MOVABLE-JAW CRUSHER FOR RUBBLE AND SIMILAR, AND RELATIVE OPERATING METHOD

TECHNICAL FIELDS

The present invention relates to a movable-jaw crusher for rubble and similar. BACKGROUND ART

As is known, movable-jaw crushers are machines for crushing rubble, rock, quarry materials, demolition or roadwork debris, and similar, using the mechanical action of two facing jaws defining two sloping lateral walls of a downward-tapering hopper, and which are moved cyclically towards each other to crush the material trapped between them, i.e. inside the hopper.

More specifically, movable-jaw crushers normally comprise a supporting structure or outer machine body, in which is formed a crushing compartment or chamber bounded laterally by two opposite parallel vertical lateral walls; two crushing jaws positioned facing each other inside the crushing chamber, i.e. between the two vertical lateral walls, to define two sloping lateral walls of a downward-tapering hopper; and a jaw actuating

device for moving the two jaws cyclically towards each other to crush the material trapped inside the hopper.

One of the jaws, known as the "fixed jaw", is normally fixed rigidly to the supporting structure of the crusher, while the other, known as the "movable jaw", is suspended at one end, inside the supporting structure, from the eccentric portion of a supporting shaft perpendicular to the two vertical lateral walls of the supporting structure« The supporting shaft is rotated by an electric or hydraulic motor; and the rear of the "movable jaw" is fixed in floating manner to the supporting structure of the crusher by a collapsible connecting member, which allows the jaw to freely oscillate about a horizontal reference axis under the bias of supporting shaft 15, concurrently allowing minor displacements in the horizontal and vertical sense.

More specifically, the collapsible connecting member normally comprises a connecting rod-strut mechanism; and one or two hydraulic thrust-bearing cylinders interposed between the strut and the supporting structure of the crusher, and designed to adjust the tilt of the movable jaw and absorb the impulsive mechanical impact stresses produced in the crusher when a large block of indestructible material gets jammed between the jaws.

More specifically, each hydraulic thrust-bearing cylinder of the collapsible connecting member comprises a passive mechanical maximum-pressure valve, which is

connected directly to the hydraulic cylinder chainber whose volume is reduced by withdrawal of the piston rod inside the cylinder, and is designed to drain oil rapidly from the chamber when the oil pressure inside the chamber exceeds a given trigger threshold _/ so as to immediately back up the "movable jaw" and prevent structural damage to the crusher.

Though widely used by most movable-jaw crusher manufacturers, by being cheap and reliable, passive mechanical maximum-pressure valves pose various problems .

Because of the way they are designed, mechanical maximum-pressure valves of the above type have an extremely slow response to variations in pressure, and fail to "sense" pressure peaks, inside the hydraulic cylinder chamber, which follow one another at a frequency higher than the response frequency of the valve. In other words, mechanical maximum-pressure valves only permit oil drainage from the hydraulic cylinder chamber when the pressure increase produced by the block of indestructible material jammed inside the crushing chamber exceeds the trigger threshold for a relatively long period of time, which, however, may be sufficient to damage the crusher. Moreover, passive mechanical maximum-pressure valves have a tendency to leak as the oil pressure inside the hydraulic cylinder chamber nears the trigger threshold, thus creating problems which reduce the

hourly output of the crusher. For example, when the oil pressure in the hydraulic cylinder remains close to the trigger threshold for a prolonged period of time, mechanical maximum-pressure valves tend to allow small amounts of oil to seep from the hydraulic cylinder, which gradually eases back the piston rod and parts the two jaws, thus increasing the size of the material from the crusher, with all the drawbacks this entails. DISCLOSURE OF INVENTION It is an object of the present invention to provide a movable-jaw crusher designed to eliminate the aforementioned drawbacks .

According to the present invention, there is provided a movable-jaw crusher for rubble and similar, as claimed in Claim 1 and preferably, though not necessarily, in any one of the following Claims depending directly or indirectly on Claim 1.

According to the present invention, there is also provided a method of operating a movable-jaw crusher for rubble and similar, as claimed in Claim 11. BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a side view, with parts in section and parts removed for clarity, of a crusher for rubble and similar, in accordance with the teachings of the present invention;

Figures 2 and 3 show two larger-scale details of the Figure 1 crusher;

Figure 4 shows a side view, with parts in section and parts removed for clarity, of a variation of the Figure 1 crusher for rubble and similar;

Figure 5 shows a view in perspective, along section line V-V, of the Figure 4 crusher for rubble and similar.

BEST MODE FOR, CARRYING OUT THE INVENTION Number 1 in Figure 1 indicates as a whole a movable-jaw crusher, which is particularly advantageous for crushing rubble, rock, quarry materials, demolition or roadwσrk debris, and similar.

Crusher 1 substantially comprises a supporting structure or outer machine body 2, in which is formed a crushing compartment or chamber 3 having a top opening through which the work material is loaded, and a bottom opening through which the crushed material is unloaded; two crushing jaws 4, 5 positioned facing each other inside crushing chamber 3 to define two sloping lateral walls of a downward-tapering hopper,- and a jaw actuating device β for moving the two crushing jaws 4 and 5 cyclically towards each . other to crush the material trapped between them, i.e. inside the hopper. More specifically, in the example shown, crushing chamber 3 is bounded laterally by two opposite parallel vertical lateral walls 7, and each crushing jaw, 4, 5 comprises a flat front plate 8 made of high-strength

metal and perpendicular to the two vertical lateral walls 7, and a rear supporting structure 9 which, depending on the type of jaw, is fixed rigidly to supporting structure 2 of the crusher, or is connected in floating manner to supporting structure 2 by actuating device 6.

In the example shown, rear supporting structure 9 of crushing jaw 4 is fixed rigidly to supporting structure 2 of the crusher, and so defines the "fixed jaw" of the crusher; whereas rear supporting structure 9 of crushing jaw 5 is suspended at one end, inside supporting structure 2, to the eccentric portion of a supporting shaft 10 - which rotates freely about a horizontal axis of rotation A perpendicular to the two vertical lateral walls 7 of supporting structure 2 - and so defines the "movable jaw" of the crusher.

More specifically, the eccentric portion of supporting shaft 10 is inserted and rotates freely inside a transverse through hole formed in the top of rear supporting structure 9 of crushing jaw 5 and coaxial with a horizontal axis parallel to axis A, so that rotation of supporting shaft 10 about axis A oscillates the whole of crushing jaw 5.

With reference to Figure 1, in addition to supporting shaft 10, actuating device 6 also comprises a motor flywheel 11 fitted rigidly to one end of supporting shaft 10 and coaxial with axis A, so as to rotate together with the shaft about axis A/ and an

electric, hydraulic, or similar motor {not shown) for rotating motor flywheel 11, and supporting shaft 10 connected to it, about axis A.

In addition, actuating device 6 also comprises a collapsible connecting member 12, which connects rear supporting structure 9 of crushing jaw 5, i.e. the movable jaw, in floating manner to supporting structure 2 of the crusher to allow crushing jaw 5 to freely oscillate about a horizontal reference axis under the bias of supporting shaft 10, concurrently allowing minor displacements in the horizontal and vertical sense.

In the example shown, collapsible connecting member 12 comprises an oscillating connecting rod 13 hinged at one end to supporting structure 2 o£ the crusher to oscillate freely about a horizontal axis B parallel to axis A; a strut 14 _r which has a first end resting on the rear of rear supporting structure 9 of crushing jaw 5, and a second end resting on the free end of oscillating connecting rod 13, which is substantially vertical; and at least one hydraulic thrust-bearing cylinder 15 interposed between the free end of oscillating connecting rod 13 and supporting structure 2 of the crusher, on the opposite side to strut 14.

More specifically, in the example shown, strut 14 comprises a flat, substantially rectangular metal plate perpendicular to the two vertical lateral walls 7 of supporting structure 2 of the crusher, and the two long lateral edges of which are positioned, one resting on

the free end of oscillating connecting rod 13, and the other on rear supporting structure 9 of crushing jaw 5; and collapsible connecting member 12 comprises two identical hydraulic thrust-bearing cylinders 15, which are located side by side, on opposite sides of the vertical mid-plane of the crusher - the plane perpendicular to axis of rotation A of supporting shaft 10 and parallel to the Figure 1 plane - and are both interposed between the free end of connecting rod 13 and a horizontal reinforcing cross member 16 rigidly connecting the two vertical lateral walls 7 of supporting structure 2 of the crusher.

With reference to Figures 1 and 2, each hydraulic thrust-bearing cylinder 15 extends along a longitudinal axis L parallel to the vertical mid-plane of the crusher, and therefore to the two vertical lateral walls 7 of supporting structure 2 of the crusher, is located on the opposite side to strut 14, and is tilted at a predetermined angle with respect to the plane of strut 14.

More specifically, each hydraulic thrust-bearing cylinder 15 substantially comprises a casing or cylindrical tubular outer body 17 coaxial with longitudinal axis L; a movable piston rod 18 coaxial with longitudinal axis L and inserted telescopically and in axially-sliding manner inside cylindrical tubular body 17,- and a piston 19, which is mounted to slide axially inside the longitudinal cavity 17a of

cylindrical tubular body 17, and is designed to engage the cavity in fluidtight manner and divide it into two complementary variable-volume chambers .

Piston 19 is fixed rigidly to the end of rod 18, so that one of the two variable-volume chambers hereinafter indicated 20 - is reduced in volume when rod 18 withdraws inside cylindrical tubular body 17, and increases in volume when rod 18 is extracted from cylindrical tubular body 17. Variable-volume chamber 20 of each hydraulic thrust-bearing cylinder 15 is obviously filled with pressurized oil, and is therefore connected in known, manner to the hydraulic circuit (not shown) of the crusher . With reference to Figures 1 and 2, collapsible connecting member 12 also comprises, for each hydraulic thrust-bearing cylinder 15, a pressure sensor 21 for detecting the instantaneous oil pressure inside variable-volume chamber 20 of hydraulic thrust-bearing cylinder 15; and an electrically controlled on-off valve 22 connected directly to variable-volume chamber 20 of hydraulic thrust-bearing cylinder 15, and for selectively draining pressurized oil from variable- volume chamber 20. More specifically, pressure sensor 21 and on-off valve 22 are preferably, though not necessarily, fitted directly to the bottom of cylindrical tubular body 17; and collapsible connecting member 12 comprises an

electronic central control unit 23, which controls on- off valves 22 of the two hydraulic thrust-bearing cylinders 15 as a function of the signals from pressure sensors 21, so as to open on-off valves 22 when the oil pressure inside variable-volume chamber 20 of either one of hydraulic thrust-bearing cylinders 15 exceeds a predetermined maximum trigger threshold, which is obviously memorized in electronic central control unit 23. In the example shown, pressure sensors 21 are conventional analog pressure transducers _/ and on-off valves 22 are proportional electrically controlled flow regulating valves already in use in oleodynaxnics for other purposes. With reference to Figures 1, 2 and 3, in the example shown, the two axial ends of each hydraulic thrust-bearing cylinder 15 rest on horizontal reinforcing crdss member 16 and the free end of connecting rod 13, respectively, with the interposition of two known spherical joints 24; and collapsible connecting member 12 also comprises an auxiliary single- or double-acting hydraulic cylinder 25, which is hinged at one end to horizontal reinforcing cross member 16, is hinged at the other end to the free end of oscillating connecting rod 13, and is connected to the hydraulic circuit (not shown) of the crusher to exert pull on horizontal reinforcing cross member Iβ and on the free end of oscillating connecting rod 13, to keep

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oscillating connecting rod 13 resting on the ends of both rods 18, and to keep cylindrical tubular body 17 of each hydraulic thrust-bearing cylinder 15 resting on horizontal reinforcing cross member 16. Xn addition, auxiliary hydraulic cylinder 25 also adjusts the tilt, with respect to the vertical, of crushing jaw 5 under the control of electronic central control unit 23, and is therefore connected to the hydraulic circuit (not shown) of the crusher with the interposition of a conventional electrically controlled hydraulic distributor (not shown) controlled directly by electronic central control unit 23.

With reference to Figures 1 and 3, collapsible connecting member 12 preferably, though not necessarily, also comprises a position sensor 26, which supplies an electric signal indicating the instantaneous tilt angle of crushing jaw 5 with respect to the vertical, or any other parameter indicating the position of crusher jaw 5 inside crushing chamber 5. In the example shown, auxiliary hydraulic cylinder 25 comprises a conventional double-acting hydraulic cylinder equipped with a magnetostriσtive or similar position transducer performing the functions of position sensor 26. That is, position transducer 26 supplies an electric signal indicating the instantaneous position of the movable piston rod 27 of auxiliary hydraulic cylinder 25 with respect to the tubular outer casing 28 of the cylinder, or more specifically, an electric

signal indicating the instantaneous length of the portion of rod 27 projecting outwards of tubular outer casing 28 of auxiliary hydraulic cylinder 25 - Which length is directly related to the position of crushing jaw 5 inside crushing chamber 3.

Electronic central control unit 23 is obviously connected to position transducer 26 of auxiliary hydraulic cylinder 25, and uses the signal from position transducer 26 to determine the actual instantaneous tilt angle of crushing jaw 5 with respect to the vertical, and the tilt angle to calculate the width of the constriction S formed by crushing jaws 4 and 5 at the hopper outlet .

In other words, double-acting auxiliary hydraulic cylinder 25, ecjuipped with position transducer 26, performs the triple function of keeping hydraulic thrust-bearing cylinders 15 resting on oscillating connecting rod 13 and horizontal reinforcing cross member 16; adjusting the tilt of crushing jaw 5 with respect to the vertical, in combination with hydraulic thrust-bearing cylinder/s 15,- and supplying an electric signal indicating an instantaneous parameter indicating the current position of crushing jaw 5 inside crushing chamber 3 , Operation of crusher 1 as a whole will be clear from the foregoing description, with no further explanation required.

Operation of collapsible connecting member 12, on

the other hand, will be described, assuming crushing jaw 5 is initially in a parked configuration, in which the width of constriction S formed by the two crushing jaws 4, 5 is maximum, and in which rods 18 of both hydraulic thrust-bearing cylinders 15 are obviously almost completely withdrawn inside cylindrical tubular bodies 17, and the volume of variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15 is minimum.

In actual use, by means of a control panel {not shown) , the operator supplies electronic central control unit 23 with, the desired size of the crushed material from crushing chamber 3, and electronic central control unit 23 determines, on the basis of various memorized operating parameters of the crusher, the ideal width of constriction S at the hopper outlet to achieve crushed material of the desired size.

Alternatively, the operator may supply electronic central control unit 23 directly with the ideal width of constriction S at the hopper outlet. On determining or acquiring the ideal width of constriction S formed by crushing jaws 4, 5 at the outlet, electronic central control unit 23 of the crusher feeds pressurized oil into variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15 to slowly extract rods 18 of both hydraulic thrust- bearing cylinders 15 and so rotate crushing jaw 5 about supporting shaft 10.

When the bottom edge of flat front plate 8 of

crushing jaw 5 comes to rest against flat front plate 8 of crushing jaw 4, thus zeroing the width of constriction S formed by crushing jaws 4 and 5, the oil pressure inside variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15 begins to rise rapidly, and, electronic central control unit 23 , which is monitoring pressure by means of pressure sensors 21, immediately cuts off oil supply to both hydraulic thrust-bearing cylinders 15, and determines, on the basis of information from position sensor 26 of auxiliary hydraulic cylinder 25, the current tilt angle of crushing jaw 5 with respect to the vertical.

Which current tilt angle corresponds to a maximum- travel configuration of crushing jaw 5, and is used as a reference by which to subsequently position crushing jaw 5.

In connection with the above, it should be pointed out that, as rods 18 are extracted, auxiliary hydraulic cylinder 25 keeps oscillating connecting rod 13 resting on the ends of rods 18, and cylindrical tubular bodies 17 of both hydraulic thrust-bearing cylinders 15 resting on horizontal reinforcing cross member 16.

On acquiring the reference parameters corresponding to the maximum-travel configuration of crushing jaw 5, electronic central control unit 23 calculates the angular displacement of crushing jaw 5, with respect to the maximum-travel configuration, required to achieve a constriction S between jaws 4 and 5 of substantially the

calculated ideal width, and then regulates pressurized- oil supply to auxiliary hydraulic cylinder 25, and pressurized-oil outflow from variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15, so as to ease rods 18 of both hydraulic thrust-bearing cylinders 15 back into respective cylindrical tubular bodies 17 and so rotate crushing jaw 5 about supporting shaft 10 in the opposite direction to before.

As rods IS withdraw, electronic central control unit 23 determines the instantaneous tilt angle of crushing jaw 5 with respect to the vertical by means of position sensor 26 inside auxiliary hydraulic cylinder 25, so as to determine when crushing jaw 5 completes the calculated angular displacement and is therefore positioned inside crushing chamber 3 to form, with crushing jaw 4, a constriction S of substantially the calculated ideal width.

As soon as crushing jaw 5 completes a rotation about supporting shaft 10 equals to the above-cited angular displacement, electronic central control unit 23 cuts off pressurized-oil outflow from variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15 to lock crushing jaw 5 in the ideal work position to crush the material to the desired size. When the crusher is running normally and a large incompressible body jams inside constriction S at the bottom opening of crushing chamber 3, rods 18 of both hydraulic thrust-bearing cylinders 15 are subjected to

severe axial thrust, which causes them, and respective pistons 19, to withdraw rapidly inside cylindrical tubular bodies 17. Seeing, however, as the variable- volume chambers 20 of both hydraulic thrust-bearing cylinders 15 are filled completely with incompressible fluid, the axial thrust transmitted by rods 18 to pistons 19 results in a rapid increase in oil pressure inside variable-volume chambers 20.

On detecting an oil pressure above the predetermined maximum threshold inside variable-volume chambers 20 of both hydraulic thrust-bearing cylinders

15, electronic central control unit 23 immediately opens on-off valve 22 of each hydraulic thrust-bearing cylinder 15 to rapidly drain pressurized oil from variable-volume chamber 20, thus enabling immediate withdrawal of rods IS of both hydraulic thrust-bearing cylinders 15 and, hence, backup of crushing jaw 5 from crushing jaw 4.

In the event partial withdrawal of rods 18 of both hydraulic thrust-bearing cylinders 15 causes the oil pressure inside variable-volume chambers 20 to fall rapidly below the maximum trigger threshold - meaning crushing jaw 5 has backed up sufficiently for the incompressible body to drop out of crushing chamber 3 - electronic central control unit 23 may reset crushing jaw 5. to the ideal work position, possibly via the maximum-travel configuration.

Replacing passive mechanical maximum-pressure

valves with electrically controlled on-off valves 22 controlled directly by electronic central control unit 23 has numerous advantages.

In particular, response of the new solution is much faster, so that crushing jaws 4 and 5 are parted as early as the first pressure peak in variable-volume chamber 20 of hydraulic thrust-bearing cylinder 15, with obvious advantages in terms of preventing structural damage to crusher 1. Control of on-off valves 22 by electronic central control unit 23 solves the problem of in-service oil leakage: as long as oil pressure remains below the maximum trigger threshold, on-off valves 22 remain perfectly closed. Moreover, the presence of electronic central control unit 23, on-off valves 22, and pressure sensors 21 gives the chance of fully automatically managing intervention times in the event of a body of incompressible material and movements of crushing jaw 5 in emergency stage, even to the extent of automatically resetting crusher 1 once the emergency has been dealt with.

Crusher 1 also provides for fully automatically compensating wear of flat front plates 8 of crushing jaws 4 and 5 caused by continual impact with the work material, thus ensuring the correct size of the crushed material from crushing chamber 3 at all times .

Clearly, changes may be made to crusher 1 as

described and illustrated herein without, however, departing from the scope of the present invention.

For example, collapsible connecting member 12 may be equipped with only one electrically controlled on-off valve 22 for simultaneously controlling pressurized-oil drainage from variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15.

Similarly, variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15 may be connected to each other, and collapsible connecting member 12 may be equipped with only one pressure sensor 21 for detecting the oil pressure in both variable-volume chambers 20.

With reference to Figures 4 and 5, in a different embodiment, collapsible connecting member 12 of crusher 1 has no oscillating connecting rod 13, and comprises a slide 29, which straddles the two vertical lateral walls 7 of supporting structure 2, in the space between the rear of rear supporting structure 9 of crushing jaw 5 and horizontal reinforcing cross member 16, and is fitted to the two vertical lateral walls 7 of supporting structure 2 to slide freely in a direction d parallel to the vertical mid-plane of the crusher and substantially parallel to longitudinal axis L of hydraulic thrust- bearing cylinders 15.

More specifically, slide 29 extends, parallel to axis A, between the two vertical lateral walls 7 of supporting structure 2, and has two ends, each designed

to engage and slide along a respective straight guide 30 on the adjacent vertical lateral wall 7.

In this variation, the two long lateral edges of the flat metal plate defining strut 14 rest, one on the lateral side of slide 29, and the other on rear supporting structure 9 of crushing jaw 5; and the two axial ends of the hydraulic thrust-bearing cylinder/s 15 rest, one on horizontal reinforcing cross member 16 of supporting structure 2, and the other on the opposite lateral side of slide 29 to strut 14.

More specifically, in this variation too, collapsible connecting member 12 has two identical hydraulic thrust-bearing cylinders 15 located side by side on opposite sides of the vertical mid-plane of the crusher, and the two axial ends of each rest on slide 29 and on horizontal reinforcing cross member 16 of supporting structure 2, respectively, with the interposition of two known spherical joints 24,

With reference to Figure 4, in this case too, collapsible connecting member 12 obviously comprises, for each hydraulic thrust-bearing cylinder 15, a pressure sensor 21 for detecting the instantaneous oil pressure in variable-volume chamber 20 of hydraulic thrust-bearing cylinder 15; and an electrically controlled on-off valve 22 connected directly to variable-volume chamber 20 of hydraulic thrust-bearing cylinder 15, and for selectively draining pressurized oil from variable-volume chamber 20.

Obviously, if variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15 are connected to each other, collapsible connecting member 12 may be equipped with only one electrically controlled on-of£ valve 22, for simultaneously controlling pressurized-oil drainage from variable-volume chambers 20 of both hydraulic thrust-bearing cylinders 15, and with only one pressure sensor 21 for detecting the oil pressure in both variable-volume chambers 20. With reference to Figure 5, in this variation too, collapsible connecting member 12 of crusher 1 comprises at least one auxiliary single- or double-acting hydraulic cylinder 31 which, like auxiliary hydraulic cylinder 25, exerts pull to keep the body of slide 29 resting on the ends of rods 18 of both hydraulic thrust- bearing cylinders 15, and to keep cylindrical tubular body 17 of each hydraulic ' thrust-bearing cylinder 15 resting on horizontal reinforcing cross member 16.

In the Figure 4 and 5 example, collapsible connecting member 12 comprises two auxiliary hydraulic cylinders 31 located outside supporting structure 2, i.e. outside crushing chamber 3 bounded laterally by the two vertical lateral walls 7, and each extending alongside a respective vertical lateral wall 7. Each auxiliary hydraulic cylinder 31 has a first end hinged to vertical lateral wall 7 , close to where wall 7 is joined to horizontal reinforcing cross member 16; and a second end hinged to an appendix 9a which

projects, substantially perpendicularly to vertical lateral wall 7, from the rear of rear supporting structure 9 of crushing jaw 5, close to the point of contact with strut 14, and which engages in sliding manner/ and projects outwards of supporting structure 2 through, a through opening (not shown) formed in vertical lateral wall 7.

Both auxiliary hydraulic cylinders 31 are obviously connected to the hydraulic circuit (not shown) of the crusher to exert pull on the rear of rear supporting structure 9 of crushing jaw 5 to keep rear supporting structure 9 of crushing jaw 5 resting on strut 14, to keep strut 14 resting on the body of slide 2S ₁ to keep slide 29 resting on the ends of rods 18 of both hydraulic thrust-bearing cylinders 15, and to keep cylindrical tubular body 17 of each hydraulic thrust- bearing cylinder 15 resting on horizontal reinforcing cross member 16.

In this case too, auxiliary hydraulic σylinder/s 31 obviously are able to adjust the tilt, with respect to the vertical, of crushing jaw 5 under the control of electronic central control unit 23, and are therefore connected to the hydraulic circuit (not shown) of the crusher with the interposition of a conventional electrically controlled hydraulic distributor (not shown) controlled directly by electronic central control unit 23.

In addition, like auxiliary hydraulic cylinder 25,

at least one of the two auxiliary hydraulic cylinders 31 may be equipped with a magnetostrictive or similar position transducer performing the functions of position sensor 26.