Patent Application
20150025772
The present invention is directed to a position indicator device, which claims priority to British Patent Application No. GB 1311856.7 filed on Jul. 2, 2013, which is incorporated herein by reference.
1. Field of the Invention
The present invention is directed to a position indicator device.
2. Description
An example of a position indicator device is given in EP 1121572 B1. That specification describes the use of pulse induction to provide the position of a target relative to one or more coils. The self inductance of a coil is given by the equation:
v=L.di/dt
in which v is the electrical voltage in volts across the coil, L is the self inductance of the coil, and i is the electrical current passing through the coil in amperes, so that di/dt is the rate of change of the electrical current passing through the coil as a function of time.
It can be seen from this that if the electrical current through the coil has a positive value as a result of a steady voltage applied across the coil, but is abruptly stopped by switching off the applied voltage, the voltage across the coil that results from the self inductance of the coil will have an extremely high negative value, well in excess of the value it had immediately prior to the instant at which the applied voltage is switched off and the current is stopped. The self inductance voltage will decay exponentially so that after a while it will have a substantially zero value. However, the exponential decay is dependent upon electrically conductive material in the vicinity of the coil. If there is an object made of an electrically conductive material close to the coil, this will lower the rate of decay of the voltage across the coil, because of the eddy currents induced in the object, and a measure of the value of the voltage at a time when, in the absence of any such object, it would be substantially zero, provides an indication of the proximity of the object, given that its size and electrical conductivity are known, or given that experiments are conducted to ascertain the different values of this voltage for different positions of the target. This method shall be referred to herein as pulse induction, pulse induction circuitry or a pulse induction circuit shall be understood as circuitry or a circuit adapted to carry out such a method, and a pulse induction coil shall be understood to mean a coil to which is connected a pulse induction circuit or circuitry.
A problem encountered with the device illustrated in EP 1121572 B1 is that the available movement of the target is limited by the coil or coils themselves.
The present invention seeks to obviate this problem.
Accordingly the present invention is directed to a position indicator device comprising a first array of uniformly spaced-apart pulse induction affecting targets fixed in position relative to a second array of uniformly spaced-apart pulse induction affecting targets, in which the spacing between the centres of adjacent targets of the first array differs from that of the second, the device further comprising a first set of pulse-induction coils comprising a plurality of such coils and a second set of pulse-induction coils comprising a plurality of such coils, with those of the first set fixed relative to those of the second set, those of the first set being located adjacent to the first array of targets, and those of the second set being located adjacent to the second array of targets, the first and second arrays of targets being movable relative to the coils of the first and second sets of pulse induction coils, the device further comprising indicator circuitry connected to the first and second sets of pulse induction coils to provide a signal dependent upon the outputs thereof indicative of the position of the coils relative to the arrays.
The pulse induction affecting targets may comprise portions of electrically conductive material. Such portions may be projections or protuberances which are integral with and extend away from a base portion of the same material.
Material which is electrically insulative relative to the said electrically conductive material, and which is magnetically permeable relative to the said electrically conductive material, may fill the spacing between the targets, and/or behind the targets. The electrically insulative magnetically permeable material may comprise metallic glass or amorphous metal.
Alternatively or in addition, the targets may comprise voids within a member or members of electrically conductive material.
Alternatively or in addition, the targets may comprise portions of material which have an electrical and/or magnetic parameter which is different from that of the material or void which surrounds the targets, provided the targets themselves and/or the material surrounding the targets are/is electrically-conductive.
It will be appreciated that it may be that the coils are moveable, or the target arrays are moveable, or that both are moveable relative to the surroundings of the device, provided relative movement between the coils and the target arrays is possible.
The first and second arrays of targets may both be linear and of the same overall length.
Alternatively, they may be circular arrays surrounding a common axis. The sets of coils may then be arranged outside, inside, or alongside those arrays. For example, the targets of the first and second arrays may comprise radially projecting portions of respective rings of electrically conductive material.
This enables the device to indicate the angle of rotation of a shaft, for example.
The number of targets in the first array may be different from the number of targets in the second array.
The number of targets in the first array may be one more than the number of targets in the second array.
The number of targets in the second array may be five.
The spacing between the respective centres of adjacent targets of the first array may be less than the spacing between the respective centres of adjacent targets of the second array.
The number of coils in the first and second sets may be three.
The coils of each set may be arranged linearly if the arrays are linear, or arcuately if the arrays are circular, concentrically therewith.
The spacing between the respective centres of the coils of the first and second sets may differ. For example, the spacing between the centres of adjacent coils of the said first set may be substantially one third the spacing between the centres of adjacent targets of the said first array. Also, for example, the spacing between the centres of adjacent coils of the said second set may be substantially one third of the spacing between the centres of adjacent targets of the said second array.
The said indicator circuitry may be such as to effect an algorithm to provide a sawtooth output for each set of coils. The algorithm may be as set out hereinbelow with reference to the accompanying drawings, or it may use a part of the algorithm set out hereinbelow with reference to the accompanying drawings.
The said indicator circuitry may effect an algorithm upon the sawtooth outputs to provide a linear output which varies in proportion to the distance of the coils from a given target. The algorithm may be as set out hereinbelow with reference to the accompanying drawings, or it may use a part of the algorithm set out hereinbelow with reference to the accompanying drawings.
The present invention further extends to a position indicator device comprising at least one pulse-induction affecting target, at least one pulse-induction coil, pulse-induction indicator circuitry connected to the said at least one pulse-induction coil to provide a signal dependent upon the output thereof indicative of the position of the said at least one pulse-induction coil relative to the said at least one pulse-induction affecting target, in which a material is arranged to shield the said at least one pulse-induction affecting target and/or the said at least one pulse-induction coil from stray signals, the said material being one which is electrically insulative relative to the material of the or each target and which is magnetically permeable relative to the or each target.
The shielding material may comprise metallic glass or amorphous metal.
This provides the advantage that in such a position indicator device, the or each such target may be mounted on a material which is different from that of the target itself, irrespective of whether the material on which the or each target is mounted is electrically conductive, because the metallic glass or the amorphous metal will shield the coil from any effect that would be present in the output in the absence of the metallic glass or the amorphous metal.
Such a position indicator device may incorporate one or more of the features set out hereinbefore in relation to the present invention or a development thereof.
The present invention extends to a control device for controlling an operating parameter of an engine or a machine or other equipment in accordance with the relative position between the coils and the targets of a position indicator device in accordance with the present invention.
The present invention also extends to an engine or a machine or other equipment provided with such a control device.
The present invention also extends to a method of indicating the position of one object relative to another using a position indicator device as set out in one or more of the foregoing paragraphs 8 to 29, and to a method of controlling a parameter of an engine or machine or other equipment using the device according to paragraph 30.
Examples of position indicator devices embodying the present invention will now be described in greater detail with reference to the accompanying drawings, in which:
The position indicator device 10 shown in
The target members 12 of the first array are each generally elongate and the target members 14 of the second array are each generally square and each set is arranged linearly with the target members of each set being generally parallel to one another. The first and second arrays are parallel to one another and spaced apart from one another by a distance which is less than the length of each target member.
The outermost target members 12 of the first array are respectively broadly in registration with the outermost members 14 of the second array, so that the first array has generally the same length as the second array, but the spacing between adjacent target members 12 of the first array is less than the spacing between adjacent target members of the second array 14.
The device 10 further comprises a combined read head 16 which is positioned to overlap both the first array and the second array of target members. Fixed within the head 16 are a first set of pulse induction coils 18 comprising three coils 18 arranged linearly, parallel to and above the first array of target members 12, and a second set of pulse induction coils 20 comprising three coils 20 arranged linearly, parallel to and above the second array of target members 14.
The spacing between the centres of adjacent coils 18 of the first set is substantially one third of the spacing between the centres of adjacent target members 12 of the first array. The spacing between the centres of adjacent coils 20 of the second set is substantially one third of the spacing between the centres of adjacent target members 14 of the second array.
Each coil has an imaginary axis around which the coil is wound which extends generally towards and away from its associated array of target members.
As is evident from
Thus the indicator circuitry 22 comprises respective pulse induction circuits 26 connected to the coils 18 and 20. The outputs from each of these circuits 26 are connected to respective inputs to an algorithm performing circuit 28 an output from which provides an indication of the relative position of the coils 18 and 20 in relation to the target members 12 and 14. That output from the algorithm performing circuit 28 is fed to an input of output circuit 24, the latter effecting a normalisation of the output from the algorithm performing circuit 28.
Each of the pulse induction circuits 26 is constructed and operated in the manner described in EP 1121572 B1, and more especially as illustrated with reference to the accompanying
The block circuit diagram shown in
A time delay 52 is also connected to the pulse generator 32, and a pulse generator 54 generating a pulse of approximately 3 usec is connected to receive a signal from a delay 52 and cause the switch 40 to be closed for that pulse period.
When the device 10 is in use, the system clock 30 causes the pulse generator 32 to close the switch 34 for a period of approximately 12 usec. This energises the coil 18 or 20 for that period such that the voltage across the coil has a step function as shown in the graph in
The algorithm performing circuit 28 may be in the form of a microprocessor programmed to effect its function.
In the embodiment shown in
The rings 50 and 52 and the head 16 are held in such a fashion that the latter is movable relative to the former about their common axis. The actual parts to which the rings 50 and 52 and the head 16 are actually attached are not illustrated, as these may be many and varied. However one example might be that the rings 50 and 52 are secured to a shaft which is coaxial with them, the shaft may be rotatable about that axis, and the head 16 may be fixed in position (although movable relative to the rings 50 and 52 by virtue of their rotation), to provide an indication of the current angular position of the shaft.
The manner of operation of the position indicator circuitry 28 is shown in
Considering first the graph shown in
Underneath the horizontal axis of the graph shown in
if amx=1 and coil 0>=coil 2 then type 1
if amx=1 and coil 0<coil 2 then type 2
if amx=0 and coil 2>=coil 1 then type 4
if amx=0 and coil 2<coil 1 then type 5
if amx=2 and coil 1>=coil 0 then type 6
if amx=2 and coil 1<coil 0 then type 7
in which coil x represents the value of the output from circuit 26 of coil x.
The algorithm performing circuit 28 then provides an output Px as indicated in
for type 1:P1=(coil 1−coil 0)/(coil 1−coil 2)
for type 2:P2=(coil 1−coil 2)/(coil 1−coil 0)
for type 4:P4=(coil 0−coil 2)/(coil 0−coil 1)
for type 5:P5=(coil 0−coil 1)/(coil 0−coil 2)
for type 6:P6=(coil 2−coil 1)/(coil 2−coil 0)
for type 7:P7=(coil 2−coil 0)/(coil 2−coil 1)
The algorithm performing circuit 28 then multiplies the outputs in the regions corresponding to types two, five and seven by −1, to obtain the output as indicated in the graph of
Offset values are then applied to each type, to form a single straight line or linear output over a distance of movement corresponding to the spacing between adjacent target members. This is achieved by way of the following calculations to give an output Qx as shown by the graph of
for type 1:Q1=6+P1
for type 2:Q1=8−P2
for type 4:Q1=4+P4
for type 5:Q1=6−P5
for type 6:Q1=2+P6
for type 7:Q1=4−P7
For the full range of movement of a combined read head 16 over the two arrays of target members 12 and 14, in which there are seven target members 12 and six target members 14, the resulting output from the algorithm performing circuit 28 is as shown in
The actual resulting output from the algorithm performing circuit 28 may appear as shown in
The algorithm performing circuit 28 subtracts one of the sawtooth outputs shown in
s(x)=a(x)−b(x)
The amplitude of the sawtooth functions in
Because this roughly linear output is created by subtracting two signals which already have a relatively high proportion of noise superimposed on what ideally would be precisely linear signals, the roughly linear output is extremely noisy and it is clearly desirable for the sake of accuracy to improve its precision. This is effected within the algorithm performing circuit 28 firstly by obtaining course steps, to determine where the position of the head 16 is in terms of those adjacent target members 14 between which its centre lies. This is achieved by subtracting the sawtooth signal obtained from the outputs of the coils 20 from the roughly linear output shown in
Approximately half the peak value of the sawtooth functions (in this case approximately 0.5) is added to the function shown in
Numerous variations and modifications to the illustrated devices may occur to the reader without taking the resulting construction outside the scope of the present invention. By way of example only, there may be seven target members 12 in the first array, and six in the second array, and indeed there may be substantially any integral number of target members in the first array with one or more less in the second array, provided that the noise of the signals obtained does not prevent a resolution of the position of the head 16. Algorithms might be used to enable there to be only two coils in each set, or there may be four or more. However a greater degree of precision might be obtained by using signals from more than three coils in each set. The target members may comprise copper instead of mild steel, for example by wrapping a strip of material comprising copper portions alternating with electrically insulative portions around the outside cylindrical surface of a hollow cylinder of mild steel.
The regions between and behind the targets 11 and 14, or between and behind such copper portions, may be filled with metallic glass or amorphous metal, so that the targets remain insulated from one another but steel for example behind the metallic glass or amorphous metal does not adversely affect the outputs of the coils 18 and 20.
The metallic glass or amorphous metal may be in the form of a layer, for example. In this case the layer insulates the targets from each other and shields the coils from the effective any electrically conductive material behind one or more of the targets. An example configuration with a single coil 64, two copper layers comprising a target 63 and a second copper layer 61 which is to be excluded from detection, and a metallic glass layer 62 (which could alternatively be a layer of amorphous metal) sandwiched between the two copper layers 61 and 63 and extending therebeyond, is shown in
The magnetic field at the coil centre immediately after the trailing end of a pulse put through the coil by the pulse-induction circuit, plotted as a function of time, is shown in solid line in
It can be seen from
It can further be seen from
Clearly, the metallic glass layer 65 shields the coil 64 from the effect of any electrically conductive material that may be behind that layer 65.
Stated briefly, the metallic glass (or amorphous metal) shields the effect on the coil output of any electrically conductive material which is behind the metallic glass (or amorphous metal), relative to the coil, but enhances the effect of any electrically conductive material which is in front of it.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1311856.7 | Jul 2013 | GB | national |
