Positioning device for a document processing device

Abstract: The invention relates to a positioning device for a document processing device such as a printing device or an image reading device. The printing device comprises a supporting plate (2), a head plate (9) provided on said supporting plate (2), and a printing portion arranged on said head plate (9), wherein at least one hole (2c) is formed in said supporting plate (2), said at least one hole (2c) being parallel to said printing portion and piercing through both sides of said supporting plate (2). The shape of said at least one hole (2c) is of a round hole or a circular groove in which a portion on the circumference of a circle forming the groove is formed as an opening connecting to one side of said supporting plate (2) and in which the width of said groove opening is smaller than the diameter of the at least one hole (2c).

Description: The present invention relates to a positioning device which facilitates the positioning of a printing portion of a printing device and an image reading portion of an image reading device with respect to a central portion of a platen roller. In the case of a printing device, for example, in which a thermal head is used, it is required to precisely position a center of a platen roller, which pushes a heat sensitive paper towards a heat element of the thermal head, with respect to the heat element of the thermal head. For this purpose, it has been known to fix a guide part by means of screws to a supporting plate of the thermal head and to incorporate this into a frame. In Fig. 3, a platen roller having this kind of a thermal head equipped with a guide portion for the thermal head are shown. Such platen rollers are mainly used for a smaller printer and the like. In Fig. 3, a supporting plate of a thermal head includes screw hole 2a which fixes a guide part 1 of a thermal head, and a positioning hole 2b. On the other hand, the guide part 1 of the thermal head includes a respectively corresponding insertion hole 1a and a positioning projecting plate 1b. An upper surface of the thermal head is applied and fixed to a back of the supporting plate 2 by means of a screw 8. After a shaft (not shown) is inserted into a pair of bearing holes 1c in the guide part 1 of the thermal head, both ends of the shaft are fixed to a frame (not shown). In this case, the frame is in advance equipped with an attaching portion of the shaft in order to position a center portion of a platen roller 5 with respect to a heat element 6 as a printing portion installed on a base plate 9 of the thermal head. In addition to the heat element 6, a driving element, a common head electrode pattern, a individual lead electrode pattern and the like are mounted on the base plate 9 of the thermal head. However, illustrations in the Figures and explanations thereof are omitted. In addition to the function of positioning with respect to the platen roller, the shaft also functions to push the thermal head towards the platen roller 5, to hold a thermal sensitive paper or the like. In the prior art device as described above, a head portion of the screw 8 for attaching the guide part 1 of the thermal head to the outer side of the thermal head, and the guide part of the thermal head project from the supporting plate 2. This is in contradiction to the need of the down-sizing the printing device by means of a thin thermal head. This problem equally applies in the case of an image reading device equipped with a platen roller. On account of the positioning mechanism of the prior printing device or image reading device being constructed as described above, when the head guide part is attached to the supporting plate, the printing device or image reading device are unnecessarily large. A document processing device according to the preamble of claim 1 is known from DE-OS-2 365 504. It is the object of the present invention to solve the above problems in the prior art. This object is solved according to the present invention by a printing device including the features of claim 1. Advantageous detailed embodiments are defined in the dependent claims. According to the present invention, the thermal head and image reading head can be mounted to the frame without a guide part. The present invention offers a printing device and positioning device with respect to platen roller in an image reading device, both in smaller scale, which enable the down-sizing. A positioning device for positioning with respect to a platen roller and pertaining to the present invention can include a supporting plate, a base plate of a head provided on the supporting plate, a printing portion or a light receiving element array installed on the head base plate, a shaft inserting portion parallel with the printing portion or the light receiving element array and formed to pierce both sides of said supporting plate, a shaft to be a supporting point for the supporting plate with the printing portion or a cover glass plate for the light receiving element array, and possibly also means to apply pressure to push the printing portion or cover glass plate toward the platen roller. Thus, the present invention provides a compact thermal printer or image reading device. Exemplary embodiments of the present invention are described in more detail in the following with respect to the enclosed drawings, in which: Fig. 1A is a perspective view of the main part of an embodiment pertaining to the present invention; Fig. 1B is a cross-sectional view of the main part of the embodiment shown in Fig. 1A; Fig. 2 is a side view of the main part of another embodiment pertaining to the present invention; Fig. 3 is a side view of a thermal head according to the prior art; Fig. 4A is an exploded view of the main part pertaining to the embodiments of the present invention; and Fig. 4B is a side view of the structure of a further embodiment pertaining to the present invention including the main part shown in Fig. 4A. Referring now to Fig. 1, a preferred embodiment will be explained in which it is easier to position a heat element of a thermal head with respect to a center portion of a platen roller. Fig. 1(A) shows a perspective view, and Fig. 1(B) shows a side view of the main components, wherein parts previously explained with respect to the prior art have the same reference signs. As shown in Fig. 1, a supporting plate 2 is provided on a base plate of a thermal head 9. A circular groove 2c parallel with a heat element 6 mounted in a longitudinal direction is provided such that it pierces both sides of the supporting plate 2, and a shaft 3 is inserted to engage the circular groove 2c. Both ends of the shaft 3 are inserted and fixed to holes 4a, 4b formed on both sides of a frame 4. Thus, an attaching position is formed as well to position a center portion of a platen roller 5, fixed to the frame, with respect to the heat element 6. In the structure as described above, the supporting plate 2 with the thermal head is in a semi-fixed state such that it can move to depict an arch around the shaft 3 as a center portion. When characters are printed in this semi-fixed state, the thermal head must be pushed against a platen roller 5 to hold a heat sensitive paper. Accordingly, a plate spring 7 to apply pressure to the back of the supporting plate 2 is mounted by means of screws or the like to at least one spring attaching portion 4c formed on the frame 4. Therefore, as the thermal head is pushed against the platen roller 5 at the shaft 3 as a supporting point, the thermal head can be in a semi-fixed state to a fixed state. In the above structure, if only a circular groove 2c is formed to insert the shaft 3 into the supporting plate 2, it becomes unnecessary to attach guide parts to the back of the supporting plate 2, and the thermal head can be formed without increasing the thickness. The supporting plate is generally formed in a continuous shape in the cross-sectional direction by extrusion or pulling-out processing of a metal such as aluminum by molding. Accordingly, the cross-sectional shape of the supporting plate can be easily formed if it is continuous, even if it is a shape, for example, equipped with the circular groove 2c as above, and it is suitable for mass production. Next, Fig. 4 shows applications of the present invention. Fig. 4(A) is a view of dismantled elements, and Fig. 4(B) is a structural side view, wherein the same or equivalent parts as described with respect to the prior art have the same reference signs and to which reference is made for explanation. As shown in Fig. 4(B), a platen roller 5 is positioned by inserting a bearing 15 into a shaft 5a, and holding it in a shaft guide portion 16a formed in a frame 16. The frame 16 is mounted on a base 17 of a thermal printer by means of screws or the like. On the other hand, as shown in Fig. 4(A), the center portion of the platen roller 5 and the heat element 6 is positioned with respect to frame 16 by means of a portion 18b of a guide pin 18 which projects from the thermal head after pushing the pin guides from an end 18a thereof into a circular groove 2c formed in both sides of the supporting plate 2 of the thermal head. Further, a groove 2d is formed on the both sides of the supporting plate 2. A supporting point is formed by holding a supporting axis plate 19 fixed on the base 17 by said groove 2d when said supporting plate 2 is pushed by the plate spring 7 fixed on the base 17 by means of a screw 20. In this example, the supporting axis plate is fixed to the base 17, but can alternatively be fixed to the frame 16. In use of the thermal head, the heat element 6 is always pushed onto the platen roller 5 with a heat sensitive paper interposed therebetween. When the heat sensitive paper is exchanged, it is necessary to detach the thermal head from the platen roller 5. In this case, said guide pin 18 is stopped at the lateral end of the pin guide 16b, which is formed, for example, with an L-shape in order to prevent the thermal head dropping. The supporting plate 2 of the thermal head can generally be formed with a continuous shape in the cross-sectional direction by extrusion or pulling-out processing of a metal such as aluminum by a molding technique. Accordingly, the cross-sectional shape of the supporting plate 2 can be easily formed to some free extent even if it is a shape, for example, provided with the circular groove 2c. As the pin guide 16b formed on the frame 16 and the shaft guide portion 16a can be formed accurately with a single metal plate or the like by pulling-out processing, the accuracy of positioning can be improved. Next, Fig. 2 shows a view of elements of an image reading device according to the present invention. The structure common with that of the example in Fig. 1 is explained by referring to Fig. 1. As shown in Fig. 2 said image reading device includes a head arranged on a supporting plate 10, a light receiving element array 14 mounted on a base plate of the head 11, a cover glass 13 fixed stepping over a manuscript stand 12 and a supporting plate 12, and a lighting element (not shown) and so on. An image such as a manuscript or photograph moving between a platen roller 5 and the cover glass 13 by pushing by the platen roller 5 is read by the light receiving element array 14. Similarly as with the printing device, a circular groove 10c parallel with the light receiving element array 14 is formed to pierce through the both sides of the supporting plate 10, and the shaft 3 (Fig. 1) matching with the circular groove 10c is inserted therein. Both ends of the shaft 3 are fixed by insertion into holes 4a, 4b formed on both sides of the frame 4 (Fig. 1). Similarly, an attaching position is formed to position a center portion of the platen roller 5 fixed to the frame 4 with respect to the light receiving element array 14. In the example above, the circular groove 2c is formed in the supporting plate 2 in order to insert the shaft 3, but a circular hole may be formed. In the example above, the thermal head was explained which is formed with the heat element, but it may be applied to a LED head including a lighting diode array. As stated above, in the present invention, as a circular groove parallel with a heat element or a round hole is formed on a supporting plate, and the shaft is directly inserted into said groove or hole and arranged on a frame, head guide parts are not required as in the prior art. Therefore, the supporting plate portion does not become thick, and a printing device or image reading device can be made compact. As the head guide parts are not used, in addition to easy assembling work, processing work for attaching the guide parts to the supporting plate are not required, and cheap printing devices and image reading devices can be manufactured.

Claims: Document processing device, comprising a supporting plate (2, 10), a head plate (9, 11) provided on said supporting plate (2, 10), a platen roller (5), and a document processing portion (6 ,14) arranged on said head plate (9, 11), wherein said supporting plate (2, 10) is molded with at least one hole (2c, 10c), said at least one hole (2c, 10c) being parallel to said document processing portion (9, 11) and piercing through both sides of said supporting plate (2, 10), characterized by the shape of said at least one hole (2c, 10c) being in the form of a circular hole or groove in which a portion on the circumference of a circle forming the hole or groove is formed as an opening connecting to one side of said supporting plate (2, 10) parallel to said document processing portion, and in which the width of said groove opening is smaller than the diameter of the at least one hole (2c, 10c) said hole (2c, 10c) being suitable for positioning said document processing portion with respect to the center of said platen roller (5). Document processing device according to claim 1, wherein the document processing portion includes a thermal head. Document processing device according to claim 1 or 2, wherein said document processing portion includes an LED head. Document processing device according to claim 1, wherein the document processing portion is an image reading portion. Document processing device according to any of the claims 1 to 4, wherein a round bar, shaft (3) or pin (18) is inserted into the at least one hole (2c, 10c) of the supporting plate (2, 10), said bar, shaft (3) or pin (18) constituting positioning means of the document processing portion and a platen roller (5), or supporting point pressing means (7), with respect to the platen roller (5).

Inventors: KUBO HIROKI, KUBO, HIROKI
Applicants: AOI ELECTRONICS COMPANY LIMITE, AOI ELECTRONICS COMPANY LIMITED
Application year: 1995
Main classification: B41J25
IPC codes: B41J25