ITUB20154142A1 - CONTACT MEASUREMENT PROBE AND ITS METHOD FOR DIMENSIONAL AND / OR POSITION AND / OR PROFILE MEASUREMENT OF A MECHANICAL PIECE - Google Patents

Description

"CONTACT MEASURING PROBE AND RELATIVE METHOD FOR THE DIMENSIONAL AND / OR POSITION AND / OR PROFILE MEASUREMENT OF A MECHANICAL PART"

TECHNIQUE SECTOR

The present invention relates to a method for the dimensional and / or position and / or profile measurement of a mechanical piece by means of an apparatus which includes a measuring probe in contact with a casing and a stem movable with respect to the casing, which comprises the steps of causing mutual movements, at a substantially constant speed of movement, between the probe and the mechanical piece, providing signals relating to the position of the probe with respect to the equipment, providing a continuous deflection signal, indicative of the deflection of the stem, sampling such signal in order to obtain samples, and process the measurements based on the signals relating to the position of the probe with respect to the equipment.

The invention also relates to a contact measuring probe, for measuring a mechanical part. The probe comprises: a casing and a stem movable relative to the casing with a feeler for touching the mechanical piece, an analog sensing device adapted to provide a continuous deflection signal indicative of the deflection of the shaft, and a processing unit, connected to the analog detection device, suitable for receiving and sampling the deflection signal to obtain samples.

The present invention finds advantageous but not exclusive application in the precision control of the profile of mechanical parts, to which the following description will make explicit reference without thereby losing generality.

ANTERIOR ART

Contact type probes or control heads are known measuring devices widely used for example in numerically controlled machine tools for measuring and / or controlling the size, position and profile of mechanical pieces being machined.

A measuring probe of the contact type is generally equipped with a stem, movable with respect to a fixed casing and connected to at least one sensor that provides signals indicative of the deflection of the stem itself, and a processing unit that processes the output signals from the sensor and generates a variation signal indicative of the contact between the probe and the mechanical piece which is transmitted, via cable or over the air, to the numerical control of the machine tool. The numerical control, as a function of the variation signal received, detects signals relating to the mutual position between the probe and the surface of the piece and processes them to obtain information on the position of the surface of the piece with respect to the machine tool. The information obtained is then suitably processed by the numerical control itself or by an electronic processor in order to obtain the required measurement. In practice, the reliability of the measurement obtained is greater the more precise and repeatable is the delay with which the variation signal is generated with respect to the instant of contact, i.e. the instant in which the actual contact between the probe and the piece takes place. .

Probes and measurement methods are known in the art which allow to obtain a high precision and repeatability of the delay introduced. Depending on the modality in which they operate, it is possible to distinguish contact detection probes, which touch a mechanical piece in a discrete sequence of points at which the detections are made, and scanning probes, which touch and maintain contact with the mechanical piece to scan and detect the entire profile. In practice, while contact detection probes are widely used in dimensional and position measurements, scanning probes are mostly used to measure complex mechanical parts, i.e. when it is necessary or at least preferable that the measuring device performs a scan of the entire profile of the workpiece, for example for roughness, concentricity and circularity measurements.

A probe with contact detection, such as that described for example in the European patent number EP 1880163 B1, is equipped with one or more sensors which give rise to signals indicative of the deflection of the rod, and with a processor which receives the output signals from the sensors and generates a trigger signal when said deflection reaches a trigger condition, for example it exceeds a predetermined threshold value. In theory, the threshold value repeatably determines the instant in which the trigger signal is generated. In practice, the processor samples the output signals from the sensors at predefined time intervals and compares the samples with the predetermined threshold value. It is highly unlikely that even just one of these samples has a value equal to the threshold value, ie that the processor samples even just one of the signals indicative of the stem deflection exactly at the instant of contact. More likely, the contact is detected in correspondence with a sample whose value is greater than the threshold value, i.e. when a not negligible delay, unknown and generally variable in the points of the aforementioned discrete sequence, has elapsed, from the instant of true contact. is exactly.

With reference, on the other hand, to a scanning probe such as the one described for example in the international patent application published with the number WO 92/20996 A1, during a measurement cycle the numerical control moves the probe towards a surface of the piece to be measured. and, when the probe touches this surface, it continues to advance the probe for a short period of time before stopping its movement. As a consequence of the touch, the stem undergoes a deflection which triggers the simultaneous reading, which lasts for such a short period of time, of the signal output from the probe and of the signals relating to the mutual position between the probe and the piece. An electronic processor calculates the relationship between the signals read and extrapolates the values in the point of zero deflection, in order to have an indication of the position of the rod at the instant of contact, obtain in a known way the position of the surface of the piece in the same instant and obtain the required measurement. In practice, the simultaneous reading of the signals requires that the time references of the scanning probe and of the machine tool are constantly in relation to each other, and a complex and frequent calibration procedure is necessary for both the probe and the machine tool, for the latter to be coordinated with each other.

DESCRIPTION OF THE INVENTION

The purpose of the present invention is to provide an extremely precise and reliable method for the measurement and control of dimensional, geometric and profile characteristics of mechanical parts by means of a contact-type measuring probe, which is easy to implement and exceeds the limits of known art.

This and other purposes are achieved by a control method described in the attached claim 1.

The main advantage of a method according to the present invention consists in the possibility of calculating a precise and repeatable delay between the time reference of the probe and that of the machine tool. There is therefore the further advantage of reconstructing in a simple and accurate way the synchronism between the probe outputs and those of the machine tool, independently, for example, of errors due to any bounce of the contact probe which measures the mechanical piece.

A further object of the present invention is to provide a measuring probe of the contact type, precise and reliable, which implements a method according to the present invention and is easy and economical to carry out.

This and other purposes are achieved by a measurement probe described in the attached claim 10.

Further objects and advantages of the present invention will become clear from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which represent exemplary and non-limiting embodiments thereof, of which:

Figure 1 schematically shows an apparatus for measuring and checking a mechanical piece according to an embodiment of the present invention, with some details omitted for clarity;

Figure 2 represents the extremely simplified trend as a function of time of a signal generated inside the apparatus shown in Figure 1;

Figure 3 represents the extremely simplified trend as a function of time of equivalent signals that can be generated inside the apparatus shown in Figure 1, each signal corresponding to a different speed of movement; And

- figure 4 represents the extremely simplified trend as a function of the time of the signal generated inside the apparatus shown in figure 1, in a time interval different from that shown in figure 2.

PREFERRED EMBODIMENTS OF THE INVENTION

Figure 1 schematically illustrates an apparatus 10 for the measurement and control of dimensions and / or position and / or profile of a mechanical part W. The apparatus can be a machine intended exclusively for measurement or a machine tool where the piece W is machined, and comprises a reference element 12 intended to position and refer to the mechanical piece W, a support device 14 suitable for supporting a probe 1 of contact measurement, for example a scanning probe of the wireless type, and a movement mechanism 11 adapted to cause mutual movements between the scanning probe 1 and the mechanical part W. A system of position transducers 13, for example optical scales, is connected to the movement mechanism 11 to provide signals relating to the position of the probe 1 with respect to the apparatus 10. A numerical control 20 is connected in a known way both to the movement mechanism 11 to control it with suitable control signals and to cause mutual movements, both to the optical ruler system 13 to read the signals relating to the position of the probe 1 with respect to the apparatus 10. Optionally, the apparatus 10 can include further devices, not shown in figure, for the transmission of signals over the air from the numerical control 20 to the probe 1, for example for the activation and / or deactivation of circuits on the probe or for the programming of some parameters, in a known way and which does not directly concern the present invention.

The probe 1 comprises a casing and a stem 2, movably connected to the casing, with a feeler 3 for touching the mechanical part W, and an analog detection device 4 of a known type, for example an LVDT transducer, suitable for providing a continuous deflection signal d, indicative of the deflection of the stem 2 with respect to the casing. A processing unit 5, connected to the transducer 4, is adapted to receive and process the deflection signal d, for example sampling, in a substantially continuous manner, i.e. with a sampling period ΔΤ5 suitably determined so as to obtain samples of the deflection d whose flow can actually be considered continuous during at least one measurement. In particular, the sampling period ΔΤ5 depends on the specific measurement, for example the roughness measurements have very stringent resolution requirements for which the sampling period ΔΤ5 is shorter than that used for profile measurements, which instead have less stringent resolution requirements. . According to the samples of the deflection signal d and a predetermined threshold value U, a variation signal is generated by the processing unit 5. In particular, the processing unit 5 is able to calculate a threshold delay ΔΤ between an unknown intersection instant TUf, in which the deflection signal d assumes a value equal to the threshold value U, and a sampling instant preceding the intersection instant Tu. As will be better described later, the sampling instant preceding the intersection instant Tu corresponds, for example, to a sampling instant immediately before the intersection instant Tu. As a function of the threshold delay ΔΤ, the processing unit 5 defines a validation instant Tve determines for example whether the probe 3 of probe 1, following the mutual approach movements between probe 1 and the mechanical piece W, has touched a surface of the latter, to consequently generate the aforementioned variation signal in the instant of validation Tv.

A transmission system 6 is connected to the processing unit 5 and, following the generation of the variation signal, transmits over the air a corresponding trigger signal to a receiver 21, located at a distance from the probe 1 and connected by means of an interface device 22 to numerical control 20 of the equipment 10. The trigger signal can be, for example, optical frequency or radio frequency and use known technologies such as Bluetooth® and Wi-Fi®. The numerical control 20 receives the trigger signal by means of the interface device 22 and controls the movement mechanism 11 with a stop signal to stop the mutual approaching movements between the probe 1 and the mechanical piece W and, possibly, with further signals command to cause other mutual movements.

The transmission system 6 is able to transmit over the air also successive samples of the deflection signal d, i.e. values of the deflection signal d sampled by the processing unit 5 of the probe 1 after the instant of validation Tv, together with relative time coordinates. . Each of the relative temporal coordinates is indicative of a sampling instant, which follows the validation instant Tve to which one of the successive samples of the deflection signal d corresponds. The sending of the relative temporal coordinates allows to know the order in time of the following samples and to restore the correct sequence even in the case of any losses. The numerical control 20, on the basis of the signals supplied by the optical ruler system 13 and taking into account said subsequent samples, processes the measurements after the instant of validation Tv.

A method for measuring and checking the dimensions and / or position and / or profile of the mechanical workpiece W by means of the apparatus 10, in particular a machine tool, with a contact measuring probe, for example, is described below. the scanning probe 1 of the wireless type described above, for checking the profile of a surface of the mechanical workpiece W.

In an initial phase, the mechanical piece W is positioned and referenced by means of the reference element 12 of the machine tool 10, so that the surface to be checked is placed in a position generally distant from the feeler 3 of the probe 1, which is located in resting condition. The numerical control 20 controls the movement mechanism 11 with a command signal, in particular an activation signal, which causes mutual approaching movements, at a substantially constant movement, in particular approaching speed, and in an approach direction, for example normal. to the surface to be checked, between the probe 1 and the mechanical piece W. The approach speed and the approach direction of the probe 1 are predetermined quantities, which the numerical control 20 does not necessarily have to transmit to the processing unit 5 of the probe 1.

Following said mutual approaching movements, the feeler 3 touches the surface of the mechanical piece W at an instant of contact Tc not known a priori, and the movement mechanism 11 continues for a given period of time to make the probe 1 advance at the speed approach and in the approach direction, whereby the stem 2 undergoes an increasing deflection and the probe 1 leaves the rest condition. The transducer 4 supplies the deflection signal d to the processing unit 5, which samples this deflection signal d, determines whether the feeler 3 has touched the surface of the mechanical part W and consequently generates the variation signal.

Figure 2 shows, with a dashed line and in an extremely simplified manner, a trend of the deflection signal d as a function of time. Before the feeler 3 touches the surface to be checked, ie when the stem 2 is not deflected and the probe 1 is in the rest condition, the deflection signal d does not vary and assumes a rest value RPC in pre-stroke. In the instants following the contact instant Tc, the deflection signal d has a rising edge which, as a first approximation, varies linearly in the given period of time in which the probe 1 continues to advance. More in detail, the deflection signal d, after the contact instant Tc, follows a substantially linear trend whose slope, defined here as "slope of the signal", is directly proportional to the increasing deflection of the stem 2, which depends on its time from the approach speed and the approach direction of probe 1. Figure 3, for example, compares the trends of the deflection signal d shown in Figure 2 with those of a rapid deflection signal d 'and a signal of slow deflection d ", relative to the same direction of approach and speed of approach of the probe 1 respectively greater and less than that with which the deflection signal d is obtained.

After the contact instant Tc, the slope of the fast deflection signal d 'is greater than that of the deflection signal d, while the slope of the slow deflection signal d "is smaller than that of both signals.

The processing unit 5 samples the deflection signal d with sampling period ΔΤ5 and compares the samples with the threshold value U. During the mutual approach movements, at the particular moment of intersection TUfin of an upward intersection, the deflection d assumes a value equal to the threshold value U, i.e. the leading edge of the deflection signal d intersects a straight line parallel to the abscissa axis (drawn in Figure 2 with a dash-dot line), indicative of the threshold value U. In a sampling sub-threshold instant TL, which follows the contact instant Tc and precedes the intersection instant Tu, the processing unit 5 samples the rising edge of the deflection signal d and identifies a sample of the deflection signal d with low value L less than threshold value U, or low sample. In an instant above the sampling threshold TH, following the rising instant of intersection Tu, the processing unit 5 samples the rising edge of the deflection signal d and identifies a sample of the deflection signal d with a high value H greater than the value U threshold, or high sample. Preferably, the sub-threshold instant TL and the sampling above-threshold instant TH correspond respectively to the sampling instants immediately before and immediately after the rising intersection instant Tu, that is to say that TH = TL + ATS. In the absence of noise and disturbances, therefore, the low sample is the largest among the samples with a value lower than the threshold value U, while the high sample is the lowest among the samples with a value greater than the threshold value U. Alternatively, the sample high can be any of the samples with a value greater than the threshold value U.

On the basis of the high and low samples, the processing unit 5 determines that the touch has occurred between the probe 3 and the surface of the mechanical piece W, and starts a computational process to calculate the threshold delay ΔΤ, which in this case corresponds to the time interval between the sampling sub-threshold instant TL and the rising intersection instant Tu. This process has a fixed computational duration ΔΤΡ (in figure 2 is represented for example 2 ΔΤ5 <ΔΤΡ <3 ΔΤ5) in which the processing unit 5 linearly interpolates the high sample at the over-threshold instant TL and the low sample at the instant under-threshold TLe calculates the threshold delay ΔΤ, applying the formula, for example

ΔΤ = (U - LHTH- TJ.

(H - L)

In correspondence with a subsequent sampling instant, for example immediately following, at the expiry of the computational duration ΔΤΡ (in figure 2, this instant corresponds to the sampling instant ΤΗ + 3 ΔΤ5), the processing unit 5 waits for a period of time equal to the threshold delay ΔΤ until defining the validation instant Tv, in which it generates the variation signal and transmits it to the transmission system 6. The transmission system 6, following the generation of the variation signal, transmits via ether the trigger signal to the receiver 21, which sends it via the interface device 22 to the numerical control 20 of the machine tool 10. The latter, having received the trigger signal, controls the movement mechanism 11 with a new command signal, in particular of stopping, to stop the mutual approaching movements between the probe 1 and the mechanical piece W, and stores the signals supplied in the instant of validation Tv by the system of lines optics 13. Then, the numerical control 20 commands a scanning movement of the probe 1 along a suitably defined path as a function of a nominal profile, so that the probe 1 maintains contact with the mechanical piece W along the entire profile to be measured .

After the validation instant Tve for the entire duration of the scanning movement of the probe 1, the processing unit 5 continues to sample the deflection signal d with the sampling period ΔΤ5, and transmits over the air via the transmission system 6 the subsequent samples of the deflection signal d together with the relative time coordinates. The numerical control 20 continues to memorize the signals supplied by the optical scale system 13 and, as a function of these signals and taking into account the subsequent samples of the deflection signal d, processes the required profile measurement, rectified by suitably calculated correction parameters. In the event that this measurement does not correspond, unless pre-set tolerances, to a reference measurement, the numerical control 20 can decide that the mechanical piece W is a waste piece and must be treated accordingly or that the machine tool 10 must work it further, or, if not, that the mechanical piece W is finished.

By transmitting to the numerical control 20 only the subsequent samples, i.e. the values of the deflection signal d sampled after the instant of validation Tv, the probe 1 according to the present invention benefits from considerable energy savings, an aspect of fundamental importance for any device powered by batteries and that uses over-the-air transmission. However, if necessary, it is possible to give up even only temporarily to this benefit and program the probe to send indiscriminately the samples of the deflection signal d to the numerical control 20, i.e. the values of the deflection signal d sampled before and after the instant of TV validation.

Furthermore, in accordance with the method described, based on the parallelism between the deflection signal d before the contact instant Tc and the straight line indicative of the threshold value U, it can easily be shown that, with the same approach speed and direction of approach of probe 1, as the contact instant Tc varies, the delay between the latter and the validation instant Tvr is constant. Furthermore, as is well known in the art, the propagation times of the electrical signals can be easily made repeatable, while the propagation times of the signals over the air are negligible compared to the delays considered up to now. Since the delay between the contact instant Tc and the validation instant Tv is precise and repeatable, this is also the delay between the contact instant Tc and the instant in which the numerical control 20 receives the trigger signal. The method according to the present invention therefore has the considerable advantage that the numerical control 20 of the machine tool 10 reconstructs in a simple and accurate manner the synchronism between the successive samples of the deflection signal d and the signals supplied by the optical ruler system 13.

Conveniently, a simple preliminary calibration operation of the probe 1 and of the machine tool 10 can be performed, in which the check is carried out on a master, ie a sample piece which comprises a reference surface whose profile is known. The master is positioned and referred to by means of the reference element 12 of the machine tool 10, so that the reference surface is distant from the feeler 3 of the probe 1 in the rest condition. The numerical control 20 controls the movement mechanism 11 with the activation signal, which causes mutual approach movements between the probe 1 and the master, at a constant approach speed and in the predetermined approach direction. Following said mutual movements, the feeler 3 touches the reference surface, the probe 1 leaves the rest condition and the stem 2 undergoes an increasing deflection. The transducer 4 supplies the deflection signal d to the processing unit 5 which, similarly to what has been described above, generates the variation signal as a function of the samples of the deflection signal d and the threshold value U at the validation instant Tw, and in the following instants it continues to sample the rising edge of the deflection signal d. By means of the transmission system 6, the processing unit 5 first sends the variation signal to the numerical control 20 of the machine tool 10, then the subsequent samples together with the relative time coordinates. The numerical control 20, having received the trigger signal, stops the mutual approach movements between the probe 1 and the master, then processes a position measurement of the reference surface according to the signals supplied by the optical scale system 13 and calculates the parameters correction, to rectify the subsequent measurements of the mechanical piece W.

As is evident to an expert in the field, the method according to the present invention is also advantageous when the probe 1 is used only for contact detection, for example to carry out dimensional and / or position measurements of the mechanical part W. In this case, unlike the previous one, probe 1 is not required to send any sample of the deflection signal over the air d. In particular, when the numerical control 20 of the machine tool 10 receives the trigger signal, it stores the signals supplied by the optical scale system 13 and commands the movement mechanism 11 with a control signal, specifically retraction, to stop the approach and cause mutual moving away between the probe 1 and the mechanical part W. According to the required measurement, the numerical control 20 can therefore command the movement mechanism 11 with further control signals, in particular of movement, so that the probe 1 touches the surface of the mechanical piece W in a discrete sequence of points and generates the related trigger signals.

According to a different embodiment of the present invention, on the basis of the samples of the deflection signal d, the processing unit 5 is able to determine whether the feeler 3, following mutual distancing movements between the probe 1 and the mechanical piece W, is about to lose contact with the surface to be measured, and consequently generate the variation signal in the instant of validation Tv. More in detail, as a consequence of the mutual approach movements already described, the feeler 3 touches the surface of the piece W mechanical and the movement mechanism 11 continues for a given period of time to advance the probe 1 at the approach speed and in the approach direction, so that the stem 2 undergoes an increasing deflection. At the expiration of the given period of time, the numerical control 20 commands the movement mechanism 11 with the stop signal and a retraction signal, to stop the approach and cause mutual withdrawal movements between the probe 1 and the mechanical piece W, at a substantially constant displacement speed, in particular withdrawn, and in a retraction direction not necessarily equal, respectively, to the approach speed and the approach direction. Following said mutual withdrawal movements, the rod 2 undergoes a decreasing deflection and the feeler 3 loses contact with the surface of the mechanical piece W in an instant of detachment Td not known a priori, moving further away until the probe 1 returns to the condition of rest.

Following the mutual moving away, the deflection signal d has a falling edge, shown in Figure 4, which varies linearly as a first approximation while the probe 1 continues to move away. The processing unit 5 samples the deflection signal d with sampling period ΔΤ5 and compares the samples with the threshold value U. The threshold value with which the samples of the falling edge of the deflection signal d are compared can be different from threshold value U with which the samples of the rising edge of the same signal are compared. During the mutual withdrawal movements, at the particular moment of intersection TUfin of downward intersection, the deflection signal d assumes a value equal to the threshold value U, i.e. the falling edge of the deflection signal d intersects the straight line indicative of the threshold value U. In the sampling over-threshold instant TH, which in this case precedes the downward intersection instant Tu, the processing unit 5 samples the falling edge of the deflection signal d in correspondence with the high sample, that is, of the sample with a high value H greater than the threshold value U. In the sampling sub-threshold TL, following the downward intersection instant Tu and preceding the detachment instant Td, the processing unit 5 samples the edge of descent of the deflection signal d in correspondence with the low sample, i.e. the sample with a low value L less than the threshold value U. On the basis of the high and low samples, the processing unit and 5 starts the computational process to calculate the threshold delay ΔΤ, that is the time elapsed between the sampling over-threshold instant TH and the downward intersection instant Tu. The continuation of the method for generating the variation signal in the instant of validation Tv is similar to what has already been described. After the instant of validation Tv, the processing unit 5 advantageously interrupts the sampling of the deflection signal d or, alternatively, continues sampling with sampling period ATs.

The behavior of the numerical control 20 which receives the trigger signal depends on the measurement required, as already seen.

As is widely known in the literature, the withdrawal movements are little or not at all subject to vibrations due to the possible rebound of the feeler 3 which touches the mechanical part W, so that the deflection signal d has a more stable trend. Consequently, the calculation of the validation instant Tv on the falling edge of the deflection signal d according to the present invention has the obvious advantage of being more accurate.

Alternatively, the transmission system 6 of the probe 1 and the receiver 21 of the machine tool 10 can be connected by cable, and in this case the trigger signal and the samples of the deflection signal d can be for example electrical or optical. In this way, although to the detriment of the handling of the probe 1, the propagation times over the air of the signals are canceled.

In reality, the deflection signal d is inevitably plagued by noisy components, both electrical and mechanical, which degrade its quality. As a first countermeasure to advantageously filter these noisy components, the processing unit 5 can for example perform a fine sampling of the deflection signal d with a shorter sampling period ΔΤ5 ', of which the sampling period ΔΤ5 is an integer multiple, and elaborate the results of the fine sampling in an appropriate manner. Specifically, assuming ΔΤ5 = Ι <· ΔΤΥ, where k is an integer, processing unit 5 samples the deflection signal d with the shortest sampling period ΔΤ5 'and obtains fine samples. To obtain the samples of the deflection signal d, the processing unit 5 calculates for example the arithmetic mean of successive fine samples, taken k at a time.

As a further countermeasure to filter the noisy components of a mechanical nature, the threshold value U can be advantageously fixed in relation to the approach and departure speeds to be suitably distant from the rest value RPC in pre-stroke. As already mentioned, in fact, due to the vibrations due to the possible rebound of the probe 3 which touches the surface of the mechanical piece W, the trend of the deflection signal d in the instants immediately following the instant of contact Tcdevia from the linear approximation in a manner the more evident the greater the approach speed of probe 1. By setting the threshold U at a certain distance from the rest value RPC in pre-stroke, since this distance depends on the approach speed of probe 1, the anomalies have the opportunity to naturally dampen .

As is well known in the art, linear interpolation is an operation that requires the calculation of very expensive products and divisions in terms of computational cost and energy efficiency compared to the limited resources of the processing unit 5 of the measurement probe 1 in contact. Alternatively, in order to calculate the threshold delay ΔΤ efficiently, the processing unit 5 can implement a bisection algorithm which identifies the instant of intersection Tu and has the advantage of defining the threshold delay ΔΤ in terms of unit of time, each unit of time being an integer multiple of the clock period of processing unit 5.

More in detail, after identifying the high and low samples of the deflection signal d, the processing unit 5 initializes a first comparison variable AUL = U-L, a second comparison variable ΔΗΙ_ = Η-Ι_ of which it calculates the half ΔΗΙ_ / 2, and a shift register. If half of the second comparison variable ΔΗΙ_ is greater than the first comparison variable Δυΐ_, i.e. ΔΗΙ_ / 2> Δυΐ_, indicative of the fact that the threshold is closer to the low sample, a new value equal to Η- is assigned to the high sample. ΔΗΙ_ / 2; otherwise, indicative of the fact that the threshold is closer to the high sample, a new value equal to Ι_ + ΔΗΙ_ / 2 is assigned to the low sample. The processing unit 5 recalculates the first or second comparison variables and repeats the procedure until the two comparison variables are equal to each other and equal to zero. At each iteration, the shift register is filled one bit at a time, starting from the most significant bit, with a "0" if the threshold is closer to the low sample or with a "1" if the threshold is closer to the sample tall. The final value contained in the shift register is representative of the threshold delay ΔΤ in terms of time units. This bisection algorithm, as described, requires the calculation of sums, divisions by 2 and binary comparisons, which are notoriously inexpensive operations in terms of computational cost and energy efficiency.

Claims (16)

CLAIMS 1. Method for the dimensional and / or position and / or profile measurement of a mechanical workpiece (W) by means of an apparatus (10) which includes a measuring probe (1) in contact, with a casing and a stem ( 2) movable with respect to the casing, and a numerical control (20), which comprises the steps of: - causing mutual movements, at a substantially constant speed of movement, between the probe (1) and the mechanical piece (W); - providing signals relating to the position of the probe (1) with respect to the equipment (10); - providing a continuous deflection signal (d), indicative of the deflection of the stem (2); - sampling the deflection signal (d) in order to obtain samples; And - process the measurements based on the signals relating to the position of the probe (1) with respect to the equipment (10); the method being characterized by the further steps of: - calculate a threshold delay (ΔΤ) between a sampling instant preceding an intersection instant (Tu) in which the deflection signal (d) assumes a value equal to a predetermined threshold value (U), and the instant of intersection (You) itself; - define a validation instant (Tv) as a function of the threshold delay (ΔΤ); And from the fact that the step of processing the measurements is performed after said validation instant (Tv). Method according to claim 1, comprising the further steps of generating by means of a processing unit (5) of the probe (1) a change signal at the validation instant (Tv) and sending a corresponding trigger signal to the numerical control (20). Method according to claim 1 or claim 2, wherein the sampling instant preceding the intersection instant (Tu) corresponds to the sampling instant immediately before the intersection instant (Tu). Method according to one of the preceding claims, comprising the further step of setting the threshold value (U) in relation to the displacement speed. Method according to one of the preceding claims, comprising the further step of linearly interpolating a low sample of the samples of the deflection signal (d), with a low value (L) less than the threshold value (U) at an instant below the threshold (TL), and a high sample of the samples of the deflection signal (d), with a high value (H) greater than the threshold value (U) at an instant above-threshold (TH), to calculate the threshold delay (ΔΤ ). Method according to claim 5, wherein the high sample is the lower of the samples with a value greater than the threshold value (U). 7. Method according to claim 5 or claim 6, in which, in the course of said mutual movements, the sub-threshold instant (TL) precedes the intersection instant (Tu), and the threshold delay (ΔΤ) corresponds at the time interval between the sub-threshold instant (TL) and the intersection instant (Tu). 8. Method according to claim 5 or claim 6, in which, during said mutual movements, the over-threshold instant (TH) precedes the intersection instant (Tu) and the threshold delay (ΔΤ) corresponds to 'time interval between the over-threshold instant (TH) and the intersection instant (Tu). Method according to one of the preceding claims, in which the step of processing the measurements based on the signals relating to the position of the probe (1) with respect to the apparatus (10) provides for taking into account the samples of the deflection signal (d). 10. Contact measurement probe (1), to carry out dimensional and / or position and / or profile measurements of a mechanical piece (W), comprising: - a casing and a stem (2) movable with respect to the casing, with a feeler (3) to touch the mechanical part (W); - an analog detection device (4) adapted to provide a continuous deflection signal (d), indicative of the deflection of the stem (2); and - a processing unit (5), connected to the analog detection device (4), suitable for receiving and sampling the deflection signal (d) in order to obtain samples; characterized by the fact that the processing unit (5) is further adapted to calculate a threshold delay (ΔΤ) between a sampling instant preceding an intersection instant (Tu) in which the deflection signal (d) assumes a value equal to a predetermined threshold value (U), and the instant of intersection (Tu) itself, define a validation instant (Tv) as a function of the threshold delay (ΔΤ), and generate a change signal at the instant of validation (Tv). Contact measuring probe (1) according to claim 10, wherein the processing unit (5) is adapted to linearly interpolate a low sample of the samples of the deflection signal (d), with a lower low value (L) of the threshold value (U) at an instant below the threshold (TL), and a high sample of the samples of the deflection signal (d), with a high value (H) greater than the threshold value (U) at an instant above threshold (TH), to calculate the threshold delay (ΔΤ). Contact measurement probe (1) according to claim 10 or claim 11, comprising a transmission system (6), connected to the processing unit (5), capable of transmitting a trigger signal following the generation of the change signal. Contact measuring probe (1) according to claim 12, wherein the transmission system (6) is adapted to transmit the trigger signal over the air. Contact measuring probe (1) according to claim 12 or claim 13, wherein the transmission system (6) is adapted to transmit over the air values of the deflection signal (d) sampled by the processing unit (5 ) of the probe (1) after the validation instant (Tv), together with relative time coordinates, each of said relative time coordinates being indicative of a sampling instant following the validation instant (Tv) and in which it was sampled one of these values of the deflection signal (d) sampled by the processing unit (5) of the probe (1) after the validation instant (Tv). 15. Apparatus (10) for measuring and checking the dimensions and / or position and / or profile of a mechanical part (W), comprising: - a reference element (12) intended to refer to the mechanical piece (W); - a support device (14) designed to support a contact measurement probe (1) according to one of claims 12 to 14; - a movement mechanism CU) adapted to cause mutual movements, at a substantially constant speed of movement, between the probe (1) and the mechanical piece (W); - a system of position transducers (13) connected to the movement mechanism (11) to provide signals relating to the position of the probe (1) with respect to the apparatus (10); And - a numerical control (20), connected both to the movement mechanism (11) to control it with suitable command signals and to cause said mutual movements, and to the position transducer system (13) to read the signals relating to the position of the probe ( 1) with respect to the equipment (10), suitable for receiving the trigger signal transmitted by the transmission system (6) of the probe (1) to process, after the validation instant (Tv), the measurements based on the signals supplied from the position transducer system (13). 16. Apparatus according to claim 15, wherein the numerical control (20) is adapted to process the measurements taking into account the samples of the deflection signal (d).