Patent Publication Number: US-2011076108-A1

Title: Swivel spindle head with gear device driven by multiple torque motors

Description:
FIELD OF THE INVENTION 
     The present invention relates to a swivel spindle head with gear device driven by multiple torque motors, and more particularly, to a swivel spindle head with gear device capable of preventing the problem of backlash from happening in its gear device and the same time reducing its output power loss by the control of a plurality of synchronized torque motors while enabling at least one of the plural torque motors to be configured with an additional rotary encoder for enhancing the control of the synchronization of the torque motors. 
     BACKGROUND OF THE INVENTION 
     With rapid advance in the calculation speed of the CNC controllers in today&#39;s machine tools and in addition to the ever-evolving CAD/CAM software, the use of multiple-axes machining technology is becoming more and more popular and common as well. In conventional multiple-axes machine tools such as five axes milling machines, the swivel spindle head is controlled by remotely mounted servo motors which use timing belts, worm gears and worm wheels, coupled to rotate the spindle head. However, it either suffers the problem of insufficient toque, or it will have a backlash problem resulting from the wear and tear of its worm gears and worm wheels as then are usually made of copper. Some prior arts had addressed the aforesaid problems by designing a swivel spindle head to be driven directly by torque motors, in short, a direct drive swivel spindle head is provided which is featuring by its ability to operate at low rotation speed and high torque. Nevertheless, when a swivel spindle head requires larger torque output, the overall volume of it will increase with the increasing of its torque motor size. Thus, it is in need of a swivel spindle head design for enabling the same to have larger torque output without the trading of the increasing of its volume, and also with lower manufacture cost as well. 
     There is a gearless, direct drive, multiple axes rotary spindle head for a machine tool, disclosed in U.S. Pat. No. 5,584,621, entitled “Direct drive multiple axes rotary spindle head for milling machine”. However, as the aforesaid spindle head has two torque motors, being arranged symmetrically for directly driving and controlling the rotation, it is required to have the two torque motors to be replaced by some other torque motors with larger torque output when the rotary spindle head requires higher torque, and thus the manufacture cost is increased. 
     Another such direct drive rotary spindle head is disclosed in U.S. Pat. No. 7,470,095, entitled “Mobile milling head with torque motor drive”. Its reduction gear system is composed of a pair of driving and driven gears while the driven gear is the assembly of two separate plates capable of rotating relative to each other for backlash compensation. However, it is noted that not every tooth of the gears in the reduction gear system can free from backlash by the aforesaid design, and also as the driven gear is composed of two separate plates, the clamping of the two can be loosen when the driven gear is subjected to a comparatively large torque so that its mechanical reliability might not be satisfactory. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide a swivel spindle head with gear device capable of preventing the problem of backlash from happening in its gear device and the same time reducing its output power loss by the control of a plurality of synchronized torque motors while enabling at least one of the plural torque motors to be configured with an additional rotary encoder for enhancing the control of the synchronization of the torque motors. 
     To achieve the aforesaid object, the present invention provides a swivel spindle head with gear device driven by multiple torque motors is disclosed, which comprises: a tool spindle, having a first shaft and a second shaft being radially disposed at two opposite sides of the tool spindle while sharing a common axial line; a plurality of torque motors, radially disposed at a side of the tool spindle; and a reduction gear set, radially disposed at a side of the tool spindle opposite to the plural torque motors, composed of a plurality of driving gears and a driven gear while each driving gear is further split into two gears; wherein the amount of the plural driving gears is the same as that of the plural torque motors while enabling each of the plural driving gears to connect with a rotor shaft of its corresponding torque motor, and the same time, connecting the driven gear on the second shaft of the tool spindle. 
     Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein: 
         FIG. 1  shows the appearance of a swivel spindle head with gear device driven by multiple torque motors according to an embodiment of the invention. 
         FIG. 2  shows the internal structure of the swivel spindle head of  FIG. 1  relating to its torque motor arrangement as the caps are removed. 
         FIG. 3  shows the internal structure of the swivel spindle head of  FIG. 1  relating to its reduction gear set as the caps are removed. 
         FIG. 4  is a front view of  FIG. 2 . 
         FIG. 5  is a front view of  FIG. 3 . 
         FIG. 6  is an A-A sectional view of  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     Please refer to  FIG. 1 , which shows the appearance of a swivel spindle head with gear device driven by multiple torque motors according to an embodiment of the invention. In  FIG. 1 , the swivel spindle head  100  of the invention has a tool spindle  10 , which is used for holding a cutting tool  70  for a milling process. 
     As shown in  FIG. 1  to  FIG. 3  and  FIG. 6 , there is a frame  20  mounted on the top of the tool spindle  10  while enabling a first space  21  and a second space  22  to be formed respectively and radially at two opposite sides of the tool spindle  10 . As shown in  FIG. 6 , there is a plurality of torque motors  50  being arranged inside the first space  21  while there is a reduction gear set  60  being arranged inside the second space  22 . Moreover, there are two caps  23 ,  24  being arranged on the frame  20  at positions corresponding to the first space  21  and the second space  22  respectively for covering the two as the two caps  23 ,  24  are being fixedly secured by use of bolts  26 , by that the plural torque motors  50  and reduction gear set  60  are sealed inside the frame  20  for protection and aesthetic purposes. It is noted that the frame  20  can be fabricated in a manner selected from the group consisting of: it is an integrally formed one-piece component and it is a combined component formed by the assembly of a plurality of parts. In addition, there is an interface  25  fitting on the top of the frame  20  to be used for fixedly securing the swivel spindle hand  100  or for coupling to a rotate component so as to integrate the swivel spindle head  100  onto a machine tool as the machine tool can be a device selected from the group consisting of: a horizontal machine tool and a vertical machine tool. 
     As shown in  FIG. 1  to  FIG. 3  and  FIG. 6 , the tool spindle  10  has a first shaft  11   a  and a second shaft  11   b , which are radially disposed at two opposite sides of the tool spindle  10  while sharing a common axial line C. Moreover, the first shaft  11   a  is arranged passing through the first space  21  while the second shaft  11   b  is arranged passing through the second space  22 . As shown in  FIG. 6 , there is at least one bearing  12  arranged at a side of the first shaft  11   a  and also the second shaft  11   b  as well, which are used for enabling the frame to perform a swivel movement. In addition, there are an angular encoder  30  and a plurality of braking elements  40  being arranged at the common axial line C of the first shaft  11   a  and the second shaft  11   b . In this embodiment, the angular encoder  30  is disposed inside the first space  21  while the plural braking elements  40  are disposed inside the second space  22 , that is, the angular encoder  30  is disposed at a side of the tool spindle  10  while the braking elements  40  are disposed at another side of the tool spindle  10  radially opposite to the angular encoder  30 . However, in another embodiment, the plural braking elements  40  can be disposed inside the first space  21  while the angular encoder  30  can be arranged inside the second space  22 , or the braking elements  40  can be disposed in a space at the same side of the angular encoder  30 . It is noted that there should be at least one braking element  40  in the swivel spindle head, however, the number of the braking elements  40  can be determined as actual required. 
     As shown in  FIG. 2 ,  FIG. 4  and  FIG. 6 , each of the plural torque motors  50  has a stator  51  and a rotor  52 , in that the stator  51 , being shaped like a hollow cylinder, is made of electromagnetic coil and is fixedly secured on the frame  20 , while the rotor, also shaped like a hollow cylinder received inside the stator  51 , is made of a magnetic material so as to generate torque under electromagnetic interaction. Moreover, there is a rotor shaft  53  arranged inside the rotor  52  which has at least one set of supporting bearing  54  mounted thereat for enhancing the rigidity and precision of the rotor shaft  53 , as shown in  FIG. 6 . In addition, for synchronizing the plural torque motors  50 , there is at least one rotor shaft  53  in the plural torque motors  50  to be configured with a rotary encoder  55 . 
     As shown in  FIG. 3 ,  FIG. 5  and  FIG. 6 , the reduction gear set  60  is comprised of a plurality of driving gears  61  and a driven gear  62 , in which each driving gear  61  is split into two gears  61   a ,  61   b . It is noted that each driving gear  61  is engaged with the driven gear  62  and the amount of the plural driving gears  61  is the same as that of the plural torque motors  50  while enabling each of the plural driving gears  61  to connect with a rotor shaft  53  of its corresponding torque motor  50  as the rotor shaft  53  is simultaneously engaged with the rotor  52 . Moreover, the driven gear  62  is disposed on the common axial line C of the first shaft  11   a  and the second shaft  11   b  while being enabled to engage with the second shaft  11   b.    
     As shown in  FIG. 4  and  FIG. 6 , when the plural torque motors  50  are being activated to rotate, the plural driving gears  61  are being driven to rotate at the same time and thus bring along the driven gear  62  to rotate accordingly. As each driving gear  61  is split into two gears  61   a ,  61   b , the two gears  61   a ,  61   b  are capable of adjusting relative to each other for compensating the backlash between the driving gear  61  and the driven gear  62 . Moreover, as the second shaft  11   b  is designed to be engaged with the driven gear  62 , the output torque through the first shaft  11   a  and the second shaft  11   b  can be amplified several times to drive the tool spindle  10  for swivel process. It is noted that the angular encoder  30 , at this moment, is used for precisely positioning the angle of the tool spindle  10  while the braking elements  40  are used for tightly and fixedly clamping the tool spindle  10 . 
     To sum up, the present invention provides a swivel spindle head with gear device driven by multiple torque motors which is capable of effectively compensating the backlash between its driving gears and driven gear so as to achieve a comparatively higher mechanical reliability as each of its driving gears is split into two gears. In addition, the cost resulting from the torque motors and gear sets can be greatly reduced comparing with those prior arts under the same torque output requirement. Moreover, for enhancing the synchronization of the plural torque motors, there is at least one rotor shaft in the plural torque motors to be configured with a rotary encoder. That is, the present invention use a plurality of synchronized torque motors as power source while enabling their cooperative output torque to be amplified by the use of a reduction gear set, by that not only it can achieve a torque output several times larger than the conventional direct drive multiple axes rotary spindle heads, but also the output torque can be increased when required simply by changing the reduction ratio of the reduction gear set without replacing its torque motors and thus the size and cost of the swivel spindle head will not be greatly increased.