Abstract:
A method and apparatus for controlling the path of movement of an automatic guided vehicle relative to a first guidepath laterally along first and second cross tracks to a second guidepath laterally offset from the first guidepath. The turn indicator is mounted relative to the first and second guide tracks. A turn indicator sensor carried on the automatic guided vehicle detects the turn indicator. A controller responsive to the sensor output positions the automatic guided vehicle for movement of the first drive wheel along one of the cross tracks and the second guide wheel along the other cross track laterally from the first guidepath to the second guidepath.

Description:
BACKGROUND 
       [0001]    The present description relates, in general, to automated guided vehicles (AGV). 
         [0002]    Unmanned, automatic guided vehicles or AGVs are used in factories, warehouses, and other applications to carry loads along a predetermined path on the facility floor typically between a load pick-up station and a load drop-off or unload station. 
         [0003]    An AGV includes a base or chassis having one or more driving wheels, at least one of which has a steering mechanism. A controller is mounted on the chassis for controlling the forward and/or rearward directional movement of the drive wheels as well as to control the steering mechanism to allow the AGV to execute a right or left hand turn. Article carrying structure, particular to the load to be carried by the AGV, is mounted on the chassis. 
         [0004]    A guidepath is laid out on the facility floor which typically defines a closed loop path defined by a magnetic or optically reflective tape strip which includes straight, curved and angular turn segments. 
         [0005]    A magnetic sensor mounted on the AGV chassis senses the magnetic tape and provides signals to the controller which in turn controls the drive wheel steering mechanism to maintain the drive wheels on the magnetic tape so that the AGV moves along the guidepath. 
         [0006]    However, AGVs having a large chassis or AGVs which carry elongated articles or parts or, simply, AGVs used in tight confined areas require excessive clearance to turn. The need for a large turn area has prevented the application of AGVs in many areas of a manufacturing plant, warehouse, or other facility; or has required a redesign of the AGV close loop path and a relocation of the manufacturing or storage facility tools or machines to provide the turning clearance for such AGVs. 
         [0007]    It would be desirable to provide a method and apparatus for an AGV which addresses this problem by allowing movement of an AGV in a small tight defined area. 
       SUMMARY 
       [0008]    An apparatus for controlling the path of movement of an automated guide vehicle along a guidepath including a first guidepath and a second guidepath laterally offset from the first guidepath. A first cross track is disposed between the first and second guidepaths. A second cross track spaced from the first cross track, is interconnected between the first and second guidepath. An automated guide vehicle movable in at least a first direction along the guidepath includes a first independently steerable drive wheel, a second independently steerable drive wheel, a first sensor associated with the first drive wheel for sensing the guidepath relative to the first drive wheel, a second sensor associated with the second drive wheel for sensing the guidepath relative to the second drive wheel, and a controller. In response to the position of the automatic guided vehicle relative to the first and second guide tracks, the controller controls the position of the automatic guided vehicle to allow the first drive wheel to follow one of the first and second cross tracks and the second drive wheel to follow the other cross track to move the automatic guided vehicle laterally in a sideways manner between the first and second guidepaths. 
         [0009]    A turn indicator is fixedly positioned relative to the first and second cross tracks. A turn indicator sensor is carried by the automatic guided vehicle for detecting the turn indicator. The controller, using an output from the turn indicator sensor, determines the position of the automatic guided vehicle relative to the first and second cross tracks to control the movement of the automatic guided vehicle along the first and second cross tracks. 
         [0010]    Optionally a third sensor is mounted rearwardly of the first drive wheel to sense the guidepath when the automatic guided vehicle is moving in a second direction opposite from the first direction. A fourth sensor is mounted rearwardly of the second drive wheel to sense the guidepath when the automatic guided vehicle is moving in a second direction opposite from the first direction. 
         [0011]    A bi-directional drive motor is coupled to each of the first and second drive wheel. 
         [0012]    In one aspect, the second guidepath is disposed to the right side of the first guidepath with respect to the direction of travel of the automatic guided vehicle in the first direction. The second guidepath can also or alternately be disposed to the left side of the first guidepath with respect to the direction of the travel of the automatic guided vehicle. 
         [0013]    The first and second cross tracks are disposed at an angle of about 45° between the first and second guidepaths. 
         [0014]    The turn indicator is fixedly located relative to the first and second cross tracks in a position such that the turn indicator sensor detects the presence of the turn indicator when the first drive wheel of the automatic guided vehicle has passed the first one of the cross tracks when the vehicle is moving in the first direction. 
         [0015]    A method of controlling the movement of an automatic guided vehicle along a guidepath including at least a first guidepath, first and second independently steerable drive wheels, comprises: 
         [0016]    providing a second guidepath laterally offset from the first guidepath, 
         [0017]    interconnecting first and second spaced across tracks between the first and second guidepaths, 
         [0018]    mounting a turn indicator in a position relative to the first and second cross tracks to indicate a sideways turn movement of the automatic guided vehicle from the first guidepath to the second guidepath, 
         [0019]    providing a turn indicator sensor on the automatic guided vehicle for detecting the turn indicator, and 
         [0020]    executing a stored program by a controller to control the movement of the automatic guided vehicle along the first guidepath and, 
         [0021]    in response to a signal from the turn indicator sensor, controlling the position of the automatic guided vehicle to allow the first drive wheel to follow one cross track and the second drive wheel to follow the other cross track to move the automatic guided vehicle laterally between the first and second guidepaths. 
         [0022]    The method includes mounting the turn indicator relative to the first and second cross tracks in a position so that the first drive wheel passes one of the first cross tracks before the turn indicator sensor detects the presence of the turn indicator. 
         [0023]    The method further includes disposing the second guidepath laterally to the right side of the guidepath and/or the left side with respect to the first direction of travel of the automatic guided vehicle. 
         [0024]    The method disposes the first and second cross tracks at an angle, about 45° angle, with respect to the first and second guidepaths. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0025]    The various features, advantages and other uses of the AGV motion control apparatus and method will become more apparent by referring to the following detailed description and drawing in which: 
           [0026]      FIG. 1  is a schematic representation of a prior art AGV turn clearance space requirement; 
           [0027]      FIG. 2  is a schematic representation of the turn space requirement for an AGV using the present method and apparatus; 
           [0028]      FIG. 3A  is a bottom elevational view of an example of an AGV which can use the present sideways movement method and apparatus; 
           [0029]      FIG. 3B  is a partial bottom perspective view of the AGV shown in  FIG. 3A . 
           [0030]      FIG. 4  is a pictorial representation of closed loop AGV guidepath; 
           [0031]      FIG. 5  is an enlarged, partial plan view of a portion of magnetic track of the guidepath showing left edge and right edge steering modes of the AGV movement along a guidepath; 
           [0032]      FIGS. 6 ,  7 ,  8  and  9  are pictorial representations of an AGV executing a right hand side step motion movement according to the present method and apparatus; 
           [0033]      FIGS. 10 and 11  are pictorial representations of an AGV executing a left hand side step motion according to the present method and apparatus; and 
           [0034]      FIG. 12  is a flow chart depicting the turn sequence control steps for an AGV executing a side step motion. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    In  FIG. 1 , there is depicted a pictorial representation an AGV  20  which has a first drive wheel  22  and a second drive wheel  24  (taken in a typical direction of forward and reverse movement of the AGV  20 ), mounted on a chassis or frame  26 . The AGV  20  follows a guidepath  28  formed of a magnetic or optical tape. 
         [0036]    Due the large length of the AGV  20 , when the AGV  20  executes a turn, such as the left hand turn shown by example in  FIG. 1 , successive rear and front corners  30  and  32  of the AGV  20  will project a considerable distance outward beyond the outline of the AGV  20  as the AGV  20  moves along the linear portions of the guidepath  28 . These large over hang areas  30  and  32  consume additional plant floor space which may cause a rearrangement of the plant facilities, such as shelves, part bins, tools, machines, or the inability to use the AGV  20  in such a tight defined location. 
         [0037]      FIG. 2  depicts a pictorial representation of the AGV  20  which utilizes a novel side step motion to enable the AGV  20  to execute a turn, such as the left hand turn illustrated in  FIG. 2 , between the first portion  36  of the guidepath  28  and a second, generally parallel portion  38  of the guidepath  28 . 
         [0038]    The side step motion according to the present method and apparatus utilizes two generally identically shaped, generally parallel disposed first cross track segment  40  and second cross track segment  42 . In general, and as will be described in greater detail hereafter, the AGV  20  moves along the first linear segment  36  of the guidepath  28  until the first drive wheel  22  passes the cross track segment  42 . At this time, the controller on the AGV  20  executes a left turn sequence for the longitudinally spaced, co-axial first drive wheel  22  and second drive wheel  24 . This causes the first drive wheel  22  to move along the first cross track segment  40  and the second wheel  24  to move along the second cross track segment  42 , generally in parallel with each other. This sidestep or crab movement translates the AGV  20  in a general parallel orientation between the first and second linear segments  36  and  38  and eliminates the overhang areas  30  and  32  in the prior art turn sequence shown in  FIG. 1 . 
         [0039]    In the following description, movement of the AGV  20  from left to right in the various orientations of the guidepath  28  will be described as a direction movement or a forward direction. An opposite movement or motion of the AGV  20  from right to left along the guidepath  28  will be termed a reverse or rearward direction of movement or simply direction B. 
         [0040]    Referring now to  FIGS. 3A and 3B , there is depicted in more detailed schematic illustration of the AGV  20 . For example, the AGV  20  depicted in  FIGS. 3A and 3B  can be a Creform FH-B35090 bidirectional AGV. A large base  23  having generally rectangular shape is mounted on the AGV  20 . The base  23  is fixed to a pair of mounting plates  21  by bolts on other fasteners. The mounting plates  21  formed by splitting the original elongated mounting plate of the AGV  20  into two separate plates  21  each fixed to one of two plates  57  and  59  each carrying one of the drive assemblies of the AGV  20 , such as a first drive assembly coupled to the plate  57  and a second drive assembly coupled to the plate  59 . A steering mechanism is provided for each drive assembly and includes a rotatable, electric motor driven, steering mechanism  56  and  58 , respectively. Activation of the steering mechanisms  56  and  58  via control signals from a controller, described hereafter, causes the electric motor of each steering mechanism  56  and  58  to rotate. The output of each steering mechanism motor is coupled through a sprocket to a drive belt which is in turn coupled to a sprocket or gear fixedly rotating with a bearing  67  for the plate  57  shown in  FIG. 3B . The bearing rotatably supports the first drive assembly which includes the first drive wheel  22 , the drive motor  50  and sensors  60  and  62 . The second drive assembly also includes a similar second drive wheel  24 , another drive motor  52  and sensors  64  and  66 . Activation of either of the drive motors of the steering mechanisms  56  and  58  causes the respective first or second drive assemblies to pivot about a vertical axis extending through the bearing  67  relative to the plates  57  or  59  in the appropriate direction to move the first and second independent drive wheels  22  and  24  of the AGV  20  along the guidepath  28  in a linear straight path of movement or in a turn or arcuate motion to follow a curved portion of the guidepath  28 . 
         [0041]    Consistent with the above-defined forward and rearward direction of movement of the AGV  20 , the plate  57  supports the first drive wheel  22  located at one edge of the chassis  21  and the plate  59  supports second located drive wheel  24  located adjacent an opposite edge of the chassis  21 . Each of the first and second drive wheels  22  and  24  is coupled to one electric drive motor  50  and  52 , respectively. The drive motors  50  and  52  are independently driven by a controller  55  also mounted on the base  23 . Each drive motor  50  and  52  is capable of opposite direction of output shaft rotation to enable the AGV  20  to move in either forward or rearward directions along the guidepath  28 . 
         [0042]    In the following discussion, the terms “forward direction of movement” and “rearward direction of movement” are taken with respect to the normal progression of the AGV  20  around the typically closed loop guide path  28  as shown in  FIG. 4  and described hereafter. This terminology is used by example as the AGV  20  is constructed for bi-directional movement in either of a first direction or direction A and an opposite second direction, such as direction B. 
         [0043]    A plurality of pivotal caster wheels  53  may be mounted adjacent opposite corners of the base  23  to provide stability for the AGV  20 . 
         [0044]    A controller  55 , which may include a central processor unit and memory, executes a control program stored in the memory to react to signals from sensors carried on each chassis  21  and other indicators located along a surface, such as a plant floor, road surface at the like, as well as the magnetic signals from the guide surface, such as the guidepath or track  28  which is typically in the form of a magnetic tape, to move the AGV  20  along the guidepath  28  in a prescribed direction of movement between one or more stop locations to load and unload parts, etc. 
         [0045]    The guidepath  28  may also be formed of an optically reflective tape which can be detected by an optical sensor carried on the AGV  20 . 
         [0046]    Consistent with the forward and rearward bi-directional movement of each of the first and second drive wheels  22  and  24 , a pair of sensors  60  and  62  for the first drive wheel  22 , and a pair of sensors  64  and  66  for the second drive wheel  24  are carried by each chassis  21 . The sensors,  60 ,  62 ,  64  and  66 , which may be Hall effect sensors, detect the magnetic field of the magnetic tape forming the guidepath  28  to provide signals to the controller  55  so that the controller  55  can direct the steering mechanisms  56  and  58  to retain the first and second drive wheels  22  and  24  on the guidepath  28  as the first and second drive motors  50  and  52  propel the AGV  20  along the guidepath  28  in the prescribed path. 
         [0047]    Turning now to  FIG. 4 , there is depicted an example of a generally closed loop guidepath. 
         [0048]    By way of example, the guidepath  28  includes a first linear portion  70  in which the AGV  20  moves between at least one or a pair of part or article load stations  72  and  74 . The parts are moved by automatic equipment carried at the article load stations  72  and  74  and/or on the base  23  of the AGV  20  to load the parts from the load stations  72  and  74  onto article support structure carried on the base  23 . 
         [0049]    After leaving the load station  74 , the AGV  20  executes a right side step motion or crab turn at location  76  on the guidepath  28 . The method and apparatus used to implement the side step turn will be described in greater detail hereafter. 
         [0050]    After completing the right side step motion, the AGV  20  then traverses along a slight curved segment  79  before making a less than 90° left turn at location  80 . 
         [0051]    The AGV  20  then traverses a second linear portion  82  of the guidepath  28  until it reaches unload station  84 . The parts carried on the chassis  21  of the AGV  20  are then unloaded by automatic conveying equipment from the support structure on the chassis  21  of the AGV  20  to the structure of the unload station  84 . 
         [0052]    After leaving the unload station  84 , the AGV  20  executes a left hand or left directed side step motion at guidepath location  86  before executing two consecutive left turns at location  88  and  90  before entering a third linear portion  92  of the guidepath  28 . 
         [0053]    By way example, the AGV  20  then executes a left turn at location  94  into a short linear segment  96  of the guidepath  28 . Upon coming to a stop, the AGV  20  reverses direction and then moves in a rearward direction along linear segment  98 , past location  76  back to a stop position at load station  72 . 
         [0054]    The details of the side step motion method and apparatus to implement the method will now be described in conjunction with  FIGS. 5-12 , for example. 
         [0055]    As shown in  FIG. 5 , the guidepath  28  is formed of a magnetic tape  100 . The guidepath tape  100  has a narrow width of generally 50 mm, for example, with a left edge  102  and a right edge  104 , as viewed in the forward movement or direction of movement of the AGV  20  along the guidepath  28 . 
         [0056]    By convention only, AGV  20  is programmed to use the left edge  102  of the magnetic tape  100  as a default guide edge. The controller  55 , in response to signals from the sensors  60  and  64  associated with the first and second drive wheels  22  and  24 , moves the first and second drive wheels  22  and  24  to the left edge  102  of the magnetic tape  100 . The sensors  60  and  64  detect the presence of the magnetic field from the magnetic tape  100  and the absence of a magnetic field adjacent to the left edge  102  to locate the left edge  102  of the magnetic tape  100 . 
         [0057]    As the AGV  20  approaches an upcoming left hand or left directed side step motion or a right hand or right directed side step motion location on the guidepath  28 , the controller  55 , with or without control signals from a programmable logic controller or PLC  54 , also mounted on the chassis  21 , determines when the AGV  20  has reached a position in advance of a right or left side step turn. In the case of a right side step turn, such as the right side step turn at location  76  shown in  FIG. 4  on the guidepath  28 , once the controller  55  has determined that the AGV  20  has reached a position to start the right side step turn, the controller  55  switches the position of the AGV  20  to the right edge  104  of the magnetic tape  100  for right edge sensing. 
         [0058]    Oppositely, when the AGV  20  is approaching a left side step turn, the controller  55  before reaching the location of the start of the left side step turn, the controller  55  will switch the position of the AGV  20  relative to the magnetic tape  100  to the right edge  104  sensing of the magnetic tape  100 . 
         [0059]    In order to facilitate the first right hand or right directed side step movement of AGV  20  along the guidepath  28  at location  76  shown in  FIG. 4 , the AGV  20  includes a turn indicator sensor  110  carried on the base  23  of the AGV  20 . The turn indicator sensor  110  is adapted for sensing a turn indicator  112 , such as a RFID tag, fixed in the plant floor at a location to provide appropriate turn signals to the controller  55  of the AGV  20 . The right directed side step turn uses a cross track segment A and a spaced, generally identical and generally parallel disposed cross track segment B, each formed of the same magnetic tape forming as the magnetic tape  100  in the main portion of the guidepath  28 . 
         [0060]    Each cross track segment B and A has a smoothly curved end segments which merge smoothly with the magnetic tape  100  of the guidepath  28  as well as the linear portions  78  of the guidepath  38 . In between the curved end portions of each cross track A and B is a generally linear segment which is disposed in parallel with the corresponding segment of the other cross track B or A. 
         [0061]    As the AGV  20  traverses along the first linear portion  70  of the guidepath  28 , the sensor  110  carried on the chassis  21  of the AGV  20  detects the turn indicator  112  when the AGV  20  reaches the location of the turn indicator  112  as shown in  FIG. 7 . 
         [0062]    When the turn indicator sensor  110  on the AGV  20  is located in proximity with or directly over a turn indicator  112  on the plant floor, the first drive wheel  22  will be positioned past the beginning curved segment of the cross track A. Since the controller  55  of the AGV  20  has previously positioned the AGV  20  so that the drive wheels  22  and  24  are moving along the left edge  102  of the magnetic tape  100  as shown in  FIG. 5 , the first drive wheel  22  continues past the curved entry portion of the cross track A and does not follow the cross track A. 
         [0063]    However, after the AGV  20  senses that it has reached the turn location position shown in  FIG. 7 , the controller  55 , upon receiving a signal from the turn indicator sensor  110  that it has sensed the turn indicator  112 , sends signals to the first and second drive wheels  22  and  24  steering mechanisms to direct the first and second drive wheels  22  and  24  to the right edge  104  of the magnetic tape  100 . In this position, the drive wheels  22  and  24  are positioned to follow the curved entry portions of the cross tracks B and A, respectively, and move along the cross tracks B and A as shown in  FIG. 8 . This moves the chassis  21  of the AGV  20  in a generally sideways, parallel, movement between the spaced linear portions  78  and  80  of the guidepath  28 , also depicted in  FIGS. 6-9  as lane 1 and lane 2, respectively. 
         [0064]    The AGV  20  continues along the first and second cross tracks A and B and follows the right edge of the magnetic tape  100  forming each of the cross tracks A and B as it moves through the curved end portions of the cross tracks A and B into the generally linear portion  78  or lane 2 of the guidepath  28 . 
         [0065]    After the drive wheels  22  and  24  of the AGV  20  have reentered the linear portion  78  of lane 2 of the guidepath  38 , either based on a measured distance traveled along the linear portions  78  or, alternately, based on time of travel along the linear portion  78 , the controller  55  switches back to left edge  102  sensing of the magnetic tape  100 . 
         [0066]    Referring back to  FIG. 4 , after executing the right side step motion at location  76  in the guidepath  28 , the AGV  20  traverses through the curved segment  79 , the left turn segment  80 , and the second linear segment  82  until it reaches the unload station  84 . 
         [0067]    At the completion of the unloading operation, a drive signal generated by the PLC  54  to the controller  55  will cause the AGV  20  to move in a forward direction on the guidepath  28  shown in  FIG. 10 . The controller  55 , based on a distance measurement from the unload station  84  or, time of travel measurement after leaving the unload station  84 , or the actual position of the AGV  20  reaching a predetermined point after leaving the unload station  84 , switches the position of the drive wheels  22  and  24  to follow the right edge  104  of the magnetic tape  100  so that the drive wheels  22  and  24  follow the first and second cross tracks D and C of the left hand side step turn  86 . As the AGV  20  moves in a generally parallel side step or crab motion between the linear portion  82  of the guidepath, as shown in  FIG. 11  to the short linear segment ahead of the left turn segment  88  of the guidepath  28 , the drive wheels  22  and  24  traverse along the first and second tracks D and C and smoothly merge and then follow the linear portion of lane 3 of the guidepath  28  ahead of the left turn segment  88 . 
         [0068]    As shown in  FIG. 10 , since the turn indicator sensor on the AGV  20  is mounted in a fixed location on the AGV  20 , the turn indicator  134 , which is mounted at a suitable location relative to the cross tracks C and D to indicate to the PLC  54  that a left side step or sideways turn is necessary, is mounted in a predetermined position relative to the cross tracks C and D, but is located outside of the lane 2 of the guidepath  28 , rather than between lane 2 and a parallel lane, referred to here as lane 3, or between the cross tracks C and D as in the previous side step turn location shown in  FIGS. 6-9 . 
         [0069]    The remainder of the movement of the AGV  20  along the guidepath  28  shown in  FIG. 4  follows left and right turns and forward and reverse directions of movement until the AGV  20  returns to the load station  72  shown in  FIG. 4 . 
         [0070]    The control sequence implemented by the PLC  54  in directing the AGV  20  in a right hand sidestep or sideways crab turn is shown in  FIG. 12 . 
         [0071]    In a forward movement direction  64 , the AGV  20  traverses along the guidepath  28  with the sensors  60  and  64  associated respectively with the first drive wheel  22  and the second drive wheel  24  detecting the magnetic tape  100  in step  160 . The output of the sensors  60  and  64  are input to the PLC  54  which then outputs to controller  55  direct to the front and rear steering mechanisms  56  and  58  to rotate in a direction to rotate the first drive assembly and the second drive assembly in the appropriate direction to position the AGV  20  toward the left edge  102  of the guidepath  28  as shown in  FIG. 5  and depicted in step  160  in  FIG. 12 . 
         [0072]    When the AGV  20  reaches the position  76  of the first sideways or crab turn as shown in  FIG. 4 , the sensor  110  will detect the turn indicator  112  mounted on or imbedded in the facility floor. At this time, the AGV  20  is in the position shown in  FIG. 7  in which the first drive wheel  22 , viewed in the direction of forward motion of the AGV  20  along the guidepath  28 , is positioned beyond the cross track A and B. 
         [0073]    Upon detecting the turn indicator  112  in step  164 , the PLC  54  activates the front and rear steering mechanisms  56  and  58  to move the AGV  20  to the right edge sensing position along the right edge  104  of the guide strip  28  as shown in  FIG. 5  in step  166  in  FIG. 12 . 
         [0074]    As the first guidepath  28  smoothly merges into the cross tracks A and B in step  168 , the front sensors  60  and  64  associated with the first and second drive wheels  22  and  24 , respectively, will follow the right edge from the linear portion  70  of the guidepath  28  to the smoothly continuous right edges of the cross tracks A and B. 
         [0075]    In step  170 , front sensors  60  and  64  detect the right turn and send signals to the PLC  54  which activates the steering mechanisms  56  and  58  to turn the first and second drive wheels  20  and  22  in a direction to allow the first and second drive wheels  20  and  22  to respectively follow the cross tracks A and B. 
         [0076]    Since a right sideways turn or movement ends in the second guidepath  78  which is, by example, substantially parallel to the first guidepath  28 , the first and second cross tracks B and A smoothly merge with the second guidepath  78  in a left turning curve. Thus, as shown in step  170 , after the AGV  20  enters the first and second cross tracks A and B as shown in  FIG. 8 , the PLC  54 , either based on distance traveled, time or a signal from a position sensor, sends signals to the steering mechanisms  56  and  58  to again drive the AGV  20  to the left edge  102  of the cross tracks A and B. In this manner, the sensors  60  and  64  track the left edge  102  of the second guidepath  78  in step  172  to enable the AGV  20  to continue traversing the linear portion of the second guidepath  78 . 
         [0077]    A left crab or sideways turn by the AGV  20  is executed in the same manner as the sequence of steps shown in  FIG. 12 , except that the turn is to the left relative to the forward direction of movement of the AGV  20 . 
         [0078]    The same sequence is also followed when the AGV  20  is moving in a rearward direction with the sensors  66  and  62  acting as the front most sensors for the AGV  20 . In reverse direction of movement, a right turn corresponds to a left turn in the forward direction or movement. A left turn in a rearward direction corresponds to a right turn in the forward direction or movement. 
         [0079]    Although a separate turn indicator sensor can be mounted on the AGV  20  and used or activated solely when the AGV  20  is moving in a reverse direction or direction B along the guidepath  28 , for economy, the same turn signal indicator  112  used for the forward direction of movement of the AGV  20 , as described above, is employed to detect turn indicators mounted in the plant floor to communicate a left or right hand side step turn when the AGV  20  is moving in a rearward direction. In this situation, the turn indicator  112  is mounted on the plant floor at a position ahead of first left or right cross track, so as to be detected by the turn indicator sensor  110  on the AGV  20 , now located along the rear edge of the AGV  20 , while at the same time, the now forward most drive wheel, such as drive wheel  24  in the rearward direction or movement of the AGV  20 , has passed the first cross track and is located between the first and second cross tracks as described above. 
         [0080]    It should be noted that the cross tracks A and B, and C and D, are disposed at an approximate 45° included or acute angle relative to the linear portion of the first guidepath  28 . It will be understood that other angular orientations of the first and second cross tracks A and B relative to the linear portion of the first guide track  28  may also be implemented, with a shallower or less than 45° angle being employed to move the AGV a smaller distance sideways or a steeper angle greater than 45° up to approximately 55°, for moving the AGV  20  a greater lateral distance between the first and second guidepaths  28  and  38 . 
         [0081]    It is also possible to move the AGV  20  in a U-turn between the first and second guidepaths  28  and  38  so that the AGV  20  traverses the second guidepath  38  in a rearward direction of movement as opposed to a forward direction of movement along the first guidepath  28 . In executing a U-turn, part way through the U-portion of the two cross tracks, the second drive wheel  22  assumes a forward leading position relative to the original first drive wheel  20  and acts as a forward or front most drive wheel as the AGV  20  traverses in a reverse direction along the second guidepath  38 .