Guiding an unmanned vehicle by reference to overhead features

• US 5,155,684 A
• Filed: 07/17/1991
• Issued: 10/13/1992
• Est. Priority Date: 10/25/1988
• Status: Expired due to Fees

• Current Assignee: Tennant Company
• Original Assignee: Tennant Company
• Inventors: Hall, Ernest L., Liang, Cao Z., Burke, Steven A.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): ZANELLI, MICHAEL J
• Application Number:
  US07/732,340
• Time in Patent Office: 454 Days
• Field of Search: 364/424.01, 364/424.02, 364/443, 364/460, 364/449, 364/448, 364/432, 364/513, 364/447, 180/167, 180/168, 180/169, 318/587, 901/1, 382/16
• US Class Current: 701/25
• CPC Class Codes: G05D 1/0221 involving a learning process
• CPC Class Codes: G05D 1/0246 using a video camera in combination with image processing means

Abstract

A vehicle primarily for unmanned operation is equipped with a video camera pointed up, and progressively records in an on-board computer memory the observed locations of points derived from overhead features such as pre-existing overhead lights in a building during a manually driven teaching mode trip along a desired course. On subsequent unmanned trips, the vehicle directs itself along the chosen course by again observing the overhead features, deriving points from them and comparing the locations of those points to the locations of the points that were recorded during the teaching mode trip. It then corrects its steering to bring the errors between the observed locations and the recorded locations to zero, thereby directing the vehicle to automatically follow the course that was followed during the teaching mode trip.

Claims

1. A method of operating a vehicle in which the vehicle automatically follows a predetermined path, including the steps of:

moving the vehicle, under operator command, over a desired path in an area unmodified for the specific use of guiding an unmanned vehicle while making a record analogous to the movement of the vehicle as such movement relates to fixed previously existing generally overhead contrasting visible areas as seen by recording means on the vehicle sensitive to such contrasting visible areas so as to record at the same time both the X and Y axis coordinates of geometric points derived from the contrasting visible areas analogous to the desired path, and

thereafter moving the vehicle, without operator control, over the desired path, the vehicle being maintained on the desired path by comparison between the analogous record and the vehicle path of movement as such movement relates to X and Y axis coordinates of geometric points derived from the fixed previously existing generally overhead contrasting visible areas as seen by the recording means to provide simultaneously Ex, Ey and Ea where Ex is lateral error, Ey is position along the desired path relative to a reference set of contrasting visible areas, and Ea is angular orientation error, and making vehicle course corrections based upon the observed Ex and Ea to cause the vehicle to follow the desired path.

2. The method of claim 1 further characterized in that the recording means is a video camera.

3. The method of claim 2 further characterized in that said video camera is pointed generally in a vertical direction.

4. The method of claim 1 further characterized in that the previously existing generally overhead contrasting visible areas are defined by spaced areas of artificial illumination.

5. The method of claim 4 further characterized in that said spaced areas of artificial illumination are disposed on or about the ceiling of a building.

6. The method of claim 4 further characterized in that the recording means defines at least a segment of the desired path of movement by the essentially simultaneous positions of geometric points derived from at least two spaced areas of artificial illumination.

7. The method of claim 6 further characterized in that the recording means defines the desired path of movement by the positions of the geometric points derived from successive groups of two or more spaced areas of artificial illumination.

8. The method of claim 6 further characterized in that the positions of said spaced areas of artificial illumination are recorded on the basis of the X, Y coordinates in a horizontal plane of the geometric point derived from each spaced area relative to a geometric point of reference on the recording means.

9. The method of claim 1 further characterized in that the vehicle is substantially continuously maintained on the desired path during the unmanned moving step by a comparison between the analogous record obtained during the manned moving step and the vehicle path of movement during the unmanned moving step.

10. A vehicle used primarily for unmanned operation including operator controls for driving the vehicle along a path determined by an operator in an area unmodified for the specific use of guiding an unmanned vehicle, means for recording the operator-determined path as it relates to fixed randomly disposed generally overhead contrasting visible areas in the locality where the vehicle operates as the vehicle is being driven over the operator-determined path so as to record at the same time both the X and Y axis coordinates of geometric points derived from the overhead features analogous to the predetermined path,

means for controlling movement of the vehicle, without operator control, including means for determining the actual position of the vehicle relative to geometric points derived from the fixed randomly disposed contrasting visible areas of unspecified location in the locality where the vehicle operates, means for comparing the actual position of the vehicle thus determined with the desired recorded position of the vehicle to determine lateral error, angular error and position along the desired path, and means for making vehicle course corrections when the actual path of the vehicle deviates from the recorded path.

11. The vehicle of claim 10 further characterized in that the means for recording the operator-determined path and for determining the actual position of the vehicle include a video camera mounted on the vehicle.

12. The vehicle of claim 11 further characterized in that said video camera is pointed generally upward so as to observe contrasting visible areas above the path of movement of the vehicle.

13. The vehicle of claim 12 further characterized in that the contrasting visible areas are provided by features of the work environment not specially positioned to define the vehicle path of movement.

14. The vehicle of claim 13 further characterized in that the contrasting visible areas are formed by ceiling lights.

15. The combination of claim 11 further comprising a light mounted on the vehicle to illuminate the surroundings generally above the vehicle so that the defined features in those surroundings may be observed by the video camera even though the vehicle may be operating in an otherwise darkened area.

16. The vehicle of claim 10 further characterized in that the means for recording include means enabling the operator to select successive sets of two or more fixed contrasting visible areas as the vehicle is moved by the operator along the predetermined path.

17. The vehicle of claim 16 further characterized in that geometric points derived from the same successive sets of two or more fixed contrasting visible areas are used to determine the actual position and angular orientation of the vehicle during operation without an operator and form the basis for vehicle course corrections.

18. The combination comprising a vehicle intended primarily for unmanned operation, having a frame supported on wheels, drive means for propelling the vehicle and steering means for steering it,

means for operating said vehicle in a manual teaching mode in an area unmodified for the specific use of guiding an unmanned vehicle and along a desired course that an operator of the vehicle wants it to follow in a subsequent unmanned mode,

a generally vertically directed video camera mounted on the vehicle, image processing means connected to the video camera, computer means including a memory connected to the image processing means,

means for successively selecting sets of two or more defined features in the surroundings generally above the vehicle in the field of view of the video camera as the vehicle is operated along the desired course in the teaching mode, observing such features with the video camera, obtaining successive representations of the locations of geometric points derived from the features in the sets of two or more features from the observations so as to obtain simultaneously both the X and Y axis coordinates of geometric points derived from the said defined features analogous to the desired path, and electronically recording these successive representations in the computer memory,

means for positioning the vehicle close to or at the start of the same desired course after the teaching mode is complete and starting the vehicle in unmanned operation with the video camera again observing the same sets of two or more features generally above the vehicle,

means for obtaining successive representations of the locations of the same geometric points derived from the same features in the same sets of two or more features as were observed while operating in the teaching mode and comparing such representations with the location representations recorded while operating in the teaching mode to simultaneously provide lateral error on the X axis, position on the Y axis and angular orientation error,

means for deriving course corrective signals from the comparisons and means to apply the course corrective signals for the X-axis error and angular orientation error to the steering means of the vehicle so as to maintain the unmanned vehicle on a course essentially the same as the course which was traveled during the teaching mode.

19. A guidance system for a primarily automated vehicle which operates on a generally horizontal surface wherein a video camera mounted on the vehicle is used to successively observe certain overhead contrasting randomly positioned features generally above the vehicle and wherein the camera images of those features are processed into digital representations of the (x,y) coordinates in a horizontal plane of geometric points derived from the features, and wherein a set of such representations obtained during a teaching mode trip along a desired route is stored in a data base and wherein another set of similarly obtained and processed representations of the (x,y) coordinates in a horizontal plane of geometric points derived from the same overhead features obtained during a subsequent automated trip along the same route is compared against the set which was stored in the data base, and wherein the comparison is processed to provide course error signals between the course followed during the teaching mode trip and the course followed during the automated trip, and wherein the course error signals are processed to provide course corrective signals to direct the steering of the vehicle to cause it to follow essentially the same route during the automated trip as was traveled during the teaching mode trip.

20. The guidance system of claim 19 wherein the video camera is mounted with the center axis of its optical system essentially perpendicular to the surface on which the vehicle operates so that the (x) and (y) coordinate information that may be derived from the observed overhead features will apply to a plane essentially parallel to the surface on which the vehicle operates.

21. The guidance system of claim 19 further characterized in that during the teaching mode the vehicle repeatedly measures the height above the video camera of each of the observed overhead features and stores the measurements in the data base.

22. A method for guiding a vehicle through a desired path in a building having an existing overhead with a discernible pattern made up of various elements generally arranged in a horizontal plane, including the steps of manually guiding the vehicle through the desired path in a first pass, recording the locations of geometric points derived from the various elements of the pattern from the vehicle from time to time while the vehicle is being so moved to establish an X and Y axis recording analogous to the desired path, thereafter causing the vehicle to move unattended through the desired path in the building, observing the locations of geometric points derived from the various elements of the pattern from the vehicle as it moves along the desired path to obtain X-axis errors, angular orientation errors and position along the Y-axis, and correcting the direction of the vehicle from time to time in accordance with the obtained X-axis errors and angular orientation errors when the vehicle departs from the desired path as detected from the recorded locations of geometric points derived from the various elements of the existing pattern.

23. The method of claim 22 further characterized in that the vehicle is substantially continuously maintained on the desired path during unattended movement by observing the locations of the various elements of the pattern and correcting the direction of the vehicle when it departs from the desired path.

24. A method of guiding a vehicle through a desired path on a generally planar surface in spaced relation to and under a generally overhead environment comprising discernable contrasting areas, including the steps of manually guiding the vehicle through a desired path on the planar surface in a preliminary pass, from time to time observing from the vehicle the coordinates in a plane parallel to the said surface of a geometric point associated with each of selected contrasting areas of the overhead environment while the vehicle is being so guided to establish a recording analogous to the desired path, thereafter causing the vehicle to move on an unattended pass through the desired path on the planar surface while observing the overhead environment from the vehicle and determining the coordinates in a plane parallel to said surface of the same geometric point associated with each of the same contrasting areas whose coordinates were observed during the preliminary pass, and correcting the direction of the vehicle from time to time when it departs from the desired path as detected from a comparison of the coordinates of the geometric points associated with the selected overhead contrasting areas obtained during the preliminary pass with coordinates of the same geometric points obtained during the unattended pass.

25. The method of claim 24 further characterized in that the coordinates of the geometric point associated with each of the contrasting areas selected from the overhead environment are in a plane generally parallel to the planar surface on which the vehicle is operating.

26. The method of claim 24 further characterized by and including the step of using existing overhead lights in an existing building as the discernable contrasting areas.

27. A method of guiding a vehicle along a desired path on a generally planar surface including the steps of defining a desired path for the vehicle on the planar surface, moving the vehicle along the desired path, from time to time observing primarily upwardly from the vehicle overhead contrasting areas while it is being so moved, making a record on the vehicle of the (x,y) coordinates of geometric points derived from such overhead contrasting areas while it is being so moved, thereafter causing the vehicle to move on its own along the desired path, observing the overhead contrasting areas while it is so moving on its own, and from time to time correcting the direction of the vehicle when it departs from the desired path based upon a comparison of the (x,y) coordinates of geometric points derived from the overhead contrasting areas observed during self-movement with the record made while guiding the vehicle along the desired path.

28. The method of claim 27 further characterized in that the vehicle is substantially continuously maintained on the desired path by correcting the direction of the vehicle when it departs from the desired path based upon the observation of the overhead contrasting areas.

29. A method of operating a vehicle having a frame supported on wheels in which the vehicle automatically follows a predetermined path, including the steps of:

moving the vehicle, under operator command, over a desired path in an area unmodified for the specific use of guiding an unmanned vehicle while making a record analogous to the movement of the vehicle as such movement relates to fixed previously existing generally overhead contrasting visible areas as seen by recording means on the vehicle sensitive to such contrasting visible areas so as to record at the same time both the X and Y axis coordinates of points derived from the contrasting visible areas analogous to the desired path,

thereafter moving the vehicle, without operator control, over the desired path, the vehicle being maintained, for at least a portion of its movement, on the desired path by comparison between the analogous record and the vehicle path of movement as such movement relates to the X and Y axis coordinates of points derived from the fixed previously existing generally overhead contrasting visible areas as seen by the recording means to provide simultaneously Ex, Ey and Ea where Ex is lateral error, Ey is position along the desired path relative to a reference set of contrasting visible areas, and Ea is angular orientation error, and making vehicle course corrections based upon the observed Ex and Ea to cause the vehicle to follow the desired path, and

wherein the vehicle can, for a portion of its movement, be maintained on the desired path during the unmanned moving step by position mode control based on wheel count.

30. A method of operating a vehicle in which the vehicle automatically follows a predetermined path, including the steps of:

moving the vehicle, under operator command, over a desired path in an area unmodified for the specific use of guiding an unmanned vehicle while making a record analogous to the movement of the vehicle as such movement relates to fixed previously existing generally overhead contrasting visible areas as seen by a video camera on the vehicle sensitive to such contrasting visible areas so as to record at the same time both the X and Y axis coordinates of points derived from the contrasting visible areas analogous to the desired path, and

thereafter moving the vehicle, without operator control, over the desired path, the vehicle being maintained on the desired path by comparison between the analogous record and the vehicle path of movement as such movement relates to the X and Y axis coordinates of points derived from the fixed previously existing generally overhead contrasting visible areas as seen by the video camera to provide simultaneously Ex, Ey and Ea where Ex is lateral error, Ey is position along the desired path relative to a reference set of contrasting visible areas, and Ea is angular orientation error, correcting for any video camera lens distortion prior to comparing the vehicle path of movement with the analogous record, and making vehicle course corrections based upon the observed Ex and Ea to cause the vehicle to follow the desired path.

31. A vehicle used primarily for unmanned operation having a frame supported on wheels and including operator controls for driving the vehicle along a path determined by an operator in an area unmodified for the specific use of guiding an unmanned vehicle, means for recording the operator-determined path as it relates to fixed randomly disposed generally overhead contrasting visible areas in the locality where the vehicle operates as the vehicle is being driven over the operator-determined path so as to record at the same time both the X and Y axis coordinates of the overhead features analogous to the predetermined path,

means for controlling movement of the vehicle, without operator control, including means for determining the actual position of the vehicle relative to the fixed randomly disposed contrasting visible areas of unspecified location in the locality where the vehicle operates, means for comparing the actual position of the vehicle thus determined with the desired recorded position of the vehicle to determine lateral error, angular error and position along the desired path, means for making vehicle course corrections when the actual path of the vehicle deviates from the recorded path, and means for controlling vehicle movement by position mode control based on wheel count.

32. The combination comprising a vehicle intended primarily for unmanned operation, having a frame supported on two independently driven wheels and one or more freely swiveling caster wheels, drive means for propelling the vehicle and steering means for steering it,

means for operating said vehicle in a manual teaching mode in an area unmodified for the specific use of guiding an unmanned vehicle and along a desired course that an operator of the vehicle wants it to follow in a subsequent unmanned mode,

a generally vertically directed video camera mounted on the vehicle, image processing means connected to the video camera, computer means including a memory connected to the image processing means,

means for successively selecting sets of two or more defined features in the surroundings generally above the vehicle in the field of view of the video camera as the vehicle is operated along the desired course in the teaching mode, observing such features with the video camera, obtaining successive representations of the locations of points derived from the features in the sets of two or more features from the observations so as to obtain simultaneously both the X and Y axis coordinates of points derived from the said defined features analogous to the desired path, and electronically recording these successive representations in the computer memory,

means for positioning the vehicle close to or at the start of the same desired course after the teaching mode is complete and starting the vehicle in unmanned operation with the video camera again observing the same sets of two or more features generally above the vehicle,

means for obtaining successive representations of the locations of the same points derived from the same features in the same sets of two or more features as were observed while operating in the teaching mode and comparing such representations with the location representations recorded while operating in the teaching mode to simultaneously provide lateral positional error (Ex) on the X axis, position on the Y axis and angular orientation error (Ea),

means for deriving course corrective signals from the comparisons and means to apply the course corrective signals for the X-axis error and angular orientation error to the steering means of the vehicle so as to maintain the unmanned vehicle on a course essentially the same as the course which was traveled during the teaching mode, and means for steering by rotating the driven wheels at speeds which may be expressed as:

space="preserve" listing-type="equation">V=Vm±

(K1Ex+K2Ea)

where V is the peripheral speed of either driven wheel, Vm is the mean velocity of the vehicle, K1 and K2 are constants of proportionality, and ±

indicates steering to right or left.

33. A guidance system for a primarily automated vehicle which operates on a generally horizontal surface wherein a video camera mounted on the vehicle is used to successively observe certain overhead contrasting randomly positioned features generally above the vehicle, which observed overhead features comprise a succession of single features which are successively observed one at a time as the vehicle progresses along a desired route, and wherein the camera images of those features are processed into digital representations of the (x,y) coordinates in a horizontal plane of points derived from the features, and wherein a set of such representations obtained during a teaching mode trip along a desired route is stored in a data base and wherein another set of similarly obtained and processed representations of the points derived from the same overhead features obtained during a subsequent automated trip along the same route is compared against the set which was stored in the data base, and wherein the comparison is processed to provide course error signals between the course followed during the teaching mode trip and the course followed during the automated trip, and wherein the lateral position error Ex of the vehicle relative to the desired route and the longitudinal location of the vehicle Ey relative to a selected point along the desired route are determined from each of these successive comparisons, and wherein the angular heading error Ea of the vehicle relative to the desired route is determined as

34. A guidance system for a primarily automated vehicle which operates on a generally horizontal surface wherein a video camera mounted on the vehicle is used to successively observe certain overhead contrasting randomly positioned features generally above the vehicle and wherein the camera images of those features are processed into digital representations of the (x,y) coordinates in a horizontal plane of points derived from the features, and wherein a set of such representations obtained during a teaching mode trip along a desired route is stored in a data base and wherein prior to or in connection with the teaching mode, the height above the video camera of a representative observed overhead feature is measured and that measurement is entered into the data base, and wherein another set of similarly obtained and processed representations of the points derived from the same overhead features obtained during a subsequent automated trip along the same route is compared against the set which was stored in the data base, and wherein the comparison is processed to provide course error signals between the course followed during the teaching mode trip and the course followed during the automated trip, and wherein the course error signals are processed to provide course corrective signals to direct the steering of the vehicle to cause it to follow essentially the same route during the automated trip as was traveled during the teaching mode trip.

35. A guidance system for a primarily automated vehicle which operates on a generally horizontal surface wherein a video camera mounted on the vehicle is used to successively observe certain overhead contrasting randomly positioned features generally above the vehicle and wherein the camera images of those features are processed into digital representations of the (x,y) coordinates in a horizontal plane of points derived from the features, and wherein a set of such representations obtained during a teaching mode trip along a desired route is stored in a data base and wherein another set of similarly obtained and processed representations of the points derived from the same overhead features obtained during a subsequent automated trip along the same route is compared against the set which was stored in the data base, and wherein the comparison is processed to provide course error signals between the course followed during the teaching mode trip and the course followed during the automated trip, and wherein an angular error (Ea) in heading of the said vehicle during an automated trip relative to a desired route is equal to the angular difference between the slope of a line connecting the images of the points derived from two features in a pattern obtained during the automated trip and the slope of a line connecting the images of the points derived from the same two features in a pattern obtained during a previous teaching mode trip along the same desired route, and wherein the course error signals are processed to provide course corrective signals to direct the steering of the vehicle to cause it to follow essentially the same route during the automated trip as was traveled during the teaching mode trip.

36. A guidance system for a primarily automated vehicle which operates on a generally horizontal surface wherein a video camera mounted on the vehicle is used to successively observe certain overhead contrasting randomly positioned features generally above the vehicle and wherein the camera images of those features are processed into digital representations of the (x,y) coordinates in a horizontal plane of points derived from the features, and wherein a set of such representations obtained during a teaching mode trip along a desired route is stored in a data base and wherein another set of similarly obtained and processed representations of the points derived from the same overhead features obtained during a subsequent automated trip along the same route is compared against the set which was stored in the data base, and wherein the comparison is processed to provide course error signals between the course followed during the teaching mode trip and the course followed during the automated trip, and wherein the angular orientation of a pattern of the points derived from the features images obtained during an automated trip along a desired route is compared to the angular orientation of a pattern of the points derived from the same feature images obtained during a previous teaching mode trip along the same desired route, and the pattern obtained during the said automated trip is mathematically rotated by an amount equal to the angular difference between the two patterns so that after the rotation a line connecting the points derived from the two features in one of the patterns will be parallel to a line connecting the points derived from the same two features in the other pattern, and wherein the course error signals are processed to provide course corrective signals to direct the steering of the vehicle to cause it to follow essentially the same route during the automated trip as was traveled during the teaching mode trip.

37. The guidance system of claim 36 wherein the lateral positional error (Ex) of the vehicle perpendicular to a desired route during an automated trip is found by a comparison between the lateral offset of the (x) coordinate of the point derived from one or more features in the pattern obtained during the said automated trip and the (x) coordinate of the point derived from the same one or more features in the pattern obtained during a previous teaching mode trip along the said desired route, said comparison being made after the feature pattern obtained during the automated trip has been rotated.

38. The guidance system of claim 36 wherein at a given time the longitudinal location of said vehicle along the desired route may be expressed as the difference (Ey) between the current longitudinal location along the route of the image of the point derived from one or more features in a pattern currently obtained during said automated trip and the longitudinal position along the route of the image of the point derived from the same one or more features in a pattern obtained during a teaching mode trip along the same desired route, said difference being taken after the feature pattern obtained during the automated trip has been routed.

39. The guidance system of claim 38 wherein the value of Ey in a particular pattern approaches zero as the vehicle progresses along the desired route, and wherein new reference patterns of the points derived from overhead features are successively recalled from memory when the value of Ey in each pattern approaches close to zero.

40. A method for guiding a vehicle having a frame supported on wheels through a desired path in a building having an existing overhead with a discernible pattern made up of various elements generally arranged in a horizontal plane, including the steps of manually guiding the vehicle through the desired path in a first pass, recording the locations of points derived from the various elements of the pattern observed from the vehicle from time to time while the vehicle is being so moved to establish an X and Y axis recording analogous to the desired path, thereafter causing the vehicle to move unattended through the desired path in the building, determining the locations of points derived from the various elements of the pattern observed from the vehicle as it moves along the desired path to obtain X-axis errors, angular orientation errors and position along the Y-axis, correcting the direction of the vehicle from time to time in accordance with the obtained X-axis errors and angular orientation errors when the vehicle departs from the desired path as detected from the recorded locations of points derived from the various elements of the existing pattern, and at times correcting the direction of the vehicle by position mode control based on wheel count.

41. A method of guiding a vehicle through a desired path on a generally planar surface in spaced relation to and under a generally overhead environment comprising discernible contrasting areas, including the steps of manually guiding the vehicle through a desired path on the planar surface in a preliminary pass, measuring the height above the vehicle of a contrasting area during the preliminary pass and establishing a recording of said height, from time to time while the vehicle is being so guided observing the contrasting areas from the vehicle, and determining with use of the recorded height the coordinates in a plane parallel to the said surface of a point associated with each of selected contrasting areas of the overhead environment to establish a recording analogous to the desired path, thereafter causing the vehicle to move on an unattended pass through the desired path on the planar surface while observing the overhead environment from the vehicle and determining with use of the recorded height the coordinates in a plane parallel to said surface of the same point associated with each of the same contrasting areas whose coordinates were determined during the preliminary pass, and correcting the direction of the vehicle from time to time when it departs from the desired path as detected from a comparison of the coordinates of the points associated with the selected overhead contrasting areas obtained during the preliminary pass with coordinates of the same points obtained during the unattended pass.

42. A method of guiding a vehicle having a frame supported on wheels along a desired path on a generally planar surface, including the steps of defining a desired path for the vehicle on the planar surface, moving the vehicle along the desired path, from time to time observing primarily upwardly from the vehicle overhead contrasting areas while it is being so moved, making a record on the vehicle derived from the observations of such overhead contrasting areas while it is being so moved, thereafter causing the vehicle to move on its own along the desired path, observing the overhead contrasting areas while it is so moving on its own, from time to time correcting the direction of the vehicle when it departs from the desired path based upon observations of the overhead contrasting areas and wherein the vehicle may at times be maintained on the desired path by position mode control based on wheel count.

43. A method for guiding a vehicle having a frame mounted on wheels through a desired path in a building having an existing overhead with a discernible pattern made up of various elements generally arranged in a horizontal plane, including the steps of manually guiding the vehicle through the desired path in a first pass, recording the locations of points derived from the various elements of the pattern observed from the vehicle from time to time while the vehicle is being so moved to establish and X and Y axis recording analogous to the desired path, thereafter causing the vehicle to move unattended through the desired path in the building, determining the locations of points derived from the various elements of the pattern observed from the vehicle as it moves along the desired path to obtain X-axis errors, angular orientation errors and position along the Y-axis, and at times correcting the direction of the vehicle in accordance with the obtained X-axis errors and angular orientation errors when the vehicle departs from the desired path as detected from the recorded locations of points derived from the various elements of the existing pattern and at other times maintaining the vehicle on the desired path by position mode control based on wheel count.