Abstract:
A digital displacement transducer to provide a digital output linear related to the displacement of a reference surface of an object. An eight track tape unit is coded with information related to displacements of 1/256 of an inch and applied to the reference surface. Means are then provided to assume the coded information of the tape unit; the means are of lesser coercivity than the tape unit. The information means is pulsed so that the information contained is the same, and a read out head is provided to read out which information was shifted, and thereby indicate the position of the reference surface of the object. A method is also provided to encode the information in the information means, switch the information therein, and obtain a read out.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method of measuring d.c. flux and a device therefor. 
     More particularly, the invention is concerned with a method and a digital displacement transducer apparatus for the measurement of a digital output which is related to the linearly displacement of a reference surface of an object. 
     A device which provides a digital output related to the displacement of a surface is a digital displacement transducer. It is desired to provide such a transducer to measure spatial displacement of approximately 0.004 inches (1/256 of an inch) of surface. One manner of providing a digital output related to spatial displacement is to provide an eight track magnetic tape or equivalent magnetic sheet and attach the tape to a reference surface of the object. The position of the reference surface could then be ascertained by reading coded information on the magnetic tape. For this purpose a stationary head would be used to read the coded information. In order to read the tape, it would be necessary to use a Hall probe or other equivalent d.c. flux measuring device; it would have to be used in the stationary head. While this technique is useful, it is quite costly. Hall probes are expensive, and they require flux condensing as small d.c. fields must be read. 
     In order to overcome the aforesaid problems and reduce the costs, the present invention proposes two embodiments to provide for the non-destructive read-out of the coded magnetic tape. 
     One embodiment is to provide a hard magnetic tape which is coded with magnetic information related to the displacement of a reference surface. A second soft magnetic tape is juxtaposed next to the hard magnetic tape and flux closed therewith. A magnetic field pulse is applied to the composite tape unit to change the magnetic stored information from a one or a positive state to a zero or negative state. The magnetic field has no effect on those already in the negative state. The magnetic field pulse is sufficiently strong to switch the information stored in the soft magnetic tape, but it is insufficient to switch the information stored in the hard magnetic tape. Therefore, the hard magnetic tape retains its coded information. 
     Another embodiment is to provide a single magnetic tape with coded information contained therein similar to the aforesaid hard magnetic tape. In this embodiment, the single tape also has eight tracks, although eight separate single track tapes can be used. A read head is provided for each track. Each read head includes a primary winding and a secondary winding. Use is made of the magnetic saturation characteristics of the read head to induce a large or small EMF into the secondary winding and provide a digital output. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of one embodiment of the invention which uses two magnetic tapes, one overlying the other, which are adapted for attachment to a reference surface of an object. FIG. 1 also shows a magnetization means in the form of a magnetization head for one of the tapes and a readout coil. While FIG. 1 shows the magnetization means as the head, a single strand wire running perpendicular to the magnetic axis can also be used in place of the magnetization head as the magnetization means to magnetize the one of the tapes. 
     FIG. 2 shows a schematic representation of an eight track tape which has been magnetically coded with stored information. 
     FIG. 3 shows a composite view of one zone of the eight track tape. The composite view includes a top view and end view of the tape together with one column indicating the Voltage Pulse and a second column indicating the Read Out. The Read Out column indicates the occurrence &#34;X&#34; or lack of occurrence &#34;-&#34; of a voltage pulse noted in the column under voltage pulse, and indicates whether a voltage pulse is produced as a result of switching the tape. A readout voltage pulse is obtained from those tracks switched. The tracks switched are those with a positive sign. 
     FIG. 4 is a schematic representation of another embodiment of the invention which uses only one magnetic tape with eight tracks or eight separate single track tapes and a magnetic read head for each track. 
     FIG. 5 is a graphical representation of the magnetization curve of the magnetic read head of FIG. 4. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to FIG. 1 of the drawings, a hard eight track magnetic tape 10 and soft magnetic tape 20 are shown. Tape 10 is shown with only a single track and containing stored information. Tape 10 is juxtaposed to and overlayed with soft eight track magnetic tape 20, also shown with only a single track. Tapes 10 and 20 are juxtaposed to each other so that the bits of stored information in tape 10 are flux closed by tape 20. It is understood that while only a single track is shown, the tapes contain eight tracks. 
     Tape 10 is shown in FIG. 2 with all eight tracks 11, 12, 13, 14, 15, 16, 17 and 18 with the bits of stored information. Tape 20 after being juxtaposed to tape 10 and flux closed therewith assumes all of the information in tape 10 and therefore stores the same magnetic code. Tape 20 is shown with the eight tracks 21, 22, 23, 24, 25, 26, 27 and 28 in FIG. 3. An end view 20a and a top view 20b of tape 20 is shown in FIG. 3. 
     A magnetization means 30 shown in the form of a magnetization head having a primary winding 32 is placed onto one of the zones on tape 20, and the composite tape unit 10, 20 is provided with a readout means, which includes means, as schematically shown, a secondary winding 34 magnetically coupled with the composite tape unit. A separate secondary winding 34 is required for each track. Secondary winding 34 is helically wound about the composite tape unit 10, 20. The read out means can be in the form of a readout head. While magnetization means 30 is shown in the form of a magnetic head, it is also within the scope of the invention to use a single wire in lieu of the magnetization head. This single wire when pulsed with a current of critical magnitude can be used to switch the magnetization in the soft magnetic tape. This offers the advantage of being simpler and intrinsically smaller in size than a yoke-based &#34;recording head&#34;. 
     It is to be understood that tape 10, coded as shown as in FIG. 2, is adapted for securement to a reference surface of an object (not shown). By this arrangement, relative linear displacement between the reference surface and the magnetization means 30 can be accurately sensed in the manner to be described hereinbelow. 
     By hard magnetic material as used herein, it is intended to designate a material which has a high coercive force and is hard to change its magnetization characteristic. Soft magnetic material as used herein is intended to designate a material which has a low coercive force and changes its magnetization characteristics easily. 
     Primary winding 32 when energized with a pulse is effective to switch the pulse (+) reading in tape 20 but ineffective to switch the (+) code in coded tape 10. Switching of tape 20 provides a voltage pulse in secondary winding 34. The column in FIG. 3 under voltage pulse indicates by means of an &#34;X&#34; that a voltage pulse is produced in the secondary winding as a result of switching of the tape. Column 2 indicates the read-out for the zone switched on tape 20 which corresponds to the zone on tape 10 under the recording head 30. As shown in FIG. 2 and as indicated in the column under read-out in FIG. 3, the position of the recording head is 10011111. 
     As noted heretofore, it is possible to use a single conductor as the magnetization means. Such a single conductor can be used to bridge all eight tracks and would normally lie perpendicular to the eight tracks. Such a conductor when pulsed with a current will generate a magnetic field along the tape axis and, depending upon the sign of the current will only switch &#34;+&#34; or &#34;-&#34; zones on tape 20. When the single conductor is used as the magnetization means, it can be generally similar to the secondary winding 34, and hence a separate drawing to show magnetization means 30 in the form of a single stand wire running perpendicular to the magnetic tape axis is considered to be unnecessary. 
     FIG. 3 shows separate conventional readout means in the form of heads 41, 42, 43, 44, 45, 46, 47 and 48 provided for each track. The readout heads may be mounted adjacent to or on the other side of the tape from the magnetization means or magnetization write head. 
     Referring now to FIG. 4 of the drawings which shows another preferred mode of practicing the invention, a portion of tape 10 is shown with a read head 50 having a primary input winding 52 and a secondary output winding 54. Tape 10 is preferably an eight track tape of the type shown in FIG. 2. Neverthless, eight single track tapes can also be used. Tape 10 carries the magnetic coded information to indicate the location or position of the reference surface. 
     Read head 50 is constructed of non-linear high permeability magnetic material, but of a lesser covercive force than tape 10. Read head 50 is magnetized by the stored magnetization dipole in the tape 10. By suitably pulsing the primary winding 52 with a current that is adjusted in magnitude so it will be large enough to switch the head but less than that required to switch the tape, only the head 50 will be switched. 
     The graphical representation of FIG. 5 which shows the magnetization curve 56 of magnetic read head 50 demonstrates the effect produced by the current applied to primary winding 52. The ordinate of the graph shows flux density and the abscissa shows the applied magnetic field. The magnetic field H, is induced into read head 50 by the flux B, produced by the dipole moment in tape 10. The read head 50 is magnetized by the tape to a near saturated condition just above the knee of the B-H curve. As a result of the current applied to primary winding 52, an applied field -ΔH or +ΔH will be produced depending on the current direction. Assuming the magnetization shown, field +ΔH will produce a small electromotive force (EMF) in secondary winding 54, and field -ΔH will produce a large EMF in secondary winding 54 and in the opposite direction to the EMF produced by the field +ΔH. An output is produced in the secondary winding 54 when the head 50 is pulsed for demagnetization thereof. 
     OPERATION 
     The device described in FIGS. 1-3 operates in the following manner. When all eight tracks of each tape are in the position shown, and tape 10 is coded as indicated in FIG. 2, a magnetic field pulse which is sent through the single conductor (not shown, but explained heretofore) or primary winding 32 switches the small bits of information stored in tape 20, but not tape 10, if the bits in tape 20 are of opposite magnetic polarity to the sense of the magnetic field produced by head 30. These bits were arbitrarily labeled with a &#34;+&#34; in FIG. 3. Simultaneously, voltage pulses appear in the secondary coil at the ends of each composite tape track when a switching event has occurred. Tracks 21, 24, 25, 26, 27 and 28 which are labeled with a &#34;+&#34; are switched, and these tracks are designated with a &#34;1&#34; under the Read Out Column in FIG. 3. In tracks 22 and 23, no switching event takes place, and they are designated with an &#34;0&#34; in the Read Out Column in FIG. 3. 
     The secondary winding 30 detects the switching events. The switching events detected then produce a &#34;1&#34; in the read out as noted in column 2 of FIG. 3. Increased resolution is obtainable by using eight tracks in parallel. 
     The device shown in FIG. 4 operates on the same principle, but somewhat differently. In FIG. 4, only a single tape is used, and tape 20 of the FIG. 1 embodiment is omitted. A separate read head 50 together with primary winding 52 and secondary winding 54 are provided for each of the eight tracks or for each track of the eight separate tapes. The read heads are magnetized by the flux in the tape and are in the saturated condition of -H or H, depending on the sense of magnetization in tape 10 underlying read head 50. If the primary winding is energized so that the magnetization +ΔH is applied, no switching takes place; but if the magnetization applied is -ΔH, switching takes place as a result of an output in secondary winding 54. Since head 50 is saturated, +ΔH produces only a small EMF, while -ΔH produces a large EMF. As noted heretofore, head 50 must be a high permeability, non-linear magnetic material. In the normal device operation, the eight head system will be simultaneously pulsed and the eight secondary induced EMF&#39;s will read as 1,0 pulses depending on the sense of magnetization in the magnetic tape under each head. 
     The position of the tape 10 is directly related to the spatial position of the reference surface of the object. Each one of the separate 256 zones on track 11 corresponds to a different space representing the 1/256 of an inch spacing. When track 28 is coded with two bits of information, track 21 will be coded with 256 bits of information and the tracks 22 to 27 will be coded in accordance with conventional practice so that the adjacent tracks above track 28 will each successively include twice as many bits of information as the preceding track. 
     In the FIG. 1 embodiment, when a pulse is applied to primary winding 32, only some of the tracks of each zone will have their magnetization changed depending upon the system used. The system used herein is to change those tracks in the zone with a &#34;+&#34; to a &#34;-&#34;. If the track is already magnetized &#34;-&#34;, then no change takes place, and the output is zero. 
     In the FIG. 4 embodiment, it will be noted that the B-H magnetization curve for read head 50 begins its saturation area above the knee which occurs at 58 in FIG. 5. The magnetization H, or maximum coercive force to flux saturate head 50 occurs at the knee 58. Any increase in magnetizing force above the knee 58 produces no further flux saturation and no change in EMF; a reverse energization of head 50 by means of primary winding 52 produces a decrease in the applied field or coercive force and therefore a change in flux density from B 1  to B 2 . The decrease in flux density from B 1  to B 2  produces a large EMF in secondary winding 56 and therefore an output voltage and current pulse therefrom. 
     It is possible to use a tape unit formed from a tape with eight separate tracks or eight separate tapes each having a single track. 
     When such a tape unit is coded with binary information in a manner shown for example in FIG. 2, there are a possible 256 unique binary combinations (2 8 ). If a one inch length of tape is utilized, each coded combination represents 1/256&#34;. 
     Thus it would be obvious to those skilled in the art, that the digital displacement transducer can be used to measure precise zone spacings of approximately 0.004 inch resolution. In effect, the tape unit 20 or the head 50 is shifted so that all the tracks of tape unit 20 or all the heads 50 contain the same information. After shifting so that all contain the same information, the output produced is characteristic of the original information. 
     It is also within the scope of this invention to increase the spatial resolution beyond 1/256 of an inch, where this should be necessary for a particular requirement. Accordingly, further spatial resolution may be obtained by increasing the number of tracks. For this purpose, separate tapes with individual tracks may be used, where tape units with nine or more tracks are required. While reference has been made to measurement in inches, any system of units may be used. What is important is that with the method and device of this invention, discrete spacings of a non-moving object can be measured with the accuracy required.