Method for docking an autonomous mobile unit with the use of a light beam

The invention includes a method for docking autonomous mobile units. Travel maneuvers are specified with which constricted space conditions can be taken into consideration. Further, different motion paths are recited that are to be sequentially traversed in order to locate a guide beam and in order to be able to dock reliably and dependably at a docking device. Preferably, a slot-shaped guide beam residing perpendicular to a travel surface of the unit is provided, and position-sensitive detectors for this guide beam are present on the unit, these being arranged parallel to the travel surface of the unit. The exact rotation (beta) of the unit relative to the docking device can be identified on the basis of the guide beam and the detectors, whereby the unit knows its approximate configuration in the space on the basis of ultrasound and odometry measurements. The invention can particularly be utilized in household robots or industrial robots.

BACKGROUND OF THE INVENTION
 The invention is directed to a method with which autonomous mobile units
 can be brought into a parked position.
 Autonomous mobile units can, for example, be employed in office, hospital
 or industrial environments in order to carry out simple tasks such as, for
 example, transport, remote manipulation or cleaning jobs. Upon utilization
 of such autonomous mobile robots, for example, it is desirable that these
 can dock precisely in order, for example, to be able to accept or hand
 over goods in a docking station, change a battery or, for example, replace
 the cleaning device in a cleaning machine. Another docking case can occur
 when the autonomous mobile unit is to travel into a garage in which it
 waits until further activity requests are made of it. During this waiting
 time, for example, an accumulator that is provided in the autonomous
 mobile unit can be charged or a self-diagnosis of the device can be
 undertaken.
 One problem that occurs when docking such units is comprised therein that
 the device must be brought from an arbitrary starting configuration into a
 fully defined final position. Known autonomous mobile units as disclosed,
 for example, by German Patent P 44 21 805 orient themselves with
 ultrasound sensors and on the basis of odometry measurements that are
 undertaken at a wheel of the unit. While the device is travelling from a
 starting point to a destination point, the configuration errors produced
 by the sensor imprecisions in the odometry measurement and in the
 ultrasound distance measurement sum up, so that an exact orientation is
 soon no longer possible when no counter-measures are undertaken. In said
 patent, counter-measures are undertaken in such a form that different
 activities that the autonomous mobile unit is to perform are evaluated and
 the configuration errors are thereby monitored. Correction measures are
 initiated when too great an error occurs.
 Another problem is comprised therein that the autonomous mobile unit should
 preferably dock in a docking station in a well-defined rotational
 orientation and with a very specific outside at the docking station. As a
 rule, however, such autonomous mobile units comprise a three-wheel
 kinematics which does not enable them to move arbitrarily on the ground.
 The three-wheel kinematics of autonomous mobile units is discussed, for
 example, in German Patent 195 21 358. The slippage that sums up over a
 planned travel path of such an autonomous mobile unit is thus determined
 therein.
 SUMMARY OF THE INVENTION
 The problem underlying the invention is thus comprised in specifying a
 method with which an autonomous mobile unit can be brought into a defined
 final position in a docking station.
 This and other problems are solved with a method for docking positioning of
 an autonomous mobile unit at a docking device using a guide beam including
 the first step of prescribing destination coordinates and a rotated
 attitude of the docking device in a world coordinate system at
 commencement of travel of the autonomous mobile unit thereby affording the
 autonomous mobile unit information concerning alignment with the guide
 beam and position and rotated attitude of the autonomous mobile unit.
 Next, self-orienting of the autonomous mobile unit is performed in
 surroundings of the autonomous mobile unit using at least one distance
 measuring sensor with which the autonomous mobile unit measures a distance
 to an obstacle in the surroundings and odometry, with which the autonomous
 mobile unit measures a path distance traversed the commencement of travel.
 Also, the autonomous mobile unit calculates coordinance of the autonomous
 mobile unit in the world coordinate system and positional uncertainty of
 the autonomous mobile unit based on at least one of the measurements of
 distance to an obstacle and the traverse path distance. The autonomous
 mobile unit is then moved to a starting position for a docking of then
 wherein the autonomous mobile unit aligns with respect to the rotated
 attitude of the autonomous mobile unit such that a detector for detecting
 the guide beam and the guide beam can interact. Finally, the autonomous
 mobile unit is moved in the direction of the destination coordinance when
 the detector does not detect the guide beam in order to seek the guide
 beam wherein the movement of the autonomous mobile unit in the direction
 of the destination coordinance in conjunction with the detector for
 detecting the guide beam is used for docking positioning of the autonomous
 mobile unit.
 One particular advantage of the method is that a good orientation aid in
 the form of a guide beam with which a signal for a travel path control of
 the unit can be generated for approaching the docking position is made
 available by employing a slot-shaped light beam residing perpendicular on
 the motion substratum of the unit in combination with a position-sensitive
 detector for this guide beam that is attached parallel to the travel
 surface of the unit.
 Another advantage of the method is that it provides two detection means for
 the guide beam that are arranged following one another in a principal
 approach direction of the unit; a more exact alignment of the unit with
 reference to the docking means can thus be achieved.
 Another advantage of the method is that it can be utilized with
 commercially obtainable position-sensitive detectors.
 An autonomous mobile unit works especially advantageously with a docking
 method wherein it determines its relative configuration vis a vis the
 docking means on the basis of the emitted guide beam and determines on the
 basis of its three-wheel kinematics whether it can designationally reach
 the docking means proceeding from this configuration in order to be able
 to dock thereat. When this is not the case, it independently moves away
 therefrom and centers itself with reference to the docking means. This
 method has the advantage that no information whatsoever are required about
 the environment of the docking means and that it can be realized in a
 simple way.
 Given the inventive docking method, however, information about the
 environment of the docking means can also be advantageously utilized in
 that, for example, a known distance of the docking means from a side wall
 is measured by the autonomous mobile unit and conclusions about the
 position of the docking means are drawn therefrom. The exact position of
 the unit can then be determined with an additional distance-measuring
 sensor, with which the distance from the docking means is measured, and
 the docking procedure can be initiated.
 The fact is especially advantageously utilized in the inventive docking
 method that the unit knows its position errors and that its starting
 configuration (i.e., the starting position and the starting rotational
 attitude in relationship to the position and rotational attitude of the
 docking means and of the guide beam) is likewise known, and the unit, on
 the basis of the estimated position error, can thus determine exactly that
 location at which the guide beam is not yet acquired by the sensors. This
 has the great advantage that the direction in which the guide beam must be
 sought is exactly known or, the unit can thus minimize its positional
 uncertainty transversely relative to the guide beam when the guide beam is
 already incident onto the detectors at this point in time.
 In a development of the inventive docking method, the fact is
 advantageously utilized that motion of the autonomous mobile unit in its
 starting configuration can be resolved into a forward motion and a rotary
 motion, so that the unit need not travel a loop in constricted
 surroundings but can implement forward travel and subsequently implements
 a rotational movement in place or, respectively, implements this motion
 event in the reverse sequence in order to proceed into a starting
 configuration for the docking event.
 In a development of the inventive method, the unit especially
 advantageously moves forward or backward to its staring position since the
 local conditions can be utilized better in this way (i.e., the unit need
 not necessarily turn in place but can turn in the starting position) and
 there is likewise the possibility that the unit always traverses the most
 direct path to the starting position.
 In a further development of the inventive method, the unit especially
 advantageously re-determines its position on the basis of the known
 position of the guide beam after this has been identified by the
 detectors. It should thereby be noted that both the unit as well as the
 docking means can emit the guide beam and that, when the docking means
 does not emit the guide beam, the detector result must be transmitted to
 the control computer of the unit by radio or infrared transmission, so
 that it is not compulsory for the invention to provide the guide beam only
 at the docking means.
 In a further development of the inventive method, the guide beam is
 especially advantageously sought by the unit such that it attempts to
 multiply cross the suspected position or, the suspected course of the
 guide beam.
 In a development of the inventive method, advantageously, the autonomous
 mobile unit moves on a meander-like path that crosses the envisioned
 course of the guide beam multiply times.
 In a further development of the inventive method, the meander shape of the
 search path for seeking the guide beam is especially advantageously varied
 in that the distance of the turning points for the departure of the
 meander-like search path from the envisioned guide beam is increased or,
 diminished since the search area for locating the guide beam is thus
 successively enlarged.
 In a further development of the inventive method, the guide beam is
 advantageously sought in that the autonomous mobile unit attempts to cross
 the envisioned course of the guide beam from one side, then attempts to
 cross it from the other side, whereby it initially moves parallel for a
 distance in between in order to again proceed into an initial position
 that lies at a similar distance from the docking means as at the beginning
 of the search event.
 In a further development of the inventive method, the guide beam is
 advantageously sought in that travel is carried out in a zig-zag course
 parallel at essentially the same distance from the docking means
 transversely relative to the guide beam, whereby the unit is aligned such
 that the detector and the guide beam can interact given forward travel and
 travel in reverse (i.e., no turning maneuvers occur on the zig-zag
 course). This has the advantage that a great breadth range can be covered
 over a slight travel distance, and that the guide beam can be dependably
 found in this way or, the docking means can be dependably localized in
 this way.
 In a development of the inventive method, the autonomous mobile unit
 especially advantageously moves along the guide beam toward the docking
 means after the guide beam has been detected.
 Additional advantages and novel features of the invention will be set
 forth, in part, in the description that follows and, in part, will become
 apparent to those skilled in the art upon examination of the following or
 may be learned by practice of the invention. The advantages of the
 invention may be realized and attained by means of the instrumentalities
 and combinations particularly pointed out in the appended claims.
 Exemplary embodiments of the invention are explained in greater detail
 below on the basis of Figures. The terms "autonomous mobile unit" and
 "robot" are thereby used synonymously, which is not intended to have any
 limiting effect whatsoever on the subject matter of the invention:
 FIG. 1 shows an autonomous mobile unit during a docking event;
 FIG. 2 provides examples of coordinate systems that are employed;
 FIG. 3 shows an embodiment of a docking means according to the present
 invention;
 FIG. 4 illustrates the geometrical relationships in the docking means;
 FIG. 5 shows an example for determining the starting configuration;
 FIG. 6 illustrates the travel to the starting configuration;
 FIG. 7 illustrates the position determinations on the basis of the guide
 beam;
 FIG. 8 illustrates the interpretation of the sensor data for detecting the
 guide beam;
 FIG. 9 illustrates a search path for localizing a docking means, which
 outputs a guide beam according to an embodiment of the present invention;
 FIG. 10 illustrates a search path for localizing a guide beam utilizing a
 zig-zag course according to another embodiment of the present invention;
 FIG. 11 illustrates a search path using a meander-like pattern according to
 another embodiment of the present invention;
 FIG. 12 illustrates problems that arise when the autonomous mobile unit
 loses the guide beam from coverage area of its sensors;
 FIG. 13 illustrates a solution to the problem illustrated in FIG. 12; and;
 FIG. 14 illustrates a flowchart of a method according to the present
 invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 As FIGS. 1 and 2 show, an autonomous mobile unit with three-wheel
 kinematics comprises, for example, a control wheel ST and drive wheels A1
 and A2. The autonomous mobile unit AE is located in its docking position
 at a docking means AV, which, for example, comprises transport rollers TR
 for handing over or receiving transport goods, in an idle position in the
 intersection of the coordinate system xy. In an arbitrary rotated attitude
 in the proximity of the docking means AV, the autonomous mobile unit is
 in, for example, a configuration P(x,y,beta) with a rotated angle beta of
 its principal approach direction HA to the docking means AV relative to
 the x-axis. After traveling over a distance of several meters, when the
 autonomous mobile unit is to dock at the docking means, the case can
 definitely be such that the error in the self-configuration estimate
 amounts to 20 cm and the orientation error amounts to up to 5.degree..
 There is thus the problem that this possible positioning error relative to
 the docking means AV must be compensated. During docking, therefore, the
 unit must exactly determine its position relative to the docking means.
 This requires sensors that enable a position identification relative to
 the docking means. Whereas when the unit is traveling and performing its
 activities, it orients itself in environment with, for example, ultrasound
 and on the basis of odometry measurements. This procedure, however,
 inadequate for having it dock precisely at a docking means. A specific
 docking means and a targeted docking method are required for this purpose.
 How the unit orients itself within its environment and how it performs and
 evaluates activities can be derived from the initially presented Prior
 Art. Another problem that arises in the docking event is that the unit AE,
 due to its three-wheel kinematics, cannot be arbitrarily maneuvered. When
 the autonomous mobile unit AE exhibits a lateral offset in the immediate
 proximity of the docking means AV, then this lateral offset cannot be
 corrected by maneuvering measures given simultaneous approach to the
 docking means. When such a case occurs, it is therefore provided that the
 unit, in turn, moves away from the docking means, whereby it centers
 itself relative to the docking means in order to be able to achieve the
 desired final configuration in a next approach to a docking position. The
 travel path to the docking position can preferably already be pre-planned
 at an adequate distance from the docking means in that the three-wheel
 kinematics and the planning algorithms from the cited Prior Art are used.
 In addition, designational placement and travel strategies are utilized
 for locating the guide beam.
 As FIG. 2 shows, different coordinate systems y_w, x_w, x_r, y_r or,
 respectively, x_l, y_l are, for example, employed in the present inventive
 methods. These indicate different positions in the local, wheel coordinate
 system of the autonomous mobile unit AE, in the local coordinate system of
 the docking means AV with x_d and y_d or, the light source LQ thereof with
 x.sub.-- 1, y.sub.-- 1. The guide beam is referenced BEA here. In this
 example, the sensor unit SE is constructed of position-sensitive detectors
 PSD1 and PSD2, the angle of incident light rays being capable of being
 determined from their measured results and their spacing upon application
 of trigonometric functions. The docking method is then comprised of the
 steps of: determination of the starting configuration; travel to the
 starting configuration; position determination; seek guide beam; docking
 event; and a specifying behavior given obstacles.
 Each object participating in the calculation has a specific configuration
 (relative to another object, relative to the world). Each of these
 configurations forms a coordinate system.
 The following notation are used:
 x.sub.a, y.sub.a point presented in the coordinate system a;
 .beta..sub.a angle presented in the coordinate system a; and
 (x.sub.a, y.sub.a, .beta..sub.a).sub.b or (x, y, .beta.).sub.a,b coordinate
 system (configuration) a presented in (i.e., relative to the coordinate
 system) b (no specification of b means relative to the world coordinate
 system).
 The following coordinate systems are established in the calculations:
 (x, y, .beta.).sub.w world coordinate system (implicit);
 (x, y, .beta.).sub.r,w robot coordinate system relative to world coordinate
 system;
 (x, y, .beta.).sub.s,r sensor unit coordinate system relative to robot
 coordinate system;
 (x, y, .beta.).sub.d,w docking station coordinate system relative to world
 coordinate system; and
 (x, y, .beta.).sub.l,d guide beam coordinate system relative to the docking
 station coordinate system.
 The following can be calculated from the above coordinate systems:
 (x, y, .beta.).sub.s,w sensor unit coordinate system relative to the world
 coordinate system; and
 (x, y, .beta.).sub.l,w guide beam coordinate system relative to the world
 coordinate system.
 As FIG. 3 shows the docking means AV in this exemplary embodiment comprises
 a light source LQ whose light is fanned by a cylindrical lens LS or by a
 slotted diaphragm to form a fan-shaped guide beam BEA that resides
 perpendicular to a travel surface FF of the autonomous mobile unit AE.
 Further, for example, an infrared receiver IRE is provided at the docking
 means AV, this being capable of activating the light source LQ when it
 receives a signal. Highly focussing lasers or, infrared lasers can
 preferably be utilized as light source LQ. However, other forms of light
 sources that allow a fan-shaped guide beam are also conceivable. The
 autonomous mobile unit shown in FIG. 3 comprises, for example, a
 position-sensitive detector PSD1 and a position-sensitive detector PSD2,
 which, in order to achieve a greater position resolution, are preferably
 arranged linearly perpendicular to HA and parallel to the travel surface
 of the unit and which allow an exact detection of the position of the
 fan-shaped guide beam BEA, as shall be shown in FIG. 4. For example, a
 filter FL that only allows light in the frequency range of the light
 source LQ to pass so that disturbances due to unwanted light can be
 suppressed is provided at the autonomous mobile unit. Further, for
 example, a control means ST is provided at the autonomous mobile unit,
 this receiving, for example, current signals I1 and I2 from the
 position-sensitive detector PSD1 and, for example, current signals I3 and
 I4 from the position-sensitive detector PSD2 via data lines DL. As FIG. 4
 shall also show, the rotated attitude of the unit relative to the light
 source LQ or, relative to the fan-shaped guide beam BEA can be determined
 on the basis of these current signals. Additionally, for example, the unit
 comprises an infrared transmitter IRS that can communicate with the
 infrared receiver IRE provided at the docking means AV in order to
 activate the light source LQ given an approach of the autonomous mobile
 unit AV to the docking means AV. Although the version of a docking means
 shown here represents the most meaningful embodiment wherein the
 evaluation means are provided in the autonomous mobile unit, which
 likewise requires these for its control procedures, it can also be
 meaningful on a case-by-case basis to provide the light source in the unit
 and the evaluation means for the position determination in the docking
 means and to communicate the data to the unit with infrared transmitters
 and receivers or other transmission means. The guide beam is preferably
 fanned perpendicular to the substratum i.e.; to the travel surface FR of
 the unit, so that a loaded condition of the unit that causes the
 position-sensitive detectors PSD1 and PSD2 to change their height position
 relative to the travel surface does not lead to a docking event becomes
 unimplementable. The guide beam or, the laser beam is preferably pulsed,
 so that an exact discrimination from ambient light can be implemented. For
 example, an evaluation electronics for the position-sensitive detectors
 PSD that synchronizes, for example, with the pulse frequency of the laser,
 is provided in the controller ST. Instead of position-sensitive detectors,
 that can be commercially acquired, however, photodiodes can also be
 provided, these enabling less of a resolution that, however, is adequate
 for a docking event on a case-by-case basis.
 As FIG. 4 shows, the two position-sensitive detectors or, on a case-by-case
 basis, two lines of photodiodes as well are arranged following one another
 at a distance d from one another with respect to a principal approach
 direction HA of the autonomous mobile unit to the docking means. The
 illustration of FIG. 4 shows a plan view onto the travel surface FF. The
 guide beam BEA transmitted by the light source LQ passes, for example, a
 filter FL and is first incident onto the position-sensitive detector PSD1
 and subsequently onto the position-sensitive detector PSD2. In this case,
 the two position-sensitive detectors PSD1 and PSD2 comprise a length L. In
 FIG. 4, the principal approach direction HA simultaneously represents the
 symmetry axis of the two detectors PSD1 and PSD2; Based on the measured
 distances Y1 and Y2 of the guide beam BEA from the principal approach
 direction HA upon incidence onto the detectors PSD1 and PSD2, the angle
 beta can therefore be determined as twist of the autonomous mobile unit
 given the assistance of the distance d of the detectors. As already
 mentioned above, the position-sensitive detectors output, for example, a
 current I1 and I2 or, I3 and I4. y1 and y2 can be determined therefrom
 according to the following equations:
 ##EQU1##
 beta derives therefrom as
EQU beta=atan((y1-y2)/d) (3)
 A filter FL is preferably provided given the inventive arrangement in order
 to minimize the influences of outside light and in order to be able to
 implement a more exact location determination of the guide beam BEA. An
 amplifier electronics that edits the signals of the detectors PSD1 and
 PSD2 is preferably provided. For example, a check is first carried out
 here to see whether pulsed laser light is present, and, when this is the
 case, the corresponding distances y1 and y2 are determined from the
 current signals output by the detectors. For example, the amplifier
 electronics in the control unit ST comprises a logic means that evaluates
 whether pulsed laser light is incident onto both position-sensitive
 detectors. When this is the case, the corresponding signals are forwarded
 to an analog-to-digital converter that, for example, makes the angle
 signal for beta available to a robot control program in the form of a
 digital value. The autonomous mobile unit or, the control program thereof
 can plan a travel path that leads it exactly to the target with the angle
 beta determined in this way.
 As FIG. 5 shows, the autonomous mobile unit AE must proceed from an initial
 position 1A with a position unreliability PU into a starting position 1B
 in order to begin with the search for the guide beam, BEA emanating from a
 light source LQ. The robot can come from an arbitrary direction for
 determining the starting configuration when approaching the docking means,
 whereby the position estimate has a certain uncertainty. It is to be
 assumed that the guide beam, due to the position uncertainty, cannot be
 initially acquired by the PSD sensor. The starting configuration
 Ks=(x_start,y_start,0), is preferably determined such that the robot is
 located at least 1 m (x_start=100) in front of the docking means and
 offset by a few centimeters (y_start=10) from the guide beam. The guide
 beam should then be quickly found with a subsequent search maneuver. In
 FIG. 5, the guide beam should be sought toward the right.
 As FIG. 6 shows, various configurations KE, K2 and K3 can be achieved on
 different paths W1 or, W2 proceeding from an initial configuration. W1
 thereby illustrates the path that would be travelled upon employment of a
 traditional controller. It can thereby be clearly seen that a wide loop
 derives when the unit attempts to proceed forward into its target
 configuration. When constricted spatial conditions are present such as,
 for example, in a narrow hall, this mode of travel is not possible and a
 different mode of travel is inventively proposed wherein the unit first
 moves forward by the distance W2 and then turns in place in P1. The exact
 approach of the starting configuration represents the first more
 significant problem. A simple configuration controller functions well when
 the target configuration is located directly in front of or, behind the
 robot and the target orientation does not deviate all too greatly from the
 starting orientation. As shown in FIG. 6,
 a) the robot orientations of Ka and Ke differ (for example, K2) by only a
 maximum angle (for example, 40.degree.); and
 b) the final configuration is located within a sector [-beta, +beta] in
 front of or, behind the starting configuration.
 Such a controller can, for example, work according to the following
 strategy:
 The control rule reads:
EQU .nu.=k.sub..rho. *.rho.
EQU .omega.=k.sub..alpha. *.alpha.+k.sub..phi. *.phi.
 whereby .nu. denotes the velocity in travel direction and .omega. denotes
 the change of travel direction (angular velocity). Further, .rho. denotes
 the distance of the current configuration from the target configuration,
 .phi. denotes then angle between current and target configuration and
 .alpha. denotes the angle between current travel direction and target
 direction.
 The target configuration Ke in FIG. 6 violates, for example, the condition
 a). The traditional controller would travel the path W1 that makes use of
 much free, traversable surrounding space. In practice, however, the
 latitude for motion on the part of the unit is often restricted by walls.
 The following method was therefore designed in the scope of the invention,
 this functioning well. When Ke is a matter of what is referred to as a
 "difficult final configuration" (condition a and/or b violated), two
 intermediate target points P1 and P2 are defined such that they are
 situated on a line to the final configuration and are respectively located
 a specific distance d (approximately 50 cm) in front of or, behind the
 final configuration.
EQU P1.x=Ke.x+d.multidot.cos(Ke.beta)
EQU P1.y=Ke.y+d.multidot.sin(Ke.beta)
EQU P2.x=Ke.x-d.multidot.cos(Ke.beta)
EQU P2.y=Ke.y-d.multidot.sin(Ke.beta)
 Subsequently, the distances d1 and d2 to the two possible intermediate
 points are identified.
 ##EQU2##
 In the travel maneuver that now follows, that point that lies closer to the
 starting configuration is preferably initially approached with arbitrary
 orientation. This is P1 in FIG. 6, whereby the robot reaches configuration
 K2. When the point has been reached, the robot turns in place, from K2 to
 K3 here, until it has reached the same rotated attitude as required by the
 final configuration. The exactly controlled approach to the final
 configuration is now relatively simple, since the robot now only has to
 travel a certain distance forward or, in reverse in reverse from K3 to Ke
 in this example. When, for example, an obstacle blocks the travel to the
 closer point P1, it is provided that the point P2 lying at the greater
 distance is initially approached and the final configuration is
 subsequently approached.
 The quality of the above-described controller suffices for the simpler
 travel maneuver. The disclosed method makes it possible for the robot,
 proceeding from a starting configuration, to travel to an arbitrary final
 configuration without great diversionary movement. The space required for
 maneuvering is kept optimally small.
 As FIG. 7 shows, the unit AE can determine its own position on the basis of
 a light source LQ and a beam BEA that is output by the light source. When
 the robot has reached the starting configuration, the continuous position
 determination, which normally ensues only in the world coordinate system
 (x,y,.beta.).sub.r,w, also additionally ensues in the guide beam
 coordinate system (x,y,.beta.).sub.r,l. Only the robot configuration in
 the guide beam coordinate system (x,y,.beta.).sub.r,l is still used for
 the entire docking maneuver. First, it is necessary to transform the
 current robot configuration and the odometry data (dx,dy,d.beta.) of the
 robot from world coordinates into guide beam coordinates:
EQU (x.sub.old,y.sub.old,.beta..sub.old).sub.r,w.fwdarw.(x.sub.old,y.sub.
 old,.beta..sub.old).sub.r,l
EQU dx.sub.w,dy.sub.w,d.beta..sub.w.fwdarw.dx.sub.l,dy.sub.l,d.beta..sub.l
 One preferably proceeds as follows in the position determination:
 1.) When the guide beam is not acquired by either of the two PSD sensors in
 the PSD sensor unit, the position determination preferably ensues
 exclusively with odometry information on the basis of the following
 equations
 ##EQU3##
 wherein W.sub.s references half the track width and u.sub.r.sub..sub.k and
 u.sub.l.sub..sub.k reference the motion changes at the two wheels. The
 index identifies the discrete condition.
 2.) When the guide beam is reliably acquired by only one of the two PSD
 sensors PSD1, only the determination of the position of the robot ensues
 normally relative to the guide beam y.sub.1 via the y1 position, the point
 of incidence of light on PSD1. The determination of the robot orientation
 .beta..sub.1 and the translational movement along the guide beam x.sub.1
 continues to be acquired via the wheel movements.
EQU x.sub.k+1 =x.sub..sub.k +dx.sub.l
EQU y.sub.k+1 =y.sub.k +y.sub.r,l,new
 =y1.multidot.cos(.beta..sub.1)-D1.multidot.sin(.beta..sub.1)
EQU .beta..sub.k+1 =.beta..sub.k +d.beta..sub.l (5)
 3.) When the guide beam is reliably acquired by both PSD sensors, the
 determination of the orientation .beta..sub.1 and the position of the
 robot ensues normally relative to the guide beam y.sub.1 ; preferably
 exclusively via the PSD data. The translational movement along the guide
 beam x.sub.1 continues to be acquired via the wheel movements according to
 the equations.
EQU x.sub.k+1 =x.sub.r,l,old +dx
EQU y.sub.k+1 =y.sub.r,l,new (by PSD sensor)
EQU .beta..sub.k+1 =.beta..sub.r,l,new (by PSD sensor) (6)
 FIG. 8 illustrates the geometrical conditions given the evaluation of the
 sensor data of the position-sensitive detectors PSD1 and PSD2.
 By evaluating the PSD data, y.sub.r,l,new and .beta..sub.r,l,new are
 calculated from y.sub.1 and y.sub.2. The angle of incidence of the guide
 beam onto the PSD sensors is:
 ##EQU4##
 .pi.is added thereto because the guide beam is modelled as a vector that
 points away from the light source:
EQU .beta.=.alpha.+.pi.
 where .beta. is the direction of the guide beam in the sensor unit
 coordinate system. In order to obtain the direction of the guide beam in
 robot coordinates, .beta. must also be transformed into robot coordinates:
EQU .beta..fwdarw..gamma.
EQU .gamma.=.beta.+.beta..sub.s,r
 In FIG. 8, .beta.(i.e., the twist of the sensor unit coordinate system
 relative to the robot coordinate system) is exactly .pi.; This will
 generally be the case since, of course, the robot usually docks moving in
 reverse along the guide beam and the sensor head is thus directed toward
 the back. However, other configurations are also conceivable if, for
 example, the robot could move sideways. .gamma. is now the direction of
 the guide beam in robot coordinates, (i.e., -.gamma. is the direction
 (=orientation) of the robot in guide beam coordinates) Thus,
EQU .beta..sub.r,l,new =-.gamma. (7)
 has been found.
 The following vectors are formed for obtaining y.sub.r,l :
 a vector which is a from the robot coordinate system origin to the point of
 incidence of the guide beam on PSD sensor 2, in robot coordinates;
 b unit which is a vector in the direction of the guide beam, in robot
 coordinates and c normal vector onto b, turned by +90.degree. .
 The distance of the guide beam from the origin of the robot coordinate
 system now derives simply as the scalar product of a and c and, thus, the
 distance of the origin of the robot coordinate system from the guide beam
 (=y.sub.r,l) derives as:
EQU yr,l=-a.multidot.c, (8)
 FIG. 8 shows that the product -a.multidot.c is negative, with the origin of
 the robot coordinate system lying over the guide beam, i.e. yr,l is
 positive.
 In practice, the position error before the docking event is often greater
 than the dimensions of the PSD sensors, i.e., the robot must place the
 sensors into the beam with suitable maneuvers. As soon as the starting
 position has been reached, suitable search positions are calculated for
 this purpose and are then approached in sequence. It should thereby be
 noted that the allowable angle of incidence of the guide beam onto the
 sensors can be limited (for example, to .+-.8.degree.: beams having too
 obtuse an incidence are reflected away by an interference filter in front
 of the PSD sensors). The search positions must thus be correspondingly
 selected. The following search strategies are advantageous since they have
 proven themselves experimentally.
 FIG. 9 shows a search path for localizing a docking means that outputs a
 guide beam BEA from a light source LQ. The autonomous unit AE is
 travelling on a search path P at this point in time that crosses the
 envisioned course of the guide beam BEA multiple times. In FIG. 9, the
 robot travels through the search region toward the left in reverse to
 point 1 on the one occasion and toward the right in reverse to point 3 on
 another occasion. It moves forward between points 1 and 2. When the guide
 beam has not yet been found when point 3 is reached, an abort is carried
 out with an error message.
 FIG. 10 illustrates another exemplary embodiment of a search path for
 localizing the guide beam and, thus, a docking means. Here, too, a light
 source LQ outputs a guide beam BEA, the unit travelling along a zig-zag
 course P5 in order to seek it. In the search maneuver shown in Figure 10,
 for example, the robot first moves a predetermined distance toward the
 right on a zig-zag course, as indicated by arrow 1. When the guide beam is
 not found, the robot moves in the other direction on the same zig-zag
 course, but this time for a longer distance, as indicated by arrow 2. This
 search toward the left and toward the right with increasing search
 distance can be arbitrarily continued, as symbolized by arrow 3.
 For localizing a guide beam BEA that is output by a light source LQ and as
 shown in FIG. 11, there is also the possibility of traveling on a
 meander-like search path on which the unit AE moves in reverse in the
 direction of the light source. When the robot already moves in reverse
 toward the docking means from far in front of the docking means, it could
 seek the beam with a simple snaking movement in reverse. The amplitude, of
 course, could in turn be modified.
 FIG. 12 illustrates problems that arise when tracking the guide beam that
 is output by a light source LQ. In FIG. 12, the autonomous mobile unit AE
 moves along a search path P20, whereby it loses the guide beam from the
 coverage area of the sensors at a point K10 and must then relocate it in
 order to proceed into a target position KE. To this end, FIG. 13 shows
 that it is meaningful for this purpose to provide, for example, an
 intermediate position x_middle toward which the autonomous mobile unit
 moves along a course P30 since it can thus avoid losing the guide beam BEA
 from the line of sight of the sensors. First, a starting configuration
 (x_start,0,0) in front of the docking means is approached. The uncertainty
 of the localization with respect to the position and the orientation will
 thereby generally be so great that the guide beam is not even seen at all
 (i.e., that the guide beam does not impinge the PSD sensors. The robot
 thus starts a search for the guide beam.
 There are two fundamental possibilities when the robot has found the beam:
 1.) With a specific controller, the robot attempts to follow the guide beam
 exactly up to the docking configuration KD.
 2.) Definition of suitable intermediate configurations that the robot
 approaches with a traditional configuration controller.
 When the robot is to exactly follow the guide beam with a controller, the
 problem arises that, due to its travel motions, the robot can again lose
 the beam. This can easily occur when, as indicated in FIG. 12 with K10,
 robot finds the beam under a relatively large angle of, for example,
 &gt;10.degree. during the beam search.
 The relocation of the guide beam is then possible with corresponding search
 strategies. Preferably, however, the traditional configuration controller
 can be utilized. To this end, two further configurations are defined in
 addition to the starting configuration. First, the middle configuration
 (x-middle,0,0) a short distance in front of the actual docking
 configuration and a final configuration (x_final,0,0) that is located
 directly behind the docking configuration KD in FIG. 13.
 First, the robot approaches the middle configuration. After successfully
 approaching the middle configuration, the robot is already exactly aligned
 such that it can travel in reverse to the docking configuration KD without
 greater steering excursions and, thus, without losing the guide beam. The
 new target, the final configuration, is already prescribed shortly before
 the middle configuration is reached. The robot can be stopped with limit
 switches before reaching the target.
 As FIG. 14 shows, a docking event can be comprised of steps 100 through
 530. The command to dock at the docking means is given with a command 100.
 In a process 150, the autonomous mobile unit travels to the starting
 position. The guide beam is sought in a step 130 until a detector acquires
 the guide beam. This is illustrated with the arrow 170. It also follows
 from arrow 180 that the starting position has been reached. Step 160 is
 implemented when both detectors already acquire the guide beam and a
 branch is thus made to process step 400. Otherwise, process step 200
 ensues wherein the different search positions of the various search path
 strategies are initialized. In step 210, the process step 250 for
 travelling to various search positions is triggered. When the
 corresponding positions are not reached, a branch back is made with step
 230. Which search position has been currently reached is answered back in
 step 270, and a check is carried out in step 310 to see which search
 positions should be approached. When the last search position has already
 been reached, the search procedure is aborted via step 305, and the
 failure of the search procedure is found in process step 310. When the
 last search position has not yet been reached, process step 350 is
 triggered via step 320, this incrementing the number of the search
 position by 1, whereupon step 220 ensues that re-initiates the process
 250. When both detectors have acquired the guide beam, step 260 is
 triggered, which likewise triggers process 400. In process step 400, the
 unit aligns exactly along the guide beam. When this is not the case, the
 position is corrected in process step 430. When the middle position has
 been reached, the process 500 is triggered with process step 410. The
 current position is checked with process step 530 and process 500 is
 implemented if the docking position has not yet been reached. Having
 reached the final position is reported in process step 510 and the success
 of the docking procedure is found in process step 520.
 While this invention has been described in connection with what are
 presently considered to be the most practical and preferred embodiments,
 it is to be understood that the invention is not limited to the disclosed
 embodiments, but, on the contrary, is intended to cover various
 modifications and equivalent arrangements included within the spirit and
 scope of the appended claims.