Abstract:
An electric compression press is disclosed comprising a frame having a fixed plate and a movable plate, a first member rotationally fixed in a stationary member and having a first gear set. A second member is rotationally fixed in the stationary member and has second gear teeth and third gear teeth, the second gear teeth being engaged with the first gear set of the first member. A third member is provided having fourth gear teeth engaged with the third gear teeth of the second member. The third member moves in a linear path when the first member is rotated, and wherein the third member is attached to the movable plate for moving the movable plate toward and away from the fixed plate.

Description:
BACKGROUND  
         [0001]    In general, compression and clamping apparatuses having stationary and movable platens have been employed in compression presses and in molding machines such as injection molding machines. The compression presses and mold-clamping apparatuses of this kind are designed to use a toggle mechanism, a crank mechanism or a ball-screw/ball-nut mechanism to translate the movable platen along a frame that interconnects the stationary platen and the movable platen for various operations.  
           [0002]    With reference to FIG. 1, a conventional press  2  has a fixed plate  3 , a movable plate  4 , and a hydraulic actuator (or “not shown”) for moving the movable plate  4 . The press  2  also has a toggle mechanism  7  having toggle points  5 . The toggle mechanism  7  is used, for example, during a clamping operation for generating a clamping force. These conventional apparatuses, however, have many shortcomings. For example, hydraulic systems are noisy and expensive to operate and maintain. Toggle devices, such as the toggle mechanism  7 , do not deliver consistent clamping force during the compression stroke, take too much time during the clamping process, and require additional components which leads to an increase in maintenance costs. What is needed is an electric high speed molding press having direct linear actuation.  
         SUMMARY  
         [0003]    The invention provides a linear actuator assembly and a press for a variety of uses. In one aspect, the invention provides a press with a linear actuator assembly comprising a stationary member, a first member rotationally fixed in the stationary member and having a first gear set, a second member rotationally fixed in the stationary member and having second gear teeth and third gear teeth, the second gear teeth being engaged with the first gear set of the first member, and a third member having fourth gear teeth engaged with the third gear teeth of the second member, wherein the third member moves in a linear path when the first member is rotated.  
           [0004]    In another aspect, the invention provides a press having a movable plate and a stationary plate, each of the movable and stationary plates having at least one of cooling elements and heating elements, an electric drive system, having a motor and a control panel, for applying a linear actuating force to the movable plate. The electric drive system further comprises a stationary member, a first member rotationally fixed in the stationary member and having a first gear set, a second member rotationally fixed in the stationary member and having second gear teeth and third gear teeth, the second gear teeth being engaged with the first gear set of the first member. Also provided is a third member having fourth gear teeth engaged with the third gear teeth of the second member, wherein the third member moves in a linear path when the first member is rotated.  
           [0005]    These and other features and advantages of the invention will be more clearly understood from the following detailed description and drawings of preferred embodiments of the present invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a perspective view of a conventional press clamping mechanism;  
         [0007]    [0007]FIG. 2 is a perspective cut-away view of a linear actuator assembly in accordance with an embodiment of the present invention;  
         [0008]    [0008]FIG. 3 is a side view of a power generation and transmission apparatus for use with the assembly of FIG. 2; and  
         [0009]    [0009]FIG. 4 is a side view of a press in accordance with an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0010]    In the following detailed description, reference is made to various specific embodiments in which the invention may be practiced. These embodiments are described with sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be employed, and that structural and procedural changes may be made without departing from the spirit or scope of the present invention.  
         [0011]    Referring now to the drawings, where like parts are designated by like reference numbers throughout, there is shown in FIG. 2 a linear actuator assembly generally designated by numeral  20 . FIG. 2 shows the linear actuator assembly  20  in a partial cutaway view for ease of description. The assembly  20  comprises a linear actuator  22 , a nut  26 , and a transmission link  44 . The linear actuator  22  has threads  24  as shown disposed along its entire length. Alternatively, a section or sections of the linear actuator  22  may be formed without threads, to save cost or for other reasons, depending upon the required length of travel of the linear actuator  22 .  
         [0012]    The nut  26  has internal threads  28  and external threads  30 . The internal threads  28  of the nut  26  engage with the threads  24  of the linear actuator  22 . In combination, the nut  26  with internal threads  28  and the linear actuator  22  with threads  24  function similar to a typical power screw or translation screw. Such a device is typically used to convert rotary motion, of one of the nut  26  and the linear actuator  22 , to linear motion of the other one of the nut  26  and the linear actuator  22 . One purpose of using a power screw is to obtain a mechanical advantage to lift weights or to exert large forces. Another purpose is to achieve precise positioning of an axial movement.  
         [0013]    The linear actuator assembly  20  further comprises a thrust collar  50 . The thrust collar  50  is positioned between a moving member (the nut  26  as will be discussed below) and a stationary member. The stationary member is an upper housing  40  which, together with a lower housing  38 , comprise a fixed portion of the linear actuator assembly  20 . The thrust collar  50  acts as a bearing surface between a stationary member and a moving or rotating member. Although one type of thrust collar is shown, a ball thrust collar or a simple bearing may be used.  
         [0014]    The transmission link  44  has a shaft portion  48  and a gear portion  46 . As will be discussed below, the shaft portion  48  may be connected to an external source of rotational energy. The gear portion  46 , as illustrated in FIG. 2, is engaged with the external threads  30  of the nut  26 . The gear portion  46  and external nut threads  30  essentially form essentially a worm gear set, which typically comprises a screw or worm (gear portion  46 ) meshing with a helical worm gear (threads  30  of nut  26 ). Rotation of the worm (gear portion  46 ) simulates a linearly advancing involute rack. The gear teeth of the worm gear (threads  30 ) are curved to partially envelop the worm.  
         [0015]    The gear portion  46  of the transmission link  44  and the nut  26  are both rotatably fixed inside the lower housing  38  and upper housing  40 . That is, rotational movement of either the transmission link  44  and the nut  26  does not result in linear movement of the components  44 ,  26  relative to the lower housing  38 .  
         [0016]    The linear actuator  20  is free to move linearly and rotationally with respect to the fixed lower housing  38  and upper housing  40 . One portion of the linear actuator  22  (shown as the lower portion in FIG. 2) is enclosed within a protective cylinder  32 . The cylinder  32  has a closed bottom end  33  which defines one limit of travel of the linear actuator  22  in the direction of arrow  53 . Alternatively, the cylinder may have an open bottom to increase the range of axial travel of the linear actuator  22 .  
         [0017]    A plate  34  is affixed to an end of the linear actuator  22  (shown as the upper end in FIG. 2). The plate  34  has holes  36  which can be used to attach to the plate  34  to move together with plate  34 . The lower housing  38  has holes  42  which can be used to attach the fixed portion (upper member  40  and lower member  38 ) of the assembly  20  to a frame of a press or the like.  
         [0018]    Referring now to FIG. 3, there is shown a simplified power generation and transmission apparatus for use with the linear actuator assembly  20  of FIG. 2. FIG. 3 shows an electric motor  60  connected to a reduction gear  62 . The reduction gear  62 , via a coupling  64 , is connected to the shaft portion  48  of the transmission link  44 .  
         [0019]    In use, rotational power is supplied in a conventional manner to the transmission link  44  from the motor  60 , via reduction gear  62  and coupling  64 . Rotation of the transmission link  44  causes the gear portion  46  to likewise rotate. Because gear portion  46  is engaged with external threads  30  of nut  26 , the nut  26  rotates. Rotation of nut  26 , and thus internal threads  28  of the nut  26  which are engaged with linear actuator threads  24 , causes linear motion of the linear actuator  22 .  
         [0020]    An example of a lifting motion by the linear actuator assembly  20  now will be described. With reference to FIG. 2, when the gear portion  46  or transmission link  44  is rotated (by an input from a rotation source) in a direction represented by arrow  54 , the nut  26  rotates in a direction represented by arrow  56 . Rotation of nut  26  in direction of arrow  56  imparts a linear motion to the linear actuator  22  in direction of arrow  52 . A rotational power input to transmission link  44  and gear portion  46  in a direction opposite to arrow  54  causes the nut  26  to rotate in a direction opposite to arrow  56 . Such rotation by nut  26  then causes the linear actuator  22  to travel in a direction represented by arrow  53 .  
         [0021]    [0021]FIG. 4 illustrates an electric press  70  having the linear actuator assembly of the present invention. The electric press  70  has a frame  84  and an electronic control panel  72  in addition to the motor  60 , gear reducer  62  and coupling  64  previously described. The electronic control panel  72  communicates with the motor  60  via a suitable link  73 , and has a controller for controlling the operational speed and force of the press as will be described below. The press  70  further comprises a movable plate  74  and a fixed plate  76 . The plates  74 ,  76  may further comprise heating elements or conduits  78  and cooling elements or conduits  80 . The heating and cooling elements  78 ,  80  may be used during a molding process, for example, to control the temperature of different stages of the process.  
         [0022]    Linear actuator(s)  22  are rigidly connected via a connecting portion  82  to the moveable plate  74 . Linear movement of the actuator(s)  22  causes the movable plate  74  to move toward or away from fixed plate  76 . As such the press  70  is capable of functioning similar to a conventional compression press or a molding press, but with enhanced capabilities made possible by the arrangement of the invention.  
         [0023]    The electronic control panel  72  can control the motor  60 , and thus the moveable plate  74 . The electronic control panel  72  can have programmable logic controllers (PLC&#39;s), computer devices, and other components, and can also incorporate artificial intelligence (AI) functions and components. The electronic control panel  72  can supply power to the motor  60 , which can be a servo motor, a variable frequency motor, or another suitable motor. In use, the electronic control panel  72  can be programmed with data corresponding to specific distances the movable plate  74  has to travel, an amount of force the movable plate  74  should apply, and the duration of time to apply such force. Other functions may be incorporated into the electronic control panel  72 . Benefits of this configuration include: faster response times; very quick acceleration and deceleration of travel of the movable plate  74 ; accurate and adjustable clamping force over the entire stroke length of the linear actuator  22 ; and accurate and adjustable position control over the entire stroke length of the linear actuator  22 .  
         [0024]    Thus, the disclosed press applies a linear, direct clamping force with positioning control that is more precise and consistent than in a hydraulic system. In contrast to conventional electric presses, the direct acting press eliminates the need for toggle clamping action. The press of the present invention, having a linear actuator assembly, need not incorporate a flywheel to multiply or increase applied force.  
         [0025]    The above description and drawings are only illustrative of preferred embodiments of the present inventions, and are not intended to limit the present inventions thereto. Any subject matter or modification thereof which comes within the spirit and scope of the following claims is to be considered part of the present inventions.