WO1985003346A1

WO1985003346A1 - Position sensor

Info

Publication number: WO1985003346A1
Application number: PCT/NL1985/000004
Authority: WO
Inventors: Johannes Petrus Jacobus Groenland
Original assignee: Stichting Centrum Voor Micro-Elektronica Twente
Priority date: 1984-01-18
Filing date: 1985-01-16
Publication date: 1985-08-01
Also published as: EP0168462A1; NL8400169A

Abstract

Device for displaying previously magnetically recorded information, said device comprising at least one pair of co-operating, relatively movable elements, the first of which carrying a dial and the second an indicator co-operating with said dial, for example for measuring the relative positions of said elements or for displaying video- or audio-information and other information such as data on credit cards, bar codes and the like, wherein the dial is constructed in the form of at least one dial strip of hard magnetic material, the indicating member is constructed in the form of a plurality of detection strips, the number of which equaling the number of dial strips, said detection strips being magnetisable by the dial strip and comprising ferromagnetic material exhibiting the anisotropic magneto-resistance effect and being connected to measuring means for measuring the electric resistance values and/or planar Hall-voltages, assessing means are provided for deriving an associated relative position from a magnetisation detected by at least one detection strip. The invention has for its object to provide such a device in which the so-called Barkhausen-noise, which may cause erroneous bits, is largely avoided. For this purpose embodying the invention is generally characterized in that the plane of the detection strip is set up by a vector having a component in the direction of length of the dial strip and a vector having a component along the normal to the plane of the dial strip.

Description

Position sensor

The invention relates to a device for displaying pre¬ viously magnetically recorded information, said device com¬ prising at least one pair of co-operating, relatively movable elements, the first of which carrying a dial and the second an indicator co-operating with said dial, for example for measuring the relative positions of said elements or for displaying video- or audio-information and other information such as data on credit cards, bar codes and the like, where¬ in the dial is constructed in the form of at least one dial strip of hard magnetic material, the indicating member is constructed in the form of a plurality of detection strips, the number of which equaling the number of dial strips, said detection strips being magnetisable by the dial strip and comprising ferromagnetic material exhibiting the anisotropic magneto-resistance effect and being connected to measuring means for measuring the electric resistance values and/or planar Hall-voltages, assessing means are provided for deri¬ ving an associated relative position from a magnetisation detected by at least one detection strip. Such a device is known from DE-A-3126806.

For measuring a relative displacement along a straight line an example is found in screw micrometers and sliding meters, whilst such devices are also known for measuring the angle between two movable elements. It should be understood, therefore, that the term "position" herein is a general con¬ cept.

The invention furthermore relates to a device of the kind set forth to be coupled with a lathe used for control¬ ling the machine tool and not serving as an independent mea¬ suring device.

It is frequently important to obtain, for example, a digital reading of the measuring value, whilst within the scope of an auxiliary device, for example, for a machine tool it may be important to have available electric signals ' associated with the measured relative positions for' control¬ ling the machine tool. In this respect it is conceivable to use a dial constructed in the form of a continuously magne- tized dial strip of hard magnetic material, the magnetisa¬ tion varies within the measuring range between two extreme values, whilst the indicating member comprises means for measuring the magnetisation which can thus be converted into an electric output signal. However, on second thought such an analogue construction appears not be obtainable in a simple manner with the desired reproduceability.

The use of magnetisation varying, for example, linear¬ ly along the length of the dial strip has the disadvantage that disturbing e fects are experienced by inter alia magne- tic interference fields, temperature fluctuations and varia¬ tions in the distance between the indicating member and the dial strip, whilst it is not simple to produce the magneti¬ sation with the required accuracy in the dial strip.

It may furthermore be conceived to construct the dial in the form of a dial strip having a plurality of paths transverse of the direction of displacement of the elements, which paths can be scanned by the associated detection ele¬ ments. Therefore, these detection elements are positioned transversely of the direction of displacement and construc- ted in the form of a single ferro-magnetic strip, the plane of which is at right angles to the dial strip. The dial strip may be subdivided in its direction of length into parts of equal lengths, which paths and cells bound the parts which may carry, for example, binary information codes discretized in the direction of displacement. A simple exam_¬ ple is a row of binary digits. The bits are read in paral¬ lel.

A disadvantage of the solution is that a relatively broad dial strip and a detection strip have to be employed. It should be noted here that the construction of the dial strip is fairly complicated, since a plurality of tracks has to be magnetized side by side but independently one of the other. A further disadvantage is that the arithmuth setting of the sensor head is critical.

A further disadvantage of the solution described is that it required relatively complicated steps for avoiding the so-called Barkhausen noise, which may give rise to erro¬ neous bits.

The invention has for its object to provide a device of the kind set forth in a manner such that the aforesaid disadvantages do not occur. For this purpose the device em- bodying the invention is generally characterized in that the plane of the detection strip is set up by a vector having a component in the direction of length of the dial strip and a vector having a component along the normal to the plane of the dial strip. _« Such a device may be adapted for carrying out incre¬ mental assessments.

The device can be free of the aforesaid Barkhausen noise by largely avoiding disturbing effects, for example, the generation of magnetic domains. For this purpose the plane of the detection strip may be arranged substantially at right angles to the plane of the dial strip. A given point of the detection strip passes in this case through such a (twodi ensional) magnetic field pattern that there is no reason for an abrupt "change-over" of the magnetisation at said point of the detection strip. It can furthermore be avoided that in the case of a field decreasing in the direc¬ tion of the so-called hard axis the magnetisation, so to say, hesitates between the two directions of the easy axis and then splits into domains. A device for measuring absolute positions may be cha¬ racterized in that at least one dial strip is premagnetized in a pattern such that a unique magnetisation is added to each position of the dial strip(s).

It is preferred in this case to use a device characte- rized in that the dial is constructed in the form of at least one dial strip of hard magnetic subdivided into parts of equal lenghts, the indicating member is constructed in the form of a detection strip, which is short with respect to the at least one dial strip and subdivided into a plurality of parts of equal pitch distances and which contains material ^"exhibiting the anisotropic magneto-resistance effect and being magnitizable by the at least one dial strip, the number of parts at least equalling to the number of parts of -the^"dial strip along the length of the detection strip, detection strip parts being connected ^• to measuring means ^"for measuring the respective electric 0 resistance values and/or planar Hall voltages, the parts of the dial strip(s) are premagnetized in a pattern such that a part pattern of a sequence along the length of the detection strip occurs only and in that assessing means are provided for deriving the associated relative relative positions from 5 the part patterns.

It is advantageous to use a variant in which each part of a dial strip is magnetized in one of two magnetisation states, in which case the dial strip preferably is in a sta¬ te of maximum remanent magnetisation and the two magnetisa- 0 tion states correspond with oppositely directed longitudinal magnetisations.

As stated above, it is required for the parts of a dial strip to be magnetized in such a pattern that a part pattern of a row occurs only once along the length of the ^ detection strip. Such an unambiguous relation between part pattern and relative position can be obtained by an embodi¬ ment in which the magnetisation transitions of the parts of a dial strip correspond to a maximum length sequence.

A very simple structure has an embodiment in which a ° detection strip consists of a single strip of material and at the transitions between the neighbouring parts electric conductors are connected to the measuring means.

In a particularly practical variant the device is cha¬ racterized in that the measuring means are adapted for ⁵ causing a predetermined current to flow through each of the parts of a detection strip and for measuring the voltage thereof. For example, the pitch distance of the parts of the dial strip may equal the pitch distance of the parts of the associated detection strip or an integer multiple thereof. The use of a multiple, for example three, has the ad- vantage that the bit pattern can be detected independently of the positioning of parts of the detection strip with respect to those of the dial strip.

The resolving power of the device embodying the inven¬ tion is determined inter alia by the minimum dimensions that can still be defined, for example, by the photolithograhic designing process. It is noted here that the minimum obtain¬ able width of the electric contacts on the detection strip is determinative thereof.

With decreasing dimensions of the parts these electric contacts will cover a proportionally increasing part of the strip and thus render it inoperative. In this situation it is advantageous to reduce the number of parts per bit inter¬ val. The optimum may then be the use of the same pitch dis¬ tance of the parts of the dial strip and the parts of the detection strip.

In order to avoid problems in the detection in the ca¬ se in which the parts of the detection strip are arranged substantially precisely between two positions of magnetisa¬ tion transitions a second detection strip coupled with the first detection strip may be used, the parts of the second detection strip having the same length the parts of the first detection strip and being off-set relatively thereto by an integer multiple, which may have zero value, plus half a pitch distance. In a preferred embodiment the device has the particu¬ lar feature that the detection strip(s) constitute(s) an in¬ tegral unit with the measuring means and the assessing means.

Further features and particularities of the invention will now be described with reference to the drawing of a few arbitrary embodiments to which the invention is not limited. The drawing shows in:

Fig. 1 a sliding gauge comprising a device embodying the invention;

Fig. 2a schematically an analogue device; Fig. 2b a graph of the magnetisation or the dial strip of Fig. 2a as a function of the place;

Fig. 3a, 3b a binary device corresponding to Figs. 2a and 2b;

Fig. 4 a schematic, perspective view of a device in which the planar Hall effect is used;

Fig. 5 an elevational view like Fig. 4 of a device ba¬ sed on the magneto-resistance effect;

Fig. 6 a fragmentary, perspective view of a detector co-operating with a dial strip; Fig. 7 an electric basic diagram for a signal-proces¬ sing device; and

Figs. 8, 9 and 10 simplified diagrams of important parts of signal-processing devices.

Fig. 1 shows a sliding gauge 1 comprising a guide 2 with a jaw 3 and a runner 4 having a jaw 5 co-operating with the former. The guide 2 is provided with a magnetized^" ial strip 6, which co-operates with a detector 7 forming part of the runner 4. The detector 7 supplies its output signals to a battery 8 fed signal-processing unit 9, which supplies output signals to a converter 10, which controls a display unit 11 with a display on the basis of fluid crystals. The design of the device is such that the numbers indicated by the display unit 11 commonly indicate the distance between the measuring faces of the jaws 3 and 5. Fig. 2 shows a dial strip 12, the magnetisation of which varies in its direction of length in the manner shown in Fig. 2b. A detector 13 is movable with respect to the dial strip 12 and designed for converting the magnetisation detected at a given place into an output signal which is supplied to a signal processing unit 14, which controls a display unit 15.

Fig. 3a shows a dial strip 16, which has the agneti- sation pattern of Fig. 3b. Two types of magnetisation are concerned here, for example, a magnetisation zero and a re- anent magnetisation of a predetermined value or a remanent magnetisation which is constant throughout the dial strip 16, the direction of which varies, however, in a predetermi¬ ned pattern. The dial strip 16, which exhibits a magnetic bit pattern in the manner described above, co-operates with a detection strip 17, which is subdivided into six parts 18, which are designed for detecting the magnetisation at the ° place concerned in the dial strip 16 and for supplying cor¬ responding signals to a signal-processing unit 19, which controls a display unit 20.

The magnetisation pattern shown in Fig. 3b has such a structure that throughout the length of the dial strip 16 ^ the detection strip 17 always detects a magnetisation pat¬ tern unambiguously related to the relative positions of the dial strip and the detection. This means that each sequence of six successive bits differs from every other sequence of six successive bits along the length of the dial strip. In a practical embodiment the bits can be grouped as a maximum length sequence. It is noted in this respect that, for exam¬ ple, three types of magnetisation may be used.

Fig. 4 shows a dial strip 16 co-operating with a de¬ tection strip 21, through which an electric current is pas¬ sed by a current source 22 shown schematically. On the side of the detection strip 21 facing the dial strip 16 nine electric contacts 23 are provided, whereas on the underside electric contacts 24 are fastened at corresponding places. Pairs or contacts ar connected to the non-inverting and the inverting inputs 25 and 26 respectively of amplifiers 27. The outputs 28 of the amplifiers are connected to a signal- processing unit (not shown in Fig. 4) which can apply sig¬ nals to a display unit indicating the position of the detec¬ tion strip 21 relative to the dial strip 16. In the configu¬ ration of Fig. 4 pairs of electric contacts 23, 24 give off the planar Hall voltage.

Fig. 5 shows a detection strip 29, with which a se- quence of electric contacts 30 is connected, which are coupled with a signal—processing unit 31, which can supply control-signals to a display unit 32. ^"~~ The configuration of Fig. 5, contrary to that of Fig.

5 4, is based on the magneto-resistance effect.

Fig. 6 shows a practical embodiment of a detector 33, which is based, like the detection strip 29, on the mag¬ neto-resistance effect. The detector 33 comprises a glass substrate 34, the front edge of the top face of which i.e.

10 the edge facing the dial strip 16 is provided with a nickel-iron strip 66 of about 50 nm. Below the glass sub¬ strate 34 is located a subplate 35 of alumina. Above the substrate plate 34 is arranged a glass cover plate 36. To the nickel-iron or permalloy strip are connected two groups

15 37, 38 of electric contacts 39. These contacts are in the form of aluminium strips having a thickness of the order of 1 urn arranged on the top face of the glass substrate plate 34. The pitch distance between the contacts 39 corresponds to the width of the "bits" on the dial strip 16. The inter-

20 val between the groups 37 and 38 corresponds to one-and-a- half times said pitch distance, which means that the con¬ tacts 39 of the group 38 are off-set with respect to the contacts 39 of the group 37 over 6.5-times said pitch dis¬ tance.

25 Fig. 6 shows the optical distorsion due to the presen¬ ce of the glass cover plate 36 so that the location of the guide paths 40 coupled with the electric contacts 39 on the top face of the glass substrate 34 is less distinct.

The top face of the subjacent plate 35 is provided

30 with guide paths 41, which are coupled by ultrasonic bonds by means of conductors 42 with the guide paths 40. The ends of the guide paths 40 serve for coupling with an electronic processing unit.

The width of the electric contacts 39 in this embodi-

35 ment is of the order of l/5th of the pitch distance, which may be 50 . By using a single group 37 or 38 the resolving power of the detector 33 is of the order of 50 urn. By using the two groups off-set through-half a pitch distance plus an integer number of off-set groups the resolving power is im¬ proved by a factor ^"2^"and is then of the order of 25 jam.

Referring of Figs. 7, 8, 9 and 10 a few embodiments of signal-processing units will be discussed, which may be em¬ ployed within the scope of the device in accordance with the invention. Reference is made to Fig. 5 showing a detection strip with a plurality of electric connections. This strip

29 is traversed by a current, either a direct current or an alternating current so that between the respective contacts

30 voltages are produced in dependence on the resistance va¬ lue between them, which resistance values in turn depend on the magnetisation in the dial strip 16 detected by the de¬ tection strip parts.^' The information to be detected is stored in the diffe¬ rence voltages between successive contacts 30. These volta¬ ges are, for example, of the order of 100 mV and as stated above, they are determined by the resistance of the.detec¬ tion strip. The magneto-resistance effect can bring about a voltage variation up to about 2% at a maximum, that is to say, about 2 mV. For detecting the presence of a resistance variation or the absence thereof the configuration of Fig. 7 can be used.

The inputs 43 of the signal-processing unit 44 are connected to the respective contacts 30 for receiving the signals there available in the form of voltages. The succes¬ sive inputs 43 are connected to the inputs of difference am¬ plifiers 45 for assessing the voltage between successive contacts. The outputs 46 of the difference amplifiers 45, there¬ fore, supply signals proportional to said difference volta¬ ges. To compensate for the fixed voltage of the order of 100 mV as indicated above the output signal 46 of each of the difference amplifiers 45 is applied to the positive input of a difference amplifier 47, which receives at its negative input a reference potential for compensating said fixed vol¬ tage. Therefore, the voltages at the outputs 48 are repre- sentative of the presence of a resistance variation of a de¬ tection strip part caused by the magneto-resistance effect. The outputs 48 are fed to a signal-processing device 49 for a further treatment of the information thus obtained. The configuration of Fig.. 7 can only be used in a case in which all connecting conductors of the detection strip are taken to the outside. A variant may be used in which a multiplexing operation is applied to the information signals so that all ouput information can be given off in a sequence format, for example, since the detection structure is arran¬ ged on a chip containing the multiplexing circuit.

Fig. 8a shows a signal-processing unit 50 having in¬ puts 51 for coupling with the contacts 30 of Fig. 5. To the inputs 51 are connected switches 52, for example, MOS swit- ches, the other side of which is commonly connected the out¬ put 53 of the signal-processing unit 50. By means not shown, for example, a digital shift register only one switch of the successive switches can be in the closed state. The control is symbolized by the arrow 54. Fig. 8b shows the output voltage at the output 53 as a function of time. The detail in Fig. 8c shows a potential waveform.

Fig. 9a shows a refined embodiment designed for only giving off a difference voltage so that the rising tendency of Fig. 8b does not occur. For this purpose the signal-pro¬ cessing device 55 of Fig. 9a uses sequences of pairwise con¬ trollable switches 56, 57, in which the outputs of the swit¬ ches 56 are connected to the one input of a difference am¬ plifier 58 and the outputs of the switches 57 to the other input thereof. By controlling so that each time only one pair of switches 56, 57 is closed as is indicated in Fig. 9a and this in a predetermined order of succession, as mul¬ tiplexed output signal is obtained at the output 59 of the difference amplifier 58, which signal contains all informa- tion described above.

Fig. 9b shows a potentially resultant waveform corre¬ sponding to Fig. 8c. Fig. 10a shows a signal-processing device 60, the inputs 51 of which are connected to an input circuit 61 for parallel writing the information and for supplying it to a charge-coupled device 62.

The input circuit 61 is designed for converting the input voltages into charge. At the same time the difference voltages to be measured can be processed and a predeter¬ mined, fixed value can be subtracted therefrom so that the requirements with respect to the relative accuracy of the charge-coupled device become less severe. The control indi¬ cated by arrows 63, 64 ensures that the difference voltages between the inputs 51 are converted into charge (charging of capacitors), the charges being inserted in parallel format into t e, charge-coupled device, after which these charges are slipped out in series from the charge-coupled device 62 through the output 65 thereof. As is known, new information can be written in the meantime through the inputs 51. An ad¬ vantage of the configuration of Fig. 10a over the multiple¬ xing circuits of Figs. 8a and 9a is that fewer problems are involved in the variation of signals during the measuring process proper.

Fig. 10b shows a possible waveform of the voltage at the output 65.

Claims

l.A device for displaying previously, magnetically re¬ corded information, said device comprising at least one pair of co-operating, relatively movable elements, the first of which carrying a dial and the second an indicating member co-operating with said dial, for example for measuring the relative positions of said elements or for displaying video- or audio-information and other information such as data on credit cards, bar codes and the like, wherein the dial is constructed in the form \nf at least one dial strip of hard magnetic material, the indicating member is constructed in the form of a plurality of detection strips, the number of which equaling the number of dial strips, said detection strips being mag- netisable by the dial strip and comprising ferromagnetic ma¬ terial exhibiting the anisotropic magneto-resistance effect and being connected to measuring means for measuring the electric resistance values and/or planar Hall-voltages, assessing means are provided for deriving an associa¬ ted relative position from a magnetisation detected by at least one detection strip, characterized in that the plane of the detection strip is set up by a vector having a component in the direction of length of the dial strip and a vector having a component along the normal to the plane of the dial strip.

2. A device as claimed in Claim 1, characterized in that at least one dial strip is premagnetized in a pattern such that a unique magnetisation is added to each position of the dial strip(s).

3. A device as claimed in Claim 2 characterized in that the dial is constructed in the form of at least one dial strip of hard magnetic material subdivided into parts of equal lengths, the indicating member is constructed in the form of a detection strip, which is short with respect to the at least one dial strip and subdivided into a plurality of parts of equal pitch distances and which contains material exhibiting the anisotropic magneto-resistance effect and being magneti- sable by the at least one dial strip, the number of parts at least equalling to..the number of parts of the dial strip along the length of the detection strip, the detection strip o parts being connected to measuring means for measuring the respective electric resistance values and/or planar Hall voltages, the parts of the dial strip(s) are premagnetized in a pattern such that a part pattern of a sequence along the 5 length of the detection strip occurs only one and in that assessing means are provided for deriving associated relative positions from the part patterns.

4. A device as claimed in Claim 3 characterized in that each part of a dial strip is magnetized in one of two 0 magnetisation states.

5. A device as claimed in Claim 4 characterized in . that the dial strip is in a state of maximum remanent magne¬ tisation and the two magnetisation states correspond with oppositely directed longitudinal magnetisations.

6. A device as claimed in anyone of Claims 2 to 5 cha¬ racterized in that the magnetisation transitions of the parts of a dial strip correspond to a maximum length sequen¬ ce.

7. A device as claimed in anyone of Claims 2 to 6, characterized in that a detection strip is formed by a sing¬ le strip of material and in that the areas of the transi¬ tions between neighbouring parts thereof electric conductors connected to the measuring means are connected to said parts.

8. A device as claimed in anyone of the preceding

Claims characterized in that the measuring means are adapted for causing a predetermined current to flow through each of the parts of a detection strip and for measuring the voltage of said parts.

9. A device as -claimed in anyone of Claims 2 to 7 cha¬ racterized in that the pitch distance of the parts of- a dial strip equals to the pitch distance of the parts of the as¬ sociated detection strip or an" integer multiple thereof.

10. A device as claimed in Claim 9 characterized by a second detection strip coupled with a first detection strip, the parts of said second strip having the same length as the parts of the first detection strip and being off-set relati¬ vely thereto by an integer multiple, which may have zero va¬ lue, plus half a pitch distance.

11. A device as claimed in anyone of the preceding Claims characterized in that the detection strip(s) consti- tute(s) an integrated unit with the measuring means and the assessing means.