Abstract:
A locking mechanism for scissors-type shear allows closing and locking of the shear even when the locking element is placed in a locked position before the shears are closed. The shear includes first and second blade assemblies pivotably connected to one another. Each blade assembly includes a blade and a handle. A locking mechanism is slidably mounted on a first handle. The locking element is moveable between locked and unlocked positions. In the locked position, the sliding lock mechanism engages a catch element on the second handle to lock the shear in the closed position. The locking mechanism includes resilient arms and the catch element includes inclined cam surfaces. When the locking mechanism is placed in a locked position before the shear is closed, the ends of the resilient arms engage the inclined surfaces of the catch element, allowing the resilient arms to flew outwardly and pass over the catch elements. When the resilient arms return to their original position, the user hears an audible click informing the user that the shears are firmly secured in a closed position.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to shears of the type having two blades pivotally connected to one another for movement between open and closed positions and, more particularly, to a locking mechanism for a spring-loaded shear to lock the shear in a closing position. 
     BACKGROUND OF THE INVENTION 
     The class of cutting tools known as a shear use two opposed and cooperating cutting edges to apply cutting force to a workpiece. Shears and scissors have a wide variety of uses. Shears and scissors are used for cutting paper, fabric, sheet metal, and many other types of sheet material. Shears are also used in gardening for pruning trees, shrubs, and other plants. Perhaps the most common type of shears is the class of shears having two blades with handles, the blades being pivotally connected at their center for pivotable movement between open and closed positions. This class of shears includes scissors and, therefore, shall be referred to herein as a scissors-type shears. 
     With scissors-type shears, it is common practice to bias the blades to an open position by means of a spring. With spring-biased shears, the user applies cutting force by squeezing the handles of the shears together, causing the blades to close. When the user relieves pressure on the handle, the spring urges the blades to an open position. Thus, the user is not required to apply force to open the blades of the shears. Spring-biased shears typically include a lock mechanism to maintain the blades in a closed position when they are not in use. Locking the blades in a closed position helps prevent damage to the cutting edges of the shears. Additionally, securing the blades in the closed position reduces the risk of injury because the cutting edges are not exposed when the blades are closed. 
     Many types of locking mechanisms have been devised in the past to secure the blades of scissors-type shears in a closed position. A common type of locking mechanism used in spring-loaded shears is a pivoting latch. Typically, a latch element is pivotally attached to one handle. The latch element includes a notch that engages with a latch pin on the opposing handle. An exemplary pivoting of latch mechanism is shown in U.S. Pat. No. Des. 406,507. Another common type of locking mechanism is a simple loop or bight element attached to one handle that engages a notch in the opposing handle when the shears are in the closed position. This type of locking mechanism is shown in U.S. Pat. No. 5,063,671. The locking mechanisms described above are relatively simple and inexpensive to manufacture. However, these locking mechanisms require two-handed operation: one hand to apply force to hold the shears in a closed position, and one hand to engage the latch or bight element. Also, while consumers may expect these types of locking mechanisms on inexpensive tools, using these mechanisms on more expensive tools could negatively impact sales since consumers may desire a more elegant locking mechanism in higher-priced tools. 
     Sliding lock mechanisms are also known for locking shears in a closed position. Examples of shears with sliding lock mechanisms are shown in the patent to Wallace et al., U.S. Pat. No. 4,156,311 and LaBarre et al, U.S. Pat. No. 5,367,774. The patent to Wallace discloses a sliding latch that slides back and forth in a slot formed in one of the handles. The opposing handle has a locking stud. The sliding latch slides into and out of engagement with the locking stud to lock and unlock the shears, respectively. The patent to LaBarre discloses a sliding lock mechanism comprising a pin that passes through aligned slots in the handles of the shears. The pin slides within the slots between locked and unlocked positions. The sliding mechanisms exemplified by these patents achieve the desired goal of one-handed operation. However, the sliding mechanisms of the prior art have various limitations. For example, some sliding mechanisms of the prior art do not retain their position during use and tend to interfere with the operation of the shears. Also, many sliding mechanisms are characterized by relatively complex construction having numerous parts. In general, an increase in the number of parts equates to greater material cost. Further, increasing the number of parts usually makes the assembly of the shears more difficult, further increasing the cost of manufacturing the tool. Additional parts also mean more opportunities for wear or failure, reducing the reliability of the tool. 
     Accordingly, there is a need for a new locking mechanism that is capable of one-handed operation, is simple in construction, and can be inexpensively manufactured. 
     SUMMARY OF THE INVENTION 
     The invention is a spring-loaded shear having a one-piece locking mechanism that can be operated with a single hand. The shear comprises first and second blade assemblies that are connected for pivotal movement between open and closed positions. Each blade assembly includes a cutting blade and a handle. A spring biases the blade assemblies to an open position. A simple, one-piece locking mechanism locks the blade assemblies in a closed position when the shear is not being used to protect the blades against damage and to prevent injury to persons. 
     In a preferred embodiment of the invention, the locking mechanism comprises a sliding latch that moves between a locked position and an unlocked position. The latch is mounted for sliding movement on one of the handles. In the locked position, the sliding latch engages a catch element on the second handle to lock the blade assemblies in a closed position. In the preferred embodiment of the invention, the sliding latch is a molded, u-shaped member, including a thumb pad and two resilient arms. The latch member mounts to the first handle with the thumb pad disposed on an upper surface of the handle and the resilient arms against lateral surfaces of the handle. The resilient arms include latch elements that engage catch elements disposed on the lateral surfaces of the handle. 
     Also, in a preferred embodiment of the invention, each of the catch elements includes an inclined, cam surface. The cam surfaces allow the blade assemblies to be closed and locked even when the latch member is in the locked position. When the user attempts to close the blade assemblies with the latch member already in a locked position, the resilient arms engage the cam surfaces on the catch elements. The cam surfaces cause the resilient arms to deflect outwardly and pass over the catch element so that the latch element can engage the catch element. Thus, to close and lock the blade assembly, the user simply slides the latch member forward to a locked position and squeezes the handles together. As the resilient arms pass over the catch element and return to their original position, an audible click is produced, alerting the user that the blade assemblies are securely locked in the closed position. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view of the shear according to the present invention in a closed position. 
     FIG. 2 is a side view of the shear in an open position. 
     FIG. 3 is a side view of the bottom blade of the shear. 
     FIG. 4 is a side view of the top blade of the shear 
     FIG. 5 is a top view of the top blade 
     FIG. 6 is a side view of the top and bottom handles of the shear. 
     FIG. 7 is a section view of the top and bottom handles taken through line A—A of FIG.  6 . 
     FIG. 8 is a detail section view of the bottom element through line B—B of FIG.  6 . 
     FIG. 9 is a perspective view of the latch member. 
     FIG. 10 is a front view of the latch member. 
     FIG. 11 is a detail section view showing the latch member being flexed outward by the inclined surfaces of the catch element. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1 and 2 of the drawings, the spring-loaded shear of the present invention is shown therein and indicated generally by the numeral  10 . The shear  10  includes first and second blade assemblies, labeled  12  and  14  respectively, which are pivotably connected by a pivot assembly  120 . The first and second blade assemblies pivot between open and closed positions. A biasing member  16 , such as a spring, biases the blade assemblies  12 ,  14  to an open position. A sliding lock mechanism  200  locks the blade assemblies  12 ,  14  in a closed position against the force of the spring. 
     The first blade assembly  12  comprises a first blade  20  and a first handle  60 . For reference, the first blade  20  is the lower blade of the shear  10  and the first handle  60  is the upper handle of the shear  10 . The first blade includes a cutting portion  22 , a connecting portion  24 , and a shank portion  26 . The cutting portion  22  includes a cutting edge  28  formed by grinding. The connecting portion  24  includes a pivot opening to receive a pivot member as will be more fully described below. The shank portion  26  includes one or more notches  32  or openings. The purpose of the notches or openings  32  is to interlock the blade  20  with the first handle  60  during the molding process when the handle  60  is formed. 
     The first handle  60  includes a top surface  62 , lateral surfaces  64 , and a bottom surface  68 . A step  70  is formed on the bottom surface  68  adjacent the forward end of the handle  60 . Step  70  includes a first abutting surface  72  that abuts a corresponding surface on the second handle, as will be described below. The top surface  62  includes a recessed portion, referred to herein as the recessed top surface  74 . Similarly, the lateral surfaces  64  include recessed surfaces which are referred to herein as the recessed lateral surfaces  76 . As will be described below, the sliding lock mechanism  200  is mounted for sliding movement along the recessed surfaces  74 ,  76 . Shoulder walls  78 ,  80  are formed along the forward and rearward edges, respectively, of the recessed surfaces  74 ,  76 . The forward shoulder wall  78  functions as a stop to limit the forward movement of the sliding lock mechanism  200 . Similarly, the rearward shoulder wall  80  functions as a rearward stop to limit rearward movement of the sliding lock mechanism  200 . Thus, shoulder walls  78 ,  80  define the permissible range of movement of the sliding lock mechanism  200 . 
     A guide rail  82  is formed on the recessed top surface  74 . The guide rail  82  extends from the rear shoulder wall  80  to the forward shoulder wall  78 . Similarly, guide slots  84  are formed in the recessed lateral surfaces  76 . The guide slots  84  extend from the rearward shoulder wall  80  to the forward shoulder wall  78 . The primary function of the guide rail  82  is to keep the sliding lock mechanism  200  aligned as it moves along the recessed surfaces  74 ,  76 . The guide slots  84  also help in keeping the sliding lock mechanism  200  properly aligned. In addition, the guide slots  84  also provide a mechanism for retaining the sliding lock mechanism  200  on the first handle  60 . This retention function will be described in more detail below. 
     The second blade assembly  14  comprises a second blade  40  and a second handle  90 . For reference, the second blade  40  is the upper blade of the shear  10 . Handle  90  is the lower handle of the shear  10 . The second blade  40  includes a cutting portion  42 , a connecting portion  44 , and a shank portion  46 . The cutting portion  42  includes a cutting edge  48  formed by grinding. The connecting portion  44  includes a pivot opening  50  to receive a pivot member as described more fully below. Notches or openings  52  in the shank portion  46  interlock with the second handle  90  when the handle  90  is molded to provide a secure attachment between the second blade  40  and second handle  90 . 
     The second handle  90  includes a top surface  92 , lateral surface  94 , and a bottom surface  96 . The top surface  92  includes a second step  98  having a second abutting surface  100 . The second abutting surface  100  abuts against the first abutting surface  72  when the shear  10  is in the closed position. The purpose of the abutting surfaces  72 ,  100  is to provide some spacing between the handles  60 ,  90  when the shear  10  is in the closed position. The lateral surfaces  94  of the second handle  90  include recessed lateral surfaces  102  corresponding to recessed lateral surfaces  76 , as shown in FIGS. 6 and 7. 
     A finger ring  104  is integrally formed on the bottom surface  96  adjacent the forward end of the second handle  90 . The finger ring  104  is positioned so that the user&#39;s index finger, or pointing finger, is inserted into the finger ring  104  during use. Also, it should be noted that the center of the finger ring  104  is vertically aligned with the center of the recessed lateral surfaces  76  on the upper handle  60 . Thus, the finger ring  104  lies centrally along the range of movement of the locking mechanism  200 . The relative positioning of the finger ring  104  and the locking mechanism  200  is advantageous from an ergonomic standpoint in that it makes operation of the sliding lock mechanism  200  easier for the user. Also, this arrangement provides a more comfortable feel as compared to other prior art shear  10 . 
     Bottom surface  96  further includes first and second contoured finger surfaces  106 ,  108 . Contoured finger surface  106  accommodates the user&#39;s middle finger, while the second contoured finger surface  108  accommodates the ring and little, or pinky, finger. The relative positioning of the finger ring  104  with respect to the sliding lock mechanism  200 , and the contoured surfaces  106 ,  108 , provide a more ergonomic and comfortable feel for the user as compared to some prior art shears. 
     To facilitate storage of the shear  10 , a support tab  110  is formed at the rear end of the second handle  90 . The support tab  110  could also be formed in the upper handle  60 . Support tab  110  includes an opening  112  formed therein. Opening  112  allows the shear  10  to be hung from a peg (not shown). Also, opening  112  can receive a loop made of string used to suspend the shear  10  from a support. 
     The blade assemblies  12 ,  14  are pivotably connected by a pivot assembly  120 . The construction of the pivot assembly  120  is not a material aspect of the invention. The pivot assembly  120  could be as simple as a bolt and lock nut passing through the aligned pivot openings  30 ,  50 . In the embodiment shown, the pivot assembly  120  includes a bolt, a first bushing, a second bushing, and a thumb nut. The first bushing is press fit into the pivot opening  30  of the first blade  20 , and the second bushing is press fit into the pivot opening  50  in the second blade  40 . The bolt is inserted through the first bushing and extends through the second bushing. The thumb nut engages the bolt to fasten the components together, completing the assembly. 
     Another pivot assembly  120  that could be used in connection with the present invention is disclosed in my co-pending U.S. patent application Ser. No. 09/148,781 filed Sep. 4, 1998 and entitled “Adjustable, Quick-Disconnect Pivot Fastener” which is incorporated herein by reference. 
     Referring now to FIGS. 9-11, the sliding lock mechanism  200  is shown. The sliding lock mechanism  200  comprises a latch member  202  and a pair of catch elements  240 . The latch member  202  is mounted to the first handle  60 . The catch elements  240  are formed on the recessed laterals surface of the second handle  90 . The latch member  202  slides forward and backward into and out of engagement with the catch elements  240 . 
     The latch member  202  includes a thumb tab  204  and two spaced-apart resilient latch arms  220 . The latch member  202  is mounted to the first handle  60  so that the thumb tab  204  occupies the area defined by the recessed top surface  74 , and the resilient latch arms  220  occupy the area defined by the recessed lateral surfaces  76 . The resilient arms  220  are disposed on opposing sides of the first handle  60  so that the first handle  60  is, in effect, captured between the resilient arms  220 . 
     The thumb tab  204  has a top surface  206  that inclines upwardly from the rear of the tab  204  to the front of the tab  204 . Ridges  208  extend across the tab from one side thereof to the other. The function of the ridges  208  is to prevent the user&#39;s thumb from slipping on the top surface  206  when pressure is applied to the thumb tab  204  by the user. The inclination of the top surface  206  enables greater force to be applied in the forward direction. The bottom surface  210  is substantially flat and smooth so as to slide easily over the recessed top surface  74 . A guide slot  212  is formed in the bottom surface  210  of the thumb tab  204 . The guide slot  212  mates with the guide rail  82  on the recessed top surface  74  of the upper handle  60 . The guide slot  212  and guide rail  82  cooperate to keep the latch member  202  properly aligned as it is moved between the locked and unlocked positions. 
     The resilient latch arms  220  are identical in construction. Each latch arm  220  extends downward in cantilever fashion from the bottom surface  210  of the thumb tab  204 . A pair of spaced-apart prongs  222 ,  224  are formed at the free end of the resilient arms  210 . The prongs  222 ,  224  define a catch area  226 . When the blade assemblies  12 ,  14  are in a closed position and the lock mechanism  200  is moved to the locked position, the catch element  240  on the recessed lateral surfaces  102  are captured in the catch areas  226  of the resilient arms  220 . 
     The inner surfaces  228  of the resilient arms  220  are preferably smooth to allow for easy sliding movement of the lock mechanism  200  over the recessed lateral surfaces  76 ,  102 . Each resilient arm  220  includes an integrally formed guide rail  230  which is formed on the inner surface  228 . The guide rails  230  fit within the guide slots  84  in the recessed lateral surfaces  76  of the first handle  60 . The guide rails  230  sliding within the guide slots  84  help to keep the latch member  202  aligned as it is moved between the locked and unlocked positions. Additionally, the guide rails  230  and guide slots  84  cooperate to retain the latch member  202  on the first handle  60 . During assembly, the first handle  60  is inserted between the resilient arms  220  of the latch member  202 . As the first handle  60  is inserted, the resilient arms  220  must be spread apart slightly to allow the guide rails  230  to pass over the portion of the recessed lateral surfaces  76  above the guide slot  84 . When the handle  60  is fully inserted, the guide rails  230  will align with the guide slots  84  in the recessed lateral surfaces  76 . When the guide rails  230  align with the guide slots  84 , the resilient arms  210  will return to their normal position and the guide rails  230  will engage in the guide slots  84 . This engagement securely attaches the latch member  202  to the upper handle  60 . 
     The catch elements  240  comprise small triangular protrusions on the opposing recessed lateral surfaces  102  as seen in FIGS. 8 and 11. The catch elements  240  have a generally triangular cross-section with a substantially vertical locking surface  244  facing downward and an aligned cam surface  246  facing upward. When the blade assemblies  12 ,  14  are in the closed position and the lock mechanism  200  is pushed forward to the locked position, the lower prong  224  engages the locking surface  244  and, thus, functions as a latch element. As previously noted, when the latch member  202  is in the locked position, the catch element  240  is captured between the upper and lower prongs  222 ,  224 . To unlock the shear  10 , the latch member  202  slides rearwardly to an unlocked position so that the prongs  224  on the resilient arms  220  clear the catch elements  240  on the second handle  90 . When the latch member  202  is in the unlocked position, the spring  16  pushes the blade assemblies  12 ,  14  apart to the open position. 
     One advantage of the present invention is that the shear  10  can be closed and locked even when the locking mechanism  200  is in a locked position. For purposes of explanation, assume that the blade assemblies  12 ,  14  are pushed apart by the spring  16  to the open position and that the latch member  202  is in the forward or locked position. When the user attempts to close the shear  10 , the bottom ends of the resilient arms  220  will engage the inclined cam surfaces  246  of the catch elements  240  as seen in FIG.  11 . The cam surfaces  246  will cause the resilient arms  220  to spread apart or flex outward so that the lower prong  224  passes over the top of the catch element  240 . 
     Once the lower prong  224  passes over the catch element  240 , the resilient arms  220  return to their original undeformed condition and the lower prongs  224  engage the locking surfaces  244  of the catch elements  240 . As the resilient arms  220  return to their un-deformed condition, the user will hear an audible click informing the user that the shear  10  is securely locked in the closed position. 
     The present invention may, of course, be carried out in other specific ways than those herein set forth without departing from the spirit and essential characteristics of the invention. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.