VEHICLE LOCATION AND HEADING COMPUTER SYSTEM

• US 3,715,572 A
• Filed: 03/05/1971
• Issued: 02/06/1973
• Est. Priority Date: 03/05/1971
• Status: Expired due to Term

• Current Assignee: AB Volvo
• Original Assignee: Dale E. Bennett
• Inventors: Bennett, Dale E.
• Primary Examiner(s): Gruber, Felix D.
• Application Number:
  US05/121,437
• Time in Patent Office: 704 Days
• Field of Search: 235/150.2,150.24,92V,92TC,92SH 318/587 340/24,52,268 250/219D,219DC,223 180/79,79.1,98 172/3
• US Class Current: 701/300
• CPC Class Codes: G05D 1/0272 comprising means for registering the travel distance, e.g. revolutions of wheels measuring distance traversed on the ground by vehicles, e.g. using odometers G01C22/00

Abstract

A system is provided in which pulses generated by the rotation of the wheels or tracks of a vehicle are processed to provide representations of the heading and location of the vehicle relative to X and Y coordinate axes. The angle between vehicle heading and the X axis is represented by the binary value stored in an angle register, the angle register being updated by the generated pulses each time the vehicle travels a predetermined distance. An associated quadrant register provides a binary representation of that one of the four quadrants of the coordinate system in which the vehicle heading is located. Binary representations of the vehicle location relative to the X and Y axes are stored in X and Y registers, which registers are updated in accordance with incremental changes in X and Y by computing the sine and cosine of the new angle stored in the angle register upon each updating of the angle register. The stored angle and X, Y representations are converted into analog values to provide a visual display of the vehicle heading and location. The stored representations are also processed by apparatus which provides for operation of the vehicle over a predetermined course without the need for a driver or operator.

Claims

1. A heading and location computer system for use with a vehicle having a pair of rotatable means which undergo rotation in response to movement of the vehicle over a surface comprising:

means associated with one of the pair of rotatable means for generating an electrical signal indication each time the one of the pair of rotatable means undergoes a predetermined increment of rotation;

means associated with the other one of the pair of rotatable means for generating an electrical signal indication each time the other one of the pair of rotatable means undergoes a predetermined increment of rotation;

means for storing a representation of the heading of the vehicle;

means associated with the means for storing a representation of the heading and responsive to the generated electrical signal indications for periodically applying the signal indications to the means for storing a representation of the heading to change the stored representation;

means for storing a representation of the location of the vehicle; and

means associated with the means for storing a representation of the location and responsive to each change in the stored direction representation for changing the stored location representation in accordance with the value of the stored direction representation.

2. A heading and location computer system according to claim 1, wherein the means for periodically applying the signal indications includes means for applying the signal indications to the means for storing a representation of the heading to change the stored direction representation each time the vehicle travels a predetermined fixed distance over the surface, the stored direction representation represents the angle between the heading of the vehicle and one of a pair of mutually perpendicular references axes, and the means for changing the stored location representation includes means for computing the sine and cosine of the angle between the heading of the vehicle and the one of the pair of reference axes.

3. A heading and location computer system according to claim 1, further including means for steering the vehicle over a predetermined course on the surface comprising means for providing a representation of a desired change in the location of the vehicle, means responsive to each change of the stored location representation for reducing the desired change representation by an amount equal to each change in the stored location representation, and means responsive to the desired change representation as reduced by changes in the stored location representation for steering the vehicle in accordance with the value thereof.

4. A heading and location system according to claim 3, wherein the means for steering the vehicle in accordance with the value of the desired change representation is responsive to the vehicle heading representation to steer the vehicle in accordance with the value of the desired change representation is responsive to the vehicle heading representation to steer the vehicle in accordance with the value of the vehicle heading representation as well as the desired change representation.

5. A heading and location computer system according to claim 1, wherein the means for storing a representation of the heading of the vehicle comprises a first register coupled to the means for periodically applying the signal indications for storing a digital number representing the angle between the heading of the vehicle and a first reference axis along the surface, and the means for storing a representation of the location of the vehicle comprises second and third registers coupled to the means for changing the stored location representation, the second register storing a digital number representing the distance between the vehicle and the first reference axis and the third Register storing a digital number representing the distance between the vehicle and a second reference axis along the surface and perpendicular to the first reference axis.

6. A heading and location computer system according to claim 5, further including means responsive to the second and third registers for providing a visual indication of the location of the vehicle relative to the first and second reference axes.

7. A computer system for use with a vehicle having first and second rotatable means which undergo rotation in response to movement of the vehicle over a surface comprising:

first pulse generating means for generating a pulse each time the first rotatable means undergoes a predetermined increment of movement;

second pulse generating means for generating a pulse each time the second rotatable means undergoes a predetermined increment of movement;

first and second pulse storing means respectively associated with the first and second pulse generating means for temporarily storing the pulses generated by the first and second pulse generating means, respectively;

counting means for storing a pulse count representing the angle between the direction of travel of the vehicle and a reference axis along the surface; and

means coupled between the counting means and the first and second pulse storing means and responsive to the pulses stored by the first and second pulse storing means for changing the pulse count stored in the counting means by an amount equal to the difference between the numbers of pulses temporarily stored in the first and second pulse storing means whenever the total number of pulses temporarily stored in the first and second pulse storing means equals a predetermined number.

8. A computer system according to claim 7, further including means coupled between at least one of the first and second pulse generating means and the associated pulse storing means and responsive to the pulses generated by the pulse generating means coupled thereto for independently providing to the pulse storing means coupled thereto a selected portion of the generated pulses to provide wheel diameter error compensation.

9. A computer system according to claim 7, further including means coupled between at least one of the first and second pulse generating means and the associated pulse storing means and responsive to the pulses generated by the pulse generating means coupled thereto for independently providing to the pulse storing means coupled thereto a selected portion of the generated pulses for subtraction from the pulses stored in the pulse storing means to provide compensation for roughness of the surface.

10. A computer system according to claim 9, wherein the means for providing compensation for roughness of the surface includes means responsive to vertical motion of that one of the first and second rotatable means to which the at least one of the first and second pulse generating means is coupled for generating signals representing the extent of vertical motion for a given increment of movement of the vehicle over the surface, means responsive to the signals representing the extent of vertical motion for providing a representation of the angle between the surface at the given increment of movement and the overall general plane of the surface, and means responsive to the pulses generated by the pulse generating means coupled thereto for determining the selected portion of the generated pulses for subtraction from the pulses stored in the pulse storing means in accordance with the representation of the angle between the surface and the overall general plane.

11. A computer system according to claim 10, wherein that one of the first and second rotatable means to which the least one of the first and second pulse generating means is coupled comprises a wheel and included axle pivotably mounted on the vehicle such that the wheel and included axle are capable of undergoing vertical motion relative to the vehicle, and wherein the means for generating signals representing the extent of vertical motion comprises an armature assembly having at least one brush and a plurality of related contacts, the brush making and breaking contact with different ones of the contacts as the axle pivots to generate the signals representing the extent of vertical motion.

12. A computer system according to claim 7, wherein the first and second pulse storing means comprise first and second binary register means normally biased to count up in response to pulses generated by the first and second pulse generating means, respectively, the counting means comprises third binary register means, and the means for changing the pulse count includes third pulse generating means, means responsive to the first and second pulse generating means for providing a signal whenever the total number of generated pulses equals a predetermined number, means responsive to the signal for coupling the third pulse generating means to the first and second binary register means to count down the first and second binary register means, and means for coupling the third pulse generating means to the third binary register means to change the pulse count in the third binary register means in response to pulses generated thereby whenever the third pulse generating means is applied to count down the first and second binary register means.

13. A computer system according to claim 12, wherein the means responsive to the signal for coupling the third pulse generating means to the first and second binary register means to count down the first and second binary register means includes means for counting down first one and then the other of the first and second binary register means, and the means for coupling the third pulse generating means to the third binary register means to change the pulse count in the third binary register means includes means for causing the third binary register means to count in one direction as the first binary register means is being counted down and in the opposite direction as the second binary register means is being counted down.

14. A computer system according to claim 7, further including means responsive to the pulse count stored by the counting means for providing a visual display of the direction of travel of the vehicle in accordance with the value of the pulse count stored by the counting means.

15. A computer system according to claim 14, wherein the means for providing a visual display includes means for generating an analog signal having a value representative of the value of the pulse count stored by the counting means, and means having a rotatable pointing device and responsive to the analog signal to rotate the pointing device through an angle according to the value of the analog signal.

16. A system for computing and storing representations of the location and heading of a vehicle relative to mutually perpendicular X and Y reference axes, the vehicle having first and second rotatable means which undergo rotation in response to movement of the vehicle over a surface, comprising:

means for storing a representation of the angle between the vehicle heading and the X axis;

means associated with the means for storing a representation of the angle between the vehicle heading and the X axis and responsive to the movement of the vehicle over the surface by a given amount for changing the stored representation of the angle between the vehicle heading and the X axis by an amount dependent upon the difference between incremental rotations of the first and second rotatable means during movement of the vehicle by the given amount;

means for storing a representation of the location of the vehicle relative to the X and Y axes; and

means associated with the means for storing a representation of the location of the vehicle relative to the X and Y axes and responsive to each change in the stored representation of the angle between the vehicle heading and the X axis for changing the stored rePresentation of the location of the vehicle relative to the X and the Y axes by an amount dependent on the value of the stored representation of the angle between the vehicle heading and the X axis.

17. A system according to claim 16, wherein the first and second rotatable means comprise wheels having axes of rotation which are fixed relative to the longitudinal axis of the vehicle.

18. A system according to claim 16, wherein the first and second rotatable means comprise wheels having endless tracks disposed thereabout, said wheels having axes of rotation which are fixed relative to the longitudinal axis of the vehicle.

19. A system according to claim 16, wherein the means for storing a representation of the angle between the vehicle heading and the X axis includes an angle register for storing a digital number representing the angle, the angle register being coupled to the means for changing the stored representation of the angle between the vehicle heading and the X axis, the means for storing a representation of the location of the vehicle includes X and Y registers for storing digital numbers representing the distance between vehicle location and the X and Y axes respectively, the X and Y registers being coupled to the means for changing the stored representation of the location of the vehicle relative to the X and Y axes, and the means for changing the stored representation of the location of the vehicle relative to the X and Y axes includes means responsive to each change in the digital number stored in the angle register for changing the digital number stored in the Y register by an amount which bears a first proportional relationship to the digital number stored in the angle register and means responsive to each change in the digital number stored in the angle register for changing the digital number stored in the X register by an amount which bears a second proportional relationship to the digital number stored in the angle register.

20. A system according to claim 19, further including means for entering in the Y register a digital number representing the actual distance between the vehicle and the X axis whenever the vehicle crosses an elongated sensor strip disposed on the surface with its axis of elongation generally parallel to the Y axis, the sensor strip having a plurality of coded surfaces parallel to the axis of elongation, each of the coded surfaces varying in digital fashion with the distance from the X axis and each coded surface corresponding to a different digit of the digital number in the Y register so as to present different binary numbers at different distances from the X axis.

21. A system according to claim 19, further including means for entering in the angle register a digital number representing the actual angle between the heading of the vehicle and the X axis whenever the vehicle crosses an elongated sensor strip disposed on the surface with its axis of elongation generally parallel to the Y axis, the sensor strip presenting electrical current paths of different resistance between different points along one longitudinal side of the strip and each of a plurality of different points along the opposite longitudinal side of the strip, and the means for entering includes an elongated element mounted on the vehicle for inducing a signal at a point along the one longitudinal side over which the elongated element lies as the vehicle crosses over the sensor strip and for sensing the resulting signal at a point along the other longitudinal side over which the elongated element lies.

22. A system according to claim 19, wherein the means for changing the digital number stored in the Y register and the digital number stored in the X register include means for changing the number stored in the Y register by the sine of the angle represented by the digital number in the angle register and means for changing the number stored in the X register by the cosine of the angle rEpresented by the digital number in the angle register.

23. A system according to claim 19, wherein the angle register comprises a plurality of stages, all of which assume binary '"'"''"'"''"'"''"'"'zero'"'"''"'"''"'"''"'"' to represent 0* and binary '"'"''"'"''"'"''"'"'one'"'"''"'"''"'"''"'"' to represent 90*, and the X and Y axes define four different quadrants of a coordinate system, and further including a quadrant register coupled to the angle register for storing a digital number representing the quadrant in which the vehicle heading is located.

24. A system according to claim 19, further including means for driving the vehicle over a predetermined course without the need for an operator, the means for driving including a Delta Y register having a pair of inputs and operative to provide at an output thereof a position error signal in the form of a digital number representing the combination of digital numbers applied to the pair of inputs, means for providing at one of the pair of inputs of the Delta Y register a digital number representing the distance in the direction of the Y axis between actual vehicle location and a desired vehicle location, means responsive to the means for changing the digital number stored in the Y register for applying each change in the Y register digital number to the other one of the pair of inputs of the Delta Y register as a position feedback signal, and means responsive to the position error signal at the output of the Delta Y register for steering the vehicle in a direction to tend to reduce the position error signal to zero.

25. A system according to claim 24, further including means for providing to the means for steering the vehicle a succession of error signals of alternating sense and relatively small size to cause oscillation of the means for driving about a null balance condition whenever the position error signal is substantially zero.

26. A system according to claim 24, further including means for providing at an output thereof a combined error signal in the form of a digital number representing the combination of digital numbers applied to a pair of inputs thereof, the output of the Delta Y register being coupled to one of the pair of inputs to provide the position error signal thereto and the angle register being coupled to the other one of the pair of inputs to provide an angle error signal thereto, and the means for steering the vehicle is responsive to the combined error signal to steer the vehicle in a direction to tend to reduce the combined error signal to zero.

27. A system according to claim 24, further including separate means for providing a turn around of the vehicle at opposite selected positions relative to the X axis, each of the means for providing a turn around including means for generating a sequence of turn around commands whenever the vehicle reaches a selected position relative to the X axis, means responsive to the sequence of turn around commands for steering the vehicle through a first turn, means responsive to the sequence of turn around commands for steering the vehicle through a second turn in a direction opposite to that of the first turn upon completion of the first turn, means responsive to the sequence of turn around commands for disabling the means for steering the vehicle in a direction to tend to reduce the position error signal to zero when the vehicle is being steered through the first and second turns, and wherein the means for providing a digital number representing the distance in the direction of the Y axis between actual vehicle location and a desired vehicle location comprises means responsive to the completion of the first turn for providing at the one of the pair of inputs of the Delta Y register a digital number representing the desired change in the location of the vehicle in a direction parallel to the Y axis after the vehicle is steered through the first and second turns.

28. A system for computing and storing represenTations of the location and heading of a vehicle relative to a coordinate system defined by two intersecting axes, the vehicle including left and right rotatable means in contact with a surface over which the vehicle travels and having axes of rotation which are affixed relative to the vehicle longitudinal axis, comprising the combination of:

left and right pulse generators respectively associated with the left and right rotatable means, each of the generators producing a pulse each time the rotatable means associated therewith undergoes a fixed increment of motion;

left and right binary register means respectively associated with the left and right pulse generators, each of the register means being operative to count pulses generated by the pulse generator associated therewith;

binary angle register means for storing a pulse count representative of the angle between the vehicle heading and one of the axes of the coordinate system;

binary quadrant register means for storing a binary value representative of the particular quadrant of the coordinate system in which the vehicle heading lies;

means coupled between the left and right binary register means and the binary angle register means and binary quadrant register means for changing the pulse count in the angle register means by an amount equal to the pulse count in the left register means in one sense and by an amount equal to the pulse count in the right register means in the opposite sense from the one sense whenever the total of the pulse counts in the left and right register means reaches a predetermined value, the one sense and opposite sense being determined by the binary value in the quadrant register means, and the binary value in the quadrant register means being changed to represent a new quadrant whenever the pulse count in the angle register means reaches a maximum or minimum value;

first binary coordinate register means for storing a pulse count representative of the vehicle location relative to one of the axes of the coordinate system;

means coupled between the binary angle register means and the first binary coordinate register means for changing the pulse count stored in the first coordinate register means by an amount corresponding to the sine of the angle represented by the pulse count in the angle register means each time the pulse count in the angle register means is changed, the sense of the change in the pulse count of the first coordinate register means being determined by the binary value in the quadrant register means;

second binary coordinate register means for storing a pulse count representative of the vehicle location relative to the other one of the axes of the coordinate system; and

means coupled between the binary angle register means and the second binary coordinate register means for changing the pulse count in the second coordinate register means by an amount corresponding to the cosine of the angle represented by the pulse count in the angle register means each time the pulse count in the angle register means is changed, the sense of the change in the pulse count of the second coordinate register means being determined by the binary value in the quadrant register means.

29. A system as defined in claim 28, wherein the means for changing the binary count in the angle register means includes second left and right pulse generators respectively associated with the left and right binary register means and coupled to change the pulse count in the angle register means when actuated, and each of the left and right binary register means includes first and second binary registers and first and second zero logic means respectively associated therewith, the first register being coupled to count up from zero value in response to the generation of pulses by the first-mentioned pulse generator associated therewith except when the second pulse generator associated therewith is actuated, the first register being coupled to count down to zero value in response to Actuation of the second pulse generator associated therewith and the first zero logic means terminating the count down of the first register whenever the first register reaches zero value, the second register being coupled to count up from zero value in response to the generation of pulses by the first-mentioned pulse generator associated therewith whenever the first register is counting down and thereafter being coupled to count down to zero value, the second zero logic means terminating the count down of the second register whenever the second register reaches zero value.

30. A system as defined in claim 29, wherein the means for changing the pulse counts stored in the first and second coordinate register means together comprise binary sine-cosine register means, means responsive to a change in the pulse count of the angle register means for temporarily storing in the sine-cosine register means a first pulse count equal to the new pulse count of the angle register means and for subsequently temporarily storing in the sine-cosine register means a second pulse count equal to the difference between the new pulse count of the angle register means and a predetermined maximum pulse count value, means responsive to the first pulse count in the sine-cosine register means for changing the pulse count in the first coordinate register means by a selected portion of the first pulse count, and means responsive to the second pulse count in the sine-cosine register means for changing the pulse count in the second coordinate register means by a selected portion of the second pulse count.

31. A system as defined in claim 30, further including timing means for initiating an eight-step sequence each time the total of the pulse counts in the left and right register means reaches the predetermined value, the first register of the left register means being coupled to count down during the first step of the sequence and up at all other times, the second register of the left register means being coupled to count up during the first step and down during the second step of the sequence, the first register of the right register means being coupled to count down during the third step of the sequence and up at all other times, the second register of the right register means being coupled to count up during the third step and down during the fourth step of the sequence, the first pulse count being temporarily stored in the sine-cosine register means during the fifth step of the sequence, the pulse count in the first coordinate register means being changed by a selected portion of the first pulse count during the sixth step of the sequence, the second pulse count being temporarily stored in the sine-cosine register means during the seventh step of the sequence, and the pulse count in the second coordinate register means being changed by a selected portion of the second pulse count during the eighth step of the sequence.

32. A system as defined in claim 30, wherein the means for changing the pulse count in the first and second coordinate register means together comprise a pulse generator, means coupled between the pulse generator and the sine-cosine register means for counting the sine-cosine register means down to zero value in response to the generation of pulses by the pulse generator, means associated with the sine-cosine register means and responsive to the pulse count stored therein to provide a continuous indication of that one of a plurality of arbitrarily defined ranges of value into which the stored pulse count is determined to fall, and means responsive to the means for providing a continuous indication of range of value for passing a portion of the pulses generated by the pulse generator to the first and second coordinate register means, the portion being variable for the different ranges and being selected in accordance with the indication of range of value.

33. A system as defined in claim 32, wherein each of the ranges represents the corresponding sine for a different range Of possible values of the angle between vehicle heading and one of the axes of the coordinate system.

34. An arrangement for providing a visual display of the location of a vehicle relative to mutually perpendicular X and Y axes, the vehicle having a pair of rotatable means which undergo rotation in response to movement of the vehicle over a surface, comprising:

means including X and Y registers and responsive to the pair of rotatable means for computing the distance between the location of the vehicle and each of the X and Y axes, the distances being represented by digital numbers stored in the X and Y registers;

X and Y digital-to-analog converter means associated with the X and Y registers respectively for converting the digital numbers stored in the associated registers to actual X and Y analog signals;

image projection tube means including an evacuated envelope having a face plate with a pair of mutually perpendicular X and Y axes superimposed thereon to correspond to the first-mentioned X and Y axes and means at least partially located within the envelope for scanning an electron beam across the face plate;

means associated with the tube means and responsive to the scanning of the electron beam for generating desired X and Y analog signals representing the distance between the electron beam and the X and Y axes superimposed on the face plate; and

means associated with the means for scanning an electron beam and responsive to the actual and desired X and Y analog signals for intensity modulating the electron beam to produce a visible spot on the face plate whenever the actual and desired X analog signals are substantially equal and the actual and desired Y analog signals are substantially equal.

35. An arrangement for providing a visual display of the heading of a vehicle relative to mutually perpendicular X and Y axes, the vehicle having a pair of rotatable means which undergo rotation in response to movement of the vehicle over a surface, comprising:

means including an angle register and responsive to the pair of rotatable means for computing the angle between the vehicle heading and the X axis, the angle being represented by a digital number stored in the angle register;

digital-to-analog converter means associated with the angle register for converting the digital number stored therein into an analog angle signal; and

means including a pointer rotatable relative to a scale having mutually perpendicular X and Y axes superimposed thereon to represent the first-mentioned X and Y axes and responsive to the analog angle signal to position the pointer at an angle relative to the superimposed X and Y axes corresponding to the value of the analog angle signal.

36. An arrangement according to claim 35, wherein the X and Y axes define four different quadrants, and the analog angle signal represents the actual value of the digital number when the vehicle heading lies in either of two of the four quadrants and the complementary value of the digital number when the vehicle heading lies in either of the other two of the four quadrants, and further including means for adding to the analog angle signal an analog signal representing the quadrant in which the vehicle lies.

37. An arrangement for driving a vehicle over a predetermined course without the need for an operator, the vehicle having a pair of rotatable means which undergo rotation in response to movement of the vehicle over a surface having a reference axis disposed therealong, comprising:

means including an angle register for periodically computing the angle between vehicle heading and the reference axis, the angle being represented by an angle digital number stored in the angle register and updated each time the angle is computed;

means including a coordinate register and responsive to the angle register to compute the change in the actual distance between vehicle location and the refeRence axis each time the angle is updated, the distance being represented by a digital number stored in the coordinate register;

means providing a digital number representing a desired distance between vehicle location and the reference axis; and

means responsive to the actual distance and desired distance digital numbers for steering the vehicle in a manner so as to tend to reduce the difference therebetween to zero.

38. An arrangement according to claim 37, further including at least one means responsive to the location of the vehicle at a particular point relative to the length of the reference axis for initiating a turn around movement of the vehicle, the means for steering the vehicle being non-responsive to the actual distance digital number during the turn around movement, means coupled to the means for steering and responsive to the initiation of the turn around movement to steer the vehicle through a first turn of predetermined duration, means coupled to the means for steering and responsive to the termination of the first turn to steer the vehicle through a second turn of predetermined duration.

39. An arrangement according to claim 37, wherein the means for steering is responsive to the angle digital number as well as the actual distance and desired distance digital numbers and is operative to steer the vehicle in a manner so as to tend to reduce both the angle digital number and difference between the actual distance and desired distance digital numbers to zero.

40. An arrangement according to claim 39, wherein the means for steering is responsive to the angle digital number as increased by a weighting factor.

41. An arrangement according to claim 37, wherein the means for steering includes a Delta Y register responsive to the desired distance digital number and to the changes in the actual distance digital number for providing a position error signal in the form of a digital number representing the algebraic combination of the desired distance digital number and the changes in the actual distance digital number, and a transfer register responsive to the position error digital number and the angle digital number for providing a combined error signal in the form of a digital number representing the algebraic combination of the position error digital number and the angle digital number.

42. An arrangement according to claim 41, wherein the angle register and the transfer register both comprise a plurality of stages arranged in binary fashion from a least significant bit stage to a most significant bit stage, and the 3 least significant bit stages of the angle register are coupled to the three stages of the transfer register which are 3 stages removed from the 3 least significant bit stages thereof to provide to the transfer register the 3 least significant bits of the angle digital number weighted by a factor of eight.

43. An arrangement according to claim 41, wherein the means for steering includes means for generating a succession of incremental biases of alternating polarity to cause oscillation of the means for steering about a null balance condition whenever the combined error signal is of substantially zero value.

44. An arrangement according to claim 41, wherein the means for steering includes a drivable steering mechanism for the vehicle, a steering register for temporarily storing the combined error signal digital number, and pulse generating means for substantially simultaneously providing pulses to drive the steering mechanism and to count down the steering register until the digital number in the steering register reaches zero value.

45. An arrangement according to claim 44, wherein the means for steering includes means for repetitively initiating the generation of successive groups of pulses by the pulse generating means whenever the digital number in the steering register is of zero value, the groups of pulses being applied to the steering register to cause the alternate driving of The steering mechanism in opposite directions.

46. An arrangement for turning around a vehicle traveling a first substantially straightline path so as to direct the vehicle onto a second substantially straightline path parallel to the first straightline path without the need for an operator, the vehicle having a mechanism for the steering thereof and a pair of rotatable means which undergo rotation in response to movement of the vehicle over a surface relative to mutually perpendicular X and Y axes, the first and second straightline paths being parallel to the X axis, comprising:

means including X and Y registers having stored digital numbers therein representing the distances between the vehicle and the X and Y axes respectively and responsive to the pair of rotatable means of the vehicle to update the digital numbers stored in the X and Y registers by appropriate changes thereof each time the vehicle travels a predetermined fixed distance;

counting means responsive to the location of the vehicle at a selected position relative to the X axis for thereafter providing a count of the number of times the X and Y registers are updated;

means responsive to a first count of predetermined value in the counting means for positioning the steering mechanism to initiate a first turning movement of the vehicle;

means responsive to a second count of predetermined value in the counting means for terminating the first turning movement of the vehicle by positioning the steering mechanism to initiate a second turning movement of the vehicle; and

means responsive to a third count of predetermined value in the counting means for terminating the second turning movement of the vehicle by positioning the steering mechanism for straight ahead travel of the vehicle.

47. An arrangement according to claim 46, further including a Delta Y step register for storing a digital number representing the desired distance in the direction of the Y axis between the first and second straightline paths, a Delta Y register having a pair of inputs and operative to provide the algebraic combination of the inputs to an output thereof, means for providing the change in the Y register digital number upon each updating to one of the pair of inputs of the Delta Y register, means for providing the desired distance digital number to the other one of the pair of inputs of the Delta Y register upon initiation of the second turning movement, and means responsive to the completion of the second turning movement for positioning the steering mechanism so as to tend to drive a non-zero digital number at the output of the Delta Y register to zero.

48. An arrangement according to claim 46, wherein the vehicle comprises a tractor having an attached plow which may be lowered to perform plowing and raised to terminate the plowing and an engine of variable torque so as to control the speed of the tractor, and further including means responsive to the location of the vehicle at the selected position relative to the X axis for raising the plow and decreasing the engine torque, and means responsive to the location of the vehicle at a second selected position relative to the X axis upon completion of the second turning movement for lowering the plow and increasing the engine torque.

49. An arrangement for periodically entering in a register a binary number representing the actual distance between a vehicle and a reference axis along a surface over which the vehicle travels comprising:

at least one elongated sensor strip disposed on the surface with its axis of elongation generally normal to the reference axis, the sensor strip including a plurality of elongated coded surfaces parallel to the axis of elongation, the coded surfaces varying in binary fashion with distance from the reference axis to present different binary numbers at different distances from the reference axis;

sensing means mounted on the vehicle for sensing the binary number presented by the coded surfaces whenever the vehicle crosses the sensor strip; and

means responsive to the sensing of a binary number by the sensing means for entering the sensed binary number in the register.

50. An arrangement according to claim 49, wherein each of the coded surfaces corresponds to a different bit position within the register and comprises a sequence of alternately light reflecting and non-reflecting surfaces, and the means for sensing comprises a different light source and reflected light detector combination associated with each of the coded surfaces.

51. An arrangement according to claim 49, further including means for effecting turn around of the vehicle after it crosses the sensor strip, means for generating a binary number representing the desired change in location of the vehicle relative to the reference axis prior to each turn around of the vehicle, means responsive to the desired change binary numbers for providing an updated sum thereof each time a new desired change binary number is generated, and Delta Y register means coupled to receive the updated sum of the desired change binary numbers and the sensed binary number in the first-mentioned register for steering the vehicle in accordance with the difference therebetween upon completion of the turn around.

52. An arrangement for periodically entering in a register a binary number representing the actual angle between the heading of a vehicle and a reference axis along a surface over which the vehicle travels comprising:

at least one elongated sensor strip disposed on the surface with its axis of elongation substantially normal to the reference axis, the sensor strip presenting electrical current paths of different resistance between different points along one longitudinal side of the strip and each of a plurality of different points along the opposite longitudinal side of the strip;

sensing means including an elongated element mounted on the vehicle for inducing a signal at a point along the one longitudinal side over which the elongated element lies as the vehicle crosses over the sensor strip and for sensing the resulting signal at a point along the other longitudinal side over which the elongated element lies; and

means responsive to the sensed signal for entering in the register a binary number corresponding to the size of the sensed signal.