Abstract:
An ergonomic cable tie installation tool includes a generally pistol-shaped housing including a grip which depends from a barrel. Pivotally connected to the lower region of the grip is a trigger linkage of a trigger mechanism. The trigger mechanism also includes an intermediate linkage pivotally connected to the trigger linkage. The intermediate linkage is supported in the housing. The intermediate linkage is, in turn, connected to a tensioning mechanism also supported in the housing. The tensioning mechanism couples the intermediate linkage to the cable tie. Pivoting the trigger linkage toward the grip, normally by the hand of a user, causes the intermediate linkage to pivot resulting in the tensioning mechanism producing an increased tension in the cable tie. The trigger linkage is oriented relative to the grip such that pivoting it toward the grip requires the stronger fingers of the user&#39;s hand to travel more than the weaker fingers thereby improving the ergonomics of the tool. The trigger linkage may also make the respective travel distances of the stronger and weaker fingers more uniform also improving the ergonomics of the cable tie installation tool. Moreover, the trigger mechanism may provide for the tension force applied to the cable tie to increase as the trigger linkage is increasingly pivoted toward the closed position. Methods of operating the tool also provide improved ergonomics of the tool.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to a cable tie installation tool, and more specifically, to such a tool having an ergonomic trigger mechanism. 
   As is well known to those skilled in the art, cable ties (or straps) are used to bundle or secure a group of articles such as electrical wires or cables. Cable ties of conventional construction include a cable tie head and an elongate tail extending therefrom. The tail is wrapped around a bundle of articles and thereafter inserted through a passage in the head. The head of the cable tie typically supports a locking element which extends into the head passage allowing the tail to be inserted through the passage but preventing retraction of the tail through the passage in the head. Two longitudinally separated portions of the tail are thereby secured to the head to define a loop for holding together the group of articles. 
   In practice, the installer manually places the tie about the articles to be bundled, inserts the tail through the head passage and then manually tightens the tie about the bundle. At this point, a cable tie installation tool is used to tension the cable tie. One type of such a cable tie installation tool includes a housing which is generally pistol-shaped where the housing has a barrel into which the tail may be inserted for application of the tension. The housing has a grip which depends from the barrel. The tool includes a trigger mechanism having a trigger member located under the barrel and in front of the grip. The trigger member is elongate and in generally depending relation relative to the barrel such that, when the heel of the hand of a user is placed against the grip such that the fingers of the user&#39;s hand extend forwardly, the fingers may encircle the forward surface of the trigger member. Forcibly drawing the fingers toward the heel of the hand, i.e., squeezing the trigger member and grip, causes the trigger member to be displaced toward the grip. The trigger mechanism extends into the housing and is able to grasp the tail, and to apply the predetermined tension thereto in proportion to the drawing or squeezing force applied to the trigger member. 
   The trigger member of such a cable tie installation tool is typically pivotally mounted adjacent to the barrel such that, when the trigger member is at the maximum displacement from the grip, the trigger member is inclined relative to the barrel and grip. This inclination results in the distance between the trigger member and grip being smallest adjacent to the barrel and increasing in the direction away from the barrel. This inclination is maximum when the trigger member is open prior to any squeezing thereof. The squeezing of the trigger member causes the trigger member to pivot toward the grip causing the angle between the trigger member and the grip to close. 
   The inclination of the trigger member prior to the squeezing thereof has ergonomic disadvantages. One such disadvantage is that the smaller fingers of the hand (i.e., the smallest and ring fingers) are more distant from the pivotal connection of the trigger member as compared to the larger fingers (i.e., the index and middle fingers). This relative distance is significant because the squeezing force applied to the trigger member is increasingly multiplied as the squeezing force is more distant from the pivotal connection. The squeezing force is translated, via the trigger mechanism, to the tension force applied to the cable tie. 
   Since the smaller fingers typically have less strength than the larger fingers, the force multiplication generated by the pivoting of the trigger member is less than it would be if the larger fingers were farther from the pivotal connection. If a substantial squeezing force is required to be applied to the trigger member, e.g., a substantial tension is required in the cable tie, then the smaller fingers may become strained. Alternatively, to generate such a substantial tension, the inclination of the trigger member may be increased to make greater the leverage of the trigger member. However, such an increase in the inclination would require the smaller fingers to extend farther to initially grasp the trigger member. This would normally be difficult due to the limited length of such fingers. 
   SUMMARY OF THE INVENTION 
   The ergonomic cable tie installation tool of the present invention includes a generally pistol-shaped housing including a grip which depends from a barrel. Pivotally connected to the lower region of the grip is a trigger linkage of a trigger mechanism. The trigger mechanism also includes an intermediate linkage to which the trigger linkage is connected. The intermediate linkage is supported in the housing. The intermediate linkage is, in turn, connected to a tensioning mechanism also supported in the housing. The tensioning mechanism couples the intermediate linkage to the cable tie. Pivoting the trigger linkage toward the grip, normally by the hand of a user, causes the intermediate linkage to pivot resulting in the tensioning mechanism producing an increased tension in the cable tie. The trigger linkage is oriented relative to the grip to provide several ergonomic advantages to the user&#39;s hand when grasping the trigger linkage and grip. 
   One ergonomic advantage of the tool is that, when the fingers of the user&#39;s hand grasp the trigger linkage, the larger fingers of the user&#39;s hand are more distant from the pivotal connection as compared to the smaller fingers. This increases the force multiplication provided by the trigger mechanism thereby increasing the tension force applied to the cable tie. Additionally, the longer fingers have a greater reach enabling the inclination of the trigger linkage to be increased providing the trigger linkage with greater leverage. 
   The trigger mechanism may be constituted by a single toggle mechanism. Additional embodiments include the trigger mechanism including a double or compound toggle mechanism. Such a mechanism has additional advantages including the capability to transmit larger tension forces to the cable tie with reduced angular displacements of the trigger linkage. Additionally, such a trigger mechanism may provide for the tension force applied to the cable tie to increase as the trigger linkage is increasingly pivoted toward the closed position. This is particularly advantageous because, typically, as the cable tie is stretched, it becomes increasingly resistant to continued stretching. Also, such a trigger mechanism may reduce the inclination of the trigger linkage relative to the grip so that squeezing of the trigger linkage results in more linear displacement of the trigger linkage relative to the grip. 
   Methods of operating the tool of the present invention also provide improved ergonomics of the tool. 
   These and other features of the invention will be more fully understood from the following description of specific embodiments of the invention taken together with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is a perspective view of the ergonomic cable tie installation tool of the present invention with outer housing being removed to show the housing frame and trigger mechanism, the trigger mechanism being shown in the open position; 
       FIG. 2  is a side elevation view of the tool of  FIG. 1 ; 
       FIG. 3  is a front elevation view of the tool of  FIG. 2  in the plane indicated by the line  3 — 3  of  FIG. 2 ; 
       FIG. 4  is a top plan view of the tool of  FIG. 2  in the plane indicated by the line  4 — 4  of  FIG. 2 ; 
       FIG. 5  is a perspective view of the tool of  FIG. 1 , with outer housing and barrel removed to show the housing frame and the trigger mechanism, the trigger mechanism being shown in the closed position; 
       FIG. 6  is a side elevation view of the tool of  FIG. 5 ; 
       FIG. 7  is a perspective view of an alternative second embodiment of the tool of  FIG. 1  with outer housing being removed to show the housing frame and trigger mechanism, the trigger mechanism being shown in the open position; 
       FIG. 8  is a side elevation view of the tool of  FIG. 7 , showing the trigger mechanism in the open position; 
       FIG. 9  is a front elevation view of the tool of  FIG. 8  in the plane indicated by the line  9 — 9  of  FIG. 8 ; 
       FIG. 10  is a top plan view of the tool of  FIG. 8  in the plane indicated by the line  10 — 10  of  FIG. 8 ; 
       FIG. 11  is a side elevation view of the tool of  FIG. 7 , showing the trigger mechanism in the closed position; 
       FIG. 12  is a side elevation view of an alternative third embodiment of the tool of  FIG. 1 , showing the trigger mechanism in the open position; 
       FIG. 13  is a front elevation view of the tool of  FIG. 12  in the plane indicated by the line  13 — 13  of  FIG. 12 ; 
       FIG. 14  is a rear elevation view of the tool of  FIG. 12  in the plane indicated by the line  14 — 14  of  FIG. 12 ; 
       FIG. 15  is a top plan view of the tool of  FIG. 12  in the plane indicated by the line  15 — 15  of  FIG. 12 ; 
       FIG. 16  is a side elevation view of the tool of  FIG. 12  with portions of the outer shell of the housing being transparent to show the trigger mechanism; 
       FIG. 17  is a rear elevation view of the tool of  FIG. 16  in the plane indicated by the line  17 — 17  of  FIG. 16 ; 
       FIG. 18  is a top plan view of the tool of  FIG. 16  in the plane indicated by the line  18 — 18  of  FIG. 16 ; 
       FIG. 19  is a side elevation view of the tool of  FIG. 12  with the outer shell of the housing being removed and the trigger cover being transparent to show the trigger mechanism; 
       FIG. 20  is a front elevation view of the tool of  FIG. 19  in the plane indicated by the line  20 — 20  of  FIG. 19 ; 
       FIG. 21  is a perspective view of the tool of  FIG. 12  with portions of the outer shell of the housing being transparent and removed to show the trigger mechanism, the trigger mechanism being shown in the open position; 
       FIG. 22  is a perspective view of the tool of  FIG. 21  with additional portions of the outer shell of the housing being removed to further show the housing frame and trigger mechanism; 
       FIG. 23  is a side elevation view of the tool of  FIG. 22  with the outer shell of the housing being removed, the trigger mechanism being shown in the open position; 
       FIG. 24  is a side elevation view of the tool of  FIG. 22  with the outer shell of the housing being removed, the trigger mechanism being shown in the closed position. 
       FIG. 25  is a perspective view of an alternative fourth embodiment of the tool of  FIG. 1  with the housing and a portion of the trigger mechanism removed to show the return spring, the trigger mechanism being shown in the open position; 
       FIG. 26  is a side elevation view of the tool of  FIG. 25  with the trigger mechanism being shown in the open position; and 
       FIG. 27  is a front elevation view of the tool of  FIG. 26  in the plane indicated by the line  27 — 27  of  FIG. 26 . 
   

   Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to the drawings and more particularly  FIGS. 1 to 6 , an ergonomic cable tie installation tool  30  is shown for securing a cable tie to a bundle of articles, such as wires or cables. 
   The tool  30  includes a pistol-shaped housing including a grip which depends from a barrel. The housing includes an outer shell and may include an internal longitudinal planar frame which is centrally located within the outer shell. Such a housing frame is shown in  FIGS. 1 to 6  and designated generally by the reference numeral  32 . The housing frame  32  has a portion contained within the grip and is designated herein as the grip frame  34 . The housing frame  32  has another portion contained within the barrel and is designated herein as the barrel frame  36 . 
   The grip and barrel frames  34 ,  36  each have a respective longitudinal plane which define a central plane  38  of the housing. The grip and barrel, including their respective frames  34 ,  36 , each have a longitudinal axis  40 ,  42  which is contained in the central plane  38 . It is possible for the respective longitudinal axes  40 ,  42  of the grip and barrel to be offset from the central plane  38 , as long as the axes are generally parallel to the central plane. 
   The barrel frame  36  has a distal end  44  and a longitudinal slot  46  which terminates at an opening  48  in the distal end. A grommet  50  is fixed to the barrel frame  36  near the distal end  44  in coaxial relation to the longitudinal slot  46  such that the slot extends through the grommet. A stop  52 , which may be a pin, is transversely mounted on the barrel frame  36 . 
   The tool  30  includes a trigger mechanism  54  having a trigger linkage  56  with an elongate trigger member  58  having a dual-member structure, as shown in  FIGS. 1 and 5 . The respective members of the trigger member  58  each have one end which is pivotally connected to the grip frame  34  generally adjacent to the distal end  44 . Each of the members of the trigger member  58  has a longitudinal axis  62  which is generally parallel to the central plane  38 , as shown in  FIG. 3 . For clarity, the pair of members of the trigger member  58  will be referred to herein collectively as the trigger member  58 . 
   As an alternative to the dual-member structure, the trigger member  58  may have a single-member structure having recesses to provide for the pivotal connections described herein. The longitudinal axis of the trigger member  58  having such a single-member structure may be generally contained in or parallel to the central plane  38 . 
   The pivotal connections  64  between the trigger member  58  and grip frame  34  provides for pivoting of the trigger member in a direction  66  toward the open position shown in  FIG. 2  and in a direction  68  toward the closed position shown in  FIG. 6 . The trigger member  58  has a distal region  70  the distance of which from the grip frame  34  is greater than the distance between the pivotal connections  64  and the grip frame when the trigger member  58  is in the open position shown in  FIG. 2 . 
   The trigger mechanism  54  includes an intermediate linkage  72  having an elongate finger member  75  with a dual-member structure, as shown in  FIGS. 1 and 5 . The respective members of the finger member  75  each have one end which is pivotally connected to the grip frame  34  generally adjacent to the distal end  60 . Each of the members of the finger member  75  has a longitudinal axis  80  which is generally parallel to the central plane  38 , as shown in  FIG. 3 . For clarity, the pair of members of the finger member  75  will be referred to herein collectively as the finger member  75 . 
   As an alternative to the dual-member structure, the finger member  75  may have a single-member structure with recesses to provide for the pivotal connections described herein. The longitudinal axis of the finger member  75  having such a single-member structure may be generally contained in or parallel to the central plane  38 . 
   The pivotal connections  77  provide for pivoting of the finger member  75  in a direction  82  toward the open position shown in  FIGS. 1 and 2 , in which the finger member abuts the stop  52 , as shown in  FIGS. 1 and 2 . The pivotal connections  77  further provide for pivoting of the finger member  75  in a direction  83  toward a closed position shown in  FIGS. 5 and 6 . The finger member  75  has a sufficient longitudinal dimension to reach the stop  52  for engagement therewith when in the open position shown in  FIGS. 1 and 2 . 
   The other ends of the finger member  75  extend to the barrel frame  36  and across the slot  46 . The other ends of the finger member  75  each have a detent  84  which extends to an axially-reciprocating pull rod  85  of a tensioning mechanism located in the slot  46 . The pull rod  85  has a proximal end  86  including a catch  87  into which the detents  84  are inserted so that the detents are longitudinally fixed relative to the pull rod thereby axially displacing the pull rod in the slot  46  when the finger member  75  is pivoted in the direction  83  toward the closed position shown in  FIGS. 5 and 6 . Alternative embodiments are possible for longitudinally fixing the detents  84  to the pull rod  85 , such as are disclosed in U.S. Pat. No. 5,915,425, the entire disclosure of which is hereby incorporated by reference herein. 
   The pull rod  85  extends from the proximal end  86 , across the distal end  44  and opening  48 , to a distal end  88  which is coupled to the cable tie by additional parts of the tensioning mechanism. Examples of mechanisms which may provide such coupling are disclosed in U.S. Pat. No. 5,915,425. The coupling between the distal end  88  and cable tie results in axial displacement of the pull rod  85  into the slot  46 , as shown in  FIGS. 5 and 6 , resulting in the application of a tensile force to the cable tie. 
   The intermediate linkage  72  further comprises an elongate intermediate link  89  having one longitudinal portion with a dual-member structure and another longitudinal portion with a single-member structure. The portion of the intermediate link  89  having the dual-member structure is pivotally connected to the finger member  75 , as shown in  FIGS. 1 ,  2 ,  5  and  6 . Each of the members of the dual-member structure of the intermediate link  89  has a longitudinal axis  90  which is generally parallel to the central plane  38 , as shown in  FIG. 3 . The portion of the intermediate link  89  having the single-member structure is pivotally connected to the trigger member  58 , as shown in  FIGS. 1 ,  2 ,  5  and  6 . The member of the single-member structure of the intermediate link  89  has a longitudinal axis  91  which is generally contained in the central plane  38 . For clarity, the members of the portions of the intermediate link  89  will be referred to herein collectively as the intermediate link  89 . 
   As an alternative to the combined single and dual-member structure of the intermediate link  89 , the link may have a single-member structure throughout its length. The longitudinal axis of the intermediate link  89  having such a single-member structure may be generally contained in or parallel to the central plane  38 . Alternatively, further, the intermediate link  89  may have a dual-member structure throughout its length. The longitudinal axes of the respective members of such an intermediate link  89  may be generally parallel to the central plane  38 . Alternatively, still further, the intermediate link  89  may have other single- or dual-member structures in other assembly configurations. 
   The pivotal connections  92 ,  95  of the intermediate link  89  are offset from one another such that the intermediate link is inclined relative to the trigger and finger members  58 ,  75 , as viewed in  FIGS. 1 ,  2 ,  5  and  6 . 
   The tool  30  may have additional parts such as are disclosed in U.S. Pat. No. 5,915,425. 
   In operation, initially, the trigger member  58  is pivoted in the direction  66  to the open position shown in  FIGS. 1 and 2 . The tail of the cable tie is coupled to the distal end  88  of the pull rod  85 . 
   The user grasps the trigger member  58  and grip such that the fingers of the user&#39;s hand partially encircle the trigger member and the heel of the user&#39;s hand abuts the grip. The fingers are oriented along the trigger member  58  so that the smaller fingers are between the larger fingers and the pivotal connections  64 . 
   The user&#39;s hand is then closed causing the trigger member  58  to pivot in the direction  68  toward the closed position shown in  FIGS. 5 and 6 . Closure of the trigger member  58  results in the travel of the larger fingers toward the grip being greater than the corresponding travel of the smaller fingers. 
   Pivoting of the trigger member  58  in the direction  68  to the closed position shown in  FIGS. 5 and 6  causes the intermediate link  89  to pivot the finger member  75  in the direction  83  about the pivotal connections  77  toward the closed position shown in  FIGS. 5 and 6 . This pivoting of the trigger and finger members  58 ,  75  causes the intermediate link  89  to pivot relative to the trigger and finger members from the angular positions shown in  FIGS. 1 and 2  toward those shown in  FIGS. 5 and 6 . 
   The pivoting of the finger member  75  in the direction  83  toward the closed position shown in  FIGS. 5 and 6  causes the detents  84  to be translated longitudinally away from the distal end  44  of the barrel frame  36 . This results in corresponding axially displacement of the pull rod  85  into the slot  46  which, due to the cable tie being coupled to the pull rod, applies a tensile force to the cable tie. 
   An alternative second embodiment of the cable tie installation tool  30   a  is shown in  FIGS. 7 to 11 .  FIGS. 7 to 11  are views which correspond to the views of  FIGS. 1 to 4 , and  6 , respectively. Parts illustrated in  FIGS. 7 to 11  which correspond to parts illustrated in  FIGS. 1 to 4 , and  6  have, in  FIGS. 7 to 11 , the same reference numeral as in  FIGS. 1 to 4 , and  6  with the addition of the suffix “a”. 
   The tool  30   a  includes an elongate outer trigger member  97 . Accordingly, the trigger member  58   a  is referred to as the inner trigger member  58   a  of the tool  30   a . The outer trigger member  97  has a dual-member structure, as shown in  FIG. 7 . 
   The respective members of the trigger member  97  each have one end which is pivotally connected to an end of the respective members of the inner trigger member  58   a  which are opposite from the pivotal connections  64   a . Each of the members of the trigger member  97  has a longitudinal axis  98  which is generally parallel to the central plane  38   a , as shown in  FIG. 9 . For clarity, the pair of members of the trigger member  97  will be referred to herein collectively as the outer trigger member  97 . 
   As an alternative to the dual-member structure, the outer trigger member  97  may have a single-member structure with recesses to provide for the pivotal connections described herein. The longitudinal axis of the trigger member  97  having such a single-member structure may be generally contained in or parallel to the central plane  38   a.    
   The pivotal connections  100  between the inner and outer trigger members  58   a ,  97  provides for the outer trigger member to pivot in a direction  102  toward the open position shown in  FIGS. 7 and 8 . The pivotal connections  100  further provide for pivoting of the outer trigger member  97  in a direction  105  toward the closed position shown in  FIG. 11 . 
   The intermediate linkage  72   a  comprises a central link  107  and inner and outer links  109 ,  111 . The central link  107  has a single-member structure. The inner and outer links  109 ,  111  each have a dual-member structure, as shown in  FIG. 7 . 
   The respective members of the links  107 ,  109 ,  111  each have an inner end which is pivotally connected to a respective inner end the members of the other links at a pivotal connection  112  such that the links have a generally Y-shaped configuration when the trigger members  58   a ,  97  are each in the respective open positions shown in  FIGS. 7 and 8 . The central link  107  has a longitudinal axis  114  which is generally contained in the central plane  38   a , as shown in  FIG. 9 . Each of the members of the inner and outer links  109 ,  111  has a respective longitudinal axis  116 ,  117  which is generally parallel to the central plane  38   a . For clarity, the pairs of members of the inner and outer links  109 ,  111  will be collectively referred to herein as the inner link  109 , and outer link  111 , respectively. 
   As an alternative to the single-member structure, the central link  107  may have a dual-member structure. As an alternative to the dual-member structure, one or more of the inner and outer links  109 ,  111  may have a single-member structure. The longitudinal axes of any of the links  107 ,  109 ,  111  having such structures may be generally contained in or parallel to the central plane  38   a.    
   The central link  107  has an outer end pivotally connected to the inner trigger member  58   a . The inner link  109  has an outer end pivotally connected to the finger member  75   a . The outer link  111  has an outer end pivotally connected to the outer trigger member  97 . 
   The portion of the grip frame  34   a  which faces the inner and outer trigger members  58   a ,  97  has a recess  118 , as shown in  FIGS. 7   8 , and  11 . 
   The stop  52   a  is located between the pull rod  85   a  and inner link  109 . The stop  52   a  is engaged by a portion of the finger member  75   a  between the detents  84   a  and inner link  109  when the finger member is in the open position shown in  FIGS. 7 and 8 . 
   In operation, the inner and outer trigger members  58   a ,  97  are pivoted in the directions  66   a ,  102  to the respective open positions shown in  FIGS. 7 and 8 . The tail of the cable tie is coupled to the distal end  88   a  of the pull rod  85   a.    
   The user grasps the outer trigger member  97  and grip of the pistol-shaped housing in generally the same manner as described herein for the tool  30 . The user&#39;s hand is then closed in generally the same manner as described herein for the tool  30 . 
   The inner and outer trigger members  58   a ,  97  and links  107 ,  109 ,  111  are shaped and sized such that displacement of the outer trigger member toward the grip frame  34   a  produces a reverse sequential pivoting of the trigger members. This reverse sequential pivoting causes the displacement to produce an initial pivoting of the outer trigger member  97  relative to the inner trigger member  58   a  in an initial direction toward the closed position shown in  FIG. 11 . This initial direction, as shown by comparing  FIGS. 8 and 11 , is the pivoting direction  105  of the outer trigger member  97  relative to the inner trigger member  58   a  about the pivotal connection  100 . During the initial pivoting of the outer trigger member  97 , pivoting of the inner trigger member  58   a  relative to the grip frame  34   a  is substantially limited. The initial pivoting causes pivoting of the links  107 ,  109 ,  111  which, in turn, cause the finger member  75   a  to pivot in the direction  83   a  toward the closed position shown in  FIG. 11 . The pivoting of the finger member  75   a  in the direction  83   a  toward the closed position shown in  FIG. 11  produces the axial displacement of the pull rod  85   a  in the same manner as for the tool  30  illustrated in  FIGS. 1 to 6 . 
   The reverse sequential pivoting provides for continued displacement of the outer trigger member  97  toward the grip frame  34   a  to cause subsequent pivoting of the inner trigger member  58   a  relative to the grip frame in a subsequent direction toward the closed position  68   a . The subsequent pivoting is initiated when the outer trigger member  97  reaches the limit at which continued pivoting of the outer trigger member in the initial direction is substantially prevented. The subsequent direction is opposite from said initial direction. As shown by comparing  FIGS. 8 and 11 , the subsequent direction is the pivoting direction  68   a  of the inner trigger member  58   a  relative to the grip frame  34   a  about the pivotal connection  64   a . During the subsequent pivoting, pivoting of the outer trigger member  97  relative to the inner trigger member  58   a  is substantially limited. The subsequent pivoting causes pivoting of the links  107 ,  109 ,  111  which, in turn, cause the finger member  75   a  to pivot further in the direction  83   a  toward the closed position shown in  FIG. 11 . The further pivoting of the finger member  75   a  toward the closed position shown in  FIG. 11  produces further axial displacement of the pull rod  85   a  in the same manner as for the tool  30  illustrated in  FIGS. 1 to 6 . 
   The reverse sequential pivoting, including the initial and subsequent pivoting of the trigger members  58   a ,  97 , causes the links  107 ,  109 ,  111  to pivot from the positions shown in  FIG. 8  to the positions shown in  FIG. 11 . 
   Pivoting of the trigger members  97 ,  58   a  in the directions  105 ,  68   a  to the respective closed positions shown in  FIG. 11  causes the links  107 ,  111  to pivot to positions where the links are received in the recess  118  in the grip frame  34   a , as shown in  FIG. 11 . This facilitates pivoting of the trigger members  97 ,  58   a  in the directions  105 ,  68   a  to the respective closed positions shown in  FIG. 11 . 
   An advantage of the reverse sequential pivoting is that the initial pivoting of the outer trigger member  97 , the portion of the member  97  most distant from the grip frame  34   a  is grasped by the smaller fingers of the user&#39;s hand since the pivoting is primarily about pivotal connections  100 . Since these fingers are weaker, the force transmitted by the trigger linkage  56   a  and intermediate linkage  72   a  to the pull rod  85   a  are initially low. When the initial pivoting is nearly complete, the portion of the outer trigger member  97  most distant from the grip frame  34   a  is grasped by the larger fingers of the user&#39;s hand since the pivoting is primarily about pivotal connection  64   a . Since these fingers are stronger, the force transmitted by the trigger linkage  56   a  and intermediate linkage  72   a  to the pull rod  85   a  increases. This is desirable because typically, as the cable tie is stretched, it becomes increasingly resistant to continued stretching. 
   An alternative third embodiment of the cable tie installation tool  30   c , which is a preferred embodiment of the present invention, is shown in  FIGS. 12 to 23 .  FIGS. 21 to 23  are views which correspond generally to the views of  FIGS. 1 ,  2  and  6 , and  FIGS. 7 ,  8  and  11 , respectively. Parts illustrated in  FIGS. 21 to 23  which correspond to parts illustrated in  FIGS. 1 ,  2  and  6 , and  FIGS. 7 ,  8  and  11  have, in  FIGS. 21 to 23 , the same reference numeral as in  FIGS. 1 ,  2  and  6 , and  FIGS. 7 ,  8  and  11  with the addition of the suffix “b”. The suffix “a”, included in some of the reference numerals of  FIGS. 7 ,  8  and  11 , is not included in  FIGS. 21 to 23 , since the correspondence to such parts in  FIGS. 7 ,  8  and  11  is sufficiently indicated by the corresponding numbers. 
     FIGS. 12 to 21  show the housing frame  32   b , and additionally show the outer shell of the housing which is designated generally by the reference numeral  119 . The outer shell  119  includes a shell  120  in which the housing frame  32   b  is supported. The portion of the shell body  120  in which the grip frame  34   b  is located is anatomically shaped to facilitate conformance thereto by the user&#39;s hand when the hand grasps the shell body and trigger cover  121 . Such grasping may be to pivot the trigger members  97   b ,  58   b  in the directions  105   b ,  68   b  from the respective open positions shown in  FIG. 23  to the respective closed positions shown in  FIG. 24 . To further facilitate such grasping, the outer surface of the portion of the shell body  120  which is so grasped may be formed of a soft comfortable material.  FIGS. 12 to 20  also illustrate additional parts of the tool  30   b  connected, either directly or indirectly, to the housing shell  119 . Some of these additional parts are disclosed in U.S. Pat. No. 5,915,425. 
   The outer shell  119  includes a trigger cover  121  pivotally connected to the shell body  120  such that the trigger cover is in depending relation to the barrel frame  36 . The trigger cover  121  is located outwardly relative to the outer trigger member  97 . The pivotal connection provides for pivoting of the trigger cover  121  from the open position shown, for example, in  FIG. 19 , in a direction  123  toward the closed position, and in a direction  125  toward the open position. 
   The trigger cover  121  includes a cover member  127  and a longitudinal window  129  formed in the cover member. The trigger cover  121  also has upper and lower flanges  131 ,  133  mounted on respective upper and lower ends of the window  129 . 
   The housing includes a roller  135  having opposite ends rotatably supported by respective ones of said upper and lower flanges  131 ,  133 . This rotatable support may be provided by the roller  135  including an axle supported between the upper and lower flanges  131 ,  133  and a sleeve which rotates about the axle in coaxial relation thereto. 
   The roller  135  has an axis of rotation  137  the orientation of which is generally the same as the longitudinal axis of the trigger cover  121 . The connections between the roller  135  and upper and lower flanges  131 ,  133  obstructs longitudinal, transverse and lateral displacement of the roller relative to the cover member  127 . The roller  135  is positioned within the window  129  such that a portion of the roller extends outwardly beyond the trigger cover  121 . 
   The inner and outer trigger members  58   b ,  97   b  are configured as shown in  FIGS. 22 and 23 . More specifically, the outer trigger member  97   b  has a lower corner portion  139  and an upper inclined portion  141 . 
   The inner trigger member  58   b  has an intermediate segment  143  between upper and lower segments  145 ,  147 . The intermediate segment  143  is inclined relative to the upper and lower segments  145 ,  147  such that the intermediate segment is outward of an inner axis  149 . The inner axis  149  is contained in or generally parallel to the central plane  38   b . The inner axis  149  intersects the pivotal connections  100   b  between the inner and outer trigger members  58   b ,  97   b . The inner axis  149  further intersects the pivotal connections  64   b  between the inner trigger member  58   b  and grip frame  34   b.    
   A stop  52   b , which may be a pin, is transversely mounted on the barrel frame  36   b . The stop  52   b  limits the pivoting of the inner and outer trigger members  58   b ,  97   b  in the directions  66   b ,  102   b  toward the open positions shown in  FIG. 23 . The engagement of the members  58   b ,  97   b  with the stop  52   b  defines the open positions shown in  FIG. 22 . 
   The outer link  111   b  has a single-member structure and a longitudinal axis  117   b  which is generally contained in the central plane  38   b , as shown in  FIG. 17 . As an alternative to the single-member structure, the link  111   b  may have a dual-member structure. The longitudinal axes of the members of such a dual-member structure may be generally parallel to the central plane  38   b.    
   The central link  107   b  has a dual-member structure, each member of which has a longitudinal axis which is generally parallel to the central plane  38   b , as shown in  FIG. 17 . As an alternative to the dual-member structure, the link  107   b  may have a single-member structure. The longitudinal axis of such a single-member structure may be generally contained in or parallel to the central plane  38   b.    
   In operation, the tool  30   b  is manipulated by the user in generally the same manner as the tool  30   a . More specifically, the inner and outer trigger members  58   b ,  97   b  are pivoted in the directions  66   b ,  102   b  into engagement with the stop  52   b  and thereby to the open positions shown in  FIG. 22 . The trigger cover  121  and roller  135  are then grasped by the fingers of the user&#39;s hand, the heel of which is in abutting relation with the grip. The portion of the roller  135  extending outwardly beyond the trigger cover  121  results in at least one of the fingers of the user&#39;s hand contacting the roller. Then, the user&#39;s hand is closed to pivot the trigger cover  121  in the direction  123  toward the closed position. The contact between at least one of the fingers and the roller  135  produces lateral translation of the finger or fingers relative to the trigger cover  121  and resultant rotation of the roller. This reduces possible friction between the fingers and trigger cover  121 . 
   The outward position of the trigger cover  121  relative to the outer trigger member  97   b  results in the trigger cover, when pivoted toward the closed position  125 , urging the outer trigger member to pivot in the direction  105   b  toward the closed position shown in  FIG. 24 . This produces reverse sequential pivoting corresponding to the reverse sequential pivoting described herein above for  FIGS. 7 to 11 . The resulting axial displacement force applied to the pull rod  85   b  is increased and the angular displacement required to pivot the inner and outer trigger members  97   b ,  58   b  in the directions  105   b ,  68   b  from the open positions shown in  FIG. 23  to the closed positions shown in  FIG. 24  is decreased, relative to the corresponding amounts for the tool  30   a . This decrease results from the configuration of the inner and outer trigger members  58   b ,  97   b , including the lower corner portion  139 , upper inclined portion  141 , intermediate segment  143 , and upper and lower segments  145 ,  147 . 
   An alternative fourth embodiment of the tool  30   c , which is a preferred embodiment of the present invention, is shown in  FIGS. 25 to 27 .  FIGS. 25 to 27  are views which correspond generally to the views of  FIGS. 1 to 3 ,  FIGS. 7 to 9 , and  FIGS. 22 ,  23  and  20 , respectively. Parts illustrated in  FIGS. 25 to 27  which correspond to parts illustrated in  FIGS. 1 to 3 ,  FIGS. 7 to 9 , and  FIGS. 22 ,  23  and  20  have, in  FIGS. 25 to 27 , the same reference numeral as in  FIGS. 1 to 3 ,  FIGS. 7 to 9 , and  FIGS. 22 ,  23  and  20  with the addition of the suffix “c”. The suffixes “a” and “b”, included in some of the reference numerals of  FIGS. 7 to 9 , and  FIGS. 22 ,  23  and  20 , are not included in  FIGS. 25 to 27 , since the correspondence to such parts in  FIGS. 7 to 9 , and  FIGS. 22 ,  23  and  20  is sufficiently indicated by the corresponding numbers. 
   As shown in  FIG. 25 , the tool  30   c  has particular correspondence to the tool  30   b  shown in  FIG. 22 . The tool  30   c  includes a return spring designated generally by the reference numeral  151 . The return spring  151  is generally elongate and connected to the outer trigger member  97   c  generally at the intersection between the lower corner portion  139   c  and upper inclined portion  141   c . The return spring  151  is further connected to the pivotal connection  77   c  of the conversion member  75   c  to the grip frame  34   c . The return spring  151  has a longitudinal axis  153  generally contained in or parallel to the central plane  38   c.    
   The inner link  109   c  shown in  FIG. 25  has a single-member structure and a longitudinal axis  116   c  which is generally contained in the central plane  38   c , as shown in  FIG. 27 . As an alternative to the single-member structure, the link  109   c  may have a dual-member structure. The longitudinal axis of the members of such a dual-member structure may be generally parallel to the central plane  38   c.    
   In operation, the tool  30   c  is manipulated by the user in generally the same manner as the tool  30   b . The return spring  151  resists pivoting of the outer trigger member  97   c  in the direction  105   c  toward the closed position of the outer trigger member. 
   The tools  30   a ,  30   b  shown in  FIGS. 7 to 11 , and  FIGS. 12 to 24 , respectively, may have a return spring corresponding to the return spring  151  shown in  FIGS. 25 to 27 . The tool  30  shown in  FIGS. 1 to 6  may have a return spring connected to the trigger member  58  which resists pivoting of the trigger member in the direction  68  toward the closed position shown in  FIGS. 5 and 6 . 
   The tools  30 ,  30   a ,  30   c  shown in  FIGS. 1 to 6 ,  FIGS. 7 to 11 , and  FIGS. 25 to 27 , respectively, may have an outer shell including a shell body and trigger cover, and a roller corresponding, respectively, to the outer shell  119 , shell body  120 , trigger cover  121 , and roller  135 . Such an outer shell and roller in  FIGS. 1 to 6 ,  FIGS. 7 to 11 , and  FIGS. 25 to 27  may operate in a manner corresponding to the operation of the outer shell  119  and roller  135 . 
   Embodiments of the ergonomic cable tie installation tool of the present invention are disclosed in the following U.S. Design Patent Applications, the entire disclosures of which are hereby incorporated by reference herein:
     Title: Cable Tie Installation Tool; Inventors: Jose Maria D. Magno, Jr., Brian A. Pope; Executed by Inventors on same date as present U.S. patent application Ser. No. 29/185,985; and   Title: Cable Tie Installation Tool; Inventors: Jose Maria D. Magno, Jr., Brian A. Pope; Executed by Inventors on same date as present U.S. patent application Ser. No. 29/185,986.   

   While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concept described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it have the full scope permitted by the language of the following claims.