BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to vehicle wheel alignment apparatus, and more particularly to the provision of an improved turning angle gauge for determining the magnitude and direction of wheel turn during the wheel alignment procedure.

2. Description of the Prior Art

The common turning angle gauge, of the character seen in HUNTER Bulletin, Form 900T-4 of October 1976, has a mechanical tracking mechanism in the base which includes a pointer which moves over a circular scale mounted in a position readily seen. A vehicle wheel alignment turn is performed, the gauge is caused to move in an X-Y direction to cause the scale and pointer to cooperate to display the degrees of turn scribed on the scale.

The problem with the mechanical turning angle gauges is that it requires an eyeball interpretation of the pointer position relative to the scale. There is also the problem of the fineness of the scale divisions, and how the scale is able totrack the wheel turn and keep its desired alignment relative to the pointer.

It is known that U.S. Pat. No. 4,394,798 of July 26, 1983 is a turning gauge equipped with electronic pick-up. The problem with such a gauge is that a belt drive potentiometer is employed, the repeatability of the belt drive is not free ofinaccuracies after a period of use, and there are a number of parts which can introduce errors.

BRIEF SUMMARY OF THE INVENTION

The present invention is an improvement in respect of accuracy of results over the visual gauges of the prior art. It also eliminates error prone drive means, with the result that results improve over scale and pointer means or belt connectedangle turn indicating devices.

A preferred turning angle gauge embodies an optical shaft encoder for tracking wheel turns in which the shaft of an encoder for tracking wheel turns is connected directly to the means which defines the rotational axis of a wheel in contact withthe top plate, and such a device is able to translate with the top plate, but without rotation, to improve on the accuracy and ease with which alignment data can be obtained.

This invention replaces the heretofore common visual reading devices, and employs a direct read-out on a digital display. An optical shaft encoder is mounted on the mechanical tracking mechanism in the turning angle gauge, while the shaft of theencoder is connected directly to a part that represents the axis of rotation of the top member of the turning angle guage. This eliminates inaccuracies experienced with belt drives found in prior turning angle gauges. The encoder body being mounted onthe tracking mechanism will not rotate, but will only translate in X-Y motion with the top member to accurately measure the rotation of the top member. The encoder means is held against rotation by means which cooperates with the cup to preventrotation.

An important object of the invention is to provide a vehicle wheel turnplate with a non-contacting direct rotary to digital encoder having a code wheel which rotates between a LED light source and a series of precisely spaced detectors to producequadrature square waves which can be electronically decoded to indicate the direction and magnitude of the rotation of the code wheel which represents the turnplate angle. An optical encoder is free of the non-linearity and contact wear problemsassociated with potentiometers, which are used in current designs.

An important object of the invention is to employ an optical shaft encoder to provide an angular readout accuracy of significantly better accuracy than visual readings provided by the prior art turnplate device equipped with a scale and pointercombination.

BRIEF DESCRIPTION OF THE DRAWINGS

The turnplate with electronic turning angle gauge is illustrated in the following drawings, wherein:

FIG. 1 is a top plan view of the turnplate;

FIG. 2 is a fragmentary sectional view taken along line 2--2 in FIG 1;

FIG. 3 is a view looking up from the under side of the turnplate seen in FIG. 1;

FIG. 4 is a fragmentary sectional view taken along the line 4--4 in FIG. 3; and

FIG. 5 is a block diagram of the turnplate shaft encoder and associated control circuit and computerized alignment display; and

FIG. 6 is a fragmentary sectional view taken along line 6--6 in FIG. 3 to show the placement of means to retain the encoder means against rotation.

DETAILED DESCRIPTION OF THE EMBODIMENT

An enabling embodiment is seen in FIG. 1 which is a top plan view of the turnplate assembly 10. The vehicle wheel supporting plate 11 is adapted to rotate about the axis XX which is established by the cup element 12 carried by the wheel contactplate 11. The base plate 13 is provided with elongated foot pads 14 directed along opposite sides of the base plate 13 and oriented to be parallel to an elongated bar 15 (FIG. 3). There are a plurality of small support feet 16 arranged about the undersurface of the base plate 13.

Between the top plate 11 and base plate 13 there is arranged a ball bearing assembly 17 comprised of an annular ball retaining ring 18 formed with tapered apertures 19 to receive a series of bearing balls 20 which support and spaced the top plate11 from the base plate 13. The bearing assembly 17 is enclosed by a dirt excluding ring 21. The ball retaining ring 18 is centered on the axis XX by four springs 22 set at 90.degree. spacing and anchored at the inner ends in a center spring retainerring 23 and anchored on the ring 18 at keepers 24 (See FIGS. 2 and 4).

Looking at FIG. 3, the underside of the base plate 13 carries spaced and parallel fixed guide bars 25 directed at 90.degree. to the foot pads 14. The bars 25 serve to guide the movement of a rectilinear tracking assembly T composed of slidebars 27 which engage and slide relative to the fixed guide bars 25. In turn, the slide bars 27 carry a second pair of guide bars 28 which span the distance between slide bars 27 and are fixed at the respective ends to the bars 27. The second pair ofbars 28 are spaced apart to receive the elongated bar 15 which is free to slide in directions parallel to the second bars 28. The tracking assembly is operably located under the base plate 13.

It is seen in FIGS. 3 and 4 that the central area of the base plate 13 is cut away to form a window opening defined by the margin 30. This opening allows the cup element 12, carried by the top contact plate 11, to penetrate into that opening soas to restrict the movement of the cup element 12 to any positions where the element 12 abuts on the margin of the window 30. Thus, the top plate 11 is able to move in the direction parallel to the bar 15 and carry with it the cup 12 until the cup abutsthe margin of the window 30. Also, the top plate 11 can move in a direction parallel to the guide bars 25 by sliding the bars 27 along the bars 25 until the cup element 12 again abuts the margin of the window 30. Likewise, the plate 11 can move inangular directions to those already identified, and in those directions the motion is limited by the margin of the window 30.

The top plate 11 has the ability to move in any direction within the limits of the opening defined by the margin 30, and in so moving the plate 11 is able to turn or rotate about the axis XX as required by the angular degree of turn of thevehicle wheel. Furthermore, as the top plate 11 moves relative to the base plate 13, the dirt excluding ring 21 will also move due to the pull of the spring 22 endeavoring to keep that ring centered to the axis XX. However, the ring 21 is preventedfrom moving out beyond its position between the plates 11 and 13 by a series of spaced retaining pins 31 carried on the underside of the top plate 11 (See FIG. 2).

The rotating function of the top plate 11 is monitored by the means of a rotary encoder device 32 disposed within the cup element 12 (FIGS. 3 and 4). The encoder device 32 is retained from rotating by the means 32B, which may consist of a bodyof pliable material, (See FIG. 6) which fits in the space between the body of device 32 and the cup element 12 to prevent rotation. That encoder device 32 may be the same as or the equivalent of a U.S. Digital SOFTPOT optical shaft encoder, identifiedas a series SP500 or SP500B, non-contacting direct rotary to digital converter. Such an encoder device eliminates wear, contact bounce and digit bobble associated with pots and analog/digital converters. The encoder device 32 has a multiple lead cable32A (FIG. 4) which is directed along beneath the bar 15 and emerges in a protective receptacle 33 positioned in an electrical junction fixture 34 which houses the receptacle 33 for receiving plug-in type cables for transmitting the signal from theencoder device 32 which has produced the signal to a suitable display. As seen in FIG. 4, the typical encoder device 32 is shown to have a projecting shaft 35 engaged in a bushing 36 fixed in the top plate 11 by welding. The bushing 36 supports thestationary (non-rotary) cup 12 by the shaft 35 and is held by a snap ring 37. Rotation of the top plate 11 drives the shaft 35 to actuate the encoder 32. However, the encoder device 32 is prevented from rotating by the means 32B.

Turning now to FIG. 5, there is shown a block diagram of a control circuit and computerized wheel alignment display processor. The control circuit has been enlarged to illustrate an arrangement of an ultimate system housing electronic turningangle gauges 40A and 40B for the steerable front wheels, and a pair of turning angle gauges 41A and 41B for steerable or other type of rear wheels. The latter pair of angle gauges are not necessary for vehicles with non-steerable rear wheels.

The angle gauge 40A has its circuit lead 42 connected into a suitable quadrature decoder and counter seen at 42A. A similar angle gauge 40B has its circuit lead 43 connected into a second suitable quadrature decoder and counter 43A. If thevehicle has steerable rear wheels, then additional angle gauges 41A and 41B are hooked into the system by circuit leads 43A and 43B connected respectively into guadrature decoders and counters 44 and 45. The respective quadrature decoders and counters42A and 43A, and 44 and 45, if needed, are connected into a common microprocessor 46 which assembles and sends that information into the wheel aligner apparatus and display seen at 47.

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