CA1217836A

CA1217836A - Control system for mobile robot

Info

Publication number: CA1217836A
Application number: CA000445143A
Authority: CA
Inventors: Katsuji Okumura
Original assignee: Katsuji Okumura; Automax Kabushiki-Kaisha
Current assignee: Automax Co Ltd
Priority date: 1983-10-26
Filing date: 1984-01-12
Publication date: 1987-02-10
Also published as: EP0142594B1; US4674048A; EP0142594A1; DE3478824D1

Abstract

ABSTRACT OF THE DISCLOSURE:

A control system for a mobile robot includes an operation unit for calculating an instantaneous position of the robot, a storage unit for sequentially storing data representative of the respective robot positions, a device for studying and storing a range to be travelled by the robot, and a device for calculating a running pattern of the robot in the specific range. The robot is allowed to travel throughly in the range without leaving any region non-travelled, while checking its own position.

Description

~he present invention relates to a control system for an unmanned, mobile robot ~hlch has drlve wheels to be capable of automatically travelllng alony a predetermined path.
A mobile robot designed for unmanned ~novement is sometimes used for cleaning the floors of buildinys.
Such a robot may be e~uipped with a vacuum cleaner and/or sweepers to clean a range of a floor which it travels.
Prior art system proposed for controlling the travel of the mobile robot includes one which lays guide cables along a predetermined path of travel of the robot so as to generate an electromagnetic wave. The robot will be guided by the cables while sensing the magnetic field by means of a sen-sor. Another prior art control system uses optical marks or tapes which are located along the path of travel so that the robot may follow the path sensing the marks or tapes.
The prior art control systems described so far commonly achieve unmanned robot movement along a predeter-mined pattern by means of guide means in one form or another.
~ problem encountered with such guide means type systems is that troublesome work is required for setting and changing a running pattern. Another problem is that the installation of such guide means on floors is undesirable for some kind of buildings. Additionally, where an obstruction is posi-tioned in a predetermined path, the robot cannot travel any further unless it is removed.
Also known in the art is a control system which loads an operation control circuitry of a mobile robot with a program, so that the robot may be automatically steered based on the program. ~his suffers from the drawback that the program has to be changed every time the dimensions and configuration of the floor to be swept are changed. Gener-ally, various e~uipments and fixtures are arranged in a room of a building which constitute obstructions to the ~ y ~

travel of the robot. Therefore, the program hAs to be designed in due consideration of such obstructions resulting in prohibitive amo~nts of time and labor required therefor.
. Furthermore, all the prior art control systems described above share a disadvantage that they lack a func-tion which allows a robot to judge the surrounding condi-tions and, therefore, the robot canno-t take an adequate measure against a change occurring therein.
It is therefore an object of the present inven-tion to provide a control system for a mobile robot which makes it.possible for the robot to study and store a range which it is to move, and, during a travel, employs its own decision while determining a travel pattern in the specific range in response to varying conditions.
It is another object of the.present invention to provide a control system for a mobile robot which allows the robot to travel in a range assigned thereto without hitting against possible obstructions and throughly in the rest of the specific range.
It is another object of the present invention to provide a generally improved control system for a mobile robot.
More particularly, according to the present invention, there is provided a.control system for a mobile robot for causing the robot to automatically run along a predetermined path, in a selected direction, and at a selected speed by controlling rotations of right and left drive wheels thereof i.ndependently o each other, this con-trol system comprising:
position identification means or sensing adistance travelled by the robot and a change in a direction of travel of the robot, calculating a position of the robot in two-dimensional coordinates in response to the sensed . -- 2 distance and the sensed change in direction, and generating a position signal representative oE the robot position;
obstruction sensor means for sensing an obstruc-tion -to generate an obstruction signal, said obstruction sensor means bein~ mounted on a Eront end and both sides of the robot with respect to an intended direction of travel of the robot;
storage means for storing a map consisting of a number of unit blocks which are defined by parallel columns and parallel rows in the two-dimensional coordinates;
teaching means for causing the robot to make a round along a boundary of a range to be travelled by the robot, so that this range is stored in the map of the storage means in response to the position signal generated by the position identification means;
first operation means ~or causing the robot to sequentially move back and forth along one of the columns and rows of the map in the range stored in the map, while sequentially shifting the robot to one of the subsequent columns and the subsequent rows;
second operation means for shifting the robot to one of ~he next column and the next row in response to detection of an obstruction by turning the robot at a posi-.5 tion where the obstruction is sensed;
non-travelled region disc~iminating means for discriminating a non-travelled region by reading out a travelled region out of the storage means and comparing the travelled region with the range to be travelled;
third operation means for returning the robot to a non-travelled region to cause the robot to resume reciprocation when the non-travelled region is present on an extension of a travelled column, at one of an instant when an obstruction ahead the robot disappears and an : - 3 -~'7`.~

instant when the travel of the robot in the ranye to be travelled is completed; an~
end-of~travel discriminating means for di~crimi~
natiny completion of the tra~el when a non~travelled reyion is eliminated in the ranye to be travelled except for an obstruction.
The above and other objects, features and advantages of the present,invention will become more apparent rom the following detailed description of pre~
ferred embodiments thereof taken in conjunction with the accompanying drawings in which:
Fig. 1 is a block diagram of a robot control system embodying the present invention;
Fig. 2 is a schematic plan view of a robot body in accordance with the present invention;
Fig. 3 is a diagram showiny a first example of running patterns of the robot in accordance with the pre-sent invention;
Fig. 4 is a flowchart demonstrating a control for effecting the run shown in Fig. 3;
Fig. 5 is a diagram showing a second example of the xobot running patterns;
Fig. 6 is a flowchart demonstrating a control for effecting the run shown in Fig. 5;
Fig. 7, which is, disposed on the same sheet of formal drawings as Figure 2, is a diagram explanatory,of a deviation of the robot from a predetermined straight path;
Fig. 8 is.a flowchart representing a control for compensating for the deviation shown in Fig. 7; and Fig. g is a diagram showing an example of a self-teaching travel of the robot.
While the control system for a mobile robot of the present invention is susceptible of numerous physical embodiments, depending upon the environment and requiremen-ts ~ 4 --~LZ~L!' ,' ~33~, of use, a substantial numbe~ o the herein shown and described embodiments have been made, tested and used, and all have p~rformed in an eminently satisf~ctor~ manner.
Referrin~ to Fig. l oE the drawiny, a distance sensor Eor producin~ a pulse signal which is proportional to a distance travelled by the mobile robot, e.~. number of rotations of drive wheels. A direction sensor 2, such as a gas rate yyro, is sensitive to a change in the travelling direction of the robot. The pulse signal,out put from the distance sensor l and the output of the direction sensor are supplied to position identification means 3. The position identification means 3 is con-structed to measure a distance travelled by the robot by counting incoming pulses from the distance sensor 1 and to identify a moving direction of the robot from the out-put of the direction sensor 2, thereby identi~ying by operation instantaneous positions of the robot in two-dimensional coordinates for each unit travel distance.
Obstruction sensors 4 are mounted on the front, opposite sides and back of the robot with respect to a direction of movement of the robot. Each of the obstruction sensors 4 is adapted to sense a wall, column or like obstruction and a distance to the obstruction by emitting a supersonic wave and receiving the reflection. Also mounted on the robo-t are touch sensors 5 which locate obstructions by mechanical contact therewith, independently of the obstruction sensors 4. The outputs of the sensors 4 and 5 are routed via an amplifier 7 and an input/output (I/O) port 8D to a control circuit 6, which comprises a microprocessor. Also, the output of the positior. identification means 3 is applied to the control circuit 6 via an I/O port 8A.
The control circuit 6 comprises a central opera-tional circuitry (CPU) 9, and a storage 10 made up of a read only memory (ROM) and a random access memory (RAM).

~2~

The control circuit 6 fur-ther comp~ises an oscillator llA
for generating clock p~llses, and an interrupt controller llB. As will be described, the CPU 9 delivers a drive signal to a drive circuit 12 via an I/O port 8C in order -ko reversibly control the rotation of drive motors (servo mokors or steppiny motors) 13 and 14, which are respec-tively associated with right and left drive wheels of therobot. At the same time, the control 6 controls the rota-tion of a drive motor 15 for cleaning sweepers which are mounted on the robot. A control console 16 is accessible -for selectively turning on and off a system power source, switching a running mode, setting a start position, adjust-in~ a sensitivity of the direction sensor 2, etc. In order to teach the robot a boundary of a travel range assigned thereto, a command ma~ be applied to the drive 12 by interruption with priority on a radio control basis. This is effected by a remotecontrol transmit unit 17 and a receive unit 18. The ou-tputs of the control console 16 and remotecontrol receive unit 18 are routed also to the con-trol circuit 6 via an I/O port 8B.
Referring to Fig. 2, a practical construction ofthe mobile robot is shown in a schamatic plan view. As shown, the robot comprises a body 30 which is substantially entirely surrounded by a front bumper 31, side bumpers 32 and 33, ~nd a rear bumper 34, each carrying the touch sensor 5 therewith. An obstruction is sensed by the con-tact of any one of the bumpers 31-34 therewith. The obstruction sensors 4 comprise, in Fi~. 2, supersonic wave sensors 4A mounted in the central and opposite corners of the front end of the robot body 30, supersonic wave sensors 4B on opposite sides, and supersonic wave sensors 4C at opposite sides, and supersonic wave sensors 4C at opposite corners of the rear end. All the supersonic wave sensors 4A, 4B and 4C operate in the manner previously described.

~2~

Usually, the supersonic wa~e sensors ~A and ~C
are capab]e of sensing obstructions be-fore -the touch sensors 5 come into contac-t therewith~ When obs~ructions exist in the dead angles of the sensors ~A ancl 4C due -to an orientation oE the robot~ the touch sensors 5 will sense them only i~ the bumpers 3~-34 lightly touch them. In this particular embodiment, the robot body 30 is freely movable on a floor by means of a front wheel ~0 and a pair of rear wheels 41 and 42~ which are the drive wheels. While the robot travels on a floor, two rotary sweepers 43 and 44 mounted on the front underside of the body 30 clean the floor.
In conjunction with a robot having the above construction, characteristic part of the present invention will be further described with reEerence to Figs. 3 and 4.
Assume a range shown in Fig. 3 which the robot is to sweep. First, the control console 16 of the robot is manipulated to set up a teaching mode and, then, the robot is led to a start position (S) shown in Fi~. 3 by use of the remotecontrol transmit unit 17 and receive unit 18. At the start position, a set button in the control console 16 is depressed to set a start point (xO, yO) in the two-dimensional coordinates and a reference ~0 of travelling directions.
As the teaching or the robot along a predeter-mined course is started as indicated by a dotted line in Fig. 3 by means of the transmit unit 17 and receive unit 18, the CPU 9 of the control circuit 6 se~uentially stores in the storage 10 instantaneous positions (x, y) and travelling directions 3 of the robot which are supplied thereto from the position identiication means 31 whereby the robot studies the boundary of the expected range of movement.
After the travel of the robot along the teaching course, the boundary is stored in a map in the two-dimensional 7~3~

coordinates and in the form of blocks which are divided at each unit distance along the x- and y-axes. Next, the robot is brou~hk to the start point or to a point A adja-cent to the start poink and, -~hen, the control console 1~
is operated -to switch the operation mode from the teaching mode to an unmanned running mode. This causes the control circuit 6 to deliver a drive signal to the drive 12 so that the robot begins an automatic run.
The automatic run of the robot is effected as follows controlled by the CPU g.
Initially, the robot advances straight ahead over the blocks in a column which extends along the y-axis in the map. At this instant, the blocks which -the robot has travelled are sequentially stored in the storage 10.
As soon as the robot reaches the boundary which is identi-fied by the position identification means 3, it is turned le~twardly from that position toward a non-travelled column of blocks (extending along the y-axis). While the robot moves the new column of blocks, the supersonic wave sensors 4B on the sides of the robot continuously watch the neigh-borhood to see if any obstruction is present at -the righ-t or left of the running column. If any obstruction is present, it is stored in the storage 10 and, if not, -the blocks are stored as clear blocks in the storage 10. The straight run is sequentially repeated thereafter so that the travelled blocks increase in number one column at a time and, at the same time, the clear blocks stored in the storage 10 are successively erase~. When the sensor 4A at the front end of the robot senses an obstruction ahead at a point F, the robot is turned toward the next non-travelled column of blocks as when the boundary is identified. Simul-taneously, the block in which the sensox 4A has sensed the obstruction is stored in the storage 10.
In the manner described, the robot moves back ~ ~tl~' 3~i and ~orth between the obstruckion and the boundary ~1hile sensing the obstruction and without hittiny thcreayainst.
When the robot comes to find no obstruction ahead, it drives Eorward along the column until the boun~ary is identified. As soon as the robot runs past the adjacent wall of the obstruction, it finds clear blocks at opposite sides -thereof. This time, the robot is caused to turn in the opposite direction after reaching the boundary, thereby running in a non travelled region of the floor at the rear of the obstruction. The point B at which the robot has turned this time is stored in the storage 10 in prepara-tion for a return to the original position as will be described. ~he robot se~uentially sweeps the non-travelled region in the manner described, repeatedly turning in the direction of the columns. At a point C, the robot identifies that a travelled block is present in the direc-tion of the next turn. Then, the robot decides that it has fully covered the non~travelled region, returns straight to the point B along the transverse train or row of blocks, and then starts another run along the columns from a point D which is in a block next to the block B.
When the robot reaches a point G after the procedure described above, it ends the movement determining that no region in the taught range of movement is left unswept. To see if any range is left unswept, the robot compares the travelled region and the obstruction region stored in the storage 10~
In the illustrative embodiment described above, if any area is left unswept in the columns which the robot has travelled, the robot immediately turns to the unswept area as soon as an obstruction is cleared. Alternatively, the robot may be programmed to move to the unswept area after completing the travel throughout the region inside the boundary. In any case, the sweepers 43 and 44 are ~ ~ ~'J~

rotated during the travel of the robot to e~fectivel~
clean all over the predetermined ranye of -the ~loor The operation of the robot control systern in accordance with the present invention will be ~urther discussed in conjunction with the pattern shown in Fig. 5.
The operation for the alternative sweepiny pattern starts with teaching the robot a predetermined range of travel (surrounded by a dotted line in Fig. 5). Thereafter, the robot is returned to a start point S to begin an automatic run. While repeating reciprocal movement in the manner described, the robot senses a first obstruction (l) at a point H so that i-t sequentially shifts to the -following columns turning at the point H. As the robot further advances column by column until sensing a pro~ecting wall as illustrated, it stores the specific column at a point J
and then repeatedly moves back and forth along the successive columns. Ater sensing a second obstruction

(2), the robot runs back and forth down to a point K
avoiding the obstruction (2), as has been the case with the pattern shown in Fig. 3. From the point K, the robot returns to the point J in the stored specific column traversing the swept columns. At the point J, the robot is redirected to follow the boundary of the predetermined range. As soon as the robot clears the protruding wall, it steers itself into a column which is the extension of the column with the point J, and then resumes a straight travel. At this instant, the robot advances into a new non travelled area updating (clearing) -the stored column.
At a point L, the robot enters an area at the back of the obstruction (l) which has been left unswept. Thereafter, the robot shifts from a point M back to the point L across the swept columns so as to start a reciprocal movement again. At a point N, the robot completes the whole movement determini.ng that it has throughly swept the taught range oE

~2~

movement.
Now, while automatically runniny in the manner described, the robot may become dislocated Erom a pre-determined or reference path as shown in Fiy. 7 due to s.lippage of the drlve wheels 41 and 42, errors in the operation of the motors 13 and 14, etc. In accordance with the present invention, the deviation of the actual path of travel from the reference path is compensated for by the following control.
A routine for the control is shown in Fig. 8 and will hereinafter be discussed with reference to Fig. 7 as well.
As shown in Fi~. 7, assume that the robot is deviated to the right from the reference path by a distance d with respect to the travelling direction of the robot, and that it is misoriented by an angle ~ relative to the reference path. Then, that the deviation of the robot is to the right of the reference path is determined. Also, whether the sign of d + tan ~ is positive or negative is determined by operation. Let it be assumed that d + tan is either d + tan 0 ~ 0 or d + tan ~ < 0.
In the first-mentioned condition, d + tan ~ > 0, the distance d is large, or the angle ~ is relatively small, or the orientation of the robot lies in the positive angular range. Then, the rotation speed V of the left drive wheel is controlled to be V = V0 - (d + tan ~) ~where the minimum value of V is assumed to be V0), while the rotation speed of the right drive wheel is kept at V0, whereby the robot is caused to make a leftward turn or rotate leftwardly abo~.t an axis thereof.
The other condition, d + tan ~ < 0 represents a situation in which the angle ~ is negative and the robo~
is directed toward the path at a large angle. In this case, while the rotation of the left drive wheel is maintained the same, the rotation speed.V of the right drive wheel is controlled to be V - ~0 -~ (d -~ tan 0), thereby -turniny or rotating the robot to the right.
In this manner, the actual p~th of the robot :is c.ontrolled ~o the reference path if dislocated there~rom, that is, the position of the robot.is corrected.
The compensation effected for rightward deviation of the actual robo-t path from.the reference path as described similarly applies to leftward deviation of the robot, except for the reversal o angles and that of -the control over the right and left drive wheels.
Due to the use of a tan function as a compensa-tion term for the angle ~, so long as MAX in the relation -~X < tan 3 < MAX is sufficiently large, there exis-t a position and an angle where a + tan ~ = 0 holds, even if the deviation d from the path is substan-tial. At such a specific point, the right and left drive wheels of the robot are equal in velocity and they approach the path at an angle to the path which becomes closer to the right 20 angle as the distance d.increases and decreases with the decrease in the distance d. Stated another way, the orientation of the robot is.compensated sharply when the distance d is large and the compensation is slowed down as the distance d becomes smaller. This insures smooth compen-sation of the orientation of the robot without huntlng orthe like due to excessive controls during -the compensation.
If desired, the term d may be multiplied by a positive constant ~ and the term tan ~ by a positive constant ~ so that any desired path compensation characteristic is established up to the point where ~d + ~tan ~ = 0 holds, that is, the point where the robot advances straight with the right and left drive wheels running at an equal speedO
Teaching the robot a desired range oE movement may be impl.emented by the supersonic wave sensors 4A, 4B and 4C and the touch sensors 5 which are mounted on the robot itself/ instead of the remotecontrol transmit and receive units. So~le of the supersonic wave sensors ~A, 4B and 4C are capable of identif~ing short and mediu~n ~anges and the others, long ranges. Such self~tea~hlny with the various sensors is optimum for cleaniny, ~or example, the floor of a room which is surrounded b~ walls;
the robot will make one round automatically along the walls of the room by sensing the walls with the sensors.
An example o~ the travelling pattern along walls is shown in Fig. 9. ~uring the straight travel from a point a to a point b, the robot is controlled on the basis of outputs of the medium range sensors S2 and S3. When the robot is too close to the wall, the rotation of the drive wheel remote from the wall is decelerated or stopped to correct the orientation of the robot away from the wall.
As the outputs of the two medium range sensors S2 and S3 coincide with each other, the robot is allowed to run straight without any further compensation. If the robot is positioned too far from the wall, the output of either one of the medium range sensors S2 and S3 will disappear to cause the control circuit to decelerate or stop the move-ment of the drive wheel closer to the wall, thereby bringing the robot c],oser to the wall.
As the robot reaches the point b where the front sensor Sl senses the wall ahead, it once stops i-ts movement and then moves backward a predetermined distance. Then, the robot rotates clockwise as viewed in Fig. 9 over a predeter~ined angle ~ (with the right drive wheel stopped and the left drive wheel rotated for a predetermined period of time?, thereafter resuming the straight run. ~hen the front sensor Sl is turned on again, the above procedure is repeated to further rotate the robot so that, eventually, the robot a-ttains a position parallel to the wall. There-7~3~

ater, the robot runs straight from the point b to the next point c.
As the robot moves past the point c, the medium range sensors S2 and S3 no longer sense the wall while only the long range sensor S~ senses it. Hence, the robot is.caused to rota~e counterclockwise at that.point as viewed in Fig. 9. As soon as the medium ranye sensors S2 and S3 come to sense the wall.again, the robot is allowed to run a straight path along the.wall.
While the robot in Fig. 9 is assumed to travel along walls which are commonly located to the left thereof with respect to the direction of travel, the same control applies to the case wherein the walls are located to the right o~ the robot, except for the reversal of the rotating directions of the robot.
Various modifications will become possible for those skilled in the art after receiving-the teachings of the present disclosure without departing from the scope thereof.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A control system for a mobile robot for causing the robot to automatically run along a predeter-mined path, in a selected direction, and at a selected speed by controlling rotations of right and left drive wheels thereof independently of each other, said control system comprising:
position identification means for sensing a distance travelled by the robot and a change in a direc-tion of travel of the robot, calculating a position of the robot in two-dimensional coordinates in response to the sensed distance and the sensed change in the direction, and generating a position signal representative of said robot position;
obstruction sensor means for sensing an obstruc-tion to generate an obstruction signal, said obstruction sensor means being mounted on a front end and both sides of the robot with respect to an intended direction of travel of the robot;
storage means for storing a map consisting of a number of unit blocks which are defined by parallel columns and parallel rows in the two-dimensional coordinates;
teaching means for causing the robot to make a round along a boundary of a range to be travelled by the robot, so that said range is stored in the map of the storage means in response to the position signal generated by the position identification means;
first operation means for causing the robot to sequentially move back and forth along one of the columns and rows of the map in the range stored in the map, while sequentially shifting the robot to one of the subsequent columns and the subsequent rows;

second operation means for shifting the robot to one of the next column and the next row in response to detection of an obstruction by turning the robot at a posi-tion where the obstruction is sensed;
non-travelled region discriminating means for discriminating a non-travelled region by reading out a travelled region out of the storage means and comparing the travelled region with the range to be travelled;
third operation means for returning the robot to a non-travelled region to cause the robot to resume reciprocation when the non-travelled region is present on an extension of a travelled column, at one of an instant when an obstruction ahead the robot disappears and an instant when the travel of the robot in the range to be travelled is completed; and end-of-travel discriminating means for discrimi-nating completion of the travel when a non-travelled region is eliminated in the range to be travelled except for an obstruction.

2. A control system as claimed in claim 1, further comprising radio control means for driving the robot by remote control, the teaching means being con-structed to cause the robot to travel along a boundary of the range to be travelled by the robot in response to manipulation through the radio control means.

3. A control system as claimed in claim 1, in which the teaching means is constructed to cause the robot to automatically travel a range which is entirely sur-rounded by walls along said walls and at a predetermined spacing from the walls, in response to the obstruction signal from the obstruction sensing means.

4. A control system as claimed in claim 1, further comprising;

means for determining whether the robot is deviated to the right or to the left from the predeter-mined path;
means for determining whether d + tan .theta. is positive or negative, where d is a deviation of the robot from the predetermined path, and .theta. is an angular differ-ence of a travelling direction of the robot from a direc-tion of the predetermined path; and means for controlling one of the right and left drive wheels to move at a rotation speed V = V0 - (d +
tan .theta.) when d + tan .theta. ? 0 and the other of the right and left drive wheels when d + tan .theta. < 0, where V0 is a reference rotation speed.