CN116457145A - System for checking tool integrity - Google Patents

Abstract

An inspection system (3) for a tool holder (e.g. a rotating shaft (5)) attached to a machine tool for inspecting the integrity of a tool while machining a metal workpiece (2). The inspection system (3) comprises a detection circuit (18), the detection circuit (18) comprising an inductor (4; 64) having a toroidal core (7) arranged in the vicinity of the tool holder and a winding (9) wound on the toroidal core. When the tool is in contact with the metal workpiece, an electrical circuit (C; C') comprising part of the support structure (1) of the machine tool and arranged crosswise to the inductor is closed, so that the electrical parameters of the detection circuit allowing the detection of the contact are varied. The detection circuit has a half-bridge structure, which is supplied by an alternating excitation voltage substantially out of phase with respect to each other by 90 DEG and comprises two resistive branches of an inductor and a reference resistor (25), respectively, and a detection branch for generating a detection signal and sending it to the control unit (10). Preferably, the reference resistor resistance is substantially equal to the inductor impedance.

Description

System for checking tool integrity

Technical Field

The present invention relates to a system for checking the integrity of metal tools present in machine tools and is particularly advantageously applied to checking rotating tools connected to the spindle of machine tools, such as drills and milling machines for machining metal workpieces.

Background

In machining in which chips are removed by a machine tool, it is extremely important to check the integrity of a tool that performs the machining. In particular, during machining using an elongated rotary tool connected to a spindle, it is important to check whether the tool is intact or damaged during machining to avoid performing incorrect and dangerous operations. This requirement for the presence of each type of tool is particularly critical in the case of very small tool sizes, since small-sized tools are more prone to breakage due to their own nature. For example, in sanding and drilling operations, by identifying and informing the tool of any breakage or damage in time (substantially in real time), workpiece waste due to improper machining can be avoided, thereby saving overall production time. The damaged tool can be replaced quickly and automatically in time through the notification. This problem also exists in this case: the tool does not rotate and in any case it is constantly approaching the workpiece (the latter usually having a rotation). This occurs, for example, on a lathe.

Various different types of systems for checking tool integrity have been proposed. Such inspection may be accomplished, for example, by an optical device such as disclosed in U.S. patent No. 5 se:Sup>A-4502823, or by se:Sup>A sensor that detects changes in physical quantities (force, vibration,) of the stress of se:Sup>A tool directly connected to the workpiece being processed, or using various combinations of sensors and measuring and inspection devices (see, for example, U.S. patent No. 5 se:Sup>A-6161055).

Inductive-type systems are also known which comprise circuit elements which are usually connected in proximity to the spindle of a machine tool (for example a milling or drilling machine) and which detect changes in these circuit elements caused by contact between a metal tool and a work piece, also of metal material. Whether such contact is detected may provide information regarding the integrity of the tool.

se:Sup>A system of this type is shown and described in US-se:Sup>A-4203691, which is similar to the known system of fig. 1. Fig. 1 schematically shows a machine tool, such as a drilling machine, for machining a metal workpiece 2. The machine tool has a support structure 1. The support structure 1 comprises a spindle 6, a tool holder and a rotary tool 3. The tool holder has a shaft 5 which rotates about an axis of rotation X. The shaft 5 is connected to the main shaft 6 by means of bearings. The rotary tool 3 is aligned along an axis X and connected to the spindle. The spindle 6 and the workpiece 2 are mutually movable in a direction defined by the rotation axis X of the shaft 5. The inductor 4 comprising windings wound on a portion of a toroidal core made of ferromagnetic material, arranged in the vicinity of the tool holder, around the rotation axis X, in particular externally and coaxially to the rotation axis 5, is part of a detection circuit or primary circuit, said inductor 4 further comprising the elements of the module 8 (fig. 2). The module 8 comprises a power supply, in particular an alternator 11, a resistor 15 and a voltage or voltage change detector 17 across the resistor 15.

When the rotating tool 3 is in contact with the metal working piece 2, the secondary circuit C defined by the circuit comprising the tool 3, the rotating shaft 5, the support structure 1 and the metal working piece 2 is closed. Closure of the secondary circuit C causes a change in the inductance parameter. Thereby, a consequent change in the voltage across the resistor 15, which is detected by the detector 17. If the tool 3 is damaged, no contact will occur, or at least when contact should occur. At this time, no change in the inductance parameter is detected. The module 8 is connected to a control unit 10. The control unit 10 controls the movement of the different parts of the machine tool. For example, the PLC programmable unit checks whether contact is detected, i.e. whether the detection circuit comprising the inductor 4 receives a detection signal, depending on the mutual position between the tool and the workpiece where the machining should be started. If not, an alarm signal is generated, the process is stopped and other known procedures are initiated, such as automatic replacement of the damaged tool with a complete tool taken from a suitable warehouse.

A problem that may occur in the known system is that it is difficult to detect the contact correctly if the contact between the tool and the workpiece is not maintained during the whole process, but only for a limited period of time. This is often the case, for example, in machining processes as well as milling operations. During machining, metal chips lead to loss of contact within a time interval that is not always predictable. In a milling operation, the rotary tool intermittently contacts the workpiece being machined. Specifically, the tool has a cutting edge. The cutting edge contacts the part during 360 deg. rotation to obtain a limited degree (e.g., 5 deg. or less) of rotation angle. In view of the high rotational speed of the tool, the contact time between the tool and the workpiece may be less than 5 microseconds. In these cases, the known detection circuits and systems do not allow to detect the inductance variations caused by the short contact between the cutting edge and the workpiece. Thus, the known detection circuits and systems are not very reliable. This is particularly the case with very small tools having a diameter of about 1mm, where the contacts are very light and of very short duration.

Another problem with the system of fig. 1 is that it is difficult to detect contact between the tool and the workpiece, in particular voltage variations across the resistance of the detector, for example, the relatively high resistance of the secondary circuit C resulting from rotation of the shaft 5. Such resistance may vary and increase significantly due to the dynamic behavior of the bearing and/or the presence of lubricant. This problem also arises if there are elements of low or zero conductivity in the path defining the secondary circuit, for example when the bearing is made of ceramic material. To overcome this problem, the aforementioned patent US-A-4203691 describes se:Sup>A solution. According to this solution, in the secondary circuit, the electrical connection between the rotating shaft and the supporting structure of the machine tool is achieved by means of suitable sliding contacts. The sliding contact may avoid (i.e., bypass) the area where the bearing is located.

This solution is an improvement over the solution of fig. 1. However, the embodiment shown in U.S. patent US-A-4203691 has brushes connected to se:Sup>A support structure. The brushes contact a ring connected to the rotating portion. This embodiment may be problematic and does not guarantee an efficient and reliable electrical connection over time.

Another problem with the system shown in fig. 1 and in US-se:Sup>A-4203691 is that in existing machine tools it is practically impossible to apply an inductor together with se:Sup>A toroidal core; in existing machine tools, other machine tool components or other limiting factors prevent access to the area surrounding the spindle.

Disclosure of Invention

It is an object of the present invention to provide a system for checking the integrity of a tool. The system is reliable and overcomes the problems of the known systems. The system allows reliable results to be obtained even in the case of tools or machine tools using the same having mechanical, electrical or application features which make inspection of the known system impossible or have uncertain results.

This and other objects and advantages are achieved by a system according to the appended claims. The accompanying claims describe embodiments of the invention and form a part of this specification.

The system for checking the integrity of a tool according to the invention comprises a detection circuit and a control unit connected to the detection circuit. The detection circuit generates a detection signal indicative of contact between the tool and a metal piece being machined on the machine tool. The detection circuit includes an inductor. The inductor has a toroidal core disposed adjacent a tool holder of a machine tool and a winding wound on the toroidal core. The detection circuit has a half-bridge structure. The half-bridge structure has two resistive branches powered by an ac excitation voltage. The two ac excitation voltages are substantially 90 ° out of phase with each other. The two resistive branches include an inductor and a reference resistor, respectively. The detection circuit comprises a detection branch with a conversion unit and a processing unit. Preferably, the reference resistor has a resistance substantially equal to the impedance of the inductor. The conversion unit is typically an RMS converter. The processing unit is used for generating the detection signal and sending the detection signal to the control unit.

The objects and advantages of the present invention will be described in detail below.

Drawings

The present invention will be described below with reference to the accompanying drawings. The accompanying drawings illustrate non-limiting embodiments of the invention, wherein:

FIG. 1 is a schematic diagram of a machine tool having a system for checking tool integrity;

FIG. 2 is a schematic diagram of components of a system for checking tool integrity according to a known embodiment;

FIG. 3 is a schematic diagram of components of a system for checking tool integrity in accordance with the present invention;

FIG. 4 is a graphical representation of electrical signal trends during operation of the inspection system of FIG. 3;

FIG. 5 is a schematic diagram of a machine tool having a system for checking tool integrity in accordance with the present invention;

FIG. 6 is an enlarged longitudinal cross-sectional view of some components of the inspection system of FIG. 5;

FIG. 7 is a perspective view of one of the components of FIG. 6;

FIG. 8 is a cross-section of FIG. 6 showing the components of FIG. 7;

FIG. 9 is a partial perspective view of some components of a system for checking tool integrity in accordance with the present invention;

FIG. 10 is a cross-sectional perspective view of a component of the present invention; and

fig. 11 is a perspective view of a portion of the component of fig. 10.

Detailed Description

Fig. 3 illustrates a detection circuit or primary circuit of a system for checking tool integrity or a part of a tool integrity checking system according to the invention, which includes the features shown in fig. 1. The primary circuit comprises an inductor 4. The inductor 4 has a core 7 of ferromagnetic material (e.g. ferrite) and windings 9. The core 7 has a toroidal shape (e.g., a toroidal shape). The winding 9 is connected to terminals t1 and t2 of the power supply and to a processing module 18 connected to the terminals t1 and t 2.

The module 18 comprises:

two power supplies, in particular voltage generators 21 and 22, respectively providing two ac excitation voltages S1 and S2, which are substantially out of phase by 90 ° with respect to each other, as shown in the graph of fig. 4;

a reference resistor 25 having a resistance substantially equal to the impedance of the inductor 4 in ohms; and

a detection branch having a filter 26, a conversion unit (in particular an effective value detector) or an RMS ("root mean square") converter 27, an analog-to-digital converter 28 and a processing unit 30 (in particular a microprocessor).

Node t3 leads to the detection branch and also to a first resistive or excitation branch (comprising generator 21 and winding 9 of inductor 4 through terminals t1 and t 2) and a second resistive or excitation branch with generator 22 and resistor 25. The excitation and detection branches thus define a half-bridge structure.

In the event that the tool and workpiece are not in contact, the secondary circuit is opened. Since resistor 25 is selected as described above, and since the appropriate phase shift between voltages S1 and S2 is substantially 90 °, the magnitude of voltage S3 at node t3 is negligible. Thus, the output signal from filter 26 (where unwanted interference and frequencies have been eliminated or attenuated) and the "average" signal S4 at the output of RMS converter 27 have a substantially constant trend, with no significant amplitude variation (trend before time T1, fig. 4).

At time T1, when the tool 3 contacts the workpiece 2, the circuit C comprising the tool 3, the workpiece 2, the tool holder with the rotation axis 5 and the support structure 1 of the machine tool with the spindle 6 is closed. In this loop C, i.e. in the secondary circuit connected to the inductor 4, a current is induced. This current in turn causes a change in the current through winding 9 of inductor 4 and thus a change in voltage S3 corresponding to node t 3. Due to the half-bridge structure of the circuit, the signal S3 may have a high crest factor. This occurs especially in the case where the tool 3 and the workpiece 2 are in continuous short or very short intermittent contact (e.g. if the tool 3 is a small knife) and the consequent change in the circuit through the inductor 4 is short or very short. Thus, the signal S3 is able to follow these short and rapid changes.

The RMS converter 27 typically has a very low average time constant, for example about 30 microseconds. In this way, it is possible to obtain a fast response to the variation of the signal output by the filter 26, which in turn reflects in substantially real time the variation of the signal S3 at the node t3 of the half-bridge circuit. Based on the above, the change can be very short and fast.

The signal S4 at the output of the RMS converter 27 is always a positive signal, eliminating the electrical noise present in the signal at the output of the filter 26. In this way, a very limited duration change of the signal S3 indicative of the short contact between the tool 3 and the workpiece 2 can be captured, for example during a milling operation or during a metal chip break resulting in a loss of contact within a generally unpredictable time interval.

The signal S4 is converted into a digital signal by the converter 28. The digital signal obtained is read by the microprocessor 30 and processed in the microprocessor 30 in a known manner, for example by comparison with a threshold value. Exceeding the threshold value indicates that contact has occurred, thereby generating a detection signal. The detection signal is sent to the control unit 10 to confirm the correct presence of the operating tool 3. If the tool 3 is damaged, the circuit C is not closed and no signal is sent to the control unit 10. If the microprocessor 30 of the module 18 fails to receive a contact signal corresponding to the mutual position between the spindle 6 and the metal workpiece 2 to be machined, the control unit 10 stops the movement of the machine tool and possibly starts an automatic tool change operation, which occurs in a manner known per se and which will not be described here. The microprocessor 30 may further process the detection signal indicating the presence of the tool 3 before sending the detection signal to the control unit 10. For example, in the case of inspection during milling operations, the microprocessor 30 can check whether the tool is present and intact by recording the continuous contact between the cutting edge and the workpiece and comparing the duration and frequency of these contacts with theoretical or predetermined values (type of tool used, rotational speed, such as removal and advance cutting parameters, etc.) associated with the particular machine tool machining.

By using a half-bridge structure comprising a secondary circuit of the inductor 4 and a suitable conversion unit such as an RMS converter 27, a high signal/noise ratio and a high sensitivity can be obtained when detecting a change in the electrical characteristics of the same circuit. In particular, the signal S3 present at the terminal t3 of the half-bridge structure may have a high crest factor, i.e. it is able to follow the rapid variation of the electrical characteristics induced in the inductor 4 by the contact between the tool 3 and the metal workpiece 2. Also, the RMS converter 27 is in turn able to detect this rapid change and provide a signal S4 with a high signal-to-noise ratio. Thus, even very small and rapid vanishing changes in electrical properties caused by light contacts (e.g. even small tools of 0.1mm diameter for very small tools) and very short durations (e.g. short contacts and intermittent contacts in the case of milling machines with tools of less than 1mm diameter) can be detected.

In the system according to the invention, the inductor 4 can be arranged in different positions with respect to the position shown in fig. 1. For example, the inductor 4 may be provided always close to the tool holder or around the shaft 5, but inside the spindle 6, for example in an intermediate position between the bearings.

Even though the filter 26 may be advantageous in eliminating or attenuating unwanted frequencies that may negatively impact proper processing of the desired signal, the filter 26 is not required.

Although the RMS converter provides better results, different embodiments of the invention may comprise a conversion unit, e.g. a peak-to-peak detector, different from the RMS converter 27, because it provides, in addition to the (further) filter, a signal that is always positive, which signal reflects changes in the input particularly fast, as already mentioned.

Although the presence of the converter 28 guarantees considerable advantages (known per se) deriving from the particular flexibility of digital processing when compared to analog signals, in this case the other different solution does not provide signal-to-digital conversion.

The above description relates to inspection of a rotary tool. However, the system according to the invention can also be applied to inspect non-rotating tools, such as tools connected to the turret of a lathe. The turret may be movable relative to the rotary element being processed, for example in a direction corresponding to the axis X of the drawing.

Fig. 5 shows an alternative to fig. 1. In particular, in the embodiment shown in fig. 5, the secondary circuit C is not closed by the bearings of the spindle 6 that allow the rotation of the shaft 5, but by a specific contact mechanism, schematically indicated by reference numeral 37. In this way, an (direct) electrical connection is produced between the shaft 5 and a portion of the support structure 1 of the machine tool (e.g. the spindle 6). Avoiding problems due to the reduced electrical conductivity of the bearing during rotation of the shaft 5 and allowing the use of the system according to the invention with zero electrical conductivity, for example in the case of bearings made of ceramic material.

The contact mechanism visible in fig. 6, 7 and 8 comprises a sliding element or shoe 40 in direct contact with the rotation shaft 5. The shoe 40 may have a particular shape and material characteristics. In particular, the shoe 40 is made of an electrically conductive and low oxidation material, such as stainless steel or bronze or a combination of both, and ensures good electrical conductivity and wear resistance. Other materials may also be used to make the shoe 40, such as graphite and silver-graphite. The skid shoe 40 is rigidly connected to the support structure 1 and comprises at least one elastically yielding portion. In particular, in the embodiment shown in fig. 7 and 8, the skid shoe 40 has a central body 41 rigidly connected to the supporting structure 1, and two arms 42 and 43 connected substantially symmetrically to the central body 41 by means of elastically yielding portions or zones 42 'and 43', characterized in that the free ends are intended to remain in contact with the shaft 5, in particular at two points of the section H of the shaft 5. At the same time, the shaft 5 rotates about the axis X. The skid shoe 40 preferably comprises a fold made of, for example, stainless steel. The folded piece defines a central body 41, arms 42 and 43 and elastically yielding regions 42 'and 43' corresponding to the folded piece. In a preferred embodiment, the shoe 40 comprises two blocks or pads 44 and 45, for example bronze blocks or pads, which define the free ends of arms 42 and 43 that are in contact with the rotation shaft 5. A reduced material may also be provided corresponding to at least one fold, as shown in fig. 7, to increase the elastic compliance of regions 42 'and 43'.

According to a possible embodiment, the skid shoe 40 is connected to the support structure 1 in an adjustable manner, as shown for example in fig. 6. Fig. 6 shows a connection assembly for connecting the skid shoe 40 to the support structure 1, in particular to the main shaft 6, with an adjustable bracket 46 provided integrally with the skid shoe 40 and with a reference bracket 48 (also partially shown in fig. 9). The adjustable bracket 46 and the reference bracket 48 are connected to each other by an adjustment element. The adjustment element has a coupler 47 comprising a screw in a slot. The connection assembly also includes elements for fixing the reference bracket 48 to the support structure, such as screws 49 with tapered contoured heads (visible in fig. 9) and other adjustment elements with spacers 50. The spacer 50 is interposed between the reference frame 48 and the support structure 1, corresponding to the fixation by the screw 49. The thickness of the spacer 50 is selected to determine the desired contact force between the shoe 40 and the shaft 5.

In particular, the procedure of registering the position of the shoe 40 in the layout schematically shown in fig. 6 provides:

after insertion of the calibrated spacer 50 'of known thickness D', the reference bracket 48 is fixed to the spindle 6 or to the support structure 1 by tightening the screw 49;

with negligible nominal zero contact force, bringing the ends 44 and 45 of the arms 42 and 43 of the shoe 40 into contact with the surface of the shaft 5,

and fixing the mutual position between the adjustable support 46 and the reference support 48 by tightening the coupling 47;

-releasing the connection between the reference bracket 48 and the support structure 1;

removing the calibrated spacer 50' and inserting the working spacer 50 having a thickness D smaller than D ', wherein the thickness difference ad=d ' -D is chosen according to the contact force desired to be present between the shoe 40 and the shaft 5. Thus, the spacers 50 and 50' can be interchanged to change the radial position of the shoe 40 relative to the axis of rotation 5, thereby defining the contact force between the shoe 40 and the shaft 5. According to the modified embodiment, by appropriately selecting the thickness of the calibration spacer 50' (d1=ad), the working spacer 50 can be omitted.

Reliable control of the number allows to obtain an optimal combination between the electrical conductivity and the wear resistance of the contact means and to ensure a proper duration of electrical contact between the components. An important feature is therefore that the possibility of contact forces is determined in a simple and safe manner.

If the contact means are fixed to the surface of the support structure 1 oriented in the opposite direction with respect to the one shown in fig. 6, the last part of the adjustment process involves: the working spacer 50, which is thicker (rather than smaller) than the calibration spacer 50', is inserted to obtain the desired contact force. In this alternative arrangement, it is also conceivable to insert no calibration spacer 50' in the first part of the process, but to insert a working spacer 50 of a certain thickness (d=ad).

In the particular embodiment shown in fig. 6, a shoe 40 is provided between the shaft 5 and the toroidal core 7 of the inductor 4. The assembly and adjustment operations of the contact mechanism are generally performed before the insertion of the inductor 4.

Regardless of the rotational speed and rotational direction of the spindle 5, an effective electrical connection between the spindle 5 and the support structure 1 can be ensured by a specific symmetrical structure of the shoe 40 and an adjustable fixation to the support structure 1 of the machine tool (e.g. to the spindle 6).

The shoe 40 may have a fold of particularly small thickness (e.g., 0.2 mm). In this case, it may not be necessary to provide the possibility of adjusting the position and fastening of the skid shoe 40 to the support structure 1. This is because the compliance characteristics of the shoe 40 itself, and in particular of the folds defining the central body 41 and the arms 42 and 43, are sufficient to ensure correct contact between the free ends of the arms 42 and 43 (in the example shown, supporting the pads 44 and 45) and the rotation axis 5, the contact being stable but without excessive force. Thus, an efficient electrical connection between the shaft 5 and the support structure 1 is achieved.

The configuration of the contact mechanism described so far and shown in fig. 6 is particularly compact and advantageous in reducing the overall size due to the particular shape of the components such as the reference bracket 48 and the adjustable bracket 46. However, other variations are also possible. For example, in some versions, the skid shoe 40 is fixed to the main shaft 6 or the support structure 1 in a manner that cooperates with the rotation shaft 5. The rotation axis 5 corresponds to a different portion, for example the portion denoted by the reference H' in fig. 6, or in any case ensures that the loop C generated when the tool 3 contacts the workpiece 2 passes through a different region of the inductor 4.

Another aspect of the invention relates to the structure of the core of the inductor 4.

As described above, the inductor 4 includes the iron core 7 of ferromagnetic material (e.g., ferrite) having a toroidal shape (e.g., toroidal shape) and the winding 9 having a certain number of copper wire coils wound on a portion of the toroidal iron core 7.

Preferably, the inductor 4 further comprises a housing 12, partially visible in fig. 6 and 9, which houses the core 7 and the winding 9. The housing 12 is typically made of non-magnetic stainless steel and allows the inductor 4 to be fixed to the spindle 6 or another part of the support structure 1 of the machine tool and in any case to be arranged coaxially with the axis X of the rotary shaft 5. The fixation is effected in a manner known per se, for example by means of screws, as is only partially visible in fig. 9. Here, a detailed description is not given for the sake of brevity.

In a known application, the inductor 4 is made in one piece. In particular, the toroidal core 7 is integral and the housing 12 is integral. The toroidal core 7 of single piece material has uniformity which ensures that the inductor 4 is operating correctly within the system. However, at least for some applications, the installation of the inductor 4 in a machine tool is relatively complex. The application of inspection systems to existing and fully assembled machine tools is particularly complex or not possible at all. Such applications require that the inductor 4 be mounted on a shaft 5 in a machine having a certain size, so that there is inevitably a mechanical limitation on the use of various components.

Fig. 11 shows an inductor 64. The toroidal core is made of two ferromagnetic material portions. The two portions have open ends and are joined to one another at the open ends. The inductor 64 is used in an inspection system according to the invention. The system also includes the features already described with reference to fig. 1.

The inductor 64 includes two interconnected half-rings 64A and 64B. Each half-ring in turn comprises a half-ring portion 67A and 67B of ferromagnetic material and a half-shell 62A and 62B of substantially C-shape. The ferromagnetic material is typically ferrite. The winding, schematically shown in fig. 11 and indicated with 69, is wound on a ferrite half-ring portion in the ferrite of one of the half-rings, in particular on a half-ring portion 67B of ferromagnetic material, and is connected to the electric wire coming out of the half-ring 64B inside the cable 71. Four reference pins 63 are fixed to the end of the half-shell and cooperate with holes 61 present at the end of the other half-shell. In the embodiment shown in fig. 10 (showing half-rings 64A) and 11, the ends of each half-shell 62A and 62B have a reference pin 63 and hole 61, respectively. But may have a different configuration (e.g., all four pins 63 at the end of one of the two half-shells 62A or 62B and four holes 61 at the end of the other, or a pair of pins 63 and one hole 61 at both ends of each half-shell 62A or 62B, etc.).

The pin 63 and the hole 61 represent mechanical references, which can be made in different ways, with suitable and per se known elements and/or surfaces, configured to align the ends of the half rings 64A and 64B.

There is a suitably shaped gasket 65 corresponding to each of the two junction areas between the half-rings 64A and 64B, i.e. to each pair of ends of the half-rings 64A and 64B facing each other. In fig. 10, both washers 65 are connected to half ring 64A.

The half-shells 62A and 62B are closed at the upper part (with reference to the orientation shown in fig. 10 and 11) by a suitably shaped element 60, typically plastic, which is partly visible in fig. 9. But this element is omitted from figures 10 and 11 for clarity.

The inductor 64 is mounted on a machine tool, such as the one schematically shown in fig. 1, by arranging the two half-rings 64A and 64B in a suitable position around the shaft 5 of the spindle 6 with their respective ends facing each other, positioned by means of the reference pins 63 and the respective holes 61, and fastened to each other by means of, for example, screws or other fastening means. In the example of fig. 11, these fastening means comprise a metal collar 66 closed and fastened by screws. The metal collar 66 has the property of distributing the load uniformly over the entire outer surface of the half-shells 62A and 62B, making the connection stable and insensitive to shocks and vibrations to which the spindle 6 is subjected.

Each half-ring portion of the ferrite 67A and 67B is accommodated in the respective half-shell 62A and 62B with a gap left therebetween such that, before installation, the respective end portions featuring flat surfaces protrude slightly from the free ends of the half-shells 62A and 62B. A resin 70 having good elasticity is present inside each half shell 62A and 62B, disposed between the ferrite half ring portions 67A and 67B and the inner walls of the half shells 62A and 62B. During the fastening by acting on the fastening means 66, the ends of the half-shells 62A and 62B are brought close to each other so that the ends of the half-rings 67A and 67B of ferromagnetic material come into contact with each other, and then the mechanical references 61 and 63 come into contact with each other, so as to couple the free ends of the half-shells 62A and 62B. The tightening then continues and eventually completes as the compression of washer 65 between the ends of half shells 62A and 62B creates a mechanical stop. At this final stage, i.e., after the ferrite half-rings 67A and 67B are in contact, the ferrites 67A and 67B are allowed to slide limitedly within the respective half-shells 62A and 62B because the resin 70 inside the half-shells 62A and 62B has elasticity.

In addition to allowing limited sliding, the elasticity of the resin 70 also exerts a constant thrust between the two ferrite half-ring portions 67A and 67B, which is a fundamental condition for the normal operation and long-term reliability of the system.

The gasket 65 closes the space between the ends of the half-shells 62A and 62B and prevents dust or other foreign matter from entering. Dust or other foreign matter entering between the end faces of the ferrite half ring portions 67A and 67B may alter and jeopardize the correct electromagnetic behavioral inductor 64. The structure of the mutually coupled two-part inductor 64 as described above ensures a repeatable assembly and a normal functioning of the system without substantial differences in terms of electromagnetic behaviour from the known solutions in which the toroidal core 7 is made in a single piece. Furthermore, with this structure, the inspection system can be applied in a case where it is physically impossible to provide the inductor 4 as one body around the rotation axis 5.

The method of mounting the inductor 64 on the machine, in particular around the rotation axis 5 of the spindle 6 of the machine, achieves the fixing of one of the half-shells 62A and 62B to the support structure 1, for example the half-shell 62B to the spindle 6 with screws, as shown in fig. 9, and as described above, namely:

-arranging the half-rings 64A and 64B with the ends of the half-rings 67A and 67B of ferromagnetic material protruding slightly from the free ends of the respective half-shells 62A and 62B;

bringing the ends of the half-rings 62A and 62B close to each other, so that the ends of the half-rings 67A and 67B of ferromagnetic material are in contact with each other, and so that the mechanical references 61 and 63 cooperate with the free ends of the half-shells 62A and 62B;

by acting on the fastening means, in particular on collar 66, fastening together half-shells 62A and 62B until the limit is reached, causing compression of elastic resin 70 inside half-shells 62A and 62B.

Claims (14)

1. An inspection system for inspecting the integrity of a tool (3) during machining of a metal piece (2) on a machine tool, the machine tool comprising a support structure (1, 6) and a tool holder (5) carrying the tool (3), the inspection system comprising:

-a detection circuit (4, 8;18; 64) for generating a detection signal indicative of a contact between the tool (3) and the metal piece (2) and having at least one power source (11; 21, 22) and an inductor (4; 64), the inductor (4; 64) comprising a toroidal core (7; 67a, 67B) provided to a tool holder (5) and a winding (9; 69) wound around the toroidal core (7; 67a, 67B); and

a control unit (10) connected to the detection circuit (4, 8;18; 64),

the inspection system is characterized in that,

the detection circuit (4, 8;18; 64) has a half-bridge structure with two resistive branches powered by an alternating voltage, which is substantially out of phase by 90 DEG with respect to each other, the two resistive branches comprising the inductor (4; 64) and a reference resistor (25), respectively, the detection circuit (4, 8;18; 64) comprising a detection branch with a conversion unit (27) and a processing unit (30) for generating the detection signal and for transmitting the detection signal to a control unit (10).

2. An inspection system according to claim 1, wherein the reference resistor (25) has a resistance substantially equal to the impedance of the inductor (4; 64).

3. An inspection system according to claim 1 or 2, wherein the conversion unit (27) is an RMS converter (27).

4. An inspection system according to claim 3, wherein the RMS converter (27) has a low average time constant.

5. The examination system according to any of the preceding claims, wherein the detection branch comprises an analog-to-digital converter (28) arranged between the conversion unit (27) and a processing unit (30).

6. The examination system of any one of the preceding claims, wherein the processing unit (30) is a microprocessor.

7. The inspection system of any one of the preceding claims, wherein the toroidal core of the inductor (64) is made of two ferromagnetic material portions (67A, 67B) having open ends and configured to be joined at the open ends, the winding (69) of the inductor (64) being wound around one of the ferromagnetic material portions (67B).

8. The inspection system of claim 7, wherein the two ferromagnetic material portions are ferrite half-ring portions.

9. The inspection system of claim 7 or 8, wherein the inductor (64) comprises two half-rings (64A, 64B) configured to be connected to each other, each half-ring comprising a half-shell (62A, 62B) housing one of the two ferromagnetic material portions (67A, 67B), the half-shells (62A, 62B) being for connection to the other half-shell (62A, 62B).

10. The inspection system of claim 9, wherein each half-shell (62A, 62B) defines two free ends with a mechanical reference (61, 63), the mechanical reference (61, 63) being configured to cooperate with the mechanical reference (61, 63) of the other half-shell (62A, 62B), the inductor (64) comprising fastening means (66), the fastening means (66) being configured to fasten the two half-rings (64A, 64B) to each other.

11. The inspection system of claim 10, wherein the fastening device comprises a metal collar (66).

12. The inspection system of any one of claims 9 to 11, wherein an elastomeric resin (70) is present within each half-shell (62A, 62B).

13. Inspection system according to any of the preceding claims, characterized by a tool (3) for inspecting rotation about an axis of rotation (X), wherein the tool holder comprises a rotation shaft (5) about the axis of rotation (X), the toroidal core (7; 67a, 67B) of the inductor (4; 64) being arranged about the axis of rotation (X).

14. The inspection system of claim 13, further comprising: -a contact mechanism (37), the contact mechanism (37) being for providing an electrical connection between the rotation shaft (5) and a support structure (1, 6), the contact mechanism (37) comprising a shoe (40) rigidly connected to the support structure (1, 6) and for maintaining contact with the rotation shaft (5).