Patent Publication Number: US-6216935-B1

Title: Adjustable force powerized stapler

Description:
BACKGROUND AND FIELD OF THE INVENTION 
     The present invention is directed to a powerized stapler device and more particularly to a stapler device wherein the driving force imparted to the head of the stapler may be varied within a wide range such that a greater driving force is applied when a multiplicity of sheets are to be stapled and conversely, a lower driving force is applied where the staple is to be clinched through a limited number of sheets. 
     1. Prior Art 
     Powerized stapling devices have been available for many years, representative examples being disclosed in U.S. Pat. Nos. 2,403,947; 2,877,461; 2,957,174; 2,975,424; 3,016,538; 3,022,512; 3,026,518; 3,101,478; 3,151,329; 3,251,524, assigned to the assignee hereof. The references noted disclose, in general, staplers integrated into a housing, carrying an electromagnetic mechanism such as a solenoid, the armature of the solenoid being disposed above the drive head of the stapler. Insertion of articles to be stapled activates a switch mechanism energizing the solenoid and causing the armature to drive the stapler through an operating cycle 
     A difficulty inhering in staplers of the type described resides in the fact that the stapling force imparted is identical for stapling jobs consisting of a multiplicity of sheets and also for jobs involving only a few sheets. Where the applied force is sufficient for joining multiple sheets and the same force is utilized in joining jobs comprised of only a few sheets, one or the other of the jobs will be defective. More particularly, if the force is insufficient to drive a staple through a multiple sheet job, an effective clinching will not result. Conversely, if a force sufficient for multiple sheet stapling is utilized in connection with a two or three sheet job, the stapler will act in the manner of a punch, the base of the overdriven staple penetrating one or more of the sheets whereby the upper most ones of the sheets are not effectively connected to the remainder of the sheets. 
     A further problem inhering in the application of overly great stapling forces when connecting a limited number of sheets, resides in the excessive impact leaving an imprint surrounding the area of staple application. 
     A still further drawback of known powerized staplers, particularly when used to fasten a limited number of sheets, resides in the staple being applied with a rolling or angular clinch. The rolling clinch results from the fact that the sheets are moving a finite distance after the sensor, which activates the stapler, is energized. As a result, the legs of the staple penetrate the sheets while the sheets are still moving, whereby the base of the staple has passed a slight distance beyond the clinching anvil, resulting in a rolling or loosely applied staple. The described problem is of lesser significance where a multiplicity of sheets are to be stapled since the multiple sheets act as a support for the staple as it is driven. Additionally, the thickness of the multiple sheets assures that impact between the stapler head and the upper most sheet occurs promptly following energizing of the power mechanism since the upper most sheet of a thick stack will be closer to the stapler head than would be the case where only a few sheets are to be connected. 
     Various means have been proposed to provide stapling devices wherein the driving power may be adjusted. These known devices utilize electronic circuitry for varying the voltage applied to the solenoid or other electromagnetic driving means. While these devices enable the user to tailor the driving force, within a limited range, to the job at hand, they do not solve the problems discussed above, and particularly the problem of avoiding a rolling staple connection when used to join a limited number of sheets. 
     A further drawback of known powerized staplers resides in the fact that the power must be manually adjusted in accordance with the job at hand. Thus, where the user will sequentially staple thin and thick stacks of articles, adjustment must be manually effected between each application, greatly slowing the stapling procedure. Additionally, manual adjustment involves discretion on the part of the user and thus is a minimal aid to the occasional powerized stapler user. 
     SUMMARY OF THE INVENTION 
     The present invention may be summarized as directed to an improved powerized stapling device characterized in that a unique means is employed for varying the force of the stapling stroke, enabling a more precise and wider range of stapling force than is available to powerized staplers utilizing electronic adjustment of stapling force. 
     The invention is further directed to a variable power-stapling device, which automatically adjusts stapling force to the thickness of the articles to be stapled. 
     A still further object of the invention resides in the provision of a variable power stapler wherein adjustment of the stapling force functions, in addition, to vary the spacing between the stapler head and the upper most of the stack of sheets to be stapled. More particularly, adjustment of the stapling force to reduce the force also functions to shift the stapler drive head closer to the upper most sheet whereby the time lag between energization and actual driving of a staple is reduced. Conversely, where a large number of sheets are to be connected adjustment of the driving force to increase the same also results in moving the stapler head further from the upper most of the thick stack of articles maximizing inertia applied to the stapler. 
     The invention is further directed a unique means for varying the stapling force thereby eliminating the use of electronic controls. Known electronic controls, namely voltage reducers do not function below a threshold voltage eliminating the desired “soft touch” where a limited number of sheets or poly bags are to be stapled. More specifically, adjustment of stapling power in accordance with the invention is accomplished by providing an electromagnetic drive mechanism and particularly a solenoid which includes an armature incorporating a high permeability portion, adjustment of the stapling force being effected by shifting the position of the high permeability portion relative to the core of the solenoid. For example, where the major portion of the high permeability material is positioned such that it will be drawn into the solenoid upon energization, a greater force is applied to the armature than is the case is where a majority of the high permeability material is already located within the solenoid. 
     It is an object of the invention to provide a force adjustable stapling device wherein adjustment of the driving force is accompanied by a concomitant movement of the stapler head toward and away from the work. 
     A further object of the invention is the provision of a variable force stapling device, wherein the driving force is automatically varied responsive to the thickness of the stack of articles to be stapled. 
     A still further object of the invention is the provision of a means for varying the force applied in a stapling operation by varying the position of an armature with respect to an electromagnetic mechanism operatively coupled to the armature. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a stapler in accordance with the invention. 
     FIGS. 2 a  and  2   b  are cross-sectional views of improperly driven staples as effected using prior art powerized stapling devices. 
     FIG. 3 is magnified cross-sectional view taken on the line  3 — 3  of FIG.  1 . 
     FIG. 4 is an exploded pre-assembly view of the driving mechanism of the stapler. 
     FIGS. 5 and 7 are vertical sectional views showing the relative positions of the driver mechanism adjusted respectively for connecting a limited number of sheets and larger number of sheets. 
     FIGS. 6 and 8 are sectional views respectively illustrating a staple clinched by the device adjusted per FIG.  5  and the device adjusted per FIG.  7 . 
     FIG. 9 is a vertical cross-section of an embodiment of the invention incorporating an automatic thickness adjustment. 
     FIG. 10 is an exploded perspective view of the embodiment of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring now to FIG. 1, a force adjustable stapler  10  includes a housing  11  having a base  12  on which is mounted a conventional stapler  13 . An adjustment knob  14  carries a microswitch or like trip mechanism (not shown) fixed to the knob  14  enabling the user to adjust the spacing from the edge of the work at which the staple will be applied. 
     In the embodiment of FIG. 1 the force with which a staple is applied is controlled by force adjustment dial  15 . 
     Details of the force adjustment mechanism are best appreciated from an inspection of FIGS. 3 and 4. The stapler  13  includes a drive head  16  carrying on its upper surface a buffer  17  of felt or elastomer. The head  16  of the stapler is biased upwardly by conventional means such as return spring  18 . 
     Driving power is provided by an electromagnetic assembly, illustratively solenoid  19 . Solenoid  19  includes a housing  20  which includes a generally U-shaped mounting bracket  21  including in-turned legs  22 , 23  (FIG.  4 ). The legs  22 , 23  are provided with threaded apertures  24 , the bracket  21  being mounted to the side wall  25  of the housing by machine screws  26  passing through apertures  27  in side wall  25  and threaded into the apertures  24  of the bracket  21 . 
     An L-shaped bracket  28  forms a support for the adjustment assembly, the bracket including a vertically directed leg  29  fixed to sidewall  25  of the housing by machine screws  30  passing through apertures  31  in the side wall and extending into complementary threaded apertures  32  in the member  29 . 
     The solenoid  19  includes an armature assembly  33 , the assembly being comprised of two components, namely an upper component  34  formed of a high permeability magnetic material such as soft iron and a lower component  35  formed of a low permeability or non-magnetic material such as brass. The armature assembly  33  is vertically movable within the core  36  of the solenoid. Force variation is a function of the position of the high permeability material  34  relative to the core  36  of the solenoid. 
     More particularly, when the high permeability component  34  is only partially disposed within the core  36  (FIG.  7  and solid line position of dial  15 , see FIG. 3) energization of the solenoid  19  will draw the high permeability component downwardly until essentially the entirety of the component  34  enters the core  36 . When the component  34  is adjusted downwardly to the position of FIG.  5  and the dot and dash position (FIG. 3) in a manner hereinafter described, the element  34  will move downwardly upon energization of the solenoid  19 , only a relatively small additional distance, i.e. until the balance of the high permeability component in introduced into the core  36 . 
     The mechanism for adjusting the relative position of the high permeability portion  34  relative to core  36 , i.e. the force adjustment mechanism will next be described. 
     Bracket  28  includes a generally horizontally directed leg  37  having formed therein a threaded aperture  38 . An adjustment rod  39  includes a threaded lower portion  40  threadedly mounted in aperture  38 . A circular flange  41  is welded as at  42  to the rod  39 , coil spring  43  being biased between the leg  37  and flange  41 . 
     Force adjustment knob  15  is keyed to rod  39  as by set screw  44 . 
     The adjustment rod  39  carries a thrust cap  45  at the lower end of the rod, the base  46  of the cap bearing against pad  47  bonded to the upper surface  48  of the high permeability portion  34  of the armature assembly  33 . The pad  48  is preferably formed of a somewhat compressible material such as a heavy felt, neoprene or like elastomer. 
     As will be apparent from the preceding description, by rotating the force adjustment dial  15  in a manner to thread rod  39  in a downward direction (see dot and dash condition FIG. 3) two complementary functions, each of which reduce the driving force of the stapler, are simultaneously effected. 
     More particularly, increments of the high permeability portion  34  of armature assembly  33  are introduced into the solenoid coil and at the same time, the inert component  35  of the armature assembly forces pad  17  downwardly moving the stapler head  16  closer to the anvil  50  of the stapler. 
     As will be appreciated, upon energization of the solenoid  19  the armature assembly  33  will always move to a predetermined lowermost position. However, the force imparted to the stapler head will vary from a maximum force wherein virtually the entirety of the high permeability component  34  is drawn into the solenoid to a minimum force wherein the majority of the high permeability portion is already situated within the core  36  of the solenoid. 
     The described force adjustment mechanism has the further advantage, where minimal force is desired, as for connecting a limited number of sheets, of bringing the head of the stapler close to the anvil whereby the time lag between penetration and clinching of a staple which passes through only a few sheets is minimized. 
     In FIG. 2 a  there is illustrated a staple S which has been applied with unduly high force. As is apparent, the staple legs are curved upwardly and the staple ends may penetrate the uppermost surface of the work providing minimal support for the lowermost sheet, the uppermost portion of the staple often being forced through the uppermost sheet. 
     In FIG. 2 b  there is illustrated the rolling effect which results from staple S′ being applied while the work piece is still moving after energizing of the switch mechanism triggering a stapling cycle. The rolling or angular configuration assumed by the staple relative to the work piece is a result of the relatively long time lag resulting from the fact that the stapler head must move through a large arc before clamping the work piece, where only a few sheets are to be processed. This results in a staple in which spaces are formed between the back of the staple and the work on the top surface and between the legs and the under surface as shown. 
     Referring to FIG. 5, the device has been adjusted to process a limited number of layers L. In this adjusted position it will be observed that the distance D between the stapler head and anvil  50  is smaller than the distance D′ (FIG. 7) where the device has been adjusted to apply maximum force. The relative positions of the parts may also be appreciated by noting the close spacing of the arrows  5 — 5  in FIG.  5  and the greater spacing of the arrows  7 — 7  of FIG.  7 . 
     FIGS. 6 and 8 illustrate the ideal clinching obtained by utilizing the adjustments provided by FIGS. 5 and 7 respectively. 
     In FIGS. 9 and 10 there is illustrated an embodiment of the invention which provides automatic adjustment of the applied force in accordance with the thickness of the work to be stapled 
     Referring now to FIGS. 9 and 10, force adjustment previously effected by adjustment of the control knob  15  is automatically accomplished in accordance with the thickness of the work to be stapled by an automatic adjustment mechanism referred to generally by reference numeral  60 . The solenoid  19  and armature assembly  33  are essentially identical to the device of the previously described embodiment. The housing front wall  61  includes an extension  62  to the side wall  63  on which is rotatably mounted an adjustment shaft  64 . The shaft  64  carries a pinion gear  65  which meshes with rack  66  guided for vertical movement by rack support brackets  67 , 68  bolted to housing wall  61 . The rack includes a drive arm  69  superposed over the high permeability component  34  of the armature assembly  33 . 
     Drive nut  70  is clamped to arm  69  as by machine screw  71 , the lower surface of the drive nut being in contact with buffer pad  47  fixed to the armature component  34 . 
     The shaft  64  includes an offset lever arm  72  on which is mounted a sensor roller  73  horizontally disposed in the path of the work W to be stapled. As is apparent from FIGS. 9 and 10, the work piece W when inserted past the sensor roller  73  will cause the shaft  64  to rotate in a clockwise direction lifting rack  66 . Contact between the pad  17  and the undersurface of the non-permeable armature component  34  is maintained by the upward springing force provided by spring  18  of the stapler. 
     As will be apparent by comparing the solid and dot and dash positions of the components as shown in FIG. 9, the thicker the work piece W the greater the rotation of the pinion gear  65  and concomitantly the greater the spacing the stapler from anvil  50 . Similarly, the high permeability portion  34  will be withdrawn from the core of the solenoid  19  providing maximum driving force and travel of the armature assembly within the solenoid core. 
     As will be apparent, insertion of a thin work piece will shift roller  73  only slightly in a clockwise condition permitting the stapler head to shift only slight distance upwardly whereby the major mass of the high permeability component will remain within the solenoid providing a relatively short stroke of the armature assembly when the solenoid is energized. 
     It will thus be recognized that the automatic adjustment assembly described controls both the spacing of the stapler from the work piece and also the force generated by the electromagnetic device upon energizing the coil  19 . 
     From the foregoing, it will be appreciated that there is described in accordance with the invention a powerized stapler device characterized in that the force with which a staple is driven may be accurately controlled, whereby greater forces are applied where a thick work piece is processed than is the case where the work piece is comprised of only a few sheets or, a readily deformed material such as a polyethylene bag. 
     A further characterizing feature of the invention resides in the device controlling both the force generated by the electromagnetic drive mechanism and also by a shifting of position of the stapler head toward and away from the work piece in accordance with the desired stapling result. 
     A further feature of the invention resides in mechanically controlling the force exerted by the electromagnetic drive mechanism as a function of the adjusted position of the high permeability component of the armature mechanism relative to the electromagnetic device. 
     A still further characterizing feature of the invention resides in a device which automatically senses the thickness of the work load to be stapled and accordingly adjusts both the position of the stapler head and the force with which the stapler is driven. 
     As will be apparent to those skilled in the art and familiarized with the instant disclosure numerous variations in structural details may be made without departing from the spirit of the invention. Accordingly, the invention is to be broadly construed within scope of the appended claims.