Patent Publication Number: US-2011074121-A1

Title: Chuck with stationary actuator

Description:
FIELD OF THE INVENTION 
     The present invention relates to chuck. More particularly this invention concerns a chuck with a stationary actuator. 
     BACKGROUND OF THE INVENTION 
     A typical chuck has a generally stationary support and a spindle centered on an axis and rotatable in the support about the axis. This spindle forming a central guide and having forward therefrom a forwardly open seat for a tool or workpiece. A plurality of jaws are shiftable along the guide between an inner position closely radially juxtaposed and capable of gripping the tool or workpiece in the seat and an outer widely radially juxtaposed position in which the tool or workpiece can be shifted into or out of the seat. A pull rod coupled to the jaws and projecting rearward therefrom. 
     An actuator is connected between the pull rod and the support and serves to axially displace it. This actuator is frequently a source of problems because it must transmit axial force between a nonrotating support and a rotating rod, with the later often moving a high speed. Thus at least a part of the actuator must be fixed or nonrotating, and another must be able to act on a rotating part without heat buildup or damage. 
     OBJECTS OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved chuck with a fixed actuator. 
     Another object is the provision of such an improved chuck with a fixed actuator that overcomes the above-given disadvantages, in particular that is of simple and reliable construction, yet which ensures actuation of the chuck even when used at high speed. As a result the assembly is often quite long and complicated. 
     SUMMARY OF THE INVENTION 
     A chuck has according to the invention a generally stationary support and a spindle centered on an axis, rotatable in the support about the axis, forming a central guide, and having forward therefrom a forwardly open seat for a tool or workpiece. A plurality of jaws are shiftable along the guide between an inner position closely radially juxtaposed and capable of gripping the tool or workpiece in the seat and an outer widely radially juxtaposed position in which the tool or workpiece can be shifted into or out of the seat. A pull rod coupled to the jaws projects rearward therefrom. A central plate is carried on the pull rod, and a rear plate spaced rearward of the central plate is rotationally fixed to the spindle. At least one push rod axially shiftable in the rear plate has a front end engageable with the central plate and a rear end projecting rearward from the rear plate. At least one spring braced between the spindle and the central plate urges the central plate, push rod, pull rod, and jaws rearward into the rear locking position of the jaws. A cylindrically tubular piston axially is shiftable in the support between a front position bearing axially forward opposite to the spring on the push rod and therethrough on the central plate, pull rod, and jaws and a rear position axially spaced rearward of the push rod. 
     This configuration has the advantage that the pull rod can be very short. Another advantage is that due to the annular face of the cylindrical piston, the push rod can be subjected to load in any rotational position of the spindle. Since, however, the actuator is only engaged with the push rod or rods to open the chuck, that is to release a tool or workpiece or take in a fresh tool or workpiece, it is acting on a stationary spindle assembly since tools or workpieces are only changed in a nonrotating chuck. 
     It has proven to be advantageous for the chuck if the cylindrical piston has an annular rear flange with a first slide-type ring seal projecting outward and a second slide-type ring seal projecting inward so that the movability and guidance of the cylindrical piston can be improved. 
     Furthermore, the actuator can include a front compartment between a front face of the flange of the cylindrical piston and a flange of the support confronting the spindle, and a rear release compartment behind the cylindrical piston&#39;s annular base flange opposite the gripping compartment, and that a third slide-type seal ring projects inward of the annular support flange against the piston. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing whose sole FIGURE is a partly schematic longitudinal cross section through the invention. 
     
    
    
     SPECIFIC DESCRIPTION 
     A chuck according to the invention has a spindle  1  supported by bearings  21  in a stationary support  2  for rotation about an axis A on which the spindle  2  is centered and along which it extends. The spindle  1  is formed at an axial front (left in the drawing) end with a rearwardly tapered seat  22  for a tool or workpiece  23 . Generally centrally it forms a standard guide  24  for an array of jaws  3  that can be shifted between the illustrated rear position in which they grip and lock the tool or workpiece  23  in the seat  22  and an unillustrated forward position in which they are radially spread so the tool or workpiece  12  can move in and out of the seat  22 . A small coil spring  25  biases the jaws  3  into the spread position. 
     A pull rod  4  axially shiftable in the spindle  1  has a front end engaging the jaws  3  and shaped to be able to shift them axially between their illustrated rear locking position and their unillustrated front releasing position. This rod  4  has a rear end fixed, typically by a screwthread, in a ring  5  that is axially shiftable in the spindle  1  but prevented from rotating relative thereto by axially extending bolts  26  screwed into the spindle  2 . At least one compression spring  8 , normally an array of angularly spaced such springs  8 , is braced axially between respective front seats in the spindle  1  and respective rear seats in the plate  5  so that the jaws  3  are forcibly biased into the rear locking position. The heads of the bolts  26  forwardly press a closing ring or plate  6  through which extends at least one push rod  7 , normally an annular array of angularly spaced such rods  7 , against a rearwardly directed shoulder  28  of the spindle  2  to axially and rotationally fix the plate  6  in the spindle  2 . The front end of each push rod  7  is screwed into a respective seat in the ring  5  and its rear end  13  projects from the rear face of the plate  6 . Thus a forward pressure on the push rods  7  will be effective on the ring  5  and through it on the rod  4  to move the jaws  3  against the force of their springs  8  into the forward releasing position. This is all generally standard and all the above-described parts rotate jointly with the spindle  3  about the axis A. 
     According to the invention a fixed actuator is formed by an annular piston  9  that can shift axially in but that does not rotate relative to the stationary support  2 . This piston  9  has a front face  10  that lies in a plane parallel to the rear faces of the rear ends  13  of the rods  7 . It also has a rear flange  16  provided with seal rings  11  and  12  that define in the support  2  a pressurizable rear compartment  15  and a front flange  17  that forms a front compartment  14  sealed by a seal ring  18  of the support  2 . Pump means shown schematically at  27  is connected to the compartments  14  and  15  by conduits  19  and  20  formed in the fixed support  2  to pressurize one or the other of these compartments  14  and  15 . 
     When according to the invention the rear compartment  15  is pressurized, the piston  9  moves out of its illustrated rear position into a front position engaging the rear ends  13  of the rods  7 , pressing them, the ring  5 , the rod  4 , and the jaws  3  forward to move these jaws  3  against the force of the springs  8  into the front releasing position. When the front compartment  14  is pressurized the piston  9  withdraws to the illustrated position and the springs  8  move the parts back into the rear locking position. 
     Thus pressurization of the rear compartment  15  opens the chuck so that it can receive or release a tool or workpiece  23 . Pressurization of the front compartment  14  allows the springs  8  to close the chuck and clamp the tool or workpiece  23 . Once the chuck is closed, the actuator is out of contact with the rotating parts, and in fact this closed compartment can be maintained simply by not letting fluid into or out of the compartments  14  and  15 .