Study of the pressure and the tension of the manuscript writings

The increasingly frequent use of Photocopie S in the daily life involves an increase in the number of documents presented to the expertise in writings and, of course, much of these documents to be appraised are themselves of the photocopies. That is strongly regrettable because, at the stage of the official expertise, the expert should not agree to work as on originals as well for the parts of Question as for the parts of Comparison.

Recalls of principles of physics

The examination of the feature appears, indeed, like a dominating element. The pressure is the most problematic variable.

In the field of physics, the arrival of the feature must be examined under a double aspect because the act to write met of work two components, one static: the mass (force) which corresponds to the depth of the furrow, other dynamics: the speed (rate/rhythm) which generally translates the width of the furrow. It results a kinetic energy from it E from a mobile point of mass M and speed v such as E = Mv ² /2. It results from it that the pressure is difficult to evaluate after the act to write.

Pressure of the feature

The pressure of the feature translates the graphic force of the script writer (support of the hand and digital pressure). Indeed, the Anglo-Saxons and German distinguish two types of pressure:

pressure of point (not presses), i.e. pressure exerted by the point of the instrument on the sheet, i.e. the support of the hand

pressure of agrippement or pressure of seizure (grip presses), i.e. pressure exerted on the instrument by the fingers of the script writer, i.e. digital pressure.

The pressure is a characteristic of general order of most interesting for the search for an identity of hand. The first work on the recording of the pressure of hand goes back to 1921. At that time, Malespine had developed an apparatus which made it possible to obtain a curve translating the kinematics of pressure: the Graphogramme.

It there has a few years, appeared a new apparatus called “profilometer” which allows a precise quantitative appreciation of the support of the hand and digital pressure which results in the formation of more or less deep furrows on the surface of a sheet of paper. This graphic characteristic is very significant for the large majority of the scipteurs because its control is difficult, even impossible. It is besides with the speed of execution (rate/rhythm), the element taken into account by the specialists in biometrics for the dynamic recognition of a signature.

The rugosimetry of surface in 2D allows a very precise measurement depth and width of a furrow ink which proves to be a graphic element determining in the checking of the writings disputed in justice to put graphically out of cause or to nominate without reserve a suspected person. In graphology, the pressure is a concrete element of graphics (W. HEGAR) whereas in graphometry, the pressure is in close relationship with graphic casting (J. Salce, m.t. Prenat).

Tension of the feature and its evaluation

In addition, the act to write can be comparable with the actuation of a particle in the horizontal plane.

In practice, the degree of tension of a feature is in direct connection with the coefficient of friction by slip (friction of the point of the instrument on paper).

R. Saudek indicates that the pressure in the writing increases in proportion with the tension. Here why one can determine the degree of tension by examining the pressure stage.

The coefficient of friction by slip depends on several factors: mainly, the depth of the furrow due to the support as well as surface quality of the support (smoothed bekk). Indeed, more surfaces of contact are smooth, more friction is weak. The borderline case is that where friction would be null, which is never carried out in practice.

The tension of the feature is higher in the formation of full, i.e. layouts written in the direction of the script writer (direction of contraction) in opposition to the layouts carried out in the opposite direction (direction of relaxation).

The classification of the writings according to R. Saudek is:

writings with normal tension, balanced like that of penmanship;
hypertensive writings (nervous or overworked subjects physically or intellectually);
hypotensive writings (lymphatic or tired subjects);
mixed writings, in turn balanced, hyper or hypotensive (anxious or distressed subjects).

These differences in degrees of tension can thus be evaluated precisely because they are in direct relationship with the depth of the furrow. A depth of approximately 80 microns corresponds to a hypertensive writing and a depth of approximately 25 micrometers ccorrespond with a hypotensive writing with the intermediaries: normal writing or of mixed type.

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