US2886676A - Potentiometer-accelerometer apparatus - Google Patents

Description

y 1959 M. E. BOURNS ETAL 2,836,675

POTENTIOMETER-ACCELEROMETER APPARATUS 2 Sheets-Sheet 2 Filed March 30, 1955 United States Patent POTENTIOMETER-ACCELEROMETER APPARATUS Marlan E. Rooms and Marvin E. Harrison, Riverside, and Alfred W. Stewart, Yncaipa, Calif.; said Harrison and said Stewart assignors to Bourns Laboratories, Inc.

Application March 30, 1955, Serial No. 498,026

7 Claims. (Cl. 201-48) The present invention relates primarily to new and improved accelerometers, although certain features of this invention are applicable to other related devices, such as, for example, potentiometers.

Those familiar with present day electrical components will realize that the term potentiometer is employed to designate a type of a variable resistor including a resistance element having end terminals designed to be connected to a voltage source and including a movable contact which may be located at any desired point along this resistance element so as to obtain a voltage dividing action. If desired those devices termed accelerometers can be considered to be a type of potentiometer since they contain the essential elements of a potentiometer, and, in addition, means intended to be moved in response to acceleration so as to shift the position of a movable contact as previously indicated with respect to a resistance element.

Potentiometers and accelerometers are widely employed at the present time in various guided missiles and related machines. As research on this type of equipment has progressed there has been a substantially constant demand for new and improved electronic instruments of the type to which this invention relates. A number of qualities are desired in such new instruments: they must be less subject to error than the preceding units; they must be accurate; they must be light in weight; they must be comparatively insensitive to damaging influences; and they preferably must be comparatively inexpensive.

A basic objective of this invention is to provide accelerometers which, when judged by the aforegoing criteria, constitute an improvement over the prior units employed for the same purpose. A broader object is to teach the construction of various new and improved means which are, it is thought, primarily useful in accelerometers, but which are capable of advantageous application in various other related devices. Such means will be described in detail in the subsequent discussion. Those skilled in the art will recognize still further objects of this invention from the remainder of this specification including the appended claims and the accompanying drawings in which:

Fig. l is a front or top view of an accelerometer of the invention;

Fig. 2 is a cross-sectional view taken at line 2-2 of Fig. 1;

Fig. 3 is a cross-sectional view taken at line 3-3 of Fig. 2;

Fig. 4 is a detail view showing the construction of a spring employed in the accelerometer shown in Figs. 1, 2, and 3 of the drawings;

Fig. 5 is a detail view showing the construction of part of the accelerometer illustrated in Figs. 1, 2, and 3 of the drawings;

Fig. 6 is a view similar to Fig. 2 of a modified accelerometer of the invention;

Fig. 7 is a detail view resembling part of Fig. 2 of a second modified accelerometer of the invention;

Fig. 8 is a view similar to Fig. 3 of a third modified accelerometer of the invention;

Fig. 9 is a detail view showing the construction of bimetallic strips employed with the invention; and

Fig. 10 is a detail view similar to Fig. 6 showing the construction of another modified accelerometer of the invention.

In all figures of the drawings like numbers are used to designate like parts wherever convenient for purposes of illustration and explanation. It is to be understood that the relative proportions of the various parts shown in the drawings have been changed from the actual proportional sizes of these parts in many cases in order to facilitate the illustration of the invention.

In Figs. 1, 2, and 3 of the drawings an accelerometer 10 is shown which includes a can-like casing 12 having an open top which is sealed by means of a lid 14 attached to the casing 12 by the use of threads 16. An appropriate conventional O-ring 18 of an elastomeric material is held within a groove 20 so as to seal this casing 12.

Mounted upon the lid 14 through the use of screws 22 is a cage 24 which fits within the casing 12. This cage is provided with an open upper end 26 in which there is positioned a disc-like bellows mounting member 28 formed of a non-conductive material. This bellows mounting member is secured to the cage 24 through the use of other screws 22. Further it includes a central opening 30 within which there is held an adjusting nut 32. This nut is provided with threads 33 which engage corresponding threads upon a projecting collar 34 forming a part of a bellows unit 36. The collar 34 is formed with an annular shoulder 38 which is intended to engage the bellows mounting member 28 as shown in Fig. 2 of the drawings. However, if desired, this shoulder 38 may be spaced from the mounting member 28 and the entire bellows unit 36 can be held in position through the use of another screw 22 located within an elongated passage 40 formed within the bellows mounting member 28. When this is done the position of the bellows unit 36 can be adjusted as desired.

The bellows unit 36 includes bellows 42 of any type of conventional construction having a centrally formed opening 44 leading to another aligned opening 46 within a valve seat 48 secured to the bellows 42 and the collar 34. The valve seat 48 is formed with a conical depression 50 forming a part of the opening 46. Within the collar 34 there is located a valve body 52 having a conical projection 54 which is adapted to fit within the conical depression 50 so as to regulate the fiow of air into and out of the bellows 42 through the valve seat 48. Air passing through the opening 46 passes into the casing 12 through passages 56 formed within the valve body 52. The position of the valve body 52 with respect to the valve seat 48 is maintained by using other threads 57 securing this valve body 52 to the collar 34. The valve body 52 may be locked in any given position through the use of a locking nut 58 which is also screwed onto the threads 57.

The construction described in the aforegoing for mounting the bellows 42 is considered to be quite important to the instant invention inasmuch as it constitutes a means whereby the flow of air into and out of this bellows may be readily regulated so as to obtain any desired air damping action. The use of air damping in the accelerometer 10 is quite advantageous inasmuch as this type of damping is substantially independent of temperature. When such damping means as liquids are employed for the same purpose the viscosity of such liquids is changed at varying temperatures causing a corresponding alteration of aeaaers S the damping effect. Further, air clamping employed herein is a distinct improvement over magnetic damping inasmuch as the parts required are relatively simple to manufacture and handle, and do not occupy any considerable space. Also with magnetic damping the parts employed are considerably heavier than the parts required for fluid damping. The term damping as used herein is intended to cover those situations in which means are employed to prevent undesired rapid movement of the various operative parts within the accelerometer 10.

This accelerometer includes a heavy disc or mass 60 which is secured to the wall of the bellows 42 remote from the bellows mounting member 28. Attached to the disc 6! is a bushing 62 which is designed to carry a rod 64 so that this rod is secured to the bellows unit 36 and projects downwardly therefrom. Screws 22 are employed for the obvious purpose of holding the rod 64 within the bushing 62.

The extremity of the rod 64 remote from the bellows 42 is attached to the central hub 66 of a spring 68 having radial arms 70. The construction of this spring 68 is best shown in Fig. 4 of the drawings. secured to the disc-shaped bottom 72 of a non-conductive support member '74. This support member is secured to the cage 24 through the use of screws 22 so as to be generally parallel to the bellows mounting member 28, and includes upstanding shaft supports 76 and a resistance support 78. The bottom 72 is formed with a centrally located opening 86 through which the rod 64 projects.

It is preferable to form either the entire spring 68 of a bi-metal sheet, although the resilient arms 70 alone may be formed of such material. When this is done the spring 68 can be constructed of such materials as to compensate for any tendency of the bellows 36 to expand or contract when heated or cooled so as to bend with such temperature variation in order to hold the rod 64 in a given location during such expansion or contraction.

The shaft supports 76 each include an opening 80 having an internal flange 84 formed therein so that a metal shaft 86 may be mounted between the supports 76 in such a manner as to be carried by rollers 88 constituting roller bearings. These rollers 88 are held in position by metal washers 90 and nuts 92 secured to the extremities of the shaft 86.

Attached to the shaft 86 so as to project therefrom is a generally channel-shaped arm 94 formed of metal upon the end of which there is located a conductive spring contact 96. If desired this contact 96 may be formed of a single sheet of material including resilient fingers 97. If desired this contact 96 may be termed a first electrical means inasmuch as it is designed to be moved along one surface of an arcuate resistance member 98 held within a correspondingly shaped slot 100 formed within the resistance support 78. The contact 96 bears against the resistance element with light spring tension, owing to the inherent resiliency of the contact. The resistance member 98 may, if desired, be termed a second electrical means and may consist of any of a number of general types of prior art constructions. It is preferred, however, that this resistance member include a non-conductive base 102 around which there is located a coil 104- of wire having appreciable electric resistance.

During the operation of the accelerometer 16 as this accelerometer is subjected to accelerating forces the disc 66 will be caused to move within the casing 12. This in turn' causes air to either be forced into or out of the bellows 42 during expansion or contraction thereof moving the rod 64 along a line within the casing .12. This motion of the rod 64 is transmitted to the shaft 86 through the use of linkage means forming a unique part of the present invention. This linkage means includes four bimetallic strips 106 of generally bowed configura- The arms 70 are tion secured together in pairs as is indicated in Figs. 2 and 3 of the drawings so that the extremities of all of these bimetallic strips 106 remote from the shaft 86 are attached to one another by means of a pin or shaft 108. All of the other extremities of the bimetallic strips 106 are secured directly to. the shaft 86. The pin 108 is designed to slide within a slot 110 formed by other pins 112 projecting from the rod 64.

The bimetallic strips 106 are preferably formed as briefly indicated in Fig. 9 of the drawings, and comprise layers 114 and 116 of different temperature coefficients of expansion. Thus, with this construction, as the bimetallic strips 106 are heated they will bend causing the pin 108 to be moved within the slot 110 away from the shaft 86. This varies the length of the effective lever arm connecting the rod 64 to the shaft 86. By appropriate selection of the material of which the bimetallic strips 106 are formed it is possible through this means to provide a construction in which the amount the contact 96 is moved along the resistance member 98 at different temperatures varies in accordance with the temperature of the accelerometer 10. Thus, it is possible to form the accelerometer It in such a manner as to compensate for expansion and contraction of the various movable parts within this unit and for the change in spring rate of the bellows 36 and of the spring 68 so that the electrical signal obtained from it is independent of the temperature at which the unit is being operated by constructing the strips 196 of such material and of such length that the expansion characteristics of these strips compensate for the expansion or the contraction and change in spring rate of the parts within the accelerometer.

The structure shown in Figs. 2 and 3 of the drawings is considered to be particularly advantageous in that the movement transmitted to the shaft 86 from the rod 64 is conveyed through linkage means disposed upon opposite sides of the rod 64. Thus with this structure the forces upon both sides of the rod 64 are substantially balanced. Further, the linkage means employed is composed of sufficient separate elements so that the effect of vibration is substantially controlled. There is substantially no tendency with this structure for the strips 106 to bend during the operation of the accelerometer 10.

In the accelerometer Ill the movement of the rod 64 is conveyed to the shaft 86 by the means previously described. It should be pointed out that these means are located intermediate the ends of the rod 64 and that this rod is supported at both of its ends by what may be termed spring means. The first of these spring means is the bellows 42; the second is, of course, the spring 68. The bellows 42 may be considered to act essentially as a spring because of the inherent resiliency of its walls.

With this type of structure the rod is held in such a manner that the desired movement of this rod is possible, but so that undesired movement of the rod, except along the intended line of travel, is effectively prevented, elimihating possible error resulting from such movement. This is considered to be a distinct advantage over the prior related constructions. The use of two spring means as herein described can be applied to other units such as, for example, absolute pressure potentiometers with substantially the same results as herein obtained.

The lid 14 is provided with a generally centrally located opening 118 in which there is mounted a rotatable member 120 having a sloping surface 122 which is designed to bear against the screw 22 attached to the rod 64 when this rotatable member 120 is turned 180 from the position shown in Figs. 1 and 2 of the drawings. The member 120 is held with respect to the lid 14 by means of a snap ring 124 fitting within a groove 126 formed in this rotatable member 120. It is secured against movement toward the casing 12 by means of what may be termed a screwhead 128 which is normally forced against an O-ring 129 located'against a flange 130 within the opening 118. The screwhead 128 is formed with arcuate recesses 132 spaced 180 from each other around this head. The purpose of the recesses 132 is to provide a convenient means by which the rotatable member 120 may be locked in either the position shown in Fig. 2 of the drawings or in the 180 position previously described when a screw 133 is secured to the lid 14 so as to engage either of these recesses.

Thus, the screw 133 may be used to lock the rotatable member 120 with the surface 122 bearing against the screw 22 attached to the rod 64 so as to prevent undesired movement of this rod and the other parts operatively connected thereto during shipment of the accelerometer This feature of the invention is considered to be quite important in preventing undesired damage to the unit due to rough handling during shipment. The surface 122 is normally of such dimension as to force the rod 64, when in such a locked position, as far away from the lid 14 as this rod will move.

In order to complete the accelerometer 10 it is necessary to provide various means by which current may be supplied to the resistance member 98 and to the contact 96. With the accelerometer 10 such means include shaftlike terminals 134 which are mounted within the lid 14 so as to project from both sides thereof. An essentially conventional dielectric resin grommet 136 surrounding these terminals may be employed to hold them in position and to insulate them from the lid 14. Wires 138 secured to the terminals 134 inside of the casing 12 are normally passed through an opening 140 within the support member 74 and then are connected to conventional terminal means 142 mounted upon the resistance support 78.

These terminal means are in turn attached to the extremities of the resistance member 98 on the surface thereof remote from the contact 96. One of the wires 138 is attached to one of the nuts 92 so as to be electrically connected to the contact 96.

In Fig. 6 of the drawings a modified accelerometer 144 of the invention is shown which differs from the accelerometer 10 in several important features. In this unit the valve means connected to the bellows 44 are omitted and replaced by a single passage 146 extending through a stud 148 which is roughly the equivalent to the collar 34 previously described. Also in this unit the rod 64 is replaced by a large diameter rod 150 formed of a comparatively very heavy material such as, for example, lead or various steel alloys. The extremity of the rod 150 adjacent to the lid 14 is secured within a bushing 152 attached to another bellows 154. This other bellows is secured to a projecting stud 156 on the wall thereof remote from the rod 150. The stud 156 is in turn located within an opening 158 formed within another bellows mounting member 160 which is fastened by means of screws 22 in the cage 24 between the lid 14 and the support members 74. A screw 22 is preferably employed to secure the stud 156 within this bellows mounting member.

The stud 156 has formed therein an opening 162 leading from the interior of the bellows 154 to adjacent to the rotatable member 120. The purpose of this opening 162 is to provide a passage through which a rod or shaft 164 can project from the Wall of the bellows 154 adjacent to the rod 150 out into the space between the mounting member 160 and the lid 14. Thus with this construction the rod 164 moves within the opening 162 during expansion or contraction of the bellows 154. It preferably fits closely within the opening 162. Further the rod 164 is provided with a periferal groove 166 serving the same purpose as the passage 146 previously described. That is, this groove 166 serves to convey air into and out of the bellows 154 so as to serve as a damping means.

With the construction shown in Fig. 6 the bellows employed may be locked in a position for shipment by adjusting the position of the movable member 120 substantially as previously described. When this is done the 6 sloping surface 122 engages the adjacent extremity of the rod 164 in the obvious manner holding both of the bellows so that undesired movement is prevented.

The accelerometer 144 also differs from the accelerometer 10 in another important regard. In this unit two bimetallic strips 168 and 170 are employed instead of the four bimetallic strips 106 previously described. These strips 168 and 170 are of substantially the same shape as the strips 106 and are secured together so that their adjacent ends are secured to the shaft 86 and the pin 108. With this construction the bimetallic strips 168 and 170 are located on one side of the rod this structure is sufliciently stable as regards to vibration for most purposes.

Frequently it is desired to form either of the strips 168 or of different metals than the other of these strips in order that the temperature characteristics of the two separate strips will differ from one another. Thus, with this type of construction not only will the efiective distance between the pin 108 and the shaft 86 change at varying temperatures but also the position of the pin 108 will change in a direction generally parallel to the axis of the rod 150.

Those skilled in the art will realize that this particular type of construction illustrated in Fig. 6 for the two bimetallic strips 168 and 170 is exceedingly advantageous in producing units having special temperature varying characteristics. That is to say units employing this feature can be manufactured so that an electrical value will change in a desired manner with respect to temperature variation. Obviously the basic feature of employing two different bimetallic strips illustrated in Fig. 6 of the drawings can be adapted to a structure such as is shown in Fig. 2 of the drawings by making the two strips 106 shown in this figure adjacent to the lid 14 of different metals than the remaining two strips. Although the use of bimetallic strips as herein described is considered to be particularly advantageous in accelerometers it is thought that it may also be applied to other related units in which motion is transmitted from one member to another member in order to vary an electrical value.

In Fig. 7 of the drawings a structure is shown in which a single bimetallic strip 172 is used to connect a shaft 86 and a rod 64 of the type shown in the initial figures of the drawings. A construction of this category can many times be advantageously employed to provide temperature compensation, and it operates in essentially the same manner as the temperature compensating construction previously described. Inasmuch as only a single bimetallic strip 172 is employed this strip may, in many cases, be subjected to vibration effects which are not material with the other constructions previously described. It is considered obvious that two curved bimetallic strips, such as the strip 172 illustrated in Fig. 7, can be employed on opposite sides of the rod 64, both of these strips being secured to the pin 112 and the shaft 86.

In Fig. 8 of the drawings a modified construction of the invention is shown which differs from the accelerometer 10 in that a single rod 174 of a material having appreciable temperature coefiicient of expansion is used instead of the bimetallic strips 106. This rod 174 is secured to the pin 108 in the obvious manner and is preferably passed through an opening 176 within the shaft 86 so as to extend within a sleeve 178 projecting from the opening 176 on the side of the shaft 86 remote from the rod 64. The rod 174 and the sleeve 178 are attached to one another by suitable means 180, such as, for example, solder. The advantage of this particular sleeve type of construction shown is that a comparatively long length may be provided for the rod 174.

A structure is shown in Fig. 10 of the drawings which is essentially a modification of the accelerometer 144 shown in Fig. 6. With this structure, a passage 182 is provided within the rod 150 so as to connect the interiors aseaere of the bellows. 154. and, 36.. Appropriate openings 184 are provided within these two bellows for the obvious purpose. With this structure the rod 150 is secured to the two bellows 36- and 154 through the use of collars 186 which are welded or otherwise fastened to these bellows. The rod 150 is also attached to the collars 186 by means of welds or other equivalent means known to the art.

With the structure indicated in Fig. the rod 164 does not have the groove 166 previously described. Thus a substantially fluid-tight fitting is obtained between this rod 164- and the stud 156 so that the quantity of fiuid within the bellows 36, the bellows 154, and the passage 182 remains constant regardless of position of this rod 164. The function of the rod 164 is substantially as previously described. If desired, it may be omitted with the corresponding omission of its function. The rod 164 in the structure shown in Fig. 10 is attached to the bellows 154 by means of a small spider Hi8, which is similar in shape to the spring 68 previously described, the spider I188 being secured to both the rod 164 and the bellows 154 by means of welds or the like.

It is possible with this structure described in the aforegoing to fill the two bellows 36 and 154 with virtually any desired fluid so that the fluid is contained within these two bellows and with the passage 182 at all times. Thus with this structure it is possible to dispense with the seal and easing previously described inasmuch as the fluid within the two bellows employed for damping is contained within a restricted area. It is considered obvious that the passage 182, being of restricted area, provides a very effective means for controlling the movement of fluid between the two bellows 36 and 154 during acceleration. If desired, temperature responsive valve means may bev disposed upon the rod 159 for governing the amount of fluid transmitted between these two bellows through the passage 182.

The structure shown in Fig. 10 of the drawings also differs from that shown in Fig. 6 in that the two bimetallic strips 168 and 170 are replaced by two strips 190 and 192 of different metals having difierent temperature coefiicients of expansion, so that as these two strips are heated the same result obtained with the bimetallic strips 168 and 170 are accomplished. The principle of using strips of different metals connecting the shaft 84 with a member movable along a line can also be applied to the structure shown in Fig. 6 of the drawing and the structure shown in Fig. 2. Normally, however, it is preferred to utilize bimetallic strips with these other consttuctions.

Those skilled in the art will realize from the aforegoing description that the accelerometer constructions described are comparatively efiicient for the purpose intended and mark a substantial improvement over prior related units on the market today. They will further realize that these accelerometer constructions may be termed air-damped, temperature compensated potentiometers. It is possible to retain certain of the advantages of the invention by omitting one or more of the various novel features herein set forth or by substituting other conventional constructions for one or more of these features. This, however, is not preferred inasmuch as the accelerometers herein described and the combination of parts set forth are exceedingly satisfactory.

Those skilled in the art will unquestionably realize that many of the features of this invention which, if desired, may be termed sub-combinations may be adapted to a number of different varieties of related electrical devices. In all of such related units a first electrical means is moved with respect to a second electrical means in order to vary an electrical value. It is considered obvious, because of this, that the instant invention is to be accorded comparatively wide scope, and is capable of a number of distinct modifications not specifically set forth in this present specification. Insofar as such modifications are within the scope of the art, and are setv forth in the appended claims, they are to be considered as part of the invention.

We claim:

1. An electrical instrument comprising a member supported for movement along a substantially linear path, a rotatable shaft disposed at right angles to said linear path of movement, an arm attached to said shaft, contact means on said arm, a resistance element wiped by said contact means, link means operatively connecting said member and said shaft, said link means including a lever arm attached at one end to said shaft and extending therefrom in a direction generally perpendicular to said linear path of movement, the other end of said lever arm being connected to said member by means providing a connection movable lengthwise of said lever arm, said link means being operable to vary the effective length of said lever arm responsive to changes of temperature, so as to compensate for variations in the output of said instrument caused by the change in temperature.

2. An electrical instrument as defined in claim 1 wherein said lever arm comprises a curved bimetallic strip operable to increase or decrease its effective length responsive to temperature changes.

3. An electrical instrument as defined in claim 1 wherein said lever arm comprises: two oppositely bowed bimetallic strips, the extremities of said strips being joined together, said other end of said lever arm being movable in the direction to vary the effective length of the lever arm responsive to temperature changes.

4. An electrical instrument as defined in claim 1 wherein said lever arm comprises: curved bimetallic strips located on opposed sides of said linearly movable member, the outer ends of said bimetallic strips being joined to a pin extending generally parallel to said shaft, said. pin engaging slot means within said linearly movable member.

5. An electrical instrument as defined in claim 1 wherein said lever arm comprises: two curved bimetallic strips, the extremities of each of said strips being joined. together, each of said strips being of. different composition, said two bimetallic strips of different composition be ing operable to move said other end of said lever arm both in the direction, to lengthen or shorten the effective length thereof, and in the direction generally parallel to the line of travel of said member responsive to changes in temperature, so as to produce a functional temperature compen: sating effect.

6. An electrical instrument as defined in claim 1 wherein said lever arm comprises a rod capable of ex'-- pending along its axis, so as to vary the length of said. link means.

7. An electrical instrument including: a can-like cas ing; a lid sealing said casing; a first bellows. mounting member positioned within said casing adjacent to the bottom thereof; a first bellows secured to said first bellows mounting member; means defining a first orifice leading from the interior of said first bellows into said casing; a second bellows mounting member positioned within said casing adjacent to said lid; a second bellows secured to said second bellows mounting member; means defining a second orifice leading from the interior of said second bellows into said casing; a rod positioned between said first and said second bellows, said rod being secured to said first and said second bellows so as to be capable of movement during the expansion and. contraction of said first and said second bellows; a shaft rotatably mounted in said casing at one side of said rod between said first and said second bellows; an arm secured to said shaft; first electrical means attached to said arm; second electrical means mounted in said casing adjacent to said first electrical means; link means connecting said shaft and said arm, said link means in,- cluding means capable of changing length at. difierent 9 10 temperatures; and means for locking said rod in a fixed 2,264,487 Smulski Dec. 2, 1941 position. 2,435,254 Ramberg Feb. 3, 1948 2,484,165 Hathaway Oct. 11, 1949 References Cited in the file of this patent 2,702,186 Head et a1. Feb. 15, 1955 UNITED STATES PATENTS 5 FOREIGN PATENTS 2,067,803 Thearle July 12, 1937 642,850 Great Britain Sept. 13, 1950 2,231,957 Shrader Feb. 18, 1941 693,958 Great Britain July 8, 1953

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