US3772490A

US3772490A - Force sensing device with adjustable mechanical amplifier

Info

Publication number: US3772490A
Application number: US00248223A
Authority: US
Inventors: P Thordarson
Original assignee: Individual
Current assignee: RAINIER NATIONAL BANK
Priority date: 1972-04-27
Filing date: 1972-04-27
Publication date: 1973-11-13
Anticipated expiration: 1990-11-13

Abstract

A force sensing device operable as a pressure switch or other triggering device or regulator includes a mechanical amplifier and deamplifier which translates motion created by changes in the applied force into larger or smaller movements for operating an output indicator or switch. An actuator arm mounted on a movable fulcrum translates motion induced by the applied force to the output indicator or switch, which responds to motion of the actuator arm in a manner determined by the position of the fulcrum. When employed as a pressure switch, for example, the shiftable fulcrum permits adjustment of the ''''deadband'''' of the switch, while other adjustments determine the position of the deadband on a pressure scale. The device is operable as a differential pressure switch or as a temperature regulator as well.

Description

United States Patent [191 Thordarson [111 3,772,490 Nov. 13, 1973 FORCE SENSING DEVICE WITH ADJUSTABLE MECHANICAL AMPLIFIER [76] Inventor: Petur Thordarson, 13700 42nd Pl.

NE, Seattle, Wash. 98125 221 Filed: Apr. 27, 1972 211 App]. No.: 248,223

[52] U.S. Cl 200/153 H, 74/522, 200/81 H, 200/83 S, 200/83 D [51] Int. Cl. H0111 35/34, I-IOlh 3/46- [58] Field of Search 200/83 Y,"83 S, .83 D, ZOO/81.5, 153 H, 81 H; 337/323; 74/510, 522

[56] References Cited UNITED STATES PATENTS 7/1951 Marcellus 200/83 S 10/1951 'Ruffle 200/83 S 1/1935 Mabey. 200/83 D UX FOREIGN PATENTS OR APPLICATIONS Canada 200/83 D France 200/83 R Primary Examiner-Robert K. Schaefer Assistant Examiner-Robert A. Vanderhye Attorney-William B. Matthews [57] ABSTRACT A force sensing device operable as a pressure switch or other triggering device or regulator includes a mechanical amplifier and deamplifier which translates I motion createdby changes in the applied force into larger or smaller movements for operating an output indicator or switch. An actuator arm mounted on a movable fulcrum translates motion induced by the applied force to the output indicator or switch, which responds to motion of the actuator arm in a manner determined by the position of the fulcrum. When emplo'yed as a pressure switch, for example, the shiftable fulcrum permits adjustment of the deadband of the switch, while other adjustments determine the position of the deadband on a pressure scale. The device is operable as a differential pressure switch or as a temperature regulator as well.

3 Claims, 4 Drawing Figures FORCE SENSING DEVICE WITH ADJUSTABLE MECHANICAL AMPLIFIER BACKGROUND AND SUMMARY OF THE INVENTION Although the invention is applicable to various types of force sensing devices, it is particularly adapted for pressure switches employed as pressure regulators and the like. Previously well accepted pressure switches have relied on Bourdon tubes ormetal bellows as the principal pressure responsive element. Both the arched metal Bourdon tube and the metal bellows are subject to fatigue and loss of linearity, however, within 10,000 to 30,000 cycles of operation. Both are subject to leakage or even explosion on occasion when overpressured. They are also subject to temperature variations, corrosion and other problems, including the cost of isolating the device where it is used in the presence of corrosive materials. Further, mechanical linkages involving as many as eight moving parts for converting motion of the tube or bellows into a snap action switch effect, are subject to wear, inaccuracy, corrosion and failure.

The mercury switch typically employed as the output indicator in Bourdon tube devices is environmentally hazardous during manufacture, dangerous in the event of breakage, and subject to vibration, rendering it useless for many purposes. Finally, neither Bourdon tube type nor bellows type pressure switcheshave provided a capability for wide adjustment of thedeadband, and both have limited pressure range capability.

The third type of prior art pressure switch employs a diaphragm made of rubber or similar flexible material which flexs in response to pressure changes. In the past, these pressure switches, too, have been characterized by narrow operating range and very limited deadband adjustment, typically 2 to 3 psi.

This invention seeks to overcome the aforementioned disadvantages of prior devices by. providing a pressure switch of the diaphragm type which includes an adjustable mechanical amplifier enabling it to operate within a broad pressure range with a wide range of adjustment of the deadband. The mechanical amplifier involves only one, moving part, so that the complicated mechanical linkages characteristic of priordevices are avoided. The device is constructed of a plastic, fireproof material which is nonconductive, noncorrosive and is not subject to significant wear. With the simple interchange of return springs of different sizes, a pressure switch in accordance with the invention is capable of operating within a range of from 1/10 psi to 300 psi. Its simplicity and durability will enable it to survive as many as 250,000 operation cycles in some applications.

In its broadest sense the invention provides a force sensing device comprising a housing having force transducer means mounted therein, including a transducer element within the housing which moves in response to application of an external force. A resilient bias means is positioned to resistmotion of the transducer element. An actuator arm mounted for rotation about a fulcrum point within the housing has one end coupled to the transducer element to translate its motion into rotation of the arm, and indicator means mounted in the housing senses movement of the actuator arm to indicate its position. Movable fulcrum means coupling the actuator arm to the housing includes a fulcrum element which is shiftable to different positions along the actuator arm to vary its response to the applied force and hence the response of the indicator.

When the device is adapted for application to a pressure switch, the transducer means comprises a port adapted to be coupled to an external source of pressure, and the transducer element comprises a flexible diaphragm responsive to changes in pressure. The bias means in such case may comprise either a spring or a second external source of pressure, including a second diaphragm responsive to changes in pressure from the second source, whereby the actuator arm responds to differences in pressures from the first and second sources. When thus arranged as a differential pressure responsive device, an adjustable secondary bias means is coupled with the opposite end of the actuator arm for further varying its response to changes in the pressure differential.

When a single source of pressure is monitored an adjustable stop means is coupled with the bias means for limiting motion of the transducer element and actuator arm. This is a self protective feature preventing damage due to excess pressure.

The adjustable fulcrum means includes a pair of opposed notched surfaces extending substantially in parallel along opposing portions of the housing and the actuator arm, and fulcrum element in the shape of a prism is insertable between the notched surfaces at different locations. A window is preferably included in the housing to observe the position of the fulcrum element.

The indicator preferably comprises a switch having an operating characteristic defining a deadband spa-cing between the respective points thereon at which it shifts from on to off and from off to on. In the preferred embodiments an electrical microswitch is employed to advantage, having its spring biased actuating element engaging the actuator arm. Adjustment of the fulcrum position adjusts the distance through which the actuator button of the microswitch moves in response to movement of the transducer element.

These and other features, objects and advantages of the invention will become more apparent from the following detailed description of preferred embodiments, shown inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded, isometric view of a pressure switch in accordance with the invention.

FIG. 2 is a sectional view of the pressure switch of FIG. 1, shown assembled.

FIG. 3 is a sectional view of a differential pressure switch in accordance with the invention.

FIG. 4 is a partially sectioned view of a temperature sensitive pressure switch in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The principal features of pressure switches constructed in accordance with the invention in its preferred forms are shownuniformly in all of the figures. FIGS. 1 and 2 show the embodiment arranged to monitor the pressure in a single fluid pressure line. Housing 10 includes a main body portion 12 and a pressure coupling portion 14 connected thereto at an angle along one end. Three screw holes 16 are provided on the main portion of the housing for mounting the unit on a panel or bracket. The removable wall 18 is secured to the main body portion by four corner screws 20 and includes an extension 22 at the left end which is secured to the pressure coupling portion 14 of the housing by a screw 24, to close the opening 26 provided for accessibility to the inside of the coupling portion 14. A moisture seal 28 fits within a recess 30 around the internal edge of the housing. The screw holes 16 are separate from those for securing the removable wall to the housing so that it can be removed while the housing is secured to a panel. The removable wall includes a window 19 for internal observation after assembly. H

In the upper righthand corner of the housing as shown is a block-like portion 32 into which is threaded an electrical conduit 34 through which electrical wiring is-passed for connection to the microswitch 36. An internal wall 38 divides the housing into a primary internal cavity 40 containing the actuator arm 41 and a secondary cavity 42 containing the wiring. The second internal wall 44 around which the wiring passes is shaped to provide a mounting bracket for one end of the 'microswitch, while wall 38 holds the other end. Three pegs 44 are provided for internal strength and for separation of the wires.

The pressure coupling portion 14 of the housing includes identical upper and lower internally threaded pressure ports 46 and 48, respectively. In the FIG. 1 embodiment pressure line 50 is coupled to the upper port 46 by means of primary

secondary fittings

52 and 54.

The port 46 would communicate with the primary internal cavity 40 of the housing through a hole 56, except that this passage is blocked by a flexible diaphragm 58, the outer rim 60 of which is held in an annular recess 62 by fitting 52. Motion of the diaphragm 58 due to pressure changes is transmitted to the actuator arm 41 by a small cylindrical rod 64'which engages the diaphragm and is seated in a recess 66 in the end of the actuator arm.

In the lower port 48 of the housing an adjustment fitting 68 holds a stop screw 70 which extends into the primary cavity 40 through a passage 72 to engage the lower recess'74 in the actuator arm 41 and limit its downward travel. The upper end of a biasing spring 76 v is also received in recess 74, its lower end being seated in a recess 78 in the fitting 68. The degree of bias or pressure against movement of actuator arm 41 is adjusted by threading the fitting 68 into or out of port 48 and locking it in place by an internally threaded lock ring 80.

The actuator arm 41 is supported within the housing on the prism-shaped movable fulcrum element 82, the base of which is corrugated to fit the notched lower wall 84 of the housing 12. Its upper edge 86 is received in the notched lower surface 88 of the fulcrum arm 41 and constitutes the fulcrum point or axis about which the arm rotates. In summary, the diaphragm 58 and associated fittings and force transmitting element 64 comprise a transducer by which pressure changes in the line 50 are first translated into linear motion and then into rotation of the actuator arm 41 about its fulcrum point 86.

The microswitch 36 is of the well known single-pole double-throw type, having a common terminal 90 and

output terminals

92 and 93, and a trigger or actuator button 37 which is depressed to actuate the switch. One of the many suitable available switches of this type is manufactured by Honeywell Incorporated, whose Model No. V3154-D8 has a pretravel distance of 0.047 in. when depressed or released and a deadband or differential travel of 0.008 in. between trigger positions. Such a switch has three operative states: its off state when the trigger 37 is in the deadband region and respective on positive and on negative states when the trigger is in its pretravel and overtravel regions, or vice versa. Different models of this type of switch are employed to obtain variations in pretravel, deadband and overtravel distances.

As previously noted, the distance through which the left-hand end of the actuator arm 41 may move is limited by the position of stop screw 70. The pressure necessary to cause it to move through the permitted distance is controlled by the compression of spring 76, which in turn is adjusted by the threaded fitting 68. The distance through which the righthand end of the actuator arm 41 moves, however, is controlled by the position of fulcrum element 82. When the fulcrum element is located at the extreme right end of notched wall 84, then the lefthand end of the arm must move through a greater distance to actuate the microswitch trigger button 37 than is required when the fulcrum element is positioned toward the lefthand end. Hence, motion of the diaphragm 58 may be either amplified or deamplified by locating the fulcrum element 82 appropriately. Conversely, the deadband of the microswitch 36 is amplified or deamplified thereby, and motion of the diaphragm 58 corresponding to travel of the microswitch trigger 37 through its deadband determines the deadband of the pressure switch itself.

While the fulcrum position thus determines the width of the deadband, adjustment of the compression of spring 76 determines the position of the deadband on the pressure scale. Both the pressure and the deadband width are precisely adjustable, and indexing scales (not shown) may be provided on the switch for visual reference during adjustment. For example, a dial type scale may be provided on the end face 96 of the fitting 68, and a linear scale may be provided along the face of the actuator arm 41, visible through the window 19 in the removable wall 18, or on the window 19.

In addition to the foregoing basic features of the pressure switch, the invention also resides in certain details of its design and construction. For example, it will be noted that the axes of the upper and lower ports 46 and 48 are slightly offset, as is most apparent in the offset of upper and

lower recesses

66 and 74 at the lefthand end of actuator arm 41. This is to compensate partially for the differences in radii due to the curve in the arm between the movable fulcrum point and the two ports, the axes of which are preferably as close as is practical to being tangential to the are through which the end of the fulcrum arm swings. Since the radius is variable, an average is taken in establishing the appropriate angle of offset of the port axes. I

It will also. be noted that the stop screw protects internal parts of the device by limiting flexing of the diaphragm 58 and travel of element 64 in response to overpressure. Since the'port axes are almost aligned, virtually all of the excess force is absorbed by the stop screw and the fitting 68, and virtually none is transmitted to the microswitch. In the event,.however, that the stop screw is positioned so as to permit a large moment of force at the righthand end of the actuator arm, the upper surface of the arm adjacent to the corner 98 thereof engages the end of the wall 100 supporting the microswitch. The lower end of the wall 100 is dimen sioned so that the actuator button 37 of the switch cannot be overdepressed.

Since the essential operation of the other two embodiments of the invention illustrated in FIGS. 3 and 4 is the same as that just described, only the differences between these embodiments and that of FIGS. 1 and 2 will be discussed.

The housing of the differential pressure switch of FIG. 3 is identical in construction, for all material purposes, to the embodiment first discussed. In place of the adjustment fitting and bias spring in port 46, how ever, a second pressure coupling 102 is employed. A second pressure line 104 is connected to the unit by primary and secondary fittings 106 and 108, and a second diaphragm 110 is included, its outer rim being held in the annular recess 112 (FIG. 2) in port 48 A second transducer element 114 is included, held between the diaphragm 110, its upper end being received in the recess 74 of the actuator arm. The pressure differential sensed by the actuator arm determines its angular position on the fulcrum element 82 and the position of actuator button 37 of the microswitch 36. I

Since it is inconvenient (though not impossible)in this embodiment to provide at the lefthand end of the actuator arm a means for adjusting the pressure difference required for actuation, the adjustment is provided at its righthand end. A hole 116 is drilled in the wall of the housing 12 and an adjustment screw 118 is inserted, together with a square nut l20,which is slideably re ceived in the auxiliary cavity 122. An auxiliary biasing spring 124 is held between the nut 120 and a flat surface 126 provided at the end of the actuator arm. Manual adjustment of screw 118 determines its absorption of a greater or lesser pressure differential, thereby adjusting the position of the deadband of the switch on the pressure scale. The width of the deadband is adjustable by positioning the fulcrum element 82 just as in the embodiment first described.

FIG. 4 illustrates an embodiment of the pressure switch employed as a temperature regulating device. The temperature sensitive element is a closed tube 128 having a bulb 130 at the end and a suitable gas captured therein having a known coefficient of expansion. The tube is mounted in a fitting 132 to which metal bellows 134 are attached in place of a rubber diaphragm. The end of bellows 134 engages recess 66 of the actuator arm 41 and rotates the arm about its fulcrum point as the gas therein expands or contracts in response to temperature changes.

A biasing spring 136 is held between the lower recess 74 in the actuator arm and an opposing recess 138 in the fitting 140 threaded into the port 48. While the type of stop screw safety feature illustrated in FIG. 2 may be employed in place of the simple fitting 140, it is not necessary where the captured expandable gas in the tube 128 will not be subjected to excessive temperatures. A pair ofgas filled tubes 128 may be installed in ports 46 and 48 where temperature differentials are to be monitored.

As has been noted, the housing, the actuator arm and the microswitch in all of the illustrated embodiments are essentially identical, and various fittings and adjustments are employed to apply the invention to different requirements. Besides selection of different microswitches and movement of the fulcrum, further adjustment-of the unit is possible by provision of different strengths of interchangeable biasing springs 76, 124 and 136. For example, with a production model of the invention four biasing springs are provided, corresponding to ranges of from zero to 60, 150, 250, and 300 psi, respectively. These ranges compare with a maximum rangefor the most popular previously known pressure switch of zero to 14.2 psi. The invention is capable of operating in higher pressure ranges up to 10,000 psi when metal bellows like that shown in FIGS. 1, 2 and 3. In addition, adjustment of the fulcrum permits varying the width of the deadband from 0.1 psi to 295 psi in the preferred embodiments.

Other capabilities and modifications of the invention within the scope of the principles disclosed will be recognized by those skilled in the art.

What is claimed is:

1. A force sensing device comprising a housing having mounted therein transducer means including an element within the housing which moves in response to application of an external force; resilient bias means positioned to resist motion of the transducer element; an actuator arm mounted for rotation about a fulcrum point and having one end coupled with the transducer element to translate its motion into rotation of the actuator arm; indicator means sensitive to movement of the actuator arm to indicate its position; and fulcrum means coupling the actuator arm to the housing, including a pair of notched surfaces extending substantially in parallel and facing one another along a portion of the housing and an opposing portion of the actuator arm, and a movable fulcrum element insertable between the notched surfaces at different locations thereon to vary its rotation in response to said force.

2. The device of claim 1 wherein said bias means comprises a spring and means for adjusting the spring to vary its degree of resistance to said force, and adjustable stop means coupled with said spring for limiting motion of the actuator arm.

3. The device of claim 1 wherein the housing includes a window through which the position of the fulcrum element is visible.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3'772'490 Dated November 13, 1973 I Petur "I'hordarson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6, lines 21, before "FIGS. insert FIG. 4 are employed in place of rubber diaphragms as shown in Signed and Scaled this fif h Day of August1975 [SEAL] A ttest.

RUTH C. MASON C. MARSHALL DANN Allesling Officer ummissinm-r uj'lan'nls and Trademarks ITED STATES PATENT OFFICE @TRTIFICATE 0F CORRECTION Patent No. 3 I 772 I 90 Dated November 13 1973 l fl Petur I'hordarson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 6 lines 21 before "FIGS insert FIG. 4 are employed in place of rubber diaphragms as shown in incd and salad this fif h Day of Augustl975 [SEAL] RUTITC. M Q SON C. MARSHALL DANN 11 ('ummissium'r nfl'alenls and Trademarks