Patent Publication Number: US-6663211-B2

Title: Printing device and roll paper

Description:
This application is a continuation application Ser. No. 09/298,877 filed Apr. 26, 1999 abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a printing device like an ink jet printer for ejecting ink onto roll paper for printing. More specifically, this invention relates to a printing device for detecting type of roll paper loaded, the presence or absence of the roll paper, the leading end of the roll paper, and a preferable roll paper to be used in a printing device. 
     PRIOR ART 
     Nowadays, it has become possible for everybody to easily perform image printings thanks to the progress of computers and printing devices. Among the characteristic examples of printing devices is known an electrophotographic copier which causes a toner to adhere onto an electrostatic potential image formed on the paper roll and transcript the toner image onto the printing paper, a printing device which is called an ink jet printer of the aforementioned ink jet type or a printing device which is called a thermal transfer printer of a thermal transfer type which is adapted to melt the ink on the ink ribbon by means of a heated thermal head or cause the heat sensitive paper to be colored. 
     While color printing in general is required to have a good color tone quality and wheatherproofness, a wide application of printing media varing from paper, cloth, film or the like is seen and in order to maintain a printing quality in an excellent condition, the printing conditions are in general subjected to review on the basis of the type or property of a printing medium. 
     While it is possible to discriminate types of paper used through its factors such as surface roughness, light transparency and rigidity, but it is not practical to mount detection mechanism for that purpose upon printing device, because one detection device is necessary for anything of said paper factors, thus increasing considerably the cost of printing device. When detecting type of paper using the factor of light transparency, only three states of paper, i.e. transparent, translucent and opaque, which limits adaptation to more and more various types of paper. As described above, direct detection of paper type has been difficult in technical and economical view points. 
     In general, users of printing device have input the type of paper used into printing device by any means. One of these means has been setting of the type of paper on the operating panel of printing device by user. More recently, the information about type of paper to be used is often transferred into printing device from personal computer together with printing data. In the last case, user selects his desired type of paper from Paper Menu printed on a software called Printer Driver containing types of paper such as common paper, coat paper, film for a overhead projector (OHP), back print film, burnished paper and the like. 
     In addition, it is essential to set printing paper sheets neatly on the printing device. If not, it is not only impossible to maintain the printing quality but also likely to lead to the trouble in which the printing head can rub the printing face of the paper sheet or perform the printing action without the printing paper sheet being fed onto the platen with the result that the paper sheet is stained or the printing head and the platen are damaged to lead to the trouble of the printing device. 
     Therefore, it is required in general to refrain from performing a printing operation when the printing paper is not set properly or has run out. 
     In the case of a printing device which uses a long roll paper which necessitates a paper cut mechanism for cutting off the roll paper, it is often observed that an immediate start of the subsequent printing operation after the paper cutting operation to create an extra margin on the leading end of the paper sheet, which must be thrown away. This is not only a waste of paper but also another cutting operation must be done after the subsequent cutting of the roll paper, causing a duplication of work. 
     In such conventional method of using the roll paper, the roll paper payed out from the paper roll is fed in an opposite direction to the regular feed direction to reduce a margin space in the leading end of the paper as much as possible. 
     On the other hand, while there are several cases where one can easily discriminate paper used by means of appearance thereof and touch feeling thereon, there are so many papers which have resembling appearance and feeling. Therefore, users erroneously set different types of papers such as common paper and coat paper, both of which have same color at a glance, though they have quite different colors when reviewed carefully. 
     In case where the printing device is constructed such that it performs the printing operation by switching the printing conditions in accordance with the type of printing paper to be used, printing can be done on a condition other than suited for the paper if the operator makes an erroneous setting concerning the type of printing paper with the result that the printing quality desired by the operator cannot be obtained. Further, if the operator uses a printing device of the ink jet type which for example can perform a printing operation in not prescribed ink quantity for some type of printing paper. In this way, if setting is done on the basis of a wrong type of paper, extra ink used can adhere to some portions of the printing device to such an extent as thus staining the printing device or the printing paper. 
     Detecting devices used in a conventional printing device are known as a lever type, an optical type, etc. 
     In said lever type printing paper detect mechanism, the lever position varies depending upon the presence or absence of the printing paper and said varied lever position is detected as ON/Off signals of the switch. On the other hand, an optical type paper detection mechanism includes a reflection type in which a light irradiated by the light emitting portion onto the paper to be reflected thereby is detected by the light receiving portion and a transmission type in which a light transmitted is detected by a light receiving portion positioned opposite the light emitting portion. 
     In said optical paper detection mechanism of reflection type permits the variation of the intensity of reflection of the light irradiated by the light emitting portion on the basis of the presence or absence of the printing paper to be converted into the variation of the electrical output for detection. On the other hand, the optical paper detection mechanism of transmission type converts into the variation of electrical output the variation of intensity of light determined depending on whether or not to interrupt the light irradiated by the light emitting portion on the basis of the presence or absence of the printing paper. 
     In the conventional printing paper detect mechanism, it is possible to detect the presence or absence of the printing paper regardless of the light transmitting property whether transparent or opaque if the mechanism is of a lever type. However, such mechanism has a problem that it is necessary to bring the lever in contact with the platen by way of the printing paper in order to detect the presence or absence of the printing paper at the printing portion, causing the lever to contact the platen directly if there is no printing paper thereat with the result that the platen can be damaged. Therefore, an optical paper detect mechanism of reflection type is used in general as a paper detection mechanism. 
     Such optical paper detection mechanism of reflection type has another problem that it is impossible as is to detect the presence or absence of the printing paper if the paper is a light transmitting transparent sheet such as OHP paper. Then, a light reflecting opaque portion is formed at an end portion (said end portion taken in a direction perpendicular to the paper feed) of the transparent sheet so that said opaque portion reflects the light to be detected. However, such method also has a problem that the opaque portion at the end of the printing paper makes it impossible to effectively use the entire surface of the printing paper and makes the opaque portion too conspicuous to prevent the printed image from viewed easily when projected by an over head projector. 
     Further, excessive rewinding of the roll paper in the user&#39;s attempt at saving the paper or any possible misalignment of the leading end of the roll paper upstream of the correct position of printing portion can cause a printing action to be performed against the platen or cause a clogging of paper as a result of excessive rearward feed. 
     SUMMARY OF THE INVENTION 
     In view of the above points, it is the object of the present invention to provide a printing device which is capable of automatically detecting the type of the roll paper. 
     It is another object of the present invention to provide a printing device which is capable of effectively detecting the presence and absence of the roll paper formed of a light transmitting transparent sheet by means of an optical printing paper detect mechanism and a roll paper which is detected in a favorable condition by the optical printing paper detection mechanism. 
     It is a further object of the present invention to provide a printing device which is capable of automatically detecting whether or not the leading end of the roll paper fed for the printing operation is positioned properly when the roll paper has been rewound in order to prevent an extra margin from being formed. 
     In order to achieve the aforementioned object, a printing device according to claim 1 is characterized by a holder engaging member which is movable and can be applied onto peripheral surface of the flange of said holders of said paper roll held by said paper roll holding mechanism, by a paper type detection unit for detecting type of said roll paper according to the position of said flange engaging correspondingly to outer diameter of said flange representing type of said roll paper used, by a paper presence/absence detection unit for detecting the presence or absence of said roll paper without contact therewith is located in said printing portion so as to oppose to said platen, by a paper leading end detection unit for detecting the leading end of said roll paper is located between said printing portion and a cutting portion, and control means for controlling actions of the relevant portions on the basis of the detection result of each detection unit. 
     In such a construction, said paper type detection unit can automatically detect type of paper only by amounting a flange, outer diameter of which is adapted to type of roll paper, said paper presence/absence detection unit can automatically detect the presence or absence of said roll paper without contact therewith, said paper leading end detection unit can automatically detect whether the paper leading end of said roll paper is in a appropriate position or not, and control means can control appropriate actions of the relevant portions on the basis of the detection result of each detection unit. 
     The printing device according to claim 2 is characterized in that the detecting unit of paper presence/absence is composed of a photosensor while the control means is constructed to determine the paper type by reversing information from the photo sensor on the basis of a result whether or not light transmission. 
     By adopting the aforementioned construction, the it is possible to automatically detect the presence/absence of the roll paper by means of the photosensor notwithstanding the result as to whether or not the roll paper is of light transmitting nature. 
     The roll paper according to claim 3 is characterized by being formed of a light transmitting transparent sheet and having a light reflector at the trailing end thereof. 
     By adopting the aforementioned construction, it is possible to effectively use the entire surface of the roll paper if said roll paper is formed of a light transmitting transparent sheet and said light reflector of the roll sheet is capable of automatically detecting the presence/absence of the paper. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an embodiment of the printing device according to the invention; 
     FIG. 2 is a partial side view of the printing device shown in FIG. 1; 
     FIG. 3 is a plan view showing the roll holding mechanism shown in FIG. 1; 
     FIG. 4 is a front view of the paper roll used in the embodiments; 
     FIG. 5 is perspective views showing the paper roll used in the embodiments; 
     FIG.  6 (A) is an enlarged perspective view of the paper type detection unit and FIG.  6 (B) is a perspective view of the essential portion of FIG.  6 (A); and 
     FIG. 7 is a control block diagram including the control means of the printing device shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of printing device  1  according to the present invention as shown in FIG.  1  and FIG. 2, has a housing  2 , in which a cylindrical platen  3  is rotatably mounted with its axis extending in horizontal direction. Said surface of platen  3  can absorb light and is controlled not to reflect light such as a coarse surface to assure diffused reflection or blacked surface to absorb light. A driven pulley (not-shown) is supported by one end to said platen  3 , a belt  5  driven by a first reversible motor  4  being wound on said driven pulley. Accordingly, said platen  3  can be driven by driving force of said first motor  4  in the normal transporting direction or in the reverse direction. 
     A paper roll  6  having an axis parallel to said platen  3  is mounted on the rear side of said platen  3  in said housing  2 . A roll paper  6   a  to be explained later, being wound on the peripheral surface of said paper roll  6 . When said paper roll  6  is rotated in counter-clockwise direction in FIG. 2, roll paper  6   a  to be used is released out of paper roll  6  to be wound on the upper side of said platen  3 . 
     Said paper roll  6  is supported as shown in FIG. 3 on a pair of holding portions  9 A and  9 B of paper roll holding mechanism over a base section  7  of the printing device  1  with a spacing therebetween in a longitudinal direction. Of the two members, the holding portion  9 B is detachably loaded at a plurality of positions on a holding portion supporting plate  10  to fit the width of the roll paper  6   a . Close to said holding portion  9 A, detection unit  11  of paper type for detecting the type of the roll paper  6   a  used as a printing paper. 
     As shown in FIG. 4, said paper roll  6  comprises said roll paper  6   a  wound on a paper tube (not-shown), said paper tube having paper tube holders  6   b ,  6   b  mounted on its both ends, and these paper tube holders being held respectively by said roll holders  9 A,  9 B. Said each paper tube holder  6   b ,  6   b  has round flange portion  6   c  having a diameter larger than that of roll paper  6   a . According to the invention, the diameter of said flange portions  6   c  has different size according to the type of roll paper  6   a  wound on said paper tube, i.e. common paper, coat paper, film for OHP, back print film, burnished film and the like. Accordingly, one can identify the paper type according to the diameter of flanges  6   c  used. 
     Further, in this embodiment, if the roll paper  6   a  is formed of a light transmitting transparent sheet  12  such as OHP paper, a light reflecting portion  12   a  is provided only at a trailing end of the light transmitting transparent sheet  12  as shown in FIG.  5 (A). In this connection, the light reflecting portion  12   a  may be provided at opposite sides perpendicular to the longitudinal direction as shown in FIG.  5 (B). So long as provided at the trailing end thereof, the structure is not limited to this embodiment. 
     As shown in FIG. 6, said detection unit of paper type  11  for outputting detection signals for detecting type of said roll paper  6   a  has abase plate  13  located adjacent to one of said roll holders  9 A. Said base plate  13  supports above it a pair of parallel guide rods  14 ,  14  which are parallel to each other and extend in horizontal direction so as to vertically cross the axis of said paper roll  6 . A sliding table  15  is mounted on said guide rods  14 ,  14  so as to shift along the extending direction of said rods  14 . A bracket  16  extends upwardly on the one end of said sliding table  15 , and said bracket  16  supports thereon a flange abutting block member  17  having its one side surface  17   a  used as a flange abutting surface. A coil spring  18  is provided between said base plate  13  and said sliding table  15  so as to urges said sliding table  15  in the direction A shown in FIG.  6 (A) for pressing said flange abutting member  17  onto said flange  6   c  of said paper roll  6 . 
     One end of a wire  19  as a manipulating member is connected to said bracket  16 . On the other hand, a hollow tube  20  is fixed on an edge portion of said base plate  13  so as to extend from the fixing point of said wire  19  on said bracket  16  in a reverse direction B to the urging direction A of said coil spring  18 . Said wire  19  passes through said tube  20  and extends outside of said base plate  13 , the other end of said wire  19  being fixed onto said cover  2 A (FIG.  2 ). Consequently, when opening said cover  2 A, said sliding table  15  is shifted by said wire  19  in the direction B against the urging force of said coil spring  18 . Accordingly, when exchanging paper roll  6 , said flange abutting member  17  as an example of roll holder abutting member is retracted into a retracted position. Further, when said cover  2 A is closed, said wire  19  is relaxed and said sliding table  15  is pulled in the direction A due to the urging force of said coil spring  18 . 
     Three photosensors  21 A,  21 B,  21 C and an output connector  23  for outputting signals from respective photosensors  21  to said controller  22  (FIG. 7) are located on said base plate  13 . Said respective photosensors  21  have respectively a U-form, and three state setting sheets  25  having each plate form to be inserted into the hollow portions of corresponding photosensors  21  are supported on the rear side surface of said sliding table  15  so as to engage into respective photosensors  21 . Each state setting sheet  25  is a shielding plate for shielding light from light emitting portion of each photosensor so as not to reach light receiving portion thereof, while said state setting sheet  25  has slits (not-shown) allowing light from light emitting portion thereof to reach light receiving portion thereof. 
     Each photosensor  21  has a construction such that it outputs signal ON when light from light emitting portion reaches light receiving portion, while it outputs signal OFF when light from light emitting portion does not reach light receiving portion. As a result, the position of sliding table  15  with respect to said base plate  13  is changed correspondingly to diameter of said flange  6   c  at the end of paper roll  6 . Thus, each photosensor  21 A,  21 B,  21 C outputs ON signal or OFF signal to said CPU board  26  (FIG. 7) according to the position of said slits of corresponding state setting sheet  25 . On the other hand, said CPU of said CPU board  26  of the control means  22  can thus detect the type of paper (roll paper  6   a ) according to the flange diameter obtained by combination of ON or OFF signals issued from respective three photosensors  21  as shown in the following Table 1. The types of paper thus detected are output to said CPU board  26  and are displayed on a displaying panel (not-shown) of the device  1 . 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Flange Diameter 
                   
                   
                   
               
               
                 Paper Type 
                 (mm) 
                 Sensor A 
                 Sensor B 
                 Sensor C 
               
               
                   
               
             
            
               
                 No Paper 
                 0 
                 ON 
                 ON 
                 ON 
               
               
                 1 
                 48-52 
                 OFF 
                 ON 
                 OFF 
               
               
                 2 
                 58-62 
                 OFF 
                 OFF 
                 ON 
               
               
                 3 
                 70-74 
                 ON 
                 OFF 
                 ON 
               
               
                 4 
                 80-84 
                 OFF 
                 ON 
                 ON 
               
               
                 5 
                 88-92 
                 ON 
                 ON 
                 OFF 
               
               
                 6 
                  98-102 
                 ON 
                 OFF 
                 OFF 
               
               
                   
               
            
           
         
       
     
     Sensors A, B and C shown in this Table 1 designated respectively said photosensors  21 A,  21 B and  21 C. 
     Said CPU board  26  can carry out image processing and driving of ink jet heads (not-shown) in Table 2 correspondingly to detected type of paper. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Paper Type 
                 Image Processing 
                 Paper Feeding 
                 Ink Jet Head 
               
               
                   
               
             
            
               
                   1 
                 Standard 
                 Standard 
                 Standard 
               
               
                 2 
                 Standard 
                 Standard 
                 Standard 
               
               
                 3 
                 Standard 
                 Standard 
                 Standard 
               
               
                 4 
                 Dedicated 
                 Standard 
                 Dedicated 
               
               
                   
                   
                   
                 (Less Ink Ejecting) 
               
               
                 5 
                 Private 
                 Dedicated 
                 Standard 
               
               
                   
                   
                 (Double Printing) 
               
               
                 6 
                 Standard 
                 Standard 
                 Dedicated 
               
               
                   
                   
                   
                 (Scan Speed 
               
               
                   
                   
                   
                 Accelerated) 
               
               
                   
               
            
           
         
       
     
     A paper hold (not-shown) to hold roll paper  6   a  to be used is released out of paper roll  6  to be kept on the peripheral surface of platen  3  is mounted in the space opposing to said platen  3  in said housing  2 . Further, an ink jet unit  27  reciprocating along said platen  3  in a direction parallel to the axis thereof is provided in the space opposing to said platen  3  in said housing  2 . A carriage  27 A of said ink jet unit  27  has thereon a plurality of ink jet heads (not-shown) which are directed against said platen  3 . The position where said ink jet heads discharge ink toward the roll paper  6   a  held against the outer periphery of the platen  3  is designated as a printing portion PP (FIG. 2) to do the printing against the roll paper  6   a.    
     A driving belt  28  is connected to said ink jet unit  27 , and said driving belt  28  is wound about a driving pulley  30  which is driven by a second motor  29  of reversible type. Accordingly, when driving said second motor  29 , said ink jet unit  27  is reciprocated along said platen  3  under the guidance of a guide shaft  31  located in parallel to said platen  3 . A pump unit  32  for covering the nozzles of restrictive ink jet heads of said ink jet unit  27  for the purpose of recovering operation thereof is located on one side of the other end portion of said platen  3 , and an exhaust liquid tank  33  is provided adjacent to said pump unit  32 . 
     Photointerrupters  34  of transmission type are located with a distance therebetween in the front and back direction of said carriage  27 A on the bottom side of said carriage  27 A of said ink jet unit  27 , and a linear encoder  35  comprising a thin plate having therein a number of small holes corresponding to printing resolution is located along the whole range of shifting ink jet unit  27 . 
     A detection unit  36  for detecting roll paper  6   a  on said platen  3  is located on the upstream side of said ink jet unit  27  in the normal conveying direction of said roll paper  6   a  so as to oppose said platen  3 . Said roll paper presence/absence detection unit  36  has photosensors  37  to emit a light from the light emitting portion toward the outer periphery of the platen  3 . The thus emitted light is reflected by the roll paper  6   a  positioned on the platen  3  such that the intensity of the reflected light is converted into an electrical signal by the light receiving portion to be sent to the control means  22  which will be explained later. 
     Cutting unit  40  consisting of long sized fixed blade  38  and movable blade  39  for cutting printed roll paper  6   a  is located below said platen  3  and ink jet unit  27 . 
     Said paper detection unit  41  for detecting roll paper  6   a  is located between said printing portion PP and said cutting portion CP. The detection unit  41  of the paper leading end is for determining whether or not the reverse feed amount of the roll paper  6   a  is adequate at such a time as the cut roll paper  6   a  to be subjected to printing is fed backwardly of the regular feed direction. When a lever switch not shown detects the leading end (cut end) of the roll paper  6   a , a detect signal is emitted to the control means  22  which will be explained later. Then, said control means  22  stops driving the first motor  4  which is feeding the roll paper  6   a  backwardly. 
     Each driving portion such as said both paper detection units  11 ,  36 ,  41  and said both motors  4 ,  29  and ink jet unit  27  is respectively connected to a control means  22 , so that when signals about roll paper  6   a  from said paper detection units  11 ,  36 ,  41  are input into said control means  22 , this control means  22  controls said respective motor  4 ,  29  and ink jet unit  27  correspondingly to the input signals. 
     As shown further in FIG. 2, the upper opening (not-shown) of said housing  2  is covered by a closing cover  2 A. 
     FIG. 7 shows a control block diagram of printing device including said control means  22 . 
     As shown in FIG. 7, said control means  22  consists of a mother board  42  having a control panel (not-shown); a CPU board  26 , a mechanical control board  43  and a head control board  44  connected to each other via said mother board  42 . 
     Said mother board  42  is connected to a paper detection unit  11  for detecting the type of roll paper  6   a  used, a paper presence/absence detection unit  36  for detecting the presence or absence of said roll paper, a paper leading end detection unit  41  for detecting the leading end of said roll paper, said pump unit  32 ; said exhaust liquid tank  33 ; a CR unit  45  for driving said second motor  29  shifting said ink jet unit  27 ; a LF unit  46  for driving said first motor  4  conveying said roll paper  6   a.    
     Said CPU board  26  has built-in CPU, ROM, RAM and the like, among which ROM has programs for operation and graphic processing, and carrying out printing based on corresponding detection result, such as type of paper, presence or absence of paper, leading end of paper by detecting signals provided by each detection unit  11 ,  36  and  41 . 
     Said mechanical control board  43  includes drivers (not-shown) for driving said detection units  11 , 36  and  41 , pump unit  32 , CR unit  45  and LF unit  46 . Further, said mechanical control board  43  can transfer signals to said CPU of said CPU board  26 . 
     Said head control board  44  has ink detection board  47  and head drive board  48 , and transfers a detection signal of residual ink quantity detected by said ink detection board  47  located on said ink jet unit  27  to said CPU of said CPU board  26 , and, in said head drive board  48 , said head control board  44  also transfers logical signals based on information from said CPU for driving said ink jet unit  27 . Based on said logical signals, said head drive board  48  generates driving signals for driving respective ink jet head  49  and respective ink cartridge  50 . 
     Further, in said CR unit  45 , said linear encoder  35  is connected in parallel to said second motor  29 , said linear encoder  35  outputting to said CPU of said CPU board  26  signals correspondingly to rotational sped of said second motor  29  for equalizing the shifting speed of said ink jet unit  27 . 
     Further, said mother board  42  is provided with interface unit  51 ,  52  for connecting this printing device  1  to personal computer and the like. 
     Further, the program stored in said CPU board  26  determines the presence of the paper upon detection of an intense reflection and outputting an electrical signal HIGH by the photosensor  37  of the detection unit  36  of paper presence/absence when the paper (roll paper  6   a ) detected by the detection unit  11  of paper type is opaque. On the other hand, if the paper detected by the detection unit  11  of the paper type is transparent, most of the light emitted by the light sensor  36  of the detection unit  36  of the paper presence/absence permeates the paper to be absorbed by the surface of the platen such that the photosensor  37  of the detection unit  36  of the paper presence/absence will not detect the reflection and emits an electrical signal LOW to determine the presence of the paper. 
     In other words, the control means  22  is constructed to perform a reverse determination concerning the information from the photosensor  37  of the detection unit  36  of paper presence/absence based on the result obtained by the detection unit  11  of the paper type as to whether the paper  6   a  is of light transmitting nature or not. 
     Next, the operation flow of said printing device  1  will be explained hereinafter. 
     First, cover  2 A is opened for mounting a paper roll  6  including a desired type of roll paper  6   a  onto roll holding mechanism  8 . Wire  19  connected to this cover  2 A is thus pulled in the direction B against the urging force of coil spring  18 , so that sliding table  15  connected to this wire  19  is also pulled in the same direction B and flange abutting member  17  is retracted into a retraction place so as not to impede inserting operation of paper roll  6 . In this state of mechanism, holders  6   b  having each flange  6   c  of outer diameter adapted to that of roll paper  6   a  mount paper roll  6  on both roll holders  9 A,  9 B of roll holding mechanism  8 . 
     Then, upon closing of cover  2 A, wire  19  is relaxed, sliding table  15  shifts in the direction A under the urging force of coil spring  18 , and abutting surface  17   a  of flange abutting member  17  is urged onto peripheral surface of flange  6   c . Correspondingly to the position of thus stopped sliding table  15 , three photosensors  21  are respectively ON state or OFF state, so that type of paper is detected as shown in Table 1. This information is output from output connector  23  to said CPU board  26  which detects type of paper based on Table 1 and can indicate predetermined image processing and head driving corresponding to detected type of paper. 
     Upon switching printing device power supply into ON, CPU of CPU board  26  initializes respective parts  26 ,  43 ,  44 ,  47 ,  48  and respective units  27 ,  32 ,  45 ,  46  and respective detection mechanism  11 ,  36 ,  41  and then recognizes type of paper used, presence or absence of paper on the printing portion PP, position of leading end of paper, by means of signals from paper detection unit, paper presence/absence detection unit and paper leading end detection unit, respectively. In this situation, the recognition of the paper by means of the photosensor of the detection unit  36  of the paper presence/absence for the control means  22  is constructed to perform a determination by reversing the information from the photosensor  37  of the detection unit  36  of the paper presence/absence on the basis of the result as to whether the paper is light transmitting or not. 
     In other words, in case where the detection result as to the type of the roll paper  6   a  by means of the detection unit  11  of the paper type is that the paper is an ordinary opaque paper which will not allow a light to permeate therethrough, the photosensor  37  of the detection unit  36  of paper presence/absence detects an intense reflection by the surface of the roll paper  6   a  to emit an electrical signal HIGH for the control means  22  to provide a determination of “paper present” when the roll paper  6   a  is on the platen  3  whereas the light emitted by the photosensor  37  is directly irradiated onto the surface of the platen  3  to be absorbed by its surface such that the photosensor  37  will not detect the reflected light and emits an electrical signal LOW for the control means  22  to provide a determination of “paper absent”. 
     On the other hand, in case where the detection result as the type of the roll paper  6   a  by means of the detection unit  11  of the paper type is that the paper is formed of a transparent sheet  12  of light transmitting paper such as a paper for the over head projector, the photosensor  37  will not detect the reflected light because most of the light irradiated by the photosensor  36  of the detection unit  36  of paper presence/absence permeates the paper directly onto the surface of the platen  3  to be absorbed thereby when the roll paper  6   a  is positioned on the platen  3 . In such situation, the photosensor emits an electrical signal LOW such that the control means  22  provides a determination of “paper present”. When the trailing end of the roll paper  6   a  is positioned on the platen  3  after the printing has been done on the roll paper  6   a , the photosensor detects an intense reflection from the light reflecting portion  12   a  formed of a transparent sheet and positioned at the trailing end of the roll paper  6   a  on the platen and outputs an electrical signal HIGH such that the control means  22  provides a determination of “paper absent”. 
     In other words, the control means  22  is constructed to perform a determination by reversing the output (information) from the photosensor  37  based on the result obtained by the detection unit  11  of the paper type as to whether the roll paper  6   a  is of light transmitting nature or not. 
     In this connection, the roll paper  6   a  is cut off at its trailing end by the paper cutting unit  40  after the printing action to form a separate sheet of paper which is discharged to complete the printing operation. When the printing operation of a sheet of paper is finished, it is needed for performing the next printing action to rewind the roll paper  6   a  by a predetermined distance by the first motor  4  because the distance from the printing portion PP to the cutting portion CP is larger than the margin formed at the leading end of the paper at the time of an ordinary printing action. The amount of reverse feed of the roll paper  6   a  is sufficiently compensated for by feeding the roll paper  6   a  backwardly a constant amount if the leading end of the roll paper  6   a  is always positioned at the cutting portion CP. Actually, however, the position of the leading end of the roll paper  6   a  varies depending on situations so that the amount of reverse feed of the roll paper  6   a  is determined by the result of detection of the leading end of the roll paper  6   a  by means of detection unit  41  of the paper leading end. In other words, the control means  22  controls the amount of reverse feed for the roll paper  6   a  by driving the second motor  29  until the detection unit  41  of the leading end of the paper detects the leading end of the roll paper after the roll paper  6   a  is cut off at its trailing end by the paper cutting mechanism  40  such that position of the leading end of the roll paper  6   a  for the printing action is done at a position suitable for printing. 
     From the information about ink type stored in a nonvolatile memory in head control board  44 , said CPU receives signals for recognizing ink type. By using the data of detected type and type of ink and/or paper, said CPU looks up data table written in ROM of said CPU board  26 , thereby to set the procedure of the printing data and to set servo constant to determine the printing speed. 
     In this way, the printing is done in accordance with the type of ink and paper. 
     In this embodiment of the invention, since type of paper can be automatically detected upon mounting of said paper roll  6  onto roll holder  9 A,  9 B as described above, double printing and/or inferior image quality due to input error of paper type by operator can be prevented. Further, since paper used is automatically detected according to outer diameter of flanges  6   c , more various types of paper can be handled by increasing the number of sensors. Further, since flange abutting member  17  is retracted when exchanging paper roll  6 , flange abutting member  17  does not impede the exchange of paper roll  6 . 
     Further, said detection unit  11  of the paper type is capable of automatically detecting the paper type from the position of the flange abutting member  17  abutting against said flange  6   c  merely by attaching a flange  6   c  to the paper roll  6 , said flange having an outer diameter corresponding to the type of the roll paper  6   a . Said detection unit  36  of the paper presence/absence is capable of automatically detecting the presence/absence of the roll paper  6   a  without contact. Said detection unit  41  of the paper leading end is capable of automatically detecting the leading end of the roll paper  6   a  subjected to printing to determine whether said leading end is properly positioned or not. Said control means  22  is capable of controlling the relevant portions such that a proper printing action onto the roll paper is assured on the basis of the detection result of the respective detection units  11 ,  36  and  41  and capable of automatically detecting the presence/absence of the roll paper to be positioned at the printing portion PP by means of the photosensors  37 , regardless of whether the roll paper  6   a  is of light transmitting nature or not. 
     The relationship between the detection result by said respective detection units  11 ,  36  and  41  and the printing action of the control means  22  based on the detection result is shown in Table 3 below. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Detection Unit 
                 Detection Unit 
                 Detection Unit 
                   
               
               
                 of 
                 of Paper 
                 of Paper 
                 Control 
               
               
                 Paper Type 
                 Presence/Absence 
                 Leading End 
                 Means 
               
               
                 11 
                 36 
                 41 
                 22 
               
               
                   
               
             
            
               
                 Paper: 
                 Light Reflection: 
                 Paper: 
                 Printing Action: 
               
               
                 Present 
                 Absent 
                 Present 
                 Suspended 
               
               
                 Transparent 
               
               
                 Paper: 
                 Light Transmission: 
                 Paper: 
                 Printing Action: 
               
               
                 Present 
                 Present 
                 Present 
                 Possible 
               
               
                 Transparent 
               
               
                 Paper: 
                 Light Reflection: 
                 Paper: 
                 printing Action: 
               
               
                 Present 
                 Present 
                 Present 
                 Possible 
               
               
                 Opaque 
               
               
                 Paper: 
                 Light Transmission: 
                 Paper: 
                 Printing Action: 
               
               
                 Present 
                 Absent 
                 Present 
                 Suspended 
               
               
                 Opaque 
               
               
                   
               
            
           
         
       
     
     Now, said detection unit  11  of paper type is adapted to output a signal indicating “paper absent” when the paper roll  6  is not loaded to the paper roll holding mechanism  8  while the control means  22  makes the printing action impossible. 
     Further, the roll paper  6   a  is formed of a transparent sheet which is light transmitting, with the trailing end of said transparent sheet  12  being formed with a light reflecting portion  12   a . Therefore, it is possible to effectively use the entire surface of the roll paper  6   a  even if the roll sheet formed of the transparent sheet  12  of light transmitting nature is used. Moreover, the light reflecting portion  12   a  of the roll paper  6   a  makes it possible for the photosensors  37  in the detection unit  36  of paper presence/absence to automatically detect the trailing end of the roll paper  6   a.    
     The present invention is not limited to the above described embodiments but can be modified if necessary. 
     As explained in the foregoing, the present invention is characterized in that the detection unit of paper type is capable of automatically detecting the paper type on the basis of the position of the flange abutting member which abuts against the flange merely if the flange having an outer diameter corresponding to the type of the roll paper is attached to the paper roll, that the detection unit of paper presence/absence is capable of automatically detect the presence/absence of the paper without contact thereto, that the detection unit of the paper leading end is capable of automatically detecting the paper leading end to determine whether said leading end is properly positioned, and that the control means is capable of controlling the relevant portions to perform the proper printing actions on the basis of the detection result of the respective detection units. 
     Further, the roll paper according to the present invention makes it possible to effectively use the entire surface of the roll paper when the roll paper formed of the transparent sheet of light transmitting nature is used and to automatically detect the trailing end of the roll paper in the detection unit of paper presence/absence by means of the light reflecting portions of the roll paper.