Abstract:
A constant pressure printing mechanism for use in a label printing machine: the platen is pivotally secured to the machine body; the pivotally supported, hand operated printing levers include a projection, which engages a pivotally supported platen lifting member, and the lifting member is pivoted by the projection to turn the platen toward the printing head, whereby the printing head and the platen are moved near to each other to perform the printing of labels.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a constant pressure printing mechanism for a portable label printing machine, or the like (hereinafter a labeler). The mechanism regulates printing pressure for obtaining clear and precise printing of labels without differences in the darkness of the printed characters on labels and without double printing. 
     2. Description of the Prior Art 
     In conventional labelers, a hand operated lever and a printing lever for carrying a printing head integrally form a working lever. A printing head is attached to the front end of the printing lever. The working lever is pivotally secured to the machine frame. The printing lever carrying the printing head is moved, and more particularly, turned downward, when the hand lever is squeezed. This moves the type faces at the underside of the printing head into contact with the surface of a tape-like label strip that is carried on a platen, thereby printing the labels. 
     In conventional labelers, however, the intensity of the squeeze of the hand lever directly influences the pressure of the printing stroke. The darkness of the printed characters is liable to vary according to the intensity of the squeezing force applied to the hand lever. Further, when the hand lever is squeezed too strongly and/or quickly, the platen is struck with great force and the printing head bounces on the label placed on the platen causing double printing. Precise printing is thus difficult to achieve. 
     In the past, even when labels were somewhat indistinctly printed by conventional labelers, they were accepted because customers can read them when they purchase commodities and cashiers can also read them when they total the purchases. In recent years, the figures, symbols (bar codes, OCR characters, etc.), and the like, that are being printed on labels are being read by computerized optical readers in place of cashiers in order to put what is called POS (point of sales) system into practice. In this system, information concerning stocks, sales, customers&#39; data, profit and loss, and other management data are memorized and processed by electronic computers. To enable accurate machine reading of labels, it has become necessary for the labels to always be printed with clear consistent quality, precise characters and symbols. 
     SUMMARY OF THE INVENTION 
     It is, therefore, the primary object of the present invention to provide an improved constant pressure printing mechanism for use in a portable label printing machine, or the like, which mechanism is quite effectively achieving clear, precise and consistent printing of labels, without double printing. 
     It is another object to provide a constant pressure printing mechanism which is reliable in operation, simple in structure and durable, even in severe use. 
     In accordance with the present invention, the constant pressure printing mechanism includes the following features. The platen that supports the tape-like label strip for being printed is pivotally secured to the machine body. When the printing lever carrying the printing head is moved toward the platen, an operator portion of the printing lever or of the printing head and a portion of the platen or of a member which is interlocked to the platen are brought into contact with each other so as to turn up the platen slightly toward the printing head. Thus, the printing head and the label strip on the platen are moved toward each other to perform the printing of a label. To turn down the printing lever, the hand lever is squeezed. In a preferred embodiment, a portion of the printing head on its underside is a pushing projection which engages a platen lifting member which is interlocked to the platen for lifting the platen. The platen is pivoted up by the lifting member. The lifting member is separately pivotally mounted to the frame and engages and lifts the platen as the lifting member is pivoted by being engaged by the pushing projection. The platen, the printing lever and the lifting member are all biased to return to their initial positions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the invention are described with respect to a preferred embodiment of the invention shown in the accompanying drawings, in which: 
     FIG. 1 is a partially cross-sectional, side elevational view of a label printing machine having the constant pressure printing mechanism of the invention, shown in the rest position; 
     FIG. 2 is the same view as FIG. 1, with the label printing machine in the printing position; and 
     FIG. 3 is an enlarged cross-sectional view of the constant pressure printing mechanism viewed along the line III--III in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an embodiment of the constant pressure printing mechanism of the present invention. The labeler includes two spaced apart machine side frames 1 between which the other labeler components are carried. On the rear parts (at the right side in FIG. 1) of both of the machine frames 1, the hand grip 2 is integrally formed. 
     There is an integral hand lever 3 and a bifurcated printing lever 4 which are pivotally secured by the pivot shaft 5 between the machine frames 1. A return spring 6 is stretched between a spring pin 7, which is formed in the hand grip 2, and a spring supporting projection 8, which is formed on the rear (right hand) part of the printing lever 4 above the pivot 5. Both the hand lever 3 and the printing lever 4 are always urged clockwise (in FIG. 1) by the return spring 6. 
     A printing head 9 is disposed in the space between the front parts of the arms of the bifurcated printing lever 4. The undersurface of the printing head 9 carries an operator, i.e. a pushing projection, 10 that is brought into engagement with the lifting member 21, as described below. Further, in front of the projection 10, the undersurface of the printing head carries types 11 for printing a label. 
     There is a platen 12 which is pivotally secured to and between the machine frames 1 by a pivot shaft 13. As shown in FIGS. 1 and 3, a respective tensioned return spring 16 is attached on each side of the platen 12. Each spring 16 is stretched between a spring supporting pin 14 that is fixed to the respective side wall of the platen 12 and another spring supporting pin 15 which is fixed to the respective side wall of the stationary bottom cover 18 of the labeler. The return spring 16 always urges the platen 12 counterclockwise (in FIG. 1). This urges the undersurface 17 at the front part of the platen 12 into contact with the bottom cover 18. A roller 20 is rotatively attached by a roller shaft 19 to each side plate of the platen 12. The roller 20 serves as an abutting means. 
     A respective one of a pair of lifting members 21 is pivotally attached to the inside wall of each machine frame 1 by a respective fitting shaft 22. Each lifting member 21 has a receiving surface 23 at its upper front portion, a lifting surface 24 at its upper rear portion, and a stopping surface 25 at its lower rear portion. The surface 24 serves as another abutting means that cooperates with the roller 20. As shown in FIG. 3, the outside of each lifting member 21 is provided with an annular projection 26 around the fitting shaft 22 and with a spring support projection 27 in the rear part of the lifting member 21. The torsion spring 28 is fitted around the annular projection 26. One end of the spring 28 is supported by the spring support projection 27 on the lifting member and the other end of the spring 28 is held against a pin 29 which is attached to the inside wall of the machine frame 1. The lifting member 21 is thus urged always clockwise to a released position. In the released position shown in FIG. 1, the stopping surface 25 of the lifting member 21 is biased into contact with the stopper 30 that is formed on the inside wall of the machine frame 1, so that the lifting member 21 can be turned only in the counterclockwise direction to the platen lifting position. 
     A stopper 31 is fixed inside the hand grip 2 and the upper surface of the hand lever 3 abuts stopper 31 when the lever 3 is squeezed, thereby limiting the extent to which the lever 3 can be squeezed. 
     There is a holder 32 for a rolled label strip 33. The tape-like label strip 34 paid out from the rolled label strip 33 is transferred onto the platen 12 by a known feeding mechanism 35. 
     The operation of the constant pressure printing mechanism of the present invention is now described. FIG. 1 shows the rest position of the labeler. When the hand grip 2 and the hand lever 3 are squeezed together to turn the hand lever upward (counterclockwise), the printing lever 4 that is formed integrally with the hand lever 3 is turned downward about the pivot shaft 5 and this moves the printing head 9 down. During this motion, an inking roller (not shown) rolls on the types 11 on the bottom of the printing head 9 to ink the type faces. As the hand lever 3 is squeezed further, the pushing projection 10 on the lower rear side of the printing head 9 first comes into contact with the receiving surface 23 of the lifting member 21 to push down the receiving surface 23 before the faces of the types 11 of the printing head 9 are moved into contact with the tape-like label strip 34 carried on the platen 12. Accordingly, the lifting member 21 is turned counterclockwise about the fitting shaft 22 against the force of the spring 28. 
     The turning movement of the lifting member 21 raises the lifting surface 24 of the lifting member 21 into engagement with the roller 20 that is attached on the side wall of the platen 12. The roller 20 is pushed up and lifted and this turns the platen 12 clockwise about the pivot shaft 13 against the force of the return spring 16. Accordingly, as shown in FIG. 2, the types 11 of the printing head 9 that is moving down come into contact with the tape-like label strip 34 on the platen 12 that is moving up. Upon such contact, the surface of a label on the platen is printed. Further, the upper surface of the hand lever 3 is squeezed into contact with the stopper 31 formed in the hand grip 2, so that the printing levers 4 and the printing head 9 are thereafter blocked from further movement, and excessive pressure contact between the faces of the types 11 and the label surface can be avoided. Therefore, excessively dark printing can be prevented. 
     Next, when the hand lever 3 is released, the hand lever 3 and the printing levers 4 are turned clockwise about the pivot shaft 5 by the tension of the return spring 6. This moves the printing head 9 upward. At the same time, the lifting member 21 is turned clockwise to the released position by the force of the spring 28 until the stopping surface 25 contacts the stopper 30. Further, the platen 12 is turned counterclockwise by the force of the return spring 16. The mechanism is thereby returned to the state shown in FIG. 1. 
     Simultaneously with the above working, the tape-like label strip 34 is shifted forward by the length of one label piece by the feeding mechanism 35, and the previously printed label 34a is paid out under the applicator 36. 
     The configurations and the positions of the pushing projection 10, the lifting member 21, etc. are not restricted to the precise form shown herein. Furthermore, the constant printing pressure mechanism of the present invention can be used not only in a portable label printing machine but also in other printing machines, such as price tag attaching machines and desk-type label printing machines. 
     As described above, in the present invention, when the type faces of the printing head are moved near the label surface by the squeezing of the hand lever, the platen carrying the label is moved toward the printing head in interlocked relationship. The type faces and the label surface are brought into contact with each other to print a label. Accordingly, the following advantages and effects can be expected. 
     (1) Even when the squeezing force is weak, the type faces and the label surface approach and press mutually, so that printing can always be accomplished under a certain pressure. Accordingly, the printed characters do not become vague and clear printing of the proper darkness can always be attained. 
     (2) Further, when the hand lever is squeezed quite strongly and/or rapidly, another part of the printing head or the printing lever first contacts the platen or a member that is attached to the platen before the type faces are brought into contact with the label surface, so that the printing pressure can be moderated properly. Furthermore, since the type faces and the label surface are brought near and then pressed to each other, the shock of impact on and the rebounding on the platen can be avoided. As a result, double printing can be prevented. 
     Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.