GB2396399A

GB2396399A - A digitiser and ball tipped stylus

Info

Publication number: GB2396399A
Application number: GB0229407A
Authority: GB
Inventors: Boaz Siman-Tov; Michael Astanovsky; Yossi Schneider
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2002-12-17
Filing date: 2002-12-17
Publication date: 2004-06-23
Anticipated expiration: 2022-12-17
Also published as: GB2396399B; GB0229407D0

Abstract

A stylus 1 for a digitiser comprises an elongate tubular member 7 with an end cap 9 enclosing a cavity 8, the end cap 9 having an aperture 9b through it, a spacer 15 fitted in the cavity 8 and having a ball seating recess, a ball 11 which extends through the end cap 9 and a spring 13 in the cavity 8 behind the ball 11 arranged to urge the ball 11 against the end cap 9, where the ball seating recess comprises a solid dry surface 15a around which the ball 11 is free to rotate. Also described is a combination of the stylus 1 and a digitiser, where the stylus 1 is used to write on the digitiser by rolling of the ball 11 on the writing surface of the digitiser, the surface comprising a compressible plastics material. The digitiser may be a device in which an electrical property of the device is changed in a region corresponding to the surface region written upon by the stylus 1.

Description

TITLE: DIGITISER AND STYLUS THEREFOR

k FIELD OF THE INVENTION

5 The present invention relates to a digitiser and stylus therefor.

BACKGROUND OF THE INVENTION

10 Digitiser devices are known for use in various applications especially as part of portable terminals for use in communication of data between a mobile user and a control terminal. The digitiser structure is often referred to as a 'tablet' which provides a stylus or pen driven 15 input device for a computer, which may also form part of the portable terminal. For example, an input signal may be provided by a writing action of the stylus on the digitiser. The computer thereby receives a digital record of the position of the stylus. Information written by the 20 stylus can thereby be recorded. Often the digitiser is combined with an electrooptical display device and the tablet' overlies the display. The position in which the digitiser is written upon may correspond in position to an image shown on the display.

25 There are several different kinds of digitiser known and commercially available. For example, the digitiser may be of the so called resistive kind in which the electrical resistivity (conductivity) of a variable resistivity layer is altered by the pressure exerted by the stylus of the 30 digitiser causing the resistivity to be reduced in a localised region adjacent to the position on the digitiser

where the stylus is applied. The variable resistivity layer may comprise an elastomer filled with conducting particles which are compressed together when the stylus is applied.

In commercially available digitiser styluses 5 the writing tips are made from low friction polymeric materials such as a polyacetal or a polytetrafluoroethylene. The tips have a curved surface, but the tip is generally designed to slide across the digitiser tablet surface. The friction 10 associated with this sliding cause the tip to become worn. The tip can thereby change its shape and can develop sharp edges, which can damage the digitiser tablet layers. For example, the layer providing the digitiser top or writing surface may 15 comprise a thin layer of a transparent compressible plastics material such as a polyester having coated on its inner surface a sensitive layer comprising a fine transparent conducting material such as indium tin oxide.

20 As a result of the stylus tip wear, the digitiser writing surface can become scratched and unreadable; the underlying sensitive layer may become damaged causing parts of the digitiser to lose functionality.

25 Another problem arising with the use of known styluses is that dust particles can stick to the stylus tip eventually damaging the tip and again resulting in excessive abrasion by a pitting effect on the digitiser tablet top surface.

30 These problems can severely limit the digitiser durability and lifetime.

Furthermore, the line width of the information written on and recorded by the digitiser can increase with wear of the stylus causing the recorded writing to become blurred.

SUMMARY OF THE PRESENT INVENTION

According to the present invention in a first aspect there is provided a stylus for a digitiser, the stylus 10 comprising an elongate member having a tubular portion and an end cap fitted in an end of the tubular portion, the tubular portion and the end cap enclosing a cavity, the end cap having an aperture there through, a spacer fitted in the cavity and having a ball seating recess, a ball seated 15 in the seating recess of the spacer and having a portion which extends through the aperture of the end cap and projects beyond the end cap and a spring in the cavity behind the ball arranged to urge the ball against the end cap, wherein the ball seating recess comprises a solid dry 20 curved surface around which the ball is free to rotate.

The ball may be made of a metal, e.g. a hard wearing metal, which may optionally carry a permanent coating of a hard wearing material, e.g. a low friction solid material such as PTFE (polytetrafluoroethylene). The spacer, 25 especially in the ball seating recess, may have a surface which comprises a low friction solid such as PTFE.

Preferably, the stylus has an annular layer between the end cap and the spacer, which serves to inhibit dust particles passing into a contact region between the ball 30 and the ball seating recess. The annular layer may comprise a metallic foil annulus or brush. The annular layer may coincide substantially with a plane perpendicular to an

axis of the elongate member. In addition, the annular layer may coincide substantially with a plane passing through the centre of the ball.

According to the present invention in a second aspect 5 there is provided a combination of a stylus according to the first aspect and a digitiser, wherein the stylus is operable by a user to write on the digitiser by rolling action of the ball on a writing surface of the digitiser, the writing surface comprising a compressible plastics 10 material. The digitiser may be a device in which an electrical property of the device is changed in a region written upon by the stylus. The conductivity of the device may be changed in the written upon region.

The invention is based on replacing a sliding 15 stylus tip in a stylus for a digitiser with a rotating tip. Beneficially, this reduces tip wear (abrasion) and avoids undesirable tip sharp edges.

By using a rotating ball as the stylus tip, wear of the tip will be uniform all around the surface of 20 the tip. The lifetime of the digitiser used with the stylus is thereby increased.

Another advantage of the stylus according to the invention is that using a rotating ball tip reduces the force needed by the user to be applied 25 to write upon the digitiser surface. It is therefore more convenient for users. The lower force required also increases the durability of the digitiser and also reduces the so called "Hertz" stress (this is the local stress applied on 30 digitiser surface, a contact stress).

Furthermore, by reducing the possibility of abrasive dust being picked up on the stylus tip

wear of the written upon digitiser surface by pitting caused by the dust is also reduced.

The stylus tip provided by the ball in the stylus according to the invention can be made from 5 metal with a hard wearing surface, which has high abrasion resistance characteristics, such as hard nickel with hard chrome plating, typically with an abrasion index of about 0.03. Such a ball will increase the stylus lifetime. It will have a better 10 resistance against adherence of unwanted dust particles. The ball tip is "self cleaning" because its rotating movement causes small particles to be removed. From an ergonomic point of view, using a 15 rotating ball tip helps users to write on the digitiser with a smoother and more continuous movement. Users can also write on the digitiser using a wide range of stylus angles. Furthermore, the width of the writing on the digitiser is kept 20 to a minimum by using the ball tip, in contrast to the prior art tips.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

Figure l is a partly cross-sectional side elevation of a digitiser stylus embodying the invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

As shown in Figure 1, a digitiser stylus 1 is provided to write on a digitiser tablet 3. The stylus 1 includes a pen shaped body 5 having an end tubular portion 7 providing an internal cavity 8. A cap 9 having an inwardly tapering S outer wall 9a is fitted in the open end of the tubular portion 7. The cap 9 has an aperture 9b through which projects part of the surface of a ball 11. The ball 11, which is made of a hard wearing metal such as stainless steel, is also partly located in the cavity 8. A spring 13 10 is located in the cavity 8 behind the ball 11. A spacer 15 is also provided in the cavity 8 between the spring 13 and the cap 9. The spacer 15 is made of a solid low friction material such as PTFE. The spacer 15 has a bowl shaped inner surface 15a in which the ball 9 is seated with a 15 close fit. The ball 11 is thereby able to rotate about a point fixed within the stylus 1. An annulus 17 made of metal foil is fitted between the spacer 15 and the cap 9.

The annulus 17 has an inner diameter, which matches the diameter of the ball 11.

20 In use, the stylus 1 is pushed by a user against the digitiser tablet 3 causing the ball 11 urged by the spring 13 to form a mild depression in the surface of the tablet 3. The stylus 1 can be moved across the surface of the tablet 3 by rotation of the ball. Positions on the tablet 3 25 where the stylus is pushed against the tablet 3 represent components of written information. Thus, information is imparted to the digitiser tablet 3 by moving the stylus 1, in particular by rolling of the ball 1, across the surface of the tablet 1 and recording the information by recording 30 the written on regions of the tablet 3 in a known manner.

Claims

1. A stylus for a digitiser, the stylus comprising an elongate member having a tubular portion and an end cap 5 fitted in an end of the tubular portion, the tubular portion and the end cap enclosing a cavity, the end cap having an aperture there through, a spacer fitted in the cavity and having a ball seating recess, a ball seated in the seating recess of the spacer and having a portion which 10 extends through the aperture of the end cap and projects beyond the end cap and a spring in the cavity behind the ball arranged to urge the ball against the end cap, wherein the ball seating recess comprises a solid dry surface around which the ball is free to rotate.

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2. A stylus according to claim l wherein the ball is made of a metal.

3. A stylus according to claim l or claim 2 wherein the ball carries a permanent coating.

4. A stylus according to claim 3 wherein the coating is 20 of a low friction solid material.

5. A stylus according to any one of claims l to 4 wherein the spacer, in the ball seating recess, has a surface which comprises a low friction solid.

6. A stylus according to claim 5 wherein the low friction 25 solid comprises polytetrafluoroethylene.

7. A stylus according to any one of the preceding claims which has an annular layer between the end cap and the spacer which serves to inhibit dust particles passing into a contact region between the ball and the ball seating 30 recess.

8. A stylus according to claim 7 wherein the annular layer may comprise a metallic foil annulus or brush.

9. A stylus according to claim 7 or claim 8 wherein the annular layer coincides substantially with a plane perpendicular to an axis of the elongate member.

10. A stylus according to claim 7, claim 8 or claim 9 and 5 wherein the annular layer coincides substantially with a plane passing through the centre of the ball.

11. A stylus according to claim 1 and substantially as herein described with reference to the accompanying drawings. 10

12. A combination of a stylus according to any one of claims 1 to 11 and a digitiser, wherein the stylus is operable by a user to write on the digitiser by rolling of the ball on a writing surface of the digitiser, the writing surface comprising a compressible plastics material.

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13. A combination according to claim 12 and wherein the digitiser comprises a device in which an electrical property of the device is changed in a region corresponding to a surface region written upon by the stylus.