Abstract:
This block and tackle window balance is based on molding a middle carriage pulley body and a cord terminal (or anchor) in a tip-to-tip position on a cord with each molded pair spaced appropriately from the next molded pair. When the cord is severed between tips, segments of cord are created with a middle carriage body already molded/connected at one end and a terminal already molded/connected at the other end and facing in the opposite direction. The molded middle carriage block component provides for attachment of the middle carriage block to the balance spring, receives a sheave and supports the sheave for rotation, retains the sash cord within sheaves, and guides the middle carriage assembly in its travel along the balance channel. The shape of its terminal provides and facilitates the ease with which the balance cord can be connected to other operative portions of the window frame or assembly. A novel snap-together sheave pair is utilized to simplify balance assembly.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims an invention which was disclosed in Provisional Application No. 60/581,477, filed 21 Jun. 2004, entitled “Block and Tackle Window Balance with integrally Molded Middle Carriage Assembly and Cord”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     My invention pertains generally to the field of block and tackle window balances. More specifically, it relates to the pulley, cord and terminal systems used in such window balances.  
       BACKGROUND OF THE INVENTION  
       [0003]     Block and tackle window balances are compact in size and relatively easy to install. They use a system of pulleys and an extension spring to convert high spring tension applied over a short working distance to a lower spring tension applied over a longer working distance. Both the spring and the pulley system are arranged within a rigid U-shaped balance channel. One end of the extension spring is anchored at a first end of the balance channel, while the other end of the extension spring is mounted to an intermediate pulley (or middle carriage) of the pulley system. The second (end) pulley of the pulley system is anchored at the second end of the balance channel. Generally, the balance channel is mounted in the jamb of the window frame and the cord for the pulley system is attached to a sash shoe that slides in the jamb with the sash. However, this arrangement can be reversed with the cord anchored to the top of the frame and the sash shoe anchored to the opposite end of the balance channel. In all cases, the extension spring and the pulley system are sized so that a desired lifting force is applied to the window sash throughout the entire range of sash travel in the window frame. Examples typical of the art in this area can be found in the following U.S. patents: 
        U.S. Pat. No. 3,358,403 issued to Dinsmore for a “Heavy Window Balance Assembly” in 1967.     U.S. Pat. No. 4,642,845 issued to Marshik for a “Balance Assembly for a Window” in 1987.     U.S. Pat. No. 5,530,991 issued to deNormand et al. for a “Block and Tackle Window Balance” in 1996.     U.S. Pat. No. 5,737,877 issued to Meunier et al. for a “Block and Tackle Balance with Integral, Non-Rotating Pulley System” in 1998.     U.S. Pat. No. 6,041,476 issued to deNormand for an “Inverted Block and Tackle Window Balance” in 2000.        
 
         [0009]     Dinsmore discloses a block and tackle window balance having a sash cord that passes alternatively over rotating sheaves positioned proximate the end of its rigid channel and rotating sheaves within an carriage assembly affixed to one end of a coil spring to form (as is typical) a tackle with five active parts. Dinsmore also teaches attachment of the sash cord to the carriage assembly and to the cord termination element by knotting the cord. Marshik discloses a block and tackle window balance powered by a gas spring and having a multipart tackle wherein the axis of a first group of sheaves is oriented at a right angle to the axis of a second group of sheaves. DeNormand et al. disclose a spring coupling, with two axle halves affixed to opposite sides, each axle half receiving a sheave and supporting it for rotation. This patent also teaches attachment of the cord to the spring coupling by means of a ring-shaped terminal affixed to the end of the sash cord. Meunier et al. teach attachment of the sash cord to the appropriate balance components by knotting. Finally, in U.S. Pat. No. 6,041,476, DeNormand discloses the structure of an end axle assembly and techniques for affixing the end axle assembly to a balance channel.  
         [0010]     As should be clear from review of the foregoing, the art in this field is well developed, but still leaves abundant room for improvement. This is particularly true in terms of reducing the number of parts involved, reducing the complexity of the structures used, and simplifying overall structure, construction, and assembly  
       SUMMARY OF THE INVENTION  
       [0011]     My invention introduces several important innovations to this field. In general, it is based on molding a middle carriage pulley body and a cord terminal (or anchor) in a tip-to-tip position on a cord with each molded pair spaced appropriately from the next molded pair. When the cord is severed between tips, segments of cord are created with a middle carriage body already molded/connected at one end and a terminal already molded/connected at the other end and facing in the opposite direction. The molded middle carriage block component provides for attachment of the middle carriage block to the balance spring, receives a sheave that it supports for rotation, retains the sash cord within sheaves, and guides the middle carriage assembly in its travel along the balance channel. The terminal provides and facilitates the ease with which the balance cord can be connected to other operative portions of the window frame or assembly. Its unique shape facilitates its functionality in these areas and it can be used in cord terminals that are not molded to the cord as in the preferred embodiments discussed herein. In addition to the foregoing, a novel sheave pair is utilized in my invention to simplify balance assembly. Finally, my middle carriage assembly is substantially shorter than current art carriages, thus enabling the use of a longer sash cord, which can provide a greater balance travel capability. These and other benefits of my invention will become obvious upon review of the text that follows and its accompanying drawing figures. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]      FIG. 1  provides a perspective view of a block and tackle balance produced in accordance with the teachings of my invention.  
         [0013]      FIG. 2  provides a perspective view of a portion of my invention&#39;s sash cord with molded cord terminal and middle carriage block, showing the top of the middle carriage block.  
         [0014]      FIG. 3  is a cross section of the sash cord, cord terminal, and middle carriage block of  FIG. 2 , taken through the centerline of the sash cord.  
         [0015]      FIG. 4  provides a perspective view of the sash cord, cord terminal, and middle carriage block of  FIG. 2 , showing the bottom of the middle carriage block.  
         [0016]      FIG. 5  provides a perspective view of a first sheave used in the construction of the block and tackle balance of  FIG. 1 .  
         [0017]      FIG. 6  is a front cross-sectional view of a second sheave used in the construction of the block and tackle balance of  FIG. 1 .  
         [0018]      FIG. 7  is an enlarged back view of a portion of the block and tackle balance of  FIG. 1 , showing the middle carriage assembly.  
         [0019]      FIG. 8  is a cross-sectional view of the middle carriage assembly taken along line  8 - 8  of  FIG. 7 , with the channel omitted for clarity.  
         [0020]      FIG. 9  provides a perspective back view of a portion of the block and tackle balance of  FIG. 1 , showing the middle carriage, end axle, and sash cord, with the channel omitted for clarity.  
         [0021]      FIG. 10  provides a perspective front view of the portion of a block and tackle balance shown in  FIG. 9 .  
         [0022]      FIG. 11  provides a perspective view of a portion of my invention&#39;s sash cord with two insert molded cord terminals.  
         [0023]      FIG. 12  provides a perspective view of a middle carriage assembly  15  designed to attach to a molded cord terminal.  
         [0024]      FIG. 13  provides a perspective view of a middle carriage assembly with integral cord grooves for a high friction balance.  
         [0025]      FIG. 14  provides a perspective view of the cord terminal of my invention connected to a typical prior art carrier.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]     A block and tackle balance  10  is constructed from a channel  100 , commonly formed from sheet metal, into which is assembled a spring  200 . First spring end  200 A of spring  200  is affixed by various means proximate a first end  100 A of channel  100 . Second spring end  200 B of spring  200  is attached to a middle carriage  300 , said middle carriage  300  comprising the first portion of a multi-part balance tackle assembly. An end axle  500 , comprising a second portion of said multipart balance tackle assembly is affixed proximate a second end  100 B of channel  100 . In commonly available block and tackle balances, a sash cord  400  is affixed at one end to middle carriage  300  and twice passes alternatively around sheaves comprising end axle  500  and middle carriage  300 , exiting finally at the second end  100 B of channel  100 , to form a five-part balance tackle assembly.  
         [0027]     When the exiting end of sash cord  400  is extended beyond the second end of channel  100 , the tackle assembly comprising middle carriage  300 , end axle  500 , and sash cord  400  is shortened and spring  200  is stretched, creating the desired restorative or counterbalancing force. Thus, when in use as a window sash balance, the first end  100 A of channel  100  can be affixed within a window frame, and sash cord  400  can be affixed to a vertically sliding sash, to counterbalance the weight of the sash. A cord terminal  600  is affixed to the second end of sash cord  400 , to facilitate attachment of the sash cord in the application of the counterbalance and to prevent the second end of the sash cord  400  from being retracted into the second end of channel  100 . Middle carriage  300  and cord terminal  600  are formed by injection molding plastic materials directly around sash cord  400 . This allows a reduction in the number of parts needed to construct a block and tackle balance, a simplification of the manufacturing steps required to produce the balance, and an improvement in the integrity of the cord attachment to the middle carriage and to the cord terminal. Thus, in  FIGS. 2 through 4 , cord terminal  600  and middle carriage block  302  are formed from a plastic material by injection molding directly onto a portion of sash cord  400 . Separate proximate cavities within the injection mold are utilized to form both cord terminal  600  and middle carriage block  302  in the same cycle or shot. Semi-circular grooves cut across both faces of the mold, in alignment with the cavities, allow a continuous length of sash cord  400  to be fed through the mold. At the end of each mold cycle, the mold opens and sash cord  400  is advanced an appropriate distance. Thus, when sash cord  400  is severed between proximate cord terminal-carriage block pairs, the length of sash cord  400  between a middle carriage block  302  on a first end of a sash cord  400  segment and the cord terminal  600  on the second end of a sash cord  400  segment is appropriate for the block and tackle balance for which it is intended.  
         [0028]     Given the intense pressures common to the injection molding process and the shrinkage of plastic materials as they cool within a mold, cord terminal  600  and middle carriage block  302  develop an intimate and strong grip on sash cord  400 . Measurement of the force required to pull sash cord  400  free of either cord terminal  600  or middle carriage block  302  consistently results in values greater than 100 pounds. Similar measurements of commonly available crimped metallic cord terminations gave force values in the range of 70 to 90 pounds. (Termination by knotting typically results in forces close to the breaking strength of the cord, but knots have the potential to slip and are difficult to form reliably and quickly in a production process.) In addition, resistance to cord pullout can be increased when sash cord  400  is manufactured from a synthetic material (such as polyester) if severance of sash cord  400  is accomplished with the aid of a hot cutting tool. This melts and fuses the fibers at the point of severance, creating an enlarged end that is difficult to pull through middle carriage block  302  or cord terminal  600 . However, it remains possible to join cord terminal  600  to sash cord  400  by other means even though it is not preferred in this invention.  
         [0029]     In the preferred embodiment, cord terminal  600  is advantageously formed with an enlarged proximal end section (shoulder  602 ), an enlarged distal end section (ball  606 ), and a narrower intermediate section (shank  604 ). This shape is preferred as it facilitates easy snap-in connection with a standard carrier  950  as illustrated in  FIG. 14 . In addition, shoulder  602  keeps the terminal from being withdrawn into the balance, retaining shank  604  in a position exterior to the balance channel where it can be easily accessed for insertion into a carrier  950 . (However, cord terminal  600  could take a variety of other shapes in keeping with its role as an anchor or hook.) Shoulder  602  is designed to pull up against the second end of channel  100  to prevent sash cord  400  from retracting into channel  100 . When applied to the task of counterbalancing, cord terminal  600  can pull upward against the slotted bracket  951  of a carrier  950  attached to a window sash. Overall, shoulder  602 , shank  604  and ball  606  form small diameter/large diameter configurations that can be used to facilitate gripping or attaching the cord end of the balance to a bracket attached to a window part or to receive adaptive parts such as specialized hooks or other attachment devices that could be added to the balance by crimping or snapping onto shank  604 .  
         [0030]     Middle carriage block  302  is formed with a spring eye  304  having a spring loop surface  306 , shaped to conform with and support spring loop  202 , when middle carriage block  302  is assembled to spring  200  in the fabrication of block and tackle balance  10 . Middle carriage block  302  also has a guide portion  308 , wherein the transverse cross-sectional shape approximates the interior shape of channel  100  and is sized to allow middle carriage block  302  to slide along the interior of channel  200 , while preventing the rotation of middle carriage block  302  about an axis parallel to the length of channel  200 .  
         [0031]      FIGS. 5 through 6  illustrate the sheaves used as cord guiding members for sash cord  500 . First sheave  700  has a sheave body  702  (with a cord groove  704 ) and a shaft  706  (with snap groove  708  and chamfer  712 ). A second sheave  800  comprises a body  802 , with groove  804  and sheave journal  806 . A plurality of snap fingers  808  encroach within sheave journal  806 , and sheave chamfer  810  facilitates assembly. These parts can all be produced simply and easily using die casting techniques of other standard molding techniques.  
         [0032]     Referring now to  FIGS. 7 through 10 , the steps for lacing block and tackle balance  10  will now be described. First, sash cord  400  is passed once around end axle  500  and then once around first sheave  700 , forming a first loop  402 , lying within cord groove  704  of sheave  700 . This first step is performed prior to the insertion of shaft  706  into journal  310  of middle carriage block  302  or when shaft  706  is only partially inserted into journal  310 . Second, shaft  706  of first sheave  700  is fully inserted into journal  310  of middle carriage block  302 , with sheave body  702  resting within first sheave pocket  314  of middle carriage block  302 , and first loop  402  of sash cord  400  entrapped within cord groove  704  of first sheave  700 , by first retainer surface  316  of middle carriage block  302 . Third, sash cord  400  is again passed once around end axle  500 , and thence, once around second sheave  800 , forming a second loop  404 , lying within groove  804  of sheave  800 , prior to the assembly of sheave  800  to middle carriage  300 . Fourth, sheave journal  806  of second sheave  800  is assembled over shaft  706  of first sheave  700 , with body  802  of sheave  800  resting in second sheave pocket  318  of middle carriage block  302 , and second loop  404  of sash cord  400  entrapped within groove  804  of second sheave  800  by second retainer surface  320  of middle carriage block  302 .  
         [0033]     When second sheave  800  is assembled onto shaft  706  of first sheave  700 , snap fingers  808  resiliently retract, then rebound, within snap groove  708  under snap lip  710 , to retain first sheave  700  and second sheave  800  in their assembled relationship. Journal chamfer  312  of middle carriage block  302  and chamfer  712  of first sheave  700  help guide shaft  706  of first sheave  700  into journal  310  of middle carriage block  302 . Likewise, sheave chamfer  810  of second sheave  800  helps guide sheave journal  806  onto shaft  706  of first sheave  700 . Finally, to complete the assembly of block and tackle balance  10 , spring loop  202  of spring  200  is rove through spring eye  304  of middle carriage block  302 , channel  100  is engaged with end axle  500 , and the first end of spring  200  is affixed to the first end of channel  100 .  
         [0034]     Some possible alternate embodiments are shown in  FIGS. 11 through 13 . In  FIG. 11 , two terminals  600  form a molding pair on a sash cord  400 . As shown in  FIG. 12 , this embodiment allows the use of an alternate middle carriage  900  with a catch  901  to which one of the terminals  600  can be attached. Further, although identical terminals are illustrated, terminals  600  can take different shapes and forms as required by the application. (Thus, this alternative avoids the use of a middle carriage  300  molded around sash cord  400 .) Another alternative middle carriage, frictional balance carriage  902 , is illustrated in  FIG. 13 . Frictional balance carriage  902  is molded with integral cord grooves  903  so as to form a high friction balance. However, while a novel block and tackle balance assembly and certain variations have been described, it should be understood that the invention is not limited to the above specific embodiments. Many additional variations can be made without exceeding the scope of the invention, as more clearly delineated in the claims that follow.