an embossed sheet forming apparatus of one embodiment according to the present invention is described with reference to fig2 to 4 . 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 . 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 . 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 fig2 ). 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 rotatable about a central axis thereof without axial movement ( lateral movement in fig2 ). 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 ). 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 . as shown in fig4 , 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 . 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 . 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 . 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 . 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 ). 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 fig5 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . 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 . fig1 b 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 . 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 .