Graphical input devices

A graphical input device is described which has a large surface divided into main regions and a small cursor divided into sub-regions. In one embodiment both the large surface and the cursor contain conductors to sense the position of a stylus used for indicating points in the large surface but the conductors of the large surface are widely spaced compared with those of the cursor. In operation the cursor is placed over a point whose position is required in the form of electrical signals and the stylus is used to indicate the point. In another embodiment only the cursor contains conductors, the large surface being divided by lines, and the position of the cursor being recorded by an operator.

The present invention relates to apparatus and methods for providing a 
signal representative of the position of a point indicated by stylus 
means, particularly but not exclusively where the point may be anywhere on 
a relatively large surface. The invention is expected to prove useful in 
the fields of graphical inputs for computers and digitisers for indicating 
the position of points in two dimensional surfaces such as on graphs or 
maps or other diagrams. 
According to a first aspect of the present invention there is provided 
apparatus for generating signals representative of the position of a point 
on a surface indicated by stylus means, including a member having a 
working surface suitable for use with stylus means to allow the stylus 
means to be used to indicate points in the working surface, first sensing 
means for sensing the position of an indicating portion of the stylus 
means in relation to the working surface to sense the position of points 
therein indicated by the stylus means, cursor means which may be placed 
on, and moved over, the working surface without materially affecting the 
operation of the first sensing means even when between the stylus means 
and the working surface, the cursor means having a working area which is 
small in relation to the working surface, second sensing means for sensing 
the position of the indicating portion of the stylus means in relation to 
the working area of the cursor means to sense the position of points 
therein indicated by the stylus means, the resolution of the second 
sensing means being high relative to that of the first sensing means, and 
means for indicating the position of the cursor means on the working 
surface. 
Preferably the working surface is divided into main regions and the working 
area of the cursor means is divided into sub-regions. 
According to a second aspect of the present invention there is provided 
apparatus for generating signals representative of the position of a point 
indicated by stylus means, including a member having a working surface, 
cursor means which may be placed on and moved over the working surface, 
the cursor means having a working area which is small in relation to the 
working surface, sensing means for sensing the position of the indicating 
portion of stylus means in relation to the working area to sense the 
position of points therein indicated by the stylus means, and means for 
indicating the position of the cursor means on the working surface. 
The means for indicating the position of the cursor means may include first 
and second groups of equally spaced parallel lines, the lines of the first 
group being at right angles to those of the second group, and the lines of 
the groups dividing the working surface into main regions, and the working 
area of the cursor means may be rectangular and of a size such that when 
on the working surface, it can be positioned to be coincident with one 
main region, or an integral number of the main regions. 
In the second aspect of the invention the working area of the cursor means 
is preferably divided into sub-regions. 
Preferably the main regions all have the same dimensions and the 
sub-regions of the cursor cover an integral number of the main regions. 
The term stylus means in the specification and claims means not only a 
writing implement but also any means which can be used to indicate the 
positions of points or lines. 
If the stylus means is constructed to interact with magnetic flux then the 
or each of the sensing means may include a plurality of sensing coils. The 
division of the working area of the cursor means into sub-regions may be 
by means of the sensing coils which may overlap in the direction of a 
required co-ordinate in the working area, and be positioned to divide the 
working area into the sub-regions with each sub-region within an 
arrangement of the sensing coils particular to that sub-region. The 
division of the working surface into main regions may be accomplished in 
the same manner by sensing coils of the first sensing means. 
Usually rectangular co-ordinates will be required to indicate the position 
of the stylus means and then two sets of sensing coils are needed for the, 
or each, sensing means, one set for each co-ordinate. 
The, or each, sensing means may include means responsive to change in flux 
linking the sensing coils and the stylus means for providing the signals 
representative of the position of the stylus means. 
Various ways in which the sensing coils can be arranged and the means 
responsive to change in flux may be constructed are described in the 
cognate complete specifications for United Kingdom Patent Application Nos. 
50200/74 and 23141/75 (Inventor: J. A. Gordon) filed on the Nov. 20, 1974 
and the May 27, 1975, respectively; and in the specification of U.S. Pat. 
No. 4,029,899 issued June 14, 1977 (Inventor: J. A. Gordon). 
In the second aspect of the invention, the apparatus may include 
manually-operable means, such as a keyboard, for providing signals 
representative of the position of the cursor means on the working surface, 
in response to operations carried out by an operator to indicate the 
cursor position. 
In use with some forms of the invention, for example in translating a map 
into a series of digital co-ordinates for storage in a computer, the map 
is placed over the area of interest and the cursor is plced on the map in 
the region where co-ordinates are required. Clearly for this application 
the cursor must be transparent but when it is placed below the map it can, 
of course, be opaque. The cursor means must be placed on the area of 
interest in such a way that the sub-regions exactly sub-divide the main 
regions and the position of the cursor means is signalled either by using 
the manually-operable means, or later when current pulses are passed 
through a coil of the stylus means. by the further sensing means. The 
stylus means is now used for example to follow a line on the map, and a 
number of least significant "bits" for each co-ordinate are derived from 
signals induced in the sensing coils of the cursor means when current 
pulses in the coil of the stylus means induce currents in the sensing 
coils. At the same time currents are induced in the sensing coils of the 
working surface, if provided, and these currents give rise to the most 
significant "bits" in each co-ordinate the position of the stylus means. 
Since the sensing coils of the cursor means and the sensing coils of the 
working surface area arranged in a pattern which is unique for every 
subregion and main region, the currents derived in the sensing coils are 
indicative of the position of the stylus. When following a line of the 
map, the cursor means may have to be moved from time to time where the 
line extends beyond the cursor. 
The main advantage of the present invention is that it allows the position 
of a point in a relatively large area to be signalled to high resolution 
without the whole area having to be divided, perhaps by means of many 
conductors, to that resolution. Indeed if the sensing coils of the working 
surface are not provided the large area need not be wired at all since 
then only the cursor means is wired.

In the arrangement of FIGS. 1 and 2 a surface of a table 16 is divided into 
main regions, such as the region 10 by nine parallel lines, such as the 
lines 11 which appear vertical in FIG. 1 and nine parallel lines such as 
the lines 12 which appear horizontal in FIG. 1. A transparent cursor 13 is 
shown overlying four of the main regions and it will be seen that this 
cursor is divided into sub-regions. The boundaries of the main regions and 
the sub-regions are physically defined by conductors 20 and 20' (see FIG. 
2) of sensing coils as described in the aforementioned cognate complete 
specification and the aforementioned U.S. patent. For example in FIG. 3, a 
first coil 17 follows the extreme edge of the working area designated 19 
of the cursor surface and a second coil 18 is positioned over the coil 17. 
A side portion 21 of the coil 18 divides the area 19 into two halves. The 
next coil in the series, coil 22, when placed over the coil 18 has side 
portions which divide the operational area together with the side portions 
of the coil 18 into four equal portions. Similarly a coil 23 having four 
side portions divides, together with the coils 18 and 22, the area of 
interest into eight equal portions. Coil 24 together with the other coils 
then divides the area into 16 equal portions. Coils 17 to 19 and 22 to 24 
are all formed by the conductors 20' of the cursor. 
The coils 17 to 24 may be placed over one another or, to prevent build-up 
of conductors at the edges, one within another. 
It will be noted that crossovers within coils are avoided. Clearly this is 
an important advantage in the manufacture of cursors since it avoids the 
necessity of locating conductors crossing the area exactly on top of one 
another. 
When this arrangement is used for the cursor 13 of FIG. 1 of the present 
invention two sets of sensing coils are provided, one for X co-ordinates 
and one for Y co-ordinates, the conductors of the coils of different sets 
being at right angles where they traverse the working area. 
Since the cursor has to be moved from place to place, it is connected by a 
flexible lead to the circuits. 
The same arrangement of coils may be used in the table 16 and the edge of a 
working surface of the table is then defined by the line designated 19. 
Two sets of coils are again required, one for each co-ordinate, the lines 
11 and 12 coinciding with the conductors 20 of the coils. 
The conductors making up the coils of the cursor are of course must more 
closely spaced than those of the working surface, and in practice many 
more sensing coils are used, at least in the cursor, than are shown in the 
figures. 
As can be appreciated from FIG. 1 showing the main regions and sub-regions 
the conductors 20 in the working surface are spaced by distances which are 
an integral multiple of the distances between the conductors 20' of the 
cursor. 
If the sensing coils are arranged as shown in FIG. 3 in both the working 
surface of the table 16 and the cursor 13, the position of a point in the 
working surface is indicated by means of a stylus 14 which includes an 
electrical coil 40 with a magnetic member 41 passing through it. When a 
pulse of current is passed through the coil 40 the flux associated with 
the magnetic member 41 varies and if the stylus is positioned adjacent to 
the cursor, currents are induced in the various coils defining the main 
regions and sub-regions. 
Although only a relatively small number of sensing elements in the form of 
coils are used a direct digital output can be obtained from the coils by 
way of the simple decoding circuit shown in FIG. 4. The output is in the 
form of a binary number having the usual arrangement of bits which are 
more significant towards the left of the number. 
In order to simplify FIG. 4 only the coils 17, 21, 22 and 23 are included 
but it will be realised that in practice depending on the resolution 
required, the coil 24 and a number of other coils may be required. 
In order that the binary numbers relating to each region can be easily seen 
they are marked above the coils in FIG. 4 between lines representing 
graduations of the X co-ordinate. 
Three subtractor circuits 26, 27 and 28 are connected to the coils 21, 22 
and 23 respectively and in addition each subtractor circuit receives half 
the output signal from the coil 17 derived by way of a potentiometer 
consisting of two equal resistors 30 and 31. In practice the subtractor 
circuits may simply be an appropriate arrangement of connections allowing 
the difference between the voltages in each of the coils 26, 27 and 28 
from that in the coil 17 to be obtained. The subtractor circuits 26, 27 
and 28 are connected to comparators 32, 33 and 34, respectively, each of 
which may conveniently comprise a saturable amplifier. The output from the 
comparator 32 is connected to an output terminal 35 at which the most 
significant bit appears and the output from this comparator is also 
connected to an exclusive OR gate 36 which also receives the output from 
the comparator 33. The output of this OR gate is connected to an output 
terminal 37 where the second most significant figure appears. A further 
exclusive OR gate 38 receives the output from the gate 36 and also that 
from the comparator 34 and its output is connected to an output terminal 
39 where the least significant bit appears. 
In operation a diagram 15 (FIG. 2) which is to be processed is placed on 
the surface of the table 16 and the cursor 13 is placed over the area of 
interest. As mentioned above care must be taken to position the cursor 
exactly in relation to the lines dividing the regions and the left-hand 
side of the cursor must be on the left-hand edge of the working surface of 
the table or an even number of main regions therefrom and the lower edge 
of the cursor (as seen in FIG. 1) must be on the lower edge of the working 
surface or an even number of main regions therefrom. For this reason the 
surface is marked, for example in the way shown, as that the cursor can be 
placed exactly in position. If apertures are provided at the corners of 
each main region and corresponding apertures exist in the cursor, the 
cursor can be pegged into position through the apertures before use. 
Taking as an example a point A in FIG. 4 the position of which on the 
cursor is in operation indicated by the stylus 14, it is seen that flux 
from the stylus in this position, when a current pulse is passed through 
the stylus coil, links only the coils 17 and 23. Thus the output from the 
subtractors 26 and 27 will be half the negative value E of the signal 
induced in the coil 17 while the output from the subtractor 28 will be E = 
(E/2) where it is assumed that the voltage induced in each of the coils is 
the same and equal to E. The application of these voltages to the 
comparators 32, 33 and 34 produces a binary output in which a negative 
signal such as (-E/2) is represented by a zero voltage, a positive signal 
such as (+E/2) is represented by a positive voltage, that is the outputs 
of the comparators 32, 33 and 34 can be represented by the binary digits, 
0, 0 and 1 respectively. Hence it can be seen that the signals appearing 
at the terminals 35, 37 and 39 represent the same digits, 0, 0, 1 which 
correspond to the X co-ordinate of the point A as shown at the top of FIG. 
4. In a similar way three more digits are generated in logic circuits 
connected to the coils of the working surface of the table. 
In a further example, the point B, is now considered. The coils 17, 21 and 
22 loop the point B but the coil 23 does not. Hence the subtractor 
circuits 26 and 27 each receive the voltage E - (E/2) and the subtractor 
circuit 28 receives the voltage -(E/2). The comparators 32, 33 and 34 then 
output signals representing the numbers 1, 1 and 0 respectively, so that 
the signals appearing at the terminals 35, 37 and 39 are 1, 0 and 0 
respectively. These digits again correspond to the binary number for the X 
co-ordinate of the point B, and again signals representing digits are 
produced from the coils of the table. 
Clearly when the stylus is used to follow a line on a map the co-ordinates 
of a series of points are generated as further current pulses are applied 
to the stylus coil. 
The coil 17 is not essential but it allows binary ones and zeros to be 
represented by voltages of opposite polarities. 
In most applications two co-ordinate signals will be required and, as is 
mentioned above, two series of coils are required for the cursor and two 
more for the table. Each series of coils is connected to its own group of 
subtractor circuits, comparators and exclusive OR gates arranged as 
indicated in FIG. 4. 
The general rule for determining the coils of FIG. 4, after coils 17 and 21 
have been chosen, is to divide each remaining portion between conductors 
in two using conductors of the next coil and then repeat the procedure for 
each further coil. However, (unless crossovers are used) no conductor 
follows the same route as a conductor of a previous coil. 
Since in FIG. 1 of the present specification there are eight rows of 
sub-regions, eight columns of such regions, and the cursor covers four 
main regions, two "bits" representing position are obtained from the table 
and three more "bits" from the cursor for each co-ordinate. Of course, if 
the cursor covered only one main region and was divided, as shown in FIG. 
1, into 64 sub-regions, three bits would be obtained from the table and 
three from the cursor. 
In another arrangement the surface of the table 16 does not contain sensing 
coils, the main regions being defined by the lines 11 and 12. In operation 
when an operator has placed the cursor in position, he keys the 
co-ordinate of the bottom left-hand corner of the cursor into receiving 
equipment for example a read-out circuit 42 (see FIG. 5) by means of a 
keyboard 43. The operator decides on the co-ordinate and keys the 
corresponding number into the equipment but since the table surface is 
divided into eight rows and eight columns of main regions and the cursor 
covers four main regions, only the first two bits of more significance are 
keyed in for each co-ordinate. Three less significant bits are obtained 
from the cursor in the way already described by means of the circuits of 
FIG. 4 represented by the logic circuit 44 in FIG. 5. 
Again, since the cursor 13 as shown covers four main regions, it must 
always be placed with the left-hand side of the cursor at the left-hand 
edge of the working surface of the table or an even number of squares from 
the left-hand edge of the working surface and with the lower edge of the 
cursor (as seen in FIG. 1) at the lower edge of the working surface or an 
even number of squares from the lower edge of the working surface. Then 
the two most significant bits in each co-ordinate are compatible with the 
three least significant bits obtained from the cursor. 
The cursor and in some cases the surface have been described as being wired 
in a specific way or in one of the ways described in the aforementioned 
complete specification but other methods of wiring and of dividing an area 
into regions may, of course, be used. Other types of graphical input 
tablets, that is devices in which the movement of stylus means in writing, 
or drawing or following lines already established, for example, is 
converted into an electrical signal, may also be used as the working 
surface and/or the cursor means.