referring now to fig1 therein is shown a conventional row crop cultivator 10 connected by hitch structure 12 to the three - point hitch 14 of a tractor or towing vehicle 16 . the row crop cultivator 10 includes a transverse tool - carrying frame or toolbar 18 supporting a plurality of transversely spaced cultivating rigs 20 each having a plurality of earth - working tools 22 . the rigs 20 are spaced such that when the cultivator 10 is towed forwardly through a field of row crops and is properly aligned with the rows , the earth - working tools 22 will work the soil between the rows without contacting the plants . as best seen in fig1 - 4 , the hitch structure 12 includes main upright framework 26 having a pair of vertically spaced and transversely extending tubular beams 28 and 30 connected by inner diagonal beam members 32 . the outer ends of the tubular beams 28 and 30 are connected by transversely spaced , parallel plates 34 which , as best seen in fig4 ., extend downwardly below the bottom of the tubular beam 28 . the lower portion of each pair of plates 34 is apertured , and a pin 38 extending through the apertures carries bushings 40 which are received in a downwardly directed recess 42 of the lower hook portion 44 of the three - point hitch 14 . a reinforced upper bracket 48 includes a rear portion 50 extending upwardly from the top of the diagonal beam members 32 . a top portion 52 extends forwardly above the tubular beam 30 . a pair of upright plates 54 are welded to the tubular beam 30 and to the rear and top portions 50 and 52 and carry a pair of vertically spaced pins 56 which are centrally located between the lower pins 38 . the upper pin 56 is received in an upwardly opening recess of upper hook portion 60 of the three - point hitch 14 . the hooked portions 44 and 60 are part of a quick attachment frame 64 connected to an upper arm 66 and a pair of lower arms 68 of the three - point hitch 14 . the frame 64 permits the hitch structure 12 to be quickly and easily connected to or disconnected from the three - point hitch . the transverse tool - carrying frame 18 is supported from , and transversely rockable with respect to , the main upright framework 26 by first and second rigid arms 70 extending above the frame 18 and by third and fourth rigid arms 72 extending below the frame 18 . each of the rigid arms 70 and 72 includes a short tubular beam 76 with front and rear hinge structure 78 and 80 welded to the opposite vertical faces of the respective ends of the beam 76 . the hinge structure 78 for the upper arms 70 is pivotally connected to the tubular beam 30 between the side plates 34 by bearings 81 . the lower arms 72 are connected in similar fashion by bearings 82 to the lower beam 28 . in the preferred embodiment , as best viewed in fig4 the upper and lower arms 70 and 72 , respectively , on each side are vertically aligned and are constrained to rock about a vertical pivotal axis 86 . the arms 70 and 72 are supported in substantially cantilever fashion from the respective beams 30 and 28 , and the structure of the main upright framework 26 prevents any significant rocking of the arms other than about the vertical axes 86 . the transverse frame 18 , which in the preferred embodiment is tubular and has a rectangular cross section , is supported from the upright framework 26 by the four arms 70 and 72 . as best seen in fig3 the beam is supported between the upper and lower arms 70 and 72 , respectively , immediately behind the framework 26 by a pair of transversely spaced brackets 90 pivotally connected to the respective arm pairs 70 , 72 . each bracket 90 includes upper and lower transverse bracket beams 92 pivotally connected to the hinge portions 80 by centrally located bearings 94 and 95 , respectively . vertical straps or plates 96 are welded to the aft faces of the bracket beams 92 and vertically space the bearings 94 and 95 a distance equal to that of the spacings between the corresponding bearings 81 and 82 located in the upright framework 26 . gussets 100 are welded to the ends of the bracket beams 92 and to the vertical straps 96 . the beam 18 is secured between the rear vertical straps 96 and forward vertical straps 102 by bolts 104 passing through the straps adjacent the opposite vertical faces of the beam . the brackets 90 are adjusted so that the four arms 70 and 72 are parallel to each other and are constrained to rock in unison with each other . the arms 70 and 72 thereby form with the upright framework 26 and the portion of the frame 18 between the brackets 90 four - bar parallel linkage structure which permits the frame 18 to rock transversely while remaining substantially perpendicular to the forward direction of travel . the arms 70 and 72 transmit the entire draft load from the cultivator 10 to the three - point hitch 14 . when the three - point hitch structure 14 is raised from the position shown in fig1 substantially the entire weight of the row crop cultivator 10 is carried by the arms 70 and 72 from the main upright framework 26 . a double - acting hydraulic cylinder 110 is connected to the upper beam 30 of the main framework 26 by a bracket 112 . the rod end of the cylinder 110 is connected to a bracket 114 which is welded to the inside face of the upper left - hand ( as viewed in the direction of travel ) arm 70 . as the cylinder 110 is extended from the position shown in fig2 the arms are rocked to the left ( broken lines ) to move the implement frame left with respect to the fore - and - aft center line of the tractor . retracting the cylinder 110 from the position shown in fig2 moves the implement to the right with respect to the center line of the tractor . the parallel linkage arrangement provided by the arms 70 and 72 permits the frame 18 to be moved laterally over a relatively wide range of positions while maintaining the frame close to the framework 26 and transverse to the forward direction of travel . the hydraulic cylinder 110 is connected to a source of hydraulic fluid on the tractor 16 and to suitable control means for extending and retracting the cylinder as necessary to align the implement 10 with the rows of crops . although the hitch structure 12 is shown with a row crop cultivator 10 , it is to be understood that the structure may also be utilized with other types of implements where it is necessary to make lateral adjustments of the frame . in the preferred embodiment , the cylinder 110 is connected to a solenoid controlled valve 120 ( fig9 ) which , when the implement is in the field - working position shown in fig1 is automatically controlled by a furrow sensor 124 to maintain a preselected lateral position of the frame 18 with respect to a preestablished furrow or groove in the ground . the valve 120 is a conventional three - position , four - way , closed center valve or the like which when unactivated prevents movement of the cylinder 110 and thereby fixes the frame 18 with respect to the three - point hitch 14 . sway blocks ( not shown ) or other conventional means are provided to prevent the hitch 14 from rocking laterally on the tractor for better implement control , particularly on sloping ground . the furrow sensor 124 includes a rigid switch box 126 connected to the forward end of a downwardly and forwardly directed support tube 128 attached to the forward face of the transverse frame 18 by a conventional bracket arrangement 130 ( fig1 and 2 ). fore - and - aft spaced vertical shafts 132 and 134 are journalled for rotation about upright axes in the bottom of the switch box 126 . pivot supports 136 and 138 are fixed to the lower portions of the vertical shafts 132 and 134 , respectively , and carry pivots 140 and 142 for rocking about generally horizontal pivotal axes . follower arms 144 and 146 are connected to the pivots 140 and 142 , respectively , for rocking vertically about the horizontal axis and for rocking laterally about the axes of the respective shafts 132 and 134 . relatively heavy round ball - shaped followers 150 are connected to the aft ends of the arms 144 and 146 and are adapted to ride in a furrow or groove in the ground formed during a preceding planting or cultivating operation . the aft end of the arm 144 is bent at ninety degree angles ( fig5 ) to provide clearance with respect to the forward ball 150 . the forward portion of the arm 146 is bent at opposite obtuse angles to provide clearance between the vertical shaft 132 and the arm . the switch box 126 is fixed with respect to the frame 18 such that when the row crop cultivator 10 is properly aligned with the rows of crops and the balls 150 are in the preestablished furrow or groove , the arms 144 and 146 will be in direct trailing relationship and parallel to each other and to the forward direction . actuator arms 152 and 154 are connected to the shafts 132 and 134 inside the switch box 126 . microswitches 160 - 166 ( fig6 ) are fixed to the switch box 126 on opposite sides of the arms 152 and 154 and include actuators 170 - 176 . the position of the actuators 170 - 176 with respect to the arms 152 and 154 are transversely adjustable , for example by an adjustable bracket assembly 180 or other conventional mounting structure . the angular position of the arms 152 and 154 can also be adjusted with respect to the shafts 132 and 134 by loosening the setscrew 182 . the microswitches 160 - 166 are normally off ( fig9 ). however , as the arms 144 and 146 move laterally from the direct trailing position of fig5 and 6 , the actuator arms 152 and 154 will activate the switches 160 and 162 , or 164 and 166 , depending on whether the arms move to the left or the right with respect to the switch box 126 . the forward ends of the arms 144 and 146 extend through apertures 192 in upright guide members 190 connected to the bottom of the switch box 126 . as best seen in fig7 each aperture 192 has an upper rectangularly shaped portion 194 and a lower v - shaped notch 196 with a center apex 198 . the forward ends of the arms 144 and 146 are so positioned that when the implement is in the field - working position shown in fig1 the arms can rock both vertically and horizontally generally between the sides of the rectangular portion 194 . as the three - point hitch 14 is raised and the implement is lifted from the ground , the arms 144 and 146 will rock about the pivots 140 and 142 , respectively , until the arms contact the v - shaped notches 196 . continued lifting of the implement causes the arms to settle toward the central apexes 198 to thereby center the arms in direct trailing relationship with respect to each other to assure that the switches 160 - 166 are in the off position when the implement is raised . to guide the implement automatically , the operator closes switch 200 ( fig9 ) which is connected via line 202 to the vehicle battery or other power source . an indicator lamp 204 is illuminated to remind the operator that this system is in the one condition . a two - position lift switch 206 , operably associated with the tractor rockshaft , includes an input terminal 208 connected to the switch 200 and a first output terminal 210 connected to the switches 162 and 166 . the switch 162 is connected in series with the switch 160 which in turn is connected to a left solenoid 212 of the solenoid control valve 120 . the switch 166 is connected in series with the switch 164 which in turn is connected to a right solenoid 214 of the valve 120 . when the rockshaft is positioned such that the three - point hitch 14 is lowered and the cultivator 10 is in the field - working position of fig1 the lift switch 206 is in the position shown in fig9 and power is supplied to the switch box 126 . as the rockshaft is rocked to raise the hitch 14 and lift the implement 10 from the ground , the lift switch 206 is switched to the second position wherein the terminal 208 is connected to the terminal 216 . in operation , assuming that the implement is lowered in the field - working position and switch 200 is closed , the switches 160 - 166 will remain in the off condition so long as the frame 18 is properly aligned with respect to the preestablished furrow in the soil so that the arms 144 and 146 trail directly rearwardly of the switch box 126 . if the frame 18 begins to move left with respect to the preestablished furrow , the balls 150 will remain in the furrow and cause the arms to pivot to the right about the vertical shafts 132 and 134 to thereby close the switches 164 and 166 . current then flows through the solenoid 214 causing the hydraulic cylinder 110 to retract and shift the frame 18 toward the right until the arms 144 and 146 are again properly centered and in direct trailing relation . if the frame 18 moves too far to the right with respect to the preestablished furrow , the switches 160 and 162 are closed and solenoid 212 is activated to extend the cylinder and rock the frame to the left . in the preferred embodiment when the frame 18 is properly positioned with respect to the preestablished furrow , neither of the valves 212 or 214 is activated and fluid flow in and out of the cylinder 110 is completely blocked so that the frame 18 is locked with respect to the upright framework 26 . in order to effect operation of one of the solenoids 212 or 214 and move the frame 18 , both switches of a series - connected pair 160 , 162 or 164 , 166 must be closed . therefore , both of the follower arms 144 and 146 must be pivoted the same direction away from center before the solenoid will be operated to shift the frame . this feature prevents unwanted shifts of the frame resulting from one of the follower balls 150 jumping out of the furrow , for example , when the ball hits a clod . the balls 150 are made of solid metal which provides sufficient weight to maintain them in the furrow . the direct in - line trailing relationship of the arms 144 and 146 functions to direct the balls 150 back towards the furrow if they happen to bounce out after hitting a clod or other obstruction . also , as the implement is raised , the arms 144 and 146 are centered with respect to the switch box 126 by the v - shaped notches 196 . the range of arm positions wherein the switches 160 - 166 will be in the off position is determined by the setting of the adjustable bracket assemblies 180 . as the implement is raised from the ground , the lift switch 206 is switched from the position shown in fig9 to provide contact between the terminals 208 and 216 . the terminal 216 is connected to a switch assembly 228 including a switch 230 connected to the solenoid 212 and a switch 232 connected to the solenoid 214 . the switches 230 and 232 include actuators 234 and 236 ( fig8 ) which contact a slide member 240 . the slide member 240 is connected by a bracket 242 to the rod end of the cylinder and moves therewith as the cylinder is extended and retracted . the slide 240 includes cam surfaces 246 and 248 which maintain both of the switches 230 and 232 in the off condition when the cylinder is extended to a preselected distance , preferably about half the stroke of the piston . retraction of the cylinder from the preselected position shown in fig8 activates the switch 230 while extension beyond the position activates the switch 232 . when the implement is raised , the switch 206 switches the power to the terminal 216 , and the switch assembly 228 activates the required solenoid to move the cylinder 110 to the preselected position . preferably the cylinder , when in the preselected position , establishes the beam 18 in a transverse position centrally between the leftmost and the rightmost lateral positions of the frame 18 . as the implement is raised , if the frame 18 is to the left of center position , switch 232 will be in the on position and will activate the solenoid 214 to retract the cylinder and move the frame 18 toward the right until both actuators 234 and 236 are in contact with the respective cam surfaces 246 and 248 . if the frame 18 is too far to the right as the implement is being raised from the ground , the switch 230 will be in the on condition and will activate the solenoid 212 to extend the cylinder and move the frame 18 to the left until the cam surface 248 causes the switch 230 to change to the off condition . therefore , as the implement 10 is raised from the ground at the end of the rows , the frame 18 will automatically be centered in a preselected position with respect to the center line of the tractor in preparation for alignment with the next set of rows to be cultivated . to provide operator adjustment independent of the switch box 126 , an operator control switch or jog switch 252 is provided in the cab of the tractor 16 . the switch 252 is a momentary on , two - position switch having output terminals connected to the solenoids 212 and 214 and having an input terminal connected to the terminal 210 of the lift switch 206 . as the implement is lowered to the ground - working position and the switch 206 assumes the position shown in fig9 the operator can move the switch to either position to momentarily turn on one of the two solenoids 212 and 214 as necessary to align the implement with the rows . until the implement is lowered sufficiently so that the balls 150 contact the ground and pivot the arms 144 and 146 upwardly , the notch 196 will maintain the arms in the central positions so that the switches 160 - 166 will be in the null or off positions as shown in fig9 and conflicting signals will not be sent to the solenoids 212 and 214 as the jog switch 252 is operated . having described the preferred embodiment , it will be apparent that modifications can be made without departing from the scope of the invention as defined in the accompanying claims .
a guidance system for use with tractor - mounted row crop cultivators and similar implements includes a pair of independent furrow followers mounted one behind the other on the implement for sensing implement position relative to a preestablished guidance furrow . series - connected switches are controlled by furrow sensor arms to activate a solenoid valve - controlled hydraulic cylinder on a laterally movable parallel linkage hitch which replaces the standard three - point hitch on the implement . when the implement is raised from the ground , v - shaped stops under the sensor arms automatically position the sensors at the null point . switches and an actuator on the hydraulic cylinder operate in response to movement of the tractor rockshaft to return the implement to center position in preparation for alignment with the next set of rows to be cultivated .