EP3990856A1

EP3990856A1 - Machine and method for inspecting mechanical parts

Info

Publication number: EP3990856A1
Application number: EP20734401.1A
Authority: EP
Inventors: Joël MOREAU; Fabrice Moreau
Original assignee: Espi France
Current assignee: Espi France
Priority date: 2019-06-27
Filing date: 2020-06-26
Publication date: 2022-05-04
Also published as: WO2020260594A1

Abstract

The invention relates to a machine for inspecting mechanical parts comprising a frame (12), a part holder assembly (14) and at least two sensors (15) arranged to inspect at least one feature of the mechanical part. The part holder assembly (14) can move relative to the frame (12) of the machine in at least four degrees of freedom, at least two of said degrees of freedom being defined by two axes of rotation (A, C). The part holder assembly (14) can move so as to allow a point of said mechanical part to be inspected to be positioned facing one of the sensors (15). The total number of degrees of freedom of the part holder assembly (14) and of the sensor (15) is at least equal to five. The inspection machine (10) further comprises measurement means arranged to determine the position of this part holder assembly (14). At least one of said sensors is supported by a gantry (13) connected to the frame (12) of the machine. The invention also relates to a method for inspecting mechanical parts using a machine as defined above, said method comprising the steps of defining a set of inspection points disposed on the mechanical part to be inspected; of selecting a sensor (15) suitable for the feature to be inspected; of positioning the mechanical part on the part holder assembly (14); of moving the part holder assembly (14) in at least four degrees of freedom in order to position an inspection point facing the selected sensor (15); of measuring, by means of the sensor (15), the feature to be inspected on the inspection point positioned facing this sensor; of storing the value of the measured features linked to a position of the sensor during the measurement; of repeating the previous three steps for the different inspection points and of processing the measurements of the features as a function of the parameter to be inspected.

Description

MACHINE AND METHOD OF INSPECTION OF MECHANICAL PARTS

TECHNICAL AREA

The present invention relates to the field of checking mechanical parts and more precisely to the field of machines for checking mechanical parts.

In more detail, this invention relates to a machine for checking mechanical parts, this machine comprising at least one frame, a workpiece carrier assembly on which the mechanical part to be checked is placed and at least two sensors arranged to check at least one characteristic. of said mechanical part.

The invention also relates to a method for checking mechanical parts by means of a machine as defined above.

Such a machine can in particular be used in the context of dimensional control of parts or control of the surface condition, both in a metrology laboratory and in a production environment.

PRIOR ART

Currently, there are several types of machines used for checking mechanical parts. Among these different types, we can mention three-dimensional measuring machines (CMM). These are generally intended to measure dimensions and / or geometric characteristics of the part. Some machines can also check the surface finish of such parts.

When they are used for dimensional and / or geometric inspection, these machines are used to determine coordinates of measured points or control points in a frame of reference linked to the inspection machine or to the inspected part. These coordinates are processed in order to verify the adequacy between the theoretical dimensions and the real dimensions of the part. These machines generally include a frame and a table fixed relative to the frame, the part to be checked being fixed on the table. The machine generally comprises a gantry mounted on slides and a measuring head mounted on the gantry. The displacement of the measuring head is carried out along three orthogonal axes defining three degrees of freedom, which makes it possible to bring the measuring head opposite the various control points.

A probe or sensor is moved until it rests against the mechanical part to be checked. The position of the probe or of the sensor at the moment of contact is determined by means of graduated rulers, encoders or by other measuring means.

CMMs with only linear axes of motion and therefore a maximum of three degrees of freedom may not necessarily access all desirable control points for any part. In some part configurations, it may be necessary to perform a certain number of measurements when the mechanical part is placed on a first fixture, then to place the part in a second fixture to take measurements on measurement points that are not accessible when the part is placed in the first pose.

This has several drawbacks. In particular, the time of a measurement cycle is greatly increased because it is necessary to release the part from the first installation, reposition it in the second installation and recalibrate the machine before starting the measurements. In addition, the risk of measurement errors is increased due to the transfer of the part from one installation to another.

To allow access to a greater variety of control points, some CMM type machines have a measuring head arranged on an arm capable of pivoting around several axes of rotation. This makes it possible to access measurement points which may be difficult to access if the measurement head is movable in translation only along three orthogonal axes.

One of the problems with these machines is due to their bulk. In fact, when the probe must be able to control complex parts, the arm carrying the probe must be able to move around the part. Given the size of the arms and probes commonly used, this implies a relatively large machine volume even for relatively small parts to be inspected. In other words, the volume of the machine is large compared to its useful volume.

Another problem with this kind of machine is due to the movement of the probe. The probe should preferably move quickly in order to minimize the measurement cycle time. The probe can be placed on a mobile gantry only with linear movements, on a mobile robot arm only with movements around the axes of rotation or on a support producing linear and rotational movements. The movements of the probe involve significant accelerations and decelerations of the probe. These significant accelerations and decelerations create distortions in the probe and generate errors and uncertainties in the measurements.

Current machines are generally designed to operate with one type of probe. When several characteristics of a part are to be checked, for example dimensional characteristics, profile characteristics, surface finish or appearance, it frequently happens that a first characteristic is checked on a first inspection machine and that a first characteristic is checked. second characteristic is checked on a second checking machine of a different type. This generates several drawbacks. First of all, it is necessary to have several specific control machines, which incurs the costs of purchasing the machines and the costs of the space required for each machine. It is necessary to move the parts to be inspected from one machine to another, which creates a relatively long cycle time which can potentially prevent an inspection during a manufacturing cycle of the parts. Positioning of the parts to be inspected must be carried out on each inspection machine, as well as a calibration of these different machines. This involves a risk of measurement errors and uncertainties.

Some existing machines have been developed in an attempt to solve some of the problems mentioned above. Japanese publication JP 2016 13691 describes a machine for measuring the shape of an object by means of non-contact measurement. This machine comprises a linearly movable plate along at least two orthogonal axes. The machine further includes a table tilting unit for pivoting the table around two axes of rotation. The translation and rotation axes of the machine make it possible to move a point of the part to measure opposite a sensor, in an orientation allowing this sensor to perform a measurement.

The machine described in this publication is only intended for measuring the shape of an object by means of an optical sensor. This measurement is made by modifying the distance between the part and a lens of the optical sensor, so as to obtain maximum intensity of the reflected light. Due to the special way of performing measurements in this invention, the machine cannot be adapted to perform other types of measurements.

Russian publication No. 2,461,839 is similar to the Japanese publication mentioned above in that it has a plate for bringing a part to be inspected opposite a lens of an optical system. In this case, this optical system is that of a microscope intended to analyze the surface of a sample.

As with the machine described above, this machine cannot be adapted for industrial control of several parameters of the same part.

The publication DE 10 2016 214307 describes a support which can be used with a conventional testing machine. This support can be placed on the platform of the measuring machine. It is formed by an arm made up of several segments, each of these segments being articulated on the adjacent segments.

This document does not describe a checking machine as such. The support is intended to present the part to be measured to a sensor of a conventional inspection machine. However, such a support is not suitable for industrial control of parts, the precision of the measurements required in this field cannot be achieved with such a device.

It would be desirable to have a machine capable of checking different types of parts, in particular parts for which a three-dimensional control is necessary. Such a machine should be able to check different characteristics of the parts, ideally without having to remove the part from the checking machine. The machine should be designed to minimize clutter or optimize the ratio between the useful volume and the total volume. Control cycle time should also be minimized while reducing measurement errors and uncertainties.

DESCRIPTION OF THE INVENTION

The control machine according to the present invention solves certain problems of the machines of the prior art by proposing a multi-sensor three-dimensional measuring machine, having a good total volume / useful volume ratio and making it possible to carry out reliable and precise measurements in a relatively short time. .

The object of the invention is achieved by a machine as defined in the preamble and characterized in that the workpiece carrier assembly is movable relative to the frame of the machine according to at least four degrees of freedom, at least two of said degrees of freedom. freedom being defined by two axes of rotation that are not collinear with one another, this part-holder assembly being movable so as to allow positioning at least one point of said mechanical part to be checked opposite one of said at least two sensors, in that the total number of degrees of freedom of the workpiece carrier assembly and of the sensor opposite which the workpiece to be checked is positioned is at least equal to five, in that the checking machine further comprises measuring means arranged to determine the position of this workpiece holder assembly and in that at least one of said sensors is supported by a gantry linked to the frame of the machine.

The object of the invention is also achieved by a method of checking mechanical parts by means of a machine comprising at least one frame, a workpiece carrier assembly on which the mechanical part to be checked and at least two sensors is placed, at least one of said sensors being supported by a gantry linked to the frame of the machine, these sensors being arranged to control at least one characteristic of said mechanical part, said part holder assembly being movable relative to the frame of the machine according to at least four degrees of freedom, at least two of said degrees of freedom being defined by two axes of rotation not collinear with each other and the total number of degrees of freedom of the workpiece assembly and of the sensor opposite which the part to be checked is positioned to be at least equal to five, this method comprising the following steps: a) definition of a set of check points arranged on the mechanical part to be checked;

b) choice of a sensor suited to the characteristic to be checked on said mechanical part;

c) positioning of said mechanical part on said part holder assembly of the checking machine;

d) movement of the workpiece carrier assembly according to said at least four degrees of freedom so as to position a control point opposite the chosen sensor; e) measuring, by means of said chosen sensor, the characteristic to be checked of the control point positioned opposite this sensor;

f) storage of the value of the characteristics measured in connection with a position of the sensor during the measurement;

g) repetition of steps d to f for the different control points; and

h) processing of the measurements of the characteristics as a function of said parameter to be checked.

The machine of the invention allows reliable and precise control of mechanical parts. This machine makes it possible in particular to carry out three-dimensional checks of these parts while minimizing the total volume of the machine in relation to the size of the part to be checked or the useful volume of the machine. This machine eliminates distortions that can occur depending on the travel speed, acceleration and deceleration experienced by the probe or sensor.

In addition, the machine respects, in most cases, certain metrological principles making it possible to obtain measurements as precise as possible, these metrological principles being often difficult to respect in practice and therefore rarely respected in conventional machines.

This machine can be adapted to measure or control different characteristics of a part to be inspected. To this end, the machine can be equipped with a whole range of sensors, detectors or suitable probes, which avoids having to transfer the part from one machine to another according to the characteristic checked on this part. This also makes it possible to carry out all the measurements having the part in the same installation, without having to recalibrate the machine. The precision and reliability of the measurements are therefore improved. This also makes it possible to reduce the cycle time since all the operations linked to the movement of the part, to the repositioning of this part on a second machine and to the calibration of this second machine are eliminated.

This machine can also be used in an environment such as a metrology laboratory, but also in an industrial environment, in particular thanks to the management of vibrations and temperature variations that can occur in such an industrial environment. A short measuring or checking cycle time and the possibility of using the machine in an industrial environment allows checks to be carried out during the manufacture of a series of parts. This makes it possible in particular to detect drifts with respect to the theoretical dimensions of the parts, these drifts possibly being due to poor settings, tool wear or any other cause. The early detection of errors makes it possible to quickly correct the machining machines or the programs managing these machines in order to compensate for errors and possible drifts during the production of the series of parts.

Due to its compact construction, the distances between the parts to be checked and the structural elements of the machine are limited, which also limits the geometric deformations of the machine and consequently the errors and uncertainties of measurement. This also makes it possible to ensure that the rulers, the encoders and in general, the measuring means arranged to determine the position of a mobile component of the machine are close to the controlled mechanical part. This feature also improves the reliability of the measurements made by this machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention and its advantages will be better understood with reference to the appended figures and to the detailed description of particular embodiments, in which: - Figure 1 schematically illustrates a first embodiment of an inspection machine according to the present invention;

- Figure 2 schematically illustrates a control machine according to a second embodiment of the invention; and Figure 3 illustrates a detail of the machine according to the invention.

EMBODIMENT OF THE INVENTION

Referring to the figures, the inspection machine 10 of the invention essentially comprises a fixed base 1 1 integral with a frame 12 of the machine, a measuring gantry 13, a workpiece carrier assembly 14 supporting the part (s) of which certain characteristics are monitored and at least two sensors 15 intended to monitor at least one characteristic of the part.

Unlike the majority of conventional CMMs, in the machine of the invention, the gantry 13 is not movable relative to the fixed base 1 1 or to the frame 12, but is immobile relative to this fixed base 1 1 or this frame 12. This characteristic allows a particularly robust and particularly rigid construction, which makes it possible to increase the precision and repeatability of the measurements.

In the embodiment illustrated in Figure 1, the workpiece carrier assembly 14 comprises in particular a table 16 cooperating with uprights 17 of the frame 12 of the machine. In this embodiment, the table 16 is movable longitudinally relative to these uprights 17.

In general, the fixed base 1 1 defines a horizontal plane. The table 16 is capable of moving in a linear direction generally perpendicular to the plane defined by the fixed base 1 1 and therefore generally vertical. The direction of movement of the table 16 may be along a vertical axis bearing the reference z.

According to an advantageous embodiment of the machine of the invention, the gantry 13 is held by the uprights 17, these uprights being arranged substantially symmetrically on either side of the fixed base 1 1. These uprights 17 include rails 18 or slides arranged to guide the table 16. There are many means for guiding the table 16 along the rails 18. By way of example, the table may include pads sliding along the rails. Other types of guidance can also be used, such as, for example, guidance on air cushions. Due to the construction of the machine, it is possible to guide the table 16 while ensuring great stability of this table, so as to guarantee that all the positions that the table can reach are mutually parallel. This stability can for example be increased by using arms or mechanical reinforcement or stabilization elements. The setting in motion of the table 16 can be carried out by means of a motor (not shown). In a preferred embodiment, this setting in motion is managed by two motors, arranged near each of the uprights 17. These motors can advantageously be linear motors.

It is possible to use known mass compensation systems, such as in particular counterweight systems, in order to facilitate the movement of the table 16 and / or of the workpiece assembly 14.

In addition to the table 16, the workpiece carrier assembly 14 includes a longitudinal displacement plate 19, also called longitudinal plate, and a transverse displacement plate 20, also called transverse plate. The longitudinal displacement plate 19 and the transverse displacement plate 20 together form the movable plate 21.

The longitudinal plate 19 is mounted on at least one linear guide disposed coplanar with a plane of the table 16. In the figures, the direction of movement of the longitudinal plate 19, or longitudinal direction, bears the reference y. In the embodiment illustrated by FIG. 1, the longitudinal plate 19 is arranged in a housing 22 of the table 16, the edges of the housing 22 cooperating with the edges of the table to ensure precise linear guidance.

In the embodiment illustrated in Figure 2, the longitudinal displacement plate 19 comprises two side members 23 sliding in two grooves 24 corresponding to table 16. It is clear that other guides can also be used.

In the embodiment illustrated in Figure 1, the transverse displacement plate 20 can be moved along an axis perpendicular to the linear displacement axis y. This perpendicular or transverse axis bears the reference x in Figures 1 and 2. The transverse plate 20 is guided in the longitudinal displacement plate 19 in the same way as the longitudinal plate 19 is guided in the table 16. It is clear that other embodiments or other types of guidance could be used.

The x and y linear axes of motion are referred to here as the basic linear axes. These basic linear axes are preferably orthogonal to each other.

The machine according to the invention and more specifically the workpiece carrier assembly 14 further comprises a caliper 25 illustrated in more detail in Figure 3 and intended to receive the workpiece to be checked. This bracket 25 can be associated with a fitting (not shown) intended to hold the part to be checked in an appropriate position and to prevent the movement of this part during its control. The caliper 25 is mounted on the movable plate 21 and more precisely on the transverse plate 20. It is clear that the order of the longitudinal plate 19 and of the transverse plate 20 could be reversed, so that the transverse plate could be guided by the table 16 and that the bracket 25 could be placed on the longitudinal plate 19.

According to an advantageous embodiment, the bracket 25 comprises a workpiece support 26 pivoting about an axis of rotation C, this workpiece support being mounted in a console 27. The console is preferably symmetrical and / or balanced and comprises two aligned cylindrical tenons 28 each disposed in a bearing 29. These tenons 28 and these bearings 29 are arranged so as to allow the rotation of the console 27 about a rotation axis A passing through the two tenons.

According to an advantageous variant, the movable plate 21 may include a recess in which the stirrup 25 can be positioned. This recess makes it possible to reduce the total mass of the workpiece-holder assembly 14. In addition, the recess makes it possible to place the bracket. part to be checked as close as possible to the movable plate 21 or to the table 16. This makes it possible to increase the rigidity of the machine and thus to minimize errors and measurement uncertainties. The part support 26 may itself include a recess allowing for example access to both sides of the part to be checked.

In practice, one of the axes of rotation A or C may be generally parallel or coincident with one of the x or y base linear displacement axes of the movable table.

According to a variant, it is possible to provide three axes of rotation on the caliper, for example the axis A parallel to the axis of linear displacement x, an axis of rotation B parallel to the axis of linear displacement y and l axis of rotation C as illustrated in Figure 3.

The movements of the console 27 and of the workpiece support 26 around the axes of rotation A and C are generated and controlled by precision motors (not shown) making it possible to ensure the greatest possible precision and repeatability of the movement of the machine. part to be checked.

The axes of rotation A and C of the console 27 and of the workpiece support 26 are also associated with means for measuring the position of this console and of the workpiece support. These measuring means can be rules associated with optical, electrical and / or mechanical means or encoders.

The axes of rotation A and C defined above materialize two degrees of freedom in rotation for the movement of the part to be checked.

As can be seen in the figures, the part to be inspected can be moved in particular in a plane of the table 16, along the two basic linear displacement axes, these axes forming two degrees of freedom. These movements can be provided for example by guides.

Each of these movements is also associated with at least one motor (not shown) which can for example be a linear motor. These motors and the corresponding guides make it possible to position the plate 21 precisely in a work zone of the checking machine.

According to an advantageous embodiment, the movement along each of the x or y axes takes place along two parallel rails, by means of a linear motor aligned with the rails and passing close to the center of gravity of the movable plate. The guides or more generally the movable elements of the workpiece carrier assembly 14 are also associated with measuring means making it possible to determine the position of the components of the workpiece carrier assembly. These measuring means can in particular be rules making it possible to determine a position by optical, electrical and / or mechanical means or encoders. The position of the components of the workpiece assembly can also be determined by the commands that have been transmitted to the motors.

As indicated previously, in the embodiment illustrated by FIG. 1, the table 16 can move along a linear displacement axis that is not coplanar with the linear displacement axes of the movable plate or vertical axis z. On the contrary, in the embodiment illustrated in Figure 2, the table 16 is not movable in the vertical direction. The sensor 15 used to perform a measurement is movable on the measuring gantry 13 in a direction orthogonal to the plane of the table 16 or along the z axis defined above or else along a vertical axis. The guidance can be achieved in different ways, for example by using the uprights 17 as a support as shown in Figure 2 or by resting on the center of the gantry 13.

In the invention, at least two sensors are available for making measurements, which sensors can be used to measure identical or different characteristics on the part to be checked. According to an advantageous embodiment, the gantry 13 supports a barrel 30 comprising several sensors 15, for example sensors capable of each measuring or controlling a different characteristic of the part to be inspected. By way of example, the barrel 30 may include a sensor 15 produced in the form of a probe intended to measure a geometric characteristic of shape, dimension and / or position in particular, a white light sensor intended to monitor a state. surface, a camera intended to determine a profile or to carry out an aspect control, etc.

In the embodiment illustrated by FIG. 1, the barrel 30 is stationary during a control or measurement cycle. This barrel may be rotating, so as to bring a sensor to a desired location, this sensor being suitable for monitoring at least one determined parameter of a monitoring cycle. This barrel 30 can be moved in rotation and / or in translation along a vertical axis, provided that a control cycle is not in progress. This mobility along a vertical axis is only used to facilitate for example the change of sensor or to place a sensor in a position in which it does not interfere with the sensor used for the following measurement cycle.

According to a particular variant, the barrel 30 is completely immobile along a vertical axis and / or an axis of rotation.

In the machine according to the invention, the fact that the sensor 15 is stationary in the vertical direction makes it possible to design a particularly stable and particularly robust barrel, which further minimizes the errors and uncertainties of the measurement.

In the embodiment illustrated in Figure 2, the table 16 is not linked to the runners or a guide, but to the uprights 17 or to the frame 12 of the machine. It is therefore fixed with respect to this frame 12.

In this case, the sensor 15 is mobile in translation along a vertical axis or z axis during a control cycle. To allow this vertical movement, the sensor 15 is integral with a column or a vertically movable cross member 31 driven by at least one motor such as for example a linear motor. The position of the column or cross member 31 must be able to be determined with precision, for example by means of a ruler or an encoder or by processing the control signals sent to the motor of the column.

As can be understood from the description and the drawings, the workpiece, held on the workpiece assembly 14, can be moved to different positions. This movement can be done by the presence of different axes of movement which can be either linear or rotary and which define different degrees of freedom. The axes of linear movement and rotation can be materialized by different components varying from one embodiment to another. However, it is important that the part to be inspected is mobile according to at least four degrees of freedom, at least two of which are in rotation.

In the embodiment illustrated by FIG. 1, the three linear axes of displacement x, y and z define three degrees of freedom. The two axes of rotation A and C of the workpiece carrier assembly define two degrees of freedom so that this workpiece assembly 14 has five degrees of freedom.

In the embodiment illustrated in Figure 2, the workpiece carrier assembly has four degrees of freedom, two in rotation and two in translation. The sensor 15 has a degree of freedom. According to other embodiments not shown, it is possible to replace the table 16, for example by a robot arm benefiting from five or even six degrees of freedom or by any equivalent support, sufficiently rigid to ensure the required measurement accuracy. In practice, the total number of degrees of freedom between the workpiece assembly and the sensor must be a minimum of five, the number of degrees of freedom of the sensor is a maximum of one and the number of degrees of freedom per axes rotation is a minimum of two.

In such configurations, the part to be checked can be positioned opposite the sensor in positions allowing measurements to be taken in the extension of the sensor. These configurations therefore make it possible to carry out measurements under optimal conditions.

The machine according to the invention can be used to control different characteristics of mechanical parts on different types of parts. A characteristic commonly checked on this type of machine is the size and more precisely the match between the actual dimensions of the part being checked and the combination of the desired size and tolerances for that part.

First, when the dimensions of a part need to be controlled, the mechanical part is placed on a suitable fixture so as to be able to prevent this mechanical part from moving relative to the fixture. The fitting is fixed to the workpiece carrier assembly 14 and more precisely to the workpiece support 26 of the caliper 25.

When a characteristic of a control point is to be measured, the sensor 15 making it possible to measure this determined characteristic is chosen and positioned in the barrel 30 so as to be operational.

The point to be checked or control point concerned is positioned opposite the sensor 15, preferably in such a way that the plane tangent to the control point is perpendicular to the measurement axis of the sensor or vertical axis z. Such positioning is possible due to the fact that the workpiece-holder assembly is capable of moving according to at least four degrees of freedom, at least two of which are linked to axes of rotation.

In the embodiment illustrated by FIG. 1, the positioning of the control point opposite the axis of the sensor is done by using in combination, the base linear guides x and y making it possible to position the movable plate 21, the guide vertical linear allowing to position the table 16 and the motors for the positioning of the console 27 and the workpiece support 26.

If the measurement is carried out by detecting a contact between the mechanical part and the sensor, the mechanical part is preferably moved along a vertical axis z by moving the table 16 along the uprights 17 until a contact is detected , but also along the x and y axes. The console 27 and the workpiece support 26 are also moved around their respective axes of rotation A and C, such that the control point is opposite the sensor, a plane tangent to this control point being substantially horizontal.

When contact between the part to be checked and the sensor is detected, the linear position of the table along the z axis is determined, as well as the linear positions of the movable plate 21 along the x and y axes. The angular positions along the axes of rotation A and C of the console 27 and of the workpiece support 26 are also determined by the means for measuring the position of the workpiece carrier assembly. The combination of these different positions makes it possible to determine the coordinates of the control point. The vertical z axis is also called the "sensor measurement axis" because the sensor measures along this z axis.

Conventionally, the coordinates of a set of control points are determined by repeating the operations described above, until all the desired control points have been measured. The coordinates of this set of points are then processed so as to provide the user with the information sought. This information can be of different kinds. In many cases, the information will be an assessment of the conformity of the checked part, i.e. an answer to the following question: do the dimensions and geometry of the part as measured conform to the theoretical part, in tolerances defined for this part. The measured and processed coordinates are compared to theoretical values of the part to be inspected, then it is determined whether the measured coordinates correspond to these theoretical values, taking into account the tolerances allowed for this part or for the different points of the part.

The mathematical treatment of the coordinates of the controlled point set is conventional and is not described in more detail here.

The characteristic checked on the mechanical part can also be a surface finish. For this purpose, a suitable sensor is used, for example a white light sensor or a laser. In the case of using light waves, it is all the more important that the tangent to the part to be checked at the level of the control point is substantially perpendicular to the vertical axis. This can be achieved as indicated above, namely by adjusting the linear movements of the table 16 and the movable plate 21 and the rotary movements of the workpiece support 26 and of the console 27.

It should be noted that the invention makes it possible to control or measure several characteristics of the same mechanical part without having to transfer the part from one machine to another. Usually, each feature is controlled by a different sensor. The various sensors can be mounted on a barrel or other similar support so that they can be available when a corresponding characteristic is checked. These sensors are therefore interchangeable, in that the sensor used to measure or control a certain characteristic of the mechanical part can be replaced by another sensor when another characteristic of the mechanical part needs to be checked.

In the method of the invention, it is possible to measure values corresponding to a given characteristic by means of a suitable sensor, then to process the measurements before going on to check another characteristic of the mechanical part. Each set of measured values, corresponding to a determined parameter of the mechanical part to be checked, is the subject of a specific treatment. It is also possible to take measurements with several sensors corresponding to different characteristics to be checked, before processing these different measurements. In this case, the measurements are processed in the same processing step, even if the measured values correspond to different characteristics of the mechanical part to be checked. It is also possible to combine these different ways of doing things, namely processing for example a set of measurements corresponding to a single parameter to be checked, before processing a set of measurements corresponding to several parameters to be checked.

In the embodiment illustrated by FIG. 2, the part is positioned similarly to the positioning explained with reference to FIG. 1. However, the vertical or z-axis movement is not performed by table 16, but by sensor 15.

The measurements are carried out in the same way, whether it is the table 16 which moves along the vertical axis or the sensor 15.

This type of checking machine is particularly interesting for several reasons. One is the fact that the sensor measures in the axis of its movement. This fully responds to Abbot's principle which says that: "If one wants to avoid parallax errors, the measuring system must be aligned with the line in which the displacement (giving the length) must be measured on the part to be measured. treat. »This displacement axis is called the sensor measurement axis.

In the majority of measuring or control machines, this Abbot principle is not respected, which implies greater imprecision in the measurements.

Another interesting point is the fact that the inspection machine according to the invention is particularly compact. Indeed, the sensor which performs a measurement is either stationary or mobile in a single direction or along a single axis and does not need to move around the part to be checked. This implies that the volume required to reach the different places where the part is to be checked can be relatively small compared to the size of the part to be checked.

This feature has an advantage in that the inspection machine can be placed in a place where available space can be limited, typically a production workshop.

The movement of the sensor along the vertical axis or z axis can also advantageously be used to allow easy change of the sensor, this sensor being suitable for the type of part to be checked, the check to be carried out and certain requirements or specificity of the check.

As regards the sensor, it is possible to provide a fixed sensor at least during one measurement cycle, linked to the measurement gantry. The fixed nature of this sensor implies that it does not undergo any acceleration / deceleration and therefore no measurement errors or uncertainties that may be related to the displacement of the sensor during a measurement cycle.

The sensor can be mobile along the vertical axis, this mobility being used only to facilitate the change of sensor, in order to adapt this sensor to the measurement or control to be performed.

One advantage of the machine according to the invention is the fact that the encoders or more generally the means for determining the position of the components of the workpiece carrier assembly are arranged near the workpiece. This makes it possible to avoid parasitic torques and increases the precision and repeatability of measurements.

The machine according to the invention therefore allows reliable and efficient control of various parameters of a mechanical part, while being compact. This compactness also makes it possible to reduce structural length variations due to temperature variations.

This machine allows the use of different sensors capable of measuring different characteristics of the mechanical parts to be controlled, which allows a complete control of a part without having to use several control machines, nor to move the part to be controlled on several fixtures. .

The machine of the invention is illustrated in a form in which the part to be inspected is arranged on a movable plate in a plane. It is clear that other embodiments could be used as long as these embodiments allow the part to be inspected to be presented opposite the sensor, in order to carry out the required inspections.

Claims

1. Machine for checking mechanical parts, this machine comprising at least one frame (12), a workpiece carrier assembly (14) on which the mechanical part to be checked is placed and at least two sensors (15) arranged to check at least one characteristic of said mechanical part, this machine being characterized in that the workpiece carrier assembly (14) is movable relative to the frame (12) of the machine according to at least four degrees of freedom, at least two of said degrees of freedom being defined by two axes of rotation (A, C) that are not collinear with each other, this workpiece carrier assembly (14) being movable so as to allow at least one point of said mechanical part to be checked to be positioned opposite the 'one of said at least two sensors (15), in that the total number of degrees of freedom of the workpiece carrier assembly (14) and of the sensor (15) opposite which the workpiece to be checked is positioned is at least equal to five, in that the control machine (10) further comprises means of e measurement arranged to determine the position of this workpiece carrier assembly (14) and in that at least one of said sensors is supported by a gantry (13) linked to the frame (12) of the machine.

2. Control machine according to claim 1, characterized in that said at least two sensors are arranged on a barrel (30) supported by said gantry (13).

3. Control machine according to claim 1, characterized in that the sensor (15) used to control a part is fixed during a measurement cycle.

4. Testing machine according to claim 1, characterized in that the workpiece carrier assembly (14) is movable according to at least five degrees of freedom.

5. Control machine according to claim 1, characterized in that the sensor (15) used to control a part is movable in translation along a linear axis during a measurement cycle.

6. Control machine according to claim 1, characterized in that the workpiece carrier assembly (14) comprises a plate (21) movable along at least two basic linear axes (x, y) defining two degrees of freedom and according to at least two axes of rotation (A, C) defining two other degrees of freedom.

7. Control machine according to claim 6, characterized in that the two basic linear axes (x, y) are mutually orthogonal and / or in that the two axes of rotation (A, C) are mutually orthogonal.

8. Control machine according to claim 6, characterized in that the plate (21) is movable along a third linear displacement axis (z) orthogonal to the two basic linear displacement axes (x, y).

9. Testing machine according to claim 1, characterized in that the sensors (15) are interchangeable.

10. Method of checking mechanical parts by means of a machine comprising at least one frame (12), a workpiece holder assembly (14) on which the mechanical part to be checked is placed and at least two sensors (15), at least one of said sensors being supported by a gantry (13) linked to the frame (12) of the machine, these sensors being arranged to control at least one characteristic of said mechanical part, said part holder assembly (14) being movable by relative to the frame (12) of the machine according to at least four degrees of freedom, at least two of said degrees of freedom being defined by two axes of rotation (A, C) not collinear with each other and the total number of degrees of freedom of the workpiece carrier assembly (14) and of the sensor (15) opposite which the workpiece to be checked is positioned being at least equal to five, this method comprising the following steps:

a) definition of a set of check points arranged on the mechanical part to be checked;

b) choice of a sensor (15) suited to the characteristic to be checked on said mechanical part;

c) positioning of said mechanical part on said part holder assembly (14) of the checking machine;

d) movement of the workpiece carrier assembly (14) along said at least four degrees of freedom so as to position a control point opposite the chosen sensor (15);

e) measuring, by means of said selected sensor (15), the characteristic to be checked of the control point positioned opposite this sensor;

f) storage of the value of the characteristics measured in connection with a position of the sensor during the measurement; g) repetition of steps d to f for the different control points; and

1 1. Control method according to Claim 10, characterized in that the mechanical part to be controlled is positioned so that a measurement axis (z) of the sensor (15) chosen to control a characteristic on said mechanical part is normal to a plane tangent to the control point.

12. Control method according to claim 10, characterized in that the selected sensor (15) is stationary during a control cycle of a characteristic of the part to be controlled.

13. Control method according to claim 1 1, characterized in that the selected sensor (15) is movable along a single linear displacement axis during a control cycle of a characteristic of the part to be inspected, this linear displacement axis being coincident with the measurement axis of the sensor (15).

14. Control method according to claim 10, characterized in that at least the position of the selected sensor (15) and the position of the workpiece carrier assembly (14) are stored with respect to each degree of freedom.

15. Control method according to claim 10, characterized in that several sensors are used to control several parameters of the part to be controlled.