EP0512956A1 - Numerically controlled grinding machine - Google Patents

Abstract

The tool-holder turret (3) is movable along the X and Z directions with respect to the workpiece-holder table (2), so that it is possible for each of the tools (9a, 10a, 11a, 12a) to machine a surface on the workpiece (6). The support (20) of the trueing unit (4) supports a rotating body (22), the arm (23) of which is provided at its end with a tracer, while the two vertical arms are equipped with diamonds. The tracer (18), which is firmly secured to the table (13) makes it possible to detect the exact positions of the trueing tools with respect to a reference which can consist of the detecting surfaces of the tracer (23). The measurements carried out by displacing the tracer (18) are stored in memory. Other measurements relating to the dimensions and to the real shape of the grinding tools (9a, 10a, 11a, 12a) are also taken by displacing the table (13), so that these tools are traced by the detecting surfaces of the tracer (23). These data make it possible to customise the trueing programme, which is thereupon carried out automatically and causes the wheels to take on a well determined reference shape. Following which, the grinding operation on the workpiece (6) can be controlled automatically. <IMAGE>

Description

Recent developments in the field of grinding machines have placed designers facing difficulties of various kinds.

As the machines became more and more powerful, they were equipped so as to be able to carry out more and more varied operations. For example, the tool turret is often equipped at the present time with two, three or even four grinding tools which can intervene successively during each sequence of grinding operations carried out on a workpiece. The workpiece table can be provided with a digital axis of rotation allowing the rectification of internal or external conical surfaces, of generally circular shapes. It must therefore be able to be oriented at will in a precise manner. In addition, the machine is often equipped with several dressing tools, for example several diamond holders of different shapes and a rotary wheel. Each of these different tools is brought into the working position during each dressing operation carried out on one or other of the grinding wheels mounted on the tool-holder turret.

We realize that this complex equipment tends to complicate and make delicate and long any operation of setting up a grinding machine for the execution of grinding operations on a series of identical parts.

On the other hand, with the increase in spindle rotation speeds and the complexity of the arrangement of tool-holder turrets, the risks run by operators who check the positioning tools during grinding wheel dressing operations increase considerably. For this reason, moreover, regulations have been imposed on manufacturers concerning safety devices to be used during the operation of grinding machines. The latter must be fitted with doors which cannot be opened without safety measures having been taken and in particular without the rotary spindles having been stopped.

These and other difficulties have therefore led to the search for solutions. However, it has been realized that it was possible to overcome the difficulties set out above, with relatively simple means, and the present invention aims to define such means making it possible, in particular, in the setting in motion of a sequence of grinding operations: to simplify the work of the operator, to greatly reduce the time of adjustment, dressing of the grinding wheels and machining until obtaining an acceptable first part, to increase safety of the operation.

It is known in the field of grinding machines working in a linear fashion (DE-37 36 463) to fix a support for dressing tools on the workpiece table and a probe integral with the tool holder. These means make it possible to determine the exact position of the dressing tools and therefore to drive knowingly the dressing dressing operations. It is also known, from the same document, to provide a second probe in a fixed position and to check, by means of this probe the final dimensions of the parts, which makes it possible to know indirectly the wear of the tools. dressage. However, the teaching of this document only applies to linear grinding machines having a grinding wheel of which only the cylindrical surface is active. In addition, the document does not suggest means for automatically controlling a training operation.

The specification EP-0 281 835 describes a dressing turret in which several dressing tools are mounted radially on a head, itself capable of pivoting about its axis on the turret. The turret is integral with a tilting arm, the working position of which can be controlled by means of a probe cooperating with a reference surface. The content of this booklet does not, however, indicate any means for carrying out a fully automatic dressing operation.

The document DE-3 524 690 relates to the measurement of the characteristics of a disc-shaped grinding wheel and in particular to the use of piezoelectric type probes for this measurement.

Finally, GB-2 002 545 relates more particularly to the conduct of grinding operations on internal cylindrical surfaces. In this case, the parts are fixed in the clamp of a rotating spindle and the table on which the spindle is mounted carries a dressing tool so that displacements of this table perpendicular to the axis of the grinding wheel allow to draw that -this. The operation is carried out according to data supplied by a measuring instrument, without any automation of the dressing operation being envisaged.

The object of the present invention is to provide a method and a machine by means of which it is possible to carry out a dressing operation fully automatically so that the difficulties indicated above are eliminated.

In a first aspect, the present invention relates to a method of starting a grinding machine equipped with a workpiece table, a tool holder carrying at least one grinding tool, a dressing turret on which are mounted one or more dressing tools having a dressing edge, and a numerical control comprising a memory, for grinding operations on several different surfaces in the same room, characterized by the following stages:
a probe having at least two detector faces is placed in a predetermined position on the tool holder,
a measurement step is carried out in which the sensing faces of the probe are brought into predetermined relative positions with respect to one or more dressing edges of the dressing tool (s) and the positions of the corresponding tool holder are recorded in the memory at each of said predetermined relative positions,
and after the measurement step, the position records stored are used to customize a program for an automatic dressing operation. In a more elaborate form of implementation of this method, a second probe is also used located in a predetermined position relative to a machine reference and by means of this second probe, measurements are taken of the positions of the surfaces of the grinding tools, so that you can determine the initial dimensions of the tools and program the automatic dressing operation accordingly.

In a second aspect, the object of the invention consists of a grinding machine comprising on a base a workpiece table, a dressing turret and a tool turret, respectively equipped with a drive spindle for a workpiece. machining, at least one dressing tool, and at least one dressing tool grinding, these turrets being capable of relative displacements at least on one of the axes X and Z between the tool-holder turret on the one hand and the workpiece carrier and the dressing turret on the other hand, characterized in that the turret carries -tools and another part of the machine are respectively equipped with a first position probe and a reference solid, the digital control being arranged for the automatic execution of a start-up operation comprising a setting step of measurements during which said probe is successively brought into predetermined relative positions with respect to at least one of the dressing tools and with respect to at least one of the surfaces of the reference solid.

• la fig. 1 est une vue en perspective schématique d'une rectifieuse équipée en vue de la mise en oeuvre du procédé,
• la fig. 2 est une vue en plan de dessus d'une rectifieuse d'un type différent de celui de la fig. 1 également équipée pour la mise en oeuvre du procédé, et
• la fig. 3 est une vue en coupe selon la ligne A-A de la fig. 2.

The essential characteristics as well as certain optional features of the start-up process and of the machine defined above are described below by way of example with reference to the accompanying drawing, of which

• fig. 1 is a schematic perspective view of a grinding machine equipped for the implementation of the method,
• fig. 2 is a top plan view of a grinding machine of a type different from that of FIG. 1 also equipped for implementing the method, and
• fig. 3 is a sectional view along line AA of FIG. 2.

The grinding machine shown in fig. 1 comprises the following main equipment: a base 1, a workpiece table 2, a grinding tool holder turret 3 and a dressing turret 4. The table 2 carries a workpiece spindle 5 driven in rotation around a horizontal axis. To this spindle is fixed a workpiece 6. A motor 7 provides the drive of spindle 5 in rotation. The workpiece table 2 is movable on the base 1, on the one hand around a vertical axis of rotation (axis B) and, on the other hand, by the fact that it is mounted on a movable table 8 moving on an axis parallel to the X axis. Table 8 could also be fixed.

The turret 3 comprises four grinding tools 9, 10, 11 and 12 which are fixed to a table 13 carried by a sliding system. This comprises, according to fig. 1, a transverse slide 14 movable along the X axis and a longitudinal slide 15 movable along the Z axis on a slide 16. As a variant, the slide system could only comprise the Z axis (slide 15 movable on slide 16) .

Finally, the dressing unit 4 comprises a support 17 on which one or more rotating or fixed dressing tools can be fixed.

To allow the implementation of the method, the machine shown in FIG. 1 comprises various elements, part of which is not shown. This machine is a numerically controlled machine, so that a computer equipped with a memory and a data input device is associated with the machine. On the other hand, on the table 13 is fixed a probe 18 with a head which carries two detectors each having a planar detector face. These are oriented along the X and Z axes, respectively. The probe 18 is therefore capable of emitting signals at the moment when one or other of its detecting faces abuts on an obstacle or is at a predetermined minimum distance from the part to be detected. The signals cause the position of the table 13 to be memorized when they are transmitted. They make it possible to order said table. The movements of the probe are controlled by the movements of the table 13, that is to say by maneuvers of the slides 15 and 14 supporting this table. The positions of the table 13 are identified, in the computer, with respect to a machine reference which can be constituted by a reference solid fixed materially at a predetermined location on the base 1 or which can also be simply incorporated in the memory of the machine. The probe 18, which can be seen in FIG. 1 the support in the form of a fixed arm, can therefore be moved throughout the space swept by the movements of tables 14 and 15. It can in particular take position measurements of two reference faces of a solid 19 which has the in the form of a rectangular parallelepiped and which is fixed to the support of the dressing unit 17. As can be seen in FIG. 1, the vertical faces of the reference solid 19 are oriented along the axes X and Z. As the probe head 18 includes two position detectors whose vertical plane surfaces are oriented in the X and Z directions, these two plane faces being fixed one with respect to the other, it is possible, by a displacement of the base 13 in the direction Z, to bring the face Z of the probe against the corresponding face of the solid 19 and to measure the exact position of the dressing unit along the Z axis. By a similar operation, the position of the dressing unit can also be measured along the X axis.

A start-up program can therefore comprise instructions which move the table 13 as indicated above, and which, moreover, bring the faces X and Z of the sensors of the probe 18 into contact with selected edges on the various diamonds. The position values thus determined and stored are then used to determine the exact positions of the diamonds relative to the machine reference. As on the one hand the positions of table 13 are constantly referenced with respect to the reference of machine and, on the other hand, it is possible to impose on the grinding wheels set values for their diameter and the position of their front face, sufficient elements to program an automatic dressing operation are combined. These elements are introduced into the program, after which the table 13 is moved so that each of the grinding wheels 9a, 10a, 11a and 12a successively come into contact with a diamond placed in the working position. The machining diameter of each grinding wheel as well as in any case the position of one of the flat faces of the grinding wheels can be entered as a target value in the program, the different dressing operations taking place until the values have been reached. Thus, the dressing operation can be carried out in several successive phases until each of the grindstones has reached the shape and dimensions of the set point. In this form of implementation of the method, the axes are positioned taking into account the maximum diameter of the grinding wheels and these are moved until contact with the diamonds.

The probe 18 can also be used to measure and store the position of one or more surfaces of the part 6. This data then makes it possible to control the approach and the implementation of the tools during the machining of the first piece in the series. The machining of this first part can therefore be accelerated. Tool controls can be carried out at accelerated speed up to a short distance from the surfaces which must come into contact with the tools or with the probe, the rest of the movement taking place at slow speed.

Storing the position of the part attached to pin 5 can be of yet another benefit. It makes it possible to know in a way absolute the displacements that must be printed on table 13 for machining a surface if this surface is machined while the workpiece table 2 is placed in an oblique position relative to the Z axis. taking measurements, by means of the probe 18, of one or more surfaces of the part 6, makes it possible to locate the position of these surfaces relative to the center of rotation of the table 2, and consequently to calculate the corresponding position of these surfaces after the table has rotated.

The memorization of the positions of the essential edges of the diamonds, relative to the reference solid 19 thanks to the probe 18, presents not only the utility of allowing fully automatic dressing operations. It also allows a repetition, along the way, of the measurement taking operation on the dressing tools. Thus, possible wear of the diamonds can be detected and this can be taken into account in the intermediate dressing operations of the grinding wheels which must be carried out during the machining of a series of identical parts. Possible dimensional deviations due to diamond wear are avoided, and series of a large number of identical parts can be machined with precision, and this fully automatically.

The sensors of the probe 18 are elements known per se. Thus, for example, the flat surface of the detector may be one side of a patch secured to an electrical contact and supported by a spring opposite another contact which is fixed, all so that the closing of the switch takes place as soon as this patch touches a foreign body, which causes the sending of a signal in the detection circuit. However, any other detector construction can be used, including those without contact allowing to approach rotating dressing tools. In order to be able to work completely, the probe 18 will include at least two detectors, in some cases even three, two of which are oriented along the Z axis in opposite directions and the third along the X axis.

On the other hand, in a preferred construction of the device described, the probe 18 will be mounted in an eclipsable manner on the table 13, the arm of the support 18 being telescopic or pivoting, so as to free, during machining, the space that it occupies during start-up and allow these machining operations to take place freely.

With regard to the advantageous effects of the process described, there may be mentioned still others than those which have been mentioned until now. Thus in particular, as the positions of the diamonds and of the workpiece have been determined by the probe and stored, the program of the digital control can at any time carry out a functional check on these positions.

In addition, from the stored positions, it is still possible to carry out an anti-collision compatibility check of the machining program introduced in the digital control. This compatibility check can, for example, trigger an alarm if there is a risk of endangering the tools or the workpiece. It is also possible to provide a graphical display of the risks of collision on the control screen.

Another embodiment of a grinding machine enabling the execution of the start-up program described will be described below. But before moving on to the description of this other embodiment, it will be mentioned that in a variant of the embodiment of fig. 1, the reference solid 19 could also be introduced into the rotary assembly of the diamond holders. In this case, this reference solid would be integral with the diamond holders, but could be brought into an active position by rotation of the crew, each other rotational movement bringing an dressing tool into the active position.

Figs. 2 and 3 represent a different grinding machine from that of FIG. 1 and in which the means allowing the implementation of the start-up process described are partly designed differently. In fig. 2 and 3, the elements of the grinding machine which are of the same nature and play the same role as corresponding elements of the grinding machine of FIG. 1, are designated by the same reference signs. Thus, there is a base 1, a workpiece table 2, a tool turret 3 and a dressing turret 4. The workpiece table also has a spindle 5 carrying a workpiece 6. It is movable in rotation around 'a vertical axis 8.

The tool-holder turret 3 is supported by a table 13. It can also move along the Z axis and along the X axis. It is equipped with four grinding devices 9, 10, 11, 12 each carrying a grinding wheel having a particular shape and dimensions. The axes of rotation of the grinding wheels are oriented either along the Z axis or along the X axis. They can be orientable on the X, Z plane. We also see in FIG. 2 the probe 18, the head of which comprises three position detectors, the surfaces of which are oriented for one perpendicular to the X axis and for the other two perpendicular to the Z axis, one in one direction, the other in the other.

The dressage turret has a special arrangement here. It has a base 20 which is mounted on a longitudinal support 21. We consider here a dressing turret according to FIG. 2, which is shown with three arms. It could however have a larger number of arms. The base 20 supports a rotary body of horizontal axis 22, oriented parallel to the axis Z. The three arms of the body 22 are designated by 23, 24 and 25, the arm 23 being, in the position of FIG. 3, oriented horizontally at the axis of the spindle 5 and the grinding tools 9 and 12. When the arm 23 is in this position, the arm 24 is oriented vertically upwards and the arm 25 vertically downwards . The dressing device therefore comprises a rest position when the body 22 is oriented so that the arm 23 is directed towards the rear of the machine. The space between the body 22 and the main axis of the machine is then completely freed.

The arm 23 constitutes a second feeler. In fact, at its end are mounted three detectors, for example detectors formed from spring contact pads controlled when the flat outer surface of a pad touches the object to be measured. The flat surfaces of these pellets are oriented for two detectors along the Z axis, one in one direction, the other in the other, and for the third along the X axis as seen in the plan view of fig. 2. The arm 24 carries a diamond, while the arm 25 carries a diamond wheel driven in rotation by a motor housed in the arm 25. In this arrangement, there is no reference solid similar to the solid 19 of the first form execution, but the function of this solid will be fulfilled by the surfaces of the detectors of the arm 23, as will be seen below. Note, however, that in a variant, a reference solid similar to that of 19 could also be fixed against the support 20 or on another arm.

The functions of the probe 23 are as follows: this probe is intended to make it possible to store data relating to the grinding wheels 9a, 10a, 11a and 12a, in particular their effective dimensions before the dressing operation, so as to allow this drive to be carried out with precision surgery.

With the grinding machine of fig. 2 and 3, the start-up process begins as described with reference to FIG. 1, by taking measurements of the positions of the determining edges of the dressing tools. The table 13 is therefore moved so that the sensing surfaces of the probe 18 come into contact with the reference solid and with each of the tools carried by the turret 20. In the case where it is the probe 23 which plays the role of the solid reference, the detectors fitted to the probe 23 will be elements whose actuating force will be a multiple of the force necessary to actuate the probe 18. These detectors can therefore play the role of the reference solid for the probe 18. Once the probe 18 has identified the positions of the dressing tools, and possibly that of the workpiece, the program includes a step of measuring the actual dimensions of the grinding wheels. The table 13 is moved along the axes X and Z, so that certain characteristic surfaces of the tools 9a, 10a, 11a and 12a come into contact with the detection surfaces of the probe 23. These characteristic surfaces will be the cylindrical surface and for example the front face for a cylindrical wheel. In the case of a conical grinding wheel, such as for example the grinding wheel 12a, the identification of the surfaces will be carried out on the front face and on the largest diameter. The data obtained will be stored in relative values, i.e. in the form of position dimensions relative to the reference machine. For this, the data obtained by the probe 18 will be used beforehand, on the positions of the detection surfaces of the probe 23.

It will also be noted that in the variant described here in which a second feeler is used in the shape of feeler 23, to determine the dimensions of the grinding wheels before dressing, the positioning of a grinding wheel on the feeler is determined according to the shape of the wheel. It is the highest point of the profile which is used for probing the diameter of the grinding tool and the most forward point for the front probing. With some specially shaped grinding wheels, it may be that the programming requires entering other values into the computer. However, the means described here allow without great difficulty to carry out all the operations automatically without exaggerated complication. It is possible to measure the dimensions between the various diamonds mounted on the dressing device with very high precision.

In some cases where one or the other of the tools mounted on the base 13 is a grinding tool, such as a diamond wheel, the characteristics of which do not allow, and do not require, dressing, the measurements taken by the second probe 23 will only be used to determine the effective position of this tool. During automatic dressing, this tool is not brought into contact with the diamonds. However, the position data recorded can be used to conduct the grinding operation on the workpiece.

As seen on the basis of the two preceding examples, the automatic start-up process can be implemented under very varied conditions. It can be implemented not only on grinding machines whose tool-holder turret is movable along X and Z with respect to the workpiece carrier and the dressing turret, but also in the case of grinding machines in which the tool-holder turret is movable only in one direction, for example the Z axis, and it is the workpiece table and the dressing turret which can be moved in the X direction.

Claims (14)

Method of starting a grinding machine equipped with a workpiece table, a tool holder carrying at least one grinding tool, a dressing turret on which are mounted one or more dressing tools having a dressing edge, and of a digital control comprising a memory, for grinding operations on several different surfaces of the same part, characterized by the following steps:
a probe having at least two detector faces is placed in a predetermined position on the tool holder,
a measurement step is carried out in which the sensing faces of the probe are brought into predetermined relative positions with respect to one or more dressing edges of the dressing tool (s) and the positions of the corresponding tool holder are recorded in the memory at each of said predetermined relative positions,
and after the measurement step, the position records stored are used to customize a program for an automatic dressing operation. Method according to claim 1, characterized in that the step of taking measurements comprises relative displacements of the probe towards a reference solid associated with the dressing turret and towards each of the dressing tools. Method according to claim 1, characterized in that, in the step of taking measurements, a second probe, located in a fixed and predetermined position relative to a machine reference, takes measurements of the surface positions of one or more grinding tools, these measurements are used to determine the initial dimensions of the grinding tool or tools, and these initial dimensions are also used to particularize the training program. Method according to claim 1, characterized in that it comprises a step of preparation for grinding in which the probe associated with the tool holder takes at least one position measurement of a surface of the workpiece and this measurement is recorded in the memory to specialize a grinding program. Method according to claim 4, applied to a grinding machine in which an angular numerical axis is associated with the workpiece table, characterized in that the workpiece surface position measurement (s) are used to determine the relative position of the workpiece relative to the center of rotation of the workpiece table, and therefore the positions of the workpiece after any angular movement of the workpiece table. Method according to claim 1, characterized in that at least part of the operations carried out during the step of taking measurements are repeated during the machining of a series of identical parts and the measurements are used to correct said dressing program taking into account a wear of the dressing tools determined by means of said measures taken repeatedly. Method according to claim 3, applied to a grinding machine comprising a grinding tool whose characteristics do not allow dressing, characterized in that the measurements of the surface positions of this tool are used only to determine the position of the tool. CNC grinding machine comprising on a base a workpiece table, a dressing turret and a tool turret, equipped respectively with a drive spindle for a workpiece, at least one dressing tool, and at least one grinding tool, these turrets being capable of relative movements at least on one of the axes X and Z between the tool-holder turret on the one hand and the workpiece carrier and the dressing turret on the other hand, characterized in that the tool-holder turret and another part of the machine are respectively equipped with a first position probe and a reference solid, the digital control being arranged for the automatic execution of a setting operation in train comprising a step of taking measurements during which said probe is successively brought into predetermined relative positions with respect to at least one of the dressing tools and with respect to at least one of the surfboards aces of the reference solid. Grinding machine according to claim 8, characterized in that the dressing turret is equipped with a second feeler whose relative positions with respect to the dressing tools are memorized, the relative displacements of the tool turret, with respect to the turret dressing, allowing position measurements to be taken on one or more surfaces of each grinding tool by said second probe. Grinding machine according to claims 8 or 9, characterized in that each probe has at least two detectors having a plane detector face, and in that these faces are oriented in pairs along the X and Z axes, the two faces of each pair being fixed one in relation to the other. Grinding machine according to claim 10, characterized in that at least one probe has a third detector, the detector face of which is oriented along the Z axis and placed so as to be able to measure the position of a rear face of a tool dressing or grinding. Grinding machine according to claim 10 or claim 11, characterized in that said detector faces of the second probe act as the surfaces of the reference solid. Grinding machine according to claim 8, characterized in that the first probe is carried by an arm and mounted eclipsably on the tool turret. Grinding machine according to claim 9, characterized in that the second feeler is integral with an arm forming part of a rotating equipment, further comprising one or more dressing tools and mounted around an axis on the dressing turret.

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