GB2160979A - Automatic machine for checking the rims of disc wheels for motor vehicles - Google Patents

Abstract

An automatic machine for checking the rims of disc wheels (R) for motor vehicles, in which the wheels (R) are fed to a measuring station by a transporter provided with gripper members. At the measuring station, the wheels (R) are rotated while first and second sensor means, (74, 76; 82, 84), one (84) of which is movable along a curved path, measure the radial (eccentricity) and axial (run-out) geometric characteristics of the rims. Means for processing the data obtained determined the angular position of the wheel (R) corresponding to the maximum of the first harmonic of the radial eccentricity of the rim and marking pincers operated by a single actuator which controls their approach and closure enable the marking of this angular position on the rims. <IMAGE>

Description

SPECIFICATION Automatic machine for checking the rims of disc wheels for motor vehicles The present invention relates in general to machines for checking the rims of disc wheels for motor vehicles.

In recent years, significant progress has been made in the constant research into reducing the weight of motor cars, lorries and buses. Unfortunately, this has made the vehicles considerably more sensitive to geometric irregularities originating from the nonsprung rotating masses. In this context, the wheel-tyre unit plays a role of primary importance in that moderate geometric imperfections could easily give rise to vibrations, cyclic jolting, and resonance phenomena at specific running speeds, particularly in conditions of a smooth and even road surface.

Until a few years ago, the evaluation of the geometric quality of a wheel was based on the measurement of the maximum value of the radial eccentricity and the axial runout in correspondence with the conical seats of the rim in which the tyre bead is fitted. Tyre and motor vehicle companies have carried out systemmatic and comparative research into the evaluation of the influence of the various factors, finding that the radial eccentricity is an important cause of unevenness in running and lack of balance. In fact, non-concentric rotation causes very marked wear on the surface of the tyre at the point of maximum eccentricity, and this becomes more pronounced with time, so that the mileage yield and the running conditions worsen.

The aforementioned practical experiments have also shown that a wheel with a relatively high but localised error may give better results than a wheel with a lower average error which extends over a greater portion of its circumference. The curve representative of the variation in the radial eccentricity detected during a complete revolution of the wheel may be compared to the superposition of several harmonics. The first harmonic corresponds to the conditions of a perfectly circular wheel mounted off-axis on the hub and is principally responsible for the harmful effects. It has in fact been proved that the successive harmonics have only a very modest influence and can thus be ignored.

For effective dimensional checking, therefore, it is necessary to change from the conventional measurement of the maximum eccentricity of the wheel to an evaluation of the first harmonic of the radial eccentricity.

Clearly, the tyres also have imperfect balancing and geometric errors and in fact all the manufacturers indicate with a red stamp the position of the minimum radial force which occurs during rotation. The combination of the position of the minimum radial force and that of the maximum eccentricity of the wheel is an advantageous method of compensating for errors, allowing the coupling of the wheel-tyre elements to be optimised. This type of assembly can be carried out without difficulty in practice, if the point of maximum eccentricity is marked or indicated on the edge of the rim, for example with a stamp made by a punch with a spherical end. The solution has been shown to be useful during the first fitting and also upon the fitting of replacements by tyre repairers who can thus reduce the harmful effect of the individual components with a considerably improved end result.

In recent years machines and apparatus have been developed for measuring the radial variations and axial displacements of the conical seats on which the tyre beads bear, calculating the first harmonic of the curve corresponding to these values during a complete revolution of the wheel, determining the relative angular position at the maximum point of the first harmonic, marking this angular position with a recognisable stamp, separating any pieces outside the tolerance limits prescribed, and moving in sequence the pieces arriving and leaving.

A known machine for carrying out such operations automatically includes a measuring station, feed means for feeding the wheels to be checked successively to the measuring station, and unloading means for unloading the checked wheels. At the measuring station there are provided means for centering and rotating the wheels, sensor means which approach the wheel rims to measure radial and axial geometric characteristics of these rims, means for processing the data obtained to determine the angular position of the wheel corresponding to the maximum of the first harmonic of the curve representative of the radial eccentricity of the rims, and marking means for marking this angular position on the rims.

In known machines ofthis type, the length of time necessary for the operations of transferring the wheels to the measuring station, obtaining the radial and axial geometric data of the rims, marking the rims at the angular position of maximum radial eccentricity, and the subsequent unloading of the wheels is considerable. These machines are thus suited to use in a laboratory or to statistical checks during production but cannot be used for systematic measuring at the end of automated production lines for the wheels or rims.

The object of the present invention, therefore, is to provide a machine of the type specified above which allows disc wheels (or rims for disc wheels) to be inspected at the end of automated production lines for a quick and very reliable systematic check of all the wheels (or rims) leaving such lines.

According to the invention, this object is achieved by virtue of the fact that an automatic machine for checking the rims of disc wheels for motor vehicles, of the type defined above, is characterised in that: -the feed means comprise a transporter having gripper members for gripping and transferring the wheels linearly to the measuring station;; -the sensor means comprise a pair of upper and lower radial sensors movable horizontally into radial contact with the wheel rim to be checked, an upper axial sensor movable vertically into axial contact with the wheel rim from the exterior, and a lower axial sensor movable along a curved path, by a single movement, into radial contact with the rim of the wheel from the interior, and -the marking means comprise movable pincers operated by a single actuator which controls both their approach to the wheel rim being checked and their closure for marking the rim.

By virtue of these characteristics, the operating times for obtaining the data and moving the wheels are very short and exactly in accordance with the pace of the assembly and welding operations in mass production lines for wheels, particularly for motor vehicles.

Furthermore, by virtue of the other measures which will become apparent below, the machine according to the invention is practically unaffected by intrinsic errors and slack, which ensures its considerable precision and reliability.

The invention will now be described in detail with reference to the appended drawings, provided purely by way of non-limiting example, in which: Figure 1 is a schematic side elevational view of a measuring machine according to the invention, Figure 2 is a partially-sectioned front elevational view of the machine, Figure 3 is a plan view of Fig. 1 from above, Figure 4 illustrates the transporter of the machine on an enlarged scale and in greater detail, Figure 5 is a sectional view on an enlarged scale, illustrating the lower axial sensor of the machine; Figure 6 is a side elevational view of the marking pincers of the machine on an enlarged scale; Figure 7 is a horizontal sectional view taken on the line VII-VII of Fig. 6, and Figure 8 is a sectional view taken on the line VIII-VIII of Fig. 6.

Referring initially to Figs. 1 to 3, the machine according to the invention includes a support frame 10 carrying on its upper part a pair of horizontal spaced-apart guides 1 2 along which disc wheels R from an automatic production line are fed successively to a measuring station, generally indicated 16, by means of a transporter 14.

At the measuring station 1 6 are a centering-raising-rotating unit 1 8 for the wheels R, two groups of sensors, radial sensors 20 and axial sensors 22 respectively, disposed on opposite sides of the unit 18, and a pincer marking device 24.

Upstream of the measuring station 1 6 along the transporter 14 are an inlet station 26 and an intermediate waiting station 28, while downstream of the station 1 6 is an unloading station including a tilting device 30.

Referring in greater detail to Fig. 4, the transporter 1 4 is constituted by a slide structure 32 having lateral rollers 34 disposed in rolling contact with guide elements 36 located beneath the sliding guides 1 2. The slide structure 32 is reciprocated in a straight line by means of a pressurised-fluid jack 38 the cylinder of which is connected to the frame 10 and the shaft of which is connected to the slide structure 32.

This slide structure 32 carries first, second and third transverse pins 40, 42, 44 spaced apart by a distance greater than the diameter of the wheels R. A lower jaw 46 and an upper jaw 48 of a rear gripper member 50 are articulated about the pin 40, while a lower jaw 52 and an upper jaw 54 of an intermediate gripper member 56 are articulated about the pin 42.

The lower jaws 46 and 52 are movable between a lowered open position and a raised closed position in which they cooperate with the respective upper jaws 48 and 54, by means of a pressurised-fluid actuator 60 and a tie rod 58.

The upper jaws 48 and 54, however, can pivot freely about the respective pins 40 and 42 between a normal raised position and a lowered position in which they are located beneath the sliding guides 12.

A pusher member 64 is articulated on each front transverse pin 44 and is freely pivotable between a normal raised positioned and a lowered position in which it is located beneath the sliding plane of the guides 1 2.

The rear gripper member 50 and the intermediate gripper member 56 are arranged to grip the lower edges of the wheels R located at the inlet station 26 and the intermediate station 28 respectively by virtue of the clamping achieved by the rotation of the lower jaws 46 and 52 towards the upper jaws 48 and 54 by the members 58 and 60. Thus, as soon as the slide structure 32 is advanced by means of the jack 38, the wheel R gripped by the intermediate gripper member 56 is transferred from the waiting station 28 to the measuring station 16, while the wheel R gripped by the rear gripper member 50 is transferred from the inlet station 26 to the waiting station 28.

Simultaneously, the pusher member 64 pushes the wheel located at the measuring station 1 6 to the unloading tilter 30. At the end of the advance of the slide structure 32, the gripper members 50 and 56 are opened by lowering of the lower jaws 46 and 52.

The subsequent return of the slide structure 32 to its starting position is allowed by the ability of the upper jaws 48, 55 and the pusher member 64 to pivot so that they can slide beneath the wheels R located at the input station 26, the intermediate waiting station 28, and the measuring station 16, respectively.

The measuring station 1 6 is defined within a mounting structure 66 projecting vertically from the support frame 1 0. At the centre of the station 1 6 is the centering-raising-rotating unit 18 which, in generally known manner, comprises a lower centering member 68 movable between a lowered position beneath the sliding guides 1 2 and a raised position in which it cooperates with an upper rotating member 70. This rotating member 70 is driven by geared electric motor 72, whereby the wheel R located at any time at the station 1 6 and raised by the centering and raising device 68 is rotated for the checking measurements to be made.

The unit 1 8 is controlled automatically in synchronism with the reciprocating movements of the transporter 1 4 so that, at the end of the measuring operations, the wheel R which has been checked has been lowered again by the centering and raising member 68, and deposited on the guides 1 2 so that it can be pushed towards the tilting device 30 by the pusher member 64.

As stated above, the measuring station 1 6 has associated therewith two groups of sensors 20 and 22, radial and axial respectively.

The group 20 includes two radial feelers 74 and 76, upper and lowr respectively, which are movable horizontally in a radial direction relative to the wheel R and are associated with electric transducers 78 and 80. The feelers 74 and 76 are movable between a withdrawn rest position in which they allow the wheel R to be positioned in the raised position, and an advanced operative position in which they are brought into contact with the edges of the rim of the wheel R, in correspondence with its inner zones which have conical surfaces and will constitute the supports for the beads of the tyre. The two feelers 74 and 76, with their transducers 78 an 80, are able to measure radial geometric variations in the said zones of the wheel rim, thus providing information on the eccentricity of the rim itself. This information is handled and processed in the manner which will be specified below.

The axial sensor unit 22 comprises an upper feeler 82 and a lower feeler 84 associated with respective electric transducers 86, 88.

The feeler 82 is movable vertically between a raised rest position and a lowered operative position in which it contacts from the exterior the upper edge of the rim of the wheel R centered and raised by the unit 1 8.

The feeler 84 is movable between a withdrawn rest position in which it allows the passage and positioning of the wheel R and an advanced operative position in which it contacts the lower edge of the rim of the wheel R from the interior. The movement of the feeler 84 from the withdrawn position to the advanced position occurs, according to the invention, by means of a single movement along a curved path. This characteristic, which allows the feeler 84 to be moved quickly and evenly towards its final position without knocks that would alter the quality and precision of the measurements, is achieved in the manner illustrated in Fig. 5. As seen in this Figure, the feeler 84 is fixed adjustably to a support member 90 mounted on a trio of pins 92 (only two of which are visible in the Figure), each of which is supported eccentrically by a sprocket 94.The sprockets 94 are carried by respective shafts 96 supported rotatably by the pillar structure 66 and meshing with a central gear wheel 98 also mounted on a shaft 100 supported for rotation by the structure 66. The positions of meshing of the sprockets 94 with the central gear wheel 98 are staggered angularly by 120 .

The shaft 100 of the central gear wheel 98 is rotated by means of a vice member 102 driven by a pressurized-fluid jack only the shaft 104 of which is partially visible in Fig.

5. The shaft 104 is articulated about a pin 106 carried by the jaw 102.

The actuation of the shaft 104 causes rotation of the shaft 100 and hence of the gear wheel 98, with a corresponding rotation through no more than 180 of each of the sprockets 94 which, through the respective eccentric pins 92, cause the feeler member 84 to approach the wheel R along a path in the form of an arc of a circle, until the feeler 84 contacts the inner side of the lower edge of the wheel R.

During the rotation of the wheel R by the geared motor 72, the two sensors of the axial unit 22 obtain any data about the axial runout of the rim of the wheel R and provide information on this data by means of the respective transducers 86 and 88.

The transducers 78, 80 and 86, 88 are connected to an electric circuit terminating at an electronic processor, not illustrated, by means of which the signals from the transducers are handled and processed in the manner explained below.

The marking pincers 24 are fixed adjustably to the mounting structure 66 close to the group of radial sensors 20, as clearly seen in Fig. 3.

With reference in greater detail to Figs. 6 to 8, the marking pincers 24 comprise an elongate central support member 108 connected to a support housing 110 fixed to the structure 66. The connection is achieved in an articulated manner by means of a pin 11 2 which passes through a tubular part 114 formed in the rear part of the element 108 and the ends of which are supported by the housing 110. Close to its front part, the element 108 has two lateral lugs 11 6 having respective holes 11 8 passed through with clearance by two vertical rods 120 fixed at their lower ends 1 22 to the base of the housing 110.Each rod 1 20 is surrounded by a pair of helical compression springs 124, 126 which act at one end against abutments 128, 1 30 on the rod and at the other end against the opposite faces of the corresponding lug 11 6. Thus, in practice, the element 108 can oscillate about the pin 11 2 and is retained in a central, substantially horizontal position by the centering action exerted by the springs 1 24 and 1 26.

An abutment jaw 1 32 is located beneath the central member 108 and is connected thereto by two pairs of front connecting rods 1 34 and two pairs of rear connecting rods 136. Each rod 134 is articulated at one end to the front part of the central member 108 and at the other end to the front part of the jaw 1 32 by respective pins 1 38 and 140, and each rear connecting rod 1 36 is articulated at one end to the rear part of the element 108 and at the other end to the rear part of the jaw 1 32 about respective pins 142 and 144.In practice, the connecting rods 1 34 and 1 36 constitute an articulated parallelogram system by means of which the lower jaw 1 32 is movable along a path in the form of an arc of a circle between the withdrawn position indicated in continuous outline in Fig.

6 and the advanced position indicated in broken outline in the same Figure. The jaw 1 32 is disposed in contact with the central member 108 in both these positions, while it is clearly spaced therefrom during its movement.

To the front end of the jaw 1 32 is fixed an abutment block 146 arranged to cooperate with a spherically-ended punch 148 carried by an upper jaw 1 50 of generally cranked form. This jaw 1 50 is articulated at its lower end 1 52 to the front end of the central member 108 and can rotate between the raised position illustrated in continuous outline in Fig. 6 and the lowered position illustrated in broken outline in the same Figure.

The movement of the lower jaw 1 32 and the rotation of the upper jaw 1 50 is effected by a single double-acting pressurized-fluid jack 154, the shaft 1 56 of which is articulated at 1 58 to the upper end of the jaw 1 50 and the cylinder 1 60 of which is articulated by two lateral pins 1 62 to the upper, upwardly-projecting ends of the two connecting rods 1 36.

The actuator 1 54 is thus freely floating and, when it is in the contracted position illustrated in Fig. 6, the lower jaw 132 is in the withdrawn position and the upper jaw 1 50 is in the raised position. The extension of the jack 1 54 clearly causes the advance of the lower jaw 1 32 and the lowering of the upper jaw 1 50. These movements occur in a controlled sequence which provides firstly for the complete advance of the lower jaw 1 32 and subsequently for the lowering of the upper jaw 1 50.In order to obtain this effect, a resilient system is provided which acts on the connecting rods 1 36 and tends to rotate them about those pins 142 corresponding to the advance of the lower jaw 1 32. In practice, this reslient system is formed by a strong compression spring 1 64 fitted onto a shaft 1 66 having a rear attachment part 1 68 articulated between the connecting rods 1 36 about a pin 1 70 carried by these rods in respective zones between the pins 142 and 162. The front part of the shaft 1 66 is slidable through an annular guide element 1 72 fixed at its upper end to the central member 108.The spring 1 64 acts between this annular guide member 1 72 and the rear attachment part 168 of the shaft 166 and thus tends to make the connecting rods 1 36 rotate about the pin 1 42 in a clockwise sense with reference to Fig. 6.

Clearly, in the contracted condition of the jack 1 54, the spring 1 64 is compressed whereby, immediately the jack is extended, it acts to cause the movement of the cylinder 1 60 and hence the movement of the lower jaw 132, while the shaft 1 56 and hence the upper jaw 1 50 remain stationary. As soon as the lower jaw 1 32 reaches its advanced position corresponding to the extension of the spring 164, the cylinder 1 60 stops while the shaft 1 56 moves relative thereto, causing the lowering of the upper jaw 1 50.

In short, the jack 1 54 is able to effect both the approach to the edge of the wheel R located at the measuring station 1 6 and the marking of this edge at the predetermined position by the pincers 24. The resilient mounting of the central element 108 by means of the pin 11 2 and the springs 124, 1 26 allows the pincers 24 to adapt automatically to the position of the edge.

The unloading tilter 30 includes a take-up member 1 74 of generally known type, which is movable by means of a pressurised-fluid jack 1 76 between a lowered receiving position illustrated in broken outline in Fig. 1 and a raised unloading position illustrated in continuous outline in the same Figure. Associated with the tilter 30 are two opposing chutes 178, 1 80 for the removal of the wheels R, by means of which the latter are separated on the basis of the measurements taken at the station 16.

The machine according to the invention is located at the end of an automated production line for disc wheels (or simply rims for disc wheels) to carry out the automatic checking of the entire production. The conveyor from the disc-rim welding, or whatever machine carries out the final operation of the cycle, automatically supplies the wheels R which are deposited at the inlet station 26 with their axes vertical. The transporter unit 14 moves each wheel R successively, in the manner explained above, firstly into correspondence with the intermediate waiting station 28 and subsequently to the measuring station 1 6. The movements of the wheels occur rapidly and safely since they are constantly held by the grippers 50 and 56.

The wheel R located at the measuring position 1 6 at any one time is raised by the raising member 68 and brought into contact with the upper rotating member 70.

At this point, the feelers 74, 76 and 82, 84 of the two units 20 and 22 are brought to predetermined points for the measurements, in the manner described above. The geared motor 72 is then actuated and rotates the wheel R through one revolution (360 ). At regular, very close intervals, the transducers 78, 80 and 86, 88 output electrical analogue signals which are registered and processed by the processor. In order to obtain more precise results, a very large number of measurements, for example 1 28 (about one every 3 ), is taken.

After one complete revolution, the input of data stops, while the wheel continues to rotate until the processor commands the geared motor 72 first to reduce the angular speed and then to stop. In the meantime, the processor connected to the transducers has determined, on the basis of the data obtained from the measurement of the movement of the various feelers 74, 76, 82, 84, the maximum values of the radial eccentricity and the axial runout of the rim. In effect, the processor is arranged to determine the maximum of the first harmonic of the curve representative of the radial eccentricity of the rim. The calculation of the first harmonic of the curve of the wheel R under inspection is carried out mathematically by the Fourier series.Together with the maximum of the first harmonic, the processor also establishes the angular position of the wheel R corresponding to this maximum and commands the stoppage of the rotation of the wheel R when this angular position is in the path of the marking pincers 24.

At this point, in the manner explained above, the approach and closure of the pincers 24 are effected so as to impress an indelible mark on the exterior of the upper edge of the rim.

The processor also calculates the values of the axial runout of the rim. If desired, it is possible to add other programs which allow the measurement, by processing of the basic data, of the effective width of the rim, the circumferential development relative to the fitting of the tyre, the degree of offset of the disc (that is the "camber" of the wheel), and any other data.

Finally, the marking pincers 24 are withdrawn and the wheel R replaced on the sliding guides 1 2 for transfer by the pusher member 64 of the transporter 14 to the unloading tilter 30. Simultaneously, the wheels lying at the intermediate station 28 and the inlet station 26 advance one step, and the cycle will be repeated in a similar manner to that described above.

It is possible to establish and preset a maximum value of the eccentricity of the first harmonic with regard to the dimensions and the requirements of use of the wheel being checked. Should the error in the wheel being checked exceed the predetermined limits, the wheel will be directed into the reject chute 178, rather than into the normal chute 1 80 intended for wheels which have been checked and found to be within the tolerance limits by a selector, not illustrated, upon unloading.

The data collected by the processor may, with the addition of specific conventional apparatus, be displayed visually on a display or video screen or documented by a printer.

The values memorised may also be used for statistical determinations relating to production times, percentages and cause of rejects, indications of quality, and other things.

The machine according to the invention is able to operate with very short measurement and movement times and with considerable reliability. Naturally, its operating field may vary in dependence on the families of existing wheels: by way of example, in the motor car sector, it is able to operate with wheels having nominal diameters of between 305 mm and 381 mm, widths of between 89 mm and 152 mm, and disc offsets of between 0 an 55 mm. For the coach, bus and industrial vehicle sectors, the field of use may be as follows; diameter-406 mm to 622 mm; widths 27 mm to 229 mm; offsets-0 to 80 mm.

Claims (8)

1. Automatic machine for checking the rims of disc wheels for motor vehicles, of the type including a measuring station, feed means for feeding the wheels to be checked successively to the measuring station, and unloading means for unloading the checked wheels, and in which the measuring station being provided with means for centering and rotating the wheels, sensor means which can approach the wheel rims respectively to detect radial and axial geometric characteristics of the rims, means for processing the data obtained to determine the angular position of the wheel corresponding to the maximum of the first harmonic of the curve representative of the radial eccentricity of the rims, and marking means for marking the angular position on the rims, in which:: -the feed means comprise a transporter having gripper members for gripping and transferring the wheels linearly to the measuring station, -the sensor means comprise a pair of radial sensors movable horizontally into radial contact with the wheel rim to be checked, an upper axial sensor movable vertically into axial contact with the wheel rim from the exterior, and a lower axial sensor movable along a curved path, by a single movement, in axial contact with the rim of the wheel from the interior, and -the marking means comprise movable pincers operated by a single actuator which controls both their approach to the wheel rim being checked and their closure for marking the rim.

2. Machine according to Claim 1, in which the means for centering and rotating the wheels include a lower member for centering and raising the wheel to be checked vertically against an upper member which is rotated continuously to put the wheel through one complete revolution for the measurement of the radial and axial geometric characteristics and then, without stoppage, to dispose it in the angular position of the wheel corresponding to the maximum of the first harmonic of the radial eccentricity determined by the processing means, in the path of the marking pincers.

3. Machine according to Claim 1, in which the transporter includes a slide structure which can reciprocate in a straight line relative to the measuring station along a guide and slide structure for the wheels and has a rear gripper member, an intermediate gripper member, a front pusher member and means for controlling the closure of the rear and intermediate gripper members during the advance of the slide structure, so as to grip first and second wheels to be checked and transfer them to the measuring station while the pusher transfers a checked wheel from the station to the unloading means, and for controlling the opening of the gripper members to allow the release of the wheels and the return of the slide.

4. Machine according to Claim 3, in which each gripper member includes a lower jaw and an upper jaw articulated about a common pin, the lower jaw being movable relative to the upper jaw by the control means between a lowered open position and a raised closed position, and the upper jaw being pivotable, like the pusher, between a raised working position and a lowered rest position, during the return of the slide structure.

5. Machine according to Claim 1, in which the lower axial sensor which is movable along a curved path comprises a feeler member mounted on a support movable along the curved path by means of a control device including a linear actuator, a drive gear rotated by the actuator, a trio of driven gear wheels meshing with the drive gear in equiangularly-spaced positions and carrying respective eccentric pins on which the support is mounted.

6. Machine according to Claim 1, in which the marking pincers include: -a central support member connected to a fixed support structure, -an abutment jaw located beneath the central support member and connected thereto by means of front and rear connecting rods which form an articulated parallelogram allowing the movement of the abutment jaw relative to the central support member between a withdrawn rest position and an advanced working position, -a marking jaw located above the central support member and articulated to the lower end thereof so as to be pivotable between a raised rest position and a lowered working position for cooperation with the abutment jaw, -a linear pressurised-fluid actuator located parallel to and above the central support member, and having one end articulated to the marking jaw and the other end articulated to the rear connecting rods, and resilient thrust means interposed between the central support member and the rear connecting rods and acting thereon so that the actuation of the actuator causes firstly the complete movement of the abutment jaw from its withdrawn position to its advanced position while the marking jaw is kept stationary, and subsequently the pivoting of the marking jaw from its raised position to its lowered working position.

7. Machine according to Claim 6, in which the central support member is connected to the fixed support structure so as to be rotatable about a transverse rear pin, and is supported at its front end by the fixed structure through resiliently yieldable centering means.

8. Automatic machine for checking the rims of disc wheels for motor vehicles, substantially as herein described with reference to, and as shown in, the accompanying draw ings.