US3673584A - Position-measuring transformer having end-detecting windings useful for positioning a magnetic head of a disc drive system - Google Patents

Abstract

Disclosed is a position-measuring transformer formed from two relatively movable members. The transformer is particularly useful for selecting and defining track positions in a magnetic disc drive system which may be used as a memory in a digital computer. One stationary member of the transformer includes cofunction windings and end-detecting windings. Those windings magnetically coupled to a reference winding on another relatively movable member of the transformer. The reference winding, which is the continuous winding of the transformer, is formed from a plurality of equally spaced active conductors. The active conductors are interconnected such that alternate ones conduct in opposite directions so that each pair of adjacent active conductors define a reference cycle. The end-detecting windings consist of one or more pairs of active conductors where the active conductors in each pair have full-cycle spacing, that is, the separation between each active conductor in a pair equals one reference cycle. The full-cycle spacing of the end-detecting winding superposed over the half-cycle spacing of the enddetecting winding induces a substantially zero resultant signal in the end-detecting winding except when the end-detecting winding is positioned over the end conductor of the reference winding as may occur when the reference winding is moved. When over the end, a limit signal is generated as a result of the unequal coupling between the end-detecting winding active conductors and the end conductor of the reference winding. The limit signal thus generated typically defines the inner or outer limit of a read/write head. Cofunction windings are formed from four winding sections with equal numbers of active conductors per section. The cofunction windings are formed using an efficient winding pattern which minimizes the number of welded or soldered connections required.

Description

United States Patent Farrand 1451 June 27, 1972 [54] POSITION-MEASURING TRANSFORMER HAVING END- DETECTING WINDINGS USEFUL FOR POSITIONING A MAGNETIC HEAD OF A DISC DRIVE SYSTEM Clair L. Far-rand, Bronxville, NY.

731 Assignee: lnductosyn Corporation, Valhalla, NY. 22 Filed: March a, 1971 [211 App]. No.: 121,951

[72] Inventor:

Primary Examiner-Bemard Konick Assistant Examiner-Vincent P; Canney Attorney-William E. Beatty and David E. Lovejoy [57] ABSTRACT Disclosed is a position-measuring transfonner formed from two relatively movable members. The transformer is particularly useful for selecting and defining track positions in a magnetic disc drive system which may be used as a memory in a digital computer. One stationary member of the transformer includes cofunction windings and end-detecting windings. Those windings magnetically coupled to a reference winding on another relatively movable member of the transformer. The reference winding, which is the continuous winding of the transformer, is formed from a plurality of equally spaced active conductors. The active conductors are interconnected such that alternate ones conduct in opposite directions so that each pair of adjacent active conductors define a reference cycle. The end-detecting windings consist of one or more pairs of active conductors where the active conductors in each pair have full-cycle spacing, that is, the separation between each active conductor in a pair equals one reference cycle. The fullcycle spacing of the end-detecting winding superposed over the half-cycle spacing of the end-detecting winding induces a substantially zero resultant signal in the end-detecting winding except when the end-detecting winding is positioned over the end conductor of the reference winding as may occur when the reference'winding is moved. When over the end, a limit signal is generated as a result of the unequal coupling between the end-detecting winding active conductors and the end conductor of the reference winding. The limit signal thus generated typically defines the inner or outer limit of a read/write head. Cofunction windings are formed from four winding sections with equal numbers of active conductors per section. The cofunction windings are formed using an efficient winding pattern which minimizes the number of welded or soldered connections required.

12 Clalns, 7 Drawing Figures POSITION-MEASURING TRANSFORMER HAVING END- DETECTING WINDINGS USEFUL FOR POSITIONING A MAGNETIC HEAD OF A DISC DRIVE SYSTEM BACKGROUND OF THE INVENTION This invention relates to position-measuring transformers of the type having two relatively movable members, one member having at least two planar windings (called polyphase windings) which are phase shifted in space relative to each other and which are inductively coupled to another planar winding carried by the other member.

When one winding on one member is energized with an altemati ng primary signal, that winding induces a secondary signal in any winding onthe other member which is in close proximity thereto.

Conventional position-measuring transformers employ, on one member, a single winding formed from uniformly spaced, series-connected active conductors. That member is therefore a single-phasemember which defines a reference pitch, that is, defines a periodic spacing of the active conductors. Two active conductors (two pitches) form a reference cycle. In practice, the single-phase member is called the scale for linear devices and is called rotor" for rotary devices.

The other relatively movable member, called the polyphase member, of conventional position-measuring transformers generally includes two cofunction windings, each phaseshifted in space with respect to the other a fractional portion of the reference cycle so that two different phases are presented as determined with reference to the single-phase member. In practice, the polyphase member is called the slider" for linear devices and the stator for rotary devices. Notwithstanding conventional practice, either or both the single-phase or polyphase members can be movable.

The phase-shift between th e polyphase windings is generally one-quarter of the reference winding cycle. Accordingly, the phase shift between the polyphase windings is a quadrature phase shift and hence is a phase shift analogous to the quadrature phase shift between sine and cosine trigonometric functions. When the polyphase windings are spaced in odd multiples of a quarter cycle, they are conventionally identified as the sine and cosine windings. While sine and cosine windings are conventional, other phase shifts, of course, may be implemented. For example, 120 shifts between each of three windings may be employed to form a three-phase system. Broadly, the term polyphase" describes all such phaseshifted windings. Additionally, the term cofunction is also generically used to describe the polyphase relations of windings of position-measuring transformers since sine and cosine, for example, are trigonometric cofunctions of the same angle.

Position-measuring transformers of the above type have been known and used for many years. For example, US. Pat. Nos. 2,799,835; 2,915,722; 2,924,798 and 3,441,888, all assigned to the assignee of the present invention, are representative examples. The V. F. Foster application, Multilayer Polyphasev Winding Member and Transformer," Ser. No. 36,913, filed May 13, 1970, assigned to the same assignee, discloses placing winding sections of cofunction windings on different layers to solve the crossover problem resulting from interconnecting winding sections. While two or more layers are useful, it is still desirable to reduce the number of crossovers required.

The development of data processing systems and particularly magnetic disc systems has produced a demand for greater information storage densities. Such greater densities are achieved in disc systems by storing data in more closely spaced magnetic tracks. While position-measuring transformers have been widely employed for accurately measuring and controlling machine elements at closely spaced positions, the magnetic disc drive systems have special requirements not heretofore readily available from position-measuring transformers. One such requirement is the ability to detect inner and outer track limits beyond which the read/write head normally does not travel while also precisely detecting crowded internal track positions between the inner and outer limits.

It is an objective of the present invention, therefore, to provide a position-measuring transformer which more efficiently and more economically provides inner and outer limit indications while also precisely indicating internal track locations.

SUMMARY OF THE INVENTION The present invention is an improved winding member and position-measuring transformer which minimizes the number of soldered or welded wire connections and which defines space positions useful, for example, in controlling the read/write-head position in magnetic disc drive systems.

The position-measuring transformer of the present invention includes end-detecting windings which are unresponsive to a reference winding except at special space positions. Additionally, cofunction windings are formed from four winding sections in a configuration which minimizes the number of soldered or welded winding connections required.

The sine and cosine windings and the end-detecting windings of the transformer are positioned on one of two relatively movable members. The other of the two relatively movable members supports a reference winding which establishes the periodic space cycle. The two members are positioned in close proximity so that the windings magnetically couple. The reference winding is formed from a plurality of equally spaced active conductors. The active conductors are positioned at half-cycle points and are interconnected by inactive conductors so that adjacent active conductors carry current in opposite directions. The end-detecting windings are formed from at least two active conductors which are spaced at full-cycle points, that is, at twice the spacing as that between the reference winding active conductors.

The active conductors of the end-detecting windings are interconnected by inactive conductors so that adjacent conductors conduct current in opposite directions. Whenever all the active conductors of the end-detecting windings are fully positioned over the active conductors of the reference windings, the total resultant magnetic coupling in the end-detecting winding is substantially zero. Whenever the relatively movable members are moved such that one or more of the active conductors of an end-detecting winding does not fully couple the reference winding, for example when positioned over the end conductors, non-cancelling unequal coupling results in the generation of a limit signal.

In a magnetic disc drive embodiment, the end-detecting windings become located over the ends of the reference winding when, for example, the reference winding member is translated. Whenever translation causes a detecting winding to exhibit a signal, that signal, as detected by a signal detector, signifies that an inner or outer limit has been reached.

For locating intermediate tracks between the inner and outer track limits, cofunction sine and cosine windings produce signals at the cyclic positions established by the spacing of the reference conductors. The efiicient cofunction winding pattern which minimizes the number of welded or soldered connections is formed with four winding sections per cofunction winding, that is, four for the sine winding and four for the cosine winding. The number of active conductors per winding section is a function of the total number of active conductors in the polyphase winding. For example, for a polyphase winding with 48 active conductors, each winding section includes six active conductors. For a linear transformer, the sine and cosine winding sections are alternated with a reversal of alternation at the center in order to employ the invention of the above-referenced US. Pat. No. 2,915,722. As a specific example, a polyphase winding member which has 48 active conductors typically includes in order six active conductors interconnected to form a sine winding section, six active conductors interconnected to form a cosine winding section, six active conductors forming a sine winding section, twelve active conductors forming two sideby-side cosine winding sections, six active conductors forming a sine winding section, six active conductors forming a cosine winding section and six active conductors forming a sine winding section.

The spacing of the active conductors in the polyphase winding member nominally equals the spacing of the active conductors in the reference winding member. The sine winding sections are, however, shifted with respect to the cosine winding sections by a quarter cycle (or any odd integral multiple thereof) of the reference winding cycle.

The end-detecting windings are typically positioned at either end of the sine and cosine windings. The end-detecting windings together with the cofunction windings operate with electronic signal detectors to define and control the positions of tracks on a magnetic disc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an enlarged schematic plan view of a polyphase member, including end-detecting windings and cofunction windings and a single-phase member, including a reference winding, where the two members, when superposed as in FIG. 3, form a position-measuring transformer.

FIGS. 2a, 2b, 2c and 2d schematically depict several representative positions of an end-detecting winding superposed over a reference winding.

FIG. 3 depicts a schematic oblique view of a position-measuring transformer of the FIG. I type mounted and connected in a magnetic disc drive system.

FIG. 4 depicts a cross-sectional front view of a portion of the position-measuring transformer represented in FIG. 1.

DETAILED DESCRIPTION General FIG. 1 depicts a position-measuring transformer including a olyphase member 49 which is stationary with respect to a translatable single phase member 50. Polyphase member 49 includes first and second end-detecting windings 30 and 31, respectively, and polyphase windings 48.

The member 50 includes the continuous reference winding 51 having a plurality of active conductors postscripted 43 and 44 which are spaced at half-cycle intervals, P, that is, with a pitch, P. The active conductors postscripted 43 are connected to the active conductors postscripted 44 by inactive conductors postscripted 45. Active conductors 43 are operative to conduct current in one direction while the active conductors 44 are operative to conduct the same current in the opposite direction. The distance between two alternate successive active conductors such as between typical conductors 43-1 and 43-2 or 44-1 and 4 L-2, defines one full cycle, 2?, of reference winding 51.

End-Detecting Windings The end-detecting windings 30 and 31 each include active conductors 30-28 and 30-27 and 31-28 and 31-27, respectively. The spacing between the active conductors 30-28 and 30-27 is one full cycle, 2?, as is the spacing between the active conductors 31-28 and 31-27. Each of the active conductors of end-detecting windings 30 and 31 are connected by an inactive conductor 30-32 and 31-32, respectively. Accordingly, any current conducted by active conductors 30-28 is in the opposite direction of an equal current carried by active conductor 30-27. Similarly, any current in active conductor 31-28 is equal and opposite to the current in active conductor 31-27. If the magnetic coupling from reference winding 51 is equal for both active conductors 30-28 and 30-27, then the resultant coupling in the end-detecting winding 30 is substantially zero.

Similarly, for equal magnetic couplings in active conductors 31-28 and 31-27, the resultant current in end-detecting winding 31 is also substantially 0.

Referring to FIGS. 20 through 2d, an enlarged view of a reference winding 51' and a superposed end-detecting winding 30 is shown. The primed numbers in FIGS. 2a through 2d correspond to the unprimed numbers of FIG. 1.

In FIG. 2a, it is assumed that terminals 40' and 41' are connected in a conventional manner to an AC signal generator and, therefore, an AC signal is carried by reference winding 51'. With such a signal, active conductor 43'-! induces a signal in active conductor 31-28'. In an analogous manner, active conductor 44'-l induces an equal but opposite signal in active conductor 31-28' so that the resultant signal in active conductor 31-28' is substantially zero. In a similar manner, the resultant signal in active conductor 31-27' is also substantially zero so that the signal between terminals 37' and 38 is also substantially zero.

Referring to FIG. 2b, end-detecting winding 31' is shifted to the right relative to its position in FIG. 2a so that active conductor 31-28 is no longer equally spaced between active conductors 43-1 and 44-l. The resultant signal in activeconductor 31-28, therefore, has a greater contribution from active conductor 44'-l than from active conductor 43'-1 since it is closer to active conductor 44'-1. In a similar manner, active conductor 31-27' has a greater component of coupling from active conductor 44'-2 than from active conductor 43'-2. Since the signals in each pair of like-numbered active conductors 44'-] and 44'-2, and 43'-l and 43'-2 are equal and of the same direction, they induce equal signal components into active conductors 31-28' and 31-27'. Since, however, active conductors 311-28 and 31-27' are interconnected by inactive conductor 31-32' so as to conduct in opposite directions, the equal signal in active conductors 31-28' and 31-27' are cancelled. The resultant signal in end-detecting winding 31', of FIG. 2b as measured between terminals 37 and 38', is substantially zero.

In FIG. 2c, again the equal resultant signals in active conductors 31-28' and 31-27 are interconnected by inactive conductor 31-32' in opposite directions so that again the resultant signal is substantially zero.

Referring to FIG. 2d, the resultant signal between terminals 35' and 36' of end-detecting winding 30', unlike FIGS. 2a, 2b and 2c is substantially greater than zero. This non-zero signal results because the end-detecting winding 31 partially extends over the end of the reference winding 51'. Because of this extension over the end, unequal coupling occurs in active conductors 31-28 and 31-27'. The greatest contribution to coupling in active conductor 31-28 is from active conductor 43-2. There is no active conductor on the right-hand side of active conductor 31-28. Accordingly, a greater signal is induced in active conductor 31-28' than is induced in active conductor 31-27'. This greater signal, as increased by the active conductor 31-28' signal, results in a substantially greaterthan-zero signal between terminals 35' and 36'.

Summarizing FIGS. 2a through 2d, whenever the end-detecting winding 31' is fully positioned over the reference winding 51', in any position relative to the reference winding cycle, the resultant signal in winding 31 is substantially zero. Whenever the end-detecting winding 31 is over the end of the reference winding 51' through translation of member 50, unequal coupling occurs and a non-zero resultant signal is produced. Because the end-detecting windings have substantially zero signal whenever fully positioned over the reference winding, they are unresponsive to the reference winding. Cofunction Windings Referring again to FIG. 1, the polyphase windings 48 on member 49, like the end-detecting windings 30 and 31, magnetically couple the reference winding 51 on member 50. A sine winding is formed between terminals 60 and 61 by interconnected active conductors having postscripts 27 or 28. Similarly, a cosine winding is formed between terminals 63 and 64 again by interconnected active conductors having postscripts 27 or 28. The active conductors of the sine winding are formed into four winding sections SI, SII, SIII and SIV. Similarly, the active conductors of the cosine winding are formed into four winding sections CI, CII, CH1 and CIV. Winding section SI includes six active conductors I-28, 1-27, 2-28, 2-27, 3-28 and 3-27. In a similar manner, winding sections SII, SIII and SW have six active conductors designated by the appropriate postscripts. In an analogous manner, cosine winding section CI includes active conductors 4-28, 4-27, and so on, to 6-27. Cosine winding sections CII, CIII and CIV similarly have six active conductors designated by the apropriate postscripts.

In FIG. 1, the spacing between active conductors in each of eight winding sections is nominally equal to the spacing, P, of the reference winding 51. While the compression of active conductors for the purpose of harmonic suppression, as described in the R. W. Tripp US. Pat. No. 2,799,835 is preferred, that compression has not been represented in the schematic representation of FIG. 1. While the spacing between active conductors in a winding section is nominally P, the sine winding sections SI, SII, S111 and SIV are shifted relative to the cosine winding sections CI, CII, CHI and CIV a quarter of the reference winding cycle, 2P, that is, /4)(2P)= (9%)). For example, the spacing between winding sections SI and CI as measured between the active conductors 3-27 and 4-28 is (3/2 )P which is equal to of a cycle, 2?. A similar 5'4- cycle spacing appears between winding sections CI and SII, SII and CII, CIII and SIII, Slll and CIV, and CIV and SIV.

The sine winding sections SI through SIV are interconnected in opposite conduction directions. Specifically, terminal 77 for winding section 51 is connected to terminal 79 of section SII so that for a current in one direction in active conductor 1-28 is matched by an equal but opposite direction current in active conductor 7-28. The position of active conductor 7-28 is midway between active conductors 43-5 and 44-5 of reference winding 51. For the same relative displacement of members 49 and 50, active conductor 1-28 is spaced midway between active conductors 43-3 and 44-3 of reference winding 51. Accordingly, while conductors 1-28 and 7-28 are interconnected so that current is in opposite directions, they are also positioned with respect to the reference winding so that they magnetically couple in the opposite sense. The effect resulting from opposite current directions cancels the effect resulting from opposite magnetic coupling in a manner which surpasses unwanted error-causing signals which would result from l-turn loop coupling. Sine winding sections SIII and SIV are interconnected so that conductors 18- 27 and 24-27 conduct in opposite directions. That opposite interconnection is compensated by the opposite magnetic couplings of winding sections SIII and SIV with the reference. Sine winding section SI and SIII can be arbitrarily defined to have a positive coupling effect and if so, sine winding sections 811 and SIII are necessarily defined to have a negative coupling effect.

In a manner analogous to the sine winding sections, the cosine winding sections have positive and negative coupling effects with respect to the reference. Cosine windings CI and CIV may be arbitrarily defined to have a positive coupling effect relative to the reference since current in active conductor 6-27 is necessarily in the same direction as current in active conductor 21-27. When winding sections Cl and CIV are defined as having a positive coupling effect with respect to the reference, winding sections CII and CIII necessarily have a negative coupling effect.

The cofunction windings 48 of FIG. 1 are an efficient design because both the sine winding sections and the cosine winding sections are symmetrically disposed on either side of the center line C. Each has an equal number (2) of positive and negative coupling winding sections, one positive and one negative, on each side of the center line C. Additionally, the number of crossovers for connecting the winding sections in the opposite sense, such as the crossover between terminal 77 and 79 (crossing over the connection from active conductor 7-28 running to terminal 78), are equal to four. The four crossover connections are from terminal 79 to terminal 77, from terminal 82 to terminal 85, from terminal 83 to 84, and from terminal 60' to 60. The four crossovers may be reduced to one if the terminal 60 is moved to 60', the terminal 64 is moved to 64 and the terminal 63 to 63. The crossover may be eliminated by making the terminals 60', 63' and 64' a connection through to the back (not shown) of member 49, thereby leaving only the crossover 79 to 77.

In FIG. 4, a cross sectional front view of the schematically shown position-measuring transformer of FIG. 1 has tripleprimed numbers identifying analogous parts bearing unprimed numbers in FIG. 1. The sine winding section SI and cosine winding section CI are shown adjacent the end-detecting winding 30". The height, Hc, of the various active conductors appropriately postscripted with a -27" and a 28"' in a typical embodiment is appropriately 0.8 inch. The center-tocenter spacing between conductors 1-28' and 1-27' is approximately 0.0l9 inch while the center-to-center spacing, E, of the end-detecting winding active conductors 3-28' and 30-27' is approximately 0.04 inch.

By way of comparison, the height, I-lr, of the active conductors 43" and 44 on the reference member 50" is approximately 0.7 inch. Similarly, the center-to-center spacing, D, between active conductors 43" and 44" is approximately 0.02 inch. Note that while the spacing of the end-detecting winding 30' is just twice that of the spacing, D, between reference active conductors, the spacing, G, between cofunction active conductors includes the compression factor useful for reducing the efiects of harmonic signals as described for example in the US. Pat. No. 2,799,835.

FIG. 3 depicts a disc drive system employing a positionmeasuring transformer like that of FIG. 1. The double-primed numbers of FIG. 3 correspond to unprimed like-numbers of FIG. 1. The disc drive system of FIG. 3 includes a translator 89 which supports the transformer member 50" which in turn carries the reference winding 51". Translator 89 is translated by drive 91, typically a motor, thereby translating the member 50" and reference winding 51" relative to the stationary member 49" while simultaneously translating the read/write head 92 relative to a magnetic disc 93. Disc 93 is rotated about its center 0 by a drive means (not shown). Member 49" is stationary with respect to disc 93 and motor 91. Member 49" supports the end-detecting windings and cofunction windings as previously described in connection with FIG. 1.

The reference winding 51" on member 50", in a typical embodiment, is energized by a signal generator 87 which may be any suitable and conventional AC signal generator. Signal generator 87 is connected to reference winding 51" via terminals 40" and 41". Signal generator 87 may be controlled with a start/stop signal via line 72. Line 72 is derived from a control unit 95 described hereinafter.

Member 49" in FIG. 3 includes the end-detecting windings and the cofunction windings 48 described with reference to FIG. 1 but which are not specifically shown in FIG. 3. The windings on member 49" magnetically couple the relatively movable reference winding 51" on member 50". Terminals 35" and 36" connect the end-detecting winding 30 shown in FIG. 1 to a signal detector 98 in FIG. 3. Similarly, terminals 37" and 38", connect the end-detecting winding 31 (shown in FIG. 1) to a signal generator 97 in FIG. 3. Signal detectors 97 and 98 are any conventional threshold detecting circuits which detect the presence or the absence of signals in the enddetecting windings. Signal detectors 97 and 98 render indications to control 95 via lines 73 and 74, respectively. Signal detectors 97 and 98 typically include bistable flip-flops so that the signals on lines 73 and 74 are appropriately bi-level signals which indicate the presence or the absence of a signal in the end-detecting windings.

The cofunction windings 48 of FIG. 1 as positioned over the member 49' in FIG. 3 are connected to a sine/cosine detector 99 via terminals 60" and 61" and 63" and 64". Sine/cosine detector 99 typically includes analog circuitry, such as amplifiers, which sense the level of the signals from cofunction windings on member 49". Detector 99 conveys those signals to control 95 via lines schematically represented by a single line 75.

Control unit 95 is any conventional disc drive control unit which is capable of carrying out the various control functions necessary for the operation of the FIG. 3 apparatus. Control 95 typically includes data processing apparatus well known to those skilled in the art of magnetic disc drive systems.

A typical implementation of conventional control 95 includes a digital command source, such as a data processing system, for commanding translator 89 to any one of a plurality of discrete track positions for head 92 between center and the periphery of disc 93. The discrete track positions are defined by the positions at which the signals in one or the other of cofunction windings 48 are a null (or other convenient level) relative to the energized reference winding 51".

The command in control 95 is typically stored in a digital register. Another digital register typically represents the present position of the reference member 50 and the translator 89. The difference between the command position and the present position is typically stored in a third register which stores, therefore, a how-far-to-go (delta) count. If the delta count differs from 0, a drive signal is commanded via line 68, through appropriate amplifier and power-driving circuits (not shown), to cause drive 91 to translate translator 89, reference winding 51" and magnetic head 92. Sine/cosine detector 99 detects each cycle (or fraction thereof) of reference winding 51" which translates with respect to member 49". Each detection by detector 99 decrements the how-far-to-go count in control 95. When the how-far-to-go counter reaches 0 count, the sine or cosine signals (or both) from detector 99 are typically employed to directly servo translator 89 to the exact track position which was commanded. For a new command, the how-far-to-go count and decrementing process described is repeated.

Whenever translator 89 receives a signal from line 73 or line 74, the limit of travel of translator 89 and therefore of head 92 is reached and appropriate control action is taken by control 95. For example, the signals on line 73 and 74 can invert the polarity of the signal on line 68 thereby causing translator 89 to rev erse direction.

Since the subject matter of the control 95 and of the signal detectors 97, 98, and 99 are well-known to those skilled in the magnetic disc art, further specific detail is not warranted in this specification. For further details relating to control mechanisms which employ command, present position, and how-far-to-go counters, reference is made to application, Ser. No. 814,670 filed Apr. 9, 1969, entitled Position Control System," and assigned to the same assignee of the present invention.

FURTHER AND OTHER EMBODIMENTS While the end-detecting windings 30 and 31 of FIG. 1 have been depicted having active conductors which are parallel to the active conductors of the reference winding 51", those active conductors may be inclined at any angle. Independent of whether the end-detecting windings are parallel or inclined with respect to the active conductors of the reference windings, the end-detecting windings are unresponsive to the reference winding except when juxtaposed to the ends of the reference winding.

While the present invention has been described with respect to linear transducers, it of course may apply to rotary devices.

Although the end-detecting windings have been depicted as consisting of only two active conductors having twice the spacing of the active conductors of the reference winding, additional pairs of active conductors at twice the spacing of the reference winding active conductors may be interconnected to form an end-detecting winding. Similarly, any integral multiple of twice the spacing (e.g., four, six, eight) may be employed. Any double spacing or multiple thereof is defined for the purpose of this specification as full-cycle spacing.

While the windings and winding sections of FIG. 1 are generally manufactured on a single layer, multiple layers may be employed. For example, half the cofunction winding sections (e.g., sine) of FIG. 1 may be manufactured on one layer, and the other half (e.g., cosine) along with end-detecting windings 30 and 31 may be added on a second layer.

As heretofore explained, the end-detecting windings are normally unresponsive to the reference winding, that is, the

resultant signals in the end-detecting windings are zero. A zero level resultant signal may be considered, in accordance with the present invention, to be due to a non-inductive relationship between the reference and end-detecting windings.

While as previously described, the end-detecting windings may be inclined at any angle without losing their unresponsiveness to the reference winding, the parallel relationship between the active conductors in the end-detecting and reference windings is preferred since that relationship renders the position measuring transformer insensitive to minor displacements of one member relative to the other member in a direction parallel to the active conductors. If inclined end-detecting windings are employed, then the detection of a limit signal becomes insensitive to minor shifts between the posi tion-measuring transformer members.

What is claimed is:

1. A position-measuring transformer including first and second relatively movable members comprising, a first winding, on said first member, formed by first active conductors spaced at half-cycle positions of a reference cycle and interconnected to cause adjacent ones of said first active conductors to conduct in opposite directions, a second winding on said second member inductively coupling said first winding, said second winding formed by second active conductors spaced at full-cycle positions and interconnected to cause adjacent ones of said second active conductors to conduct in opposite directions, said second winding producing a non-zero resultant signal only when said second active conductors unequally couple said first winding.

2. The transformer of claim 1 wherein said second active conductors are substantially parallel to said first active conductors.

3. The position-measuring transformer of claim 1 further including,

a signal generator for energizing said first winding, and,

a signal detector for detecting any signal induced in said second winding.

4. The position-measuring transformer of claim 1 wherein said second member further includes,

a first polyphase winding spaced from said second winding for detecting cyclic positions relative to said reference cycle.

5. The position-measuring transformer of claim 4 further including a second polyphase winding spaced relative to said first polyphase winding any odd integral multiple of onequarter of said reference cycle and wherein each of said polyphase windings includes two winding sections having a positive coupling efi'ect to said reference winding and two winding sections having a negative coupling effect to said reference winding.

6. The positiommeasuring transformer of claim 5 wherein each of said first and second polyphase windings has one posi tive coupling and one negative coupling winding section symmetrically disposed on either side of a center line whereby the number of conductor crossovers interconnecting the winding sections does not exceed four.

7. The position-measuring transformer of claim 6 wherein said polyphase windings include terminals through-connected to the back of said second member whereby the number of conductor crossovers equals one.

8. A disc drive system for positioning a magnetic head at a plurality of track locations including an inner limit and an outer limit, on a magnetic disc, comprising,

a first member rigidly-fixed with respect to said magnetic head and relatively movable with respect to said magnetic disc, said first member having a reference winding formed by first active conductors spaced at half-cycle positions of a reference cycle and interconnected to cause adjacent ones of said first active conductors to conduct in opposite directions.

a second member rigidly fixed with respect to said magnetic disc having first and second end-detecting windings each having second active conductors spaced at full-cycle posithird and fourth detectors for detecting the signals in said member further includes,

first and second polyphase windings each spaced relative to each other by any odd integral multiple of one-quarter of 10 said reference cycle and wherein each of said polyphase windings includes two winding sections having a positive coupling effect to said reference winding and two winding sections having a negative coupling effect to said reference winding, the said polyphase winding sections formed from active conductors having a nominal spacing equal to one-half said reference cycle where said track locations are defined by the null positions of said polyphase windings with respect to said reference winding.

10. The disc drive system of claim 9 further including,

a signal generator for energizing said reference windings,

first and second signal detectors for detecting any signals induced in said first and second end-detecting windings,

. respectively,

first and second polyphase windings, respectively. 1 l. Position-measuring transformer comprising relatively movable inductively related members in close space relation, one of said members having a single-phase winding, another of said members having a polyphase winding and a limit winding with first and second active conductors at one end of said polyphase winding, said limit winding being in close space, non-inductive relation with said single phase winding when said single phase winding is juxtaposed to both said active conductors of said limit winding, said limit winding being inductively related to said single phase winding and supplying a limit signal when said single phase winding is juxtaposed to only one of said active conductors.

l2. Position-measuring transformer comprising relatively movable inductively related members in close space relation, one of said members having a single-phase winding formed by reference active conductors spaced at half-cycle position of a reference cycle, another of said members having a limit winding with first and second active conductors spaced at full-cycle positions of said reference cycle, said limit winding being in close-space, non-inductive relation with said single phase winding when said single-phase winding is juxtaposed to equally couple both said active conductors of said limit winding, said limit winding being inductively related to said single phase winding and supplying a limit signal when said single phase winding is juxtaposed to unequally couple said singlephase winding.

Claims (12)

1. A position-measuring transformer including first and second relatively movable members comprising, a first winding, on said first member, formed by first active conductors spaced at halfcycle positions of a reference cycle and interconnected to cause adjacent ones of said first active conductors to conduct in opposite directions, a second winding on said second member inductively coupling said first winding, said second winding formed by second active conductors spaced at full-cycle positions and interconnected to cause adjacent ones of said second active conductors to conduct in opposite directions, said second winding producing a non-zero resultant signal only when said second active conductors unequally couple said first winding.

2. The transformer of claim 1 wherein said second active conductors are substantially parallel to said first active conductors.

3. The position-measuring transformer of claim 1 further including, a signal generator for energizing said first winding, and, a signal detector for detecting any signal induced in said second winding.

4. The position-measuring transformer of claim 1 wherein said second member further includes, a first polyphase winding spaced from said second winding for detecting cyclic positions relative to said reference cycle.

5. The position-measuring transformer of claim 4 further including a second polyphase winding spaced relative to said first polyphase winding any odd integral multiple of one-quarter of said reference cycle and wherein each of said polyphase windings includes two winding sections having a positive coupling effect to said reference winding and two winding sections having a negative coupling effect to said reference winding.

6. The position-measuring transformer of claim 5 wherein each of said first and second polyphase windings has one positive coupling and one negative coupling winding section symmetrically disposed on either side of a center line whereby the number of conductor crossovers interconnecting the winding sections does not exceed four.

7. The position-measuring transformer of claim 6 wherein said polyphase windings include terminals through-connected to the back of said second member whereby the number of conductor crossovers equals one.

8. A disc drive system for positioning a magnetic head at a Plurality of track locations including an inner limit and an outer limit, on a magnetic disc, comprising, a first member rigidly-fixed with respect to said magnetic head and relatively movable with respect to said magnetic disc, said first member having a reference winding formed by first active conductors spaced at half-cycle positions of a reference cycle and interconnected to cause adjacent ones of said first active conductors to conduct in opposite directions. a second member rigidly fixed with respect to said magnetic disc having first and second end-detecting windings each having second active conductors spaced at full-cycle positions and interconnected to cause adjacent ones of said second active conductors to conduct in opposite directions, said first and second end-detecting windings operative to detect ends of said reference winding to thereby define said inner and outer limits on said magnetic disc.

9. The disc drive system of claim 8 wherein said second member further includes, first and second polyphase windings each spaced relative to each other by any odd integral multiple of one-quarter of said reference cycle and wherein each of said polyphase windings includes two winding sections having a positive coupling effect to said reference winding and two winding sections having a negative coupling effect to said reference winding, the said polyphase winding sections formed from active conductors having a nominal spacing equal to one-half said reference cycle where said track locations are defined by the null positions of said polyphase windings with respect to said reference winding.

10. The disc drive system of claim 9 further including, a signal generator for energizing said reference windings, first and second signal detectors for detecting any signals induced in said first and second end-detecting windings, respectively, third and fourth detectors for detecting the signals in said first and second polyphase windings, respectively.

11. Position-measuring transformer comprising relatively movable inductively related members in close space relation, one of said members having a single-phase winding, another of said members having a polyphase winding and a limit winding with first and second active conductors at one end of said polyphase winding, said limit winding being in close space, non-inductive relation with said single phase winding when said single phase winding is juxtaposed to both said active conductors of said limit winding, said limit winding being inductively related to said single phase winding and supplying a limit signal when said single phase winding is juxtaposed to only one of said active conductors.

12. Position-measuring transformer comprising relatively movable inductively related members in close space relation, one of said members having a single-phase winding formed by reference active conductors spaced at half-cycle position of a reference cycle, another of said members having a limit winding with first and second active conductors spaced at full-cycle positions of said reference cycle, said limit winding being in close-space, non-inductive relation with said single phase winding when said single-phase winding is juxtaposed to equally couple both said active conductors of said limit winding, said limit winding being inductively related to said single phase winding and supplying a limit signal when said single phase winding is juxtaposed to unequally couple said single-phase winding.

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