WO2002095324A1

WO2002095324A1 - Precision measuring apparatus

Info

Publication number: WO2002095324A1
Application number: PCT/AU2002/000648
Authority: WO
Inventors: Trevor Dinning
Original assignee: Dinning Light Engineering Pty Ltd
Priority date: 2001-05-24
Filing date: 2002-05-23
Publication date: 2002-11-28
Also published as: AUPR525101A0

Abstract

A linear measuring apparatus, especially for measuring the misalignment of vehicle wheels, the apparatus including a plate (4) freely moveable at right angles to the direction of movement of a vehicle wheel over the plate, and detecting means to measure the movement of the plate as the wheel passes along the length of the plate.

Description

PRECISION MEASURING APPARATUS

TECHNICAL FIELD

This invention relates to precision measuring apparatus, more particularly to an apparatus for precisely measuring linear movement.

BACKGROUND ART

Apparatus for measuring linear movements are well known, these including optical devices for measuring linear movement. One of the desired applications for measuring linear movement is the checking of the wheel alignment of vehicles, that is to ensure the wheels of the vehicle are tracking and rolling correctly with the wheel rolling along the intended path.

Wheels of vehicles are supported by a suspension which is adjustable relative to the chassis of the vehicle to ideally position the wheel so that it rolls along the intended path without any sideways forces being applied by misalignment to the wheel when rolling in contact with the surface over which it is passing.

In the suspension of a motor vehicle the two most critical factors in controlling rolling contact are camber and toe-in, and if either or one of these is incorrectly adjusted in relation to the other the wheel will not tend to roll along the intended path without applying a sideways force to the surface on which it rolls. This results in a sideways force on the wheel resulting in tyre wear and thus a corresponding undesired effect on the handling of the vehicle, in control and cornering. Increased noise from tyre contact on the surface increased rolling resistance resulting in greater fuel consumption.

Many wheel alignment systems and apparatus are known, however these usually rely on the wheel alignment technician adjusting the suspension system to the manufacturers recommendations. However these instructions often list a variable range, and not a precise figure and do not include measurements of sideways forces when rolling in contact with the intended surface.

However this may not be satisfactory for every vehicle of the manufacturer. The vehicle maybe fitted with tyres with a profile different to those fitted by the manufacturer. Also the vehicle may be continuously operated in a laden condition. When a vehicle is laden the movement of the suspension to the laden position may alter either or both of the camber and toe-in of the wheel. Hence the wheel does not roll or track correctly in the laden condition.

Apparatus is known which attempts to check the sideways movements of a vehicle, and these include apparatus including a plate over which the wheel rolls, the intention being the plate moves at right angles to the direction of movement of the vehicle when a wheel is misaligned, and means are provided to indicate the degree of sideways movement of the plate. However various of these while giving an indication of the degree of misalignment are not particularly sensitive to the forces applied to the plate due to the frictional resistance to the movement of the plate.

Such checking apparatus known to the applicant are permanently installed in a floor or other surface with the plate level with the surface of the floor, and a rigid plate has rollers on its under surface rolling on a track or base plate. Difficulty arises in preventing dirt and debris from entering into the apparatus and the rigid plate when it moves has to move all rollers supporting the plate. This creates undesired friction resulting in a nil reading until the friction is overcome. Thus this creates a false reading. Also the process of commencing and terminating the measurement period or distance is imprecise.

DISCLOSURE OF THE INVENTION

It is an object of this invention to provide a linear measuring apparatus which can be used for testing the sideways movements of a vehicle's wheels when rolling in contact with the surface over which it passes. A further object of the invention is to provide a wheel alignment apparatus which can be either portable or permanently installed in position.

A further object of the invention is to provide a wheel alignment tester having a freely moving plate over which the wheel of the vehicle passes from one end of the plate to the other, the plate being adapted to move only in a direction at right angles to the direction of passage of the wheel over the plate.

A further object of the invention is to provide a wheel alignment tester having means receptive to movement of the plate and to transmit this movement to a display and or recording means.

A further object is to allow the tyre to be fully on the moving plate before readings begin allowing the suspension to "unload" and not include this element in the measured reading.

A still further object of the invention is to provide switching means to initiate the indicating and or recording means when the vehicle wheel enters the plate and further switching means to terminate the indicating and/or recording means when the vehicle wheel exits the plate.

Thus there is provided according to the invention a linear measuring apparatus said apparatus consisting of a frame, a freely movable plate constrained to move in only opposite linear directions, and means to detect and indicate the linear movement.

Preferably the apparatus tests the wheel alignment of a vehicle, the plate being constrained to move only in a direction at right angles to the passage of the wheel over the plate as the wheel passes over the plate.

Preferably the plate freely rests on a series of low friction rollers mounted on the base of the frame, the frame including an end frame member locating the plate to prevent upward movement of the plate. Also it is preferred the plate is flexible so that the downward force of the wheel is supported by the rollers generally under the footprint of the wheel on the plate.

Preferably the means to detect the movement of the plate include a rotary increment indicator and a cord or the like connected to each side of the plate and looping around the shaft of the rotary increment indicator.

Preferably the apparatus includes a switch mechanism at each end of the plate to initiate the indicating and display mechanism as the wheel enters the plate and to switch off the indicating and display mechanism as the wheel leaves the plate.

Preferably also the apparatus includes a spring mechanism to return the plate to a central position irrespective of which lateral direction the plate moves.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more fully describe the invention reference will now be made to the accompanying drawings in which:-

Figure 1 is an overall view of one form of the invention, Figure 2 is an exploded view of an entry switch plate, Figure 3 is a partially exploded view of the plate and supporting rollers, Figure 4 is a view of the encoder and plate returning mechanism, Figure 4a shows an alternative encoder assembly, and

Figures 5 and 6 show the operation of the plate returning mechanism.

The invention will now be described in some detail as used for indicating the correctness of the wheel alignment of a vehicle.

The wheel alignment tester can be a portable unit or can be fixed in a supporting surface such as a floor. As shown in the drawings the apparatus includes a frame 1 and a ramp 2 at each end. However if the frame 1 is a fixture in a floor, the upper surface of the frame being level with the surface of the floor in which case the ramps 2 are not required.

At each end there is a switch plate 3 adjacent the freely movable plate 4, the switch plate 3 being biased upwardly by springs 5 on pegs 6 so that on depression of the switch plate 3 by the passage of a vehicle there over, the switch 7 is activated. The wheel passing from the switch plate onto the movable plate 4 the switch releases and initiates a control and display later to be described.

The movable plate 4 is supported on a series of rollers 8 in this embodiment mounted in channels 9 attached to the base 10 internal frame 10a. As shown there are seven pairs of rollers in each channel with seven channels spaced along the length of the frame. However it is realised that the numbers of rollers and channels will vary depending upon whether the apparatus is to be used on lightweight passenger vehicles or heavier vehicles such as buses and heavy transport vehicles. The rollers are positioned such that their upper surfaces are above the edge 11 of the base frame.

The plate 4 has a surrounding edge 12 so that when placed in position it is freely supported on the rollers with the edge spaced outwardly of the edge 11 of the base, thus permitting the plate 4 to move on the rollers. The base 10 at each end has an extending flange 13 over which the plate is positioned. The edge flange 12 of the plate 4 at each end of the plate has at least a pair of rollers 14 one adjacent each comer of the plate, these rollers being adapted to engage the under surface of the flange 13 of the base. These rollers prevent the upward movement of the plate 4.

It to be noted the plate 4 is not a rigid plate but has a degree of flexibility. Thus when a vehicle wheel passes over the plate, due to the flexible nature of the plate, the rollers beneath the footprint of the tyre of the wheel support the weight of the vehicle. The flexure of the plate thus ensures that only a minimum number of rollers are supporting the vehicle and thus the frictional resistance is decreased, for the plate away from the footprint is not in contact with the rollers. The rollers 14 on the plate thus limit any upward movement of the plate 4.

The movement of the plate 4 is detected by a rotary increment detector 15 mounted on the base 10 and a cord 16 or the like attached to opposite sides of the plate 4 and looping around the shaft 17 of the detector. A spring or springs maintains the tension in the cord so that as the plate moves the cord will correspondingly rotate the shaft of the detector. Hence as the plate 4 moves in one direction the shaft will rotate in one direction of rotation and when the plate moves in the opposite direction the shaft will rotate in the opposite direction of rotation. The detector or detectors are preferably sensitive to rotation and in one instance the detector will emit 2000 pulses during one rotation of the shaft. These pulses are transmitted to an electronic control and display 18. As the wheel moves over the plate the plate will progressively move so that pulses are continuously transmitted until the wheel initiates the exit switch to cancel transmission and store and display 19 the information in the control unit. The degree the wheel is rolling/tracking off parallel can then be calculated by reference to the length of the tyre travel and the distance the plate has moved. Also the display indicates the direction of movement of the plate, thus indicating for example the tracking/rolling in or tracking/rolling out of the wheel. Additionally the displayed limit is set depending on the type of tyre profile 21.

Alternatively the plate movement can be detected as shown in Figure 4(a). The cord 16 after passing around shaft 17 passes around idler pulley 32. One end is connected to a lug 33 on the moving plate, a tension spring 34 attaching the other end to the lug.

The base 10 also houses a mechanism for returning the plate to the central position after passage of a wheel there over. A T-shaped lever 22 is pivoted by pivot pin 23 to the base 10, rollers 24 and 25 are on the ends of the lever, the stem 26 of the T-shaped lever extending to contact limit switches 27 and 28. A tension spring 29 returns the lever to the position governed by a stop pin, this being the central position of the plate 4 with the stem 26 contacting switch 28.

A pair of lugs 30 and 31 are provided on the under surface of the plate 4 the lug 30 positioned to engage roller 24 on the side opposite to the stem 26, and lug 31 engages roller 25 on the side of the stem 26. Thus it will be seen that whether the plate 4 moves to the right or to the left, the T-shaped lever will pivot in the same direction, the stem disengaging from switch 18 and moving towards switch 27.

Spring 29 returns the T-shaped lever back to the rest position, the appropriate roller 24 or 25 engaging its respective lug 31 or 30 to move the plate back to its central rest position. When the stem disengages from the switch 28 the display is initiated and if the displacement of the plate is such that switch 27 is engaged, the display shows the maximum movement.

When the apparatus is used as a portable unit a dummy unit is provided for the opposite wheel of the vehicle to ensure the vehicle is level and any variation in height of the vehicle from side to side is eliminated. Any variation in height would cause a sideways movement on the plate 4.

Thus it can be seen that the invention provides in one embodiment of the invention a measurement of the misalignment of a wheel of a motor vehicle. The invention provides a freely movable plate over which the wheel passes. If the wheel has a misalignment as it passes over the plate it will cause the plate to move in a direction at right angles to the direction of passage of the wheel. The plate is of known length and the total lateral movement of the plate is measured and recorded as the wheel passes over the length of the plate. This is processed to give a reading of the degree of misalignment of the wheel.

While the invention has been described in some detail as applied to the wheel alignment of a motor vehicle, it is to be realised the invention can be used to measure movement of any apparatus or member. Due to the sensitive nature of the apparatus it can be used for example to measure the expansion and contraction of a member or structure, such as a bridge, or other structure such as a building.

Hence it can be seen that the invention provides an apparatus which is sensitive to movement. Due to the plate being virtually a floating plate, the plate being unconstrained and resting on the plurality of rollers mounted on the base. The force moving the plate has to overcome the negligibly friction of the rollers and the small returning force provided by spring 9. Also the sensing unit provides a virtually continuous output of pulses, i.e. in the example 2000 pulses for each 20mm of movement of the plate, for each 20mm movement will cause the sensing unit to make one revolution.

Although one form of the invention has been described in some detail it is to be realised the invention is not limited thereto but can include variations and modifications like multiple encoders for improved performance falling within the spirit and scope of the invention.

Claims

1. A linear measuring apparatus, said apparatus including a frame, a freely movable plate constrained to move only in opposite linear directions, and means to detect and indicate the degree of linear movement .

2. A linear measuring apparatus as defined in claim 1 herein the apparatus tests the wheel alignment of a vehicle as the wheel traverses along the length of the plate, and wherein the plate is constrained to move in directions at right angles to the direction of passage of the wheel over the plate.

3. A linear measuring apparatus as defined in claim 2 wherein the frame includes a plurality of low friction rollers supporting the plate, the plate being flexible whereby the weight of the vehicle is supported by the rollers positioned at that time under foot print of the wheel as the wheel passes over the plate whereby any frictional resistance is provided only by the rollers under the plate supporting the weight of the vehicle.

4. A linear measuring apparatus as defined in claim 2 or 3 wherein the means to detect the movement of the plate include a rotary increment indicator and a cord or the like connected to each side of the plate and looping around the shaft of the rotary increment indicator.

5. A linear measuring apparatus as defined in any one of the preceding claims wherein the frame includes an end frame member locating the plate to prevent upward movement of the plate.

6. A linear measuring apparatus as defined in any one of the preceding claims wherein the apparatus includes an indicating and display mechanism to display the movement of the plate.

7. A linear measuring apparatus as defined in claim 6 wherein the means to detect the movement of the plate is connected to the indicating and display mechanism.

8. A linear measuring and display mechanism as defined in claim 6 or 7 wherein the apparatus includes a switch mechanism at each end of the plate to initiate the indicating and display mechanism as the wheel first engages the plate and to switch off the indicating and display mechanism as the wheel leaves the plate.

9. A linear measuring and display mechanism as defined in any one of the preceding claims including means to return the plate to its central position irrespective of the direction the plate moves.

10. A method of measuring the misalignment of a vehicle wheel, the method including the steps of providing means for measuring the lateral displacement of a plate at right angles the direction of movement of a vehicle wheel as the wheel passes over the length plate, and processing said measurement to display the misalignment of the wheel.

11. A method as defined in claim 10 including the steps of providing a plate of predetermined length, and processing the total displacement of the plate as the wheel passes over the length of the plate to display the amount of misalignment of the wheel.

12. A method as defined in claim 10 or 11 including the steps of providing a flexible plate supported on a plurality of rollers whereby the wheel is supported by the rollers under the foot print of the wheel to minimise any frictional resistance provided by the rollers

13. A method as defined in any one of claims 10 to 12 including means to analyze the total displacement of the plate as the wheel passes over the length of the plate to display the misalignment of the wheel.

14. A linear measuring apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.