US2432029A - Correction of selsyn transmitter errors - Google Patents

Description

1947- J. F. MANILDl 2,432,029

' CORRECTION OF SELSYN TRANSMITTER ERRORS Filed Oct. 5, 1945 3 Sheets-Sheet 1 a j 5. 5 l

.Z'zwvezvfar Jnsspb 11775171721 1 .1. F. MANILDI v qonascnouoz" SELSYN wmusmwma muons Dec. 2, 1947.

Filed Oct. 5, 1945 3 Sheets-Sheet 2 Dec. 2, 1947. AN| D 2,432,029

CORRECTION OF SELSYH TRANSMITTER ERRORS Filed Oct. 5, 1945 3 Sheets-Sheet 3 T it J if) M) J0 I 4 m 4 INVENTOR. Jaszaa/ Fjflan /Hi BY A TTORNEYS l ,siPatg nted r resistor;

T-jPAIENT OFFICE CORRECTION OF SEIiSYN TRANSMITTER ERRORS J0seph F.'-=Manildi, Pasadena; Calif., assignor, by

* mesne assignments; to :Howe& Fa'nt. Inc., South.

-Norwalk,aGonn.,: a corporation 'of Delaware .:SAppIication October 52,1945; Serial No. 620.548

This "invention relates to the correction. of

i transmission errorsiinherent in Selsyntransmission'systems.

lselsyn 'Z transmission systems, whether of I the 'I haveiadiscoveredthatallsuch inherenterrors may;be corrected-'byx'suit'able modifications of' the., transmitter res stancelfroml-the linear formin -"w'h'ichit is ordinarily :used. The following de-- sxscriptiorrwillcsetnout,in preferred and illustrative form, the details of theiatpplication of my inven- 1 tion to athree wirefsystem: and will then po nt out the .applica'bili'tywof .the invention 'stO 0l5h8I systems. *For the'purpose of suchdescription I refer 130 the accompanying drawings, in which Fig. Lisa circuit diagram showing the essentials'of a-usual'three-wire .Selsyn system; .3 'Fig. v2 is a'idiagramxshowing the varia'tion 'be- :tween "transmitter I angle :and receiver angle;

Fig. 3 is a diagramshowing the angular error of the receiveriplottcd against transmitter angle;

Fig. 4 is adiag-ranr showing the variation of the 1 resistance modification factor with transmitter wangle;

Bis ardiagram showing the dei' elop edshape 0f a sectoriof ar'nodified resistance; g 7.

Fig. -6 'is a diagram showing the;develop"edshape giof a complete resistor; Fig; 'I isarfragmentary perspe'c ti eof the re- 's lstor'ofFlgfi;

i Fig. -8 is a dla gramishowing another "typefiof 5 Fig. 9- is a dia'grar'ii:showing(another-resistor *modification; and v 'Fig. "10 is a view-inxperspective"of'afiriodified 'form'iofthe new resis'tor;---and V "Figs. '11 and. 12 "are. diagrams showing; circuits "thatinay beused with the resistor-of Fig. 10. I

.Fig. ishows the essential electrical c rcuiting of a,typical"three-wireselsyn'system, consisting essentially (of a circulart'ransmitter resistance R, to

which a potential difference is applied bydiarnetgrically' opposed brushes-D and E}, and which is connected by the three wire circuit I' 'CCT, tothe delta wi-ndingsfi'. T. 8. of the receiver.

. ":"rh-e receivermaybe considered to be of the usual type with its delta-connected coils rotatingin a on two-pole magnetic field; orl as indicated in Fig.

I 1'. may be considered as having a two-pole magnet 'M rotating in the field of thecoils.

In such a system, where transmitter resistance R is linear with relation to the angle 0. of transmitter rotation, it can be shown that Z 120 tang I 3 +tan 6 where 0 denotes the angle of rotation of the transmitter brush from any zero point (such as marked vi 0 in Fig. l) where. a brush makes direct connection with a circuit lead; and where 0 denotes the corresponding angle of rotation of the rotary element of the receiver, assuming that the receiver stands at .all times in an equilibrium position with reference to the distribution of magnetic forces'which are controlled by the transmitter. As seen by inspection of Equation 1 the angle 0' becomes equal to 0 for values of 0 equal to 0; 30, and, so on, as might be expected from the fact thatone of the transmitter brushes B is in direct contact with a lead and the other brush B is in mid-position between two leads for every 60 position,- and that the two brushes have a symmetric relation to one of the leads, andto the other two leads considered as a pair, at every intermediate 30 point (e. g. such a brush positionas shown in Fig. 1.) Fig. 2 shows receiver angle 0' plotted against transmitter angle 0, and

for comparison shows 0 plotted ideally as equal to 0/ Comparison of the two curves shows the variation between 0' and 0 for the first 60 of transmitter rotation from a zero position. From Equation 1 it may be deduced that where 5 denotesth di'fierence'between 0 and 0;

that is, denotes the angle by which receiver angle 0 "-va'rie iromf transmitter angle 0...; Inspection 10f Equation 2 shows that B is equal to zerom ll,

transmitter angles-of 0, 30, 60 etc.; that B varies 'symr netricall with relation toany one of those angular positions; and that s is negative (receiver lags) for the first 30 of transmitter ro- "tation from a zero position, and is positive (receiver leads) through the next 30 of transmitter rotation from that zero position. Fig. 3 shows [3 plotted against 0 for the first 60 of transmitter angle. Negative maximum of 1 6' occurs at 0:1318', and an equal positive maximum oc- The curve repeats itself for each 60 of transmitter rotation following that shown in Fig. 3.

As may be noted from Equationswi and 2, the

error ,8 in-the standard Sels-yn system is inde pendent of the resistance values used in the transmitter, or the relation oii'liose values to the ,resistancevalucs; in the receit'erinthc paper which I later refer to. I show among other things that, to obtain maximum torque in the receiver in where R1 is the resistance of the transmitter resistance per degree, R: the similar unit resistance of the receiver winding, E the applied E, M. F., and P the maximumpower consumed in the system. However, those considerations of maximum torque do not affect the receiver error, nor do they eifect the correction provided by my invention.

In my invention, the transmitter resistance is varied from its usual linear form by a factor which is a function of the transmitter angle 0. As a result of that resistance variation receiver angle is made to be equal to transmitter angle 0 for all values of the latter. The requisite variation of the transmitter resistance is arrived at as outlined below.

Since the receiver error, in a system having a linear transmitter resistance (Ri=constant) is symmetric with relation to each 30 position of the transmitter, it is only necessary to ascertain the required deviation of transmitter resistance for transmitter angles from 0 to then to make the deviations from 30 to 60 symmetrical with those from 30 to 0, and then to repeat the cycle of deviation for each succeeding 60 of transmitter angle.

Referring to Fig. 1, and assuming that the resistance of a linear transmitter resistance element is R1 per degree, or 120 R1 for each leg between leads C, we let (1R1 represent the ideal unit resistance of a transmitter. That is, a is a function of a, the transmitter angle, such that 0', receiver angle, will become equal to 0, transmitter angle.

From consideration of the circuit of Fig. 1, and equivalent electrical circuits derivable therefrom, it can be shown that the receiver angle 0' will be given as follows. Equation 1 above may be written,

In that equation, receiver angle a will be given with a substituted for 0; thus,

Solving for or under those conditions, we obtain,

. 22m (h) 05 tan 0 which gives the necessary variation of a with 0 for zero error, and hence the variation of transmitter resistance with 0, since the resistance of the transmitter resistor element is, by definition, ClRl. a is the variable modification factor for R1, for zero error, expressing the variation of the resistance with 0, the transmitter angle. Here again it is noted that the modification factor is independent of R1 and R2. and hence is applicable to any transmitter and any receiver or set of paralleled receivers. Fig. 4 shows the variation of a 4 with I. along with a linear variation for comparison. v

The usual physical form of transmitter resistance element is one in which a toroidal coil -is wound helically about a toroidal form which has the shape of a section of thin walled tube with the ends of the section normal to the axis. Fig. 5 shows at OABC a development of the superficial area of such an element from 0 to 30, and shows at OABC' the corresponding development of a resistance element in which one edge, C'B, is shaped for zero error. In any such resistance element. the resistance at any transmitter angle 0 is equal to the area under C'B' between 00' and the vertical corresponding to 0.

Using Equation 6 and the fact that the area under CB represents non-varying resistance with respect to 0, and that the area under C'B' represents the same for a function of 0 which satisfies Equation 6, it can be shown that,

as 1 3 (ficosH-sind) where L is equal to the height or length of an equivalent (equal total resistance) resistor-the dimension 00 in Fig. 5. Fig. 5 shows 1"(0) as the curve C'B' plotted against 8 from 0' to 30. The plot for 30 to 60 is symmetric with C'B'. about the 30 axis. The developed shape of the whole toroidal resistor then follows with five successive duplications of the shape of the first 60; such complete developed shape being indicated in F g. 6.

Fig. 7 is a fragmentary perspective illustrating the physical form of the resultant resistor. In Fig. 7 the thin tubular body is shown at 20, and the helically wound resistance wire is fragmentariiy shown at I. As here shown all of the resistance variation is applied to one edge of the resistor body; but it will readily be understood that the. variations which are represented by Equation '7 above may be as well distributed between the two edges.

The fully detailed derivations of the several formulae given here are contained in a paper by this applicant, published in Trans. A. I. E. E. July 1945, vol. 64. A copy of that paper is filed here-- with for reference.

Other physical forms of resistor may be used. For instance, as indicated in Fig. 8, the modifying factor represented by Equation 6 may be applied to a varying thickness of a toroidal body 20a on which the coil wire Ila is wound. "And Fig. 9 shows a commutator type resistor with resistance elements Rs between successive commutator segments 22. In such a resistor the resistance variation will follow Equation 6 step by step.

By considerations and developments which are v tan 0 i-i-tan 0 and the following equation Equation 7 above.

recti'on factor) -as given by Equations 6 and 6a above the following. generalization may be made.

where (1 represents the numeric value in degrees of the angle between successive connections to the resistor, and where n represents a numeric constant. v

Similarly the following generalization can be made as between Equations 7 and 7a where n equals the angle between successive con.

nections to the resistor, in degrees, divided by 180, and where n represents a numeric constant.

A form of the new resistor R having four equi-.

angularly spaced leads is illustrated in Fig. 10. This resistor includes a thin tubular core 30. upon which is helically wound the resistance wire 3|. One end edge of the core is formed with projections spaced 90 to produce the desired variations and the connecting wires 32, II, M, 35 tap the resistor at the points of the projections F, G, H, and J.

In Fig. 11, the system shown includes the resistor R. of Fig. 10 with the connecting wires 32, I3, 34, leading, respectively, from points F, G, H, and J on the resistor to the ends F, G. H, and J or independent receiver coils 36, 31, extending at right angles to one another. The receiver is shown as including a magnet M rotating in the field of the coils.

In Fig. 12, the system shown includes the resistor R of Fig. 10 with connecting wires 32, 33, I4, 36 leading. respectively. to the ends F", G", H", and J" of delta-connected coils 38, 39, 40, and ll 01' the receiver, which includes the magnet M.

I claim:

l. A circular resistor for a transmitter of a Selsyn system in which the resistor is tapped by equi-angularly spaced leads and is engaged by relatively rotating contact members, said resistor having a resistance which varies in substantial accordance with the expression 1.2211. n'+ tan 8 resistance which varies in substantial accordance with the expression 120 tan 0 /+tan a I where 0 represents the relative angle of rotation with respect to a predetermined zero point.

3. A circular resistor for a transmitter of a where 0 represents the relative angle of Selsyn system in which the resistor is tapped by iour equi-angularly spaced leads and is engaged by two diametrically opposed and relatively rotating contact members. said resistorhaving a J resistance which varies in substantial accordance with the expression rotation from a predetermined zero point.

4. A- toroidally wound resistance coil for a Selsyn system havinga transmitter in which the resistance coil is tapped by equi-angularly spaced leads and is engaged by relatively rotating contact members, said resistor having a superficial area which, measured from a predetermined zero point, varies insubstantial accordance with the expression I 1 cNamara-0 where n is equal to the angle between successive lead connections to the resistor, in degrees, divided by 180, where n" represents a numeric constant, where 0 represents rotational angle from the predetermined zero point, and L represents a numeric constant.

5. A toroidally wound resistance coil for a Selsyn system having a transmitter in which the resistance coil is tapped by three equi-angularly spaced leads and is engaged by two diametrically opposed and relatively rotating contact members, said resistor having a superficial area which, measured from the predetermined zero point, varies in substantial accordance with the expression a (43' cos 0+sin 0) where L represents a numeric constant, and 0 represents rotational angle from the predetermined zero point.

6. A toroidally wound resistance coil for a Selsyn system having a transmitter in which the resistance coil is tapped by four equi-angularly spaced leads and is'engaged by two diametrically opposed and relatively rotating contact members, said resistor having a superficial area which, measured from the predetermined zero point, varies in substantial accordance with the expression 2 (cos 6+sin 0) where L represents a numeric constant and where 0 represents rotational angle from the predetermined zero point.

JOSEPH F. MANILDI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain Jan. 7, 1943 Certificate of "Correction Patent No. 2,432,029. Decemb'er'r2, 194?. JOSEPH F..'MANILDI It is hereby certified that error appears in the printed-specificationioi vthe..-above numbered patent requiringcorrection aslfollowsz Column 3,"line,.3,rforthattportion of the equation reading (8=30, read (0'==30,; and thatthe. saridzLettersiPiatent should be read with thus correction thereinthat thesame'may conform to the' record of the case in the Patent- Oflice.

Signed and sealed" this 24th; day oiFebruary A. D.i1948.

THOMAS F; MURPHY,

Auiatmnt aIPatenu.

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