Abstract:
An embossed sheet forming apparatus has phase controlling means ( 33, 34 ) axially shifting a second embossing roller  11 , a front embossed profile detector  74  for detecting an embossed profile on a front surface of a both-sided embossed sheet  100 , a rear embossed profile detector  75  for detecting an embossed profile on the rear surface, both surfaces phase difference computing means  80  comparing a detection signal from the front embossed profile detector  74  and a detection signal from the rear embossed profile detector  75  for calculating an embossing phase difference in a sheet width direction between the embossed profiles on the both surfaces, and phase adjustment control processing means  77  inputting a phase difference signal representing the embossing phase difference from the both surfaces phase difference computing means  80  for outputting a command to the phase controlling means ( 33, 34 ) to cancel a deviation of the phase difference.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to embossed sheet forming apparatuses and related rotary phase difference control methods and, more particularly, to an embossed sheet forming apparatus and a related rotary phase difference control method for forming an optical high-precision both-sided embossed sheet.  
         [0002]     An optical high-precision both-sided embossed sheet such as a lenticular sheet for use in a rear projector screen has front and rear surfaces, both of which are formed with embossed patterns. Such a both-sided embossed sheet is, as disclosed in Japanese Patent Provisional Publication No. 2004-142182, formed by an extrusion molding method using an embossed sheet forming apparatus. This embossed sheet forming apparatus includes two embossing rollers, having outer peripheries engraved with patterns, which are juxtaposed in parallel with each other.  
         [0003]     The embossed sheet forming apparatus has issues as follows: When the embossed sheet forming apparatus is continuously operated, since the respective rolling speeds of the two embossing rollers are fluctuated, the speed ratio (draw ratio) of the two embossing rollers is also fluctuated. Consequently, the rotary phase difference of the two embossing rollers is fluctuated. The fluctuation of such a rotary phase difference (rotary phase deviation), as shown in  FIG. 1A , causes swell-like deviation (embossing phase deviation) to occur in the embossing phase difference of front and rear surfaces of the both-sided embossed sheet along a roller axis direction (sheet width direction).  
         [0004]     In  FIG. 1A , “LPs1” denotes the embossing phase of the front surface of the both-sided embossed sheet in a roller axis direction; “LPs2” the embossing phase of the rear surface of the both-sided embossed sheet in the roller axis direction; and “A” the phase difference of the phases LPs 1  and LPs 2 . The phase difference A shows that it cyclically and widely fluctuates the embossing phase deviation of the front and rear surfaces along the roller axis direction (sheet width direction).  
         [0005]     This embossed sheet forming apparatus therefore faces a difficulty in forming a both-sided high-precision embossed sheet that the embossing phase deviation of the front and rear surfaces falls within a tolerance.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention has been completed with the above issues in mind and has an object to provide an embossed sheet forming apparatus and a related rotary phase difference control method for preventing the cyclic remarkable embossing phase deviation of the front and rear surfaces of a both-sided embossed sheet, which arises from the fluctuation of the rotary phase difference of two embossing rollers, and for allowing the embossing phase deviation to fall within a tolerance.  
         [0007]     A first aspect of the present invention provides an embossed sheet forming apparatus having first and second embossing rollers juxtaposed in parallel with each other to allow the first and second embossing rollers to form a both-sided embossed sheet, comprising first-roller rotational origin position detecting means for detecting a rotational origin position of the first embossing roller, second-roller rotational origin position detecting means for detecting a rotational origin position of the second embossing roller, rotary phase difference computing means for computing a rotary phase difference equivalent to a difference between the rotational origin position of the first embossing roller detected by the first-roller rotational origin position detecting means and the rotational origin position of the second embossing roller detected by the second-roller rotational origin position detecting means, and rotary phase difference correction-amount computing means for computing a correction amount to correct a rotary speed ratio between the first and second embossing rollers such that when fluctuation occurs in a rotary phase difference computed by the rotary phase deviation computing means, the fluctuation in the rotary phase difference is cancelled, wherein the rotary speed ratio between the first and second embossing rollers is corrected based on the correction amount computed by the rotary phase difference correction-amount computing means.  
         [0008]     A second aspect of the present invention provides a method of controlling a rotary phase difference of an embossing sheet forming apparatus having first and second embossing rollers juxtaposed in parallel with each other to allow the first and second embossing rollers to form a both-sided embossed sheet, comprising detecting a rotary phase difference between the first embossing roller and the second embossing roller, and correcting a rotary speed ratio between the first and second embossing rollers so as to cancel a deviation of the rotary phase difference when fluctuation occurs in the rotary phase difference. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1A  is a graph illustrating a phase difference in a both-sided embossed sheet formed by an embossed sheet forming apparatus of the related art, and  FIG. 1B  is a graph illustrating a phase difference in a both-sided embossed sheet formed by an embossed sheet forming apparatus according to the present invention.  
         [0010]      FIG. 2  is a plane view showing one embodiment of an embossed sheet forming apparatus according to the present invention.  
         [0011]      FIG. 3  is a front view of a roller targeted for adjusting an axial phase in one embodiment of the embossed sheet forming apparatus according to the present invention.  
         [0012]      FIG. 4  is a skeletal view of a drive system and a phase control system of the roller targeted for adjusting the axial phase in one embodiment of the embossed sheet forming apparatus according to the present invention.  
         [0013]      FIG. 5  is a block diagram showing one embodiment of a control system of the embossed sheet forming apparatus according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     An embossed sheet forming apparatus of one embodiment according to the present invention is described with reference to FIGS.  2  to  4 .  
         [0015]     The embossed sheet forming apparatus includes a frame  10  as a base. The frame  10  has an operating station  10 A and a driving station  10 B, those on which roller bearing boxes  12 ,  13  are fixedly mounted.  
         [0016]     The roller bearing boxes  12 ,  13  have roller radial bearings  16 ,  17  that support roller shafts  14 ,  15 , the support roller shafts  14 ,  15  integrally formed with both ends of a second embossing roller  11 , respectively. The roller radial bearings  16 ,  17  allow the second embossing roller  11  to be rotatable about a center axis thereof and to be movable in the center axis direction.  
         [0017]     The operating station  10 A and the driving station  10 B of the frame  10  have linear guides  44 ,  45  that carry on roller bearing boxes  46 ,  47 , respectively. The roller bearing boxes  46 ,  47  are configured to be movable toward and away from the second embossing roller  11  in a radial direction thereof (vertical direction in  FIG. 2 ).  
         [0018]     The roller bearing boxes  46 ,  47  include roller radial bearings  51 ,  52  that support roller shafts  49 ,  50 , the roller shafts  49 ,  50  integrally mounted on both ends of a first embossing roller  48 , respectively, with a roller thrust bearing  54  (mounted only in the roller bearing box  47 ). The roller radial bearings  51 ,  52  allow the first embossing roller  48  to be roratable about a central axis thereof without axial movement (lateral movement in  FIG. 2 ).  
         [0019]     The first and second embossing rollers  48 ,  11  face with each other in parallel and play a role as embossing rollers that have outer peripheral surfaces, each of which is engraved with a circumferentially formed recess-shape embossing pattern (not shown).  
         [0020]     The second embossing roller  11  has a roller shaft  15 , carrying on a second roller measurement reference ring  78 , in a driving side thereof. Mounted on the frame  10  at a position close proximity to the second roller measurement reference ring  78  is a second-roller rotational origin position sensor (second-roller rotational origin position detecting means)  75  such as a proximity switch. The second-roller rotational origin position sensor  75  senses a rotational origin position detection magnet  76  mounted on the second roller measurement reference ring  78  to detect a rotational origin position of the second embossing roller  11 .  
         [0021]     As shown in  FIG. 4 , the roller shaft  15  has one axial end connected to a roller drive shaft  19  by means of a coupling (flange coupling)  18 . The roller drive shaft  19  extends in a roller axis direction thereof through a gear box  20  fixedly mounted on the frame  10  at the driving station  10 B and a hollow gear shaft  22  rotatably supported by a roller radial bearing  21  in the gear box  20 .  
         [0022]     The roller drive shaft  19  is coupled to the hollow gear shaft  22  by means of a slide key, a spline  23 , or the like with a torque transcript relationship satisfying displacing capability in the roller axis direction. The hollow gear shaft  22  carries on a drive gear  24 . Mounted inside the gear box  20  is a second roller drive motor (servomotor)  25  with a reduction gear unit.  
         [0023]     Mounted on an output shaft  26  of the second roller drive motor  25  is an output gear  27  that is held in meshing engagement with the drive gear  24 . Mounted on the second roller drive motor  25  is a pulse generator (rotary position detector)  72  for detecting a motor rotating position of the second roller drive motor  25 .  
         [0024]     The second roller drive motor  25  generates rotational force that is transcribed to the roller shaft  15  through the motor shaft  26 , the output gear  27 , the drive gear  24 , the slide key or the spline  23 , the roller drive shaft  19  and the coupling  18 . This transmission of the rotational force causes the second embossing roller  11  to rotate about the center axis thereof.  
         [0025]     The roller drive shaft  19  has an axial end that is connected to a shift member  34  of a phase controller means  33  in a roller axis direction (widthwise direction of a product) by means of a rotary sliding coupling  28 . The rotary sliding coupling  28  includes a rotary case  29 , to which an axial end of the roller drive shaft  19  is fixedly connected, and a coupling shaft  32  disposed in coaxial relationship with the roller drive shaft  19 . The coupling shaft  32  is support to a radial rotary bearing  30  mounted in the rotary case  29  and a thrust roller bearing  31  for relative rotation capability without movement in an axial direction (roller axis direction).  
         [0026]     The rotary sliding coupling  28  shuts off the transmission of the rotation of the roller drive shaft  19  to the shift member  34  by means of the combination of the radial roller bearing  30  and the thrust roller bearing  31 , while permitting an axial force of the shift member  34  to be transcribed to the roller drive shaft  19 . The thrust roller bearing  31  is also applied with a preload such that the rotary case  29  is connected to the coupling shaft  32  without looseness in the roller axis direction.  
         [0027]     The shift member  34  of the phase controller means  33  is comprised of a slide base  35  and a ball-nut member  36  fixedly secured to the slide base  35  without rotation. The shaft member  34  is movable in the same direction as the roller axis direction by means of a linear guide  37  mounted on the driving station  10 B of the frame  10 . The ball-nut member  36  is coaxially aligned with a central axis of the second embossing roller  11  and held in screwing engagement with a ball screw rod  38 .  
         [0028]     The ball screw rod  38  is rotatably supported by a radial roller bearing  40  and a thrust roller bearing  41  mounted in a bearing box  39  and drivably connected to an output shaft (not shown) of a phase control reduction gear motor (servomotor)  43  by means of a shaft coupling  42 .  
         [0029]     When the phase control reduction gear motor (servomotor)  43  rotatably drives the ball screw rod  38 , the shift member  34  involving the ball-nut member  36  is shifted in the same direction as the roller axis direction. Since such shifting movement is transcribed to the roller drive shaft  19  and the roller shaft  15  through the rotary slide coupling  28 , the second embossing roller  11  is axially moved. With such axial movement, phase control is performed in the roller axis direction.  
         [0030]     The bearing boxes  46 ,  47  of the first embossing roller  48  are moved in parallel with each other in a roller-to-roller gap direction (radial direction of the roller) by means of feed screws  58 ,  59  driven by roller-to-roller gap adjustment motors  56 ,  57 , respectively. With such movements, a roller-to-roller gap between the first and second embossing rollers  11 ,  48  is adjusted.  
         [0031]     The roller shaft  50  of the driven station of the first embossing roller  48  has a first roller measurement reference ring  77 . The frame  10  carries on a first-roller rotational origin position sensor (first-roller rotational origin position detecting means)  73  such as a proximity switch, at a position close proximity to the first roller measurement reference ring  77 . The first-roller rotational origin position sensor  73  senses a rotational origin position detection magnet  74  mounted on the first roller measurement reference ring  77  to detect a rotational origin position of the first embossing roller  48 .  
         [0032]     The roller shaft  50  has an axial end drivably connected to a motor shaft  62  of a first roller drive motor (servomotor)  61  by means of a constant velocity universal joint  60  using a Schmidt coupling and others.  
         [0033]     The first roller drive motor  61  is of a type that includes a reduction gear and generates rotational force of the first roller drive motor  61  that is transcribed to the roller shaft  50  through motor shaft  62  and the constant velocity universal joint  60 . This transmission of the rotational force causes the first embossing roller  48  to rotate about a central axis thereof. Mounted onto the first roller drive motor  61  is a pulse generator (rotary position detector)  71  for detecting a motor rotary position of the first roller drive motor  61 .  
         [0034]     A T-die (not shown) is located in a position just above a gap portion between the first and second embossing rollers  11 ,  48 . The T-die supplies embossing sheet forming resin to the gap portion between the first and second embossing rollers  11 ,  48  under a melted condition. Melted resin supplied to the gap portion between the first and second embossing rollers  11 ,  48  is formed in a sheet-like configuration between the rollers by extrusion molding. After an embossed sheet (product) whose both surfaces are embossed is produced, the following step is executed.  
         [0035]     One embodiment of a control system for controlling a rotary phase difference with the embossed sheet forming apparatus according to the present invention is explained with reference to  FIG. 5 .  
         [0036]     The embossing sheet forming apparatus performs rotary phase difference control using a microcomputer  80 . The microcomputer  80  includes a CPU for executing various computing operations, a ROM  82  storing an operational sequence and computer programs, a RAM  83  used for working memories, a liquid crystal display  84 , a touch panel  85 , D/A converters  86 ,  88 , and I/O port (interface)  90 .  
         [0037]     Connected to the D/A converter  86  is a motor driver  87  for the first roller drive motor  61 . Connected to the D/A converter  88  is a motor driver  89  for the second roller drive motor  25 .  
         [0038]     Based on a command, inputted from the microcomputer  80 , for rotation of the first embossing roller and a pulse signal, inputted from the pulse generator  71 , resulting from detecting a motor rotary position of the first roller drive motor  61 , the motor driver  87  drives the first roller drive motor  61 , that is, rotates the first embossing roller  48  in feedback control.  
         [0039]     Based on a command, inputted from the microcomputer  80 , for rotation of the second embossing roller and a pulse signal, inputted from the pulse generator  72 , resulting from detecting a motor rotary position of the second roller drive motor  25 , the motor driver  89  drives the second roller drive motor  25 , that is, rotates the second embossing roller  11  in feedback control.  
         [0040]     The microcomputer  80  has the I/O port  90  to which the motor drivers  87 ,  89  and the first and second roller rotational origin position sensors  73 ,  75  are connected. The microcomputer  80  is thus applied with pulse signals (rotary position detection signals) output from the pulse generators  71 ,  72 , a rotational origin position signal of the first embossing roller  48  delivered from the first-roller rotational origin position sensor  73 , and a rotational origin position signal of the second embossing roller  11  delivered from the second-roller rotational origin position sensor  75 .  
         [0041]     The CPU  81  of the microcomputer  80  realizes a rotary phase deviation computing means  101  and a rotary phase-deviation correction-amount computing means  102  by executing various computer programs.  
         [0042]     The rotary phase difference computing means  101  computes a rotary phase difference ΔP, which is equivalent to a difference in a rotational direction between a rotational origin position of the first embossing roller  48  and a rotational origin position of the second embossing roller  11 . Here the rotational origin position of the first embossing roller  48  is detected by the first roller rotational origin position sensor  73 , and the rotational origin position of the second embossing roller  11  is detected by the second roller rotational origin position sensor  75 . In particular, the rotary phase difference computing means  101  computes the rotary phase difference ΔP by counting either one of pulse signals delivered from the pulse generators  71 ,  72 , during a time interval between a time when the first roller rotational origin position sensor  73  detects the rotational origin position of the first embossing roller  48  and a time when the second roller rotational origin position sensor  75  detects the rotational origin position of the second embossing roller  11 . Here the pulse signals is PG-frequency-divided pulses in the present embodiment.  
         [0043]     When the rotary phase difference ΔP computed by the rotary phase difference computing means  101  is varied, the rotary phase difference correction-amount computing means  102  computes a draw ratio correction amount Cd for correcting a rotary speed ratio (draw ratio) between the first and second embossing rollers  48 ,  11  so as to cancel the deviation of the rotary phase difference ΔP. In particular, the rotary phase difference correction-amount computing means  102  computes the draw ratio correction amount Cd with the following steps: (1) By subtracting a reference value ΔPd from a rotary phase difference ΔPr, where the reference value ΔPd is the average value of the rotary phase difference ΔP at a time when the reference value ΔPd is set up, and the rotary phase difference ΔPr is a rotary phase difference at a time when the rotary phase difference ΔP is corrected; (2) By multiplying the difference (ΔPr−ΔPd) by a correction coefficient (%/deg.). Here the correction coefficient (%/deg.) is set up on the touch panel  85 .  
         [0044]     The time when the reference value ΔPd of the rotary phase difference ΔP is set up can be regarded to be a time at which a preset button is pressed on the touch panel  85 . The time when the rotary phase difference ΔP is corrected may be cyclically determined for a specified seconds time interval, a specified number of rotations, or the like.  
         [0045]     The microcomputer  80  corrects the rotary speed ratio of the first and second embossing rollers  48 ,  11 , based on the draw ratio correction amount Cd computed by the rotary phase difference correction-amount computing means  102 .  
         [0046]     With the correction of such a rotary speed ratio, the difference (ΔPr−ΔPd) of the rotary phase difference is cancelled, thereby avoiding the variation of the rotary phase difference of the first and second embossing rollers  48 ,  11 .  
         [0047]     This can avoids cyclic remarkable embossing phase deviation on the front and rear surfaces of an embossed sheet, which arises from the fluctuation of the rotary phase difference of the first and second embossing rollers  48 ,  11 , and consequently, a double-sided high precision embossed sheet can be formed with a embossing phase deviation falling within a tolerance.  
         [0048]      FIG. 1B  shows a phase difference B between an embossing phase LPs 1  in the axis direction of an upper roller, which corresponds to a front surface of a both-sided embossed sheet, and an embossing phase LPs 2  in the axis direction of a lower roller, which corresponds to a rear surface of the both-sided embossed sheet, according to the embossed sheet forming apparatus of the present embodiment. The phase difference B shows that any remarkable embossing phase deviation does not cyclically occur on the front and rear surfaces of the both-sided embossed sheet along a widthwise direction thereof, and the embossing phase deviation falls within a tolerance.  
         [0049]     The entire content of Japanese Patent Application No. P2005-123749 with a filing data of Apr. 21, 2005 of which is expressly incorporated herein by reference in its entirety.