US2799821A - Mechanical-electrical analog converter - Google Patents

Description

1957 w. A. HANNIG ETAL 2,7

MECHANICAL-ELECTRICAL ANALOG CONVERTER Filed Oct. 13, 1953 Inventors: 1 Wi||iamA.Hanni Arnoldl-ifiilver",

by v ll7/saz TheirAttoPney.

Sttes MECHANICAL-ELECTRICAL ANALGG CONVERTER William A. Hannig, chenectady, and Arnold H. Silver, Troy, N. Y., assignors to General Electric Company, a corporation of New York Application October 13, 1953, Seriai No. 385,812

tllaiins. (Cl. 323-79) This invention pertains to voltage dividing devices, and more particularly to a mechanical-electrical analog converter of the type used to convert a mechanical quantity into an electrical quantity, and, in some applications, to perform a mathematical operation on the electrical quantity obtained from the conversion.

Computing machines of the analog type, which operate on measurable physical quantities rather than on numbers, are well-known in the art. When a problem which is expressed in numbers is to be solved by an analog machine, the numbers are translated into physical form, such as light intensities, electric voltages, lengths, or angular positions of shafts, and the computing operations are performed on these physical quantities.

In some applications it is desirable to convert a mechanical quantity, such as the angular position of a shaft, into an electrical quantity on which specific operations may be performed more easily than on a mechanical quantity. A known method of making such a conversion is to connect the shaft, Whose angular position is variable, to the rotating arm of a rheostat or potentiometer, and thus establish a value of current or voltage which is controlled by the angular position of the shaft. The present invention is directed toward this type of mechanical-electrical converter.

In many instances, the electrical quantity, whose value is determined by the angular position of a rotatable shaft, must be controlled with great precision, and this requires that the rheostat or potentiometer which is connected to the incoming data driving shaft be extremely accurate. It is difiicult, as well as costly, to obtain a potentiometer which is physically suitable for use in an analog converter and which has better than 0.1% accuracy, that is, in which the resistance of the winding departs from its proper value at any point by less than 0.1%. Accordingly, an object of the present invention is to provide a converter of the type described, which utilizes conventional potentiometers of readily obtainable accuracy, wherein the possible error in the output voltage is substantially less than the possible error in previously known converters using such otentiometers.

Another object of the invention is to provide a mechanical-electrical analog converter employing a plurality of potentiometers which may be arranged to minimize the possible error in any desired region or regions of the output voltage range.

A further object is to provide an analog converter in which the ratio of the analog to the variable represented remains constant over the entire range of operation.

A form of the invention which attains the foregoing objectives comprises a fixed voltage divider for connection across a voltage source. The voltage divider includes a plurality of resistors connected in series, and across each of these resistors is connected a potentiometer, so that only a portion of the total input voltage appears across each potentiometer. The potentiometer shafts, whose angular positions control the positions of the potentiometer pick-off contacts, are mechanically connected together so that when one shaft is rotated all of the shafts rotate simultaneously. The input data driving shaft whose angular position is to be converted to an electrical potential, is connected to drive one of the potentiometer shafts.

The relationships between the resistors of the voltage divider, the resistances of the otentiometers, and the gears which connect the potentiometer shafts are such that each potentiometer covers a specific range of output voltage corresponding to a specific range of rotation of the input data driving shaft, and means are provided to select the output from the various potentiometer pickotf contacts as the input data driving shaft rotates through its various ranges. Thus, the output of each potentiometer is independent of any error of the other potentiometers.

Further features and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawing, which is a diagrammatic view of a mechanical-electrical analog converter embodying the invention.

In the form of the invention illustrated, it is desired to convert the mechanical rotation of an input data driving shaft 1 into an electrical potential, whose value is determined by the angular position of the driving shaft 1. A voltage source E1 (not shown), from which the output voltage is derived, may be connected across input terminals 2?; and 3, between which resistors 4, 5, 6, and 7 are connected in series to form a voltage divider. Resistors 4, 5, 6, and 7 may be either individual fixed resistors or sections of a large resistor having fixed or movable taps. In many instances, the latter arrangement is preferable in order that all sections of the divider may respond the same way to temperature variations. Input terminal 2 may be grounded (as shown), or, as will be later pointed out, the ground connection may be omitted or placed at other points in the voltage divider.

An output voltage, which carries in accordance with the position of the driving shaft 1, is taken from potentiometers 3, 9, l0, and 11, whose ends are electrically connected to the ends of resistors 4, 5, 6, and 7, respectively, with the resistance of each potentiometer being, in general, equal to or greater than the resistor across which it is connected. The ratio of the resistance of each potentiometer to the resistor across which it is connected need not be the same for all combinations. However, if the resistors 4, 5, 6, and 7 all have the same temperature vs. resistance characteristics, as when they are sections of a single large resistor, it is desirable to select the potentiometers 8, 9, 1d, and 11 so as to disturb the uniform characteristics as little as possible. It has been found that when the resistance of each potentiometer is ten or more times the value of the resistor across which it is connected the slight diiferences in the temperature vs. resistance characteristics of the potentiometers cause only a negligible change in the characteristics of the parallel sections.

The potentiometers 8, 9, 10, and 11 have movable pickoff contact arms 12, 13, 14, and 15, respectively, mounted on. shafts 16, 1'7, 18, and 19, respectively. In this instance, each of the potentiometers is of the continuously rotatable type, in which the movable contact arm can pass from one end of the resistance winding across a small gap to the other end, and need not be rotated in a reverse direction to reach the opposite end of the winding. Also, in the form of the invention here shown, the potentiometers are linearly Wound; that is, the resistance of each winding is uniformly distributed throughout its length.

The potentiometer shafts l6, 17, 12%, and w, are mechanically connected together for simultaneous rotation, in this instance, by means of gears 20, 21, 22, and 23, respectively, mounted on the shafts. The ratio between the gears associated with adiacent potentiometers is such that the ratio of the amounts of rotation of the shafts is the inverse of the ratio of the parallel resistances of the resistors and potentiometers, or, to state it another way, the ratio of the amounts of rotation of the shafts is the inverse of the ratio of the voltage drops across their otentiometers. For example, if resistors 4 and 5 had resistances of 1000 ohms and 2000 ohms, respectively, and otentiometers 8 and 9 had resistances of 10,000 ohms and 20,000 ohms, respectively, thereby causing twice the voltage drop across potentiometer 9 as across potentiometer 8, gear 21 would be twice the circumference of gear 20, so that for one revolution of the gear 20 the gear 21 would make one-half revolution. Similarly, if the resistors 5 and 6 have equal resistances and if potentiometers 9 and 10 have equal resistances, the gear ratio between the gears 21 and 22 would 1:1; and if the resistors 6 and 7 have resistances of 2000 ohms and 1000 ohms, respectively, and the potentiometers 10 and 11have resistances of 20,000 ohms and 10,000 ohms, respectively, the ratio of gears 22 and 23 would be such that the shaft 19 would make two revolutions for every revolution of the shaft 18. This coordination between the parallel resistances of the resistors and otentiometers and the amounts of rotation of the potentiometer shafts is-the basis for one of the outstanding advantages derived from our invention, because, when the potentiometers are linearly wound, as in this embodiment, the voltages present on the pickotf contact arms all change by the same amount for any given rotation of a potentiometer shaft, although the absolute values of the various voltages are different.

The input data driving shaft 1 is connected into the gear train by any convenient means, such as by being connected directly to the shaft 16 of potentiometer 8. If desired, the driving shaft might be connected to the gear train through a gear of the proper size mounted on the driving shaft and meshing with any one of the gears of the train.

The rotatable pick-01f contacts 12, 13, 14, and of the potentiometers are electrically .connected to the con tacts of a selector switch 24, which is mechanically connected to the driving shaft '1 by conventional means, such as a gear train 25, and the amount of rotation of the driving shaft determines which one of the potentiometer pickoff contacts will be connected through the selector switch to its output terminal 26. The selector switch 24 may be of any conventional type, which may be so modified that the change from any input connection to "its adjacent ones may be made smoothly and Without discontinuity. In the example shown, the connection between the selector switch and the input data driving shaft would be such that .during the first revolution of the driving shaft 1 the contact arm 12 of potentiometer 8 would be connected through the selector switch to the output terminal 26; during the second and third revolutions of the driving shaft, potentiometer v9 would have its contact arm 13 connected to the output terminal;

during the fourth and fifth revolutions the arm 14 of potentiometer 10 would be so connected; and during the sixth revolution of the driving shaft the contact arm 15 of potentiometer 11 would be connected through the switch to the output terminal..

In order to illustrate clearly the operation of this form of the invention, specific values have been assigned to the various elements. These values have been arbitrarily chosen, with due regard to the teachings of the invention, as follows: resistor 4, 1000 ohms; resistor 5, 2000 ohms; resistor 6, 2000 ohms; resistor 7, 1000 ohms; potentiometer 8, 10,000 ohms; potentiometer 9, 20,000 ohms; potentiometer 10, 20,000 ohms; potentiometer 11, 10,000 ohms. If the voltage E1 applied between terminals 2 and 3 is taken to be 60 volts, and terminal 2 is .connected to ground as shown, the potentials at points 27, 28, 29, 30, and 31 will be 0 volts, 10, volts, 30 volts, volts, and volts, respectively.

The various potentiometer contact arms are illustrated in the position corresponding to zero rotation of the driving shaft 1. At this time, contact arm 12 of potentiometer 8 is connected through the selector switch to the output terminal 26 and, because there has been no rotation of the driving shaft, the output terminal is at zero potential. As the driving shaft 1 rotates counterclockwise in response to incoming data, the contact arm 12- moves around the potentiometer in the same direction, and the voltage appearing at the output terminal 26 increases from zero volts to 10 volts as the driving shaft makes one complete revolution. After one revolution, the driving shaft causes the selector switch 24 to disconnect contact arm 12 from the output terminal and connect contact arm 13 thereto. The potentiometer contact aims are so arranged with respect to each other that when the arm 12 of potentiometer 8 has made one revolution and is at the high potential end of the winding,

arm 13 of potentiometer 9 is at the low potential end of its winding. Thus, the arms 12 and 13 are at the same potential .and the transition from one to the other may be made smoothly. Similar relationships exist between all of the potentiometer contacts arms.

.As :the :incoming data driving shaft 1 continues to rotate through its second and third revolutions, the contact arm 13 of potentiometer 9 rotates once around the winding of the potentiometer, and the voltage appearing at output terminal 26 rises from 10 volts to 30 volts. This action results because, as previously stated, the ratio of the amounts-of rotation of the shafts of potentiometers 8 and 9 is the inverse of the ratio of the resistances of the parallel combination of resistor 4 and potentiometer 8 'andthe parallel combination of resistor 5 and potentiometer 9. That is, the parallel resistance of resistor 5 and potentiometer 9 'is twice that of resistor 4 and potentiometer 8, and, therefore, the shaft 17 of potentiometer 9 rotateshalf as fast as the shaft 16 of potentiometer 8. At the end of three revolutions of the driving shaft 1 from its reference point, the potential on the contact arm 13 and output terminal 26 is 30 volts, and the driving shaft 1 causes the selector switch to disconnect contact arm 13 from the output terminal and connect contact arm 14 thereto.

The resistance ratio of the parallel combinations which include resistors 5 and 6 andpotentiometers 9 and '10 is 1:1, and, therefore, the gears 21 and 22 are so selected that the shafts of potentiometers .9 and 10 rotate at the same speed. At the end of three revolutions of driving shaft 1, contact arm 14 of potentiometer .10 is .at :thelow potential end of .the winding and, during the next .two revolutions, .it will rotate once around the potentiometer. During these two revolutions the potential vonoutput terminal .26 will rise from 30 to 5.0 volts. Upon completion of five revolutions of the driving shaft, the selector switch is caused to disconnect contact arm 14 and to connect contact arm 15 to the output terminal.

Because the parallel combination ofresistor 6 and potentiometer-10 has twice the resistance of the parallel combination of resistor 7 and potentiometer 11, the gears 22 and 23 are so selected that the contact arm 15 of potentiometer 11 rotates twice as rapidly as contact .arm 14 of potentiometer 10. Therefore, during the sixth revolution of "the driving shaft 1, contact arm 15 of potentiometer :11 will rotate once, and the output voltage on terminal 26 will rise from 50 to :60volts.

Atthe .end .of six revolutions of the driving shaft, all of the otentiometers have again reached the positions shown, and contact arm 12 of potentiometer 8is again connected through-the elector switch to the output terminal. It is apparent, therefore, that the illustrated embodiment of our invention'may be used only in'a system wherein the range .of input data is such that it rotates driving shaft 1 less than six revolutions. It is to be understood, however, that any number of resistors of various values may be employed in the fixed voltage divider in association with a corresponding number of potentiometers. That is, although we have shown only a four section arrangement, any number of sections may be used so long as the fundamental relationships between the resistances of the sections and the gears connecting the potentiometer shafts are maintained.

In this form of the invention, it is seen that the relationship between the output voltage and the amount of rotation of the driving shaft from a reference point is a constant ratio. For example, if a single revolution of the driving shaft produces an output voltage change of volts, two revolutions of the driving shaft will produce an output voltage change of 20 volts. It is to be understood, however, that this invention is not limited to such a linear relationship, and this form of the invention is shown only for purposes of illustration and description.

By the use of our novel arrangement the error in the output voltage due to the error in accuracy of any potentiometer can be greatly reduced over prior known systems. For example, the voltage drop between points 27 and 31 is 60 volts, which is divided among four potentiometers with 10 volts appearing across potentiometer 8, 20 volts across potentiometer 9, 20 volts across potentiometer l0, and 10 volts across potentiometer 11. If it is assumed that the acuracy of potentiometer 11, for example, is 0.1%, the possible error due to this potentiometer would then be .001 10 or .01 volt. If the entire 60 volts were applied across a single potentiometer having 0.1% accuracy, the possible error could be .00l 60 or .06 volt.

A further advantage of our invention is that the possible output error may be minimized in any desired region or regions of the total range requiring high accuracy by employing a plurality of potentiometers in these regions, that is, by covering the regions in small steps rather than in large steps. In the embodiment shown and described, the greatest accuracy was desired at the beginning and end of the 60 volt, 6 revolution range. Therefore, potentiometers and resistors of the proper value to have only 10 volts voltage drop across them were employed in these two regions. If additional accuracy were required in these two areas, the combination of resistor 4 and potentiometer 8 might be replaced by ten resistor-potentiometer combinations connected in series, with each combination having one-tenth the resistance of the combination of resistor 4 and potentiometer 8. Similarly, such an arrangement might have been employed instead of the resistor 7 and the potentiometer 11. Therefore, assuming the voltages and potentiometer accuracies to be the same as in the example given above, the maximum output error in the range covered by one of these potentiometers would be .001 volt instead of .01 volt, as previously explained. Thus, we have provided an analog converter having a great advantage over prior devices, and one which has solved a troublesome problem in the computing machine field.

The embodiment of the invention which has been described herein is constructed to produce an electrical output signal which is either always positive or always negative, depending on how the voltage source is connected to the input terminals. It will be apparent that many different arrangements may be used, however. For example, the ground connection might be made to a point intermediate the ends of the voltage divider, instead of to one of the input terminals, as shown. In that case, the output signal could be either positive or negative, depending on the position of the input data driving shaft. In addition, the input may be from either an alternating current or direct current source, and the operation as previously explained will remain unchanged.

This embodiment of the invention is suitable for use in converting incoming data from mechanical shaft rotation to an electrical potential. However, there are many other uses for the device and the invention is not to be limited to any particular application.

For example, the converter may be used as a multiplier of two variables. In the above description of operation, it was assumed that the voltage E1 applied between input terminals 2 and 3 was constant. Therefore, the output potential on terminal 26 was proportional only to the incoming data driving shaft position. However, it is apparent that the voltage applied between the input terminals, as well as the position of the driving shaft 1, may be varied. In this instance, the output voltage will-be proportional to both the voltage E1 and the position of the driving shaft 1, and will be proportional to the product of these two variables.

Similarly, the device may also be used as an arbitrary function generator of one variable. The series of potentiometers may be wound non-linearly to represent the function, each covering a portion of the function and being switched in and out by the driving shaft 1, as previously indicated. The driving shaft 1 would represent the independent variable, and the output voltage would represent the arbitrary function of this variable varied in accordance with the voltages appearing across the sections of the voltage divider and in accordance with the non-linear windings of the potentiometers. If it is desired to use linearly wound potentiometers, a similar result may be obtained by properly adjusting the voltage divider voltages to produce a straight-line approximation of an arbitrary function of the input variable.

It is apparent that we have provided a device which has many applications, and it is our intention not to be limited by the specific embodiment or application shown or described. Various changes and modifications may be made by one skilled in the art without departing from the spirit of the invention, which is to be limited only by the scope of the appended claims.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A precision mechanical-electrical analog converter, comprising a voltage divider for connection across a voltage source, said voltage divider comprising a plurality of resistors connected in series, a potentiometer connected across each of said resistors, each potentiometer having a continuously rotatable pick-off contact arm connected to a rotatable shaft, means connecting the rotatable shafts of the potentiometers for simultaneous rotation, the means connecting the rotatable shafts of the potentiometers comprising a motion translating means interrelated to produce equal voltage changes on all of the potentiometer pick-off contact arms for a given rotation of a shaft, a selector switch having a plurality of input terminals and an output terminal, means electrically connecting said potentiometer pick-off contact arms to the input terminals of said selector switch, and means responsive to rotation of the potentiometer shafts for operating said selector switch.

2. A precision mechanical-electrical analog converter, comprising a voltage divider for connection across a voltage source, said voltage divider comprising a plurality of resistors connected in series, a potentiometer connected across each of said resistors, each potentiometer having a continuously rotatable pick-ofi contact arm connected to a rotatable shaft, means for connecting the rotatable shaft of a potentiometer to a driving shaft for rotation therewith, a gear fixed to each rotatable potentiometer shaft, the gears fixed to adjacent potentiometer shafts being meshed with each other and their ratio of teeth being the same as the ratio of the voltage drops across their respective potentiometers, a selector switch, means electrically connecting said pick-ofl contact arms to said selector switch, and means responsive to the amount of rotation of said driving shaft from a reference point to operate said selector switch.

3. A precision mechanical-electrical analog converter comprising at least two potentiometers connected in series for connection across avolta-ge source, each potentiometer having a continuously movable pick-E contact arm, actuating means for said contact arms for simultaneous movement thereof in response to movement of an input data shaft, said actuating means including a variable motion transmitting means coupled to said arms so that movement thereof is inversely proportional to the ratio ofthe voltage drops across their associated potentiometers, and means-responsive tome-movement of said pickotfi arms for successively selecting-the output voltage existing ateach of said pick-off arms.

4. A precision mechanical-electrical analog converter comprising a plurality of potentiometers connected in series for connection across avoltage source, each potentiometer having a continuously rotatable pick-off contactarm, actuating meansforsaid contact arms for simultaneous rotation thereof in response to rotation of an input data shaft, said actuating means including a rotatable shaft secured to each of said contact arms and variable motion transmitting means coupled to said shafts so that the, rotationthereof is inversely proportional to' the ratio of the, voltage drops across their associated potentiometers, andselector means operable by'said input shaft for successively selecting the output voltage existing at each of said potentiometers pick-off contact arms.

5. A precision mechanical-electrical analog converter,

8 comprising ac voltage divider for'connection across a voltage source; said voltage divider comprising aplurality'ofi resistors connected in scri es; a potentiometer connected across each'of'said resistors, each potentiometer having-a continuously rotatable picleo'ifcontact arm; actuating means for said contact arms for simultaneous rotation thereof in* response to rotation of an input data shaft, said actuating means including a rotatable shaft secured to each of said contact arms, and variable motion transmitting means coupled to said shafts so that the rotation" thereof is inversely proportionalto the ratio of the voltage drop across their associated otentiometers, a selector switch having a plurality of input t'errninalsand an output'terrninal and means electrically connecting said p0 tentiometer pick-oft contact arms to the input terminals of said selector switch, and means" responsive to rotationof said input data shaft for operating said selector switch;

References-(iited in the file ofthis patent UNITED STATES PATENTS

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