CA1152218A

CA1152218A - Handwriting position and force sensing device

Info

Publication number: CA1152218A
Application number: CA000374237A
Authority: CA
Inventors: Francis Omoruto; Peter D. Lawrence; Grant B. Anderson
Original assignee: Canadian Patents and Development Ltd
Current assignee: Canadian Patents and Development Ltd
Priority date: 1981-03-24
Filing date: 1981-03-24
Publication date: 1983-08-16

Abstract

T I T L E

HANDWRITING POSITION AND FORCE SENSING DEVICE

I N V E N T O R S

Francis Omoruto Peter Donald Lawrence Grant B. Anderson ABSTRACT OF DISCLOSURE
A handwriting position and force sensing device comprising a rigid plate mounted on three pressure sensing devices positioned at the corners of a triangle such that when the plate is written upon, pressure signals are obtained from the pressure sensing devices than can be utilized to record, analyze, verify, or validate the hand-writing.

Description

~lSZ218 This invention relates to a handwriting position and force sensing device and more particularly to a transducer arrangement ~or providing pen position and normal vertical force data normal to the writing surface than can be used for signature analysis and verification or graphical data acquisition.
Systems for distinguishing between valia and forged signatures have been developed using the positlon and force of a pen on a writing surface. The following are patents in this field 3,962,679 R.S. Engelbrecht June 8, 1976 3,988,93~ Kamphoefner et al Nov. 2, 1976 4,008,457 A.J. Radcliffe Feb. 15, 1977 4,035,768 Boldridge et al July 12, 1977 4,143,~57 Baver et al March 6,1979 It is an object of the present invention:to provide a means of sensing the position of a pen on a writing surface and also a measurement of the total downward force on the surface. I
This and other objects of the inventlon are achieved by a handwriting position and force sensing device comprising a rigid plate mounted on three pressure sensing devices positioned at the corners of a triangle such that when the plate is written upon, pressure signals are obtained from the pressure sensing devices than can be utilized to record, analyze, verify, or validate the handwriting~
In drawings which illustrate an embodiment of the invention, Figure 1 is a top view of the signature sample writing plate, Figure 2 is a side view of the plate with a schematic of the da'a processing and output plotter, ~1522i8 Fi~ure 3 is a yiew of the signature verifying device in a housing, Figure 4 is a flow diagram of an overall signature verifying apparatus, Figure 5 is a flow diagram of a digital data processing arrangement, and Figure 6 is a flow diagram of an analogue processing arrangement.
Referring to figure 1, a generally rectangular plate 10 forms a sample signature writing tablet and is mounted on three force sensing transducers Tl, T2, T3, positioned as shown at the corners of an Isosceles triangle 11 having a base of length "b" and a height "h". As shown in figure 2 the transducers are mounted on a fixed surface 12. The input force p from the pen of the writer translates into three force signals from the transducers which after amplication in amplifiers Al, A2, and A3 give force values pl, p2, p3. These are fed to the processing system 13 which computes X and Y coordinate and force (p) values. Algorithms for this are as follows:

2 (P3 P2)/ i =

y 3 (2pl P2 P3 p = 3 i=l The x and y outputs are shown driving a plotter 14 that displays a reconstructed representatior. of the input sample signature.
Figure 3 shows the transducer device in a suitable housing 15 designed with opening 16 for the writing - of sample signatures on the exposed tablet 1~ surface. A

~1522i8 strip of writing paper would normally be arranged to pass over the suxface o~ the writing tablet.
The device described above is a means of sensing the position o~ a pen on a writing surface and also provides a measurement of the total normal force on the surface. The same transducers are used to measure the normal force as well as pen position. This feature is not shown in the patents listed above nor in any known system.
The structure is very simple and can be self-levelling by virtue of the location of the force transducers at the corners of a triangle. The force transducer outputs can be used to completely describe (a) the pen position and movement in the plane ~i.e. time derivatives of the position coordina-tes (b) the force normal to the writing surface and (c) the forces on the pen in the plane of the surface through'~knowled-ge of the coefficient of friction, The device has application as a part of larger systems e.g. automatic banking terminals and credit check systems. In a typical arrangement, the customer enters a credit card which has on it numerical information describing the customer's signature dynamics and the sensor, together with a programmed microcomputer, compares characteristics of the individual's handwriting dynamics (writing force, velocity, acceleration parameters) to the numerical information on the card. Figure 4 is a flow diagram of such a set-up.
Figure 5 is a more detailed flow chart of the processing system using a small computer. The force inputs pl, p2, and p3 are applied to an analogue multiplexor 17, and an analogue-to-digital (A/D) converter lB. The computation is done in a microprocessor programmed to give digital data to appropriate output and/or storage devices.
- Figure 6 shows an analogue arrangement for solving the ~lSZZ18 algorith~s using summing ampli~iers 20 and operational ampli-~iers 2I to provide the appro~riate x~ y, and p outputs~
These would be passed to A/D convertors to provide the digital outputs as required by output and/or storage devices.

Claims

CLAIMS:

1. A handwriting position and force sensing device comprising.
a) a handwriting tablet in the form of an extended rigid plate, b) three force sensing devices mounted on fixed supports and positioned at the corners of a triangle under and supporting said plate such that when the plate is written upon, dynamic force data signals are obtained from the three force sensing devices useful in analysing and verifying the handwriting.

2. A handwriting position and force sensing device comprising:
a) a handwriting tablet in the form of an extended rigid plate, b) three force sensing devices mounted on fixed supports and positioned at the corners of an isosceles triangle having a base length "b" and a height "h" under and supporting said plate such that when the plate is written upon, dynamic force data signals (p1, p2, and p3) are obtained from the three force sensing devices, c) computational means for processing the three signals p1, p2, and p3 according to the following algorithms:

said x, y, and p values being useful in analysing and veri-fying the handwriting.

3. A handwriting position and force sensing apparatus as in claim 2 further comprising plotting means for accepting the x, y, and p signals and reconstructing and displaying the input handwriting sample.