Abstract:
A door check wherein a housing is affixed to the pivotable panel and a guide rail is affixed to the frame of a door. The housing contains a shaft which is rigidly connected with one end of an arm the other end of which is slidably guided by the rail. The shaft carries a disc cam having two asymmetric sections one of which is tracked by a spring-biased follower tending to return the panel to its closed position and the other of which is tracked by the piston of a damper which yieldably opposes the movement of the panel back to its closed position. The configuration of the two cam sections is selected with a view to allow for a reduction of the resistance which the follower offers to opening of the door shortly after the panel leaves its closed position as well as to ensure that the damper can operate independently of the follower and vice versa.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to door closers or door checks in general, and more particularly to improvements in door checks of the type wherein a shaft is caused to rotate in response to pivoting of a door panel to open or closed position under the action of an arm one end portion of which is non-rotatably affixed to the shaft and the other end portion of which is slidable along a guide mounted on the door frame if the shaft is mounted on the panel or vice versa. 
     In door checks of the above outlined character, the panel is pivoted to open position against the opposition of resilient means serving to return the panel to the closed position as soon as a person, a vehicle or a holding device ceases to apply a force which causes the panel to move toward its fully open position or to dwell in the open or partly open position. Moreover, such door checks comprise suitable dampers which ensure a more or less gradual closing of the panel, i.e., the damper prevents the panel from slamming against the frame of a door under the action of the resilient means. The just described door checks are preferred under circumstances when the appearance is important and/or when the available space does not allow for the installation of other types of door checks, especially those wherein the shaft is rotated by a linkage normally including a first link which is non-rotatably connected to the shaft and a second link which is articulately connected to the first link and to a fixed pivot member on the panel or on the door frame. However, the presently known door checks of the type wherein the shaft is connected with an arm which is slidable along a guide rail or the like exhibit a number of serious drawbacks so that their popularity is rather limited. One of the most serious drawbacks of such door checks is that the closing force is often a small fraction of the closing force of door checks which employ a linkage between the rotatable spring-biased shaft and the door frame or door panel. The difference between the closing forces of the two types of door checks can be as high as 60 percent. An undesirable consequence of the relatively small closing force of door checks with a single arm is that the magnitude of the force which is required to pivot a door panel from its closed position increases during the initial stage of pivoting through an undesirably large angle (up to and even in excess of 60 degrees). This is in contrast with the door checks wherein the shaft is connected to a linkage and the force with which the panel must be pivoted from open position decreases from a maximum value to a much lower value upon completion of an angular movement through a few degrees and thereupon decreases gradually to reach a constant value (which is much smaller than the maximum value) not later than when the panel has been caused to pivot through an angle of approximately 50 degrees. 
     It has been found that presently known door checks wherein the shaft is connected with a single arm offer a very pronounced resistance to movement of the door panel from its closed position through an excessive angle which causes discomfort to the person attempting to move the panel to its open position, even to a person who is accustomed to encounter a rather pronounced resistance to such movement but only during a small initial stage. This is the reason for the lack of popularity of presently known single-arm type door checks in spite of the fact that their appearance is much more pleasing to the eye than that of the door checks wherein the shaft is connected with several links and none of the links are slidable along a guide rail or the like. As a rule, door checks with a single arm are presently used only on doors wherein the required closing force is small or negligible. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     An object of the invention is to provide a novel and improved door check of the type wherein the shaft is connected to and is caused to turn by a single arm which is slidable along a guide on the stationary part or on the pivotable part of a door. 
     Another object of the invention is to provide a door check of the just outlined character which is of eye-pleasing appearance and whose performance is at least as satisfactory as that of door checks wherein the shaft is rotated by a set of interconnected links. 
     A further object of the invention is to provide novel and improved means for transmitting torque to the shaft of the above outlined door check. 
     An additional object of the invention is to provide a door check with a novel and improved damper. 
     Still another object of the invention is to provide a door check wherein the resistance to opening of a door panel and the force with which the panel is closed can be regulated within a wide range in a simple and efficient way. 
     A further object of the invention is to provide novel and improved cam means for use in the above outlined door check. 
     An additional object of the invention is to provide a novel and improved method of regulating the forces which oppose the opening of a door panel and which cause the panel to reassume its closed position. 
     A further object of the invention is to provide a simple, compact and eye-pleasing door check which can be used as a superior substitute for heretofore known door checks wherein the shaft is connected to a single arm or to one link of a set of articulately connected links. 
     The invention resides in the provision of a door check which comprises a first component connectable to the frame of a door and a second component connectable to the pivotable panel of such door. One of the two components comprises elongated guide means and the other component comprises an arm having a first end portion reciprocable along the guide means in response to movements of the panel between open and closed positions, a shaft which is non-rotatably connected with the second end portion of the arm so that it turns about its own axis in response to movements of the panel with reference to the frame, cam means provided on the shaft and having preferably different first and second sections, means for transmitting to the first section of the cam means torque so as to urge the shaft to rotate in a panel-closing direction, and damper means in contact with the second section of the cam means and serving to yieldably oppose rotation of the shaft in the panel-closing direction. 
     In accordance with a presently preferred embodiment of the invention, the cam means comprises a disc cam (e.g., a heart cam) and the torque transmitting means comprises a follower and means for biasing the follower against the first section of the cam so that the follower tends to turn the shaft in the panel-closing direction. The damper means can comprise a fluid-operated piston and a cylinder which reciprocably receives the piston. 
     The just mentioned cylinder can form part of a housing which contains bearings for the shaft and further accommodates the torque transmitting as well as the damper means. In accordance with a feature of the invention, the follower of the torque transmitting means and the piston of the damper means are movable in the housing independently of each other. The torque transmitting means (and more particularly the follower of the torque transmitting means) can comprise a first rotary element (e.g., a roller or wheel) which tracks the first section of the cam means and the damper means (and more specifically the aforementioned piston) preferably comprises or carries a discrete second rotary element (e.g., a roller or wheel) which tracks the second section of the cam means. Energy storing means is preferably provided to urge the damper means (i.e., the rotary element of the piston) against the cam means with a predetermined force and in a sense to effect an opening of the panel. The torque transmitting means comprises means for biasing the follower (i.e., the rotary element of the follower) against the first section of the cam means with a second force which can greatly exceed the predetermined force of the energy storing means. This ensures that the energy storing means does not interfere with the operation of the torque transmitting means but merely serves to maintain the rotary element of or on the piston in contact with the second section of the cam means. 
     The two sections of the cam means are or can be asymmetrical to each other with reference to a plane which includes the axis of the shaft, i.e., the throw of one of the sections can deviate from the throw of the other section. 
     The axis of the rotary element on the piston of the damper means is preferably disposed at one side of the plane which includes the axes of the piston and the shaft. The same preferably applies for the axis of the rotary element on the follower, i.e., such axis is preferably located (at least slightly) at one side of the plane including the axes of the shaft and that (preferably cylindrical) portion of the housing wherein the follower is reciprocable axially toward and away from the shaft. 
     The improved door check preferably further comprises means for adjusting the bias of the means (e.g., one or more helical springs) which biases the follower toward the cam means. The adjusting means can comprise a retainer for the spring or springs of the biasing means and means for moving the retainer radially of the shaft in the interior of the housing so as to increase or reduce the initial stressing of the spring or springs. 
     The guide means of the one component can comprise an elongated rail which can be affixed to the frame, i.e., the shaft, the housing, the damper means and the torque transmitting means are then mounted on the pivotable panel of the door. 
     The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The improved door check itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain specific embodiments with reference to the accompanying drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a fragmentary perspective view of a door with the panel shown in partly open position and further showing a door check which embodies one form of the invention; 
     FIG. 2 is a greatly enlarged horizontal sectional view of the major part of one component of the door check substantially as seen in the direction of arrows from the line II--II of FIG. 1; and 
     FIG. 3 is a vertical sectional view as seen in the direction of arrows from the line III--III of FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the upper portion of a door including a frame 11 and a panel 10 which is pivotable with reference to the frame 11 between open and closed positions about the common axis of several vertical hinges of which only one can be seen in the drawing. The panel 10 is shown in a partly open position; as a rule, this panel is pivotable through an angle of approximately 180 degrees between a closed and a fully open position. 
     The improved door check comprises two components one of which includes an elongated guide 15 in the form of a hollow rail having an elongated slot and being installed on the upper horizontal member of the frame 11 close to the pivot axis for the panel 10. The other component of the improved door check comprises a substantially horizontal arm 14 one end portion of which extends through the slot and into the interior of the hollow rail 15 where it carries a roller or another suitable follower arranged to roll or slide back and forth in response to pivoting of the panel 10 between its closed and open positions. The follower on that end portion of the arm 14 which extends into the rail 15 is remote from the pivot axis of the panel 10 when the latter is held in the closed position and such follower advances toward the pivot axis in response to movement of the panel 10 toward its fully open position. The second component of the improved door check further comprises an elongated box-shaped unit 12 which is mounted on the upper portion of the panel 10 and includes a vertical shaft 13 whose upper end portion constitutes a stub 17 (see FIG. 3) which is non-rotatably connected to the other end portion of the arm 14. Thus, the shaft 13 is compelled to rotate in an elongated housing or case 16 of the unit 12 when the panel 10 is caused to pivot with reference to the frame 11 of the door. 
     The housing 16 contains a supply of a liquid medium, preferably oil, and the shaft 13 is mounted substantially or exactly midway between the longitudinal ends of the housing. As can be seen in FIG. 3, the top wall of the housing 16 has a tapped bore for an externally threaded annular holder 19 which surrounds an antifriction bearing 18 for the adjacent portion of the shaft 13. The stub 17 at the upper end of the shaft 13 has a polygonal or other suitable outline to facilitate the establishment of a rotation-preventing connection with the corresponding end portion of the arm 14. The lower end portion of the shaft 13 constitutes a second stub 17 which also extends from the housing 16 and can be used for attachment to the respective end portion of an arm 14 if the housing 16 is to be attached to a door in a position turned through 180 degrees with the position shown in FIG. 1 or if the door check employs two arms. The lower wall of the housing 16 has a recess for a portion of a second antifriction bearing 20 which surrounds the lower portion of the shaft 13 in the housing. Suitable seals (e.g., O-rings), of which only two are specifically identified in FIG. 3 by reference characters 21, are provided in the housing 16 in the regions of the end portions of the shaft 13 to prevent escape of the confined liquid medium. 
     The median portion of the shaft 13 is connected or made integral with a disc-shaped cam 22 which, as shown in FIG. 2, can constitute or resemble a heart cam. The circumferentially extending face of the cam 22 comprises a first section 23, 24 which is tracked by a first rotary element in the form of a roller 26 mounted on a vertical pivot member 27 parallel to the shaft 13, and a second section 25 which is tracked by a rotary follower element in the form of a roller 35 mounted on a pivot member 36 which is also parallel to the shaft 13. The portion 23 of the section 23, 24 has a concave shape and defines a seat or socket for a portion of the roller 26 when the cam 22 and its shaft 13 assume the angular positions of FIG. 2 in which the panel 10 is assumed to be held in the closed position. The portion 24 of the first section 23, 24 of the face on the cam 22 is tracked by the roller 26 as soon as the panel 10 is pivoted from its closed position, and the section 25 is tracked by the roller 35 whenever the panel 10 is caused to leave its closed position. In FIG. 2, the roller 35 contacts the tip of a lobe on the cam 22 substantially but not exactly diametrically opposite the socket 23. The sections 23, 24 and 25 are asymmetrical to each other with reference to a plane which includes the axis of the shaft 13, i.e., the throw of the section 23, 24 for the roller 26 is different from the throw of the section 25 for the roller 35. 
     The roller 26 and its pivot member 27 constitute two elements of a follower which is mounted on a reciprocable support or plunger 28. The follower and the plunger form part of a torque transmitting device which further includes two coaxial helical springs 29 and 30 serving to urge the roller 26 against the section 23, 24 of the cam face for the purpose of urging the panel 10 toward the closed position, namely in a clockwise direction, as viewed in FIG. 2. That portion of the housing 16 which reciprocably receives the plunger 28 can be said to constitute a cylinder of the aforementioned torque transmitting device, and the axis of the pivot member 27 for the roller 26 is located at one side of the plane which is common to the axes of such cylinder and the shaft 13. In the embodiment of FIGS. 1 to 3, the axis of the pivot member 27 is located slightly below the just mentioned plane, as viewed in FIG. 2. 
     The means for adjusting the bias of the resilient means including the helical springs 29 and 30 comprises a disc-shaped retainer 31 which is reciprocable in the housing 16 behind the rearmost convolutions of the springs 29, 30 and means for moving the retainer 31 in the housing 16 toward or away from the shaft 13. Such moving means comprises a feed screw 33 which meshes with the central portion of the retainer 31, a stopper or plug 34 which is in mesh with the respective end portion of the housing 16, and a slotted or recessed motion transmitting element 32 which is rotatable in but cannot move axially of the plug 34 and is non-rotatably connected with the adjacent end portion of the feed screw 33. The recess in the exposed end face of the element 32 can receive the working end of a screw driver or the like in order to change the axial position of the retainer 31 and to thereby increase or reduce the bias of the springs 29, 30 upon the plunger 28, i.e., upon the roller 26. In the illustrated embodiment of the improved door check, the biasing means for the plunger 28 comprises a very strong helical spring 29 which operates between the retainer 31 and the rear end face of the plunger 28, and a much weaker helical spring 30 which is surrounded by the spring 29 and operates between the retainer 31 and a washer which is inserted into a counterbore of and bears against an internal shoulder in the plunger 28. Suitable sealing elements are provided to prevent the escape of confined liquid medium from the housing 16 in the region of the plug 34 and motion transmitting element 32. 
     The pivot member 36 for the roller 35 is mounted at the front end of a piston 37 which forms part of a damper. The latter further includes that portion of the housing 16 in which the piston 37 is reciprocable, i.e., such portion of the housing 16 constitutes a cylinder for the piston 37. The chamber of the cylinder for the piston 37 is shown at 38; this chamber is adjacent to the left-hand end wall of the housing 16. The chamber 38 is normally sealed from the space which accommodates the central portion of the shaft 13, the cam 22 on the shaft 13 and the torque transmitting device including the plunger 28, roller 26, shaft 27 and helical springs 29, 30. The internal surface of the housing 16 is formed with a circumferentially extending groove 39 which communicates with the chamber 38 and is connected with the space receiving the cam 22 by a channel which is machined into the housing 16 and includes a first radially extending portion 40 in communication with the groove 39, a second radially extending portion 42 in communication with the space around the cam 22 and an axially parallel portion 41 connecting the portions 40, 42 and containing a preferably adjustable flow restrictor 43. The flow restrictor 43 produces the damping action when the shaft 13 is caused to turn clockwise back toward the angular position which is shown in FIGS. 1 and 2 and thereby causes the cam 22 to push the roller 35 and the piston 37 to the left, as viewed in FIGS. 2 or 3, so that the liquid medium which fills the chamber 38 is expelled via channel 40-42 and back into the space around the cam 22. 
     The piston 37 resembles a cup and its bottom wall 45 and its interior receives the major portion of an energy storing device 44 in the form of a helical spring which reacts against the left-hand end wall of the housing 16 and bears against the bottom wall 45 to maintain the roller 35 in contact with the respective section 25 of the face on the cam 22. The bottom wall 45 of the piston 37 contains a check valve 46 which opens when the pressure in the space around the cam 22 exceeds the pressure in the chamber 38. The bottom wall 45 is further formed with a substantially centrally located tapped bore 47 for a removable safety relief valve 48 wherein a spring-biased valving element opens when the pressure in the chamber 38 exceeds the pressure in the space around the cam 22. 
     The bias of the helical spring 44 is a fraction of the combined bias of the springs 29 and 30 which together constitute the means for biasing the roller 26 against the section 23, 24 of the face on the cam 22. All that counts is to ensure that the spring 44 is at least barely able to maintain the roller 35 in contact with the section 25 of the cam 22 when the shaft 13 is rotated in response to movement of the panel 10 from its closed position. 
     As mentioned above, FIGS. 2 and 3 show the shaft 13 in that angular position in which the panel 10 is closed. As soon as a person begins to pivot the panel 10 from the closed position, the arm 14 causes the shaft 13 to turn in a counterclockwise direction as indicated in FIG. 2 by the arrow 49. During the initial stage of such angular movement through a few degrees, the roller 26 is expelled from the concave part 23 of the section 23, 24 of the face on the cam 22 whereby the person pivoting the panel 10 from the closed position encounters a rather substantial resistance to such pivotal movement because the plunger 28 is caused to cover a substantial distance against the opposition of the springs 29, 30 in response to relatively small angular displacement of the panel 10 and shaft 13. The roller 26 thereupon contacts the gradually sloping portion 24 of the cam face section 23, 24 so that the rate of axial displacement of the plunger 28 in a direction away from the shaft 13 increases more gradually which is felt by the person pivoting the panel 10 toward open position as a relaxation of the resistance. In other words, the panel 10 must be pivoted through a relatively large angle in order to enable the cam 22 to shift the plunger 28 through the same distance as during the initial stage of opening movement when the roller 26 was in contact with the portion 23 of the cam face section 23, 24. It will be noted that, by the simple expedient of altering the configuration (throw) of the cam face section 24, the manufacturer can select the resistance which the panel 10 offers to movement toward the fully open position and also the difference between the resistance to the initial stage and the resistance to the next-following major stage of movement of the panel 10 from the closed to the fully open position. A first important consideration in the selection of the slope of the portion 24 is the comfort to the user of the door and a second important consideration is the reliability of the closing action of the improved door check. 
     While the roller 26 tracks the portion 24 of the section 23, 24 of the cam face, i.e., while the plunger 28 continues to move toward the retainer 31 against the opposition of the helical springs 29 and 30, the roller 35 tracks the second section 25 of the cam face under the action of the helical spring 44. The roller 35 then rotates in a clockwise direction because the cam 22 turns in the direction which is indicated by the arrow 49. The check valve 46 opens automatically because the volume of the chamber 38 increases and the liquid medium is free to flow through the bottom wall 45 of the piston 37 and into the chamber 38. 
     When the user of the door has pivoted the panel 10 through an angle which is required or sufficient for convenient passage through the door, the panel 10 is released so that the springs 29 and 30 can take over and push the plunger 28 in a direction toward the shaft 13 to thereby turn the cam 22 in a clockwise direction, as viewed in FIG. 2 and back toward the illustrated angular position. Thus, the panel 10 pivots back toward the closed position. The section 25 of the cam face then moves the roller 35 away from the shaft 13 so that the piston 37 expels liquid medium from the chamber 38 via groove 39 and channel 40-42 whereby the flow restrictor 43 throttles the flow of such liquid medium from the chamber 38 into the space around the cam 22. The relatively weak coil spring 44 is caused to store energy to thus ensure that it can hold the roller 35 in contact with the section 25 of the cam face when the panel 10 is again pivoted from its closed position. 
     The disc cam 22 can be replaced with a different cam without departing from the spirit of the invention. For example, the cam can have a groove or track for the rollers 26 and 35. Also, the axis of the piston 37 need not coincide with the axis of plunger 28. The springs 29, 30 can be replaced with or used in addition to a package of dished springs, the housing 16 can be mounted on the frame 11 (in which case each of the two stubs 17 can be connected to a discrete arm 14), the flow restrictor 43 can be installed in the bottom wall 45 of the piston 37, the bias adjusting means can comprise a discrete adjuster for each of the springs 29 and 30, and the cam 22 can be replaced with two cams one of which is tracked by the roller 26 and the other of which is tracked by the roller 35. 
     An important advantage of the improved door check is that the resistance which the panel 10 (and hence the shaft 13) offers to movement from closed position can be selected practically at will, not only during the initial stage of pivotal movement of the panel 10 from its closed position but also during the major part of the entire angular movement between open and closed positions. Moreover, the manufacturer can select the variations of resistance to movement of the panel 10 to open position during the aforementioned major part of such movement by the simple expedient of adequately selecting the configuration or throw of the portion 24 of that section (23, 24) of the face on the cam 22 which is tracked by the roller 26 while the shaft 13 performs the major part of its angular movement in the counterclockwise direction, as viewed in FIG. 2. Still further, by properly selecting the configuration of the section 25 of the cam face, the manufacturer can regulate the action of the damper which yieldably opposes a movement of the panel 10 back to its closed position. 
     The cam 22 (or an analogous cam) replaces the customary rack and pinion drive which is used in many conventional door checks and wherein a portion of the rack constitutes a piston which is reciprocable in its cylinder to thereby rotate the pinion or vice versa. A rack and pinion drive does not allow for any changes in the resistance which the panel offers to pivotal movement during different stages of such movement. Thus, were the plunger 28 replaced with a rack meshing with a pinion on the shaft 13, each and every movement of the shaft through a given angle would entail or require a fixed axial displacement of the rack. This would prevent the door check from offering a different resistance to each of a series of different stages of angular movement of the door panel from its closed to its fully open position. The improved door check renders it possible to vary the angle of attack of the roller 26 upon the face of the cam 22 and the extent of axial movement of the plunger 28 in response to angular displacement of the cam 22 so as to obtain a practically infinite number of different characteristic curves for the torque transmitting device even though the helical springs 29, 30 exhibit linear characteristics. The relationship between the angle of attack of the roller 26 and the axial displacement of the plunger 28 is preferably selected in such a way that the door check offers a rather pronounced initial resistance to movement of the panel 10 from its closed position (i.e., the springs 29, 30 exert upon the panel a rather pronounced force during the last stage of movement toward closed position) and that the resistance of the panel to movement from closed position decreases abruptly or at least substantially as soon as the panel has completed a relatively small angular movement (e.g., through an angle of approximately two degrees) from its fully closed position. The resistance to further pivoting of the panel 10 to fully open position can remain constant or can even decrease or increase during certain stages of angular movement from 2 degrees to approximately 180 degrees, depending upon the maximum angle through which the panel must or can turn between its closed and fully open positions. All this is accomplished in a surprisingly simple and effective way, i.e., by the expedient of selecting a cam or a pair of cams whose throw varies in dependency on the desired resistance which the shaft 13 is to offer to rotation during pivoting of the panel between open and closed positions. As mentioned above, the damping action can be regulated in an equally simple and effective way by the expedient of properly selecting the throw of the section 25 of the face on the cam 22. 
     An important advantage of the feature that the torque transmitting device including the parts 26-30 and the damper means including the parts 35-37 are two discrete units, which are movable in the housing 16 independently of one another, is that the damping action need not vary as a function of the torque transmitting action and/or vice versa, i.e., that the roller 35 of the damper can track the section 25 of the cam face independently of the roller 26 which tracks the section 23, 24. Such arrangement further improves the efficiency of the door check and ensures a less pronounced and more uniform wear upon the face of the cam 22. 
     The feature that the spring 44 is weaker than the springs 29, 30 for the plunger 28 ensures that the roller 35 invariably contacts the section 25 of the face on the cam 22 but does not interfere with or adversely influence the action of the torque transmitting device including the plunger 28 and the springs 29, 30. 
     As mentioned above, the sections 23, 24 and 25 of the face on the cam 22 are asymmetrical to each other with reference to a plane which includes the axis of the shaft 13 and the axis of the follower 28, i.e., the throw of the section 23, 24 is different from that of the section 25. This is the presently preferred configuration of the cam face because it allows for different axial displacements of the plunger 28 and piston 37 in response to a given angular displacement of the cam 22. The lack of symmetry can exist between certain parts of the two sections of the cam or during each and every stage of angular movement of the panel 10 between its closed and fully open positions. The placing of the roller 35 at least slightly off center (i.e., to one side of the plane which includes the axes of the piston 37 and shaft 13) is often desirable and advantageous because this renders it possible to more accurately relate the axial positions of the piston 37 to the angular positions of the cam 22. It was further found that the aforediscussed positioning of the axis of the roller 26 at one side of the plane including the axes of the plunger 28 and shaft 13 facilitates the actuation of the door check. The distance between the axis of the roller 26 and the just mentioned plane can be small or very small. 
     The provision of the axially adjustable retainer 31 enhances the versatility of the improved door check because it allows for a change in the combined bias of the springs 29 and 30, i.e., for a change in the magnitude of the force with which the springs 29, 30 resist manual pivoting of the panel 10 or with which such springs force the panel to reassume its closed position. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the appended claims.