WO2013154507A2

WO2013154507A2 - Method and etalon for calibrating tire balancing machines

Info

Publication number: WO2013154507A2
Application number: PCT/SI2013/000021
Authority: WO
Inventors: Tomaž FRAKELJ; Primož HAFNER; Marko LOTRIČ
Original assignee: Nela, Razvojni Center Za Elektoindustrijo In Elektroniko, D.O.O.
Priority date: 2012-04-12
Filing date: 2013-04-05
Publication date: 2013-10-17
Also published as: WO2013154507A3; SI24059A

Abstract

The object of the present invention is an etalon and a calibration method pertaining to the field of metrology and used for calibrating tire balancing machines. To check and/or calibrate centering devices, tire service and repair shops employ ordinary rims, which is not very suitable. Nobody can ensure that the rim being used as an etalon is properly balanced, and consequently the question arises as to whether the machine is functioning correctly. According to the present invention the balancing of the etalon is carried out on a rotor balancing machine capable of balancing a body to within 0.1 gmm. The calibration of tire balancing machines is comprised of various tests whereby the operation of tire centering machines can be verified.

Description

Method and Etalon for Calibrating Tire Balancing Machines

FIELD OF THE INVENTION

The object of the present invention is an etalon pertaining to the field of metrology and used for calibrating tire balancing machines.

PRIOR ART

Beside tire mounting machines, tire centering machines are essential to performing tire change operations correctly. On mounting devices the tire is mounted onto the rim. By means of a tire centering machine the wheel is made ready for proper operation. It is important that the wheel be properly centered. To check and adjust the machine, tire service and repair shops employ ordinary rims, which however do not ensure that after calibration the machine will function faultlessly.

It is obvious that centering machines must be checked by means of a precise etalon having known characteristics. It is advantageous for the etalon used to be as similar as possible to a rim. After being manufactured, the etalon must be adjusted on a balancing machine, instructions for performing the calibration procedure of the centering machine and for the calculation of the measurement uncertainty must be written, and a certification template must be produced. Given that calibration of centering machines is performed in the field, the etalon must be made ready for transport so that any external effect or potential damage is prevented.

The problem solved by the present invention is a metrological problem related to checking tire balancing machines. When fashioning an etalon, the material employed and the method of fabrication are very important. It is obvious that an etalon should have a circular body with a uniformly distributed mass and dimensions identical to those of the selected rim. It would be advantageous if it was adaptable in various dimensions.

The classic steel rim is not strong enough. After repeatedly force-clipping lead weights onto the rim, the lead weight would gradually get deformed at the edge. Many weights would have to be employed, since it would be advisable to use new lead weights each time. Substituting the mass of the tire in such a way as to keep it uniformly distributed would be difficult.

Aluminum rims allow holes to be made for receiving dedicated weights. A problem may arise with the machine's centering software because for aluminum rims weights of a different type are used, applied by bonding. Replacing the mass of the tire in such a way as to keep it uniformly distributed is difficult.

The mass of the body should be similar to the mass of the rim and the tire combined, which amounts to about 20 kilograms. Even when dealing with wheels of identical dimensions, however, their mass can vary considerably because rims and tires designed for cars of greater mass are manufactured in a sturdier variety, and vice versa. DETAILED DESCRIPTION OF THE INVENTION

The invention shall hereinafter be described with reference to the embodiments thereof and the accompanying drawings:

Figure 1: Etalon of the invention.

Figure 2: Represents a 40-gram and a 90-gram weight completed state.

Figure 3: Figure showing the positions of the weights.

Conception of the Etalon

It is important that the weights be positioned at precisely the same distance from the center of the body and spaced apart from one another by 165 mm (6.5 inches). Every 90° along the circumference receiving spaces for the weights must be provided, so that the calibration procedure may be performed, and weights must be provided which replace the original lead weights with adjusted M8 screws and additional metal plates.

An etalon which is adaptable to the dimensions of the tires while at the same time being accurate is hard to manufacture. Therefore, an etalon was tested fashioned from a circular tube, preferably from tool engineering steel for a seamless thickwalled tube ST 372, with an internally welded 10 mm thick plate, and then dressed to the desired dimensions. When workpieces of large diameters are being machined, high forces are involved. The central plate represents a challenge. The central plate must be at least 15 mm thick, or it will shift away during dressing, which will result in an inaccurately machined workpiece. In the case where the resulting wall after machining was somewhere around 8 mm thick, the etalon would weigh in at around 20 kilograms, and if the walls were thicker than that, its weight would exceed 23 kilograms, which is excessive. Adjusted screws are employed as weights, with added metal plates in order to achieve the desired mass. The etalon may be balanced on a machine since it has a circular shape. Due to the thickness of the central plate, the problem of the mass of the etalon as such arises, which is why the said embodiment is only partially useful.

Because of the challenges presented by the mass of the etalon, a central plate with a thickness of 15 mm was also tested, wherein 5 uniformly disposed holes with a diameter of 80 mm had been cut. This allowed the mass of the etalon to be reduced by 3 kilograms despite it having a stronger plate. At each quarter of the tube along the curvature, M8 holes are made at predetermined intervals for fixing the weights. Weights consist of M8 screws and plates.

Fashioning the Ring along with the Central Plate

As an upgraded version of the above-described embodiment, an etalon (Figure 1) was fashioned having the following characteristics, which correspond to the best-selling rim dimension, namely 195/65-16 X 6.5 ET 40: a rolled tube having a diameter of 406.4 mm, a wall thickness of 15 mm, a length of 195 mm and a 15 mm thick central plate.

First, the tube which will constitute the ring is straightened out. Thereupon the central plate is prepared, the diameter is adjusted and the holes are cut out by wire erosion. Once prepared, the plate must be welded into the center of the tube. The whole is then machined to dimensions on the lathe. Subsequently, the bores are drilled and the threads are cut. When the machining is completed, the etalon is powder coated in order to protect it against corrosion.

Centering the Etalon

Turning is a machining process used mainly for producing cylindrical bodies. Accurate machining on the lathe ensures that the machined workpiece will have a cylindrical shape. Due to previously undergone operations, however, it can not be assured that its mass will be uniformly distributed around its axis. The body must be centered on a machine that is more accurate than a tire balancing machine. Such operation was carried out on a rotor balancing machine capable of balancing a body to within 0.1 gmm, which is 10 times better than what is achievable with centering machines .

Due to the structure of the etalon as such, in order to center viz. to secure the ring an additional shaft for securing the etalon to the machine must be fashioned. Given that the imbalance of the etalon is modest, the mass of the etalon may be balanced simply by boring holes into the region having excess mass.

Fashioning the Weights

The procedure for calibrating the machine requires weights to be fashioned which have the following mass:

2 g (screw) ,

5 g (screw) ,

10 g (screw 10 g) ,

50 g (screw 10 g + 40 g circular weight),

100 g (screw 10 g + 90 g circular weight) .

The weights are fashioned from M8 screws and a circular steel rod with a diameter of 30 mm. The screws utilized for 2 g and 5 g weights have a bore drilled through part of the thread. This still leaves enough thread to allow for fastening, while making sure at the same time that a predetermined mass is not exceeded. The screws for 10 gram weights, on the other hand, have their head shaped into a cone first, whereupon they are ground off to a predetermined mass. To meet the needs for weights of greater mass, the conically shaped heads are also used for fastening the plates with precision, whereby 50 and 100 gram weights are obtained.

The circular rod is machined on a lathe. First, the rod is turned off to a diameter of 25 mm, whereupon a 9 mm bore is drilled therethrough and subsequently shaped into a cone matching the heads of the screws. After machining the rod is cut to a length of approximately 14 mm and subsequently weighed and progressively cut off until the predetermined mass of 40 grams is reached (Figure 2) . The 90 gram weight is fashioned in the same manner. The only difference is in that the weight is 18 millimeters longer (Figure 2) .

Adjustment of the Weights

The weights must be adjusted. The weight adjustment operation consists in cleaning, verifying the functionality of the measure and its accuracy as per the requirements of the pertinent standards and recommendations. Adjustment is carried out according to the comparative method. The limit of maximum allowed deviations of the mass of the weights from the nominal values complies with the international recommendation OIML Rill.

Calibration of Tire Balancing Machines

The etalon according to the present invention is subsequently utilized for calibrating tire balancing machines. The etalon is secured to the machine in the manner foreseen by the manufacturer. All the provided clamps supplementing the machine are used. The dimensions of the etalon are selected or entered via the software interface of the machine. Thereupon the zero position is tested according to the following procedure:

a) the etalon without the weights is secured to the test shaft ,

b) the normal routine, used for wheel centering, is started on the machine,

- if the values displayed fall within tolerance limits, we proceed to the "Mass linearity test",

- if the values displayed fall outside the tolerance limits, we repeat point a) with the etalon rotated by 45°,

- (if the imbalance is ≥ 5 g it is possible that the etalon is not centered on the machine, or possibly the cones, covers, or the fixing nut are damaged/dirty and consequently unfit for use) ,

c) if the machine does not display results within tolerance limits in any position, the following should be done:

- set the zero position,

- service the machine (confer with the client) .

Thereupon, mass linearity is tested according to the following procedure:

a) the etalon is secured to the test shaft, and a 5 g weight is fastened in position 1 (Figure 3),

b) the normal routine, used for wheel centering, is started on the machine, c) by turning the etalon the accuracy position deviation is determined as well, and from the periphery of the etalon the angle deviation is read out with a 5° resolution.

d) the machine readouts are annotated in the protocol, e) points a), b) , c) and d) are repeated by carrying out the test with the following weights as well:

- 2 g

- 5 g

- 50 g

- 100 g.

f) The 2 g weight is only used when the machine is capable of 1 g resolution.

The next stage is the dimensional linearity test, performed by following this procedure:

a) the etalon is secured to the test shaft, and a 50 g weight is fastened in position 1 (Figure 3),

b) the normal routine, used for wheel centering, is started on the machine,

c) by turning the etalon the accuracy position deviation is determined as well, and from the periphery of the etalon the angle deviation is read out with a 5° resolution.

d) the machine readouts are annotated in the protocol, e) points a) , b) , c) and d) are repeated by also carrying out the test in positions:

- 2, 3, 4 and 5.

In conclusion, the 90° angle test is performed.

The angle test is performed by fastening one 10 g weight in position 1 (Figure 3) . Another 10 g weight is fastened in the same position 1, but spaced apart by 90° along the circumference from the weight fastened previously. At 180° from the center of the added weights, the machine must show a mass of 1.41 times the mass of a single weight. In the case that the machine yields an incorrect result, the test must be repeated with the 5 g and 50 g weights as well.

Claims

Patent Claims

1. Etalon for calibrating tire balancing machines, characterized in that the etalon is balanced on a machine that is more precise than a tire machine and enables specially adjusted weights to be secured thereto, the mass of the etaloft being equal to the mass of a wheel, which is to say, of a rim and a tire combined .

2. Etalon according to Claim 1, characterized in that it is made from rim dimensions 195/65-16 X 6.5 ET 40.

3. Etalon according to Claims 1 to 2, characterized in that the balancing thereof is carried out on a rotor balancing machine which is capable of balancing a body to within 0.1 gmm.

4. Etalon according to Claims 1 to 3, characterized in that specially adjusted weights are used for balancing, fashioned from MB screws and a steel rod with a diameter of 30 mm.

5. Method for calibrating tire balancing machines, characterized in that an etalon according to Claims 1 to 3 and specially adjusted weights are employed for balancing, the mass of the etalon being equal to the mass of a wheel, which is to say, of a rim and a tire combined .

6. Method according to Claim 5, characterized in that the method is comprised of the following stages: securing the etalon to the machine, testing the zero position, testing the mass linearity, testing the dimensional linearity, and testing the 90° angle.

7. Method according to Claims 5 to 6, characterized in that specially adjusted weights are used, fashioned from M8 screws and a steel rod with a diameter of 30 mm.