Patent Publication Number: US-2004047701-A1

Title: CNC machine tool for rotating a workpiece by a preset angle per one-revolution rotation of a rotating shaft on a worktable

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001] This application claims priority of Taiwanese Application No. 91214140, filed on Sep. 9, 2002.  
       BACKGROUND OF THE INVENTION  
       [0002] 1. Field of the Invention  
       [0003] This invention relates to a CNC (Computer Numerical Control) machine tool, and more particularly to a CNC machine tool, which can rotate a workpiece by a preset angle per one-revolution rotation of a rotating shaft on a worktable.  
       [0004] 2. Description of the Related Art  
       [0005] Referring to FIG. 1, a CNC machine tool  10  is shown to include a workpiece-rotating device  11 , which is disposed on a worktable  12  that is mounted movably on a machine bed and that can move in horizontal directions (X, Y) under CNC control. A vertical working disk ill is connected rotatably to the worktable  12  by means of the workpiece-rotating device  11  for holding a workpiece (not shown) to be cut thereon. The workpiece-rotating device  11  is provided with a stepping motor  13  for rotating the working disk  111 . A carrier  14  is disposed on the machine bed, and can move in a vertical direction (Z). A cutter  15  is mounted fixedly on the carrier  14 . As such, the workpiece (not shown) can be rotated on the worktable  12  by a preset angle by the workpiece-rotating device  11  upon each output of the motor  13 .  
       [0006] The aforesaid conventional CNC machine tool  10  suffers from the following disadvantages:  
       [0007] (1) To drive the motor  13 , a power cable (not shown) and a signal cable (not shown) are connected thereto. It is expensive to arrange the power cable and the signal cable on the machine  10 . Furthermore, some elements, which are disposed among the motor  13 , the power cable, and the signal cable, are required to often replace, thereby resulting in difficulties in maintenance and repair.  
       [0008] (2) Because no means is provided for preventing rotation of the working disk  111  relative to the worktable  12 , the working disk  111  is kept in a rotatable condition with respect to the worktable  12 , thereby resulting in poor cutting quality, especially for comparatively heavy workpieces.  
       SUMMARY OF THE INVENTION  
       [0009] The object of this invention is to provide a CNC machine tool, which includes a working disk that is rotated mechanically by a rotating unit so that a stepping motor for driving the working disk can be omitted, and means for preventing rotation of the working disk relative to a worktable only when the working disk does not rotate.  
       [0010] According to this invention, a CNC machine tool includes a worktable disposed movably on a machine bed and having a fixed first engaging element, a working disk mounted rotatably on the worktable for holding a workpiece to be cut, and a rotating unit with a rotating shaft journalled on the worktable. A second engaging element is fixed to the working disk. The working disk is rotated mechanically by a preset angle by the rotating unit per one-revolution rotation of the rotating shaft on the worktable. When the rotating unit does not rotate the working disk during rotation of the rotating unit, it activates the first and second engaging elements to engage each other so as to fix the working disk relative to the worktable. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] These and other features and advantages of this invention will become apparent in the following detailed description of the preferred embodiments of this invention, with reference to the accompanying drawings, in which:  
     [0012]FIG. 1 is a perspective view of a conventional CNC machine tool;  
     [0013]FIG. 2 is a perspective view of the preferred embodiment of a CNC machine tool according to this invention;  
     [0014]FIG. 3 is a perspective view showing a rotating unit, a driven unit, a clutch unit, and a positioning unit of the preferred embodiment, in which a casing is shown in phantom lines;  
     [0015]FIG. 4 is another perspective view showing the rotating unit, the driven unit, the clutch unit, and the positioning unit of the preferred embodiment, but viewed from another angle;  
     [0016]FIG. 5 is a schematic fragmentary sectional view of the preferred embodiment taken along a vertical direction, illustrating connection between a guiding wheel and a plurality of driven elements;  
     [0017]FIG. 6 is a schematic fragmentary sectional view of the preferred embodiment taken along a horizontal line when a central shaft is disposed at a connecting position, where first and second engaging elements engage each other;  
     [0018]FIG. 7 is a view similar to FIG. 6 when the central shaft is disposed at a disconnecting position, where the first and second engaging elements are removed from each other;  
     [0019]FIG. 8 illustrates movement of a roller on one of the driven elements along a guiding slot in the guiding wheel; and  
     [0020]FIG. 9 illustrates movement of a roller on a driven swing arm of the rotating unit along a periphery of a driving cam wheel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0021] Referring to FIGS. 3, 4, and  5 , the preferred embodiment of a CNC machine tool according to this invention is shown to include a machine bed  21 , a worktable  22 , a carrier  23 , a numerical control unit  24 , a casing  3 , a rotating unit  4 , a driven unit  5 , a clutch unit  6 , and a positioning unit  7 .  
     [0022] The worktable  22  is disposed movably on the machine bed  21 , and is movable on the machine bed  21  under CNC control in horizontal directions (X, Y) (see FIG. 2). The carrier  23  is disposed vertically and movably relative to and above the machine bed  21 , and is movable relative to the machine bed  21  in a vertical direction (Z) (see FIG. 2) under the CNC control of the numerical control unit  24  in a known manner.  
     [0023] The casing  3  is fixed on the worktable  22 , and has an outer surface that is provided with a toothed first engaging element  31  fixed thereon.  
     [0024] The rotating unit  4  includes a horizontal rotating disk  41 , a vertical rotating shaft  42 , a driving cam wheel  43 , and a guiding wheel  44 . The rotating shaft  42  is journalled on and is disposed axially and movably within the casing  3 . The rotating disk  41  is connected fixedly to a top end of the rotating shaft  42 , and has a top surface that is provided with a fixed rotating center element  411 , which is eccentric from the axis of the rotating shaft  42 . In this embodiment, the positioning element  441  is configured as a cylindrical sleeve.  
     [0025] The driving cam wheel  43  is sleeved fixedly on the rotating shaft  42 . Referring to FIG. 9, the driving cam wheel  43  includes a small-radius cam surface ( 431   a ), a driving cam surface ( 431   b ), a large-radius cam surface ( 431   c ), and a transitional cam surface ( 431   d ). The small-radius cam surface ( 431   a ) has a uniform radius, a leading end, and a tail end. The leading and tail ends of the small-radius cam surface ( 431   a ) are spaced apart from each other by an angle of 25°. The large-radius cam surface ( 431   c ) has a uniform-radius that is larger than that of the small-radius cam surface ( 431   a ), a leading end, and a tail end. The leading and tail ends of the large-radius cam surface ( 431   c ) are spaced apart from each other by an angle of 190°. The driving cam surface ( 431   b ) has a leading end coupled with the tail end of the small-radius cam surface ( 431   a ) at a point (A 2 ), a tail end coupled with the leading end of the large-radius cam surface ( 431 C) at a point (A 3 ), and a diameter increasing gradually from the leading end of the driving cam surface ( 431   b ) to the tail end of the driving cam surface ( 431   b ) The leading and tail ends of the driving cam surface ( 431   b ) are spaced apart from each other by an angle of 60°. The transitional cam surface ( 431   d ) has a leading end coupled with the tail end of the large-radius cam surface ( 431   c ) at a point (A 4 ), and a tail end coupled with the leading end of the small-radius cam surface ( 431   a ) at a point (A 1 ). The leading and tail ends of the transitional cam surface ( 431   d ) are spaced apart from each other by an angle of 85°.  
     [0026] Referring to FIGS. 3, 4 and  8 , the guiding wheel  44  is sleeved fixedly on the rotating shaft  42 , and has an annular outer surface that is formed with a guiding slot  441 . Referring to FIG. 8, the guiding slot  441  has an entrance slot portion ( 441   a ) (not visible in FIGS.  3  and  4 ), a helical slot portion ( 441   b ), and an exit slot portion ( 441   c ) (not visible in FIGS. 3 and 4). The entrance slot portion ( 441   a ) is formed at a lower end of the guiding wheel  44 , extends from a point (B 1 ) to a point (B 2 ) along a circumferential direction of the guiding wheel  44 , and has a leading end ( 441   a ′) and a tail end ( 441   a ″). The helical slot portion ( 441   b ) extends from the point (B 2 ) to a point (B 3 ) along a helical path, and has a lower leading end ( 441   b ′) coupled with the tail end ( 441   a ″) of the entrance slot portion ( 441   a ), and an upper tail end ( 441   b ″). The exit slot portion ( 441   c ) extends from the point (B 3 ) to a point (B 4 ) along the circumferential direction of the guiding wheel  44 , and has a leading end ( 441   c ′) coupled with the tail end ( 441   b ″) of the helical slot portion ( 441   b ) and a tail end ( 441   c ″). The guiding slot  441  extends about the axis of the guiding wheel  44  by an angle of 360°. That is to say, the points (B 1 , B 4 ) are aligned along a vertical direction.  
     [0027] Referring again to FIGS. 3, 4,  5 , and  6 , the driven unit  5  includes a horizontal central shaft  51 , a vertical working disk  52 , a toothed second engaging element  53 , a spring member  54  in the form of a coiled compression spring, a ring  55 , and a plurality of angularly equidistant driven elements  56 . The central shaft  51  is journalled on and is disposed movably within the casing  3 , and has an inner end  51 ′ (see FIG. 6) that is disposed in the casing  3 , and an outer end  51 ″ that is disposed outside of the casing  3 . The working disk  52  is adapted to mount a workpiece (not shown) to be cut thereon, is connected fixedly to the outer end  51 ″ of the central shaft  51 , and is disposed outside of the casing  3 . The second engaging element  53  is disposed fixedly on the working disk  52 . The ring  55  is sleeved fixedly on the inner end  51 ′ of the central shaft  51 . The driven elements  56  are connected fixedly to and extend radially and outwardly from the central shaft  51 , and are arranged along a circumferential direction of the central shaft  51 . Each of the driven elements  56  has an outer end, which is provided with a rotatable roller  561  that is movable along the guiding slot  441  in the guiding wheel  44 . The number of the driven elements  56  is N.  
     [0028] The spring member  54  biases the central shaft  51  inwardly relative to the casing  3  so as to move the working disk  52  toward the casing  3 , thereby permitting engagement of the second engaging element  53  with the first engaging element  31 . In this embodiment, the spring member  54  is sleeved on the central shaft  51 , and is disposed between the ring  55  and a stop member  32  (see FIG. 6). The stop member  32  is fixed in the casing  3 , and is disposed between the ring  55  and the driven elements  56 .  
     [0029] The clutch unit  6  includes a vertical clutch shaft  61  (see FIG. 3) journalled within the casing  3 , a driven swing arm  62  cooperating with the driving cam wheel  43 , and a driving swing arm  63  cooperating with the ring  55 . The driven and driving swing arms  62 ,  63  extend integrally, radially, and outwardly from the clutch shaft  61  so as to rotate synchronously with each other. The driven swing arm  62  has a free end, which is provided with a rotatable roller  621  that is movable along the small-radius cam surface ( 431   a ) (see FIG. 9), the driving cam surface ( 431   b ) (see FIG. 9), the large-radius cam surface ( 431   c ) (see FIG. 9), and the transitional cam surface ( 431   d ) (see FIG. 9) of the driving cam wheel  43 .  
     [0030] The spring member  54  biases the ring  55  to press against the driving swing arm  63 . Because the driven and driving swing arms  62 ,  62  are connected fixedly to the clutch shaft  61 , the roller  621  of the driven swing arm  62  is brought into engagement with the driving cam wheel  43  of the rotating unit  4 .  
     [0031] The positioning unit  7  includes a positioning element  71 , which is disposed fixedly on the carrier  23 , and is configured as a projecting post that extends downwardly from the carrier  23 . In this embodiment, the positioning element  71  is a cutter.  
     [0032] In operation, the rotating shaft  42  is rotated with respect to the worktable  22  by controlling the numerical control unit  24  in a known manner that will be described in the succeeding paragraph.  
     [0033] The numerical control unit  24  is operated to move the worktable  22  horizontally so as to align the positioning element  71  with the rotating center element  411 . The carrier  23  is moved downwardly under the control of the numerical control unit  24  so as to permit the positioning element  71  to engage fittingly the rotating center element  411  such that the rotating center element  411  is sleeved rotatably on the positioning element  71 , thereby preventing displacement of the rotating center element  411  relative to the positioning element  71  while permitting rotation of the rotating center element  411  relative to the positioning element  411 . At this time, the worktable  22  can be moved horizontally on the machine bed  21  under the control of the numerical control unit  24  so as to rotate the rotating disk  41  about the rotating center element  411 , thereby permitting rotation of the rotating shaft  42  within the casing  3 .  
     [0034] Referring to FIGS. 3 through 9, during rotation of the rotating shaft  42  relative to the worktable  22 , the roller  621  of the driven swing arm  62  of the clutch unit  6  is biased to press against the periphery of the driving cam wheel  43  due to the presence of the spring member  54 .  
     [0035] When the roller  621  of the driven swing arm  62  of the clutch unit  6  moves from the point (A 1 ) to the point (A 2 ) along the small-radius cam surface ( 431   a ), the second engaging element  53  engages the first engaging element  31  so as to prevent rotation of the working disk  52  relative to the worktable  22 .  
     [0036] When the roller  621  moves from the point (A 2 ) to the point (A 3 ) along the driving cam surface ( 431   b ), the driving swing arm  63  of the clutch unit  6  contacts and pushes the ring  55  toward the stop member  32  so as to compress the spring member  54  such that the central shaft  51  in the casing  3  moves from a connecting position shown in FIG. 6, where the first and second engaging elements  31 ,  53  engage each other, to a disconnecting position, shown in FIG. 7, where the first and second engaging elements  31 ,  53  are removed from each other.  
     [0037] When the roller  621  of the driven swing arm  62  of the clutch unit  6  moves from the point (A 1 ) to the point (A 3 ), the roller  561  of one of the driven elements  56  of the driven unit  5  enters the leading end ( 441   a ′) of the entrance slot portion ( 441   a ) of the guiding slot  441 , and moves from the point (B 1 ) to the point (B 2 ) along the entrance slot portion ( 441   a ). As such, the driven elements  56  are fixed relative to the worktable  22  so that the working disk  52  cannot rotate on the worktable  22 .  
     [0038] When the roller  621  of the driven swing arm  62  of the clutch unit  6  moves from the point (A 3 ) to the point (A 4 ) along the large-radius cam surface ( 431   c ), the driven and driving swing arms  62 ,  63  are fixed relative to the worktable  22  so that the central shaft  51  of the driven unit  5  is kept in the disconnecting position shown in FIG. 7, thereby permitting rotation of the working disk  52  on the worktable  22 . At the same time, the roller  561  of the one of the driven elements  56  moves from the point (B 2 ) to the point (B 3 ) along the helical slot portion ( 441   b ) so that the driven elements  56  are rotated by a preset angle of 360/N degrees (N is the number of the driven elements  56 ).  
     [0039] When the roller  621  of the driven swing arm  62  of the clutch unit  6  moves from the point (A 4 ) to the point (A 1 ) along the transitional slot portion ( 431   d ), the driving swing arm  63  is rotated back to its original position, where the central shaft  51  is disposed at the connecting position shown in FIG. 6. At the same time, the roller  561  of the one of the driven elements  56  moves from the point (B 3 ) to the point (B 4 ) along the exit slot portion ( 441   c ), and exits from the tail end ( 441   c ″) of the exit slot portion ( 441   c ) so that the driven elements  56  and the working disk  52  cannot rotate on the worktable  22 . When the roller  621  of the driven swing arm  62  of the clutch unit  6  moves to the point (A 1 ), the roller  561  of the one of the driven elements  56  exits from the tail end ( 441   c ″) of the exit slot portion ( 441   c ), and the roller  561  of a succeeding one of the driven elements  56  enters the leading end ( 441   a ′) of the entrance slot portion ( 441   a ). As such, the driven elements  56  can engage the guiding slot  441  in the guiding wheel  44  of the rotating unit  4  in turn when the rotating unit  4  rotates.  
     [0040] From the forgoing description, it can be seen that the working disk  52  can rotate by an angle of 360/N degrees per one-revolution rotation of the rotating shaft  42  on the worktable  22 , thereby permitting intermittent rotation of the central shaft  51  on the worktable  22 .  
     [0041] This invention has the following advantages:  
     [0042] (1) Because the central shaft  51  is driven mechanically by the rotating shaft  42 , there is no need to provide a stepping motor, a signal cable, and a power cable for driving the working disk  52 .  
     [0043] (2) When the rotating shaft  42  does not rotate the central shaft  51  during rotation of the rotating shaft  42 , the central shaft  51  is prevented from rotation relative to the worktable  22  due to engagement of the first and second engaging elements  31 ,  53 , thereby resulting in good cutting quality. Furthermore, the CNC machine tool of this invention is suitable for cutting comparatively heavy workpieces.  
     [0044] With this invention thus explained, it is apparent that numerous modifications and variations can be made without departing the scope and spirit of this invention. It is therefore intended that this invention be limited only as indicated by the appended claims.