GB2270765A - Position recognition apparatus - Google Patents
Position recognition apparatus Download PDFInfo
- Publication number
- GB2270765A GB2270765A GB9319486A GB9319486A GB2270765A GB 2270765 A GB2270765 A GB 2270765A GB 9319486 A GB9319486 A GB 9319486A GB 9319486 A GB9319486 A GB 9319486A GB 2270765 A GB2270765 A GB 2270765A
- Authority
- GB
- United Kingdom
- Prior art keywords
- signal
- measuring apparatus
- sensor
- signal generating
- generating elements
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
- G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
- G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
- G06F3/046—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means by electromagnetic means
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B7/00—Measuring arrangements characterised by the use of electric or magnetic techniques
- G01B7/004—Measuring arrangements characterised by the use of electric or magnetic techniques for measuring coordinates of points
Abstract
Apparatus for measuring the position of a member arranged to be movable on a surface comprises a plurality of signal generating elements 25a, 25b which may comprise elongate conductors or point sources each of which is responsive to a signal supply means; a sensor 35 movable in relation to the signal generating elements in association with the movements of the member, said sensor being adapted to produce sensor-signals in response to signals generated by the signal generating elements; means for monitoring a characteristic of the sensor-signals produced by the sensor; means for determining, for each particular sensor-signal, which of the signal generating elements generated the signal in response to which the particular sensor-signal was produced; and calculating means responsive to the monitoring means and the determining means for calculating the position of the sensor relative to the grid of signal generating elements. <IMAGE>
Description
Position Recognition Apparatus
This invention relates to an apparatus for monitoring the position or condition of an object able to move over a surface, for example the position of a measuring head in gauging apparatus.
Gauging apparatus is well known and involves the direct measurement of linear dimensions from a known fixed point in a co-ordinate system by means of scales, such as glass gratings and lasers for example. These versions identify the position of a measuring head by use of linear scales fixed independently to an X-axis and a Y-axis. They often require careful calibration via relative measurements of distance, the results of all such measurements being dependent on accurate measurement of the fixed point and careful positioning of the scales relative to the axes.
The apparatus of the present invention identifies the position of a measuring head, and hence any object with which the measuring head is in contact, directly without the use of linear scales fixed independently to the axes. The apparatus requires no parts other than the measuring head itself to be on the surface, the position being measured via signals monitored by the measuring head whose characteristics vary continuously over the measuring surface. From these signals, the position of the measuring head can be determined, approximately by a direct method and more accurately by means of suitable analysis of the signals, the position being identified with respect to purely notional fixed points and axes.
According to the present invention, there is provided an apparatus for measuring the position of a member arranged to be movable on a surface, comprising a plurality of signal generating elements each of which is responsive. to a signal supply means; a sensor movable in relation to the signal generating elementsin association with the movements of the member, said sensor being adapted to produce sensor-signals in response to signals generated by the signal generating elements; monitoring means for monitoring a characteristic of the sensor-signals produced by the sensor; determining means for determining, for each particular sensor-signal, which of the signal generating elements generated the signal in response to which the particular sensor-signal was produced; and calculating means responsive to the monitoring means and the determining means for calculating the position of the sensor relative to the grid.of signal generating elements.
Preferably each signal generating element is an elongate portion of a closed loop of electrically conductive material, the direction of elongation of each portion being parallel to a direction that lies within the plane of the measuring surface of the apparatus. A set of such signal generating elements each parallel to the same direction, spaced at intervals in substantially the same plane, form a row for measuring position in the direction on the surface that is perpendicular to the direction of the major portion of the elongate portions. The portions themselves may be on or below the base-surface of the measuring apparatus.
Each closed loop may be regarded as having an outward section and a return section. The outward and return sections of each closed loop may both be in the form of elongate portions forming signal generating elements, carrying current in equal and opposite directions. Alternatively, the return section may be positioned away from the plane of the measuring surface, so as to have a negligible effect on the sensor.
Preferably the apparatus has two independent rows of signal generators such as the portions of conducting material described above, aligned so that one row generates signals whose main direction of variation allows position measurements to be made in the direction of a notional X-axis on the measuring surface, while the other row generates signals whose main direction of variation allows position measurements to be made in the direction of a notional Y-axis perpendicular to the Xaxis. This apparatus may then monitor the position of a measuring head moving over a surface in two dimensions in terms of Cartesian co-ordinate. For measurements of position in one dimension however, one such row of signal generators would be sufficient.Other layouts of rows, for example with non-perpendicular rows, can also be used for more specialized applications, and with suitable means to move the measuring head, for example.
The apparatus may alternatively have a matrix of signal generators in the form of point-sources, such as small coils of conductive wire, preferably positioned regularly across the measuring surface in two dimensions. These may be energized one-by-one, or on a row-by-row and/or column-by-column basis, or concurrently but so as to cause them to generate signals which may be differentiated from each other, so as to provide signals that may be picked up by the sensor.
If the signal generators are chosen to be closed loops or coils of conductive material, then in use, they may be caused to generate a signal if they are energized by an electrical input signal. A sensor suitable for picking up the resulting electromagnetic signal from the signal generators would be an inductive pick-up coil. For different types of signal from alternative types of signal generators, however, other types of sensor could be chosen.
Using the preferred layout of rows of lengths of conductive material as signal generators and an inductive pick-up coil as a sensor, the position of the sensor and hence the measuring head can be monitored accurately if it is possible to differentiate between the signals picked up by the inductive pick-up from different signal generators. The input signal for the signal generators may be an alternating signal or a pulsed signal. In either of those cases, the signal generators may also be pulsed on a time base so that only one is energized at a particular time, thus allowing the knowledge that any signal picked up by the inductive pick-up coil at that time was generated by the contemporaneously energized signal generator.Suitable analysis of the signals picked up over time by the sensor in comparison with the input signals to the signal generators allows the position of the sensor to be calculated with respect to the positions of the signal generators. Alternatively, each may be energized by an alternating input signal of a different frequency.
In this case, suitable analysis of the signals picked up by the sensor in comparison with the input signals using a frequency dependent analyzer allows the position of the sensor with respect to the positions of the signal generators to be calculated.
With the versions of the apparatus referred to above, two levels of accuracy of measurement of the position are possible, using data relating, for example to the strength of the signal from each signal generator picked up by the sensor at a particular position. The strength of the signal picked up relative to the input signal for a particular signal generator is dependent on the distance of the sensor from that signal generator.
Thus an approximate measurement of position can be made from the knowledge that the sensor must be nearest to the signal generator from which the signal of greatest relative strength is being picked up. A measurement of greater accuracy can be made by further analysis of the relative strengths of the signals picked up from each signal generator. A similar choice of level of accuracy is possible if some characteristic of the signal other than strength is picked up, providing suitable analysis of the signal is done.
Preferably the apparatus for measurement of position includes a base-surface on which a one or two dimensional grid of signal generators is mounted. The signal generators may be wholly or partly on or below the base-surface, provided it is possible to connect to each of them means to energize them with an input signal sufficient to cause them to generate suitable signals themselves. Over the base surface is a measuring surface parallel to the one or two dimensional grid of signal generators and means four moving a measuring head over the measuring surface in mechanical contact with a work-piece which may be supported on or above the measuring surface or be supported by other means away from the measuring surface.A sensor, mounted so as to move with the measuring head, is able to pick up signals generated by the signal generators and relay data relating to those signals picked up to a means for analyzing said data. Suitable analysis of said data allows the position of the sensor, and hence of the measuring head, to be calculated.
Embodiments of the invention will now be described in more detail with reference to the accompanying drawings in which:
Figure 1 is a perspective view of the apparatus for position recognition according to an embodiment of the invention, showing the base-surface with signal generators and the measuring head. No workpiece is shown;
Figure 2 shows in symbolic form the electrical part of the apparatus for measurement of position in one dimension, according to an embodiment of the invention.
Figure 3 shows in symbolic form the electrical part of the apparatus for measurement of position in two dimensions, according to an embodiment of the invention;
Figure 4 and 5 show a- set of input signals pulsed on a time-base to each of the signal generators, and a graph of possible signals picked up by which the position of the measuring head may be estimated roughly or calculated accurately, for measurement of position in one dimension; and
Figure 6 shows a set of input signals pulsed on a time-base to each of the signal generators, and a graph of possible signals picked up by which the position of the measuring head may be determined, for measurement of position in two dimensions.
In Figure 1, an embodiment of the apparatus for position recognition is shown in simplified form.
There is a base-surface (10) in which is mounted a grid (20) of lengths of a conducting material (25). Pairs of these lengths are in fact portions of the same closed loop and thus carry equal and opposite currents when the loop is energized. The lengths (25a) in a row aligned parallel to a first direction and spaced apart regularly in direction X have a function to generate electromagnetic signals, a characteristic of which varies predominantly with position along direction X.
The lengths (25b) in a row aligned parallel to a second direction and spaced apart regularly in direction Y have a function to generate electromagnetic signals, a characteristic of which varies predominantly with position in direction Y. (The means by which the lengths (25) are caused to generate electromagnetic signals are not shown in Figure 1.)
Above the grid (20), which may be above or below the base-surface (10), a measuring-head (30) is able to move on a measuring-surface (not shown) by means of a servo-system (not shown) or otherwise. Mounted to the measuring-head (30) is a sensor (35) such as an inductive pick-up coil, and a contact-arm (32) for mechanical contact to a work-piece (not shown).
Figures 2 and 3 show the electrical part of the apparatus for measurements of position in one and two dimensions respectively, in symbolic form.
Referring to Figure 2, the input signal to the row of loops (25a) for measurement of position along direction
X is denoted by Vin. According to an embodiment of the invention, signal Vin is an alternating signal of radiofrequency, although the frequency can be chosen depending on the response time and accuracy required.
The lengths (25a) are also activated by pulses from a time-base, represented by switches S1 to Sn, with the result that one neighbouring. pair of lengths at a time is driven by the input signal Vin. The resulting signal to each length is that which is allowed to pass through switches S1 to Sn, represented in Figure 4 by signals V1 to Vn.
Returning to Figure 2, the pulses of alternating current in each successive pair of lengths cause them to generate electromagnetic signals in turn.
These electromagnetic signals will induce a current in the inductive pick-up coil (35) whose size depends on the input signal, the dimensions of the closed loops and the coil, their relative orientations, and the size of the distance between lengths and the coil. All other factors being equal, the distance of the inductive pickup coil (35) from each of the lengths (25a) determines the strength of the signal Vout induced by each pair of lengths as it is pulsed on the time-base.
An initial estimate of the position along direction X of the pick-up coil (35) can be made from determining from which signal generator the maximum signal is received. Thus on Figure 5, the maximum signal received Vout(max) lies within the area above the pair of lengths activated by switch S2. The position of this loop can therefore be taken to be a first order estimate of the position along direction X of the pickup coil (35).
For a more accurate measurement of the position along direction X, denoted by tx' in Figure 5, more detailed mathematical analysis of the set of output signals Vout(Sl, 52 ....Sn) is carried out, using iteration methods or otherwise. The accuracy able to be achieved by such methods is dependent on the sensitivity of the pick-up coil (35) to the signals from the signal generators (25a), the amount of signal generators, and the accuracy of their alignment with respect to each other amongst other factors.
Figures 2, 4 and 5 relate to an embodiment of the apparatus for position recognition in one dimension.
They also serve to facilitate the understanding of a similar embodiment of the apparatus for position recognition in two dimensions. Figures 3 and 6 relate to this embodiment which function similarly to the embodiment described with reference to Figs. 2, 4 and 5.
Only the significant differences will be summarized in the following paragraph.
In Figure 3 the electrical part of the apparatus for measurement of position in two dimensions is shown in simplified symbolic from. Referring also-to
Figure 5, two rows of signal generators (25a-25b) for measuring position in the two directions X and Y are activated successively by pulses from the same timebase, represented by switches Sl(x) to Sn(x) and Sl(y) to Sn(y) so that one at a time is driven by the input signal Vin. As with the embodiment of Figs. 2, 4 and 5, the pulses of alternating current in each successive signal generator cause them to generate electromagnetic signals which induce a current in the pick-up coil (35).
The treatment of the output signal Vout must be divided into a part for determining the position along the X direction and a part for determining the position along the Y direction. Thus for initial estimates of the positions along directions X and Y and for more accurate measurements of these positions, data relating to the two directions are treated separately. The final result of the two pairs of determinations are then combined to give the position in two dimensions in terms of
Cartesian co-ordinates based on notional axes in the X and Y directions and fixed points chosen as required.
Claims (23)
1. An apparatus for measuring the position of a member arranged to be movable on a surface, comprising a plurality of signal generating elements each of which is responsive to a signal supply means; a sensor movable in relation to the signal generating elements in association with the movements of the member, said sensor being adapted to produce sensor-signals in response to signals generated by the signal generating elements; monitoring means for monitoring a characteristic of the sensor-signals produced by the sensor; determining means for determining, for each particular sensor-signal, which of the signal generating elements generated the signal in response to which the particular sensor-signal was produced; and calculating means responsive to the monitoring means and the determining means for calculating the position of the sensor relative to the grid of signal generating elements.
2. A measuring apparatus according to claim 1, wherein in use said signal generating elements are caused to generate signals in a predetermined order, such that they are differentiable from each other in time by the determining means.
3. A measuring apparatus according to claim 1 or 2, wherein in use said signal generating elements are caused to generate signals which cause the sensor to produce sensor-signals which are differentiable from each other by the determining means by virtue of a predetermined characteristic.
4. A measuring apparatus according to any of the preceding claims, wherein the signal generating elements are elongate elements, the signals from each of which are substantially constant along its length.
5. A measuring apparatus according to claim 4, wherein a first set of said elongate signal generating elements comprises a first plurality of said elements arranged in a regular pattern parallel to each other, such that the main direction of variation of signals produced therefrom is in a first direction perpendicular to the direction of elongation of said elements of said first plurality.
6. A measuring apparatus according to claim 5, wherein a second set of said elongate signal generating elements comprises a second plurality of said elements arranged in a regular pattern parallel to each other, such that the main direction of variation of signals produced therefrom is in a second direction perpendicular to the direction of elongation of said elements of said second plurality, said first direction being transverse to said second direction.
7. A measuring apparatus according to claim 6, wherein said first direction and second direction are perpendicular directions.
8. A measuring apparatus according to any of claims 4 to 7, wherein each signal generating element is a portion of a closed loop of an electrically conductive material for generating an electromagnetic signal when energized by an electrical input signal from said signal supply means.
9. A measuring apparatus according to claim 8, wherein an outward and a return portion of each closed loop are positioned parallel to each other.
10. A measuring apparatus according to claim 9, wherein said outward and return portions of the closed loops are all positioned in substantially the same plane.
11. A measuring apparatus according to claim 8, wherein each signal generating element is an outward portion of a closed loop, said outward portions being substantially parallel to each other and in the same plane, the return portions of the closed loops being positioned at such a distance from theplane containing the outward portions that they have a negligible effect on the sensor.
12. - A measuring apparatus according to claim 1, 2 or 3, wherein the signal generating elements are substantially point sources.
13. A measuring apparatus according to claim 12, wherein the signal generating elements are arranged in a regular two-dimensional array.
14. A measuring apparatus according to claim 13, wherein the signal generating elements are arranged in rows and columns, the rows being perpendicular to the columns.
15. A measuring apparatus according to claim 12, 13 or 14, wherein each signal generating element is a portion of a closed loop of an electrically conductive material for generating an electromagnetic signal when energized by an electrical input signal from said signal supply means.
16. A measuring apparatus according to claim 15, wherein each signal generating element is a coil.
17. A measuring apparatus according to any of the preceding claims, wherein the signal supply means is an electrical signal supply means.
18. A measuring apparatus according to claim 17, wherein said signal supply means is arranged to supply alternating currents to the signal generating elements.
19. A measuring apparatus according to claim 18, wherein said alternating currents differ in frequency from each other.
20. A measuring apparatus according to claim 17, 18 or 19, wherein said signal supply means is arranged to supply pulses of current to the signal generating elements successively.
21. A measuring apparatus according to any of the preceding claims, wherein the sensor is adapted to produce electrical sensor signals in response to signals generated by the signal generating elements.
22. A measuring apparatus according to any of the preceding claims, wherein the sensor is an inductive pick-up coil.
23. A measuring apparatus substantially as hereinbefore described with reference to the figures.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB929219918A GB9219918D0 (en) | 1992-09-21 | 1992-09-21 | Position recognition apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9319486D0 GB9319486D0 (en) | 1993-11-03 |
| GB2270765A true GB2270765A (en) | 1994-03-23 |
Family
ID=10722232
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB929219918A Pending GB9219918D0 (en) | 1992-09-21 | 1992-09-21 | Position recognition apparatus |
| GB9319486A Withdrawn GB2270765A (en) | 1992-09-21 | 1993-09-21 | Position recognition apparatus |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB929219918A Pending GB9219918D0 (en) | 1992-09-21 | 1992-09-21 | Position recognition apparatus |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB9219918D0 (en) |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2032115A (en) * | 1978-08-14 | 1980-04-30 | Fadden B J | Graphic digitizer |
| GB2038482A (en) * | 1977-12-21 | 1980-07-23 | Telediffusion Fse | Graphic tables |
| GB2089045A (en) * | 1980-11-11 | 1982-06-16 | Osawa Shokai Kk | Tablet for an X-Y Co-ordinate Digitizer |
| GB2124773A (en) * | 1982-07-10 | 1984-02-22 | Sony Corp | Coordinate position digitising systems |
| GB2131955A (en) * | 1982-11-04 | 1984-06-27 | Sony Corp | Coordinate position digitizing systems |
| GB2134760A (en) * | 1983-02-09 | 1984-08-15 | Secr Defence | Interactive display system |
| GB2140562A (en) * | 1983-04-22 | 1984-11-28 | Robert John Collins | Current-ratio digitisers |
| GB2227319A (en) * | 1988-12-09 | 1990-07-25 | Qudos Sa | Digitising device |
-
1992
- 1992-09-21 GB GB929219918A patent/GB9219918D0/en active Pending
-
1993
- 1993-09-21 GB GB9319486A patent/GB2270765A/en not_active Withdrawn
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2038482A (en) * | 1977-12-21 | 1980-07-23 | Telediffusion Fse | Graphic tables |
| GB2032115A (en) * | 1978-08-14 | 1980-04-30 | Fadden B J | Graphic digitizer |
| GB2089045A (en) * | 1980-11-11 | 1982-06-16 | Osawa Shokai Kk | Tablet for an X-Y Co-ordinate Digitizer |
| GB2124773A (en) * | 1982-07-10 | 1984-02-22 | Sony Corp | Coordinate position digitising systems |
| GB2131955A (en) * | 1982-11-04 | 1984-06-27 | Sony Corp | Coordinate position digitizing systems |
| GB2134760A (en) * | 1983-02-09 | 1984-08-15 | Secr Defence | Interactive display system |
| GB2140562A (en) * | 1983-04-22 | 1984-11-28 | Robert John Collins | Current-ratio digitisers |
| GB2227319A (en) * | 1988-12-09 | 1990-07-25 | Qudos Sa | Digitising device |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9219918D0 (en) | 1992-11-04 |
| GB9319486D0 (en) | 1993-11-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |