Apparatus and method for providing a weighted average of time varying characteristic of handwriting

The stress wave activity produced during a first generation of a piece of handwriting in an enrollment procedure is put into a store and the stress wave activities produced for subsequent generations of the piece of handwriting in the enrollment procedure are used sequentially to produce a weighted average of the stored stress wave activity and the stress wave activity of the subsequent generation of the piece of handwriting and replaces the stored stress wave activity; the weighted average includes a weighted average of amplitudes and times of events. For subsequent generations of the piece of the handwriting are resequenced in order of increasing difference from the respective stored stress wave activity. The subsequent generations of the piece of handwriting are again used to sequentially produce weighted averages and replace the stored stress wave activity. The subsequent generations of the piece of handwriting are again resequenced in order of increasing difference from the respective stored stress wave activity. Each of the four subsequent generations of the piece of handwriting are used to produce weighted averages and replace the stored stress wave activity if the difference from the respective stored stress wave activity is less than a predetermined value.

FIELD OF THE INVENTION 
The present invention relates to an apparatus and method for verifying 
personal handwriting. 
BACKGROUND OF THE INVENTION 
It is known from British Patent No. 2159998B to detect and store a time 
varying characteristic, e.g. the stress wave activity produced in a body 
by a writing instrument during the generation of a given piece of 
handwriting. The time varying characteristic, e.g. the stress wave 
activity, produced by a subsequent generation of the given piece of 
handwriting is compared with that produced by the stored piece of 
handwriting in order to determine whether the stored and subsequent 
handwriting pieces have a common author. 
In our copending European Patent Application No. 90313505.1, filed on 12 
Dec. 1990, if it is determined that the subsequent and stored time varying 
characteristic produced during the generation of the handwriting pieces 
have a common author, a weighted average of the stored time varying 
characteristic and the subsequent time varying characteristic is produced. 
The stored time varying characteristic is then replaced by the weighted 
average of the stored time varying characteristic and the subsequent time 
varying characteristic produced during the generation of a piece of 
handwriting by a common author. The weighted average is a weighted average 
of the magnitudes of the time varying characteristic between the stored 
time varying characteristic and the time distorted subsequent time varying 
characteristic and is a weighted average of the time of events. 
In this procedure it is necessary that the stored time varying 
characteristic is either produced from a single sample piece of 
handwriting of the author generated during an enrollment procedure, or is 
an average produced from a number of sample pieces of handwriting of the 
author generated during an enrollment procedure. 
A problem associated with the production of the stored time varying 
characteristic is that the single sample piece of handwriting of the 
author, or one or more of the number of sample pieces of handwriting of 
the author, is often not a typical piece of handwriting of the author. 
This is often because the author is not relaxed during the enrollment 
procedure, or is because the author is not used to writing or for other 
reasons. If the time varying characteristic produced from the untypical 
sample of the piece of handwriting, or untypical samples of the piece of 
handwriting, is stored and subsequently compared to the time varying 
characteristic produced by an authentic piece of handwriting it is 
possible that the authentic piece of handwriting will be determined to be 
generated by a person other than the author of the stored time varying 
characteristic, i.e the piece of handwriting will be determined to be a 
forgery. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide a novel apparatus and method for 
verifying personal handwriting which overcomes the above problem. 
Accordingly the present invention provides a method of verifying personal 
handwriting comprising the steps of detecting a time varying 
characteristic produced by the motion of a writing instrument on a surface 
of a body during the generation of a given piece of handwriting, storing 
random noise or the time varying characteristic produced by the motion of 
the writing instrument on the surface of the body during a first 
generation of the piece of handwriting by an author at an enrollment 
procedure to produce a stored time varying characteristic, sequentially 
producing a weighted average of the stored time varying characteristic and 
the time varying characteristic produced by the motion of the writing 
instrument on the surface of the body during each one of a plurality of 
subsequent generations of the piece of handwriting by the author at said 
enrollment procedure and replacing the stored time varying characteristic 
with the weighted average of the stored time varying characteristic and 
the time varying characteristic produced by the motion of the writing 
instrument on the surface of the body during the said one of the 
subsequent generations of the piece of handwriting by the author at the 
enrollment procedure, characterised in that the step of sequentially 
producing a weighted average includes comparing the stored time varying 
characteristic and the time varying characteristic produced by the motion 
of the writing instrument on the surface of the body during each one of 
the plurality of subsequent generations of the piece of handwriting by the 
author at the enrollment procedure to give a measure of the difference, 
resequencing the time varying characteristics of the plurality of 
subsequent generations of the piece of handwriting by the author at the 
enrollment procedure in order of increasing difference from the respective 
stored time varying characteristic, sequentially producing a weighted 
average of the stored time varying characteristic and the time varying 
characteristic produced by the motion of the writing instrument on the 
surface of the body for each of the resequenced plurality of subsequent 
generations of the piece of handwriting by the author at the enrollment 
procedure and replacing the stored time varying characteristic with the 
average of the stored time varying characteristic and the time varying 
characteristic produced by the motion of the writing instrument on the 
surface of the body during said one subsequent generation of the piece of 
handwriting by the author at the enrollment procedure if the difference is 
less than a predetermined value to produce an average of the time varying 
characteristic produced by the motion of the writing instrument on the 
surface of the body from the subsequent generations of the piece of 
handwriting by the author at the enrollment procedure. 
Preferably the method further comprises the step of determining if a 
predetermined number of the plurality of subsequent generations of the 
piece of handwriting have a difference from the stored time varying 
characteristic equal to or greater than the predetermined value and 
aborting the enrollment procedure if the predetermined number is equalled 
or exceeded. 
Preferably, after resequencing the time varying characteristics of the 
plurality of subsequent generations of the piece of handwriting and before 
sequentially producing and storing the weighted average of the stored time 
varying characteristic and the time varying characteristic produced by the 
motion of the writing instrument on the surface of the body for each one 
of the subsequent generations of the handwriting piece if the difference 
is less than a predetermined value, sequentially producing a weighted 
average of the stored time varying characteristic and the time varying 
characteristic produced by the motion of the writing instrument on the 
surface of the body during each one of the plurality of subsequent 
generations of the piece of handwriting by the author at said enrollment 
procedure and replacing the stored time varying characteristic with the 
weighted average of the stored time varying characteristic and the time 
varying characteristic produced by the motion of the writing instrument on 
the surface of the body during the said one of the subsequent generations 
of the piece of handwriting by the author at the enrollment procedure, 
resequencing the time varying characteristics of the plurality of 
subsequent generations of the piece of handwriting by the author at the 
enrollment procedure in order of increasing difference from the respective 
stored time varying characteristic. 
Preferably comparing the stored time varying characteristic with the time 
varying characteristic produced by the motion of the writing instrument on 
the surface of the body includes distorting the time varying 
characteristic in time to obtain a best match with the stored time varying 
characteristic and storing the value of time distortion required to obtain 
the best match. 
Preferably producing a weighted average of the stored time varying 
characteristic and the time varying characteristic produced by the motion 
of the writing instrument on the surface of the body includes distorting 
the time varying characteristic in time by the values stored to obtain the 
best match with the stored time varying characteristic, producing weighted 
average magnitudes of the time varying characteristic between the stored 
time varying characteristic and the time distorted time varying 
characteristic produced by the motion of the writing instrument on the 
surface of the body and producing weighted average of time of events by 
displacing the weighted average magnitudes of the time varying 
characteristic in time towards the time varying characteristic produced by 
the motion of the writing instrument on the surface of the body. 
Preferably the time varying characteristic is stress wave activity. The 
time varying characteristic may be capacitance, load, pressure, velocity 
or acceleration. 
The present invention also provides an apparatus for verifying personal 
handwriting comprising means for detecting a time varying characteristic 
produced by the motion of a writing instrument on a surface of a body 
during the generation of a given piece of handwriting, means for storing 
random noise or the time varying characteristic produced by the motion of 
the writing instrument on the surface of the body during the first 
generation of the piece of handwriting by an author at an enrollment 
procedure to produce a stored time varying characteristic, means for 
sequentially producing a weighted average of the stored time varying 
characteristic and the time varying characteristic produced by the motion 
of the writing instrument on the surface of the body during each one of a 
plurality of subsequent generations of the piece of handwriting by the 
author at said enrollment procedure and for replacing the stored time 
varying characteristic with the weighted average of the stored time 
varying characteristic and the time varying characteristic produced by the 
motion of the writing instrument on the surface of the body during the 
said one of the subsequent generations of the piece of handwriting by the 
author at the enrollment procedure the means for sequentially producing a 
weighted average includes means for comparing the stored time varying 
characteristic and the time varying characteristic produced by the motion 
of the writing instrument on the surface of the body during each one of 
the plurality of subsequent generations of the piece of handwriting by the 
author at the enrollment procedure to give a measure of the difference, 
means for resequencing the time varying characteristics of the plurality 
of subsequent generations of the piece of handwriting by the author at the 
enrollment procedure in order of increasing difference from the respective 
stored time varying characteristic, second means for sequentially 
producing a weighted average of the stored time varying characteristic and 
the time varying characteristic produced by the motion of the writing 
instrument on the surface of the body for each of the resequenced 
plurality of subsequent generations of the piece of handwriting by the 
author at the enrollment procedure and replacing the stored time varying 
characteristic with the average of the stored time varying characteristic 
and the time varying characteristic produced by the motion of the writing 
instrument on the surface of the body during said one subsequent 
generation of the piece of handwriting by the author at the enrollment 
procedure if the difference is less than a predetermined value to produce 
an average of the time varying characteristic produced by the motion of 
the writing instrument on the surface of the body from the subsequent 
generations of the piece of handwriting by the author at the enrollment 
procedure. 
Preferably the apparatus further comprises means for determining if a 
predetermined number of the plurality of subsequent generations of the 
piece of handwriting have a difference from the stored time varying 
characteristic equal to or greater than the predetermined value and for 
aborting the enrollment procedure if the predetermined number is equalled 
or exceeded. 
Preferably the apparatus comprises third means for sequentially producing a 
weighted average of the stored time varying characteristic and the time 
varying characteristic produced by the motion of the writing instrument on 
the surface of the body for each one of the plurality of subsequent 
generations of the piece of handwriting by the author at said enrollment 
procedure resequenced by the means for resequencing the time varying 
characteristics of the plurality of subsequent generations of the piece of 
handwriting and replacing the stored time varying characteristic with the 
weighted average of the stored time varying characteristic and the time 
varying characteristic produced by the motion of the writing instrument on 
the surface of the body during the said one of the subsequent generations 
of the piece of handwriting by the author at the enrollment procedure, 
second means for resequencing the time varying characteristics of the 
plurality of subsequent generations of the piece of handwriting by the 
author at the enrollment procedure in order of increasing difference from 
the respective stored time varying characteristic. 
Preferably the means for comparing the stored time varying characteristic 
with the time varying characteristic produced by the motion of the writing 
instrument on the surface of the body distorts the time varying 
characteristic in time to obtain a best match with the stored time varying 
characteristic and stores the value of time distortion required to obtain 
the best match. 
Preferably the means for producing a weighted average of the stored time 
varying characteristic and the time varying characteristic produced by the 
motion of the writing instrument on the surface of the body is arranged to 
distort the time varying characteristic in time by the values stored to 
obtain the best match with the stored time varying characteristic, and is 
arranged to produce weighted average magnitudes of the time varying 
characteristic between the stored time varying characteristic and the time 
distorted time varying characteristic produced by the motion of the 
writing instrument on the surface of the body and is arranged to produce a 
weighted average of time of events by displacing the weighted average 
magnitudes of the time varying characteristic in time towards the time 
varying characteristic produced by the motion of the writing instrument on 
the surface of the body. 
Preferably the means for detecting the time varying characteristic is an 
acoustic emission transducer for detecting the stress wave activity 
produced by the motion of the writing instrument on the surface of the 
body. 
The means for detecting the time varying characteristic may be a capacitor 
defined between the writing instrument and the surface of the body, the 
time varying characteristic is capacitance. 
The means for detecting the time varying characteristic may be a load cell 
for detecting load, or pressure, produced by the motion of the writing 
instrument on the surface of the body.

DETAILED DESCRIPTION OF THE INVENTION 
An apparatus for verifying personal handwriting is shown in FIG. 1. An 
acoustically conductive plate 12 is mounted on isolating blocks 14 in 
order to acoustically isolate it from the surface upon which it is 
located. A conventional resonant acoustic emission transducer 16 is 
acoustically coupled to the plate 12 for the purpose of detecting stress 
wave activity associated with the plate 12. Such stress wave activity is 
produced by the generation of a piece of handwriting on a surface of the 
plate 12 using a writing instrument 13. A piece of paper or other 
similarly surfaced material may be present on the plate 12 to receive the 
piece of handwriting, or alternatively, the piece of handwriting may be 
written directly on the plate 12. The writing instrument 13 may be a pen, 
or a pencil, but other writing instruments may be used. The plate 12 may 
be steel. The essential requirement is that when the piece of handwriting 
is generated, the friction between them should be sufficient to produce 
detectable stress waves within the plate 12, and that the plate 12 is 
acoustically conductive. 
The transducer 16 detects the stress wave activity within the plate 12 over 
a narrow band of frequencies around the resonant frequency of the 
transducer 16. The transducer 16 is selected to have a resonant frequency 
which is well above audio frequencies so that substantially only stress 
wave activity produced by the interaction between the writing instrument 
13 and the writing surface on the plate 12 is detected by the transducer 
16. 
The transducer 16 converts the detected stress wave activity into an 
electrical signal. This electrical signal is supplied in series to an 
amplifier 18, which amplifies the electrical signal and to a root mean 
square converter 20, which demodulates the electrical signal to an 
envelope of the stress wave activity associated with the generation of the 
piece of handwriting. The bandwidth, dynamic range and duration of this 
envelope are suitably limited to those values which are relevant to and 
characteristic of the particular piece of handwriting under investigation. 
The output of the root mean square converter 20 is fed to an analogue to 
digital converter 22 which produces a digitised time record of the stress 
wave activity produced by the generation of the piece of handwriting. The 
digitised time record of the stress wave activity is supplied to a 
processing unit 24. 
If an author of a piece of handwriting has not previously used the 
apparatus, the author is required to enroll onto the apparatus. The 
enrollment procedure is shown in the form of a flow chart in FIG. 2. In 
the enrollment procedure the author is required to generate the piece of 
handwriting for a first time. The digitised time record of the stress wave 
activity produced during the first generation of the authentic piece of 
handwriting is supplied to a store 26. The author is then required to 
produce the piece of handwriting at least a further two times, preferably 
a further four times. The digitised time records of the stress wave 
activity produced during each of the at least two further generations of 
the piece of handwriting are used to update the stored digitised time 
record to store 26. 
The processing unit 24 compares the stored digitised time record of the 
stress wave activity of the first generation of the piece of handwriting 
and the digitised time record of the stress wave activity of the second 
generation of the piece of handwriting and gives an indication of the 
degree of conformity between them. The comparison procedure involves using 
a dynamic time warping algorithm which takes a point, or portion , of the 
stored digitised time record of the stress wave activity of the first 
generation of the piece of handwriting and compares it with the digitised 
time record of the stress wave activity of the second generation of the 
piece of handwriting. The digitised time record of the stress wave 
activity of the second generation of the piece of handwriting is displaced 
in time relative to the stored digitised time record of the first 
generation of the piece of handwriting through different time periods, to 
obtain many better matches, and the best match is selected i.e. the match 
with least errors. Subsequent points, or portions, of the stored digitised 
time record of the stress wave activity of the first generation of the 
piece of handwriting are then compared with the digitised time record of 
the stress wave activity of the second generation of the piece of 
handwriting in a similar fashion to obtain best matches. 
The comparison of a point, or portion, of the stored digitised time record 
of the stress wave activity of the first generation of the piece of 
handwriting and the best match of the digitised time record of the stress 
wave activity of the second generation of the piece of handwriting 
involves taking a measurement of the difference in amplitude ofthe stress 
wave activities and squaring the difference, and taking a measure of the 
time displacement to obtain the best match. This is a running least 
squares method which gives an indication of the errors between the two 
digitised time records of the stress wave activity of the first and second 
generations of the piece of handwriting The total error for the best match 
for each point, or portion, of the stored digitised time record of the 
stress wave activity of the first generation of the piece of handwriting 
is the sum of the square of the amplitude error and the time distortion 
errors. The total error for the best match of all the points, or portions, 
of the stored digitised time record of the stress wave activity of the 
first generation of the piece of handwriting is the sum of all the squares 
of the amplitude errors and all the time distortion errors. The total 
error, or differences, between the digitised time record of the stress 
wave activity of the second generation of the piece of handwriting and the 
stored digitised time record of the stress wave activity of the first 
generation of the piece of handwriting is stored. 
The processing unit 24 stores the values of time displacement required to 
distort the digitised time record of the stress wave activity of the 
second generation of the piece of handwriting piece to a best match 
position with the stored digitised time record of the stress wave activity 
of the first generation of the piece of handwriting for each point, or 
portion, of the stored digitised time record of the stress wave activity 
of the first generation of the piece of handwriting. The time displacement 
values are stored in a back pointer array. 
The stored digitised time record of the stress wave activity of the first 
generation of the piece of handwriting is replaced by a weighted average 
of the stored digitised time record of the stress wave activity of the 
first generation of the piece of handwriting and the digitised time record 
of the stress wave activity of the second generation of the piece of 
handwriting. The weighted average of the two digitised time records 
includes a weighted average of the amplitudes and a weighted average of 
the times of events. In order to produce the weighted average of the 
stored digitised time record of the stress wave activity of the first 
generation of the piece of handwriting and the digitised time record of 
the stress wave activity of the second generation of the piece of 
handwriting, the time displacement values stored in the backpointer array 
are again used to distort the digitised time record of the stress wave 
activity of the second generation of the piece of handwriting to the best 
fit time scale with the stored digitised time record of the stress wave 
activity of the first generation of the piece of handwriting. 
The weighted average of each point on the stored digitised time record of 
the stress wave activity of the first generation of the piece of 
handwriting and the time warped digitised time record of the stress wave 
activity of the second generation of the piece of handwriting are then 
calculated to give a weighted average amplitude of the two digitised time 
records. 
The weighted average of times of events is produced by displacing each new 
stress wave amplitude in value in time towards that of the digitised time 
record of the stress wave activity of the second generation of the piece 
of handwriting, the time displacement is weighted by the same value as 
that used for the weighted average of the stress wave amplitudes. This new 
digitised time record of stress wave activity is stored in the store as a 
stored first average digitised time record of the stress wave activity of 
the piece of handwriting and replaces the original stored digitised time 
record of the stress wave activity of the first generation of the piece of 
handwriting. 
The processing unit 24 compares the stored first average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the third generation 
of the handwriting piece and gives an indication of the degree of 
conformity between them. The comparison procedure involves using the 
dynamic time warping algorithm which makes a point, or portion, of the 
stored first average digitised time record of the stress wave activity of 
the handwriting piece and compares it with the digitised time record of 
the stress wave activity of the third generation of the handwriting piece. 
The digitised time record of the stress wave activity of the third 
generation of the handwriting piece is displaced in time relative to the 
stored first average digitised time record of the stress wave activity of 
the handwriting piece through different time periods, to obtain many 
better matches, and the best match is selected i.e. the match with least 
errors. Subsequent points, or portions, of the stored first average 
digitised time record of the stress wave activity of the handwriting piece 
are then compared with the digitised time record of the stress wave 
activity of the third generation of the handwriting piece in a similar 
fashion to obtain best matches. 
The comparison of a point, or portion, of the stored first average 
digitised time record of the stress wave activity of the handwriting piece 
and the best match of the digitised time record of the stress wave 
activity of the third generation of the handwriting piece involves taking 
a measurement of the difference in amplitude of the stress wave activities 
and squaring the differences, and taking a measure of the time 
displacement to obtain the best match. This is a running least squares 
method which gives an indication of the errors between the stored first 
average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the third generation of the handwriting piece. The total error 
for the best match for each point, or portion, of the stored first average 
digitised time record of the stress wave activity of the handwriting piece 
is the sum of the square of the amplitude error and the time distortion 
errors. The total error for the best match of all the points, or portions, 
of the stored first average digitised time record of the stress wave 
activity of the handwriting piece is the sum of all the squares of the 
amplitude errors and all the time distortion errors. The total error, or 
difference, between the digitised time record of the stress wave activity 
of the third generation of the handwriting piece and the stored first 
average digitised time record of the stress wave activity of the 
handwriting piece is stored. 
The processing unit 24 stores the values of time displacement required to 
distort the digitised time record of the stress wave activity of the third 
generation of the handwriting piece to a best match position with the 
stored first average digitised time record of the stress wave activity of 
the handwriting piece for each point, or portion, of the stored first 
average digitised time record of the stress wave activity of the 
handwriting piece. The time displacement values are stored in a back 
pointer array. 
The stored first average digitised time record of the stress wave activity 
of the handwriting piece is replaced by a weighted average of the stored 
first average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the third generation of the handwriting piece. The weighted 
average of the two digitised time records includes a weighted average of 
the amplitudes and a weighted average of the times of events. In order to 
produce the weighted average of the stored first average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record ofthe stress wave activity of the third generation 
of the handwriting piece, the time displacement values stored in the 
backpointer array are again used to distort the digitised time record of 
the stress wave activity of the third generation of the handwriting piece 
to the best fit time scale with the stored first average digitised time 
record of the stress wave activity of the handwriting piece. 
The weighted average of each point on the stored first average digitised 
time record of the stress wave activity of the handwriting piece and the 
time warped digitised time record of the stress wave activity of the third 
generation of the piece of handwriting are then calculated to give a 
weighted average amplitude of the two digitised time records. 
The weighted average of times of events is produced by displacing each new 
stress wave amplitude value in time towards that of the digitised time 
record of the stress wave activity of the third generation of the 
handwriting piece. the time displacement is weighted by the same value as 
that used for the weighted average of the stress wave amplitudes. This new 
digitised time record of stress wave activity is stored in the store as a 
stored second average digitised time record of the stress wave activity of 
the handwriting piece and replaces the stored first average digitised time 
record of the stress wave activity of the handwriting piece. 
The processing unit 24 compares the stored second average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the fourth generation 
of the handwriting piece and gives an indication of the degree of 
conformity between them. The comparison procedure again involves using the 
dynamic time warping algorithm. The total error, or difference, between 
the digitised time record of the stress wave activity of the fourth 
generation of the handwriting piece and the stored second average 
digitised time record of the stress wave activity of the handwriting is 
stored. 
The processing unit 24 stores the values of time displacement required to 
distort the digitised time record of the stress wave activity of the 
fourth generation of the handwriting piece to a best match position with 
the stored second average digitised time record of the stress wave 
activity of the handwriting piece for each point, or portion, of the 
stored second average digitised time record of the stress wave activity of 
the handwriting piece in a back pointer array. The stored second average 
digitised time record of the stress wave activity of the handwriting piece 
is replaced by a weighted average of the stored second average digitised 
time record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the fourth generation 
of the handwriting piece. The weighted average of the two digitised time 
records includes a weighted average of the amplitudes and a weighted 
average of the times of events and is produced in the same manner as 
disclosed above. This new digitised time record of stress wave activity is 
stored in the store as a stored third digitised time record of the stress 
wave activity of the handwriting piece and replaces the stored second 
average digitised time record of the stress wave activity of the 
handwriting piece. 
The processing unit 24 compares the stored third average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the fifth generation 
of the handwriting piece and gives an indication of the degree of 
conformity between them. The comparison procedure again uses the dynamic 
time warping algorithm. The total error, or difference, between the 
digitised time record of the stress wave activity of the fifth generation 
of the handwriting piece and the stored third average digitised time 
record of the stress wave activity of the handwriting piece is stored. 
The processing unit 24 stores the values of time displacement required to 
distort the digitised time record of the stress wave activity of the fifth 
generation of the handwriting piece to a best match position with the 
stored third average digitised time record of the stress wave activity of 
the handwriting piece for each point, or portion, of the stored third 
average digitised time record of the stress wave activity of the 
handwriting piece in a back pointer array. 
The stored third average digitised time record of the stress wave activity 
of the handwriting piece is replaced by a weighted average of the stored 
third average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the fifth generation of the handwriting piece. The weighted 
average of the two digitised time records includes a weighted average of 
the amplitudes and a weighted average of the times of events and is 
produced in the same manner as disclosed previously. This new digitised 
time record of stress wave activity is stored in the store as a stored 
fourth average digitised time record of the stress wave activity of the 
handwriting piece and replaces the stored third average digitised time 
record of the stress wave activity of the handwriting piece. 
It can be seen that the procedure up to now differs from that disclosed in 
our European Patent Application No. 90313505.1 in that the digitised time 
records of the stress wave activity for the second, third, fourth and 
fifth generations of the handwriting piece have each been used once to 
update the stored digitised time record of the stress wave activity 
produced during the generation of an authentic handwriting piece no matter 
how great the difference between the stored digitised time record and the 
digitised time record of the particular handwriting piece. 
The digitised time records of the stress wave activity for the second, 
third, fourth and fifth generations of the handwriting piece are 
resequenced in order of increasing error or difference, from the 
particular stored digitised time record of the stress wave activity of the 
handwriting piece with which it was compared. For example the digitised 
time record of the stress wave activity of the third generation of the 
handwriting piece was compared with the stored first average digitised 
time record of the stress wave activity of the handwriting piece. 
Similarly the digitised time record of the stress wave activity of the 
fifth generation of the handwriting piece was compared with the stored 
third average digitised time record of the stress wave activity of the 
handwriting piece. 
The processing unit 24 compares the stored fourth average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the one, of the 
second, third, fourth and fifth generations of the handwriting piece, 
which has the least error and gives an indication of the degree of 
conformity between them using the same method as described previously. 
The stored fourth average digitised time record of the stress wave activity 
of the handwriting piece is replaced by a weighted average of the stored 
fourth average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the one of the second third, fourth and fifth generations of 
the handwriting piece which has the least error. The weighted average of 
the two digitised time records includes a weighted average of the 
amplitudes and a weighted average of the times of events and is produced 
in the same manner as disclosed previously. This new digitised time record 
of stress wave activity is stored in the store as a stored fifth average 
digitised time record of the stress wave activity of the handwriting piece 
and replaces the stored fourth average digitised time record of the stress 
wave activity of the handwriting piece. 
The processing unit 24 compares the stored fifth average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the one, of the 
second, third, fourth and fifth generations of the handwriting piece, 
which has the second lowest error and gives an indication of the degree of 
conformity between them using the same method as described previously. 
The stored fifth average digitised time record of the stress wave activity 
of the handwriting piece is replaced by a weighted average of the stored 
fifth average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the one of the second third, fourth and fifth generations of 
the handwriting piece which has the second lowest error. The weighted 
average of the two digitised time records includes a weighted average of 
the amplitudes and a weighted average of the times of events and is 
produced in the same manner as discussed above. This new digitised time 
record of stress wave activity is stored in the store as a stored sixth 
average digitised time record of the stress wave activity of the 
handwriting piece and replaces the stored fifth average digitised time 
record of the stress wave activity of the handwriting piece. 
The processing unit 24 compares the stored sixth average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the one, of the 
second, third, fourth and fifth generations of the handwriting piece, 
which has the third lowest error and gives an indication of the degree of 
conformity between them using the same method as described previously. 
The stored sixth average digitised time record of the stress wave activity 
of the handwriting piece is replaced by a weighted average of the stored 
sixth average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the one of the second third, fourth and fifth generations of 
the handwriting piece which has the third lowest error. The weighted 
average of the two digitised time records includes a weighted average of 
the amplitudes and a weighted average of the times of events and is 
produced in the same manner as disclosed above. This new digitised time 
record of stress wave activity is stored in the store as a stored seventh 
average digitised time record of the stress wave activity of the 
handwriting piece and replaces the stored sixth average digitised time 
record of the stress wave activity of the handwriting piece. 
The processing unit 24 compares the stored seventh average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the one, of the 
second, third, fourth and fifth generations of the handwriting piece, 
which has the greatest error and gives an indication of the degree of 
conformity between them using the same method as described previously. 
The stored seventh average digitised time record of the stress wave 
activity of the handwriting piece is replaced by a weighted average of the 
stored seventh average digitised time record of the stress wave activity 
of the handwriting piece and the digitised time record of the stress wave 
activity of the one of the second third, fourth and fifth generations of 
the handwriting piece which has the greatest error. The weighted average 
of the two digitised time records includes a weighted average of the 
amplitudes and a weighted average of the times of events and is produced 
in the same manner as discussed previously. This new digitised time record 
of stress wave activity is stored in the store as a stored eighth average 
digitised time record of the stress wave activity of the handwriting piece 
and replaces the stored seventh average digitised time record of the 
stress wave activity of the handwriting piece. 
The digitised time records of the stress wave activity for the second, 
third, fourth and fifth generations of the handwriting piece have each 
been used a second time to update the stored digitised time record of the 
stress wave activity produced during the generation of an authentic 
handwriting piece no matter how great the difference between the stored 
digitised time record and the digitised time record of the particular 
handwriting piece. 
The digitised time records of the stress wave activity for the second, 
third, fourth and fifth generations of the handwriting piece are again 
resequenced in order of increasing error, or difference, from the 
particular stored digitised time record of the stress wave activity of the 
handwriting piece with which it was compared during the second updating of 
the stored digitised time record. 
The processing unit 24 compares the stored eighth average digitised time 
record of the stress wave activity of the handwriting piece and the 
digitised time record of the stress wave activity of the one, of the 
second, third, fourth and fifth generations of the handwriting piece, 
which has the lowest error to give an indication of the degree of 
conformity between them using the same method as described previously. 
If the total error is less than a predetermined value the digitised time 
record of the one, of the second, third, fourth and fifth generations of 
the handwriting piece, which has the lowest error has a good degree of 
conformity with the stored eighth average digitised time record of the 
stress wave activity of the handwriting piece. 
The stored eighth average digitised time record of the stress wave activity 
of the handwriting piece is replaced by a weighted average of the stored 
eighth average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the one of the second third, fourth and fifth generations of 
the handwriting piece which has the lowest error if the total error is 
less than the predetermined value. A new digitised time record of stress 
wave activity is stored in the store as a stored ninth average digitised 
time record of the stress wave activity of the handwriting piece and 
replaces the stored eighth average digitised time record of the stress 
wave activity of the handwriting piece. 
If the total error is equal to or greater than the predetermined value the 
digitised time record of the one of the second, third, fourth and fifth 
generations of the handwriting piece, which has the lowest error is not in 
conformity with the stored eighth average digitised time record of the 
stress wave activity of the handwriting piece. 
The stored eighth average digitised time record of the stress wave activity 
of the handwriting piece is not updated by the digitised time record of 
the stress wave activity of the one of the second, third, fourth and fifth 
generations of the handwriting piece which has the lowest error if the 
total error is equal to or greater than the predetermined value. 
The processing unit 24 compares either the stored eighth or ninth average 
digitised time record of the stress wave activity of the handwriting piece 
and the digitised time record of the stress wave activity of the one, of 
the second, third, fourth and fifth generations of the handwriting piece, 
which has the second lowest error and gives an indication of the degree of 
conformity between them using the same method as described previously. 
If the total error is less than a predetermined value the digitised time 
record of the one, of the second, third, fourth and fifth generations of 
the handwriting piece, which has the second lowest error has a good degree 
of conformity with the stored eighth or ninth average digitised time 
record of the stress wave activity of the handwriting piece. 
The stored eighth or ninth average digitised time record of the stress wave 
activity of the handwriting piece is replaced by a weighted average of the 
stored eighth or ninth average digitised time record of the stress wave 
activity of the handwriting piece and the digitised time record of the 
stress wave activity of the one of the second third, fourth and fifth 
generations of the handwriting piece which has the second lowest error if 
the total error is less than the predetermined value. A new digitised time 
record of stress wave activity is stored in the store as a stored ninth or 
tenth average digitised time record of the stress wave activity of the 
handwriting piece and replaces the stored eighth or ninth average 
digitised time record of the stress wave activity of the handwriting 
piece. 
If the total error is equal to or greater than the predetermined value the 
digitised time record of the one of the second, third, fourth and fifth 
generations of the handwriting piece, which has the second lowest error is 
not in conformity with the stored eighth or ninth average digitised time 
record of the stress wave activity of the handwriting piece. 
The stored eighth or ninth average digitised time record of the stress wave 
activity of the handwriting piece is not updated by the digitised time 
record of the stress wave activity of the one of the second, third, fourth 
and fifth generations of the handwriting piece which has the second lowest 
error if the total error is equal to or greater than the predetermined 
value. 
The processing unit 24 compares either the stored eighth, ninth or tenth 
average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the one, of the second, third, fourth and fifth generations of 
the handwriting piece, which has the third lowest error and gives an 
indication of the degree of conformity between them using the same method 
as described previously. 
If the total error is less than a predetermined value the digitised time 
record of the one, of the second, third, fourth and fifth generations of 
the handwriting piece, which has the third lowest error has a good degree 
of conformity with the stored eighth, ninth or tenth average digitised 
time record of the stress wave activity of the handwriting piece. 
The stored eighth, ninth or tenth average digitised time record of the 
stress wave activity of the handwriting piece is replaced by a weighted 
average of the stored eighth, ninth or tenth average digitised time record 
of the stress wave activity of the handwriting piece and the digitised 
time record of the stress wave activity of the one of the second third, 
fourth and fifth generations of the handwriting piece which has the third 
lowest error if the total error is less than the predetermined value. A 
new digitised time record of stress wave activity is stored in the store 
as a stored ninth, tenth or eleventh average digitised time record of the 
stress wave activity of the handwriting piece and replaces the stored 
eighth, ninth or tenth average digitised time record of the stress wave 
activity of the handwriting piece. 
If the total error is equal to or greater than the predetermined value the 
digitised time record of the one of the second, third, fourth and fifth 
generations of the handwriting piece, which has the third lowest error is 
not in conformity with the stored eighth, ninth or tenth average digitised 
time record of the stress wave activity of the handwriting piece. 
The stored eighth, ninth, tenth or eleventh average digitised time record 
of the stress wave activity of the handwriting piece is not updated by the 
digitised time record of the stress wave activity of the one of the 
second, third, fourth and fifth generations of the handwriting piece which 
has the third lowest error if the total error is equal to or greater than 
the predetermined value. 
The processing unit 24 compares either the stored eighth, ninth, tenth or 
eleventh average digitised time record of the stress wave activity of the 
handwriting piece and the digitised time record of the stress wave 
activity of the one, of the second, third, fourth and fifth generations of 
the handwriting piece, which has the greatest error and gives an 
indication of the degree of conformity between them using the same method 
as described previously. 
If the total error is less than a predetermined value the digitised time 
record of the one, of the second, third, fourth and fifth generations of 
the handwriting piece, which has the greatest error has a good degree of 
conformity with the stored eighth, ninth, tenth or eleventh average 
digitised time record of the stress wave activity of the handwriting 
piece. 
The stored eighth, ninth, tenth or eleventh average digitised time record 
of the stress wave activity of the handwriting piece is replaced by a 
weighted average of the stored eighth, ninth, tenth or eleventh average 
digitised time record of the stress wave activity of the handwriting piece 
and the digitised time record of the stress wave activity of the one of 
the second third, fourth and fifth generations of the handwriting piece 
which has the greatest error if the total error is less than the 
predetermined value. A new digitised time record of stress wave activity 
is stored in the store as a stored ninth, tenth, eleventh or twelfth 
average digitised time record of the stress wave activity of the 
handwriting piece and replaces the stored eighth, ninth, tenth or eleventh 
average digitised time record of the stress wave activity of the 
handwriting piece. 
If the total error is equal to or greater than the predetermined value the 
digitised time record of the one of the second, third, fourth and fifth 
generations of the handwriting piece, which has the greatest error is not 
in conformity with the stored eighth, ninth, tenth or eleventh average 
digitised time record of the stress wave activity of the handwriting 
piece. 
The stored eighth, ninth, tenth or eleventh average digitised time record 
of the stress wave activity of the handwriting piece is not updated by the 
digitised time record of the stress wave activity of the one of the 
second, third, fourth and fifth generations of the handwriting piece which 
has the greatest error if the total error is equal to or greater than the 
predetermined value. 
The digitised time records of the stress wave activity for the second, 
third, fourth and fifth generations of the handwriting piece are each used 
a third time to update the stored digitised time record of the stress wave 
activity produced during the generation of an authentic handwriting piece 
if the difference between the stored digitised time record and the 
digitised time record of the particular handwriting piece is less than the 
predetermined value. 
If any two of the second, third, fourth and fifth generations of the 
handwriting piece result have digitised time records of stress wave 
activity which have differences from the stored digitised time record 
greater than the predetermined value, the enrollment procedure is aborted 
and the whole procedure is repeated. The final stored digitised time 
record of the stress wave activity of the handwriting piece is a better 
average of the digitised time records of the several generations of the 
handwriting piece. Any poor, or untypical, samples of the generation of 
the handwriting piece made during the enrollment procedure are rejected 
when the stored digitised time record is updated a third time by the 
digitised time records of each of the handwriting piece. 
When the digitised time record of the stress wave activity of a subsequent 
authentic generation of the piece of handwriting is compared with the 
final stored digitised time record, produced during the enrollment 
procedure, the subsequent authentic generation of the handwriting piece is 
not determined to be a forgery. 
Alternatively if an author of a handwriting piece has not previously used 
the apparatus, the author is required to enroll onto the apparatus. In the 
enrollment procedure random noise is supplied to a store 26. The author is 
required to produce a handwriting piece at least two times, preferably 
four times. The digitised time records of the stress wave activity 
produced during each of the at least two generations of the handwriting 
piece are used to update the stored digitised time record in store 26. 
The same procedure of comparing the digitised time records of the stress 
wave activity of each generation of the handwriting piece sequentially 
with the stored digitised time record is followed as discussed before. 
A suitable weighting factor used during the procedure is four times the 
stored digitised time record to one times the digitised time record being 
compared to the stored digitised time record. 
Although the description has referred to the use of stress wave activity as 
the time varying characteristic, other suitable time varying 
characteristics may be used. One example is the use of a load cell to 
detect the force, load or pressure applied on the writing instrument, or 
body, during the generation of the piece of handwriting. A further example 
is the use of a capacitor to detect the capacitance defined between the 
writing instrument and the surface of the body. Other suitable time 
varying characteristics derived from the dynamics of the production of a 
piece of handwriting are position, velocity and acceleration.