Pressure sensitive pen

Details Pressure sensitive pen Pressure sensitive pen

2002-01-28

2004-04-27

Shankar, Vijay (Department: 2673)

Telegraphy

Systems

Position coordinate determination for writing

C345S179000

Reexamination Certificate

active

06727439

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a positional indicator used in a digitizer tablet, and more particularly to a pen-like device that can detect pen press pressure or that comprises pen pressure sensitive mechanisms.
2. Description of the Prior Art
Currently, widely used computer input devices include the keyboard and the mouse. Due to the advances of digital technologies, more and more computer users have begun working with digitizer-based devices such as digitizer tablets, which allow a user to write and draw upon the working area of the tablet and have the signals and codes interpreted by a computer. Specifically, the working area of the tablet provides a writing surface for capturing the position, pressure and key status of an object, such as a pen or a mouse, and information related to pressure and actuated keys etc. In cooperation with the tablet, a pen-like device is required to create such objects. Most existing pen-like devices, which can be corded or cordless, are not able to generate lines with variable width according to different depressed forces upon the working area of the tablet applied by the pen-like devices. To overcome this shortage, pressure sensitive pens were invented.
FIG. 1A
shows a schematic cross-sectional view of a prior pressure sensitive pen
10
, which comprises a casing
12
having a cylindrical outer body, a core body
14
provided on the axis of the casing
12
, a ferrite core
16
having a through-hole for slidably housing the core body
14
, coil
20
wound around the ferrite core
16
, a movable magnetic body
18
that can move in relation to the core body
14
, a spring
22
, and a capacitor
24
. The core body
14
has a generally cylindrical form, while its upper neighboring portion, which touches the positional detecting plane, has a tapered form such that the operation allows it to easily indicate a specified point.
The ferrite core
16
is fixed to the casing
12
. The core body
14
moves backward along its axis by a depressing force when the pen top
13
is depressed against the positional detecting plane. The moveable magnetic body
18
is positioned to move in conjunction with the core body
14
. The relative distance to the ferrite core
16
is therefore varied as the magnetic body
18
moves. The coil
20
and the capacitor
24
form a resonant circuit. Conditions of this resonant circuit are determined such that the circuit resonates with the coil
20
while inducing and transmitting an electromagnetic field between them. The inductance of the coil
20
can be changed when the gap between the ferrite core
16
and the magnetic body
18
is changed. It thus detects the depressing force against the pen top
13
by sensing the change in the resonant conditions caused by the placement of the pen.
However, if the pressure sensitive pen
10
is operated in an inclined position against the detecting plane, the direction of the depressing force is then no more coincident with the axial direction of the core body
14
. In such a case, only the axial component of the depressing force is transferred to the core body
14
so that the amount of the depressing force contributing to detection is decreased. Thus, the inductance change generated by the displacement of the magnetic body is reduced. The sensitivity of the pen pressure detection is also reduced if the pressure sensitive pen
10
is operated in an inclined position so that it cannot detect a weaker pen pressure.
Normally, it is natural for an operator to hold the pen in an inclined position, rather than in an orthogonal position while inputting with the pen in hand onto a horizontal plane.
To attain an increased absolute sensitivity by compensating for such a defect, it is desirable to provide a structure that provides the movable magnetic body
18
with a larger area, and has its end face opposed to the face of the fixed magnetic body
16
, such as shown in
FIG. 1B
rather than to use the movable magnetic body
18
having a smaller area shown in FIG.
1
A. In
FIG. 1B
, it is however required to assemble the pen with the initial gap predetermined as the interval between the two magnetic bodies when the pen not depressed by its tip. That requires high accuracy when placing the movable magnetic body. Moreover, ferrite material normally used for the fixed magnetic body is made by powder metallurgy, so that its dimensional tolerance is large and thus it is difficult to ensure the accuracy mentioned above.
Accordingly, it is an intention to provide an improved pressure sensitive pen to overcome the drawbacks mentioned-above.
SUMMARY OF THE INVENTION
It is one objective of the present invention to provide a pressure sensitive pen, which uses a fixed magnetic body having one coil formed of at least a wire wound around and a movable magnetic body. A predetermined distance between the fixed magnetic body and the movably magnetic body is changed when applying a depressing force on a core body of the pen. As a result, an inductance generated by the coil is changed and a frequency of electromagnetic field emitted from the pen is thereby changed.
It is another objective of the present invention to provide a pressure sensitive pen, which utilizes an annular member disposed in a hollow cylinder to separate a fixed magnetic body having one coil formed of at least a wire wound around and a movable magnetic body such that a predetermined distance between the fixed magnetic body and the movable magnetic body is accurately and properly controlled when there is no force applied on a core body of the pen. An initial frequency of electromagnetic field emitted from the pen is kept constant and not influenced by a common difference of the magnetic bodies in dimension.
It is a further objective of the present invention to provide a pressure sensitive pen, in which one coil is formed of at least a wire wound around a fixed magnetic body so that the coil obtains a high Q value. Hence, the capability of the coil for inducing/emitting electromagnetic field is very excellent. The pen can directly induce an electromagnetic field coming from an underlying tablet to serve as power source, and does not require an additional power supply such as a battery.
It is still a further objective of the present invention to provide a pressure sensitive pen, in which one coil is formed of at least a wire wound around a fixed magnetic body so that the coil obtains a high Q value. Hence, the capability of the coil for emitting electromagnetic field is very excellent. As a result, an underlying tablet for detecting pressure variation of the pen has a higher S/N ratio, and the resolution of the tablet is improved. The signal transformation of the tablet from a frequency value into a pressure value is facilitated.
In order to achieve the above objectives of this invention, the present invention provides a pressure sensitive pen having a pressure sensitive mechanism. The pressure sensitive mechanism comprises a supporting member, an elastic element, a hollow cylindrical body, a first magnetic body, a second magnetic body, a sliding member, a core body and one coil formed of at least a wire wound around the first magnetic body. One end of the supporting member is provided with a first housing. The elastic element is disposed in the first housing. One end of the hollow cylindrical body is leaned against the end of the supporting member having the first housing. The hollow cylindrical body has an inner surface and an outer surface. The inner surface of the hollow cylindrical body is formed with an annular member for dividing the hollow cylindrical body into a second housing and a third housing. The third housing is formed between the annular member and the first housing. The first magnetic body is provided with a first central through-hole. One end of the first magnetic body is engagely received in the second housing and against the annular member. The second magnetic body is provided with a second central through-hole. The second magnetic body is movably disposed in the third hou

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