US3487401A - Digitizer with long contacts - Google Patents

Abstract

1,157,641. Selective signalling. MOORE REED (INDUSTRIAL) Ltd. 15 July, 1966 [28 July, 1965], No. 32250/65. Heading G4H. A shaft 64, Fig. 6, position digitizer includes a 10<SP>-3</SP> stage 61 in which brushes 0/9, 1/8, 2/7, 3/6, 4/5 and A, B, C, C o , C e and COM, Fig. 5, are moved over stationary conductive segments 53, 54, 55, and 10<SP>-2</SP> and 10-1 stages 62, 63 in which coded scales (e.g. as in Fig. 7, not shown, or as in Specification 1,135,204, which is referred to) are moved past stationary brushes, the arrangement being such that each stage produces a " choosing signal " which selects which brushes in the next higher stage are to be operative. The lowest denominational stage 61, Fig. 6, includes two brushes A, B, Fig. 5, whose outputs when suitably combined (Fig. 2, not shown) produce inverse signals a, b, Fig. 3a, which are used to energize the C e and C 0 brushes respectively, Fig. 5, so that each numbered brush (e.g. 0/9) produces a signal when in a position corresponding to either of its numbers, the ambiguity being resolved by reference to brush C.

Description

Dec. 30, 1969 s. EVANS 3,487,401

DIGITIZER WITH LONG CONTACTS Filed July 18, 1966 5 Sheets-Sheet 2 All I A y f (/m/n 5= 40) Dec. 30, 1969 D. s. EVANS 3,487,401

DIGITIZER WITH LONG CONTACTS Filed July 18, 1966 5 Sheets-Sheet 4 Dec. 30, 1969 D. s. EVANS 3,437,401

DIGITIZER WITH LONG CONTACTS Filed July 18, 1966 5 Sheets-Sheet 5 m (an/ads afar/77rd [mg/b United States Patent US. Cl. 340-347 Claims ABSTRACT OF THE DISCLOSURE A digitizer for converting an analogue position into numerals with a plurality of contacts disposed on a support so as to form at least a single contact track and a plurality of parallel contact paths in that track with each contact track representing a numeral scale, a given division of length being associated with each numeral of that scale and each contact extending along its path for a distance equivalent to at least two of the given divisions of length of the scale. Brushes fixed with respect to each other are mounted for movement along the paths to produce signals which are then transmitted to an external device for determining the numerals into which the position is converted.

This invention relates to contact type digitizers having contacts longer than a scale division and to means for deriving therefrom signals corresponding to each division.

In this specification the terms contact and brush will be used, the operative association of a contact and a brush being referred to as connection. The meaning I of such terms, with reference to electric circuits, is wellknown but these terms will be used herein to refer also to other equivalent arrangements; such as, for example, optical, pneumatic, hydraulic and, particularly, to magnetic arrangements such as those wherein a discrete area of a material in a certain magnetic state corresponds to a contact and a sensor, corresponding to a brush, is provided to obtain one or other of two signals (one of which may correspond to a state of no signal), according as the sensor is or is not operatively coupled (connected) to such a discrete area of the material.

The base of a scale of nototion is the number of distinct digits which are required to express all the readings of the scale; for example, a binary scale requires two digits (0 and 1), and a decimal scale requires ten digits (0, 1 9). In explaining this invention, reference will be made to a decimal scale but it is to be understood that the principles can be applied to scales having other bases.

The term reflected half-base will be used to describe apparatus in which signals related to the digits of the lower half of the base of a scale are the same as those related to the corresponding complementary digits in the upper half of the base.

In our co-pending patent application No. 26346/ 65 there is described a reflected half-base digitizer wherein the lengths of the contacts do not exceed the track length corresponding to a single digit. The scale tracks are preferably arranged in closed circles. Since practical considerations set a lower limit to the length of a conveniently constructed contact, there is a corresponding upper limit to the resolution of a practical scale, for any particular scale diameter.

One object of the invention is therefore to provide means whereby contacts of a digitizer may be longer than the track length corresponding to a single digit of the scale.

3,487,401 Patented Dec. 30, 1969 According to this invention, a digitizer comprises a track having a plurality of contact paths, the track corresponding to a scale of notation; contacts, corresponding to the digits of the scale, distributed over the paths, each contact extending along its path by a distance substantially equivalent to at least the distance corresponding to two adjacent digits of the scale; and a plurality of brushes mounted in fixed relationship with one another and in movable relationship with the paths, each path having associated therewith a brush capable of sequentially connecting with and disconnecting from the contacts of the paths, both leading and trailing edges of the contacts having significance in reading; the contacts and brushes being so relatively disposed that, in use, each brush carries one of two signals, according as the brush is or is not connected to a contact, combined brush signals being logically related to the scale reading, as defined by the position of brushes along the track.

According to a first aspect of this invention, a digitizer may comprise as brush choosing drive means an arrangement as just described wherein the said track has two parallel contact paths, respectively corresponding to two groups of digits into which the scale is separated; and wherein there is provided means whereby, in use, the brush signals may be connected to logic devices for combining the brush signals and providing one of two choosing signals, according to the group of digits in which the scale reading lies.

When the said drive means is to be connected to choosing means for a reflected half-base digitizer, and/or a multiscale digitizer, the contacts may be so arranged that the resulting choosing signals are inverted at the centre of the scale and/ or at the junction of two scales.

When the contacts and brushes are conventional electric contacts and brushes, the means for connecting each brush signal to the logic devices may comprise a return brush, so associated with the signal brush that both the signal and return brushes connect with one contact simultaneously; the return brushes all being connected to a common line. A preferred alternative arrangement is, however, a continuous common contact, arranged along a path parallel to the said contact paths and having associated therewith a return brush connected to the common line, all the contacts being electrically connected together; such an arrangement makes it possible to avoid using a plurality of return brushes.

When equivalent optical, pneumatic or hydraulic devices are used as contacts and brushes, the contacts will usually be apertures; the passage of a beam of light, gas, or liquid through an aperture to a receiver providing one signal, while no beam reaching the receiver will correspond to the other signal.

Magnetic equivalents of contacts and brushes include arrangements analogous to a light-beam arrangement, the contact comprising a magnetic coupling between a transmitting device, disposed close to one side of the contact, and a receiving device similarly disposed on the other side of the contact; and an arrangement wherein both transmitter and receiver are disposed on one side of the contact, the coupling between the transmitter and the receiver being increased by the presence of the contact. A single device may then, in effect, comprise both transmitter and receiver, the presence or absence of a contact affecting the signal transfer properties of the device sufiiciently to provide two distinguishable signals.

In the equivalent optical, pneumatic, hydraulic and magnetic arrangements just described, the outputs of the receivers are connected to the common line.

In certain cases, for example when a brush choosing driving means is to be used in a reflected half-base digitizer, a yet further contact path may be arranged,

parallel to the driving contact paths and carrying complementing contacts for distinguishing between the upper and lower groups of the scale base. This complementing path will have associated with it a complementing brush, and the complementing contacts may be connected to the common contact of the choosing drive track. Such an arrangement will hereinafter be referred to as a complementing signal means.

The nature of this invention will be made clear in the following description, in which:

FIGURE 1 illustrates a brush choosing driving means, according to this invention;

FIGURE 2 shows logic devices connected to a brush choosing means, for selecting one of two brushes in response to drive signals from driving means such as is shown in FIGURE 1;

FIGURES 3A and 3B show modifications of the arrangement of FIGURE 1;

FIGURE 4 shows an exemplary single decade refiected half-base digitizer according to this invention;

FIGURE 5 illustrates one decade of a multidecade decimal digitizer and choosing drive track, according to this invention; and,

FIGURE 6 illustrates, in block form, a 1000 division digitizer according to this invention; and to the accompanying drawings in which:

FIGURE 7 illustrates another exemplary single decade reflected half-base digitizer, particularly suitable for use in a thousand-division digitizer;

FIGURE 8 shows, in block form, a logic circuit device for use with the digitizer of FIGURE 7; and

FIGURE 9 shows a logic circuit of FIGURE 8 in greater detail.

One embodiment of the first aspect of this invention is illustrated in FIGURE 1, which shows a movable set of three contact paths 10, 11 and 12, corresponding to the digits 0, 1 9, 1' of a decimal scale shown at 13. The path 10 carries a continuous contact 110, forming a common return connection. The path 11 carries three contacts 111, 112 and 113, positioned along the path so as to correspond with digits 1 and 2, and 6, and 9 and 0 respectively; and the path 12 similarly carries contacts 121, 122 and 123, corresponding to digits 2 and 3, 6 and 7, and 0 and 1. The length of each of the contacts on the paths 11 and 12 corresponds to two digits. Three brushes A, B and COM, shown as solid dots in a position corresponding to digit 0, are fixed relative to one another and are in movable relation to the contacts, along the paths. It will be seen that, as the brushes and contacts are moved relative to one another in the first decade 09, brush A is connected to the brush COM only when its position corresponds to digits 2, 3, 6 and 7; similarly brush B is connected to brush COM only when its position corresponds to digits 1, 2, 5, 6 and 9, as shown for example by the open dots at digit 1. Signal lines connected to brushes A and B will thus be correspondingly connected, or not connected, to a common signal line connected to brush COM, and will carry one of two corresponding brush signals. These brush signals can be combined, by means of known logic devices, to provide one of two signals, a and b as shown at 14, according as the reading of the scale, as defined by the position of the brushes, is even or odd; that is, the logic devices are arranged to perform the logical operations,

where A and B are the negation of A and B, and signifies disjunction (or).

FIGURE 2 shows a suitable logic device for performing the required logic operations, together with brush choosing means to be driven by the logic device.

In FIGURE 2, signal lines designated A and B respectively, are for connection to brushes A and B of FIGURE 1. Line A is connected directly to AND gates 20 and 21 and through an inverter 22, to AND gates 23 and 24; line B is connected directly to AND gates 20 and 24, and through an inverter 25 to AND gates 21 and 23. The inverters provide negation signals A and E as shown and the AND gates 20, 21, 23 and 24 pass signals according to the respective logic relations AB, A E, AIS and AB, as shown. The signals from the AND gates are passed to switches 26 and 27 of a bistable trigger circuit 28, capable of connecting one or the other of two signal lines 29 and 30 to a common line (not shown).

When the contacts and brushes comprise devices other than conventional electrical contacts and brushes, the common contact and the brush COM may not be necessary, the common connection being otherwise provided; the operating principle will, however, be the same. Even with conventional contacts and brushes, the common contact 110 and brush COM may be dispensed with, if a return brush is associated with each of brushes A and B, as hereinbefore described.

FIGURE 3A shows an alternative arrangement which is particularly suitable for driving choosing means for a reflected half-base digitizer.

In FIGURE 3A, contact paths 10, 11' and 12' correspond to paths 10, 11 and 12 of FIGURE 1, but contact pairs 130, 131 and 132 (corresponding to the contact pairs of FIGURE 1) are spaced apart by path lengths equivalent to three digits, instead of two digits, as in FIG- URE 1. Relative movement of the brushes and contact paths then result in brush signals which, when combined by suitable logic devices, provide two signals, a and b, as shown at 14'. It will be seen that the signals are inverted, when the brushes pass from digit 4 to digit 5 (that is, at the center of the base); and again, when the brushes pass from digit 9 to digit 0 (that is, from one decade to the next). The application of this feature will be made clear, hereinafter.

Instead of displacing the contacts on the path 12 or 12', relative to those on path 11 or 11, as shown in FIGURES 1 and 3A, one of the brushes may be displaced correspondingly. Such a modification, applied to the arrangement of FIGURE 3A, is shown in FIGURE 313, where the contacts on both path 11 and path 12 each correspond to digits 2 and 3, 7 and 8 and 2 and 3', respectively. The brushes A, B and COM are shown, as soild dots, in a position corresponding to digit 0 of the scale; since the contacts on path 11 have been advanced by one digit, relative to FIGURE 3A, brush B has also been advanced by one digit, relative to brush A. Since the common contact on path 10' is continuous, the position of brush COM is immaterial. Contacts and brushes so arranged will provide brush signals which can be combined, as described with reference to FIGURE 3A, to provide even and odd signals a and b as shown at 14 in FIGURE 3A.

If, for any purpose, more than two signals are required from a contact track and brush assembly such as has just been described, a corresponding number of parallel contact paths, with associated brushes, may be used. In such a case, the contacts on the individual paths may be aligned, after the manner described in connection with FIGURE 3B, and the brushes staggered; such an arrangement of the contacts simplifies the manufacture of the contact assembly.

The principle of distributing contacts, corresponding to the digits of a scale of notation, over a plurality of parallel paths, and making the path length of at least most of the contacts greater than the path length corresponding to a single digit, may be applied to digitizer scales; particularly to high resolution digitizers having a large number (for example 1000) divisions.

According to a second aspect of this invention a reflected half-base digitizer comprises a plurality of contact tracks, the tracks in combination corresponding to a scale of notation whose digits are separated into two complementary groups, each of which is related to a corresponding contact track; wherein each track comprises at least two parallel paths, there being disposed on each path contacts separated from one another along the path, and each path has movably associated therewith a brush capable of sequentially connecting with the contacts on the path, each complementary pair of digits if the base of the scale is even, or each complementary pair of digits and the center digit, if the base is odd, being associated with one brush; means being provided for connecting brush choosing means to the digitizer whereby, when the true reading of the scale is represented by a particular digit, the output of the digitizer carries signals related only to the group of digits including said particular digit.

Choosing drive means and complementing signal means, as hereinbefore described, may also be included. These means are respectively capable of providing drive signals, for driving choosing means for selecting a desired brush, and logic means control signals, for selecting one of the complementary pair of digits associated with the selected brush; both actions being performed according to the reading of the brushes. The various tracks of the digitizer, choosing drive means and complementiing signal means will, in use, have fixed relationship one with another; the brushes will have similar fixed relationship.

The second aspect of the invention will now be made clear by describing an exemplary embodiment of a single decade reflected half-base digitizer, having conventional electric contacts and brushes. A second related embodiment, wherein the digit contacts are distributed over a single track will also be described.

The first embodiment is shown in FIGURE 4, wherein there are two contact tracks 40 and 41; track 40 comprises four paths 42, 44, 46 and 48, and track 41 comprises three paths 43, 45 and 47. Each of paths 42 to 46 has two digit contacts, shown in full lines and respectively identified by the digits and 9, the contacts being disposed along the paths in positions corresponding to the positions of the respective digits on the scale, shown at 49. Paths 47 and 48 have continuous contacts C and C forming common contacts for the tracks 41 and 40, respectively. Contacts 0 and 9 are connected to contact C and contacts 1 and 8 to C although not so shown, contacts 2, 4, and 7 are also connected to C and 3 and 6 to C It will be seen that track 40 carries contacts positionally corresponding to a first group of digits comprising the even digits 0, 2 and 4, in the lower half of the scale, and complementary digits 5, 7 and 9 on the upper half of the scale. Track 41 similarly carries a second group comprising the odd digits 1 and 3 and the complementary digits 6 and 8. Track 40 will hereinafter be referred to as the evens tracks, and the common contact C as the evens common contact; track 41 will be referred to as the odds track, and contact C as the odds common contact.

With each of the paths 42 to 46 there is associated a brush, the brushes being respectively designated 0/9, 1/8, 2/7, 3/6 and 4/5, referring to the digits corresponding to the contacts with which a designated brush can connect. With the paths C and C there are similarly associated corresponding brushes C and C All the brushes are mounted in fixed relationship one with another, the brushes being movable with respect to the contact tracks, to establish a scale reading according to the relative position of the brushes and the contacts.

It will be seen that, when the brushes are in the positions shown in FIGURE 4 by solid dots, brush 0/ 9 is connected to brus'h if the brushes are moved to the positions shown by the open dots, brush 1/ 8 is connected to brush C in either case, all other brushes are disconnected from C and C Thus, the brushes 0/ 9 to 4/5 are capable of providing a signal indicating to which complementary pair of digts the scale is set, at any reading,

but there is a first ambiguity as to which of the two digits of the pair is the true reading. This first ambiguity can be resolved in a manner to be explained hereinafter.

Each of the digit contacts shown in FIGURE 4 may be extended, in both directions, along the relevant paths, as indicated by the dotted lines; it may be possible to manufacture such extended contacts even if, in a particular design, the path length corresponding to a single digit is too small for a practicable contact of single digit size. With such extended contacts, a second ambiguity will be introduced; when, for example, the brushes are in the position shown in FIGURE 4 by the open dots, odds brush 1/8 is connected to odds common brush C as before, but evens brushes 0/9 and 2/7 are also connected to evens common brush C It will be seen that the second ambiguity always arises in the track which is not related to the digit representing the true scale reading; the ambiguity can therefore be resolved by isolating the common brush of the track in which the ambiguity arises. Such a choice of one of the common brushes C and C can be made by suitable brush choosing means, driven by means according to the first aspect of this invention, described hereinbefore.

The second embodiment is illustrated in FIGURE 7 and comprises a single contact track having five code paths identified as V, W, X, Y and Z, and a common path COM; each path has an associated brush, the brushes being identified generally by 101. Portions of the paths correspond to the digits 0 to 9 as indicated in FIGURE 7. The five code paths carry discrete contacts as shown, while the common path carries a continuous contact.

Of the five code paths only three, namely W, X. and Z, have the edges of their contacts accurately positioned relative the scale (and the corresponding brushes accurately aligned); the contacts and brushes of these three paths therefore determine changes from one digit to the next. The function of the contacts on the two paths V and Y is to distinguish 0 and 9 from 4 and 5 and the positions of the edges of these contacts, and the alignment of the corresponding brushes, are therefore less critical than in the cases of the paths W, X and Z. The theoretical maximum tolerance permissible in the brush positions on the paths V and Y is il /2 divisions of the scale. The paths V and Y are complementary and the signals of one could be derived electrically from those of the other; both are, however, preferably included so that there is never a no-signal condition, even for the digit 0.

All the contacts of the digitizer shown in FIGURE 7 are connected together; the whole contact assembly may, in fact, be formed integrally, by printed circuit techniques or other known methods.

In use, the brushes corresponding to the paths V and Y may be connected to a logic circuit} arranged to provide outputs corresponding to the digits 0 to 4. A suitable logic circuit is shown at 102 in FIGURE 8 and includes AND gates, an OR gate and inverters, respectively designated &, OR and Inv. The path Z provides complementing signals C and C, by means of a logic circuit such as 103 in FIGURE 8.

In FIGURE 8 the signals from the digitizer paths are identified by the corresponding letters; the inverses of signals W, X and Z are designated W, X and Y.

When the digitizer of FIGURE 7 forms the low decade part of a multidecade digitizer, the cmplementing signals C and 6 may be used to drive choosing means for the next higher decade.

In FIGURE 4, the digit contacts of each track are arranged in staggered formation, the corresponding brushes all being in line with the common brush. A reverse arrangement is, however, preferable, one at least of the brushes being displaced so that some, at least, of the contacts can be arranged in line. One such arrangement is shown in FIGURE 5, where the contacts of an evens track, 50 and an odds track 51, are, in each case,

combined into single conducting bodies or layers, 53 and 54 respectively, whereby all the digit contacts of a track are connected to the corresponding common contact, in manufacture.

FIGURE 5 illustrates one decade (digits to 9, shown at 56) of a multidecade decimal digitizer, having an evens track, 50, an odds track 51, and a choosing drive track, 52, all according to the principles described hereinbefore. Although the paths of the tracks are shown as straight lines, it is to be understood that the paths are, in fact, closed circles, the tracks being continuous. The paths of the evens and odds track, and paths 10", 11 and 12' of the choosing drive track, correspond respectively with the paths designated by the same numbers in FIGURE 3A, 3B and 4; brushes associated with these paths also have the same references as in FIGURES 3A, 3B and 4. Path 57 of the choosing drive track 52 carries complementing contacts, a brush C being associated therewith.

It will be seen that, with the relative positions of the brushes and contacts shown, neither brush A nor brush B is connected to brush COM; thus, logic devices such as are shown in FIGURE 2 will give a signal Providing brush choosing means, such as is shown in FIGURE 2, are arranged to select the evens common brush C and disconnect the odds common brush C brush 0/9 will be connected to brush C and the scale reading is either 0 or its complement 9. The ambiguity is resolved by the complementing path 57, the complementing brush C being connected to the brush COM, indicating that the true reading lies in the upper half of the decade; the true reading is therefore 9.

If all the brushes are moved one digit to the right, in FIGURE 5, the choosing drive signal will become and the odds common brush will be selected; the complementing contact C, however, now indicates that the true reading is in the lower half of the next higher decade and the true reading is digit 0 of that decade.

Digitizers such as that illustrated in FIGURE may have any number of divisions, so long as the total number is an integral multiple of the base of the scale. Since the path length of the shortest contact is twice that corresponding to a single digit, a decimal digitizer having, for example 1000 divisions can. be manufactured sub stantially smaller than a prior art digitizer of the same resolution. Such a 1000 division digitizer is illustrated, in block form, in FIGURE 6.

In FIGURE 6, 61, 62 and 63 represent contact track assemblies and associated brush assemblies, for scales having respectively one thousand, one hundred and ten divisions. Each track assembly comprises a disc of insulating material on which electrical contacts are laid out on closed concentric paths. The contact disc of assembly 61 is rigidly mounted on a shaft 64, 64', for rotation therewith, the associated brushes being mounted in fixed po ition within the housing containing the assembly so that, when the contact disc is rotated through a particular angle relative to a datum position by means of the end 64 of the shaft, the contacts and brushes define a corresponding scale reading, one unit of the scale corresponding to of a revolution of the shaft 64. Assembly 61 thus gives signals corresponding to units of the scale.

Assembly '61 comprises three contact tracks, 65, 66 and 67; these tracks correspond respectively to the tracks '52, 50 and 51 of FIGURE 5, repetitively extended to include one thousand digits. The common brush of track 65 (corresponding to brush COM of FIGURE 5) is connected to a terminal COM for connection to one side of a voltage source; the brushes A and B are connected, through corresponding terminals A and B, to a choosing logic and choosing device 68, such as is shown in FIGURE 2. The

choosing means chooses one or other of two lines, which are respectively connected, through terminals C and C to corresponding common brushes (C and C in FIGURE 5) of the evens contact track 66 and the odds contact track 67. The evens digit bushes (0/9, 2/7 and 4/5 in FIGURE 5) are connected, through sets of terminals 69, to an amplifier 70, to which the odds digit brushes 1/8 and 3/6 in FIGURE 5) are also connected, through sets of terminals 71. The amplifier 70 is also connected to receive complementing signals from the brush C, via terminal C, of the track 65. The amplifier 70 is similar to that described in our aforementioned copending application and similarly comprises logic devices, for directing a digit signal to the appropriate one of a set 72 of t n unit digit output terminals according to the complementing signal.

The contact discs of assemblies 62 and 63 are mounted in fixed positions within their housings, the associated brushes being rigidly mounted on the shaft 64, 64', for rotation therewith. These assemblies are arranged to act as reflected half-base digitizers, in the manner described in our co-pending application No. 2.6346/65.

The assembly 62 has a digit track 73 having one hundred contacts, arranged in ten sequential decade sets, each contact corresponding to ten units of the scale of assembly 61. The contacts of each set are connected together in complementary pairs, symmetrically disposed about the centre of the decade, and to corresponding pairs of contacts of the other sets. A pair of bushes is connected, through terminals 93, to terminals C and O, of the amplifier 70, which provide complementing choosing signals, each of which corresponds to five units of the scale of assembly 61 that is to one half of a division of the track 73; one or other of the pair of brushes is thereby chosen, according to the true scale reading, to provide a tens digit signal representing a decade of the scale of assembly 61.

A complementing track 74 has ten sequential complementing sets of contacts arranged to provide, in co-operation with a pair or brushes movable by the shaft 64, one of two further complementing signals, according as the reading of the scale of track 73 is in a lower or upper half of a decade.

Signal lines connected respectively to the five complementary pairs of contacts of the track 73 are connected, through five sets of terminals 76, to an amplifier 78; which amplifier also receives appropriate complementing signals from the complementing track 75, through. sets of terminals 79. The amplifier operates in a manner similar to amplifier 70, directing each tens digit signal to the appropriate one of a set 80 of ten tens digit output terminals, according to the complementing signal received through the terminals 79.

The assembly 63 has a digit track 81, having ten contacts, each corresponding to one hundred units of the scale of assembly 61, forming a single decade set; the contacts are connected together in complementary pairs, symmetrically disposed about the centre of the decade. A brush pair is driven by the complementing signals from the complementing track 75, each signal corresponding to one half division of the track 81, and thereby provides a hundreds digit signal representing ten decades of the scale of assembly 61. A complementing track 83 has one complementing set of contacts arranged to provide, in co-operation with a pair of brushes movable by the shaft 64, one of two complementing signals, according as the reading of the scale of track 81 is in the lower or upper half of the decade.

Five sets of terminals 84 convey signals from the five complementary pairs of contacts of track 81 to an amplifier 86; which amplifier also receives complementing signals from the track 83, via sets of terminals 87. The amplifier 86 operates in a manner similar to amplifier 78, directing each hundreds digit signal to the appropriate one of a set 88 of ten hundreds digit output signal lines,

according to the complementing signal received through the terminals 87.

The assembly 61, may alternatively, comprise a contact track such as is illustrated in FIG. 7, repetitively extended to include one thousand digits. In such a case the choosing logic device 68 is not required, while an amplifier similar to the amplifier 78 is used instead of the amplifier 70. The amplifier receives digit signals from a logic device. such as is illustrated at 102 in FIGURE 8, together with complementing signals from the logic device 103. These. complementing signals are also passed to the assembly 62 as complementing choosing signals.

A coarser digitizer, preferably of the kind described in our aforementioned co-pending application, may be coupled, through a reduction gear train, to the end 64' of the shaft 64, 64. Such a digitizer may derive choosing signals from the complementing track 83, through the terminal set 89.

If desired, a one hundred division digitizer may comprise assemblies 62 and 63, for use with amplifiers 78 and 86, assembly 61 and associated devices 68 and 70 being omitted. Assembly 62 therefore comprises a fourth contact track 90, for providing, at terminals 92, a choosing means drive similar to that described in our aforementioned co-pending application. A suitable choosing means (not shown) can then supply choosing signals to terminals 93.

Any of the digitizer outputs may be inhibited, except on interrogation, by means similar to those described in our aforementioned co-pending application. The choosing device may also similarly be adapted to act as a short term memory.

In use, each assembly always provides two output signals to represent a digit (including zero); the absence of either one or both output signals therefore indicates a fault.

The output of the digitizers so far described is a full decimal output; a binary coded decimal output may be obtained by applying the full decimal output to a diode logic matrix, in known manner. It is thus possible to provide both a full decimal and a binary coded decimal output, simultaneously.

It is preferred, in practice, that a digitizer comprise necessary isolating diodes; which may be connected for positive or negative signal outputs, as desired. Choosing means, inhibiting gates and other associated electronic circuits are preferably provided as separate items.

What is claimed is:

1. A reflected half-base digitizer comprising first support means; a set of electrical contacts disposed on the first support means to form a plurality of tracks, the contacts of the tracks in combination corresponding to a scale of notation whose digits are separated into a corresponding plurality of groups of complementary digits, each track being related to one group of digits, the contacts being electrically connected together and distributed over at least two parallel paths, there being disposed on each path contacts separated from one another along the path each contact extending along its path a distance equivalent to at least the distance corresponding to two adjacent digits of the scale; second support means; a brush corresponding to each contact path and mounted on the second support means, all the brushes being in fixed relationship with one another; movement means for imparting relative movement between the first and second support means, whereby each brush is capable of sequentially connecting with and disconnecting from the contacts of its associated path, both leading and trailing edges of the contacts having significance in reading; and connection means for connecting brush choosing means to the digitizer whereby, when the true reading of the scale is represented by a particular digit, the output of the digitizer carries signals related only to the groups of digits including the said particular digit.

'2. A reflected half-base digitizer comprising first support means; a set of electrical contacts disposed on the first support means to form a single track having at least four contact paths one of which is a complementary contact path, the contacts of the paths in combination corresponding to the digits of a scale of notation, the digits being considered in two complementary groups, the contacts being electrically connected together, each contact extending along its path a distance equivalent to at least the distance corresponding to two adjacent digits of the scale, the contacts of each path which has a plurality of contacts being separated from one another along the path; second support means; a brush corresponding to each contact path and mounted on the second support means, all the brushes being in fixed relationship with one another; movement means for imparting relative movement between the first and second support means, whereby each brush is capable of sequentially connecting with and disconnecting from each contact of its associated path, both leading and trailing edges of the contacts having significance in reading; and connection means connected to the brushes and the sets of contacts for providing output signals from each of the said brushes.

3. A digitizer as claimed in claim 2 wherein the base of the scale is ten and wherein there are provided at least five contact paths, three of which have contacts each corresponding to at least two adjacent digits and longitudinally dimensioned and located with an accuracy at least as great as the accuracy with which the scale is to be read.

4. A digitizer as claimed in claim 2 wherein the paths are a set of concentric closed circles.

5. A digitizer as claimed in claim 2 wherein there are provided a plurality of contact tracks, each track corresponding to a scale, the several scales having bases which are sequentially rising powers of the base of the lowest scale, the corresponding tracks being joined together in sequence so that the joined paths form a set of concentric closed circles; each set of joined corresponding paths being provided with a common brush.

6. A digitizer for converting an analogue position into numerals comprising:

first support means,

a plurality of contacts disposed on said first support means to form at least a single contact track and to form a plurality of parallel contact paths in each said track so that each said contact track represents .a numerical scale with a division of length associated with each numeral of said scale with each said contact extending along its path for a distance equivalent to at least the distance corresponding to two adjacent given divisions of length on said scale, a contact track being associated with each of the numerals into which said position is converted,

brush means associated with each said contact path,

means for applying a source of electrical energy to at least some of said brushes to generate electrical information signals,

means for connecting said brushes and contacts to external means for receiving said information signals and determining said numerals into which said position is converted,

second support means for holding each of said brushes in each of said tracks in fixed relationship to each other, and

means for causing relative movement between said first and second support means to produce said analog position.

7. A digitizer comprising:

a member carrying a contact track having a plurality of contact paths, a scale of notation adjacent the tracks, contacts (as defined herein) corresponding to the digits of the scale distributed over the paths, each contact extending along its path a distance equivalent to at least the distance corresponding to two adjacent digits of the scale; and

a plurality of signal brushes (as defined herein) arranged in a first (even or odd) group and a second (odd or even) group, mounted in fixed relationship with one another and in movable relationship with the paths, each path having associated therewith a brush capable of sequentially connecting with and disconnecting from the contacts of the path, both leading and trailing edges of the contacts having significance in reading;

the contacts and brushes being so relatively disposed that, in use, each brush carries one of two signals, according as the brush is or is not connected to a contact, combined brush signals being logically related to the scale reading, as defined by the position of brushes along the track cars being provided whereby said first or second group is chosen in accordance with signals derived from an additional contact path on the member, and the arrangement of the contacts and brushes being such that relative movement therebetween along a brush path will produce different combinations of brush signals, one for each digit of the scale, by the connections effected between the contacts and the brushes.

8. A digitizer as claimed in claim 7 the said track having two parallel contact paths, respectively corresponding to two complementary groups of digits comprising the scale.

9. A digitizer as claimed in claim 8, wherein the contacts are so arranged that the choosing signals will be inverted at the center of the scale and/ or at the junction of two scales.

10. A digitizer as claimed in claim 7 arranged as a reflected half-base digitizer comprising a plurality of contact tracks, the tracks in combination corresponding to a scale of notation whose digits are separated into two complementary groups, each of which is related to a corresponding contact track;

wherein each track comprises at least two parallel paths, there being disposed on each path contacts separated from one another along the path, and each path has movably associated therewith a brush capable of sequentially connecting with the contacts on the path, each complementary pair of digits, if the base of the scale is even, or each complementary pair of digits and the center digit, if the base is odd, being associated with one brush;

means being provided for connecting brush choosing means to the digitizer whereby, when the true reading of the scale is represented by a particular digit, the output of the digitizer carries signals related only to the group of digits including said particular digit.

References Cited UNITED STATES PATENTS 2,873,442 2/1959 Ziserman 340-347 3,054,996 9/ 1 962 Spaulding et al 340-347 3,056,956 10/1962 Retzinger 340-347 3,070,787 12/1962 Waldron et a1. 340-347 3,143,730 8/1964 McIntyre 340-347 MAYNARD R. WILBUR, Primary Examiner J. GLASSMAN, Assistant Examiner

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