Eraser for electronic blackboard

An eraser for an electronic blackboard. System whose erasing area is variable according to the size and accuracy of the figure to be erased. The eraser includes a main unit carrying a small area erasing unit, and a large area erasing unit which is detachably engaged to the main unit. Detectors installed in the main unit detect when the eraser is touched on the surface of the board, and/or that the large area erasing unit is being used, and send an appropriate signal to the system controller. When the system controller receive the signal, it blanks the memories corresponding to the area covered by the erasing units and erases the corresponding area of figures displayed on the display unit.

BACKGROUND OF THE INVENTION 
This invention relates to an electronic blackboard, especially to an eraser 
used for it and more particularly the present invention provides an eraser 
which has a variable erasing area. 
An electronic blackboard is a device developed for displaying a signal, 
written by hand on an input board using a hand-held input instrument, on 
an electronic display unit. Such a device has been proposed for use in a 
conference system by interconnecting isolated conference rooms using 
telephone lines etc. Such a system is beginning to be put into actual use 
under trade names "Gemini 100" by AT&T or "OA Board" by Fujitsu Ltd. etc. 
The electronic blackboard detects the positional coordinates of the 
hand-held input instrument, such as chalk, pencil, felt pen or some 
special input instrument, when it contacts the surface of the input board 
(such an input board is sometimes called as digitizer). The coordinates of 
the touched points are detected and stored in a memory or transmitted to a 
display unit, and the trace of touched points (figures) are displayed on 
the display unit. 
Electronic blackboard systems can be roughly classified into two kinds by 
the method of how detection of the coordinates of touched points occurs. 
One is a pressure sensing type, which detects the contact point of the 
hand-held instrument on the input board by using a pressure sensitive 
board. The other is an electro magnetic types which can be further 
classified into electric and magnetic type, according to whether the 
coordinate detection is performed by electric or magnetic coupling of the 
detector to the electronic blackboard or input board. 
The electromagntic detection type can be further classified into two types. 
One is an active board and passive pen type system, that is a position 
signal is generated by the the input board (active board) and detected by 
the pen or eraser (passive pen). The other one is a passive board and 
active pen type system, that is the pen or eraser generates a signal 
(active pen) detected by the input board (passive board). 
The present invention is related to an eraser used for erasing a figure 
written on the surface of the input board, and blanking the locations in a 
memory corresponding to the erased part of the figure, to erase the 
corresponding part of the figure displayed on display unit. It is 
especially intended to provide a new eraser, whose erasing area can be 
varied for user convenience to erase a large or small area of the 
displayed figure. 
The following explanation will be given with respect to a magnetic type 
electronic blackboard, and especially with respect to an active board and 
passive pen type system. However the explanation is essentially the same 
for the other types of systems, and can be extended to any type of 
electronic blackboards except the method of detecting the positional 
coordinate of the input instrument or eraser on the surface of the input 
board. 
The essential parts of a magnetic type electronic blackboard are shown in 
FIG. 1. In a blackboard (tabulator of figures written on an input board) 1 
is installed a number of coils arranged in X and Y directions with the 
interval between the coils depending upon the desired resolution. The 
coils are fabricated usually by printed circuit technology and are called 
X-coils 2 and Y-coils 3 respectively, according to their direction of 
arrangement as shown in FIG. 1. These x-coils 2 and Y-coils 3 are excited 
using electric current and generate magnetic fields at specified intervals 
in the order of the X and Y directions. When a figure or letter 6 is 
written on the board 1 (it is not necessarily black in color) using a felt 
pen 5, a detection coil 4 installed in the felt pen 5, detects the 
magnetic field emanation from the surface of the board. From the timing or 
phase of the magnetic field detected by the coil 4, the positional 
coordinate of the felt pen 5 on the board 1 is detected and the FIG. 6' 
written on the board 1, can be shown on a display unit 7. 
An eraser for such a system is similar to the input pen. When the figure on 
the input board is erased by hand with an eraser having a felt point for 
example, a detection coil installed in the eraser detects the magnetic 
field produced by the input board. The positional coordinates of the 
eraser are detected in the same way as those of the input pen, and the 
memory locations corresponding to the trace of contacted points by the 
eraser on the surface of the input board (that is the part of the figure 
erased by the eraser) are blanked or cleared. Thus the corresponding part 
of figure on the display unit is erased. 
When using the prior art electronic blackboard, the person who uses the 
blackboard eraser experiences inconvenience when erasing figures because 
the point of the eraser is fixed to an appropriate size or area, and if 
the person wants to erase a large area, he has to use the eraser many 
times. However, if he wants to erase a fine or sharp figure, a wrong part 
can be erased by the improperly large eraser. And if the user tries to 
erase a fine figure by leaning the eraser on its edge similar to when 
using a general blackboard eraser, errors occur in positional detection 
and the displayed figure can be deleted incorrectly. 
Simple method of responding this problem is provide two erasers, large and 
small. However this method results in an increased number of components 
and an increased in cost. The inconvenience caused by the need of changing 
the eraser in hand is not overcome. 
SUMMARY OF THE INVENTION 
An object of the present invention, therefore, is to improve or avoid the 
above mentioned inconveniences and to provide a new type of eraser for an 
electronic blackboard which is able to change the size of its erasing 
area, for erasing large or a small area of the figure. 
Another object of the present invention is to provide an eraser for 
electronic blackboard which is convenient for practical use. 
The objects can be attained by providing a detachable large area eraser for 
erasing a large area, at the top of the fine area eraser, and providing a 
means to detect whether the large area eraser is being used. Based on this 
detection, the area to be deleted on the display unit can be controlled. 
The eraser of the present invention comprises a main unit, a small area 
erasing unit attached to the main unit, a position sensor installed in the 
main unit and a detachable large area erasing unit. 
A sensor to detect whether the large area eraser unit is attached 
comprises, for example a lead relay, which is switched by the magnetic 
field of a permanent magnet installed in the large area eraser unit. 
These together with other objects and advantages, which will be 
subsequently apparent, reside in the details of construction and operation 
as fully hereinafter described and claimed.

Like reference numerals designate like or corresponding parts throughout 
the figures. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As mentioned above, two kinds of erasers are required for the convenience 
of the user, in order to erase a figure written on an electronic 
blackboard. One for erasing a small area (fine) and another for erasing a 
large area. 
One method of responding to this requirement is provide a large eraser 
attachable to a small (fine) eraser. The erasing process is similar to 
that described before. Namely, the positional coordinates of the center of 
the eraser touching the surface of the input board are detected, and the 
memory locations associated with and around the center of the radius of 
the eraser is blanked or cleared. Thus the figure corresponding to this 
part on the display unit is erased. 
In this method it is necessary to detect whether the large area eraser is 
in use to determine the radius to blanked in the memory. There were some 
experiments conducted to discover the best method to determine what size 
eraser investigated was in use. One method is to make a holder for the 
large area eraser, and keep the large area eraser in the holder when it is 
not in use. The use of large area eraser is detected by the holder. That 
is, if the eraser is not in the holder, it is in use and a large area 
erasing signal is sent to the controller. However it was noted as 
troublesome for a lecturer to return the eraser back to the holder and if 
he concentrated on his lecture, the eraser was often not returned to the 
holder, and caused trouble due to erroneous operation. 
So, it was determined that it is necessary to detect the use of an 
attachable large area eraser unit by using the eraser itself. 
FIG. 2 illustrates a structure of an eraser according to the present 
invention. FIG. 2 (a) shows a condition when the eraser for the large area 
is not attached, and 2(b) shows a case when the large area eraser is 
attached. The figure shows only the essential parts of the invention. The 
eraser comprised a main unit 10, a small area erasing unit 10' and large 
area erasing unit 10" made from a non-magnetic material. It is to use a 
lightweight material such as plastic to reduce the weight and to make the 
handling easy. Material to be used is all similar for all the embodiments 
which will be described hereinafter. The main unit 10 (hand held rod) is 
provided with a detection coil 11 and contact points 13 and 14. which are 
separated from each other by a separating device which will be explained 
later with regard to FIG. 4. The small area erasing unit 10' comprises a 
small area eraser 12, attached to the surface of eraser head 19 and 
supported by a rod 19' which is inserted into the main unit 10, and held 
in a manner slidable along its axis. Of course the rod 19 is prevented 
from slipping out of the main unit 10 by a retaining device. However these 
mechanism are not essential to the present invention, and have been 
omitted from the explanation and drawings hereinafter. 
The large area erasing unit 10" is detachably fitted to the main unit 10. 
And a large area eraser 15 is attached to the surface of large area 
erasing unit 10" as shown in FIG. 2(b). 
The small area eraser 12 and the large area eraser 15 are made of felt or 
rubber, for example, and are used to erase figures written on the surface 
of the electronic blackboard (not shown). The size and material of the 
erasers depends on what kind of material is used to write figures on the 
electronic blackboard, and the size and/or accuracy of figures to be 
erased. The shape of the eraser may be freely chosen but circular shape is 
preferable for the reasons set forth hereinafter. 
The contact points 13 and 14 are closed by pressure transmitted by rod 19' 
attached to the small eraser unit 10', when the small area eraser 12 is 
touched to the surface of the input board, and send an erasing signal to a 
control unit or the display unit. 
Contact points 16 and 17 are provided on the main unit 10 and the large 
area erasing unit 10", respectively, as can be seen in FIG. 2(b). These 
points contact each other and send a large eraser signal when the large 
area erasing unit 15 is attached to the main unit 10. Control of the 
electronic blackboard by these signals will be described hereinafter with 
respect to FIG. 5. Wiring for the contact points is also omitted from the 
figures for simplicity. Only a cable 55 to connect the eraser to a 
controller unit of the system or display unit is shown. It is preferable 
to make one or both of the contact points 16 or 17 in a ring form, to make 
them contact each other regardless of the rotational direction around the 
main unit in which the large area erasing unit is attached. If a point 
contacts are used, it is necessary to provide a guide on both erasing 
units to determine the direction of insertion. 
When the large area erasing unit 10" is attached to the main unit 10, the 
small area eraser 12 is projected out slightly from the surface of the 
large area eraser 15, as can be seen in FIG. 2(b). When the large area 
eraser is pressed to the surface of the electronic blackboard, the small 
area eraser is pushed into the main unit 10 and the surface of the erasers 
become flat. The projection depends on the size of the large area eraser, 
and the margin of the space between the contact points 13 and 14. More 
details with respect to about this portion of the invention will be 
described later with respect to FIG. 4. 
In the eraser as shown in FIG. 2, the contact points 16 and 17 are exposed. 
Resulting in problems of safety and reliability. An embodiment of the 
present invention which overcomes this problem is shown in FIG. 3. FIG. 3 
shows a cross-sectional view of another eraser according the present 
invention to illustrate its construction. FIG. 3 also shows the essential 
parts of the invention which comprises a main unit 20, a small area 
erasing unit 20' and a large area erasing unit 20". The main unit contains 
a coil 21 which detects the positional coordinates, a contact points 23 
and 24, and a magnetic field sensible lead switch 27. Contact points 23 
and 24 in the main unit 20 are separated from each other by separating 
device which may be a spring inserted in proper portion for which more 
details will be provided later with respect to FIG. 4. The small area 
erasing unit 20 comprises a small area eraser 22, attached to the surface 
of eraser head 29 and supported by a rod 29' which is inserted into the 
main unit 20, and held in a similar manner as described with respect to 
FIG. 2. The large area erasing unit 20 comprises a large area eraser 25 
attached to the surface of the unit and a permanent ring magnet 26. The 
large area eraser unit 20 is detachable from the main unit 20, to which it 
is engaged by an engagement device. In FIG. 3 it is held by the friction 
of a rubber ring 28 fitted on the inner surface of the large area eraser 
unit 20" as shown in the figure. 
The contact point 23 is pushed toward the contact point 24 by the rod 29', 
when the eraser is pressed to a surface of a board to erase figures 
written on it. and the contact points 23 and 24 are closed to send an 
erasing signal that the eraser is in use. When the large area unit 20 is 
attached to the main unit 20, the lead switch 27 installed in the main 
unit 20 is closed by the magnetic field of the permanent magnet 26, and a 
signal that the large area erasing unit is in use is sent to the system 
controller. In FIG. 3, the wiring for the lead switch 27 also omitted for 
the sake of simplicity. 
When the system controller receives the erasing signal, it blanks the 
portion of memory corresponding to the area of the small size eraser 
around the positional coordinates for the main unit 20, and the portion of 
the figure corresponding to the area of the small area eraser on the 
display unit is deleted. If the system controller further receives the 
signal that the large area eraser is in use, it further blanks the memory 
portions corresponding to the area of the large size eraser around the 
positional coordinate for the main unit 20. And on the display unit, a 
large area corresponding to the large area eraser is deleted, which 
corresponds to the area deleted on the surface of the electronic 
blackboard. More details of this erasing process will be described later 
with respect to FIG. 5. 
The surface of the small area eraser 22 project out slightly from the 
surface the large area eraser 25 as shown in FIG. 3, similar to FIG. 2. 
More details of this projection will be described hereinafter with respect 
to FIG. 4. 
In the erasers described above, the shape of the eraser may be any shape. 
However it is the most practical to use a circular erasing area, because 
the system controller only has to delete an area within a constant radius 
determined by the size of the eraser, around the point detected by the 
coordinate detecting coil. If for example a rectangular or some other 
shaped erasing area is used, it is necessary to provide additional means 
to detect the direction of the eraser touched on the surface of electronic 
board, where the shape of the eraser is determined beforehand. 
FIG. 4 shows still another embodiment of an eraser giving according to the 
present invention. FIG. 4 shows more details of the eraser, however the 
essential principles of the eraser are similar to the preceding 
embodiments, therefore, only some of the details and some of the points 
different from the preceding embodiments will be described. 
The eraser comprises from main unit 30, small area erasing unit 30' and 
large area erasing unit 30". Function and performance of these units are 
all similar to that of FIGS. 2 and 3. The contact points for detecting the 
small area erasing unit 30' have been replaced by a magnetic sensible lead 
relay 34 and a small permanent magnet 33. In the figure, wiring for the 
position detecting coil 31, lead relay 37 and 34 are shown respectively by 
51, 52 and 53. The wires are passed through holes or spaces properly made 
in the main unit 30, bonded to a small terminal plate 54. and then wired 
to the multi-conductor cable 55. The terminal plate 54 is fixed properly 
to the main unit 30, and prevents the fine wires from breaking or becoming 
disconnected. The permanent magnet 33 is pressed by a spring 41 toward the 
far end away from the magnetic sensible lead relay 34, in a case 42 which 
accommodates the lead relay 34 and the spring 41. When the small area 
eraser 32 is touched to the surface of the board (not shown) to erase the 
figures written on it, the permanent magnet 33 is pushed toward the near 
side or closest side to the lead relay 34 in the case 42, as can be seen 
in FIG. 4. Then the lead relay 34 closes and sends a signal that the 
eraser is in use. 
As can be seen in FIG. 4, the rod of the small area erasing unit 30', which 
corresponds to the rod 19' or 29' in FIGS. 2 or 3, is made from plurality 
of rods or pistons and sleeves, each coupled to each other and which slide 
along the axis. Piston 43 is inserted into sleeve 44 and pressed toward 
the eraser head 39 by a spring 48. The means to support and prevent the 
piston 43 from sliding out of the sleeve 44 is not shown for the sake of 
simplicity, because it does not relate directly to the invention. The 
sleeve 44 is connected to rods 45 and 46 successively, which conduct the 
pressure at eraser 32 to the magnet 33 through a pin 47. The means to 
support or hold these parts properly is also omitted from the description 
for the sake of simplicity. 
The gap 61 between the head of rod 46 and stopper 49 is narrower than the 
margin allowed for the spring 41 to shrink in the holder 42, to prevent 
the damage to magnet 33 when pressed by the small area eraser 32. The 
marginal space 62 between the end of the piston 43 and the bottom of the 
sleeve 44 where the spring 48 is inserted, is wider than the gap 61, so 
that a strong pushing stroke on the eraser head which is larger than the 
gap 61 is absorbed by the gap 62. Finally, the gap 63 between the back of 
eraser head 39 and the top of the main unit 30 is narrower, than the total 
width of gaps 61 and 62, so that a shock of a rough touching of the eraser 
to something is absorbed and the eraser is protected from damage. 
The spring 48 is selected to have its elasticity stronger than that of 
spring 41. When the eraser is touched to the blackboard, therefore, the 
spring 41 is caused to shrink and the magnet 33 is moved first to activate 
(close) the lead relay 34. Further pressure is absorbed by the 
above-mentioned process. The process and function of the eraser is similar 
to the one explained with respect to FIG. 2 or 3. 
One more note should be added with regard to the setting position of 
position detecting coil 11, 21 or 31. In the preceding embodiments, these 
coils were placed in the main unit 10, 20 or 30 respectively. They can be 
placed at any other place, for example in the head of small area erasing 
unit 19, 29 or 39. According to the experience of the inventors, there is 
an optimum distance from the surface of the board (more precisely from the 
X and Y coils). This is the distance where the accuracy of position 
detection is high, and errors due to the improper use of the eraser such 
as leaning of the eraser become a minimum. In the case shown in the 
figures, the above described position preferred is a position for the 
coordinate detection coils. More details about this condition have been 
disclosed in Japanese Laid Open Pat. No. Tokukaisho 56-147280 by T. Kohno, 
issued on Nov. 16, 1981. 
Next it will be explained briefly how the the electronic blackboard is 
controlled by a control system. It the method is a common method and will 
be described briefly with respect to FIG. 5, which shows a block diagram 
of control system for an electronic blackboard. 
A positional coordinate signal picked up by the coil 11, 21 or 31 in the 
forgoing figures is amplified by a buffer amplifier BA, filtered by a 
band-pass filter BPF, and then fed to a sample-hold circuit S/H. The 
sample-hold circuit S/H sends the signal to an analog to digital converter 
(A/D converter) ADC, synchronized to the period of a clock pulse generator 
PG. The A/D converter converts the input signal to a 12 bit signal, and 
loads it in a 12 bit input buffer resister IBR. On the other hand the 
signals sent from the contact points 13 and 14, 23 and 24 or lead switch 
34, which indicate that the eraser is in use, are send to a first receiver 
R1. The signal sent from the contact points 16 and 17, or lead relay 27 or 
37, which indicate that the large area erasing unit is in use, is received 
by a second receiver R2. The out put of these receivers are loaded in a 
device status resister DSR. 
A processor PRO reads out the memory of device status resister DSR at a 
predetermined interval (usually about 10 msec) according to the processing 
program stored in read only memory ROM (capacity of which is about 32K 
bytes). When a flag is set indicating the "eraser is in use", the 
processor PRO reads out the signal in the input buffer register IBR and 
the signal in the device status resister DSR indicating the use or not of 
the large erasing unit, and stores same in a random access memory RAM, 
having a capacity of about 8K bytes. For the transportation of this data 
between PRO, DSR, RAM and ROM a first data bus BUS1 is used. 
At the same time, the signals are converted into serial data by a first 
serial interface controller SIC1, and fed to a second serial interface 
controller SIC2 via a driver D, and a receiver R4 of a host processor 
H-PRO. The seconc serial interface controller SIC2 converts the input 
serial signal into a parallel signal and sends it out onto a second data 
bus BUS2. 
A host processor H-PRO reads the data on the second data bus BUS2, and 
recognizes the area which is to be erased in the figure displayed on the 
display unit DISP. Then the host processor H-PRO sends out to the second 
data bus BUS2, the address corresponding to the area to be erased in a 
refresh memory REF, and the writing signal "0". The refresh memory stores 
the figure displayed on the display unit DISP. 
The above-mentioned address is comprises an address which corresponds to a 
circular area having a center corresponding to the coordinate detected by 
the coil, and a radius corresponding to the size of the eraser used. These 
data are sent to the refresh memory REF via a graphic display controller 
GDC. In the refresh memory, the displayed data (drawing displayed) is 
written as "1", and replacing this data by "0" the displayed data to be 
erased. 
The clock pulse generator PG generates a signal to drive the X coils 2 and 
Y coils 3 of the electronic blackboard 1 shown in the FIG. 1. It also 
generates a signal X/Y to switch the X coil and Y coil. The signal from 
the coil 4 in the write pen 5 is also sent to the processor PRO. It is 
necessary, therefore, to distinguish a write an erase. For this purpose, 
the writing pen 5 is provided with a switch, which sends a signal 
indicating the writing pen is in use. This signal is sent to the device 
status resister DSR via a third receiver R3, and registered in a different 
bit position of the device statue register DSR. Thus the processor can 
distinguish the signals. 
In the above disclosure of the present invention, the explanation has been 
made with respect to a magnetic type active board and passive pen type 
electronic blackboard. As will be clear as mentioned above, the spirit of 
the present invention is not limited to this type, but can be extended to 
any type of electronic blackboard with a slight modification which would 
be easy for one skilled in the art. For example by an replacing the X 
coil, Y coil and detection coil by appropriate electric coupler, such as a 
condenser plate for example, it is possible to realize an electrostatic 
type board. Replacement of passive board and active pen or eraser is also 
easy. 
Moreover, it will be clear that many variations in the embodiments may be 
possible. For example, the position sensor and the magnetic sensible lead 
relay may be replaced by some other magnetic field sensors, such as Hall 
effect elements. The lead relays may be replaced any kind of detectors 
such as photo detector and light emitting diode, for example. The 
particular mechanical structure of the eraser which has been disclosed is 
also not essential for the invention. For instance the rod may be of any 
shape, the means to hold the large area erasing unit and the small area 
erasing unit in their proper position may be replaced by many 
alternatives. Further, the magnet mounted on the large area erasing unit 
needs not be a ring magnet. A modification such as eraser having a battery 
and transmitter in it, to eliminate the cable to connect the eraser by 
wireless transmission system is also possible. 
These variations and modifications are all within the scope and spirit of 
the present invention. Accordingly, it should be understood that the 
embodiments as set forth in the explanation show the essential part and 
practical shape of the invention.