Abstract:
Apparatus for providing linear motion to a generally flat flexible material, comprising: (a) at least one piezoelectric ceramic motor situated on a first side of the flat flexible material and having a contact surface which contacts the flat flexible material and which imparts said linear motion; and (b) a bearing surface situated on a second side of the flat flexible material opposite said contact surface.

Description:
RELATED APPLICATIONS 
     The present application is a U.S. national application of PCT/IL97/00410, filed Dec. 15, 1997. 
     FIELD OF THE INVENTION 
     The present invention relates to linear motion and to piezoelectric motors generally and more particularly to the use of piezoelectric motors for moving delicate materials, such as paper. 
     BACKGROUND OF THE INVENTION 
     Linear motion and piezoelectric motors are known in the art. SU 693493 describes a piezoelectric motor comprising a flat rectangular piezoelectric plate having one electrode covering essentially all of one large face of the plate (“the back face”) and four electrodes each covering a quadrant of the front face. The back electrode is grounded and the electrodes of the front face are electrically connected on the diagonal. Two ceramic pads are attached to one of the long edges of the plate and these pads are pressed against the object to be moved by a spring mechanism which presses the other long edge. 
     The long and short edges of the piezoelectric ceramic have similar resonant frequencies (for different mode orders) such that, when one pair of connected electrodes is excited with an alternating current (AC) voltage to which the ceramic is responsive, the object moves in one direction, and when the other pair of electrodes is excited, the object moves in the other direction. 
     SUMMARY OF THE PRESENT INVENTION 
     One aspect of the present invention is concerned with the transport of flexible materials such as paper and cloth. 
     In a preferred embodiment of the invention a piezoelectric motor is used to move the material. 
     There is thus provided, in accordance with a preferred embodiment of the invention, apparatus for providing linear motion to a generally flat flexible material, comprising: 
     (a) at least one piezoelectric ceramic motor situated on a first side of the flat flexible material and having a contact surface which contacts the flat flexible material and which imparts said linear motion; and 
     (b) a bearing surface situated on a second side of the flat flexible material opposite said contact surface. 
     In one preferred embodiment of the invention the bearing surface is the surface of a roller. In other preferred embodiments of the invention, the bearing surface is a contact surface associated with a second piezoelectric motor. 
     In these other preferred embodiments of the invention, the bearing surface is a contact surface of a second piezoelectric motor and the second piezoelectric motor also imparts said linear motion to the flat flexible material via said contact surface, preferably the at least one and the second piezoelectric motors both impart linear motion to the flexible material in the same direction. 
     In one of these other preferred embodiments of the invention, the at least one and second piezoelectric motors impart said linear motion in a given direction during motion periods which alternate with periods during which said motion is not applied and the motion periods of the at least one and the second piezoelectric motors at least partially overlap. Preferably, the motion periods of one of the at least one and the second piezoelectric motors is fully contained within the motion period of the other piezoelectric motor. Preferably, the motion periods of the at least one and the second piezoelectric motors coincide. 
     Preferably, the contact surfaces of the at least one piezoelectric motor and the second piezoelectric motor are displaced toward the flexible material during their respective periods of motion such that the material is pinched between the respective contact surfaces. 
     Alternatively the contact surface of the at least one piezoelectric motor is displaced toward the flexible material during the period of motion of the at least one piezoelectric motor and wherein the contact surface of the second piezoelectric motor is displaced away from the flexible material during the period of motion of the at least one piezoelectric motor. Preferably, the contact surface of the second piezoelectric motor is displaced toward the flexible material during the period of motion of the second piezoelectric motor and the contact surface of the at least one piezoelectric motor is displaced away from the flexible material during the period of motion of the second piezoelectric motor, such that the at least one piezoelectric motor and second piezoelectric motor alternately apply motion to the flexible material. While it might be expected that this apparatus would not operate since the flexible material would move from side to side, remaining in contact with both motors and thus not moving at all. However, it appears that even the relatively low mass and stiffness of paper is sufficient to allow for the motors to independently move the material. 
     In a preferred embodiment of the invention, the at least one piezoelectric motor comprises: 
     a second contact surface which contacts and is operative to apply linear motion to a second portion of the flexible material; 
     and further comprising: 
     a second bearing surface situated on a second side of the flat flexible material opposite said second contact surface. 
     As with the first bearing surface, the second bearing surface may be a roller or a contact surface of an additional piezoelectric motor. The additional piezoelectric motor preferably cooperates with the second contact surface in the same way as the second piezoelectric motor cooperates with the contact surface. 
     There is further provided, in accordance with a preferred embodiment of the invention, a method for providing linear motion to a generally flat flexible material, comprising: 
     (a) contacting a contact surface of at least one piezoelectric ceramic motor with a first side of the flat flexible material, said at least one motor being operative to impart linear motion to surfaces which are in contact with the contact surface; and 
     (b) providing a bearing surface on a second side of the flat flexible material opposite said contact surface. 
     In one preferred embodiment of the invention the bearing surface is the surface of a roller. In other preferred embodiments of the invention, the bearing surface is a surface associated with another piezoelectric motor. 
     In these other preferred embodiments of the invention, the bearing surface is a contact surface of a second piezoelectric motor and wherein the second piezoelectric motor also imparts said linear motion to the flat flexible material via said contact surface, preferably the at least one and the second piezoelectric motors both impart linear motion to the flexible material in the same direction. 
     In one of these other preferred embodiments of the invention, the at least one piezoelectric motor and the second piezoelectric motor impart said linear motion in a given direction during motion periods which alternate with periods during which said motion is not applied and the motion periods of the at least one piezoelectric motor and the second piezoelectric motor at least partially overlap. Preferably, the motion periods of the at least one piezoelectric motor and the second piezoelectric motor is fully contained within the motion period of the other piezoelectric motor. Preferably, the motion periods of the at least one piezoelectric motor and the second piezoelectric motor coincide. 
     Preferably, the contact surfaces of the at least one piezoelectric motor and the second piezoelectric motor are displaced toward the flexible material during their respective periods of motion such that the material is pinched between the respective contact surfaces. 
     Alternatively the contact surface of the at least one piezoelectric motor is displaced toward the flexible material during the period of motion of the at least one piezoelectric motor and wherein the contact surface of the second piezoelectric motor is displaced away from the flexible material during the period of motion of the at least one piezoelectric motor. Preferably, the contact surface of the second piezoelectric motor is displaced toward the flexible material during the period of motion of the second piezoelectric motor and wherein the contact surface of the at least one piezoelectric motor is displaced away from the flexible material during the period of motion of the second piezoelectric motor, such that the at least one piezoelectric motor and the second motor alternately apply motion to the flexible material. 
     In a preferred embodiment of the invention the method includes: 
     (a) contacting a second contact surface of the at least one piezoelectric ceramic motor with a first side of the flat flexible material, said motor being operative to impart linear motion to surfaces which are in contact with the second contact surface; and 
     (b) providing a second bearing surface on a second side of the flat flexible material opposite said second contact surface. 
     As with the first bearing surface, the second bearing surface may be a roller or a contact surface of an additional piezoelectric motor. The additional piezoelectric motor preferably cooperates with the second contact surface in the same way as the second piezoelectric motor cooperates with the contact surface. 
     Additionally, in accordance with a preferred embodiment of the present invention, the piezoelectric ceramic motor has two upper and two lower electrodes and wherein the two upper electrodes are of the same size but different than the size of the two lower electrodes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
     FIG. 1 is a schematic illustration of apparatus for providing linear motion for a flat flexible material, constructed and operative in accordance with a first embodiment of the present invention; 
     FIG. 2 is an enlarged elevational detail of the apparatus of FIG. 1; 
     FIG. 3 is a schematic illustration of a second embodiment of the present invention in which a single piezoelectric motor and a pair of roller devices are used in combination for providing horizontal linear motion; 
     FIG. 4 is a schematic illustration of a third embodiment of the present invention in which a piezoelectric motor is configured to provide differential movement of the material to be moved; 
     FIG. 5 is a schematic illustration of apparatus for providing linear motion to two individual lines of flat flexible material, constructed and operative in accordance with a fourth embodiment of the invention; and 
     FIG. 6 is a schematic illustration of a fifth embodiment of the present invention in which a three piezoelectric motors provide horizontal linear motion. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Reference is now made to FIG. 1 which illustrates apparatus  10  for providing linear motion for a delicate material  12 , constructed and operative in accordance with a first embodiment of the present invention. 
     Apparatus  10  comprises upper and lower piezoelectric motor units  14 A and  14 B, respectively, located along a vertical line, on two opposing sides of delicate material  12 . Delicate material  12  is any relatively soft material, which is fragile and flexible, such as paper or cloth. The piezoelectric motor units, generally designated  14 , are connected to a power source  15 . 
     Upper and lower piezoelectric motor units  14 A and  14 B have similar elements and thus similar reference numerals are used throughout. The suffix “A” refers to the upper piezoelectric motor unit  14 A and the suffix “B” refers to the lower piezoelectric motor unit  14 A. 
     The piezoelectric motor units  14  can be any type of piezoelectric motor unit, which can provide the desired amount of dynamic force in the desired amount of time. The piezoelectric motors commercially manufactured by Nanomotion Ltd. of Haifa, Israel, are suitable. 
     The operation of a piezoelectric motor is briefly described herein; the details of its operation can be found in U.S. Pat. No. 5,616,980 to the common assignees of the present invention, the disclosure of which is incorporated by reference. 
     Four electrodes  16 ,  17 ,  18  and  20  are plated or otherwise attached onto the face (hereinafter “the first face”) of a piezoelectric ceramic  22  to form a checkerboard pattern of rectangles, each substantially covering one-quarter of the first face. The opposite face (“the second face”) of the piezoelectric ceramic  22  is substantially covered with a single electrode (not shown). Diagonally located electrodes ( 17  and  18 ,  16  and  20 ) are electrically connected by wires  24  and  26  preferably placed near the junction of the four electrodes. The electrode on the second face is preferably grounded. 
     A relatively hard spacer  28  is attached to a short edge of piezoelectric ceramic  22 , preferably at the center of the edge. 
     Piezoelectric ceramic  22  vibrates when electrified. The dimensions of the rectangular large face are preferably chosen such that piezoelectric ceramic  22  has closely spaced resonance frequencies in an X and a Y direction (the short and long directions of the rectangular face of the piezoelectric ceramic  22 , respectively), albeit in different modes. Typically, the resonances have overlapping response curves; thus, excitation of the piezoelectric ceramic is achieved by connecting an alternating current (AC) voltage at a frequency at which both modes are excited, to selected ones of the electrodes. When excited, standing waves at the resonant frequencies are formed in ceramic  22  in both the X and Y directions. 
     Piezoelectric ceramic  22  is generally constrained by a pair of fixed supports  32  and by a pair of resilient supports  34 . Supports  34  are typically formed of rubber. Supports  32  and  34  contact piezoelectric ceramic  22  at points of zero movement in the standing wave in the Y direction. The points of zero movement are along a pair of long edges of the ceramic  22 . These supports are designed to slide in the Y direction. A resilient support  38  is pressed against the middle of a second short edge, labeled  40 , of ceramic  22 , opposite the short edge having spacer  28 . Support  38  continually supplies pressure (a “preload”) between ceramic  22  and the body to be moved, such as material  12 , which causes the motion of ceramic  22  to be transmitted to the body to be moved. 
     It is noted that, when a piezoelectric motor ( 14 A or  14 B) is operated, it moves its spacer  28  in both the X and Y directions, where the X and Y directions are defined, as above, as being along the short and long axis, respectively, of the piezoelectric motor. The net effect of the movement of the spacer  28  in both X and Y directions, is elliptical, as described hereinbelow with respect to FIG.  2 . 
     In a preferred embodiment of the present invention, piezoelectric motors  14 A and  14 B are electrified in the same direction (shown by arrows  25 A and  25 B). That is, both the upper and lower piezoelectric motor units  14 A and  14 B, respectively operate in concert. Thus, both spacers  28 A and  28 B move together alternately, in either the X and Y directions. The diagonally located electrodes ( 16  and  20 ) of upper piezoelectric motor  14 A, and the opposite diagonally located electrodes ( 17  and  18 ) of lower piezoelectric motor  14 B are electrically connected together. 
     Reference is now made to FIG. 2 which is an enlarged elevational detail showing the movement of material  12  in a forward direction  50 . Material  12  is being pressed by the spacers  28  of both piezoelectric motors  14  at the same time. That is, material  12  is subject to pressure in a vertical Y direction. The combination of this vertical Y pressure and forward X movement distorts the material  12  slightly, creating a convex shape, as shown. 
     The spacers  28  have a two stage cyclical movement., a first stage (a movement period) during which material  12  moves forward and a second stage during which material  12  does not move. The movement of each spacer, in both the Y and X directions, can be defined as having a positive aspect, indicated by arrow “+” and a negative aspect, indicated by arrow “−”. Upper spacer  28 A moves forward in a positive X direction while it is displaced in a downwards negative Y direction (dashed structure). At the same time, lower spacer  28 B moves forward in a positive X direction but upwards in a positive Y direction (dashed structure). 
     During a second stage the spacers move away from material  12  and in the −x direction.(solid line structure). They then move toward the material and contact the material again and move to the right. 
     The motion of the upper and lower spacers  28 A and  28 B is illustrated by arrows  54  and  56  respectively. 
     In an alternative preferred embodiment of the invention piezoelectric motors are electrified to transfer motion to material  12  alternatively. While each of the spacers moves in the same manner as the spacers of FIG. 2, the spacers move “out of phase” such that they alternatively impart motion in the +x direction. It might be expected that the flexible material would follow this alternating motion and move transverse to the x direction, remaining in contact with both spacers and having no net motion in the +x direction. Surprisingly, this does not happen. It appears that material  12 , even if it is flexible, remains generally in place so that it is alternatively contacted by spacers  28 A and  28 B such that it is alternatively moved by the two motors in the +x direction. 
     While it is difficult to make measurements of the transverse motion of material  12 , it is possible that the material does move up and down together with the motion of the spacers, however, its motion is less than that of the spacers such that net motion is provided in the +x direction. 
     Reference is now made to FIG. 3 which illustrates a further embodiment of the present invention utilizing a single piezoelectric motor  70  and rollers, generally designated  71 . First and second rollers  71 A and  71 B are situated on opposite sides of material  12 . Embodiments having similar elements have similar reference numerals throughout. 
     First and second rollers  71 A and  71 B are used in place of the upper piezoelectric motor  14 A of the embodiment of FIG. 1 to provide pressure on material  12 . Rollers  71  are any cylindrical type rollers, known in the art, which are freely rotatable. Pre-loading is provided to the piezoelectric motor  70  and rollers  71  by pre-loading supports  38 , as described hereinabove with respect to the embodiment of FIG.  1 . 
     Piezoelectric motor  70  is distinguished from piezoelectric motors  14 , described hereinabove with respect to the embodiment of FIG. 1, by having a pair of spacers  72 A and  72 B attached to short edges  74 A and  74 B, respectively of piezoelectric ceramic  22 . Piezoelectric motor  70  comprises upper electrodes  76  and  77 , adjacent to spacer  72 A, and lower electrodes  78  and  79  adjacent to spacer  72 B. In this embodiment, material  12  is moved around through 180° by the action of piezoelectric motor  70  on both rollers  71 A and  71 B. 
     When piezoelectric motor  70  is operated, both spacers  72 A and  72 B move simultaneously in both the X and Y directions. In this case, both spacers  72 A and  72 B behave in a manner similar to lower spacer  28 B, as described hereinabove with respect to the embodiment of FIG.  1 . Spacer  72 A moves in an upward direction (+y) and in a forward direction (+x) as in the embodiment of FIG.  1 . 
     The net elliptical effect of the movement of spacer  72 A causes material  12  to be pushed along in the X direction (arrow  50 A). Roller  71 A which is in contact with material  12  is rotated in an anti-clockwise direction by the movement of the material  12 , as illustrated by arrow  75 A. 
     The lower part of piezoelectric motor  70  is a mirror image of the upper part. Spacer  72 B attached to lower electrodes  78  and  79 , acts in a similar manner to spacer  72 A. Thus, the material  12  is also moved along in a clockwise direction, indicated by arrow  50 B. Roller  71 B which is rotated in an anti-clockwise direction by the movement of the material  12 , as illustrated by arrow  75 B. 
     It will be appreciated by persons skilled in the art that the combination of a single piezoelectric motor  70  have a spacer at either end, as described hereinabove can also be used to move two separate lines of material  12 . That is, one line of material moves in one direction indicated by arrow  50 A while a second line of material moves in the opposite direction, indicated by arrow  50 A. 
     Reference is now made to FIG. 4 which schematically illustrates a further embodiment of the present invention in which piezoelectric motor  80  is configured to provide differential movement of the material to be moved. Since this embodiment is identical to the embodiment of FIG. 3, except for the piezoelectric motor unit  80 , only this unit is further described in detail hereinbelow. 
     Four electrodes  81 ,  82 ,  83  and  84  are plated or otherwise attached onto the first face of a piezoelectric ceramic  22  to form a checkerboard pattern of rectangles. The opposite face of the piezoelectric ceramic  22  is substantially covered with a single electrode (not shown). Diagonally located electrodes ( 81  and  83 ,  82  and  84 ) are electrically connected by wires  85  and  86  preferably placed near the junction of the four electrodes. The electrode on the second face is preferably grounded. 
     Adjacent electrodes  81  and  82  have the same dimensions, each electrode having a length a Similarly, adjacent electrodes  83  and  84  also have the same dimensions of a length b, where b is greater than a. Spacers  86 A and  86 B are attached to edges of piezoelectric ceramic  22  which are adjacent to pairs of electrodes  81 / 82  and  83 / 84  respectively. 
     Movement in the X direction, indicated by arrow  88 , by spacers  86 A and  86 B depends on the length of the electrodes. The material  12  is thus moved further by spacer  86 B than by spacer  86 A and is effectively pulled along. Rollers  71 A and  71 B rotate in an anti-clockwise direction (arrow  75 ). 
     Reference is now made to FIG. 5 which schematically illustrates a further embodiment of the present invention in which a single piezoelectric motor  90  and a pair of rollers  71 A and  71 B are configured to provide horizontal movement of two separate lengths of material designated  12 A and  12 B. Since this embodiment is identical to the embodiment of FIG. 3, except for the piezoelectric motor unit  90 , only this unit is further described in detail hereinbelow. 
     Piezoelectric motor  90  comprises two longitudinal electrodes  91  and  92  which are plated or otherwise attached onto the first face of a piezoelectric ceramic  22 , each substantially covering one-half of the first face. The opposite face of the piezoelectric ceramic  22  is substantially covered with a single electrode (not shown) which is preferably grounded. Spacers  72 A and  72 B are attached to short edges  74 A and  74 B (hidden), respectively of piezoelectric ceramic  22 . 
     In this embodiment, when piezoelectric motor  90  is operated, both spacers  72 A and  72 A move simultaneously in both the X and Y directions. However, in contrast to the embodiment of FIG. 3, since electrodes  91  and  92  extend longitudinally between spacers  72 A and  72 B, the net elliptical movement of each spacer causes sheets of material  12 A and  12 B to move in the same direction, as illustrated by arrows  94 A and  94 B, respectively. 
     During the cycle stage when spacer  72 A moves in an upward direction (+y) and in a forward direction (+x), spacer  72 B moves in an upward direction (−y) and in a backward direction (−x) and is not in contact with material  12 B. Thus, when material  12 A is pushed along by the vibrations induced by spacer  72 A, material  12 B is stationary. 
     During the second part of the cycle, spacer  72 B induces material  12 B to move and material  12 A is stationary. 
     It will be appreciated by persons skilled in the art that each of longitudinal electrodes  91  and  92  may be replaced by two half size electrodes to create the same effect as described hereinabove. 
     Reference is now made to FIG. 6 which illustrates a yet further embodiment of the present invention utilizing three piezoelectric motors  14 A,  14 B and  70 , described hereinabove, to move material  12  around through 180° or to move two separate lines of material in opposite directions. The upper and lower piezoelectric motors  14 A and  14 B comprise spacers  28 A and  28 B, respectively, and are similar to the piezoelectric motors described hereinabove with respect to the embodiment of FIG.  1 . Piezoelectric motor  70  comprises a pair of spacers  72 A and  72 B, respectively, and is similar to the piezoelectric motor described hereinabove with respect to the embodiment of FIG. 3, and are therefore not described in any further detail. 
     Thus, when the three piezoelectric motors  14 A,  14 B and  70  are operated together, spacers  28 A and  72 A from piezoelectric motors  14 A, and  70 , respectively act in a similar manner to spacers  28 A and  28 B, as described hereinabove with respect to the embodiment of FIG.  1 . Thus material  12  moves horizontally in the direction of arrow  50 A. 
     Similarly, spacers  28 B and  72 B from piezoelectric motors  14 B, and  70 , respectively also act in a similar manner to spacers  28 A and  28 B and material  12  moves horizontally in the opposite direction (arrow  50 B). 
     It will be appreciated by persons skilled in the art that the present invention is not limited to AS what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined by the claims which follow: