Impact relief pressure switch for roadway vehicle detector

[57] ABSTRACT

A pressure switch is disclosed for use in a roadway vehicle detector system. The pressure switch includes a cylindrical metal case which has a diaphragm of resilient material secured on the open top thereof. The diaphragm is formed with a protruding solid bulb on the upper surface thereof. A spring assembly comprised of an outer spring with a shorter and smaller diameter inner spring nested therein is enclosed within the case with the diaphragm bulb located above the outer spring. A cable having a plurality of conductors has one of its conductors connected to the lower end of the outer spring and another of its conductors connected to an isolated conductive member centrally located on the bottom of the case. When a tire of a vehicle passes over the switch it depresses the solid bulb of the diaphragm into the case to thereby depress the outer spring and enable a contact on the end of the inner spring to close the electrical circuit between the conductors of the cable.

Primary Examiner— David Smith, Jr.

Attorney—Vernon D. Beehler et al.

Claims, 22 Drawing Figures

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PATENTEDMAR2OI973

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SHEET 1 OF 5

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PATENTE0KAR2O1973

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SHEET 2 Of 5

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PATENTEDMAR2OI973

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SHEET 3 OF 5

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PATENTEDMAR2OI973

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SHEET USE 5

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PATENTEDHAR2OI973

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SHEET 5 OF 5

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IMPACT RELIEF PRESSURE SWITCH FOR ROADWAY VEHICLE DETECTOR

This invention relates to roadway switches for use in traffic detecting and classifying systems and more particularly to an improved pressure actuated switch for use in such systems.

In conducting studies of traffic, it is highly desirable to provide a switching device across a roadway for the purpose of detecting the number and wheel types of vehicles traveling thereover. Such switching devices provide for a number of spaced individual sets of contacts extending across the lane of a roadway. Each set of contacts includes an upper contact and a lower contact. A cable comprised of a plurality of conductors extends across the lane of the roadway and each of the sets of contacts has one of its contacts connected to a common conductor of the cable and the other of its contacts connected to one of the circuit conductors of the cable. In response to the passage of a wheel of a vehicle over a set of contacts, the upper and lower contacts engage to close an electrical circuit included in electronic apparatus provided on the side of the roadway, thus providing for counting and classifying the vehicles passing over the roadway.

It should be appreciated that when such a traffic detecting system is installed on a heavily travelled roadway, the individual sets of contacts are subjected to considerable impact by the wheels of the vehicles passing thereover and the large number of actuations of the switching device can cause severe wear of the active elements such as to require continual maintenance to insure that the system operates reliably.

Accordingly, one of the objects of the present invention is to provide an improved individual switch which incorporates a set of contacts and which switch is especially useful in a traffic detecting and classifying system as desctibed above.

Another object of the present invention is to provide an improved roadway switch for use in a traffic counting and classifying system wherein the switch is simple in its construction, easy to install in the roadway, and easy to service.

Yet another object of the invention is to provide an improved roadway switch for use in a traffic counting and classifying system wherein the active elements of the switch are designed to have a long operating life.

Still another object of the invention is to provide a roadway pressure switch with a diaphragm of a resilient material such as rubber or the like formed with a protruding solid bulb on the upper surface thereof wherein the bulb serves to minimize the impact of a tire of a vehicle passing over the switch by moving down and effectively getting out of the way of the tire while also closing the contacts of the switch.

With these and other objects in view, the invention consists in the construction, arrangement, and combination of the various parts of the device, whereby the objects contemplated are attained, as hereinafter set forth, pointed out in the appended claims and illustrated in the accompanying drawings.

Referring to the drawings:

FIG. 1 illustrates a roadway vehicle detector system arrangement using the pressure switches of the present invention.

FIG. 2 is a view of one of the pressure switches of FIG. 1 installed in the roadway.

FIG. 3 is an exploded view of one embodiment of the pressure switch.

FIG. 4 is a cross-sectional view of the pressure switch taken along lines 4—4 of FIG. 2.

FIG. 5 is a top plan view of the pressure switch taken along lines 5—5 of FIG. 4.

FIG. 6 is a plan sectional view of the pressure switch taken along lines 6—6 of FIG. 4.

FIG. 7 is a side elevational view of the diaphragm in an unstressed condition.

FIG. 8 is a cross-sectional view of the pressure switch similar to that of FIG. 4 showing the tire of a vehicle passing over the switch to close the contacts thereof.

FIG. 9 is a fragmentary cross-sectional view showing how the upper surface of the lower button engages with the lower surface of the upper button when the switch is closed.

FIG. 10 shows a cross-sectional elevational view of another embodiment of the pressure switch.

FIG. 11 is a plan cross-sectional view of the pressure switch of FIG. 10 taken along lines 11—11 thereof.

FIG. 12 is a bottom, partly sectional, view of the pressure switch of FIG. 10.

FIG. 13 is a view of modified form of the spring assembly for the embodiment of FIG. 10.

FIG. 14 is a schematic electrical circuit diagram of the roadway vehicle detector system shown in FIG. 1.

FIG. 15 is a cross-sectional elevational view of another embodiment of the pressure switch.

FIG. 16 is perspective view of the spring assembly used in the embodiment of FIG. 15.

FIG. 17 is a cross-sectional elevational view of another modified form of the pressure switch.

FIG. 18 is a plan view of the pressure switch of FIG. 17 as taken along lines 18—18 thereof.

FIG. 19 is a cross-sectional elevational view showing a modified version of the embodiment of the pressure switch in FIG. 15.

FIG. 20 is a cross-sectional elevational view showing another modified version of the embodiment of the pressure switch in FIG. 15.

FIG. 21 is a plan cross-sectional view of the pressure switch of FIG. 20 as taken along lines 21—21 thereof, and

FIG. 22 is another embodiment of the pressure switch utilizing pneumatics.

Referring to FIG. 1, a perspective view is shown of a roadway vehicle detector 10 including a row of spaced pressure switches 12 connected at their bases to cable 13. The detector 10 is shown with the switches 12 in position to be inserted in respective spaced wells 14 formed across the lane of a roadway 16. A narrow slot 15 is cut between each of the wells 14. Thus to install the roadway vehicle detector 10 the individual switches 12 are lowered in their respective wells 14 with the cable 13 settling in the slots 15. Then the slots are filled with a moisture proof material to protect the cable 13. FIG. 2 shows one of the switches after being lowered in the well 14 of the roadway 16. The end of the cable 13 near the roadside is connected to a box 17 of electronic apparatus which responds to signals produced by closing one or more of the individual switches 12 in response to the wheel of a vehicle passing over the roadway to thereby provide the counting and classifying of the vehicles.

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A preferred embodiment of the switch 12 of the present invention is shown in FIGS. 3-9 of the drawings. As shown by an exploded view of the parts of the switch 12 in FIG. 3, and a cross section of the assembled switch 12 as taken along lines 4—4 in FIG. 2, each of the switches 12 includes a cylindrical metal case 19 with a central opening 20 in the bottom thereof. The upper end of the case 19, which is open, is provided with a circumferential flange 21. A number of bosses 22, preferably six, with threaded holes are equally spaced about the top of the flange. Fitted on the opening 20 on the bottom of the case 19 is an upper circular insulator 24 and a lower circular insulator 25. An upright conductive support member 23 protruding upward from the central opening 20 on the bottom of the case has a threaded lower portion which passes through the circular insulators 24 and 25. Nuts 26 and 27 on the threaded portion of the conductive support member 23 bear against the respective insulators 24 and 25 to hold the support member 23 in position on the bottom of the case 19. The conductive support member 23 may be a well known type of electrical connector that can be purchased commercially and is known as a banana plug.

Inside the case 19 is a spring type contact assembly comprised of an outer spring 30 with a smaller diameter inner spring 32 nested therein. The outer spring 30 is tapered, being wider at the bottom, and its lower end rests firmly on the inner bottom of the case 19 such as to make electrical contact therewith. The coils forming the lower portion of the inner spring 32 are positioned over the upper portion of the conductive support member 23 and are in secure electrical contact therewith. A contact button 34 is secured on the upper end of the outer spring 30 and a smaller diameter contact button 36 is secured on the upper end of the inner spring 32. The inner spring 32 is shorter than the outer spring 30 such that in its assembled position the contact button 36 is normally spaced below the contact button 34.

Fastened on the top of the case 19 is a diaphragm 38 formed of resilient material such as rubber. The diaphragm 38 is comprised of a circumferential flat portion integrally formed with a flexible web 44 connected to the lower end of a centrally positioned solid bulb 39. The bulb 39 thus protrudes upwardly from the center of the diaphragm 38. The circumferential portion of the diaphragm 38 is provided with a number of holes 37 spaced to fit over the bosses 22 on the flange 21 of the case 19. A lid 40 having a central opening 41 is provided with spaced holes 42 about the periphery thereof matching those on the circumferential portion of the diaphragm 38 such that, when the lid 40 is placed over the diaphragm with the bulb 39 protruding up through the central opening 41 thereof, cap screws 43 can be inserted through holes 42 to engage the threaded holes in the bosses 22 and thereby firmly secure the diaphragm 38 to the top of the case 19.

Referring to the showing of the assembled switch in FIG. 4, it is noted that the lower end of the bulb 39 rests on the contact button 34 on the top of outer spring 30 and that the contact button 36 on the top of inner spring 32 is spaced away from the contact button 34. The switch 12 is thus shown in its open contact position. As also shown in FIG. 4, when the switch 12 is in4 serted in well 14 in the roadway, the outer flange 21 of the case and hence the circumferential periphery of the diaphragm 38 are actually supported by the sides of the roadway 16.

In the embodiment of the switch 12 shown in FIGS. 3-9, the electrical connections to cable 13 are made inside the case 19. As shown in FIGS. 4 and 8, holes 47 are drilled through diametrically opposite lower sides of the case 19 through which cable 13 passes. Since the ¹⁰ lower end of the outer spring 30 is intended to rest firmly on the interior bottom of the case 19 so as to make electrical contact therewith, the insulated cable 13 passes over the coil 31 of the spring 30.

The portion of cable 13 within the case 19 has its in* 5 sulation removed such as to expose a number of conductors or wires which would be at least three and typically five or seven conductors. The electrical schematic circuit diagram of the system of the present invention 20 in FIG. 14 shows the seven conductors included in cable 13. One of the conductors of cable 13 is common to all of the switches 12 and this is schematically indicated as the bottom conductor 49 in FIG. 14. In the embodiment of FIGS. 3-9, the common conductor 49 25 is soldered at 45 to the inside bottom of the case 19, as shown in FIG. 6. Thus note, that for each switch 12 in FIG. 1 there will also be one conductor of the cable 13 referred to as a circuit conductor which is switched to be connected by the active element for that switch to 30 the common conductor 49. The remaining six conductors, such as 50, 51, etc. in FIG. 14, correspond to the circuit conductors of cable 13. Thus in the embodiment of FIGS. 3-9, the circuit conductor 51, for example, is connected to the center conductive support member ³⁵ 23 on which the lower portion of the coils of the inner spring 32 is firmly positioned to have electrical contact therewith. It should be clear that each of the switches 12 in FIG. 1 is connected to a different circuit conduc₄₀ tor such as 50, 51, etc. of cable 13. Thus when a tire of a vehicle passes over a particular switch 12 in FIG. 1, the closing of its contacts provides for energizing selected ones of the circuits in box 17 which are used for counting and classifying the vehicles passing over ₄₅ the switches.

FIG. 5 is a top view of the switch 12 taken on lines 5—5 in FIG. 4 showing the switch in position in the well 14 of the roadway 16 with the bulb 39 protruding above the lid 40. In order to more clearly show the 50 parts of the assembled switch 12 in FIG. 5, the lid 40 is partly broken away to reveal the underlying circumferential portion of diaphragm 38, and the diaphragm 38 is partly broken away to reveal the underlying outer flange 21 of the case 19 and the coils of the tapered 55 outer spring 30 positioned within the case 19. FIG. 6 which is a cross-sectional plan view of the assembled switch 12, as taken along lines 6—6 in FIG. 4, shows the cable 13 passing through the openings 47 on the lower sides of the case 19, and the electrical connec⁶⁰ tion of the common conductor 49 to the inner bottom of the case 19 and the circuit conductor 51 to the conductive support member 23. FIG. 6 also shows the lower portion of the tapered outer spring 3®, and the lower end of the inner spring 32 bearing on the nut 26 of support member 23.

Reference will next be made to FIG. 8 which is a cross section of the assembled switch 12 installed in the

3,721,784 roadway, similar to that in FIG. 4, but showing the bulb 39 depressed as a result of the tire S3 of a vehicle passing thereover. Thus when the bulb 39 of the diaphragm 38 is depressed by the tire 53, as shown, the contact button 34 on the upper end of the outer spring 30 moves down and engages the contact button 36 on the upper end of the inner spring 32. FIG. 9 is a fragmentary cross-sectional view showing, in greater detail, how the upper surface of the lower button 36 engages with the lower surface of the upper button 34. The top of the lower button 36 is provided with a small contact point 35 which aids in assuring that a good electrical contact is made between the buttons.

It should be noted that a significant feature of the diaphragm 38 is that the solid rounded mass of rubber which forms the bulb 39 is flexibly connected at its lower end by web 44 to the circumferential portion of the diaphragm 38, as particularly shown in FIGS. 4 and 8. As a result of this flexible connection, when the bulb 39 receives the impact of the tire 53 it effectively disappears, that is, the bulb is readily depressed into the case 19. Accordingly, the bulb 39 of the switch 12 can be hit very hard by the tire 53 and the impact is dissapated to some extent but is largely avoided by the fact that the bulb 39 moves down into the case 19 and gets out of the way of the tire. This is a highly advantageous feature since it reduces the strain of the impact on the bulb 39 of diaphragm 38 resulting in a longer operating life of the switch.

Another important feature of the embodiment of the switching FIGS. 3-9 is the accessability of the active elements of the switch for maintenance purposes. It should be noted, as shown in FIG. 4, that the screws 43 may be removed in order to take off the lid 40 and diaphragm 38. The outer spring 30 can then be removed from the insulated cable 13 by rotating or unscrewing it relative thereto. Then the inner spring 32 is simply lifted out. It is further noted that the diaphragm 38 extending across and secured to the top of the case 19 provides for the active contact elements therein to be rendered weatherproof.

Next to be described is the embodiment of the switch shown in FIGS. 10-13. This switch, similarly to the switch shown in FIG. 4, is provided with a case having a diaphragm 38 with a bulb 39 which protrudes upwardly through the central opening 41 of lid 40 therefor. This switch differs from the switch shown in FIG. 4 primarily by the fact that the electrical connections between the conductors of cable 13 and the elements of the switch are made outside the case which is here designated by reference numeral 56. Thus in FIG. 10, a potting compound 58 underneath the case 56 encapsulates the cable 13 and the connections of the conductors to the elements of the switch. The potting compound 58 is permanently self-bonded to the underside of the case 56. A conductive support member 61, similar to the banana plug support member 23 shown in FIG. 3, protrudes upwardly through an insulator 62 provided on an opening 60 in the bottom of case 56. This insulator 62 is simply a section of rubber hose which is stretched around a nut 63 on the base of the support member 61. Thus, when the lower end of support member 61 is forced upward through the opening 60 in the bottom of the case 56, the edge of the opening in the case creates its own groove in the rubber hose.

The spring type contact assembly in FIG. 10 includes an outer spring 65 and an inner spring 66, neither or which is tapered. A cylindrical hard rubber grommet 67 provided with a central opening is used as a structural base for holding the lower ends of the two springs at a desired relative position. Thus, as shown in FIG. 11 which is a cross-sectional view of FIG. 10 taken along lines 11—11 thereof, the inner spring 66 slips inside and the outer spring 65 slips over the outside of grommet 67. A rubber glue 73 or other similar bonding agent is then used to secure the coils of the springs to the sides of the grommet 67. Contact buttons 68 and 69 are secured to the tops of springs 65 and 66, respectively. The spring assembly is positioned in the case 56 with the coils on the lower portion of the inner spring 66 snugly fitting on the lower portions of the support member 61 so that a good electrical contact is made between the lower end of the inner spring 66 and the member 61. Also note that the lower end of the outer spring 65 rests on the interior bottom surface of the case 56 so as to make an electrical contact therewith. As shown by the bottom view of the switch in FIG. 12, as taken along lines 12—12 of FIG. 10, the common conductor 49 of the cable 13 is soldered at point 70 to the outside bottom of the case 56 and one of the circuit conductors such as circuit conductor 51 of the cable 13 is held by a lower bolt 71 against the nut 63 so as to make electrical contact with conductive support member 61. It should now be clearly evident that when the bulb 39 of diaphragm 38 is depressed into case 56, the top contact button 68 on outer spring 65 is pushed down and engages the smaller contact button 69 on the top of the inner spring 66 such as to close the circuit between the common conductor 49 and the circuit conductor 51 of cable 13.

FIG. 13 is a separate view of a spring contact assembly very similar to the one used in FIG. 10 in that a grommet 67 having a central opening is used to support the lower ends of the outer spring 65 and the inner spring 66 relative to each other. However, the contact elements on the top of these springs are not buttons but rather plain flat discs 68a and 69a that are attached to the upper ends of the respective springs 65 and 66 by spot welding, for example.

It should be noted that inasmuch as the embodiment of the switch 12 in FIG. 10-12 has its electrical connections to the conductors of cable 13 made externally of the case 56, the ease of access from the top of the roadway 16 is even better than the embodiment of the switch shown in FIGS. 3-9 because it is not necessary to unscrew the outer spring 65 from the cable 13. The whole spring contact assembly lifts out as one piece. Accordingly, it is merely necessary to take off the lid 40 and the diaphragm 38 and then remove the entire spring assembly.

Next to be described in connection with FIGS. 15 and 16 is another embodiment of the switch 12 which uses a different spring contact assembly and arrangement for electrically connecting the conductors of cable 13 to the contacts of the switch. Thus FIG. 15 uses a switch contact assembly in which an inner spring 74 and an outer spring 75 are integrally formed of a single wire construction. As shown in FIG. 16 the upper end of the outer spring 75 extends inwardly to form the upper end of the inner spring 74. The inner spring 74

3,721,784 tapers from the top to bottom being narrowest at the bottom. Inner spring 74 is shorter than outer spring 75 such that the lower end 81 of the inner spring 74 is normally spaced above the bottom of outer spring 75. The lower coil of the outer spring 75 rests on a cylindrical base 78 formed of an insulating material, and the lower wire end 79 (FIG. 15) of the outer spring 75 is bent over at a right angle and passes down through the base 78. When the spring contact assembly of FIG. 16 is positioned in case 76 to form a complete switch, as shown in FIG. 15, the wire end 79 of the outer spring passes through a central opening 72 in the bottom of case 76 and is connected below the case 76 to the common conductor 49 of the cable 13. Base 78 is provided with a center contact 77 in the form of the head of a screw 80. Screw 80 is supported only by the insulating base 78 and its lower protruding end is connected to one of the circuit conductors of the cable 13, such as conductor 51, by a nut 82. It should be now clear that when the switch 12 shown in FIG. 15 is in its open contact position, the bulb 39 held on the top of case 76 rests on the common upper end 84 of the composite spring assembly, and the lower end 81 of the inner spring 74 is spaced away from the center contact 77. Then when the bulb 39 is depressed by the tire of a vehicle passing thereover, the spring assembly is depressed causing the lower end 81 of the inner spring 74 to make contact with the fixed center contact 77, thus connecting circuit conductor 51 to the common conductor 48 of cable 13. It should be noted that only one of the contacts in this embodiment is movable, the contact formed by the lower end 81 of inner spring 74. The other contact 77 being fixed adds to the reliability of the switch.

FIG. 19 shows a modification of the switch of FIG. 15 which differs primarily in that the spring contact assembly is formed of a separate outer spring 75α and inner spring 74α. The upper ends of both springs 75α and 74α are secured to a single contact disc 84α by spot welding, for example. As in FIG. 15, the lower end 79α of the wire forming the outer spring 75α is bent at a right angle and passes through base 78 which is of a cylindrical configuration and made of an insulating material such as a resinous potting compound. The lower end 79α of the outer spring 75α passes through one side of opening 72 in the bottom of the case 76 and is connected to the common conductor 49 of the cable 13. When both springs 74α and 75α are fully extended, the outer spring 75α is significantly longer than the inner spring 74α. Therefore, the condition of the rest of the switch, that is, its open contact condition, is as shown in FIG. 19. When a vehicle tire travels over the switch, the diaphragm bulb 39 is depressed, depressing the common disc 84α at the top of the spring contact assembly, and this causes the lower end 81α of the inner spring 75α to contact the center contact 77 in the form of the head of a screw 80 in the center of the bottom of the case.

FIG. 20 is another form of the switch similar to that in FIGS. 15 and 19 in that the upper ends of both an outer spring 86 and an inner spring 87 is provided with a common top button 89. The outer spring 86 tapers from the bottom to top, being widest at the bottom. In addition, outer spring 86 is wide enough at the bottom to occupy the full width of the metal case 90. In the switch ofFIG. 20, the bottom of outer spring 86 makes an electrical contact with the inner bottom of the case 90 and the common conductor 49 (not shown) is connected to the bottom of the case in a manner similar to ⁵ that shown in FIG. 12. The bottom of the inner spring 87 has a contact button 92 which is spaced above the lower center contact 94 in the form of the head of a screw 95 which is supported in the central opening on the bottom of case 90 by an insulator 91. Similarly to ¹⁰ FIG. 10, a potting compound 58α underneath the case 90 encapsulates the cable 13 and the connections thereto. FIG. 21, which is a cross-sectional view of the switch as taken along lines 21—21 of FIG. 20 shows the 15 relative positions of springs 86 and 87 and contact button 92 on the lower end of the inner spring 87.

FIGS. 17 and 18 show another configuration of the spring contact assembly and the connections provided therefor to the conductors of cable 13. Thus, as shown, 20 an insulating base 96 formed of a block of resin is used and the lower coil of both an inner spring 97 and an outer spring 98 rest on the base 96. A contact disc 101 is spot welded to the top of outer spring 98. The top coil 93 of the inner spring 97 forms a contact therefor 25 and is spaced away from the disc 101. The lower end 99 of the wire forming inner spring 97 is bent at a right angle and passes through the center of the base 96. Similarly the lower end 100 of the wire forming outer ₃₀ spring 98 is bent at a right angle and passes through the outer portion of base 96. Both ends 99 and 100 of the springs pass through the large opening 72 in the bottom of the case 76 and are connected externally to the circuit conductor 51 and common conductor 49 of the 35 cable 13. FIG. 18 is a cross-sectional view taken along lines 18—18 of FIG. 17 which shows the inner spring 97 and the outer spring 98 resting on the insulating base 96 with their wire ends 99 and 100 bent to pass through the base 96.

it should be noted that with regard to all of the embodiments of the switch 12, except the form shown in FIGS. 15 and 16, the top button such as the button 89 in FIG. 20, may if desired be bonded to the lower surface of the bulb 39 on diaphragm 38. If this is done, the ⁴⁵ purpose is to avoid any mechanical instability of the spring contact assembly in the lateral direction. However, a better way to avoid that instability is by using an outer spring whose width at the bottom is substantially ₅₀ the full width of the case, such as shown by outer spring 86 in FIG. 20, for example.

Thus, in general, the spring contact assembly of the switch of the present invention connects two springs, an outer spring and an inner spring with the inner 55 spring being shorter, and the two springs being mechanically supported relative to each other either at their tops or at their bottoms. Form an electrical point of view, either the inner spring is in firm electrical contact with the outer spring at their upper ends, as shown ⁶⁰ in FIGS. 15,19 and 20, in which event the lower end of the inner spring makes switching engagement when depressed with a fixed contact at the bottom center of the case, or else the lower end of the inner spring is in ₆₅ fixed contact with the bottom center of the case and its upper end makes switching engagement with the contact on the upper end of the outer spring, as shown in FIGS. 2,10, and 17, for example.

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Referring next to FIG. 22, it should be noted that the same diaphragm 38 of the present invention may be used with a modified case 102 for a displaced volume type of roadway vehicle switch. In this version of the switch the diaphragm 38 is held onto the top of the flange of case 102 by lid 40 such that the case is substantially air-tight. An air tube 103 leading out of the side of the closed case 102 is then connected to a data recording unit 105. By providing for the air system so . provided to be sealed on all ends, the depressing of the bulb 39 on diaphragm 38 down into the case 102 by the tire of a vehicle passing over the switch creates an impact in case 102 which when transmitted by tube 103 to unit 105 operates a sensing switch 106 therein which is used for counting the number of vehicles passing over the roadway switch, for example.

From the above discription it will be apparent that there is thus provided switching devices of the character described and possessing the particular features of advantages before enumerated as desirable but which obviously are susceptable of modification in their form, proportion, detailed construction and arrangement of parts without departing from the principle involved or sacrificing any of their advantages.

While in order to comply with the statutes, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown but the means and construction herein disclosed comprise the preferred forms of several modes of putting the invention into effect and the invention is therefore, claimed in any of its forms or modifications within the ligitimate and valid scope of the appended claims.