Patent Publication Number: US-7708268-B2

Title: Separator and feeder with vibrator for sheets of paper medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-143113, filed May 23, 2006, the entire contents of which are incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a separator/feeder for sheets of paper or paper-like medium for taking out such a medium. More particularly, the present invention relates to a separator/feeder for sheets of paper or paper-like medium that separates and feeds sheets of such a medium one by one from a pile of sheets of the medium. 
   2. Description of the Related Art 
   An apparatus adapted to check and process sheets of paper or paper-like medium (to be simply referred to as paper-like medium hereinafter) such as a printer, a copying machine, an automatic teller machine, a banknote processing machine, a mail matter processing machine or the like handles sheets of paper-like medium such as sheets of printing paper, banknotes, sheets of copying paper, sealed letters, postcards, cards securities or the like, whichever appropriate. More specifically, such an apparatus is required to take out sheets one by one from a pile of a plurality of sheets of paper-like medium. Therefore, such a checking apparatus is equipped with a separator/feeder for separating and feeding sheets of paper-like medium one by one from a pile of sheets of paper-like medium. For example, a banknote processing section of an automatic teller machine repeats an operation of taking out a banknote from a pile of banknotes stored in an input/output section or a depository and examines it. Thus, an automatic teller machine is equipped with a separator/feeder for separating banknotes one by one from a pile of banknotes. 
   Conventionally, separators/feeders for separating and feeding sheets of paper-like medium from a pile of sheets of paper-like medium are required to accurately feed sheets one by one without duplication as the most important requirement that have to meet. Sheets of paper-like medium are apt to be adsorbed by each other in a pile because some of the sheets are inevitably frayed at the time of manufacturing, if slightly, and loosened fibers become entangled or the sheets are held in tight contact with each other or generate static electricity. To date, such sheets of paper-like medium are mostly separated by applying a strong force to the uppermost surface of the piled sheets and a predetermined number of sheets of paper-like medium are stripped off from the pile. Then, the sheets that are stripped off are separated from each other by a duplicate feeding prevention mechanism or the like and fed into the host apparatus one by one. Various techniques are selectively employed in such duplicate feeding prevention mechanisms and the sheets that are laid one on the other and taken out from the pile as a bunch are forced into a narrow gap and separated from each other by the most popular one of the known techniques. For example JP-A 2003-261238 (KOKAI) discloses a technique with which rollers are arranged at the opposite sides of a narrow gap to rotate in various different directions and sheets that are laid one on the other are forced to pass through the gap. Then, the sheets are subjected to forces in opposite directions and separated from each other. However, in many occasions, it is difficult to reliably and satisfactorily separate sheets into individual ones by means of such a mechanism. In other words, sheets of paper-like medium that are strongly adhering to each other can be caught by the gap and locked there to give rise to a trouble of bringing the apparatus to a halt. 
   Techniques of applying vibrations to the uppermost surface of a pile of sheets of paper-like medium to separate the sheets with ease have been discussed. For example, JP-A 2004-2044 (KOKAI) discloses a technique of applying vibrations to sheets of paper-like medium. With this technique, a beam-shaped vibrating part is applied to the entire surface of a pile of sheets of paper-like medium in the transversal direction at a position located immediately upstream relative to a feed mechanism to reduce the adhesion of the sheets so as to operate as an auxiliary means of a duplicate feeding prevention mechanism. For this purpose, a bar-shaped vibrating part having a length greater than the width of the sheets of paper-like medium is arranged upstream relative to a takeout roller and sheets of paper-like medium are fed while it is being vibrated. 
   However, the arrangement of applying vibrations to sheets of paper-like medium when taking out the sheets of paper-like medium as disclosed in JP-A 2004-2044 (KOKAI) is accompanied by a problem as described below. As a result of an experiment conducted by the inventors of the present invention, it is indispensably necessary to apply appropriate pressure between the vibrator and the sheets of paper-like medium in order to vibrate the piled sheets of paper-like medium and loosen them. In other words, the effect of separating sheets of paper-like medium is not obtained simply by controlling the height of the uppermost sheet as described in JP-A 2004-2044 (KOKAI). 
   A mechanism for separating sheets of paper-like medium by applying vibrations to the sheets of paper-like medium until they start vibrating as disclosed in JP-A 2002-356240 (KOKAI). However, the disclosed mechanism can be used only in an apparatus where a paper-like medium having certain predetermined characteristics is supplied and additionally it is not possible to separate sheets of paper-like medium by means of the mechanism unless pressure of an appropriate pressure level is applied to the vibrator. The mechanism disclosed in FIG. 3 of JP-A 2000-177869 (KOKAI) cannot separate sheets of paper-like medium for a similar reason. 
   Additionally, the paper-like medium feeding position of conventional paper-like medium processing machine is fixed and the machine is so devised that a take out mechanism such as a takeout roller operates to take out sheets of paper-like medium while applying appropriate pressure to the sheets. More specifically, JP-A 2000-219334 (KOKAI) discloses a mechanism comprising a movable lever that is held in contact with the top surface of piled sheets of paper-like medium to detect the position of the top surface and constantly keep the top surface of the piled sheets of paper-like medium to a same position. In short, it is possible for the prior art to take out sheet of paper-like medium reliably without depending on the type of paper-like medium only by means of such a mechanism. 
   However, the mechanism of using a vibrator held in contact with the surface of piled sheets of paper-like medium is accompanied by a problem that the pressure being applied by the vibrator resists the operation of taking sheets of paper-like medium one by one. Particularly, when sheets of paper-like medium is soft, the sheets of paper-like medium are pressed down by and engaged with the vibrator to adversely affect the operation of taking them out. Therefore, it may be necessary to regulate the pressure according to the state of being pressed down. 
   As pointed out above, mechanisms for preventing duplicate feeding that takes place when sheets of paper-like medium tightly adhere to each other by means of ultrasonic vibrations are accompanied by a problem that the technique of controlling the pressure applied to piled sheets of paper-like medium by means of a vibrator is not reliably established. 
   BRIEF SUMMARY OF THE INVENTION 
   According to an aspect of the present invention, there is provided a separator/feeder comprising: 
   a holding mechanism configured to hold a pile of sheets of paper-like medium; 
   a vibrator which is held in contact with a first region of the top surface of the pile under a first contact pressure to apply high frequency vibrations to sheets of paper-like medium; 
   a takeout mechanism configured to take out the sheets of paper-like medium one by one from top surface of the pile in a state of being held in contact with the top surface of the pile to apply a second contact pressure to the top surface of the pile; 
   a first sensor which detects a first position of the vibrator held in contact with the pile and output a first detection signal; 
   a second sensor which detects a second position of the top surface of the pile in a second region of the pile and outputs a second detection signal; and 
   a control section configured to determine the first and second contact pressures according to the first and second detection signals and maintain the first and second contact pressures respectively in first and second predetermined ranges. 
   According a second aspect of the present invention, there is provided a separator/feeder comprising: 
   a holding mechanism configured to hold a pile of sheets of paper-like medium; 
   a vibrator which is held in contact with a first region of the top surface of the pile under a first contact pressure to apply high frequency vibrations to the sheets of paper-like medium; 
   a takeout mechanism configured to take out the sheets of paper-like medium one by one from top surface of the pile in a state of being held in contact with the top surface of the pile to apply a second contact pressure to the top surface of the pile; 
   a first sensor which detects the first position of the vibrator held in contact with the pile and outputs a first detection signal; 
   a second sensor which detects the second position of the top surface of the pile in a second region and outputs a second detection signal; and 
   a control section configured to determine the first and second contact pressures according to the outcome of a comparison of a first displacement of the first position and a second displacement of the second position before and after taking out the sheet of paper-like medium from the top surface of the pile according to the first and second detection signals and maintain the first and second contact pressures respectively in first and second predetermined ranges. 
   According to a third aspect of the present invention, there is provided a separator/feeder comprising: 
   a holding mechanism configured to hold a pile of sheets of paper-like medium; 
   a vibrator which is held in contact with a first region of the top surface of the pile under a first contact pressure to apply high frequency vibrations to sheets of paper-like medium; 
   a takeout mechanism configured to take out the sheets of paper-like medium one by one from top surface of the pile in a state of being held in contact with the top surface of the pile to apply a second contact pressure to the top surface of the pile; 
   a first sensor which detects the first position of the vibrator held in contact with the pile and outputs a first detection signal; 
   a second sensor which detects the second position of the top surface of the pile in a second region of the pile and outputs a second detection signal; and 
   a control section configured to compare the first and second detection signals to estimate the undulations of the first region of the pile, determine the first and second contact pressures according to the undulations and maintaining the first and second contact pressures respectively in first and second predetermined ranges. 
   Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a schematic illustration of a separator/feeder for sheets of paper-like medium subjected to an experiment of observing the effect of loosening sheets of paper-like medium by means of vibrations; 
       FIG. 2  is a graph summarily illustrating the results of the experiment conducted by using the separator/feeder for sheets of paper-like medium illustrated in  FIG. 1 ; 
       FIG. 3  is a schematic illustration of a first embodiment of separator/feeder for sheets of paper-like medium; 
       FIG. 4  is a schematic lateral view of the vibrating part of the vibrator of  FIG. 3 ; 
       FIG. 5  is a schematic lateral view of the ultrasonic horn of the vibrator of  FIG. 3 ; 
       FIG. 6  is a schematic lateral view of an ultrasonic horn obtained by modifying the ultrasonic horn of the vibrator of  FIG. 3 ; 
       FIG. 7  is a schematic lateral view of another ultrasonic horn also obtained by modifying the ultrasonic horn of the vibrator of  FIG. 3 ; 
       FIG. 8  is a schematic illustration of a separator/feeder obtained by modifying the embodiment of separator/feeder for sheets of paper-like medium of  FIG. 3 ; 
       FIG. 9  is a flowchart of the separation/feed operation of the separator/feeder of  FIG. 3 ; 
       FIGS. 10A to 10D  are schematic illustrations of the method of controlling pressure by comparing relative positional changes in the separator/feeder of  FIG. 3 ; 
       FIG. 11  is a flowchart of the operation of controlling the pressure of the vibrator of the separator/feeder of  FIG. 3  according to the outcome of comparison of relative positional changes in the separator/feeder; 
       FIGS. 12A and 12B  are schematic illustration of the method of comparing the absolute value of the position of the vibrator and that of the position of the uppermost surface of sheets of paper-like medium in the separator/feeder of  FIG. 3 ; 
       FIG. 13  is a flowchart of the operation of controlling the pressure of the vibrator of the separator/feeder of  FIG. 3  according to the outcome of comparison of positions in terms of absolute values in the separator/feeder; 
       FIG. 14  is a flowchart of the operation of continuously comparing the sensor outputs and controlling pressure in the separator/feeder of  FIG. 3 ; 
       FIG. 15  is a schematic illustration of a separator/feeder obtained by modifying the separator/feeder of  FIG. 3 ; 
       FIGS. 16A to 16C  are schematic illustrations of a second embodiment of separator/feeder for sheets of paper-like medium; 
       FIGS. 17A and 17B  are schematic illustrations of the operation of the separator/feeder for sheets of paper-like medium of  FIG. 16A  when the entire pile of sheets of paper-like medium is warped upward; 
       FIGS. 18A and 18B  are schematic illustrations of the operation of the separator/feeder for sheets of paper-like medium of  FIG. 16A  when the entire pile of sheets of paper-like medium is warped downward; 
       FIG. 19  is a schematic illustration of the operation of the separator/feeder for sheets of paper-like medium of  FIG. 16A  when the entire pile of sheets of paper-like medium is undulated; 
       FIG. 20  is a schematic illustration of a third embodiment of separator/feeder for sheets of paper-like medium; 
       FIG. 21  is a schematic illustration of a separator/feeder obtained by modifying the separator/feeder of  FIG. 20 ; and 
       FIG. 22  is a schematic illustration of the operation of reducing the moving distance of the sheets of paper-like medium in the vertical direction of the separator/feeder for sheets of paper-like medium of  FIG. 20 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Now, embodiments of separator/feeder for sheets of paper-like medium according to the invention will be described with referring to the accompanying drawings. 
   Before describing the embodiment of separator/feeder for sheets of paper-like medium, the observations of the inventors of the present invention on a separator/feeder for sheets of paper-like medium will be firstly described by referring to  FIGS. 1 and 2 . 
   The inventors of the present invention conducted an experiment of observing the effect of loosening sheets of paper-like medium by means of vibrations in a separator/feeder for sheets of paper-like medium as illustrated in  FIG. 1  and obtained results as summarily illustrated in  FIG. 2 . 
   The separator/feeder illustrated in  FIG. 1  and driven to operate in the experiment comprises a backup table  2  for delivering sheets. Sheets  11  of paper-like medium are laid one on the other to form a pile  6  of sheets of paper-like medium on the backup table (sheet delivery table)  2 . A vibrator  10  is arranged on and held in contact with the pile  6  to apply vibrations to the pile of sheets  11  of paper-like medium that are apt to adhere to each other. A takeout roller  3  for delivering sheets  11  of paper-like medium is also arranged on the pile  6 . In other words, the sheets  11  of paper-like medium are fed onto the backup table  2  from below so as to be piled on the backup table  2  and then the backup table  2  is raised until the top surface of the pile  6  comes into contact with the takeout roller  3 . As the takeout roller  3  is driven to rotate while it is held in contact with the pile  6 , the uppermost sheet is taken out in the direction of arrow S in  FIG. 1  and put into a sheet processing apparatus (not shown) due to the frictional force generated between the takeout roller  3  and the uppermost sheet  11  of paper-like medium of the pile  6 . The vibrator  10  is driven to vibrate in the directions indicated by arrow V in  FIG. 1  while backup force FE is applied to the pile  6  as the backup table  2  is raised in the direction indicated by arrow E in  FIG. 1 . Thus, the pile  6  is pressed against the takeout roller  3  and, at the same time, the vibrator  10  is also pressed against the pile  6  with a predetermined vibrator pressure FV. 
   In the separator/feeder for sheets of paper-like medium illustrated in  FIG. 1 , the pile  6  is pressed by the takeout roller  3  and the vibrator  10  is by turn pressed against the pile  6  with a predetermined vibrator pressure FV. Then, as the vibrator  10  is driven to vibrate and the vibrations of the vibrator  10  are applied to the pile  6 , the sheets of paper-like medium of the pile  6  become ready for being taken out one by one from the top. As the roller  3  is driven to operate in this state, the sheets of paper-like medium are fed out one by one in the direction indicated by arrow S in  FIG. 1 . 
   The experiment was conducted in a condition where the position of the takeout roller  3  of the separator/feeder for sheets of paper-like medium having the above-described configuration is fixed relative to the piled sheets  11  of paper-like medium and the pressure FE of the backup table  2  is made to change. In this experiment, the vibrator  10  is driven to vibrate at a frequency of 20 kHz and the pressure FV of the vibrator  10  is made to change and brought into contact with the uppermost surface of the sheets  11  of paper-like medium to observe the effect of the vibrations for loosening the sheets of paper-like medium.  FIG. 2  summarily illustrates the results of the experiment. In  FIG. 2 , the vertical axis indicates the backup force FE and the horizontal axis indicates the vibrator pressure FV, whereas the regions R 1 , R 2 , R 3  where a loosening effect is observed are indicated by respective broken lines. The broken line region R 1  is a region where piled envelopes are loosened appropriately and the broken line region R 2  is a region where piled official post cards are loosened appropriately, whereas the broken line region R 3  is a region where piled picture postcards are loosened appropriately. From the results of the experiment shown in  FIG. 2 , it was found to be important that the pressure of the vibrator  10  is regulated appropriately according to the backup force FE and the state of adhesion of the sheets  11  of paper-like medium is controlled properly in order to achieve a good effect of loosening sheets  11  of paper-like medium by bringing the vibrator  10  into contact with the surface of the piled sheets  11  of paper-like medium and applying high frequency vibrations. 
   It was found that a good loosening effect can be achieved for any type of sheets in terms of size and thickness when the pressures are limited to a predetermined range as indicated in  FIG. 2 . In other words, it was found that a good loosening effect can be achieved for a variety of types of sheets  11  of paper-like mediums when an appropriate condition is defined for the pressures. Such an appropriate pressure may vary from machine to machine depending on the frequency and the amplitude of the vibrator  10 , the design of the takeout roller  3  and other factors. From the above-described results of the experiment, it was found that a mechanism that can determine the pressures appropriately depending on machines is required to stably achieve a good loosening effect. 
   As seen from  FIG. 2 , it was also found that the vibrator  10  needs to be driven to vibrate sheets of paper-like medium with a frequency of an ultrasonic wave (a low frequency above the audible band or about 18 kHz to 28 kHz) and pressed against the sheets of paper-like medium with a pressure FV from 100 to 800 g, preferably from 180 to 450 g, with a backup force FE found within a range between 400 g and 1,200 g as requirements applicable to any type of paper-like medium. 
   When taking out sheets  11  of paper-like medium at high speed in a state where the vibrator  10  is held in contact with them, there arises a problem that the surface of the sheets  11  of paper-like medium is curved and deformed to show undulations. For example, when soft envelopes are to be loosened, the sheets  11  of paper-like medium is depressed and engaged with the vibrator  10  as they are pressed by the vibrator  10  so that it will be expected that they are fed in duplication and blocked by the vibrator  10  to give rise to tragic consequences. Additionally, it will be expected that the vibrator  10  cannot persistently follow the recessed or bulged surface of the pile  6  of sheets  11  of paper-like medium and jumps up to give rise to a situation where the vibrator  10  can no longer be stably held in contact with the sheets  11  of paper-like medium due to the relationship between the vibrator  10  and the proper vibration of the holding section holding the vibrator  10 . It is important that the vibrator  10  is constantly held in contact with the sheets  11  of paper-like medium in order to apply vibrations and effectively achieve a good loosening effect. Therefore, it is important to prevent a situation where the vibrator  10  cannot be stably held in contact with the sheets  11  of paper-like medium. 
   In order to avoid such tragic consequences, it is necessary to variably control the pressure FV according to the position where the vibrator  10  contacts the surface of the sheets  11  of paper-like medium. More specifically, when the sheets  11  of paper-like medium are curved to produce a recess due to the pressure of the vibrator  10 , it is necessary to control the vibrator  10  to reduce the pressure FV thereof in order to suppress the recess. When, on the other hand, the sheets  11  of paper-like medium are curved to produce a bulge that the vibrator  10  contacts, it is necessary to increase the pressure FV thereof in order to increase the contact area. 
   Now, this embodiment of separator/feeder for sheets of paper-like medium invented by the inventors of the present invention on the basis of the above observation will be described below. The separator/feeder for sheets of paper-like medium according to the embodiment comprises a mechanism for controlling the pressures FE and FV, a sensor for detecting the contact position of the vibrator  10  and a sensor for detecting the position of the uppermost surface of the piled sheets  11  of paper-like medium. Thus, it can control the pressures FE and FV. 
     FIG. 3  is a schematic illustration of the first embodiment of separator/feeder  100  of sheets of paper-like medium. The separator/feeder  100  comprises a backup table  26  bearing and supporting a pile  27  of sheets of paper-like medium. The backup table  26  is driven to move up and down by a drive mechanism  28 . Thus, the uppermost position of the pile  27  can be adjusted by means of the drive mechanism  28 . The uppermost position of the pile  27  is detected by a non-contact sensor  25  such as an optical non-contact displacement gauge. A takeout roller  21  of a takeout/feed mechanism  31  for taking out an uppermost sheet  29  of paper-like medium of the pile  27  is held in contact with the pile  27 . The takeout roller  21  is driven to rotate according to a drive signal from the roller drive circuit  40  and pressed against the pile  27  by means of a torque motor  33  of the feed mechanism  31 . A vibrator  22  is arranged to apply vibrations to the pile  27  by way of its front end that is held in contact with the pile  27 . The vibrator  22  is mechanically linked to a pressure adjustment mechanism  53  for pressing the vibrator  22  against the pile  27 . Thus, the pressure applied to the pile  27  by the vibrator  22  can be adjusted by the pressure adjustment mechanism  53 . The pressure adjustment mechanism  53  includes a torque motor  23  and pressure is provided to the vibrator  22  from the torque motor  23 . Since the torque motor keeps on pressing the vibrator  22  with a constant turning effort, the motor stops rotating to keep on applying a constant pressure when the vibrator is held in contact with the surface of the medium. The torque motor  23  is connected to a potentiometer  24 , which potentiometer  24  detects the position where the rotation of the torque motor  23  is stopped (rotational phase of the torque motor). The torque motors  23 ,  33  are driven by drive signals from respective torque motor drive circuits  30 ,  35 . The detection signal of the potentiometer  24  is output from potentiometer output circuit  36  to a control unit  101 . The control unit  101  controls the drive signal of the roller drive circuit  40  so as to drive the feed motor  21  to operate at a predetermined timing. The control unit  101  controls the outputs of the torque motors  23 ,  33  so as to respectively control the pressure adjustment mechanism  53  and the feed mechanism  31  and also controls the drive mechanism  28  so as to control the operation of driving the backup table  26  to move up and down. Additionally, the vibrator  22  is driven to operate by a drive signal from vibrator drive circuit  38 , which vibrator drive circuit  38  is also controlled by the control unit  101 . 
   The vibrator  22  is illustrated in  FIG. 3  in a simplified form. It has a structure where a vibrating part  12  as shown in  FIG. 4  is linked to an ultrasonic horn  14  as shown in  FIG. 5 . The vibrating part  12  is referred to as so-called bolt-held type vibrating part having a structure where a piezoelectric ceramic section  18 , or a piezoelectric element, having electrodes extending from the inside to the outside thereof is held tightly in position between a pair of blocks  15 ,  16  by means of a bolt  17  as shown in  FIG. 4 . The cylindrical block  15  and the disk-shaped piezoelectric ceramic section  18  are provided respectively with central through holes  15   a ,  18   a , which through holes  15   a ,  18   a  are threaded so as to be engaged with the bolt  17 . The cylindrical block  16  is also provided with a recess/hole  16   b  at the center of the side of the piezoelectric ceramic section  18 , which recess/hole  16   b  is also threaded so as to be engaged with the bolt  17 . Thus, as the bolt  17  is driven into the through holes  15   a ,  18   a  of the cylindrical block  15  and the disk-shaped piezoelectric ceramic section  18  and the recess/hole  16   b  of the cylindrical block  16 , the cylindrical block  15 , the disk-shaped piezoelectric ceramic section  18  and the cylindrical block  16  are mechanically linked to each other. 
   In the vibrating part  12 , as the disk-shaped piezoelectric ceramic section  18  is vibrated as a function of the drive voltage applied to the electrodes  13 , the entire vibrating part  12  vibrates and the vibrations of the vibrating part  12  are transmitted to the vibration surface  16   a  of the cylindrical block  16 . The amplitude of vibration of the piezoelectric ceramic section  18  is relatively small so that, if the ultrasonic vibrations of the vibration surface  16   a  of the cylindrical block  16  are taken out and applied to the surface of the pile  20 , it is not possible to apply vibrations that are large enough for loosening the sheets  2 . Thus, the vibrating part  12  is mechanically linked to the ultrasonic horn  14  in order to amplify the ultrasonic vibrations. 
   The vibration surface  16   a  of the cylindrical block  16  is provided with a threaded recess/hole  16   c  for the purpose of mechanically linking itself to the ultrasonic horn  14  shown in  FIG. 5 . The ultrasonic horn  14  is provided at the end facet of one of the opposite ends of cylindrical block section  19  thereof with a link section  19   a  to be engaged with the recess/hole  16   c . As the link section  19   a  is driven into and engaged with the recess/hole  16   c , the cylindrical block  16  and the cylindrical block section  19  are tightly brought into contact with each other and linked to each other. Thus, they become integral with each other. The total length of the cylindrical block section  19  is defined to be λ/4, where λ is substantially equal to the vibration wavelength. An extension  19   b  having a diameter smaller than the diameter Sb of the cylindrical block section  19  is extended from the opposite end facet of the cylindrical block section  19 . The front end of the extension  19   b  is made flat because it is brought into contact with the sheets  2 . In the ultrasonic horn  14 , the position of the opposite end of the cylindrical block section  19  is typically defined to be the position of the vibration mode (λ/4) and the diameter of the extension  19   b  extended from the opposite end is increased or decreased from that of the cylindrical block section  19  so that the amplitude of vibration transmitted through the cylindrical block section  19  is changed by the extension  19   b  and transmitted to the sheets  2  from the extension  19   b.    
   With the above-described structure of the ultrasonic horn  14 , the rate of vibration at the front end of the ultrasonic horn  14  is boosted to V1/V2=Sb/Sa. Due to such a structure of the ultrasonic horn  14 , it is possible to produce a large amplitude at the front end thereof and apply a sufficient acceleration to the sheets (medium)  2 . Note that V2 represents the rate of vibration transmitted to the cylindrical block  16  and V1 represents the rate of vibration output from the front end of the ultrasonic horn  14 . 
   In an experiment where ultrasonic horns  14  having respective front end diameters of Sa=5 mm, 10 mm and 20 mm are alternately linked to a 20×60 mm vibrating part  12 , it was proved that the vibration amplifying ratio Sb/Sa of the ultrasonic horn  14  is doubled. In this experiment, it was found that the friction reducing effect is strongest when Sa=5 mm. This is because, as the front end diameter of the ultrasonic horn  14  increases, the intra-planar vibration component increases relatively to obstruct the axial vibration component that operate for the vibrations. On the other hand, from the viewpoint of the contact of the ultrasonic horn  14  and the sheets (medium)  2 , the contact pressure falls as the diameter Sa increases when the force applied to the sheets as pressure remains the same so that the risk of damaging the medium falls. Therefore, it was found that the front end diameter Sa of the horn is effective when it is between about 5 and 20 mm from a realistic viewpoint for designing the ultrasonic horn. It was proved that no friction reducing effect is achieved when a vibrating part  12  is used without an ultrasonic horn  14 . 
   With the above-described vibrator  22 , as the ultrasonic horn  14  is pressed against the top of the piled sheets (pile)  20 , both the friction between the front end of the ultrasonic horn  14  and the uppermost sheet  2  and the friction between the upper most sheet  2  and the sheet  2  of the pile under it fall sufficiently so that it is possible to separate and bring out the uppermost sheet without duplication. 
   While a titanium alloy that is hard and least subjected to fatigue/failure is most suitable as the material of the ultrasonic horn  14 , an aluminum alloy or a nickel alloy may also be used depending on the frequency of use and other conditions. The profile of the ultrasonic horn  14  is not limited to the one illustrated in  FIG. 5 , where a large diameter cylindrical block and a small diameter cylindrical block are aligned and linked to each other along the same axial line with a step formed between them. For example, the diameter of the extension  19   b  may be decreased not abruptly but gradually toward the front end thereof as shown in  FIGS. 6 and 7 . More specifically, the extension  19   b  may be tapered from the cylindrical block  19  to show a curved profile as illustrated in  FIG. 6 . Alternatively, the extension  19   b  may be tapered linearly from the cylindrical block  19  as illustrated in  FIG. 7 . 
   While the contact area of the front end of the ultrasonic horn  14  is normally made to show a flat profile, it may be rounded when it can damage the medium, when its resistance is too strong and/or when it can catch an envelope at a small step of the latter. Additionally, the contact area of the front end of the ultrasonic horn  14  preferably does not have any undulations. 
   In the separator/feeder  100  of sheets of paper-like medium as shown in  FIG. 3 , firstly the drive mechanism  28  is driven to operate and raise the backup table  26  bearing a pile  27  of sheets of paper-like medium thereon under the control of the control unit  101 . Then, as a result, both the takeout roller  21  and the vibrator  22  press the uppermost surface of the pile  27 . Then, drive signals are applied respectively from the torque motor drive circuits  35 ,  30  to the torque motors  23 ,  33  to drive the torque motors  23 ,  33  so as to adjust the pressure between the vibrator  22  and the pile  27  and the pressure between the takeout roller  21  and the pile  27  under the control of the control unit  101 . Under this condition, the vibrator  22  starts vibrating according to the drive signal from the vibrator drive circuit  38 . Thus, the vibrator  22  vibrates with a frequency in an inaudible zone not lower than 18 kHz while pressing the pile  27 . Then, as a result, the sheets  29  of paper-like medium of the pile  27  are loosened by the vibrations applied to them from the vibrator  22 . Thereafter, the takeout roller  21  is pressed against the pile  27  due to the turning effort of the torque motor  33 . The takeout roller  21  is driven to rotate according to the signal from the roller drive circuit  40  while pressing the sheets  29  of paper-like medium. Thus, the sheets  29  of paper-like medium are sequentially scraped off from the pile  27  as the uppermost sheet and delivered in the sense of rotation of the takeout roller  21  due to the frictional force between the takeout roller  21  and the sheets of paper-like medium. 
   The torque motors  23 ,  33  are controlled by the control unit  101  for their rotary torque and the takeout roller  21  and the vibrator  22  are pressed against the sheets  29  of paper-like medium by predetermined respective forces. The potentiometer  24  indirectly detects the position of the vibrator as it is connected to the torque motor  23 , which is by turn connected to the vibrator  22 , to detect the rotational halting position of the torque motor  23  and outputs a detection signal that corresponds to the observed value to the control unit  101 . 
   The potentiometer  24  may be replaced by an optical position sensor  44  to directly observe the position of the vibrator  22  as shown in  FIG. 8 . In the separator/feeder  100  of sheets of paper-like medium illustrated in  FIG. 8 , the non-contact displacement gauge  25  detects the position of the uppermost surface of the pile of sheets of paper-like medium and outputs the observed value to the control unit  101 . The backup table  26  that operates as holding section bears a pile  27  of sheets of paper-like medium and holds the lowermost surface of the pile  27  of sheets of paper-like medium. The drive mechanism  28  for driving the backup table  26  actuates the backup table  26  according to the output of the control unit  101  to control the position of the uppermost surface of the pile  27  of sheets of paper-like medium. The control unit  101  is connected to the torque motor  23 , the optical position sensor  44 , the non-contact displacement gauge  25  and the drive mechanism  28  and controls the rotary torque of the torque motor  23  and the operation of the drive mechanism  28  according to the inputs from the optical position sensor  44  and the non-contact displacement gauge  25 . 
   In the separator/feeder  100  of sheets of paper-like medium illustrated in  FIG. 8 , the vibrator  22  is also vibrated by a drive signal from the vibrating part drive circuit  38  so that it vibrates while pressing the pile  27 . Thus, as a result, the sheets  29  of paper-like medium of the pile  27  are loosened by the vibrations applied by the vibrator  22  and the takeout roller  21  is driven to rotate by the turning effort of the torque motor  33  according to the signal from the roller drive circuit  40 , while pressing the pile  27 . Then, the sheets  29  of paper-like medium are sequentially scraped off from the pile  27  as the uppermost sheet and delivered in the sense of rotation of the takeout roller  21  due to the frictional force between the takeout roller  21  and the sheets  29  of paper-like medium. 
   The torque of the torque motor  23  is set to such a value that the pressure of the takeout roller  21  and that of the vibrator  22  that are applied to the sheets of paper-like medium get to respective target values. The optimum pressure of the takeout roller  21  and that of the vibrator  22  are defined in advance by referring to the results of one or more than one experiments conducted for the effect of loosening sheets of paper-like mediums because they are variable depending on the machine and the vibrator. For example, from the results of the experiment illustrated in  FIG. 2 , it is preferable that the pressure FE of the takeout roller is defined to be within a range between 600 [gf] and 900 [gf] and the pressure FV of the vibrator  22  is defined to be within a range between 200 [gf] and 350 [gf]. Therefore, the torque of the torque motor  23  is controlled so as to confine the pressures FE and FV within the respective ranges. 
   Now, the operation of the separator/feeder  100  for separating and taking out sheets of paper-like medium from a pile of sheets will be described below by referring to the flowchart of  FIG. 9 . Firstly, in Step S 1 , the control unit  101  starts the separator/feeder  100  of sheets of paper-like medium. When no sheet  27  of paper-like medium is found on the backup table  26 , a pile  27  of sheets of paper-like medium to be processed is set on the backup table  26  by an operator as indicated by Step S 2 . Subsequently, in Step S 3 , the control unit  101  starts controlling the separator/feeder. In Step S 4 , the control unit  101  sets the pressures FV, FE and the vibrator  22  is operated while applying the pressure FV to the sheets  29  of paper-like medium, whereas the pressure FE is also applied to the sheets  29  of paper-like medium and the operation of the takeout roller  21  for taking out the sheets  29  of paper-like medium is started as the position of taking out the sheets  29  of paper-like medium of the takeout roller  21  is controlled. Thus, the sheets  29  of paper-like medium are taken out sequentially. As the operation of taking out the sheets  29  of paper-like medium ends in Step S 5 , the control unit  101  controls the operation of controlling the set pressures FV, FE and the position of taking out sheets  29  of paper-like medium in Step S 6 . In Step S 7 , it is determined if a sheet  29  of paper-like medium to be taken out next is still found or not and the process returns to Step S 2  when there is a sheet  29  of paper-like medium to be taken out. If there is not any sheet  29  of paper-like medium to be taken out, control unit  101  stops the separator/feeder  100  of sheets of paper-like medium and ends the process in Step S 8 . 
   Now, the operation of controlling the pressures of Step S 4  shown in  FIG. 9  will be described in greater detail below. 
   The pressures FV, FE are controlled according to the undulations of the sheets  29  of paper-like medium. More specifically, each time a sheet  29  of paper-like medium is taken out, the position of the vibrator  22  and the uppermost position of the sheets  29  of paper-like medium are compared to detect undulations, if the sheets  29  of paper-like medium. For the comparison, either a technique of comparing relative positions for a change or a technique of comparing absolute values of the positions is used. These two techniques will be described in greater detail below. 
   Referring to  FIGS. 10A to 10D , the technique of controlling the pressures by comparing relative positions for a change will be described firstly. With the technique of comparing the relative positions for a change, the quantity of the positional move of the vibrator  22  between before and after taking out the uppermost sheet  29  of paper-like medium is detected by the sensor  24  or  44  and the quantity of the displacement of the uppermost sheet  29  of paper-like medium is detected by the sensor  25  and the quantity of the positional move and the quantity of the displacement are compared. 
   Firstly, as shown in  FIG. 10A , the takeout roller  21  is stopped and the position of the vibrator  22  before the uppermost sheet  29  of the pile of sheets of paper-like medium is taken out is detected. In other words, the sensor  24  or  44  detects the contact position X 1  of the vibrator  22  in a state where the vibrator  22  is held in contact with the uppermost surface of the pile  27  of sheets of paper-like medium and outputs the detection output X 1 . Similarly, the sensor  25  measures the height X 2  of the uppermost surface of the sheets  29  of paper-like medium and outputs the measurement output X 2 . 
   In  FIGS. 10A to 10D , the X-axis indicates the direction perpendicular to the uppermost surface of the pile  27  of sheets of paper-like medium and the upward direction as indicated by arrow X (which corresponds to the X-axis) is the positive direction. 
   Then, as shown in  FIG. 10B , the takeout roller  21  rotates to start taking out the uppermost sheet  29  of paper-like medium and the uppermost sheet  29  of paper-like medium is removed from the contact point of the vibrator  22  and the detection point of the sensor  25 . In the state where the uppermost sheet  29  of paper-like medium in  FIG. 10A  is removed as shown in  FIG. 10B , the sensor output changes and the vibrator  22  is lowered by the quantity of displacement a so that the sensor  24  or  44  outputs the sensor output (X 1 −a). Similarly, as the detection point on the uppermost surface of the sheets of paper-like medium of the pile  27  falls by the displacement b, the sensor  25  outputs the sensor output (X 2 −b). 
     FIG. 10C  shows the state where the uppermost sheet  29  of paper-like medium is completely taken out and the backup table  26  is raised in the direction of arrow X so that the height of the uppermost surface of the sheet  29  of paper-like medium of the pile  27  is adjusted. The sensor output changes in this state. If the state of  FIG. 10B  is switched to the state of  FIG. 10C  and the vibrator  22  is raised by the quantity of displacement c, the sensor output of the sensor  44  is changed to output (X 1 −a+c). As the uppermost surface detection point is raised by the quantity of displacement d, the sensor output of the sensor  25  is changed to output (X 2 −b+d). In other words, the quantity of the change ΔX 1  of the position of the vibrator  22  and the quantity of the change ΔX 2  of the uppermost surface position before and after the uppermost sheet  29  of paper-like medium is taken out are respectively (−a+c) and (−b+d). 
   By paying attention to the value of the quantity of the change ΔX 1 , it will be found that the displacement a is increased and the displacement c is decreased so that the quantity of change ΔX 1  is decreased when the sheet  29  of paper-like medium that is used to be the second sheet and newly becomes the uppermost sheet after taking out the former uppermost sheet  29  of paper-like medium is soft and the vibrator  22  is driven into the sheets  29  of paper-like medium. When, on the other hand, the contact section of the vibrator  22  contacts a hard raised part of the second sheet  29  of paper-like medium and pushed up by the latter, the displacement a is decreased and the displacement c is increased so that the quantity of change ΔX 1  is increased. Meanwhile, the sensor for detecting the uppermost surface position detects the position in such a way that it does not touch or touches the top surface only very weakly and hence does not press down the top surface of the sheets of paper-like medium so that the quantity of change ΔX 2  does not change depending on the type of sheets of paper-like medium. Thus, it is possible to determine the state of being raised or lowered of the contact point of the vibrator  22  by comparing the quantity of change ΔX 1  and the quantity of change ΔX 2 . If it is found that ΔX 1 &lt;ΔX 2  as a result of the comparison, the vibrator  22  is driven into the sheets of paper-like medium. If, on the other hand, it is found that ΔX 1 &gt;ΔX 2 , the vibrator  22  is pushed up by a raised section of the surface of the sheets of paper-like medium. Thus, the pressure FV of the vibrator  22  is determined according to the value of (ΔX 1 −ΔX 2 ). Once the pressure FV is determined, the values of the positions X 1 , X 2  are quickly reset. 
     FIG. 10D  shows a state where the values of the sensor outputs X 1 , X 2  are reset and the operation of taking out the sheet  29  of paper-like medium that newly becomes the uppermost sheet is started after determining the pressure. From the state of  FIG. 10D , the sheet  29  of paper-like medium is taken out as shown in  FIGS. 10B and 10C  and the pressure FV is determined once again. The operation of sequentially taking out sheets of paper-like medium is conducted as a result of repeating the above-described control operation. 
   In the description given above by referring to  FIGS. 10A through 10D , it is assumed for the sake of convenience that the uppermost sheet  29  of paper-like medium does not show any undulations in the state of  FIG. 10A  to describe the control process of the control unit for successively taking out sheets  29  of paper-like medium. When taking out a sheet  29  of paper-like medium for the first time after starting the separator/feeder, the values of the sensor outputs X 1  and X 2  are reset immediately before starting the takeout operation. Then, the quantity of change ΔX 1  and the quantity of change ΔX 2  are observed and the pressure FV to be applied to the uppermost sheet  29  of paper-like medium is determined when the backup table  26  is raised to set the uppermost sheet  29  of paper-like medium to be taken out first in position. 
     FIG. 11  is a flowchart of the operation of controlling the pressure FV of the vibrator  22  according to the outcome of the above-described comparison of the relative positions for a change. Referring to  FIG. 11 , as the takeout operation is started in Step S 21  after starting the separator/feeder, the sensor output X 1  and the sensor output X 2  are set to the respective initial values. Then, the sheets  29  of paper-like medium are moved by the backup table  26  in Step S 22  and the position of the uppermost surface of the sheets  29  of paper-like medium is set. At this time, the quantity of displacement ΔX 1  and the quantity of displacement ΔX 2  are detected. Then, the difference between the quantity of displacement ΔX 1  and the quantity of displacement ΔX 2  is computed and the relative position of the vibrator  22  is determined in Step S 23 . Thereafter, the pressure FV of the vibrator  22  is determined by means of a function (a function where the quantities of displacement are variables) according to the outcome of the computation of the difference of the quantities of displacement (ΔX 1 −ΔX 2 ) in Step S 24 . If, for example, the difference of the quantities of displacement is negative (ΔX 1 −ΔX 2 =−1 mm) and a recess is formed on the piled sheets  29  of paper-like medium, the pressure FV that is normally 250 [gf] may be reduced to 100 [gf]. If, on the other hand, the difference of the quantities of displacement is positive (ΔX 1 −ΔX 2 =1 mm) and a bulge is formed on the piled sheets  29  of paper-like medium, the pressure FV that is normally 250 [gf] may be raised to 300 [gf]. The function that is required in Step S 24  is appropriately defined according to the specifications of the separator/feeder. After the quantities of displacement ΔX 1 , ΔX 2  are reset, an operation of taking out the uppermost sheet  29  of paper-like medium is started in Step S 25 . After ending the operation of taking out the uppermost sheet  29  of paper-like medium in Step S 26 , it is determined if there is still a sheet of paper-like medium to be taken out successively or not in Step S 27 . The end of the operation of taking out the uppermost sheet  29  of paper-like medium in Step S 25  is defined appropriately depending on the situation. In other words, the operation may be ended when only a sheet  29  of paper-like medium is taken out or only when a predetermined number of sheets  29  of paper-like medium are taken out. If it is found in Step S 27  that there is still a sheet  29  of paper-like medium to be taken out successively, the process returns to Step S 22  and the position of the uppermost surface of the sheets  29  of paper-like medium is adjusted once again. If, on the other hand, it is found in Step S 27  that there is not any sheet  29  of paper-like medium to be taken out, the takeout operation of the separator/feeder is ended in Step S 28 . 
     FIGS. 12A and 12B  are schematic illustration of the technique of comparing the position of the vibrator  22  and the position of the uppermost surface of sheets  29  of paper-like medium in terms of absolute value. The position of the vibrator  22  immediately before the uppermost sheet  29  of paper-like medium is take out is detected by the sensor  24  or  44  and the uppermost position of the sheets  29  of paper-like medium is detected by the sensor  25  so that the sensor outputs of the two sensors  24  or  44  and the sensor  25  are compared with each other. 
     FIG. 12A  illustrates a state where the vibrator  22  touches the uppermost surface of the piled sheets  29  of paper-like medium and the front end position thereof X 1  is detected by the sensor  44  so that the sensor output X 1  is output, while the position of the uppermost surface X 2  of the pile  27  of sheets of paper-like medium is detected by the sensor  25  so that the sensor output X 2  is output. The direction perpendicular to the uppermost surface of the pile  27  of sheets of paper-like medium is the direction of the X-axis. The numerical values of the sensor outputs X 1 , X 2  immediately before the uppermost sheet of the pile  27  of sheets of paper-like medium is taken out is read in and compared to detect the undulations, if the pile  27  of sheets of paper-like medium that the vibrator  22  touches. More specifically, if the sensor output X 1  is smaller than the sensor output X 2  (X 1 &lt;X 2 ), the part where the vibrator  22  touches the pile  27  of sheets of paper-like medium is depressed. If, on the other hand, the sensor output X 1  is greater than the sensor output X 2  (X 1 &gt;X 2 ), the part where the vibrator  22  touches the pile  27  of sheets of paper-like medium is raised. Thus, the pressure of the vibrator  22  is determined according to the difference of the sensor outputs X 1 , X 2 . For example, if the difference of the sensor outputs X 1 , X 2  is negative (X 1 −X 2 =−1 mm), the pressure of the vibrator  22  that is normally 250 [gf] may be decreased to 100 [gf]. If, on the other hand, the difference of the sensor outputs X 1 , X 2  is positive (X 1 −X 2 =1 mm), the pressure of the vibrator  22  that is normally 250 [gf] may be increased to 300 [gf]. 
   After the pressure FV is determined, the uppermost sheet  29  of paper-like medium is taken out from the pile  27  of sheets of paper-like medium in the state where the pile  27  of sheets of paper-like medium is being vibrated. As the operation of taking out the uppermost sheet  29  of paper-like medium ends as shown in  FIG. 12B , the position of the uppermost surface of the sheets  29  of paper-like medium is put back to the state of  FIG. 12A . Then, the process where the numerical values of the sensor outputs X 1 , X 2  immediately before the uppermost sheet of the pile  27  of sheets of paper-like medium is taken out is read in and the pressure FV is set is repeated. 
   The process of controlling the pressure FV of the vibrator  22  according to the outcome of the comparison of the positions in terms of absolute value will be described by way of the flowchart of  FIG. 13 . After the control unit  101  starts to operate the separator/feeder and the operation of taking out a pile  27  of paper-like medium is started in Step S 31 , the values of the sensor outputs X 1 , X 2  are calibrated also in Step S 32 . Then, in Step S 33 , the pile  27  of paper-like medium are moved by the backup table  26  and the position of the uppermost surface of the pile  27  of paper-like medium is determined. Then, the values of the sensor outputs X 1 , X 2  are detected in Step S 34  and the pressure FV of the vibrator  22  is determined by means of a function that is defined according to the specifications of the separator/feeder depending on the different of the sensor outputs X 1 , X 2  in Step S 35 . Thereafter, a sheet  29  of paper-like medium is or a predetermined number of sheets  29  of paper-like medium are taken out in Step S 36 . When the operation of taking out a sheet  29  or the predetermined number of sheets  29  of paper-like medium ends, it is determined if there is a sheet  29  of paper-like medium to be taken out successively or not in Step S 37 . If there is a sheet  29  of paper-like medium to be taken out successively, the process returns to Step S 33  and the uppermost position of the pile  27  of paper-like medium is adjusted. If, on the other hand, it is found in Step S 37  that there is not any pile  27  of paper-like medium to be taken out, the sheet taking out operation ends in Step S 38 . 
   With this technique of comparing the positions in terms of absolute value, the values of the sensor outputs X 1 , X 2  may be continuously compared with each other to constantly control the pressure FV.  FIG. 14  is a flowchart of the process of constantly controlling the pressure FV. With the technique of continuously comparing the output values, after the control unit  101  starts to operate the separator/feeder and the operation of taking out a sheet  29  of paper-like medium is started in Step S 41 , the values of the sensor outputs X 1 , X 2  are calibrated also in Step S 41 . Then, in Step S 42 , the position of the uppermost surface of the sheets  29  of paper-like medium is adjusted and defined by the backup table  26 . Then, the values of the sensor outputs X 1 , X 2  are detected in Step S 43  and the pressure FV of the vibrator  22  is determined to a predetermined value according to the difference of the sensor outputs X 1 , X 2  and by means of a function that is defined according to the specifications of the separator/feeder in Step S 44 . Then, in Step S 45 , the operation of taking out the uppermost sheet  29  of paper-like medium is started by the takeout roller  21 . When it is found in Step S 46  that the uppermost sheet  29  of the paper-like medium has not been taken out yet, the process returns to Step S 43  and the pressure of the vibrator  22  is redetermined. When, on the other hand, it is found in Step S 46  that the uppermost sheet  29  of the paper-like medium has already been taken out, it is determined in Step S 47  if there is the next sheet  29  of paper-like medium to be taken out or not. If it is determined in Step S 47  that there is the sheet  29  to be taken out, the process returns to Step S 42  to adjust the uppermost position of the sheets  29  of paper-like medium. If, on the other hand, it is determined in Step S 47  that there is not any sheet  29  to be taken out, the sheet taking out operation ends in Step S 48 . The cycle period of the loop from Step S 43  to Step S 46  is determined so as to make the process most optimum depending on the separator/feeder. 
   With the above-described techniques, the pressure of the vibrator  22  is so controlled as to bring the uppermost surface of the sheets  29  of paper-like medium and hence the sensor output X 1  of the sensor  25  to a constant level when the backup table  26  is raised and the uppermost position of the sheets  29  of paper-like medium is moved. However, the present invention is by no means limited to such a control process. Alternatively, the control process may be such that the backup table  26  is not moved and held to a fixed position and a feed mechanism  31  including the vibrator  22  and the takeout roller  21  is moved toward the sheets  29  of paper-like medium until the feed mechanism  31  touches the uppermost surface of the sheets  29  of paper-like medium as shown in  FIG. 15 . 
   With the separator/feeder of  FIG. 15 , the feed mechanism  31  is mounted on a holding/moving mechanism  39  and controlled by the mechanism  39  so as to be movable toward the sheets  29  of paper-like medium. More specifically, as shown in  FIG. 15 , the feed mechanism  31  including the vibrator  22 , the torque motor  23 , the potentiometer  24 , the non-contact displacement sensor  25  is mounted on and anchored to the moving mechanism  39  and the moving mechanism  39  is moved with the feed mechanism  31  at the same time. With a separator/feeder equipped with such a moving mechanism  39 , it is possible to detect undulations of the pile  27  of sheets of paper-like medium at the contact point of the vibrator  22  by comparing the position of the vibrator  22  and the position of the uppermost surface of the sheets  29  of paper-like medium in terms of either relative value or absolute value. Then, it is possible to appropriately control the pressure FV. 
     FIGS. 16A and 16B  are schematic illustrations of the second embodiment of separator/feeder  100  of sheets of paper-like medium according to the invention. In the separator/feeder  100  of sheets of paper-like medium illustrated in  FIGS. 16A and 16B , the sensor  25  is arranged at the upstream side of the contact point of vibrator  22  where the vibrator  22  touches the uppermost sheet  29  of paper-like medium of a pile on a backup table as viewed in the direction of taking out sheets  29  of paper-like medium. Thus, the sensor  25  detects the position of the uppermost sheet  29  of paper-like medium in the X-direction at an upstream position relative to the contact point of the vibrator  22 . With this arrangement, it is possible to substantially control the pressure of the vibrator  22  according to the state of the surface of the uppermost sheet  29  of paper-like medium passing the contact point of the vibrator  22  during the operation of taking out the sheet  29  of paper-like medium. More specifically, the recess and the bulge, if the sheet  29  of paper-like medium are detected in advance immediately before the recess or the bulge comes into contact with the vibrator  22  so that it is possible to control the pressure of the vibrator  22  according to the extent (state) of recess or bulge of the sheet  29  of paper-like medium. For example, if the sheet  29  of paper-like medium is recessed at the position where it contacts the vibrator  22  and the bulge of the sheet  29  of paper-like medium that is coming to contact the vibrator  22  can be caught by the latter as shown in  FIG. 16C , the pressure FV of the vibrator  22  is reduced so that the sheet  29  of paper-like medium may smoothly pass under the vibrator  22 . It is desirable that the real time pressure control technique of controlling the pressure of a vibrator  22  as described above by referring to  FIG. 14  is applied to the separator/feeder illustrated in  FIGS. 16A and 16B . 
   As described above, the separator/feeder  100  can be used with a machine that handles various sheets of paper-like mediums that are different in terms of thickness, shape and size. 
   According to an experiment conducted by the inventors of the present invention, it was found that any change in the thickness of sheets  29  of paper-like medium does not substantially adversely affect the effect of reducing the frictional force of the vibrator  22 . This is because sheets of paper-like medium that are thicker than about 1.0 mm can hardly been taken out in duplicate. The inventors of the present invention conducted an experiment on sheets  29  of paper-like medium having a thickness between 0.1 mm and 1.0 mm. As a result of the experiment, it was found that the effect of loosening sheets  29  of paper-like medium is reduced slightly as the thickness of sheets  29  of paper-like medium increased but still conspicuously observed for thick sheets  29  of paper-like medium. On the other hand, no adverse effect such as a torn sheet  29  of paper-like medium was observed when the vibrator  22  touched a sheet  29  that was thin to a certain degree and the effect of loosening sheets  29  of paper-like medium was also conspicuously observed. In short, if the sheets  29  of paper-like medium to be treated show changes in the thickness, the above-described separator/feeder  100  of the embodiment operates effectively with respect to sheets  29  of paper-like medium having various thicknesses. 
   Now, the influence of a deformed sheet  29  of paper-like medium such as a warped sheet  29  on the operation of taking out the sheet  29  of paper-like medium and a control method that can accommodate the influence will be described below. When sheets  29  of paper-like medium show various shapes, it is possible to smoothly take out sheets  29  of paper-like medium by means of the technique of detecting the surface profile of the uppermost sheet  29  of paper-like medium in advance as described above in terms of the separator/feeder illustrated in  FIGS. 16A and 16B . 
   When the entire pile  27  of sheets of paper-like medium is bulged as shown in  FIG. 17A , the uppermost sheet  29  of paper-like medium will be lifted during an operation of being taken out as shown in  FIG. 17B  so that the vibrator  22  may no longer be able to follow the surface profile of the sheet  29  of paper-like medium. However, with the separator/feeder illustrated in  FIGS. 16A and 16B , if the uppermost sheet  29  of paper-like medium is lifted and the vibrator  22  is pushed up by the lifted sheet  29  of paper-like medium, no problem arises for detecting undulations of the sheet  29  of paper-like medium and the pressure of the vibrator  22  is raised immediately after the rear edge of the sheet  29  of paper-like medium passes the detection point of the sensor  25  because the relative position of the vibrator  22  is high so that the lift of the next sheet  29  of paper-like medium is suppressed and the next sheet  29  can be moved smoothly. Thus, the separator/feeder illustrated in  FIGS. 16A and 16B  can reliably take out the uppermost sheet  29  of paper-like medium if the entire pile  27  of sheets of paper-like medium is bulged. 
   When the entire pile  27  of sheets of paper-like medium is recessed as shown in  FIGS. 18A and 18B , there is a risk that the front end of the vibrator  22  damages the uppermost sheet  29  of paper-like medium. In this case again, with the separator/feeder illustrated in  FIGS. 16A and 16B , the recess and the bulge, if the sheet  29  of paper-like medium are detected in advance immediately before the recess or the bulge comes into contact with the front end of the vibrator  22  so that it is possible to reduce the pressure of the vibrator  22  and prevent the front end of the vibrator  22  from damaging the sheet  29  of paper-like medium. If the pile  27  of sheets of paper-like medium shows undulations as shown in  FIG. 19 , it is possible to take out the uppermost sheet  29  of paper-like medium without any problem by controlling the pressure FV of the vibrator  22  depending on the undulations of the sheet  29  of paper-like medium as detected at the position immediately before contacting the vibrator  22 . 
   Actual machines are devised to suppress changes in the profile of the pile  27  of sheets of paper-like medium. For example, an idle roller is pressed against the surface of the pile  27  of sheets of paper-like medium to suppress the warp, if the uppermost sheet  29  of paper-like medium. Therefore, it may be safe to assume that the deformation of the sheet of paper-like medium, if any, practically does not influence the operation of the vibration/loosening mechanism (vibration mechanism). As described above, the separator/feeder illustrated in  FIGS. 16A and 16B  can reliably loosen sheets  29  of paper-like medium, if the profile of the pile  27  of paper-like medium is deformed. 
   Now, the influence of the size of sheets  29  of paper-like medium on the loosening effect of vibrations will be discussed below. It may be safe to assume that the loosening effect of vibrations appears as the entire uppermost sheet  29  of paper-like medium vibrates. Therefore, when the sheets  29  of paper-like medium are very large, vibrations may not propagate over the entire uppermost sheet  29  and hence the loosening effect may not be satisfactory. When, the power of vibrations is weak, a satisfactory loosening effect can be achieved by arranging a plurality of vibrators  22  and a plurality of pressure mechanisms  53  for pressing the vibrators  22 . 
   If, on the other hand, the size of sheets  29  of paper-like medium is extremely small and the sheets  29  cannot brought into contact with the vibrator  22 , it is not possible to loosen such small sheets  29  of paper-like medium by vibrations. However, the present invention can be applied to sheets  29  of paper-like medium having the size of ordinary name cards or that of post cards, which is about 92 mm×52 mm. Thus, the above-described embodiments of separator/feeder according to the present invention can be applied to sheets of paper-like medium in general. 
     FIG. 20  is a schematic illustration of the third embodiment of separator/feeder  100  of sheets of paper-like medium according to the invention. Unlike the separator/feeder of  FIG. 3 , the separator/feeder  100  illustrated in  FIG. 20  is equipped with a displacement sensor  46  for detecting the position of the uppermost surface of a pile  27  of sheets of paper-like medium in place of the position sensor  25  of the separator/feeder of  FIG. 3 . The potentiometer that operates as the sensor  46  is connected to the torque motor  23  for driving the takeout/feed mechanism  31  and indirectly observes the position where the takeout/feed mechanism  31  touches the uppermost sheet  29  of paper-like medium by detecting the rotational position of the torque motor  23 . 
   Alternatively, an optical position sensor may be used as the sensor  46  to directly observe the position of the takeout/feed mechanism  31  as shown in  FIG. 21 . In  FIG. 21 , the sensor  46  observes the position of the pile  27  of sheets of paper-like medium like the sensor  25  of  FIG. 3 . In the case of the separator/feeder illustrated in  FIG. 21 , the pressure FV of the vibrator  22  is controlled according to the output of the sensor. 
   When a mechanism with which the vibrator  22  is pressed against sheets  29  of paper-like medium along the rotational trajectory thereof typically by a torque motor as illustrated in  FIGS. 3 ,  20  and so on, it is necessary to be careful about the observation coordinates of the sensors  24 ,  44 . The position of the vibrator  22  needs to be observed as the distance to the surface of the pile  27  of sheets of paper-like medium in the vertical direction. The distance of movement of the vibrator  22  on the rotational trajectory is reduced to the distance of movement in the direction perpendicular to the sheets  29  of paper-like medium as shown in  FIG. 22 . In the coordinate system shown in  FIG. 22 , the center of rotation of the torque motor  23  is selected as the origin of the coordinate system and the axis X running in the direction perpendicular to the uppermost surface of the pile  27  of sheets of paper-like medium is defined as reference axis. In the rotational coordinate system, the front end of the vibrator  22  is arranged with the initial angle of rotation θ1 and separated from the pile  27  of sheets of paper-like medium by distance X 1 . In this state, assume that the front end of the vibrator  22  is rotated with a radius of rotation of r by an angle of rotation of θ2 as a result of that the uppermost sheet  29  of paper-like medium is removed under the above conditions. Then, the distance X 1  is determined by the formula shown below.
 
 X   1   =r ·cos θ2 −r ·cos θ1
 
   The distance X 1  corresponds to the distance by which the front end of the vibrator  22  is moved linearly toward the sheets  29  of paper-like medium as a result of that the uppermost sheet  29  of the paper-like medium is removed. Thus, the pressure FV of the vibrator  22  is controlled by the sensor output X 1  that corresponds to the distance X 1  to give appropriate vibrations to and exert a loosening effect on the pile  27  of sheets of paper-like medium. Any computational technique may be used for reducing the distance into the sensor output X 1  so long as it is based on the above-described formula. Additionally, the difference between the quantity of movement on the rotational coordinate system and the quantity of movement after the reduction can be within the range of error depending on the machine. In such a case, the quantity of movement on the rotational coordinate system, or {r·(θ2−θ1)} may be directly used to determine the right position. 
   It is desirable that the largest permissible displacement of the position of the vibrator  22  is defined for each machine by referring to the thickness of the sheets  29  of paper-like medium to be handled in order to prevent any abnormal motion of the vibrator  22  from taking place. Additionally, it is desirable to stop the vibrations of the vibrator  22  when a positional change of the vibrator  22  that exceeds the largest permissible displacement is detected by the sensor  24  or  44 . For example, sheets  29  of paper-like medium that are handled by mail sorters has a thickness of 10 mm at most so that it may be so arranged that the vibrations of the vibrator  22  are stopped when the vibrator  22  is displaced by more than ±11 mm. 
   Displeasing resonating sounds arise when the vibrator  22  hits a structural part of the separator/feeder such as the backup table  26  that is a holding section, while vibrating. For the purpose of avoiding generation of noises that takes place when the vibrator  22  contacts some other part of the separator/feeder, it is desirable that the separator/feeder designed in such a way that the vibrating part of the vibrator  22  is free from any structural part made of metal, plastic or the like within the movable range of the vibrating part. 
   The above-described takeout/feed mechanism  31  is not limited to the takeout roller  21  of the friction/takeout type and may alternatively be a belt of the friction/takeout type, a roller or a belt mechanism of the vacuum suction type. 
   The mechanism for providing the contact pressure FV may be a torque motor, a pneumatic cylinder, a hydraulic cylinder or a spring structure. While a direct-acting mechanism is desirable for supporting the takeout/feed mechanism  31  and the vibrator  22 , a rotary mechanism may alternatively be used for supporting them. 
   The vibration frequency of the vibrator  22  needs to be higher than 18 kHz that is in the inaudible frequency range. The amplitude of vibrations of the front end of the vibrator  22  is required to be not less than 1 μm in order to reliably realize the effect of loosening a bundle of sheets of paper-like medium. 
   The holding section for holding a pile  27  of sheets of paper-like medium is not limited to the above-described backup table  26  and may be replaced by any other holding structure such as a structure for supporting the rear side of a pile  27  of sheets of paper-like medium by means of a plate-like member, a roller or a belt. 
   Any of various sensors that can detect the quantity of displacement of the pressure adjustment mechanism  53  and that of displacement of the vibrator  22  may be used for the sensors  24 ,  44 . Sensors that can be used for the purpose of the present invention include optical position sensors of the LED type and the laser type, sensors like potentiometers for detecting the rotational position of a torque motor and solenoid type sensors. 
   Any of various sensors that can detect the top position of the pile  27  of sheets of paper-like medium can be used for the sensor  25 . Sensors that can be used for the sensor  25  include optical position sensors of the LED type and the laser type and movable levers that touch the top surface of sheets of paper-like medium with a light pressure not greater than 100 [gf]. Alternatively, as described above, the sensor  46  may be arranged at the takeout/feed mechanism  31  to detect the top surface position of the pile  27  of sheets of paper-like medium from the position where the takeout/feed mechanism  31  contacts the pile  27  of sheets of paper-like medium. A sensor of the type same as the sensors  24 ,  44  may be used for the sensor  46 . 
   Preferably, the vibrator  22  and the sensor  25  are arranged with such a positional relationship that the distance between the contact point of the vibrator  22  with the pile  27  of sheets of paper-like medium and the detection point of the sensor  25  is about 5 to 20 mm and no undulations appear on the pile  27  of sheets of paper-like medium between them. 
   While a pile  27  of sheets of paper-like medium is placed on the backup table  26  in each of the above-described embodiments, it may alternatively be so arranged that the backup table  26  is standing and the pile  27  of sheets of paper-like medium is held by the backup table  26  in such a way that it is juxtaposed with a lateral surface of the backup table  26  so that a sheet  29  of paper-like medium of the pile  27  is taken out upwardly or downwardly from the front of the lateral side of the pile  27  of sheets of paper-like medium that is most remote from the backup table  26 . If the pile  27  of sheets of paper-like medium is not placed on the backup table  26  but the pile  27  of sheets of paper-like medium is held by the backup table  26  differently, the front of the lateral side of the pile  27  of sheets of paper-like medium where the sheet  29  of paper-like medium to be taken out is located is the top surface of the pile  27  of sheets of paper-like medium. Thus, the top surface of a pile  27  of sheets of paper-like medium may be the front of a lateral side of the juxtaposed pile  27  of sheets of paper-like medium for the purpose of the present invention. 
   As described above, with a separator/feeder for sheets of paper-like medium according to an aspect of the present invention, it is possible to reliably provide a loosening effect by means of vibrations regardless of the type of sheets of paper-like medium and reliably prevent sheets of paper-like medium from taken out in duplicate. 
   Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.