Abstract:
A hammer device generates a magnetic moving force in a magnetic member by energizing a coil, whereby a hammer strikes a recording sheet to form a record thereon by means of its moving force, the striking force of the being capable of regulation by changing the relative position of the coil and the magnetic member without changing the position of the hammer.

Description:
This application is a continuation division, of application Ser. No. 370,122 filed June 20, 1989, which is a continuation of Ser. No. 124,446 filed Nov. 23, 1987, which is a continuation of Ser. No. 935,128 filed Nov. 26, 1986, which is a continuation of Ser. No. 827,673 filed Feb. 10, 1986 which is a continuation of Patent application Ser. No. 625,640 filed June 28, 1984, all now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hammer device in which a hammer is moved to strike a recording sheet by attraction of an armature with a coil. 
     2. Description of the Prior Art 
     In the field of electronic typewriters and computer terminal printers, there are already employed impact printers in which a magnetic force obtained by energizing a coil is used for displacing a movable hammer toward a platen, thereby causing a type to strike a printing sheet on the platen through an ink ribbon to print on the sheet. 
     In such impact printers, the printed characters will not be uniform unless types of smaller areas exert a weaker striking force while types of larger areas exert stronger striking force. 
     In order to prevent such drawback there have been made various proposals, but such proposals invariably involve excessive complication in structure or in control. 
     Also there is required an exact positional adjustment among the hammer, coil and yoke in order to obtain the above-mentioned characteristic of the hammer, but such adjustment is generally extremely difficult and is scarcely achievable in uniform manner on all units. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a hammer device in which the striking force is easily adjustable. 
     Another object of the present invention is to prevent noise or repeated advancement of the hammer when the hammer is returned. 
     Still another object of the present invention is to provide a printing apparatus in which the striking force of the hammer is easily adjustable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The attached drawings illustrate an embodiment of the present invention, wherein FIG. 1 is a perspective view of a hammer unit before it is mounted on a base; 
     FIG. 2 is a perspective view of the hammer unit mounted on the base; 
     FIGS. 3A and 3B are cross-sectional plan views showing the method of adjusting the output power of the hammer. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now the present invention will be clarified in detail by an embodiment shown in the attached drawings. 
     FIGS. 1 and 2 show a hammer unit respectively before and after it is mounted on a base functioning as a support member therefore. The hammer device of the present invention is composed of the hammer unit and the base integrally connected thereto, and a printing apparatus is composed of the hammer device and other components such as a platen, a type font wheel, etc. to be explained later. 
     In FIGS. 1 and 2, the hammer unit 1 is assembled on a support frame 2. 
     The support frame 2 is provided, at the front and rear part thereof, with support plates 2a, 2a between which is positioned a coil 1a, and a cylindrical hammer 4 is slidably fitted in the center of the coil 1a. 
     There is also provided a yoke 3. On both ends of the support frame 2 there are formed elongated slots 2b which are disposed parallel to the hammer 4 and are respectively fitted with guide pins 6, 6 projecting from a base 5. As will be explained later, the elongated slots 2b and guide pins 6, 6 allow regulation of the relative position of the coil 1a with respect to the hammer 4 and a magnetic member 4a, seen in FIG. 3, fixed on the rear end thereof. 
     From the base 5 projects a shaft 8 on which a rotatable lever 9 is rotatably supported at an end thereof. The lever 9 engages with the rear end of the magnetic member 4a and functions as a stopper for stopping the magnetic member 4a and the hammer 4 at a determined position. The rotatable lever 9 is provided, at the free end thereof, with an elongated finger 9a which is extended toward the base 5 and engages with a recess 5a formed at the rear end of the base 5. 
     The shaft 8 is provided thereon with a torsion coil spring 7 for biasing the rotatable lever 9 counterclockwise in the drawing. In this manner the rotatable lever 9 resiliently receives the rear end of the magnetic member 4a to stop the magnetic member 4a and the hammer 4 at a determined home position. Thus, since the hammer is resiliently received by the rotatable lever 9 when returned to its home position, the impact force is decreased and the impact noise reduced. 
     As shown in FIGS. 3A and 3B, the hammer 4 composed of a non-magnetic material such as stainless steel is provided at the rear end thereof with the magnetic member 4a composed of a magnetic material such as soft steel, and between the magnetic member 4a and the yoke 3 there is provided a returning spring 10 to constantly bias the hammer 4 in the retracted position. 
     The torsion coil spring 7 and the spring 10 are so selected that the finger 9a of the rotatable lever 9 remains in the recess 5a of the base 5 in the normal state and in a state when the hammer unit 1 is displaced on the base toward the rotatable lever 9 until the pins 6, 6 are in contact with the end portions of the elongated slots 2b. 
     In the above-described hammer unit, the magnetic flux generated by energizing the coil 1a functions to magnetically attract the magnetic member 4a to the yoke 3 against the force of the spring 10, and the magnetic attraction causes the hammer 4 to project to the front. In front of the hammer 4 there is rotatably provided a so-called daisy type font wheel 11 having a printing type on the front end of each spoke. Further in front of the daisy wheel 11 there is provided a platen 12 bearing printing sheet (not shown) thereon. In the abovedescribed structure, upon energization of the coil 1a, the hammer 4 causes the type to strike the recording sheet, thus to generate a print thereon. 
     The hammer unit 1 is fixed on the base 5 by fitting the guide pins 6, 6 in the elongated slots 2b of the support frame 2 and fixing nuts (not shown) or the like on the threaded guide pins 6. 
     Consequently the hammer unit 1 is positionally adjustable front and back within the length of the elongated slots 2b, with respect to the base 5. The adjustment within the range of pins 6,6 and slots 2b,2b does not change the relation of the forces provided by springs 7 and 10. More detailedly, such positional adjustment does not alter the position of the hammer 4 with respect to the font wheel 11 but alters the relative position of the magnetic member 4a with respect to the coil 1a. Consequently it is rendered easily possible to regulate the striking force of the hammer without moving the same. 
     In the assembled state as shown in FIGS. 3A and 3B, the rear end of the magnetic member 4a provided at the rear end of the hammer 4 is maintained in contact with a lateral face of the rotatable lever 9 which is constantly biased by the torsion coil spring 7. 
     Also in such state, the rotary force of the torsion coil spring 7 on the rotatable lever 9 is larger than the elastic force of the returning spring 10, so that the finger 9a always sits in the recess 5a of the base 5 without displacement of the lever 9. 
     In the above-described structure, when the coil 1a is energized according to print instructions, there is generated a magnetic field in a direction to move the magnetic member 4a of the hammer 4 toward the platen 12, whereby the hammer 4 performs a forward movement to strike the type font wheel 11, thus impacting against the platen 12 on the unrepresented recording sheet and printing through an ink ribbon. 
     Since the hammer unit 1 engages, in the aforementioned manner, with the guide pins 6, 6 through the elongated slots 2b and is movable within the length thereof while the returning spring 10 constantly biases the hammer 4 in such a manner that the rotatable lever 9 is in contact with the magnetic member 4a, the distance B between the front end of the magnetic member 4a and the yoke 3 is arbitrarily adjustable without any change in the relative positional relationship between the hammer 4 of the hammer unit and the rotatable lever 9. 
     The distance B affects the attractive force on the hammer when the coil 1a is energized. 
     If the distance B is selected small as indicated by B&#39; in FIG. 3B, the hammer 4 can be activated even with a small energizing current. On the other if the distance is selected large as shown in FIG. 3A, the hammer 4 does not perform the printing operation unless a relatively large energizing current is supplied. 
     Thus the printing force of the hammer 4 can be adjusted by regulating the position of the hammer unit 1 with respect to the base 5. 
     In practice the printing force can be quite easily adjusted since the printing force can be regulated by the measurement of the output power of the hammer. 
     In the foregoing embodiment the hammer unit 1 has an integral structure including the support frame and the coil, but it is possible also to render the coil (including the yoke) movable with respect to the support frame 2, and permanently fix the support frame to the base. In such case the unrepresented support member of the coil can be made movable with respect to the support frame 2 or to the base 5 through the combination of elongated holes and guide pins. 
     In the foregoing embodiment the hammer 4 is composed integral with the magnetic member 4a, but it is also possible to separate the hammer from the magnetic member 4a. Also the hammer need not necessarily be cylindrical but may assume other forms such as a wire-shape. It will further be evident that the present invention is subject to various other modifications.