Patent Publication Number: US-9417597-B2

Title: Power assist scissor lift

Description:
This is a divisional of U.S. application Ser. No. 13/867,272, filed Apr. 22, 2013, Moore et al, and claims priority therefrom. This divisional application is being filed in response to a restriction requirement in that prior application. 
    
    
     This disclosure relates in general to an image forming apparatus, and more particularly, to an image forming apparatus employing an improved lift mechanism for a finisher connected to the image forming apparatus. 
     It is well known to use scissor lift platforms to facilitate stacking or un-stacking of sheets or booklets of media, for example, those exiting an image forming apparatus. The typical lift table incorporates a support platform and a mechanism for selectively raising or lowering the support platform into a position facilitating its loading or unloading. Vertical movement of the support platform usually is accomplished by use of a scissor arm mechanism that supports the support platform on an underlying base and that is raised and lowered by way of conventional means. 
     A scissor lift generally consists of two elongated members connected together, usually at or near their midpoints, forming a pivoting mechanism. The scissor lift works by starting the members in an orientation favored towards the horizontal, rather than vertical. To create a change in vertical height, or lift, the members are counter rotated relative to each other from the starting orientation to a more vertical orientation. 
     Scissor lifts can be driven using many different mechanisms, for example, using hydraulic cylinders, pneumatics, or lead screws as shown in U.S. Pat. Nos. 3,246,876; 5,722,513 and 6,679,479 which are included herein by reference to the extent necessary to practice the present disclosure. The mounting of the drive mechanisms can also vary greatly. Some systems mount the drive mechanism at an optimal angle and allow the drive mechanism to rotate with the scissor arms. Other scissor lifts use a lead screw mounted in a permanent horizontal position. 
     It has been found that in a current scissor lift mechanism employing a single lead screw mounted in a permanent horizontal position used to raise a stack of paper in a cut-sheet finisher with a large stack height being ideal, a limitation is presented as to how low the scissor lift can collapse. Another limitation dealt with in this type of lift mechanism is the amount of weight that can be lifted from a low, collapsed position. A large stack weight is desirable to enable stacking of large heavy weight media. 
     The basic operation of a conventional or standard scissor lift  60  that includes a permanently horizontal lead screw drive, as shown in prior art  FIGS. 1 and 2 , requires that force through a lead screw represented by arrow  61  is applied to legs  62  and  64  that pivot about a shaft at pivot point  65  to lift tray  66 . One of the inherent problems with this setup is that the force to drive the scissor lift grows exponentially as the angle of the scissor arms approach horizontal. Because of this, such systems have to be designed with a minimum practical starting height so the lead screw drive can apply enough force to lift the mechanism. This characteristic prevents the scissor lift design from being a very low profile unit.  FIG. 3  shows an example of the lead screw drive force for a mechanism lifting 60 lbs., starting with a scissor arm angle of 8° inclined from horizontal. As shown by line A, the total force on the lead screw lessens as the travel of the lead screw increases. 
     These and other problems in the prior art reveal the need for a new scissor lift mechanism which overcomes one or more of the above-mentioned problems. 
     Accordingly, disclosed herein is an improved scissor lift mechanism that includes the addition of a sliding carriage member and a pivoting linkage assist device to the scissor lift that will lower the force required to lift a tray during the initial portion of the lifting action when the scissor lift is fully compressed. With a typical scissor lift, the initial force required to raise the lift from a fully compressed state is quite high, requiring a large actuator as well as a sturdy scissor linkage. 
    
    
     
       Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the example(s) below, and the claims. Thus, they will be better understood from this description of these specific embodiment(s), including the drawing figures (which are approximately to scale) wherein: 
         FIG. 1  is a frontal schematic view of a prior art scissor lift at a low angle; 
         FIG. 2  is a frontal schematic view of the prior art scissor lift of  FIG. 1  at a high angle; 
         FIG. 3  is a chart showing the lead screw drive force necessary to lift media of a particular weight with the scissor lift of  FIG. 1 ; 
         FIG. 4  is a partial, frontal view of an exemplary modular xerographic printer that includes the improved scissor lift system of the present disclosure; 
         FIG. 5  is a frontal schematic view of an improved scissor lift at a low angle employing a spring assist device; 
         FIG. 6  is a frontal schematic view of the scissor lift of  FIG. 5  at a high angle; 
         FIG. 7  is a chart showing the lead screw drive force necessary to lift media of a particular weight with the improved scissor lift of  FIG. 5 ; 
         FIG. 8  is a frontal schematic view of an alternative scissor lift at a low angle employing a power assist lift device; 
         FIG. 9  is a frontal schematic view of the improved scissor lift of  FIG. 8  at a high angle; 
         FIG. 10  is a chart showing individual force-to-drive curves resulting from lifting media by employing the power assist spring scissor lift device of  FIG. 8 ; 
         FIG. 11  is a chart showing individual platform-height curves for the improved power assist spring lift device of  FIG. 8 ; 
         FIG. 12  is a chart showing power assist scissor lift lead screw force resulting from use of the mechanism of  FIG. 8 ; and 
         FIG. 13  is a chart showing power assist scissor lift platform-height curves resulting from use of the mechanism of  FIG. 8 . 
     
    
    
     The disclosure will now be described by reference to preferred embodiment xerographic printing apparatus that includes a finisher with an improved media scissor lift system. 
     For a general understanding of the features of the disclosure, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. 
     Referring now to printer  10  in  FIG. 4  that, as in other xerographic machines, and as is well known, shows an electrographic printing system including the improved scissor lift method and apparatus of the present disclosure. The term “printing system” as used here encompasses a printer apparatus, including any associated peripheral or modular devices, where the term “printer” as used herein encompasses any apparatus, such as a digital copier, bookmaking machine, multifunction machine, etc., which performs a print outputting function for any purpose. Marking module  12  includes a photoreceptor belt  14  that advances in the direction of arrow  16  through the various processing stations around the path of belt  14 . Charger  18  charges an area of belt  14  to a relatively high, substantially uniform potential. Next, the charged area of belt  14  passes laser  20  to expose selected areas of belt  14  to a pattern of light, to discharge selected areas to produce an electrostatic latent image. Next, the illuminated area of the belt passes developer unit M, which deposits magenta toner on charged areas of the belt. 
     Subsequently, charger  22  charges the area of belt  14  to a relatively high, substantially uniform potential. Next, the charged area of belt  14  passes laser  24  to expose selected areas of belt  14  to a pattern of light, to discharge selected areas to produce an electrostatic latent image. Next, the illuminated area of the belt passes developer unit Y, which deposits yellow toner on charged areas of the belt. 
     Subsequently, charger  26  charges the area of belt  14  to a relatively high, substantially uniform potential. Next, the charged area of belt  14  passes laser  28  to expose selected areas of belt  14  to a pattern of light, to discharge selected areas to produce an electrostatic latent image. Next, the illuminated area of the belt passes developer unit C, which deposits cyan toner on charged areas of the belt. 
     Subsequently, charger  30  charges the area of belt  14  to a relatively high, substantially uniform potential. Next, the charged area of belt  14  passes laser  32  to expose selected areas of belt  14  to a pattern of light, to discharge selected areas to produce an electrostatic latent image. Next, the illuminated area of the belt passes developer unit K, which deposits black toner on charged areas of the belt. 
     As a result of the processing described above, a full color toner image is now moving on belt  14 . In synchronism with the movement of the image on belt  14 , a conventional registration system receives copy sheets from sheet feeder module  100  through interface module  50  and brings the copy sheets into contact with the image on belt  14 . Sheet feeder module  100  includes high capacity feeders  102  and  104  that feed sheets from sheet stacks  106  and  108  positioned on media supply trays  107  and  109  into interface module  50  that directs them either to purge tray  118  through sheet feed path  52  or to imaging or marking module  12  through sheet feed path  54 . Additional high capacity media trays could be added to feed sheets along sheet path  120 , if desired. 
     A corotron  34  charges a sheet to tack the sheet to belt  14  and to move the toner from belt  14  to the sheet. Subsequently, detack corotron  36  charges the sheet to an opposite polarity to detack the sheet from belt  14 . Prefuser transport  38  moves the sheet to fuser E, which permanently affixes the toner to the sheet with heat and pressure. The sheet then advances to stacker module F and onto platform  66  as shown in  FIG. 5 , or to duplex loop D. 
     Cleaner  40  removes toner that may remain on the image area of belt  14 . In order to complete duplex copying, duplex loop D feeds sheets back for transfer of a toner powder image to the opposed sides of the sheets. Duplex inverter  90 , in duplex loop D, inverts the sheet such that what was the top face of the sheet, on the previous pass through transfer, will be the bottom face on the sheet, on the next pass through transfer. Duplex inverter  90  inverts each sheet such that what was the leading edge of the sheet, on the previous pass through transfer, will be the trailing on the sheet, on the next pass through transfer. 
     Turning now to  FIG. 5 , an alternative improvement to the prior art scissor lift of  FIG. 1  is shown that is positioned in stacker or finisher F of  FIG. 4  to receive sheets advanced from marking module  12  that includes a spring assist assembly that comprises an L-shaped arm  200  attached to a fixed pivot  202  at the elbow of the L-shaped arm  200 . A roller  206  on one end of the arm contacts the platform  66  of the scissor lift  60 . The other end of the arm is connected to an extension spring represented by arrow  210 . When the scissor lift is at the bottom of its range, the extension spring is extended, applying a force to the arm. The arm transmits the force to the scissor lift platform  66 . As the scissor lift rises, the spring assist arm applies a force for a determined distance as shown in  FIG. 6  before hitting a hard stop  215 . The hard stop prevents the arm from over rotating. When the arm hits the hard stop, the spring assist actuation comes to an end. For the remaining duration of the lift, the lead screws are acting directly on the leg(s) of the scissor lift. Essentially, the remaining motion is identical to that of a conventional scissor lift. 
     The chart in  FIG. 7  shows in line B an example of the lead screw drive force for the scissor lift of  FIGS. 5 and 6  lifting 60 lbs., starting with a scissor arm angle of 8° inclined from horizontal with a spring assist assembly. Compared to the forces for the conventional scissor lift of  FIG. 1 , it can be seen that the peak drive forces are lowered by approximately 40%. 
     In accordance with the present disclosure, an improved scissor lift apparatus embodiment is shown in  FIGS. 8 and 9  and includes a power assist assembly that utilizes extending the travel of a lead screw (not shown). A force  61  is applied to arm  200  by the lead screw instead of spring(s), thereby providing a power assist assembly. In order to drive the power assist assembly separate from the scissor lift, the force from the lead screw assembly must be decoupled from the scissor lift members. A sliding carriage member  300  is added and directly driven by the lead screw assembly. The power assist assembly of  FIGS. 8 and 9  includes sliding carriage member  300 . From the lift in a lowered position, the sliding carriage member  300  initially applies a force directly to the power assist assembly as shown in  FIG. 8  which includes an L-shaped arm  200  attached to a fixed pivot  202  at the elbow of the L-shaped arm  200 . A roller  206  on one end of the arm contacts the platform  66  of the scissor lift  60 . When the scissor lift is at the bottom of its range, the sliding carriage is moved by a force  61  thereby applying a force to the arm  200 . The arm  200  transmits the force to the scissor lift platform  66  to start vertical motion. Carriage member  300  is also designed to transmit force from the lead screw assembly to the scissor members. An offset is designed into the carriage so the lead screws drive the power assist arm a given distance before the carriage catches up to the scissor members and begins directly driving. An example of the carriage driving the scissor members directly can be seen in  FIG. 9 . 
     An example of the force curves and the displacement curves is shown in  FIGS. 10 and 11 , respectively.  FIG. 10  shows individual curves broken down into each component. Line C represents the individual force-to-drive curve of the conventional scissor lift of  FIG. 1  and line D represents the individual force-to-drive curve employing the power assist arm. The critical point M in  FIG. 11  is where the platform heights are equal, approximately 45 mm of lead screw travel. At this point, the lead screw assembly force is handed off from the power assist assembly and power assist arm to the scissor members. From this point forward, the lead screws drive the scissor members directly, exactly the same as in the conventional scissor lift shown in  FIG. 1 . 
     In  FIG. 12 , the motion of the power assist scissor lift that comprises the sliding carriage member is represented by the force curve G which shows that less force is required to lift 60 lbs., starting with a scissor arm angle of 8° inclined from horizontal than with the conventional scissor lift. The force curve G shifts from the power assist assembly to the conventional scissor lift at the point of handoff after approximately 45 mm lead screw travel. The lead screw force at the start of movement, from a fully down position, is reduced by up to 70% for this particular configuration. The power assist scissor lift platform-height curve H in  FIG. 13  shows increased platform height in less lead screw travel time over conventional scissor lifts when using the power assist scissor lift of the present disclosure. 
     In recapitulation, an improvement to conventional scissor lifts used in a finisher of a xerographic device to lift tray supported heavy weight copy sheets or media is shown that includes the addition of a sliding carriage member and a pivoting linkage to a conventional scissor lift that will lower the force required to lift the tray during the initial portion of the lifting action where the scissor lift is fully compressed. The lower forces involved results in a cost savings for both the actuator and scissor linkage as well as increased lift capacity. As an additional benefit, the profile of the scissor lift is lowered by use of the sliding carriage member and pivoting linkage scissor lift improvement. 
     The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others. Unless specifically recited in a claim, steps or components of claims should not be implied or imported from the specification or any other claims as to any particular order, number, position, size, shape, angle, color, or material.