Balancing machine for vehicle wheels with analog to digital conversion and adjustable sampling frequency

The upgraded balancing machine for vehicle wheels comprise a supporting frame for gripping and rotation means for gripping and rotating a wheel to be balanced around a rotation axis, a first sensor for detecting the unbalance of the wheel with respect to the rotation axis suitable for generating a first analog signal, a second sensor for detecting at least one portion of the profile of the wheel suitable for generating a second analog signal, at least one analog to digital converter associated with at least one of the first and the second detection sensors and suitable for converting at least one of the first and the second analog signals into a corresponding digital signal, a processing and control unit associated with the conversion device and suitable for processing the digital signal, and an adjustment unit for adjusting the sampling frequency of at least one of the first and the second analog signals associated with the conversion device. The adjustment unit responds to a first signal generated by a shaft encoder, and responds to a programmable timer, so that the frequency of the sampling operation can be altered.

The present invention refers to an upgraded balancing machine for vehicle wheels.

BACKGROUND OF THE INVENTION

It is known that vehicle wheels are generally made up of a cylindrical metal rim having, at the axial ends, ring-shaped flanges between which is defined a channel for the interlock of an elastic tire, the side portions of which, the so-called “beads”, are positioned fast up to the ring-shaped flanges.

The need is also known to perform frequent balancing operations that consist in applying weights, made of lead or other material, at predetermined points of the wheel and along the rim.

The fitting of the weights offsets the presence of any tire and/or rim irregularities during the rotation of the wheel.

To perform such operations, balancing machines are commonly used that comprise a supporting structure for wheel gripping and rotation means, such as a horizontal shaft that can turn axially by means of motor means and onto which the wheel rim is keyed.

The measurement of the wheel unbalance is detected during rotation by suitable electronic or electromechanical devices, such as force transducers fitted along the horizontal shaft.

Other characteristic measurements are generally added to the unbalance measurement such as the measurement of the wheel roundness, the eccentricity of the wheel, the amount of tread wear, etc. Such measurements are normally performed by means of suitable measuring sensors, with or without contacting the wheel (for example feeler pins or optical sensors).

Each of the detected measurements is normally related to a respective angular position of the wheel on the rotation axis detected by an angular position transducer (encoder) associated with the horizontal shaft.

In particular, the unbalance and the other specific measurements made on the wheel are performed by sampling the signals coming from the respective measuring sensors at preset and constant angular intervals determined by the technical characteristics of the encoder.

These known balancing machines are however susceptible to upgrading, in particular, in order to upgrade the quality and the precision of the measurements taken.

In fact, the frequency of samplings made by the measuring devices on the wheel is closely tied to predetermined angular positions and is restricted by the technical characteristics of the encoder. In particular, the angular resolution of the encoder, generally suitable for measuring unbalance, can be insufficient and not allow sufficiently accurate measurements in case, for example, of measuring the roundness or the eccentricity of the wheel. In fact, the low resolution of the measurements made, together with the presence of numerous branched grooves that extend irregularly on the surface of the tread, tends to falsify the testing of the tire characteristics.

BRIEF SUMMARY OF THE INVENTION

The main aim of the present invention is to provide an upgraded balancing machine for vehicle wheels that permits upgrading the quality and the precision of the measurements taken without having to increase the angular resolution of the encoder.

Within the scope of this technical aim, another object of the present invention is to achieve the above-noted aims with a simple structure, of relatively practical implementation, safe to use and with effective operation, as well as having a relatively low cost.

The objects indicated above are all achieved by the present upgraded balancing machine for vehicle wheels, comprising a supporting frame for gripping and rotation means for gripping and rotating a wheel to be balanced around a rotation axis, first detection means for detecting the unbalance of said wheel with respect to said rotation axis suitable for generating a first analog signal, second detection means for detecting at least one portion of the profile of said wheel suitable for generating a second analog signal, at least one conversion device associated with at least one of said first and said second detection means and suitable for converting at least one of said first and said second analog signal into a corresponding digital signal, a processing and control unit associated with said conversion device and suitable for processing said digital signal, and adjustment means which are suitable for adjusting the sampling frequency of at least one of said first and said second analog signal and which are associated with said conversion device.

DETAILED DESCRIPTION

With reference to such figures, an upgraded balancing machine for vehicle wheels has been designated generally by reference number1.

The machine1comprises a frame2that supports gripping and rotation means3for gripping and rotating a wheel R to be balanced around a substantially horizontal rotation axis A.

Particularly, the frame2is made up of a base block2a, containing the support and motorization system of the gripping and rotation means3, and of a vertical wall2bassociated with a side of the base block2a.

The gripping and rotation means3comprise a shaft4defining the rotation axis A which extends horizontally and overhanging from the base block2a. The free end of the shaft4has a bush suitable for fixing and centering the rim of the wheel R.

The machine1comprises first detection means5of the unbalance of the wheel R with respect to the rotation axis A.

In particular, the first detection means5can comprise a pair of force transducers, of the load cell type or the like, associated together spaced along a section of the shaft4and suitable for detecting variations in the forces exercised by the wheel R along the shaft4during rotation.

The machine1also comprises second detection means6for scanning at least a portion of the profile of the wheel R.

The second detection means6, in the particular embodiment of the invention illustrated inFIG. 1, comprise a first sensor7, of the non-contact type, such as an optical sensor or a distance laser sensor, which can slide along on straight guiding means8.

The straight guiding means8extend in a direction parallel to that of the rotation axis A and are made up, for example, of two supporting bars fastened to the upper portion of the vertical wall2b. The sliding of the first sensor7along the supporting bars is obtained by means of movement means made up, usefully, of a flexible body, of the belt type or the like, which is closed on itself like a ring, is associated with the first sensor7and is wrapped on two rotating disks, one of which is the drive disk and the other the drive disk (note shown).

Advantageously, the second detection means6scans a portion of the side surface of the wheel R.

In particular, the machine1can envisage a pair of second sensors such as feelers, optical sensors or distance laser sensors, associated moving with, or fixed to the frame2, and arranged facing the two opposite side surfaces of the wheel R.

The potential cannot, however, be ruled out of first and second different detection means5and6, with different number and arrangement of the force transducers, of the first sensor7and of the second sensors.

Advantageously, the force transducers of the first detection means5generate, during the rotation of the wheel R, a first analog output signal SA1, modulated according to the changes in force detected along the shaft4.

In the same way, the first sensor7(and possibly the second sensors) of the second detection means6generates, during the rotation of the wheel R, a second analog output signal SA2, modulated according to the particular shape and position of the surface along the circumference of the tire, at the tread.

As the diagram ofFIG. 2shows, the first and second detection means5and6are operatively associated with a conversion device9, of the analog-digital converter type, which receives the first and/or the second analog signal SA1and SA2and converts these analog signals into respective digital signals SD.

Advantageously, the machine1comprises adjustment means10associated with the conversion device9and suitable for piloting the sampling frequency of the first and second analog signal SA1and SA2.

In particular, the adjustment means10are made up of a determination device for determining the above sampling frequency starting with the frequency generated by a programmable timer13, if necessary synchronized with a reference signal SR.

Usefully, the reference signal SRcan be an electrical signal or pulse produced by first generation means11, during the rotation of the wheel R and triggered at just one predetermined angular position.

The first generation means11are made up of a first detection device of the non-contact type, for example, an optical sensor suitable for scanning or viewing a determined area of reference on the surface of the tire or of the rim of the wheel R.

Alternatively, the first generation device11is an encoder which is associated with the shaft4and which measures the rotation around its own axis for determining just one, or more, angular positions of the wheel R and for the generation of corresponding reference signals SR.

The reference signal SRso determined is then sent to the determination device in adjustment means10which, by means of the programmable timer13, generates a piloting signal SPfor the conversion device9. The sampling frequency of the conversion device is a multiple of the frequency of the reference signal SRor, in any case, the sampling frequency is substantially greater and synchronous with respect to the frequency of the reference signal SR.

Usefully, a management and control unit12is associated with the determination device in adjustment means10for selecting the multiplication factor M of the input reference signal SRand, therefore, for changing the frequency of the output piloting signal SP.

Advantageously, in specific measurement phases and in the event of the wheel R rotating at a preset angular speed, the timer13can be suitably programmed according to the angular speed of the wheel R. In this case, therefore, there is no need to synchronize the piloting signal SPwith respect to the reference signal SRand, consequently, the measurement of just one or more angular positions of the wheel R is superfluous.

Conveniently, the management and control unit12is suitable for controlling the determination device10for the dynamic adjustment of the sampling frequency during a same measuring cycle. In particular, the frequency of the piloting signal SPis increased in case of a higher speed of change in the first and/or the second analog signal SA1and SA2or, on the contrary, the frequency of the piloting signal SPis reduced in case of a reduction in the speed of change of the first and/or the second analog signal SA1and SA2.

The machine1can also comprise second generation means for generating the reference signal SRin relation to the movement of the first sensor7along the straight guiding means8and at predefined axial positions of the first sensor7itself.

In particular, the second generation means can comprise a second sensor device, of the type of an encoder, suitable for detecting one or more angular positions of at least one between the rotating disks for the movement of the first sensor7.

The digital signal SDresulting from the sampling of the first analog signal SA1and/or the second analog signal SA2is sent to the management and control unit12, which is a microprocessor system, and is processed for testing unbalance, roundness, eccentricity, tread wear, etc., on the wheel R.

The data thus processed can be sent to display means14, such as a monitor, for analyzing the results on the part of an operator.

It has been found that the described invention achieves the proposed objects, and, in particular, the fact is underlined that the presence of the adjustment means for the sampling frequency upgrades the quality and the precision of the measurement taken.

In fact, the possibility of sampling the input analog signals at frequencies higher than those commonly used permits a greater resolution of the digital signal obtained, ensuring a precise measurement even in the case of irregular surfaces, such as those of the tire tread.

Furthermore, the presence of the programmable timer permits the execution of particular measurements on the tire, such as taper or roundness, quite apart from the measurement of just one or more angular positions of the wheel.

To this must be added the fact that, in case of the synchronization of the sampling frequency with the frequency of the reference signal, a correct association is in any case ensured between the measurement taken and the corresponding angular position of the wheel.

The invention thus conceived is susceptible of numerous modifications and variations, all of which fall within the scope of the inventive concept.

Furthermore all the details may be replaced by other elements which are technically equivalent.

In practice, the contingent shapes and dimensions may be modified while still falling within the scope of protection of the following claims.