Abstract:
The present invention provides an apparatus for moving a member including a first clamp assembled to a fixed surface for selectively clamping the member and a second clamp moveable with respect to the first clamp for selectively clamping the member. A piezo actuator is disposed between the first and second clamps for moving the member in response to expansion of the actuator. Resilient means bias the second clamp toward the first clamp.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/180,239 filed Feb. 4, 2000, U.S. Provisional Application No. 60/198,056, filed Apr. 18, 2000, and U.S. Provisional Application No. 60/220,542, filed Jul. 25, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to a linear motor having piezo actuators.  
         BACKGROUND OF THE INVENTION  
         [0003]    Throughout industry there are numerous applications requiring a motor which is compact or small in size, powerful, precise, efficient, reliable, low cost, etc. Some prior known motors meet one or more of these desired characteristics, however, such motors have shortcomings. Some motors provide the required power but not the required precision. Other motors meet the required size but not provide the required power. Still other motors provide the required precision but are very expensive. Accordingly, it would be desirable to provide a linear motor which is capable of overcoming the shortcomings of the prior art.  
         SUMMARY OF THE INVENTION  
         [0004]    An apparatus for moving a member including a first clamp assembled to a fixed surface for selectively clamping the member and a second clamp moveable with respect to the first clamp for selectively clamping the member. A piezo actuator is disposed between the first and second clamps for moving the member in response to expansion of the actuator. Resilient means bias the second clamp toward the first clamp. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein:  
         [0006]    [0006]FIG. 1 is a schematic, cross-sectional view of a linear motor in accordance with the present invention showing the internal components of the motor;  
         [0007]    [0007]FIG. 2 is a perspective view of internal components of the linear motor;  
         [0008]    FIGS.  3 A- 3 G are a series of schematics illustrating an operation of the linear motor of FIGS. 1 and 2 for moving a member in one direction; and  
         [0009]    [0009]FIG. 4 is a cross-sectional view of one embodiment of an actuator for use in the linear motor. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0010]    [0010]FIG. 1 is a schematic, cross-sectional view of a linear motor  10  in accordance with the present invention showing the internal components of the motor. The linear motor  10  is shown in schematic illustration for descriptive purposes. The linear motor  10  is encased in a housing  12 . The housing  12  is designed to protect the linear motor  10 . In one embodiment of the present invention, the linear motor  10  is assembled to a fixed surface or member (not shown). In this embodiment, the fixed linear motor  10  is capable of moving a member, such as an actuating rod or shaft  14 , in either direction along axis A in FIG. 1. In other words, the fixed linear motor  10  is capable of moving the rod  14  left or right relative to the linear motor  10  as illustrated in FIG. 1. In another embodiment of the present invention, the rod  14  is assembled to a fixed surface or member (not shown). In this embodiment, the linear motor  10  is capable of linear movement along the fixed rod  14  in either direction along axis A in FIG. 1. To accomplish either movement, the linear motor  10  operates in a walking beam feeder fashion, shown in FIG. 3 and described in greater detail below. To perform the walking beam feeder movement, the linear motor  10  includes three piezo or piezoelectric actuators  16   a,    16   b,  and  16   c  (piezo actuators  16   a  and  16   c  are shown in FIG. 2), a pair of clamps  18  and  20 , and a resilient means  22 . The first clamp  18  is fixed to the housing  12  and the second clamp  20  is free from the housing  12 . In alternative embodiments of the present invention, the resilient means  22  may comprise an actuator retractor spring (as shown in FIG. 1), an o-ring or other similar type of resilient structure, or another piezo actuator. The resilient means  22  is disposed between the second clamp  20  and the housing  12 . The linear motor  10  further includes an electrical connector (not shown) for receiving power to operate the motor  10 .  
         [0011]    [0011]FIG. 2 is a perspective view of selected internal components of the linear motor  10  used to accomplish the walking beam feeder movement. The two clamps  18  and  20  are adapted to clamp or hold the rod  14 . The axis of the rod  14  is aligned perpendicular to the two clamps  18  and  20 . The rod  14  is disposed within the jaws of the two clamps  18  and  20 . In one embodiment of the present invention, a flexible structure  26 , such as a wire, cable, string or the like, may be secured to the end  28  of the rod  14  adjacent to the first clamp  18 .  
         [0012]    The two outermost actuators  16   a  and  16   c  are operated between an energized state, wherein voltage is applied to the actuator, and a de-energized state, wherein no voltage is applied to the actuator. The two outermost actuators  16   a  and  16   c  are normally de-energized. When the first actuator  16   a  is de-energized, the first clamp  18  is closed, or clamps to or engages the rod  14 . When the third actuator  16   c  is de-energized, the second clamp  20  is closed, or clamps to or engages the rod  14 .  
         [0013]    Each of the three actuators  16   a - c  is energized by applying a voltage to the respective actuator. Energizing the first actuator  16   a  disengages the first clamp  18  from the rod  14 . Energizing the third actuator  16   c  disengages the second clamp  20  from the rod  14 . In other words, energizing the first actuator  16   a  opens the first clamp  18  thereby releasing the rod  14  and energizing the third actuator  16   c  opens the second clamp  20  thereby releasing the rod  14 .  
         [0014]    The second or central actuator  16   b  is disposed between the first and second clamps  18  and  20  providing a nominal displacement between the first and second clamps  18  and  20 . When energized, the second actuator  16   b  provides an increase in the displacement between the two clamps  18  and  20 . In other words, when energized, the second actuator  16   b  provides an expansion force which pushes the two clams  18  and  20  apart or away from each other. Within the normal or typical operating voltage range, the amount of increase in the displacement between the two clamps  18  and  20  is proportional to the amount of voltage applied across the second actuator  16   b.    
         [0015]    When de-energized, the second actuator  16   b  provides an decrease in the displacement between the two clamps  18  and  20 . Piezo actuators, especially piezo stacks, provide a contraction force significantly lower or weaker than the aforementioned expansion force and are suspectible to failure caused by tension during contraction. Accordingly, the resilient means  22  is adapted to bias or push the second clamp  20  toward the second actuator  16   b.  In alternative embodiments, the resilient means  22  can provide all or part of the force necessary to move the two clamps  18  and  20  back to the nominal displacement.  
         [0016]    The operation of the three actuators  16   a - c  may be sequenced to move the rod  14  in one direction or the opposite direction along axis A of the rod  14 . FIGS.  3 A- 3 G are a series of schematics illustrating an operation of the linear motor  10  for moving the rod  14  in one direction. In other words, FIGS.  3 A- 3 G illustrate a sequence of operations performed by the linear motor  10  to move the rod  14  in a direction of travel as indicated by arrow  30 .  
         [0017]    [0017]FIG. 3A illustrates the linear motor  10  in a first position. The second actuator  16   b  is de-energized and the first and second clamps  18  and  20  are clamped to the rod  14 . The first clamp  18  is fixed to the housing  12  or anchored in a fixed location or to a fixed surface. During the first operation, voltage to each of the three actuators  16   a - c  is switched off and the displacement between the first and second clamps  18  and  20  is nominal.  
         [0018]    [0018]FIG. 3B illustrates the linear motor  10  in a second position. The first clamp  18  is opened by energizing the first actuator  16   a.  During the second operation, the rod  14  is released by the first clamp  18 .  
         [0019]    [0019]FIG. 3C illustrates the linear motor  10  in a third position. A voltage is applied to the second actuator  16   b  thus energizing the second actuator  16   b  and providing an increase in the displacement between the first and second clamps  18  and  20 . During the third operation, the expansion of the second actuator  16   b  forces the second clamp  20  and the rod  14  in a direction of travel as indicated by arrow  30 . Movement of the second clamp  20  compresses the resilient means  22  against the housing  12 .  
         [0020]    [0020]FIG. 3D illustrates the linear motor  10  in a fourth position. The first clamp  18  is closed by de-energizing the first actuator  16   a.  During the fourth operation, the first clamp  18  clamps to the rod  14 .  
         [0021]    [0021]FIG. 3E illustrates the linear motor  10  in a fifth position. The second clamp  20  is opened by energizing the third actuator  16   c.  During the fifth operation, the rod  14  is released by the second clamp  20 .  
         [0022]    [0022]FIG. 3F illustrates the linear motor  10  in a sixth position. The second actuator  16   b  is de-energized. During the sixth operation, the resilient means  22  pushes the second clamp  20  in the direction of travel indicated by arrow  32 .  
         [0023]    [0023]FIG. 3G illustrates the linear motor  10  in a seventh position. The second actuator  16   b  is de-energized and the first and second clamps  18  and  20  are clamped to the rod  14 . During the seventh operation, voltage to each of the three actuators  16   a - c  is switched off and the displacement between the first and second clamps  18  and  20  is nominal. The seventh position is similar to the first position but with the rod  14  moved in the direction of travel as indicated by arrow  30  relative to the linear motor  10 .  
         [0024]    The linear motor  10  is capable of performing the seven step operational sequence in less than or equal to approximately 400 to 4,000 microseconds. A single cycle of the seven step operational sequence will nominally move or displace the rod  14  approximately 12 micrometers. To move or displace the rod  14  a distance greater than the nominal displacement produced by the second actuator  16   b,  the seven step operational sequence may be repeated or cycled two or more times. To move or displace the rod  14  a distance less than the nominal displacement produced by the second actuator  16   b,  the amount of voltage applied to the second actuator  16   b  is reduced proportionally. For example, to move or displace the rod  14  a distance of one-half the nominal displacement produced by the second actuator  16   b,  one-half the nominal voltage is applied to the second actuator  16   b.  To move or displace the rod  14  a distance of one-quarter the nominal displacement produced by the second actuator  16   b,  one-quarter the nominal voltage is applied to the second actuator  16   b.    
         [0025]    The sequence of operations performed by the linear motor  10  may be modified to move the rod  14  in the direction opposite of arrow  30 . Further, the present invention may be practiced by combining one or more operations into a single step.  
         [0026]    [0026]FIG. 4 is a cross-sectional view of one embodiment of an actuator  16  for use in the linear motor  10  of the present invention. The actuator  16  is designed to produce a positional or spatial displacement along one predetermined axis when energized. In other words, the cross-section of the actuator  16  is designed to expand along at least one predetermined axis when energized. In one embodiment of the present invention, the actuator  16  includes a ceramic substrate  34  sandwiched between two opposing end caps  36  and  38 . The two end caps  36  and  38  are preferably formed in the shape of truncated cones. In one embodiment of the present invention, the two end caps  36  and  38  are made from sheet metal. Each end cap  36  and  38  includes a contact surface  40  and  42  respectively. In one embodiment of the present invention, the entire periphery of each end cap  36  and  38  is bonded to the ceramic substrate  34 . This type of actuator  16  is commonly referred to in the art as a cymbal actuator.  
         [0027]    The actuator  16  is operated between a de-energized state, illustrated in FIG. 4 with solid lines, providing a spatial displacement equal to the nominal thickness of the actuator, and an energized state, illustrated in FIG. 4 with dashed lines, providing a spatial displacement greater than the nominal thickness of the actuator. The actuator  16  is normally de-energized.  
         [0028]    The actuator  16  is energized by applying a voltage or potential across the ceramic substrate  34 . The voltage causes the substrate  34  to expand along the Z axis and contract along the X and Y axes as designated in FIG. 4. As a result, both end caps  36  and  38  flex or bow outwardly from the substrate  34  about flex points  44 ,  46  and  48 ,  50  respectively. Thus, the contraction of the ceramic substrate  34  shortens the distance between the sidewalls of each end cap  36  and  38  and increases the distance between the contact surfaces  40  and  42 . In this manner, a substantial increase in the displacement between the contact surfaces  40  and  42  is produced.  
         [0029]    Within the normal or typical operating voltage range, the increase in the displacement between the contact surfaces  40  and  42  for a given cymbal geometry is proportional to the amount of voltage applied across the ceramic substrate  34 . In other words, a nominal voltage produces a nominal displacement, one-half the nominal voltage produces one-half the nominal displacement, one-quarter the nominal voltage produces one-quarter the nominal displacement, etc.  
         [0030]    The large, flat contact surfaces  40  and  42  of each end cap  36  and  38  render it practical to stack several actuators in order to achieve greater displacements.  
         [0031]    The present invention may also be practiced with other similar types of actuators including, but not limited to, a single or individual piezoelectric element, a stack of individual piezo elements, a mechanically amplified piezo element or stack, or a multilayer cofired piezo stack.  
         [0032]    The linear motor  10  has numerous advantages, attributes, and desirable characteristics including, but not limited to, the characteristics listed hereafter The present invention incorporates relatively simple, inexpensive, low power, reliable controls. More specifically, the linear motor  10  is compact in size (i.e. less than or equal to approximately 1 in 3 ) yet physically scalable to dimensions as least as much as a factor of ten greater and highly powerful (i.e. capable of exerting a drive thrust of 35 lbs.). The present invention is highly precise (i.e. capable of producing movement increments of approximately 0.0005 inch), highly efficient (i.e. having an average power consumption of less than 10 Watts when operating and negligible power consumption when idle), and highly reliable (i.e. having a component life expectancy of approximately 250,000,000 cycles). Further, the linear motor  10  produces minimal heat during operation, generates minimal EMI (Electromagnetic Interference) and RFI (Radio-Frequency Interference), and is relatively unaffected by stray EMI and RFI in the area. Additionally, the present invention is capable of producing an accumulated linear travel distance in excess of 2 kilometers. Finally, the linear motor  10  can operate in extreme environmental conditions including high vacuum.