Apparatus and method for recognizing carpets and stairs by cleaning robot

Apparatus and method for determining the condition of the floor to be cleaned by a cleaning robot. The apparatus comprises an ultrasonic wave signal transmitting circuit for transmitting an ultrasonic wave signal to an ultrasonic wave signal transmitter under the control of a microcomputer, a receiving amplifying unit for amplifying the ultrasonic wave signal transmitted from the ultrasonic wave signal transmitter and received in a ultrasonic wave signal receiver, a receiving demodulating unit for smoothing the output signal from the receiving amplifying unit to demodulate it and then apply it to the microcomputer. According to the control of the microcomputer, the ultrasonic wave signal is transmitted for a predetermined period. The period from the time when the ultrasonic wave signal is transmitted to the time when the ultrasonic wave signal is received in the ultrasonic wave signal receiver is measured. Then, the distance between the position of the ultrasonic wave signal receiver and the floor to be cleaned is calculated from the measured period. Accordingly, it can be determined whether the floor to be cleaned is a normal floor, a floor covered with a carpet, or stairs, thereby enabling correct recognition of the condition of the floor to be cleaned, without being adversely affected from environment.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for recognizing floor 
condition of a cleaner, and more particularly to an apparatus and a method 
for recognizing carpets and stairs of a cleaning robot, which can 
determine whether the floor to be cleaned is a normal floor, a floor 
covered with a carpet, or stairs. 
FIGS. 1A and 1B are a side view and a bottom view showing a conventional 
cleaner with infrared ray transmitter and receiver, respectively. As shown 
in the drawings, the infrared ray transmitter 4 and the infrared ray 
receiver 5 are mounted to the front portion of the bottom surface of a 
cleaner body 1 such that they are vertically spaced about 5 cm apart from 
the floor to be cleaned. In the drawings, the reference numeral "2" 
designates wheels and the reference numeral "3" designates a caster. 
Referring to FIG. 2, there is shown a circuit for transmitting infrared ray 
in the conventional cleaner. As shown in the drawing, the circuit which is 
designated by the reference numeral "6" comprises an oscillating element 7 
to which a resistor R21 for supplying a power from a power source Vcc, 
resistors R22 and R23, a condenser C21 for setting a time constant by 
cooperating with said resistors R22 and R23, and a transistor Q21 having a 
base connected with the output terminal P3 via a resistor 24 and a 
collector connected to a light emitting element, that is the infrared ray 
transmitter 4 via a resistor R25. 
Referring to FIG. 3, there is shown a circuit for receiving infrared ray in 
the conventional cleaner. As shown in the drawing, the circuit comprises a 
receiving detector unit 71 which includes resistors R31 to R33, diodes D31 
and D32, condensers C31 and C32 and a transistor Q31 and functions to 
detect the infrared ray received in the infrared ray receiver 5, that is a 
light receiving element, as a sine wave, a receiving amplifier unit 72 
which includes resistors R34 to R40, condensers C33 to C37 and an 
operational amplifier OP31 and functions to compare the output signal from 
the infrared ray receiver 5 with an offset voltage and then amplify it, 
and a receiving demodulator unit 73 which includes inverters IN31 to IN33, 
a diode D33, a condenser C38 and a resistor R41 and functions to smooth 
the output signal from said receiving amplifier unit 72 to demodulate it 
and then apply it to the input terminal PAO of a microcomputer 73. 
Operations of the above-mentioned circuits will now be described. 
The oscillating element 7 of the infrared ray transmitting circuit 6 
generates square wave of 1 KHz according to the time constant set by the 
resistors R22 and R23 and the condenser C21. The 1 KHz square wave which 
is outputted from the output terminal P3 of the oscillating element 7 is 
applied to the base of the transistor Q21 via the resistor R24 so that the 
transistor Q21 is turned on or off, thereby causing the infrared ray 
transmitter 4 to transmit infrared ray at the period of 1 msec (=1/1 KHz). 
The infrared signals outputted from the infrared ray transmitter 4 as 
above-mentioned are reflected against the floor and then received in the 
infrared ray receiver 5. Accordingly, the infrared ray receiver 5 also 
repeats to be turned on and off at the period of 1 msec so that sine waves 
are outputted, at the period of 1 msec, from the output terminal of the 
receiving detector 71 which is connected to the collector of the infrared 
ray receiver 5. 
On the other hand, the amount of the infrared ray signals received in the 
infrared ray receiver 5 varies depending on the floor condition. 
For example, in the case of a normal floor shown in FIG. 4A, all infrared 
ray signals are directly reflected and received in the infrared ray 
receiver 5, so that the amount of infrared ray signals received in the 
infrared ray receiver 5 is greatly different from that in the case that 
the infrared ray receiver 5 receives no infrared ray. In the case of a 
carpet covered floor shown in FIG. 4B, however, a part of infrared ray 
signals transmitted from the infrared ray transmitter 4 are absorbed in 
the carpet and only the remained part of transmitted infrared ray signals 
are reflected against the carpet. As a result, the amount of infrared ray 
signals received in the infrared ray receiver 5 is slightly different from 
that in the case that the infrared ray receiver 5 receives no infrared 
ray. On the other hand, in the case of stairs or a very steep surface as 
shown in FIGS. 4C to 4E, infrared ray signals transmitted from the 
infrared ray transmitter 4 are reflected from a distant surface and then 
received in the infrared ray receiver 5. Accordingly, the amount of 
infrared ray signals received in the infrared ray receiver 5 is slightly 
different from that in the case that the infrared ray receiver 5 receives 
no infrared ray. 
Depending on such difference in amounts of infrared ray signals received in 
the infrared ray receiver 5, the amount of current passing through the 
infrared ray receiver 5 varies. On the other hand, sine wave signals are 
outputted, at the period of 1 msec, from the output of the receiving 
detector unit 71 connected to the collector of the infrared ray receiver 
5. The amplitude of the sine wave signals is in proportion to the 
difference between the amount of infrared ray signals received in the 
infrared ray receiver 5 is slightly and the amount of infrared ray signals 
in the case that the infrared ray receiver 5 receives no infrared ray. 
Consequently, the amplitude of sine wave signals outputted from the 
receiving detector unit 71 is large in the case of FIG. 4A, while it is 
small in the case of FIGS. 4B to 4E. 
These sine wave signals outputted from the receiving detector unit 71 are 
applied to the inverting input terminal of the operational amplifier OP31, 
via the condenser C33, the resistor R39 and the condenser C35 of the 
receiving amplifier unit 72 and then compared with the DC offset voltage 
predetermined by the variable resistor R35. Thereafter, the compared sine 
wave signals are amplified at the rate of R38/R39 and then applied to the 
inverter IN31 of the receiving demodulator unit 73. At this time, if the 
DC offset voltage is predetermined to the voltage applied to the inverting 
input terminal of the operational amplifier OP31, when sine wave signals 
of large amplitude are outputted from the receiver detector unit 71 as in 
the case of FIG. 4A, low potential signals are outputted from the 
operational amplifier OP31. Accordingly, the inverter IN31 outputs peak 
signals of high potential, which is then smoothed at the condenser C38 and 
the resistor R41, via the diode D33. At this time, the voltages smoothed 
at the condenser C38 are maintained above a predetermined value, since 
high potential peak signals are outputted from the inverter IN31, at the 
period of 1 msec. This smoothed voltages are inverted into low potential 
signals at the inverter IN32. At the inverter IN33, the low signals are 
then inverted into high potential signals which is applied to the input 
terminal PAO of the microcomputer 8. Thus, the microcomputer 8 recognizes 
that the floor to be cleaned is a normal floor. 
On the other hand, when sine wave signals of small amplitude is outputted 
from the receiving detector unit 71, as in the cases of FIGS. 4B to 4E, 
the operational amplifier OP31 outputs continuously high potential 
signals, thereby causing the inverter IN31 to output low potential 
signals. As a result, low level signals are applied to the input terminal 
PAO of the microcomputer 8, so that the microcomputer 8 recognizes that 
the floor to be cleaned is not a normal floor, but a carpet covered floor. 
Although the above-mentioned conventional circuit can determine a normal 
floor and a carpet covered floor, it may mistake stairs or a very steep 
surface for the carpet covered floor. As a result, there is a disadvantage 
of providing no protection of cleaning robots from stairs or a very steep 
surface. 
In addition, external light beams may cause malfunction of the circuit in 
discriminating between a normal floor and a carpet covered floor. 
SUMMARY OF THE INVENTION 
Therefore, an object of the invention is to provide an apparatus and a 
method for recognizing carpets and stairs of a cleaning robot, which can 
determine whether the floor to be cleaned is a normal floor, a floor 
covered with a carpet, or stairs, without being affected by external light 
beams. 
In one aspect, the present invention provides an apparatus for recognizing 
carpets and stairs of a cleaning robot, comprising: ultrasonic wave signal 
transmitting means adapted to frequency-divide an oscillating signal and 
transmit the frequency-divided oscillating signal under a control of a 
microcomputer; receiving amplifying means adapted to receive an ultrasonic 
wave signal transmitted from said ultrasonic wave signal transmitting 
means and compare-amplify the received ultrasonic wave signal with a DC 
offset voltage; and receiving demodulating means adapted to demodulate an 
output signal from said receiving amplifying means smoothly and apply the 
demodulated signal to the microcomputer. 
In another aspect, the present invention provides a method for recognizing 
carpets and stairs of a cleaning robot comprising the steps of: 
transmitting an ultrasonic wave signal for a predetermined period (t1) by 
an ultrasonic wave signal transmitter and according to the control of a 
microcomputer; measuring the period from the time when the ultrasonic wave 
signal is transmitted to the time when an ultrasonic wave signal detecting 
signal is generated as the ultrasonic wave signal is received in an 
ultrasonic wave signal receiver and then calculating a distance from the 
measured period; if the calculated distance is no more than the sum of the 
vertical distance (d1) from the vertical position of said ultrasonic wave 
signal transmitter and receiver to the floor to be cleaned and a tolerance 
(e), recognizing the floor to be cleaned as a normal floor; and if the 
calculated distance is more than the sum of the vertical distance (d1) and 
the tolerance (e), transmitting the ultrasonic wave signal again for a 
predetermined period (t1+a) which is sufficiently longer than said 
predetermined period (t1), calculating a new distance according to the 
procedure executed at said calculating step, and if the calculated 
distance is no more than the sum of the vertical distance (d1) and the 
tolerance (e), recognizing the floor to be cleaned as a carpet covered 
floor, while if the calculated distance is more than the sum of the 
vertical distance (d1) and the tolerance (e), recognizing the floor to be 
cleaned as stairs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 5 is a circuit diagram of a circuit for transmitting and receiving an 
ultrasonic wave signal in a cleaner according to the present invention. As 
shown in the drawing, the circuit comprises ultrasonic wave signal 
transmitting means 11 adapted to frequency-divide an oscillating signal 
and transmit the frequency-divided oscillating signal under a control of a 
microcomputer 8, receiving amplifying means 121 adapted to receive an 
ultrasonic wave signal transmitted from the ultrasonic wave signal 
transmitting means 11 and compare-amplify the received ultrasonic wave 
signal with a DC offset voltage, and receiving demodulating means 122 
adapted to demodulate an output signal from the receiving amplifying means 
121 smoothly and apply the demodulated signal to the microcomputer 8. The 
ultrasonic wave signal transmitting means 11 comprises an oscillating 
integrated element IC4 for generating the oscillating signal of 1 MHz, a 
ten frequency-dividing integrated element IC1 for frequency-dividing the 
oscillating signal from the oscillating integrated element IC4 by ten, a 
flip-flop IC2 for frequency-dividing an output signal from the ten 
frequency-dividing integrated element IC1 by two, a flip-flop IC3 for 
receiving a clear signal from the microcomputer 8 and frequency-dividing 
an output signal from the flip-flop IC2 by two, and an ultrasonic wave 
signal transmitter 9 for receiving the two frequency-divided signal from 
the flip-flop IC3 to transmit the ultrasonic wave signal to the receiving 
amplifying means 121. 
On the other hand, the receiving amplifying means-121 comprises an 
ultrasonic wave signal receiver 10 for receiving the ultrasonic wave 
signal from the ultrasonic wave signal transmitter 9 in the ultrasonic 
wave signal transmitting means 11, an operational amplifier OP51 including 
its inverting input terminal connected to an output stage of the 
ultrasonic wave receiver 10 via a condenser C51 and a resistor R51, its 
non-inverting terminal connected to power source Vcc terminal via a 
resistor R55 and its output terminal feedback-connected to the inverting 
input terminal via a resistor R52, and another operational amplifier OP52 
including its inverting input terminal connected to the output terminal of 
the operational amplifier OP51 via a condenser C52 and a resistor R53, its 
non-inverting terminal connected to the power source Vc terminal via the 
resistor R55 and its output terminal feedback-connected to the inverting 
input terminal via a resistor R56. Herein, between the power source Vcc 
terminal and the non-inverting terminals of the operation amplifiers OP51 
and OP52 are connected in parallel to a resistor R54 and a condenser C53. 
Also, the receiving demodulating means 122 comprises an inverter IN51 
connected to the output terminal of the operational amplifier OP52 in the 
receiving amplifying means 121, a diode D51 connected to an output 
terminal of the inverter IN51, an inverter IN52 connected to the diode 
D51, an inverter IN53 including its input terminal connected to an output 
terminal of the inverter IN52 and its output terminal connected to an 
input terminal PAO of the microcomputer 8, and a resistor R57 and a 
condenser C54 connected in parallel between the diode D51 and the inverter 
IN52. 
The ultrasonic wave signal transmitter 9 and the ultrasonic wave signal 
receiver 10 are used in place of the infrared ray transmitter 4 and the 
infrared ray receiver 5 shown in FIG. 1. In this case, they are mounted to 
be vertically apart 10 cm from the floor to be cleaned. 
The operation of the circuit with the above-mentioned construction in 
accordance with the present invention will be described in detail. 
First, the oscillation signal of 1 MHz is generated from the oscillating 
integrated element IC4, which is then frequency-divided by ten by the ten 
frequency-dividing integrated element IC1. Then, the ten frequency-divided 
signal is sequentially frequency-divided by two by the two 
frequency-dividing flip-flops IC2 and IC3. As a result, a square wave 
signal of 25 MHz is outputted from the flip-flop IC3. 
Noticeably, if a low potential signal is outputted from the transmission 
control terminal PBO of the microcomputer 8, the flip-flop IC3 is cleared 
so that the ultrasonic wave signal transmitter 9 is not driven; if a high 
potential signal is outputted from the transmission control terminal PBO 
of the microcomputer 8, the flip-flop IC3 is released from the clear state 
and thus outputs the square wave signal of 25 MHz as mentioned above to 
the ultrasonic wave signal transmitter 9, thereby allowing the transmitter 
9 to transmit the ultrasonic wave signal according to the square wave 
signal of 25 KHz. 
Hence, when a high potential signal is outputted from the transmission 
control terminal PBO of the microcomputer 8 for a predetermined period of 
transmission time t, the ultrasonic wave signal transmitter 9 transmits 
the ultrasonic wave signal according to the square wave signal of 25 KHz 
for the predetermined period of transmission time t, wherein the 
transmission time t can be controlled softwarely by the microcomputer 8. 
Then, the ultrasonic wave signal of 25 KHz transmitted from the ultrasonic 
wave signal transmitter 9 is reflected from the floor and is then received 
to the ultrasonic wave signal receiver 10, which then outputs a sinusoidal 
wave signal of 25 KHz. The amplitude of the sinusoidal wave signal is 
proportional to the magnitude of the received ultrasonic wave signal. The 
sinusoidal wave signal outputted from the ultrasonic wave signal receiver 
10 is amplified by R52.times.R56 and the amplified signal is then DC 
offset by Vcc.times.R55+R54 by the operational amplifiers OP51 and OP52. 
Then, the DC offset signal is applied to the input stage of the receiving 
demodulating means 122. 
At this time, the DC offset voltage according to Vcc.times.R55+R54 is set 
to a high potential signal which is barely recognized by the inverter IN51 
in the receiving demodulating means 122. As a result, a low potential 
signal is outputted from the operation amplifier OP52 only when the 
sinusoidal wave signal having the amplitude larger than that of the DC 
offset voltage is outputted from the ultrasonic wave signal receiver 10, 
so that a peak signal of high potential is outputted from the inverter 
IN51. The peak signal of high potential from the inverter IN51 is charged 
into the condenser C54 through the diode D51 for smoothness. At this time, 
since the peak signal of high potential is outputted from the inverter 
IN51 at the period of 25 MHz, the voltage smoothed by the condenser C54 is 
maintained above a predetermined value. This smoothed voltage is inverted 
into a low potential signal by the inverter IN52, which is then inverted 
into a high potential signal by the inverter IN53. In result, this high 
potential signal is applied to the input terminal PAO of the microcomputer 
8. 
On the other hand, when the sinusoidal wave signal having the amplitude 
smaller than that of the DC offset voltage is outputted from the 
ultrasonic wave signal receiver 10, a high potential signal continues to 
be outputted from the operational amplifier OP52, thereby causing a low 
potential signal to be outputted from the inverter IN51. As a result, the 
charged voltage on the condenser C54 is maintained below a predetermined 
value, thereby causing a low potential signal to be applied to the input 
terminal PAO of the microcomputer 8. 
In result, when the ultrasonic wave signal receiver 10 receives the 
ultrasonic wave signal having the magnitude above a predetermined value, a 
high potential signal is applied to the input terminal PAO of the 
microcomputer 8 by means of the receiving amplifying means 121 and the 
receiving demodulating means 122. 
The procedure for determining whether the floor to be cleaned is a normal 
floor, a carpet covered floor, or stairs will now be described in 
conjunction with the flowchart of FIG. 6. 
During the travel of the cleaning robot, the microcomputer 8 outputs high 
potential signal at its output terminal PBO, for 0.1 msec, so as to 
transmit an ultrasonic wave signal for 0.1 msec. Subsequently, the 
microcomputer 8 checks continuously whether a high potential signal is 
received in its output terminal PAO, in order to detect the receipt of the 
ultrasonic wave signal. If the receipt of the ultrasonic wave signal is 
detected, the period from the time when the ultrasonic wave signal is 
transmitted to the time when the ultrasonic wave signal is received is 
measured. At this time, if the receipt of ultrasonic wave signal is not 
detected until 2 msec lapses after the transmission of ultrasonic wave 
signal, the ultrasonic wave signal receiving period is regarded as 2 msec. 
From this measured ultrasonic wave signal receiving period, the distance 
from the floor can be calculated. That is, the distance is equal to the 
product of the ultrasonic wave signal receiving period by the acoustic 
velocity/2. 
In the case that the cleaning robot travels on a normal floor as shown in 
FIG. 4A, the ultrasonic wave signal transmitted from the ultrasonic wave 
signal transmitter 9 is directly reflected against the floor which is 
vertically apart 10 cm from the bottom of the cleaning robot and then 
received in the ultrasonic wave signal receiver 10. 
Therefore, the calculated distance will be 10 cm .+-.2 cm, even though a 
maximum tolerance is taken into consideration. 
On the other hand, in the case that the cleaning robot travels on a carpet 
covered floor as shown in FIG. 4B, the ultrasonic wave signal transmitted 
from the ultrasonic wave signal receiver 10. Accordingly, the ultrasonic 
wave signal receiving period is regarded as 2 msec, so that the distance 
is calculated as 34 cm. 
In cases of a very steep surface or carpet covered stairs as shown in FIGS. 
4D and 4E, the results are similar to that of the carpet covered floor. 
In the case that the cleaning robot travels toward stairs as shown in FIG. 
4C, the ultrasonic wave signal transmitted from the ultrasonic wave signal 
transmitter 9 is hardly received in the ultrasonic wave signal receiver 10 
because the stair bottom surface is distantly apart from the bottom of the 
cleaning robot. When the ultrasonic wave signal is hardly received as 
above-mentioned, the distance is calculated as 34 cm. When the ultrasonic 
wave signal is received, the distance from the stair bottom surface is 
measured as the sum of 10 cm+the stair height .+-.2 cm. 
Accordingly, when the measured distance is no more than 12 cm as the 
ultrasonic wave signal is transmitted for 0.1 msec, according to the 
control of the microcomputer 8, the floor to be cleaned is recognized as a 
normal floor shown in FIG. 4A. 
If not the above case, the ultrasonic wave signal is transmitted again for 
1 msec. The distance is then measured again in the above-mentioned manner. 
Even though in the case that the cleaning robot travels on a carpet as 
shown in FIG. 4B, the ultrasonic wave signal is greatly absorbed in the 
carpet, it is received in the ultrasonic wave signal. This is because the 
magnitude of the transmitted ultrasonic wave signal is high, in virtue of 
the transmission of ultrasonic wave signal for a relatively long period, 
that is 1 msec. As a result, the distance from the floor to be cleaned is 
measured as 10 cm.+-.2 cm. 
In the case that the cleaning robot travels toward stairs as shown in FIG. 
4C, the distance from the stair bottom surface is measured as the sum of 
10 cm+the stair height.+-.2 cm. On the other hand, when the cleaning robot 
travels toward a very steep surface or carpet covered stairs as shown in 
FIGS. 4D and 4E, the distance is measured as 34 cm, because the ultrasonic 
wave signal receiver 10 receives no ultrasonic wave signal. 
Therefore, when the measured distance is no more than 12 cm as the 
ultrasonic wave signal is transmitted for 1 msec, according to the control 
of the microcomputer 8, the floor to be cleaned is recognized as a carpet 
covered floor shown in FIG. 4B. If not the above case, the floor to be 
cleaned is determined as stairs or a very steep surface as shown in FIGS. 
4C to 4E, so that the microcomputer 8 recognizes that the cleaner robot 
should travel no longer. 
As apparent from the above description, the present invention enables to 
determine correctly whether the floor to be cleaned is a normal floor, a 
floor covered with a carpet, or stairs. In accordance with the present 
invention, there is any possibility of occurring malfunction due to 
environment. 
Although the preferred embodiments of the invention have been disclosed for 
illustrative purpose, those skilled in the art will appreciated that 
various modifications, additions and substitutions are possible, without 
departing from the scope and spirit of the invention as disclosed in the 
accompanying claims.