Abstract:
An automatic tool changer in which the load produced when a turret is rotation-driven is reduced, and abrasion in the balls and the like of a speed reducer, and mal-distribution of an axial pressing force are prevented. The speed reducer that drives the turret in the automatic tool changer is constructed by superposing a driving plate, a holder, and a driven plate in the order named. In the driven plate fitted with tools, there is formed a ball groove in a concave-convex shape having the number of cycles corresponding to the number of the tools. In the driving plate, there is provided a ball groove obtained by enlarging the ball groove of the driven plate in the angular direction and copying two cycles. The holder is provided with a plurality of guide holes in the radial direction, which hold their respective balls. The driving plate is rotated by spindle rotation, and the driven plate is driven at a reduced speed of (the number of tools/2) through the balls. It is possible to reduce the load by setting the ball groove of the driven plate at the optimum pressure angle. The balls are dispersed, so that the axial pressure is even, to thereby reduce the abrasion of the balls and ball grooves, and the like.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an automatic tool changer for automatically changing a tool in a machine tool.  
         [0003]     2. Description of Related Art  
         [0004]     As a device for automatically changing a tool to be fixed to the spindle of a machine tool, an automatic changer, in which an impact generated during tool change is lessened, and the moving amount of a spindle head during tool change is reduced, was already developed by the applicant and has been well known (see JP 6-738A).  
         [0005]      FIG. 1  is a schematic view of this automatic tool changer. The automatic tool changer has a vertically movable arm member  4 , a turret  13  having a plurality of tool grippers  12  and holding tool holders  11  (tools). The turret  13  is provided with a speed reducer  5  for selecting a desired tool through the allocating operation, and the tool grippers  12  are so constructed as to rotate to be maintained in a tool change position due to the output of the speed reducer  5 . A spindle  2  to which the tool holders (tools)  11  are fixed is rotatably supported by a spindle head  1 .  
         [0006]     The spindle head  1  has swing cams Csa and Csb for swinging the turret  13  in order to move each of the tool holders  11  held by the corresponding tool gripper  12  to a position where it is fixed to the spindle  2 , and a lift cam CL for mounting and detaching the tool holder  11  with respect to the spindle  2  by moving the turret  13  up and down to move the corresponding tool gripper  12  in the vertical direction. The tool grippers  12  are fastened to a flange of a driven plate of the speed reducer disposed in the turret  13 . Biasing means  18  is fixed in the middle portion of a turret base  13   a  with a fixing pin. One end of the turret base  13   a  is fixed to a turret slider  16  through a rotary shaft  20 , and a swing roller  17  that cooperates with the swing cams Csa and Csb is rotatably fitted in the end portion on the opposite side of the rotary shaft  20 . The biasing means  18  is fixed in the middle portion of the turret base  13   a  with the fixing pin, and the turret base  13   a  is biased anticlockwise around the rotary shaft  20 . The swing roller  17  is so constructed as to be biased against cam faces of the swing cams Cs by the biasing means  18 . With this structure, the swing roller  17  is supported by the swing cams Csa and Csb to be moved relatively on the swing cams Csa and Csb, to thereby swing the turret  13  according to the shapes of the swing cams Csa and. Csb.  
         [0007]     The rotary shaft  20  is coupled to the turret slider  16 . The turret slider  16  is constructed vertically movable along a linear guide, not shown, which is fixed to the arm member  4 . A lift-adjusting member  15  is fixed to the other end of the turret slider  16  with a ball joint  10 , and a lift lever  14  is fixed to the other end of the lift-adjusting member  15 . The lift lever  14  is bent at an angle of about  90  degrees and is rotatably fitted to the arm member  4  at its bending point. A lift roller  9  engaged with the lift cam CL is rotatably fitted to the other end of the lift lever  14 . In  FIG. 1 , reference numeral  3  represents a spindle motor for driving the spindle.  
         [0008]     With the above-described structure, once a tool change command is given, the orientation of the spindle is carried out. At the same time, the spindle head  1  moves upward at fast speed, and the swing roller  17  moves on a flat supporting surface of the swing cam Csa ( FIG. 1  shows a position where the spindle head  1  is raised. Before tool change operation is started, the spindle head  1  is in a descended position, whereas the turret  13  is positioned in an upper position in relation to the spindle head  1 , and the swing roller  17  is positioned in an upper end portion of the swing cam Csa). The lift roller  9  moves in a straight-line portion of the lift cam CL, and the lift operation is not performed. Subsequently, due to the upward motion of the spindle head  1 , the swing roller  17  moves in a curved portion of the swing cam Csa, thereby turning the turret base  13   a  anticlockwise around the rotary shaft  20  and beginning the swing motion of the turret  13 . The tip end of the tool gripper  12  approaches a V-groove of the tool holder  11 . After a roller provided to the tip end portion of the tool gripper  12  is engaged with the V-groove, the roller accurately moves on the V-groove.  
         [0009]     Furthermore, due to the upward motion of the spindle head  1 , the swing roller  17  moves to a flexion of the swing cam Csa and the swing cam Csb. Immediately before the swing motion therebetween is finished, the lift roller  9  is engaged with a flexion of the lift cam CL, thereby turning the lift lever  14  anticlockwise around the rotary shaft, moving the lift-adjusting member  15  and the turret slider  16  in the upward direction, and accelerating the turret base  13   a,  namely the turret  13 , in the same direction with respect to the upward motion of the spindle head  1 . As a result, when the swing motion is finished, due to the upward motion of the spindle head  1  and the lift operation of the turret  13 , the relative speed becomes virtually zero, so that the impact is drastically reduced.  
         [0010]     After the swing motion is finished, the spindle head  1  moves upward at fast speed, and simultaneously the turret  13  begins the lift operation for pulling out the tool holder  11  from the spindle. In other words, the swing roller  17  moves on the swing cam Csb, and the lift roller  9  moves from the top of the flexion of the lift cam CL in a descending direction. This makes the swing motion slight. Additionally, since the lift roller  9  moves in the opposite direction to the direction of moving to the top of the lift cam CL, the lift acceleration acts in the opposite direction, which slows down the upward lift operation. The downward lift operation is started. Due to the relative downward lift operation with respect to the spindle head  1 , the tool holder  11  is pulled out from the spindle  2 .  
         [0011]     After the upward motion of the spindle head  1  is finished, a spindle gear  19  of the spindle  2  and a turret gear  5 c of the speed reducer  5  are engaged with each other. The spindle  2  rotates to rotate the turret  13  through the speed reducer  5 , to thereby carry out the allocation of the desired tool. After the turret-allocating operation is finished, the spindle head  1  descends in the inverse order to the above-mentioned order, and the tool change operation is completed.  
         [0012]      FIG. 5  are explanatory views of the speed reducer used in the above-described conventional automatic tool changer. The speed reducer is formed of a holder  51 , a driving plate  52 , and a driven plate  53 . As shown in  FIG. 5   c,  the driving plate  52  is provided with cogs in its circumferential surface to serve as a turret gear  5   e.  In the end face of the driving plate  52 , a circular cam groove  52   a  with radius r is formed to be eccentric from the rotational center of the turret gear  5   e  by an eccentricity amount Q. In the holder  51 , as shown in  FIG. 5   b,  n+1 oval groove portions  51   a  extending longitudinally along the radial direction are arranged at regular angle intervals on the condition that the speed reduction ratio is n (n=2, 3, 4 . . . ). The examples illustrated in  FIG. 5  show the case where the speed reduction ratio n equals 6. The longitudinal length of each of the oval groove portions  51   a  along an axis is twice or more as great as the eccentricity amount Q in the eccentric circular cam groove  52   a  of the driving plate  52 . Balls  54  are held in the respective groove portions  51   a.  On the surface of the driven plate  53 , as shown in  FIG. 5   a,  there is provided a virtually circular member having a cam groove  53   a  in the shape of petals or a starfish including as many concaves and convexes as the speed reduction ratio n in the radial direction, engaging with the balls  54 . The examples of  FIG. 5  show the case where the speed reduction ratio is 6.  
         [0013]     The driving plate  52  is rotatably fitted to the turret base  13   a,  and the holder  51  is fixed to the turret base  13   a  in a state superposed upon the driving plate  52 . The oval groove portions  51   a  of the holder  51  are made to hold the respective balls  54 , and the balls  54  and the cam groove  52   a  of the driving plate  52  are engaged with each other. Moreover, the driven plate  53  is fitted to the holder  51  to be rotatable and superposed thereupon. The cam groove  53   a  of the driven plate  53  and the balls  54  held by the holder  51  are engaged with each other. The tool grippers  12  are fixed to the driven plate  53 .  
         [0014]     While the driving plate  52  makes one rotation, the balls  54  make one reciprocating motion in the radial direction within the respective groove portions  51   a  of the holder  51  in the state engaged with the cam groove  53   a  of the driven plate. As to the motion of the balls  54  within the groove portions  51   a,  in the cam groove  53   a  of the driven plate  53 , the balls  54  for example move from the top to the top and press the side faces of the cam groove  53   a  between the tops, to thereby move the driven plate  53  for one cycle of the cam groove  53   a.  In other words, since the number of concaves and convexes of the cam groove  53   a  is n, the driven plate  53  moves only by 2π/n with respect to a center angle φ. Therefore, if the speed reduction ratio is 6, the driven plate  53  makes ⅙ rotation while the driving plate  52  makes one rotation, making it possible to obtain ⅙ speed reduction.  
         [0015]     In the above-described conventional automatic tool changer, when the turret  13  is rotation-driven, the load is great, so that it is necessary to moderate the acceleration/deceleration. Furthermore, abrasion of the balls  54  of the speed reducer and a pressing force of the balls  54  are unevenly generated. As a result, there arises the problem that undulation occurs in the rotation of the turret.  
         [0016]     As described, with the speed reducer used in the conventional automatic tool changer, the cam groove  52   a  formed in the driving plate  52  has the circular shape as shown in  FIG. 5 , so that the degree of freedom in design is small, and it is impossible to set a sufficiently small pressure angle. In order to decrease the pressure angle, the eccentricity amount Q of the cam groove  52   a  of the driving plate  52  is made large to increase the motion amount of the balls  54 . By so doing, however, there generates an undercut in the cam groove  53   a  of the driven plate  53 , or a curvature radius of the cam groove  53   a  of the driven plate  53  becomes extremely small. Therefore, the pressure angle should not be reduced. Due to the great pressure angle, the load created when the turret is rotation-driven is great, so that it is necessary to moderate acceleration/deceleration in order to smooth the turret rotation. Therefore, the tool change takes time.  
         [0017]     Furthermore, because of the eccentricity of the cam groove  52   a  of the driving plate  52 , the axial pressing force borne by each of the balls  54  becomes eccentric and uneven, so that the surface pressure borne by each of the balls is locally increased. As a result, the cam grooves  52   a  and  53   a  or balls abrade away, and occasionally do not last for a full duration of life. Moreover, since the balls  54  are unevenly distributed with respect to the surfaces of the driving plate  52  and the driven plate  53 , due to deviation in the axial pressing force borne by each of the balls  54 , there generates undulation during the rotation of the driving plate  52  due to the eccentricity of the axial pressing force borne by each of the balls  54 . Consequently, when the spindle-side gear  19  and the turret gear  5   e  rotate in the state engaged with each other, a backlash in cog surfaces of the gears fluctuates, so that the backlash cannot be properly regulated. As a consequence, there is the problem of loud noises.  
       SUMMARY OF THE INVENTION  
       [0018]     According to one aspect of the present invention, an automatic tool changer for a machine tool includes a speed reducer for reducing a rotational speed of a driving force for turning a plurality of tools to be changed. The speed reducer comprises; a driving plate to which the driving force is inputted, provided rotatably and having a ball-driving groove; a holder provided fixedly on a base of the speed reducer and having guide holds for respectively holding and guiding a plurality of balls movably in a radial direction by restricting circumferential motion of the plurality of balls; and a driven plate to which a tool-holding device for detachably holding the plurality of tools is fixed, provided rotatably and having a ball-driven groove. The driving plate, the holder and the driven plate are coaxially arranged such that the balls respectively held by the guide holes of the holder are engaged with the ball-driving groove of the driving plate and the ball-driven groove of the driven plate, thereby the driven plate is rotated by the driving force inputted to the driving plate. The ball-driven groove of the driven plate is defined by a continuous curved line having a plurality of cycles along a circumference of the driven plate, and the ball-driving groove of the driving plate is defined by a continuous curved line obtained by enlarging two or more cycles of the continuous curved line of the ball-driven groove of the driven plate in a circumferential direction thereof.  
         [0019]     According to another aspect of the present invention, an automatic tool changer comprises: a first gear provided to be rotated with a spindle of a machine tool; a second gear brought into engagement with the first gear at the time of tool selection; and a tool-holding device for detachably holding a plurality of tools to be changed; a speed reducer arranged between the first gear and the tool-holding device, the speed reducer comprising; a driving plate provided rotatably with the second gear and having a ball-driving groove, a driven plate provided rotatably with the tool-holding device and having a ball-driven groove, and a holder fixedly provided between the driving plate and the driven plate and having guide holes for respectively holding and guiding a plurality of balls to be movable in a radial direction by restricting circumferential motion of the plurality of balls. The driving plate, the holder and the driven plate are coaxially arranged such that the balls respectively held by the guide holes of the holder are engaged with the ball-driving groove of the driving plate and the ball-driven groove of the driven plate, thereby rotary motion of the driving plate is converted into radial motion of the balls and then converted into rotary motion of the driven plate to be rotated with a reduced rotational speed. The ball-driven groove of the driven plate is defined by a continuous curved line having a plurality of cycles along a circumference of the driven plate, and the ball-driving groove of the driving plate is defined by a continuous curved line obtained by enlarging two or more cycles of the continuous curved line of the ball-driven groove of the driven plate in a circumferential direction thereof.  
         [0020]     The number of cycles of the continuous curved line defining the ball-driven groove of the driven plate may correspond to the number of plurality of tools detachably held by the tool-holding device.  
         [0021]     The continuous curved line defining the ball-driving groove of the driving plate is slightly enlarged in a radial direction with respect to an average radius of radial strokes of the ball-driven groove of the driven plate.  
         [0022]     A ratio of a rotational speed of the driven plate to a rotational speed of the spindle may be set to a value obtained by dividing an integral multiple of the number of plurality tools detachably held by the tool-holding device by 2.  
         [0023]     Paths of the ball-driving groove and the ball-driven groove may be partially biased in accordance with surface pressure produced on the paths between the driving plate and the driven plate.  
         [0024]     The ball groove formed in the driven plate may be an arbitrary continuous curved line, and it is possible to set a sufficiently small pressure angle. Therefore, the load created during the turret driving can be reduced. This enables rapid acceleration/deceleration of the turret driving at the time of tool selection, which shortens the time for tool change. Since the ball groove is designed to have a plurality of cycles in one round of the driving plate. As a result, the balls equally bear the axial pressing force, which prevents abrasion of the ball grooves of both the driving and driven plates and of the balls, and improves durability. Furthermore, the balls are dispersedly positioned on the surfaces of the driving plate and the driven plate, so that the balls equally bear the axial pressing force, which prevents undulation in rotation of the turret gear. Consequently, the fluctuation of a backlash in the cog surfaces of the gears is suppressed, and it is possible to constantly retain a proper backlash and reduce the noise level during turret allocation. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a schematic view of an automatic tool changer according to one embodiment of the present invention;  
         [0026]      FIG. 2  is a partial sectional view of a speed reducer according to the same embodiment;  
         [0027]      FIG. 3   a  to  FIG. 3   c  are explanatory views showing a speed reduction principle of the speed reducer;  
         [0028]      FIG. 4   a  to  FIG. 4   d  are explanatory views showing the operation of the speed reducer; and  
         [0029]      FIG. 5   a  to  FIG. 5   c  are explanatory views showing the operation of a speed reducer used in a conventional automatic tool changer. 
     
    
     DETAILED DESCRIPTION  
       [0030]     The present invention is obtained by improving a speed reducer applied to an automatic tool changer shown in  FIG. 1 , and is an improvement of the speed reducer for causing a turret to make a reduced rotation.  
         [0031]     According to the present invention, a construction of the automatic tool changer other than the speed reducer is identical to that of a conventional automatic tool changer, and the operation thereof is the same as that of the conventional automatic tool changer shown in  FIG. 1 , apart from an operating portion of the speed reducer. Therefore,  FIG. 1  is a schematic view of an automatic tool changer according to one embodiment of the present invention at the same time.  
         [0032]      FIG. 2  is a partial sectional view of the speed reducer applied to the automatic tool changer according to the one embodiment of the present invention. A speed reducer  5  disposed in a turret  13  is formed of a driving plate  5   a,  a holder  5   b,  a driven plate  5   c,  and balls  5   d.  The driving plate  5   a  is rotatably fitted to a turret base  13   a  by using a bearing  5   i,  and the holder  5   b  is fixed to the turret base  13   a.  A flange  5   f  of the driven plate  5   c  constructing tool-holding means is rotatably fitted to an axis portion of the holder  5   b  by using a bearing  5   j.  The holder  5   b  is so fixed as to be sandwiched between the driving plate  5   a  and the driven plate  5   c  from both sides. As mentioned below, the balls  5   d  are held in guide holes provided to the holder  5   b,  and ball grooves formed in the driving plate  5   a  and the driven plate  5   c  are engaged with the balls.  
         [0033]     Cogs are formed in a circumferential surface of the driving plate  5   a,  thereby constructing a turret gear  5   e  engaged with a spindle gear  19  provided to a spindle  2 . Between the turret base  13   a  and the driving plate  5   a,  a positioning ball  5   h  for positioning the driving plate  5   a  in a tool change position is so disposed as to press the driving plate  5   a  with a spring  5   g.  In the driving plate  5   a,  there are formed hollows  5 L in positions for engaging with the positioning ball  5   h  so that the positioning is carried out each time the driving plate  5   a  makes ½ rotation.  
         [0034]     A plurality of tool grippers  12  are fitted to the flange  5   f  formed integrally with the driven plate  5   c.  In short, the flange  5   f  forms the tool-holding means. Reference character  5   k  represents a nut for holding the bearing  5   j.    
         [0035]      FIG. 3   a  is a plan view of the driving plate  5   a,    FIG. 3   b  is a plan view of the holder  5   b,  and  FIG. 3   c  is a plan view of the driven plate  5   c.    
         [0036]     In this embodiment, the number of tools is  14 . A gear ratio between the spindle gear  19  and the turret gear (driving plate  5   a )  5   e  is 1:2, and a speed ratio between the driving plate  5   a  and the driven plate  5   c  of the speed reducer  5  is 7:1.  
         [0037]     First, the driven plate  5   c  will be described. In an end face of the driven plate  5   c,  there is formed a ball groove  6   c  that is engaged with the balls  5   d  and forms a cam groove. The ball groove  6   c  is made up of a groove formed into a continuous curved line having cycles in the concave-convex shape like sine waves in a radial direction in a state where a circle with an average radius R is positioned at the center. The ball groove  6   c  is formed so that inner corners of the ball groove  6   c,  shown by reference characters A and B in  FIG. 3   c,  are not extremely small convex bent portions, and so that an area shown by reference character C in the drawing may have a minimum pressure angle that is sufficiently small (30 degrees or less). In this embodiment, the turret is capable of holding the  14  tools. Therefore, according to the number of the tools, the concaves/convexes of the ball groove  6   c  of the driven plate  5   c  is a continuous curved line repeating 14 cycles (1 cycle α=360 degrees/14) in one round of the driven plate  5   c.    
         [0038]     In this embodiment, as shown in  FIG. 3   b,  the holder  5   b  is provided with guide holes  6   b  radially arranged in positions determined by dividing 360 degrees into 16 equal parts, so as to stretch in a radial pattern. The balls  5   d  are fitted into the respective guide holes  6   b.  The balls  5   d  are restrained in circumferential motion, and are movable only in the radial direction. The number of the guide holes  6   b  that can be disposed in the holder  5   b  is (the number of cycles of the ball groove  6   a  in one rotation of the driving plate  5   a )×(the required speed ratio+1). In this embodiment, the number of cycles of the ball groove  6   a  in one rotation of the driving plate  5   a  is 2, and the speed reduction ratio of the speed reducer is 7, so that the equation, 2×(7+1)=16, is established. Needless to say, even if some of the guide holes  6   b  are thinned out after disposition, the equation can be established in principle.  
         [0039]     The driving plate  5   a  is also provided with the ball groove  6   a  forming a cam groove. In this embodiment, the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1. The ball groove  6   a  of the driving plate  5   a  is a virtually oval-shaped curved line obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be seven times larger in an angular direction and copying the same. In short, the ball groove  6   a  has a cam-curved line with two cycles corresponding to one round of the driving plate  5   a.  As mentioned, two conical hollows are formed in a back surface of the driving plate  5   a  such that they are positioned each time the driving plate  5   a  makes ½ rotation, and the ball  5   h  is biased with the spring  5   g.    
         [0040]     Moreover, in the present embodiment, the ball groove  6   a  of the driving plate  5   a  is slightly enlarged in the radial direction to be greater than the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be seven times larger in the angular direction and copying the same. When the average radius R of radial strokes is taken as the center, and the average R and a radial distance of the ball groove  6   c  of the driven plate  5   c  are enlarged and copied to be about 1.03 times larger, this creates a state where the balls  5   d  are in tighter contact with the concave portions of the ball groove  6   c  of the driven plate  5   c.  This makes it possible to further reduce the surface pressure produced in the convex portions A and B of the ball groove  6   c  of the driven plate  5   c.    
         [0041]     In other words, according to the present invention, the ball groove  6   c  of the driven plate  5   c  is formed in a waved shape including the number of concaves and convexes, which is obtained by multiplying the number of cycles of the ball groove of the driving plate  5   a  by the speed ratio required in the speed reducer so that the ball groove  6   c  has a desired pressure angle (ideal pressure angle) γ. Subsequently, the ball groove  6   c  of the driven plate  5   c  is slightly enlarged in the radial direction with the average radius R of the radial strokes of the ball groove  6   c  in the driven plate  5   c  at the center, and is also enlarged to be several times (seven times in the embodiment) larger in the angular direction and copied, to thereby obtain the shape of the ball groove  6   a  of the driving plate  5   a  in order to be matched with the shape of the ball groove  6   c  of the driven plate  5   c.  As described, the present invention is characterized in that the desired pressure angle γ is first decided to determine the shape of the ball groove  6   c  of the driven plate  5   c,  and the ball groove  6   a  of the driving plate  5   a  is formed to be matched with the shape of the ball groove  6   c  of the driven plate  5   c,  which makes it possible to carry out the driving at the desired pressure angle.  
         [0042]     At the time of allocating the tools, when the turret gear  5   e  is engaged with the spindle gear  19 , and the driving plate  5   a  having the turret gear  5   c  is rotated by rotation of the spindle  2 , the balls  5   d  held in the respective guide holes  6   b  of the holder  5   b  receive a force from the ball groove  6   a  of the driving plate  5   a.  However, since the circumferential motion thereof is restrained by the guide holes  6   b,  they move in the radial direction. Due to the radial motion of the balls  5   d,  the ball groove  6   c  of the driven plate  5   c  receives the force on concave-convex waved side surfaces (a portion shown by reference character C in  FIG. 3   c ) of the ball groove  6   c,  to thereby rotate the driven plate  5   c.  The flange (tool-holding means)  5   f  formed integrally with the driven plate  5   c  also rotates together. This rotates the tool grippers  12  fitted with the flange (tool-holding means)  5   f.  Since the ball groove  6   c  of the driven plate  5   c  is set to have the ideal small pressure angle γ, the load created when the turret is driven is reduced.  
         [0043]      FIG. 4  show a state in which the driven plate  5   c,  the holder  5   b  and the balls  5   d  according to the embodiment are disposed, and each of the balls  5   d  moves while the driven plate  5   c  moves through a rotation angle between two adjacent tools in order to allocate one of the tools.  
         [0044]      FIG. 4   a  shows a state in which the motion is started,  FIG. 4   b  shows a state in which the driven plate  5   c  moves through ⅓ cycle (one cycle α=360/14, and α/3=8.57 degrees),  FIG. 4   c  shows a state in which the driven plate  5   c  moves through  2 / 3  cycle (=17.14 degrees), and  FIG. 4   d  shows a state in which the driven plate  5   c  moves through one cycle (α=25.71 degrees).  
         [0045]     In  FIG. 4 , along with the rotation of the driving plate  5   a,  the disposition of the balls  5   d  is rotated by a sevenfold moving amount in a rotating direction opposite to the driven plate  5   c  because of the oval-shaped ball groove  6   a.  While the driven plate  5   c  rotates through an angle of 25.71 degrees corresponding to an angle between two adjacent tool grippers  12 , the oval-shaped ball disposition is rotated at an angle of 180 degrees. In other words, the driving plate  5   a  makes a half rotation, and the half rotation of the driving plate  5   a  causes the motion only through the angle between the tool grippers  12  fitted to the flange (tool-holding means)  5   f  of the driven plate  5   c.    
         [0046]     In the embodiment described above, with respect to the  14  tools on the turret  13 , the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1, and the speed ratio between the driving plate  5   a  and the driven plate  5   c  is 7:1. As a result, the speed ratio between the spindle and the turret is 14:1. In other words, the driving plate  5   a  makes ½ rotation each time the spindle makes one rotation, and the driven plate  5   c  makes a 360/14=25.71 degree rotation due to ½ rotation of the driving plate  5   a,  to thereby allocate one of the tools.  
         [0047]     Although in the above embodiment, the rotational speed ratio of the turret (driven plate  5   c ) to the speed of the spindle  2  is 14:1, the speed ratio is not limited to this. To be brief, an object is to complete the positioning of the spindle into a phase where the tool can be held at the point when the allocation of the turret is finished. Therefore, the tool holder can be fixed to the spindle in a phase where keys in two places of the end surface of the spindle and key grooves formed in two places of a tool flange portion are matched with each other. Accordingly, if it is not necessary to recreate two sides of the phase of the tool to be held by the spindle, it is possible to set the speed ratio to be half with respect to the  14  tool holders  11  on the turret  13 , that is to say, 7:1, and it is also possible to set a greater speed ratio.  
         [0048]     To be specific, a tool position can be allocated by setting the rotational speed of the turret (driven plate  5   c ) to be  1 , and setting the rotational speed of the spindle  2  to be a value equal to the number found by dividing an integral multiple of the number of the tool grippers (the number of the tools) provided to the turret by 2. To put it the other way around, the driven plate  5   c  should be designed to make a (2/an integral multiple of the number of the tools) rotation while the spindle makes one rotation. If this is formularized, assuming that the value by which the number of the tools is multiplied is X, the number of rotations Y of the turret (driven plate  5   c ) should be set to correspond to a rotation of the following equation 1 with respect to one spindle rotation. 
 
 Y =2/the number of tools× X    (1) 
 
         [0049]     For example, correspondence between the practicable number of tools and the speed ratio between the spindle and the turret can be organized as below.  
         [0050]     Where the number of tools is 10, the speed ratio is: 
        5:1, 10:1, 15:1, 20:1 . . .        
 
         [0052]     Where the number of tools is 14, the speed ratio is: 
        7:1, 14:1, 21:1, 28:1 . . .        
 
         [0054]     Where the number of tools is 21, the speed ratio is: 
         21 : 2 ,  21 : 1 ,  42 : 3 ,  42 : 1  . . .        
 
         [0056]     Formed in the driven plate  5   c  is the ball groove  6   c  in the concave-convex shape in which the number of cycles equals (the number of cycles of the ball groove of the driving plate)×(the speed ratio required in the speed reducer). Provided in the driving plate  5   a  is the ball groove  6   a  having the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be (the speed ratio required in the speed reducer) times larger in the angular direction and copying the same. Formed in the holder  5   b  are the guide holes  6   b  as many as (the number of cycles of the ball groove  6   a  of the driving plate  5   a )×(the speed ratio required in the speed reducer+1).  
         [0057]     The Case Where the Number of Tools is 10, and the Speed Ratio is 5:1  
         [0058]     Let us say that the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1. In the driven plate  5   c,  there is formed the ball groove  6   c  in the shape concave-convex having (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer=2.5)=5 cycles. In the driving plate  5   a,  there is provided the ball groove  6   a  (2 cycles) having the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be (the speed ratio required in the speed reducer=2.5) times larger in the angular direction and copying the same. In the holder  5   b,  there are formed the guide holes  6   b  as many as (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer+1=3.5)=7.  
         [0059]     In this example, the spindle  2  makes five rotations, and the turret (driven plate  5   c,  tool-holding means  5   f ) makes one rotation. While the spindle makes one rotation, the turret (driven plate  5   c,  tool-holding means  5   f ) makes ⅕ rotation. Every time the spindle makes one rotation, the driving plate  5   a  makes ½ rotation. Due to the ball groove  6   a,  the balls  5   d  are caused to make one reciprocation and moved through one cycle of a concave-convex cycle of the ball groove  6   c  of the driven plate  5   c,  to thereby cause the turret (driven plate  5   c,  tool-holding means  5   f ) to make ⅕ rotation.  
         [0060]     The Case Where the Number of Tools is 10, and the Speed Ratio is 10:1  
         [0061]     Let us say that the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1. In the driven plate  5   c,  there is formed the ball groove  6   c  in the concave-convex shape having (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer=5)=10 cycles. In the driving plate  5   a,  there is provided the ball groove  6   a  (2 cycles) having the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be (the speed ratio required in the speed reducer=5) times larger in the angular direction and copying the same. In the holder  5   b,  there are formed the guide holes  6   b  as many as (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer+1=6)=12.  
         [0062]     The turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/10 rotation while the spindle makes one rotation. Since the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1, while the spindle makes one rotation, the driving plate  5   a  makes ½ rotation to rotate for one cycle of the ball groove  6   a,  thereby causing the balls  5   d  to make one reciprocation, moving the balls  5   d  through one cycle of the concave-convex cycle of the ball groove  6   c  of the driven plate  5   c,  and causing the turret (driven plate  5   c,  tool-holding means  5   f ) to make 1/10 rotation.  
         [0063]     The Case Where the Number of Tools is 10, and the Speed Ratio is 15:1  
         [0064]     Let us say that the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1. In the driven plate  5   c,  there is formed the ball groove  6   c  in the concave-convex shape having (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer=7.5)=15 cycles. In the driving plate  5   a,  there is provided the ball groove  6   a  (2 cycles) having the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be (the speed ratio required in the speed reducer=7.5) times larger in the angular direction and copying the same. In the holder  5   b,  there are formed the guide holes  6   b  as many as (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer+1=8.5)=17. While the spindle  2  makes 15 rotations, the turret (driven plate  5   c,  tool-holding means  5   f ) makes one rotation. Each time the spindle makes one rotation, the turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/15 rotation. Since the driving plate  5   a  makes ½ rotation to rotate for one cycle of the ball groove  6   a  of the driving plate  5   a  while spindle makes one rotation, the balls make one reciprocation and move for one cycle of the concave-convex cycle of the ball groove  6   c  in the driven plate  5   c.  Accordingly, the turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/15 rotation. Similarly, while the spindle makes 1.5 rotation, the driven plate is caused to make 1/10 rotation corresponding to one tool.  
         [0065]     The Case Where the Number of Tools is 14, and the Speed Ratio is 7:1  
         [0066]     Let us say that the speed ratio between the spindle gear  19  and the turret gear  5   e  is 2:1. In the driven plate  5   c,  there is formed the ball groove  6   c  in the concave-convex shape having (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer=3.5)=7 cycles. In the driving plate  5   a,  there is provided the ball groove  6   a  (2 cycles) having the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be (the speed ratio required in the speed reducer=3.5) times larger in the angular direction and copying the same. In the holder  5   b,  there are formed the guide holes  6   b  as many as (the number of cycles of the ball groove of the driving plate=2)×(the speed ratio required in the speed reducer+1=4.5)=9.  
         [0067]     While the spindle  2  makes 7 rotations, the turret (driven plate  5   c,  tool-holding means  5   f ) makes one rotation. Therefore, every time the spindle makes one rotation, the turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/7 rotation. Since the driving plate  5   a  makes ½ rotation to rotate for one cycle of the ball groove  6   a  every time the spindle makes one rotation, the balls are caused to make one reciprocation and move for one cycle of the concave-convex cycle of the ball groove  6   c  in the driven plate  5   c,  and the turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/7 rotation.  
         [0068]     The same applies to the case in which the number of tools is 21, so that descriptions will be omitted.  
         [0069]     In the above embodiment, the number of cycles of the driven plate  5   c,  which is enlarged and copied to the driving plate  5   a,  is 2. However, the concave-convex cycle of the driven plate  5   c  may be enlarged and copied such that the number of cycles to be copied to the driving plate  5   a  is an integral value.  
         [0070]     For example, in case that the number of tools is 21, that the speed ratio between the spindle  2  and the turret (driven plate  5   c,  tool-holding means  5   f ) is 21:1, and that the number of cycles of the driving plate is 3,  
         [0071]     the speed ratio between the spindle gear  19  and the turret gear  5   e  is 3:1. In the driven plate  5   c,  there is formed the ball groove  6   c  in the concave-convex shape having (the number of cycles of the ball groove of the driving plate=3)×(the speed ratio required in the speed reducer=7)=21 cycles. In the driving plate  5   a,  there is provided the ball groove  6   a  (3 cycles) having the shape obtained by enlarging the ball groove  6   c  of the driven plate  5   c  to be (the speed ratio required in the speed reducer=7) times larger in the angular direction and copying the same. In the holder  5   b,  there are formed the guide holes  6   b  as many as (the number of cycles of the ball groove of the driving plate=3)×(the speed ratio required in the speed reducer+1=8)=24.  
         [0072]     While the spindle  2  makes 21 rotations, the turret (driven plate  5   c,  tool-holding means  5   f ) makes one rotation. Therefore, each time the spindle makes one rotation, the turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/21 rotation. While the spindle makes one rotation, the driving plate  5   a  makes ⅓ rotation to rotate for one cycle of the ball groove  6   a  of the driving plate  5   a,  so that the balls are caused to make one reciprocation and move for one cycle of the concave-convex cycle of the ball groove in the driven plate  5   c,  and the turret (driven plate  5   c,  tool-holding means  5   f ) is caused to make 1/21 rotation.  
         [0073]     As described above, by determining the number of cycles of the ball groove  6   c  of the driven plate  5   c,  which is copied to the driving plate  5   a,  the speed reduction ratio in the speed reducer  5  is determined. Based on the speed reduction ratio, the speed reduction ratio between the spindle  2  and the speed reducer  5  (speed reduction ratio between the spindle gear  19  and the turret gear  5   e ), which is an input to the speed reducer  5  to be the final speed reduction ratio of the turret  13  (driven plate  5   c,  tool-holding means  5   f ) with respect to the spindle  2 , may be determined.