Abstract:
A roll paper printer having a cover movable between an open and closed position with the printer having hooks on locking levers disposed to the cover to hold the cover in the locked position upon engaging pins located on the printer body side and having an opening lever to unlock the cover. The printer also includes a paper cutter device having a stationary knife which is attached to the cover and contact plate parts which extend from the stationary knife for contacting the front panel part on the printer body and having extension springs disposed in tension for pulling the stationary knife towards the back of the printer such that upon closing the cover the contact plate parts push the cover to the front of the printer. This causes the hooks of the locking levers to press from the back against the engagement pins to eliminate any play in the cover when in cover is in the locked position and to assist in opening the cover when the cover opening lever is operated.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of, and claims priority under 35 U.S.C. §120 on, U.S. patent application Ser. No. 11/646,038, filed Dec. 27, 2006. The content of this related application is incorporated by reference herein in its entirety. Japanese patent application nos. 2005-374481 and 2005-374482 are also incorporated by reference herein in their entirety. 
     
    
     BACKGROUND 
       [0002]    1. Field of Invention 
         [0003]    The present invention relates to a printer having a mechanism for locking a cover in a closed position and for releasing the mechanism so that when the cover is closed it is held tightly without permitting play in the closed position while also improving operability when releasing the lock and opening the cover. 
         [0004]    2. Description of Related Art 
         [0005]    In order to enable easily loading and replacing the roll paper in roll paper printers such as used for printing sales receipts, some roll paper printers have a mechanism that opens the paper transportation path from the roll paper compartment to the paper exit when the cover to the roll paper compartment is opened. This type of roll paper printer may have a platen member that opposes the print head, an opposing pressure roller that presses the paper to the paper feed roller, and a stationary knife of a scissor type paper cutter device which includes a stationary knife and a movable knife. The platen member, pressure roller, and stationary knife are disposed to the cover. When the cover opens the platen member, pressure roller, and stationary knife move away from the corresponding opposing members, i.e., the print head, paper feed roller, and movable knife, which causes the paper transportation path to open. As a result, opening the cover, loading the roll paper into the roll paper compartment, pulling the leading end of the roll paper out from the roll paper compartment, and closing the cover results in the paper being automatically threaded through the paper transportation path as is taught in JP-A-2002-308482. 
         [0006]    JP-A-2001-158141 teaches a lock mechanism for locking the cover in the closed position using an engagement pin disposed to the printer body and a locking lever having a hook formed on the distal end disposed to the cover for engaging the engagement pin. 
         [0007]    The locking lever is urged to the locking side by the force of a spring. When the cover closes, the distal end of the locking lever meets the engagement pin and the engagement pin pushes the locking lever up (or down) as the cover continues to close so that the hook rides over the engagement pin. When the hook rides over the engagement pin the force of the spring moves the hook from the front in the closing direction of the cover (from the back side of the engagement pin) to the locking position where the hook engages the engagement pin, thereby locking the cover closed. 
         [0008]    If the hook of the locking lever cannot ride over the engagement pin on the printer body side, this lock mechanism cannot reach the locked position. Extra space is therefore provided behind the engagement pin so that the cover can be pushed beyond the closed position and the hook part of the locking lever can reliably engage the engagement pin. 
         [0009]    Because the cover can be pushed beyond the closed position, the cover can move slightly in the opening/closing direction when locked by the lock mechanism. As a result, in some situations, the cover cannot be positioned without having play in the closed position. If the closed position of the cover shifts, the paper pressure roller mounted to the cover may not be able to apply appropriate pressure to the paper feed roller on the printer body side. If the contact position of the rollers shifts, the nipping position of the paper conveyed between the rollers shifts and the paper nipping force of the rollers changes. This causes the paper feed pitch to vary and lowers paper feed precision. 
         [0010]    Furthermore, to open the cover a cover opening lever must be operated to move the locking lever in resistance to the force of the spring to the release position, and the cover must be moved in the opening direction while holding the cover opening lever in the lock-release position. More specifically, the cover must be moved in the opening direction to a position where the locking lever will not re-engage the engagement pin when the cover opening lever is released. 
         [0011]    Simply operating the cover opening lever thus leaves the locking lever positioned to engage the engagement pin, and if the cover opening lever is released immediately the spring causes the locking lever to return to the locked position engaging the engagement pin and the cover cannot be opened. 
         [0012]    The printer of this invention enables the cover to lock in the closed position without play and to reliably open the cover by operating the cover opening lever only once. 
       SUMMARY OF INVENTION 
       [0013]    A printer according to a first aspect of the invention has a body; a cover movably attached to the body for movement into an open or closed position; a lock mechanism for locking the cover in the closed position or for unlocking the cover; and a positioning and urging mechanism for directing the cover to move in an opening/closing direction relative to the open or closed position of the cover so as to minimize play when the cover is locked in the closed position. The lock mechanism has a body-side engaging unit disposed to the printer body, a cover-side engaging unit disposed to the cover, and a lever for moving the cover-side engaging unit for disengaging the cover-side engaging unit from the body-side engaging unit. The positioning and urging mechanism has a cover-side contact part disposed to the cover in an arrangement relative to the printer body such that when the cover is in the closed position the cover-side contact part is pressed into the body to cause the cover to move into the open position in response to the unlocking of the cover by the control lever; and an urging member connected between the cover-side contact part and the cover for urging the cover-side contact part toward the cover closing direction. 
         [0014]    According to embodiments of the invention, when the cover closes the cover-side contact part contacts the printer body-side contact part and is pushed in the cover opening direction. Substantially at the same time the cover-side engaging unit of the lock mechanism rides over and engages the body-side engaging unit, and the cover is locked closed. The contact part of the cover is pushed away from the printer body in the cover opening direction and this pressure acts on the cover. Force pushing the cover in the opening direction is thus applied from the printer body to the cover when the cover is locked in the closed position. The cover-side engaging unit is thus reliably pressed against the body-side engaging unit from the front in the cover closing direction, and the cover is locked without play in the closed position. When the lock release lever is operated to release the cover lock, the force applied from the printer body to the cover compels the cover in the opening direction. Because the cover is unlocked and compelled automatically in the opening direction by simply operating the lock release lever once, the operation required to open the cover is extremely simple. 
         [0015]    In a roll paper printer, for example, a paper cutter device is typically disposed near the paper exit. In such a printer the stationary knife is attached to the cover and the movable knife is disposed to the printer body, the stationary knife is used as the cover-side contact part and the urging member can be a spring member disposed in tension between the stationary knife and a position offset in the cover closing direction from the stationary knife on the cover. A separate member is therefore not needed to function as the cover-side contact part, and the cover-side contact part can be easily disposed. 
         [0016]    When the invention is applied to a roll paper printer, the cover can be used as a cover for opening and closing an opening for loading and unloading roll paper in the roll paper compartment. To simplify the task of loading roll paper, a body-side roller for conveying the paper is disposed to the printer body and a cover-side roller contacting the body-side roller is disposed to the cover; and when the cover opens, a paper transportation path for conveying paper from the roll paper compartment between the body-side roller and cover-side roller and between the stationary knife and movable knife of the paper cutter device is opened. 
         [0017]    A positioning and urging mechanism in this roll paper printer constantly pushes the locked cover in the cover opening direction. The cover can therefore be locked without play in the closed position, and the cover-side roller can be set with good precision in contact with the body-side roller. Problems resulting from a drop in paper transportation precision due to deviation in where the rollers contact can therefore be reliably prevented. 
         [0018]    A printer according to another aspect of the invention has a housing for storing continuous paper; a moveable cover for opening and closing an opening in the housing; a housing-side engaging unit disposed to the housing; a locking lever that is pivotably disposed to the cover for engaging and disengaging the housing-side engaging unit, wherein the pivot of the lever, the housing-side engaging unit, and the engaging part of the lever are positioned in this order when the cover is closed; a cutting mechanism having a movable knife disposed on the housing side and a stationary knife disposed on the cover side for cutting the paper when the cover is closed; a contact part disposed to the stationary knife for contacting the housing side when the cover is closed; and an urging member connected between the stationary knife and the cover for urging the stationary knife in the closing direction of the cover. When the cover is closed the contact part of the stationary knife touches the housing side and the cover is urged by the urging member in the cover opening direction. 
         [0019]    A printer according to another aspect of the invention has a housing for storing continuous paper; a cover pivotally disposed to the housing such that the cover can be moved in cover closing direction to a closed position or in a cover opening direction to an open position; a lock mechanism having a first engaging unit disposed to the housing and a second engaging unit disposed to the cover for locking the cover when in the closed position; a release member for moving the second engaging unit to release the engagement of the first and second engaging units; and a cutting mechanism having a movable knife disposed on the housing side, a stationary knife disposed on the cover side, and an urging member for urging the stationary knife in the cover closing direction. When the cover is in the closed position, the stationary knife contacts the housing and is positioned to the movable knife by being urged by the urging member to the housing side. The stationary knife contacts the housing and is positioned to the movable knife by being urged by the urging member to the housing side when the cover is in the closed position. A contact part disposed to the stationary knife contacts the housing side when the cover is closed. The urging member is connected between the stationary knife and the cover for urging the stationary knife in the closing direction of the cover such that when the cover is in the closed position the cover is pressed in the cover opening direction which causes the cover to move forward in the cover opening direction when unlocking the locking mechanism and releasing the engagement of the first and second engaging unit. 
         [0020]    Accordingly, in embodiments, resistance to the urging force of the urging member acts on the stationary knife when the cover is in the closed position, and the cover is pressed in the cover opening direction and the second engaging unit is pressed to the first engaging unit by said resistance, and when engagement of the first and second engaging units is released by the release member when the cover is in the closed position the cover is pushed by said resistance in the cover opening direction. 
         [0021]    Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is an external oblique view of a roll paper printer according to a preferred embodiment of the invention. 
           [0023]      FIG. 2  is an external oblique view of the roll paper printer with the cover open. 
           [0024]      FIG. 3  is an oblique view of the print mechanism unit in the roll paper printer. 
           [0025]      FIG. 4  is a schematic side section view of the print mechanism unit. 
           [0026]      FIG. 5  is an oblique view shows the print mechanism unit with some portions removed for clarity. 
           [0027]      FIG. 6  describes the cover lock mechanism and positioning and urging mechanism. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]    A preferred embodiment of a printer according to the present invention is described below with reference to the accompanying figures. 
       General Configuration 
       [0029]      FIG. 1  shows the appearance of an inkjet roll paper printer according to the present invention, and  FIG. 2  shows the printer with the paper compartment cover fully open. The roll paper printer  1  has a body  2  with a basically rectangular box-like shape, and a cover  3  attached to the front of the body  2 . 
         [0030]    A paper exit  4  of a specific width is formed at the front of the outside case  2   a  of the body  2 . An exit guide  5  protrudes to the front below the paper exit  4 , and a cover opening lever  6  (lock release lever, release member) is located beside the exit guide  5 . A square opening  2   b  for loading and removing roll paper is formed below the exit guide  5  and cover opening lever  6  of the outside case  2   a,  and the cover  3  closes this opening  2   b.    
         [0031]    Operating the cover opening lever  6  releases the cover lock and pushes the cover  3  in the opening direction. Pulling forward on the exit guide  5  then causes the cover  3  to pivot and swing forward from the bottom end part of the cover  3  to a substantially horizontal position as shown in  FIG. 2 . Opening the cover  3  also opens the roll paper compartment  11  rendered inside the printer so that roll paper can be loaded and replaced from the front of the printer. 
         [0032]    Another opening  2   c  is also formed on the right beside the cover  3 , and a cover  7  that pivots at the bottom to open and close is attached at this opening  2   c . Opening this cover  7  opens the ink cartridge compartment  18  (ink supply unit) so that ink cartridges can be replaced. 
         [0033]    An operating panel  2   d  having a number of LEOs used as state indicators as well as a paper feed button, for example, is disposed on the left beside the cover  3 . 
         [0034]      FIG. 3  is an oblique view of the printer mechanism unit  10  inside the outside case  2   a  of the roll paper printer  1 .  FIG. 4  is a schematic vertical side view of the printer mechanism unit  10  shown in section. 
         [0035]    The printer mechanism unit  10  has a roll paper compartment  11  substantially in the widthwise center of the printer mechanism unit  10 . The roll paper  12  is placed sideways to the printer inside the roll paper compartment  11  so that the roll paper  12  rolls as paper is pulled off. A head unit  13  is disposed horizontally above the roll paper compartment  11 . 
         [0036]    The head unit  13  has a head unit frame  14 . A carriage guide shaft  15  passes horizontally between the right and left side panels  14   a  and  14   b  of the head unit frame  14 . A carriage  17  carrying an inkjet head  16  facing down can move bidirectionally along the carriage guide shaft  15 . 
         [0037]    As shown in  FIG. 3 , the ink cartridge compartment  18  and head maintenance unit  20  are disposed below the head unit  13  on the right side of the roll paper compartment  11 . Ink cartridges not shown can be loaded into the ink cartridge compartment  18  below the head maintenance unit  20 . Similarly to a head maintenance unit as known from the literature, a wiper for wiping the nozzle face  16   a  of the inkjet head  16  and a recovery unit for recovering waste ink discharged or purged from the nozzles of the nozzle face  16   a  are disposed in the head maintenance unit  20  above the ink cartridge compartment  18 . A circuit board housing  22  containing the control circuit board is located below the head unit  13  on the left side of the roll paper compartment  11 . 
         [0038]    As shown in  FIG. 4 , a paper guide  32  is disposed horizontally widthwise to the printer at a position behind and between the roll paper compartment  11  and head unit  13  inside the printer mechanism unit  10 . A platen guide  33  is disposed horizontally in the front to back direction of the printer in front of and above the paper guide  32 . The inkjet head  16  carried on the carriage  17  is directly above the platen guide  33 . The nozzle face  16   a  of the inkjet head  16  is opposite the top surface  33   a  of the platen guide  33  with a constant gap therebetween, and the printing position is determined by this top surface  33   a.    
         [0039]    A first paper feed roller  34  is disposed horizontally widthwise to the printer between the platen guide  33  and paper guide  32 . A first paper pressure roller  35  of a specific width is pressed from below with a predetermined force against the first paper feed roller  34 . The first paper feed roller  34  is driven by a paper feed motor  36  disposed to the head unit  13  by means of an intervening belt and pulley power transfer mechanism  36   a  (see  FIG. 5 ). A second paper feed roller  37  is disposed to a position at the front edge side of the platen guide  33 . A second paper pressure roller  38  is pressed from above against the second paper feed roller  37  with a predetermined force. 
         [0040]    The carriage  17  is moved bidirectionally along the printer width (the printing width direction) by a carriage transportation mechanism including a carriage motor  39  and timing belt  40  (see  FIG. 3 ). As the carriage  17  travels back and forth, the inkjet head  16  mounted on the carriage  17  is driven to print on the surface of the printing paper  12   a  delivered from the roll paper  12  passed the printing position. 
         [0041]    An ink damper  41  is mounted on the carriage  17 , and a flexible ink tube  42  is connected to the ink damper  41 . Colored ink is supplied from the ink cartridges in the ink cartridge compartment  18  through the ink tube  42  to the inkjet head  16  enabling full color printing by the inkjet head  16 . 
         [0042]    A scissor-type paper cutter device  44  is located near the paper exit  4  on the upstream side. The stationary knife  45  of the paper cutter device  44  is disposed vertically with the cutting edge up, and the movable knife  46  is disposed vertically with the cutting edge down. The movable knife  46  pivots at one end thereof widthwise to the printer and is driven bidirectionally up and down by a movable knife drive mechanism  47 . As the movable knife  46  rotates downward the point of contact with the stationary knife  45  moves across the width of the printer and thus cuts across the width of the printing paper  12   a  located between the knives. 
         [0043]    The platen guide  33 , paper guide  32 , first paper pressure roller  35 , second paper feed roller  37 , and stationary knife  45  are disposed to the cover frame  51  of the cover  3 . The cover opening lever  6  and exit guide  5  are attached to the front portion of the cover frame  51 . Opening the cover  3  both opens the opening  2   b  for loading and removing roll paper to the roll paper compartment  11  and opens the paper transportation path from the roll paper compartment  11  to the paper exit  4 . As a result, when roll paper  12  is then placed in the roll paper compartment  11 , a printing paper  12   a  leader of a certain length is pulled off the roll paper  12  and the cover  3  is then closed, the printing paper  12   a  pulled from the roll paper  12  in the roll paper compartment  11  is guided by the paper guide  32  and is automatically threaded through the paper transportation path passing from between the first paper feed roller  34  and first paper pressure roller  35  over the top surface  33   a  of the platen guide  33  (the printing position), between the second paper feed roller  37  and second paper pressure roller  38 , and to the outside from the paper exit  4 . 
         [0044]    Transportation of the printing paper  12   a  begins when the first paper feed roller  34  and second paper feed roller  37  then begin to turn. The inkjet head  16  is driven synchronized to printing paper  12   a  movement to print on the surface of the printing paper  12   a  as the paper passes the printing position. After printing ends conveying the printing paper  12   a  stops with the printed portion discharged from the paper exit  4 , the paper cutter device  44  then cuts the printing paper  12   a , and the printed portion severed from the roll can be issued as a sales receipt, for example. 
       Cover Lock Mechanism And Positioning And Urging Mechanism 
       [0045]    The lock mechanism for locking the cover  3  in the closed position, and the positioning and urging mechanism for positioning the cover  3  in the closed position and urging the cover  3  in the opening direction when the cover  3  lock is released, are described next with reference to  FIG. 4  to  FIG. 6 . 
         [0046]      FIG. 5  is an oblique view of the printer mechanism unit  10  with the head unit  13  other than the paper feed motor  36  and power transfer portion thereof, the ink cartridge compartment  18 , the head maintenance unit  20 , and the circuit board housing  22  removed.  FIG. 6  describes the main parts of the lock mechanism and the positioning and urging mechanism. 
         [0047]    The lock mechanism for securing the cover  3  in the closed position includes a support shaft  52  disposed at the front portion of the cover frame  51  to rotate freely in the opening and closing direction of the cover  3 , a pair of left and right locking levers  53  (cover-side engaging unit) fixed at opposite ends of the support shaft  52 , and a pair of left and right engagement pins  54  (body-side engaging unit, frame-side engaging unit) disposed to the body  2 . Note that these parts on only one side of the printer are shown in the figure. 
         [0048]    The cover opening lever  6  is fixed on the end of the support shaft  52  so that pressing on the cover opening lever  6  causes the support shaft  52  to rotate and the distal end portion (the end towards the back of the printer) of the locking levers  53  fixed on both ends of the support shaft  52  to rotate up. The locking levers  53  are constantly urged in the locking direction (downward in this arrangement) by a torsion spring. 
         [0049]    The locking levers  53  are vertical plates of a substantially constant width protruding from both ends of the support shaft  52  toward the back of the printer, and the bottom edge of the distal end part of each lever slopes from the back to the front of the printer, rendering incline  53   a.  A hook  53   b  that can engage the engagement pin  54  from the back side of the printer (the front in the direction in which the cover closes) is formed at the bottom end of the incline  53   a : More specifically, an engaging surface  53   c  curves upward continuously from the bottom end of the incline  53   a,  and a bottom edge  53   d  curves continuously from the top end of this engaging surface  53   c  toward the front of the printer. 
         [0050]    The left and right engagement pins  54  on the body  2  side are studs that protrude to the outside widthwise to the printer almost perpendicularly to the outside surfaces of the side panel portions  55  and  56  on opposite sides of the roll paper compartment  11 . When the cover  3  closes the incline  53   a  of the locking lever  53  contacts the engagement pin  54 . As the cover  3  continues to close the locking levers  53  are pushed up, the hooks  53   b  ride over the engagement pins  54 , and the hooks  53   b  drop into the locked position engaging the engagement pins  54  from the back side of the printer. 
         [0051]    When the cover opening lever  6  is then depressed when in this locked position, the distal ends of the left and right locking levers  53  pivot up, the hooks  53   b  rise and disengage the engagement pins  54 , and the cover is thus unlocked. 
         [0052]    So that the locking levers  53  can reliably lock onto the engagement pins  54 , the cover  3  can be pushed a slight extra distance towards the back side of the printer from this closed position. As a result, the cover  3  can move slightly in the front to back direction of the printer when in this locked position. To prevent such movement, this embodiment of the invention has a positioning mechanism (positioning and urging mechanism) for positioning the cover  3  in the Closed position. 
         [0053]    The positioning and urging mechanism according to this embodiment of the invention includes the stationary knife  45  disposed to the cover  3  and two coil extension springs  61  (urging members) that pull the stationary knife  45  toward the back of the printer (in the closing direction). The stationary knife  45  is disposed so that it can be moved slightly by means of the front end part  51   a  of the cover frame  51  in the front to back direction of the printer (the cover opening and closing direction). The extension springs  61  are disposed with one end attached to the left and right ends of the stationary knife  45  and the other end attached to spring catches  51   b  disposed to the cover frame  51  at a position towards the back of the printer from the stationary knife  45 . These extension springs  61  constantly urge the stationary knife  45  towards the back of the printer (in the cover closing direction). 
         [0054]    A pair of left and right contact plate parts  45   a  (cover-side contact units) are formed projecting up at the left and right ends of the stationary knife  45 . These contact plate parts  45   a  can contact front parts  14   d  (body-side contact units) rendered at the bottom edge parts of both ends of the front panel part  14   c  of the head unit frame  14  of the head unit  13 . This embodiment of the invention is configured so that the contact plate parts  45   a  contact the front panel part  14   c  just before the hooks  53   b  of the locking levers  53  of the lock mechanism engage the engagement pins  54  when the cover  3  is closed. The stationary knife  45  is thus positioned to the movable knife  46  with the contact plate parts  45   a  touching the front panel part  14   c  and the contact plate parts  45   a  pressed against the front panel part  14   c  by the extension springs  61 . 
         [0055]    The operation of the lock mechanism and positioning and urging mechanism thus arranged is described next. 
         [0056]    As shown in  FIG. 6 , when the cover  3  is closed the left and right contact plate parts  45   a  of the stationary knife  45  contact the left and right front parts  14   d  of the front panel part  14   c  on the body  2  side just before the hooks  53   b  of the left and right locking levers  53  of the lock mechanism engage the left and right engagement pins  54  on the printer body  2  side. As the cover  3  is pressed further in the closing direction so that the lock mechanism locks, the stationary knife  45  is pressed with a specific amount of force to the front from the body side. 
         [0057]    The stationary knife  45  is connected (supported) on the cover frame  51  of the cover  3  through an intervening pair of left and right extension springs  61 . As a result, the pressure on the stationary knife  45  from the body  2  side pushes the cover  3  toward the front of the printer, and the engaging surface  53   c  of the hook  53   b  of the left and right locking levers  53  of the lock mechanism is pressed from the back side of the printer against the corresponding left and right engagement pin  54 . More specifically, the cover  3  is locked with no play in the closed position. 
         [0058]    When the cover  3  is in the closed position, the first paper pressure roller  35  and second paper feed roller  37  disposed to the cover  3  are reliably positioned in contact with the first paper feed roller  34  and second paper pressure roller  38  disposed on the body  2  side. The nipping force of the rollers can therefore be held constant, and problems such as a drop in print quality resulting from inconsistent nipping force resulting in a variable paper feed pitch due to deviation in the roller contact position can be prevented. 
         [0059]    Operation when the cover  3  that is locked in the closed position is opened is described next. 
         [0060]    When the cover opening lever  6  is depressed, the left and right locking levers  53  of the lock mechanism pivot, the hooks  53   b  on the ends of the levers move up and disengage the left and right engagement pins  54  on the body  2  side, and the lock is released. 
         [0061]    As described above, the urging mechanism (positioning and urging mechanism) works from the body side to apply a predetermined force on the cover  3  in the opening direction. When the lock is disengaged, the pressure of this force causes the cover  3  to automatically pop forward (in the opening direction). This causes the hooks  53   b  of the locking levers  53  of the lock mechanism to move to a position to the front of the printer from the engagement pins  54  so that even if the cover opening lever  6  is released the cover  3  will not be locked again. 
         [0062]    Once the cover  3  is thus pushed forward, the weight of the cover causes the cover  3  to pivot on its bottom end and open automatically to the full open position. To control the speed with which the cover  3  opens a coil spring that urges the cover  3  with a predetermined force in the closing direction can be connected between the cover  3  and body  2 . Alternatively, a torsion spring could be disposed to the support shaft on which the cover  3  pivots. 
         [0063]    The simple operation of depressing the cover opening lever  6  once thus unlocks the cover  3  and automatically pushes the cover  3  in the opening direction. The operation of opening the cover  3  is thus improved. 
       Variations of the Preferred Embodiment 
       [0064]    The invention is described above using a roll paper printer by way of example, but the invention can also be applied to covers on printers other than roll paper printers. 
         [0065]    Furthermore, while an inkjet type roll paper printer is described above, the invention can also be applied to printers using a non-inkjet type print head such as thermal or impact types. 
         [0066]    Yet further, the same mechanism is used for the positioning mechanism for positioning the cover in the closed position and the urging mechanism for pushing the cover in the opening direction, but different mechanisms could be used. 
         [0067]    Yet further, the stationary knife of the paper cutter mechanism is used in the cover positioning mechanism, but a location or part on the cover other than the stationary knife could be used. 
         [0068]    Yet further, the stationary knife of the paper cutter mechanism is used in the urging mechanism for automatically pushing the cover in the opening direction, but a different part could be affixed to the cover to function as the cover-side contact unit. 
         [0069]    In addition, the locking levers are disposed to the cover in the lock mechanism described above, but the locking levers could be disposed to the body and the engagement pins to the cover. The shape and construction of the body-side engagement parts and cover-side engagement parts can also be varied in many ways. 
         [0070]    Although the present invention has been described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will be apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims, unless they depart therefrom.