METHOD AND DEVICE FOR OBTAINING POSITIONAL INFORMATION

Abstract: A method of obtaining positional information utilising a device (10) comprising a first member (11) having at least two electrically isolated conducting parts (13-16), and a second electrically conducting member (12) adjacent to and capacitively coupled to the first member (11), the first and second members (11, 12) being relatively movable such that the proportions of the respective parts (13-16) of the first member (11) in overlapping relationship with the second member (12) may be varied, the method comprising the steps of providing a first square waveform signal (26) to one of the parts (13-16) of the first member (11) and a second square waveform signal (27) to the other of the parts (13-16) of the first member (11), analysing a signal arising in the capacitively coupled second member (12) to obtain a device output signal (50) containing information about the relative positions of the first and second members (11, 12).

Description: METHOD AND DEVICE FOR OBTAINING POSITIONAL INFORMATION Description of Invention This invention relates to a method of and device for obtaining positional information, particularly but not exclusively for providing positional information for a computer, controller, game playing console or the like. It is known for example from GB-A-872152 to apply sinusoidal voltages of constant magnitude but of differing phasing to two electrically isolated members and to detemiine positional information from an output signal from a relatively movable member ,which output signal varies in phase depending upon the extent of the relative movement. I have proposed in my previous patent application GB2321108a device which operates on this principle but is able to provide positional information in two dimensions. In order to obtain two constant substantially similar sinusoidal signals of different phase, it has been necessaiy to generate such signals digitally and to filter each of the digital signals with respective filters in order to obtain sinusoidal waves. The provision of two filters adds a penalty to the cost of generating the waves and thus to the overall cost of the device. According to one aspect of the invention I provide a method of obtaining positional information utilising a device comprising a first member having at least two electrically isolated conducting parts, and a second electrically conducting member adjacent to and capacitively coupled to the first member, the first and second members being relatively movable such that the proportions of the respective parts of the first member in overlapping relationship with the second member may be varied, the method comprising the steps of providing a first square waveform signal to one of the parts of the first member and a second square waveform signal to the other of the parts of the first member, analysing a signal arising in the capacitively coupled second member to obtain a device output signal containing information about the relative positions of the first and second members. Thus utilising the present invention it is unnecessary to provide a filter to filter each of the digitally generated (square) waveforms before applying these to the parts of the first member. Preferably the first and second square waveform signals are of the same frequency but are 90° out of phase with each other and thus may be obtained from a single oscillator. In one arrangement, the method may comprise filtering the signal arising in the second member so that the signal which is analysed comprises a filtered output signal from the second member which thus may comprise a sine wave. Thus the phase of the signal arising in the second member may be compared with the phase of one (or both) of the first and second square waves. However this would still require the provision of a filter, albeit a single filter, to filter the output signal from the second member. It will be appreciated that the signal arising in the second member will comprise a complex waveform, which, assuming the first and second square waveform signals are of the same frequency but out of phase with one another, will be of the same frequency as the first and second square wavefomis but having steps either side of a dominant step level. The method may comprise analysing the relative step heights which will vary as the first and second members are relatively moved, to obtain the positional information. Although simple step height determination can be used to detemiine changes in the relative positions of the first and second members if greater accuracy is required, for example for actually measuring changes in relative position, if desired the method may comprise analysing the difference between at least one of the steps in the complex waveform either side of the dominant step level and the dominant base or peak step level to obtain the positional information. Thus the method will be substantially self correcting in the event of component drift for example. In each case no filtering would be required to obtain the positional infoπnation. According to a second aspect of the invention I provide a device for obtaining positional infoπnation by a method according to the first aspect of the invention the device comprising a first member having at least two electrically isolated conducting parts, and a second electiically conducting member adjacent to and capacitively coupled to the first member, the first and second members being relatively movable such that the proportions of the respective parts of the first member in overlapping relationship with the second member may be varied, means to provide a first square waveform signal to one of the parts of the first member and a second square waveform signal to the second part of the first member, means to analyse a signal arising in the capacitively coupled second member to obtain a device output signal containing information about the relative positions of the first and second members. The first member of the device may comprise two electrically isolated parts relative to which the second member moves whereby the device is able to obtain positional infoπnation about relative movement in a single linear direction, or the first member may comprise more than two electrically isolated parts relative to which the second member may move, square waveform signals being applied to each of the plurality of parts whereby the device is able to obtain positional infoπnation about relative movement between the first and second member in two dimensions. The invention will now be described with reference to the accompanying drawings in which: FIGURE 1 is an illustrative plan view of part of a device in accordance with the invention; FIGURE 2 is'an illustrative end view of the part of the device of figure 1; FIGURE 3 is a diagram illustrating a possible electronic circuit for the device of figures 1 and 2. FIGURE 4 is an illustration showing first and second square waveform inputs for the device of figures 1 and 2 and a resultant output signal containing positional infoπnation. Refeπing to the drawings an input device 10 for inputting positional information into a computer, controller, game playing console or the like comprises a first member 11, and a relatively moveable second member 12. The first member 11 comprises in this example, four isolated electiically conducting generally flat pails 13, 14, 15 and 16 airanged in a generally rectangular array such that the parts 13 to 16 are isolated from one another by a generally cross shaped isolating element indicated at 17. In this example, the second part 12 is moveable over the first part 11 by means hereinafter explained. The total area of the first part 1 1 is at least four times that of the area of the second member 12 in this example. Conveniently the first member 1 1 is made from single sided printed circuit board material or is otherwise a mixed construction of conducting and insulating parts. The first part 1 1 may comprise a discrete member, or may comprise part of or an extension to an existing printed circuit board. Each of the parts 13 to 16 of the first member 1 1 is provided with a connection 20 to 23 respectively. The device 10 further comprises an oscillator signal source 25 which produces two substantially identical square wavefoπn output signals 26,27 which are however 90° out of phase with one another. One of the signals, namely the signal indicated at 26. is connected via a conductor 30 to the teπninal 20 of the first part 1-3 of the first member 11. The signal 26 may, in dependence upon the condition of an electronic switch 31, simultaneously be connected via a conductor 32 either to the second part 14 of the first member 11, or the fourth part 16 of the first member 11 depending upon whether the device 10 is operating to provide positional information along an X axis indicated at 33, or a Y axis indicated at 34. The second signal 27 is connected via a conductor 36 to terminal 22 of the third part 15 of the first member 11, and depending upon the condition of the electronic switch 31, may simultaneously be connected either to terminal 21 of the second part of 14 of the first member 11, or to terminal 23 of the fourth part 16 of the first member 1 1. The device 10 further comprises a signal analyser means indicated at 40 which has a first input connected to conductor 30 carrying the first signal 26 from the oscillator signal source 25 to the first member 1 1 , and a second input 42 connected, in this example via a flexible wire 43, to the second member 12. The signal analyser means 40 provides an output signal 50 indicative of the relative position of the second member 12 to the first member 11. Of course, the second member 12 may be connected by any other desired kind of conductor to the input 42, such as conductor incorporating one or more wiping contacts or the like. The second member 12 may also comprise a printed circuit board and is positioned adjacent to the first member 1 1 with there being an air gap 46 between the first 1 1 and second 12 members. The second member 12 ma)' be constrained by any desired known means to move relative to the first member 1 1 such that distance d between the first 11 and second 12 members remains substantially constant and the first member 11 and second member 12 remain substantially parallel. It will be appreciated therefore that as the second member 12 is moved over the first member that the proportions of the respective parts 13-16 of the first member 11 in overlapping relationship with the second member 12 will be varied. The air in the -air gap 46 between the first 1 1 and second 12 members is a di-electiic and as such, the first and second members 11, 12 will be capacitively coupled. Of course, if desired, instead of providing an air gap 46 between the first 11 and second 12 members, an insulating material may be provided. In one example, a polythene or other thin membrane may be placed on the first member 11, and the second member (12) may cany a conductive foam rubber which is moved over the first member 1 1 as the second member 12 moves. In that way, the spacing D between the first and second members 11, 12 would remain constant duiing movement of the second member 12. Other airangements are no doubt possible. When the electronic switch 31 is in a condition such that the first signal 26 is connected to the two parts 13 and 16 and the second signal 27 is connected to the second and third parts 14, 15, movement of the second member 12 relative to the Y axis 34 (i.e. along the X axis 33) will thus change the wavefoirn of the signal arising in the second member 12 by virtue of its capacitive coupling to the first member 1 1. The fonn of the signal arising will depend upon the relative extents of overlap of the second member 12 and the parts 13, 16 and 14, 15 of the first member 1 1. The signal from the second member 12 may according to the invention, be analysed in at least the following two alternative ways. First, refeπing to figure 4, it will be appreciated that the signal 52 arising in the second member 12 by virtue of its capacitive coupling to the first member 1 1 will comprise a complex waveform 52 comprising dominant base 55 and peak 56 step levels, with steps 57,58 between the dominant base and peak levels 55,56. As the proportion of overlap of the second member 12 with the respective parts 13, 16 and 14, 15 of the first member 1 1 is changed, this will affect the levels of the steps 57,58 above and below the base and peak levels 55,56 respectively . For example as the second member 12 is moved so that a greater proportion of the parts 14 and 15 of the first member 1 1 are overlapped, the height of step 58 above the base level 55 may rise whilst the height of the step 57 above the base level 55 may fall. Thus the steps 57,58 heights will be indicative of the position of the second member 12 relative to the first member 1 1 along the X axis 33 and so by analysing the signal output from the second member 12 to sense the step 57,58 heights infoπnation concerning the relative position of the second member 12 to the first member 1 1 along the X axis may be deteimined. When the electronic switch 31 is in a condition such that first signal 26 from the oscillating signal source 35 is connected to parts 13 and 14 of the first member 11, and the second signal 27 is connected to third and fourth parts 15 and 16 of the first member 1 1, then the output signal 50 from the analyser means 40 will be indicative of the relative position of the second part 12 relative to the X axis 34 i.e. along the Y axis 34. In each case, the frequency of the signal 52 arising in the second member 12, which is analysed will be nominally the same as the frequency of the first and second square waveform signals 26,27. In a practical airangement because the levels of both of the steps 57 and 58 in the signal 52 will vary as the second member 12 is moved relative to the first member 1 1, the level of only one of the steps 57,58 may be deteimined. However it will be appreciated that in a practical airangement the resultant wavefoim signal 52 arising in the second member 12 may not remain constant due to. for example only, component drift, which may affect the accuracy of the square wavefomis 26,27 provided to the first member 1 1. Hence preferably the signal 52 is analysed by comparing the level of step 57 or 58 with the base 55 or peak 52 dominant step levels so that any variations in the square wavefonn signals 26,27 do not affect the accuracy of the positional infoπiiation. It will be appreciated that there will be a ratiometric relationship between the base 55 and peak 52 dominant step levels and the step levels of the steps 57,58 to either side in the complex wavefoim. Analysing the signal 52 arising in the second member 12 in this way, it is envisaged that the method and device described may subject to calibration, be sufficiently accurate to be used for measurement. When the device 10 is operating such that the device output signal 50 is indicative of the position of the second member 12 relative to the X axis 33, it will be appreciated that movement of the second member 12 relative to the Y axis, i.e. along X axis 33 will not affect the signal 52 arising in the second member 12 by virtue of its capacitive coupling to the first member 11, and conversely, when the output signal 50 is indicative of the position of the second member 12 relative to the Y axis 34, movement of the second member 12 relative to the X axis 33 i.e. along the Y axis 34, will not affect the signal 54 arising in the second member 12. The output signal 50 from the analyser means 40 thus may, depending on the condition of the electronic switch 31, be indicative of the position of the second member along the X or Y axes 33,34. A second way of analysing the wavefonn arising in the second member 12 is to filter haimonics from the complex waveform 52 in order to obtain a simple sinusoidal waveform. In figure 4 the resultant filtered sinusoidal wavefonn is indicated in dotted lines at S. This waveform S will still be of the same frequency as the two square wavefomis 26,27 which are provided to the parts 13-16 of the first member 1 1 although the phase of the filtered signal will vary depending on the relative position of the second member 12 to the first member 1 1 i.e. the proportion of overlap of the second member 12 to the respective two parts 13, 14 to 15, 16 or 13, 16 to 14, 15of the first member 11. Thus the analyser means 40 may comprise a phase comparator to compare the phase of the filtered signal 60 derived from the output signal arising the second member 12, with the phase of one or both of the square wavefoim signals 26,27 provided to the first member 11. The phase comparator 40 may compare the relative phases of the signals at the two inputs 41 and 42 by any applicable means such as a (software) timing loop or (hardware) ASIC counter or the like. In all cases the electiOnic switch 31 may be manually controlled but most conveniently, the electronic switch 31 is airanged to provide the respective first and second square wavefonn signals 26, 27 to the different parts 13 - 16 of the first member 11 automatically and in sequence. A multiplexer or like airangement may therefore be provided as the elecft'onic switch 31 and it will be appreciated that the device output signal 50 may need appropriately to be switched to different inputs of a computer controller, game console or the like, which may thus utilise the device output signal 50 appropriately to detemiine X-Y axis positional information in real time. It will appreciated that in many items of electiOnic equipment or other apparatus which contain electronic control means, there will be an existing microcontroller or ASIC, and that the existing microcontroller or ASIC may be utilised both to obtain one or more square wavefonn signals such as signals 26 and 27 for use in the device 10, and that the microcontroller or ASIC may also comprise the means necessary for step level detennination and/or phase comparison. It will be appreciated that the oscillator signal source 25 may provide appropriate signal wavefonn signals to a plurality of position sensing devices. Thus for example in a graphic equalizer which may have a substantial number of individual channels, thirty say, only one oscillator signal source 25 would be required. A dedicated analyser means 40 may be provided for each positional sensor, or using a multiplexing type airangement, a single analyser means 40 may be used for each of the plurality of positional sensing devices. Various modifications may be made without departing from the scope of the invention. In particular, the present invention has been described in the embodiment above with reference to a device for obtaining positional information along mutually generally orthogonal X and Y axis 33 and 34. The invention may be utilised to obtain omnidirectional infoimation only, and that direction may be linear or otherwise. For example, a conventional slider type control having wiping contacts may be replaced by a device in accordance with the invention in which the first member has only two parts which are isolated electrically conducting parts. Altematively, the device may provide positional infoimation relative to three axes at 120° to one another in which case the first member may comprise three isolated electrically conducted parts in a suitably aπay. It is envisaged that a device in accordance with figures 1 to 3 may be constructed in which the first member 1 1 has an area of about 25 x 20 mm. The oscillator signal source 25 may generate a square wave signal at a frequency of about 10 kHz. Stability of frequency is not critical but should remain stable whilst positional movement of the second member 12 relative to the first member is performed. The oscillator signal source 25 may generate the square waveform signal or signals 26, 27 digitally or otherwise. Whereas it is prefeπed for the distance d between the moving member 12 and the fixed member 1 1 to remain generally constant, slight variations in distance d during second member movement need not have a severe effect on the positional movement deteimined provided that the air gap 46 is sufficiently great. In Figure 3 it can be seen that there is an input 41 to the analyser means 40 from the conductor 30. This is used to facilitate tuning in the analyser means 40 but is not essential. A timing pulse may be provided direct from oscillator means 25 if desired. The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific foims or in terms of a means for peifoiming the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately or in any combination of such features, be utilised for realising the invention in diverse foims thereof.

Claims: CLAIMS 1. A method of obtaining positional infoimation utilising a device comprising a first member having at least two electrically isolated conducting parts, and a second electrically conducting member adjacent to and capacitively coupled to the first member, the first and second members being relatively movable such that the proportions of the respective parts of the first member in overlapping relationship with the second member may be varied, the method comprising the steps of providing a first square wavefonn signal to one of the parts of the first member and a second square wavefoim signal to the other of the parts of the first member, analysing a signal arising in the capacitively coupled second member to obtain a device output signal containing infoimation about the relative positions of the first and second members. 2. A method according to claim 1 wherein the first and second square wavefoim signals are of the same frequency but are 90° out of phase with each other. 3. A method according to claim l or claim 2 wherein the signal which is analysed comprises a filtered output from signal arising in the second member. 4. A method according to claim 3 wherein the filtered output signal comprises a sine wave the phase of which is compared w ith the phase of one of the first and second square waves. 5. A method according to claim 1 or claim 2 wherein the output signal from the second member is a complex wavefonn of the same frequency as the first and second square waveforms having steps either side of a dominant step level, the method comprising analysing at least one of the step heights to obtain the positional infoimation. 6. A method according to claim 1 or claim 2 wherein the output signal from the second member is a complex wavefoim of the same frequency as the first and second square wavefoπns having steps either side of a dominant step level, the method comprising analysing the difference between at least one of the steps and the dominant base or peak step level to obtain the positional infoimation. 7. A method of obtaining positional infoimation substantially as herinbefore described with reference to the accompanying drawings. 8. A device for obtaining positional information by a method according to any one of the preceding claims the device comprising a first member having at least two electrically isolated conducting parts, and a second electiically conducting member adjacent to and capacitively coupled to the first member, the first and second members being relatively movable such that the proportions of the respective parts of the first member in overlapping relationship with the second member may be varied, means to provide a first square wavefonn signal to one of the parts of the first member and a second square wavefonn signal to the second part of the first member, means to analyse a signal arising in the capacitively coupled second member to obtain a device output signal containing infoimation about the relative positions of the first and second members. 9. A device according to claim 8 wherein the first member of the device comprises more than two electrically isolated parts relative to which the second member may move, square waveform signals being applied to each of the plurality of parts whereby the device is able to obtain positional information about relative movement between the first and second member in two dimensions. 10. A device for obtaining positional infoimation substantially as hereinbefore described with reference to and as shown in the accompanying drawings. 11. Any novel feature or novel combination of features described herein and/or shown in the accompanying drawings.

Inventors: WOODFIELD DAVID, WOODFIELD, DAVID
Applicants: WOODFIELD DAVID, WOODFIELD, DAVID
Application year: 1998
Main classification: G01D5
IPC codes: G01D5, G06F3