Dual type thermal printer

Abstract: A conventional dual type thermal printer has only one drive roller and one motor, and the guide portion of its paper feed mechanism is fixed, and thus, there is a problem that the width of paper to be printed is fixed and the print speed has to be the same with regard to two systems. Two platen rollers (2a, 2b) positioned coaxially and rotatably supported independently of each other are provided in parallel with one opposing thermal head (3), and, there are provided paper feed means (9a, 9b) for separately transporting heat sensitive paper inserted between these platen rollers and the thermal head, respectively, and a movable frame (20) for holding the thermal head, having regulating pieces (24a, 24b) at both ends thereof for regulating end portions of the heat sensitive paper and slidably attached in the axial direction of the platen rollers.

Description: The present invention relates to a printing apparatus and a multiple type printing apparatus capable of printing on a plurality of pieces of paper. More specifically, the present invention relates to a technique effective when applied to, for example, a thermal printing apparatus provided with a thermal head (what is called a thermal printer). Printers used as information output apparatus are broken down into impact printers such as wire dot printers and non-impact printers. Non-impact printers include laser printers and thermal printers. Since impact printers make a large noise and are inferior in the print quality, non-impact printers have been more popularly used recently. Among non-impact printers, thermal printers are suited for miniaturization, and thus, they have been used in a wide range of fields. In particular, in the field of POS (point-of-sales) terminals, since output paper for a receipt to be handed to a customer and output paper for a journal to be kept as a copy for the shop have to be printed simultaneously, two printers are provided in parallel with each other or a dual type printer that has two heads has been put to practical use. However, since a printhead of a printer costs considerably, with a multiple type printer having heads for the respective paper, though it can be made compact to some extent, satisfactory effects with regard to the cost can not be obtained. Accordingly, an invention has been proposed with regard to dual type thermal printer which, by sharing a thermal head and providing two paper feed units in parallel with each other with respect to the shared thermal head, attains improvement with regard to both miniaturization and economical efficiency (Japanese Patent No. 2819595). Another proposal is a printer where two sheets of paper of different width are set through a left and right tractor feed unit and a left and right platen. Then both sheets are printed by a printing head slidably mounted on a carriage (JP 63 001565). However, though the thermal printers according to the patented prior inventions mentioned in the above has an advantage that it is a low-priced apparatus capable of printing on two pieces of paper simultaneously, since the guide portion of its paper feed mechanism is fixed, the width of paper to be printed is fixed and thus, it is found that there is a problem that the printer is difficult to use for general purposes. Especially with regard to POS terminals, there are many cases where the outputted information and the amount thereof are required to be different between output paper for a receipt to be handed to a customer and output paper for a journal to be kept as a copy for the shop. Accordingly, when the thermal printer according to the patented prior invention mentioned in the above is used for a POS terminal, two kinds of such printers must be prepared for two kinds of paper different in size ratio, preventing drastic decrease in the cost. In addition, since the thermal printer according to the patented prior invention mentioned in the above has only one drive roller and one motor, the print speed for the two kinds of paper can not be made different. Therefore, it is found that, in case the difference in the amount of the outputted information is large, i.e., the amount of the information is extremely different, there is a problem that paper having the smaller amount of information wastes large blank portions. Accordingly, an object of the present invention is to provide a dual type thermal printer capable of changing the size ratio of paper to be used, and thus, capable of decreasing the total cost. Another object of the present invention is to provide a dual type thermal printer capable of making different the print speed for two kinds of paper and thus, capable of accommodating a case where the difference in the amount of the outputted information is large without changing the size ratio of paper so much. Still another object of the present invention is to provide a dual type thermal printer capable of avoiding excessive waste blank portions of paper having the smaller amount of information. The present invention is made in view of the above problems. According to the present invention, two platen rollers positioned coaxially and rotatably supported independently of each other are provided in parallel with one opposing thermal head, and, there are provided paper feed means for separately transporting heat sensitive paper inserted between these platen rollers and the thermal head, respectively, and a movable frame for holding the thermal head, having regulating pieces at both ends thereof for regulating end portions of the heat sensitive paper and slidably attached in the axial direction of the platen rollers. According to the means mentioned in the above, by just sliding the movable frame, the size of paper to be used can be changed. Further, since the two platen rollers and the paper feed means for separately transporting heat sensitive paper are provided, the paper feed speed for the two pieces of heat sensitive paper can be made different. For a more better understanding of the present invention, reference is made of a detailed description to be read in conjunction with the accompanying drawings, in which: Fig. 1 is a perspective view showing an embodiment of a thermal printer according to the present invention; Fig. 2 is a sectional side view illustrating a thermal head in the thermal printer of the embodiment shown in Fig. 1, away from a platen roller; Fig. 3 is a sectional side view illustrating the thermal head in the thermal printer of the embodiment shown in Fig. 1, pressed against the platen roller; Fig. 4 is a perspective view showing a specific example of a movable frame; and Fig. 5 is a perspective view showing a specific example of a stopper and conducting member inserted into a space between the movable frame and a main body frame. A preferred embodiment of the present invention is now described in the following based on the drawings. Fig. 1 is a perspective view showing an embodiment of a thermal printer according to the present invention. Fig. 2 is a sectional side view illustrating a thermal head away from a platen roller. Fig. 3 is a sectional side view illustrating the thermal head pressed against the platen roller. In Fig. 1, reference symbol 1 denotes a main body frame of the printer, 2a and 2b denote platen rollers provided horizontally at a front end portion of the main body frame 1, 3 denotes a line dot type thermal head attached to the main body 1 frame approachably to and separably from the platen rollers 2a and 2b, and 4 denotes a rotating and pressing member for making the thermal head 3 approach to and away from the platen roller 2. The rotating and pressing member 4 has a pressing piece 4a positioned at the rear surface of the thermal head 3 and an operating lever 4b provided on one side thereof so as to protrude upward. The main body frame 1 is formed of plastic, and the outer peripheral surfaces of the platen rollers 2a and 2b are covered with an elastic material. As shown in Fig. 2, the thermal head 3 is fixed between a pair of head supporting pieces 6a and 6b on the left and right sides fitted to a head supporting shaft 5 disposed at a center lower portion of the main body frame 1, and is held so as to be rotatable about the head supporting shaft 5. When assembled, the thermal head 3 is away from the platen roller 2 as shown in Fig. 2. The thermal head 3 is configured to be pressed against the platen rollers 2a and 2b by pushing forward the operating lever 4b as shown by an arrow B in Fig. 3. In this embodiment, a plurality of leaf springs 7 are fixedly attached to the rear surface of the thermal head 3, though the present invention is not limited thereto. The tip sides of the leaf springs 7 are in contact with a rear wall 25 of a movable frame 20 described in the following. By this, when the operating lever 4b is pushed forward, the pressing piece 4a rotates and at the same time, presses the leaf springs 7 forward, curving the leaf springs 7, as shown in Fig. 3 such that the thermal head 3 is pressed against the platen roller 2 at predetermined pressure caused by the elastic force of the leaf springs 7. Also, as shown in Fig. 2, a pushing-up piece 4c is provided at a lower end of the operating lever 4b, and an engaging pin 3a is provided on one side of the thermal head 3 so as to protrude sideward. When the operating lever 4b is rotated backward as shown by an arrow A, immediately after the pressing piece 4a comes out of contact with the leaf springs 7, the pushing-up piece 4c comes in contact with and pushes up the engaging pin 3a, thereby compulsorily moving the thermal head 3 away from the platen roller 2. In this embodiment, the platen roller 2 is, as shown in Fig. 1, divided into two: a first platen roller 2a axially supported by a rotational shaft 8a between a side wall portion 1a of the main body frame 1 and a supporting wall 1c provided at the center of the front end of the frame; and a second platen roller 2b axially supported by a rotational shaft 8b between a side wall portion 1b and the supporting wall 1c. In this embodiment, the platen roller 2a is formed so as to be shorter than the platen roller 2b, though the present invention is not limited thereto. Drive motors 9a and 9b are attached to both sides of a back end portion of the main body frame 1 correspondingly to the two divided platen rollers 2a and 2b, respectively. It is structured such that the rotational driving force of the drive motors 9a and 9b are transmitted to the platen rollers 2a and 2b by reduction gear mechanisms built in the side wall portions 1a and 1b of the main body frame 1, respectively. It is to be noted that a pin 10 horizontally provided between the side wall portion 1a of the main body frame 1 and the supporting wall 1c and substantially in parallel with and a little above the platen roller 2a is a pin as a stopper for regulating the forward position of the operating lever 4b. The pin 10 also has a function such that when a cutter is attached in front of the platen roller 2b, it introduces paper after printing so that the paper forms a predetermined angle with regard to the cutter. The pin 10 is provided only on the side of the platen roller 2a because it is assumed that, when the printer is used for a POS terminal, paper on the right side is for a journal of the shop to be kept as a record and paper on the left side is for a receipt to be handed to a customer, and thus, it is assumed that a cutter is attached only to the left side. On the other hand, though the thermal head 3 is integrally formed so as to oppose both of the platen rollers 2a and 2b as shown in Fig. 1, its length is set so as to be a little shorter than the total of the widths of the platen rollers 2a and 2b and the space between the platen rollers 2a and 2b. It is to be noted that the difference between the length of the thermal head 3 and the above total length of the platen rollers is determined according to the amount of the slide of the thermal head described in the following. In other words, the length of the thermal head 3 is the total length of the platen rollers minus the amount of the slide of the thermal head. Next, a sliding mechanism of the thermal head 3 is described. In this embodiment, a movable frame 20 made of a conductive material is attached to a front end lower surface of the main body frame 1. The movable frame 20 has at both ends thereof a pair of retaining pieces 21a and 21b bent upward as shown in Fig. 4, and is configured to be slidable to the left and to the right of the main body frame 1 by fitting through holes 22a and 22b formed in lower portions of the retaining pieces 21a and 21b to the head supporting shaft 5. Further, a supporting pin 11 for rotatably supporting the rotating and pressing member 4 is horizontally provided between engagement holes 23a and 23b formed in tip portions of the retaining pieces 21a and 21b. It is to be noted that the pair of head supporting pieces 6a and 6b on the left and right sides for supporting the thermal head 3 is fitted to the head supporting shaft 5 inside the retaining pieces 21a and 21b at both ends of the movable frame 20. When the frame 20 is moved along the head supporting shaft 5 with the operating lever 4b held up as shown in Fig. 2, since the retaining pieces 21a and 21b laterally pushes the head supporting pieces 6a and 6b, the thermal head 3 is slid together. Further, regulating pieces 24a and 24b for regulating ends of paper are provided in the movable frame 20, and the width of paper to be used is determined by the space between the regulating pieces 24a and 24b and the supporting wall 1c at the front end of the main body frame 1. When the movable frame 20 is slid, since the space between the regulating piece 24a and the supporting wall 1c and the space between the regulating piece 24b and the supporting wall 1c changes simultaneously, the respective widths of paper to be fed by the platen rollers 2a and 2b are changed. More specifically, in a state where the movable frame 20 is moved to the left in Fig. 1, the space between the regulating piece 24a and the supporting wall 1c equals the space between the regulating piece 24b and the supporting wall 1c, so that the platen rollers 2a and 2b are capable of feeding heat sensitive paper for printing having the same width. On the other hand, in a state where the movable frame 20 is moved to the right in Fig. 1, the space between the regulating piece 24a and the supporting wall 1c is made smaller and the space between the regulating piece 24b and the supporting wall 1c is made larger, so that the platen roller 2a feeds narrower heat sensitive paper for printing and the platen roller 2b feeds heat sensitive paper for printing wider than that for the platen roller 2a. In other words, by sliding the movable frame 20 to the left or to the right, the combination of the widths of heat sensitive paper to be used can be changed. In addition, in this embodiment, the regulating pieces 24a and 24b are formed such that the lower ends thereof are in contact with a guide wall 1d provided at the front end of the main body frame 1. Further, guide pieces 25a and 25b opposing side front walls 1e and 1f of the main body frame 1 are projectingly provided at a front end of the movable frame 20. These regulate the rotation of the movable frame 20 about the head supporting shaft 5 to make the movable frame 20 slidable to the right and to the left in a stable posture. In this embodiment, in a state where the movable frame 20 is moved to either end, a stopper and conducting member 30 made of a conductive metal plate or the like and having a shape as shown in Fig. 5 is detachably inserted from below the main frame 1 into a space C2 (or C1) between the movable frame 20 and an inner surface of a side wall portion of the main body frame 1, through the present invention is not limited thereto. Though, in Fig. 1, the space between the movable frame 20 and the inner surface of the side wall portion of the main body frame 1 is denoted by C2, in a state where the movable frame 20 is slid to the right end, i.e., oppositely to the case shown in Fig. 1, such a space C1 is on the opposite side (on the left side), and thus, the stopper and conducting member 30 is symmetrically shaped so as to be insertable into both of the left space and the right space. A substantially rectangular notch 31 at a front lower portion of the stopper and conducting member 30 shown in Fig. 5 is formed so as to be capable of engaging with the head supporting shaft 5. Notches 32 and 33 formed from both ends in the middle toward the center are for facilitating curving of both wing pieces 34 and 35 in attachment and detachment. Further, a contact piece 36 provided so as to extend diagonally downward from an upper end and stopper pieces 37 and 38 bent outward from tip portions of the both wing pieces 34 and 35 are provided in the stopper and conducting member 30. Among them, the stopper piece 37 or 38 is engaged with an engagement hole formed in proximity to a motor attaching portion on an inner surface of a side wall portion of the main body frame 1 to prevent misalignment of the stopper and conducting member 30. On the other hand, the contact piece 36 is pressed against and in contact with a housing made of metal for the drive motor 9a or 9b by the elastic force of the stopper and conducting material 30 in a state where it is inserted in the space C1 or C2. Further, the wing pieces 34 and 35 of the stopper and conducting member 30 are in contact with the retaining pieces 21a and 21b at both ends of the movable frame 20, and is assembled such that the movable frame 20 is in contact with the tips of the leaf springs 7 at the rear surface when the thermal head 3 is pressed against the platen rollers 2a and 2b. This makes the electric potential of the housing of the drive motor 9a or 9b equal to that of the thermal head 3. Further, as shown in Fig. 1, a sheet metal 50 formed such that its front end has a protrusion 51 a tip of which protrudes from the side front wall surface 1f (1e) and its back end reaches the position where the drive motor 9b (9a) is attached in each of the inner walls of the side wall portions 1b (1a) of the main body frame 1. The drive motor 9b (9a) is fixed to the sheet metal 50 with a screw, and the guide piece 25b (25a) of the movable frame 20 is configured so as to be contactable therewith. This makes the electric potential of the drive motor 9a or 9b without the stopper and conducting member 30 inserted therein equal to that of the movable frame 20 through the sheet metal 50. By grounding them through an earth wire (not shown), breakage of the thermal head due to static electricity is prevented. It is to be noted that, in Figs. 2 and 3, reference symbol 42 denotes a detector formed of a microswitch and the like for detecting whether the thermal head 3 is in the up state or in the pressed state. Next, the method of using the thermal printer according to the above embodiment is described. The thermal printer of this embodiment has two set states: a first set state where the movable frame 20 is moved to the left end with the stopper and conducting member 30 inserted in the space C2; and a second set state where the movable frame 20 is moved to the right end with the stopper and the conducting member 30 inserted in the opposite space (C1). In the second set state, the effective width of printing of the left platen roller 2a is smaller than that in the first set state, and, in contrast, the effective width of printing of the right platen roller 2b is larger. Besides, the thermal printer of this embodiment is provided with the drive motors 9a and 9b for the platen rollers 2a and 2b, respectively. This makes it possible for the respective platen rollers 2a and 2b to control the paper feed amount, that is, the print speed, and the size of the printed characters independently of each other. As a result, the necessity to prepare two kinds of printing apparatus for two sheets of print paper different in width ratio as with a conventional thermal printer is eliminated, a single printer that can cope with two sheets of print paper different in width ratio can be provided, and thus, the total cost can be lowered. It is to be noted that, though in the above embodiment, lateral movement of the movable frame 20 in operation is prevented by inserting the stopper and conducting member 30 into the space C1 or C2 between the movable frame 20 and a side wall portion of the main body frame 1 with the movable frame 20 slid to one end, the means for preventing movement of the movable frame 20 is not limited thereto. For example, in the embodiment shown in Fig. 1, slits for engagement 1g (the right slit is not seen because the regulating piece 24b is in engagement therewith) are provided on the front end surface of the main body frame 1 so as to oppose the regulating pieces 24a and 24b when the movable frame 20 is moved to the left end and to the right end, respectively, and movement of the movable frame 20 can be fairly prevented just by the slits for engagement 1g. However, it is to be noted that, as in this embodiment, by inserting the stopper and conducting member 30 into the space C1 or C2 between the movable frame 20 and a side wall portion of the main body frame 1, movement of the movable frame 20 can be prevented with more certainty. Further, though the driving force of the drive motors is transmitted to the platen rollers to rotate in this embodiment, a paper feed roller may be provided separately from the platen rollers. As described in the above, a thermal printer according to the invention as claimed in claim 1 comprises a main body frame, one thermal head, first and second platen rollers provided in parallel with the thermal head, positioned coaxially, and rotatably supported independently of each other, paper feed means capable of separately transporting two pieces of heat sensitive paper inserted between the first platen roller and the thermal head and between the second platen roller and the thermal head, respectively, and a movable frame for holding the thermal head, having a pair of regulating pieces at both ends thereof for regulating end portions of the heat sensitive paper and slidably attached in the axial direction of the platen rollers, and thus, there is an effect that the size of paper to be used can be changed just by sliding the movable frame, and the feed speed of the two sheets of paper can be made different. According to the invention as claimed in claim 2, a supporting wall is provided between the first platen roller and the second platen roller of the main body frame, a supporting shaft of the first platen roller is provided horizontally between the supporting wall and one side wall portion of the main body frame, a supporting shaft of the second platen roller is provided horizontally between the supporting wall and the other side wall portion of the main body frame, and side surfaces of the supporting wall form guide surfaces for regulating the other end portions of the two pieces of heat sensitive paper inserted between the first platen roller and the thermal head and between the second platen roller and the thermal head, respectively, and thus, there is an effect that the supporting wall of the platen rollers can also serve as a guide member of heat sensitive paper, making the configuration simpler. According to the invention as claimed in claim 3, a stopper member insertable into any space between the movable frame and a side wall portion of the main body frame with the movable frame slid to one end is provided, and thus, there is an effect that movement of the movable frame in operation is prevented with certainty, and in addition, since only one stopper member is necessary, the number of parts is small. According to the invention as claimed in claim 4, the paper feed means comprises two drive motors provided correspondingly to the platen rollers and two sets of reduction gear mechanisms for transmitting driving force of the drive motors, respectively, and thus, there is an effect that output to two sheets of paper with the print speed and the size of the printed characters can be changed. According to the invention as claimed in claim 5, the stopper member is formed of a conductive material and is configured such that, in an inserted state, a portion thereof is in contact with a conductive housing of one of the drive motors forming the paper feed means, and thus, there is an effect that the electric potential of the movable frame is made to be equal to that of the housing of the drive motor through the stopper member, and grounding as measures against static electricity is made easier. According to the invention as claimed in claim 6, an elastic member for pressing the thermal head against the platen rollers is disposed on a rear surface of the thermal head, a portion of the elastic member is in contact with the movable frame, and thus, there is an effect that the electric potential of the thermal head is made to be equal to that of the movable frame and that of the housing of the drive motor, and the grounding is further made easier. According to the invention as claimed in claim 7, the movable frame is configured to have guide pieces in contact with a surface of the main body frame, the surface formed in parallel with the supporting shafts of the platen rollers, and thus, there is an effect that the movable frame can be slid with stability. According to the invention as claimed in claim 8, a head up/down mechanism is provided at the back of the thermal head for pressing the thermal head against the platen rollers or moving the thermal head away from the platen rollers by rotation of an operating lever, and a positional regulation pin for regulating the rotational position of the operating lever is provided in the vicinity of a platen roller on the side where the operating lever is disposed so as to be in parallel with the platen rollers, and thus, there is an effect that the force pressing the thermal head against the platen rollers can be made constant. According to the invention as claimed in claim 9, the operating lever and the positional regulation pin are provided so as to be in parallel with one platen roller having a smaller distance from the thermal head when the movable frame is slid, and thus, there is an effect that the positional regulation pin can also serve as an introducing member of the paper, and the number of parts can be decreased. According to the invention as claimed in claim 10, the length of the thermal head is set so as to be shorter than the total of the widths of the first and second platen rollers and the space therebetween, and thus, there is an effect that the length of the thermal head can be made minimum and the cost can be lowered. The aforegoing description has been given by way of example only and it will be appreciated by a person skilled in the art that modifications can be made without departing from the scope of the present invention.

Claims: A dual type thermal printer comprising: a main body frame (1); one thermal head (3); first and second platen rollers (2a, 2b) provided in parallel with said thermal head, positioned coaxially, and rotatably supported independently of each other; paper feed means capable of separately transporting two pieces of heat sensitive paper inserted between said first platen roller and said thermal head and between said second platen roller and said thermal head, respectively; and a movable frame (20) for holding said thermal head, characterised by having a pair of regulating pieces (24, 25) at both ends thereof for changing the spaces available for said heat sensitive paper and slidably attached in the axial direction of said platen rollers. A dual type thermal printer as claimed in claim 1, characterised in that a supporting wall (1c) is provided between said first platen roller and said second platen roller of said main body frame, a supporting shaft of said first platen roller is provided horizontally between said supporting wall and one side wall portion of said main body frame, a supporting shaft of said second platen roller is provided horizontally between said supporting wall and the other side wall portion of said main body frame, and side surfaces of said supporting wall form guide surfaces for changing the spaces available for the end portions of said two pieces of heat sensitive paper inserted between said first platen roller and said thermal head and between said second platen roller and said thermal head, respectively. A dual type thermal printer as claimed in claim 1 or 2, characterised by further comprising a stopper member (30) insertable into space (c1, C2) between said movable frame and a side wall portion of said main body frame with said movable frame slid to one end. A dual type thermal printer as claimed in claim 1, 2, or 3, characterised in that said paper feed means comprises two drive motors (9a, 9b) provided correspondingly to said platen rollers and two sets of reduction gear mechanisms for transmitting driving force of said drive motors, respectively. A dual type thermal printer as claimed in claim 4, characterized in that said stopper member is formed of a conductive material and is configured such that, in an inserted state, a portion thereof is in contact with a conductive housing of one of said drive motors forming said paper feed means. A dual type thermal printer as claimed in claim 5, characterized in that an elastic member for pressing said thermal head against said platen rollers is disposed on the rear surface of said thermal head, a portion of said elastic member being configured to be in contact with said movable frame. A dual type thermal printer as claimed in claim 1, 2, 3, 4, 5, or 6, characterized in that said movable frame is configured to have guide pieces in contact with a surface of said main body frame, the surface formed in parallel with said supporting shafts of said platen rollers. A dual type thermal printer as claimed in claim 1, 2, 3, 4, 5, 6, or 7, characterized in that a head up/down mechanism is provided at the back of said thermal head for pressing said thermal head against said platen rollers or moving said thermal head away from said platen rollers by rotation of an operating lever, and a positional regulation pin for regulating the rotational position of said operating lever is provided in the vicinity of a platen roller on the side where said operating lever is disposed so as to be in parallel with said platen rollers. A dual type thermal printer as claimed in claim 8, characterized in that said operating lever and said positional regulation pin are provided so as to be in parallel with one platen roller having a smaller distance from said thermal head when said movable frame is slid. A dual type thermal printer as claimed in claim 1, 2, 3, 4, 5, 6, 7, 8, or 9, characterized in that the length of said thermal head is set so as to be shorter than the total of the widths of said first and second platen rollers and the space therebetween.

Inventors: AKIHIKO ITO, WATANABE HIDEKI, AKIHIKO, ITO, WATANABE, HIDEKI
Applicants: SEIKO INSTR INC, SEIKO INSTRUMENTS INC.
Application year: 2000
Main classification: B41J3
IPC codes: B41J11, B41J3