FR2486264A1 - Localisation system for tool position on machine tool - uses probe at reference location to produce electrical position signal for control processor - Google Patents

Abstract

The appts. uses a probe (2) with four flat surfaces (3-6) coupled into a box (1) by a moving element (10). The box is attached to a cross member at a reference point on the machine and contains hydraulic and electrical connections for the probe movement. Contact between the tool point (7) and the probe is transmitted into the box for conversion to an electrical signal to indicate the displacement whatever its direction. Instructions for the measurement are issued from the machine tool control system. The measurements for the probe are limited to a vertical axis and one longitudinal axis.

Description

Method and device for introducing tool corrections on a numerically controlled machine.

The present invention relates to a method for introducing tool corrections on a numerically controlled machine of the type comprising a type command director.
CNC (Computer Numerical Control; in French: Numerical control with calculator), carrying out tool corrections and having in memory the reference origins of the measurements in a longitudinal direction, called the axis
X, in a vertical direction, perpendicular to the X axis, called the Z axis and possibly in other directions belonging to the plane containing the X and Z axes and called the Ul ... .U2n axes.

The invention also relates to a device for introducing tool corrections on a numerically controlled machine.

Certain types of parts machined on a machine tool require numerous dimension checks, the cost of which may be equivalent in certain cases to the cost of performing the part. This is so in certain known methods where it is frequent, for example, to use a measurement station independent of the machine for the automatic control of the part as soon as it is executed. The information collected can in this case be used for the execution of the next part in order to be within the desired tolerance.

Improvements have been proposed which make it possible, for example, to carry out part of these checks on the machine in an automatic manner and then to introduce the information collected in the command director of the numerically controlled machine. The information is thus used to carry out a finishing pass taking into account the measurement of the pre-finish or even for the execution of the following parts.

One or other of these known methods also makes it possible to detect the wear of the tool during the control of the finished part. The introduction of tool corrections in the "command director" however presents the risk of possible errors at this stage.

 It is also known to use presetting benches for very precise adjustment of tools outside the machine. This operation introduces long adjustment times, requires the use of fairly sophisticated equipment and constitutes an unfavorable element in the search for minimum cost.

It will also be noted that the known methods which have been recalled use, for dimension measurements on workpieces, feelers whose contact key is spherical or of substantially equivalent shape, and it turns out that these shapes are unsuitable for measuring a precise dimension on the tool tip.

In order to avoid the various drawbacks of the previous methods, the object of the invention is to propose a method for controlling and measuring tools directly on the machine which exploits the possibility offered by known equipment of a numerically controlled machine for enter the tool corrections in the command director.

To this end, the method according to the invention is characterized in that a measurement of the location of the tool tip along the X axis and an identical measurement along the Z axis are introduced into the command director of so as to automatically update the tool correctors existing in said command director. Optionally, the same is done for the measurements along the axes U1 ... U2n.

According to the invention, said location measurement is advantageously obtained along the X axis by the emission of a signal corresponding to the contact of the tool with a material plane, perpendicular to the X axis, when the tool moves in the direction of said X axis. The location measurement is advantageously obtained respectively along the Z axis in a similar manner and possibly likewise along the axes U1 ... U2n.

In an advantageous embodiment, the displacement of the tool tip in the direction of any one of said materialized planes is, according to the invention, at high speed, from the origin of the measurement to a point Al (respectively A2 and A3) located on the X axis (respectively Z and U1) and corresponding to the position of the tool tip given by the instruction program appearing at the command director for the execution of the machining of a part. Said movement is done at slow speed, from said point Ai (respectively A2 and A3) to a point Mi (respectively M2 and M3) located on the X axis (respectively Z and U1) and corresponding to the contact of the tool with said material plane, at the theoretical point where the tool tip should have been located in the absence of a defect.

Advantageously, said updating of the tool correctors in the command director takes place with respect to said point M1 (respectively M2 and M3) taken as a reference.

The device according to the invention is used for the introduction of tool corrections on a numerically controlled machine of the type comprising a command director of the CNC (Computer Numerical Control) type, in French: Numerical Control with calculator) making the corrections tool and having in memory the reference origins of the measurements along a longitudinal direction, called the X axis, following a vertical direction perpendicular to the X axis, called the Z axis and possibly along other directions belonging to the plane containing the axes X and Z and called axes U1 ... U2n. This measuring device is characterized in that it comprises a probe of polygonal shape with 2 (2n + 2) sides coming into contact along any one of its sides with the tip of the tool, two of said sides being parallel to the X axis, two other sides being parallel to the Z axis and the other sides being parallel by two respectively to the axes
U1 ... U2n and in that said contact triggers an electrical signal in a box associated with said probe which introduces into the control director the measurement of the position of the tool tip relative to the reference point of origin and causes , from this measurement, the automatic updating of the tool correctors existing in said command director.

Advantageously, a square or octagonal shape probe is used, one corresponding to the axes X, Z and the other to the axes X, Z, U1, U2, U1 and U2 being oriented at 450 with respect to X and Z .

Advantageously, said probe can occupy two pre-established positions: an "out" position during the approach of the tip of the probe tool and a "retracted" position, the execution of which is triggered by an order from the command director. In the event of a system failure, the retraction order is triggered safely by the contact of the probe on the tool.

Advantageously, said probe and associated housing are fixed to a cross member of said machine.

The process according to the invention has many advantages. It contributes in fact to advantageously reduce the operating costs and the costs of controls in the operation of numerically controlled machines which represent a large part of financial fixed assets and on which parts are generally machined with high cost prices. .

The method according to the invention thus makes it possible to obtain a reduction in the dead times for checking the machined parts. I1 allows, by controlling the factors relating to the wear of the tool, to obtain precise, correct dimensions on the machined parts. This process dispenses with a measurement of a machined part which involves the axes of the machine and risks being distorted by errors.

The method according to the invention when the measurements are limited to the two axes X and Z is suitable for tool corrections for machining of the paraxial type. On the other hand, for contouring machining, the method using one or more additional measurements along axes belonging to the plane containing the axes X, Z and for example along one or two axes oriented at an angle of 450 relative to the axes X and Z, makes it possible to detect the presence of any possible defect on the tool tip and to check the tool radius or the centering of a tool of circular shape.

The method according to the invention also avoids that, when changing a tool, an error in the positioning of the tool tip, due to various causes coming from the machine or its size, resulting in finishing , faults on the workpiece, because the process allows this type of anomaly to be detected.

The method according to the invention finally dispenses, when a tool presetting is carried out, which is usual for numerically controlled machines, of great precision for this presetting of tools outside the machine and consequently makes it possible to reduce the time devoted to this operation and to operate a simplification of the adjustment benches.

The characteristics and advantages of the invention will be better understood on reading the description which follows of an embodiment of the invention. This description is made with reference to the accompanying drawings in which
- Figure 1 is a schematic representation
of an operating cycle in a first
embodiment of the method according to the invention;
- Figure 2 is a schematic elevational view
of a tool measuring device according to a mode
of the invention, shown assembled
on a CNC machine
- Figure 3 is a schematic view, taken in view
from above of figure 2
- Figure 4 is a schematic representation
partial of an operating cycle in a
second embodiment of the method according to
the invention.

An example of an operation for introducing tool corrections on a numerically controlled machine, according to the method according to the invention, can be described as follows, in a first embodiment, with reference to the operating cycle schematically represented in FIG. 1. This figure represents the displacements of the tool in a plane (X, Z), the X axis corresponding to a longitudinal direction relative to the machine and the Z axis corresponding to a vertical direction relative to the machine, perpendicular to the X axis.

The machine control director has a specific program for tool measurements. This program is triggered for an axis, for example, the X axis.

At the start of the cycle, the tool after a movement Z1 in a direction parallel to the axis Z, of one of the carriages is in alignment with a measuring device D, at a point Po at the start of the measuring cycle. A fast speed is then engaged on the other carriage and the tool tip moves to a point A1, in a direction parallel to the axis X and covering a distance X1.

At point A1, a slow speed is engaged and the tool tip moves to a point M1, where it comes into contact with a material plane, parallel to the Z axis and perpendicular to the X axis, which is represented by its trace EF in the plane (X, Z). This contact corresponds to the emission of a signal which introduces the measurement into the command director. In fact, during this phase, at the level of the command director's program, the instructions defining the tool offset made it possible to reach point A1, and a special register then counts down the distance X2 separating point A1 from point M1.

This distance is added algebraically to the tool offset. A special sequence updates the active tool offset along the X axis.

The "updating" cycle of the tool corrector which has just been described thus makes it possible to introduce into the command director a measurement corresponding to the difference between the theoretical position of the tool tip represented by a plane materialized and the actual position of the tool tip, this deviation being due for example to wear of the tool or to a preset error. This updating of the tool corrector prevents the said deviation of the position of the tool tip from being fully reflected through the instructions supplied to the machine by the order director, on the dimensions of the finished part obtained after the machining cycle. , but it thus allows to obtain precise, correct dimensions of the workpiece. Dimension accuracy as good as + 0.005 mm is thus obtained.

The cycle described for the X axis is reproduced in a similar manner for the Z axis. As soon as it comes into contact at the point
Mid of the tool tip with the materialized plane, the movement of the carriage is reversed and by traveling a distance X3 in a direction parallel to the axis X, the tool tip returns to the point Po at the start of the measurement cycle. The tool, carrying out a displacement Z2 in a direction parallel to the axis Z to a point P2 then a displacement X4 in a direction parallel to the axis
X, returns to alignment with the measuring device D, at a point P4. A fast speed is then engaged on the vertical movement carriage and the tool tip moves to a point A2 in a direction parallel to the axis Z and covering a distance Z3.

At point A2, a slow speed is engaged and the tool tip moves to a point M2 where it comes into contact with a material plane, parallel to the X axis and perpendicular to the Z axis, which is shown. by his trace
FG in the plane (X, Z). In a similar way to what has been described for the measurement along the X axis, this contact corresponds to the emission of a signal which introduces the measurement into the command director where a special register counts down the distance Z4 separating the point A2 from point M2.

This distance is again added algebraically to the tool offset and a special sequence makes it possible to update the active tool offset along the Z axis.

As soon as the tool tip comes into contact at point M2 with the materialized plane, the movement of the carriage is reversed and by traveling a distance Z5 in a direction parallel to the Z axis, the tool tip comes to the point P4 end of the measurement cycle.

Other measurement cycles according to the method according to the invention are possible although they have not been shown in the drawings. In particular, all the distances represented in FIG. 1 (X1, X2, X3, X3> X4, and Zi, Z2, Z3, Z4, Zg) can vary. The measurement cycle has been represented with respect to two perpendicular material planes whose traces on the plane (X, Z) are
EF and Ft, but this cycle can be performed with respect to
any combination of two mat planes
perpendicular to each other, taken from among the four planes
whose traces on the plane (X, Z) form a square, of
sides EF, FG, GH and HE which can be in a mode of
realization of the sides of a square probe 2. Other modes
approach of the tool tip to one of the material planes
read, different from that which has been described in the mode
of realization which has been proposed by way of example not
limiting, can also be carried out within the limits
of the process according to the invention.

A second embodiment is shown schematically
and partly in Figure 4. The operating cycle
reproduces the elements previously described with reference
in the first embodiment according to FIG. 1. On
found in this second mode the axes X and Z, the materialized planes respectively perpendicular to the axis X,
represented by their traces JK and RN, and at the Z axis, represented
felt by their traces LM and ST. Additional management
shut up called axis U1, belonging to the plane containing the
X and Z axes and oriented at an angle of 450 relative to
to the X and Z axes is used for displacements of
the tool obtained by composition of movements according to
X and Z axes. Material planes perpendicular to
the axis U1, are represented in the plane by their traces
KL and RS. A direction called axis U2, belonging to the plane
containing the X and Z axes and perpendicular to the U1 axis
can also be combined. The cycle described for
axes X and Z is reproduced similarly for the axis
United . From a point Po at the start of the measurement cycle,
the tool carrying out a displacement Z2 in a direction
parallel to the axis Z, comes into alignment with the measuring device D 'at a point P2. Following a combined movement of rapid speed movement on the carriages, the tool tip moves to a point A3 in a direction parallel to the axis U1 and traveling a distance ul.

At point A3, slow speeds are engaged and the tool tip moves by traveling a distance u2 to a point M3 where it comes into contact with the materialized plane of trace KL. Similar to the measurements along the X or Z axes, the measurement is again introduced into the command director and an update of the tool offset is performed.

In this embodiment, a measurement along the axis U2 is still possible. Other embodiments which will not be described in more detail since they are evident from those which have been described can be obtained. The materialized plans can for example be in higher number such as 2 (2n + 2) and additional directions can be defined for the measurements, such as U1 ... U2n-
The device for introducing tool corrections is shown in Figures 2 and 3 in place for use, mounted on a numerically controlled machine.

In this embodiment, shown by way of nonlimiting example, the machine is a vertical lathe. This type of machine can pose, with respect to the aims pursued by the invention, some specific problems linked to the size of the machine and to that of the large parts being machined. The previously noted advantages of the invention thus find a particularly interesting application in this case.

As shown in FIGS. 2 and 3, the device for introducing tool corrections according to the invention consists of a housing 1 which is fixed with reference to the machine, on a cross member 11, and of a probe 2 associated with this case 1. The probe 2 has four flat faces 3, 4, 5 and 6, arranged in a square. The location of the tool tip 7, mounted on a tool holder 5, placed on the slide 9 of the machine, is made by contact on one of the four flat faces 3, 4, 5 or 6 of the probe. 2, during a movement and approach cycle, following the instructions provided by a command director equipping the machine and which is provided with a specific program of instructions for this purpose.

The probe 2 is connected to the housing 1 by a movable part 10 which allows the exit of the probe 2, represented in position 2a in FIG. 3, and the retraction of the probe 2 in the housing, represented in position 2b in FIG. 3. In one embodiment, the output of the probe 2 is triggered during the approach cycle of the tool tip 7, when this approach changes from a fast speed to a slow speed and the retraction of the probe 2 is triggered by an order from the command director and; in the event of a fault, in safety by the contact of the tool tip 7 on the probe 2. These movements of the probe 2 are controlled by the instructions of the program with which the command director is provided and they are executed by any appropriate means, for example a double-acting hydraulic cylinder. This contact between tool tip 7 and feeler 2 causes an appropriate mechanical transmission known per se, which will not be described here in more detail for this reason (reference may be made to French patents 1 504 799 and 1 594,566 previously filed by the Applicant). By this transmission, contained in the housing 1, any contact on the probe 2 is transformed, whatever its direction, into an axial displacement. This movement acts in the housing 1 on a high precision electrical contact which causes the emission of an electrical measurement signal transmitted to the machine control director where, according to the specific program of instructions with which it is provided for this purpose , a special sequence allows an automatic "update" of a corresponding tool offset.

The box 1 has the necessary electrical and hydraulic connections, and the connections to the machine are provided by an electric cable and two hydraulic hoses.

In another embodiment, the probe 2A, schematically represented in FIG. 4 by its projection in the plane (X, Z), has eight planar faces arranged in a regular octagon. These faces are used in a similar way to the four faces of the square probe which has just been described and the device also allows the automatic updating of the tool correctors.

According to embodiments not shown, the probe can have 2 (2n + 2) planar faces arranged in a regular polygon with 2 (2n + 2) sides and the probe can also have a cylindrical shape.

Claims (12)

1. Method for introducing tool corrections into a numerically controlled machine of the type comprising a command director of a known type CNC carrying out tool corrections and having in memory the reference origins of the measurements following at least two directions, namely a longitudinal direction called the X axis and a vertical direction, perpendicular to the X axis, called the Z axis, characterized in that at least two measurements of location of the tool tip, namely a measurement along said X axis and an identical measurement along said axis Z are introduced into the command director so as to automatically update the tool correctors existing in said command director. 2. Method for introducing tool corrections on a numerically controlled machine according to claim 1, characterized in that said measurements of location of the tool tip are limited to the X and Z axes. 3. Method for introducing tool corrections on a numerically controlled machine according to claim 1, characterized in that said measurements of location of the tool tip are made along said X axis, along said Z axis and along at least a direction, belonging to the plane containing the X and Z axes, called the U1 axis. 4. A method of introducing tool corrections on a numerically controlled machine according to claim 3, characterized in that said measurement of location of the tool tip along said axis X (respectively, Z and U1) is obtained by l 'emission of a signal corresponding to the contact of the tool with a material plane, perpendicular to the X axis (respectively, Z and U1) when the tool moves in the direction of said X axis (respectively, Z and U1) . 5. Method for introducing tool corrections on a numerically controlled machine according to any one of claims 3 and 4, characterized in that the displacement of the tool tip, from the origin of the measurement up to '' at a point AI (respectively, A2 and A3) on the X axis (respectively, Z and U1) and corresponding to the position of the tool tip given by the instruction program given to the command director for the execution of the machining of a part, is done at high speed and from said point Al (respectively, A2 and A3) up to a point M1 (respectively, Mz and M3) located on the X axis (respectively, Z and U1) and corresponding to the contact of the tool with said materialized plane, at the theoretical point oli should have been located tool tip in the absence of a fault, the movement is made at slow speed. 6. A method of introducing tool corrections on a numerically controlled machine according to claim 5, characterized in that said updating of the tool correctors in the command director takes place with respect to said point Mi (respectively, M2 and M3) taken as a reference. 7. Device for the introduction of tool corrections on a numerically controlled machine of the type comprising a CNC type command director carrying out tool corrections and having in memory the reference origins of the measurements along a longitudinal direction called the X axis , in a vertical direction perpendicular to the X axis, called the Z axis and in an even number 2n of combined directions, in a plane containing the X and Z axes and called the axes U1 ... U2n, characterized in that it comprises a polygonal probe (2; 2A) with 2 (2n + 2) sides coming into contact along any one of its sides with the tool tip, two of said sides being parallel to the X axis, two other sides being parallel to the axis Z and the other sides being parallel by two respectively to the axes Uî. . .U2n, and in that said contact triggers in an enclosure (1) associated with said probe (2; 2A) an electrical signal which introduces into the command director the measurement of the position of the tool tip (7) relative to the reference point of origin and causes from this measurement the automatic updating of the tool correctors existing in said command director. 8. Device for introducing tool corrections according to claim 7, on a numerically controlled machine of the type comprising a command director of the CNC type making the tool corrections and having in memory the reference origins of the measurements according to a longitudinal direction called axis X and in a vertical direction perpendicular to axis X and called axis Z, characterized in that it comprises for n = O, a square-shaped probe (2) coming into contact according to any one of its sides (3, 4, 5, 6) with the tool tip (7), two of said sides (4, 6) being parallel to the X axis and the other two sides (3, 5) being parallel to the axis Z, and in that said contact triggers in an enclosure (1) associated with said probe (2) an electrical signal which introduces into the control director the measurement of the position of the tool tip (7) relative to the point of reference origin and causes from this measurement the automatic updating of the correctors of tool existing in said command director. 9. Device for introducing tool corrections according to claim 7, on a numerically controlled machine of the type comprising a command director of the CNC type making the tool corrections and having in memory the reference origins of the measurements according to a longitudinal direction called X axis, in a vertical direction perpendicular to the X axis, called Z axis, in a combined direction, in a plane containing the X and Z axes, oriented at an angle of 450 relative to the previous ones, called U1 axis , and along another combined direction of the first two, in a plane containing the axes X and Z, perpendicular to the axis U1 and called the axis U2, characterized in that it comprises for n equal to 1 a probe of octagonal shape (2A) coming into contact along any one of its sides with the tip d tool (7), said sides being parallel by two respectively to each of the axes X, Z, U1> U2, and in that said contact triggers in a housing (1) associated with a probe (2A) an electrical signal which introduces in the command director, the measurement of the position of the tool tip (7) relative to the reference point of origin and, on the basis of this measurement, automatically updates the tool correctors existing in said command director. 10. Device for introducing tool corrections on a numerically controlled machine according to any one of claims 7, 8 and 9, characterized in that said probe (2; 2A) can occupy two preset positions an "out" position (2a) during the approach of the tool tip (7) of the probe (2) and a "retracted" position (2b) whose execution is triggered by an order from the command director. 11. Device for introducing tool corrections on a machine. Numerical control according to claim 10, characterized in that the retraction order in the event of a system failure is triggered safely by the contact of the probe (2) on the tool tip (7). 12. Device for introducing tool corrections on a numerically controlled machine according to any one of claims 7 to 11, characterized in that said associated housing (1) and probe (2) are fixed on a cross-member (11 ) of said machine.