Robotic lawn mower

A lawn mower, having an engine for driving the mower itself, is provided with a memory unit of a paper-tape type for storing a route of travel for the mower and an optical reading unit for reading the stored route of travel. The paper tape is operable with a lead wheel which guides the movement of the mower, so that the paper tape is advanced when the lead wheel rotates and the route of travel of the mower is recorded on the paper tape with a writing member when the mower moves. The optical reading unit is installed in place of the writing member for operating the mower automatically. The optical reading unit reads the recorded route of travel and delivers a signal to control the direction of the lead wheel.

BACKGROUND OF THE INVENTION 
This invention generally relates to a lawn mower, more particularly a 
robotic lawn mower that is capable of mowing a lawn by itself after having 
been programmed. 
Although a variety of lawn mowers, are commercially available ranging from 
small, manual types to large, motor-driven mowers, lawn mowing is still 
hard work for many people as all conventional lawn mowers require a person 
to operate and maneuver them. A riding mower provides a convenience in 
that the operator rides on the mower during the lawn mowing; however, the 
operator still has to work with the machine through the entire work 
process. 
Therefore, this invention offers a robotic lawn mower that is capable of 
mowing a lawn by itself, more specifically, capable of being programmed 
and then later repeating the operation by itself according to what has 
been programmed. 
SUMMARY OF THE INVENTION 
This invention presents a robotic lawn mower capable of mowing a lawn by 
itself after having been programmed. The robotic lawn mower of this 
invention is generally provided with a power unit, which may be an 
internal combustion engine or an electric motor, for providing power for 
driving cutting blades and moving the mower. A reduction gear set and a 
driving wheel is provided for propelling the mower. A lead wheel is for 
leading the mower. A control unit is for controlling the movement of the 
mower. The control unit includes a memory unit for memorizing or recording 
a program of the operation. A reading unit is for reading the stored or 
recorded program and a control circuit is for converting the program read 
by the reading unit into an operation signal. A steering unit receives the 
operation signal and operates the lead wheel so as to lead the mower to 
move along a route according to the program. 
In use, the robotic lawn mower of this invention is first guided by man to 
move or travel along a certain route over a lawn to be mowed, so as to 
program the mower on the route it should move along. The route, which 
includes the angles of turns and the length of travel in any given 
direction, is stored or recorded in the memory unit according to the path 
of travel of the lead wheel. For automatic lawn mowing, the mower is moved 
to the starting point to start its own operation, without being maneuvered 
by man, to move along the path or route recorded in the memory device, or 
to follow the program. The same mowing route recorded in the memory unit 
can be used repeatedly for mowing the same lawn. 
In a preferred embodiment the memory unit includes a paper tape, which 
moves while the mower travels, and a writing device having a pen for 
marking on the paper tape the route of travel of the mower in a certain 
scale. The reading unit includes an optical sensor for reading the 
recorded route of travel or programming of the mower and for producing a 
certain signal representing the route of travel, of the operation of the 
mower. The paper tape can be any appropriate sheet material that 
withstands solar heat without substantially deforming, so that the mower 
can operate accurately during the hot summer. 
Therefore it is the main object of the present invention to provide a 
robotic lawn mower capable of mowing a lawn by itself upon being 
programmed.

DETAILED DESCRIPTION OF THE INVENTION 
In FIG. 1 there is shown an embodiment of the robotic lawn mower of this 
invention, which is provided with a power unit 1, a lead wheel 2, a drive 
wheel 3, a control unit 4, safety devices 5 and 6, a reduction gear set 8, 
a casing 9 in which a set of cutting blades (not shown) is disposed, and a 
steering unit 30S. Power unit 1 may be an internal combustion engine 
(hereafter as engine) provided with an alternator and a rechargeable 
battery (not shown), wherein the alternator is mechanically coupled to the 
engine and capable of cranking the engine to start when energized by the 
battery, and also capable of charging the battery when the engine is 
running. A clutch, now shown, is provided to selectively transfer the 
rotary power produced by the engine to reduction gear set 8 which drives 
drive wheel 3 thus causing the entire mower to move forward. The cutting 
blades are also driven by the engine to rotate within casing 9. 
As shown in FIG. 2, control unit 4 includes a memory unit 28 which is 
preferably a paper tape cassette having a paper tape 28A wound around 
first and second reels 28B and 28C, paper tape 28A having a portion 
passing over a flat plate disposed between first and second reels 28B and 
28C. Paper tape 28A is capable of reflecting light. A driving device is 
provided to advance the paper tape 28A when lead wheel 2 rotates. The 
driving device includes first sprocket 22 coaxially fixed onto lead wheel 
2, a second sprocket 24 driven by the first sprocket 22 with a timing belt 
23, a third sprocket 25 coaxially fixed onto the second sprocket 24, and a 
fourth sprocket 26A driven by the third sprocket 25 with another timing 
belt 26B. Fourth sprocket 26A advances and also controls the linear speed 
of paper tape 28A to synchronize the tape 28A with the rotational speed of 
lead wheel 2. Lead wheel 2 is rotatably supported by fork member 27 which 
is journaled onto a frame member 29 on which memory unit 28 is mounted. 
Timing belt 23 is so designed that it is allowed to twist when fork member 
27 is caused to rotate to change the direction of lead wheel 2, without 
affecting the operation of the driving device. 
Memory unit 28 also includes a writing device consisting of an arm member 
30 having a first end fixedly mounted on an upper end of fork member 27 
and a second end provided with a writing element 34, which may be a pen or 
pencil of black or dark color, to write on paper tape 28A. Steering unit 
30S includes a worm wheel 30A fixedly mounted on the upper end of fork 
member 27 and an electric motor 31 provided with worm gear 32 for engaging 
with worm wheel 30A. Steering unit 30S is to operate fork member 27, or to 
steer lead wheel 2 with electric motor 31, which is controlled by a 
circuit 36 to be explained later. Writing element 34 is removably inserted 
into a receptacle 33 provided at the other second end of arm member 30. 
Control unit 4 further includes a reading unit having an optical sensor 35 
adapted to be selectively inserted in receptacle 33 in place of writing 
element 34 of the writing device, and a control circuit 36. Optical sensor 
35 is capable of reading a mark on paper tape 28A to produce a certain 
signal to control circuit 36 which then delivers operational signals to 
electric motor 31 to steer leading wheel 2 accordingly. 
The principles of recording, or the programming process, will be described 
below. 
To carry out the programming process, writing element 34 is first inserted 
in receptacle 33 of arm member 30. Then the engine is started and the 
mower is maneuvered manually to travel along a certain route over the lawn 
to be mowed. While the mower travels, paper tape 28A of memory device 28 
is caused to advance from second reel 28C to first reel 28B, allowing 
writing implement 34 of writing device to draw a line 28G on paper tape 
28A, as shown in FIG. 3. Line 28G shows the mower traveling distance along 
the tape advancement direction, and also shows the lead wheel angle in the 
direction perpendicular to the tape advancement. 
In order to prevent lead wheel 2 from slipping, lead wheel 2 is provided 
with a plurality of stings 21 extending from the periphery of lead wheel 2 
as shown in FIG. 3. 
FIGS. 4 and 5 illustrate an example of the programming process. When the 
mower M, as shown in FIG. 4, moves along a straight course of length L1, a 
corresponding straight line L1 is drawn on the paper tape of the memroy 
device as shown in FIG. 5. When the mower M makes a right turn of an angle 
.theta.R1 and then travels along a second straight course of length L2, a 
corresponding curve .theta.R1 and a second straight line L2 are drawn on 
the paper accordingly. The same principles are followed to complete the 
recording of the intended route of travel of the mower, or the teaching of 
the mowing operation. 
The principles of automatic mowing operation, or "play-back" operation, 
will now be described. 
FIG. 6 shows an electric circuit diagram of the control unit including a 
reading unit 35 and a control circuit 36. Reading unit 35 is an optical 
sensor unit consisting of a light source 41, which may be a lamp or light 
emitting diode (LED), preferably a LED, a first photosensing cell 42 on 
one side of LED 41, and a second photosensing cell 43 on the opposite side 
of LED 41. Control circuit 36 consists of a comparator 44 and an amplifier 
45. 
In operation LED 41 casts light on to an area of the paper tape 28A. First 
photosensing cell 42 is adapted to detect the light reflected from paper 
tape 28A and deliver a first signal to comparator 44 (FIG. 6), while 
second photosensing cell 43 is adapted to detect the light reflected from 
paper tape 28A and deliver a second signal to comparator 44 to be compared 
with the first signal. As line 28G on paper tape 28A absorbs lights, it 
reduces current or voltage output of the photosensing cell closer to line 
28G. The comparator 44 delivers an operation signal depending upon the 
difference between the first and second signals, the operation signal then 
being amplified by amplifier 45 and delivered to electric motor 31. 
When the first signal is identical with the second signal, i.e., when line 
28G is at the center between two photosensing cells 42 and 43, the lights 
received by two photosensing cells are balanced and there is no difference 
between the two signals and thus no operation signal will be delivered 
from comparator 44, as in the case when the reading device is reading a 
straight line from the intended route of travel recorded on paper tape 28A 
of the memory device, and electric motor 31 will not be energized. As a 
result the mower will keep moving along a straight line. 
When one of the first signal and the second signal differs from the other, 
as in the case when the distances of the two photosensing cells 42 and 43 
from line 28G are not equal, an operation signal corresponding to the 
difference between the two distances is produced by comparator 44. The 
operational signal then is amplified and delivered to electric motor 31, 
thus causing electric motor 31 to rotate and drive arm member 30 to move 
the two photosensing cells, so as to cause the two photosensing cells to 
deliver equal outputs again. At the same time the movement of arm member 
30 also causes fork member 27 to rotate to steer lead wheel 2 to make a 
turn in the corresponding direction. 
The operation of the reading unit, or optical sensor 35, in association 
with the steering device will be described in more detail with reference 
to FIGS. 8-13. 
As shown in FIG. 8, when optical sensor 35 is reading a straight line L1 of 
the intended course recorded on paper tape 28A which moves in direction A 
relative to optical sensor 35, signals produced by first and second 
photosensing cells 42 and 43 are identical and no operation signals will 
be delivered to electric motor 31 (FIGS. 3 and 6); therefore lead wheel 2 
remains in a straight-forward position. As shown in FIG. 9, as the mower 
travels to a point where the program shows that the mower should make a 
left turn, for example, paper tape 28A moves to such point that first 
photosensing cell 42 starts reading curve R of the route recorded on paper 
tape 28A, thereby causing first photosensing cell 42 to produce a signal 
different from that of second photosensing cell 43. As a result an 
operation signal is delivered from control circuit 36 (FIGS. 2 and 6) to 
electric motor 31, causing electric motor 31 to rotate in such a direction 
that lead wheel 2 is turned left, or in direction X, as shown in FIGS. 9 
and 10. Arm member 30 (FIG. 3), which carries optical sensor 35, is also 
rotated together to shift the position of optical sensor 35 to follow line 
28G. As shown in FIG. 11, two photosensing cells 42 and 43 trace line 28G 
to balance with each other, and the angle .alpha. of lead wheel 2 is 
determined. In the meantime the mower keeps making the left turn. As shown 
in FIG. 12, as the mower keeps moving, paper tape 28A keep moving in 
direction A relative to optical sensor 35. Now line 28G leans more to 
second photosensing cell 43. That causes second photosensing cell 43 to 
produce less output than first photosensing cell 42. The difference 
between the outputs from the two photosensing cells causes control circuit 
36 (FIG. 5) to deliver a new operational signal to electric motor 31 to 
cause electric motor 31 to rotate in an opposite direction. As a result 
lead wheel 2 is caused to turn in a reversed direction, or to make a 
"return". As shown in FIG. 13, as soon as lead wheel 2 returns to the 
original straight forward position, arm member 30 (FIG. 3), which carries 
optical sensor 35, also returns to its original position, as the mower has 
completed its turning operation and continues to move straight forward. 
To prevent any accident from occurring, which might involve children 
playing, moving subjects, or standing obstacles, the robotic lawn mower of 
this invention is equipped with safety devices, as shown in FIG. 1 and 
FIG. 2, including a bumper member 5 which is very similar to most 
automatic guided vehicle applications, and an elongated bar member 6 which 
is like a rod antenna. Both provide a switching means for emergency 
shutting-off of the ignition system of the engine. They also activate a 
brake to stop the operation of the machine, and generate a sound alarm and 
a warning light to call for help. The mower will not start again until the 
object is removed and the mower manually reinitialized. The rod antenna 
type safety device is very useful in limiting the accessible area of the 
robotic mower. Some lawns may lie right on a busy street and may not have 
fences separating the lawns and the street. A wire or a rope temporarily 
set up along the lawn boundary could prevent the robotic mower from 
erroneously running into the street as shown in FIG. 14. With the 
combination of the bumper and the antenna safety devices, the robotic 
mower can be operated safely without human attendance. 
One of the most difficult problems for the robotic mower, a problem similar 
to the development of automated guided vehicles, is the tracking 
problem--following the prescribed path. Error is mainly caused by slippage 
between the wheel and the ground. The robotic mower of this invention has 
a unique wheel system arrangement. The lead wheel 2 and the rear wheel 3 
have a sting ring as shown in FIGS. 1, 2 and 3. The sting can be engaged 
into the ground. This limits the wheel movement to only one degree of 
freedom, i.e., either rolling forward or rolling backward without 
slippage. The sting ring also helps healthy grass growth. 
Rear wheel 3 is the drive wheel. It is powered by the engine (or motor) 
through a transmission box with suitable speed reduction and directional 
adjustment. The sting annulus can help the tracking and reduce slippage 
and power loss. 
Front wheel 2 is the driven wheel, which rotates passively as the mower 
moves forward. The rotation of the front wheel causes the advance of the 
paper tape through the timing belts. The front wheel is also a steering 
wheel, through the swing angle to set the turning of the mower. The sting 
annulus on front wheel 2 not only helps to hold better on the ground, but 
also accurately controls the advancement of the recording tape. 
Both front wheel 2 and rear wheel 3 assume the majority of weight of the 
lawn mower. The course of the mower movement is determined by the distance 
between these two wheels and their relative angle. 
The robotic lawn mower can have either one or two side wheels. In the case 
of two side wheels, the four wheels of the mower are located at the 
corners of a rhomb as shown in FIG. 1. The side wheels are spring 
supported for self height adjustment so that the front wheel and the rear 
wheel are always in contact with the ground and assume the majority of the 
load. In the case of one side wheel, the mower is stable and less affected 
by the flatness of the lawn surface because of the advantage of a three 
point setting in a plane in geometry. 
The side wheel is an idle wheel, mainly for balancing the mower and 
assuming some load. It does not matter whether it has sting annulus on it 
because it is not concerned with slippage. While operating, no matter 
whether the mower goes straight or makes turns, the front wheel and rear 
wheel are expected to always rotate at the same speed. However the speed 
of the side wheel is self adjustable, depending on the radius difference 
of the turn. 
The wheel design with sting, the functional assignment of each wheel, and 
the geometrical layout of the wheels make this wheel system very special 
and provide unbeatable tracking capability over other available 
arrangements. 
The robotic lawn mower of this invention can also be operated manually, as 
described below. 
The manual operation of this automatic lawn mower is different from 
operating a push/walk-behind lawn mower or a riding mower (tractor). The 
maneuverability of the mower is controlled by a hand unit for programming 
and for manual control. The hand unit may have push button switches to 
control two motors (D.C. streeting Motor 31 and engine starting motor), 
the clutch, and emergency stop devices through a multiple wire cable or by 
radio signals. Thus the operator does not need to follow and push the 
mower as most walk behind type mowers, neither does the operator need to 
turn the steering wheel as in the case of riding mowers. The operator can 
precede, walk behind, or stand on the side of the mower as desired. After 
the mower starts and moves forward, the operator pushes the appropriate 
button on the hand unit to control the rotational direction of steering 
motor 31. Motor 31 then makes fork member 27 swing through worm 32 and 
gear segment 30A on arm member 30. Front wheel 2 on fork member 27 thus 
turns at an angle to lead the mower to make turns. In this way the mower 
can be manipulated to run all over the lawn to be mowed. As the mower 
moves forward, making left or right turns on the lawn, high grass is cut 
to an uniform height by rotating cutting blades 7 under the mower chasis. 
The principles of automatic operations of the robotic lawn mower of this 
invention are further emphasized as follows. 
The automatic lawn mower of this invention can be programmed to follow a 
mowing path. The programming process is for the mower to store the mowing 
path. It is similar to the manual operation described in the previous 
paragraph except that a blank memory tape cassette 28 and writing elements 
34 are mounted in place before starting the mower. As in manual 
operations, front wheel 2 rotates passively as rear wheel 3 drives the 
mower. This rotation motion is transmitted to the tape advancement through 
two timing belts 23, 26 and four sprockets 22, 24, 25 and 26. The linear 
speed of paper tape 28A is thus proportional to the linear travel of front 
wheel 2. Writing element 34 is inserted in receptacle 33 on arm member 30 
during the programming process; it can move in the transverse direction of 
memory tape 28A advancement as arm member 30 swings when front wheel 2 
rotates at an angle to make a turn. Writing element 34 therefore makes 
markings of a line or a continuous curve on a paper tape 28A. This line or 
curve indicates the travel of front wheel 2 in the direction of the tape 
advancement, and indicates the angle of front wheel 2 in the transverse 
direction. 
Using the hand unit, the operator controls the mower to move all over the 
lawn during this process, the traveling distance and turning angles are 
recorded as a continuous curve on the memory tape 28A, i.e., the history 
of the mowing path in the memory of the automatic lawn mower. 
The programming process is for mowing the lawn manually for the first time 
with writing element 34 and memory tape 28A working inside the mower. 
After rewinding the memory tape, the programming process is completed. 
Automatic lawn mowing is a repeat of manual mowing operation in the 
programming process. Writing element 34 used in the programming process is 
replaced by a reading unit (Optical sensor) 35 in the automatic mode 
operation. With the same initial setup (position & direction) as in the 
programming process, the mower of this invention is started and moves 
forward. As the mower moves forward and cuts the grass, memory tape 28A is 
driven forward through the relationship of front wheel rotation, timing 
belt and driving mechanism. Reading element 35 (optical sensor) has the 
capability to trace curve 28G on memory tape 28. This is done because the 
control circuit drives steering motor 31 to swing arm member 30 where the 
optical sensors seat. Any deviation of the sensor scanning area from line 
28G will result in elecrical voltage for motor 31 driving arm member 30 
back to follow pre-recorded line 28G. Note that front wheel 2 is steered 
with arm member 30 as an integral part. That means the swing angle of the 
front wheel is controlled by the pre-recorded curve. The mower repeats the 
pre-programmed route after a series of instructions: how long to travel 
and what angle to turn,--etc.; and finally mows over the entire lawn area. 
During the automatic mowing process, attendence by an operator is not 
required. The safety devices will stop the running of the mower and signal 
the operator for help in case something happens. 
In conclusion, the robotic lawn mower of this invention, of which the 
entire concept is shown in the block diagram in FIG. 15, consists of an 
internal combustion engine as a power unit which drives a mowing cutter 
and the mower itself through a reduction gear set and a drive wheel, an 
alternator to be used as a generator and as a starting motor, a storage 
battery, a lead wheel for guiding the movement of the mower; a control 
unit for controlling the movement of the mower, the control unit including 
a paper tape device operable in association with the lead wheel, a writing 
member for recording a teaching on the paper tape device, an optical 
reading unit for reading the teaching i.e., the recording from the paper 
tape device, a comparator-amplifier unit for producing an operation signal 
in response to the reading of the optical reading unit, an electric motor 
operable by the operation signals for controlling the steering angle of 
the lead wheel, a worm gear and worm wheel set for transferring the power 
from the electric motor to the lead wheel to cause the lead wheel to 
change its steering angle. 
While a preferred embodiment of the robotic lawn mower of this invention 
has been described and illustrated, it is to be understood that certain 
modifications are possible by persons skilled in the art without departing 
from the principles of this invention. For example, the timing belts can 
be replaced by chains, and the arm member that carries the writing device 
or the reading unit can be coupled to the fork member with an appropriate 
gear trains or the like. Therefore, the scope and spirit of this invention 
are to be defined by the appended claims.