US2451439A - Control instrument - Google Patents

Description

Oct, 12, 1948. A. H. JQRDAN 294539439 COHTRCL INSTRUMENT Film! Jan. 15, 1.946 3 Shasta-Sheet l HNVENMR, ARTHUR H. mmzm MNE Get. 12 1948 A. H. JORDAN GCETROL INSTRUMEHT 3 Shasta-Sheet 2 Filed Jan. 159 1948 N mA m m V mH R U H T. R n

BKZ/W 971W ATTORNEY.

Patented Oct. l2,

UNITED STATES PATENT OFFICE CONTROL INSTRUMENT Arthur H. Jordan, Norrlstown, Pa., asslgnor to The Brown Instrument Company, Philadelphia, Pa., a corporation of Pennsylvania Application January 15, 1946, Serial No. 641,387

(cl. zoo-4s) Claims. 1

The present invention relates to control systems, and more particularly to a control system that can be used with a potentiometer type in strument and one in which a mercury switch is used to control the application of a conditionchanging medium in response to variations in the value of that condition from some desired value.

It is an object oi the present invention to'provide a mercury switch control mechanism to be used with control instruments in which the switch is actuated by a differential gear mechanism. In the embodiment disclosed there is provided a planetary differential in which .a normally stationary part is moved to some position proportional to the value at which it is desired to maintain the condition; a normally rotating part is moved in response to condition variation, and a third part is used to operate a switch in accordance with the joint positions of the first two parts. The third part has a cam movable with it to tilt a switch supporting member.

It is a further object of the invention to provide a control instrument in which a simple and readily adjusted gear mechanism may be used between the condition responsive mechanism and the control switch thereof. V

It is a further object of the invention to provide an accurate and inexpensive mercury switch operatingmechanism. The switch moving parts of the present invention are moved by the same potentiometer drive motor which adjusts the recording pen so that the parts are moved in syn= chronism. Adjustable gearing is provided be.

tween the motor and the switch, however, so that the switch may be opened or closed at any point in the pen travel.

While the control mechanism is disclosed herein as being used with a potentiometer type instrument and is designed particularly for use therewith, it will be readily apparent that other types of instruments such as thermometers, pressure gauges and flow meters may be used. It. is only required that the instrument have a part moved with sufficient force proportional with the change in the condition being controlled to move the switch operating mechanism.

The various features of novelty which characterlze this invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying drawings and descriptive matter in which is illustrated and de- 2 scribed a preferred embodiment of the invention.

In the drawings:

Figure 1 is a wiring diagram for a potentiometer circuit, 7 I

Figure 2 is a diagrammatic view of various of the moving parts of a potentiometer,

Figure 3 is a partial front view of the instrument showing the switches and the switch actuatingmechanism, and

Figure 4 is a view taken on 4-4 of Figure 3. Referring first to Figure 1 there is shown a wiring diagram of a potentiometer circuit. In an instrument of this type there is provided a slidewire I across which a potential is placed by a battery 2. A portion of this potential is opposed by the E. M. F. developed by a thermocouple 3, and to this end the thermocouple is connected in the potentiometer circuit by means of a collector 4 that is attached to one of the thermocouple terminals. This collector is connected electrically with the slidewire l by means of a movable contact B, The other thermocouple terminal is connected to the circuit through a switch 6 and an amplifier I. When the contact ii is so positioned along the slidewire i and collector 1 that there is no'current fiow in the circuit, the instrument is in balance. Ii, however, the thermocouple'shou'ld be subjected to a change in temperature, the voltage produced thereby would change and a current flow would take place through the potentiometer circuit. This current flow is detected and ampli fied by the amplifier l to produce an energlzationof a rebalancing motor 8 in a direction depending upon the current flow in the circuit. The motor is mechanically connected to contact ii to move this contact along slidewire i in such a direction that the thermocouple voltage is exactly opposed by the voltage drop across the slidewire. When contact 5 reaches this point along the slidewire i, current will cease to flow in the circuit and the motor will again be deenergized so that the contact will remain still until a further change in thermocouple voltage takes place. At times it is necessary to recallbrate or standardize the po= tentiometer circuit. This is accomplished by movinga contact 9 of switch 6 to the right to disconnect the thermocouple from the circuit and to connect a standard cell i l in its place. This standard cell is connected in the circuit and a suitable resistance i2 is simultaneously connected in the circuit around the amplifier 7. The standard cell produces a given voltage drop across a portion of the potentiometer circuit so that if this voltage is not exactly opposed by the voltage of the battery 2, a resistance 13 may be adjusted in suitable manner until the voltages are equal. Thereafter the contact 8 is moved to the left to again connect the thermocouple in the. circuit. For further details of the potentiometer circuit and the amplifier, attention is called to the copending application of Walter P-Wills, Serial No. 421,173, filed December 1, 19%1, now patent number 2,423,540, July 8, 1947.

The mechanism of the instrument, or at least that which is necessary for an understanding of the invention, is shown in Figures 2 to 4. It will be seen in Figure 2 that themotor B is provided with a pinion ll which meshes with the teeth of a large gear l5 that is mounted upon a shaft IS. The gear is provided with a stop or enlarged -prtion it that bears against one side or the other of pinion H to limit the rotation thereof in both directions. Also mounted on the shaft 56 is a small gear l8 that meshes with teeth which are formed in the lower edge of a segment member l8. This segment is movable with a pivoted shaft 2! that has attached to it in a manner to be described later a pen arm. The shaft it is also used to operate the control mechanism to which the invention is more particularly related.

Rotation of shaft it also serves to adjust the contact along the slidewire i and the conductor 4. To this end there isprovided a pulley 22 that is also attached to the shaft it. This pulley has wrapped around it a cable 23 which passes over a series of guide pulleys 24, 25, and 26. The first of these pulleys is mounted for movement on a lever arm 21 that is biased in a downward direction by means of a spring 28. This mounting for the pulley 24 serves to take up any slack which may occur in the cable and thus prevent undesirable play between the drive motor 8 and the contact 5. As is shown in Figure 2 the cable 23 also passes around a drive pulley 29 that is mounted up a shaft 3|. This shaft is suitably journaied in a supporting member 32 made of insulating material upon which the slidewire i and the collector 4 are helically wound side by side. The contact 5. travels inla helical path around member 32 and is held iifengagement with the slidewire and collector byv means of a spring member 34. This spring has a slot in it extending in a direction parallel to the axis of shaft 3|. Spring 34 is attached to a vertically extending arm of a part 33,'the other arm of which extends across the bottom'of support 32 and is fastened to the shaft 3|.

From the above description it will be seen that as the motor 8 is energized in response to pctentiometer unbalance, it will rotate the pulley 22, and through the cable 23, the pulley 29. When this pulley moves, shaft 3| will be rotated to move part 33 around the supporting member 32. During this movement contact 5 which engages the slidewire and collector bar will move up and down in the slot formed in spring 34 as the latter is moved around theoutslde of the supporting member 32. Therefore, the contact 5 moves in a helical path along the slidewire I and collector l to the proper position so that the motor 8 is deenergized when the potentiometer circuit is again balanced. The slidewire and collector are protected by a cover 36 that is placed around them and heldin position by clips 36.

The parts of the potentiometer which have just been described are mounted on a frame member or casting 31, on the front of which is disposed the recording and control mechanism. It will be seen from Figures 3 and 4 that the shaft 2|, which is moved by segment it. extends t rough this casting and has attached to its front end a driving arm 38 which is formed with a rearwardly extending tongue 32. Rotatably mounted on shaft 2! is a pen arm di that is held in engagement with the tongue 89 by means of a spring 52. Because of this construction the pen arm ll will move a pen on its end across a suitable chart (not shown) as the shaft ii is rotated but that this pen arm may be manually moved to the right in Figure 3 without disturbing the position of shaft 2|.

As shaft 2! moves the pen arm, it also serves to operate the control mechanism. This is accomplished by means of a segment #33 that is attached to the shaft 2! and which has gear teeth formed on its lower curved surface. Movement of the segment acts through idler gears dd and 65, which are mounted for rotation upon shafts Q8 and Q1, respectively, to drive a planet gear 69 that forms part of a planetary differential. A second planet gear 39 along with gear 59 is attached to a shaft 5i that is journaled in a hub 52. This hub is eccentrically mounted on a large gear 56 that is in turn attached to a hub 55 which rotates on shaft Q7. It will be seen from an inspection of Figure 4 of the drawing that'hub E55 projects to the right and has mounted for rotation on that end thereof the gear all. In a like manner hub 55 extends to the left and has several parts to be described below mounted for rotation on it. Rotation of planet gear as is imparted to asmall gear 68 that is attached to a hub 5? which is rotatable upon the left hand extension of hub 55. From the above it will be seen that gear 56 may be rotated either by maintaining gear 54 in some given position and moving segment 63 or by holding segment 63 and gears 663 and 35 from rotation and rotating the large gear 56. v

Gear 56 is manually'rotated by an attendant in order to adjust the control point of the instrument. This is accomplished by means of a gear 58 in mesh therewith and a pinion 5s. The

pinion is mounted on a shaft that extends to the front of the instrument and is rotated by a knob .68 on it. Simultaneously with the rotation of gear El i an indexis moved across a suitable chart (not shown) upon which the pen on arm :3! makes a record in order to indicate the control point for which the instrument is set. This is accomplished by means of a second gear 6| which is also in mesh with the pinion 59, a pinion em rotatable with gear, 6!, and a segment member 62 which is formed with gear teeth on its outer curved edge.

The segment is pivoted at a suitable point in the instrument at 63 and has formed as a part thereof an index pointer 66 that projects down in front of the above mentioned chart which has not been shown.

Mounted on the hub 57 of gear 58 is a composite cam which is indicated by the numeral 6!. The composite cam is made of four cam members of which two 66 and 61, are indicated by reference numerals. Each cam member is formed of adisc having an active surface of two diameters, with the large diameters of the cam control may be obtained, the control surfacecomprising the small diameter of the small cam member and the large diameters of each of the cam members. These cam members may be adjusted relative to each other and held in their adjusted positions by clamp screws 69 which extend through slots 08 in the front cam members and are firmly threaded into the back cam member. By loosening the screws the cam members may be adjusted relative to each other for a purpose to be described. The cam members are on hub I1 and are held in place and against relative rotation with this hub by a thumb screw or knob II. It is also noted that a spring 10 is provided in the instrument, which spring has one end attached to hub 81 and the other end attached to a stationary part of the instrument. The purpose of this spring is to take up any play between the teeth oi the various gears in the differential gear train.

Rotation of the cam 65 moves a control switch by engagement between the edge of this cam and a roller 12 that projects from a lever 13. This lever is freely movable on a shaft H and is attached by a screw and slot connection 15 to a second arm or lever 16 which has a hub 11 projecting to the right therefrom in Figure 4. Fastened to the rear end of hub ll are a pair of switch supports 18 and 19 that have mercury switches 8| and 82, respectively, mounted upon them.

In the operation 01' the instrument the cam members are adjusted relative to each other so that the high portion of each cam member will be circumferentially spaced some given distance beyond the end of the high portion of the next adjacent cam member as shown in Figure 3. This means that cam has five different radii within the range of rotation of the cam relative to roller 712. Therefore, as the cam is rotated past roller it, this roller will cause lever '36 to be rotated around shaft it and will move the switches ill and 322 to five distinct positions. If cam is rotated in a counter-clockwise direction in Figure 3 of the drawing, the high portion of each cam member will successively be brought into engagement with roller 12.

If switches 8i and 82 are of the type having contacts in each end their supports may be soadjusted, on hub l1, for example, thatall contacts and control circuits are opened when the high portion of cam member 61 engages roller 12. As cam 85 rotates in one direction or the other from this position the circuits including the contacts in the opposite ends of the switches will be closed to actuate suitable control mechanisms. it will be seen that in the normal operation of the device, an attendant will rotate knob 6t, and through the gearing, rotate large gear E i and the cams until index 64 has been moved to a designated point on the chart. This indicates the control point of the instrument. Generally speaking, at this time the high portion of the cam member ill will be under roller i2 indicating that the temperature under measurement is at the control point. Thereafter, variation of the temperature under measurement will cause unbalance of the potentiometer circuit and produce energization of the motor 8 in one direction or the other. This motor drives the pen across the scale and simultaneously acts through the gearing described above to rotate cam 65. Depending upon whether the temperature increased or decreased, the cam will be rotated to bring higher portions or lower portions under roller 12 and therefore close one or the other of the control circuits. Closure of these circuits is intended to act through suitable, conventional relay mechanisms in order to properly control the application of various gears have diameters and tooth numbers so that rotation of shaft 2| and rotation oi knob Bil in the proper directions and speed will move the gears so that no movement of the cam is produced. In other words it the control point of the instrument is being changed in the same direction and at the same speed as the temperature under measurement is varying, no motion will be imparted. to the cam and the control switches.

From'the above it will be seen thatI have utilized a simple planetary gear arrangement in order to provide an instrument with control mechanism that may be accurately operated. Because of the gearin'g'arrangement that is used, only a small amount of power is required from the actuating element and any desired movement 01' the'switches within reason may be obtained for a comparatively small variation of the temperature being measured. Also, using the particular gearing arrangement disclosed herein, the control point of the instrument may be easily and accurately adjusted to any value at which it is desired to maintain the temperature. By. having the control cam made of a plurallty'oi sections, it is possible to use more than one switch and obtain a neutral in the control system of any desired extent. If the instrumentls to be fairly insensitive the neutral step of the cam 55 that is formed by the large diameter portion of cam member 61 will be longer in extent than it will be if more sensitive instrument is desired. Obviously any desired number of cam members may be used, and, if desired, only one cam meinber may be used to give an on-off action to the controller.

tus disclosed without departing from the spirit of the invention as set forth in the appended claims, and that in some cases certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what F. claim as new and desire to secure by Letters Patent is:

1. In a control instrument, a control switch, means to mount said switch for tilting movement between open and closed positions, a cam mounted for rotation and operative to tilt said switch mounting means, differential gearing to rotate said cam including a normally stationary but manually adjustable portion to adjust initially the position of said cam, and a portion rotatable to positions corresponding to the variable values of a condition under control, and resilient means to bias normally said gearing in one direction to take up back lash in the gears thereof.

2. In a control instrument, the combination of a mercury control switch, a support to mount said switch for tilting movement between open and closed positions, a roller projecting from said support, a rotatable cam, means to mount said cam for rotation with the edge thereof engaging said roller whereby as said cam rotates said support will be moved to tilt said switch, a first set of gears to rotate said cam, a second set of gears including a portion of said first set of gears to also rotate said cam, manually operated means to ro= enema!) tate said first set of gears to position initially said cam, and means operated in accordance with variations in the value of a condition being controlled to rotate said second set of gears.

8. In a control instrument, the combination 0! a support, a shaft projecting from said support, a planetary gear arrangement mounted on said shaft including a normally stationary part, a normally rotating part and a third part rotated by either of said first mentioned parts, a shaft Journaled in said support, means to rotate said shaft positions depending upon the value of a condition, means connected to said shaft to rotate naeans operative upon rotation thereof to move said means to thereby actuate said switch, and means to rotate said cam including a first gear rotated to positions proportional to the value of a-condition under control, a second gear connected to said cam to rotate the same, drive means extending between said gears, a member carrying said drive means, and means to rotate said member to positions proportional to the value at which it is desired to maintain said conditii'ln.

5. In a control instrument, the combination of control means, an element mounted for movement around a pivot and operative upon pivotal movement to actuate said control means, a rotatable cam cooperating with said element to pivot the same as said cam is rotated, means to rotate said cam includinga first gear rotatable around an axis to positions corresponding to the value of a variable condition, a second gear rotatable around said axis and connected with said cam, drive means extending between said gears, a member rotatable around said axis and carrying said drive means, and means to rotate said memher to positions corresponding to the desired value of said condition.

ART n. JORDAN.

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