Digitizer utilizing heat source detection to receive input information

A heat sensing digitizer is formed on an input area by providing at least two heat sensors at positions fixed relative to the input area. The heat sensors detect heat provided by a heat source, such as a pen with a heated tip. Based on the calculated distance of the tip to each of the heat sensors, the location of the heat sensitive tip in the input area is determined. Multiple sensors further permit detection of the intensity of the heat source or three-dimensional position of the heat source.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to computer user input devices, and more 
specifically, to a computer digitizer that senses a heated pen. 
2. Description of the Related Art 
The explosion of the personal computer market has lead to great advances 
and ease of use of those personal computers. The keyboard and text display 
has given way to a variety of user input devices for control of graphical 
interfaces. These input devices either augment or totally replace the 
keyboard, and include mice, track balls, digitizers pads, touch sensitive 
screens, among other things. 
Touch sensitive screens are used both for displays on standard personal 
computers, but more commonly in conjunction with notepad computers and 
dedicated automated stations, such as automated airline ticket dispensers 
and automated tellers. A requirement of a touch sensitive screen, of 
course, is that it be clear--as opposed to digitizers, which do not need 
to transmit light, since a user must see on the screen what is available 
or present to be able to make a choice or control decision. 
So far as is known, there have been three principal technologies used for 
touch sensitive screens. These are known as capacitive technology, 
resistive technology, and surface acoustic wave (SAW) technology. 
Resistive technology typically used a voltage gradient on a plastic on 
glass membrane overlay to sense touch. For example, a five wire sense 
system created a voltage gradient on the bottom layer, and the top layer 
senses that voltage. The screens two layers were coated with a thin, dear 
conductive metal oxide on their facing sides and held apart by a layer of 
materials composed of spacer dots. Along the edges of the sensor was 
electrode pattern. The controller dispersed a uniform voltage field across 
the sensor and then measured the voltage on the glass layer at the 
location where a user's finger or other indicator object pressed the two 
layers together. The sensed voltage was then translated into a set of 
digital touch coordinates by a controller and sent to a host computer. 
Capacitive digitizer technology typically used an all glass sensor with a 
transparent, thin film conductive coating fused to its surface. Along the 
edges was a narrow, precisely printed electrode pattern that uniformly 
distributed low voltage, AC field over the conduct layer. When a finger 
made contact with the screen surface, it "capacitively coupled" with the 
voltage field, drawing a minute amount of current to the point of contact. 
The current flow from each corner was proportional to the distance to the 
finger and the ratios of these flows were measured by the controller and 
used to locate the touch. 
Surface acoustic wave (SAW) technology provided a glass panel with 
transducers that transmitted and received surface waves over the face of 
the screen. When a finger or other object touched the screen, a portion of 
the energy of the wave was absorbed at the touch location. This location 
could then be determined based on the presence of interference patterns 
caused in the acoustic wave. 
SUMMARY OF THE INVENTION 
Briefly, the present invention provides a new and improved system for 
receiving input information from a user based on the location of a heat 
source. The heat sensing digitizer according to the present invention 
includes an input area with at least two heat sensors located at fixed 
locations relative to the surface. The heat sensors detect the presence of 
a heat source and provide a signal representative of the distance from 
each heat sensor to the heat source. The location of the heat source on 
the surface is then calculated from the two determined distances. 
Further, multiple heat sensors can provide an indication of the intensity 
of the heat source, representing the pressure of a heat sourcing pen on 
the input area, for example. Multiple sensors can also provide a 
three-dimensional location of the heat source.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning to FIG. 1, a typical computer system C is shown according to the 
invention. The computer system C includes a primary circuit board (not 
shown) within a chassis 100. The circuit board provides system storage 
through various storage devices, including a CD ROM drive 102, a floppy 
disk drive 104, and a hard disk drive 106. The circuit board also provides 
a keyboard 108 and a mouse 110. The circuit board provides display data 
for a video display 112, which includes a heat sensing digitizer 114 
according to the invention. A heat source pen 116 forms the heat source 
for the digitizer 114 and is either coupled to the computer system C or is 
standalone with internal batteries. The details of the heat sensing 
digitizer 114 are further discussed in conjunction with FIG. 6, and 
details of the heat source pen 116 are discussed in conjunction with FIG. 
5. 
Turning to FIG. 2, a notepad computer N is shown implemented according to 
the invention. Again, a heat sensing digitizer 118 is provided for use 
with the heat source pen 116, which may be the sole input device for the 
notebook computer N. A chassis 120 houses the electronics necessary to 
operate the notebook computer N. 
Turning to FIG. 3, an automated teller system A is shown implemented 
according to the invention. The automated teller system A preferably 
includes a dispenser 122 for money, tickets, and other materials typically 
provided by automated tellers and has an input 124 for, for example, 
credit cards. A display 126 again has a heat sensing digitizer 127 
according to the invention. 
Turning to FIG. 4, a retrofit device R is illustrated for use with existing 
displays, such as the display 112 of FIG. 1. The retrofit device R has a 
clear screen 132, a frame 128, an input/output (I/O) cable 130, and the 
heat source pen 116. This retrofit device R optionally omits the clear 
screen 132, instead using as an input area the actual screen of the 
display 112 of FIG. 1. 
Turning to FIG. 5, the details of the heat source pen 116 implemented 
according to the invention are shown. The heat source pen 116 includes 
batteries 134, an on/off switch 136, and drive electronics 138. The drive 
electronics 138 heat a heat conducting tip 140, for example between 
140.degree. and 200.degree. F. An activation tip 142, which can be 
pressure sensitive, activates the heat conducting tip 140. Further, if the 
activation tip 142 is pressure sensitive, the electronics 138 sense the 
amount of pressure on the tip 142 and heat the tip 140 to varying degrees 
depending on that pressure. Alternatively, a user can simply turn the tip 
140 on and off with the switch 136, or can use the switch to turn on the 
electronics 138 to heat the tip 140 to a fixed temperature in response to 
the activation tip 142. One skilled in the art will appreciate that a wide 
variety of point heat sources can be used according to the invention. In 
appropriate cases, even the heat of a fingertip can provide the heat 
necessary to activate the heat sensing digitizer 114, 118, or 127 
according to the invention. 
Turning to FIG. 6, a diagram of a screen 200 illustrates the operation of 
the heat sensing digitizer 114, 118, or 127 according to the invention. 
The screen 200 forms the boundaries of a two-dimensional input area, with 
three pyroelectric sensors S.sub.1, S.sub.2, and S.sub.3 located at a 
lower left corner, a lower fight corner, and an upper middle position of 
the screen 200 (such as along the periphery of the frame 128 of FIG. 4). 
The pyroelectric sensors S.sub.1, S.sub.2, and S.sub.3 are preferably 
standard pyroelectric sensors known to the art. Such sensors typically 
source either voltage or current (preferably voltage sourcing in the 
disclosed embodiment), and provide that voltage or current as a rising 
function of a sensed temperature. Other sensors, such as infrared sensors, 
could also be adapted for sensing the heat source. 
When the heat source pen 116 is brought into contact with the screen 200 
illustrated in FIG. 6, the tip 140 heats responsive to the activation tip 
142. Each of the three pyroelectric sensors S.sub.1, S.sub.2, and S.sub.3 
then provide an elevated reading in response to sensing the heat from the 
tip 140. Pyroelectric sensors are not directional, but do vary in response 
depending on their distance from a heat source. Therefore, each of the 
pyroelectric sensors S.sub.1, S.sub.2, and S.sub.3 will provide a voltage 
level (in the disclosed embodiment) representing the heat intensity it is 
sensing; here, illustrated as intensities I.sub.1, I.sub.2, and I.sub.3. 
The distance versus intensity function will be known, and is preferably 
the same for each of the pyroelectric sensors. Therefore, three distance 
curves 202, 204, and 206 at distances d.sub.1, d.sub.2, and d.sub.3 from 
the corresponding sensor S.sub.1, S.sub.2, and S.sub.3 are determined from 
the intensities I.sub.1, I.sub.2, and I.sub.3. These three distance curves 
202-206 intersect at a point P(x,y). 
Each distance d.sub.1, d.sub.2, and d.sub.3 for the corresponding sensor 
S.sub.i, S.sub.2, and S.sub.3 is a function of both that sensor's returned 
intensity I.sub.1, I.sub.2, and I.sub.3, and a base intensity I.sub.0 of 
the pen 116. This results in the following equations. 
EQU d.sub.1 =f(I.sub.1, I.sub.0) 
EQU d.sub.2 =f(I.sub.2, I.sub.0) 
EQU d.sub.3 =f(I.sub.3, I.sub.0) 
It will be appreciated from FIG. 6, however, that the point P(x,y) can be 
determined from just two of the intensities I.sub.1 and I.sub.2. That is, 
the distances d.sub.1 and d.sub.2 are sufficient to determine P(x,y). 
However, if the y-axis deflection is low, any error in the distance 
d.sub.1 or d.sub.2 would result in rather large changes in the calculated 
y-axis position. Therefore, the third sensor S.sub.3 improves accuracy. 
As will be further appreciated, by using three sensors the system does not 
need to know the actual pen intensity I.sub.0. Assuming a linear, 
exponential, or inverse square type of function (or another rising 
function) for each distance d.sub.n as a function of intensity I.sub.n, 
I.sub.0 can be calculated based on the three intensities I.sub.1, I.sub.2, 
and I.sub.3. That is: 
EQU I.sub.0 =f(I.sub.1, I.sub.2, I.sub.3) 
Therefore, it is possible to calculate P(x,y) without knowing I.sub.0 : 
EQU P(x,y)=f(I.sub.1, I.sub.2, I.sub.3,) 
Alternatively, the initial I.sub.0 can be determined based on a calibration 
routine by having the user press the pen 116 on a certain point whose 
distance from each sensor S.sub.n is known. I.sub.0 can then be determined 
based on the known distances d.sub.1, d.sub.2, and d.sub.3 from that point 
in conjunction with the returned intensities I.sub.1, I.sub.2, and 
I.sub.3. 
But the capability of determining I.sub.0 as a function of I.sub.1, 
I.sub.2, or I.sub.3 further allows the system to calculate "z-axis" 
information. In two-dimensional digitizer terminology, "z-axis" generally 
represents a sensed pressure. If the intensity of the tip 140 varies based 
on the pressure on the activation tip 142, I.sub.0 will therefore vary 
based on that pressure. But I.sub.0 can be calculated as a function of 
I.sub.1, I.sub.2, and I.sub.3, so the intensity values I.sub.1, I.sub.2, 
and I.sub.3 can be used to determine both P(x,y) and a z-axis value (i.e., 
a pressure value). 
Turning to FIG. 7, an alternative implementation using two sensors S.sub.1A 
and S.sub.2A in the upper left and lower right corners of a screen 208 is 
illustrated. Such a configuration is not preferable, because the distance 
curves not only intersect at points (x,y) but also at (x.sub.S, y.sub.S), 
leading to an ambiguity of pen 116 location. Therefore, if only two 
sensors are used, it is preferable to implement a two sensor system as 
illustrated in FIG. 8, where two sensor, S.sub.1B and S.sub.2B are located 
in the lower left and lower right corners of a screen 210. The (x,y) 
position illustrated in FIG. 8, however, could suffer from rather large 
errors in the determined y-axis value if the distances from the sensors 
S.sub.1B and S.sub.2B are at all in error. 
Turning to FIG. 9, shown is a four sensor implementation with sensors 
S.sub.1C, S.sub.2C, S.sub.3C, and S.sub.4C, each positioned at a corner of 
a screen 212. Using this configuration, the system is more accurate both 
in the z-axis calculation and in determining the position P(x,y) of the 
heat source. 
Turning to FIG. 10, an embodiment with a screen 214 and a fan 216 is shown. 
This fan 216 can blow cool air, either from a cool air source or across a 
thermoelectric cooler 218, to maintain the surface of the screen 214 
fairly constant. This may be desirable in environments in which the 
temperature can vary on the screen 214. 
FIG. 11 shows another alternative embodiment of a display screen according 
to the invention. A display screen 216 in this case is surrounded by an 
array of sensors, designated S.sub.(x,y). This array of sensors further 
enhances the accuracy of position location as well as the ability to 
determine the intensity of the heat from the pen 116. 
As will be appreciated from FIGS. 6-10, a wide variety of sensor locations 
are possible. Further, as will be appreciated, a wide variety of heat 
sources can be used. This is especially true in a three or four sensor 
system, because the intensity of the heat source can be calculated from 
the intensities detected by the sensors. Further, not only the pen 116 
could be used, but a finger may be suitable for certain controlled 
environments. It should also be appreciated that the heat sensing 
digitizer can be used absent a display screen, as a standard digitizer 
pad. 
It will be appreciated that a wide variety of other embodiments could be 
implemented without departing from the spirit of the invention. For 
example, using multiple pyroelectric sensors positioned in three 
dimensions, a true three-dimensional input can be achieved using a 
three-dimensional input area. Also, virtually any device that requires x,y 
or x,y,z type input can use the heat sensing digitizer according to the 
invention. 
Further, although the input areas of FIGS. 1-11 are shown as the boundaries 
of a screen, it should be appreciated that the input area could in fact 
extend beyond the edges of the plane bounded by the sensors, or could 
instead be contained inside the area bounded the sensors. That is, it is 
not necessary that the sensors be located precisely along the corners or 
sides of the input area, but they could be further away from the input 
area, or contained within the input area. One will appreciate that the 
techniques according to the invention still have application regardless 
the size of the input area and its relationship to the sensors. 
Turning to FIG. 12, electronics are shown for detecting the intensities 
I.sub.1, I.sub.2, and I.sub.3 from the sensors S.sub.1, S.sub.2, and 
S.sub.3, and for calculating the position of the pen 116. Three amplifiers 
300, 302, and 304 are connected to the outputs of the sensors S.sub.1, 
S.sub.2, and S.sub.3 of FIG. 6. These amplifiers can be constructed within 
the frame of the digitizer itself, such as the frame 128 of FIG. 4, or can 
be implemented within the control system of the computer, such as within 
the notebook computer N of FIG. 2. Precise location is not critical. 
Preferably, the output of each amplifier 300-304 is provided to a high 
speed analog multiplexer 306, so the outputs of each amplifier 300-304 can 
be selectively switched by the multiplexer 306 into an analog-to-digital 
(A/D) converter 308. In this way, a single A/D converter 308 suffices, 
although separate A/D converters could instead be used for each amplifier 
300-304. The output of the A/D converter 308 is provided to a 
microcontroller 310, which controls the A/D converter 308 and the 
multiplexer 306. The microcontroller 310 preferably executes a routine to 
repeatedly calculate both the position of a heat source 226 and its 
intensity. This microcontroller 310 provides output location and z-axis 
(i.e., pressure) signals over an I/O link 312, preferably digital, for use 
by one of the systems of FIGS. 1-4. 
Turning to FIG. 13, a flowchart illustrates the operation of the 
microcontroller 310. Preferably the microcontroller 310 repeatedly 
executes a routine beginning at step 350, where the microcontroller 310 
reads the intensities I.sub.1, I.sub.2, and I.sub.3 from the sensors 
S.sub.1, S.sub.2, and S.sub.3 through the amplifiers 300, 302, and 304. 
This is done by switching the multiplexer 306 to first connect the output 
of the amplifier 300 to the input of the A/D converter 308 and then 
performing a conversion through the A/D converter 308, providing a digital 
signal representative of the intensity I.sub.1 from the sensor S.sub.1. 
The microcontroller 310 reads this data value through an input port. Next, 
the multiplexer 306 is switched to the amplifier 302 whose output is 
digital by the A/D converter 308, with the digitized intensity I.sub.2 
being provided to the microcontroller 310. Finally, the output of the 
amplifier 304 is coupled to the A/D converter 308 through the multiplexer 
306, thus providing the intensity 13 to the microcontroller 310. 
Proceeding to step 352, the (x,y) position and pressure (z-axis position) 
are calculated. As an initial step, if none of the sensors S.sub.1, 
S.sub.2, or S.sub.3 has provided an intensity I.sub.1, I.sub.2, or I.sub.3 
high enough to indicate the presence of the pen 116, the microcontroller 
310 provides an output signal indicating that the pen 116 is not present 
or has not been activated. If the heat source from the tip 140 is present, 
however, the intensities are used to calculate the P(x,y) position of the 
heat source, as well as the intensity I.sub.0 of the heat source (and the 
corresponding pressure on the activation tip 142). 
Proceeding to step 354, the microcontroller 310 transmits the P(x,y) 
position data and the pressure data over the communications link 312, such 
as to one of the computers of FIGS. 1-4 for use by a graphical user 
interface. 
Turning to FIG. 14, a block diagram illustrates typical components of the 
computer system S of FIG. 1 for using the data from the microcontroller 
310. Preferably the data from the microcontroller 310 is received over the 
communications link 312 by an I/O device 400, such as a high speed serial 
I/O device or a parallel I/O device. This data is then sent over a bus 402 
for processing by a microprocessor 404, such as a Pentium.RTM. type 
microprocessor by Intel Corporation. The microprocessor 404 also 
preferably responds to an I/O device 406, which controls, for example, the 
keyboard 108, the mouse 110, and the floppy drive 106. The microprocessor 
404 also preferably responds to an I/O device 408, which controls the hard 
disk drive 104. Based on the input from the mouse 110 and the keyboard 
108, and the digital data from the data link 312, the operating system 
software of the computer controls the display 112 through a video 
controller 412. In this way, data from the digitizer 114 of FIG. 1 forms 
an input to the graphical user interface. 
The foregoing disclosure and description of the invention are illustrative 
and explanatory thereof, and various changes in the size, shape, 
materials, components, circuit elements, wiring connections and contacts, 
as well as in the details of the illustrated circuitry and construction 
and method of operation may be made without departing from the spirit of 
the invention.