  11  of the linear roller guideway  1  with the deformation of the low stiffness region, and comprises a contact surface for directly or indirectly abutting against the rail surface  111 . 
     The contact surface of the high stiffness region can be made in any of a variety of forms that satisfy the nonlinear contact characteristics of the bilinear sections shown in  FIG. 5 . Further, the nonlinear component  2  is not limited to geometric or material nonlinear stiffness, however, in this embodiment, geometric nonlinearity is explained to support the effectiveness of the present invention. 
       FIG. 6  is a schematic sectional view of a nonlinear component  2  that satisfies the stiffness curve shown in  FIG. 4 .  FIG. 7  illustrates the nonlinear component  2  mounted on a rail  11 . When a vertical load is transferred from the aforesaid work platform  3  and/or workpiece  4  to the nonlinear component  2  through a jacket  20  of the nonlinear component  2 , the middle low stiffness region  21  of the nonlinear component  2  receives the weight of the vertical load at first and is caused to elastically gradually deform, the stiffness of this low stiffness region  21  is the stiffness value of k S,BC  obtained in Step II, and, the amount of deformation is determined according to the amount of the vertical load. When the amount of deformation surpasses the predetermined amount of deformation x B , the contact surfaces  23  of the high stiffness regions  22  at opposing left and right sides relative to the low stiffness region  21  will be forced into contact with the rail surface  111  (see  FIG. 8 ), increasing the stiffness to the level of the high stiffness region to achieve the surface contact characteristic of nonlinearity or bilinearity. 
       FIG. 9  illustrates an alternate form of the nonlinear component  2 . According to this second embodiment, the nonlinear component  2  comprises two low stiffness regions  21  respectively disposed at opposing left and right sides, and a high stiffness region  22  located on the middle between the two low stiffness regions  21 . This high stiffness region  22  comprises a contact surface  23  adapted for contacting the rail surface  111  to achieve the same effects as the aforesaid first embodiment. 
     Step IV: Mount the Nonlinear Component. 
     As illustrated in  FIG. 3 , slidably mount the nonlinear component  2  thus prepared on a rail  11  of a linear roller guideway  1  between two slide units  12  of the linear roller guideway  1  to have one wall (for example, the top wall of the nonlinear component  2 ) be joined to a work platform  3 , enabling the nonlinear component  2  and the slide units  12  to concomitantly bear the vertical load of the work platform  3  and/or a workpiece  4 . 
     Referring to  FIG. 10  and  FIG. 11 , a nonlinear component  2  for improving the dynamic characteristics of a linear roller guideway in accordance with a third embodiment of the present invention is shown. According to this third embodiment, the nonlinear component  2  is a rectangular metal block, comprising a bearing surface  24  located at a top side thereof for joining to a bottom surface of the work platform  3  (see  FIG. 3 ), sliding groove  25  located in an opposing bottom side thereof and extending through opposing front and rear sides thereof and fitting the aforesaid linear roller guideway  1  (rail  11 ) and a hardening contact structure  26  located between the bearing surface  24  and the sliding groove  25 . This hardening contact structure  26  specifically comprises at least one low-stiffness deformable portion  261  for bearing a vertical load from the bearing surface  24 , a high-stiffness first support surface  262  capable of bearing the vertical load from the bearing surface  24  and downwardly movable with the loading of the vertical load, a high-stiffness second support surface  263  corresponding to the high-stiffness first support surface  262 , and an allowable clearance  264  defined between the high-stiffness first support surface  262  and the high-stiffness second support surface  263  (see  FIG. 12 ). This allowable clearance  264  is preferably in the range of 0.05 mm˜0.1 mm. 
     Referring to  FIGS. 10 and 11  again, the hardening contact structure  26  of the nonlinear component  2  further comprises a pass-through portion  265  in the form of, for example, a slot that extends through the opposing front and rear sides of the nonlinear component  2  and defining an inner top wall  266  and an opposing inner bottom wall  268  that forms the aforesaid high-stiffness second support surface  263 , a first protruding block  267  downwardly extending from the inner top wall  266  of the pass-through portion  265  and terminating in the aforesaid high-stiffness first support surface  262 , and two circular through holes  269  respectively disposed in the opposing left and right sides of the pass-through portion  265  in communication with the pass-through portion  265 . The diameter of the through holes  269  is larger than the height between the inner top wall  266  and the inner bottom wall  268  of the pass-through portion  265  so that the thickness of the part between the through holes  269  and the bearing surface  24  is smaller than the thickness of the part between the inner top wall  266  and the bearing surface  24 . Thus, the part between the through holes  269  and the bearing surface  24  and the part between the inner top wall  266  and the bearing surface  24  form the aforesaid low-stiffness deformable portion  261 . When the bearing surface  24  bears a vertical load, the low-stiffness deformable portion  261  is forced to deform, moving the high-stiffness first support surface  262  into abutment against the high-stiffness second support surface  263 . 
     Referring to  FIGS. 10 and 11  again, the aforesaid sliding groove  25  preferably comprises a top groove wall  251 , two opposing side groove walls  252 , a second protruding block  253  downwardly extending from the top groove wall  251 , and two third protruding blocks  255  respectively extending from the two side groove walls  252  toward a vertical midline of the groove  25 . The second protruding block  253  comprises a first sliding surface  254  located at a bottom side thereof and kept in contact with the top surface of the rail  11  of the linear roller guideway  1 . Each third protruding block  255  comprises a second sliding surface  256  kept in contact with one respective side surface of the rail  11  of the linear roller guideway  1 . Thus, the nonlinear component  2  is precisely coupled to the rail  11 . 
     The aforesaid nonlinear component  2  is preferably a one-piece metal block of rectangular form that defines the said bearing surface  24 , the said sliding groove  25  and the said hardening contact structure  26 . Alternatively, as shown in  FIGS. 13 and 14 , the nonlinear component  2  can be implemented as a modular structure, consisting of a first block member  27  and a second block member  28 . The top wall  271  of the first block member  27  is downwardly processed to form the inner bottom wall  268  and through holes  269  of the pass-through portion  265 , allowing the inner bottom wall  268  to work as the high-stiffness second support surface  263 . The bottom side of the first block member  27  is processed to provide the aforesaid sliding groove  25 . The second block member  28  is affixed to the top wall  271  of the first block member  27  with fastening elements  29 , for example, screws. The bottom wall of the second block member  28  works as the inner top wall  266  of the said pass-through portion  265 , and is processed to provide the said first protruding block  267  having the said high-stiffness first support surface  262 . After the first block member  27  and the second block member  28  are assembled, the allowable clearance  264  is defined between the high-stiffness first support surface  262  and the high-stiffness second support surface  263 . Preferably, this allowable clearance  264  is in the range of 0.05 mm˜0.1 mm. 
     Referring to the simplified curve of surface contact having a nonlinear contact characteristic of hardening of  FIG. 5 , the structural characteristics of the low-stiffness deformable portion  261  and allowable clearance  264  of the hardening contact structure  26  of the nonlinear component  2  enable the nonlinear component  2  and the rail  11  to achieve a soft contact or a contact of lower stiffness, facilitating installation of the nonlinear component  2  in the rail  11 , and thus no vertical load or only a small amount of vertical load will be produced when mounting the nonlinear component  2  on the rail  11 , and the nonlinear component  2  can be smoothly moved on the rail  11  and then quickly positioned in the desired position without incurring any significant damping force. More specifically, before the vertical load on the nonlinear component  2  reaches the stiffness of the low-stiffness deformable portion  261 , the status of the low-stiffness deformable portion  261  is in the slope of the OB section. 
     However, in a machining operation, the vertical load is transferred from the work platform  3  through the nonlinear component  2  to the hardening contact structure  26 , the at least one low-stiffness deformable portion  261  is firstly elastically deformed. The stiffness of the low-stiffness deformable portion  261  is a rated stiffness value. Thus, when the amount of deformation reaches the predetermined stiffness value and the amount of deformation of the low-stiffness deformable portion  261  surpasses the predetermined stiffness value, the high-stiffness first support surface  262  is lowered to reduce the allowable clearance  264 . When the allowable clearance  264  is reduced to the extent that the high-stiffness first support surface  262  touches the high-stiffness second support surface  263 , the stiffness of the nonlinear component  2  is largely increased, achieving the surface contact characteristic of nonlinear of bilinear. 
     Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications and enhancements may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims.