Abstract:
Toe adjustment apparatus for an alignment machine includes wheel position and body height sensors for providing input to a controller, and a power wrench carried by an adjustment mechanism for engaging and adjusting the vehicle tie rod under control of the controller. Power operated multi-axis actuators approximately align and couple the wrench head with the tie rod and multi-axis passive adjustments perfect registration of the head on the tie rod. The wrench head includes an open end socket configured to mate with a jam nut at one end and a tie rod hex portion at the other end so that both elements are selectively engaged by lateral shifting along the rod from one to the other for turning the jam nut and the rod as required for proper toe set. An encoder on the wrench produces pulses representing rotation increments and thus wheel adjustment increments. A method of correcting toe angle comprises measuring the toe angle and determining the error, calculating the rotation target value require to correct the error, adjusting the tie rod with the wrench and counting the encoder pulses, and comparing the counted pulses with the target value to determine when to stop adjustment.

Description:
This application is a continuation of application Ser. No. 175,037, filed Mar. 29, 1988 and now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to automatic toe adjustment method and apparatus for a wheel alignment machine and particularly to such toe adjustment method and apparatus utilizing a power wrench for tie rod nut adjustment. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of automotive vehicles automatic equipment plays an important role in accurate and inexpensive assembly and adjustment of the vehicle components. One of the operations where such automatic equipment has been employed is in the toe adjustment of wheels during wheel alignment. As a matter of design, each vehicle type has an assigned toe angle which is parallel to the longitudinal axis or at a small angle to the axis. To provide an adjustment capability, the tie rod has a threaded adjustment allowing relative rotation of male and female shaft members to cause lengthening or shortening of the tie rod, and a jam nut on the threaded part to lock the assembly against relative rotation. An adjustment machine then must be capable of measuring the toe angle and alternately rotating the jam nut and one of the shaft members for making any needed correction to a high degree of accuracy. The machine then is required to make the measurement and then, without exact information on the location of the tie rod, quickly make the adjustment by finding the tie rod, securely attaching a wrench to the jam nut and the shaft, and rapidly making the proper rotation of each part. 
     U.S. Pat. No. 4,679,327 to Fouchey et al discloses a toe set alignment system having a track for positioning a vehicle over a pit, adjustment apparatus in the pit, an apparatus for measuring the toe set, a sensor for detecting the vehicle height, and a programmable controller for reading the measurements and controlling the adjustment apparatus. The adjustment apparatus has a mechanism carried on a guideway for positioning relative to the tie rod and an adjustment head having drive rollers for contacting and adjusting the tie rod. A separate nut runner head is used to operate the jam nut. To use the nut runner the adjustment head must first be removed from the tie rod and then, as a separate operation, the nut runner is applied, thereby adding extra time to the adjustment. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a toe adjustment method and apparatus for an alignment machine that can rapidly make a tie rod adjustment and tighten the jam nut. It is another object to provide an apparatus to perform those functions without removing the adjusting mechanism from the tie rod. 
     The invention is carried out in a wheel alignment machine having measurement means for determining wheel attitude and a programmable controller for machine control, automatic toe adjustment means for engaging a tie rod and controllably turning a threaded tie rod part and an associated jam nut comprising; a power wrench having an open end head for fitting on the tie rod, the head having a first side conforming to the jam nut and a second side configured to drive the tie rod part, and multi-axis support means under control of the controller for holding the power wrench and for moving it into engagement with the tie rod, the support means including means for laterally shifting the power wrench head in one direction along the tie rod axis for selectively engaging and turning one of the nut and the tie rod part, and for laterally shifting the wrench head in the opposite axial direction for engaging and turning the other nut or part. The invention further comprehends an encoder coupled to the wrench to measure the amount of corrective rotation for use in determining the completion of the adjustment. 
     The invention is further carried out in a wheel alignment machine having a tie rod rotating apparatus for adjusting toe angle by the method comprising the steps of; measuring the toe angle, determining the required correction, calculating a target rotation amount, adjusting the angle by rotating the tie rod, measuring the actual rotation amount during the adjusting step, comparing the measured rotation amount with the target rotation amount, and stopping the adjusting when the measured rotation amount equals the target rotation amount, whereby the adjustment is made rapidly and accurately. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other advantages of the invention will become more apparent from the following description taken in conjunction with the accompanying drawings wherein like references refer to like parts and wherein: 
     FIG. 1 is a perspective view of a vehicle at an alignment station having a toe adjustment apparatus according to the invention; 
     FIG. 2 is a perspective view of a toe adjustment mechanism according to the invention; 
     FIG. 3 is a partly broken away sectional view of a spring biased cylinder for support of the power wrench according to the invention; 
     FIGS. 4 and 5 are partly broken away isometric views of a power wrench according to the invention; 
     FIG. 5A is an isometric view of a gear in the wrench head; 
     FIG. 6 is a partly broken away elevation of the wrench of FIGS. 4 and 5; 
     FIG. 7 is a View of a wrench detail as viewed along line 7--7 of FIG. 6; and 
     FIG. 8 is a side elevation of the wrench according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 depicts a vehicle 10 on a positioning track 12 including stops 14 for establishing fore and aft position, a pit 16 between the tracks 12 and under the vehicle 10 for accommodating two toe adjustment mechanisms 18, one for the right wheel 20 and one for the left wheel 22. The wheels are rotated by a conventional arrangement wherein the stops 14 are rollers supporting the respective wheel and one of which is motor driven. A wheel attitude sensing device 24 at each wheel 20 and 22 includes a wheel engaging probe 26 for determining the respective wheel position. The devices 24 are coupled to a programmable controller 28 which assesses the wheel position information and issues correction signals to the adjustment mechanism 18. As thus far described, the system and its operation are well known and further details are not necessary except as follows. 
     FIG. 2 shows the adjusting mechanism which comprises a power wrench 30 having a head 32 mounted on supporting mechanism. The wrench 30 is movable toward and away from a tie rod 34 and all the supporting mechanism is devoted to providing that motion in a way to assure accurate engagement of the wrench head 32 with the tie rod. To facilitate the engagement a locating fork 33 is provided at each end of the head 32 for guiding the head toward the tie rod 34. The head 32 is coupled to a bracket 36 by a pivot connection 38 which allows the head to self adjust about one axis upon contacting the tie rod. The bracket 36, in turn, is attached to a transverse carrier 40 having a motor 42 for adjustably positioning the bracket 36 and thus the head 32 in a direction generally parallel to the tie rod. A shaft 44 carried in a spring cylinder 46 is attached to the transverse carrier 40. A pivot pin 48 generally parallel to the tie rod secures the spring cylinder 46 to a slide 50 and permits limited rocking movement of the cylinder about the axis of the pin 48. The cylinder 46 itself permits limited rotation about the shaft 44 axis as will be further described. The slide 50 is slidably mounted on an inclined guideway 52 and is moved toward and away from the tie rod by a linear actuator 54. The guideway 52 is attached to a movable vertical carrier 56 which is positioned by a motor driven lead screw 58. The vertical support 56 assembly is mounted on a horizontal carrier 60 which is movable on rails 62 parallel to the vehicle longitudinal axis. A probe 64 carried by the guideway 52 is extendable upwardly to engage a cross member 66 on the vehicle to judge the vehicle height and relay that information to the controller 28. 
     In operation, the horizontal carrier 60 is prepositioned to suit the particular vehicle model to be aligned. The vehicle 10 is moved onto the track 12 with the front wheels against the stops 14. The probes 26 are moved into position against the wheels 20, 22 to gauge the lateral position of the wheels relative to the track 12 as well as to sense each wheel angular attitude. Underneath the vehicle, the height probe gauges the height of the vehicle cross member 66. Since manufacturing tolerances lead to different vehicle heights, even in the same model, and the height affects the position of the tie rod, the height information is useful in the automatic location process. The position information from probes 26 and 64 is fed to the controller 28 which causes the appropriate positioning of the vertical carrier 56 and the transverse carrier 40, so that the wrench head 32 is approximately aligned with the tie rod 34. Then the slide 50 can be advanced to carry the head to the tie rod. During engagement of the head with the tie rod the locating forks 33 guide the head for accurate and firm seating of the head. Movement about three axes to accommodate any small misalignment is permitted by the passive pivot connections 38 and 48 and by the rotation offered by the spring cylinder 46. 
     Referring to FIG. 3, the spring cylinder 46 comprises a tubular housing 70 containing a set of bearings 72 at either end to slidably support the shaft 44 for axial movement. The lower end of the housing 70 has a closure 74 with a threaded central aperture 76 which receives a threaded plug 78 secured by a lock nut 80. The plug 78 has an inner end 82 of reduced diameter which defines a shoulder 84. The inner end 82 serves as a spring locator and the shoulder 84 is a seat for a coiled compression spring 86. The shaft 44 is hollow at its lower end and receives the spring 86 and the inner end of the plug 78 which is adjustable to adjust the spring force which serves to thrust the shaft 44 upwardly. A cam aperture 88 in the side of the housing 70 has a triangular portion with its apex 90 directed upwardly and with its base adjoining a square portion of the aperture. A pin 92 threaded into the side of the shaft 44 extends into the cam aperture 88 and is normally pressed into the apex by the spring force to establish the normal angular position of the shaft 44. When, during engagement of the head against the tie rod 34, sufficient axial force is applied to compress the spring 86 the shaft moves to a depressed position to withdraw the pin 92 from the apex 90 to a less restrictive position 92&#39; shown in phantom lines. Then the shaft can rotate about its axis a limited amount to accommodate a small misalignment of the head and the tie rod. Thus the cylinder 46 and shaft 44 arrangement allows lost motion during the forceful application of the head to the tie rod and maintains a predetermined angular disposition of the head about the shaft axis until the lost motion occurs. 
     The tie rod itself as well as the wrench head details are shown in FIGS. 4 and 5. The tie rod 34 has a threaded coupling comprising a knuckle 94 with a threaded female part, a rod 96 with a threaded end 98 received in the knuckle 94, a jam nut 100 on the rod 96 for locking the threaded parts against relative rotation, and a hex shaped portion 102 on the rod spaced from the knuckle 94. The tie rod 34 is lengthened or shortened by loosening the jam nut, turning the rod 96 in the knuckle 94, and tightening the jam nut 100. The head 32 of the power wrench 30 is designed to engage the rod 96 in a space between the threaded end 98 and the hex portion 102 and accomplish the operations on both the shaft 96 and the nut 100 while remaining engaged with the rod 96. 
     As best seen in FIGS. 4 through 6, the wrench head 32 has an open end socket 104 with two spaced, coaxial socket cavities. One cavity 103 is configured to fit the hex part 102 and the other cavity 105 is formed to fit the jam nut 100. Thus the same head is used for rotating both parts and is merely shifted laterally to selectively engage them. The socket 104 has a hex shaped outer surface and is loosely held in a gear 107 having a hex cavity and an end opening 109 aligned with the socket end opening. The gear 107 is driven through a special gear train 106 by a conventional pneumatic power tool driver 108. The gear train is enclosed in a housing 110 which includes a pair of side plates 112 and 114 which support the gears. The gear train 106 has a driving gear 116 directly driven by the tool driver 108 which has an output shaft 118 journaled in a bearing assembly 120. An intermediate gear 122 meshes with the driving gear 116 and is rotatably mounted on a pin 124 which is mounted by its end in apertures in the side plates 112, 114. Two pinions 126, journaled on pins 127, mesh with the intermediate gear 122 as well as with the gear 107 to drive the socket 104. As the gear 107 turns about its axis the pinions 126 will, one at a time, encounter the opening in the gear so that at least one pinion will be in driving relation to the gear 107. The gear 107 has laterally extending hubs 128 journaled in the plates 112, 114. The plates cannot completely encompass the hubs 128 due to the necessary open end feature, but they do wrap around the hubs enough to retain the gear 107. A hub extension 130 on one side of the socket 104 has an annular groove 132 mating with a stationary guide 134 to prevent lateral movement of the socket 104. The locating forks 33 are mounted as outriggers on either side of the socket 104 and are spaced so that as the socket is applied to the rod between the jam nut 98 and the hex portion 102 one fork 33 will engage the knuckle 94 and the other will engage the rod 96. Each fork has a flared opening 136 to catch the rod when the head approaches the rod and terminates in a seat 138 tailored to the size of the part that it engages. The opening of each fork 33 faces the same direction as the opening of the socket when in its index position. 
     Provision is made for assuring that the socket 104 stops at its index position to allow the engagement and disengagement with the tie rod. As shown in FIGS. 5A and 6 the intermediate gear 122 has an arcuate groove 140 in one face 142 which has a bottom ramp 144 to define an abutment 146 at the lowest end of the ramp while the other end of the ramp terminates flush with the face 142. A stop pin 150 is positioned to move axially into the groove 140. The pin carries a piston 152 which slidably fits within a cylinder 154 mounted on the side plate 114 opposite the gear 122. An opening 156 in the cylinder for connection to an air pressure line, not shown, provides for admitting pressure to force the pin 150 into the groove 140. A spring 158 surrounding part of the pin 150 and bearing against the piston urges the pin out of the groove 140 in the absence of the air pressure. A cam 160 carried on an end of the socket 10 helps to stop the socket at its index position by operating a switch 162 (FIG. 7) which signals the socket position to the controller 28 which can then remove power to the wrench at an appropriate time to stop. The cam operates the switch 162 through a linkage comprising a slidable pin 164 which follows the cam 160, a bell crank 166 which translates the pin 164 movement to the switch 162 operating arm, and a spring biased pin 168 in line with and opposed to the pin 164 to bias the linkage toward switch off position. 
     In operation of the indexing feature, the socket is initially in the index position prior to engaging the tie rod 34 so that the open end of the socket 104 allows entry of the rod. Then under control of the controller 28, air pressure is removed from the cylinder 154 to permit the stop pin 150 to retract from the groove 140. To assure that the pin has indeed withdrawn, the wrench motor is initially driven in a direction that rotates the gear 122 such that the ramp 144 pushes the pin 150 out of the groove. Then the socket may be rotated in either direction. To remove the head from the rod 96 the controller causes the gear 122 to slowly rotate opposite to the initial direction, apply air pressure to the cylinder 154 to drive the pin 150 into the groove 140, and remove power when the switch 162 is operated. The pin 150 contacts the abutment 146 to positively stop the gear at the index position to allow withdrawal of the head. 
     A sensor 170 in the head 32 determines when the head has made engagement with the rod 96. A pin 172 spring biased outwardly toward the rod 96 slides in a bore 174 so that the presence of the rod determines the position of the pin 172. The pin has a laterally projecting shoulder 176 at one end. A switch 178 has an operating arm 180 in the path of the shoulder 176 so that the switch 178 is actuated by the shoulder 176 when the head moves against the rod 94. The signal from this switch informs the controller 28 when to apply power to the wrench. 
     Still another sensor for supplying information to the controller 28 is a rotary optical encoder 182 secured to the plate 112 on the head and covered by a housing 184. The encoder 182 has an input shaft 186 extending through an aperture 188 in the plate 112 and threaded into the end of the wrench driving shaft 118 for rotation by the shaft 118. The encoder input shaft 186 rotates whenever the wrench head rotates and produces output pulses on lines 190 marking increments of rotation. The rotation of the tie rod part 96 changes the toe angle by an amount proportional to the amount of rotation. The exact relationship depends on the geometry of the steering linkage, the thread size, and other factors, but for a given system the wrench rotation and thus the number of encoder pulses during an adjustment interval is directly related to the change in toe angle. A typical system has an encoder which yields 82 counts per revolution of the encoder input shaft and the corresponding wrench rotation effects a toe angle change of 0.62 degrees. Thus 0.01 degree is equivalent to 1.32258 counts. Resolution of this sort is appropriate since wheel toe angle specifications require accuracy within a few hundredths of a degree. 
     Overall operation of the automatic toe adjustment apparatus comprises positioning the vehicle on the track 12, applying the wheel probes 26 and the height sensor 64 to determine the vehicle position, adjusting the vertical position of the support 56 and the lateral position of the head 32 via the transverse carrier 40, and operating the slide 50 from its idle retracted position to its extended position to engage the rod 96 by the head 32. The sensor 170 determines the time of engagement and the controller uses that information to arrest the upward slide movement. The powered adjustments align the head with the rod 96 well enough for the locating forks 33 to find the rod and the pivot connections 38 and 48 and the spring cylinder 46 allow passive adjustments for exact alignment as the slide 50 moves to its final position. Then the wrench is moved laterally by the transverse carrier 40 to engage the socket portion 105 with the jam nut 100, the socket being turned slowly to obtain registration and coupling with the nut. The nut is loosened to allow free adjustment of the rod 96 in the knuckle 94. Then the head is shifted in the same way to engage the hex part 102 and the rod is turned under control of the controller to lengthen or shorten the tie rod 34 until the toe specification is met. Then the head is moved back to the jam nut 100 to tighten it and is then moved to a neutral position on the rod 96 where the socket is indexed for removal from the rod and the slide 50 is retracted. 
     The apparatus will operate in two modes: static and dynamic. In each mode toe angle is measured by rotating the wheel and averaging hundreds of angle measurements and the error is calculated by comparison with the angle specification. Thus the true toe angle is not available instantaneously. The static mode is a closed loop system wherein the wheel is stopped after the measurement is made and the static wheel attitude is constantly measured during tie rod adjustment and the adjustment continues until the wheel is moved an amount equal to the error. 
     In the dynamic mode, the rotary encoder is used to provide adjustment information to the controller. An error is calculated in terms of the number of encoder pulses needed to correct the error and the encoder pulses are counted to determine when to stop the adjustment. The wheel continues to rotate during the adjustment and a verifying measurement is made after the adjustment. If necessary, another adjustment is made. More particularly, the dynamic mode operates as follows: the toe angle is measured, the error is calculated, the necessary correction value or target rotation amount is calculated in terms of the required number of encoder pulses, the power wrench turns the rod to make the adjustment, the encoder measures the rotary displacement of the wrench (in terms of encoder pulses), the rotation is compared to the target rotation amount and the wrench rotation is stopped when the rotation equals the correction value or target amount. 
     It will thus be seen that the apparatus of the invention is an improvement over prior proposals particularly in its ability to use the same wrench part to turn the jam nut and the rod without removal of the wrench from the rod, its superior self adjustment mechanisms for accurate and secure coupling of the wrench with the tie rod, and its ability to provide adjustment feedback to the controller. Likewise, the method of the invention affords the ability to accomplish accurate adjustments using encoded feedback from the adjusting mechanism.