Title of Invention	A GRINDING MACHINE IN PARTICULAR A TOOL GRINDING MACHINE WITH CONCENTRICITY CORRECTION
Abstract	The invention relates to a grinding machine (1), in particular a tool grinding machine, comprising a workpiece receptacle (5), which is arranged for receiving an elongated rotationally symmetrical blank (7) or a workpiece (7); a rotary positioning device, which is arranged for rotating the workpiece receptacle (5) about a predetermined receptacle axis (C), and having a rotary position detection device, which are connected to the workpiece receptacle (5); a grinding head (3), which has a rotary drive mechanism and carries at least one grinding tool (15); a positioning device (14), which is connected to the workpiece receptacle (5) and/or to the grinding head (3), for effecting a relative motion between the grinding tool (15) and the blank (7) or workpiece (7); a measuring device (8,9), which is arranged for determining the eccentricity and the alignment error of the blank (7) or workpiece (7) with respect to the receptacle axis (C) ; and a machine control unit (6), which is connected to the rotary positioning device, the rotary position detection device, the positioning device (14), and the measuring device (8,9), and which has a computation module (11), which determines control commands for the positioning device (14), taking into consideration the alignment error and the eccentricity in order to cause the grinding tools (15) to track an unsteady workpiece (7) so that the workpiece is machined concentrically and to the correct dimension.

Title of Invention

A GRINDING MACHINE IN PARTICULAR A TOOL GRINDING MACHINE WITH CONCENTRICITY CORRECTION

Abstract

The invention relates to a grinding machine (1), in particular a tool grinding machine, comprising a workpiece receptacle (5), which is arranged for receiving an elongated rotationally symmetrical blank (7) or a workpiece (7); a rotary positioning device, which is arranged for rotating the workpiece receptacle (5) about a predetermined receptacle axis (C), and having a rotary position detection device, which are connected to the workpiece receptacle (5); a grinding head (3), which has a rotary drive mechanism and carries at least one grinding tool (15); a positioning device (14), which is connected to the workpiece receptacle (5) and/or to the grinding head (3), for effecting a relative motion between the grinding tool (15) and the blank (7) or workpiece (7); a measuring device (8,9), which is arranged for determining the eccentricity and the alignment error of the blank (7) or workpiece (7) with respect to the receptacle axis (C) ; and a machine control unit (6), which is connected to the rotary positioning device, the rotary position detection device, the positioning device (14), and the measuring device (8,9), and which has a computation module (11), which determines control commands for the positioning device (14), taking into consideration the alignment error and the eccentricity in order to cause the grinding tools (15) to track an unsteady workpiece (7) so that the workpiece is machined concentrically and to the correct dimension.

Full Text	FIELD OF INVENTION The present invention relates to grinding machines, in particular tool grinding machines with concentricity correction. BACKGROUND OF INVENTION With grinding machines, especially tool grinding machines, high accuracy must now be attained, which makes stringent demands in terms of precision on all the machine elements involved, especially with regard to the bearing and guidance of the workpiece as well as the bearing and guidance of the grinding head. Inaccurate chucks represent a considerable problem in this respect. EP 0611630 discloses a torsionally-rigid portal (9) is fixed to the machine bed (2), having a gantry (11) between two lateral uprights (10). The spindle mounting (20) is adjustable along the gantry on a first axis (-Y). The bed protrudes in front of the portal to one side. The uprights can be at the opposite sides of the bed, and can be supported from its protruding end. A closed stiffening rear wall (13) can be mounted between the uprights, and can also be rigidly secured to the bed. OBJECT OF INVENTION With this as the point of departure, it is the object of the invention to create a grinding machine, in particular a tool grinding machine, with which tools can be made with highly accurate concentricity in a simple and reliable way. DE19753426 discloses the invention relates to a device for correcting radial run- outs during the fabrication of cylindrical parts (9). The device comprises a rotating spindle (4) which can be driven and a chuck (5, 6) which is fastened to the spindle (4) and accommodates a cylindrical part (9). The invention is characterized in that the chuck (5, 6) can be transversally displaced on the spindle (4) relative to the spindle axis (3) by being actuated with a defined force. In addition, a measuring device (12) is provided in order to determine a radial run-out of the cylindrical part (9) relative to the spindle axis (3). The invention is also characterized in that a final control element (14) can be controlled according to the measurement result of the measuring device (12) in order to generate the defined force which thus displaces the chuck (5,6) relative to the spindle (4). The device permits the middle axis (13) of a cylindrical part (9) to be centered opposite the spindle axis (3) in a fully automatic manner. SUMMARY OF INVENTION In a first aspect of the invention there is provided a grinding machine in particular a tool grinding machine, comprising a workpiece receptacle which is arranged for receiving an elongated rotationally symmetrical blank or a workpiece a rotary positioning device, which is arranged for rotating the workpiece receptacle about a predetermined receptacle axis, and having a rotary position detection device, which are connected to the workpiece receptacle a grinding head, which has a rotary drive mechanism and carries at least one grinding tool; a positioning device which is connected to the workpiece receptacle and/or to the grinding head, for effecting a relative motion between the grinding tool and the blank or workpiece; a measuring device which is arranged for determining the eccentricity and the alignment error of the blank or workpiece with respect to the receptacle axis; and a machine control unit, which is connected to the rotary positioning device, the rotary position detection device, the positioning device, and the measuring device, and which has a computation module, which determines control commands for the positioning device, taking into consideration the alignment error and the eccentricity in order to cause the grinding tools to track an unsteady workpiece so that the workpiece is machined concentrically and to the correct dimension. In a second aspect of the invention, there is provided a method for controlling a grinding machine, in particular a tool grinding machine, comprising the steps of receiving an elongated rotationally symmetrical blank or a workpiece in a workpiece receptacle; rotating the workpiece receptacle in a rotary positioning device about a predetermined receptacle axis, the rotary positioning device having a rotary position detection means, which are connected to the workpiece receptacle; providing a grinding head, which has a rotary drive mechanism and carries at least one grinding tool; effecting a relative motion between the grinding tool and the blank or workpiece in a positioning device, which is connected to the workpiece receptacle and/or to the grinding head; determining the eccentricity and the misalignment of the blank or workpiece with respect to the receptacle axis in a measuring device; determining control commands for the positioning device, in a machine control unit, connected to the rotary positioning device, the rotary position detection device, the positioning device, and the measuring device, and having a computation module, taking into consideration the alignment error and the eccentricity in order to cause the grinding tools to track an unsteady workpiece so that the workpiece is machined concentrically and to the correct dimension. The grinding machine of the invention performs the required grinding machining on the basis of a coordinate system defined by the clamped workpiece. This can be done either by working directly with tool coordinates, or, which is preferred, by first determining the location and orientation of the workpiece coordinate system by means of a measurement and then converting this workpiece coordinate system to the machine coordinate system by means of a kinematic transformation. For the kinematic transformation, a transformation matrix is used, which is obtained from the orientation of the workpiece and its oordinate system within the machine coordinate system. As a result, the machine control unit takes a virtually arbitrary misorientation of the workpiece in the machine coordinate system into account. If the machine coordinates for instance include cartesian coordinates x, y, z, which characterize a relative motion between the grinding wheel and the workpiece, as well as one or more pivot axes about which the grinding head and/or the............................................. workpiece holder is to be pivoted, then in addition to the machine coordinates a receptacle axis of the workpiece receptacle is used, which describes a rotation of the workpiece receptacle about the longitudinal direction of the workpiece to be clamped. The machine coordinate system thus in the most general case has six degrees of freedom; that is, it has three linear axes and two pivot axes as well as one rotary axis. This last axis is formed by the receptacle axis. The tool coordinate system is for instance a cartesian or a polar coordinate system. This system is designed such that at least one axis forms the axis of symmetry of the preferably cylindrical blank. This coordinate direction, also called the workpiece axis, is determined in a first measurement step. This is done in the machine coordinate system by means of a suitable measuring device, such as an optical measuring device or a mechanical tracer, which traces the blank, which initially is cylindrical as a rule, on its jacket face in the course of one or more revolutions of the workpiece receptacle about the receptacle axis. The tumbling motion that exists is recorded. From the path that the blank takes, the location of the workpiece axis can be calculated relative to the receptacle axis. The receptacle axis and the workpiece axis need not intersect one another. The location of the workpiece axis to the receptacle axis is determined by two vectors x0, r0. The two vectors characterize the eccentricity and the misalignment of the two axes to one another. The control unit converts the position of the blank, taking these vectors into account, into the machine coordinate system and takes this into account in triggering suitable control motors, which are associated with the various directions of motion (axes) of the components, that is, of the grinding head or of the workpiece holder of the grinding machine. Taking this into account can be done in such a way that the existing and previously determined commands for the actions of the individual control motors of the individual axes are modified. However, it can also be done in such a way that the tumbling motion of the workpiece is taken into account in advance when creating the individual control commands for the control motors. This last can be done by setting up a transformation specification T, which converts the kinematic transformation of a point PW in the workpiece coordinate system into a point PM of the machine coordinate system (PM = T (PW)), taking the vectors x0, r0 into account. The new transformation Tnew (T, x0, r0) is then in turn used for converting (copying) a point PW in the workpiece coordinate system into a point PM in the machine coordinate system; PM = Tnew (PW). It should be noted that the vectors x0, r0 are dependent on the coordinate C of the machine coordinate system that describes a rotation of the receptacle about the receptacle axis. The determination of the vectors xo, ro is preferably done at the beginning of each machining operation on the still un-machined blank. For each machining operation, an individual transformation specification Tnew (T, x0, r0) is therefore set up. Thus for the individual blanks, different chucks can be used, whose accuracy is no longer critical. Even with very inexpensive chucks, highly precisely machined tools can thus be produced, whose ground cutting edges and other functional faces are positioned in the very best way possible to the tool axis. The tool axis is defined by the predetermined tool shaft on the blank. The latter can be shaped cylindrically or conically. Precise concentricity in precision chucks is assured, even though the workpiece may have been ground in a substantially less-precise chuck. Further details of advantageous embodiments of the invention will become apparent from the drawings, the description, and the claims. In the drawings, one exemplary embodiment of the invention is shown. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Fig. 1, an extremely schematic illustration of a tool grinding machine; Fig. 2, a top view on the tool holder and the grinding head; Fig. 3, a schematic view of the tool holder and a clamped blank during the initial measurement; Fig. 4, a schematic, exaggerated view of the machine coordinate system and the position of the blank in it; and Fig. 5, a block circuit diagram of the machine controller of the grinding machine of Fig. 1. DETAIL DESCRIPTION OF INVENTION In Fig. 1, a tool grinding machine 1 is shown in a schematic illustration. It includes a machine frame 2, which carries a grinding head 3 and a tool holder 4. As schematically indicated in Fig. 1 by arrows, the tool holder 4 and the grinding head 3 are adjustable relative to one another in three coordinate directions X,Y and Z. The corresponding guides for the X direction, the Y direction and the Z direction, and the drive mechanisms not otherwise shown for moving the tool holder 4 or-the grinding head 3 in these directions are represented here as "axes" or "CNC axes". The tool holder 4 is furthermore pivotably supported about a vertical axis B. The tool holder 4 furthermore has a workpiece receptacle 5, which is rotatable about a receptacle axis C. The motions along all the directions X,Y,Z and about the axes B and C are monitored, or in other words controlled/regulated, by a machine control unit 6, as schematically shown in Fig. 5. The grinding head 3 serves to produce the desired workpiece, such as a drill or milling cutter or the like, from a blank 7 that is held in the workpiece receptacle 5. The blank 7 is preferably a cylindrical body. As Fig. 3 shows, it is as a rule clamped by the workpiece receptacle 5 not entirely coaxially with the receptacle axis C. Instead, the axis of symmetry of the cylindrical blank 7, or in other words the workpiece axis D, deviates from the receptacle axis C. As a rule, the deviation is stochastic, and it is all the greater, the lower the accuracy of the workpiece receptacle 5 is. The receptacle axis C and the workpiece axis D need not intersect one another at all; that is, they can be skewed relative to one another. Upon a rotation of the blank 7 about the receptacle axis C, the blank 7 executes a tumbling motion. The machine control unit 6 has a measurement module 8, to which one or more measuring tracers 9 (Fig. 3) or other measuring means belong that are capable of detecting the position of the blank 7. If tracers 9 are used, they serve for instance, during one or more revolutions of the blank 7, to trace the blank on its outer circumference, or in other words its jacket face, for instance at various points. It is for instance possible to trace a blank at three or more points on its circumference, by providing that from one tracing operation to another it is rotated in each case about a fixed angular amount about the receptacle axis C and then traced again. If the tracing operation is done over multiple rotations, periodic errors whose period extends over a plurality of revolutions of the blank and which originate for instance in the drive gear or in ball bearings, can also be detected. The measurement module 8 also includes an evaluation program, which on the basis of new measurement points obtained draws a conclusion about the location of the workpiece axis D. The tracing operations may, as indicated by dashed lines in Fig. 3, be performed at a plurality of places spaced apart axially from one another with respect to the receptacle axis C. The measurement module 8 also serves, on the basis of the measurement values obtained, to draw a conclusion about the eccentricity and the misalignment with which the blank 7 is held relative to the receptacle axis C. The eccentricity and the misalignment can be described by vectors x0, r0, as are shown greatly exaggerated in Fig. 4. The blank 7 is adjusted in a skewed fashion to the receptacle axis C. The concentricity error is described by an orientation vector ro, which is located parallel to the center axis of the blank 7 or some other workpiece, and a further vector x0, which describes the offset of the workpiece fr0m the ideal position. The vectors x0, r0 ascertained by the measurement module 8 are transferred to a computation module 11, with which the coordinates of the workpiece or blank 7 are converted fr0m a workpiece-specific coordinate system into the machine coordinate system X, Y, Z, B, C. In addition to the usual transformation T with which a given point PW in the tool coordinate system is to be converted into a point PM in the machine coordinate system if no tumbling motion is occurring, or in other words, when the vector r0 has the same direction as the receptacle axis C and when the vector x0 disappears (is zer0), the transformation Tnew now takes into account the vectors x0/ r0 (Tnew (T, x0, r0) ) as well. The computation module, which may be formed by a pr0gram running in the machine contr0l unit 6, receives data or commands fr0m a contr0l module 12 that can be considered as positioning commands for the individual guide motors associated with the axes X, Y, Z, B and C. These contr0l commands are modified by the computation module 11 and sent onward, as corrected contr0l commands, to the drive mechanisms 14. The tool grinding machine described thus far functions as follows: For machining a workpiece, or in other words for pr0ducing a tool fr0m a blank 7, first the blank 7 is clamped in the workpiece receptacle 5 and measured in it. To that end, the computation module 11 initially triggers the appr0priate drive mechanism of the tool holder 4 such that the blank 7 is r0tated in increments about the receptacle axis C. The tracer 9, which may be connected to the grinding head 3 or guided in some other way, traces the jacket face of the blank 7 at various places in the same axial position and furnishes the corresponding measurement values to the computation module 11. After at least one but preferably a plurality of revolutions of the blank 7, the tracer 9 is axially adjusted, in order to trace the blank 7 again along its circumference. To that end, the computation module 11 causes the blank 7 to r0tate onward in increments. If needed, the blank 7 can be traced at further places. Once the at least two axially spaced-apart annular regions of the blank 7 have been traced, then fr0m that, the measurement module 8 or the computation module 9 calculates the vectors x0, r0, which characterize the eccentricity and the misorientation of the blank 7. The two vectors x0, r0 are then kept in readiness individually for the workpiece or blank 7 that has just been measured and are further used for transforming the workpiece-related coordinates into the machine-related coordinates. If the blank 7 is then to be machined in a grinding machining operation, as indicated in Fig. 2, and if a cylindrical face is for instance to be created, then the grinding head 3 is br0ught as Fig. 2 shows to the blank 7. For creating the cylindrical face, the blank 7 is r0tated about the receptacle axis C while the grinding wheel 15 is in engagement with it. The wobble runout of the blank 7 has been determined in the previous measurement operation and stored in memory by the machine contr0l unit 6. The contr0l unit now takes the wobble runout into account in triggering the grinding head 3, so that the grinding head executes a recipr0cating motion, as indicated by the arr0w 16 in Fig. 2. The motion is adapted such that the circle on the blank 7 described by the point of contact between the grinding wheel 15 and the circumference of the blank 7 is located concentrically to its workpiece axis D. It is therefore possible, regardless of clamping inaccuracies on the part of the workpiece receptacle 15, to create cylindrical faces on the blank 7 which are concentric and dimensionally accurate relative to the workpiece axis D. Other surfaces, such as flanks, faces, and cutting edges, can also be created symmetrically and precisely relative to the location of the workpiece axis D. A tool grinding machine 1 has a machine contr0l unit 6, which by means of a suitable measuring device, which for instance comprises a tracer 9 and a measuring module 8, first determines the wobble runout with respect to the ideal receptacle axis C of a workpiece receptacle. In the grinding machining of the blank 7 or a workpiece, this wobble runout is taken into account and compensated for; that is, the grinding tools are made to track a tumbling workpiece in such a way that the workpiece is machined to the exact intended dimensions and concentrically. WE CLAIM; 1. A grinding machine (1), in particular a tool grinding machine, comprising: a workpiece receptacle (5), which is arranged for receiving an elongated r0tationally symmetrical blank (7) or a workpiece (7); a r0tary positioning device, which is arranged for r0tating the workpiece receptacle (5) about a predetermined receptacle axis (C), and having a r0tary position detection device, which are connected to the workpiece receptacle (5); a grinding head (3), which has a r0tary drive mechanism and carries at least one grinding tool (15); a positioning device (14), which is connected to the workpiece receptacle (5) and/or to the grinding head (3), for effecting a relative motion between the grinding tool (15) and the blank (7) or workpiece (7); a measuring device (8,9), which is arranged for determining the eccentricity and the alignment err0r of the blank (7) or workpiece (7) with respect to the receptacle axis (C); and a machine contr0l unit (6), which is connected to the r0tary positioning device, the rotary position detection device, the positioning device (14), and the measuring device (8,9), and which has a computation module (11), which determines control commands for the positioning device (14), taking into consideration the alignment error and the eccentricity in order to cause the grinding tools (15) to track an unsteady workpiece (7) so that the workpiece is machined concentrically and to the correct dimension. . The grinding machine as claimed in claim 1, wherein the measuring device (8,9) comprises at least one measuring tracer (9), with which the blank (7) or workpiece (7) is traced at a plurality of places spaced apart from one another in the axial direction. . The grinding machine as claimed in claim 1, wherein the measuring device (8,9) comprises at least one measuring tracer (9), with which the blank (7) or workpiece (7) is traced at a plurality of places spaced apart from one another in the circumferential direction. . The grinding machine as claimed in claim 1, wherein for measuring the eccentricity and the misalignment of the blank or workpiece (7), the latter (7) is rotated step by step and it is traced initially in a first axial position and then in at least one other axial position. . The grinding machine as claimed in claim 1, wherein the computation module (11) determines from the obtained measured values two vectors (x0, ro), which characterize the amount of deviation of the workpiece axis (D) from the receptacle axis (C ) and the orientation of the workpiece axis (D) relative to the receptacle axis ( C). 6. The grinding machine as claimed in claim 5, wherein the computation module converts the workpiece coordinates, in the course of a coordinate transformation, into machine coordinates and takes the vectors (x0, ro) into consideration in the course of transformation. 7. The grinding machine as claimed in claim 1, wherein the eccentricity and the misalignment is determined on the basis of the determination of the vectors after each clamping operation, in which a workpiece or blank (7) has been clamped in the workpiece receptacle (5). 8. A method for controlling a grinding machine, in particular a tool grinding machine (1), comprising the steps of: - receiving an elongated rotationally symmetrical blank (7) or a workpiece (7) in a workpiece receptacle (5); - rotating the workpiece receptacle (5) in a rotary positioning device about a predetermined receptacle axis (C ), the rotary positioning device having a rotary position detection means, which are connected to the workpiece receptacle (5); - providing a grinding head (3), which has a rotary drive mechanism and carries at least one grinding tool (15); - effecting a relative motion between the grinding tool (15) and the blank (7) or workpiece (7) in a positioning device (14), which is connected to the workpiece receptacle (5) and/or to the grinding head (3); - determining the eccentricity and the misalignment of the blank (7) or workpiece (7) with respect to the receptacle axis (C) in a measuring device (8,9); - determining control commands for the positioning device (14), in a machine control unit (6), connected to the rotary positioning device, the rotary position detection device, the positioning device, and the measuring device, and having a computation module (11), taking into consideration the alignment error and the eccentricity in order to cause the grinding tools (15) to track an unsteady workpiece (7) so that the workpiece (7) is machined concentrically and to the correct dimension. 9. The method as claimed in claim 8, wherein the workpiece or blank is traced at a plurality of places spaced apart from one another in the axial direction by means of at least one measuring tracer allocated to the measuring device. lO.The method as claimed in claim 9, wherein the workpiece or blank is traced at a plurality of places spaced apart from one another in the circumferential direction. 11.The method as claimed in claim 8, wherein the workpiece is rotated step by step for measuring the eccentricity and the misalignment of the workpiece, and during the process it is traced initially in a first axial position and then in at least one other axial position. 12. The method as claimed in claim 8, wherein two vectors (x0, ro) are determined from the measurement values obtained by means of the computation module, which vectors characterize the amount of deviation of the workpiece axis from the receptacle axis and the orientation of the workpiece axis relative to the receptacle axis. 13.The method as recited in claim 13, characterized in that the computation module converts the workpiece coordinates, in the course of a coordinate transformation, into machine coordinates and in this transformation takes the vectors (x0, ro) into account. 14.The method as recited in claim 8, characterized in that the determination of the eccentricity and the misalignment is done on the basis of the determination of the vectors after each clamping operation, in which a workpiece or blank has been clamped in the workpiece receptacle. The invention relates to a grinding machine (1), in particular a tool grinding machine, comprising a workpiece receptacle (5), which is arranged for receiving an elongated rotationally symmetrical blank (7) or a workpiece (7); a rotary positioning device, which is arranged for rotating the workpiece receptacle (5) about a predetermined receptacle axis (C), and having a rotary position detection device, which are connected to the workpiece receptacle (5); a grinding head (3), which has a rotary drive mechanism and carries at least one grinding tool (15); a positioning device (14), which is connected to the workpiece receptacle (5) and/or to the grinding head (3), for effecting a relative motion between the grinding tool (15) and the blank (7) or workpiece (7); a measuring device (8,9), which is arranged for determining the eccentricity and the alignment error of the blank (7) or workpiece (7) with respect to the receptacle axis (C) ; and a machine control unit (6), which is connected to the rotary positioning device, the rotary position detection device, the positioning device (14), and the measuring device (8,9), and which has a computation module (11), which determines control commands for the positioning device (14), taking into consideration the alignment error and the eccentricity in order to cause the grinding tools (15) to track an unsteady workpiece (7) so that the workpiece is machined concentrically and to the correct dimension.

Full Text

FIELD OF INVENTION
The present invention relates to grinding machines, in particular tool grinding
machines with concentricity correction.
BACKGROUND OF INVENTION
With grinding machines, especially tool grinding machines, high accuracy must
now be attained, which makes stringent demands in terms of precision on all the
machine elements involved, especially with regard to the bearing and guidance
of the workpiece as well as the bearing and guidance of the grinding head.
Inaccurate chucks represent a considerable problem in this respect.
EP 0611630 discloses a torsionally-rigid portal (9) is fixed to the machine bed
(2), having a gantry (11) between two lateral uprights (10). The spindle
mounting (20) is adjustable along the gantry on a first axis (-Y). The bed
protrudes in front of the portal to one side. The uprights can be at the opposite
sides of the bed, and can be supported from its protruding end. A closed
stiffening rear wall (13) can be mounted between the uprights, and can also be
rigidly secured to the bed.
OBJECT OF INVENTION
With this as the point of departure, it is the object of the invention to create a
grinding machine, in particular a tool grinding machine, with which tools can be
made with highly accurate concentricity in a simple and reliable way.
DE19753426 discloses the invention relates to a device for correcting radial run-
outs during the fabrication of cylindrical parts (9). The device comprises a
rotating spindle (4) which can be driven and a chuck (5, 6) which is fastened to
the spindle (4) and accommodates a cylindrical part (9). The invention is
characterized in that the chuck (5, 6) can be transversally displaced on the
spindle (4) relative to the spindle axis (3) by being actuated with a defined force.
In addition, a measuring device (12) is provided in order to determine a radial
run-out of the cylindrical part (9) relative to the spindle axis (3). The invention is
also characterized in that a final control element (14) can be controlled according
to the measurement result of the measuring device (12) in order to generate the
defined force which thus displaces the chuck (5,6) relative to the spindle (4). The
device permits the middle axis (13) of a cylindrical part (9) to be centered
opposite the spindle axis (3) in a fully automatic manner.
SUMMARY OF INVENTION
In a first aspect of the invention there is provided a grinding machine in
particular a tool grinding machine, comprising a workpiece receptacle which is
arranged for receiving an elongated rotationally symmetrical blank or a
workpiece a rotary positioning device, which is arranged for rotating the
workpiece receptacle about a predetermined receptacle axis, and having a rotary
position detection device, which are connected to the workpiece receptacle a
grinding head, which has a rotary drive mechanism and carries at least one
grinding tool; a positioning device which is connected to the workpiece
receptacle and/or to the grinding head, for effecting a relative motion between
the grinding tool and the blank or workpiece; a measuring device which is
arranged for determining the eccentricity and the alignment error of the blank or
workpiece with respect to the receptacle axis; and a machine control unit, which
is connected to the rotary positioning device, the rotary position detection
device, the positioning device, and the measuring device, and which has a
computation module, which determines control commands for the positioning
device, taking into consideration the alignment error and the eccentricity in order
to cause the grinding tools to track an unsteady workpiece so that the workpiece
is machined concentrically and to the correct dimension.
In a second aspect of the invention, there is provided a method for controlling a
grinding machine, in particular a tool grinding machine, comprising the steps of
receiving an elongated rotationally symmetrical blank or a workpiece in a
workpiece receptacle; rotating the workpiece receptacle in a rotary positioning
device about a predetermined receptacle axis, the rotary positioning device
having a rotary position detection means, which are connected to the workpiece
receptacle; providing a grinding head, which has a rotary drive mechanism and
carries at least one grinding tool; effecting a relative motion between the
grinding tool and the blank or workpiece in a positioning device, which is
connected to the workpiece receptacle and/or to the grinding head; determining
the eccentricity and the misalignment of the blank or workpiece with respect to
the receptacle axis in a measuring device; determining control commands for the
positioning device, in a machine control unit, connected to the rotary positioning
device, the rotary position detection device, the positioning device, and the
measuring device, and having a computation module, taking into consideration
the alignment error and the eccentricity in order to cause the grinding tools to
track an unsteady workpiece so that the workpiece is machined concentrically
and to the correct dimension.
The grinding machine of the invention performs the required grinding machining
on the basis of a coordinate system defined by the clamped workpiece. This can
be done either by working directly with tool coordinates, or, which is preferred,
by first determining the location and orientation of the workpiece coordinate
system by means of a measurement and then converting this workpiece
coordinate system to the machine coordinate system by means of a kinematic
transformation. For the kinematic transformation, a transformation matrix is
used, which is obtained from the orientation of the workpiece and its oordinate
system within the machine coordinate system. As a result, the machine control
unit takes a virtually arbitrary misorientation of the workpiece in the machine
coordinate system into account. If the machine coordinates for instance include
cartesian coordinates x, y, z, which characterize a relative motion between the
grinding wheel and the workpiece, as well as one or more pivot axes about
which the grinding head and/or the.............................................
workpiece holder is to be pivoted, then in addition to the
machine coordinates a receptacle axis of the workpiece
receptacle is used, which describes a rotation of the
workpiece receptacle about the longitudinal direction of the
workpiece to be clamped. The machine coordinate system thus
in the most general case has six degrees of freedom; that is,
it has three linear axes and two pivot axes as well as one
rotary axis. This last axis is formed by the receptacle axis.
The tool coordinate system is for instance a cartesian
or a polar coordinate system. This system is designed such
that at least one axis forms the axis of symmetry of the
preferably cylindrical blank. This coordinate direction, also
called the workpiece axis, is determined in a first
measurement step. This is done in the machine coordinate
system by means of a suitable measuring device, such as an
optical measuring device or a mechanical tracer, which traces
the blank, which initially is cylindrical as a rule, on its
jacket face in the course of one or more revolutions of the
workpiece receptacle about the receptacle axis. The tumbling
motion that exists is recorded. From the path that the blank
takes, the location of the workpiece axis can be calculated
relative to the receptacle axis. The receptacle axis and the
workpiece axis need not intersect one another. The location
of the workpiece axis to the receptacle axis is determined by
two vectors x0, r0. The two vectors characterize the
eccentricity and the misalignment of the two axes to one
another.
The control unit converts the position of the blank,
taking these vectors into account, into the machine
coordinate system and takes this into account in triggering
suitable control motors, which are associated with the
various directions of motion (axes) of the components, that
is, of the grinding head or of the workpiece holder of the
grinding machine. Taking this into account can be done in
such a way that the existing and previously determined
commands for the actions of the individual control motors of
the individual axes are modified. However, it can also be
done in such a way that the tumbling motion of the workpiece
is taken into account in advance when creating the individual
control commands for the control motors. This last can be
done by setting up a transformation specification T, which
converts the kinematic transformation of a point PW in the
workpiece coordinate system into a point PM of the machine
coordinate system (PM = T (PW)), taking the vectors x0, r0
into account. The new transformation Tnew (T, x0, r0) is then
in turn used for converting (copying) a point PW in the
workpiece coordinate system into a point PM in the machine
coordinate system; PM = Tnew (PW). It should be noted that
the vectors x0, r0 are dependent on the coordinate C of the
machine coordinate system that describes a rotation of the
receptacle about the receptacle axis.
The determination of the vectors xo, ro is preferably
done at the beginning of each machining operation on the
still un-machined blank. For each machining operation, an
individual transformation specification Tnew (T, x0, r0) is
therefore set up. Thus for the individual blanks, different
chucks can be used, whose accuracy is no longer critical.
Even with very inexpensive chucks, highly precisely machined
tools can thus be produced, whose ground cutting edges and
other functional faces are positioned in the very best way
possible to the tool axis. The tool axis is defined by the
predetermined tool shaft on the blank. The latter can be
shaped cylindrically or conically. Precise concentricity in
precision chucks is assured, even though the workpiece may
have been ground in a substantially less-precise chuck.
Further details of advantageous embodiments of the invention will become
apparent from the drawings, the description, and the claims. In the drawings,
one exemplary embodiment of the invention is shown.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1, an extremely schematic illustration of a tool grinding machine;
Fig. 2, a top view on the tool holder and the grinding head;
Fig. 3, a schematic view of the tool holder and a clamped blank during the initial
measurement;
Fig. 4, a schematic, exaggerated view of the machine coordinate system and the
position of the blank in it; and
Fig. 5, a block circuit diagram of the machine controller of the grinding machine
of Fig. 1.
DETAIL DESCRIPTION OF INVENTION
In Fig. 1, a tool grinding machine 1 is shown in a schematic illustration. It
includes a machine frame 2, which carries a grinding head 3 and a tool holder 4.
As schematically indicated in Fig. 1 by arrows, the tool holder 4 and the grinding
head 3 are adjustable relative to one another in three coordinate directions X,Y
and Z. The corresponding guides for the X direction, the Y direction and the Z
direction, and the drive mechanisms not otherwise shown for moving the tool
holder 4 or-the grinding head 3 in these directions are represented here as
"axes" or "CNC axes". The tool holder 4 is furthermore pivotably supported about
a vertical axis B. The tool holder 4 furthermore has a workpiece receptacle 5,
which is rotatable about a receptacle axis C. The motions along all the directions
X,Y,Z and about the axes B and C are monitored, or in other words
controlled/regulated, by a machine control unit 6, as schematically shown in Fig.
5.
The grinding head 3 serves to produce the desired workpiece, such as a drill or
milling cutter or the like, from a blank 7 that is held in the workpiece receptacle
5. The blank 7 is preferably a cylindrical body. As Fig. 3 shows, it is as a rule
clamped by the workpiece receptacle 5 not entirely coaxially with the receptacle
axis C. Instead, the axis of symmetry of the cylindrical blank 7, or in other words
the workpiece axis D, deviates from the receptacle axis C. As a rule, the
deviation is stochastic, and it is all the greater, the lower the accuracy of the
workpiece receptacle 5 is. The receptacle axis C and the workpiece axis D need
not intersect one another at all; that is, they can be skewed relative to one
another. Upon a rotation of the blank 7 about the receptacle axis C, the blank 7
executes a tumbling motion.
The machine control unit 6 has a measurement module 8,
to which one or more measuring tracers 9 (Fig. 3) or other
measuring means belong that are capable of detecting the
position of the blank 7. If tracers 9 are used, they serve
for instance, during one or more revolutions of the blank 7,
to trace the blank on its outer circumference, or in other
words its jacket face, for instance at various points. It is
for instance possible to trace a blank at three or more
points on its circumference, by providing that from one
tracing operation to another it is rotated in each case about
a fixed angular amount about the receptacle axis C and then
traced again. If the tracing operation is done over multiple
rotations, periodic errors whose period extends over a
plurality of revolutions of the blank and which originate for
instance in the drive gear or in ball bearings, can also be
detected. The measurement module 8 also includes an
evaluation program, which on the basis of new measurement
points obtained draws a conclusion about the location of the
workpiece axis D. The tracing operations may, as indicated by
dashed lines in Fig. 3, be performed at a plurality of places
spaced apart axially from one another with respect to the
receptacle axis C.
The measurement module 8 also serves, on the basis of
the measurement values obtained, to draw a conclusion about
the eccentricity and the misalignment with which the blank 7
is held relative to the receptacle axis C. The eccentricity
and the misalignment can be described by vectors x0, r0, as
are shown greatly exaggerated in Fig. 4. The blank 7 is
adjusted in a skewed fashion to the receptacle axis C. The
concentricity error is described by an orientation vector ro,
which is located parallel to the center axis of the blank 7
or some other workpiece, and a further vector x0, which
describes the offset of the workpiece fr0m the ideal
position. The vectors x0, r0 ascertained by the measurement
module 8 are transferred to a computation module 11, with
which the coordinates of the workpiece or blank 7 are
converted fr0m a workpiece-specific coordinate system into
the machine coordinate system X, Y, Z, B, C. In addition to
the usual transformation T with which a given point PW in the
tool coordinate system is to be converted into a point PM in
the machine coordinate system if no tumbling motion is
occurring, or in other words, when the vector r0 has the same
direction as the receptacle axis C and when the vector x0
disappears (is zer0), the transformation Tnew now takes into
account the vectors x0/ r0 (Tnew (T, x0, r0) ) as well. The
computation module, which may be formed by a pr0gram running
in the machine contr0l unit 6, receives data or commands fr0m
a contr0l module 12 that can be considered as positioning
commands for the individual guide motors associated with the
axes X, Y, Z, B and C. These contr0l commands are modified by
the computation module 11 and sent onward, as corrected
contr0l commands, to the drive mechanisms 14.
The tool grinding machine described thus far functions
as follows:
For machining a workpiece, or in other words for
pr0ducing a tool fr0m a blank 7, first the blank 7 is clamped
in the workpiece receptacle 5 and measured in it. To that
end, the computation module 11 initially triggers the
appr0priate drive mechanism of the tool holder 4 such that
the blank 7 is r0tated in increments about the receptacle
axis C. The tracer 9, which may be connected to the grinding
head 3 or guided in some other way, traces the jacket face of
the blank 7 at various places in the same axial position and
furnishes the corresponding measurement values to the
computation module 11. After at least one but preferably a
plurality of revolutions of the blank 7, the tracer 9 is
axially adjusted, in order to trace the blank 7 again along
its circumference. To that end, the computation module 11
causes the blank 7 to r0tate onward in increments. If needed,
the blank 7 can be traced at further places.
Once the at least two axially spaced-apart annular
regions of the blank 7 have been traced, then fr0m that, the
measurement module 8 or the computation module 9 calculates
the vectors x0, r0, which characterize the eccentricity and
the misorientation of the blank 7. The two vectors x0, r0 are
then kept in readiness individually for the workpiece or
blank 7 that has just been measured and are further used for
transforming the workpiece-related coordinates into the
machine-related coordinates.
If the blank 7 is then to be machined in a grinding
machining operation, as indicated in Fig. 2, and if a
cylindrical face is for instance to be created, then the
grinding head 3 is br0ught as Fig. 2 shows to the blank 7.
For creating the cylindrical face, the blank 7 is r0tated
about the receptacle axis C while the grinding wheel 15 is in
engagement with it. The wobble runout of the blank 7 has been
determined in the previous measurement operation and stored
in memory by the machine contr0l unit 6. The contr0l unit now
takes the wobble runout into account in triggering the
grinding head 3, so that the grinding head executes a
recipr0cating motion, as indicated by the arr0w 16 in Fig. 2.
The motion is adapted such that the circle on the blank 7
described by the point of contact between the grinding wheel
15 and the circumference of the blank 7 is located
concentrically to its workpiece axis D. It is therefore
possible, regardless of clamping inaccuracies on the part of
the workpiece receptacle 15, to create cylindrical faces on
the blank 7 which are concentric and dimensionally accurate
relative to the workpiece axis D.
Other surfaces, such as flanks, faces, and cutting
edges, can also be created symmetrically and precisely
relative to the location of the workpiece axis D.
A tool grinding machine 1 has a machine contr0l unit 6,
which by means of a suitable measuring device, which for
instance comprises a tracer 9 and a measuring module 8, first
determines the wobble runout with respect to the ideal
receptacle axis C of a workpiece receptacle. In the grinding
machining of the blank 7 or a workpiece, this wobble runout
is taken into account and compensated for; that is, the
grinding tools are made to track a tumbling workpiece in such
a way that the workpiece is machined to the exact intended
dimensions and concentrically.
WE CLAIM;
1. A grinding machine (1), in particular a tool grinding machine, comprising:
a workpiece receptacle (5), which is arranged for receiving an elongated
r0tationally symmetrical blank (7) or a workpiece (7);
a r0tary positioning device, which is arranged for r0tating the workpiece
receptacle (5) about a predetermined receptacle axis (C), and having a
r0tary position detection device, which are connected to the workpiece
receptacle (5);
a grinding head (3), which has a r0tary drive mechanism and carries at
least one grinding tool (15);
a positioning device (14), which is connected to the workpiece receptacle
(5) and/or to the grinding head (3), for effecting a relative motion
between the grinding tool (15) and the blank (7) or workpiece (7);
a measuring device (8,9), which is arranged for determining the
eccentricity and the alignment err0r of the blank (7) or workpiece (7) with
respect to the receptacle axis (C); and
a machine contr0l unit (6), which is connected to the r0tary positioning
device, the rotary position detection device, the positioning device (14),
and the measuring device (8,9), and which has a computation module
(11), which determines control commands for the positioning device (14),
taking into consideration the alignment error and the eccentricity in order
to cause the grinding tools (15) to track an unsteady workpiece (7) so
that the workpiece is machined concentrically and to the correct
dimension.
. The grinding machine as claimed in claim 1, wherein the measuring device
(8,9) comprises at least one measuring tracer (9), with which the blank
(7) or workpiece (7) is traced at a plurality of places spaced apart from
one another in the axial direction.
. The grinding machine as claimed in claim 1, wherein the measuring device
(8,9) comprises at least one measuring tracer (9), with which the blank
(7) or workpiece (7) is traced at a plurality of places spaced apart from
one another in the circumferential direction.
. The grinding machine as claimed in claim 1, wherein for measuring the
eccentricity and the misalignment of the blank or workpiece (7), the latter
(7) is rotated step by step and it is traced initially in a first axial position
and then in at least one other axial position.
. The grinding machine as claimed in claim 1, wherein the computation
module (11) determines from the obtained measured values two vectors
(x0, ro), which characterize the amount of deviation of the workpiece axis
(D) from the receptacle axis (C ) and the orientation of the workpiece axis
(D) relative to the receptacle axis ( C).
6. The grinding machine as claimed in claim 5, wherein the computation
module converts the workpiece coordinates, in the course of a coordinate
transformation, into machine coordinates and takes the vectors (x0, ro)
into consideration in the course of transformation.
7. The grinding machine as claimed in claim 1, wherein the eccentricity and
the misalignment is determined on the basis of the determination of the
vectors after each clamping operation, in which a workpiece or blank (7)
has been clamped in the workpiece receptacle (5).
8. A method for controlling a grinding machine, in particular a tool grinding
machine (1), comprising the steps of:
- receiving an elongated rotationally symmetrical blank (7) or a
workpiece (7) in a workpiece receptacle (5);
- rotating the workpiece receptacle (5) in a rotary positioning device
about a predetermined receptacle axis (C ), the rotary positioning
device having a rotary position detection means, which are
connected to the workpiece receptacle (5);
- providing a grinding head (3), which has a rotary drive mechanism
and carries at least one grinding tool (15);
- effecting a relative motion between the grinding tool (15) and the
blank (7) or workpiece (7) in a positioning device (14), which is
connected to the workpiece receptacle (5) and/or to the grinding
head (3);
- determining the eccentricity and the misalignment of the blank (7)
or workpiece (7) with respect to the receptacle axis (C) in a
measuring device (8,9);
- determining control commands for the positioning device (14), in a
machine control unit (6), connected to the rotary positioning
device, the rotary position detection device, the positioning device,
and the measuring device, and having a computation module (11),
taking into consideration the alignment error and the eccentricity in
order to cause the grinding tools (15) to track an unsteady
workpiece (7) so that the workpiece (7) is machined concentrically
and to the correct dimension.
9. The method as claimed in claim 8, wherein the workpiece or blank is
traced at a plurality of places spaced apart from one another in the axial
direction by means of at least one measuring tracer allocated to the
measuring device.
lO.The method as claimed in claim 9, wherein the workpiece or blank is
traced at a plurality of places spaced apart from one another in the
circumferential direction.
11.The method as claimed in claim 8, wherein the workpiece is rotated step
by step for measuring the eccentricity and the misalignment of the
workpiece, and during the process it is traced initially in a first axial
position and then in at least one other axial position.
12. The method as claimed in claim 8, wherein two vectors (x0, ro) are
determined from the measurement values obtained by means of the
computation module, which vectors characterize the amount of deviation
of the workpiece axis from the receptacle axis and the orientation of the
workpiece axis relative to the receptacle axis.
13.The method as recited in claim 13, characterized in that the computation
module converts the workpiece coordinates, in the course of a coordinate
transformation, into machine coordinates and in this transformation takes
the vectors (x0, ro) into account.
14.The method as recited in claim 8, characterized in that the determination
of the eccentricity and the misalignment is done on the basis of the
determination of the vectors after each clamping operation, in which a
workpiece or blank has been clamped in the workpiece receptacle.
The invention relates to a grinding machine (1), in particular a tool grinding
machine, comprising a workpiece receptacle (5), which is arranged for receiving
an elongated rotationally symmetrical blank (7) or a workpiece (7); a rotary
positioning device, which is arranged for rotating the workpiece receptacle (5)
about a predetermined receptacle axis (C), and having a rotary position detection
device, which are connected to the workpiece receptacle (5); a grinding head
(3), which has a rotary drive mechanism and carries at least one grinding tool
(15); a positioning device (14), which is connected to the workpiece receptacle
(5) and/or to the grinding head (3), for effecting a relative motion between the
grinding tool (15) and the blank (7) or workpiece (7); a measuring device (8,9),
which is arranged for determining the eccentricity and the alignment error of the
blank (7) or workpiece (7) with respect to the receptacle axis (C) ; and a
machine control unit (6), which is connected to the rotary positioning device, the
rotary position detection device, the positioning device (14), and the measuring
device (8,9), and which has a computation module (11), which determines
control commands for the positioning device (14), taking into consideration the
alignment error and the eccentricity in order to cause the grinding tools (15) to
track an unsteady workpiece (7) so that the workpiece is machined concentrically
and to the correct dimension.

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Patent Number

223763

Indian Patent Application Number

00403/KOLNP/2006

PG Journal Number

39/2008

Publication Date

26-Sep-2008

Grant Date

23-Sep-2008

Date of Filing

22-Feb-2006

Name of Patentee

WALTER MASCHINENBAU GMBH

Applicant Address

DERENDINGER STRASSE 53 72072 TUBINGEN

Inventors:

#	Inventor's Name	Inventor's Address
1	SIMAKOV, MIKAIL	18, BOXSHALL STREET, BRIGHTON, VICTORIA 3186
2	DILGER, CHRISTIAN	HIRSCHSTRASSE 43, 70771 LEINFELDEN-ECHTERDINGEN

PCT International Classification Number

B24B 19/04

PCT International Application Number

PCT/EP04/010660

PCT International Filing date

2004-09-23

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10344293.6	2003-09-23	Germany